EPA-600/3-80-080
August 1980
SEDIMENTS OF SOUTHERN LAKE HURON:
ELEMENTAL COMPOSITION AND ACCUMULATION RATES
by
John A. Robbins
Great Lakes Research Division
The University of Michigan
Ann Arbor, Michigan 48109
Grant No. R803086
Project Officer
Michael D. Mullin
Large Lakes Research Station
Environmental Research Laboratory-Duluth
Grosse He, Michigan 48138
ENVIRONMENTAL RESEARCH LABORATORY—DULUTH
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
DULUTH, MINNESOTA 55804
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DISCLAIMER
This report has been reviewed by the Environmental Research Laboratory-
Duluth, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency, nor does mention of
trade names or commercial products constitute endorsement or recommendation
for use.
ii
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FOREWORD
The presence of hazardous materials in the environment is a topic of
major interest to the Environmental Protection Agency. Most metal contam-
inants in lakes are primarily associated with particulate matter and are
conveyed to underlying deposits in association with fine-grained materials
such as organic debris, hydroxides of iron, and manganese or clay minerals.
In order to develop an understanding of this sedimentation process, it is
necessary to determine the amounts and locations of these sediments.
This report describes the composition and rates of accumulation of
metal contaminants in the depositional basins of southern Lake Huron.
Appendix A appears in a separate volume, which is available from National
Technical Information Services (NTIS).
Norbert Jaworski, Ph.D
Director
Environmental Research Laboratory
Duluth
iii
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ABSTRACT
It is widely recognized that most metal contaminants in lakes are
primarily associated with particulate matter and are conveyed to underlying
deposits in association with fine-grained materials such as organic debris,
hydroxides of iron, and manganese or clay minerals. In the Great Lakes the
fine-grained sediments and associated contaminants are not deposited
uniformly over the bottom but are confined to "pockets" or depositional
basins which are of more limited extent and generally found in deeper areas
of each lake. This report is the first in a series of three comprehensive
reports which describes the composition and rates of accumulation of metal
contaminants in the depositional basins of Lake Huron. This first report
deals with the two principal depositional basins in southern Lake Huron: the
Port Huron basin and the Goderich basin.
Over a period of a year (1974-1975) nearly 100 sediment cores were taken
within these two basins. Cores were carefully sectioned aboard ship and
subsequently analyzed for large number of elements using state-of-the-art
methods. Elements determined include Al, As, Ba, Br, Ca, Cd, Ce, Co, Cr, Cs,
Cu, Eu, Fe, K, La, Lu, Hg, Hf, Mg, Mo, Mn, Na, Ni, P, Pb, Rb, Sb, Sc, Si, Sm,
Sn, Sr, Ti, Th, U, V, Yb and Zn. Most of the known or potential metal
contaminants are included in this list. Many of the cores were dated by
radiometric methods using lead-210 and cesium-137. In addition, for a
limited set of cores the distribution of dissolved substances was determined
to estimate possible exchanges with overlying water.
Results of this study include: (1) greatly improved estimates of
sediment accumulation rates, (2) recognition of the role of sediment mixing
by benthic organisms in modifying metal contaminant and radioactivity
profiles, (3) estimates of the rates of accumulation of metal contaminants in
these depositional basins, (4) identification of which metals are
contaminants and their degree of surface enrichment (in particular, the
discovery of tin as a contaminant metal), and (5) limited comparisons of
accumulation rates with lake loadings. The extent of contamination of
sediments relative to natural levels is greatest for Hg and then, in
decreasing order Sn, Pb, Sb, As, Cd, Zn, Ni, U, Cu, and Br. Data presented
include: (1) contour maps of surface concentrations of major and trace
constituents, enrichment factors, total anthropogenic metal accumulation
since about 1800, vertically integrated cesium-137, depth of sediment mixing,
mass and mean linear sedimentation rates, the intrinsic time resolution,
rates of accumulation of major constituents and contaminant metals, (2)
vertical distributions of major, trace, and dissolved constituents, (3)
models for the behavior of cesium-137 in water, sediment mixing, and silicon
dissolution in sediments, (4) area-wide loadings of major and trace
constituents plus contaminant metals.
iv
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CONTENTS
Page
Foreword iii
Abstract iv
Figures viii
Tables xvi
Acknowledgments xx
Introduction 1
Conclusions and Recommendations 8
Methods 14
Field Methods 14
Sediment collection 14
Sample processing 14
Laboratory Methods 20
Wet Sediment 20
Bulk density 20
Zoobenthos 20
Dry Sediment 20
Fraction dry weight 20
Cesium-137 23
Trace elements (NAA) 23
Total and inorganic carbon 24
Acid-peroxide extracts 25
Soluble fraction 25
Trace elements (AAS) 25
Lead-210 26
Base Extracts 28
Amorphous silicon 28
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Pore Water 29
Soluble reactive PC>4 and Si 29
Other constituents 29
Accuracy of Results 29
Neutron activation analysis 29
Timed Extractions 33
Metals (AAS) 33
Amorphous silicon 36
Pore water air-exposure effect 40
Results and Discussion 43
Physical properties of sediments 43
Composition of surface sediments 48
Average composition 64
Distribution and interelement associations 67
Major constituents 67
Trace constituents 88
Vertical distribution of elements 118
Major constituents 122
Trace constituents 131
Cores at station 18 140
Enrichment factors 159
Vertically integrated concentrations 183
Sediment mixing and sedimentation rates 195
Cesium-137 195
Lead-210 213
Stable lead 223
Time resolution in cores 234
Rate of accumulation of sedimentary constituents 244
Computation 244
Distribution 246
Mean and total accumulation rates 253
Comparison with external loadings 265
Vertical distribution of dissolved constituents 277
VI
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Literature Cited 301
Publications and presentations receiving EPA support 308
Appendix
vii
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FIGURES
Number Page
1 Surficial sediment distribution in Lake Huron 2
2 Sediment coring locations in Lake Huron 4
3 Southern Lake Huron study area 5
4 Surficial sediment distribution in southern Lake Huron 7
5 Shipboard collection and processing scheme 17
6 Cross-sectional view of cassette sediment squeezer 19
7 Sample analysis scheme 21
8 A comparison of analytical precision and accuracy in
determination of trace element composition of standard
lake sediment via neutron activation analysis 33
9 Elemental concentration ascribed to standard lake sediment
versus extraction time 35
10 Silicon released from standard lake sediment versus
extraction time 39
11 Concentration of selected elements in successive 3 ml
aliquots of pore water 41
12 Fraction dry weight of sediment versus bulk density for
540 sediment samples 45
13 Vertical distribution of porosity in selected cores
(Saginaw and Port Huron Basins) 46
14 Vertical distribution of porosity in selected cores
(Goderich Basin) 47
15 Vertical distribution of porosity in two contrasting cores 49
16 Distribution of surface porosity 50
17 Distribution of porosity at depth 51
viii
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18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
Relative variability of element concentrations in
Distribution of fraction soluble component in surface sediments
Relation between calcium and inorganic carbon in
Relation between magnesium and inorganic carbon in
Relationship between calcium and magnesium in surface sediments
Distribution of iron in surface sediments
Relation between the fraction soluble component (corrected for
Relation between observed and predicted values of dolomite-
corrected fraction soluble content of surface sediments
Relation between iron and organic carbon in surface sediments
Distribution of phosphorus in surface sediments
Relation between iron (NAA) and cobalt (NAA)
Degree of correlation of element concentrations with the organic
52
65
71
73
74
75
76
77
78
80
83
84
85
87
89
90
91
92
93
94
95
97
ix
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40 Distribution of antimony (NAA) in surface sediments 99
41 Distribution of arsenic (NAA) in surface sediments 100
42 Distribution of bromine (NAA) in surface sediments 101
43 Distribution of cadmium in surface sediments 102
44 Distribution of chromium in surface sediments 103
45 Distribution of copper in surface sediments 104
46 Distribution of lead in surface sediments 105
47 Distribution of mercury in surface sediments 106
48 Distribution of nickel in surface sediments 107
49 Distribution of thorium (NAA) in surface sediments 108
50 Distribution of tin in surface sediments 109
51 Distribution of uranium (NAA) in surface sediments 110
52 Distribution of zinc in surface sediments Ill
53 Hierarchical trees resulting from cluster analysis of
surface sediment concentrations 113
54 Association of calcium family and related constituents based on
principal components analysis 114
55 Association of non-calcium family elements in the most complete
data set based on principal components analysis 115
56 Results of principal components analysis of complete data set
including calcium-family elements 116
57 Hierarchical tree resulting from cluster analysis of the
complete set plus additional non-enriched elements 117
58 Vertical distribution of the fraction soluble component for selected
cores from the Port Huron and Saginaw Depositional Basins ... 123
59 Vertical distribution of the fraction soluble component for selected
cores from the Goderich Basin 124
60 Vertical distribution of calcium in selected Port Huron and
Saginaw Basin cores 125
61 Vertical distribution of calcium in selected
Goderich Basin cores 126
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62 Vertical distribution of iron in selected Port Huron and
Saginaw Basin cores 127
63 Vertical distribution of iron in selected Goderich Basin cores 128
64 Vertical distribution of magnesium in selected Port Huron cores 129
65 Vertical distribution of magnesium in selected
Goderich Basin cores 130
66 Vertical distribution of mercury in a Goderich Basin core 132
67 Vertical distribution of manganese in selected Port Huron
and Saginaw Basin cores 133
68 Vertical distribution of manganese in selected
Goderich Basin cores 134
69 Vertical distribution of phosphorus in selected Port Huron
and Saginaw Basin cores 135
70 Vertical distribution of phosphorus in selected
Goderich Basin cores 136
71 Vertical distribution of potassium in selected Port Huron
and Saginaw Basin cores 137
72 Vertical distribution of potassium in selected
Goderich Basin cores 138
73 Vertical distribution of amorphous silicon in selected
Goderich Basin cores 139
74 Vertical distribution of cadmium in a Port Huron basin core .... 141
75 Vertical distribution of chromium in selected
Port Huron Basin cores 142
76 Vertical distribution of chromium in selected
Goderich Basin cores 143
77 Vertical distribution of copper in selected Port Huron and
Saginaw Basin cores 144
78 Vertical distribution of copper in selected
Goderich Basin cores 145
79 Vertical distribution of lead in selected Port Huron and
Saginaw Basin cores 146
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80 Vertical distribution of lead in selected
Goderich Basin cores 147
81 Vertical distribution of nickel in selected Port Huron and
Saginaw Basin cores 148
82 Vertical distribution of nickel in selected
Goderich Basin cores 149
83 Vertical distribution of tin in a Goderich Basin core 150
84 Vertical distribution of zinc in selected Port Huron and
Saginaw Basin cores 151
85 Vertical distribution of zinc in selected
Goderich Basin cores 152
86 Vertical distribution of major elements (NAA) in
Goderich Basin core (74-18-2) 156
87 Vertical distribution of minor elements (NAA) in
Goderich Basin core (74-18-2) 157
88 Vertical distribution of elements in Goderich Basin core (74-18-2)
possessing a significant degree of enrichment 158
89 Distribution of the cadmium enrichment factor 175
90 Distribution of the calcium enrichment factor 176
91 Distribution of the copper enrichment factor 177
92 Distribution of the lead enrichment factor 178
93 Distribution of the manganese enrichment factor 179
94 Distribution of the nickel enrichment factor 180
95 Distribution of the zinc enrichment factor 181
96 Relationship between the mean enrichment factor and the degree of
unrelatedness between surface and underlying element
concentrations 182
97 Enrichment factors for elements in the fine-grained sediments
of southern Lake Huron 184
98 Distribution of vertically integrated excess manganese 186
99 Distribution of vertically integrated excess copper 187
xii
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100 Distribution of vertically integrated excess nickel ............ 188
101 Distribution of vertically integrated excess lead .............. 189
102 Distribution of vertically integrated excess zinc .............. 190
103 History of cesium-137 deposition in Lake Huron ................. 197
104 Vertical distribution of cesium-137 in selected cores
(74:3-8) [[[ 200
105 Vertical distribution of cesium-137 in selected cores
(74:9-13, 19) ................................................ 201
106 Vertical distribution of cesium-137 in selected cores
(74: 14-18) [[[ 202
107 Vertical distribution of cesium-137 in selected cores
(74: 20-32) [[[ 201
108 Vertical distribution of cesium-137 in selected cores
(74: 33-36) [[[ 202
109 Vertical distribution of cesium-137 in a series of cores at
station 14 collected in 1974 (14-1,2) and in 1975 (14A-2, SC) 203
110 Relation between the expected and observed distribution of
cesium-137 at station 14 (Core 14A-2) ........................ 205
111 Relation between the depth of sediment mixing as indicated by
either cesium-137 or lead-210 and the depth above which 90% of
benthic macroinvertebrates occur (Zgg) ....................... 207
112 Distribution of mixed depth based on cesium-137 ................ 210
113 Distribution of vertically integrated cesium-137 activity ...... 211
114 Vertical distribution of lead-210 and cesium-137 in
core 74-13 [[[ 217
115 Vertical distribution of lead-210 and cesium-137 in
core 74-12 [[[ 218
116 Vertical distribution of excess lead-210 in selected
Port Huron and Saginaw Basin cores ........................... 219
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119 Distribution of vertically integrated excess lead-210
(standing crop) 222
120 Relationship between the mass sedimentation rates estimated from
cesium-137 and lead-210 224
121 Estimated regional atmospheric emissions of lead from the
combustion of coal and leaded fuel additives 226
122 Vertical distribution of major elements in core
EPA-SLH-75-18A 227
123 Vertical distribution of trace elements in core
EPA-SLH-75-18A 228
124 Vertical distribution of lead in selected radiometrically
dated cores 229
125 Relationship between the mass sedimentation rates calculated from
stable lead and lead-210 profiles 231
126 Rate of accumulation of fine-grained sedments in southern
Lake Huron 237
127 The average linear sedimentation rate in the upper ten cm
of sediment in southern Lake Huron 238
128 The effect of rapid steady-state mixing on the sedimentary record
of two events occurring ten years apart 242
129 The approximate time-resolution expected in sampling cores in
southern Lake Huron 243
130 The rate of accumulation of organic carbon in surface sediments 247
131 The rate of accumulation of iron (AAS) in surface sediments .... 248
132 The rate of accumulation of chromium (AAS) in surface sediments 249
133 The rate of accumulation of inorganic carbon in surface sediments 250
134 The rate of accumulation of calcium in surface sediments 251
135 The rate of accumulation of magnesium in surface sediments 252
136 The distribution of the factor converting surface concentrations
to present (1980) values 254
137 Rate of accumulation of anthropogenic antimony
(adjusted to 1980) 255
xiv
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138 Rate of accumulation of anthropogenic copper
(adjusted to 1980) 256
139 Rate of accumulation of anthropogenic mercury
(adjusted to 1980) 257
140 Rate of accumulation of anthropogenic lead
(adjusted to 1980) 258
141 Rate of accumulation of anthropogenic nickel
(adjusted to 1980) 259
142 Rate of accumulation of anthropogenic tin
(adjusted to 1980) 260
143 Rate of accumulation of anthropogenic zinc
144
145
146
147
148
149
150
151
152
153
^ CfcU 1 U«3 1
Vertical
Vertical
Vertical
Vertical
Vertical
U^U L> V/
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TABLES
Number Page
1 Area of surficial sediments in Lake Huron 6
2 Southern Lake Huron stations 15
3 A summary of physical and chemical parameters determined 22
4 Composition of standard sediment determined via nutron
activation analysis 30
5 Results of repeated analysis of standard lake sediment and
U.S.G.S. samples 32
6 Composition of standard lake sediment determined via atomic
absorption spectrophotometry 37
7 Extraction efficiencies for selected trace elements 38
8 Composition of pore water with and without air exposure 42
9 Composition of surface sediments 53
10 A summary of surface concentration data 59
11 Correlation matrix for surface concentration data 60
12 Mercury and tin in surface sediments 62
13 Regression data for mercury 68
14 Regression data for tin 69
15 Comparison of mean surface concentration data with other
reported values 70
16 Concentration of dolomite in surface sediments 81
17 Multiple regression coefficients for FSOL* versus organic
carbon plus iron plus manganese 86
18 Comparison of acid soluble and whole sediment element
concentrations 96
xvi
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19 Results of principle components analysis 119
20 Significant interelement associations 120
21 Summary of vertical distribution measurements 121
22 Vertical distribution of major elements in whole sediment
(station 18) 153
23 Vertical distribution of minor elements in whole sediment
(station 18) 154
24 AAS to NAA element concentration ratios 160
25 Mean whole-sediment element concentrations in surface and in
underlying sediments. Station EPA-SLH-74-18(2) 161
26 Vertical distribution of elements in the acid-soluble
fraction (AAS). Station SPA-SLH-75-18A(2) 162
27 Concentration of major elements (AAS) in surface and in
underlying sediments 165
28 Concentration of minor elements (AAS) in surface and in
underlying sediments 168
29 Correlations between enrichment factors 172
30 Summary of mean concentration ratios and enrichment factors 173
31 Comparison of mean enrichment factors by depositional basin 174
32 Vertically integrated excess element concentrations 185
33 Correlations between total excess deposition of
selected elements 191
34 Storage of anthropogenic elements in sediments of
southern Lake Huron 193
35 Inventory of cesium-137 in southern Lake Huron 194
36 Vertically integrated activity of cesium-137 and
mixing-model parameters 208
37 Values of the mixing depth versus hypothetical
sediment losses 212
38 Summary of lead-210 data, sedimentation rates, and
mixed-depths 216
39 Sedimentation rates derived from stable lead profiles 230
xvii
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40 Exponential source function parameters 233
41 Summary of sedimentation rate data 235
42 Summary of mixed depth estimates 239
43 Mean and total accumulation of fine-grained sediments
and non-enriched elements 262
44 Coefficients used to estimate missing background
concentrations of enriched elements 264
45 Accumulation rates of enriched eler.^nts
Port Huron Basin 266
46 Accumulation rates of enriched elements
Goderich Basin 267
47 Accumulation rates of enriched elements
southern Lake Huron 268
48 Sensitivity of mean accumulation rates to changes in
estimated background levels 269
49 Comparison of element composition of dolomitic
sediment with the composition of Canadian Lake Huron
shoreline materials 272
50 Comparison of mean anthropogenic element accumulation
rates with other loading data 274
51 Summary of dissolved element concentration data 278
52 Comparison of accumulation rates of amorphous silicon
with regeneration rates 294
APPENDIX TABLES
A-l Physical properties of sediment cores Al
A-2 Vertical distribution of metals A71
A-3 Vertical distribution of amorphous silicon A138
A-4 Vertical distribution of cesium-137 A139
A-5 Vertical distribution of lead-210 A147
xviii
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A-6 Vertical distribution of benthic macrofauna A153
A-7 Vertical distribution of dissolved species A163
A-8 Coefficients associated with pair-wise regression of surface
sediment concentration data A174
xix
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ACKNOWLEDGMENTS
It would not have been possible to do this work without the generous
help from a great many individuals. I should like to thank James Murphy,
Captain of the R/V Laurentian and his crew, and Richard Thibault, Captain of
the R/V Laurentian and his crew for their dedicated and effective help in the
collection of samples from southern Lake Huron. I am especially grateful to
John Krezoski and Kjell Johansen for their long-standing commitment to this
work and the help they have given in so many ways both in the field and in
the laboratory. Thanks are due K. Remmert for her help in the preparation
and analysis of samples and to J. Jones and the staff of the Phoenix Memorial
Laboratory for help in Neutron Activation Analysis. I wish to thank
W. Ullman and L. Hess for their help in data reduction and J. Gustinis for
the assistance in the design and fabrication of the sediment pore water
extraction system. Thanks are due M. Barron for the cadmium analyses and to
V. Hodge for the mercury and tin analyses.
Finally a tribute to those whose contributions too often go
unrecognized: the people who have had to read my handwriting and convert it
into recognizable English prose. I wish to thank L. Ayers, J. Thomas, L.
Trost, L. Gardner, and B. McClellan for their help in manuscript preparation.
Special thanks go to S. Schneider for his patience and help in producing this
document.
xx
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INTRODUCTION
This is the first in a series of three reports dealing with the
composition of recent sediments of Lake Huron and the rate of accumulation of
metal contaminants. The aims of the series are many and include: (1)
determination of recent sedimentation rates by both radiometric and other
means, (2) identification of elemental contaminants by examination of
concentration profiles in dated sediment cores, (3) development of contour
maps for the Lake which show the concentration of metal contaminants and
their historical and present rates of accumulation, (4) estimation of the
total amount of various contaminants stored in the sediments, (5)
identification of the origins of metal contaminants in selected cases and (6)
recognition and quantitative treatment of processes affecting sedimentary
records of radioactivity and metal contaminants and the exchange of
substances between sediments and overlying water. The results of the
research reported in this Lake Huron sediment series represent a natural
extension of the work of Thomas et al. (1973) who provided the first
extensive and systematic mapping of the surficial sediments of Lake Huron and
that of Kemp and Thomas (1976b) who provided the first limited exploratory
study of the distribution of metal contaminants in pollen-dated cores from
this Lake.
On the basis of extensive grab sampling and echo sounding, Thomas et al.
(1973) identified several major lithological units in Lake Huron: (1)
glacial till and bedrock; (2) glaciolacustrine clay; (3) postglacial mud and
(4) sand. The areas of sand, bedrock, till and glaciolacustrine clay are
considered as non-depositional. These areas are not currently receiving any
long-term input of sediments. Fine-grained materials entering the lake at
the present time accumulate primarily in the comparatively limited areas of
the Lake as shown in Figure 1. This is a very general feature of
sedimentation in the Great Lakes: accumulation is not uniform over the Lake
bottom. Instead, there is strong sediment focusing (cf. Lehman, 1975;
Kamp-Nielsen and Hargrave, 1978). In Lake Huron, less than half and perhaps
as little as a third of the area, receives modern sediments (see Table 1).
Postglacial muds occur in basins of three distinct types as indicated in Fig.
1: (1) Type A. Regular basins in which mud forms a continuous cover; (2)
Type B. Irregular basins with undulating bottom topography. Mud cover is
greater than 50%; (3) Type C. As for Type B but with mud cover less than
50%. Postglacial mud accumulation is continuous in the southern basins of
the Lake due to the gentle relief of the Lake bottom. In the northern region
of the Lake, mud accumulation is discontinuous due to the undulating nature
of the Lake bottom. Mud fills the hollows leaving glacio-lacustrine clay
exposed at the top of undulations in this region. As most metal and other
contaminants are associated with the fine-grained sedimentary materials, they
preferentially accumulate in the depositional basins in combination with
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Sand Alpeno
Undifferentioted till or bedrock
Glaciotacustrine clay (V*
Type A basin sediments (muds)
Type B basin sediments (muds >50%)
Type C basin sediments (muds<50%)
85W P'W 83'00'
Figure 1. Surficial sediment distribution in Lake Huron,
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postglacial muds. For this reason, emphasis is placed in the reports on the
composition of sedimentary materials within these depositional basins.
Each of the three reports deals with a specific area of Lake Huron as
indicated in Fig. 2. This report is concerned with southern Lake Huron as
defined by the enclosed rectangular region in Fig. 2. The second report in
the series is devoted to the sediments of lower Saginaw Bay and the third
report treats recent sediments of northern Lake Huron as indicated in each
case by the enclosed rectangular regions. The symbols in Figure 2 indicate
the locations of sediment sampling sites where, in general, multiple cores
were taken.
Within the southern Lake Huron study area, there are two principal
depositional basins, the Port Huron basin to the west having a mean depth of
88 m and the Goderich basin to the east, having a mean depth of 119 m
(Fig. 1). As can be seen in Fig. 3, these two basins reflect the bathymetry
of this part of tfhe Lake and are separated by a mid-Lake, north-south
trending escarpment referred to as the Ipperwash scarp (Thomas et al., 1973).
Along the escarpment there is no significant accumulation of postglacial
muds, and surficial deposits are characterized as a narrow band of
undifferentiated till and bedrock. Included within the southern Lake Huron
study area is a small portion of a lesser basin termed the Saginaw basin
located just beyond the entrance to Saginaw Bay. In southern Lake Huron
about 40% of the bottom is covered by Type A mud. Approximately 13% of the
total area corresponds to the Port Huron basin, which is contained entirely
within the study area. Approximately 27% of the area of southern Lake Huron
corresponds to the Goderich basin and approximately 90% of this basin is
contained within the study area (See Table 1). As can be seen in Fig. 4, the
sediment sampling sites have been chosen to provide extensive coverage of the
two primary depositional basins within the southern Lake Huron study area.
In comparison with previous work in this part of the Lake, the present study
represents a considerable advance. Kemp and Thomas (1976) based a whole-lake
contaminant metals inventory on only three dated cores from Lake Huron of
which only one was taken from the southern part. It is the intent of this
study to provide sufficient coverage of the depositional basins that there
can be an improved understanding of the variability of composition of
sediments within depositional basins and an improved accuracy and
comprehensiveness in mass-balance calculations for major and minor
sedimentary constituents and for metal contaminants in particular.
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46'Od
45'0tf
44-00
43"0(
84°00
83"00'
e2"00'
Figure 2. Sediment coring locations in Lake Huron.
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44°00
43°30
43°00'
EPA-SLH
Stations
October 1974
August 1975
SOUTHERN LAKE HURON
10
20 Miles
83°00'
82°30'
82°00'
8I°30'
Figure 3. Southern Lake Huron study area.
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TABLE 1. AREA OF SURFICIAL DEPOSITS IN LAKE HURON ( IN UNITS OF 1013 cm2)
Sediment Northern Lake
type1 Huron2
Sand 0.3
Undif ferentiated
till or bedrock 9.0
Glaciolacus trine
clay 6.2
Postglacial muds:
Type A 2.6
Type B 9.5
Type C 0.9
Undiffer-
entiated
Total areas 28.5
Southern Lake Georgian Saginaw Total
Huron2 Bay3 Bay^
2.6 - 2.5 5.4
2.5 5.317 0 16.8
0.6 8.20 0 15.0
3.86 - 0.36 6.8
0 - 0 9.5
0 - 0 0.9
5.29 - 5.29
9.5 18.8 2.8 59. 65
1 Based on the classification of Thomas et al. (1973).
2 Northern and southern portions divided along latitude 44° 15'N.
Data of Thomas et al. (1973).
3 Data from IJC (1977) p. 354.
* Based on the data of this study.
5 The total surface area of Lake Huron is 23,000 sq. mi. or 5.96 x 1014ctn2.
U. S. Dept. of Commerce, NOM-National Ocean Survey, General Great Lakes
Chart 0.
0 The area of the Port Huron Basin is 1.22 x lO^cm2,
and the area of the Goderich Basin is 2.59 x 1013cm2.
7 1.84 x 1013cm2 glacial till, plus 3.47 x 1013cm2, melange, bedrock,
till and glaciolacustrine clay.
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44°00' -
43°30
43°00'
SOUTHERN LAKE HURON
83°00'
82°30
8I°30'
Figure 4. Surficial sediment distribution in southern
Lake Huron.
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CONCLUSIONS AND RECOMMENDATIONS
Intensive coring combined with radiometric and multielement analysis of
carefully-sectioned cores has led to an improved view of the patterns and
processes of accumulation of sedimentary constituents in the two principal
depositional basins of southern Lake Huron. As a result of a combination of
factors including bathymetry, hydrodynamics, and the distribution of source
materials, the two basins are very different in character. The Port Huron
basin is comparatively inefficient as a collector of fine-grained materials
and associated m^tal contaminants. This is due partly to its lesser size and
to much lower sedimentation rates. In contrast, the Goderich basin is
roughly five times more efficient in accumulation of sediments. In addition,
there is a considerable degree of systematic variability in concentrations
and accumulation rates within this basin, partly as a result of the markedly
enhanced deposition of silt-sized materials toward the eastern margin.
The preferential deposition of fine-grained materials in limited areas of the
lake bottom, or sediment focusing, has been clearly demonstrated by the work
of Thomas and Kemp (1973). This report shows that rate of accumulation of
certain sedimentary constituents is even more sharply focused within
depositional basins. These general features are apparent in many of the
conclusions which follow.
Porosity profiles are generally exponential in shape within depositional
basins but tend to show discontinuities toward basin margins. Surface
sediments are least consolidated toward the escarpment side of the
depositional basins, and possess a maximum porosity of 0.9 or greater. In
the Goderich basin surface sediments are considerably more consolidated
toward the eastern margin and may have porosities as low as 0.6 or less.
The mean concentration of elements (37) determined in this study are
generally consistent with the limited concentration data published by others.
However, mean concentrations of contaminant elements tend to be somewhat
higher than previously reported and this is shown to be due to improvements
in the sampling methods adopted for this study. An exception is mercury,
which is found to be significantly less in the Port Huron basin than
previously reported. If not due to analytical or methods differences, this
result could imply a decrease in the amount of mercury stored in this basin
during the five-year period between surveys. Two major groups of elements
occur in surface sediments: the calcium family elements and those associated
with organic carbon and other fine-grained constituents. The calcium family
elements (Ca, Mg, and IOC) are strongly associated with each other and occur
in proportions which indicate dolomite as their primary source. The amount
of material which dissolves on acid treatment is principally composed of
dolomite plus organic carbon and iron compounds. In the Goderich basin up to
92% of the acid-soluble fraction is composed of dolomite. Subtraction of the
8
-------
dolomite fraction from the total amount which is acid-soluble leaves a
residual fraction which correlates well with the organic carbon and iron
content of surface sediments. Multiple linear regression of the residual
fraction soluble on iron and organic carbon concentrations indicates the mean
composition of organic carbon as C^O. A very high degree of correlation
exists between organic carbon and iron and other minor and trace
constituents. Hydrodynamic as well as geochemical processes result in the
co-deposition of trace constituents with fine-grained materials such as clay
minerals, organic carbon, and iron compounds. As a result, considerable
redundancy exists in the distribution of most non-calcium family elements in
surface sediments of the two depositional basins. The distribution in
surface concentrations of such elements as As, Br, Cd, Cr, Cu, Pb, Hg, Ni,
Th, Sn, U, and Zn are very similar and are highest toward the escarpment
sides of the depositional basins where sediments are least consolidated. In
contrast, the calcium family elements have the highest concentration in
surface sediments toward the eastern margin of the Goderich basin.
Of the 37 elements determined only a few exhibit an enrichment of
surface concentrations above background levels. Elements enriched in surface
sediments are, in decreasing order, Hg, Sn, Pb, Mn, Sb, As, Cd, Zn, Si, Ni,
U, Cu, and Br. The enrichment of Mn is confined to the upper 1 to 2 cm in
all cores and is probably the result of natural diagenesis. The enrichment
of Si (amorphous) may be either natural or the result of enhanced fixation of
soluble silicon in overlying water. Enrichments of the other elements
probably are due to recent anthropogenic loadings to the lake. The
concentration of Hg is four to five times higher in surface sediments than in
background sediments. Tin (Sn) is second only to Hg in terms of enrichment
and has a maximum concentration in surface sediments of about 6 ppm. On the
basis of profiles in dated cores, tin is recognized as a significant
contaminant. This study represents the first reported observation of tin as
a metal contaminant in sediments of the Great Lakes. As recent sediments of
Lake Huron are in general relatively less contaminated with metals than
sediments of lakes such as Michigan, Erie, and Ontario, it is likely that
appeciably higher concentrations may be found in certain sediments of these
other lakes. The degree of enrichment shows a systematic variation within
the depositional basins similar to that for surface concentrations of
non-calcium family elements. Hence, the degree of enrichment of elements is
not a unique characteristic of the lake or even of depositional basins but
shows nearly as much spatial variability as do element concentrations.
With the exception of Mn and possibly Si, concentrations of enriched
elements are subdivided into natural levels corresponding to concentrations
deep in cores (generally below about 15 cm) and anthropogenic concentrations
taken as the amount above natural levels. Vertically integrated
anthropogenic concentrations in individual cores indicate the total amount of
an element accumulated at a location resulting from human activity. The
greatest vertically integrated concentrations occur toward the center of the
Goderich basin. There has been relatively little accumulation of
anthropogenic elements in the Port Huron basin. The total storage of
anthropogenic elements in southern Lake Huron as of 1975 was 700, 2400, 1000,
and 3000 metric tons of Cu, Pb, Ni, and Zn respectively. For cesium-137, a
radionuclide produced by nuclear testing in the atmosphere, the total stored
-------
was about 400 Curies. This amount is less than the relatively well-known
decay-corrected deposition on the southern part of the lake since the mid
1950s (950 Curies). Over half the cesium-137 deposited on the lake surface
did not accumulate in underlying sediments. Without an inventory of the
entire lake, it is not possible to tell if this deficit is located in other
parts of the lake. An alternative possibility is that there is storage over
nondepositional areas. Only a few tenths gram of material per cm^ in the
water column overlying nondepositional areas is sufficient to achieve the
proper materials balance for this radionuclide.
Analysis of cesium-137, lead-210, and stable lead profiles in a large
number of sediment cores generally leads to self-consistent estimates of
recent sedimentation rates. The mean sedimentation rate in the Goderich
basin is 35.7 mg/cmVyr, while the mean rate in the Port Huron basin is
12.8 mg/cm^yr. These values imply that about 1 million metric tons of
fine-grained sediments are deposited annually, corresponding to a mean
area-wide sedimentation rate of 11.4 mg/cm^yr. Thus the mean accumulation
rate in southern Lake Huron is not greatly different from the main lake
average of 10 mg/cnrVyr reported by Kemp et al. (1974). A considerable
fraction (20%) of the material accumulating in the southern Lake Huron basins
is dolomite. Mass sedimentation rates on the eastern side of the Goderich
basin are very high as a result of intense deposition of dolomite. Within
this basin rates toward the escarpment side are under 20 mg/cm /yr while
values on the eastern side may exceed 100 mg/cm^/yr. High mass sedimentation
rates are associated with sediments which are relatively consolidated. As a
result, the distribution of the linear sedimentation rate (cm/yr) is very
different. Because of compaction, the linear rate is not uniquely defined in
a given sediment core but is taken in this report to be the average rate over
the upper 10 cm of sediment. This rate is very low in the Port Huron basin
(0.5-1 mm/yr) and also in the southern half of the Goderich basin. Highest
values are around 1.5 mm/yr in the northern section of the Goderich basin.
Both radioactivity and anthropogenic element profiles often possess a
zone at the sediment-water interface where concentrations are essentially
constant. This feature is interpreted as being due to the mixing of sediment
solids. A model developed for this report of rapid steady-state mixing over
a zone of well-defined depth accounts satisfactorily for observed profiles.
The vertical distribution of benthic macroinvertebrates in a series of
replicate cores from two locations (as well as data from Saginaw Bay)
indicates that benthos can be the active agents in sediment mixing
(bioturbation). Ninety percent of the benthos are located within the zone of
mixing as determined radiometrically. Because of sediment mixing, profiles
of cesium-137 are of limited usefulness in determining sedimentation rates.
The greatest depth of sediment mixing tends to occur toward the escarpment
sides of the depositional basins where sediments are least consolidated.
Sediment mixing may be the principal determinant of the resolution
attainable in reconstruction of historical events from sedimentary records.
The resolution is given approximately by the residence time of particles
within the mixed zone (the ratio of the mixed depth in g/cm^ to the
sedimentation rate g/cm^yr). On the average this time is about 20 years in
southern Lake Huron. The resolution varies systematically in the Goderich
10
-------
basin, decreasing to values less than 10 years in certain areas contiguous
with the eastern margin. Sediment mixing serves to increase the contact time
between contaminated sediments and overlying water. In the absence of
additional metal contaminant fluxes to sediments, concentrations in surface
sediments would be expected to decrease by about 5% per year according to the
steady-state mixing model. Because of sediment mixing, it is not likely that
any recent improvements in water quality will have as yet had a measurable
effect on sedimentary profiles in this area of the lake.
Stable lead profiles have been given particular attention in this report
and it has been shown that stable lead can be used as a geochronological
tool. Since lead profiles in radiometrically dated cores exhibit the same
time- dependence from one location to another, the local rate of deposition
may evidently be expressed in terms of separated variables: one part
containing the spatial dependence and the other containing the time variable.
This latter part is referred to as the source function. The source function
for lead is shown to be given in terms of the regional lead loadings
reconstructed from emissions inventories based on combustion of coal and
leaded fuel additives. This source function is essentially exponential over
the pertinent time period (from about 1900) and indicates a twenty year
doubling time for anthropogenic lead inputs. Application of the exponential
source function formalism to other anthropogenic element profiles indicates
that anthropogenic Cu, Sn, and Zn also have doubling times of about twenty
years. Anthropogenic Ni has a 14 year doubling time which may not be
significantly different. Mercury, on the other hand, has a 40 year doubling
time. This higher value is probably an artifact resulting from migration of
the element within sediments.
The rate of accumulation of an anthropogenic element is computed as the
product of the anthropogenic element concentration and the mass sedimentation
rate. Because the anthropogenic concentration has been increasing over time,
accumulation rates must be referred to a specific date. By means of the
steady-state mixing model and use of the exponential source functions, metal
contaminant profiles are adjusted so as to provide estimates of 1980
accumulation rates. To convert measured concentrations (1-2 cm interval) to
surface values (1975), the typical adjustment for the effects of sediment
mixing and finite-interval sampling is about 40%. Another 20% increase is
due to adjustment of values from 1975 to this report date (1980). The mean
anthropogenic accumulation rates (ug/cm^/yr) for southern Lake Huron are:
As (0.32); Br (0.24); Cd (0.022); Cu (0.24); Hg (0.002); Ni (0.42); Pb
(0.94); Sb (0.014); Si (79); Sn (0.047); Zn (1.3). Values refer to amounts
deposited per unit area of southern Lake Huron. The mean accumulation rates
are generally comparable to measured or estimated loadings from the
atmosphere. Direct municipal and industrial discharges as estimated by the
International Joint Commission (IJC, 1977) are far too low to be of
importance while tributary inputs often far exceed the measured accumulation
rates. Differences are undoubtedly due both to analytical problems with
tributary measurements and to insufficient distinction of chemical and
physical forms of the elements in the water samples. In general,
anthropogenic element accumulation rates tend to be highest toward the center
of the Goderich basin and show limited variability within the Port Huron
basin. The mean rate of accumulation of anthropogenic bromine is consistent
11
-------
with the lead data and suggests combustion of fuel additives as the primary
source. Because of the high degree of variability in the anthropogenic
element concentrations and accumulation rates within the Goderich basin
especially, inventories based on a single core or on a few cores can lead to
considerable error. On the other hand, because of the high degree of
correlation of anthropogenic constituents with organic carbon and iron, a
sampling and analysis scheme can be devised which takes optimal account of
these correlations in estimating anthropogenic sediment loadings.
The concentration of several elements in pore water are sensitive to
exposure to air. In addition to those of known sensitivity such as Fe, K>4
and Mn, additional sensitive elements include Co, La and Sb. Profiles of
some dissolved elements (Fe, Mn, PO^ and Si) exhibit large gradients either
at or just below the sediment-water interface. Very rough comparisons of
upward fluxes based on gradients at z=0 with excess accumulation rates
suggest a steady-state diagenetic cycle involving burial, dissolution, upward
migration and reprecipitation for Fe, Mn, and possibly P04. The P04 data are
of marginal quality because of air exposure effects. Careful calculations of
soluble reactive silicon fluxes (SRS) based on interstitial gradients at z=0
imply fluxes ranging from 750 to 1700 yg Si/cm^/yr. Such fluxes are
consistent with values obtained in postglacial muds of northern Lake Huron
(for the third in this report series) ranging from about 1000-2000 yg
Si/cnrVyr. If such fluxes are representative of annual average releases of
silicon to overlying water, then the sediments are a major source of SRS in
the water column. In two cores the outward SRS flux is matched by the
downward supply of available (amorphous) silicon. In two other cores the
outward SRS flux considerably exceeds the supply of available silicon.
Reasons for the imbalance are unclear. Relations between amorphous
(available) Si and that dissolved in pore water suggest a theoretical
treatment developed for marine sediments which can be modified to take
account of the finite range of bioturbation as encountered in sediments of
the Great Lakes.
The postglacial deposits of the Great Lakes serve as repositories for
particle-bound contaminants entering the Lakes. As seen in this report, the
sediments provide a literal "ground truth" for attempts to develop
contaminant mass balances and play an important role in some of the nutrient
cycles in the lakes. For these reasons the recent sediments should be
accorded considerable attention and effort should be made to obtain accurate
sedimentation rate information in cores in combination with measurements of
the vertical distribution of metal contaminants and available nutrient
elements such as PO^ and Si. Because of the recognition that the fate of
many toxic organic substances are also transported in association with
particulate matter, the distribution of organic constituents in carefully
dated sediment cores should also be undertaken not only for purposes of
reconstructing the history of organic pollutant accumulation (where
diagenesis may be neglected) but so as to properly model the role of the
sediments in the exchange of substances with overlying water.
This study has demonstrated the desirability of using several methods in
combination to obtain information on sedimentation rates and sediment mixing.
Of particular interest is the lead-lead-210 pair. As these two forms of lead
12
-------
have significantly different sources but probably the same geochemistry and
hydrodynamics in the lakes, lead-210 has the potential ability to serve as a
tracer for atmospheric lead contributions. This property should be exploited
not only in order to understand the behavior of lead contaminants in the
lakes but for the wider implications. Use of stable-radioactive element
pairs as well as radionuclides such as cesium-137 can play a very important
role in the calibration of ecosystems models of other pollutants such as
toxic organics. The preliminary mass balance for the cesium-137 suggests
that nondepositional areas of the lake should be examined for possible
boundary layer storage of contaminants.
The phenomenon of sediment mixing as identified previously in Lake
Michigan (Robbins and Edgington, 1975) is also occurring in sediments of Lake
Huron. As sediment mixing serves to prolong the contact time between
sediments and overlying water, this process may be an important factor in the
ability of lakes to resolve themselves following implementation of pollutant
abatement strategies. Laboratory studies should be undertaken to define the
role of natural benthos communities on the mixing of sediments and exchange
of substances across the sediment-water interface. Of particular interest
would be laboratory simulations of the role of benthos and sediment mixing on
the long-term exchange of contaminants with water.
As tin is shown to be a significant sedimentary contaminant, further
studies of the concentration and distribution of tin in selected areas of the
Great Lakes should be undertaken. Since tin can be converted to biologically
active organotin compounds by bacterial action, the chemical forms of tin in
sediments, water and biota should be investigated as should the potential
effect of such compounds on sensitive members of the biota in the Lakes.
\
Because of the importance of the sediments in the cycling of silicon in
the lake, realistic models of particulate and soluble silicon in sediments
need to be developed. Such models sould be tested by careful laboratory
studies of the kinetics of silicon dissolution as well as by concurrent
measurements of pore water concentration profiles and fluxes of silicon (SRS)
across the sediment-water interface.
13
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METHODS
FIELD METHODS
Sediment Collection
Sediment samples were collected at 65 stations in southern Lake Huron
(Table 2) during October 1974 and August 1975. The locations of sediment
sampling stations, shown in Figure 3, cover with considerable detail most of
the corable areas of southern Lake Huron. This can be seen in Figure 4 which
shows the location of stations in relation to the distribution of major types
of surficial sediments (Thomas et al., 1973). The locations are largely
within the two depositional basins (Port Huron, and Goderich basins) which
contain recently deposited muds with only a few stations located where there
are glaciolacustrine clays, or sandy and coarser deposits. Most of the cores
were taken in the Goderich Basin and only three were taken in the Saginaw
Basin (25, 71, 73) which mostly lies outside the study area (Figure 4). In
areas with coarse-grained deposits samples were collected by means of a Ponar
grab. Elsewhere, core samples were recovered using a 3-inch diameter (7.6
cm) gravity core (Benthos, Inc., N. Falmouth, Massachusetts). The inner
diameter of the core liners is 6.66 + 0.03 cm. (Area = 34.8 cnr). To
minimize disturbance of the surface sediments which are often extremely
loosely consolidated and flocculent, several steps were taken. The plastic
core liners were outfitted with a butterfly valve which presents little
resistance to water flow through the tube during descent of the corer through
the water column and during impact with the sediments. In addition, the
corer was lowered to a position 5-10 meters above the sediments before
allowing it to fall freely. Free fall from this position allowed the corer
to penetrate sediments at velocities over 1 m/sec. For cores of this
diameter minimum core distortion occurs for velocities over 1 m/sec. (Hongve
and Erlandsen, 1979). These procedures aided in the retreival of cores
possessing an interface remarkably intact. In some cases the delicate
detrital mounds produced by tubificid worms or by Chirononid larvae were
present in recovered cores (see also Robbins et al., 1977).
Sample Processing
The shipboard processing of cores and grab samples is summarized in
Figure 5. Sediment cores contained in plastic liners were placed on a
hydraulic extruding stand. The sediment column within the liner was forced
upward by filling the bottom of the liner with water under pressure. A
precisely controlled amount of sediment (+ 0.1 cm) was extruded into a
14
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TABLE 2. SOUTHERN LAKE HURON STATIONS
STATION NUMBER
EPA-SLH-74-3
EPA-SLH-74-4
EPA-SLH-74-5
EPA-SLH-74-6
EPA-SLH-74-7
EPA-SLH-74-8
EPA-SLH-74-9
EPA-SLH-74-10
EPA-SLH-75-10A
EPA-SLH-74-11
EPA-SLH-74-12
EPA-SLH-74-13
EPA-SLH-74-14
EPA-SLH-74-15
EPA-SLH-74-16
EPA-SLH-74-17
EPA-SLH-74-18
EPA-SLH-74-19
EPA-SLH-74-20
EPA-SLH-74-21
EPA-SLH-74-22
EPA-SLH-74-25
EPA-SLH-74-29
EPA-SLH-74-30
EPA-SLH-74-3 1
EPA-SLH-74-3 2
EPA-SLH-74-33
EPA-SLH-74-34
EPA-SLH-74-3 5
EPA-SLH-74-36
EPA-SLH-75-37
EPA-SLH-75-38
EPA-SLH-75-39
EPA-SLH-75-40
EPA-SLH-75-41
EPA-SLH-75-42
EPA-SLH-75-43
EPA-SLH-75-44
EPA-SLH-75-45
EPA-SLH-75-46
EPA-SLH-75-47
WATER DEPTH GROSS SEDIMENT
LOCATION (METERS) CHARACTERISTICS
43° 30.0' N
43° 40.0'
43° 40.0'
43° 40.0'
43° 40.0'
43° 45.0'
43° 45.0'
43° 50.0'
43° 50.3'
43° 50.0'
43° 50.0'
43° 50.0'
43° 55.0'
44° 00.0'
44° 00.0'
44° 00.0'
44° 00.0'
44° 05.0'
44° 05.0'
44° 10.0'
44° 10.0'
44° 15.0'
44° 15.0'
44° 15.0'
43° 35.0'
43° 35.0'
43° 55.0'
43° 30.0'
43° 25.0'
43° 25.0'
43° 15.4'
43° 20.0'
43° 20.0'
43° 22.5'
43° 25.0'
43° 25.0'
43° 25.0'
43° 25.0'
430 30.0'
43° 30.0'
43° 30.0'
82° 00.0' W
82° 25.0'
82° 16.3'
82° 04.0'
81° 55.0'
82° 20.0'
82° 00.0'
82° 25.0'
82° 28.5'
82° 16.0'
82° 05.0'
81° 55.0'
82° 07.5'
32° 30.0'
82° 19.0'
82° 10.0'
82° 00.0'
82° 29.0'
82° 15.0'
82° 15.0'
82° 05.0'
82° 55.0'
82° 15.0'
82° 05.0'
82° 20.0'
82° 00.0'
82° 20.0'
82° 22.5'
82° 22.5'
82° 00.0'
82° 07.4'
81° 55.0'
82° 00.0'
82° 02.9'
82° 09.2'
82° 02.6'
81° 55.0'
81° 50.0'
81° 50.0'
81° 55.0'
82° 05.0'
58
51
61
77
51
63
80
62
54
69
91
40
96
57
69
102
68
70
96
63
77
62
95
64
53
69
69
44
40
42
20
21
24
40
43
43
27
18
21
37
52
Gray Mud
—
—
—
—
—
—
—
—
—
—
—
Dr. Gray Silt
Red Sandy Clay
Dk. Gray Silt
Dr. Gray Silt
Dk. Gray Sandy Silt
Lt. Gray Sandy Mud
Dk. Gray Silt
Dk. Gray Silt
Pink Sandy Mud
Gray Silt
Dk. Gray Silt
Tan Sandy Clay
Gray Sandy Silt
Lt . Gray Sandy Mud
Gray Silt
—
—
Gray Sandy Mud
Sand
Brown Silty Sand
Olive Sandy Mud
—
Sand
Gray Mud
Olive Sandy Mud
Gray Sandy Clay
Gray Sandy Clay
Gray Sandy Mud
Dk. Gray Sandy Silt
(continued)
15
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TABLE 2. (continued)
STATION NUMBER
EPA-SLH-75-48
EPA-SLH-75-49
EPA-SLH-75-50
EPA-SLH-75-51
EPA-SLH-75-52
EPA-SLH-75-53
EPA-SLH-75-54
EPA-SLH-75-55
EPA-SLH-75-56
EPA-SLH-75-57
EPA-SLH-75-58
EPA-SLH-75-59
EPA-SLH-75-60
EPA-SLH-75-61
EPA-SLH-75-62
EPA-SLH-75-63
EPA-SLH-75-65
EPA-SLH-75-66
EPA-SLH-75-67
EPA-SLH-75-58
EPA- SLH-7 5-69
EPA-SLH-75-70
EPA-SLH-75-71
EPA-SLH-75-73
WATER DEPTH GROSS SEDIMENT
LOCATION (METERS) CHARACTERISTICS
43° 35. O1
43° 35.0'
43° 35.0'
43° 35.0'
43° 40.0'
43° 40.0'
43° 45.0'
43° 45.0'
43° 45.0'
43° 50.0'
43° 50.0'
43° 55.0'
43° 55.0'
43° 55.0'
44° 00.0'
44° 00.0'
44° 05.0'
44° 05.0'
44° 05.0'
44° 10.0'
44° 15.0'
44° 15.0'
44° 15.0'
44° 15.0'
82° 10.0'
82° 05.0'
81° 55.0'
81° 50.0'
81° 50.0'
82° 00.0'
82° 55.0'
82° 05.0'
82° 10.0'
32° 10.0'
82° 00.0'
82° 10.0'
82° 00.9'
81° 55.0'
81° 55.0'
82° 05.0'
82° 10.0'
82° 05.0'
82° 00.0'
82° 10.0'
82° 10.0'
82° 20. O1
82° 50.0'
83° 00.0'
46
58
43
21
21
73
46
73
64
76
64
67
76
40
37
73
91
82
55
91
82
91
61
58
Brown Mud
Gray Sandy Mud
Gray Sandy Clay
—
Brown Gravelly Mud
Gray Clayey Silt
Dk. Gray Sandy Silt
—
Dk. Gray Sandy Silt
Brown Clayey Sand
Brown Sandy Silt
Gray Sandy Mud
Gray Silt
Gray Sandy Silt
Gray Sandy Silt
Gray Sandy Silt
Gray Sandy Silt
Gray Mud
Gray Brown Sandy Silt
Gray Sandy Silt
Dk. Gray Sandy Mud
Gray Sandy Silt
Gray Sandy Mud
16
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CORES
GRABS
i
SECTIONING
COARSE / FINE
BENTHOS
SAMPLES
PORE
WATER
SAMPLES
L
SOLIDS-
LIQUID
i
Si 8 P04
ANALYSIS
Eh,pH
MEASUREMENTS
FORMALIN ACIDIFY/ FREEZE
REFRIGER-
ATE
PRESERVATION
REFRIGERATE
Figure 5. Shipboard collection and processing scheme,
17
-------
plastic collar made of a section of liner having centimeter graduations. By
this means even unconsolidated material could be sectioned without
appreciable loss of material and with adequate preservation of the
relationship between sediment depth and cumulative dry mass per unit area.
Two general sectioning schemes were used: (1) coarse sectioning; 1 cm
intervals to 14 cm, 2 cm intervals to 30 cm, and 5 cm intervals to a depth of
60 cm or to the bottom of the core; (2) fine sectioning; 0.5 cm intervals to
10 cm, 1 cm intervals to 20 cm, 2 cm intervals to 30 cm, and 5 cm intervals
to a depth of 60 cm or to the bottom of the core. Recovery of sediment was
quantitative for all one and two centimeter sections while only about half of
each 5 cm section was kept. The maximum time cores were allowed to stand at
ambient temperature before sectioning was one hour. Expansion of the cores
or the formation of gas pockets during this period was not significant
although such problems are significant in high sedimentation areas such as
the eastern basin of Lake Erie. Sediment sections were stored in preweighed
polyethylene bottles and frozen aboard ship.
Cores from four stations were sampled for interstitial water. The
method is described here very briefly as it has already been described in
detail by Robbins and Gustinis (1976). Immediately following collection, the
core in its liner was mounted on an extruding stand and a set of insulated
copper coils was slipped over the outside of the liner. The coils were
cooled by circulating a mixture of antifreeze and water using a constant
temperature pumping system (Lauda model K-2/RD). Sediments were extruded
into a glove box (550 cc volume) filled with nitrogen supplied by a
pressure-building dewar of liquid nitrogen which provided about 10^ 1 of N2
gas at STP. Within the glove box, sediments were transferred to a modified
(Robbins and Gustinis, 1976) gas-operated diaphragm squeezer (Reeburgh,
1967). A cross-sectional view of the squeezer is shown in Fig. 6. Pore
water was forced through a 0.45 micron 90 mm dia. Millipore filter under
about 100 p.s.i.g pressure. Approximately 30 ml of pore water was obtained
within 20 minutes from each one centimeter sediment section. A portion of
this sample was analyzed immediately for reactive Si and PO^ by
spectrophotometric methods described below while the remainder was acidified
with about 1 ml of ULTREX concentrated nitric acid and refrigerated for later
analysis.
At each of two stations in southern Lake Huron (EPA-SLH-75-14 and 18)
twelve cores were taken for determination of the composition, density and
vertical profile of zoobenthos. Each core was hydraulically extruded and
sectioned in 1 cm intervals to 10 cm within 30 minutes of collection. It is
presumed that short storage times reduced the extent of migration of animals
in response to altered conditions of temperature and light intensity. The
effect of coring and storage on the vertical distribution of benthos was not
investigated. Sediment sections were preserved with buffered formalin and
stored in plastic bags for analysis in the laboratory.
18
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Top clamp plate (aluminum)-
Top (Delrin)-
"0" Ring (Viton)
Gasket (Dental Dam rubber)-
Prefilter (70 mm Whatman 541}
Sediment Tray (Delrin)
Cemented support mesh (nylon)
"0" Ring (Won)
Membrane Filter (90 mm Millipore GSTF)
Support mesh (nylon)
Base (Delrin)-
Bottom clamp plate (aluminum)
I—I—h
Scale (cm)
10
Figure 6. Cross-sectional view of cassette sediment squeezer,
-------
LABORATORY METHODS
In the laboratory sediment samples were processed according to the
scheme indicated in Fig. 7. The analytical methods and measured quantities
are summarized in Table 3. Description of the methods below is organized by
sediment phase.
Analysis of Wet Sediment
Bulk Density
The bulk density of wet sediment was determined by weighing tared
bottles containing frozen sediments. Uncertainty in the bulk density is
largely due to inaccuracies in specifying the section thickness (j^O.l cm).
Hence the uncertainty is around 10% for 1 cm sections and 5% for 2 cm
sections. The data are provided in Table A-l of the Appendix.
Zoobenthos
Formalin-preserved wet sediment samples were suspended in approximately
one liter of tap water and sieved using a No. 10 Nitex screen (mesh size:
0.15mm). Organisms were isolated under 10X or greater magnifications.
Chironoimids and oligochaetes were identified under a compound microscope.
Additional information on methods can be found in Robbins et al. (1977) and
Krezoski et al. (1978). Based on previous sampling experience with
oligochaetes in deeper parts of the Great Lakes (S.C. Mozley, personal
communication) the estimated standard error in the vertically integrated
density is about 20% for analysis of twelve cores. This precision is
desirable for studies of benthic invertebrates (Elliot, 1971). Zoobenthos
data are given in Table A-6 of the Appendix. Standard errors in estimating
the vertical distribution of benthos can be very large (>100%) at some depths
because of the very low benthos densities and the large variability between
replicate cores.
Dry Sediment
Fraction Dry Weight
Weighed frozen sediment samples in preweighed polyethylene bottles were
freeze-dried for at least 4-5 days. Samples remained frozen during removal
of moisture even when additional heat was applied via hot plate to facilitate
drying. Following freeze-drying, samples were again weighed to obtain the
fraction dry weight, the cumulative dry weight per unit area of the core and,
by inference, the sediment porosity. Uncertainties in the estimate of the
fraction dry weight are less than 5%. Uncertainties in calculation of the
cumulative dry weight are around 10% or less provided the error in estimating
section thickness is truly random. Any systematic error involved in
sectioning the core will result in an increasing absolute error in the
estimate of the cumulative dry weight of sediment. The error in estimating
the porosity which is calculated from the fraction dry weight assuming a
constant density of sediment solids ( Ps = 2.54 g/cm^) is 15% or less.
20
-------
FROZEN SAMPLES
FROM CORES
WEIGH
FREEZE DRY
IDENTIFY AND
COUNT BY
MICROSCOPE
(MACROINVERTEBRATES)
[WEIGH
~
HOMOGINIZE
SOLIDS
LIQUID
GASOMETRIC
ANALYSIS
(TOTAL 8 INORGANIC
CARBON)
GAMMA SPECTROSCOPY
(CESIUM-137)
ACID/PEROXIDE
DIGESTION
I I
SOLIDS LIQUID
WEIGH
(INSOLUBLE
FRACTION)
NEUTRON ACTIVA-
TION ANALYSIS
Ag,AJ,As,Ba,Br,
Ca.Ce.Co, Cr, Cs,
Eu.Fe.Hf.Hg, K,
La, Li, Mn,Na, Ni,
Rb, Sb,Sc, Se, Sm
Th, Ti.U, V, Yb
EVAPORATE TO
DRYNESS
REDISSOLVE IN HCl|
ALPHA PROPORTIONAL
COUNTING
(LEAD - 210)
ATOMIC ABSORPTION
SPECTROPHOTOMETRY
Ba, Co, Cd, Cr, Cu,
Fe, K, Mg, Mn, No,
Ni, P, Pb, Sr, Zn
SIEVING AND
PIPETTE ANALYSIS
(GRAIN SIZE
DISTRIBUTION)
Figure 7. Sample analysis scheme.
-------
TABLE 3. A SUMMARY OF THE PHYSICAL AND CHEMICAL PARAMETERS DETERMINED
FOR SEDIMENTS OF SOUTHERN LAKE HURON AND SAGINAW BAY
Sediment Fraction
Parameter
Method
1. Wet sediment
2. Dry sediment
3. Acid-peroxide
extracts
4. Base extracts
5. Pore water
a. bulk density
b. zoobenthos
c. Eh/pH*
d. grain size*
weighing
sieving/microscopic study
electrode
sieving/pipette
a. fraction dry weight, weighing
cumulative mass per unit area
b. cesium-137
c. Trace elements Ag, Al, As,
Ba, Br, Ca, Ce, Co, Cr, Cs,
Eu, Fe, Hf, Hg, K, La, Lu,
Mn, Na, Ni, Rb, Sb, Sc, Se,
Sm, Th, Ti, U, V, Yb
d. Organic/Inorganic Carbon
a. Fraction soluble
b. Trace elements: Ba, Ca, Cd,
Cr, Cu, Fe, Hg, K, Mg, Mn,
Na, Ni, P, Pb, Sn, Sr, Zn
c. lead-210
a. Amorphous silicon
a. Reactive Si and P04
b. Trace elements: Ba, Ca, Fe,
Mg, Mn, K, Na, Sr, Zn
gamma spectroscopy
neutron activation
analysis (NAA)
gasometric
centrifuging/weighing
atomic absorption
spectrophotometry (AAS)
alpha proportional
counting
colorimetric
colorimetric
(AAS)
*for Saglnaw Bay samples only
22
-------
Fraction dry weight, cumulative dry weight and porosity data are given in
Table A-l of the Appendix.
Cesium-137
The cesium-137 activity of sediment samples was determined by gamma
spectroscopy using a well-shielded 3x5 inch Nal(Tl) crystal gamma detector
connected to a multichannel analyzer (Nuclear Data 100). Prior to counting,
sediment samples were ground by mortar and pestle and compacted into a
cylindrical plastic container. Standardization of the sample geometry is
necessary for accurate measurement of absolute activity. The cylindrical
configuration of sediment was placed concentrically on the axis of the
detector several millimeters from the crystal face and counted for times
ranging from 2 to 60 hours. Standards of the same geometry were prepared by
doping inactive sediments with known amounts of cesium-137 (Amersham Searle
Corp.). Doped samples were then counted to obtain the counting efficiency of
the system for different sample volumes (variable height, constant
cross-sectional area). The total activity of cesium-137 (vertically
integrated) is given in Table 36 while vertical distribution data are given
in Table A-4 of the Appendix. Uncertainties indicated refer only to the
Poisson statistical error in counting the sample. Other sources of error are
negligible.
Trace Elements (via neutron activation analysis, NAA)
Up to 25 trace elements were determined in portions of freeze dried
sediments via non-destructive neutron activation analysis using the Ford
Nuclear Reactor at the Phoenix Memorial Laboratory (University of Michigan,
Ann Arbor, Michigan). Both pneumatic-tube and in-pool irradiations were
carried out. The pneumatic tube method is applicable to measurement of
elements with half lives the order of a few hours or less where short
exposure times are required. In-pool irradiations involve insertion of
samples into the core of the reactor to obtain maximal thermal neutron
fluxes. This method is used to achieve long exposure times for measuring
elements with long half lives.
For the pneumatic-tube irradiations, 50-75 mg splits of each sample,
ground well to avoid homogeniety problems, were weighed into small
polyethylene vials. For each four such samples, two comparative standards
were prepared: U.S. Geological Survey Standard Rock Sample USGS-BCR-1; (See
Flanagan, 1973) and PML primary standard. Samples and standards were
initially irradiated for 25 seconds at a thermal neutron flux at about lO1^
n/cm^/sec, allowed to undergo decay for 20 minutes, and counted for 30
seconds. When all residual activity from the 25 second irradiation had
decayed (in 3 to 4 days), four samples and two standards were again
irradiated, this time for 10 minutes, allowed to decay for 12 hours and
counted for 400 seconds. The first irradiation yielded data for Al, Ca, Mn,
Ti and V. The second provided a measurement of K, Na and Mn.
For the in-pool irradiations, 60-70 mg portions of four sediment samples
and two standards were weighed into ultra-pure Synthetic quartz tubing
(Suprasil T-21, Amersil, Inc., Hillside, New Jersey). Standards used were
U.S.G.S. rock samples, USGS-BCR-1 and USGS-RGM-1. The quartz tubes
containing sediments or standards were flame-sealed and groups of seven were
Irradiated for ten hours within the core at a thermal neutron flux of about
23
-------
1 O
10 n/cmVsec. then allowed to decay for eight days. Following this
"cooling" period, samples were separated, the outside surface of the quartz
tubes cleaned, dried and counted for 1800 seconds. After two weeks,
following decay of the intermediate lived isotopes, the samples were counted
for 7200 seconds to obtain data for the long-lived constitiuents. The first
counting yielded data for Ag, As, Ba, Br, La, Lu, Na, Ni, Rb, Sc, Sm, Th, Yb
and U. Second counting provided a measurement of Ce, Co, Cr, Cs, Eu, Fe, Hf,
Hg, Sb, Sc and Se.
A specially prepared sample of standard lake mud (SLM-1) was analyzed
via this method (NAA) to ascertain the reproducibility of the method. A
large (>10 1) sample consisting of the upper 20 cm of several cores of
fine-grained sediment from Lake Michigan was placed in a multilayered
polyethylene bag and homogenized thoroughly by kneading the outside of the
bag. The sample was then frozen and on return to the laboratory was
freeze-dried, ground in a mortar and pestle, sieved to 250 mm mesh size and
split into sixteen subsamples using a conventional riffle sample splitter.
Two subsamples, SLM-1-1 and SLM-1-10 were further subdivided into 4 and 3
splits respectively for a total of 7 replicate NAA analyses. In each case
about 200 mg of sample was irradiated. These original analyses were
completed in early 1976; in Jan. 1978 a 200 mg sample of SLM-1-1 was
re-analyzed by the method thus providing another replicate sample.
Gamma spectra were obtained using an lithium-drifted germanium detector
(Ortec, Inc., Oak Ridge, Tenn.) having a resolution of 2.0 - 2.3 Kev fwhm for
the 1332 KeV cobalt-60 gamma ray. Intrinsic detector efficiency is about
12-15%. The detector was interfaced to a semiautomated nuclear data 4420
minicomputer pulse height analysis system. Spectral data were stored on
magnetic disk immediately following the end of each counting period and
subsequently reduced by computer. Details of the irradiation procedures,
sources of uncertainty, corrections for interferences and data reduction
methods are given, by Dams and Robbins (1970). The reliability of the method
is discussed further below.
Total and Inorganic Carbon
A gasometric technique was used to obtain the total and inorganic carbon
content of the sediment samples. Total carbon was determined by combustion
of 2-3 grams of sediment. The C02 evolved is assumed to result from complete
oxidation of organic carbon and conversion of inorganic carbonate to C02-
The procedure was carried out using the LEGO carbon analyzer (Furnace Model
No. 507-100 and Volumetric System Model No. 572-200). Inorganic carbon was
determined on the same system by titrating the sediment with acid to evolve
C02 from the carbonate phases. The organic carbon content is inferred to be
the difference between total and inorganic carbon.
The precision of the method (e.g. Kolpack and Bell, 1968; Bien, 1952)
was examined by analyzing 15 standard lake mud samples (SLM-1-8). The
average value of total organic carbon was 5.45 +_ 0.15 percent by weight.
Thus the standard deviation in the estimate of the mean is about 3% (Table
6). There is an additional source of uncertainty which must be built in to
the overall error which results from variable uptake of moisture by
sediments. Before processing, sediments were first dried at 100° C for 24
24
-------
hours. The reduction In weight for Standard Lake Mud (SLM-1-8) was 1.5%.
This was not corrected for in estimating the total carbon concentration
because the re-uptake of moisture after drying but before combustion was not
determined. Hence the overall error (including calibration errors) in
estimating the total carbon content of a single sample is probably less than
10%.
The method for inorganic carbon analysis follows that described by
Kolpack and Bell (1968) with the following exceptions: (1) 10 ml of 2N HC1
were added per gram of sample, (2) 4 ml of 5% FeS(>4 were added to each sample
and (3) a temperature of 70-80° was maintained throughout digestion.
Analyses of CaC03 and standard lake mud samples indicate the overall error in
estimating inorganic carbon in a single sample to be less than 5%. The mean
concentration of inorganic carbon in six replicate samples was 3.26 + 0.07
percent by weight.
All measurements were corrected for temperature and pressure
variations. The organic and inorganic carbon data are given in Table 9.
Acid - peroxide Extracts
Soluble Fraction
A slurry of 2-3 g of ground freeze-dried sediment and 25 ml of distilled
water was prepared in 250 ml glass beakers. 25 ml of cone. HN03 are added
slowly to control the extent of foaming. After foaming subsided, 5 ml of 30%
y.2^2 were carefuly added. The beakers were then covered with watch glasses
and placed in an 30-95° C water bath for 96 hours. 5 ml 30% 1^02 were added
every 24 hours. Following this sequence, the watch glasses were removed and
the mixture was evaporated to near but not complete dryness (i.e. about 2 mm
of solution on top of settled sediment). Evaporated samples were removed
from the bath, allowed to cool and combined with 10% HN03 into 50 ml
pre-weighted (+0.0001 g) centrifuge tubes. The tubes were spun for 20 min at
1800 rpm, the supernatant decanted and the sediment residue resuspended with
a few ml of HN03 and the mixture recentrifuged. The rinse supernatant was
combined with the original supernatant and the entire volume was diluted to
100+0.02 ml with 10% HN03. Half of this solution was set aside for AAS
analysis while the remaining solution was bottled separately for lead-210
analysis. The sediment residues in the centrifuge tubes were dried at 100° C
overnight, weighed (+_ 0.0001 g) and stored in labeled Whirlpack^™) bags.
The fraction soluble is computed as the ratio of the original sample
weight minus the weight of this residue divided by the original sample
weight. The uncertainty in the estimate of the fraction soluble can be as
high as 15% because of the uncertainties in recovery and in weighing the
sample residue. Data on the fraction soluble are given in Table 9.
Trace Elements (via Atomic Absorption Spectrophotometry, AAS)
The concentration of up to 16 elements (Ba, Ca, Cd, Cr, Cu, Fe, K, Mg,
Mn, Mo, Na, Ni, P, Pb, Sr, and Zn) in sediment acid extracts and up to 11
elements (Ba, Ca, Fe, K, Mg, Mn, Ni, P, Si, Sr, and Zn) in interstitial
waters were determined by Atomic Absorption Spectrophotometry.
25
-------
Determinations of all elements except Cd were made on a Perkin-Slmer, Model
403 Spectrophotometer according to the standard conditions recommended for
flame atomization in the Perkin-Elmer Operating manual (Perkin-Elmer Corp.,
Norwalk, Connecticut). Where necessary, dilution of extracts were made using
10% HN03- Cd concentrations were obtained by flameless atomization using a
Varian Technion Model 1200 Atomic Absorption Spectrophotometer with a Model
60 Carbon Rod Atomizer (Varian Inc., Palo Alto, California).
Phosphorus concentrations were measured by the addition of an ammonium
molybdate tetrahydrate solution to the acid extracts and the subsequent
extraction of the resulting phosphomolybdic acid by iso-butyl acetate. The
concentration of phosphorus could then be determined by measuring the
absorption of Mo by AAS. This method is described in detail by Ramakrishna
et al. (1969).
Toward the completion of this report it became feasible to analyze a
number of samples for two additional elements, mercury and tin. New portions
of freeze-dried material were allowed to leach in 6M HC1 for about one month.
Comparison of lead concentrations in samples from core ISA determined from
50% HN03 leaches made in 1977 with those determined in recent (Marc, 1980)
6 M HC1 extraction gave the following results:
Pb (1980 HC1 leach) = 1.010 x Pb (1977 HN03 leach) - 3.9
with r = 0.995 and N = 10.
On the average there was a 6 (+5) percent difference in concentrations of
lead as determined in separate portions of samples extracted by different
methods, and analyzed by different people on different atomic absorption
instruments. Concentrations of mercury were determined by means of the
cold-vapor method described by Lawrence et al. (1980). One ml of the lechate
was sonicated after addition of SnCl2 and Hg vapors produced by this method
were flushed into a cold vapor tube for analysis via AAS. Concentrations of
tin were determined by reaction of the lechate with NaBH4 to produce volatile
tin hydrides which are detected via AAS. The method is essentially
interference-free and capable of determining subnanogram quantities of Sn(IV)
and the halides of many organotin compounds. As used here, the method gave
values for total Sn(IV) concentrations. The method is described in detail by
Hodge et al. (1979). Concentrations of mercury and tin in surface sediments
are given in Table 12. Atomic absorption data for the other elements are
given in Table 9 and in A-2 of the Appendix. Concentrations of dissolved
constituents determined primarily via AAS are given in Table A-7.
Lead-210
The lead-210 activity of the sediment samples was determined by
measurement of the alpha activity of its daughter, polonium-210. It is
assumed that polonium-210 and lead-210 are in secular equilibrium in each
sediment sample so that the activity of polonium-210 is exactly equal to the
activity of lead-210. In most samples this condition will be met
automatically because the age of the sample is large in comparison with the
half-life of polonium-210 (138 days) and because neither lead-210 nor
polonium-210 have appreciable mobility in the sedimentary column. Therefore
in physically undisturbed sediments, each layer (subsample) is a closed
26
-------
system with respect to these two isotopes (see Rabbins, 1978). Eakins and
Morrison (1974) found evidence of polonium-210/lead-210 disequilibrium in
near surface sediments but the effect is small. The long storage time of
isolated sediment sections prior to analysis (about 1 year) favors
establishment of secular equilibrium even in sections where the possibility
exists of a small degree of in situ disquilibrium.
The method of determining the activity of polonium is adapted from the
procedure of Holtzman (1963), Flynn (1968), and Robbins and Edgington (1975)
which takes advantage of the ability of polonium to selectively self-plate
onto polished silver discs. The 50 ml extract of the sample (in 10% HN03)
set aside for Pb-210 analysis, was dried at a temperature of 90° C. Then 10
ml of concentrated HC1 and a few drops of H202 were added and the sample
re-evaporated to dryness. Caution was taken to keep the temperature at or
below 90° C. Polonium chloride sublimes at 190° C. The steps of adding HC1
and H202 and evaporation were repeated twice for a total of three
evaporations to dryness with HC1 to thoroughly eliminate traces of N03 ions.
Their presence in strong acid will cause etching of the silver disc and
prevent complete self-plating of polonium. The extract was then dissolved in
10 ml of hot 10% HC1, and 1.0 gram of ascorbic acid plus 10 ml of distilled
water was added. The pH was adjusted to 1.4 j^ 0.1 by addition of
concentrated NIfyOH via pipette. This solution of less than 40 ml final
volume was then transferred to plating containers made from 8 ounce "Nalgene"
square linear polyethylene wide-mouth bottles. A 1 ml Eppendorf pipette tip
inserted through a hole in one of the bottom corners of the bottle served as
a stopper and vent.
Approximately 1/8 inch of bottle tip was removed and smoothed by
pressing on a hot plate, trimmed and ground flat with 0.7 micron abrasive. A
washer intended for 3/4 in bolts inside the bottle cap served to press a
0.005 inch thick 1.5" diameter silver disc against the ground surface to
create a seal. The silver discs (Handy and Harmon Corp., New York, New York)
were polished by means of a slurry of 0.3 micron "Alpha Micropolish" (Bueler
Inc.). Each container was rinsed with distilled water and then with 10% HC1
prior to filling with pH adjusted extracts. The plating containers (15) were
installed in a water bath shaker (Eberbach, Co.) and shaken for two hours at
85-90° C. Efficiency of plating was occasionally checked by replating the
solution. The ratio of the activity on second plating to that on first
plating indicated an efficiency consistently better than 90%. Then
containers were disassembled and silver discs were rinsed first with
distilled water, then with methanol and counted on a 2-pi gas-flow
proportional counter (NMC Model DS-2P, Sealer and PCC-11T proportional
counter, Nuclear Measurements Corporation, Indianapolis, Ind.). The
efficiency of the counter was determined using a standard lead-210
(polonium-210) source. Raw counts are corrected for decay of polonium
following plating and converted into absolute activity per unit weight of
sediment (pCi/g). Lead-210 data are given in table A-5 of the Appendix.
Uncertainties indicated refer only to the Poisson statistical error in
counting the sample. The overall uncertainty is significantly larger because
of the variability in plating efficiency. The estimated error introduced by
this factor combined with other sample processing errors yields a 10% error
which must be combined with the counting error provided in table A-5.
27
-------
Basic Extracts
Amorphous Silicon
To determine the amorphous silicon content of the sediments a modified
version of the method of Mckeys et al. (1974) was used. The method takes
advantage of the differing rates of dissolution for various forms of silicon.
Authigenic particulate silica, diatoms and possibly other non-crystalline
(amorphous) phases (see Nriagu, 1977) dissolve rapidly (within one to two
hours) in 0.5N NaOH at room temperature. In contrast, silicon associated
with clay mineral dissolves under such conditions at a very much slower rate,
while silicon as quartz is resistant to dissolution to any significant degree
over time periods of 6 hours or so.
In the method of McKeys et al., sediment samples are treated
alternatively with strong acid and weak base. They found that alternating
acid-base treatment dissolved more amorphous silica than the base treatment
alone. McKeys et al. conjectured that strong acid removes iron and other
metal coatings on surfaces of amorphous silica which hinder dissolution (see
also Hurd, 1973). Because of time constraints, the alternating acid-base
treatment was not followed. Rather, samples were pre-treated with acid as a
one shot exposure. It was found that the difference between a one shot
exposure and alternate acid-base treatments was not large. The latter
treatment dissolved about 10% more amorphous silicon than the single acid
treatment (SLM-1-8).
30 mis of 8N HC1 were added to poly-propylene centrifuge tubes
containing 0.1-0.4 g crushed dried sediment previously squeezed to obtain
pore water. After 30 minutes, the mixture was centrifuged, the supernatant
discarded and the sediment washed with distilled water and transferred to a
polyethylene bottle with 200 ml 0.5N NaOH. The bottle was tightly capped and
agitated on a rotary arm shaker at room temperature. Approximately each
hour, 4 ml of solution were removed via polyethylene syringe, filtered
through a 0.45 micron filter and stored at 40° C.
After about six hours a suite of filtered samples were analyzed for
reactive dissolved silicon colorimetrically (Bausch and Lomb Spec 100
Spectrophotometer) using the method outlined by Strickland and Parsons
(1960). The method was modified for use with 0.5N NaOH rather than water.
Analysis of replicate samples indicated an overall error of about 10% in
estimating the amount of reactive dissolved silicon in solution.
The amorphous silicon concentration was estimated by extrapolating the
amount of silicon dissolved per gram of dry sediment back to zero time.
Error in replicating of the amorphous silicon content is around 15%. Limits
to the acccuracy of the method are discussed below.
28
-------
Pore Water
Reactive Si and P04-
The concentration of dissolved reactive phosphate and silicon in pore
water was determined colorimetrically by the method of Sutherland et al.
(1966). Samples were stored under refrigeration (4° C) for not more than
about two hours following sediment "squeezing". A mixed reagent of ammonium
molybdate and potassium antimony tartrate was used to form a blue
phosphomolybdate complex for the determination of phosphate. Absorbance was
measured at 690 nm. An ammonium molybdate solution was used to complex the
reactive dissolved silicon. The absorbance of the resulting yellow
silicomolybdic complex was measured at 400 nm. Shipboard colorimetric
determinations were made on a Bausch and Lomb Spectronic 100
Spectrophotometer (Bausch and Lomb, Rochester, New York). Analytical
uncertainty in silicon and phosphate concentrations are generally around 10%
and 15% respectively. Limitations in the accuracy of the methods are further
discussed below.
Other Constituents
The concentrations of Ba, Ca, Fe, Mg, Mn, K, Na, Sr and Zn were
determined using Atomic Absorption Spectrophotometry (Perkin Elmer 403
spectro- photometer). As sample volumes were extremely limited, replicate
analyses were not possible. However the approximate uncertainty of
replication can be inferred from comparison of concentrations in a set of
contiguous pore water samples toward the bottom of sediment cores where real
variations should be negligible. Analysis of 1-6 such samples shows that the
replication error is roughly 20% for Ba, 5% for Ca, 10% for Fe, under 5% for
Mg and Mn, about 30% for P04, 10% for K, under 5% for Si, about 5% for Sr and
over 40% for Zn. The high uncertainties for Ba and Zn arise because
concentrations are near the limits of detection. The high value for P04 is
probably at least in part due to air exposure effects discussed further below.
Accuracy of Results
Neutron Activation Analysis
The results of analysis of seven replicate s.tandard lake mud samples are
given in Table 4. It can be seen that the precision of the analytical
results is excellent for most elements. The percent deviation from the mean
is mostly under 10% and only a few elements have concentrations deviating by
more than 20% from the mean. With 7 replicate analyses, the error in
estimating mean concentration of most elements is better than 5% and all
elements are determined to better than 10%. There is no significant
difference between mean concentration of split 1 and split 10 for any
specific element. However, taken as a whole, mean concentrations are 2%
higher in split 10 (weighted average) than in split 1. As the samples were
analyzed randomly it is unlikely that this systematic variation arises from
differential treatment of samples or standards. Most likely it is the result
of sample inhomogeneity.
The reproducibility of the neutron activation method was further
29
-------
TABLE 4. COMPOSITION OF STANDARD LAKE MUD SAMPLES (SLM-1-1 AND SLM-1-10)
DETERMINED VIA NEUTRON ACTIVATION ANALYSIS (CONCENTRATIONS IN yg/g DRY WEIGHT)
CO
o
Element
AI
As
Ag
Ba
Br
Ca
Ce
Co
Cr
CR
Eu
Fe
Hf
Hg
K
La
Lu
Mg
Mn
Na
Ni
Rb
Sb
Sc
Sc
Se
Sm
Th
Tl
U
V
Yb
1
53596
3.64
<2.38
439
45.2
70397
53.4
11.94
81.7
4.38
0.99
33288
4.37
•CO. 10
22088
25.8
0.36
37381
600
5003
<64.3
100.6
1.00
9.54
9.54
<5.5
4.66
7.04
2344
2.26
76.86
2.35
SLM-1-1
Subsample
2 3
52375
7.97
<1.94
361
38.4
52846
51.7
11.79
97.3
5.23
0.89
32347
4.08
<1.17
15442
27.0
0.36
26225
572
4702
O5.1
75.6
1.08
9.23
9.55
2.99
4.73
8.45
3656
3.94
68'. 9
2.85
48332
<10.0
<2.00
526
40.8
70321
51.5
11.95
87.9
4.86
0.94
33912
4.22
<1.39
23754
27.4
0.51
27113
689
4754
<72.1
57.5
1.76
9.52
9.43
<2.77
4.52
7.10
3402
4.68
60.7
1.99
4
53193
<10.3
<2.02
290
38.6
77576
48.1
11.64
87.9
4.38
3.87
32598
4.10
<1.41
21734
26.1
0.45
25865
597
4514
<72.3
70.4
1.85
9.27
9.28
<2.S1
4.46
6.75
3312
3.68
75.0
1.94
Mean Standard
N=4 dev .
51874
8.0
-
400
41.
70310
51.2
11.8
88.7
4.71
0.92
33036
4.19
-
21005
26.6
.42
29145
539
4758
-
75.3
1.42
9.39
1.45
-
4.6
7.3
3219
4.0
68.3
2.3
ni5
3.0
-
100
4.0
6055
2.2
0.15
6.4
o.4i
0.05
705
0.13
-
3167
0.8
0.08
5515
63.0
167
-
18.0
0.44
0.16
0.13
-
0.1
0.3
664
1.0
6.7
0.4
1
53135
<10.5
<2.08
488
42.7
74349
51.1
12.45
92.8
4.94
0.9?
34522
4.65
<1.43
24277
27.4
0.5'
27364
553
4704
<74.17
73.9
1.90
9.83
9.53
<2.88
5.15
7.59
4290
3.34
7i.4
2.04
SLM-1-10
Subsample
2 3
54175
<10.4
<2.05
566
43.0
59417
52.7
12.13
88.9
4.82
0.91
33392
4.32
<1.43
20496
28.3
0.54
27898
566
4535
<74.4
66.0
2.21
9.51
9.53
<2.86
5.05
7.48
2905
3.41
83.1
2.00
53839
6.82
<2.02
370
37.4
65871
54.6
12.08
85.2
4.08
0.89
32921
3.60
<1.07
26668
27.7
0.31
28716
589
6670
<56.8
73.39
1.25
9.38
9.55
2.75
4.47
7.16
4382
5.57
104.9
2.22
Combination
Mean Standard
N=3 dev .
53716
9.2
-
475
41.0
69879
52.8
12.2
89.0
4.61
0.91
33612
4.19
-
23814
27.8
0.47
27993
574
5303
-
71.1
1.79
9.56
9.55
-
4.89
7.41
3879
4.11
87.1
2.09
530
2.1
-
98.7
3.15
4257
1.75
0.20
3.8
0.47
0.02
822
0.54
-
3112
0.46
0.15
681
12.7
1187
-
4.4
0.49
0.25
0.03
-
0.37
0.22
793
1.27
16.1
0.12
Mean Standard
N=7 dev .
52700
5.14
-
434
41.0
70100
51.9
12.0
88.8
4.57
0.91
33300
4.19
-
22200
27.10
0.44
28700
654
5000
-
74.1
1.58
9.46
9.25
-
4.72
7.37
3510
3.84
76.4
2.20
2000
2.24
-
99
3
5000
2.0
0.3
5
0.4
.04
800
0.3
-
3000
0.9
0.1
4000
50
800
-
13
0.5
0.2
0.8
-
0.3
0.6
700
1.0
14
0.3
%
dev.
4
36
-
23
8
7
4
2
5
9
4
2
8
-
15
3
22
14
7
15
-
18
29
2
8
-
6
8
21
27
19
15
% error
in ave.
est.*
1.4
12.5
_
8.0
2.8
2.5
1.4
0.7
2.1
3.2
1.4
0.7
2.8
_
5.3
1.1
7.7
4.9
2.5
5.3
-
6.3
10.1
0.7
2.8
-
2.2
2.8
7.4
9.5
5.7
5.3
*100 *
* standard Deviation/mean
-------
investigated by reanalysis of the standard lake mud sample (SLM-1-1) two
years later. The results are summarized in Table 5. In general, the long
term reproducibility is good. Agreement with the mean concentrations is
usually better than 10%. Thus the level of precision survives variability in
laboratory techniques, use of new standards and minor modifications in
analysis of raw data over a two year period. Only for one element, Lu, is
the reproducibility poor. Reasons for the significantly lower value on
reanalysis are obscure but are probably due to use of new PML or USGS
standards in combination with interferences which affect the accuracy of the
results.
To investigate the accuracy of the method five USGS, rock standards
other than BCR-1 and RGM-1 were analyzed as unknowns. The "unknowns" were
two samples of USGS-GSP-1, two USGS-G-2 and one sample of USGS-AGV-1. A
measure of the accuracy of the determination is given as
N
(100/N) E^
where C^ is the measured concentration of a given element in the itn standard
while CA is the accepted concentration of the itn standard (N=5). Thus Q^ is
the mean percent deviation from accepted values. This value may be compared
with the mean deviation of the concentration of a given element (C^) in SLM-1
samples (N=7) from the mean concentration (C)
N
(100/N) I (C. - C) / C (2)
This measure of the precision is compared with the measure of accuracy in
Figure 8. It can be seen that for most elements both Q^ and Qp are under
10%. Exceptions occur for Ba and Lu where the precision is significantly
less than the accuracy of the method and for Cr, Sb, and particularly for U
where the accuracy of the method is considerably poorer than the precision.
For these elements there are probably significant uncompensated interferences
which limit the validity of the results. There may be an accuracy problem
with Br as well. In most rock standards values of Br are unspecified.
Results of an additional analysis of AGV-1 given in Table 5 show a
dramatically higher measured concentration than the accepted value. Yet,
bromine can be determined via NAA without interferences. Moreover
contamination is unlikely to have occurred. Furthermore analysis of Br in
SLM-1 samples gives a mean concentration (41 ppm) which is very comparable to
31
-------
TABLE 5. RESULTS OF A SECOND ANALYSIS OF STANDARD LAKE MUD (SLM-1-1) AND OF A
U.S. GEOLOGICAL SURVEY ROCK STANDARD (AGV-1) BY NEUTRON ACTIVATION ANALYSIS
Concentration (Mg/g)
Element
As
Ag
Bu
Br
Ce
Co
Cr
Cs
Eu
Fe
Hf
Hg
La
Lu
Na
Ni
Rb
Sb
Sc
Se
Sm
Th
U
Zn
1975
Analysis^
<8
<2
400+100
41+4
51+2
11.8+0.2
89+6
4.7+0.4
0.92+0.05
3300+700
4.2+0.1
<1.4
26.6+0.8
0.42+0.08
4800+200
<72
76+1.8
1.4+0.4
9.4+0.1
<3
4.6+0.1
7.3+0.8
4.0+1.0
"
SLM-1-1
AGV-1
1978 % differ- %
Analysis ^
<6
<1.2
390+28
39+0.4
49+. 2
10.0+0.07
83.2+1
3.8+. 07
0.89+0.02
2900+100
4.4+0.06
<.5
27.0+0.2
0.20+.01
408+50
<35
77+2
1.4+0.06
9.9+0.03
<1 . 5
4.4+0.02
7.2+0.1
2.7+0.3
86+2
ence
-
3
5
4
16
7
21
3
13
5
-
2
66
1
-
1
0
5
-
4
1
9
•~
Accepted3
0.8
-
1208
0.6
63
14.1
12.2
1.4
1.7
47300
5.2
-
35
0.28
31600
18.5
67
4.5
13.4
—
5.9
6.4
1.88
84
Measured^
<6
-
1300+50
2.3+0.4
53+0.2
11.8+0.1
9.9+0.5
1.1+0.1
1.4+0.02
36000+100
4.6+0.06
-
38.7+0.2
0.14+0.01
30000+100
<35
57+2
3.7+0.1
12.0+0.03
_
5.0+.02
6.0+0.1
2.3+. 28
30+1
differ-
ence
_
7
300
16
15
19
21
18
24
11
-
11
50
5
-
15
18
11
_
15
6
22
64
mean and standard deviation from analysis of four subsamples.
2 analytical error associated with a single analysis.
3 USGS standard values (Flannagan et al. 1973).
32
-------
As
u>
CH % Deviation from Std.
§• % Deviation from Mean
80
loo
Figure 8. A comparison of analytical precision and accuracy in determination of trace
element composition of standard lake sediment via neutron activation analysis,
-------
concentrations reported by Shimp et al. (1971) for sediments collected in the
same area of the lake. Therefore it is likely that the published value of Br
is incorrect in this case. The inaccuracy in the Zn value is due to the
presence of Sc. It is very difficult to properly correct for Sc interference
and for this reason no NAA results are reported for Zn. The measured
concentrations of elements in the AGV-1 sample (Table 5) are systematically
too high by 10% primarily due to error in weighing small sample as well as to
sample homogeneity. A comparison of the percent difference between first and
second analyses for Lu (66%) and the apparent accuracy (AGV-1, 50%) indicates
the possibility of significant inaccuracies in the determination of this
element even though Q^ and Qp defined above (Fig. 8) are under 20%.
No determination of the accuracy of measuring the concentration of the
elements corresponding to short-lived isotopes (i.e. Al, Ca, Mg, Ti, V) was
made. For most of these elements the interference corrections are negligible
(see Dams and Robbins, 1970). However there is a major interference in the
determination of magnesium due to fast neutron production of Mg^' through the
(n,p) reaction on aluminum. That is, if the gamma-emitting isotope Mg^',
which serves as the measure of the amount of the Mg present can be produced
either by Mg^6 (n,y) Mg^? or by Al^7 (n,p) Mg^?. The interference correction
is given approximately by (Dams & Robbins, 1970)
[Mg]actual = Mobserved - 0.15 [Al] (3)
As [Al] = 53,000 ppm roughly 0.15 x 53,000 = 8000 ppm of the measured
concentration or about 8000/29,000 = 25% is due to an interference. As the
interference correction is only approximate, the values for Mg may be in
error by as much as 20%.
In summary, neutron activation analysis is a precise and accurate method
for the determination of many elements in sediments. Exceptions occur for U,
Lu and possibly Cr, Sb and Mg where the data may be of limited accuracy
because of uncompensated interferences. The multiple analysis of SLM-1
splits makes it a useful standard for intercomparison of analytical methods
and results in laboratories undertaking metal analysis of lacustrine
sediments. Portions of this material are available from our laboratory on
request.
Timed Extractions
Metals (AAS)
The standard procedure for extracting sediments involved treatment in
hot 50% HN03 (+ H202) for 96 hours. The efficiency of this method was
checked by determining the release of metals from standard lake mud for
shorter treatment times and for the alternative, more conventional, treatment
with 50% HC1 (-1- H202). (Samples were extracted in HN03 to provide
chloride-free extracts for neutron activation analysis. Chloride is a major
interference in the determination of shortlived elements via NAA.) The
results are illustrated in Figure 9. For most elements the release is
complete within a few hours. Included in the rapid release group are Ca, Cr,
Cu, Fe, Mg, Mn, Ni, Pb, Sr and Zn. For sodium the release is considerably
34
-------
^O
~ 3
Mg
"0 20 40 60 80 100
SLM SAMPLES
*HN03 •HOB
1
i I i I i I i
0 20 40 60 80 100
Pb
0 20 40 60 80 100
t
160
140
120
100.
i
I 1
0 20 40 60 80 100
160
2:130
100
0 20 40 60 80 100
HOURS
2000
0 20 40 60 80 100
HOURS
Figure 9. Elemental concentration ascribed to standard lake
sediment versus extraction time.
35
-------
slower but nevertheless complete by the end of the four day extraction
period. For two elements, K and Ba, the extraction is evidently not complete
even after four days. This result is understandable since K is a principal
constituent of the clay minerals which resist dissolution on acid treatment.
That Ba is also in the incomplete category indicates that a considerable
fraction of it too is bound in the resistant clay mineral phase.
There are significant differences between HNC>3 and HC1 treatments. The
biggest effect is for Cu. The HNC>3 treatment is about 25% more efficient for
extraction of copper. It is also slightly more efficient for Ni and Zn
(CLO%). For Mg there is no significant difference in treatment. An
independent analysis of six replicate SLM-1 samples in this laboratory
(R. Rossmann, personal communication) was undertaken using 2 g of sediment
ground in a mixer mill extracted in 10% HC1 with repeated additions of 30%
H2^2 (R« Rossmann, 1975). Samples were allowed to extract for a 48 hour
period at 90° C and extracts analyzed via AAS. These results are given in
Table 6. For most elements (Ca, Fe, Mg, Mn, Zn) the agreement is
satisfactory (10% or better). However the 10% HC1 extraction yields
significantly higher concentrations (about 20%) of Cr, Ni and Sr. Reasons
for this effect have not been investigated.
For selected elements there are both NAA results for whole sediment as
well as for acid-peroxide extracts. These data provide a measure of the
efficiency of the extraction method. Results are summarized in Table 7. For
calcium and magnesium,the efficiency is essentially 100%; for the transition
elements Fe, Mn and Cr the efficiency is over 80% while for Ba, K and Na the
efficiency is below 40%. These latter elements are in good part contained in
resistant clay minerals. The low efficiencies are very consistent with the
results of the timed extraction study discussed above. An important result
for this study is that the transition elements are efficiently extracted by
the acid-peroxide treatment. It is therefore likely that efficiency of
extracting the anthropogenic components is essentially 100%.
Amorphous Silicon
The results of a timed extraction of a standard sediment sample
(fine-grained mud) and a standard sample of illite (see Robbins et al., 1977)
are given in Fig. 10. The rapid increase in dissolved silicon in 0.5 m NaOH
during the first ten minutes or so corresponds primarily to the dissolution
of amorphous silica. The slower, essentially constant rate of dissolution of
the silicon in mud samples beyond about one hour corresponds to the release
of the element from clay minerals. The rate of dissolution of "pure" illite,
a principal clay constituent of these muds, is essentially the same beyond an
hour. According to McKeyes et al. (1974) the amorphous silicon content may
be inferred by linear extrapolation of the concentration time curve for
(t > 1 hr) back to t = 0. This is an accurate method only if the release
rate of Si from the clay mineral fraction is constant over the initial
extraction period. The illite extraction curve shows that this is not true.
More rapid release occurs during the first 10 minutes. If this rapid initial
increase is not due to contamination of the illite sample with "amorphous"
materials, but due to release of silica from illite, then the linear
extrapolation is probably underestimating the amount of silica in the 0.5N
NaOH attributable to clay minerals. From Figure 10, it can be seen that the
36
-------
TABLE 6. COMPOSITION OF REPLICATE STANDARD LAKE MUD SAMPLES
(SLM-1-3; SLM-1-7; SLM-1-8)
DETERMINED BY GASOMETRIC OR ATOMIC ABSORPTION ANALYSIS (AAS)
Concentration (yg/g)
Element
Ba
Ca*
Cu
Cr
Fe*
K
Mg*
Mn
Na*
Ni
Pb
Sr
Zn
C
(total)
C
(inorganic)
30% HN03 extract 30% HC1
Mean
7.5+0.14
41.8+0.9
64.5+2.6
3.0+0.1
-
3.77+0.05
540+6
-
37.2+0.5
96+2
42.0+0.7
163+5
5.45+. 15*
3. 26+. 07*
% N Mean
— -— —
1.9 4
2.2 12 31.2+0.5
45
3 12 3.2+0.1
_
1 12 3.64+0.08
1.1 12 610+4
- -
1.3 8 33.3+0.7
28
1.7 12
3 12 155+2
3 15
2 6
extract 10% HC1 extract1
% N Mean
_ _ —
7.18+0.05
1.6 5 42.3+0.1
78.9+1.7
3 5 3.1+0.2
0.87+0.04
2 5 3.66+0.03
0.7 5 605+3
0.09+0.007
2.1 5 46.9+0.1
_
51.0+0.9
1 5 168+14
%
_
0.7
0.2
2.2
6.5
4.6
0.8
0.5
7.8
0.2
-
1.8
8.3
N
__
6
6
6
6
6
6
6
6
f>
-
6
6
1 Independent analysis of six SLM-1 samples by R. Rossmann (pers. comm.).
* Concentrations in percent by weight.
37
-------
TABLE 7. EFFICIENCY OF EXTRACTION OF SELECTED TRACE ELEMENTS
VIA ACID-PEROXIDE TREATMENT (SLM-1 SAMPLES)
Concentration (yg/g)
Element Whole Sediment2 Acid-Peroxide Extract Efficiency
(NAA) (Mean)
Ba
Ca
Cr
Fe
K
Mg
Mn
Na
434
7.00*
88.8
3.33*
2.20*
2.87*
654
0.50*
176
7.3*
71.7
3.10*
0.87*
3.7*
578
0.09
40
>1003
81
93
40
>1004
88
18
* Concentration in percent by weight
1 100 x concentration from acid-peroxide extract/whole sediment concentration
2 Data from table 3
3 >100 because of statistical uncertainties
^ MOO because of interference effects in NAA analysis for Mg (see text)
38
-------
UX
FIGURE 10. Silicon released from standard lake sediment versus extraction time.
-------
amount of SI released by clay minerals could be as much as 4 mg/g lower than
that Implied by a linear extrapolation. For this particular sample, which is
fairly representative, corresponds to a (3.5/(15.4-3.5)) * 100 = 30% effect.
As the actual data cannot be corrected accurately for such effects, the
inaccuracy in the results could be as much as about 30% and will increase for
low measured amorphous Si values. The precision of the method is far better,
around 15%.
Pore water air-exposure effects
It is now well-known that even very limited exposure of anoxic sediments
to air prior to sampling for pore water can have a drastic effect on the
concentration of certain dissolved species (phosphate: Bray et al., 1973;
Weiler, 1973; iron: Troup et al., 1974). Using the method described above
and in Robbins and Gustinis (1976), the sensitivity of the concentration of
the elements Ba, Ca, Fe, K, Mg, Mn, Na, P, Si and Sr has been studied.
A 5 cm section of fine grained anoxic sediment was split under
nitrogen. Half the sample was squeezed in an inert nitrogen atmosphere. The
other half was exposed to air for 15 seconds. As the sediment plug was
fairly well-consolidated the sectioned pieces retained their shape and
limited surface area was in momentary contact with air. Following exposure
to air, the section was returned to the nitrogen-filled glove box, loaded
into the cassettes and squeezed. In squeezing the unexposed sample, care was
taken to eliminate traces of air within the squeezer system by purging it
with nitrogen using a rubber diaphragm with a pin hole leak (see Robbins and
Gustinis, 1976). Application of N2 pressure to the assembled, clamped
squeezer forced nitrogen through the system eliminating traces of air as well
as nitrogen-purged distilled water used to clean the parts. For the exposed
section, the system was not purged with N2- Therefore it necessarily
contained both traces of air and residual distilled water. On squeezing,
aliquots of pore water were taken from each of the squeezers after each 3 ml
had been produced.
The results for the elements showing the greatest sensitivity to air
exposure are shown in Figure 11. The concentration of Si is reduced by about
8% on brief exposure to air. The initial low values in the concentration of
Si in pore water from exposed sediment is due to residual distilled water in
the system. For Mn the reduction on air exposure is about 14%. For both Fe
and P04 the effect is drastic. Concentrations of these constituents never
reach an equilibrium value during squeezing. By the end of squeezing, the
concentration of Fe in pore water remains approximately half of the value
obtained from squeezing unexposed samples. For P04 the reduction is nearly a
factor of 4. In normal operation, the first six mis of pore water are
discarded as they contain some distilled water. The subsequent 20-25 mis are
collected. Therefore in such an integrated sample, brief exposure of
consolidated sediments to air and squeezing in an incompletely purged system
can result in nearly order of magniture decreases in the concentration of P04
and Fe. There were no measurable effects for Ba, Ca, K, Mg or Sr. -These
results are of importance for interpreting interstitial profiles of Si, Mn,
Fe and P04. Radical departures from smooth variations in contiguous samples
40
-------
ppm
ppm
ppm
ppm
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
2.4
2.0
1.6
1.2
0.8
0.4
0
1.0
0.8
0.6
0.4
0.2
0
14
12
10
8
6
4
2
0
_i I I I I
i i i i i i i i i
A Anoxic
• Exposed to Air
l l I i I I I I I I i i
\ r
i i i
i r
I I I I I I I I I I I
I _
_ I I I I I I I I I I I I
0 6 12 18 24 30 36
VOLUME OF PORE WATER (rr\l)
42
Figure 11.
Concentration of selected elements in successive 3 ml
aliquots of pore water. For some elements brief ex-
posure of sediments to air drastically reduces dis-
solved concentrations.
41
-------
are likely to result from inadvertent contamination with air. The effects of
limited air exposure on concentrations of the above elements and others in
pore water are summarized in Table 8.
TABLE 8. CONCENTRATION OF SELECTED ELEMENTS IN PORE WATER SAMPLES
WITH AND WITHOUT BRIEF EXPOSURE TO AIR
Concentration (ppm)
Element
Ba
Br
Ca
Ca
Co
Fe
Fe
K
La
Mg
Mn
Na
Na
P04
Sb
Si
Sr
Unexposad
0.51
0.091
25.4
22.6
6.4*
2.3
3.0
1.2
5.7*
8.8
0.71
5.7
6.3
2.9
2.7*
12.5
0.11
Exposed
0.59
0.085
26.1
30.0
<1.0*
0.89
0.80
1.3
2.5*
8.2
0.59
5.0
6.7
0.46
0.76*
11.6
0.14
Ratio (%)1
MOO
93
^100
MOO
<16
39
27
0,100
44
93
83
88
MOO
16
28
93
MOO
Method'
AAS
NAA
AAS
NAA
NAA
AAS
NAA
AAS
NAA
AAS
AAS
AAS
NAA
COLOU
NAA
COLOR
AAS
Concentration in ppb
Ratios >100% reflect analytical and other errors.
42
-------
RESULTS AND DISCUSSION
PHYSICAL PROPERTIES OF SEDIMENTS
To develop an accurate estimate of the flux of metal contaminants to
sediments it is necessary to know the mass per unit area as a function of
depth in individual cores. This has been accomplished in two ways: (1) by
direct measurement of the mass per unit area and (2) by determination of the
fraction of the total sediment section weight which is due to solids, the
fractional dry weight, f. The direct measurement would suffice if it were
not for the fact that some sediment is occasionally lost on sampling, so that
the actual volume of sediment recovered in sectioning is less than the volume
corresponding to a section of thickness dz in the core liner of cross-
sectional area A. If the wet weight of sediment is w then the directly
measured bulk density is:
p = w / (A dz)
b
(4)
and if D is the dry weight of sediment in the section, the mass per unit area
is:
dm = D / (A dz)
the second measure of dm may be obtained from determination of:
(5)
f = D / w
(6)
Clearly the measured value of f does not depend on loss of sediment
during sampling. The fraction dry weight of a section is related to dm in
the following way. If the mean density of sediment solids, p , is
essentially constant within the depositional basins then the porosity of
sediment is given by:
*
V
and
f •
Vs Ps
(Vsps
(7)
(8)
43
-------
where v^ and vg are the partial volumes of liquid and solids in a given
section (p^ = density of water = 1). From there it can be seen that
(eliminating vs and v )
X*
4 = P (l - f) / (p (i - f) + f)
S (9)
and since
dm = (1 - <(>) p dz
s
(10)
subtracting Eq. 9,
dm = f pg dz / (f + Pg (1 - f) )
(11)
furthermore the bulk density of sediment is given either by Eq. 4 above or by
Pb H ('svs + V£) / (Vg + v£) - ps / (ps (i _ f) + f) ^^
In figure 12 values of Pb (the bulk density) are plotted against f for 2
cm thick sediment sections where sediment losses on sectioning are minimal.
The line shown is the relationship expected if Ps is about 2.5 + 0.2 g/cm3.
The large uncertainty in the estimate of ps primarly reflects the
insensitivity of pb and f to changes in the value. Comparison of the two
measures of p, provides an estimate of loss of material. This comparison is
,
provided in the Appendix (Table A-l). For five centimeter sections
Pb/Pb = I/2 since approximately 1/2 of the section
sampling the core. In compiling the cumulative mass,
z
M = / dm
o (13)
Eq. 11 was used. Physical properties of approximately sixty cores are
tabulated in the Appendix (Table A-l).
Examples of the vertical distribution of porosity are shown in Fig. 13
for stations 5, 10, 19 from the Port Huron basin and 25 from the Saginaw
basin. In Fig. 14 are shown porosity profiles for stations 14A, ISA, 53 and
63 in the Goderich Basin. Because of the very large number of profiles
determined, only selected examples are illustrated in the report. The above
eight stations will serve to illustrate not only the vertical dependence of
physical properties but the vertical dependence of chemical and radioactivity
parameters as well.
Smoothly decreasing porosity (and f) profiles are found throughout most
of the depositional areas with discontinuities such as those seen at stations
10, 14A and 53 occurring generally toward basin margins. Smoothly varying
profiles are characterized by an approximately exponential porosity profile
(5, 25, 14A, ISA, 63) described by the equation
44
-------
CP
.0.6
LU
cr
Q
2 0.4
o
<
o:
0.2
1.0 1.5
BULK DENSITY (g/cm3)
2.0
Figure 12
Fraction dry weight of sediment versus bulk density
for 540 sediment samples. Solid curve expected if
all samples have the same density of solids (2.54
g/cm3).
45
-------
LAKE HURON CORES (EPA-SLH-74)
50
25
0.84 0.90 0.96 0.74 0.80 0.86 0.92 0.72 0.78 0.84 0.90 0.86 0.92
POROSITY
Figure 13. Vertical distribution of porosity in selected cores
(Saginaw and Port Huron Basins).
-------
LAKE HURON CORES (EPA-SLH-75)
63'
0.86 0.92 0.98 0.78 0.84 0.90 0.96 0.70 0.76 0.82 0.88 0.94 0.80 0.86 0.92 0.97
POROSITY
Figure 14. Vertical distribution of porosity in selected cores
(Goderich Basin).
-------
4> - (*0 - f) e~z + *f
Where $=4O at z=o and •jiH'f at sufficiently great depths. Units of the
compaction parameter 3 are cm"*-. Within the upper few cm, the water content
(porosity) is generally somewhat underestimated by this relationship (Eq. 7)
as can be seen in Fig. 15 which shows a least squares fit to porosity profile
in a core from Station 18 using Eq. 14. Also shown is a contrasting
irregular profile, having no meaningful description in terms of Eq. 14, for
another marginal location (station 22; see Figs. 3 and 4). Eq. 14 predicts
a surface porosity of 0.90 while the measured value is 5% higher. (Note that
Hongve and Erlandsen (1979) found that the water content of cores were not
affected by coring compression during sampling.) Because <|> is essentially
discontinuous at z=0, Eq. 14 has been used to obtain an average $, roughly
over the 1-2 cm interval for purposes of illustrating the systematic
variation over the depositional areas. In cases where discontinuities occur
$Q and $f have been estimated from actual values around z=l-2 cm and z=50
cm without aid of Eq. 14.
Shown in Figures 16 and 17 are values of $Q and <(>,. for the two
depositional basins in southern Lake Huron. Variations are similar for both
and $f are quite systematic. High porosity sediments tend to occur in
deepest parts of the basins, mid lake toward the central escarpment and in
fine grained, organic rich deposits. Particularly within the Goderich Basin,
sediments are considerably more consolidated toward the eastern, shoreward
margin in areas of high inorganic carbon deposition (Thomas et al., 1973).
The variation in the compaction parameter, 3 (cm"*-), with location is less
systematic as can be seen from Fig. 18. However, 3 tends to be highest in
marginal areas not either toward the escarpment nor in the area of highest
inorganic carbon deposition (see Fig. 17). A large 3> indicates a
comparatively rapid decrease in sediment porosity with depth.
COMPOSITION OF SURFACE SEDIMENTS
The composition of surface sediments (1-2 cm) is given for 62 cores in
Table 9. Concentrations of mercury and tin are given separately in Table 12.
Concentrations based on neutron activation analysis are given for 39 of the
62 cores. Care should be exercised in using this table as the AAS data refer
to acid-extractable element concentrations while the NAA data are for whole
sediments. Quantities starred in Table 9 are NAA data. Also where confusion
could arise, acid-soluble (AAS) concentrations are given the suffix 1 whereas
whole sediment (NAA) concentrations are given the suffix 2. Thus, for
example, Nal refers to acid-soluble sodium while Na2 refers to whole-
sediment sodium. Unless explicitly stated in the text element concentrations
refer to acid-soluble quantities.
Since as many as 36 parameters have been determined in these sections,
the data set is the largest and most complete elemental analysis of sediments
in this part of the lake yet available. In Table 9 Fsol (g/g) refers to the
fraction of dry sediment soluble by acid-perioxide treatment. IOC and OC
refer respectively to inorganic and organic carbon in weight percent. Cs37
-------
0
0.65 0.70
POROSITY (ml/ml)
0.75 0.80 0.85 0.90
0.95
T
1.0
u
X
a.
Ld
Q
Figure 15. Vertical distribution of porosity in two contrasting
cores.
49
-------
SOUTHERN LAKE HURON
Figure 16. Distribution of surface porosity.
50
-------
SOUTHERN LAKE HURON
10 20 30 40
KILOMETERS
Figure 17. Distribution of porosity at depth.
51
-------
-------
TABLE 9. COMPOSITION OF SURFACE (1-2 CM) SEDIMENTS IN SOUTHERN LAKE HURON*
STN
3.
4 .
5.
6.
7.
8.
9.
10.
11 .
12 .
13.
14.
15.
16.
17.
18.
19.
20.
21 .
22.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41 .
42 .
43.
44 .
45 .
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61 .
62 .
63.
65.
66 .
67.
68 .
69.
70.
71 .
FSOL
0.243
0.26C
~
0.428
0.260
0.283
-
—
0.326
0.463
0. 317
_
0.250
0.318
0.354
-
-
-
_
0.317
_
0. 187
_
0.262
_
_
_
„
_
0.242
0.212
_
0.452
0.397
0.375
0. 303
_
0.311
0.401
0.411
_
0.434
0.296
0.270
0. 211
0.278
0.322
0.430
0.391
0.276
C.272
0.327
0.306
0.297
0.310
0.205
0.267
IOC
(%)
C.10
4.78
O.C9
2.41
_
_
1.21
4.85
C.95
C.14
C.64
2.37
-
-
-
„
0.78
C.10
_
C.16
_
_
_
_
_
_
2.67
_
1.C8
_
5. 39
4.71
4.40
0.27
_
C.26
4.68
4.72
_
_
4.68
C.32
_
1.67
_
3.36
1.30
C.61
_
2.13
_
"
OC
(%)
_
4.54
_
0.63
4.91
2.48
-
_
4.11
1.22
4.27
_
4.73
4.16
3.44
-
-
-
_
4.11
_
3.70
_
4.94
_
_
_
_
_
_
0.55
_
3.92
_
1.44
0.67
C.80
5.35
_
5.77
0.99
_
-
_
1.93
4.91
_
_
1.62
_
_
2.78
3.91
4.66
_
3.01
_
_
_
AS*
(PPM)
17.2
20.7
_
_
24.8
-
-
_
21.6
_
21.2
_
24.9
22.9
-
-
-
-
-
24.2
_
16.2
_
28.1
-
-
-
-
-
_
_
_
23.1
_
_
_
_
50.2
_
54.0
_
_
-
_
_
48.8
_
22-5
_
33.8
14.7
_
_
23.6
23.9
17.6
_
27.7
20.4
31.9
27.8
BAl
(PPM)
_
138.1
—
66.5
_
-
-
—
147.2
90.2
256.4
—
177.4
171.3
122.9
-
-
-
-
189.4
_
-
-
-
-
-
-
-
-
_
58.3
_
121.9
-
109.2
77.3
88.6
1 98.5
_
172.5
91.7
93.6
-
_
122.0
221.2
_
213.0
79.6
134.8
156.2
_
140.7
164.8
201."
182.7
173.8
192.9
_
202.3
192. 9
BA2*
(PPM)
471.
442.
—
457.
458.
433.
-
—
366.
358.
391.
—
370.
398.
420.
-
~
~
-
418.
-
474.
-
593.
-
-
-
-
-
-
297.
-
443.
-
231.
339.
366.
468.
-
501.
279.
397.
-
_
327.
463.
_
540.
298.
500.
480.
409.
363.
504.
547.
521.
530.
503.
428.
528.
538.
BR *
(PPM1
22.8
26.2
—
12.6
22.1
16.0
-
—
23.3
13.5
31.3
—
27.9
27.5
63.0
~
~
~
-
27.7
-
18.4
-
118.1
-
-
-
-
-
-
14.7
-
81.4
-
9.4
11.8
16.2
157.8
-
165.2
14.8
8.1
-
-
23.1
106.3
—
97.4
31.7
106.4
59.5
30.6
38.1
79.0
96.2
78.4
45.8
88.7
82.5
100.4
106.6
(continued)
*Values are either in PPM = yg/gram whole dry sediment or in % = percent by
weight. Starred values refer to neutron activation analysis or whole
sediments. Other metal concentrations based on acid-peroxide extracts.
53
-------
TABLE 9 (continued)
STN
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
1*.
15.
16.
17.
18.
19.
20.
21.
22.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42 .
43.
44 .
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62 .
63.
65.
66.
67.
68.
69.
70.
71 .
CA
(%)
2.00
0.11
0.47
0.64
7.37
0.62
3.99
0.47
0.54
2.33
7.68
2.46
0.15
0.64
1.37
4.21
0.38
1.07
1.29
0.67
1.68
0.65
0.64
0.55
0.59
0.40
0.28
3.33
2.78
6.66
2.68
4. 18
1.18
1.84
6.66
9.44
8.33
7.51
0.87
0.45
0.82
7.17
8.33
2. 85
1.95
7.97
1.08
0.27
0.85
2.86
0.69
3.78
6.24
5.80
2.22
1.44
2.80
3.33
1.84
2.05
0.87
1.09
CD
(PPM)
2.81
_
3.06
_
_
_
2.00
_
_
_
_
3.30
_
2.83
3.22
1.51
_
-
-
-
3.02
_
2.11
_
3.86
_
_
_
_
_
_
2.05
_
2.54
_
3.19
2.77
3.14
3.16
_
2.97
2.54
3.08
_
_
3.47
4.27
_
4.24
1 .55
2.06
2.44
4.22
2.70
2.57
3.28
2.84
2.45
2.81
2.93
2.98
2.57
Cf*
(PPM)
54.8
-
65.8
_
41.3
65.6
41.3
_
_
63.0
37.9
62.9
-
64.9
62.6
-
-
-
-
-
64.4
-
55.2
-
59.2
-
-
-
-
-
-
26.9
-
-
-
-
-
-
-
-
_
33. £
?5.5
-
_
38.2
63.0
-
65.8
37.9
67.6
50.9
42.4
51. 5
59. 3
65.2
59.5
57.8
65.6
61.7
63.0
62.7
CO *
(PPM)
10.4
_
11.8
_
6.7
12.3
7.6
_
_
12.6
6.1
12.5
-
13.3
13.7
l
-------
TABLE 9 (continued)
STN
3.
4.
5.
6 .
7.
8.
9.
10.
11 .
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22 .
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41 .
42.
43.
44 .
45.
46.
47.
48.
49.
50.
51.
52 .
53 .
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
65.
66.
67.
68.
69.
70.
71,
CS37
(pCi/g)
9.60
7.70
1.7C
8.30
3.60
9.90
2.60
12.50
6.90
1C. 50
<;.9G
_
_
_
11.80
6.30
_
7.80
_
_
_
1.07
6.01
0. 12
C.60
2.34
17.74
8.75
1.63
1.18
4.32
14.60
9.00
2.94
12.50
9.90
5.90
5.40
10.50
13.40
10.70
3.13
11.80
13.20
14.00
11.80
CU
(PPM)
47.5
7.38
65.4
64.4
16.5
62.0
_
37.7
61.1
51.3
22.8
49.9
5.56
63.3
62.2
41 .3
31 .6
62.9
57.9
16.4
59.3
8.25
45.7
35.5
55.9
22.9
9.48
31.7
?2.1
9.86
12.2
10.4
27.9
39.7
8.86
12.2
6.29
12.6
71.1
22.4
65.3
16.5
8.63
3.26
46.1
21.7
63.1
21.1
67.2
20.6
45.2
38.3
26. 2
32.5
49.5
59.0
49.6
41 .4
53.9
49.6
61.2
63.4
EU*
(PPM)
1.30
_
1.42
_
0.92
1.54
0.98
_
_
1.29
0.86
1.28
_
1.33
1.43
1.34
_
_
_
_
1.16
_
1.14
_
1.40
_
_
_
_
_
_
0.74
_
1.02
_
0.65
0.69
0.70
1.26
_
1.30
0.75
0.59
_
0.82
1.32
1.37
0.75
1.38
1.04
0.95
1.10
1. 19
.27
.29
.22
.27
.24
.33
.24
FE1
(%)
2.42
0.94
3.32
4.06
1.27
3.01
2.01
1.92
3.80
3.33
1.38
3.26
0.85
3.83
3.67
2.43
1 .99
3.78
3.56
1.90
3.99
1.27
2.22
2.30
3.53
1.61
1.28
1.77
2.11
1.00
1.27
0.92
1.82
2.24
0.89
1.16
0.87
1 .14
3.59
1 .37
3.52
1.19
0.87
0.89
2.67
1.43
3.96
1.45
4.10
1.53
2.46
2.60
1.92
2.13
3.28
3.79
3.19
2.71
3.32
3.71
3.91
3.45
FE2 *
(%)
3.02
—
3.54
-
2.09
3.76
2.20
_
_
3.8C
1.78
3.58
_
4.00
3.84
4.00
_
_
_
_
4.09
_
2.61
_
3.98
_
_
_
_
_
_
1.23
_
2.79
_
1.46
1.39
1.39
3.91
_
3.58
1.43
1. 15
_
_
1.79
4.31
_
4.14
i.ao
4. 11
2.93
2.30
2.54
3.72
4.01
3.43
3. 11
3.82
3.77
4.30
3.94
K
m
0.52
-
0.65
-
0.25
0.69
C.32
_
_
0.72
0.37
0.73
_
0.56
0.84
0.62
-
-
-
_
0.87
-
C.45
-
0.70
-
-
-
-
-
_
0.26
_
C.62
-
0.37
0.15
0.31
1.19
_
O.S7
0.23
C.20
_
_
0.51
1.26
_
j.
-------
TABLE 9 (continued)
STN
3.
4.
5.
6.
7.
8.
9 .
10 .
11 .
12.
13 .
14.
15.
16.
17.
IB.
19 .
20.
21 .
22.
29.
30.
31.
32 .
33.
34.
35 .
36.
37.
38.
39.
40.
41 .
42.
43 .
44.
45.
46.
47.
48 .
49.
50.
51 .
52.
53 .
54.
55.
56.
57.
58.
59.
60 .
61 .
62 .
63 •
65.
66.
67.
68.
69.
70.
71 .
LU*
(PPM)
0.35
-
0.35
-
0.26
0.40
0.27
-
-
0.36
0.23
0.34
_
0.34
0.38
0.32
-
-
-
-
0.36
-
0.33
-
0.44
-
-
-
-
-
-
0.26
-
0.36
-
C.20
0.26
0.21
0.4T
_
0.41
0.22
0.17
-
_
0.25
0.43
_
0.39
0.23
0.30
0.36
0.25
0.29
0.37
0.32
0.35
0.31
0.34
0.38
C.41
0.44
MG
(%)
1.46
0.16
O.B2
0. 76
5.19
0. 86
3.06
0.46
0.66
1.96
5.41
2.10
0. 12
0.87
1.46
3.17
0.55
1.14
1.28
0.66
1.73
0.25
0.16
0.61
0.89
0.40
0.?5
2.59
1.6?
3.91
1.72
2.83
D.91
1 .49
4.27
5.00
5.18
4.68
1.05
0. 38
1.01
4. 97
4.58
1.66
1.73
5.30
1.23
0.12
1 .27
2.18
0.83
3.11
4.38
4.38
2.04
1.49
2.47
2. 76
1.77
1.83
1.14
1.24
MN
m
0.075
0.020
C.048
0.231
0.023
0. 119
C.068
0.192
0.409
0.250
C.038
0. 130
0.031
0.245
0.227
0.045
C.034
0.309
0.234
0. 116
0.351
0.568
0.03?
0.102
0. 127
0.193
0.038
C.045
0.041
C.040
0.036
0.018
C.C61
0.153
0.026
0.033
O.C26
0.036
C.242
0.078
C.273
0.024
0.029
C.014
C.140
0.034
0.273
0.095
0. 149
0.064
0. 188
C.I 50
0.045
O.C38
0.122
C. 243
0. 159
0.043
0.258
0.225
0.245
0.1C6
NA1
(%)
_
_
0.205
_
0.111
_
_
_
0.148
0.121
0.330
0.075
0.203
0.114
_
_
_
0.180
_
_
_
_
_
_
_
0.254
_
0.156
_
0.160
0.154
0.154
0.384
0.300
0.204
0.165
_
0.156
0.259
0.409
0.163
0.150
0.171
_
0.265
0.181
0.240
0.221
0.161
0.169
0.184
0.268
NA2 *
(%)
0.749
_
0.799
0.778
0.846
0.772
0.664
0.668
0.715
0.738
0.671
0.650
0.678
0.869
0.795
0.875
0.719
0.728
0.843
0.830
0.668
0.735
0.791
0.838
0.672
0.701
0.713
0.866
0.710
0.672
0.652
0.641
0.685
0.688
0.653
0.685
0.672
0.655
0.709
0.794
NI
(PPM)
53.5
8.4
46.8
76.2
25.8
60.4
42 .2
62.8
74.6
62.7
34.1
63.5
5.3
71.7
87.1
51.5
38 .6
96.6
87.3
31 .1
85.6
26.2
45.5
42.2
53.0
50.9
22.5
42.5
34.4
22.0
24 .2
30.2
38.1
81 .5
36.0
23.9
21.4
24.8
85.2
31 .7
74.7
31 .0
21.6
14.0
64.1
34.7
82.1
29.6
81.3
37.0
54.2
54.7
48.1
44.3
72.1
79.5
64.9
52.8
70.3
72.8
80.6
67.6
P
m
0. 120
0. 199
0. 142
0.230
0. 220
0. 180
0.210
0.049
0.079
0.040
0. 108
0.059
0. 131
0. 159
0.063
0.085
0.068
0. 175
0. 172
0.062
0. Ill
0. Ill
0. 130
0.091
0.210
0.239
0.245
0.226
0. 144
0.240
0. 159
0.205
(continued)
56
-------
TABLE 9 (continued)
STN
3.
it.
5.
6.
7.
8.
9.
10.
11 .
12.
13.
1*.
15.
16.
1 7.
18.
19.
20.
21 .
22.
29.
30.
31 .
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43 .
44.
45.
46.
47.
48.
49.
50.
51 .
52.
53.
54.
55.
56.
57.
58.
59.
60.
61 .
62.
63.
65.
66.
67.
68.
69.
70.
71 .
PB
(PPM)
90.0
_
98.5
173. C
39.4
110.0
65.5
55.7
105.0
115.0
49.8
96.9
9.7
109.5
ICC. 3
88. 2
19.5
112. C
114.0
26.7
125.0
50.6
83. P
66.7
95.3
55.3
22.0
68.0
36.3
31.8
38.8
35.4
50.3
83.1
35.8
31.1
33.9
41 .3
14C.O
44 .5
133.0
3<5.4
33. e
14.1
92.2
51.4
12C.C
40.1
121.0
46.9
80.8
81.3
64. 1
69.0
S7.3
112.0
94.8
64.8
1C5.C
109.0
114. C
108.4
PB21
(pCi/g)
8.9
_
7.4
_
2.4
5.4
5.0
_
_
14.0
2.9
12.6
_
3.2
8.2
8.8
_
-
_
_
_
_
4.3
_
7.9
_
_
_
-
-
_
_
_
_
_
_
1.5
_
_
_.
_
2.2
2.4
_
_
_
_
_
6.2
_
_
_
3.7
11.4
-
-
_
_
7.3
_
-
SB*
(PPM)
0.94
_
1.13
_
0.34
1.13
0.54
_
_
0.78
0.43
0.79
_
0.90
0.78
1.44
-
-
-
_
I. 00
_
0.8D
_
1.26
-
-
-
-
-
_
0.41
_
0.78
_
C.21
C.17
0.33
1.39
_
1.49
0.38
0.26
_.
_
0.40
1.36
_
1.19
0.4?
1.15
0.89
0.50
0.80
0.95
l.ll
0.99
1.09
1.37
0.92
1.30
1.63
SC *
(PPM)
11. 1
_
13.4
„
8.2
13.8
8.6
_
_
13.1
7.9
12.9
_
13.4
13.6
11 .7
-
-
-
_
14.0
_
11 .2
_
14.?
-
-
-
-
-
_
5.B
_
13.5
_
6.4
5.°
5.8
13.6
_
14.5
6.3
4.9
_
_
7.5
14.?
_
14.6
6.8
14.4
11. 1
9.4
11.1
12.8
14.0
12. 6
12.?
13.6
13.4
14.5
13.0
SM *
(PPM)
5.42
_
6.51
_
4. 16
6.57
4.20
_
_
6.15
3.84
6.24
_
6. 19
6.24
5.36
-
-
-
_
6.23
_
5.39
_
6.66
-
-
-
-
-
_
3.09
_
5. 16
_
2.86
3.11
2.80
6.10
_
6.38
3.07
2.74
_
_
3.80
7.02
_
6.93
3.07
6.32
5.34
4.69
5.05
6.17
6.46
5.32
5.22
5.80
6.10
5.9B
6.38
SR
(PPM)
_
_
37.2
_
48.0
_
_
-
_
43.4
55.6
44.9
_
36.2
45.2
38.8
-
-
-
_
41 .1
_
-
_
-
-
-
-
-
-
_
36.1
_
32.7
_
49.5
46.5
42.2
47.9
_
43.1
45.1
45.4
_
_
49.6
47.3
_
48.4
42.7
29.5
42.9
_
49.2
42.5
46.6
46.4
43.9
44.6
41.0
41 .6
43.6
TH *
(PPM)
8.20
-
10.08
-
6.01
10.48
6.00
-
_
9.83
5.13
8.93
_
10.19
9.65
8.55
-
-
-
_
10.14
_
8.42
_
10.83
-
-
-
-
-
_
4.35
_
8. 18
_
4.17
4.49
3.86
9.78
_
10.94
5.55
3.96
_
_
5.14
10.96
_
10.60
5.08
10.94
7.44
7.07
8.97
9.33
10.32
10.56
8.66
8.93
9.43
9.64
10.76
(continued)
57
-------
TABLE 9 (continued)
STN
3.
4.
5.
6 .
7.
8.
9.
10.
11.
12.
13.
1*.
15.
16.
17.
18.
19.
20.
21.
22.
29.
30.
31 .
32.
33.
3*.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46 .
47.
48.
40.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61 .
62.
63.
65.
66 .
67.
68.
69.
70.
71.
U *
(PPM)
2.65
_
3.17
_
2.35
3.96
2.22
_
_
2.98
2.04
2.56
_
3.80
2.91
2.48
_
_
_
_
3.19
3.30
_
3.6?
_
_
_
_
_
_
2.27
_
2.09
_
2.21
1.68
1.91
2.9S
_
3.78
2.72
1.24
_
1.94
1 .86
2~.05
2.55
4.22
1 .69
1.68
2.88
2.34
2.90
4.16
4.17
3.91
3.07
3.49
2.95
ZN
139.2
20.7
184.9
196.8
55.6
175.3
96.2
117.0
1S8.5
155.5
7B.O
171.7
8.2
192.7
173.8
140.6
61.2
199.2
182. 1
40.8
193.0
35.1
133.0
1C2.8
1«3.7
96. 5
45. 1
98.9
72. 1
45.fi
54.4
47.2
78.4
122.7
'32. 1
27.8
22.0
74. 3
201.1
62.2
190.2
54.2
34.6
9. 1
145.7
68.8
190.8
52.9
203. 4
62.5
135.9
120.0
96.5
126. 1
163.7
188.0
156.2
131.0
152.4
199.2
204. 3
178.3
58
-------
TABLE 10. SUMMARY OF SURFACE CONCENTRATION DATA
Range
Minimum
FSOL (g/g)
IOC (%)
OC (%)
As
Bal
Ba2
Br
Ca (%)
Cd
Ce
Co
Crl
Cr2
Cs
Csl37 (pCi/g)
Cu
Eu
Fel (%)
Fe2 (%)
K (%)
La
Lu
Mg (%)
Mn (%)
Nal (%)
Na2 (%)
Ni
P (%)
Pb
Pb210 (pCi/g)
Sb
Sc
Sm
Sr
Th
U
Zn
0.19
0.09
0.55
14.7
58.3
231
8.1
0.11
1.5
25.5
3.8
15.4
31.9
0.75
0.12
3.3
0.59
0.85
1.15
0.15
13.0
0.18
0.12
0.014
0.075
0.64
5.3
0.40
9.7
1.5
0.17
4.9
2.7
29.5
3.86
1.24
8.2
Maximum
0.46
5.4
5.8
54.0
256
593
118
9.4
4.3
67.6
14.8
82.6
86.4
5.41
17.7
71.1
1.54
4.10
4.30
1.26
40.7
0.45
5.4
0.57
0.41
0.88
96.7
0.25
140
14.0
1.63
14.6
7.02
55.6
11.0
4.2
204
Average
0.31
2.1
3.2
26.7
148
432
51.2
2.67
2.87
54.3
10.6
47.1
66.5
3.64
7.73
37.0
1.12
2.37
3.06
0.68
31.1
0.33
2.00
0.13
0.20
0.73
50.6
0.15
73.6
6.54
0.87
11.2
5.23
43.6
8.24
2.79
116
Standard
Deviation
0.07
1.9
1.6
10
51
84
37
2.6
0.66
13
3.6
19
18
1.4
4.6
21
0.26
1.1
1.0
0.31
8.7
0.072
1.6
0.11
0.076
0.072
23
0.064
35
3.6
0.40
3.1
1.3
5.2
2.4
0.81
63.
Ratio*
0.23
0.90
0.52
0.39
0.34
0.19
0.72
0.98
0.23
0.23
0.34
0.39
0.28
0.38
0.59
0.57
0.23
0.46
0.34
0.45
0.28
0.22
0.79
0.87
0.38
0.98
0.45
0.44
0.48
0.55
0.46
0.28
0.26
0.12
0.29
0.29
0.54
N
39
29
28
24
32
39
39
62
35
32
39
62
39'
39
39
61
39
62
39
38
39
39
62
62
32
39
62
32
61
20
39
39
39
33
39
39
62
Values in yg/g unless indicated. * Ratio = SD/mean.
59
-------
TABLE 11. CORRELATION COEFFICIENTS BASED ON PAIR-WISE LINEAR REGRESSION OF SURFACE SEDIMENT
CONCENTRATION DATA
FSOL
me
oc
AS
BA1
BA2
BR
CA
CD
CE
CO
r« i
CR2
C S
CS37
Cu
EU
FE1
FE2
K
LA
LU
MG
MN
NA1
NA2
NI
P
PS
PB21
SB
SC
SM
SR
TH
U
7N
FSOL
1.00
0.83
-0.53
0.15
-0.43
-0.48
-0.41
3.85
0.29
-0.43
-0.53
-3.50
-0.51
-3.48
-0.44
-0.59
-0.54
-3.52
-3.52
-0.35
-0.5?
-0.59
0.87
-0.37
-0.25
-0.26
-3.53
-0.32
-0.53
-3.48
-0.53
-0.52
-3.52
0.63
-0.52
-0.43
-0.56
IOC
0.83
1.00
-0.90
-0.30
-0.73
-0.61
-0.57
0.99
-0.12
-0.83
-0.85
-0.80
-0.83
-0.81
-0.76
-0.91
-C.84
-0.87
-C.S5
-0.71
-0.89
-0.86
0.99
-0.68
-0.41
O.C9
-0.81
-0.68
-0.87
-0. 66
-0.80
-0.86
-0.87
0.49
-0.87
-0.64
-C.89
OC
-0.53
-0.90
1.00
0.82
0.85
0.66
0.67
-0.87
0.40
0.95
0.94
0.89
0.92
0.92
0.84
0.97
0.90
0.94
0.93
0.83
0.96
0.91
-0.86
0.75
0.43
-0.34
0.86
0.71
0.96
0.72
0.88
0.95
0.94
-0.?5
0.95
0.60
0.96
AS
0.15
-0.30
0.82
l.CO
0.19
0. 16
0.59
-C.45
0.30
C.48
C.6C
0.43
0.62
0.58
C.46
C.55
3.19
0.35
0.55
C.50
C.50
0.46
-0.38
C.48
0.38
-0.10
C.42
-C.20
0.65
C.10
0.69
C.54
0.44
0.14
0.51
C.H
3. 44
BA1
-0.43
-0.73
0.85
C.1S
l.OC
0.62
C.64
-C.71
0.52
C.82
0.83
0.85
0.82
C.R2
C.33
C.35
0.7fi
O.SC
C.83
0.86
0.85
0.78
-C.6S
C.74
0.54
-o.5£
C.83
C.76
0.85
C.74
0.74
C.35
0.84
0.05
0.81
0.42
C.87
8A2
-C.48
-0.61
C.66
0.16
0.63
l.CO
0.73
-0.65
C.1Q
C.62
C.70
0.67
0.74
C.67
C.60
C.67
C.6°
C.65
C.70
C.66
C.72
0.73
-0.61
C.40
0.30
-0.20
0.53
C.72
0.62
C.22
0.76
C.72
0.72
-0.13
C.71
0.43
0.63
BR
-0.41
-0.57
0.67
0.59
0.^4
0. 73
1.00
-0.61
0.2?
0. 58
0. 74
0. 75
0. 74
0. 71
0.72
0.64
0.57
0. 66
0. 71
0.77
0.67
0. 70
-0.58
0.57
0.48
-0.36
0. 6?
0.49
0.66
0. 37
0. 80
0. 69
0. 65
-0.18
0.69
0.34
0.66
CA
0.85
0.99
-0.87
-0.45
-0. 71
-0.65
-0.61
1.00
-0.01
-0.84
-0.85
-0. 36
T0.84
-0.82
-0. 75
-0.51
-0 . 86
-3.51
-0. 85
-0.68
-0. 90
-0.84
0.98
-0.48
-0. 38
O.C9
-0.42
-0.61
-0.43
-0. 64
-0. 80
-0. 87
-0. 87
0.47
-3.96
-0.62
-0.45
CD
0.29
-0 .12
0.40
0.30
0.52
0.19
0.22
-0.01
1.00
0.27
3 .17
0.31
0.19
0.19
0.22
0.26
0.17
0.35
0.21
0.32
0 .24
0.26
-0 .00
0.28
0 .48
-0.27
0.28
0 .13
0-29
-0 .01
0.09
0.25
0.31
0.53
0.?4
-0.19
0.30
CE
-0.48
-3.83
0.95
0.48
3.82
0.62
0.5P
-0.84
0.27
1 .00
0.97
0.82
0. 96
0.96
3.84
0.95
0.95
0. 92
0.97
j.79
0. 98
0 .82
-0. 76
0. 71
0.22
-0. 36
0.84
0.75
0.92
0.72
0.85
0. 98
0.96
-0.27
0. 96
0.6?
0.94
CO
-0. 53
-0. 85
0.94
0. 6C
0.83
0. 7C
0. 74
-0.85
0. 17
0.97
1. CC
0. 88
0.97
3.98
0. SC
0.94
0.92
0.91
0.99
0.85
0.96
0.8ft
-0. 8C
0.7£
0.33
-0.51
0.9C
0. 73
0. S3
0. 77
3. SC
0. 97
0.94
-0. 2-6
0.94
0. 60
0. 95
CR1
-0.50
-0.80
0.89
0.43
0.35
0.67
0.75
-0.36
0.31
0.82
0.88
1.00
0.83
0.88
0.85
0.89
0.78
0.39
0.86
0.90
0.87
0.83
-0.24
0.42
0.53
-0.47
0.35
0.65
0.87
0.57
0.83
0.88
0.86
-0. 10
0.86
0.44
0.90
CR2
-0.51
-0.83
0.92
C.62
0.82
0.74
C.74
-0.84
C.19
0.96
C.97
0.83
1.00
C.95
0.88
C.91
0.93
0.90
G.Q7
0.81
0.95
C.87
-0.78
C.72
0.38
-0.42
0.84
0.75
C.91
0.75
0.91
0.96
0.95
-0.25
0.94
0.57
0.92
cs
-0.48
-0.81
0.92
0.58
0.83
0.67
0.71
-0.82
0.19
0.96
0.98
0.88
0.95
1.00
O.P3
0.93
0.93
0.9 3
0.93
0.8 4
0.95
0.34
-0.76
0.74
0.30
-0.55
0.87
0.74
0.92
0.75
0.89
0.97
0.94
-0.21
0.93
0.58
0.94
CS37
-0.44
-0.76
0.34
0.46
0.83
0.60
0.72
-0.75
0.22
0.34
0.90
0.85
0.88
0.88
1.00
0.84
0.78
0.85
3.88
0.85
0.83
0.78
-0.71
0.79
0.44
-0.51
0.85
0.62
0.89
0.84
0.80
0.85
0.84
-0.16
0.81
0.41
0.86
CU
-0.59
-0.91
0.97
0.55
0.85
0.67
0.64
-0.51
0.26
0.95
0.94
0.89
0.91
0.93
0.84
1.00
0.92
0.97
0.94
0.83
0.96
0.89
-0.39
0.56
0.44
-0.34
0.91
0.71
0.95
0.67
0.88
0.95
0.95
-0.17
0.94
0.58
0.98
EU
-0.54
-0.84
0.90
0.19
0.78
0.69
0.57
-O.R6
0.17
0.95
0.92
0.78
0.93
0.93
0.78
0.92
1.00
0.87
0. 94
0.73
0.96
0.35
-0.81
0.60
0.31
-0.36
0.77
0.76
0.86
0.69
0.85
0.95
0.95
-0.26
0.94
0.65
0.91
FE1
-0.52
-0.8T
0.94
0.35
0.90
0.65
0.66
-0.51
0.35
0.92
0.94
0.89
0.90
0.93
0.85
0.97
0.87
1.00
0.95
0.86
0.94
0.87
-0.39
0.63
0.41
-0.44
0.92
0.76
0.94
0.74
0.82
0.95
0.94
-0.14
0.92
0.54
0.97
FE2
-0.52
-0. 85
0.93
0.55
0.83
0. 70
0.71
-0. 85
0.21
0.97
0. 99
0. 86
0. 97
0.98
0. 83
0.94
0.94
0.95
1.00
0.83
0.97
0.87
-0.80
0.78
0.31
-0.46
0. 88
0.75
0. 93
0.78
0.90
0.98
0. 96
-0.26
0.95
0.59
0.95
(continued)
-------
TABLE 11 (continued)
FSOL
IDC
nc
AS
BA1
BA2
RR
CA
CD
CE
cn
CRl
CP2
cs
CS37
CU
FU
Fei
FF2
K
LA
LU
MG
MN
MA 1
NA2
NI
P
PB
PR21
SB
SC
SM
SP
TH
U
ZN
K
-3.35
-0.71
0.83
0.50
0.86
0.66
0.77
-3.68
0.32
0.79
0.85
0.90
0.81
0.84
0.85
0.83
0.73
0.86
0.83
1.00
0.81
0.76
-0.62
0.69
0.51
-0.55
0.83
3.64
0.83
0.73
0.83
0.84
0.81
0.02
0.82
0.44
0.83
LA
-0.58
-0.89
0.96
0.50
0.65
0.72
0.67
-0.90
0.24
0.98
0.96
0.87
0.95
0.95
0.83
0.96
0.96
0.94
0.97
0.81
1.00
0.90
-0.85
0.73
0.37
-0.37
0.85
0.74
0.92
0.69
0.88
0.99
c.<;8
-0.26
0.98
0.67
0.96
LU
-0.59
-0.86
0.91
0.46
0.78
3.70
0.70
-0.84
0.26
0.82
0.86
0.83
0.87
0.84
0.78
0.89
0.85
O.R7
0.87
0. 76
0.90
1.00
-0.80
0.66
0.46
-0.26
0.82
0.66
0.38
0.65
0.85
0.88
3.90
-0.1 a
0.88
0.46
0.89
fG
C.87
C.99
-C.66
-0.38
-C.69
-C.61
-0.58
C.98
-C.CO
-0.18
-C.80
-C.24
-C.78
- C.76
-C.71
-C.39
-C.81
-C.39
-c.eo
-C.62
-0.85
-C.80
1.C3
-0.44
-C.37
-o.co
-C'.30
-0.55
-0.32
-0.41
-C.76
-0.82
-0.82
0.52
-0.82
-C.60
-C.33
MN
-0.37
-0.66
C.75
0.48
C.74
C.4C
0.57
-C.48
o.2e
0.71
0.7E
0.42
0.72
C.74
o.7<;
0.56
0.6C
0.63
C.7E
0.6S
C.73
0.6t
-C.44
l.OC
C.25
-C.4f
0.66
C.45
0.63
C.71
0.6C
C.75
0.71
-C.I?
C.7C
C.46
0.5£
NA1
-C.25
-0.41
C.43
0.38
C.54
0.30
0.48
-0.38
0.43
0.22
C.33
0.53
C.38
C.30
C.44
C.44
0.31
0.41
C.31
0.51
C.37
C.46
-C.37
0.25
l.CO
-C.07
0.41
C.27
C.47
C.19
0.40
C.36
C.39
0.23
C.38
C.CO
C.44
NA2
-0.26
0. 09
-0. 34
-0. 10
-0.56
-0.20
-0.36
0.09
-0.27
-0. 36
-0.51
-0.47
-0.42
-0.55
-0.51
-0.34
-0.36
-0.44
-0.46
-0. 55
-0.37
-0.26
-0.00
-0.46
-0.07
1.00
-0.51
-0.34
-0.41
-0.49
-0.33
-0. 46
-0.40
-0. 21
-0.39
-0.13
-0.40
NI
-0.53
-0.81
0. 86
0.42
0.83
0. 58
D.68
-0.42
0.28
0.84
0.90
0. 85
0.84
0. 87
0. 85
0.91
0.77
0.92
0.88
0.83
0.85
0. 82
-0. 30
0.66
0.41
-0.51
l.CO
0.61
0.92
0. 70
0.75
0. 87
0.85
-0. 19
0. 83
0.43
0.93
P
-0.32
-0.68
0.71
-0.20
0.7t
0.72
0.49
-0.61
0.13
0.75
0 .73
0.65
0.75
0.74
0.62
0.71
0.76
0.76
0.75
0 .64
0 .74
0.66
-0.55
0.45
0.27
-0.34
0.61
1.00
0.67
0.74
0.66
0.74
0.75
0.07
0.74
0.48
0 .75
PB
-3.53
-0.87
0.96
0.65
0.85
0.62
0.66
-0.43
0.29
0.92
0.93
O.at
0.91
0. 92
0 .89
0.95
0.86
0.04
0.93
0.83
0.92
0. 33
-0.32
0.63
0.47
-0.41
0.92
3.67
1.00
0.77
0 .85
0.93
0.92
-0.15
0. 91
0.52
0.96
P821
-0.48
-0.66
0.72
0.1C
0.74
0.22
0.37
-0.64
-0.01
0. 72
0. 77
0. 57
0.75
0. 75
0.84
0. 67
0.6S
0.74
0. 78
0. 73
0.69
0. 65
-0.61
0. 71
0. IS
-0.49
0. 7C
0.74
0.77
l.CC
0.6C
0.73
0. 73
-0.45
0. 7C
0. 38
0.71
S3
-0.53
-0.80
0.88
0.69
0.74
0.76
O.flO
-0.80
0.09
0.85
0.90
0. 83
0.91
0.89
0.80
0.88
0.85
0.«2
0.90
0.83
0.88
0.85
-0.76
0.60
0.40
-0.33
0.75
0.66
0.85
0.60
1.00
0.88
0.85
-0.23
3.88
0.58
0.86
SC
-0.52
-0.86
0.95
0.54
C.85
0.72
C.69
-0.87
0.25
0.98
0.97
0.88
0.96
0.97
0.85
0.95
0.95
0.95
0.98
C.84
0.99
0.88
-0.82
0.75
0.36
-0.46
0.87
0.74
C.°3
0.73
C.88
1.00
C.9R
-0.22
0.97
C.65
0.96
SM
-0.52
-0.87
0.94
0.44
0.84
0.72
0.65
-0.87
0.31
0.96
3.94
0.86
0.95
0.94
0.84
0.95
0.95
0.94
0.96
o.ai
0.98
0.90
-0.82
0.71
0.39
-0.40
0.85
0.75
0.92
0.73
0.85
0.9R
1.00
-0.21
0.97
0.54
0.95
SR
0.63
0.49
-0.25
0.14
0.05
-0.13
-0.18
0.47
0.53
-0.27
-0.28
-0.10
-0.25
-0.21
-0.16
-0.17
-0.26
-0.14
-0.26
0.02
-0.26
-0.18
0.52
-0.19
0.23
-0.21
-0.19
0.07
-0.15
-0.45
-0.23
-0.22
-0.21
I. 00
-0.25
-0.33
-0.19
TH
-0.52
-0.87
0.95
0.51
0.81
0.71
0.69
-0.86
0.24
0.96
0.94
0.86
0.94
0.93
0.81
0.94
0.94
0.92
0.95
O.fl2
0.98
0.88
-0.82
0.70
0.38
-0.39
0.83
0.74
0.91
0.70
0.88
0.97
0.97
-0.25
1.00
0.66
0.93
U
-0.43
-0.64
0.60
0.11
0.42
0.43
0.34
-0.62
-0. 19
0.62
0.60
0.44
0.57
0.58
0.41
0.58
0.65
0.54
0.59
0.44
0.67
0.46
-0.60
0.46
0.00
-0. 13
0.43
0.48
0.52
0.38
0.58
0.65
0.54
-0.33
0.66
1.00
0.57
ZN
-0.56
-0.89
0.96
0.44
0.87
0.68
0.66
-0.45
0.30
0.94
0.95
0.90
0.92
0.94
0.86
0.98
0.91
0.97
0.95
0.83
0.96
0.89
-0.33
0.53
0.44
-0.40
0.93
0.75
0.96
0.71
0.86
0.96
0.95
-0.19
0.93
0.57
1.00
-------
TABLE 12. MERCURY AND TIN IN SURFACE SEDIMENTS
OF SOUTHERN LAKE HURON (yg/g)
Station
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Mercury
0.18
N.D.
-
-
-
0.14
-
-
-
-
-
-
0.04
-
-
0.16
0.05
-
-
-
0.18
0.07
0.03
0.07
-
-
0.05
-
0.13
-
0.06
0.05
-
0.20
-
0.17
~
Tin
4.2
N.D.
4.0
5.0
2.0
4.1
1.8
3.3
3.8
6.4
1.5
4.0
0.3
3.8
4.0
3.1
0.7
3.7
4.6
1.0
4.1
0.8
3.7
2.0
2.0
1.6
0.8
2.0
1.5
1.0
1.4
1.3
1.4
2.3
1.2
0.6
1.0
1.2
5.0
1.7
3.6
0.8
(continued),
62
-------
TABLE 12. (continued).
Station
51
52
53
54
55
56
57
58
59
60
61
62
63
65
66
67
68
69
70
Min
Max
Avg.
SD
SD/Mean
N
Mercury
_
-
-
0.07
0.22
0.07
0.19
-
-
-
-
-
-
-
-
-
-
-
-
0.03
0.22
0.11
0.06
0.59
19
Tin
0.6
0.2
2.4
1.3
4.4
1.5
4.2
1.2
-
2.2
1.6
1.8
3.4
4.4
4.0
2.1
4.0
3.7
4.4
0.2
6.4
2.5
1.5
0.60
59
N.D. Not Detectable
63
-------
refers to the average activity of cesium-137 within the thickness of sediment
where it is found.
1 z max
i.e., Cs37 = / Cs-137(z)dz (15)
z max o
Contour maps showing the spatial variation in surface sediment concentration
values are in subsequent figures. To conserve space, concentration isopleths
are shown for only about half of the elements. This does not represent a
significant limitation because of the considerable redundancy in the
concentration data-
Average Composition
The average concentrations of elements in surface sediments within the
two depositional basins in southern Lake Huron given in Tables 10 and 12 are
compared with other concentration data in Table 15. The relative variability
of element concentrations in surface sediments is illustrated in Fig. 19.
Anthropogenically or diagenetically enriched elements generally exhibit a
high degree of variability within depositional basins as do the calcium
family elements. Surface concentration data are given in terms of each
depositional basin based upon the study of Kemp and Thomas (1976) and
reported by the International Joint Commission (1977). Also given in Table
15 are average elemental concentration values for fine-grained sediments of
Lake Michigan (Shimp et al. 1971). Concentrations in the single core (115)
refer to the upper ten centimeters of sediment (Frye and Shimp 1973). This
core was taken from a depositional environment in the eastern part of
southern Lake Michigan possessing characteristics comparable in many respects
to the Goderich Basin in Lake Huron.
Most of the major elements determined in this report have concentrations
which are comparable to values reported by IJC (1977). Note that the calcium
values in the Goderich Basin as reported by the IJC are significantly higher
than those in the Port Huron Basin. The observation is consistent with the
results of this study (see below) which indicate significantly (order of
magnitude) higher dolomite deposition in the Goderich Basin. Note also that
potassium values are roughly a factor of four lower in this study. Values
reported by the International Joint Commission are for whole sediment while
those reported here are for the acid-soluble fraction. Similarly the silicon
concentrations reported by the International Joint Commission are for whole
sediment while the values reported here are for amorphous silicon. On the
average approximately 4% of the total silicon of the fine-grained sediments
is in an amorphous, easily-leached form.
Some discrepancies are apparent on comparison of previously reported
concentrations of trace elements with the results of this study. The present
study indicates arsenic concentrations of 27 +_ 10 ppm whereas the IJC reports
1+2 ppm for the Goderich Basin. As can be seen from inspection of Table 5,
neither the accuracy nor the precision of the method of instrumental
activation analysis is particularly good for determination of this element.
Moreover Walter et al. (1974) report surface concentrations of arsenic of
64
-------
Ln
< 0.9
LU
Q
c/)
• 0.8
0.7
i o.e
cc
§0.5
h- M
Z-
UJ
o 0.3
o
c_>
0.2
Co
No2
IOC
Mg
ft
OC
m
;NI
^
CM
Not
Cs
Co
Bol
:e2
Th
Lo
Sc
Cr2
Sm|-
Wi
$®&^
Ce
Eu
Lu
^
ELEMENT
Figure 19. Relative variability of element concentrations in surface sediments.
Anthropogenically or diagenetically enriched elements (shaded regions)
generally exhibit a high degree of variability within depositional basins,
-------
around 1-2 ppm for Lake Erie sediments and values no higher than 10 ppm
even in grossly polluted harbor sediments. These results suggest that the As
levels reported here are too high, perhaps because of unidentified
interferences. On the other hand, surface sediments from comparable
depositional environments in Lake Michigan indicate values of around 15 ppm
(Frye and Shimp 1973). Furthermore Ruch et al. (1970) found that recent
sediments in Lake Michigan had concentrations ranging from 5 to 30 ppm. As
they used radiochemical separation procedures following neutron activation
analysis, their results should be interference-free. The results reported
here for southern Lake Huron are quite consistant with the Lake Michigan
data. Reasons for this situation are not yet clear. Other elements reported
here are also higher on the average than values reported by IJC. The ratios
of mean concentration in surface sediments for the Goderich Basin as
determined here to those determined by IJC are 2.9, 1.5, 1.3, and 1.9 for Cd,
Ni , Pb, and Zn respectively. Levels of Cd reported by Walters et al. (1974)
for recent sediments of Lake Erie range from about 1 to 4 ppm. Values
reported by Barron (1976) for recent sediments of Lake Michigan average about
4 ppm. While part of the difference in surface concentrations of Cd reported
here and by IJC may be due to analytical inaccuracies, at least part is
probably due to the sampling methods. The data reported by IJC are based on
analysis of the upper 3 cm of sediments collected by Shipex grab sampler.
Losses of surface sediment by grab samplers can significantly reduce the
measured concentration of enriched (see below) elements in what is defined as
surface sediments. It is easy to see how the approximately 50% higher levels
of Ni, Pb and Zn reported here could result from a slight loss of surface
sediments. Consider the case of lead. For purposes of illustration suppose
that the real concentration, CQ , at the surface (z = 0) is 100 ppm and that
the natural level Cf is 30 ppm. It is shown below that the anthropogenic
loading of lead to the Lake has an approximate 20 year doubling time. Thus,
the actual profile of lead in sediments would then have the form:
C = C e + C = C e + Cf
o f o f (16)
where 3 = 0.69315/20 years and u> is the mean linear sedimentation rate about
0.08 cm/yr. The concentration of lead in the section from 0 - 3 cm (used by
Kemp and Thomas, 1976) is then
C „ = 1 /3 C(z) dz = 69.5 (ppm)
°~3 I o (17)
If there were just a 1 cm loss of sediment the expected concentration would be
"C0-3" "I'* C(Z) dz = 55.8 (ppm) (ig)
A two cm loss of material would give:
"C0_3"= I ^ C(z) dz = 46.9 (ppm)
Thus for realistic sedimentation rates and doubling times, just a two cm loss
66
-------
of sediment would reduce the apparent concentration of lead by a factor of
1.5. Clearly the effect of sediment loss of other sediment disturbance by
Shipex sampling depends on the degree of enrichment of the element over
background levels. The determination of elements possessing a significant
degree of enrichment will be sensitive to losses of surface material. For
non-enriched elements measured concentration are insensitive to sediment
disturbances.
In contrast with most enriched elements, concentration of mercury as
determined for this report are significantly less than those reported by the
IJC and by Thomas (1973). Mean surface concentrations of mercury for the
Port Huron and Goderich Basins are not significantly different and average
0.11 ppm. Values reported by IJC are 0.44 and 0.25 for these respective
depositional basins. The analytical method used here is interference-free
and values obtained agree with those reported by Kemp and Thomas (1976) for a
core in the Goderich Basin. In their core the surface concentration (0-2 cm)
was found to be 0.20 ppm whereas in two adjacent cores (Stn. 55 and 57)
collected for this report surface (1-2 cm) concentrations were .22 and .19
ppm respectively. To some degree the distribution of mercury in surface
sediments as found for this report are the mirror image of the distribution
reported by Thomas (1973). In the sediments collected in 1969, Thomas found
highest concentrations of mercury in the Port Huron Basin. Values were not
only generally lowar in the Goderich Basin but there was an indication that
the areas identified in this report as being high in organic carbon were
somewhat depleted in mercury. In contrast, in this present study mercury
concentrations in surface sediment were found to follow the same general
pattern as do concentrations of iron, organic carbon and most other trace
elements and contaminants associated with fine-grained sedimentary materials.
Like mercury, strontium concentrations are found to be lower significantly
than previously reported by IJC. The reasons for these differences are not
clear but are probably due at least in part to analytical inaccuracies. An
intriguing alternative explanation is that there has been a net movement of
mercury out of the Port Huron Basin and into the Goderich Basin during the
five year period between the two sample collection dates; 1969 and 1974-1975.
Additionally there could perhaps have been a net loss of mercury from
sediments during this period.
Distribution and Interelement Associations
Major Constituents
Inspection of the correlation matrix (Table 10) shows that many elements
are extremely well-correlated with each other. Linear regression
coefficients are tabulated in Table A-8 of the Appendix. Regression
coefficients for mercury and tin are given in Tables 13 and 14 respectively.
An outstanding feature seen in looking the correlation matrix is the
appearance of a set of elements correlated well with each other but
negatively correlated with most other elements. This group is comprised of
the calcium family elements, Ca, Mg, IOC and to a lesser extent Fsol, Sr, and
Na2. In Figure 20 are shown the isopleths for inorganic carbon (IOC). This
distribution is consistent with that found by Thomas et al. (1973) both in
terms of absolute values and the strong trend toward high carbonate carbon
67
-------
TABLE 13. RESULTS OF PAIR-WISE REGRESSION ANALYSIS
OF MERCURY SURFACE CONCENTRATION DATA
Intercept
Element
FSOL
IOC
OC
AS
BA1
BA2
BR
CA
CD
CE
CO
CR1
CR2
CS
CS-137
CU
EU
FE1
FE2
K
LA
LU
MG
MN
NA1
NA2
NI
P
PB
PB-210
SB
SC
SM
SN
SR
TH
U
ZN
N
13
11
11
8
11
13
13
19
12
7
13
19
13
13
13
19
13
19
13
13
13
13
19
19
11
13
19
12
19
5
13
13
13
19
11
13
13
19
Value
0.258
0.184
0.029
0.145
-0.024
-0.106
0.081
0.128
0.052
-0.051
-0.006
-0.022
-0.046
0.013
0.055
0.019
-0.059
-0.006
-0.010
0.028
-0.046
-0.114
0.124
0.059
0.055
0.462
0.000
0.040
0.013
0.046
0.033
-0.041
-0.057
0.017
0.106
-0.033
0.065
0.016
Standard
Error*
0.10
0.02
0.02
0.04
0.03
0.06
0.03
0.03
0.10
0.07
0.02
0.02
0.03
0.02
0.02
0.01
0.05
0.02
0.02
0.03
0.04
0.06
0.03
0.02
0.06
0.22
0.02
0.5
0.01
0.05
0.02
0.03
0.03
0.01
0.23
0.03
0.08
0.01
Slope
Value
-0.379
-0.026
0.030
0.001
0.001
0.001
0.001
-0.006
0.029
0.004
0.014
0.003
0.003
0.035
0.011
0.003
0.177
0.052
0.048
0.159
0.006
0.738
-0.007
0.454
0.346
-0.440
0.002
0.747
0.001
0.016
0.115
0.016
0.037
0.039
0.001
0.021
0.028
0.001
Standard
Error*
0.30
0.01
0.01
0.00
0.00
0.00
0.00
0.01
0.03
0.00
0.00
0.00
0.00
0.01
0.00
0.00
0.04
0.01
0.01
0.03
0.00
0.17
0.01
0.14
0.26
0.30
0.00
0.32
0.00
0.01
0.02
0.00
0.01
0.00
0.01
0.00
0.03
0.00
Correlation
Coefficient
-0.47
-0.85
0.91
0.47
0.92
0.86
0.73
-0.29
0.36
0.89
0.94
0.94
0.92
0.92
0.93
0.94
0.86
0.92
0.94
0.89
0.92
0.88
-0.18
0.73
0.53
-0.53
0.89
0.71
0.95
0.86
0.90
0.93
0.93
0.97
0.06
0.93
0.37
0.95
[Hg] = intercept + slope [element]* 90% confidence limits.
Note: regression data for other element pairs in Table A-8 of Appendix.
68
-------
TABLE 14. RESULTS OF PAIRWISE REGRESSION ANALYSIS
OF TIN SURFACE CONCENTRATION DATA
Intercept
Element
FSOL
IOC
OC
AS
BA1
BA2
BR
CA
CD
CE
CO
CR1
CR2
CS
CS-137
CU
EU
FE1
FE2
HG
K
LA
LU
MG
MN
NA1
NA2
NI
P
PB
PB-210
SB
SC
SM
SR
TH
U
ZN
N
37
29
28
22
30
37
37
57
33
30
37
57
37
37
37
56
37
57
37
19
36
37
37
57
57
30
37
57
30
57
20
37
37
37
31
37
37
57
Value
6.092
4.085
0.469
3.490
-0.480
-0.979
2.009
3.337
1.487
-2.202
-0.643
-0.366
-1.482
-0.204
0.889
0.155
-2.327
-0.339
-0.698
-0.247
0.567
-1.490
-2.313
3.342
1.648
1.484
8.470
-0.292
0.603
-0.309
0.820
0.601
-1.490
-1.871
5.036
-1.311
0.341
0.030
Standard
Error*
1.32
0.38
0.53
0.75
0.78
1.55
0.51
0.36
1.51
0.83
0.56
0.50
0.70
0.52
0.35
0.26
0.82
0.34
0.53
0.28
0.59
0.66
1.03
0.43
0.36
1.06
3.23
0.38
0.65
0.27
0.62
0.56
0.66
0.73
3.69
0.69
1.07
0.28
Slope
Value
-10.035
-0.641
0.734
0.016
0.023
0.009
0.019
-0.264
0.466
0.098
0.340
0.062
0.067
0.869
0.270
0.065
4.700
1.211
1.202
23.609
3.428
0.144
16.061
-0.356
7.032
7.035
-7.592
0.056
14.706
0.039
0.333
2.762
0.399
0.925
-0.048
0.521
0.938
0.022
Standard
Error*
4.05
0.13
0.15
0.03
0.00
0.00
0.01
0.09
0.51
0.02
0.05
0.01
0.01
0.14
0.04
0.01
0.72
0.13
0.17
2.17
0.79
0.02
3.08
0.16
2.02
4.94
4.40
0.01
4.13
0.00
0.08
0.61
0.06
0.14
0.08
0.08
0.37
0.00
Correlation
Coefficient
-0.51
-0.79
0.81
0.18
0.77
0.52
0.46
-0.47
0.22
0.86
0.85
0.77
0.84
0.84
0.85
0.90
0.84
0.87
0.86
0.97
0.72
0.85
0.78
-0.38
0.55
0.35
-0.38
0.84
0.69
0.92
0.80
0.73
0.85
0.85
-0.15
0.83
0.51
0.89
[Sn] = intercept + slope [element]* 90% confidence limits.
Note: regression data for other element pairs in Table A-8 of Appendix.
69
-------
TABLE 15. COMPARISON OF MEAN SURFACE CONCENTRATION DAT\ WITH OTHER REPORTED VALUES
Mean Concentration
(Frye and Shimp, 1973)
Element
Major (%)
Al
Ca
K
Mn
Na2
P
Si
Ti
Fe2
Minor (ug/g)
As
Cd
Co
Cr
Cu
Hg
Ni
Pb
Sr
V
Zn
This Report
Basins Combined3
(5.9)b
2.7 + 2.7
0.68 + 0.3
0.13 + 0.11
0.73 + 0.07
0.15 + 0.06
1.2
(0.30)
3.1 + 1.0
27 + 10
2.9 + 0.7
11 + 4
47 + 19
37 + 21
0.11 + 0.06
51 + 23
74 + 35
44 + 5
(90)
120 + 60
IJC,
Port Huron Basin
5.5 + 0.6
0.93 + 0.07
2.7 + 0.2
0.08 + 0.05
0.7 + 0.04
0.06 + 0.01
31 + 1.9
0.33 + 0.03
3.2 + 0.6
-
1 +0.4
14 + 7
36 + 8
42 + 11
0.44 + 0.17
43 + 8
38 + 27
74 + 17
56 + 19
50 + 27
1977
Goderich Basin
4.6 + 1.3
3.9 + 3.3
2.3 + 0.6
0.08 + 0.03
0.72 + 0.06
0.08 + 0.02
28 + 3.1
0.31 + 0.07
3.0 + 1.2
1 + 2
1 + 0.5
22 + 21
29 + 11
30 + 16
0.25 + 0.13
35 + 17
58 + 12
79 + 26
40 + 23
63 + 37
fe — ' •
Lake
Michigan
Core 115 Average
5.0
6.7
2.0
0.06
0.45
0.15
22
0.31
3.1
15
-
15
80
45
0.24
40
125
-
66
270
—
5.6
-
0.06
-
0.07
25
-
2.6
14
4.9C
13
77
37
0.20
34
88
—
48
206
c Value from B.irron (1976).
-------
INORGANIC CARBON
SOUTHERN LAKE HURON
10 20 30
KILOMETERS
Figure 20. Distribution of inorganic carbon i
sediments.
in surface
71
-------
deposition along the eastern side of Lake Huron. Thomas et al. attribute the
high carbonate values on the eastern side of the Lake to the proximity of
carbonate bedrock of the Bruce Peninsula and the shoreline exposures of
glacial sediments on the eastern shore. Their x-ray diffraction studies
indicate that the carbonate in the eastern portion of the lake consists
predominantly of dolomite with subsidiary calcite. The calcium family
element data support that observation.
Both calcium (Fig. 21) and magnesium (Fig. 22) as well as Fsol (Fig. 23)
have distributions very similar to that of IOC. The scatter plot of Ca vs.
IOC shown in Fig. 24 indicates the excellent degree of correlation between
these quantities (R = 0.995; N = 29). The regression equation is
Ca = 0.39 + (1.58 + .04) IOC. (20)
If the calcium and IOC were due entirely to dolomite, the expected ratio
would be
Ca/IOC - 40/24 = 1.66 (21)
if the composition of dolomite is taken to be CaMg(C03)2. The 4% difference
between the observed and expected slopes is within experimental
uncertainties. Hence the relationship between Ca and IOC suggest that
essentially all the inorganic carbon present is due to non-substituted
dolomite.
The magnesium data are also consistent with this analysis. A scatter
plot of Mg vs. IOC (Fig. 25) shows that provided Mg > 1% the correlation with
IOC is excellent. Regression analysis of all data yields
Mg = 0.824 + (0.829 4- .04) IOC r = 0.987 N = 34 (22)
whereas regression on data for which Mg> 1% yields:
Mg = 0.87 + (0.89 +_ .05) x IOC r = 0.98 N = 29. (23)
This latter slope may be compared with that expected if both Mg and IOC were
due exclusively to dolomite:
Mg/IOC = 24/24 = 1.00. (24)
Again the observed slope is consistent with expectation, although some Mg is
evidently associated with non-dolomitic material. Similarly the regression
of Ca on Mg (Fig. 26) for Mg > 1% yields
Ca = -0.95 + 1.72 Mg r = 0.97 N = 42 (25)
while the expected slope is
Ca/Mg = 40/24 = 1.65.
72
-------
43°30'—
~
CALCIUM
Sornio
SOUTHERN LAKE HURON
10 20 30
KILOMETERS
Figure 21. Distribution of calcium i
surface sediments,
73
-------
43°00'—
SOUTHERN LAKE HURON
82° 30'
10 20 30 40
KILOMETERS
82°00
Figure 22. Distribution of magnesium in surface sediments,
74
-------
43°30—
FRACTION SOLUBLE
(PERCENT)
D
D 10-20
M 20-30
• 30-40
• 40-50
43°00'—
Port
Huron
N
SOUTHERN LAKE HURON
82° 30'
10 20 30
KILOMETERS
82°00'
40
Figure 23.
Distribution of fraction soluble component in
surface sediments.
75
-------
o\
Figure 24.
12345
INORGANIC CARBON (wt%)
Relation between calcium and inorganic carbon in surface sediments,
-------
LJ
1
234
INORGANIC CARBON (wt %)
Figure 25. Relationship between magnesium and inorganic carbon
in surface sediments.
77
-------
oo
12345
MAGNESIUM (wt%)
Figure 26. Relation between calcium and magnesium in surface sediments,
-------
As can be seen from inspection of the correlation matrix and regression
Table (A-8), the correlation of Sr with major calcium family constituents is
significant but considerably poorer:
Sr = 40.59 + 0.86 Ca r - 0.47 N = 33. (26)
The strontium associated with calcium occurs in the ratio of:
Sr/Ca = 0.86 x 10 ~4 (g/g).
The three independent estimators of dolomite, Ca, Mg, and IOC, are used
in Table 16 to obtain the best estimate of dolomite in surface sediments.
The resulting distribution of dolomite is shown in Fig. 27. Toward the
eastern margin of the Goderich Basin dolomite can account for over 40% of the
total weight of dry sediment.
It is therefore, not surprising that Fsol is well-correlated with the
calcium family elements. Much of what goes into solution on acid-peroxide
treatment is evidently due to dissolution of dolomite. Regression of Fsol on
Ca gives:
Fsol = 0.241 + 0.022 Ca r = 0.85 N = 39. (27)
As Fsol must include dissolution of nondolomitic materials as well, its
correlation with Ca is predictably less than major calcium family and IOC
inter-correlations. Given in Table 16 is the fraction of dry sediment which
dissolves on acid treatment which is not due to dolomite dissolution, Fsol*:
Fsol* = Fsol - (Dolomite (wt. %) / 100.0) (28)
The ratio Fsol*/Fsol, also shown in Table 16 is the fraction of sediment
dissolved which is non-dolomitic. At some stations such as 44 where
Fsol*/Fsol = 0.06, 94% of the material in solution is due to dissolution of
dolomite. In contrast at Station 5 where Fsol*/Fsol = 0.92, 92% of the
material dissolved is not due to dolomite.
With the dolomite contributions removed from Fsol by introducing Fsol*,
this latter quantity should correlate strongly with the complementary major
sedimentary constitutents which go into solution, organic carbon and iron.
Their isopleths are shown in Figures 28 and 29 respectively. A scatter plot
of Fsol* versus OC, shown in Figure 30, shows that Fsol* is well-correlated
with organic carbon (and Fe).
Pair-wise regression analysis yields:
Fsol* = -1- 0.001 + 0.0480C r = 0.96 N = 28. (29)
Fsol* is also well-correlated with iron:
Fsol* = - 0.033 + 0.074 Fe r = 0.96 N - 28. (30)
As Fsol* is most certainly made up of contributions from both Fe and OC
79
-------
Horbor
Beach
DOLOMITE
(wt%)
a 1-5
5-10
10-20
20-40
>40
SOUTHERN LAKE HURON
Figure 27.
Distribution of dolomite in surface sediments.
Values are based on analysis of calcium, magnesium
and inorganic carbon content.
80
-------
TABLE 16. CONCENTRATION OF DOLOMITE IN SURFACE SEDIMENTS BASED ON CALCIUM,
MAGNESIUM AND INORGANIC CARBON CONTENT (WT %)
00
Station
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
29
30
31
32
33
34
35
36
37
38
39
Calcium
2.01
0.11
0.48
0.64
7.37
0.62
4.00
0.48
0.54
2.33
7.68
2.46
0.16
0.64
1.38
4.22
0.39
1.08
1.30
0.68
1.69
0.65
0.64
0.55
0.60
0.40
0.29
3.33
2.79
6.66
2.69
Magnesium
1.47
0.17
0.82
0.77
5.19
0.87
3.06
0.47
0.67
1.96
5.42
2.11
0.12
0.88
1.47
3.17
0.55
1.14
1.29
0.67
1.73
0.26
0.73
0.61
0.90
0.40
0.26
2.60
1.62
3.92
1.72
IOC
0.10
4.78
0.09
2.41
0.08
1.21
4.85
0.95
0.14
0.64
2.37
0.78
0.10
0.16
0.08
3.79
1.59
Dol(Ca)
9.3
0.5
2.2
3.0
34.0
2.9
18.4
2.2
2.5
10.7
35.4
11.4
0.7
3.0
5.3
19.4
1.8
5.0
6.0
3.1
7.8
3.0
3.0
2.6
2.8
1.8
1.3
15.3
12.8
30.7
12.4
Dol(Mg)
7.2
0.0
2.1
1.7
36.7
2.5
19.3
0.0
0.9
11.1
38.4
12.3
0.0
2.5
7.2
20.7
0.0
4.6
5.8
0.9
9.3
0.0
1.4
0.4
2.7
0.0
0.0
16.1
8.4
26.6
9.2
Dol(IOC)
2.2
37.8
2.1
19.8
2.0
10.6
38.3
8.7
2.5
6.3
19.4
7.4
2.2
2.6
2.0
30.2
13.5
Dol
8.2
0.3
2.2
2.3
36.1
2.5
19.3
1.4
1.7
10.8
37.4
10.8
0.4
2.7
6.6
19.9
0.9
4.8
5.9
2.0
8.1
1.7
2.2
1.5
2.7
0.9
1.1
15.7
10.6
29.2
11.7
Fsol
0.243
0.260
0.428
0.260
0.283
0.326
0.463
0.317
0.250
0.318
0.354
0.317
0.137
0.262
Fsol*
0.161
0.238
0.067
0.235
0.090
0.218
0.089
0.209
0.223
0.252
0.155
0.236
0.165
0.235
Fsol*/Fsol
0.562
0.917
0.156
0.905
0.317
0.668
0.193
0.661
0.893
0.792
0.439
0.743
0.883
0.897
(continued)
-------
TABLE 16. (continued)
oo
ISJ
Station
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
65
66
67
68
69
70
71
73
Calcium
4.18
1.19
1.84
6.66
9.45
8.34
7.51
0.88
0.46
0.82
7.17
8.34
2.85
1.95
7.97
1.09
0.28
0.85
2.86
0.77
3.79
6.25
5.81
2.22
1.44
2.81
3.33
1.84
2.05
0.88
1.21
1.08
Magnesium
2.83
0.91
1.50
4.27
5.01
5.18
4.68
1.05
0.39
1.01
4.97
4.58
1.66
1.73
5.31
1.23
0.32
1.28
2.19
0.92
3.12
4.38
4.38
2.04
1.50
2.48
2.76
1.78
1.83
1.14
1.39
1.40
IOC
2.67
1.08
3.93
5.39
4.71
4.40
0.27
0.26
4.68
4.72
1.41
4.68
0.32
1.67
3.36
1.30
0.61
2.13
Dol(Ca)
19.3
5.5
8.5
30.7
43.5
38.4
34.6
4.0
2.1
3.8
33.0
38.4
13.1
9.0
35.7
5.0
1.3
3.9
13.2
3.5
17.4
28.8
26.7
10.2
6.6
12.9
15.3
8.5
9.5
4.0
5.6
5.0
Dol(Mg)
18.0
2.8
7.4
29.4
35.2
36.6
32.6
3.9
0.0
3.6
34.9
31.8
8.8
9.3
37.5
5.3
0.0
5.7
12.9
2.9
20.3
30.3
30.3
11.7
7.4
15.2
17.4
9.6
10.1
4.6
6.6
6.7
Dol(IOC)
21.7
9.6
31.3
42.4
37.2
34.9
3.5
3.4
37.0
37.3
12.1
37.0
3.9
14.1
27.0
11.3
6.1
17.6
Dol
19.7
4.1
8.5
30.5
40.4
37.4
34.0
3.8
1.0
3.6
35.0
35.9
11.4
9.1
37.1
4.7
0.6
4.8
13.4
3.2
18.8
29.5
28.0
11.1
6.7
14.1
16.8
9.1
9.8
4.3
6.1
5.8
Fsol
0.242
0.212
0.452
0.397
0.375
0.303
0.311
0.401
0.411
0.434
0.296
0.270
0.211
0.278
0.322
0.430
0.391
0.276
0.272
0.327
0.306
0.297
0.310
0.205
0.267
Fsol*
0.045
0.127
0.048
0.023
0.035
0.265
0.275
0.051
0.052
0.063
0.249
0.222
0.077
0.246
0.134
0.135
0.111
0.165
0.205
0.186
0.138
0.206
0.212
0.152
0.206
Fsol*/Fsol
0.188
0.598
0.107
0.058
0.092
0.874
0.884
0.128
0.128
0.145
0.840
0.822
0.365
0.835
0.415
0.313
0.284
0.598
0.753
0.570
0.451
0.695
0.685
0.788
0.773
-------
43°00'—
Kincardine
Goderich
SOUTHERN LAKE HURON
10 20 30
KILOMETERS
40
82° 30'
82°00'
Figure 28. Distribution of organic carbon in surface sediments,
83
-------
SOUTHERN LAKE HURON
10 20 30 40
KILOMETERS
Figure 29. Distribution of iron in surface sediments,
84
-------
00
Ui
0
Figure 30.
3 4
ORGANIC CARBON (wt%)
6
Relation between the fraction soluble component (corrected for dolomite
contributions) and organic carbon.
-------
as well as Mn to a lesser extent it should be best described in terms of a
linear combination of these elements; i.e.,
Fsol* = a + g OC + y Fe + 6 Mn
multiple regression analysis yields the values given in Table 17.
(31)
TABLE 17. COEFFICIENTS FROM MULTIPLE LINEAR REGRESSION OF
FSOL* VS OC, FE AND MN
Coefficient
a
3 (OC)
T (Fel)
6 (Mn)
Value
- 0.0202
0.0251
0.0358
0.0207
Standard
Error
+ 0.012
+ 0.007
+ 0.013
4- 0.072
Level of
Significance
0.1
0.001
0.01
0.8
N = 28
Most of the significance is determined by OC and Fe. The unexplained
variance and the contribution of manganese to the proper description of Fsol*
are negligible. The parameters, a and g , have associated uncertainties of
28% and 36% respectively. The relationship between Fsol* determined by
dolomite subtraction and that predicted by equation 26 is shown in Figure 31.
If the contribution of organic carbon to Fsol* were due solely to
compounds having the empirical formula, (CH20)n (sugars, cellulose, etc.)
Fsol(org.C) = 12 + 18 x 1 = 0.025 OC
12
100
(32)
This is precisely the value found from the regression analysis. Thus
the above empirical formula is consistent with the inferred contribution of
organic carbon to the acid-peroxide extractable material in sediments. Such
close agreement between the value of beta and that in Eq. 32 above is
undoubtedly accidental, however.
Values of y an
-------
0.3
•o
0)
5 0.2
(/>
o
0>
o
u.
0.1
O.t
0.2
Fso*( multiple regression)
0.3
Figure 31. Relation between observed and predicted values of
dolomite-corrected fraction soluble content of
surface sediments.
87
-------
Fsol* (Mn) = 54.93 + 4 x 17 1 = 0.022 Mn (%) • (34)
54.93 100
Both values are consistent with those obtained from the regression
analysis within experimental errors, 0.036 + 0.013 and 0.02 + 0.07
respectively. The coefficient in Eq. 33 would increase for contribution from
iron compounds having less iron by weight per molecule, such as iron
phosphates and iron in humic materials.
The distribution of organic carbon in surface sediments is consistent
with the observations of Thomas et al. (1973) both in terms of absolute value
and trend toward higest concentrations in deeper parts of each depositional
basin. As shown in Fig. 32, Fe and organic carbon are well-correlated.
Distributions of other major elements are shown in Figures 33-36. Mn,
acid-soluble P and K have distributions similar to those of OC and Fe. The
distribution of Na2 (NAA) tends to follow that of the calcium family elements
with highest concentrations along the eastern margin of the Goderich Basin.
Trace Constituents
Many of the 27 trace elements are intercorrelated to a very high degree
as can be seen by inspection of the correlation matrix (Table 11). The
highest correlation occurs for the pair, Fe2(NAA) - Co(NAA), with r = 0.99
for N = 39 (Fig. 37). Among acid-extracted .elements, the highest correlation
occurs for Zn and Cu with r = 0.98 and N = 61 (Fig. 38). Many other element
pairs have correlations exceeding 0.90 for a sizeable number of observations.
On the other hand, trace element concentrations in the acid soluble
sediment fraction and in whole sediment are not necessarily as well-
correlated. The results of pair-wise linear regression analysis of AAS and
NAA data are in Table 18 for Ba, Cr, Fe, and Na. If the dependent variable
is taken to be the acid-extractable element concentration (AAS) and the
independent variable is taken as the whole sediment concentration (NAA) then
the slope derived from the regression analysis is a measure of the average
extraction efficiency. This value may be directly compared with the value
obtained from replicate analysis of standard sediment given in Table 6. From
Table 18 it can be seen that for Ba, Cr and Fe the average extraction
efficiencies are very comparable to those obtained using standard sediment.
For Na, the average extraction efficiency is significantly smaller than for
standard sediment although there is a large uncertainty in estimating the
value. Particularly in the case of Ba and Na, AAS values are poorly,
correlated with those obtained from NAA because the portion which is
acid-leachable is largely unrelated to the Ba and Na present in the unleached
sediment matrix.
Nearly all of the trace elements have a significant degree of
correlation with organic carbon (and iron) and most correlations are very
high as can be seen in Fig. 39. In this figure elements are ordered
according to their degree of correlation with organic carbon. Cu, Pb and Zn
plus the rare earth elements as well as Co, Fe, Sc and Th all have
88
-------
00
VO
z
o
cr
234
ORGANIC CARBON (wt%)
Figure 32. Relation between iron and organic carbon in surface sediments.
-------
43°30'
D <500
D 500-1000
B 1000-2000
• 2000-2500
• >2500
43°00'-
Port
Huron
82°30'
SOUTHERN LAKE HURON
0 10 20 30 40
KILOMETERS
82°00'
Figure 33. Distribution of manganese in surface sediments,
90
-------
43°30'—
PHOSPHORUS
D 3000
43°00'-
Port
Huron
Kincardine
^Goderich
N
SOUTHERN LAKE HURON
10 20 30
KILOMETERS
40
82° 30'
82°00'
Figure 34. Distribution of phosphorus in surface sediments,
91
-------
Harbor
Beach
POTASSIUM
(WT%)
<0.4
0.4-0.7
0.7-10
1.0-1.5
Sarnio
SOUTHERN LAKE HURON
,0 20 30 40
KILOMETERS
Figure
35. Distribution of potassxum
82!QQ_
in surface sediments,
92
-------
43°30'—
SODIUM
(wt.%)
CD 0.60-0.70
EH 0.70-0.80
• 0.80-0.90
• >0.90
43°00'—
Port
Huron
SOUTHERN LAKE HURON
82°30'
10 20 30
KILOMETERS
82°00'
40
Figure 36. Distribution of sodium (NAA) in surface sediments,
93
-------
o
Q_ ^H
— 2
0
0
4 8 12
COBALT-NAA(^g/g)
16
Figure 37. Relation between iron (NAA) and cobalt (NAA) in
surface sediments.
94
-------
200-
0
20 40 60
COPPER (/ig/g)
Figure 38. Relation between zinc and copper in surface sediments,
95
-------
TABLE 18. COMPARISON OF ACID-SOLUBLE (AAS) AND WHOLE SEDIMENT (NAA)
ELEMENT CONCENTRATIONS USING PAIR-WISE LINEAR REGRESSION ANALYSIS
Dependent
Variable
(Element
via AAS)
Bal
Crl
Fel
Nal
Independent
Variable
(Element
via NAA)
Ba2
Cr2
Fe2
Na2
N
32
39
39
32
Regression
Intercept
- 9.1 + 50**
- 1.5 +9
- 0.28 + 0.23
0.26 + 0.2
Parameters*
Slope r
0.37 + 0.11
0.83 + 0.13
0.95 + 0.07
- 0.08 + 0.3
Extraction Efficiency (%)
r
0.63
0.83
0.95
- 0.07
Average
This Data
37
83
95
0
Standard
Sediment
(Table 6)
40
81
93
18
* From Table A-8 of the Appendix.
**Standard error (90% confidence limits).
-------
vo
C CARBON
b
COEFFICIENT OF CORRELATION WITH ORGANI
O O O O O O O
CM '.b en ^ o> 10
Cu
—
-
Lo
Pb
Zn
Ce
Sc
Th
Co
Fel
Sm
Cs
Lu
Eu
CM
Sb
Ni
Bo
i
;7Cs
K
As
Mn
i
iop|
P
i
Br
U
ijnl
Nolcd
ELEMENT
FIGURE 39.
Degree of correlation of element concentrations with the organic carbon
content of surface sediments.
-------
correlation coefficients of 0.90 or greater. Hence distributions of most
trace elements conform to that of organic carbon, exhibiting highest
concentrations in the fine-grained sediments occurring in the deeper areas of
each depositional basin. It should be emphasized that the high degree of
correlation between trace elements and organic carbon (or iron) does not
necessarily mean a chemical affinity in every case. The correlation results
from a combination of geochemical and hydrodynamic processes which result in
the codeposition of trace elements with organic carbon, iron, and clay
minerals. The selective deposition of fine-grained sediments in restricted,
low energy areas of lakes, or sediment focusing, as it is popularly termed is
coming to be recognized as a general feature of sediment transport and
deposition in lakes (cf. Kamp-Nielsen and Hargrave, 1978). In most cases,
trace constituents are found to be codeposited with fine-grained materials
(cf. Clay and Wilhm, 1979). As considerable redundancy exists in the
distribution of trace elements only those for several selected elements,
particularly those shown later to be anthropogenically enriched, are
presented in Figures 40-52.
While a detailed discussion of interelement associations is beyond the
scope of this report, a limited statistical analysis reveals some important
relationships. In this report, we have examined the data in terms of cluster
analysis and principle components analysis. In cluster analysis, elements
are grouped according to the degree of similarity in their behavior. While
several alternative measures of similarity have been developed, we have
chosen to base the degree of similarity on the correlation coefficient. The
degree of similarity is taken to be, 1 - r, where r is the correlation
coefficient. Clustering is performed by stepwise addition of elements to the
set. Principle components analysis provides a means of identifying a set of
independent variables, a linear combination of which provides a statistically
adequate representation of measured concentration values. In the present
case the number of truly independent variables is far less that the number of
elements determined. Like cluster analysis, principal components analysis
provides a means of summarizing the associations between elements. Because
of the frequency of missing observations the two statistical methods were
applied to subsets of the data. Nine elements (Ca, Crl, Cu, T?el, Mg, Mn, Ni,
Pb, Zn) comprise the most complete set of data of 60 observations with no
missing data. Other sets including those with either OC, IOC or neutron
activation data are more limited, consisting of about 30 observations. Five
subsets of data examined are:
1. IOC set (IOC, Ca, Mg, Fsol, Sr, Na2, Bal; N = 25)
2. OC set (OC, Cu, Zn, Fel, Pb, Ni, Crl, Mn; N = 27)
3. Complete data set (N = 60)
4. Complete data set plus surface-enriched elements (N = 22)
5. Complete data set plus non-enriched elements (N = 30)
Results of the cluster analysis are shown in Figures 53 and 57. From
the discussion of the calcium family elements in the earlier section, it
should be expected the IOC, Ca and Mg would bear a close relation to each
other, while Fsol, being comprised of both dolomitic and non-dolomitic
contributions, would be less strongly related. The cluster analysis
illustrates this relationship in terms of a hierarchical tree (Fig. 53, IOC
98
-------
-------
Harbor
Beach
SOUTHERN LAKE HURON
0 10 20 30 40
KILOMETERS
Figure 41. Distribution of arsenic (NAA) in surface sediments
100
-------
SOUTHERN LAKE HURON
O 10 20 30 40
KILOMETERS
Figure 42. Distribution of bromine (NAA) in surface sediments
101
-------
SOUTHERN LAKE HURON
10 20 30 40
KILOMETERS
Figure 43. Distribution of cadmium in surface sediments,
102
-------
]<20
20-40
40-60
60-80
>80
N
SOUTHERN LAKE HURON
82° 30'
10 20 30
KILOMETERS
82°00'
40
Figure 44. Distribution of chromium in surface sediments.
103
-------
SOUTHERN LAKE HURON
82°30'
»0 20 30
KILOMETERS
82°00'
40
Figure 45. Distribution of copper in surface sediments,
104
-------
o
N
SOUTHERN LAKE HURON
82° 30'
10 20 3O
KILOMETERS
82°00'
40
Figure 46. Distribution of lead in surface sediments,
105
-------
43°30 —
MERCURY
(/ig/g)
CDO.02-0.10
i \ 0.10-0.15
mi 0.15-0.20
B 0.20-0.25
•i 0.25-0.30
43°00'—
Port
Huron
^Goderich
Sornio
SOUTHERN LAKE HURON
82° 30'
10 20 30
KILOMETERS
82°00'
40
FIGURE 47. Distribution of mercury in surface sediments,
106
-------
SOUTHERN LAKE HURON
10 20 3O 40
KILOMETERS
FIGURE 48. Distribution of nickel in surface sediments,
107
-------
SOUTHERN LAKE HURON
Figure 49. Distribution of thorium (NAA) in surface sediments
108
-------
Horbor
Beoch
<0.5
CD 0.5-2.0
2.0-3.5
3.5-5.0
5.0-6.0
Sornio
SOUTHERN LAKE HURON
FIGURE 50. Distribution of tin
in surface sediments.
109
-------
SOUTHERN LAKE HURON
Figure 51. Distribution of uranium (NAA) in surface sediments
110
-------
N
SOUTHERN LAKE HURON
82° 30'
0 10 2O 30
KILOMETERS
82°00'
40
Fiaure 52. Distribution of zinc in surface sediments.
Ill
-------
set). In successive stages elements are attached to discreet clusters. At
the first stage, Ca is associated with IOC. Next Mg is added to form a three
element cluster. Fsol, while added next, is not attached to a specific
element, but rather to the three element cluster. Sr, Na2 and particularly
Bal, are weakly coupled to this group. Inspection of the correlation matrix
shows that Bal should not even be included in the "calcium family" element
group. Na2 should be included in this group because it was a small but
positive correlation with Ca. Use of alternative distance (similarity)
measures (Euclidean, Hinkowski, etc.) does not result in a different
clustering. This configuration is stable with respect to changes not only in
association measures but with respect to weighting given to neighboring data
points. Similar results are obtained using principal components analysis.
Two components account for over 95% of the variance. Elements are located in
the plane defined by these two components as shown in Fig. 54. Groupings can
be seen to be consistent with the results of cluster analysis. IOC, Ca, and
Mg are tightly grouped; Fsol is more distant as are the elements Sr and Nal
while Bal is essentially unrelated.
Because the correlation between organic carbon and iron is very high the
possibility of using statistial techniques to determine the relative
importance of these two variables in the deposition of trace contaminants is
marginal at best. The only hope lies in examination of a limited set of
variables including both OC and Fe. For the nine elements in the complete
set, replicate samples were run and they are therefore the set with minimum
experimental uncertainties. To further provide a separation in terms of
cluster and principle components analysis the calcium family elements were
left out of the set while organic carbon was included. The results (Fig. 53,
OC sat) show that Cu and Zn form the principle cluster. Fel is attached to
this cluster at the next level and at the third level OC is attached to this
three-element group. Beyond that point elements are progressively added to
this single cluster in the order: Pb, Ni, Crl, and Mn. Trials with other
measures of association show that the pair Zn - Cu is stable but that OC and
Fe may "trade places". This is reflected in the results of principle
components analysis (Fig. 51) where two components suffice to account for 95%
of the variance. As can be seen in Fig. 55, Zn, Cu and OC are most closely
associated while Fel is somewhat removed. Lead, while further removed is
principally described by component 1. In contrast, Mn is principally
described in terms of component 2 and is, in fact, the reason for the
existence of a two-component description of the data set. On balance, there
is a trend toward association of Zn and Cu with OC but even with very high
quality data such as this, the distinction between OC and Fe is marginal.
The clustering of elements revealed by treatment of data subsets is
preserved when the complete data set is used. As can be seen in Fig. 53
(complete set), Ca and Mg are strongly associated and form a cluster which is
only remotely connected to other elements. Cu and Zn again are most strongly
associated and Fel is added at the third stage to form a three-element
cluster. To this cluster are added Pb and Ni in order, while Mn is
essentially an independent element. Similar relationships are seen on
principle components analysis (Fig. 56). The anthropogenically enriched
elements (see below) form a close association (Pb, Zn, Ni, Cu). Crl and Fel
are slightly removed from this group while both Mn and Ca + Mg are distant
112
-------
1. IOC Set
2. OC Set
oc
Cu
Zn
Pel
Pb
Ni
CM
Mn
3. Complete Set
Co
Mg
CM
Cu
Zn
Pel
Pb
Ni
Mn
4. Complete Set + Surface-enriched
As
Br
Sb
Cd
Cu
Pel
Zn
Pb
Mn
Ni
Cr 1
Cs-137
Co
Mg
Figure 53.
Hierarchical trees resulting from cluster analysis
of surface sediment concentrations.
113
-------
Bo I
0.4 h
0.2-
OJ
UJ
O
Q_
8-0.2
-0.4
-0.6
Sr
FSOL
No 2
1
-0.2
0 0.2
COMPONENT 1
0.4
Figure 54
Association of calcium family and related constit-
uents based on principal components analysis.
114
-------
COMPONENT 2
fD
Ul
Ul
•
P) 3 >
3 O W
PJ co en
I-1 rt o
CO O H-
p- O £<
co 3 rt
• "T3 H-
M 0
fD 3
rt
fD O
Hi
pj y
rt 0
p 3
I
co o
fD fa
rt M
O
cr H-
co 3
fD
CL hh
0 3
3 H-
H
n
H- fD
0 fD
H-3
13 fD
P 3
I-1 rt
CO
O
O H-
3 3
0 rt
fD fD
3
rt
CO
1 1 1
O O O O P
CD ^ ro O K) 4^
P
04
ro
o
O
«^
1 P
O OJ
2 •*
m
*"*"
O
OJ
CD
1 1 1
"3
—
^M*
^^^
•o
o-
1 1
o
•^
-------
0.6
0.4
CO
I-
z
bJ
z 0.2
o
a.
8
-0.2
Pel
Mn
I
-0.2
0 0.2
COMPONENT 1
0.4
Figure 56.
Results of principal components analysis of complete
data set including calcium-family elements.
116
-------
5. Complete Set + Non- enriched
Co
Mg
Ce
La
Sm
Th
Eu
Cu
Pel
Zn
Pb
Ni
Lu
CM
K
Mn
U
Co 177-1
Fe2 -3_L
5hn
Figure 57.
Hierarchical tree resulting from cluster analysis of
the complete data set plus additional non-enriched
elements.
117
-------
elements. On the basis of the complete (N = 60) data set the principle
components analysis recognizes three components accounting for 96% of the
variance. The first and second, used to locate elements in Fig. 56,
correspond to the transition metal group + lead and to calcium family
elements respectively. The third component corresponds to Mn. The
uniqueness of Mn may be attributed to its ability to undergo diagenetic
remobilization in near-surface sediments. This attribute would not normally
be revealed on application of multivariate techniques to gross sediment
samples. The uniqueness of Mn is emphasized as a result of using a sediment
section close to the surface whose Mn concentration is often dominated by the
remobilized fraction. This effect may be better appreciated by comparison of
manganese concentration profiles with those of other elements (see below).
The results of principle components analysis on the complete set are
summarized in Table 19.
If all surface-enriched elements are added to the complete data set, an
additional group emerges from cluster analysis as can be seen in Fig. 53. In
addition to the groups (Cu, Zn, Fel, Pb) and (Ca - Mg) there is (As-Br-Sb).
Reasons for this association are not clear although As and Sb, at least, are
in the same chemical family and might reasonably be expected to have similar
geochemical behavior. Elements such as Cd, Crl, and Cs-137 are not strongly
related to any group although they are clearly not associated with calcium
family elements. The association of Ni with Mn is unstable and does not
survive changes in the measure of similarity.
The hierarchical tree resulting from cluster analysis of the non-
enriched elements plus the basic data set is shown in Fig. 57. Two new
associations are apparent. In addition to the Cu-Zn-Pb-Fel and the Ca-Mg
groups, there are Ce-La-Sc and Co-Fe2. Both of these latter sets involve
elements determined via NAA on whole sediments. With the exception of Fe2
these elements are primarily lattice-bound constituents not readily leached
by acid. Both sets are probably characteristic of the clay minerals present
and are themselves connnected together early on in the stepwise clustering
process. To the largar cluster defined by Ce-La-Sc-Co-Fe2 are progressively
added the other rare earth elements (Sm, Eu) and Cs, Cr2 and Th. Elements
loosely connected to any cluster are Ni, Crl, K, Mn, U and the rare earth
element, Lu. Thus with the exception of Lu, the rare earth elements are a
part of a major cluster (Ce, Sm, Eu) which includes La, Sc, Co, Fe2, Cs, Th,
and Cr2.
In summary, five principal groupings of elements are identified: (1)
IOC Group: lOC-Ca-Mg-Fsol; (2) OC group: OC-Fel-Cu-Zn-Pb-(Ni); (3) Diagenetic
Group: Mn only; (4) Sb-As group: Sb-Br-As; and (5) Clay mineral group: two
sub groups A = Ce-La-Sc and B = Co-Fe2 which in turn are connected so that
the major cluster is A-B-Cs-Sm-Th-Cr2-Eu. These results are presented in
Table 20.
VERTICAL DISTRIBUTIONS OF ELEMENTS
Vertical distribution of metals and radioactive constituents have been
measured in 32 cores as summarized in Table 21. NAA elements were determined
in only one of the cores at Station 18 (Tables 22, 23). The vertical
118
-------
TABLE 19. RESULTS OF PRINCIPLE COMPONENTS ANALYSIS OF COMPLETE DATA SET*
Component
Element
Ca
Crl
Cu
Pel
Mg
Mn
Ni
Pb
Zn
Cumulative
Explained
Variance (%)
-0.
0.
0.
0.
-0.
0.
0.
0.
0.
1.
252
343
378
380
211
269
367
371
377
73
2.
0.601
0.234
0.108
0.097
0.669
-0.181
0.146
0.189
0.159
90
3.
0.207
-0.304
-0.158
-0.037
0.171
0.887
0.109
0.056
-0.085
96
4.
0.019
-0.840
0.337
0.121
0.210
-0.217
0.012
0.190
0.285
98
*N = 60.
119
-------
TABLE 20. SIGNIFICANT INTERELEMENT ASSOCIATIONS
IN SURFACE SEDIMENTS OF SOUTHERN LAKE HURON
Group Elements in order of decreasing degree of association
I. Inorganic Carbon lOC-CA-Mg-Fsol Sr Na2
II. Organic Carbon/ Cu-Zn-(Fel-OC)-Pb—Ni Crl
Iron
III. Diagenic Mn only
IV. Sb-As Sb-Br-As
V. Clay Mineral A: La-Sc-Ce B: Co-Fe2
Cs-Sm-Th-Cr2-Eu
120
-------
TABLE 21. A SUMMARY OF VERTICAL DISTRIBUTION MEASUREMENTS IN CORES FROM SOUTHERN LAKE HURON.
Physical AAS NAA
Station Properties Elements Elements
3
4
5
6
7
8
9
10
12
13
14
15
16
17
13
19
25
29
31
33
35
38
39
41
45
50
51
53
57
61
63
69
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Cesium-
137
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Lead- Amorphous Dissolved* Benthic
210 Silicon Elements Invertebrates
X
X
X
X
X
X
X
X
X
X
XX X X
X
X
XX X X
X
X
X
X
X
X
X
X
X
X
X
XX X
X
X
XX X
X
* Pore water concentrations.
(Table A-2).
A complete listing of vertical profile data is contained in the Appendix
-------
distributions of amorphous silicon and dissolved elements were determined for
4 cores (Stns. 14A, ISA, 53 and 53) and the distributions of zoobenthos were
determined at two locations (Stns. 14A and ISA) with a high degree of
replication. Discussion of the vertical distribution of zoobenthos is
deferred to the section on radioactivity profiles. To conserve space, only
eight locations are selected for illustration. The stations include 5, 10
and 19 in the Port Huron Basin; 25 from the Saginaw Basin and stations 14A,
ISA, 53, and 63 in the Goderich Basin. As can be seen from Table 21, these
stations in the Goderich Basin are particularly well-characterized. As the
primary focus of this report is the characterization of anthropogenic
elements in sediments, their increase in concentration and rates of
deposition, the discussion below emphasizes trends in element concentration
profiles and the significance of concentration increases toward the
sediment-water interface. The general behavior of concentration profiles is
expressed in terms of the ratio of the concentration of an element of near
surface sediments (1-2 cm) to its average concentration in deeper sections of
the cores where variations with depth are usually minimal. For cores in
southern Lake Huron, element concentrations are generally constant below
about 20 cm except in cores from stations located in basin margins and
possessing a high degree of inhomogeniety. Surface-to-depth concentration
ratios for the entire set of cores is given in Table 27 and summarized in
Table 30 and 31. Values are given also for the enrichment factor defined
below.
Major Constituents
Vertical profiles of major constituents are shown in Figs. 58-85. Each
profile is accompanied by a trend line to facilitate visualization. As can
be seen in Figs. 58 and 59, Fsol is essentially constant with depth within
experimental errors for most stations except 25 and 53 where there is a
slight but systematic increase over the upper 5 cm or so. In contrast, Fsol
is lower at the surface at station 19. This core is inhomogeneous with
respect to grain size, possessing a lens of sandy mud in the upper 7 cm. On
the average, as can be seen in Table 27, Fsol is about 10% higher in surface
sediments than in deeper sections of cores. Calcium profiles (Figs. 60, 61)
are essentially constant for Stations 5, 10, 19, 14A, and ISA. Cores at
stations 25 and 53 exhibit a small increase in Ca concentration near the
surface while at 63 there is a small subsurface maximum at around 10 cm. On
the average the concentration of calcium is about 30% higher in surface
sediments (Table 27). Iron consistently shows a slight increase in
concentration within the upper 5 cm or so as can be seen in Figs. 62 and 63.
The exception is the core at the marginal station, 19, where surface iron
concentrations are reduced. The average surface-to-depth concentration for
iron (Table 27) is similar to that of Fsol, about 1.08, indicating an 8%
increase in surface values. For Mg, concentration profiles at stations 5, 8,
16, and 14A are remarkably constant while those at ISA and 63 exhibit small,
broad subsurface maxima but are otherwise essentially constant (Fig. 64 and
65). Alternative stations were selected for Mg because no measurements were
made at 10, 19 or 25 for this element. Stations 8, 15 and 16 are all located
in the Port Huron Basin. The core at station 15 is grossly inhomogenous with
respect to sediment type, possessing a 5 cm section of fine sand which grades
into glaciolacustrine clay with increasing sediment depth. This progressive
122
-------
LAKE HURON CORES (EPA-SLH-74)
NJ
E
o
0
5
10
15
20
25
Q_
LoJ
Q 30
35
40 -
45 -
50
25
0 O.I 0.2 0.3 0 O.I 0.2 0.3 0 O.I 0.2 0.3 0 O.I 0.2 0.3
FRACTION SOLUBLE
Figure 58. Vertical distribution of the fraction soluble component for selected
cores from the Port Huron and Saginaw Depositional Basins.
-------
LAKE HURON CORES (EPA-SLH-75)
ro
5
10
15
E 20
o
h-
Q_
UJ
Q 30
35
40
45
50
I4A
ISA
I i |
63
0 O.I 0.2 0.3 0 O.I 0.2 0.3 0.4 0.5 0 O.I 0.2 0.3 0 O.I 0.2 0.3 0.4
FRACTION SOLUBLE
Figure 59. Vertical distribution of the fraction soluble component for selected
cores from the Coderich Basin.
-------
LAKE HURON CORES (EPA-SLH-74)
ho
Ln
\J
5
10
15
"E 20
o
fE 25
Q_
LU
Q 30
35
40
45
50
-
-
•
•
-
-
-
• i i
, •
5
10
25
0246024602460246
CALCIUM (wt. %)
Figure 60. Vertical distribution of calcium in selected Port Huron and Saginaw
Basin cores.
-------
LAKE HURON CORES (EPA-SLH-75)
w
5
10
15
20
1= 25
0
I 30
Q_
LU
Q 35
40
45
50
-
-
-
-
-
_
•
•
•
I4A
-
-
i i
. ISA
0246 0246 0246 0246
CALCIUM (wt. %)
Figure 61. Vertical distribution of calcium in selected Goderich Basin cores,
-------
0
5
10
LAKE HURON CORES (EPA-SLH-74)
o
X
I-
Q_
LU
Q
E 20
25
30
35
40
45
50
10
19
25
01 234501 2 301 2 340
IRON (wt. %)
2 3
Figure 62. Vertical distribution of iron in selected Port Huron and Saginaw Basin
cores.
-------
LAKE HURON CORES (EPA-SLH-75)
S3
oo
0
5
10
15
20
o
X25
Q_
LU
Q 30
35
40
45
50
4A
. ISA
0123
1234 12340123
IRON (wt. %)
Figure 63. Vertical distribution of iron in selected Goderich Basin cores.
-------
LAKE HURON CORES (EPA-SLH-74)
ho
w
5
10
15
20
IE 25
o
I 30
Q_
UJ
Q 35
40
45
50
•
i
-
i
i
-
-
-
I 1
i
5
l i
0246
8
15
i i
16
0246 0246 0246
MAGNESIUM (wt. %)
Figure 64. Vertical distribution of magnesium in selected Port Huron cores,
-------
U)
o
0
5
10
15
E 20
o
X 25
Q_
UJ
Q 30
35
40
45
50
LAKE HURON CORES (EPA-SLH-75)
I4A
0246
ISA
024 6 0246
MAGNESIUM (wt. %)
63
0246
Figure 65. Vertical distribution of magnesium in selected Goderich Basin cores
-------
shift in sediment type is illustrated by the concentration profile of Mg
(Fig. 64). On the average there is no significantly higher concentration of
magnesium in surface sediments than there is in underlying sediments. It is
therefore plausible that the reduction in Ca with increasing sediment depth
is primarily the result of dissolution of non-dolomitic calcium, perhaps
authigenic calcite. In contrast with other major element profiles, those of
manganese are very strongly peaked at the sediment-water interface in every
case including station 19, as can be seen in Figs. 67 and 68. Within the
upper 3 cm or less, the concentration of Mn rises to a maximum in the
uppermost sediment section and greatly exceeds underlying values. Very large
near-surface Mn enrichment has now been widely observed in sediments of the
Great Lakes and elsewhere (Robbins and Callender, 1975; Kemp et al., 1976)
and is almost certainly due to diagenetic remobilization of the element. On
the average the surface to depth concentration ratio is about 2.5 for Mn.
This value is sensitive to the use of the 1-2 cm interval to define the ratio
because of the rapid increase in Mn concentration toward the sediment
surface. For the other elements including those which show enrichments due
to anthropogenic loadings, concentration ratios and enrichment factors are
not nearly as sensitive to the choice of the surface interval. The
concentration of mercury (Fig. 66) shows a dramatic increase toward the
sediment-water interface. Large surface enrichments have been observed
earlier in cores from Lake Huron (Kemp and Thomas 1976), Lake Ontario (Thomas
1972), Lake Erie (Walters and Wolery 1974) and elsewhere and are attributed
to anthropogenic additions of the element to the Lakes. For acid-soluble
phosphorus (Figs. 69 and 70) there is a very slight increase in surface
sediments except for the core at station 25 where there is a small but
systematic decrease toward the sediment surface. On the average (Table 22)
there is a small and marginally significant increase in acid soluble P, 7%.
For potassium (Figs. 71 and 72) there are large excursions in the values of
the concentration in individual sediment sections owing partly to
experimental errors and to variable extractability of K from sediment matrix.
As can be seen from Table 27, potassium is not on the average, enriched in
surface sediments. Perhaps the most interesting major constituent is
amorphous Si which in the four cores studied, shows a large increase in
surface sediments (Fig. 73). Unlike Mn, the concentration of Si increases
gradually from a depth of up to 15 cm toward the sediment water interface.
Its profile is more closely related to those of the anthropogenically
enriched elements than to Mn, showing concentration ratios on the average of
2 in these four cores (Table 27). Near-surface sediment enrichment of
amorphorus Si first reported by Robbins et al. (1974) for Lake Michigan has
subsequently been observed by Parker and Edgington (1976) and in other of the
Great Lakes by Nriagu (1978). It is not yet clear whether the enrichment is
a steady-state feature resulting from deposition of authigenic particulate
silica and its progressive dissolution during burial in sediments or whether
it is the result of recent increases in the rate of biological fixation of
silicon and increased deposition of particulate forms.
Trace Constituents
The vertical distributions of minor elements are illustrated in Figs.
74-85. The only complete profile of cadmium is for a core at station 10
(Fig. 74). At this location there is a four-fold increase in Cd at the
131
-------
10
20
u
Q.
LJ
Q
30
40
50
ISA-2
0.05 0.10 0.15 0.20
MERCURY (fJLQ/g)
Figure 66.
Vertical distribution of mercury in a Goderich Basin
core.
132
-------
LAKE HURON CORES (EPA-SLH-74)
H
U)
w
5
10
15
IE 20
o
X 25
Q_
LU
Q 30
35
40
45
50
•
-
-
-
-
•
T~^
i
9
5
10
0 0.05 0.10 0.15 0.20 0 0.05 0.10 0.15 0.20 0.25 0 0.05 0.10 0 0.05 0.10 0.15 0.20
MANGANESE (wt. %)
Figure 67. Vertical distribution of manganese in selected Port Huron and Saginaw
Basin cores.
-------
LAKE HURON CORES (EPA-SLH-75)
0
5
10
15
E 20
o
Q_
LJ
30
35
40
45
50
1 I
14A
ISA
53'
J I I
0 0.05 0.10 0.15 0.20 0.25 0 0.05 0.10 0.15 0 0.05 0.10 0.15 0.20 0.25 0.30 0 0.05 0.10 0.15 0.20
MANGANESE (wt. %)
Figure 68. Vertical distribution of manganese in selected Goderich Basin cores.
-------
LAKE HURON CORES (EPA-SLH-74)
Ol
\J
5
10
15
20
1 25
o
^ 30
Q_
LJ
Q 35
40
45
50
/ '
•
•
-
"
•
31
-
-
i i
10
19
25
0 0.2 0.4 0.6 0 0.2 0.4 0.6 0 0.2 0.4 0.6 0 0.2 0.4 0.6
TOTAL PHOSPHORUS (wt. %)
Figure 69. Vertical distribution of phosphorus in selected Port Huron and Saginaw
Basin cores.
-------
LAKE HURON CORES (EPA-SLH-75)
CO
ON
VJ
5
10
15
'E 20
o
K 25
Q_
LU
Q 30
35
40
45
50
I
- •
- •
-
r
I4A
-
-
- •
_ •
- *
•
•
— 4
• 1
»
*
ISA
-
1
•
- •
-
_
-
-
t
53'
•
-
•i
(•
i •
-
| 63
•
- •
-
-
0 0.2 0.4 0.6 0 0.2 0.4 0.6 0 0.2 0.4 0.6 0 0.2 0.4 0.6
TOTAL PHOSPHORUS (wt. %)
Figure 70. Vertical distribution of phosphorus in selected Coderich Basin cores,
-------
LAKE HURON CORES (EPA-SLH-74)
OJ
0
5
10
15
20
o
Q.
LjJ
Q 30
35
40
45
50
10
0.8 1.0 1.2 0.2 0.4 0.6 0.8 0.4 0.6 0.8 0.6 0.8 1.0
POTASSIUM (wt. %)
Figure 71. Vertical distribution of potassium in selected Port Huron and Saginaw
Basin cores.
-------
LAKE HURON CORES (EPA-SLH-75)
00
0
5
10
E 20
o
I 25
Q_
UJ
Q 30
35
40
45
50
I4A
ISA
0.6 0.8 1.0 0.4 0.6 0.8 1.0 1.2 0.4 0.6 0.8 1.0 1.2 1.4 0.6 0.8 1.0 1.2
POTASSIUM (wt. %)
Figure 72. Vertical distribution of potassium in selected Goderich Basin cores.
-------
u>
VO
0
5
10
15
E 20
Q_
LJ
Q
25
30
35
40
45
50
LAKE HURON CORES (EPA-SLH-75)
I4A-SC
I8A-SC
53-SC
63-SC
J I L
0 0.5 1.0 1.5 2.0 0 0.5 1.0 1.5 0 0.5 1.0 1.5 0 0.5 1.0 1.5 2.0
AMORPHOUS SILICON (wt. %)
Figure 73. Vertical distribution of amorphous silicon in selected Goderich Basin
cores.
-------
sediment-water interface. While only one complete profile of Cd is
available, concentration data for other cores includes not only surface
values given in Table 9 but concentrations in underlying sediments (22-24 cm)
given in Table 28. From Table 28, it can be seen that on the average the
concentration of Cd in the 1-2 cm interval of sediment is 2.3 times higher
than in the 22-24 cm section. Enrichment of Cd in surface sediments of Lake
Huron has been previously reported by Kemp and Thomas (1976). In a core from
the western margin of the Goderich Basin Kemp and Thomas observed a
concentration ratio of 1.2 for Cd. While this value is significantly lower
than the average, it is shown below that the enrichment factor itself is
subject to large systematic variations within a given depositional basin, a
result of considerable importance in assessing the impact of man's activities
on the composition of recent sediments. The profiles of chromium shown in
Figs. 75 and 76 suggest that this element is not significantly enriched.
Apart from station 19 and 25 where Cr concentrations are depressed in surface
sediments, profiles at other locations are essentially constant. As can be
seen from Table 28, on the average Cr is not significantly enriched in
surface sediments. For copper (Figs. 77 and 78) the sediments are
consistently enriched near the surface. The exception is the profile at
station 19 where sediments are inhomogeneous. On the average the
surface-to-deep concentration ratio for Cu is 1.5 (Table 28). Kemp and
Thomas (1976) observed a ratio of 1.7 in their single core from southern Lake
Huron. Surface enrichment is even more pronounced for lead (Figs. 78 and
80). All profiles indicate a major increase in the concentration of lead
(except 19) toward the sediment surface. In the one southern Lake Huron core
described by Kemp and Thomas (1976) a six-fold increase in Pb concentration
was found between the 20-30 cm section and 0-1 cm. Nickel is also
consistently enriched in surface sediments located away from basin margins as
can be seen in Figs. 81 and 82. The average surface to depth concentration
ratio for this element is 1.7 (Table 28). The vertical distribution of tin
(Fig. 83), exhibits a marked increase in the vicinity of the sediment-water
interface. The more than five-fold enrichment of tin in core 18A-2 indicates
that this is probably one of the most significantly enriched elements in
sediments of the Great Lakes. Data below indicate that enrichments of this
newly observed element probably are the result of anthropogenic loadings.
Zinc is also appreciably enriched as can be seen in Figs. 84 and 85. With
the exception of station 19, all profiles show a marked increase toward the
sediment-water interface. The average concentration ratio for zinc is 2.2
(Table 28).
Cores at Station 18
All sections of the core (EPA-SLH-74-18-2) at station 18 were analyzed
by neutron activation analysis. The data are given for major elements in
Table 22 and for minor elements in Table 23. Profiles for the major elements
are shown in Figure 86. It can be seen that with the exception of sodium,
the concentration of major elements is essentially constant over the 50 cm
length measured. The sodium (Na2) concentration increases by about 30% with
increasing sediment depth and may reach a maximum value at around 30 cm depth.
In Figure 87 are shown examples of minor element (NAA) profiles while in
Figure 88 are shown profiles of Zn, Pb, Ni, Cu (AAS) together with Cr and Sb
140
-------
CADMIUM (pg/g)
2 3
0
10
E
o
Q_
LU
Q
20
25
SLH-74-IO
Figure 74. Vertical distribution of cadmium in a Port
Huron Basin core.
141
-------
LAKE HURON CORES (EPA-SLH-74)
\J
5
10
15
"? 20
o
^ 25
Q_
LJ
Q 30
35
40
45
50
i i
i
<
*
-
_ 5 •
•
-
-
-
_ 10
19
0 50 100 0 50 100 0 50 100 0 50 100
CHROMIUM (/^g/g)
FIGURE 75. Vertical distribution of chromium in selected Port
Huron Basin cores.
142
-------
LAKE HURON CORES (EPA-SLH-75)
V
5
10
15
*E 20
o
X 25
Q_
LJ
0 30
35
40
45
50
i
<
(
•
•
•
. I4A
-
-
•
•
•
-
-
. ISA
_ 53
. 63
0 50 100 0 50 100 0 50 100 0 50 100
CHROMIUM (^g/g)
Figure 76. Vertical distribution of chromium in selected
Goderich Basin cores.
143
-------
LAKE HURON CORES (EPA-SLH-74)
u
5
10
15
'i 20
o
I 25
h-
Q_
LJ
Q 30
35
40
45
50
j
i
— <
<
•
~
-
I
*
i
5
•
/
\
*\
•
-
•
i
-
_
~
-
10
-
-
,
.\
•
_
••
-
i
t
19
•
-
-
,
i
1
_ •
•
•
<
•
_
f
i
25
~
-
-
-
,
0 50 100 0 50 100 0 50 100 0 50 100
COPPER (^g/g)
Figure 77. Vertical distribution of copper in selected
Port Huron and Saginaw Basin cores.
144
-------
LAKE HURON CORES (EPA-SLH-75)
E
0
DEPTH
w
5
10
15
20
25
30
35
40
45
50
J
-
- •
-
-
-
/
I4A
-
-
ISA
53
0 50 100 0 50 100 0 50 100
COPPER (^g/g)
63
0 50 100
Figure 78. Vertical distribution of copper in selected
Goderich Basin cores.
145
-------
0
5
10
15
20
LAKE HURON CORES (EPA-SLH-74)
o
Q_
LU
Q 30
35
40
45
50
0
25
0 50 100 150 0 50 100 0 50 0 50 100
LEAD (^g/g)
Figure 79. Vertical distribution of lead in selected Port Huron and Saginaw
Basin cores.
-------
LAKE HURON CORES (EPA-SLH-75)
0
5
10
15
E 20
o
CL
LJ
Q 30
35
40
45
50
I4A
•ISA
53'
• 63
0 50 100 150
0 50 100 150 0 50 100 0 50 100
LEAD (^g/g)
Figure 80. Vertical distribution of lead in selected Coderich Basin cores.
-------
LAKE HURON CORES (EPA-SLH-74)
00
0
10
15
E 20
o
X 25
QL
LU
Q 30
35
40
45
50
0
19
0 50 100 0 50 100 0 50 100 0 50 100
NICKEL Ug/g)
Figure 81. Vertical distribution of nickel in selected Port Huron and Saginaw
Basin cores.
-------
LAKE HURON CORES (EPA-SLH-75)
\J
5
10
15
'i 20
o
X 25
Q_
LU
0 30
35
40
45
50
i i "i»
•
•
•
—
_ i
-
.
-
/
>
I4A
»
-
i i i
ISA
53'
63
0 50 100 0 50 100 0 50 100 0 50 100
NICKEL (//g/g)
Figure 82. Vertical distribution of nickel in selected Goderich Basin cores,
-------
0
iO
20
Q.
LJ
Q
30
40
50
i r i 471
18A-2
I I I I I I
1 2 3
TIN(/ig/g)
Figure 83.
Vertical distribution on tin in a Goderich Basin
core.
150
-------
LAKE HURON CORES (EPA-SLH-74)
u
5
10
15
*E 20
o
K 25
Q_
LiJ
Q 30
35
40
45
50
•
_
— i
<
-
-
-
r
.
i
5
»
l i l
19
25
0 50 100 150 200 250 0 50 100 150 200 0 50 100 0 50 100 150 200
ZINC
Figure 84. Vertical distribution of zinc in selected Port Huron and Saginaw
Basin cores.
-------
LAKE HURON CORES (EPA-SLH-75)
N3
0
5
10
15
E 20
o
h-
Q_
L±J
30
35
40
45h
50
I4A
ISA
J I I
53
63
0 50 100 150 200 0 50 100 150 200 0 50 100 150 200 0 50 100 150 200
ZINC (//g/g)
Figure 85. Vertical distribution of zinc in selected Goderich Basin cores.
-------
TABLE 22. VERTICAL DISTRIBUTION OF MAJOR ELEMENTS IN WHOLE SEDIMENTS (NAA),
STATION EPA-SLH-74-18(2).
Element (percent by
Depth (cm)
0.5-1
1-2
2-3
3-4
4-5
5-6
6-7
7-8
8-9
9-10
10-12
12-14
14-16
16-18
18-20
20-25
25-30
30-35
35-40
40-45
45-50
Al
5.7
5.9
6.2
5.5
6.4
5.9
5.9
6.9
5.7
6.5
6.5
5.9
5.7
-
6.0
6.3
-
5.6
5.9
6.1
6.3
Ca
4.9
4.9
5.3
4.7
4.6
4.9
4.7
5.5
5.4
5.5
5.1
5.3
5.1
-
5.7
5.5
-
4.5
5.4
4.8
4.9
Fe
3.3
3.0
3.1
3.0
3.3
3.2
3.1
3.0
3.0
3.2
3.0
3.0
3.1
-
2.9
2.9
2.9
2.8
3.0
2.9
2.9
K
2.2
2.0
1.9
2.6
1.8
2.4
2.4
-
2.5
2.3
-
1.9
2.9
-
2.6
2.6
-
3.0
1.9
-
2.2
Mg
3.0
2.3
2.7
3.4
2.6
3.1
3.6
3.2
2.6
2.7
3.3
2.8
3.4
-
3.6
4.0
-
2.1
2.6
2.1
2.1
weight)
Mn
.130
.054
.054
.047
.050
.054
.052
.060
.048
.056
.060
.048
.048
-
.042
.045
-
.041
.039
.045
.039
Na
0.70
0.77
0.71
0.75
0.64
0.69
0.73
-
0.76
0.80
-
0.77
0.80
-
0.82
0.88
-
0.93
0.75
-
0.72
Ti
0.38
0.30
0.45
0.36
0.39
0.37
0.31
0.31
-
0.40
0.34
0.32
0.32
-
0.38
0.25
-
0.29
0.37
0.36
0.44
153
-------
TABLE 23. VERTICAL DISTRIBUTION OF MINOR ELEMENTS IN WHOLE SEDIMENT (NAA)
STATION EPA-SLH-74-18(2)
Concentration
Depth (cm)
0.5-1
1.2
2-3
3-4
4-5 .
5-6
6-7
7-8
8-9
9-10
10-12
12-14
14-16
16-18
18-20
20-25
25-30
30-35
35-40
40-45
45-50
represent.
uncertainty
As
16.1
10.6
9.5
9.7
8.9
3.6
9.4
15.0+2
4.1
8.5
<7.0
9.2
4.9
<7. 1
7.5
4.0
<6.8
2.9
7.9
7.2
5.7
+.6
Ag
<1.7
<1.9
<2.0
<1.7
<2. 1
<2.6
<1.7
<2.0
<2.3
<2. 1
<2.1
<1.9
<2.5
<2. 1
<1.7
<2.3
<2. 1
<2.5
<2.0
<2. 1
<2.4
+2
Ba
300
600
400
450
400
1200
300
900
900
600
800
500
500
500
500
300
400
800
500
700
300
+150
Br
65.2
50.0
48.0
48.4
44.0
51.8
46.2
38.5
46.2
43.6
47.1
44.9
52.8
41.4
45.7
44.7
45.4
43.5
45.5
40.7
42.0
+3
Ce
56.1
58.1
59.7
59.0
62.9
62.7
60.0
58.9
59.4
62.2
56.9
58.2
62.1
59.8
60.1
58.9
58.7
60.3
63.0
60.6
61.4
+1.0
Co
12.0
11.8
12.3
12.0
13.4
13.0
12.0
11.9
11.7
12.9
11.7
11.8
12.3
12.2
11.4
11.5
11.6
11.7
12.3
11.7
12.2
+.2
(yg/g)
Cr
86.5
83.5
80.0
86.0
92.2
92.2
81.4
67.3
76.4
71.5
69.5
79.8
79.7
63.7
83.8
65.8
69.6
75.0
73.8
69.6
66.9
+1
Cs
4.5
4.5
4.5
4.7
5.1
4.2
4.7
3.9
3.7
4.5
3.8
4.2
3.5
4.1
3.8
4.2
4.1
3.7
4.3
4.0
4.2
+.2
Eu
1.0
1.0
1.1
1.0
1.0
1.0
1.0
1.0
0.95
1.1
1.9
1.0
1.1
1.1
1.0
1.1
1.0
0.96
1.1
1.0
1.2
+.06
Hf
4.1
4.7
4.7
4.8
4.1
4.7
4.6
3.9
4.3
4.9
3.8
4.3
4.3
4.6
5.0
4.9
4.3
4.5
5.1
4.3
4.9
+.2
Hg La
<1.0 29.1
<1.0 31.2
<1.2 32.1
<1.1 31.1
<1.2 34.3
<0.14 31.4
<1.0 31.2
<1.1 31.6
<0.1 29.6
1.3 35.2
<1.2 31.1
<1.1 32.1
<0.13 31.5
<1.3 32.0
<1.0 32.4
<0.1 29.3
<1.1 31.0
<0.14 29.9
<1.2 34.8
<1.2 32.4
<0.1 31.6
+1 +.8
(continued),
-------
TABLE 23. (continued).
Ln
Concentration (yg/g)
Depth (cm)
0.5-1
1-2
2-3
3-4
4-5
5-6
6-7
7-8
8-9
9-10
10-12
12-14
14-16
16-18
18-20
20-25
25-30
30-35
35-40
40-45
45-50
represent.
uncertainty
Lu
0.34
0.30
0.41
0.32
0.37
0.40
0.39
0.26
0.35
0.41
0.30
0.21
0.44
0.34
0.35
0.54
0.37
0.34
0.47
0.41
0.45
+.1
Ni
<42.7
55.0
<47.2
68.7
56.5
<76.6
57.4
<57.7
<69.9
<48.0
<61.5
50.7
<76.1
<75.6
<42.9
<62.0
<60.0
<75.0
<46.0
66.0
76.0
+60
Rb
59.1
90.0
86.3
55.8
80.7
95.2
61.3
95.5
77.6
87.6
94.8
70.8
85.7
96.3
60.4
114.0
103.0
80.0
81.9
95.8
102.0
+8
Sb
0.89
0.85
0.87
1.10
0.94
1.28
1.00
0.79
1.10
0.57
0.54
0.56
0.41
0.46
0.35
0.23
0.41
0.59
0.27
0.35
0.34
+.2
Sc
9.8
10.2
10.3
10.4
11.0
10.7
10.7
10.0
10.0
11.0
10.1
10.4
10.8
10.8
10.6
10.2
10.1
10.2
10.8
10.5
10.3
+.1
Se
2.8
<3.1
<3.2
<2.0
<2.6
4.3
2.7
<2.5
3.7
<3.3
<2.6
<2.4
<3.9
<2.8
<2.0
<5.3
<2.6
<4.9
3.9
<2.6
<5.7
+2
Sm
5.5
5.1
5.6
5.4
5.7
5.5
5.8
4.8
5.2
5.8
4.5
5.5
5.5
5.5
5.8
4.8
5.1
5.4
6.0
5.2
5.6
+.1
Th
12.1
8.0
9.0
10.4
10.9
9.3
10.8
8.6
9.1
9.0
7.9
9.6
10.0
10.5
11.1
7.6
8.7
9.5
8.3
8.3
8.0
+.9
U
2.8
4.8
2.7
3.5
3.7
2.7
2.6
2.8
2.1
3.7
3.4
3.5
2.5
3.6
2.3
3.4
2.2
2.4
2.9
2.1
2.2
+.8
V
79
90
95
83
102
77
85
85
73
93
99
87
76
-
80
96
-
78
85
91
120
+8
Yb
2.4
2.5
2.2
2.6
2.6
2.2
2.3
2.6
1.9
2.7
2.4
3.1
2.1
2.7
2.5
3.0
2.4
2.1
2.1
2.7
2.6
+.5
-------
ALUMINUM (wt %)
2468
10
O
10
o
- 20
I
L
o.
40
50
0
10
1 2°
I
^
2i 30
Q
40
SO
,'''i
1
1 '
-1900
i
-1800
-1700 1
IRON (wt %)
024 6 8 1C
.
i
-
-
CALCIUM (wt %)
0 2 4 6 6 10
0
10
Izo
I
ui 30
a
40
50
MAGNESIUM (wt %)
034 6 8 1C
T-J i i i 1
' "'','
1
1
|
' 1
POTASSIUM (wt %)
2 4 6 8
10
SODIUM (wt %)
0 0.2 O.4 O.6 O.6 lO
Figure 86. Vertical distribution of major elements (NAA)
in Goderich Basin core (74-18-2).
156
-------
MANGANESE (jjg/g)
0 400 800 1200 1600 2000
ARSENIC l)
-------
ZINC
40 80 120
160 200
LEAD
0 40 80 120
10
20
3°
40
50
10-
20 -
Si 30
O
40
NICKEL (ug/g)
20 40 60 80
100
CHROMIUM (ug/g)
20 40 60 80 100
160 200
0
10
•g
3 20
I
U 30
O
40
Rn
l l i i, i
'i.
i
i
-1900 1
, 1
-1800
_
-1700
•
1 1 1 1 1
! •
, '
, i
i '
i '
-
.
i
i
COPPER
0 20 40 60 80 100
ANTIMONY (ug/g)
0.0 0.4 0.8 1.2 1.6 2.0
Figure 88.
Vertical distribution of elements in Goderich
Basin core (74-18-2) possessing a significant
a significant degree of enrichment. (Cu, Ni, Pb,
Zn : via AAS ; Cr and Sb via NAA) .
158
-------
(NAA). From these figures it can be seen that Mn and perhaps Br are enriched
only in the uppermost sediment layer while two elements determined via NAA
show the characteristic anthropogenic profile, As and Sb. The mean ratio of
element concentrations determined via AAS and via NAA for this core are given
in Table 24. The ratios (extraction efficiencies) compare favorably with
those determined for surface sediments (Table 18) and for standard mud
samples (Table 6). The surface-to-depth concentration ratios and enrichment
factors (defined below) are summarized in Table 25 for this core. Vertical
distribution of elements determined via AAS in core ISA are given in Table 26.
ENRICHMENT FACTORS
This study as well as many others has shown that nearly all minor
sedimentary constituents are associated with fine-grained materials. To
eliminate the effect of small inhomogeneities in the distribution of fine or
inert materials on measures of the degree of surface enrichment of trace
elements, Kemp et al. (1976) introduced the concept of the sediment
enrichment factor (SEF) defined in terms of the ratio of element
concentrations to that of aluminum. Aluminum is taken as a measure of the
clay mineral, or fine-grained sediment concentration. The SEF is defined as:
(CS/A1S) - (Cd/Ald)
SEF =
(Cd/Ald) (35)
where Cs = the observed elemental concentration in the surface cm of
sediments (1-2 cm)
Cd = the precultural elemental concentration in a sufficiently deep
layer
Alc = the aluminum concentration in surface sediments (1-2 cm)
o
Ald = the aluminum concentration in a sufficiently deep layer
Kemp et al (1976) took layers of sediment below the Ambrosia horizon
(ragweed) corresponding to about 130 years b.p. for estimating Cd and Ald. A
simpler but valid technique is to choose these values as the average over an
interval sufficiently deep that concentrations are constant. This approach
has been taken in the construction of SEFs in Table 25. In this Table values
of Cd and Ald are calculated as the average of concentrations in the
lowermost four sediment sections. When there is essentially no change in the
concentration of aluminum with depth, as in the case of the core at station
18, the SEF reduces to (Cs - Cd)/Cd. When there is a significant variation
in the concentration of Al with depth, the unnormalized enrichment factor
might give a false picture of the extent of surface enrichment. As can be
seen in Table 25 only a few elements (Fe, Mn, As, Br, Cr, and Sb) have any
significant degree of enrichment in this core. The rest are not enriched and
are "conservative" (Kemp et al., 1976) in that their relative proportion in
sedimentary materials has not been changed as a result of mans' recent impact
on the Lakes. (Sodium shows a slight negative "enrichment").
159
-------
TABLE 24. MEAN RATIO OF ELEMENT CONCENTRATIONS
DETERMINED VIA AAS AND VIA NAA
FOR CORE EPA-SLH-74-18-2
Element Ratio (+ Standard Error)*
Ca 0.83 + 0.01
Cr 0.71 + 0.02
Fe 0.89 + 0.01
K 0.31 + 0.01
Mg 1.06 + 0.04
Mn 0.96 + 0.02
Na 0.14 + 0.01
*Ratio = cone, via AAS/conc. via NAA averaged over all depth intervals.
160
-------
TABLE 25. CONCENTRATION OF ELEMENTS DETERMINED VIA NAA
IN SURFACE AND IN UNDERLYING SEDIMENTS,
CONCENTRATION RATIOS AND ENRICHMENT FACTORS
(BASED ON Al NORMALIZATION) FOR CORE EPA-SLH-74-18-2
Concentration*
Element
Major
Al
Ca
Fe
K
Mg
Mn
Na
Ti
Minor
As
Ba
Br
Ce
Co
Cr
Cs
Eu
Hf
La
Lu
Rb
Sb
Sc
Sm
Th
U
V
Yb
Surface
5.93
5.0
3.1
2.0
2.7
.08
.73
.38
12.1
433
54.4
58.0
12.0
83.3
4.5
1.0
4.5
30.8
35.0
78.4
0.87
10.1
5.4
9.7
3.4
88
24.0
Deep
5.98
4.9
2.9
2.4
2.3
.04
.82
.37
5.9
580
42.9
61.3
12.0
71.3
4.1
1.1
4.7
32.0
34.3
90.0
0.38
10.2
5.5
8.5
2.4
94
23.0
Ratio
1.0
1.0
1.1
0.83
1.1
2.0
0.89
1.0
2.1
.75
1.30
0.95
1.0
1.2
1.1
.91
.96
.96
1.0
.87
2.3
1.0
0.98
1.0
1.4
0.94
1.04
Enrichment
Factor**
0
0
0.
0
0
1.
-0
0
1.
0
0.
0
0
0.
0
0
0
0
0
0
1.
0
0
0
<\, o
0
0
07
0
.11
1
27
17
3
* major elements in (wt %) minor elements in (yg/g).
is the average over upper 3 cm. Deep concentration =
deepest four sections.
**set = to zero if not statistically significant.
Surface concentration
average of values in
161
-------
TABLE 26. VERTICAL DISTRIBUTION OF ELEMENTS (AAS) IN CORE EPA-SLH-75-18A-2
Interval
(cm)
0.0-0.5
0.5-1.0
1.0-1.5
1.5-2.0
2.0-2.5
2.5-3.0
3.0-3.5
3.5-4.0
4.0-4.5
4.5-5.0
5.0-5.5
5.5-6.0
6.0-6.5
6.5-7.0
7.0-7.5
7.5-8.0
8.0-8.5
8.5-9.0
9.0-9.5
9.5-10
10-11
11-12
12-13
13-14
14-15
15-16
16-17
Fraction
Soluble
(g/g)
0.343
0.315
0.385
0.350
0.375
0.365
0.375
0.364
0.370
0.345
0.345
0.355
0.394
0.372
0.382
0.332
0.354
0.330
0.361
0.340
0.361
0.366
0.336
0.327
0.449
0.354
0.345
Major Elements (wt %)
Ca
4.31
4.30
4.91
4.82
4.77
4.82
4.55
4.46
4.62
4.66
4.71
5.18
5.23
4.82
5.03
5.38
4.81
4.50
5.12
5.38
5.53
5.22
4.76
4.76
5.38
5.13
4.97
Fe
3.14
3.42
3.13
2.90
3.64
3.27
3.61
3.36
3.05
3.45
3.28
3.26
2.42
2.83
3.02
3.26
3.01
2.79
2.89
3.02
2.89
3.01
2.98
3.23
3.33
2.92
2.80
Mg
2.72
3.03
3.22
3.17
3.16
3.20
3.03
3.07
3.10
3.08
3.16
3.45
3.32
3.10
3.23
3.40
3.16
2.97
3.25
3.42
3.60
3.44
3.22
3.19
3.56
3.39
3.26
Mn
(xlO-2)
4.60
8.00
4.49
4.23
4.27
4.46
4.83
4.92
4.55
4.49
4.26
4.36
3.96
4.45
4.36
4.03
4.45
4.07
4.35
5.01
4.73
4.45
4.08
3.98
3.99
3.80
3.70
Cr
52.9
50.2
52.9
55.7
55.6
58.3
60.9
59.5
55.7
55.3
43.5
44.9
42.4
51.0
52.3
46.1
43.5
44.8
49.7
51.0
51.9
45.8
45.8
48.2
49.5
47.1
45.8
Cu
37.2
34.9
39.1
38.9
40.7
39.8
41.4
41.7
39.5
35.9
34.3
30.8
30.3
32.4
31.1
27.9
28.3
26.8
27.2
26.6
25.0
24.3
23.3
23.3
22.7
21.9
21.7
Minor Elements (ppm)
Hg
0.14
0.15
0.14
0.11
0.14
0.17
0.14
0.13
0.12
0.12
0.12
0.10
0.11
0.11
0.11
0.09
0.10
0.11
0.06
0.06
0.05
0.03
0.03
-
-
0.04
—
Nl
59.0
53.9
55.6
50.0
62.8
61.1
64.6
61.7
55.3
47.4
48.0
46.3
42.6
42.7
44.0
39.8
39.2
39.7
39.1
39.2
38.0
38.5
37.3
36.8
35.6
35.7
33.8
Pb
90.9
97.8
98.2
91.9
94.6
89.9
88.9
85.1
80.3
66.3
61.9
55.3
54.6
59.1
55.3
50.0
51.4
46.6
44.7
44.7
38.0
36.1
33.7
32.2
32.3
31.3
26.7
Sn
1.6
2.5
2.8
2.6
2.3
2.4
2.5
2.2
2.1
1.7
2.0
1.6
1.4
1.2
1.2
1.0
1.0
0.9
0.9
-
0.8
-
-
0.6
-
-
—
Zn
114
108
129
126
136
129
136
136
120
110
100
94.6
94.0
114
90.3
79.1
77.9
71.1
63.4
65.2
62.5
61.2
60.1
58.9
53.5
55.7
52.3
(continued)
-------
TABLE 26. (continued)
ON
Co
Interval
(cm)
17-18
18-19
19-20
20-22
22-24
24-26
26-28
28-30
30-35
35-40
40-45
45-50
Fraction
Soluble
(g/g>
0.227
0.340
0.372
0.358
0.366
0.243
0.342
0.362
0.351
0.380
0.376
0.348
Major Elements (wt %)
Ca
4.97
4.87
4.81
5.08
5.28
4.81
5.16
5.64
5.07
5.64
5.38
4.90
Fe
2.40
2.86
2.92
3.58
3.20
2.08
2.58
2.55
3.01
2.53
2.71
2.52
Mo
3.26
3.22
3.28
3.39
3.51
3.13
3.38
3.64
3.32
3.67
3.51
3.26
Mn
(xlO-2)
3.71
4.40
4.21
3.89
4.17
3.42
3.74
4.04
3.89
3.80
3.66
3.62
Cr
42.3
49.5
53.0
47.1
50.7
47.0
47.0
48.3
49.5
49.5
53.1
50.8
Cu
21.1
23.3
24.3
23.0
23.5
21.4
22.6
23.0
23.3
24.0
23.0
24.3
Minor
Hg
__
0.02
-
-
0.04
-
-
0.03
-
0.03
0.03
-
Elements (ppm)
Ni
33.9
38.6
40.3
37.4
38.0
32.7
35.0
36.2
35.6
36.2
36.3
35.7
Pb Sn
29.4
30.3 0.6
31.2
31.3
29.4
27.4
28.4
30.3
30.8 0.5
30.3
30.4
30.9
Zn
50.2
54.6
56.7
52.4
56.8
47.9
53.4
52.4
53.5
53.5
53.5
56.4
-------
In Tables 27 and 28 are listed the enrichment factors for 29 additional
cores. Because Al concentrations were not determined for these cores, an
alternative normalization was used. As shown previously, the fraction
soluble (Fsol) is, as expected, a composite of carbonate materials and
organic carbon and iron-associated constituents. Thus normalization to Fsol
eliminates the effect of dilution of sediments by inert (non acid-soluble)
materials on the estimate of the enrichment factor. A normalization to Fe
rather than Fsol is probably somewhat more analogous to the Al normalization
used by Kemp et al. (1976) but in the present case the values of the
enrichment factors are largely independent of whether Fsol or Fe is used.
The degree of near-surface enrichment for the non-conservative elements
varies strongly with location as can be seen in Figs. 89-95. The
distribution of enrichment factors tends to follow the distribution of
fine-grained constituents with highest values tending to occur toward the
centers of the two depositional basins. However, the distribution patterns
are generally not strongly correlated as can be seen in Table 29. Zn and Cu
have the best correlated enrichment factors, with r = 0.89 (N = 26); those
for Pb and Mn also are significantly correlated, with r = 0.67 (N = 26). The
remaining correlations between enrichment factors are appreciably less. This
study represents the first observation of the systematic spatial variability
in enrichment factors. The degree of enrichment of surface sediments
relative to background levels is not a unique characteristic of the lake or
even of a given depositional basin but rather shows nearly as much spatial
variability as do element concentrations themselves.
Mean surface-to-deep concentration ratios and enrichment factors for all
elements measured in more than one core are given in Table 30. Also given in
Table 30 is the coefficient of correlation between elemental concentrations
in near-surface and in underlying sediments. Clearly when surface and deep
concentrations are identical not only must Ef = 0 but the correlation
coefficient must equal 1.00. On the other hand, for elements with a high
degree of enrichment there is no a priori reason why the correlation between
surface and deep concentrations should remain high. Defining the degree of
unrelatedness as -In r, a linear regression of the enrichment factor versus
this variable shows that the greater the degree of surface enrichment, the
less related is the composition of underlying sediments. This relationship
is illustrated in Figure 96. The regression line gives
Ef = 0.06 - 2.121nr or r e~°'5Ef (36)
which satisfies the requirement that when Ef = 0 r = 1.
Table 31 provides a comparison of mean enrichment factors for each
depositional basin. Only two elements show significant differences in
enrichment factors between basins, Mn and Pb. Both elements are
significantly more enriched in the Port Huron basin. Enhancement of
enrichment factors in the Port Huron basin could be the result of generally
lower sedimentation rates. In cores where the sedimentation rate is high,
surface concentrations may be reduced as a result of higher deposition of
inert material. Other anthropogenic elements such as Cd, Cu, Ni and Zn also
have higher average enrichment factors in this basin but the differences
164
-------
Ul
TABLE 27. CONCENTRATION OF MAJOR ELEMENTS IN SURFACE1 AND IN UNDERLYING2 SEDIMENTS,
CONCENTRATION RATIOS, AND ENRICHMENT FACTORS
Fraction Soluble (g/g)
Station
3.
4.
5.
7.
8.
9.
10.
12.
13.
14.
15.
16.
17.
18.
19.
25.
29.
31.
33.
35.
39.
50.
53.
57.
61.
63.
69.
S
0.23
0.071
0.26
0.43
0.26
0.27
0.16
0.33
0.46
0.30
0.045
0.25
0.33
0.37
0.15
0.29
0.32
0.19
0.26
0.07
0.20
0.38
0.28
0.23
0.43
0.34
0.31
D
0.18
0.17
0.23
0.43
0.23
0.26
0.19
0.25
0.44
0.27
0.34
0.23
0.27
0.37
0.21
0.24
0.26
0.19
0.24
0.26
0.26
0.41
0.27
0.22
0.42
0.28
0.27
R3
1.278
0.418*
1.130
1.000
1.130
1.038
0.842*
1.138
1.045
1.111
0.132*
1.087
1.222
1.000
0.714*
1.208
1.231
1.000
1.08
0.269*
0.769*
0.927
1.037
1.046
1.024
1.214
1.148
S
1.90
0.40
1.80
8.60
0.57
3.50
0.49
2.20
4.00
1.50
0.16
0.61
3.30
4.40
0.42
1.12
1.60
0.62
0.56
0.33
1.50
5.30
1.70
0.73
5.50
2.70
2.00
Calcium
D
0.60
1.60
1.30
8.40
0.45
2.80
0.40
1.40
4.00
1.40
2.60
0.41
2.50
4.40
0.43
0.56
1.02
0.46
0.43
1.62
2.20
6.10
1.98
0.59
5.60
3.14
1.67
(wt %)
R
3.167
0.250
1.385
1.024
1.267
1.250
1.225
1.571
1.000
1.071
0.064
1.488
1.320
1.000
0.977
2.000
1.569
1.348
1.302
0.204
0.682
1.033
0.859
1.237
0.982
0.861
1.200
Iron (wt %)
E4
1.478
-0.401
0.225
0.024
0.121
0.204
0.455
0.381
-0.043
-0.036
-0.518
,0.369
0.080
0.000
0.367
0.655
0.275
0.348
0.202
-1.266
0.114
0.114
-0.872
0.184
-0.041
-0.292
0.043
S
2.60
1. 10
3.60
1.24
3.00
2.10
1.90
3.30
1.74
3.60
0.98
3.50
3.70
2.80
2.00
3.20
3.60
2.40
3.50
1.51
1.20
1.10
2.60
3.30
2.00
3.40
3.40
D
2.10
2.40
3.10
1.34
2.80
2.70
2.20
3.10
1.58
3.10
4.00
2.90
3.60
2.70
2.50
2.80
3.50
2.40
3.00
3.01
0.98
1.30
3.30
3.20
1.80
1.25
3.20
R
1.238
0.458
1.161
0.925
1.071
0.778
0.864
1.065
1.101
1.161
0.245
1.207
1.028
1.037
0.800
1.143
1.029
1.000
1.167
0.502
1.224
0.846
0.788
1.031
1.111
2.720
1.062
S4
-0.031
0.097
0.027
-0.075
-0.052
-0.251
0.026
-0.065
0.053
0.045
0.851
0.110
-0.159
0.037
0.120
-0.054
-0.164
0.000
0.077
0.863
0.592
-0.087
-0.340
0.031
0.085
1.240
-0.075
1 Derived from vertical profiles. Average of upper 3 cm or 1-2 cm interval.
2 Average of approximately the lower 20-50 cm.
^ R = Surface concentration (Cs)/deep concentration (C
-------
TABLE 27. (continued)
Magnesium (wt. %)
Manganese (wt %)
Phosphorus (wt %)
Station
3.
4.
5.
7.
8.
9.
10.
12.
13.
14.
15.
16.
17.
18.
19.
25.
29.
31.
33.
35.
33.
50.
53.
57.
61.
63.
69.
S
__
0.24
0.89
5.40
0.91
2.70
—
1.90
5.20
1.50
0.148
0.88
1.50
2.90
—
—
1.50
0.78
0.91
—
—
4.70
1.50
1.20
4.40
2.20
_-.
D
1.922
0.85
5.40
0.89
3.00
—
1.60
5.40
1.50
3.40
0.83
1.40
3.20
—
—
1.50
0.73
0.92
—
—
4.90
1.90
1.13
, 4.40
2.09
™"~
R
0.125
1.047
1.000
1.022
0.900
—
1.187
0.963
1.000
0.044
1.060
1.071
0.906
—
—
1.000
1.068
0.989
—
--
0.959
0.790
1.06
1.000
1.053
~"~~
E
-0.745
-0.074
0.000
-0.096
-0.133
—
0.044
-0.079
-0.100
-0.671
-0.025
-0.123
-0.094
—
—
-0.188
0.068
-0.084
—
—
0.035
-0.239
0.016
-0.023
-0.133
__
S
0.073
0.040
0.080
0.032
0.085
0.070
0.160
0.170
0.052
0.180
0.034
0.170
0.160
0.067
0.045
0.150
0.262
0.049
0.100
0.038
0.038
0.027
0.180
0.140
0.048
0.150
0.170
D
0.030
0.027
0.028
0.022
0.034
0.026
0.020
0.053
0.028
0.056
0.048
0.046
0.044
0.040
0.026
0.033
0.066
0.027
0.036
0.023
0.017
0.025
0.053
0.054
0.035
0.034
0.050
R
2.433
1.429
2.857
1.231
2.500
2.692
8.000
3.208
1.857
3.214
0.708
3.696
3.536
1.675
1.731
4.545
3.964
1.815
2.778
1.652
2.235
1.080
3.40
2.59
1.371
4.425
3.400
E
0.904
2.421
1.527
0.231
1.212
1.593
8.500
1.819
0.776
1.893
4.352
2.400
1.975
0.675
1.423
2.762
2.236
0.815
1.564
5.121
1.865
0.165
2.275
1.430
0.340
2.634
1.961
S
0.12
0.076
—
—
0.23
0.14
0.19
—
—
0.33
—
—
—
0.22
0.22
0.11
—
0.18
0.21
0.14
0.106
—
0.21
0.16
0.13
0.31
0.24
D
0.15
0.140
—
—
0.15
0.13
0.20
—
—
0.27
—
—
—
0.17
0.20
0.20
—
0.15
0.19
0.180
0.096
—
0.210
0.18
0.14
0.20
0.24
R
0.800
0.543
—
—
1.533
1.077
0.950
—
—
1.222
—
—
—
1.294
1.100
0.550
—
1.200
1.105
0.778
1.104
—
1.00
0.889
0.929
1.550
1.000
E
-0.374
0.300
—
—
0.356
0.037
0.128
—
—
0.100
—
—
—
0.294
0.540
-0.545
—
0.200
0.020
1.889
0.435
—
-0.036
-0.111
-0.093
0.277
-0.129
(continued)
-------
TABLE 27. (continued)
Potassium (wt. %)
Silicon (wt %)
Sodium (wt
Station
3.
4.
5.
7.
8.
9.
10.
12.
13.
14.
15.
16.
17.
18.
19.
25.
29.
31.
33.
35.
39.
50.
53.
57.
61.
63.
69.
s
0.53
0.28
0.89
0.26
0.68
0.34
0.36
0.72
0.38
0.83
0.188
0.560
0.85
0.70
0.50
0.76
0.90
0.45
0.70
0.17
0.28
0.19
0.71
0.43
0.57
0.92
0.77
D
0.49
0.72
1.10
0.36
0.71
0.48
0.65
0.83
0.40
0.82
0.940
0.570
1.100
0.63
0.75
0.77
0.78
0.51
0.75
0.83
0.28
0.27
1.08
0.47
0.52
0.82
0.75
R
1.082
0.389
0.809
0.722
0.958
0.708
0.554
0.867
0.950
1.012
0.200
0.982
0.773
1.111
0.667
0.987
1.154
0.882
0.933
0.205
1.000
0.704
0.657
0.915
1.096
1.11
1.027
E S D RE
-0.154
-0.069
-0.284
-0.278
-0.153
-0.318
-0.342
-0.238
-0.091
-0.089 1.9 1.1 1.73 0.56
0.511
-0.096
-0.368
0.111 1.3 0.69 1.88 0.88
-0.067
-0.183
-0.063
-0.118
-0.138
-0.239
0.300
-0.241
0.366 1.0 0.62
-0.085
0.071
-0.087 1.7 0.68 2.50 1.35
-0.106
S
—
—
0.10
—
—
—
0.14
0.110
—
0.118
0.074
0.21
0.12
—
—
—
—
—
—
—
—
—
—
—
—
—
D
—
—
0.10
—
—
—
0.10
0.106
—
0.064
0.056
0.20
0.11
—
—
—
—
—
—
—
—
—
—
—
—
—
R
—
—
1.00
—
—
—
1.40
1.04
—
0.72
1.32
1.05
1.09
—
—
—
—
—
—
—
—
—
—
—
—
—
E
—
—
0.00
—
—
—
0.23
0.00
—
4.44
0.21
-0.14
0.09
—
—
—
—
—
—
—
—
—
—
—
—
—
-------
TABLE 28. CONCENTRATION OF MINOR ELEMENTS IN SURFACE AND IN UNDERLYING SEDIMENTS,
CONCENTRATION RATIOS AND ENRICHMENT FACTORS
00
Barium (yg/g)
Station S D
3.
4.
5. 152. 151.
7. 107. 120.
8.
9.
10.
12. 133. 62.
13. 92. 80.
14. 213. 154.
15. 44. 200.
16. 170. 96.
17. 167. 197.
18. 181. 150.
19.
25.
29.
31.
33.
35.
39.
50.
53. 172. 201.
57.
61.
63. 203. 192.
69.
R
—
—
1.00
.89
—
—
—
2.15
1.15
1.30
.22
1.77
.85
1.21
—
—
—
—
—
—
—
—
0.855
—
—
1.06
"
E
—
—
-0.12
-0.11
—
—
—
0.89
0.10
0.17
0.66
0.63
.30
0.21
—
—
—
—
—
—
—
—
-0.175
—
—
-0.129
"
2
1
3
2
2
3
3
2
3
1
1
2
3
2
3
3
2
4
4
2
2
S
.81
.50
.06
—
—
.00
.36
—
—
.22
.02
.83
.22
.61
.50
.86
.020
.11
.86
—
.26
—
.51
.24
.22
.57
.93
Cadmium (yg/g)
D
1.75
1.52
1.23
—
—
1.50
1.50
—
3.78
1.89
—
0.56
1.04
0.95
1.73
2.03
0.57
1.24
1.79
—
2.30
—
1.13
—
2.53
1.02
1.91
R
1.506
0.987
2.391
--
—
1.333
1.573
—
—
1.704
—
4.233
3.095
1.695
0.343
1.409
5.293
1.702
2.155
—
1.417
—
2.221
—
1.568
2.520
1.534
E
0.257
1.363
1.115
—
—
0.284
0.863
—
—
0.533
—
2.945
1.533
0.695
0.180
0.166
3.305
0.702
0.991
—
0.343
—
0.507
—
0.629
1 . 37 1
0.335
S
58.0
24.0
57.0
19.4
62.0
38.0
34.0
53.0
34.0
65.0
16.8
55.0
67.0
59.0
43.0
—
69.0
50.0
62.0
16.
24.0
31.0
62.0
55.0
37.0
71.0
— —
Chromium (yg/g)
D
58.0
52.0
66.0
30.3
58.0
45.0
51.0
55.0
30.0
58.0
82.6
51.0
66.0
53.0
59.0
—
62.0
48.0
60.0
50.
24.0
33.
65.0
55.1
.36.0
53.0
___
R
1.000
0.452
1.015
0.630
1.069
0.826
0.667
0.964
1.133
1.121
0.203
1.098
1.015
1.113
0.729
—
1.113
1.042
1.033
0.320
1.000
0.539
0.954
0.933
1.028
1.224
E
-0.217
0.105
-0.102
-0.370
-0.054
-0.205
-0.208
-0.153
0.084
0.009
0.537
0.010
-0.159
0.113
0.020
—
-0.096
0.042
-0.046
0.189
0.300
0.014
-0.030
-0.053
0.00'+
0.152
— ~~
(continued)
-------
TABLE 28. (continued)
vo
Copper (yg/g)
Station
3.
4.
5.
7.
8.
9.
10.
12.
13.
14.
15.
16.
17.
18.
19.
25.
29.
31.
33.
35.
39.
50.
53.
57.
61.
63.
69.
S
47.
15.0
72.
16.2
56.
33.
35.
50.
24.0
59.
5.8
64.
65.
40.
31.
54.
60.
46.
53.
9.77
12.0
17.
42.
59.
24.
51.
46.
D
31.
32.6
44.
15.2
34.
33.
26.
31.
14.6
33.
36.0
41.
38.
26.
39.
34.
35.
34.
35.
19.4
8.4
17.
28.2
40.,
18.
25.
29.
R
1.516
0.460
1.536
1.066
1.647
1.000
1.346
1.613
1.544
1.788
0.161
1.561
1.711
1 . 538
0.795
1.588
1.714
1.353
1.514
0.503
1.524
1.000
1.489
1.480
1.333
2.040
1.586
E
0.187
0.102
0.448
0.066
0.457
-0.037
0.599
0.417
0.572
0.609
0.217
0.436
0.400
0.538
0.113
0.314
0.393
0.353
0.393
0.871
0.981
0.079
.446
0.411
0.302
0.920
0.382
S
87.
13.7
132.
74.2
103.
62.
57.
101.
78.
122.
13.
108.
143.
93.
20.
108.
128.
81.
92.
20.
40.
41.
93.
118.
56.
105.
98.
Lead
D
14.
22.0
44.
37.9
20.
25.
13.
22.
48.0
27.
50.9
17.
43.
33.
15.
21.
35.
21.
22.
15.
28.
27.
27.5
24.
31.
24.
25.
(pg/g)
R
6.214
0.623
3.000
1.958
5.150
2.480
4.385
4.591
1.625
4.519
0.257
5.353
3.326
2.818
1.333
5.143
3.657
3.857
4.182
1.333
1.429
1.519
3.382
4.917
1.806
4.375
3.920
Lead-210 (pCi/g)
E
3.863
0.497
1.654
0.958
3.556
1.388
4.207
3.034
0.554
3.067
0.930
4.845
1.721
1.818
0.867
3.256
1.971
2.857
2.86
3.952
0.857
0.638
2.261
3.917
0.764
3.118
2.414
S
8.9
0.55
7.4
2.4
5.4
5.0
4.6
14.0
2.9
12.6
—
3.2
8.2
8.8
1.6
10.9
—
4.3
7.9
—
2.7
2.2
8.3
6.2
3.7
11.4
7.3
D
0.49
0.26
0.49
0.33
0.49
0.43
0.46
0.70
0.31
0.78
—
0.77
0.66
0.444
0.62
0.63
—
0.51
0.57
—
0.27
0.37
0.51
0.35
0.27
0.67
0.85
R
18.163
2.115
15.1
7.27
11.020
11.628
10.000
20.000
9.355
16.154
—
10.649
12.424
19.820
2.581
17.302
—
8.431
13.860
—
10.000
5.946
16.275
17.714
13.704
17.015
8.583
E
13.215
4.065
12.36
6.27
8.749
10.197
10.875
15.576
7.948
13.538
—
8.797
9.165
18.820
2.613
13.319
—
7.431
11.79
—
12.000
5.415
10.043
16.714
12.385
15.014
6.430
(continued)
-------
TABLE 28. (continued)
Molybdenum (yg/g)
Station S D RE
0 __ __. _._
4.
5___ ___
•
7.
8.
9_. _ _
•
10.
12. 6.7 6.9 0.97 -0.15
13. 11.0 8.2 1.3 0.25
14. 11.0 10.0 1.1 -0.01
1 5 • "** ~™ "~
16.
17.
18.
19.
25.
29.
31.
33.
35.
39.
50.
53.
57.
51.
63.
69.
S
63.0
19.6
75.0
28.0
50.0
41.0
71.0
61.0
38.0
75.0
11.2
71.0
80.0
50.0
40.0
71.0
85.0
52.0
61.0
21.0
22.0
26.0
56.0
78.0
37.0
68.0
68.0
Nickel
D
32.0
41.4
21.0
28.0
36.0
33.0
37.0
34.0
28.0
39.0
52.0
41.0
46.0
33.0
42.0
36.0
44.0
37.0
39.0
29.3
16.8
26.0
35.5
44.0
26.0
29.0
37.0
ipg/g) Strontium (yg/g)
R
1.969
0.473
3.571
1.000
1.667
1.242
1.919
1.794
1.357
1.923
0.215
1.732
1.739
1.515
0.952
1.972
1.932
1.405
1.564
0.717
1.310
1.000
1.578
1.773
1.423
2.345
1.838
E S D
0.541
0.134
2.159 38. 33.
0.000 48. 44.
0.474
0.196
1.279
0.577 42. 31.
0.298 54. 48.
0.731 46. 35.
0.627 15.6 48.
0.593 36. 24.
0.423 45. 37.
0.515 39. 41.
0.333
0.632
0.570
0.405
0.444
1.662
0.702
0.079
0.521
0.696
0.390
1.207
0.601
R
—
—
1.15
1.10
—
—
—
1.35
1.13
1.31
0.32
1.50
1.22
0.95
—
—
—
—
—
—
—
—
—
—
—
—
~~~
E
—
—
0.01
0.09
—
—
—
0.19
0.08
0.18
1.45
0.38
0.00
-0.05
—
—
—
—
—
—
—
--
—
—
—
—
"
(continued)
-------
TABLE 28. (continued)
Zinc (yg/?)
Station
3.
4.
5.
7.
8.
9.
10.
12.
13.
14.
15.
16.
17.
IB.
19.
25.
29.
31.
33.
35.
39.
50.
53.
57.
61.
63.
69.
S
145.
42.
200.
50.
167.
94.
114.
157.
74.
186.
20.
195.
195.
146.
67.
156.
191.
133.
165.
46.4
60.
52.
139.
178.
85.
171.
150.
0
62.
68.
85.
34.
67.
58.
60.
69.
34.
73.
80.
35.
86.
59.
70.
62.
70.
65.
72.
49.
38.
33.
68.7
74.6
47.
58.
65.
R
2.339
0.613
2.353
1.471
2.493
1.621
1.900
2.275
2.176
2.548
0.250
2.294
2.267
2.475
0.957
2.516
2.729
2.046
2.292
0.947
1.579
1.368
2.023
2.386
1.809
2.9^3
2.308
E
0.830
0.479
1.081
0.471
1.205
0.561
1.256
1.000
1.082
1.293
0.839
1.111
0.855
1.475
0.340
1.082
1.217
1.046
1.115
2.517
1.053
0.476
0.951
1.232
0.766
1.775
1.010
-------
TABLE 29. CORRELATIONS BETWEEN ENRICHMENT FACTORS
FOR ELEMENTS WITH A SIGNIFICANT DEGREE OF ENRICHMENT
Mn
Cd
Cu
Ni
Pb
Pb-210
Zn
Mn
0.32
0.29
0.37
0.67
0.34
0.35
Cd
0.26
0.09
0.14
-0.18
0.27
Cu Ni Pb Pb-210
0.37
0.21 0.24
0.31 0.37 0.45
0.89 0.38 0.43 0.53
172
-------
TABLE 30. SUMMARY OF MEAN SURFACE-TO-DEPTH CONCENTRATION RATIOS,
ENRICHMENT FACTORS AND CORRELATION COEFFICIENTS FOR SOUTHERN LAKE HURON CORES
(ALL DEPOSITIONAL BASINS COMBINED)
Element
Soluble fraction
Calcium
Iron
Magnesium
Manganese
Phosphorus
Potassium
Silicon
Sodium
Barium
Cadmium
Chromium
Copper
Lead
Laad-210
Molybdenium
Nickel
Stronium
Zinc
Mean
Ratio
1.
1.
1.
1.
2.
1.
0.
2.
I.
1.
2.
1.
1.
3.
12
1.
1.
1.
2.
09
30
08
00
48
07
99
04
15
22
31
04
51
54
.9
12
70
21
23
+ 0
+ 0
+ 0
± °
+ 0
+ 0
+ 0
+ 0
+ 0
+ 0
+ 0
+ 0
+ 0
+ 0
+ 1
± °
+ 0
± °
+ 0
.02
.11
.03
.02
.21
.07
.06
.24
.07
.13
.31
.03
.06
.32
.0
.1
.11
.06
.08
Mean
Enrichment Factor*
0.
0.
- 0.
- 0.
1.
0.
- 0.
0.
0.
0.
1.
- 0.
0.
2.
10
0.
0.
0.
1.
00
18
01
07
26
00
09
93
07
12
06
03
39
21
.9
03
55
11
05
+ 0.
+ 0.
+ 0.
+ 0.
+ 0.
+ 0.
+ 0.
+ 0.
+ 0.
± °-
+ 0.
± °-
+ 0.
+ 0.
-I- 0.
± °-
+ 0.
± °-
+ 0.
00
08
02
02
17
07
05
23
06
12
26
03
05
27
9
12
09
05
07
Correlation
Coefficient (N)
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
96
97
97
99
87
78
88
74
97
87
50
97
95
49
79
96
85
73
96
(22)
(22)
(22)
(17)
(21)
(14)
(22)
(3)
(6)
(9)
(14)
(20)
(2)
(22)
(21)
(3)
(22)
(8)
(22)
*Factors underlined are significantly greater than zero. (+2 o ).
173
-------
TABLE 31. COMPARISON OF MEAN ENRICHMENT FACTORS BY DEPOSITIONAL BASIN
Depositional Basin
Element
Fraction Soluble
Calcium
Iron
Magnesium
Manganese
Phosphorus
Potassium
Cadmium
Chromium
Copper
Lead
Lead-210
Nickel
Zinc
Port Huron (N = 4)
—
0.23 + 0.05*
0.04 + 0.04
- 0.07 + 0.02
1.67 + 0.25
0.19 + 0.17
- 0.17 + 0.04
1.68 + 0.63
- 0.05 + 0.02
0.44 + 0.01
3.11 + 0.18
10.43 4- 0.96
0.92 + 0.42
1.13 + 0.03
Goderich (N = 17)
__
0.14 + 0.09
- 0.02 + 0.03
- 0.07 + 0.02
1.06 + 0.18
0.02 + 0.06
- 0.06 + 0.06
0.96 + 0.29
0.03 + 0.04
0.38 + 0.06
1.94 + 0.29
10.83 + 1.09
0.46 + 0.07
1.03 + 0.09
Difference
0.09 + 0.10
0.06 + 0.05
0.00 + 0.03
0.61 + 0.31
0.17 + 0.18
- 0.13 + 0.07
0.72 + 0.69
- 0.02 + 0.04
0.06 + 0.06
1.17 + 0.34
- 0.04 + 1.5
0.46 + 0.43
0.10 + 0.09
* Mean 4^ standard error in estimate of mean.
Underlined values are significantly (+a ) different from zero.
174
-------
CADMIUM
ENRICHMENT
FACTOR
43°00'—
Kincardine
Goderich
Sarnia fsj
SOUTHERN LAKE HURON
10 20 3O
KILOMETERS
82° 30'
82°QO'
Figure 89. Distribution of the cadmium enrichment factor.
175
-------
43°30 —
CALCIUM
ENRICHMENT
FACTOR
CH < 0
pPPI n - n n*s
ksSfit&.jiS N-/ V-/, \J \*J
005-0.15
> 0.15
43°00'—
Port
Huron
Kincardine
^Goderich
SOUTHERN LAKE HURON
82° 30
10 20 30
KILOMETERS
82°00'
40
Figure 90. Distribution of the calcium enrichment factor.
176
-------
Harbor,
Beach
43°30'—
COPPER
ENRICHMENT
FACTOR
EH < 0.2
O3 0.2-0.5
• > 0.5
43°00'—
Kincardine
Goderich
SOUTHERN LAKE HURON
82° 30
10 2O 30
KILOMETERS
82°00'
40
Figure 91. Distribution of the copper enrichment factor
177
-------
Harbor^
Beach
43°30'—
LEAD
ENRICHMENT
FACTOR
CH < 0.5
CD 0.5-1.0
EH 1.0-2.0
ffi 2.0-30
• > 3 0
43°00'—
Kincardine
^Goderich
Sornia
SOUTHERN LAKE HURON
82° 30'
10 20 30
KILOMETERS
82°00'
40
Figure 92. Distribution of the lead enrichment factor,
178
-------
MANGANESE
ENRICHMENT
FACTOR
CU <0.2
["I 0.2-0.5
H! 1.0-1.5
• > 1.5
43°00'—
SOUTHERN LAKE HURON
82° 30'
10 20 30
KILOMETERS
82°00
40
Figure 93. Distribution of the manganese enrichment factor
179
-------
44°00'
Harbor;
Beach
43°30'-
NICKEL
ENRICHMENT
FACTOR
Q < 0.2
• 0.5-1,0
• > 1.0
43°00'—
Kincardine
Goderich
SOUTHERN LAKE HURON
82°30
10 20 30
KILOMETERS
82°00'
40
Figure 94. Distribution of the nickel enrichment factor
180
-------
43°30 —
ZINC
ENRICHMENT
FACTOR
r i 1.5
43°00'—
Port
Huron
^Goderich
SOUTHERN LAKE HURON
10 20 30
KILOMETERS
40
82° 30'
82°00'
Figure 95. Distribution of the zinc enrichment factor,
181
-------
0
Figure 96. Relationship between the mean enrichment factor and
the degree of unrelatedness between surface and un-
derlying element concentrations.
182
-------
between basins are only significant at the one sigma level as can be seen in
Table 31.
In Fig. 97 the elements are ordered according to their degree of
enrichment in core EPA-SLH-74-18-2. Of all the elements determined only a
limited number show any significant degree of enrichment. Also shown in the
same figure are the average values for the study area (shaded parts) and
enrichment factors for additional elements based on the core taken by Kemp et
al. (1976).
It should be kept in mind that the enrichment factors of the single Kemp
et al. core could be very different from average values for the elements
shown. Elements showing significant enrichment in southern Lake Huron
include: Pb, Mn, Cd, Sn, Zn, Si, Ni, Cu, As, Sb, P, Br as well as Hg, IOC,
OC, and N as determined by Kemp et al. (1976).
VERTICALLY INTEGRATED ELEMENT CONCENTRATIONS
The total anthropogenic loading of the sediments may be estimated by
vertical integration of net concentration profiles. This integration is
accomplished as follows:
N
Total excess deposition (yg/cm2) = Z (C± - Cbg) x dm-^ (37)
1=1
where dm^ is the dry weight of sediment per unit area (g/cm2) in the ith
interval, C^ is the element concentration (yg/g) in the interval and C^g is
the mean background concentration (yg/g). Elements possessing enrichment
factors of zero will have no significant total excess deposition (TED).
Values for individual cores are given in Table 32. The element Mn is
included for comparison although its excess is attributable to diagenetic
effects rather than to cultural ones. Values reported in this table with the
exception of Mn are estimates of the total amount of an element deposited at
the given location as a result of man's activities to date (i.e. 1975). Part
of the usefulness of these numbers lies in the fact that they are largely
model-independent and therefore the estimate is not dependent on knowing the
rate of sediment deposition.
The horizontal distribution of the TED for Mn, Cu, Ni, Pb and Zn are
given in Figs. 98-102. Without exception, the greatest excess element
accumulation occurs toward centers of the basins and patterns of the TED are
very similar as can be seen from the correlation matrix given in Table 33.
Strong intercorrelations exist between all anthropogenic element pairs
(Cu, Ni, Pb, and Zn) while Mn excess "deposition" patterns are not as
well-correlated for reasons indicated previously. The particularly strong
correlation between surface concentrations of Cu and Zn are also found in the
TED values. Excess element deposition values for other elements such as As,
Cd and Sb cannot be computed because of the lack of complete vertical
profiles.
183
-------
oo
ENRICHMENT FACTORS FOR ELEMENTS
IN SEDIMENTS OF SOUTHERN
LAKE HURON
ELEMENT
Figure 97. Enrichment factors for elements in the fine-grained sediments of southern
Lake Huron. Values are either means (shaded regions) or based, where
necessary, on individual cores.
-------
TABLE 32. VERTICALLY INTEGRATED EXCESS ELEMENT CONCENTRATIONS
(TOTAL EXCESS DEPOSITION)
Total excess deposition (tnicrograms/cm^)
Station
3-2
4-2
5-2
7-2
8-2
9-2
10-2
12-2
13-2
14-2
14A-SC
14A-SC2
15-2
16-2
17-2
18-2
18A-SC
19
25-1
29-2
31-2
33-2
35-2
38
39
41
45
50
51
53-SC
53-SC2
57
61
63-SC
69
Mean + SD
Manganese*
370.
432.
255.
128.
201.
278.
1083.
895.
426.
1598.
1243.
829.
0.
601.
583.
707.
263.
139.
255.
1410.
149.
334.
334.
277.
405.
279.
137.
108.
217.
414.
561.
542.
139.
717.
837.
504 + 380
Copper
21.6
0.0
19.8
3.0
14.7
4.9
7.3
32.8
24.0
59.2
56.5
36.3
0.0
13.9
20.0
59.0
46.6
0.0
11.1
33.3
9.1
11.8
0.0
5.3
10.5
12.8
3.0
0.6
9.9
13.3
14.0
27.5
13.4
39.1
42.7
19.4 + 18
Lead
74.0
0.8
59.9
135.0
56.1
34.2
30.9
134.8
55.0
233.2
198.5
133.4
0.0
57.1
76.6
241.7
90.8
4.1
54.4
123.0
42.4
48.0
14.0
26.4
31.6
21.7
29.0
42.3
36.5
58.6
56.3
116.6
53.2
113.3
147.3
75.2 + 62
Nickel
31.4
0.0
32.1
1.6
16.2
7.7
24.7
42.8
22.7
82.3
60.4
54.5
0.0
18.2
23.8
62.0
28.4
0.13
18.68
46.4
10.9
13.7
0.0
7.1
13.4
16.3
16.0
4.5
10.9
184.9
22.6
32.9
20.1
46.5
62.9
24.9 + 21
Zinc
91.2
0.0
62.0
47.8
69.8
31.7
40.5
165.2
102.2
282.1
239.2
170.9
0.0
68.2
91.3
274.9
211.7
1.55
62.4
173.2
47.0
65.1
7.6
34.3
54.7
42.1
36.7
46.7
44.3
57.5
65.9
146.2
66.4
171.1
211.7
93.8 + 79
* Diagenetic excess
185
-------
43°30'—
(/ig/cm2)
CHi 100- 400
C±S 400- 800
• 800-1200
•11200-1600
43°00'—
Port
Huron
N
SOUTHERN LAKE HURON
10 20 30 40
KILOMETERS
82° 30'
82°00'
Figure 98. Distribution of vertically integrated excess
manganese.
186
-------
1 -10
10-20
20-40
40-60
SOUTHERN LAKE HURON
10 20 30 40
KILOMETERS
Figure 99. Distribution of vertically integrated excess copper.
187
-------
43°30'—
/cm2)
2-20
20-50
50-90
43°00'—
Port
Huron
Kincardine
Goderich
SOUTHERN LAKE HURON
82° 30'
10 20 30
KILOMETERS
82°00
40
Figure 100. Distribution of vertically integrated excess nickel,
188
-------
43°30'—
10-100
100-200
200 -250
43°00'-
Port
Huron
SOUTHERN LAKE HURON
82° 30'
10 20 30 40
KILOMETERS
82°00'
Figure 101. Distribution of vertically integrated excess lead,
189
-------
-------
TABLE 33. CORRELATIONS BETWEEN TOTAL EXCESS DEPOSITION
(TED) OF SELECTED ELEMENTS
Mn
Cu
Ni
Pb
Zn
Mn Cu Ni Pb
.71
.81 .94
.69 .90 .88
.72 .99 .93 .93
N = 35 r = 0.43 at 0.01 level of significance.
191
-------
On the basis of the distribution of TED values in each depositional
basin, it is possible to arrive at an area-wide estimate of anthropogenic
loadings. These loadings, expressed in metric tons (Table 34), are computed
from the contour plots shown in Figs. 98-102. Values for As, Cd, and Sb are
computed indirectly as follows: The mean surface concentrations of the four
elements (Cu, Pb, Ni, and Zn) minus the mean "background" concentration or
mean net concentrations are well-correlated with the total excess element
stored (r = 0.996 for N = 4 significant at 0.01 level). Thus the regression
of mean net surface concentrations on excess stored may be used to predict
the excess storage of Cd, As and Sb from their mean net surface
cncentrations. Because of the limitations of this method of calculation, the
values shown (in parentheses) in the table for these elements should be
regarded as very approximate.
An important result of this study is the recognition that limited
sampling of sediments can lead to considerable error in construction of
materials budgets for the Lakes. As has all too often been the case in the
past, sediment and contaminant budgets have been built on the analysis of an
exceedingly limited number of sediment cores. In some cases inventories have
been developed on the basis of a single core within a depositional basin. As
can be seen from Table 32 there are up to order of magnitude differences in
the total excess deposition from core to core within each depositional basin.
There are sufficient data in this report to estimate the number of cores
required per unit area of each depositional basin to arrive at a desired
level of accuracy in estimating total inventory of a given contaminant.
However, it is beyond the scope of this report to undertake such an analysis.
It should be borne in mind that any relationship worked out for this study
area is not generalizable to other parts of the lake.
Of particular interest is the total inventory of cesium-137 in southern
Lake Huron. Integration of contours of vertically-integrated cesium-137
activity indicate a storage of about 60 Curies as of 1975 in the Port Huron
Basin. In the Goderich Basin in 1975 there were about 320 Curies of
cesium-137 present. At an aqueous concentration of about 0.02 pCi/1 in 1975,
inferred from the concentration-time model using the data of Barry (1973),
the amount contained in the water in southern Lake Huron in 1975 was about 20
Curies. Thus the total stored in the water or in depositional basins
amounted to about 400 Curies. In contrast the decay-corrected total
deposition on this area of the lake is about 950 Curies (based on the data of
Lerman 1970). Thus over half the cesium-137 deposited on the surface of
southern Lake Huron did not end up in the underlying depositional basins.
The hydraulic residence time of the lake is so long in comparison with the
apparent residence time of cesium-137 in the water, that very little could
have been lost by outflow. Hence either the numbers are wrong, or there has
.been a net export of the radionuclide out of the southern part of the Lake
into other areas or there is storage of cesium-137 in non-depositional
regions. The numbers are not likely to be off by a factor of two and until
the inventory is made for the whole lake the second possibility cannot be
ruled out. However, it does not take much mass per unit area overlying the
non-depositional regions of the Lake to account for the missing cesium-137.
Concentrations of cesium-137 in the very fine flocculent material overlying
sediments has concentrations of cesium-137 approaching 30 pCi/g. One to two
192
-------
TABLE 34. ANTHROPOGENIC ELEMENT STORAGE
IN SEDIMENTS OF SOUTHERN LAKE HURON
(METRIC TONS)
Element Port Huron Goderich Combined
Regression* Ratio**
Copper
Lead
Nickel
Zinc
Antimony
Arsenic
Bromine
Cadmium
Mercury
Tin
100
410
157
344
_
-
-
-
-
—
611
2000
788
2580
-
-
-
-
-
"
710
2400
950
2900
(110)
(1000)
-
(150)
-
"
600
2300
1000
3100
40
800
600
60
5
120
*Values in parentheses are approximates and based on regression of the net
mean surface concentration vs. stored excess of Cu, Pb, Ni, and Zn
**Values based on the mean ratio of 1980 anthropogenic accumulation rates to
the stored excess of Cu, Pb, Ni, and Zn.
193
-------
TABLE 35. STORAGE OF CESIUM-137 IN SEDIMENTS OF SOUTHERN LAKE HURON
Region
Area
(xlO13 cm2)
Cesium-137 (1975)
(Curies)
Water Column
Port Huron Basin
Goderich Basin
Non-depositional areas
Total Cesium-137 in
southern Lake Huron
Estimated time-integrated input
decay-corrected to 1975
Unattributed cesium-137
9.5
1.22
2.59
5.93
600
*Arbitrarily assumes a 0.1 g/cm2 flocculent/nephloid layer overlying non-
depositional areas and having an average activity of 30 pCi/g.
194
-------
cm of flocculent material may have a mass per unit area (dry weight) of 0.1
g/cm . This much mass per unit area if present over non-depositional areas
could add 200 Curies to the cesium-137 inventory. Such calculations are
summarised in Table 35. Such a layer of this characteristic mass per unit
area could be present either in the form of a relatively well-defined layer
in juxtaposition with non-depositional boundaries or in the form of a
nephloid layer of some appreciable extent above the lake bottom. Evidence
for the existence of such layers has been reported by Chambers and Eadie
(1980) and confirms the sediment trap studies of Wahlgren et al. (1980).
Whether it is necessary to postulate the existence of boundary-layer storage
to realize accurate mass-balance calculations must remain a matter of
speculation until critical experiments are performed.
SEDIMENT MIXING AND SEDIMENTATION RATES
In the preceding discussion, it has been possible to investigate
patterns of contaminant metal deposition, inter-element associations and even
total anthropogenic element loadings without reference to sedimentation
rates. To gain information about the rates of contaminant deposition,
however, it is necessary to associate a time scale with concentration
profiles in individual cores. Three independent methods have been used for
sediment geochronology in this report. The first relies on measurement of
the vertical distribution of cesium-137 and the occurrence of a horizon
corresponding to the onset of nuclear testing about 25 years ago. This
method provides a measure on the average sedimentation rate over the past 25
years. The second method is based on the radioactive decay of lead-210
(ti/2 = 22.26 years) following burial in sediments. In principle this method
is capable not only of yielding average sedimentation rates over a period of
roughly 100 years, but is capable of revealing changes in the rate of
sedimentation over this period of time. The third method involves use of the
anthropogenic element profiles themselves. The technique is based on the
evidence that profiles of metals from diverse areas of a given lake or
depositional basin reflect a common pollution history which is
reconstructable in terms of regional contaminant loadings. The validity of
this latter approach has been demonstrated by Edgington and Robbins (1976).
Each of the three methods is investigated in this report and in combination,
they lead to an internally consistent view of the local sedimentation process.
The computation of contaminant fluxes is sensitive to the interpretation
given to individual profiles. This fact has been emphasized in a number of
recent studies (Robbins et al., 1977, Robbins and Edgington, 1975, Edgington
and Robbins, 1976, Robbins et al., 1978) which show that the mixing of
surface sediments, probably by benthic organisms, has a significant influence
on radioactivity and metal contaminant profiles and on the estimate of
contaminant fluxes (Edgington and Robbins, 1976). In the section below on
cesium-137, the effects of sediment mixing on radioactivity and contaminant
profiles are discussed.
Cesium-137
Cesium-137 is a uniquely anthropogenic radionuclide first introduced
into the environment as a result of atomic weapons testing which began
195
-------
roughly 25 years ago. Many studies have now demonstrated the utility of
cesium-137 for investigation of sedimentation processes in aquatic systems
such as lakes and reservoirs. Cesium-137 is an especially useful tracer
because its input to the lakes may be accurately inferred from atmospheric
and precipitation radioactivity measurements (Sr-90) made for about a 20 year
period within the watershed of the Great Lakes and elsewhere. Shown in
Figure 103 is the record of deposition of cesium-137 onto Lake Huron since
about 1955. Two maxima are apparent, one in 1958-59 and a larger one in
1963-1964. In the middle panel of Fig. 103 is shown the average annual
concentration of cesium-137 in waters of the Lake from about the mid 1960s
(Barry, 1973). The smooth curve is the predicted concentration based on a
time-dependent coupled-lakes model developed for this report and analogous to
that used by Lerman (1970) for Sr-90. The theoretical fit is best in the
least squares sense for an assumed residence time of 1.1 years for cesium-137
in the water column. Thus the radionuclide is rapidly removed from the water
and changes in its aqueous concentration mimic the history of atmospheric
deposition as a result. Since the hydraulic retention time of the Lake is
long (about 30 years) in comparison with the overall residence time of the
radionuclide, the dominant process for removal of cesium-137 is particle
scavenging and sedimentation. This inference is consistent with the known
high affinity of radiocesium for certain clay minerals present in the water
column. It is therefore expected that the flux of cesium-137 to the
sediments would follow the time-dependence of aqueous concentrations as well
as that of atmospheric inputs. While the flux may do so, the profile of
cesium-137 often does not as can be seen in the bottom panel of Fig. 103. In
the core from station 18, dated by the lead-210 method, the cesium
concentration is smeared out and details of the time-dependence of the input
~from the overlying water are entirely lost. This smeared-out character of
the cesium-137 profiles is seen in other cores such as those shown in Figs.
104-108 for selected (1974) stations. The data for all cores are given in
Table A-4 of the appendix. In most cases there is no detailed structure, and
often there is a zone of nearly constant activity extending downward from the
sediment-water interface. Subsurface maxima are sometimes but not always
seen. These features are strikingly illustrated for a series of cores taken
at station 14 (Fig. 109). At this location the reproducibility of profiles
taken one year to the next is excellent. The open symbols in Fig. 109 refer
to two cores collected in 1974 while the solid symbols refer to 1975
collections. In both cases there is a zone of nearly constant activity which
extends down to about 4 cm, with a suggestion of a peak at around 5 cm,
followed by a gradual decrease in activity below this point down to 10 cm.
As a part of this report, a model has been developed to account for the
observed discrepancy between observed and expected cesium-137 profiles. The
details are presented in Robbins et al. (1977). The smearing is assumed to
occur only in the sedimentary column and as a result of the rapid
steady-state mixing of sediments over a zone of fixed depths, at the sediment
water interface. This depth is referred to as the mixing depth. It can be
shown (Robbins et al., 1977) that if the activity of radiocesium added to the
sediments at time t (with t = 0 corresponding to a very deep sediment layer)
is As(t), the expected cesium-137 distribution is given by:
196
-------
Cs'37m Lake Huron
•£30
10
§ 0
^
0.4
0.3
o
Q.
£0.2
>
H
^0.1
0
25
20
.
o
Q.
> 10
5
AIR
(HAS.L Data)
Coupled
lakes model
TR=1.1yr
WATER
(Data of Barry, 1973.)
J
I
SEDIMENTS
/CORE: EPA-SLH-75\
\ I8A-2 I
1940 1950 1960 1970
YEAR (A.D.)
1980
Figure 103.
History of cesium-137 deposition in Lake Huron.
(Upper panel: estimated flux to the lake surface;
Middle panel: observed mean and predicted concen-
tration in surface waters; Bottom panel: distri-
bution observed in a dated sediment core.)
197
-------
00
^ 137
Cs DISTRIBUTION IN LAKE HURON SEDIMENTS
STATIONS EPA-SLH-74 3-8
ACTIVITY (pCi/grom)
0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 18 20 22
1
2
3
4
<
1 1 1 1 1 1 |J 1 1 1
L J o
A) i
! i
3 <
5^ 5
i i i i i i i i i i i
!•
U
6
0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 18 2O 22
1
2
4
i i || i i i i i i i
2
3
4
4
sl- 5
i 1J I I I i I i i i i
['
_
7
2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 18 20 22
1
p
(
3
t
\
4
5
i i i i i i i ii j i i
B
>i
i ^
jj 4'
5
I 1 1 1 1 1 ' 1
D-
$
>_ 8
24
• '
o
24
1
24
1
Figure 104.
Vertical distribution of cesium-137 in selected cores (74:3-8). (Rectan
gular regions correspond to measured activities. Height indicates sam-
pling interval, width represents analytical errors. Solid circles cor-
respond to values predicted by steady-state mixing model.)
-------
VO
Cs137DISTRIBUTION IN LAKE HURON SEDIMENTS
STATIONS EPA-SLH-74 9-13,19
ACTIVITY
0 2 4 6 8 10 12 14 16 18 20
0 2 4 6 8 10 12 14 16 18 20
1
2
3
i
4
(
£
0
X
• ^ 2
Q. <
UJ 3
0 i
4
5
1 1 1 1 \9 1 1 1 i 1 1
— .-.I-J i
:, ' :
L II 94
|
L 5
) 2 4 6 8 10 12 14 16 18 20 '
1 1 1 1 1 IJ 1 1 1 1 6,
n H ^
1 1 1 1 1 1 ILII 1 1
[«
T«
n ° 12
r°
K 0 2 4 6 8 10 12 14 16 18 20
1
Jj 1
1
L 10 2
t
\
L 3
0 2 4 6 8 10 12 14 16 18 20 J
1
1
2
3
(
4
t
\
5'
i i iy i i i i i i i
11
I
f 13
»
1 1 1 1 1 1 1 1 1 Jl 1 '
•|J 0 2 4 6 8 10 12 14 16 18 20
—— 1 j •
Db
{
1 II 3
L 4
1 1 U 1 1 1 1 1 1 1
[ *
1
19
_
DEPTH IN CM. ACTIVITY IN pCi/GRAM
Figure 105. Vertical distribution of cesium-137 in selected cores (74:9-13,19)
-------
Cs137 DISTRIBUTION IN LAKE HURON SEDIMENTS
STATIONS EPA-SLH-74 14-18
ACTIVITY
2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 IO 12 14 16 18 20 22
1
2
3
4
5
6
7
8
E
o f 9
° UJ '
| i
-I 2
IT 3
1 1 I
^
— i i 5
! -o "' ;
-•0 14 3
[D
1
5
O 2 4 6 8 10 12 14 16 18 20 J
1
g\ i i i i i iii
1*
r '
L- 2
15 3
5"- 4
5
1 1 1 1 1 1 I9| 1 1 1
n ^
~ n
Tl 16
> I I
32 4 68 10 12 14 16 18 20 22
1 1 1 1 1 1 1 1 1 9 1
i & ^
> I
I
) 2 4 6 8 10 12 14 16 18 2O 22
1 1 1 i i i i im
; "«
- n l8
* U
DEPTH IN CM. ACTIVITY IN pCi/GRAM
Figure 106. Vertical distribution of cesium-137 in selected cores (74:14-18).
-------
N3
O
Cs DISTRIBUTION IN LAKE HURON SEDIMENTS
STATIONS EPA-SLH-74 20-32
ACTIVITY
0 2 4 6 8 10 12 14 16 18 20 22 24 0 2 4 6 8 10 12 14 16 18 20 22 24
1
2
3
4
5
(
6
<
7 1
I C
0.
ll 1 1
Q
2
3
4
5
i
6
C
1
2
<
3
1 I 1 1 1 1 1 1 1 1 1 <(
i
!•
:1 fl •
1 <
H 20 6
HI 71
) 2 4 6 8 10 12 14 16 18 20 22 24 C
1 1 1 1 1 1 1 1 1 ! <(l
1
Wf '
fl
^ ti 2,* *<
31 2I ,
) 2 4 6 8 10 12 14 16 18 20 22 24 n
1 1 1 IU 1 1 1 1 1 1 1
~ fl
- " 22 4'
»
- 5
1 1 1 1 1 1 1 1 1 1 II
.[
: i "'•
b1
) 2 4 6 8 10 12 14 16 18 20 2
1 1 1 1 1 i 111 1 1 1
[' " -
) 2 4 6 8 10 12 14 16 18 20 2
i i i i i i i i y i
B
D
32
i i
»2 24
1 1
>2 24
1 1
DEPTH IN CM. ACTIVITY IN pCi/GRAM
Figure 107. Vertical distribution of cesium-137 in selected cores (74:20-32)
-------
Cs137 DISTRIBUTION IN LAKE HURON SEDIMENTS
STATIONS EPA-SLH-74 33-36
ACTIVITY
24 6 8 IO 12 14 16 18 2O O 2 4 6 8 IO 12 14 16 18 2O
1
2
3
<
41
i i i i yi i i i i i i i i ii i i i I I 1
71 3 ~J
33 4( ~ 36
5L
C
— 1
r-o r~
o t" 2
N3 Q_
UJ (
U»J
Q 3
4
C
1
2
1
3
4
5
> 2 4 6 8 10 12 14 16 18
1 1 1 IU 1 1 1 1 1 1
r ^
34
—
> 2 4 6 8 10 12 14 16 18 20
i y i i i i i i i i i
35
DEPTH IN CM. ACTIVITY IN pCI/GRAM
Figure 108. Vertical distribution of cesium-137 in selected cores (74:33-36)
-------
SOUTHERN LAKE HURON STATION 14
o
OL
LJ
Q
6
7
8
9
10
Cs-137 ACTIVITY (pCi/g)
8 12 16 20 24 28
I T
T I
I I I IQ I
I I
O
O
• D
O
-• D
O
O
O
O
O
Dl
o 14-1
D 14-2
• 14A-2
• 14A-SC
Figure 109.
Vertical distribution of cesium-137 in a series
of cores at station 14 collected in 1974(14-1,2)
and in 1975(14A-2,SC).
203
-------
and
A = Am(T) zs
(38)
where Y = r/s, t = T corresponds to the sediment water interface and u> is
the sedimentation rate (cm/yr) neglecting the effects of compaction. is
the radioactive decay constant for cesium-137 (Y= 0.69315/ti/2» tl/2 = 30.0
years) and z is the depth below the sediment-water interface. The effects of
compaction are automatically taken into account by expressing z in terms of
the cumulative mass per unit area and jw in terms of the mass sedimentation
rate (g/cm2/yr). The mixing depth, in consistent units, is expressed in
terms of mass/unit area.
A computer program was developed to find the value of the mixing depth,
sedimentation rate and surface activity AS(T) giving the best least squares
fit of the above equation to the observed profiles. The results are
summarized in Table 36 and indicated in Figs. 104-108 in terms of the solid
points of selected profiles. In general, the agreement is satisfactory but
often, because of the limited range of penetration of radiocesium into these
sediments, the inferred values, both the sedimentation rates and mixed
depths, are subject to large uncertainties. The effect of steady-state
mixing on the radio-cesium profile is illustrated in Fig. 110 which shows the
distribution expected in a lead-210 dated core in the absence of mixing (left
panel). With a short overall residence time in the Lake, radiocesium should
have a sedimentary profile which corresponds to the history of atmospheric
deposition. Because of mixing, however, the activity is found deeper in the
core and is smoothly distributed as indicated in the right panel of Fig. 110.
In most cores from the study area, the observed vertical distribution of
radiocesium is largely the result of mixing rather than sedimentation. Thus
limited reliable information is obtained on sedimentation rates via
cesium-137 measurements. This is easily seen by examination of Fig. 107 for
such stations as 20 and 21. In cores from these stations the activity is
essentially constant over the upper 4 cm or so and drops abruptly in deeper
sections. In such cores the sedimentation rate could be almost zero and yet,
because of mixing, activity will appear at appreciable depths in the core.
Moreover both the sedimentation rate and mixing depth are sensitive to
small losses of material from the tops of the cores. This may be illustrated
by repeated analysis of the cesium-137 profile at station 14 via the mixing-
model for progressive losses of sediment (i.e. the model was evaluated using
the station 14 profile with top and successive layers of data left out and
the surface (z=0) redefined). The results are shown in Table 37. As Cs-137
is found more deeply in this core than in most others, station 14 represents
an optimal case. Cores in which Cs-137 is only a few cm deep will be far
more sensitive to disturbances of the sediment-water interface. Thus, at
best, cesium-137 can be used only as a rough indication of sedimentation
rates in southern Lake Huron and an alternative measure of sedimentation
204
-------
nCi/m /yr
10 15 20
pCi/g
10 15
20
1950
N>
O
Ul
ANNUAL FALLOUT OF
Cs'37
TO THE SURFACE OF
LAKE HURON
Cs'37 ACTIVITY
CORE 14
EPA-SLH-74
6CVI
C
O -
1.0
•o
0)
1.4'5
o»
c
0>
1.8
2.2
E
& O
b —
JC
"a.
O
JIO
Figure 110.
Relation between the expected and observed distribution of cesium-137 at
station 14 (Core 14A-2). (Left panel: Distribution expected if transfer
from air to sediments were instantaneous and if there were no sediment
reworking. Right panel: Observed distribution and predicted profile us-
ing the steady-state mixing model.)
-------
rates must be employed. Lead-210 is suitable in this respect partly because
the average sedimentation rate determined by this method is almost completely
insensitive to any realistic losses of sediment on coring or other
short-range (cm) disturbances of the sediment-water interface. Sedimentation
rates determined via cesium-137 and lead-210 are discussed further below.
As part of this report, the vertical distribution of benthos was
determined in a series of replicate cores at stations 14A and ISA (Krezoski
et al., 1978) to establish if their distribution and density could account
for the inferred effects of mixing. Robbins et al. (1977) successfully
showed that benthos were primarily found in the zone of mixing as defined by
cesium-137 and lead-210 profiles and that they were present in sufficient
numbers to account for estimated mixing rates. Further studies, sponsored by
EPA in Saginaw Bay, have shown (Batac-Catalan et al. 1980) that the mixed
depth is well-correlated with the depth above which 90% of the benthos occur.
A summary plot for cores examined to date from this study area, from Saginaw
Bay and from Lake Erie is given in Figure 111. The 90% cutoff depth is very
well correlated with the depth of the mixed zone (S = -0.2 + 1.16 Z ; r =
0.91, N = 10). Thus, there is strong circumstantial evidence that benthic
organisms are primarily responsible for the mixing of near-surface sediments
and the resultant alteration of radioactivity and contaminant metal profiles.
Previously it had been suggested (Lerman & Lietzkie, 1975) that profiles of
cesium-137 as well as those of strontium-90 might be affected or even largely
determined by diffusional migration. However, Robbins et al. (1977) showed
that cesium-137 cannot migrate significantly its sediments by molecular
diffusion since it is strongly bound to sediment solids. This result cannot
be generalized to include other contaminants, tracers, or sedimentary
environments however. Cesium-137 can experience significant diffusional
migration in sediments which do not contain minerals with a specific affinity
for this radionuclide (cf. Alberts et al. 1979). Also a nearly conservative
tracer such as Sr-90 undergoes considerable diffusion in sediments of the
Great Lakes (Lerman & Lietzkie, 1975).
In Table 36 the mixing depth derived from the steady-state mixing model
is given both in linear terms (cm) and in terms of mass per unit area. For
both measures, there is a systematic variation within each depositional
basin. A major increase in the depth of sediment mixing occurs toward the
deepest, central region and northward within the Goderich Basin (Fig. 112).
Values range from essentially zero to over 4 cm. Reasons for the observed
distribution are not clear, but the depth of mixing is directly related to
the porosity of surface sediments. Less consolidated sediments are mixed to
a greater depth (compare Figs. 16 and 112). This trend may be related to the
nature of benthos-sediment interactions.
Also given in Table 36 is the vertically integrated activity of
cesium-137 (or total deposition), the analogue of TED for soluble elements
and computed using Eq. 37 with C^g = 0. Mean vertically integrated
activities (pCi/cm^) for the Port Huron and Goderich Basins are respectively
4.8 + 2.6 (N = 12) and 11.2 + 7.7 (N = 47). The horizontal distribution of
the total cesium deposition is shown in Fig. 113. Highest deposition occurs
toward the center of the Goderich Basin but values often do not exceed that,,
expected from atmospheric fallout, decay-corrected to 1975 (about 10 pCi/cm ).
206
-------
16
12
E
o
8
•o
o Soginow Boy
• Lake Huron
• Lake Erie
0
8
Z90 (cm)
12
16
Figure 111,
Relation between the depth of sediment mixing as
indicated by either cesium-137 or lead-210 and the
depth above which 90% of benthic macroinvertebrates
OCCUr (
207
-------
TABLE 36. VERTICALLY INTEGRATED ACTIVITY OF CESIUM-137
AND MIXING MODEL PARAMETERS
INTEGRATED
STATION CS-137
(pel/cm^)
EPA-SLH-74-3-2
EPA-SLH-7 4-4-2
EPA-SLH-74-5-2
EPA-SLH-74-6-2
EPA-SLH-74-7-2
EPA-SLH-74-8-2
EPA-SLH-74-9-2
EPA-SLH-74-10-2
EPA-SLH-7 4-1 1-2
EPA-SLH-74-12-2
EPA-SLH-74-13-2
EPA-SLH-7 4- 14-1
EPA-SLH-74-14-2
EPA-SLH-75-14A-2
EPA-SLH-75-14A-SC
EPA-SLH-74-15-2
EPA-SLH-74-16-2
EPA-SLH-74-17-2
EPA-SLH-74-18-2
EPA-SLH-7 5- 18A-SC
EPA-SLH-75-18A-2
EPA-SLH-74-19-2
EPA-SLH-74-20-2
EPA-SLH-74-21-2
EPA-SLH-74-22-2
EPA-SLH-74-25-1
EPA-SLH-74-29-2
EPA-SLH-74-30-2
EPA.-SLH-74-31-2
EPA-SLH-74-32-2
EPA-SLH-74-33-2
EPA-SLH-74-34-2
EPA-SLH-74-35-2
EPA-SLH-74-35-2
EPA-SLH-75-39
EPA-SLH-75-40-2
EPA-SLH-7 5-4 1-1
EPA-SLH-7 5-42-1
EPA-SLH-7 5-4 3
EPA-SLH-75-44
11.30
1.45
5.35
10.01
3.79
7.30
8.50
4.83
8.32
14.91
5.67
22.57
23.69
29.35
28.20
1.68
7.11
12.01
15.25
12.35
12.07
1.00
16.47
15.91
4.06
9.30
16.70
3.60
6.19
5.78
5.07
5.13
3.40
9.21
4.85
3.18
5.36
11.92
2.06
0.33
MIXING DEPTH
(cm) (g/cm2)
1.42
0.00
1.41
2.52
1.07
1.96
2.00
1.08
2.24
3.80
1.05
3.79
3.62
3.20
5.28
0.88
1.69
2.96
2.05
1.78
1.90
0.18
3.53
3.38
0.76
1.72
1.96
0.35
1.06
1.04
0.82
1.17
0.05
2.40
1.12
1.40
1.58
2.81
0.88
0.85
0.24
0.00
0.22
0.36
0.64
0.28
0.54
0.22
0.34
0.72
0.34
0.65
0.61
0.55
0.95
0.80
0.22
0.46
0.48
0.40
0.43
0.04
0.55
0.52
0.18
0.25
0.62
0.07
0.22
0.17
0.10
0.36
0.28
0.70
0.70
1.25
0.23
0.68
0.85
1.13
SEDIMENTATION RATE
CS-137
(cm/yr) (mg/cm2/yr)
0.188
—
0.204
0.069
0.039
0.051
0.099
0.057
0.050
0.085
0.074
0.500
0.487
0.341
0.152
0.030
0.093
0.095
0.340
0.098
0.167
0.044
0.115
0.156
0.051
0.123
0.130
0.077
0.058
0.063
0.138
0.060
0.052
0.090
0.133
0.056
0.096
0.140
0.110
0.026
28.
0.
28.
7.
23.
6.
19.
11.
6.
11.
23.
49.
56.
45.
20.
27.
10.
10.
32.
18.
19.
10.
13.
17.
12.
13.
17.
12.
12.
10.
17.
16.
31.
20.
80.
45.
5.
20.
40.
35.
(continued).
208
-------
TABLE 36. (continued).
INTEGRATED
STATION CS-137
(pci/cm2)
EPA-SLH-75-45
EPA-SLH-75-46
EPA-SLH-7 5-47-2
EPA-SLH-7 5-48
EPA-SLH-7 5-49-2
EPA-SLH-7 5-50
EPA-SLH-7 5-5 1-1
EPA-SLH-7 5-5 2
EPA-SLH-75-53-SC
EPA-SLH-7 5-54
EPA-SLH-7 5-55
EPA-SLH-7 5-56
EPA-SLH-7 5-57
EPA-SLH-7 5-58
EPA-SLH-7 5-59
EPA-SLH-7 5-60
EPA-SLH-7 5-61
EPA-SLH-7 5-62
EPA-SLH-75-63-SC
EPA-SLH-7 5-65
EPA-SLH-7 5-66
EPA-SLH-7 5-67
EPA-SLH-7 5-68
EPA-SLH-7 5-69
EPA-SLH-7 5-70
EPA-SLH-7 5-71
2.42
9.80
26.80
0.06
11.24
4.89
4.09
0.44
12.92
15.33
28.57
2.26
8.43
5.59
18.31
22.63
13.69
9.92
15.16
23.57
17.79
3.26
22.90
24.93
15.99
11.44
MIXING
(cm)
1.42
2.82
4.84
0.00
1.64
1.63
1.54
0.00
2.97
3.72
4.98
0.78
2.40
1.10
3.33
0.70
1.31
1.14
2.26
4.00
3.27
0.86
3.10
3.78
3.80
1.33
DEPTH
(g/cm2)
1.70
2.15
0.72
0.00
0.30
1.03
1.40
0.00
0.62
1.52
0.84
0.21
0.38
0.19
0.48
0.67
0.42
0.28
0.39
0.62
0.60
0.13
0.66
0.66
0.58
0.43
SEDIMENTATION RATE
CS-137
(cm/yr) (mg/cm2/yr)
0.071
0.148
0.318
—
0.088
0.062
0.106
—
0.092
0.238
0.266
0.041
0.114
0.075
0.217
0.327
0.167
0.117
0.167
0.303
0.216
0.040
0.264
0.268
0.106
0.071
80.
70.
28.
0.
14.
32.
90.
0.
12.
54.
29.
11.
13.
11.
20.
55.
48.
27.
22.
27.
24.
6.
29.
34.
9.
7.
209
-------
Harbor
Beach
MIXING DEPTH
(cm)
SOUTHERN LAKE HURON
10 20 30 40
KILOMETERS
Figure 112. Distribution of mixed depth based on cesium-137
210
-------
Harbor;
Beach
43°30-
CESIUM-137
(pCi/cm2)
5-10
10-15
'5-20
>20
43°00'-
Port
Huron
Kincardine
^Goderich
82°30'
N
SOUTHERN LAKE HURON
0 tO 20 30 40
KILOMETERS
82°00'
Figure 113. Distribution of vertically integrated cesium-137
activity.
211
-------
TABLE 37. VALUES OF THE MIXING DEPTH AND
SEDIMENTATION RATE VERSUS THE EXTENT OF
SURFACE SEDIMENT LOSS DURING CORING
Loss (cm) S (g/cm2) r (mg/cm2/yr)
0 0.61 56
1 0.55 50
2 0.43 47
3 0.34 37
212
-------
If the non-depositional areas within the study area contain insignificant
amounts of cesium-137, then considerably less is stored at this part of the
lake than expected on the basis of atmospheric fallout and estimated losses
via outflow and storage of the radionuclide in the water column. This
apparent mass balance discrepancy is considered in greater detail above.
Lead-210
The lead-210 method of dating coastal marine and lacustrine sediments
has been used with increasing frequency since its first application by
Krishnaswami et al. (1971). The extensive literature concerning radioactive
lead isotopes and lead-210 in particular has been recently reviewed by
Robbins (1978). The method has been shown to be of value in dating
fine-grained sediments from all of the Great Lakes (Superior: Bruland et al.
1975; Michigan: Robbins and Edgington 1972, 1975; Edgington & Robbins 1976;
Huron: Robbins et al. 1977; Robbins 1977; Erie and Ontario: Robbins et al.
1978; Farmer 1978). Generally, the method has been applied to a very limited
set of cores. This report represents one of the first extensive applications
of the method to determination of sedimentation rates in lakes. Only a brief
account of the lead-210 method of dating sediments is given in this report.
For a detailed discussion of the principles underlying the method, see
Robbins (1978).
Lead-210 is produced as the indirect result of the decay of uranium
present in crustal and sedimentary materials. The principal components in
the decay scheme are:
U238 -> Ra226(t1/2 = 1620 yr) -> Rn222(ti/2 - 3.8 d)
-> Pb210(t1/2 = 22.26 yr) -> Po210(t1/2 - 138 d)
-> Pb206
Short-lived products in the decay scheme are not shown.
Some lead-210, present in sediments, is produced by in situ decay of
radium-226. Generally this is a small and nearly constant activity referred
to as supported lead-210. In addition to supported lead-210, there is an
excess which is supplied to sediments from atmospheric deposition.
Atmospheric lead-210 originates from a unique property of the uranium series
decay scheme shown above. Radium-226 decays to form the radioactive noble
gas, radon-222, which diffuses out of crustal materials into the atmosphere.
Radon-222 decays through a series of very short-lived nuclides to lead-210
which has a high affinity for atmospheric particulate matter and is rapidly
scavenged from the air. The flux of lead-210 over the Great Lakes has not
yet been measured but is expected to be around 0.5 pCi/cm2/year and quite
constant from year to year. Once in the water, lead-210 is rapidly
transferred to sediments and this excess, not being supported by radium
activity, decays toward supported levels during burial. In sediment cores
from the Great Lakes excess lead-210 may be roughly twenty times higher than
supported levels (cf. Robbins and Edgington, 1975).
In undisturbed cores where the sedimentation rate is constant, the
activity of excess lead-210 is given by
213
-------
. / N A ~^t A -Xm/r
A(m) = AQ e = AQ e
where Ag is the excess activity at one surface (m = o), t is the time before
collection (years), m is the cumulative dry weight of sediment (g/cm^) and r
is the mass sedimentation rate (g/cm^/yr). The radioactive decay constant
is given by 0.69315/22.26 = 0.0311 yr-1.
The total (observed) activity is given by
Atot = A(m) + Af (40)
where Af is the activity of supported lead-210.
The above equations suffice to describe profiles in sediments where
there is no mixing. Incorporation of the effects of rapid steady-state
mixing is comparatively straight-forward for lead-210 (Robbins et al. 1977)
since As(t) in Eq. 38 is essentially constant over time. Using mass units
rather than linear (cm) units and substituting AQ for As(t) in that equation,
the distribution of excess lead-210 is given by
A,,, = A0 / (1 + As/r)
A(m) = V m < 8 (41)
- Ame-XCm-sVr r>s.
This is the equation used to obtain sedimentation rates and mixed depths from
excess lead-210 profiles. Eq. 41 describes a theoretical profile in which
the activity of lead-210 is constant from the sediment-water interface down
to depths. Below that depth (mixed depth) the activity fall off exponentially.
Because of sediment compaction, the decrease in porosity with increasing
sediment depth, the sedimentation rate in linear terms is not uniquely
defined (Robbins and Edgington, 1975) even when the mass sedimentation rate
is well-defined and constant. Layers of sediment are brought closer together
on burial as a result of the loss of water so that the apparent linear
sedimentation rate decreases with sediment depth. In an interval of
thickness dz, the mass, dm, is given by
dm = (1 - ) p dz (42)
s
Thus the mass sedimentation rate r is related to the linear rate 01 by
r = dm / dt
= (1 - <)>(z)) P dz/dt (43)
S
= (i -
s
If the density of sediment solids, ps, is constant for a given core and
(j)(z) is the porosity, then when r is constant
214
-------
u> = u (1 - (z))
where w is the linear sedimentation rate at z = 0.
o
In the foregoing brief discussion of sedimentation rates based on
cesium-137, is is computed (Table 38) as the average rate over the upper 5 cm
or so while r remains uniquely but imprecisely defined. In the discussion of
lead-210, To , is defined as the average over the upper 10 cm (^ = 10/A t where
At = m(10)/r) and is given only to provide a rough indication in linear terms.
Vertical distributions of lead-210 and in some cases cesium-137 as well
are given in Figures 114-117. The complete data set is given in Table 5A of
the Appendix. In Fig. 114 (core EPA-SLH-74-13), it can be seen that excess
lead-210 decreases in an essentially exponential way with increasing sediment
depth as expected on the basis of simple radioactive decay, constant lead-210
flux and constant sedimentation rate. Total lead-210, indicated by the open
circles, departs from excess lead-210 at around 10 cm depth and the supported
level in this core is about 0.3 pCi/g, about an order of magnitude lower than
excess lead-210 at Z = 0. Both lead-'VO and cesium-137 profiles indicate
essentially no (<1 cm) mixing at this location. In contrast, profiles of
lead-210 and cesium-137 at station 12 (Fig. 115) both possess a zone of
constant activity down to about 4 cm. In Figs. 116-117 are shown additional
excess lead-210 profiles which illustrate the variety of profiles encountered
in the study area. In core 19 (Fig. 116) excess lead-210 is measurable only
over the upper two cm, and the rate is very poorly determined as a result.
In contrast, in Core 25 (Fig. 116) there are many values down to 8 cm which
fall on a well-defined line (log plot). There is also about 1-2 cm of mixing
in this core. In each case the solid line is the theoretical (least squares
fit) using Eq. 41. In Core 53 (Fig. 117) non-exponential features exist in
the upper 3-4 cm which are not well-described in terms of rapid steady-state
mixing. In this core there is a change in gross sediment composition at
around 4 cm. Fig. 118 (upper panels) presents unsupported lead-210 (excess)
and cesium-137 profiles for stations 14 and 18. In the lower panels are
presented the vertical distribution of benthic organisms. This data set has
been discussed in detail by Robbins et al. (1977). The mixed depths inferred
from lead-210 in both cases is consistently higher than that determined from
cesium-137.
Sedimentation rate, and mixing parameters derived from the steady-state
mixing model are given in Table 38. The uncertainty in estimating the
activity of excess lead-210 increases without limit as background
(unsupported) levels are approached. For this reason, a weighted least
squares analysis was used to extract parameter values from the model.
Weights were chosen proportional to the reciprocal of the square of the error
associated with the estimate of excess lead-210.
The distribution of vertically integrated excess lead-210 or standing
crop shown in Fig. 119 illustrates the strong focusing effect seen as well
(in greater detail) for the distribution of total cesium-137 (Fig. 113). If
the excess lead-210 were deposited uniformly over the lake bottom and there
were no transfers into or out of the study area, the expected standing crop
would be given by the ratio of the atmospheric flux to the radioactive decay
215
-------
TABLE 38. SUMMARY OF LEAD-210 DATA AND MODEL-DERIVED SEDIMENTATION RATES
AND MIXED DEPTHS
Activity (pCi/g)
Station
3
4
5
7
8
9
10
12
13
14ASC
16
17
18-2
18A2
19
21b
25
31
33
35
38
39
41
45
50
51
53C
57
61
63
69
Mean
Surface
8.9
1.3
11.1
3.3
7.2
5.9
7.1
15.0
3.9
11
9.4
8.6
7.5
8.8
3.5
-
10.2
5.8
10.3
2.4
2.8
3.1
11.7
2
3.0
2.8
10.2
6.6
3.7
10.8
7.1
Mean
Supported
0.49
0.25
0.59
0.32
0.49
0.45
0.47
0.77
0.34
0.7
0.76
0.65
0.45
0.55
0.62
-
0.70
0.50
0.57
0.51
0.29
0.26
0.19
0.18
0.36
0.25
0.52
0.35
0.27
0.67
0.84
Sedimentation
(mg/cm^/yr)
16.3
<5
7.5
65.6
14.0
21.0
16.0
38.2
94.2
24.0
11.2
13.5
53.2
41.4
<1.7
11.6
13.4
11.4
11.9
<19
<28
<27.8
12.3
49.4
61.0
114
<11.1
20.6
103
34.2
39.7
Rate
(cm/yr)a
0.063
0
0.038
0.087
0.071
0.041
0.054
0.16
0.15
0.12
0.060
0.066
0.20
0.13
0
0.072
0.067
0.054
0.062
<0.02
<0.02
<0.029
-
-
0.084
0.088
<0.031
0.10
0.19
0.14
0.18
Mixed
(cm)
2.5
0
0
0
0
1.7
0
3.5
0
4.5
1.5
2
3
2.5
0
3.5
1.5
0
0
1.0
0
2
0
0
0
0
0
2
3
4.5
4
Depth
(g/cm2)
0.47
0
0
0
0
0.5
0
0.66
0
0.71
0.2
0.3
0.75
0.78
0
0.5
0.2
0
0
0.5
0
1.5
0
0
0
0
0
0.3
1.2
0.97
0.71
a mean sedimentation rate over the upper 10cm
° data only in counts/min/gram
c discontinuity around 4 cm
216
-------
Cs137 Activity (pCi/g)
30-
4 8
12 16
1974
-1939
o
o>
-1905
- 1870
0.2 0.5 1.0 2.0
Pb210 Activity (pCi/g)
Figure 114. Vertical distribution of lead-210 and cesium-137
in core 74-13. (Open circles: total lead-210;
X: excess lead-210.)
217
-------
Cs Activity (pCi/g)
30-
0.5
CORE 12
EPA-SLH-74
0 = 1.4 mm/yr
s = 4 cm
I
Pb
25
Activity (pCi/g)
10
1974
1939
o
0)
1903
1867
20
Figure 115. Vertical distribution of lead-210 and cesium-137
in core 74-12.
218
-------
0
EXCESS LEAD-210 (pCi/g)
0.5 I 2 5
10
20
Figure 116. Vertical distribution of excess lead-210 in selec-
ted Port Huron and Saginaw Basin cores.
219
-------
O.I
EXCESS LEAD-210 (pCi/g)
0.2 0.5 I 2
0
2
10
6
0
1 2
SLH-75-53
Q-
LJ
Q
4
6
8
10
12
14
SLH-75-63
Figure 117. Vertical distribution of excess lead-210 in selec-
ted Goderich Basin cores (75-53,63).
220
-------
H
(D
ho
N3
MEAN NUMBER OF ORGANISMS
210 ,
O -^ oo
PERCENT SOLIDS BY VOLUME
UNSUPPORTED Pt) (pCi/g)
O
ro
o
m
T>
o
3
oo
6
Fo
^
cr>
o CD
137
ro
Cs'37(pCi/g)
O
z
00
-------
y2io
2L
(pCi/cm2)
ED 5-10
1 0 - 20
20-30
>30
Sornia
SOUTHERN LAKE HURON
Figure 119.
Distribution of vertically integrated excess lead-
210 (standing crop).
222
-------
constant or about 0.5 pCi cm~2 yr * / 0.0311 yr 1 = 16 pCi/cm2. Within the
Goderich depositional basin this value is often exceeded as can be seen in
Fig. 119. But on the average the standing crop is lower in this part of the
lake than expected from atmospheric deposition. This result is consistent
with that inferred from the cesium-137 analysis: the depositional basins do
not store as much of either radionuclide as expected on the basis of known
atmospheric inputs.
The comparison of sedimentation rates based on lead-210 and cesium-137
illustrates the difficulties in obtaining accurate estimates from cesium
profiles in the study area. Shown in Fig. 120 is the relation between
rPb-210 anc^ rCs-137* Regression analysis yields:
rCs-137 = 3.24 + 1.08 rPb_2i0 (45)
with a correlation coefficient of 0.84 for N=25. While the relationship is
highly significant there are none the less very large discrepancies in some
cases between the two measures. Because of the uncertainties in the estimate
from cesium-137 profiles, a simpler treatment of the data does equally well
in predicting sedimentation rates. The first order effect of steady-state
mixing on the cesium-137 profile is a downward displacement of the horizon by
an amount equal to the depth of mixing. As a result, the sedimentation rate
may be inferred from visual identification of the mixed depth and the
location of the horizon, z^. As cesium-137 was introduced into the
environment in significant quantities just after 1952, the mixing-corrected
horizon (z^ - s) should correspond to a time of 1975 - 1952 = 23 years so the
sedimentation rate may be approximated as r = (z^ - s)/23 with s and z^
expressed in g/cm2. Results of these two methods, least squares and
simplified, are compared in Table 33 below. Also shown in Fig. 120 (open
circles) is the relation between r Cs-137 anc* the mass sedimentation rate
inferred from linear extrapolation or interpolation from lead-210 rates at
nearby locations. Essentially the same degree of correlation (rcorr = 0.8,
N = 22) exists for this set as for the lead-210/Cs-137 set. At locations
where neither lead-210 nor stable lead data are available, sedimentation rate
values are based on regression analysis of the two methods of treating
cesium-137 profiles and on interpolation between grid points. (Table 40
below).
Stable Lead
An alternative means of determining sedimentation rates is based on
analysis of pollutant metal concentration profiles. Walters and Wolery
(1974) found that the mercury profiles in sediment cores from western Lake
Erie possessed several horizons which tended to correspond to the development
of local industrial mercury use over the past 40 years or so. In principle
such features could be used to infer sedimentation rates. Edgington and
Robbins (1976) showed that the vertical distribution of stable lead in the
fine-grained sediments of Lake Michigan reflects the history of cultural lead
inputs. Lead distributions in dated cores were quantitatively described by a
universal time-dependent loading or source function taken to be a linear
combination of the estimated annual inputs of atmospheric lead derived from
the combustion of leaded gasoline and the burning of coal in the Great Lakes
223
-------
100-
0
20
40 60
rpb-2io (mg/cm2/yr)
80
Figure 120. Relationship between the mass sedimentation rates
estimated from cesium-137 and lead-210.
224
-------
region since about 1800. Robbins and Edgington (1974) showed that
application of this source function to lead profiles in other sediment cores
from Lake Michigan yielded sedimentation rates consistent with rates inferred
from seismic profiling data. The source function developed for Lake Michigan
should be applicable to the entire Great Lakes region and therefore provide
an alternative sediment dating method for Lake Huron as well.
The estimated loading of the lake in relative units (or source function)
is shown in Fig. 121. Two sources have contributed most (>95%) of the
anthropogenic lead in the environment today: coal and leaded fuel combustion
(Winchester and Nifong, 1971). Until about the mid 1920's the dominant
contributor was coal burning but not long after the introduction of leaded
gasoline, combustion of this latter product became the principal source of
lead pollution in the Great Lakes region. Details of construction of the
source function are given by Edgington and Robbins (1976). It is assumed
that non-atmospheric inputs are proportional to this source function (i.e.
have the same time-dependence but different magnitude). Because of the
presumed short residence time of lead in the lakes (cf. Nriagu et al. 1979)
stable lead profiles should reflect this loading history apart from the
effects of sediment mixing. The effects of mixing may be taken into account
in the same way as done above for cesium-137 except that in the case of lead
there is no radioactive decay so that in Eq. 41,\ = 0 while As(t) is taken to
be proportional to the source function. Details of the theoretical treatment
are given by Edgington and Robbins (1976).
Values of the mixed depth and sedimentation rate are determined by trial
and error and chosen to minimize the differences between observed and
predicted lead concentration profiles in the least squares sense. The
results for one of the most finely sectioned cores (EPA.-SLH-75-18A-2) are
given in Figures 122 and 123. The vertical distribution of major elements
(Fig. 122) indicates that this core is of uniform composition with respect to
many principal constituents. Dates assigned to sediment intervals in the
figures are based on lead-210. In Fig. 124 vertical profiles of other
elements are given in addition to lead for comparison. The solid line
indicates the predicted lead profile corresponding to a sedimentation rate
41.5 mg/cnrvyr as compared with a value of 41.4 mg/cm^/yr based on lead-210.
Clearly such close agreement is accidental in view of the over all relation
between rates based on these two methods. The results of applying the method
to lead profiles in the other cores are given in Table 39. Both lead and
lead-210 profiles give a very consistent picture of sedimentation rates.
Shown in Fig. 124 are other profiles of lead plotted against dat*e as
determined by lead-210. In each case the lead records indicate the onset of
excess lead deposition as just prior to 1900. Shown in Fig. 125 is the
relationship between sedimentation rates determined by the two methods.
Regression analysis yields:
r Pb-210 = --04 + °-89 r Pb (46)
with a correlation coefficient of 0.94 for N=24. This result indicates that
1) within the study area, profiles of stable lead are everywhere consistent
with a lead loading history developed previously for Lake Michigan (note: not
in absolute magnitude, however) and 2) stable lead may be used as an
225
-------
N3
500
y>
•E 200
ID
O)
•5 100
_g
o>
£ 50
en
LJ
O
LJ
_l
O
cr.
LJ
X
Q.
20
10
5
2
1
0.5
EXPONENTIAL SOURCE
FUNCTION
= 0.034yrH)
LEADED FUEL
ADDITIVES
LEADED FUEL
ADDITIVES
PLUS COAL
1860
1880 1900 1920
YEAR (A.D.)
1940
1960
Figure 121.
Estimated regional atmospheric emissions of lead from the combustion of
coal and leaded fuel additives.
-------
K)
N>
u
5
10
15
I20
t 25
LJ
Q
30
35
40
45
5O
1 I U
t
{
i
.
-
-
t
-
-
i i i
i i
»
»
•
j
•
'
t
•
i i
i i i ii .
•*
••
-
•
4
t
- Co
_
4
-
-
1 1 1 I
1
\
1
:
,
•
•
i
-
•
-
_
-
•
-
i i
t- '
••„
c
•
•
•
Fe
•
i i
i i •;.
|
4
•
- Mg •
_
<
-
-
4
1 1
1
•
•
•
1
1
-
^
•
- -
-
-
•
i
.1 U 1 I *1
/
t
*
i
»
•
* —
Mn
•
SLH-75
18A(2) -
i i i i i
1 ^ / J
1950
1900
1850
1800
1700
1600
1500
o:
LJ
0 0.2 0.4 0 2 4
FRACTION Co(wt.%)
SOLUBLE
60 2 40 2 40 0.05 0.10 0.15
Fe(wt.%) Mg(wt.%) Mn(wt.%)
Figure 122. Vertical distribution of major elements in core EPA-SLH-75-18A.
-------
u
5
10
15
~ 20
o
JE25
LU
Q
30
S3
M
00
35
40
45
50
t '
-/
_ /
r
- r
I
—
-
-
_
Cu
>
<
»
il < i
1 1 4U 1
n
P
\
•I
|.
"
-Cr •
h-
| |
1
•
I
j
V
- •/'
V
i
-
-
—
—
-
_
i/
*
Hg
i i i
1 '\ '
/
_ ?
f
r f
- f
- •
—
—
-
—
i
Ni
i i i
i i i 14.1
_ K
I'
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- -j Pb
i
—
i
i i i i
ii i » .
- /
/
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-
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—
<
—
-
—
i
.
Sn
i i i i
i i i i i • m
*7 —
I
- i
l-
*
L
•| Zn
*\
i
u_
4
-
—
1 I
—
SLH-75
18A(2)
i i i i i
\^i u
1950
1900
1850
1800 ~
ci
-
1700
1600
1500
0. 40 0 40 0 0.050100.15 0 40 80 0 40 80 0 1 2 0 40 80 120 160
CONCENTRATION (ppm)
Figure 123.
Vertical distribution of trace elements in core EPA-SLH-75-18A. The
solid lines are the predicted concentrations based on the historical
emissions inventory (lead) or exponential source function (other
elements).
-------
K)
VO
I975
LEAD
60
80 100 120
LEAD (ug/g>
20 40 60 80 100 120
140 160
I900
I800
a
<
cr
<
LJ
I700
1600
1500
Figure 124.
1 1 1 1 ! £T~0 '
• so
• A 0^*
0 ^
o A"
• o
• A
0
-------
TABLE 39. SEDIMENTATION RATES BASED ON ANALYSIS OF LEAD PROFILES'1
Station
3
4
5
7
8
9
10
12
13
14A-SC
16
17
18-2
18A2
19
25
29
31
33
35
38
39
50
51
57
61
63
69
Sedimentation Rate
(mg/cm^/yr)
21.0
0
12.9
100
14.4
17.0
6
36.4
14.0
38.0
12.3
12.0
60.0
41.5
<2
13.3
32.0
13.5
17.2
0
<25
37
78
110
32.0
90.0
38.0
40.0
Mixed Depth (g/cm2)
(cm)
3
0
2
2
2
0
0
4
0
4.5
3
3
5
3
0
2
3
2
0
0
0
0
0
0
2
2
3
6
a Using the source function shown in Fig. 121.
230
-------
e
o
140
120
100
80
e 60
*—.»
Q.
40
20
I
0
20 40 60 80 100
rpb-2io (mg/cm2/yr)
120
Figure 125.
Relationship between the mass sedimentation rates
calculated from stable lead and from lead-210
profiles.
231
-------
alternative if not exclusive means of determining recent sedimentation rates
in this and possibly other of the Great Lakes. This is an important result
as it suggests the possibility of obtaining accurate sedimentation rate
information for a considerably reduced expenditure of time and effort if
lead-210 analysis may be discontinued. As suggested above, there are other
reasons for retaining the analysis of lead-210 in sediments and in water,
however.
It is important to note that excess concentration profiles of other
elements such as copper, mercury, nickel, tin and zinc in core 18A-2 (Fig.
123) as well as in other cores imply a deposition history which is consistent
with treating the excess as anthropogenic in origin and in fact is largely
consistent with the source function developed for lead. It is possible to
develop source functions for several of these elements based on historical
records of regional population growth and metals usage but this approach is
beyond the scope of this report. However, as a first approximation, the
source function for the anthropogenic (excess) component of each element may
be taken as essentially exponential. In such case the time-dependence is
given by, e —$t where t is the time before present (1975). The increase
in anthropogenic loading of the sediments can be expressed in terms of the
doubling time = 0.69315/g which is analogous to the lead-210 half-life in
terms of the treatment by the steady-state mixing model. If the exponential
source function is used instead of the one based on historical records of
lead usage, the best fit to the observed lead profile in core 18A-2 (which
occurs for a g value of 0.034 yr"1 or doubling time of 20 years) is
essentially indistinguishable from that based on the historical records. The
reason for this is evident from inspection of Fig. 121. The exponential
source function after 1900 has essentially the same time-dependence (slope)
as that of the one based on historical records. Only before that date is the
time-dependence of the exponential source function in error. But the
pre-1900 contribution of anthropogenic lead is very small. As a result, lead
profiles are dominated by post 1900 contributions which are essentially
exponential in character.
Application of the exponential source function to other minor element
profiles yields predicted distributions indicated as the solid lines in
Figure 123. While there are some small systematic departures of theoretical
from observed profiles the quality of the fits are generally excellent.
Least squares values of g and the corresponding doubling time are given in
Table 40. As can be seen from this table, the majority of elements have
essentially the same doubling time, around 23 years (Cu, Pb, Sn and Zn), and
very close to the half-life of lead-210 (22.6 years). The small enrichment
of Cr seen in this, but not all cores, implies a smaller doubling time
(roughly 7 years). The doubling time of Ni is also significantly shorter (14
years) and indicates a comparatively more recent onset of significant
addition of anthropogenic Ni to the lake if this result can be generalized to
other cores. Mercury is the only element with a significantly longer
doubling time (40 years). This longer doubling time is probably inconsistent
with historical records of mercury use and could arise from remobilization of
the element within the core. It is beyond the scope of this report to
consider this question in further detail.
232
-------
TABLE 40. EXPONENTIAL SOURCE FUNCTION PARAMETERS DERIVED FROM
APPLICATION OF THE STEADY-STATE MIXING MODEL
TO MINOR ELEMENT PROFILES IN CORE EPA-SLH-75-18A-2
Doubling time or
Element (3 (yr"1) half life (yr)
Cr 0.1 7
Cu 0.029 24
Hg 0.017 40
Ni 0.048 14
Pb 0.034 20
Pb-210 0.031 22
Sn 0.033 21
Zn 0.027 26
233
-------
The use of the linear regression expressions for the relation between
cesium-137 and lead-210 sedimentation rates (Eq. 45) and between stable lead
and lead-210 sedimentation rates (Eq. 46) leads to a set of independent
predictions of the sedimentation rate at each location. The values are
summarized in Table 41. In most cases where there are lead-210 rates the
adopted value is based on lead-210. In cases where there are no lead-210 or
stable lead rates, the adopted value is based on cesium-137 rates in
combination with values based on linear interpolation or extrapolation of
lead-210 rates to the locations in question. The adopted value is generally
taken as the approximate average of two of the three most similar measures of
the sedimentation rate.
The mass sedimentation rate in southern Lake Huron is shown in Fig. 126,
the numbers in parenthesis are approximate and derived from the cesium-137
profiles and grid interpolation as indicated above. The value enclosed by
the square in Fig. 126 (33 mg/cur/yr) is based on analysis of the ragweed
(Ambrosia) pollen profile in a core taken at the indicated location by Kemp
et al. (1974). The sedimentation rate determined by Kemp et al. is very
consistent with values determined at adjacent sites for this report.
It can be seen (Fig. 126) that there is a very systematic trend toward
higher mass sedimentation rates on the eastern side of the Goderich Basin.
Within this Basin rates toward the escarpment side are under 20 mg/cm^/yr
while on the eastern side values may exceed 100 mg/cm^/yr. The high
sedimentation rates toward the eastern part are associated with the intense
deposition of dolomitic materials. Because the materials are capable of
relatively greater compaction than the organic and clay mineral phases, the
high mass sedimentation rates are not generally accompanied by high linear
rates. Values of the mean linear sedimentation rate (Fig. 127) have a very
different distribution. They tend to follow a north-south trend with higher
values occurring toward the northern part of the Goderich Basin. Mass
sedimentation rates within the Port Huron Basin are very much lower and
exhibit very limited spatial variability.
Time Resolution in Cores
The fidelity of sediments in recording events occurring in the lake is
limited in part by postdepositional particle and solute movements. Several
lines of evidence partly developed in this report indicate that there is a
zone extending downward from the sediment water interface which is rapidly
mixed probably by benthic invertebrates. Development of a model envisioning
the mixing process as steady-state and confined to a precisely defined
interval leads to self-consistent interpretation of metal and radioactivity
profiles. Shapes are quantitatively and adequately described and within
experimental uncertainties and sedimentation rates derived from application
of the model are generally consistent. Values obtained for the mixed depth
from application of the model are also consistent as can be seen from the
summary in Table 42. Agreement is poorest for mixed depths under 2 cm
because in this case the mixed depth is often comparable to the size of the
sampling interval. Regression analysis of lead and lead-210 mixed depths
yields spb-210 = 0.13 + 0.72 sp^ with r = 0.80 and N = 24. While the
correlation is highly significant, mixed depths derived from analysis of
234
-------
TABLE 41. SEDIMENTATION RATES ESTIMATED FROM ANALYSIS OF
CESIUM-137, LEAD-210, AND LEAD PROFILES
Mass Sedimentation Rate
(mg/cm^/yr)3
Cs-137
Station
3
4
5
6
7
8
9
10
11
12
13
14ASC
15
16
17
18-2
18A-2
19
20
21
22
25
29
30
31
32
33
34
35
36
38
39
40
41
42
43
44
45
46
(d)
17
0
25
5
52
13
65
34
5
16
84
52
0
20
15
34
15
6
14
15
55
10
21
39
25
23
16
33
21
28
45
38
<45
26
33
-
51
58
"
(e)
38
0
38
14
32
12
28
18
13
18
32
29
37
17
17
43
28
17
21
25
20
21
25
20
20
17
25
24
42
29
-
99
-
11
29
<52
47
99
87
Pb
125.1
0
11.5
-
89.2
12.9
15.2
5
-
32.5
125
34
0
11.0
10.7
53.5
37.0
<2
-
-
-
11.9
28.6
-
12.1
-
13.6
-
0
-
<22
33
-
-
-
-
-
-
•"
Pb-210
16.3
<5
7.5
-
65.6
14.0
21.0
16.0
-
38.2
94.2
24.0
0
11.2
13.5
53.2
41.4
<1.7
-
11.6
-
13.4
-
-
11.4
-
11.9
-
<19
-
<28
<28
-
12
-
-
-
49
"~
Gridb
(16.3)
5.
(7.5)
0
(65.6)
(14.0)
(21.0)
(16.0)
10
(38.2)
(94.2)
(21.0)
0
(11.2)
(13.5)
(53.2)
(41.4)
«1.7)
13
(11.6)
56
(13.4)
15
12
(11.4)
14
(11.9)
10
«19)
22
«28)
«28)
23
( 12)
17
31
50
( 49)
33
Adopted
Value
16.3
0
7.5
0
65.6
14.0
21.0
16.0
10
38.2
94.2
30.0
0
11.2
13.5
53.2
41.4
0
14
11.6
55
13.4
28.6
40
11.4
20
11.9
25
<20
25
<30
<30
<20
12
25
<25
50
50
0
Mean Linear
rate (cm/yr) Intrinsic
Adopted Resolution
Valuec (yr)
0.063
0
0.038
0
0.087
0.071
0.041
0.054
0.05
0.16
0.15
0.17
0
0.060
0.066
0.20
0.13
0
0.07
0.072
0.08
0.067
0.14
0.03
0.054
0.064
0.06
0.02
<0.02
0.05
<0.02
<0.03
<.02
-
0.05
<0.02
0.04
-
0
22
_
47
>90
10
21
20
20
48
21
6
30
_
24
35
9
15
—
46
43
9
30
30
17
20
11
15
18
24
38
>40
>82
_
18
15
38
27
50
-
(continued).
235
-------
TABLE 41. (continued).
Mass Sedimentation Rate
Cs-137
Station
47
49
50
51
53
54
55
56
57
58
59
60
61
62
63
65
66
67
68
69
70
71
(d)
15
21
34
52
12
65
24
25
14
56
23
38
19
13
27
25
19
26
29
45
22
17
(e)
38
6
43
110
20
69
40
18
21
18
29
70
62
37
31
37
34
13
40
45
16
14
Pb
_
-
69.6
98.2
-
-
-
-
28.6
-
-
-
80.3
-
33.9
-
-
-
-
35.7
-
—
Pb-210
_
-
61.0
110.
<11.1
-
-
-
20.6
-
-
-
103
-
34.2
-
-
-
-
39.7
-
~~
(mg/cm2/yr)a
Gridb
24
31
(61.0)
(110)
(41.1)
70
20
20
(20.6)
66
18
62
(103)
72
(34.2)
23
42
65
31
(39.7)
6
—
Adopted
Value
20
20
61.0
110
<11.1
65
25
20
20.6
60
20
60
103
40
34.2
25
30
50
30
39.7
20
15
Mean Linear
rate (cm/yr)
Adopted
Value0
0.1
0.07
0.084
0.088
<0.031
0.07
0.13
-
0.10
0.02
0.1
0.18
0.19
0.09
0.14
0.12
0.12
0.16
0.12
0.18
0.10
0.08
Intrinsic
Resolution
(yr)
48
20
12
19
60
23
42
35
15
8
30
18
11
15
16
33
20
5
28
18
21
24
a Rates adjusted to lead-210 values by regression analysis (see text).
b Linear interpolation or extrapolation from values of rp^_2io at neighboring
locations. Values in parentheses are measured lead-210 rates.
c Mean sedimentation rate over 10 cm intervals = 10.0 cm / At where
At = cumulative weight at 10 cm / mass sedimentation rate.
d Derived from the simplified treatment using the mixing-model (see text).
e Derived from mixing-model.
236
-------
13 (15)
Harbor;
Beach
43°30'—
MASS
SEDIMENTATION
RATE
(mg/cm2/yr)
43°00'—
V20) (29) 40 (40V
Kincardine
^Goderich
SOUTHERN LAKE HURON
10 20 30
KILOMETERS
40
82°30'
82°00'
Figure 126.
Rate of accumulation of fine-grained sediments in
southern Lake Huron. Numbers in parenthesis are
approximate estimates. The value enclosed by the
square is based on analysis of an Amborsia (ragweed)
pollen profile (Kemp et al., 1974).
237
-------
43°30
MEAN LINEAR
SEDIMENTATION
RATE (mm/yr)
rn
-------
TABLE 42. MIXED-DEPTHS MEASURED OR CALCULATED FROM CESIUM-137,
LEAD-210 AND LEAD PROFILES
Mixed
Depth (g/cm2)
Cesium-137
Station
3
4
5
6
7
8
9
10
11
12
13
14A-SC
15
16
17
18-2
18A-2
19
20
21
22
25
29
30
31
32
33
34
35
36
38
39
40
41
42
43
44
45
(a)
0.36
0
0
0.45
0
0.29
0
0
0.48
0.76
0
0.95
0
0.27
0.47
.46
0.61
0
0.64
0.64
0
.40
.60
0
0
0
.18
0
0
.94
0
2.45
0
.21
.38
1.5
0
2.49
(b)
0.24
0
0.22
0.36
0.64
0.28
0.54
0.72
0.34
0.72
0.34
0.95
0.8
0.22
0.46
0.48
0.43
0.04
0.55
0.52
0.18
0.25
0.62
0.07
0.22
0.17
0.10
0.36
0.28
0.70
-
0.70
1.3
0.23
0.68
0.85
1.13
1.70
Lead-210
0.47
0
0
-
0
0
0.53
0
-
0.66
0
.71
-
0.2
0.3
0.75
0.78
0
-
0.5
-
0.20
-
-
0
-
0
-
0.5
-
0
1.5
-
0
-
-
-
0
Lead
0.59
0
.32
-
1.4
.29
0.20
0
-
.76
0
.71
-
.46
.47
1.3
.36
0
-
-
-
0.30
-
-
.45
-
0
-
0
-
0
-
-
-
-
-
-
~™
Adopted
Value
0.47
0
0.27
0.4
0.5
0.29
0.4
0
0.4
0.73
0
0.71
0
0.29
0.43
0.74
0
0.60
0.55
0
0.29
.61
0
0.17
0
0.14
0.2
0.2
0.8
0
1.6
0.7
0.2
0.5
1.2
0.6
2.1
(continued),
239
-------
TABLE 42. (continued).
Mixed
Depth (g/cm^)
Cesium- 137
Station
46
47
49
50
51
53
54
55
56
57
58
59
60
61
62
63
65
66
67
68
69
70
71
(a)
3.2
.95
.38
0
2.06
.63
1.5
1.1
0
0.3
0
.6
1.1
1.2
0.59
0.55
0.82
0.78
0
0.85
0.71
0.42
0.36
(b)
2.15
0.72
0.30
1.0
1.4
0.62
1.5
0.84
0.21
0.38
0.19
0.48
0.67
0.42
0.28
0.39
0.62
0.60
0.13
0.66
0.66
0.58
0.43
Lead-210 Lead
_ _
-
-
0 0
0 0
0
-
-
-
0.3 0.30
-
-
-
1.2 0.71
-
0.97 0.56
_
-
-
_
0.71 1.2
-
— _
Adopted
Value
2.7
0.8
0.3
0
0.8
0.6
1.5
1.0
0.1
0.32
0
0.5
0.9
0.9
0.4
0.6
0.7
0.7
0
0.8
0.82
0.5
0.4
a Derived from simplified model of mixing.
b Derived from least-squares fit or mixing model.
240
-------
metals and radioactivity profiles are not as consistent as are sedimentation
rates. In some cores, reported for Lakes Erie and Ontario (Robbins et al.,
1978) profiles of Cs-137 are consistent with significant sediment mixing even
when lead-210 profiles are not. While the concept of mixing is essentially
established, it is clear that other factors such as areal resuspension
effects (see Robbins et al., 1978), delayed watershed contributions,
remobilization and particle-selective bioturbation may be important in the
generation of observed profiles. Within these limitations an approximate
mixed depth may be associated with each core based on the combined analysis
of cesium-137, lead-210 and lead profiles. These values are provided in
Table 39.
To the extent that steady-state mixing is a satisfactory representation
of the principle postdepositional particle transport process in sediments, an
intrinsic time resolution may be assigned to cores. The effect of
steady-state mixing on the sedimentary record of two discreet events
occurring ten years apart is illustrated in Fig. 128. For a hypothetical
sedimentation rate of 2 mm/yr the expected distribution is shown for various
assumed depths of sediment mixing. As the depth of sediment mixing
increases, the record is increasingly smeared out and the events are
essentially unresolvable for times greater than the residence time of the
event record within the mixed zone. This time, which may be referred to as
the intrinsic resolution, is given by the ratio of the mixed depth to
sedimentation rate: t(yr) = s (g/cm2) / r (g/cm2/yr). Thus, for example, an
intrinsic resolution of 10 years corresponds to a mixed depth of 2 cm when
the sedimentation rate is 2 mm/yr. For this intrinsic resolution the ten
year discreet events produce a profile in which the full width at half
maximum of the recorded peaks is approximately equal to their separation
(Fig. 128).
Adding to the loss of sediment record fidelity is the practical size of
sediment sections. While several cores were sectiond in half cm intervals, a
practical limit is generally 1 cm. The resolution associated with this
thickness is given by the ratio of mass per unit area corresponding to 1 cm
to the sedimentation rate (g/cm2/yr). Choosing whichever of the two measures
above is largest, a practical intrinsic resolution may be estimated. These
values are given in Table 40 and shown in Fig. 129 in terms of a contour map.
This figure is useful as it provides an indication of the resolution which
can be expected in reconstructing the pollution history of this lake by
taking cores from various locations within the two depositional basins. Over
much of the Goderich Depositional basin the practical intrinsic resolution is
about twenty years while in a certain limited region toward She eastern
margin of this basin the resolution may be under ten years and primarily
limited by the 1 cm condition. This area is characterized by a combination
of comparatively high sedimentation rates and small depth of sediment mixing.
In the Port Huron basin the resolution is generally greater than twenty years.
Because of the time resolution inherent in sediments of these
depositional basins, it is not likely that any recent improvements in water
quality will as yet have had a measureable effect on sedimentary profiles.
Another important aspect of this intrinsic resolution or characteristic
integration time concept, is its bearing on the availability of pollutants
241
-------
CONCENTRATION
x
i-
0.
UJ
o
N3
4>
N3
S = 0 cm
t = Oyr
lOyears
S = I cm
t =5yr
=0.2 cm/yr
S= 2 cm
t =IOyr
S = 4 cm
t =20yr
S = 8 cm
t =40yr
Figure 128.
The effect of rapid steady-state mixing on the sedimentary record of two
events occurring ten years apart.
-------
43°30'
INTRINSIC
RESOLUTION
(yr)
• 10-20
I 1 20-50
f I >60
43°00'—
Port
Huron
SOUTHERN LAKE HURON
0 10 20 30 40
KILOMETERS
82°30'
Figure 129.
The approximate time-resolution expected in samp-
ling cores in southern Lake Huron. The validity of
the distribution depends on the correctness of the
steady-state mixing model.
243
-------
for exchange with overlying water. Sediment mixing serves to increase the
contact time between water and polluted sediments. In the absence of any
further anthropogenic metal additions to this area, the concentration of
pollutant metals in surface sediments in contact with overlying water will
decrease at a rate characteristic of the mean integration time, which for the
two depositional basins in southern Lake Huron is on average about 20 years,
corresponding to a rate constant of about 5% per year.
It should be emphasized that these results are strongly model-dependent
and valid only to the extent that the concept of steady-state mixing is
valid. Moreover, the results apply only to substances which remain strongly
associated with sediment particles and are not subject to any appreciable
post-depositional migration.
RATE OF ACCUMULATION OF SEDIMENTARY CONSTITUENTS
Computation
The rate of accumulation of non-enriched elements is computed as the
product of the concentration of a given element in surface sediments (1-2 cm)
and the mass sedimentation rate. For the non-enriched elements this value of
the accumulation rate is both a measure of the most recent rate of
accumulation (z=0) and of the precultural accumulation rate as well.
For elements possessing a significant degree of surface enrichment the
rate of accumulation can be described in terms of two components, the
background or natural rate and the portion attributable to anthropogenic
loadings (Kemp and Thomas, 1976; Edgington and Robbins, 1976). The natural
accumulation rate is computed as the product of the mass sedimentation rate
and the average concentration of an element below the depth where there is
any significant degree of enrichment. For sediment cores where the mean
background concentration is not known, it can be adequately inferred from the
regression relation between surface iron concentrations and background values
in other cores. In some instances only one background value is known. In
such cases approximate background levels are taken to be proportional to
surface iron concentrations. (Note that there is very little (<_ 8%) surface
enrichment of iron.) Linear regression parameters used to determine missing
background concentrations from surface iron data are given in Table 44. In
the cases of the elements Cd, Cu, Mn, Ni, Pb and Zn there is very little
uncertainty in the estimate of background data because (1) there are many
measured values and (2) correlations between measured values and surface iron
concentrations are generally high. In the case of such elements as Sn, Hg,
As and Br where there are very few measurements of background concentrations,
uncertainties in the method of background assignments are unknown.
The rates of accumulation of the anthropogenic components are time-
dependent and should, in principle, be referred to a specific time. In most
previous analyses of anthropogenic element profiles some sort of ambiguous
time-averaging has introduced biases into reported anthropogenic accumulation
rates. For example, in the core collected by Kemp et al. (1974) in 1970 from
the Goderich Basin, the so-called surface concentration refers to an interval
from 0-2 cm. As the sedimentation rate is about 0.14 cm/yr at this location,
244
-------
this interval corresponds to 2/0.14=14 years. Hence the anthropogenic
concentrations and accumulation rates for this core actuall refer to a mean
date of (1970-7 )+7 = 1963+7 years. In this regard, the valvas reported for
rates of anthropogenic element accumulation in Lake Huron by the IJC (1977)
are based on this and two other cores which were sampled in a way which leads
to an assigned date of 1962+8 years.
In the present report the so-called surface concentration values refer
to the 1-2 cm sections of cores. Because of the great variability of
sedimentation rates within each depositional basin, this section does not
have a uniquely defined date from core to core. Moreover, because of
averaging over the 1 cm section, the 1-2 cm interval may correspond to an
appreciable span of years as discussed above. Because both the sedimentation
rate and source function have been determined as part of this study, it is
possible to correct concentration data for the effect of finite interval
sampling in the way indicated above. If Co is taken as the net anthropogenic
concentration (total-background) of a given element at the sediment surface
(z=0 corresponding to 1974 or 1975) then the expected profile is:
(47)
where m is the cumulative mass per unit area and 3 is the source function
parameter (see above). When the cores are sectioned in finite intervals, the
expected concentration in the 1-2 cm interval, for example, is then
Cl-2 = (Co /(m2 ~ ml}) ' e dm (48)
1
or in terms of dates associated with depths m^ and m2 (t^=m^/r and t2=ni2
Cl-2 " \-i by
Co = Cl-2 6 (t2 - V
Thus the concentration in the 1-2 cm interval may be used to infer the most
recent accumulation rate (Co x r) when the mass sedimentation rate and source
function parameter are known.
245
-------
In the tables below, the present accumulation rate is adjusted to the
date of this report (1980). It is assumed that the values of the doubling
times calculated above for the enriched elements hold as well for the period
between the collection date 1974 or 1975 and 1980. As the source function
parameter is approximately 0.034 yr~l the correction is given by
C(1980) = C(1975) e+0. 034 (1980-1975)
o o
which represents an 18% increase during the 5 year period.
The above corrections apply to unmixed sediments (s=0). When there is a
zone of rapid steady-state mixing greater than about 1 cm depth, the
concentrations in the 1-2 cm interval may be affected primarily by the mixing
process. The effect of mixing is to suppress the concentration in the mixed
zone. It can be shown (Robbins, 1978) that provided the 1-2 cm interval
falls within the mixed zone the observed concentration is given by,
C1-2 - GO y / (Y + 3) so that (52)
CQ(1975) = C±_2 (Y + 3) / Y (53)
where Y= r/s (vr ) anc* s ^s tne depth of the mixed zone in g/cm^. Hence in
computing the present accumulation rates either Eq. 50 or Eq. 53 is used
depending on whether s is zero or not. A more rigorous treatment of the
combined effects of mixing and finite interval sampling is given by Edgington
and Robbins (1976).
Distribution of Accumulation Rates
Examples of the distribution of the rate of accumulation of non-enriched
elements are shown in Figures 130-135. To conserve space only a few examples
are given. As expected from the previous discussion of interelement
associations, there is considerable redundancy in patterns of accumulation.
There are two primary patterns, that of organic carbon-iron and that of the
calcium family elements. The patterns of accumulation representative of the
first group are organic carbon (Fig. 130), iron (Fig. 131) and chromium
(Fig. 132). In each case there is a systematic trend toward increased rates
of accumulation in the northern part of the Goderich Basin. Also in the
northern sector the rates increase toward the eastern margin of the basin.
Accumulation rates of the organic carbon-iron group of elements are
considerably lower in the Port Huron Basin and exhibit less spatial
variability. The considerable variability in the organic carbon-iron group
of elements in the Goderich Basin is brought about in part by the dramatic
gradients in the deposition of the calcium family elements. In contrast
however with the first group, the calcium family elements do not possess a
significant north-south trend. Inorganic carbon (Fig. 133), calcium (Fig.
134) and magnesium (Fig. 135) all exhibit marked and systematic increases in
rates of accumulation toward the eastern margin of the Goderich Basin.
Within this basin more than an order of magnitude decrease in the rate of
deposition of the calcium family elements occurs in traversing from east to
west. In comparison with calcium family element accumulation rates in the
246
-------
43°30'
ORGANIC
CARBON
ACCUMULATION
RATE
(mg/cm2/yr)
D <0,5
EB 1.0-2,0
•I >2.0
43°00'—
Kincardine
Goderich
SOUTHERN LAKE HURON
82° 30'
10 20 30 40
KILOMETERS
82°00'
Figure 130. The rate of accumulation of organic carbon in sur-
face sediments.
247
-------
43°30'—
IRON
ACCUMULATION
RATE
(mg/cm2/yr)
CH <0.2
CD 0.2-0.5
C53 0.5-i.o
Hi 1.0-1.5
• > 1.5
43°00'—
Port
Huron
N
SOUTHERN LAKE HURON
82° 30'
10 20 30
KILOMETERS
82°00'
40
Figure 131. The rate of accumulation of iron (AAS) in surface
sediments.
248
-------
43°30'
CHROMIUM
ACCUMULATION
RATE
(mg/cm2/yr)
1.0-2.0
2.0-3.0
43°00'—
Port
Huron
82° 30'
SOUTHERN LAKE HURON
0 10 20 30 40
KILOMETERS
82°00
Figure 132.
The rate of accumulation of chromium (AAS) in sur-
face sediments.
249
-------
Figure 133.
Harbor
Beoch
'NORGANfC
A CARBON
ACCUMULATION
o.ot-o.i
0.1-0.3
0.3-
1-0-3.0
SOUTHERN LAKE HURON
250
-------
43°30'—
CALCIUM
ACCUMULATION
RATE
(mg/cm2/yr)
[~~1 0.05-0.2
EH 0.2-1.0
•I >5
43°00'
SOUTHERN LAKE HURON
10 20 30 40
KILOMETERS
82° 30'
82°00'
Figure 134. The rate of accumulation of calcium in surface
sediments.
251
-------
43°30'—
MAGNESIUM
ACCUMULATION
RATE
(mg/cm2/yr)
m 3
43C00'—
Port
Huron
SOUTHERN LAKE HURON
82° 30'
10 20 3O 40
KILOMETERS
82°00'
Figure 135. The rate of accumulation of magnesium in surface
sediments.
252
-------
Goderich Basin, those in the Port Huron Basin are virtually neglible.
The spatial distribution of the factor required to convert 1-2 cm
anthropogenic concentration data to 1980 values is shown in Fig. 136.
Highest values tend to occur toward the escarpment sides of the depositional
basins. The mean conversion factor is 1.9 of which 18% (1.18) results from
extrapolation of surface values in 1975 to those expected in 1980 (see
above). That part of the factor associated with converting 1-2 cm
concentrations to values at z=0 (1975) is on the average equal to
1.9/1.18=1.6. Thus the use of the 1-2 cm section to represent surface
concentrations of anthropogenic components, plus the effects of finite
interval sampling and steady-state mixing combine to produce about a 60%
average upward adjustment.
The present (1980) rates of accumulation of selected elements are shown
in Figs. 137-143. The patterns are very similar for most of the elements and
show highest values in the northern sector of the Goderich Basin and toward
the western margin. Anthropogenic accumulation rates in the Port Huron Basin
are substantially less and show less spatial variability.
Mean and Total Accumulation Rates
The mean and total accumulation rates of fine-grained sediments and
non-enriched elements are summarized in Table 43. Mean rates for the two
depositional basins have been computed as the mean of accumulation rates
calculated for individual cores within each basin. Because of the large
number of cores and their regular spacing within basins this method of
estimation is not significantly different from that based on integration of
isopleths.
In Table 43 the mean accumulation rates for southern Lake Huron are
expressed in terms of the combined accumulation in the Goderich and Port
Huron Basins divided by the total area of southern part of the Lake. Thus,
for example, the mean accumulation rate of fine-grained sediment in southern
Lake Huron, 11.4 mg/cm2/yr, is calculated as follows: the total accumulation
rate in the Port Huron Basin is 12.8 mg/cm2/yr x 1.22 x 1013 cm2. The total
accumulation rate in the Goderich Basin is 35.7 mg/cm2/yr x 2.59 x lO^-3 cm2
while the total area of the southern Lake Huron is 9.5 x 10*-3 cm2 (see Table
1). Therefore, the mean accumulation rate in the southern part of the Lake
is (12.8 x 1.22 + 35.7 x 2.59)/9.5 = 11.4 mg/cm2/yr. Note that in Table 43,
mean accumulation rates of the fine-grained sediments and major constituents
are expressed in terms of mg/cm2/yr whereas for the trace constituents the
units are micrograms/cm2/yr. In the above calculation it is implicitly
assumed that the areas of sand, till, glaciolacustrine clay and exposed
bedrock are non-depositional. That is, at the present time there is no
significant permanent accumulation of fine-grained sediments in those areas.
Note that this assumption is open to question in view of the results obtained
above for cesium-137 and lead-210. The utility of expressing accumulation
rates in terms of the total per unit area of the southern part of the Lake is
that, to the extent that there is no net export or import of particulate
matter form the southern part of the lake, there is some basis for comparison
of these mean rates with other loading data.
253
-------
43°30'
CONVERSION
FACTOR
CD 1.1 - 1-5
n 1.5-1.9
O t.9-2.3
Ol 2.3-2.7
•I 2.7-3.1
43°00'
SOUTHERN LAKE HURON
82*30'
Figure 136.
10 20 30
KILOMETERS
82°00'
40
The distribution of the factor converting surface
concentrations to present (1980) values. Only 18%
of the factor results from conversion from 1975 to
1980 values. The remainder results from sediment
mixing and finite sampling corrections (see text).
254
-------
Horbon
Beach
43°30'—
PRESENT
ACCUMULATION
RATE OF
ANTHROPOGENIC
ANTIMONY
(fig/cm2/yr)
H30.01 -0.03
53 0.03 - 0.05
• 0.05 - 0.07
• 0.07 - 0.09
Kincardine
43°00'-
Goderich
N
SOUTHERN LAKE HURON
o
10 20 3O
KILOMETERS
40
82°30'
82°00'
Figure 137.
Rate of accumulation of anthropogenic antimony
(adjusted to 1980).
255
-------
43°30'
PRESENT
ACCUMULATION
RATE OF
ANTHROPOGENIC
COPPER
(yu.g/cm2 /yr
F~l 0.t -0.4
I 1 0.4 - 0,8
0.8- 1.2
•I 1.2-1.6
•I 1.6-2.0
43°00'—
Port
Huron
SOUTHERN LAKE HURON
10 20 30
KILOMETERS
4O
82° 30'
82°00'
Figure 138.
Rate of accumulation of anthropogenic copper (ad-
justed to 1980}.
256
-------
43°30'
PRESENT
ACCUMULATION
RATE OF
ANTHROPOGENIC
MERCURY
(/ug/cm2/yr}
CZ3 0.001-0.003
O 0.003-0.006
Bi OO06-0.009
0.009-0.012
43°OQ'-
Port
Huron
-Sarma
SOUTHERN LAKE HUf^ON
82°30'
0 10 20 30
KILOMETERS
82°00'
40
Figure 139.
Rate of accumulation of anthropogenic mercury (ad-
justed to 1980).
257
-------
43°30'—
PRESENT
ACCUMULATION
RATE OF
ANTHROPOGENIC
LEAD
t 1 <1.0
CH 1.0-2.5
EH 2.5-4.0
U 4.0 5.5
•I 5.5 7.0
43°00'—
?$arnia
SOUTHERN LAKE HURON
82° 30'
10 20 30
KILOMETERS
82°00'
40
Figure 140.
Rate of accumulation of anthropogenic lead (adjust-
ed to 1980) .
258
-------
43°30'-
PRESENT
ACCUMULATION
RATE OF
ANTHROPOGENIC
NICKEL
C/xg/cm2/yr)
CD < 0.50
CD 0.50-1.25
EH 1.25-2.00
2.00-2.75
2.75-3.50
43°00'-
Port
Huron
Kincardine
Goderich
Sarnia N
SOUTHERN LAKE HURON
10 20 30 40
KILOMETERS
82° 30'
82°QO'
Figure 141.
Rate of accumulation of anthropogenic nickel (ad-
justed to 1980).
259
-------
43°30'—
PRESENT
ACCUMULATION
RATE OF
ANTHROPOGENIC
TIN
(/ig/cm2/yr)
O0.02-0.10
CD 0.10-0.20
0.20 - 0.30
• 0.30 0.40
• > 0.40
43°00'—
Port
Huron
SOUTHERN LAKE HURON
10 20 30
KILOMETERS
40
82°30'
82°00'
Figure 142.
Rate of accumulation of anthropogenic tin (adjust-
ed to 1980).
260
-------
PRESENT
ACCUMULATION
RATE OF
ANTHROPOGENIC
ZINC
SOUTHERN LAKE HURON
Figure 143.
Rate of accumulation of anthropogenic zinc (adjust-
ed to 1980).
261
-------
TABLE 43. MEAN AND TOTAL ACCUMULATION RATES OF FINE-GRAINED SEDIMENTS AND NON-ENRICHED ELEMENTS
Port Huron Basin
Goderich Basin
Southern Lake Huron
Mean
Accumulation
Ratea Total
(mg/cm2/yr)
or pg/cm^/yr) (metric tons/yr)
Mean
Accumulation
Rate3 Total
(mg/cm^/yr)
or yg/cm^/yr) (metric tons/yr)
Mean
Accumulation
Rateb Total
(mg/cm^/yr)
or yg/cm^/yr) (metric tons/yr)
Mass
(total)
(acid sol.)
12.8
3.5
1.6 x 105
0.43 x 105
35.7
12.6
9.3 x 105
3.3 x 105
11.4
3.9
1.1 x 106
0.37 x 106
NJ
Major Constituents
OC
IOC
Ca
Fel
Fe2
K
Mg
Na2
P
.47
.24
.07
.35
.41
.08
.08
.11
.021
5700
2900
850
4300
5000
980
980
1300
250
.93
1.0
1.6
.77
.93
.21
1.1
.27
.046
24000
26000
41000
20000
24000
5400
28000
7000
1200
.31
.30
.44
.25
.31
.068
.31
.088
.015
30000
30000
42000
24000
29000
6000
29000
8300
1000
Minor Constituents
Ba2
Ce
Co
Crl
Cr2
Cs
Eu
^6
.74
.14
.59
.90
.048
.016
70
9
1
7
11
.7
.2
.59
.19
^15
1.
.
1.
2.
.
•
7
32
6
1
11
036
390
44
8.
41
54
2.
•
3
8
93
4.9
.56
.10
.51
.69
.036
.012
460
53
10
48
65
3.
1.
4
1
(continued).
-------
TABLE 43. (continued).
Port Huron Basin
Goderich Basin
Southern Lake Huron
Mean
Accumulation
Rate3 Total
(mg/cm^/yr)
or yg/cm^/yr) (metric tons/yr)
Mean
Accumulation
Total Rateb Total
. ^ (mg/cm2/yr)
or yg/cm^/yr) (metric tons/yr) or yg/cm^/yr) (metric tons/yr)
Mean
Accumulation
Rate*
Minor Constituents
La
Lu
Sc
Sm
Sr
Th
U
.44
.0046
.15
.073
.57
.12
^.04
5.4
0.056
1.9
.89
7
1.4
.5
.96
.011
.35
.17
1.6
.26
-v.09
25
.28
9.1
4.4
41
7.5
2.3
.32
.0036
.11
.056
.51
.086
.030
30
0.33
11
5.3
48
8.9
2.8
a Sediment and major element accumulation rates in mg/cm^/yr;
minor element accumulation rates in yg/cm^/yr
" Mean accumulation rate for all of southern Lake Huron = total accumulation/
total area of southern Lake Huron (9.5 x 10^ cm^). Non-depositional areas
(glacio-lacustrine clay and sand") are assigned zero accumulation rates.
-------
TABLE 44. COEFFICIENTS USED IN THE REGRESSION RELATION TO DETERMINE
ENRICHED ELEMENT BACKGROUND LEVELS FROM SURFACE IRON CONCENTRATIONS
Coefficient3
Element
As
Br
Cd
Cu
Hg
Mn
Ni
Pb
Sb
Si
Sn
Zn
a
0
0
3.0
5.0
0
0.008
19.8
26.8
0
-0.31
0
20.6
B
2.11
15.32
-0.51
8.87
0.0096
0.011
5.15
0
0.136
0.35
0.16
15.4
Correlation
Coefficient
-
-0.52
0.84
-
0.71
0.63
-
-
0.75
-
0.88
N
1
1
17
24
1
23
24
_
1
4
1
24
a [Element]BG = a + 3
Note: Fe, Mn and Si in wt. %,
1-2.
all others in yg/g.
264
-------
The mean and total rates of accumulation of anthropogenic elements in
the Port Huron and Goderich Basin and in southern Lake Huron are given in
Tables 45, 46 and 47 respectively. Near-surface values are computed as the
product of the mass sedimentation rate and uncorrected net surface
concentrations in the 1-2 cm interval. This value is included both for
completeness and because it is minimally dependent on model assumptions.
Because of the necessity to construct some missing background values by
regression analysis, the sensitivity of estimated mean concentrations was
tested by varying calculated background levels by 20% while leaving known
values unchanged. The results are given in Table 48 for the Goderich Basin
data. For elements such as Hg, Sn, Zn, Pb where the degree of surface
enrichment is high, a 20% change in calculated backgrounds results in only a
3-13 % change in mean accumulation rates. For other elements a 20% change
results in approximately the same percent change in the estimate of mean
accumulation rates.
From comparison of data in Tables 45 and 46 it can be seen that the mean
accumulation rate of most elements is roughly twice (2.2) as high in the
Goderich Basin as in the Port Huron Basin. This elevation occurs principally
because sedimentation rates are considerably higher on the average in the
Goderich Basin while mean concentrations of most elements other than the
calcium family group are comparable in both basins. In addition to
possessing a considerably higher average sedimentation rate, the Goderich
Basin has roughly twice the area of the Port Huron Basin and therefore
receives the lion's share of accumulating sedimentary constituents. On the
average, the Goderich Basin receives 5 times more loading of most
constituents than the Port Huron Basin. For the calcium family elements the
Goderich Basin receives roughly 30 times as much per year as the Port Huron
Basin.
Comparison with External Loading
It is premature to develop an accurate mass balance for Lake Huron which
takes proper account of the accumulation of sedimentary materials, since the
data for the northern part of the lake are not yet available. However,
trends may be meaningfully examined by apportioning the loadings estimated by
others for the main lake to the southern part. This approach is successful
particularly in considering the accumulation of anthropogenic constituents
since comparison of their accumulation rates with lake loadings does not
depend on an accurate evaluation of the sources and composition of background
constituents.
Fine-Grained Sediments — The accumulation of fine-grained sediments in
southern Lake Huron amounts to about 1 million metric tons annually and
corresponds to a mean accumulation rate of 11.4 mg/cm^/yr. This value is
only slightly higher than the mean value for the main lake computed from the
data of Kemp et al. (1976) as 10 mg/cm^/yr corresponding to a lake-wide
accumulation of 3.9 million metric tons annually. It therefore appears that
the mean accumulation rate in the southern part of the lake is not greatly
different from the lake-wide average. This is an important result in
considering the representativeness of the southern lake for calculating
265
-------
TABLE 45. ACCUMULATION RATES OF ENRICHED ELEMENTS IN THE PORT HURON BASIN
Mean Accumulation Rate
(Ug/cm2/yr)
Element
As
Br
Cd
Cu
Hg
Mn
Ni
Pb
Sb
Si
Sn
Zn
Natural
0.073
0.53
0.023
0.41
3xlO~4
5
0.47
0.33
0.0047
78
0.0055
0.87
Anthropogenic
Near-
Surface
0.21
0.12
0.017
0.19
13xlO~4
0.28
0.72
0.0068
60
0.033
1.0
Corrected
to 1980
0.40
0.22
0.034
0.38
26xlO~4
0.55
1.4
0.013
120
0.065
2.0
Total Accumulation Rate*
(metric tons/yr)
Natural
0.89
6.5
0.28
5.0
0.004
61
5.7
4.0
0.057
950
0.067
11
Anthropogenic
Near-
Surface
2.6
1.5
0.21
2.3
0.016
3.4
8.8
0.08
730
0.40
12
Corrected
to 1980
4.9
2.7
0.41
4.6
0.032
6.7
17
0.16
1500
0.79
24
* Mean accumulation rate x area of the Port Huron Basin.
266
-------
TABLE 46. ACCUMULATION RATES OF ENRICHED ELEMENTS IN THE GODERICH BASIN
Mean Accumulation Rate
(Ug/cm2/yr)
Element
As
Br
Cd
Cu
Hg
Mn
Ni
Pb
Sb
Si
Sn
Zn
Natural
0.16
1.18
0.074
0.81
7xlO"4
11
1.1
1.0
0.011
156
0.012
1.8
Anthropogenic
Near-
Surface
0.52
0.39
0.033
0.36
32xlO~4
-
0.65
1.4
0.014
117
0.068
1.9
Corrected
to 1980
1.0
0.78
0.064
0.69
61xlO~4
-
1.3
2.8
0.028
235
0.14
3.7
Total Accumulation Rate*
(metric tons/yr)
Natural
4.1
30
1.9
21
0.018
285
28
25
0.28
4000
0.31
47
Anthropogenic
Near-
Surface
13
10
0.85
9.3
0.083
-
17
36
0.36
3000
1.8
49
Corrected
to 1980
26
20
1.9
17
0.16
-
34
72
0.72
6100
3.6
96
* Mean accumulation rate x area of the Goderich Basin.
267
-------
TABLE 47. ACCUMULATION RATES OF ENRICHED ELEMENTS IN SOUTHERN LAKE HURON
Element
Mean Accumulation Rate*
(Ug/cm2/yr)
Total Accumulation Rate
(metric tons/yr)
Natural
Anthropogenic
Natural
Anthropogenic
Near-
Surface
As
Br
Cd
Cu
Hg
Mn
Ni
Pb
Sb
Si
Sn
Zn
0.
0.
0.
0.
053
39
022
27
2.3xlO~4
3.
0.
0.
0.
53
0.
0.
6
36
32
004
004
60
0
0
0
0
.17
.12
.011
.12
10xlO~4
-
0
0
0
40
0
0
.21
.47
.005
.023
.64
Corrected
to 1980
0.
0.
0.
0.
32
24
022
24
20xlO~4
-
0.
0.
0.
79
0.
1.
42
94
014
047
3
5.0
37
2.1
26
0.022
350
34
30
0.34
5000
0.38
57
Near-
Surface
16
11
1.0
11
0.10
-
20
45
0.44
3800
2.2
61
Corrected
to 1980
30
23
2.
23
0.
-
40
89
1.
7500
4.
120
1
19
3
5
* Total accumulation/area of southern Lake Huron. Non-depositional areas
(sand and glaciolacustrine clay) assigned zero accumulation rates.
268
-------
TABLE 48. SENSITIVITY OF CALCULATED ANTHROPOGENIC ACCUMULATION RATES*
TO VARIATIONS IN THE ESTIMATE OF BACKGROUND CONCENTRATIONS
Accumulation Rate (yg/cm^/yr)
Element Optimal Background Estimate 20% increment % change
As
Br
Cd
Cu
Hg
Ni
Pb
Sb
Si
Sn
Zn
1.0
0.78
0.064
0.69
61 x 10~4
1.3
2.8
0.028
235
0.14
3.7
0.96
0.52
0.051
0.55
59 x 10~4
1.1
2.6
0.024
180
0.13
3.22
4
33
20
20
3
15
7
14
23
7
13
* Goderich Basin. Note: only values based on the regression analysis were
allowed to change. Known background levels were kept fixed.
269
-------
anthropogenic loadings. Because of the absence of adequate information
concerning the extent of contributions from shoreline erosions to the total
accumulation of fine-grained sediments, a mass-balance calculation primarily
gives information on the magnitude of shoreline erosion inputs.
Contributions of particulate matter to the main Lake from municipal and
industrial waste discharges calculated as part of the IJC (1977) report are
77,700 kg/day corresponding to a mean lake-wide loading of 0.075 mg/cm^yr.
Tributary inputs contribute about 2.2 x 106 kg/day corresponding to about 2.1
mg/cm2/yr while atmospheric inputs contribute about 0.55 mg/cm2/yr. The
combined inputs from the Lakes Michigan and Superior and from Georgian Bay
amount to approximately 0.42 mg/cm2/yr while the outflow of suspended matter
through the St. Glair River is about 0.53 mg/cm2/yr (assuming a mean
particulate matter concentration of 1 mg/1). Hence the net loading of
fine-grained materials from sources other than shoreline erosion is about
0.075 + 2.1 + 0.55 + 0.42 - 0.53 = 2.6 mg/cm2/yr. Comparison of this value
with the mean accumulation rate, of 10 mg/cm2/yr indicates the relative
importance of shoreline erosion as a source of fine-grained sediments.
Roughly 2/3 of the material in the depositional basins are apparently derived
from this source which remains to be adequately characterized.
Sodium — An understanding of the difficulties in comparing the
sedimentary accumulation data for natural components may be gained by
considering the case of sodium. For Na2, neutron activation analysis sodium,
the analytical method is interference-free and values represent the
whole-sediment concentrations of the element. The total deposition in the
southern part of the lake is about 3000 metric tons per year corresponding to
a mean accumulation rate of about 0.9 mg/cm2/yr over the main lake area.
This accumulation rate cannot be reproduced or even approximated by
considering sodium inputs and outputs from the lake because most reported
sodium values refer to dissolved sodium or, at best, to total sodium for
which that contained in the particulate fraction is only a small part. The
total loading of sodium to the lake is approximately equal to the mean
concentration of total sodium in the lake water times the outflow of the St.
Clair river or 1.6 mg/cm2 of main lake area per year. Thus the mean
accumulation of Na2 is only 0.09/1.6=6% of the total loss of sodium from the
lake per year. Since Na2 is essentially a label of the fine-grained
particulate fraction, the proper comparison is with concentrations of Na
exclusively in the suspended solids fraction of lake loadings but these data
are not yet available.
Calcium — Another example of the difficulties in developing a
mass-balance for non-anthropogenic constituents may be seen in considering
the element calcium. Like sodium, calcium is primarily a conservative
element in the lake and particulate calcium (neglecting authigenic CaC03
formation) is a minor fraction of the total calcium in the lake water. The
estimated rate of loss of calcium from the lake is about 14 mg/cm2/yr whereas
the rate of calcium accumulation in southern Lake Huron is only 0.44
mg/cm2/yr. From the previous discussion it is clear that in southern Lake
Huron (at least in the Goderich Basin) most of the calcium in sediments is
derived from local erosion of shoreline material rich in dolomite. Hence for
this element a lake-wide inventory of the particulate calcium loading would
still not accurately reflect the accumulation in the Goderich Basin. A
270
-------
proper mass balance for this element could be constructed only if the extent
of shoreline erosion were accurately known and in a fairly detailed way since
the hydrodynamics of dolomitic materials (silt-size particles) is such that
sedimentary dolomite tends to be locally-derived. Based on analysis of the
calcium family elements (Ca, Mg and IOC), the annual rate of deposition of
dolomite (CaMg(003)2) in southern Lake Huron is about 200,000 metric tons per
year. This value could be usefully compared with the composition and rate of
erosion of material from the Canadian shoreline adjacent to the Goderich
Basin.
A comparison of the trace element composition of materials eroded from
the Canadian shoreline generally is compared with the composition of
dolomitic sediments collected for this report in Table 49. Values reported
by the IJC (1977) do not include major constituents so it is impossible to
tell whether the eroded materials are primarily dolomitic or not. However
the minor element composition reported by IJC generally agrees with that
found for sediments containing over 35% dolomite by weight.
Phosphorus — According to the IJC report (1977), the total loading of
total phosphorus to the main lake is 3720 tonnes per year while the amount
lost by outflow was calculated to be 1080 tonnes per year. If the inventory
of phosphorus is not increasing in the lake, the difference between these
values which is 2640 tonnes must be deposited each year. This latter value
corresponds to a mean accumulation rate of 0.006 mg P/cm^/yr on a lake-wide
basis. This value is approximately 40% of the total, acid-soluble P, found
to accumulate in the southern part of the Lake which is 0.015 mg P/cm2/yr.
Thus removal of phosphorus from the water via sedimentation is consistent
with measured rates of acid-soluble phosphorus accumulation in this part of
the lake. Further refinements of the comparison would necessitate careful
identification of sedimentary phosphorus constituents perhaps via chemical
separation techniques such as those employed by Williams et al. (1976).
Silicon — Comparison of the accumulation rates of silicon with mass
balance calculations is particularly intriguing. According to the IJC report
(1977), there is a net annual increase in soluble reactive silica (Si02) of
183,000 tonnes in the main lake. This increase corresponds to a value of 200
micrograms Si/cm2/yr which is quite close to that expected as the
anthropogenic plus natural (total) mean accumulation rate of amorphous
silicon in southern Lake Huron (1980). The computed total from Table 47 for
the natural plus anthropogenic mean accumulation rate is 534-79=132 micrograms
Si/cm2/yr. Such agreement would be expected if the dissolved reactive
silicon in the lake is converted to the particulate form (either as diatoms
or as other forms of amorphous silicon) and removed permanently from the
water column. Because of the many uncertainties in the calculation the close
agreement may be accidental. If not, that data suggest that the increases
seen toward the sediment-water interface in the concentration of amorphous
silicon in the cores examined for this report, may reflect the increased rate
of conversion of soluble silicon to particulate form in the lake as a result
of the stimulation of diatom growth by phosphorus additions. Note that the
most satisfactory agreement between the net loading of soluble reactive
silicon to the lake and the mean accumulation rate is obtained by adding the
anthropogenic component to background levels. The favorable comparison
271
-------
TABLE 49. COMPARISON OF THE COMPOSITION OF DOLOMITE SEDIMENTS
WITH THE COMPOSITION OF CANADIAN LAKE HURON SHORELINE MATERIALS
Major Elements
(wt %)
Ca
Fe
K
Mg
Mn
Nal
P
Dolomitic
7.5
0.96
-0.18
5.0
0.024
0.11
0.11
Sediments3
+ 1.0
+ 0.2
+ 0.06
+ 0.3
+ 0.01
+ 0.04
Shoreline Material
IJC (1977)
_
-
-
-
-
-
-
Minor Elements
(ug/g)
As
Cd
Co
Cr
Cu
Hg
Mo
Ni
Pb
Sr
V
Zn
-
-
-
23 +
12 +
0.05
-
20 +
36 +
49
-
35 +
5
6
5
6
10
3.1
1.3
11
25
19
0.025
3.1
15
17
183
38
30
+ 4
+ 0.5
+ 6
+ 23
+ 50
+ 0.02
+ 3
+ 9
+ 12
+ 50
+ 20
+ 26
a Dolomite >_ 35% by weight, mean of 4 cores,
272
-------
further suggests that the result of increased conversion of silicon to
particulate form has on the average enhanced the accumulation rate of
amorphous Si by 79/53=1.49 or about 50% since the onset of such changes.
Were it not for the possibility, if not likelihood, that silicon undergoes
significant dissolution in the sediments, this result would in turn imply
corresponding changes in the water column. The alternative explanation for
observed amorphous Si profiles, and one offered by Parker and Edgington
(1976), is that they result from steady-state postdepositional dissolution of
diatoms and possibly another amorphous materials and do not reflect changes
in the diatom productivity of overlying waters. The truth may well lie
between these extreme possibilities and further discussion is provided below
in connection with an examination of profiles of dissolved silicon in
selected cores.
In considering the mean accumulation rate of anthropogenic trace
constituents, several features are apparent on inspection of Table 50.
First, direct municipal/industrial runoff does not contribute significantly
to anthropogenic element accumulation rates. Second, tributary inputs
generally far exceed anthropogenic accumulation rates. This is likely to be
due to a combination of effects. Both natural and anthropogenic components
are typically present in tributary water samples and are lumped together in
reporting concentration values. In addition, as noted before, concentrations
refer to both soluble plus some fraction of the particular matter present
depending on the sampling and analytical methods. As the form and amount of
the anthropogenic components are not distinguished in reporting tributary
loadings, it is difficult to properly compare such loadings with
anthropogenic accumulation rates. In the discussion below, the relation
between atmospheric inputs and anthropogenic accumulation rates is emphasized
It is shown that generally these rates are comparable to the atmospheric
loading rates. This result suggests that the anthropogenic loading by
tributaries may be relatively unimportant for many elements considered. It
should also be noted that even for a background-free contaminant like
cesium-137 whose inputs to the Great Lakes are relatively well-known, there
are factor of two discrepancies between the amount stored in sediments in the
southern part of the lake and the time-integrated loading (see Table 35
above). Because of the many approximations inherent in making comparisons
between anthropogenic accumulation rates in sediments and existing loading
data, a factor of two agreements may be considered as a satisfactory
comparison at this point.
Arsenic — Information on atmospheric contributions of arsenic to the
lakes Is sparse. Zinc-normalized values obtained from the data pf Gatz
(1975) indicate a characteristic deposition rate of around 0.046 micrograms
per cm2/yr. To the degree that any valid comparison can be made with
sediment accumulation data, indications are that atmospheric deposition
cannot account for anthropogenic loadings to the sediments, which for
southern Lake Huron are about 0.32 micrograms/cm2/yr. Municipal and
industrial runoff to the main lake also cannot account for the inferred
accumulation rate. In contrast, tributary inputs (0.73 micrograms/cm2/yr)
are sufficient but as indicated above, there are problems with the tributary
data as to how much of the element is in the soluble phase initially, how
much is anthropogenic, and how much may be converted to particulate form or
273
-------
TABLE 50. COMPARISON OF MEAN ANTHROPOGENIC ELEMENT ACCUMULATION RATES IN
SOUTHERN LAKE HURON WITH VARIOUS MAIN-LAKE LOADING ESTIMATES3 (yg/cm2/yr)
NJ
Mean Anthropogenic
Accumulation Rate in
Southern Lake Huron
Element
As
Br
Cd
Cu
Hg
Ni
Pb
Sb
Si
Sn
Zn
This
studyb
0.32
0.24
0.022
0.24
0.002
0.42
0.94
0.014
79
0.047
1.3
Kemp &
Thomas0
(1976)
_
-
0.01
0.56
0.002
-
1.7
-
-
-
2.2
Municipal &
Industrial
Runoff
Tributary
Inputs
Atmospheric Inputs
Lake Ontario
Lake Shiomi
IJC (1977)
0.005
-
0.002
0.02
0.0002
0.017
0.013
-
-
-
0.26
Huron
IJC (1977) IJC (1977)
0.73
-
1.2 0.12
2.1 1.1
0.007
2.2 0.31
1.8 1.2
-
-
-
2.0
& Kuntz
(1973)d
-
0.085
0.42
-
0.22
1.4
-
-
-
5.2
Lake
Michigan
Gatz
(1975)e
0.046
-
0/045
0.59
-
0.15
2.6
-
-
-
1.3
Lake Michigan
Fingleton &
Robbins
(1980)e
_.
0.50
-
0.21
0.001
-
-
0.012
-
-
1.3
a Whole lake loadings are expressed in terms of element weight per unit area of the main lake
(excluding Saginaw and Georgian Bay).
b Values corrected to 1980 (18% increase since 1975) and based on approximately 60 cores.
c Values based on a single core from the Goderich Basin.
"• Bulk precipitation measurements.
e Based on emissions inventories, and over-water sampling. Values are arbitrarily normalized to the
observed value of the zinc accumulation rate for comparison.
-------
become associated with particulate matter in the lake. Because of analytical
uncertainties associated with determination of this element and the limited
number of observations, the mean anthropogenic accumulation rate reported
here should be regarded as very approximate.
Bromine — Like arsenic there are limited observations of bromine,
especially in underlying sediments and anthropogenic accumulation rates are
very approximate. The limited data on atmospheric inputs derived on the
basis of zinc normalization of the over-lake (Michigan) sampling of
particulate matter by Fingleton and Robbins (1980), the rate of deposition of
bromine is about 0.5 micrograms/cm^/yr. This value is quite comparable to
the calculated accumulation rate (0.24 micrograms/cm^/yr) in southern Lake
Huron. In continental air nearly all bromine as well as lead at the present
time, originates from the combustion of leaded fuel additives which contain,
among other ingredients, ethylene dibromide (cf. Robbins and Snitz, 1972).
The ratio of bromine to lead in TEL Motor Mix (Ethyl Fluid) is 0.39 which
compares very well with the mean ratio of Br to Pb observed in continental
air. Fordyce (1975) reported a mean Br/Pb ratio in air sampled in Cleveland,
Ohio for an entire year of 0.31. The ratio of mean anthropogenic
accumulation rate of Br to that of Pb in southern Lake Huron is
0.24/0.94=0.26. Thus the mean rate of accumulation of bromine is consistent
with the data for lead and indicates combustion of fuel additives as the
primary source.
Cadmium— Reported tributary loadings (IJC, 1977) exceed the
anthropogenic accumulation rate by more than a factor of 50. For other
elements, the contrast between tributary loads and anthropogenic accumulation
rates is not nearly as pronounced, being generally a factor of 2 to 9. As
cadmium is not found to any great degree in the soluble phase in natural
waters, it is surprising that the values are so far apart. The atmospheric
inputs are much closer to the mean anthropogenic accumulation rate of cadmium
but both the IJC values and those reported for Lake Ontario (Shiomi and
Kuntz, 1973) are still about a factor of four higher. The most consistent
comparison is with the zinc-renormalized data of Gatz (1975).
Copper — Values reported for atmospheric inputs by IJC (1977) are
appreciably higher than the observed anthropogenic accumulation rate. In
contrast, values derived from the three other studies are very consistent
with the measured accumulation rate.
Mercury — The measured accumulation rate of mercury 0.002 micrograms/
cm^/yr is consistent with the zinc-renormalized data of Fingleton and Robbins
(1980) of 0.001 microgram/cm^/yr. The values reported by Fingleton and
Robbins, however, could well be low because significant amounts of Hg may be
in the vapor phase and not collected by their sampling method.
Nickel — The mean anthropogenic accumulation rate of nickel, 0.42
micrograms/cm^/yr, is quite consistent with values derived from three studies
including the IJC report.
Lead — It is known that much of the lead entering the Great Lakes comes
from atmospheric deposition. Therefore, the good agreement between the
275
-------
anthropogenic accumulation rate (0.94 micrograms/cm^/yr) and several
estimates of rates of atmospheric input (1.2, 1.4 and 2.6 micrograms/cnrvyr)
support the idea that the mean anthropogenic accumulation rates for southern
Lake Huron are representative of the entire main lake. The rates of
anthropogenic lead accumulation found in this study are very comparable to
those found in Lake Ontario by Farmer (1978) ranging from 1.2 - 6.7 Vg/cnrvyr
and in southern Lake Michigan by Edgington and Robbins (1976) (mean of 1.3
pg/cnrVyr). Mean anthropogenic rates observed by Nriagu et al. (1979) in Lake
Erie are significantly higher. Average accumulation of excess lead in the
fine-grained sediments of the Western, Central and Eastern Basins of Lake
Erie are 13, 2.5 and 16 yg/cm^/ yr. The agreement supports the impression
that for lead and for other trace contaminant metals, the mean anthropogenic
accumulation in sediments is representative primarily of regional atmospheric
loading (except possibly Lake Erie). To the extent that trace metal
contaminants are atmospherically derived, the results of this study further
underscore the importance strong focusing effects occurring on this and other
of the Great Lakes. Constituents (including cesium-137 and lead-210 as well)
which are deposited for the most part uniformly on the lake surface are
eventually stored in very selective areas of the Lake bottom.
Antimony — There are but very limited comparisons for antimony. The
measured anthropogenic accumulation rate (.014 micrograms/cm^/yr) is in
excessively good agreement with the zinc-renormalized data of Fingleton and
Robbins (1930), 0.012 micrograms/cm2/yr.
Tin — This element has not been previously reported for the Great Lakes
and is identified in this report as a contaminant. There are no comparisons
with loading data available. Because of the likelihood that tin is subject
to methylation and partial remobilization out of sediments into the water
column, it would be desirable to develop a better picture of the mass-balance
for this element, its chemical forms and potential availability to the biota.
The mean anthropogenic accumulate rate of tin in southern Lake Huron is 0.047
micrograms/cm^/yr, corresponds to an annual total accumulation rate of about
4.5 metric tons per year as of this report date and represents a total
sediment inventory of 120 metric tons.
Zinc — The anthropogenic accumulation rate of zinc is comparable to
that of lead. The data of Shiomi and Kuntz (1973) based on bulk
precipitation measurements show zinc to have about a four-fold greater
loading rate than that of lead. The zinc-renormalized data of Gatz (1975)
show the opposite trend with lead loading from the atmosphere being twice as
high as that of zinc. It is beyond the scope of this report to consider
reasons for these differences in any great detail.
276
-------
VERTICAL DISTRIBUTION OF DISSOLVED CONSTITUENTS
The vertical distribution of dissolved constituents in selected cores is
shown in Figs. 144-153. The vertical distribution data are given in Table A7
of the Appendix. A summary of concentration data and information on
concentration gradients is given in Table 51. In the discussion that
follows, emphasis is placed on the possible exchange of dissolved species
across the sediment-water interface. It is beyond the scope of this report
to give much accord to geochemical factors affecting the distribution of
dissolved constituents. Diffusional fluxes of solutes across the
sediment-water interface are computed as the product of the diffusion
coefficient and the concentration gradient at Z = 0, (dC/dZ)z=g. With the
exception of Si the gradient is estimated by a linear least squares fit using
data points near the sediment-wajer interface. Approximate values for the
diffusion coefficients of ions l.i free solution are taken from the work of Li
and Gregory (1974) unless otherwise Indicated. With the exception of Si, the
mass-balance calculations below are only approximate.
Bar'urn — The vertical distribution of barium (Fig. 144) is poorly
defined because of the appreciable analytical uncertainties. There are
indications in cores such as ISA and 63 of a gradient in concentration around
z=0. However, the data are best summarized in terms of a mean pore water
concentration (Table 51) which ranges from 0.32+0.20 (ppm) for core 53 to
0.73+0.22 (ppm) for core 63. Concentrations for cores 14A, ISA and 63 are
not significantly different and average 0.61+0.2 ppm.
Calcium — In contrast with the barium data, the profiles of calcium
(Fig. 145) are extremely well-defined because of the very low analytical
uncertainties. The striking feature of these profiles is the linear increase
in concentration with increasing sediment depth in each core. Such profiles
may indicate a very slow approach of dissolved calcium toward saturation
concentrations. In all of the cores the saturation value is not reached even
in the deepest interval sampled. Therefore the values of Cf given in Table
51 are only approximate and probably are a lower limit. The average gradient
in each of the cores is obtained from a linear least-squares fit and ranges
from 0.16 (53) to 0.47 (63) micrograms/cm^. Gradients at the sediment-water
interface are essentially the same as the average in the cores. For a
molecular diffusion coefficient of around (5 x 10""^ cm^/sec or about
160 cm^/yr) these gradients imply an outward flux at z=0 of about 25 to 75
micrograms Ca/cm^/year.
Iron — Profiles of dissolved iron (Fig. 146) increase greatly with
increasing sediment depth in three of the four cores. In core 53 there is
essentially no significant change with depth below 3 cm. Iron concentrations
in this core remain constant and low. This core is collected from a low
sedimentation area where sediments are perhaps less anoxic. In cores 53 and
63, concentrations reach undetectable limits appreciably below the
sediment-water interface. Thus there is no appreciable gradient of dissolved
Fe at z=0 for these two cores and the diffusional flux is essentially zero.
If the profiles are steady-state, the existence of the large gradient in
these two cores below the sediment-water interface implies the build-up of
277
-------
TABLE 51. A SUMMARY OF PORE WATER CONCENTRATION DATA
Concentration (yg/ml)
Element
Barium
Calcium
Iron
Magnesium
Manganese
Phosphate
(soluble
reactive)
Potassium
Silicon
(soluble
reactive)
Core
14
18
53
63
14
18
53
63
14
18
53
63
14
18
53
63
14
18
53
63
14
18
53
63
14
18
53
63
14
18
53
63
C GO
0.61 + 0.15
0.50 + 0.21
0.32 + 0.20
0.73 + 0.22
26.2
26.2
27.2
o-26
<0.01
<0.01
<0.01
<0.01
7.6
7.2
7.6
7.5
<0.01
<0.01
<0.01
<0.01
- -
-
-
- -
6.86
0.84
0.82
0.87
0.96
0.97
0.94
1.1
Cf
_
-
-
-
^50
o,47
0,40
0,55
24
Ml
^ 0.2
Ml
14.5
11.8
11.3
M3.3
3.6
1.4
0.24
1.6
-
-
-
—
1.6
1.3
1.2
1.3
19.2 + 1.0
18.0 + 1.0
9.0 + 0.7
17.2 + 0.5
Gradient
z=0
.
-
-
-
0.34
0.30
0.16
0.47
1.3
1.9
0
o,0
2.5
4.0
0.7
-
0.69
o,0.7
0
o,0
0.5
0.6
0
0.8
o,0.44
a,0.8
a.0.3
0.06
3.6
5.9
3.4
4.2
(yg/cm^)
Average
_
-
-
-
0.34
0.30
0.16
0.47
0.47
0.34
0
0.31
0.10
0.12
0.073
0.16
-
-
-
-
-
-
-
-
-
-
-
—
-
-
-
(continued).
C = the mean + sd for elements with no significant gradients,
CQ = concentration in overlying water, Cf = mean concentration in deep
sediments for sediments with significant gradients around z=0 or elsewhere.
278
-------
TABLE 51. (continued).
Element
Concentration (yg/ml)
Gradient
Core
z=0
Average
Sodium
14
18
53
63
3.3 + 0.4
2.7 + 0.2
3.7 + 0.3
3.5 + 0.5
._ _ _
_
_
_
Strontium
14
18
53
63
0.13 + 0.02
0.13 + 0.01
0.14 + 0.01
0.15 + 0.01
279
-------
LAKE HURON CORES (EPA-SLH-75)
. I4A
30
40
55
60
65
ISA
. 63
0 0.5 1.0 0 0.5 1.0 0 0.5 1.0 0 0.5
DISSOLVED BARIUM (^g/ml)
1.0
Figure 144. Vertical distribution of dissolved barium in selec-
ted cores.
280
-------
LAKE HURON CORES (EPA-SLH-75)
u
5
10
15
20
-25
o
x 30
h-
Q_
0 35
40
45
50
55
60
65
-
I
-
-
-
-
-
-
(
I4A
,
*
ISA
63
0 50 100 0 50 100 0 50 100 0
DISSOLVED CALCIUM (/^g/ml)
50 100
Figure 145. Vertical distribution of dissolved calcium in se-
lected cores;
281
-------
LAKE HURON CORES (EPA-SLH-75)
ro
CO
NJ
0
5
10
15
20
IE 25
IE 30
h-
Q_
Q 35
40
45
50
55
60
65
ISA
53
63
0 5 10 15 20 25 0 5 10 15 0 5 10 0 5 10 15
DISSOLVED IRON (//g/ml)
Figure 146. Vertical distribution of dissolved iron in selected cores,
-------
iron in the solid phase in the same region. In cores 14A and ISA.,
concentrations approach the limits of detection at z=0 and gradients at this
interface at 1.3 and 1.9 micrograms Fe/cm^ respectively. These gradients
imply a flux at the sediment-water interface of about 165 and 240 micrograms
Fe/cm^/yr in cores 14A and ISA. respectively, assuming an effective molecular
diffusion coefficient of about 4 x 10~6 cnr/sec or 126 cm^/yr. Because of
the sensitivity of dissolved Fe concentrations on sedimentary redox
conditions (see Fig. 11), it is likely that much of the dissolved iron
transferred through the sediment-water interface is reprecipitated.
Therefore, there should be a buildup of iron in near surface sediments.
Inspection of Fig. 63 shows that there is a slight increase of Fe in the
vicinity of the sediment-water interface which could be due to diagenetic
remobilization. In core ISA, for example, the upward flux of 240
micrograms/cm^/yr may be compared with the "excess" iron accumulation rate.
The concentration at the surface is about 3.1 wt % while the average
underlying concentration is 2.75+0.22 wt %. The iron enrichment amounts to
about 3.1-2.75=0.35 wt % or 0.0035 g/g. As the sedimentation rate in this
core is 0.0414 g/cm /yr, the steady-state rate of loss of iron on burial of
solid phase iron is 0.0035 x 0.0414 = 140 micrograms/Fe cwr/yr which is
comparable (within a factor of two) to that given in the approximate flux
calculation. Thus the loss of Fe on burial may be counter-balanced by that
supplied to the surface by diffusion, as must be the case if the process of
diagenesis is steady-state.
Magnesium — The vertical profiles of dissolved magnesium (Fig. 147)
exhibit a roughly linear increase with sediment depth. Average gradients
found by linear least squares analysis, as in the case of calcium, range from
0.073 to 0.16 mirograms/cm^/yr. In contrast with calcium, there is a
significant decrease in the concentration of dissolved magnesium in the
vicinity of the sediment-water interface, so that the average gradient does
not well-represent the concentration gradient at z=0. Values at the
interface are from 10 to 30 times higher at the interface than on average.
This feature suggests that the overlying water is undersaturated with respect
to certain forms of magnesium occurring in sediments and that, on burial,
pore waters rapidly become saturated with respect to such components. In
addition to this, there are other components which result in higher
saturation levels after very long times. Diffusional fluxes implied by
surface gradients range from 112 to 600 micrograms/cm^/yr for Mg assuming an
effective diffusion coefficient of 160 cm^/yr.
Manganese — Profiles of dissolved manganese, such as those shown in
Fig. 148, have been found in the Great Lakes by Bobbins and Callender (1975)
and elsewhere by others. As is the case for iron, concentrations of Mn
approach undetectable levels in cores 53 and 63 well below the sediment-water
interface. In cores 14A and ISA, concentrations approach undetectable levels
at the sediment-water interface. In each of these latter cores the gradient
at z=0 is about 0.7 micrograms/cm , corresponding to a flux of 77
micrograms/cm^/yr assuming a diffusion coefficient of 110 cm^/yr. Using core
ISA again as an example, the concentration of manganese at the surface is
0.11 wt % while the average concentration of Mn in underlying sediments is
0.0352 + 0.003 wt %. Hence the net loss of Mn on burial is given by
0.11 - 0.0352 = 0.0748 wt % or 7.48 x 10~4 g/g. The rate of loss then is
283
-------
LAKE HURON CORES (EPA-SLH-75)
5 -
10
15
20
t
o
X 30
I-
Q_
0 35
40
45
50
55
60
65
0
I4A
ISA
53
63
10 15 0 5 10 15 0 5 10 0 5
DISSOLVED MAGNESIUM (/^g/ml)
10 15
Figure 147.
Vertical distribution of dissolved magnesium in se-
lected cores.
284
-------
LAKE HURON CORES (EPA-SLH-75)
0
E
o
5 -
10-
15 -
20 -
25
I 30
K
Q_
40
45
50
55
60
65
0
Figure 148.
I4A
_ ISA
53
_ 63
I 2 3 4 0 I 2 0 I 0
DISSOLVED MANGANESE (/xg/ml)
Vertical distribution of dissolved manganese in se-
lected cores.
285
-------
approximately this difference times the sedimentation rate or 7.48 x 10^ x
0.0414 = 31 micrograms/cm^/yr. Since the concentration of Mn increases so
rapidly toward z = 0 over the upper few cm, it is difficult to accurately
estimate the actual concentration at z = 0. The value used here is
undoubtedly an underestimate as it does not take account of the effect of
finite interval sampling. Hence upward diffusion of manganese is essentially
(within a factor of 2) counterbalanced by formation of an excess Mn in the
solid phase. Such a diagenetic process has been well-documented (cf. Robbins
and Callender, 1975) and leads to marked enhancement of Mn in the uppermost
sediment layers in the fine-grained sediments of the Great Lakes. This
surface enrichment is an invariant feature of intact cores as can be seen
from Figs. 67 and 68. That surface enrichments of manganese are seen in
virtually all cores attests to the fact that cores recovered are essentially
undisturbed.
Phosphorus — Of all the elements determined in sediment pore waters for
this report, phosphorous exhibits an extreme sensitivity to contamination
with air. The large fluctuations seen (Fig. 149) in the concentration of
soluble reactive phosphate (SRP) versus depth in various cores, particularly
ISA and 63, are most probably due to inadvertent contamination of the
sediment squeezing system with small amounts of air. For this reason the
lowest concentrations should almost certainly be discarded and higher levels
should be regarded as minimum values. In contrast with Fe and Mn profiles,
concentrations of SRP in each core decrease toward the sediment-water
interface but not to undetectable levels. Actual values in overlying water
should be essentially undetectable in terms of the analytic methods employed.
Concentration gradients in three cores (14A, 18A and 63) are either nearly
correct or are lower limits and are 0.5, 0.6 and 0.8 micrograms PO^cm^
respectively. Assuming an effective diffusion coefficient of about 5 x 10~"
cm2/sec or about 160 cm /yr, the apparent flux at the sediment-water
interface is about 100 micrograms/cm^/yr in core ISA (or greater).
Inspection of the distribution of acid-soluble phosphorus in the
corresponding cores (Fig. 70) shows that there are very small increases in
concentrations near the sediment-water interface in cores 14, 18A, and 63 but
not in 53. This result is consistent with the presence of surface gradients
in all but core 53. The increase seen in ISA is very marginal. The
concentration at the surface (0-1 cm) is about 0.267 wt % while the mean
concentration in deeper layers is 0.20 j^ 0.02 wt %. Hence the net loss of
P04 on burial is 0.267 - 0.20 = 0.067 wt % which corresponds to a rate of
about 30 micrograms P04 cm^/yr. Not enough to balance the upward diffusional
flux. However, the numbers are too uncertain to be sure that the difference
in this case is real. In core 63 the surface concentration of acid-soluble
P04 is 0.33 wt %, whereas the mean concentration in underlying sediments is
0.236 +_ 0.04 wt %. Hence, the net P04 lost on burial is 0.33 - 0.24 = 0.09
wt %. As the sedimentation rate in this core is 34.2 mg/cm^/yr, the loss
rate is 0.09 x 10^ x 0.034 = 31 micrograms P04 cm^/yr. The approximate flux
is 0.8 x 160 = 130 micrograms/cm^/yr. Again in this core there may not be
enough loss of acid-soluble P04 to counter-balance the upward flux. The same
result applies to core 14. Thus the indications are that although some
phosphorus may be involved in diagenetic cycling, a significant amount may be
contributed to overlying water as a result of interstitial diffusion. It
should be emphasized that this indication is based on the assumption of
286
-------
LAKE HURON CORES (EPA-SLH-75)
00
0
5
10
15
20
1 25
o
I 30
Q.
S 35
40
45
50
55
60
65
I4A
ISA
.53
01 234501
450
20123
DISSOLVED REACTIVE PHOSPHATE (//g/ml)
Figure 149. Vertical distribution of dissolved reactive phosphate in selected cores,
-------
steady-state conditions and on phosphorus concentrations of very marginal
quality.
Potassium — In all cores there is a two-fold increase in equilibrium
concentrations of dissolved potassium over concentrations in overlying water
(Fig. 150). In general, equilibrium concentrations are reached within the
upper five centimeters of the cores studied and for cores ISA and 53 this
increase in concentration is confined to the upper cm or so. Assuming an
effective diffusion coefficient of about 10 x 10~° cm/sec, or 316 cnr/yr,
calculated fluxes range from about 20 to 250 micrograms K/cm^/yr.
Sodium — With the possible exception of core 63, profiles of sodium
exhibit no significant gradients (Fig. 152). The values are essentially
constant and average 3.30 +_ 0.4 ppm for the four cores (Table 51). This
result contrasts with the observations of Lerman and Weiler (1970). In
sediment cores from Lake Ontario these authors found about a 20% increase in
the concentration of sodium above background levels near the sediment-water
interface. The increase was successfully attributed to increases in the
concentration of sodium in Lake Ontario waters since the 1900s.
Strontium — Profiles of dissolved strontium (Fig. 153) exhibit no
significant variations with sediment depth. Concentrations average
0.14 + 0.0.01 ppm for the four cores.
Silicon — The data on dissolved and amorphous silicon are of sufficient
quality and detail to warrant a more accurate treatment than given above for
the other elements. Profiles of dissolved silicon (Fig. 151) exhibit
dramatic gradients at the sediment-water interface. Such profiles have been
seen before in sediments of Lake Michigan (Robbins et al. 1974) and in Lakes
Superior, Erie, and Ontario (Nriagu 1978). Concentrations increase from
about 1 ppm Si above z = 0 to saturation levels within each core. Saturation
concentrations given in Table 51 range from 9.0 ppm in core 53 to 19.2 ppm Si
in core 14. Concentration values increase smoothly with sediment depth
showing very little scatter. Note that in contrast to soluble reactive
phosphate, the concentration of soluble reactive silicon (SRS) is only
slightly affected by exposure of sediments and pore water samples to small
amounts of air (See Fig. 11 and Table 8).
As stated previously, the outward flux of SRS may be computed as the
product of the concentration gradient as z = 0 and the effective diffusion
coefficient, provided the release of SRS to overlying water is
diffusion-limited. Recent direct measurements of the SRS flux from cores
suggest that this method of calculation may underestimate real fluxes because
the flux is in part determined by surface reactions as well as by transport
properties (Robbins and Edgington, 1979). In the absence of information
concerning actual fluxes, the exchange is assumed to be diffusion-limited.
The gradient, in principle, can be found by linear least squares fit of the
concentration data around z = 0 if the sampling intervals are sufficiently
small. Values based on a linear fit are given in Table 52. However, this
method can lead to a significant underestimate of the surface gradient of SRS
because the concentrations increase so rapidly just below the sediment-water
interface. Anikouchine (1967) and others have shown that for sediments
288
-------
LAKE HURON CORES (EPA-SLH-75)
00
VO
0
5
10
15
20
E 25
o
X 30
35
40
45
50
55
60
65
I4A
ISA
53
-0 0.5 10
1.5 20 0 0.5 10 15 0 05 10
DISSOLVED POTASSIUM (//g/ml)
63
0 05 10 1.5
Figure 150. Vertical distribution of dissolved potassium in selected cores
-------
VO
O
0
5
10
15
E 20
o
Q.
LJ
? 25
30
35
40
45
50
0
I4A
J I
LAKE HURON CORES (EPA-SLH-75)
ISA
I I
I
10 15 20
0 5 10 15 20 0
DISSOLVED SILICON
53
i r
63
J I
10 15 0 5 10 15 20
Figure 151. Vertical distribution of dissolved silicon in selected cores.
-------
LAKE HURON CORES (EPA-SLH-75)
E
o
LU
Q
0
5
10
15
20
25
30
35
40
45
50
55
60 -
65
. I4A
J L
.ISA
. 53
_ 63
024 024024 024
DISSOLVED SODIUM (uq/ml)
Figure 152. Vertical distribution of dissolved sodium in selec-
ted cores.
291
-------
LAKE HURON CORES (EPA-SLH-75)
0
E
o
Q_
10 -
15 -
20
25
30
35
40
45
50
55
60
65
_I4A
. ISA
. 53
. 63
0 O.I 0.2 0 O.I 0.2 0 O.I 0.2 0 O.I 0.2
DISSOLVED STRONTIUM (^g/ml)
Figure 153. Vertical distribution of dissolved strontium in se-
lected cores.
292
-------
accumulating at a constant rate with a constant flux of silicon, and the
solid phase dissolving according to first order kinetics, the steady-state
distribution of SRS is approximately given by
D 32C - k (C - C,) - 0 (54)
* a 2
9 z
where the effects of compaction and advection are neglected. De is the
effective diffusion coefficient (cm'/yr), k is the first-order rate constant
(yr *"*•), and Cf is the equilibrium concentration of SRS. Under such
conditions the solution to the above equation is
C - (C - C,) e~3z, 3 = *^/Do (55)
O I S
Thus, even the most elementary model of silicon dissolution indicates that
the increase in concentration with sediment depth is not linear but involves
an exponential term over any appreciable sediment interval. Inspection of
the distribution of amorphous silicon in the cores as well as the SRS profile
in core 53 show that the above formalism is not sufficient for describing the
overall relations between amorphous and dissolved silicon, but the above
equation (55) is adequate for estimating surface gradients. A least squares
fit of the above equation, using values of CQ and Cf given in Table 51 and
the first four data points below z = 0, gives a estimate of the parameter, 8 ,
and a second estimate of the gradient at z = 0 for each core is 8 (C,. - C ) .
The effect of finite sampling may be taken into account by averaging the
theoretical profile (Eq. 55). Thus, the predicted of concentration is really
the average of the theoretical concentration over the sampling interval or
C ' 72^1 f^ (Co - V 6"eZ + Cf]dZ (56)
zl
Inclusion of the sampling effect leads to a second estimate of beta, 8*, and
the gradient. Each of the estimates is given in Table 52, along with other
relevant values.
From values given in Table 52, it can be seen that: (1) provided only
the first two points (z » 0 and z « 0-1 cm) are used in a linear calculation
the inferred gradients are generally consistent with those based on a
theoretical distribution with inclusion of sampling effects; (2) the
inclusion of four points in a linear fit leads to appreciable underestimates
of the gradient; and (3) the effect of including sample averaging is to
slightly increase the estimated gradient in three of the four cases. The
values of the surface SRS gradients are very comparable to those obtained by
Nrigau (1973) and Robbins et al. (1974). Re-analysis of Nriagu's Lake
Ontario core data in terms of the theoretical profile, plus sample averaging
(Eq. 56), shows that the four profiles of SRS in Lake Ontario sediments yield
a gradient of 7.1 +_ 0.5 yg Si/cm^. Values in Table 52 range from 5.8 to 15.9
yg Si/cnr*.
293
-------
TABLE 52. PARAMETERS DERIVED FROM ANALYSIS OF DISSOLVED AND AMORPHOUS SILICON PROFILES
N>
v£>
Quantity
Exponent coefficient (cm )
B
e*
2
Gradient at z=0 ( yg Si/cm /yr)
linear (two points)
linear (four points)
B (Cf-Co)
B*(Cf-Co)
Mean porosity, $
2
Apparent diffusion coefficient (cm /yr)
* De
First order rate constant (yr )
k
2
SRS Flux ( pg Si/cm /yr)
F.
i
14A
0.31
0.32
8.4
3.6
5.7
5.8
0.93
130
21
750
Core
18A
0.86
0.94
11.6
5.9
14.6
15.9
0.89
107
87
1700
53
0.66
0.68
7.1
3.4
7.2
7.5
0.93
130
55
980
63
0.44
0.42
7.0
4.2
7.0
6.7
0.92
124
28
830
(continued)
-------
TABLE 52. (continued)
S3
M3
Ui
Amorphous
Quantity
Si Concentration ( wt% )
mean surface
mean deep
net (uncorrected)
net (corrected)
2
Sedimentation rate (mg/cm /yr)
Available
2
Si Flux (pg Si/cm /yr)
F*
Core
14 A ISA 53 63
1.91 1.28 1.13 1.75
1.09 0.70 0.60 0.69
0.82 0.58 0.53 1.06
2.62 1.13 1.47 2.17
30 41.4 ~11 34.2
790 470 160 740
Note: in core 53, C, - 11.9 yg/ml for estimating the gradient at z=0.
-------
The effective diffusion coefficient for silicon in pore water is not
well known and should be measured for sediments of the Great Lakes. Nriagu
(1978) adopted the value given by Lerman (1975) of 94.6 cm2/yr in his
treatment of SRS profiles. This value is certainly reasonable. The
self-diffusion coefficient of SRS in seawater at 25° C is 1 x 10~5 cm2/sec
(Wollast and Garrels 1971). At the in situ temperature of 6° C this value
should be about 5.5 x 10~6 cm2/sec or 173 cm2/yr (cf Li and Gregory 1974).
This value characterizes diffusion in ocean water. In fresh water the
diffusion coefficient should be about 5% higher because of a lower viscosity
(Li and Gregory 1974) or about 183 cm2/yr. The effective diffusion
coefficient is smaller than that in free solution because of the interference
of sediment particles with the movement of ions. While there are no
absorption effects under steady-state conditions, there are sediment
tortousity effects. The tortuosity is the average ratio of the actual
tortuous diffusion path of ions around sediment particles to the straight
distance of that path. Kurd (1973) used an empirical relationship derived
from measurement with clays between the free solution, Do, and effective
diffusion coefficients, De:
(W - 1-65 ( *-l). (57)
This formula gives an adequate correction for tortuosity effect. <|> is the
sadiment porosity which in the present case is around 0.9 in each core near
the sediment-water interface. In calculating the flux, a correction must be
made (Berner 1975) for the fraction of the area across which solutes diffuse
which is not blocked by sediment particles. This fraction is simply <)> .
Thus, the best estimate of the flux if SRS is
F = 183 x 101-65 C*-1) x 4 x (dC/dz) . (58)
•V Z~~U
The term 4>DP corresponds to the value used by Nriagu (1973) and generally is
about 13-30% higher than his value. Nriagu did not attempt to adjust the
value of De for the effects of sediment porosity and tortuosity. Values of
(|>D are given in Table 52.
Values of the SRS flux (Table 52) range from 750 to 1700 yg Si/cm2/yr.
As has been noted by Robbins et al. (1974), Robbins (1976), and Nriagu
(1978), if such fluxes are representative of the annual silicon release from
sediments of the Great Lakes then regeneration of silicon from sediments is a
major process in the cycling of silicon in the water column. The calculated
fluxes reported here are very consistent with the values based on direct
measurement of releases from eight cores taken in July 1976 from northern
Lake Huron by Remmert et al. (1977). These authors report actual fluxes
ranging from 1015 to 2050 yg Si/cm-/yr. Their results suggest that measured
release rates can be reconciled with values estimated from concentration
gradients and thus that the process of exchange may be adequately described
in terms of diffusional and advective transport.
In this regard, advective contributions to silicon exchange have been
assumed to be small in comparison with diffusional transport in calculating
296
-------
the outward SRS flux above. The advectlve flux is given approximately by
toC and is less than about 0.15 yg/cm^/yr for each core, (Table 52) and
thus indeed may be neglected.
The first-order rate constant, k, is computed from the value of beta.
In the above calculations the value of beta was found using only points in
the vicinity of the sediment water-interface in order to best infer the
concentration gradient at z=0. For purposes of computing the rate constant
it is appropriate to use all the data. Values of k given in Table 52 are
based on least squares fit of Eq. 56 to all the data. The first-order rate
constant is then given by
,2
e
k=<|>D_e (59)
Values listed in Table 52 range from 21 to 87 yr *•. Less variation from core
to core might be expected if an accurate formalism were used to describe
solid phase Si dissolution and solute transport. An appropriate formalism
which includes the effect of sediment mixing is provided below. Reanalysis
of the SRS profiles in the Lake Ontario cores (Nriagu 1978) yields values of
the first-order rate constant ranging from about 11 to 15 yr~l.
Under steady-state conditions the upward flux of SRS is exactly matched
by sedimentation of silicon. Comparison of the upward flux with sedimenting
silicon is rendered difficult because of at least two important effects: (1)
not all of the silicon reaching the sediments is available for dissolution.
Therefore a means must be found for isolating or identifying that portion of
the total silicon which participates in diagenetic transformations (i.e.
available Si) and (2) while the downward flux is given as the product of the
mass sedimentation rate and the concentration of available silicon in
sedimenting material, this concentration is not necessarily the same as the
concentration of available silicon in surface sediments. There are at least
two reasons for possible differences: (1) rapid dissolution at and near z=0
causes the concentration of available silicon on incoming material to be
different from material actually deposited at z=0 as practically defined and
(2) post-depositional movement (such as that due to bioturbation) of sediment
solids carrying available silicon can redistribute the initially-deposited
silicon downward in the sediment core. In the absence of a unified formalism
for these processes, an approximate calculation can be made which at least
takes account of mixing. The available silicon may be taken as the
concentration of amorphous silicon in surface sediments minus the amount
which remains in deeper sediment layers. Because of sediment mixing the
concentration at the surface will be reduced over that in initially deposited
materials. The effects of mixing may be corrected approximately on the
assumption that in the absence of mixing the profile of amorphous Si would be
exponential. Thus, the theoretical profile is assumed to have the form
C(Z)=CQ e~az + Cf (60)
where CQ is the concentration at z=0 and Cf is the concentration at
sufficient depth. The coefficient a can in turn be expressed in terms of an
apparent reciprocal life-time', so that « = "X"/u, and the correction for the
effects of mixing takes the form
297
-------
Y + "X" (u)/s) + otto . ^
Y = (d/s) = 1 + as
See Eq. 41 for comparison. The value of alpha is determined graphically from
the exponential portion of each amorphous silicon profile. The downward flux
of available silicon, F •(•, is taken to be
F+ - r (Co - CP (1 + as) (62)
The values of the rate of sedimentation of available silicon, F.J., are given
in Table 52. The product of the two terms in parentheses is referred to as
the corrected available silicon.
A comparison of the downward flux of available silicon with the upward
flux of SRS indicates that for cores 14A and 63 there is essentially a
balance. In cores ISA. and 53 there appears to be a considerably greater SRS
flux than can be matched by the supply of available silicon. Because of the
many uncertainties in the comparisons it is not possible to identify the
probable reasons for the mismatch. It should be emphasized that the
calculation of SRS fluxes based on surface gradients is extremely sensitive
to small losses of sediment or other disturbances of sediment during coring.
Thus, in a core such as ISA where the gradients at z=0 is very large, a loss
of even a few mm of sediment can introduce a factor of two change (increase)
in the computed value. In core 53 there is a stratigraphic discontinuity
around 4 cm so that the formalism developed above may not be applicable at
all to Si profiles in this core. In addition, the above formalism does not
properly incorporate conservation of mass or solid/solution reaction kinetics
and assumes steady-state conditions. A useful approach to rigorous
quantitative modeling of the effect of bioturbation on the sediment-water
interactions has been formulated specifically for the dissolution of silicon
in marine sediments by Schink and Guinasso (1977) and Schink et al. (1975).
The formalism is transferrable to the case of Great Lakes profundal sediments
with certain modifications. While it is beyond the scope of the present
report to actually develop solutions to a unified model for silicon
dissolution, it is of value to provide an outline of the formalism as it
emerges from the insights gained in this study.
In the original formulation of Schink et al. (1975) the non-steady state
distributions of soluble reactive silicon and amorphous silicon were
represented by two separate differential equations describing transport of
these phases.
The equations given by Schink et al. (1975) are:
(<|> + K*) 3C = 3 (
-------
Where the terms have the following meaning:
= the porosity which is depth-dependent
K* = the effective adsorption coefficient of dissolved species on
associated solids
C = the concentration of SRS (Vg Si/cm3)
Cf = aqueous phase saturation concentration
C0 = concentration in overlying water
t = time in years
z = depth below the sediment-water interface (cm)
De = effective diffusion coefficient (cm2/yr)
v = velocity of the sediment-water interface relative to incoming
sediment particles (cm/yr)
KJJ = first order dissolution rate constant (yr~l)
B = concentration of available silicon in the bulk phase
(solids+fluids) of the sediment (Vg Si/cm3)
Dfc = rate of vertical (biological) mixing of solid phases (cm2/yr)
The most important boundary condition for the model is that the input flux of
available silicon is equal to mixing redistribution plus advection, i.e.
F, = - D^ OB/9z) + v B (64)
r b o o
Note that in the absence of mixing, F^ = vBQ as assumed in the approximate
calculations above. For non-steady-state problems the time-dependence of
the sediment silicon profiles results from the time-dependence of F^ and Co.
Note that the mixing is described in terms of an eddy diffusion process.
Robbins et al. (1977) have shown that this representation is acceptable for
the action of the amphipod, Pontoporeia Hoyi, on sediments. The conveyor
belt species such as Oligochaete worms transport sediment in a different way
but the above formalism may still provide an adequate representation of their
long-term interaction with sediments. The above formalism of Schink et al.
(1975) assumes that the range of bioturbation is essentially infinite. In
contrast, the results of the present study indicate that the range is quite
limited in the Great Lakes, often not exceeding 3 or 4 cm depth. This is the
principal modification required of the above set of equations. Another is
that the advective terms are negligible. Thus, the equations above can be
used as a basis for describing SRS and amorphous Si profiles if the proper
depth-dependence of D^ is introduced. The simplest being that, below the
depth of the mixed zone, Dfo=0. it may also be necessary to introduce a
depth-dependent effective diffusion coefficient De. Recent studies by
Krezoski and Robbins (1980) using radiotracers have shown that the presence
of benthos significantly enhances the value of De within the mixed zone.
Guinasso and Schink (1977) and Schink et al. (1975) assume that the
change in SRS concentration in a given segment of sediment due to reactions
with solid phases is given by a term which couples solid and solution phase
concentrations, namely:
( + K*) 9£ = K^ B (Cf - C)/Cf (65)
3t reactions
299
-------
While this form is probably adequate to describe the SRS and amorphous silicon
profiles, its validity needs to be ascertained for freshwater sediments under
carefully controlled laboratory conditions.
300
-------
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Lerman, A. and T. A. Lietzke. 1975. Uptake and migration of tracers in
lake sediments. Limnol. Oceanogr. 20: 497-510.
Lerman, A. and R. Weiler. 1970. Diffusion and accumulation of chloride and
sodium in Lake Ontario sediment. Earth Planet. Sci. Lett. 10: 150-156.
Li, Y. and S. Gregory. 1974. Diffusion of ions in sea water and in deep sea
sediments. Geochim. Cosmochim. Acta. 38: 703-714.
McKyes, E., A. Sethi, and R. N. Young. 1974. Amorphous coatings in particles
of sensitive clay soils. Clays and Clay Miner. 22: 427-433.
Nriagu, J. 0. 1978. Dissolved silica in pore waters of Lakes Ontario, Erie
and Superior sediments. Limnol. Oceanogr. 23: 53-67.
Nriagu, J. 0., A. L. W. Kemp, H. K. T. Wong, and N. Harper. 1979. Sedimen-
tary record of heavy metal pollution in Lake Erie. Geochim. Cosmochim.
Acta. 43: 247-258.
Parker, J. I. and D. N. Edgington. 1976. Concentration of diatom frustules
in Lake Michigan sediment cores. Limnol. Oceanogr. Note 21: 887-893.
Parker, J. I., H. L. Conway, and E. M. Yaguchi. 1977. Dissolution of diatom
frustules and recycling of amorphous silicon in Lake Michigan. J. Fish.
Res. Board Can. 34: 545-551.
Ramakrishna, T. V., J. W. Robinson, and P. W. West. 1969. Determination of
phosphorus, arsenic or silicon by atomic absorption spectrometry of
molybdenum heteropoly acids. Anal. Chim. Acta. 45: 43-49.
Reeburgh, W. 1967. An improved interstitial water sampler. Limnol.
Oceanogr. 12: 163-165.
Remmert, K. M., J. A. Robbins, and D. N. Edgington. 1977. Release of
dissolved silica from sediments of the Great Lakes. 20th Annual
Conference on Great Lakes Research of the International Association for
Great Lakes Research. May 10-12.
Robbins, J. A. 1976. The role of sediments in the silica budget of the
Great Lakes. 10th Great Lakes Regional Meeting of the American Chemical
Society, Northwestern University, Evanston, II. June 17-19. Abstracts,
pp. 206-207.
Robbins, J. A. 1977. Recent sedimentation rates in southern Lake Huron and
in Saginaw Bay. 40th Ann. Meeting of the American Society of Limnology
and Oceanography, Lansing, Michigan. June 20-23, 1977. Abstr.
304
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Robbins, J. A. 1978. Geochemical and geophysical applications of radioactive
lead. Ln J. 0. Nriagu (ed), The Biogeochemistry of Lead in the
Environment. Elsevier/North-Holland Biomedical Press, New York.
pp. 285-393.
Robbins, J. A. and E. Callender. 1975. Diagenesis of manganese in Lake
Michigan sediments. Am. J. Sci. 275: 512-533.
Robbins, J. A. and D. N. Edgington. 1974. Stable lead geochronology of
fine-grained sediments in southern Lake Michigan. Radiological and
Environmental Research Division Annual Report, Ecology, Argonne National
Laboratory, Argonne, 111. Jan.-Dec., 1974, ANL-75-3 Part III. pp.
32-39.
Robbins, J. A. and D. N. Edgington. 1975. Determination of recent sedimen-
tation rates in Lake Michigan using Pb-210 and Cs-137. Geochim.
Cosmochim. Acta. 39: 285-304.
Robbins, J. A., and D. N. Edgington. 1979. Release of dissolved silica
sediment of Lake Erie. 22nd Annual Conference on Great Lakes Research
of the International Association for Great Lakes Research, May 1-13.
Abstracts, pp. 19.
Robbins, J. A. and J. Gustinis. 1976. A squeezer for efficient extraction of
pore water from small volumes of anoxic sediment. Limnol. Oceanogr.
21: 905-909.
Robbins, J. A. and F. Snitz. 1972. Bromine and chlorine loss from lead
halide automobile exhaust particulates. Environ. Sci. Technol. 6:
164-169.
Robbins, J. A., D. N. Edgington, and J. I. Parker. 1974. Distribution of
amorphous, diatom frustule and dissolved silica in a lead-210 dated core
from southern Lake Michigan. Radiological and Environmental Research
Division Annual Report, Ecology, Argonne National Laboratory, Argonne,
111. Jan.-Dec., 1974. ANL-75-3 pp. 14-31.
Robbins, J. A., J. R. Krezoski, and S. C. Mozley. 1977. Radioactivity in
sediments of the Great Lakes: Post-depositional redistribution by
deposit-feeding organisms. Earth Planet. Sci. Lett. 36: 325-333.
Robbins, J. A., D. N. Edgington and A. L. W. Kemp. 1978. Comparative
lead-210, cesium-137 and pollen geochronologies of sediments from Lakes
Ontario and Erie. Quater. Res. 10: 256-278.
Rossmann, R. 1975. Chemistry of nearshore surficial sediments from
southeastern Lake Michigan. Great Lakes Res. Div., Spec. Rept. No. 57,
Univ. of Michigan, Ann Arbor. 62 pp.
Ruch, R. R., E. J. Kennedy, and N. F. Shimp. 1970. Distribution of arsenic
in unconsolidated sediments from southern Lake Michigan. 111. State
Geological Survey, Environmental Geology Notes, EGN-37. 16 pp.
305
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Shimp, N. F., J. A. Schleicher, R. R. Ruch, D. B. Heck, and H. V. Leland.
1971. Trace element and organic carbon accumulation in the most recent
sediments of southern Lake Michigan. 111. State Geol. Surv., Environ.
Geol. Notes, No. 41. 25 pp.
Schink, D. R. and N. L. Guinasso, Jr. 1977. Effects of bioturbation on
sediment-seawater interaction. Marine Geol. 23: 133-154.
Schink, D. R., N. L. Guinasso, and K. A. Fanning. 1975. Processes affecting
the concentration of silica at the sediment-water interface of the
Atlantic Ocean. J. Geophys. Res. 80: 3013-3031.
Shiomi, M. T. and K. W. Kuntz. 1973. Great Lakes precipitation chemistry:
Part I. Lake Ontario Basin. _In. Proc. 16th Conf. Great Lakes Res. of the
Internat. Assoc. Great Lakes Res., pp. 581-602.
Strickland, J. D. H. and T. R. Parsons. 1960. A manual of sea water
analysis. Fisheries Research Board, Canada, Bull. No. 125. Ottawa.
185 pp.
Sutherland, J. C., J. R. Kramer, L. Nichols, and T. D. Kurtz. 1966.
Mineral-water equilibria, Great Lakes: Silica and phosphorus. In Proc
9th Conf. Great Lakes Res. of the Internat. Assoc. Great Lakes Res.,
pp. 439-445.
Thomas, R. L. 1972. The distribution of mercury in the sediments of Lake
Ontario. Can. J. Earth Sci. 9: 636-651.
Thomas, R. L. 1973. The distribution of mercury in the surficial sediments
of Lake Huron. Can. J. Earth Sci. 10: 194-204.
Thomas, R. L., A. L. Kemp, and C. F. M. Lewis. 1973. The surficial sediments
of Lake Huron. Can. J. Earth Sci. 10: 226-271.
Troup, B. N., 0. P. Bricker, and J. T. Bray. 1974. Oxidation effect on the
analysis of iron in the interstitial water of recent anoxic sediments.
Nature 249: 237-239.
Wahlgren, M. W., J. A. Robbins, and D. N. Edgington. 1980. Plutonium in the
Great Lakes, Ln Transuranics in the Environment (W. C. Hanson, Ed.),
U. S. Dept. of Energy (TID-22800). (In Press, April 1980).
Walters, L. J. and T. J. Wolery. 1974. Transfer of heavy metal pollutants
from Lake Erie bottom sediments to the overlying water. State of Ohio
Water Resources Center, Completion Report No. 421X. 84 pp.
Walters, L. J., T. J. Wolery, and R. D. Myser. 1974. Occurrence of As, Cd,
Co, Cr, Fe, Hg, Ni, Sb and Zn in Lake Erie sediments. Ln Proc 17th
Conf. Great Lakes Res. of the Internat. Assoc. Great Lakes Res. Part I.
pp. 219-234.
306
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Weiler, R. 1973. The interstitial water composition in the sediments of the
Great Lakes. I. Western Lake Ontario. Limnol Oceanogr. 18: 918-931.
Williams, J. D. H., T. P. Murphy and T. Mayer. 1976. Rates of accomulation
of phosphorus forms in Lake Erie sediments. J. Fish. Res. Board Can.
33: 430-439.
Winchester, J. W. and G. D. Nifong. 1971. Water pollution in Lake Michigan
from pollution aerosol fallout. Water, Air and Soil Pollut. 1: 50-64.
Wollast, R. and R. M. Garrels. 1971. Diffusion coefficient of silica in sea
water. Nature Phys. Sci. 229: 94-95.
Zobell, C. E. 1946. Studies of redox potentials of marine sediments. Bull.
Am. Assoc. Petrol. Geologists. 30: 477-513.
307
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ARTICLES PRESENTED OR PUBLISHED RECEIVING EPA SUPPORT
Robbins, J. A. The role of sediments In the silica budget of the Great Lakes.
Invited paper for the 10th Great Lakes Regional Meeting of the American
Chemical Society, Northwestern University, Evanston, 111., June 17-19,
1976. Abstracts p. 206-207.
Burin, G. and J. A. Robbins. Polychlorinated byphenyls (PCBs) in dated
sediment cores from southern Lake Huron and Saginaw Bay. 20t'1 Annual
Conferences on Great Lakes Research of the International Association
for Great Lakes Research, Ann Arbor, Michigan. May 10-12, 1977.
Johansen, Kjell A. and J. A. Robbins. Fallout cesium-137 in sediments of
southern Lake Huron and Saginaw Bay. Ibid.
Krezoski, J. R. and J. A. Robbins. Radioactivity in sediments of the Great
Lakes: post-depositional redistribution by deposit-feeding organisms.
Ibid.
Remmert, K. M., J. A. Robbins and D. N. Edgington. Release of dissolved
silica from sediments of the Great Lakes. Ibid.
Robbins, J. A. Recent sedimentation rates in southern Lake Huron and Saginaw
Bay. Ibid.
Ullman, W. and J. A. Robbins. Major and minor elements in sediments of
southern Lake Huron and Saginaw Bay: patterns and rates of deposition,
historical records and intarelement associations. Ibid.
Robbins, J. A., Limnological applications of natural and fallout
radioactivity in the Great Lakes, Symposium on limnology of the Great
Lakes, 40th annual meeting of the American Society of Limnology and
Oceanography, East Lansing, Michigan, June 20-23, 1977.
Robbins, J. A., McCall, P., Fisher, J. B. and Krezoski, J. R. Effect of
deposit feeders on migration of radiotracers in lake sediments.
American Society of Limnology and Oceanography, 41st Annual Meeting,
Victoria, British Columbia, June 19-22, 1978.
Robbins, J. A., and Johansen, K. A., Cesium-137 in the sediments of Lake
Huron. Ibid., p. 10.
Robbins, J. A. Radiotracer studies of sediment reworking by freshwater
macrobenthos. Forty-second Annual Meeting of the American Society of
Limnology and Oceanography, Inc. Marine Sciences Research Center,
State University of New York, Stoney Brook, N. Y. June 18-21, 1979.
Abstracts P. 100.
Robbins, J. A. Aspects of the interaction between benthos and sediments in
the North American Great Lakes and effects of toxicant exposures.
Invited paper for the Symposium on the Theoretical Aspects of Aquatic
Toxicology, Borok, USSR, July 3-5, 1979.
308
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Robbins, J. A. Accumulation of tin and other metal contaminants in sediments
of southern Lake Huron. The XXIst Congress of the International
Association of Theoretical and Applied Limnology, Kyoto, Japan,
Aug. 24-31, 1980.
Robbins, J. A. and J. Gustinis, A squeezer for efficient extraction of pore
water from small volumes of anoxic sediment. Limnol. and Oceanogr., 21,
(1976) 905-909.
Robbins, J. A. Geochemical and geophysical applications of radioactive lead
isotopes. In: Biogeochemistry of lead in the Environment, Part A., J.
0. Nriagu (Ed.), Elsevier Scientific Publishers, Amsterdam,
Netherlands. Vol. 1A. (1978) 285-393.
Robbins, J. A., J. R. Krezoski and S. C. Mozley. Radioactivity in sediments
of the Great Lakes: postdepositional redistribution by deposit-feeding
organisms. Earth Planet. Sci. Lett. 36, (1977) 325-333 .
Krezoski, J. R., S. C. Mozley and J. A. Robbins. Influence of benthic
macroinvertebrates on mixing of profundal sediments in Lake Huron.
Limnol. Oceanogr. 23 (1978) 1011-1016.
Robbins, J. A., P. L. McCall, J. B. Fisher and J. R. Krezoski, Effect of
deposit feeders on migration of cesiura-137 in lake sediments. Earth
Planet. Sci. Lett. 42 (1979) 277-287.
Meyers, P. A., Takeuchi, N. and Robbins, J. A. Petroleum hydrocarbons in
sediments of Saginaw Bay, Lake Huron. Environ. Sci. Technol.
(submitted Aug. 1979).
Robbins, J. A. Aspects of the interaction between benthos and sediments of
the North American Great Lakes and effects of toxicant exposures. In
Proc. of the US-USSR Symposium on Theoretical Aspects of Aquatic
Toxicology, Borok, Jaroslavl, USSR, July 3-5, 1979.
309
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-80-080
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Sediments of Southern Lake Huron: Elemental
Composition and Accumulation Rates
5. REPORT DATE
August 1980 Issuing Date.
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
John A. Robbins
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Great Lakes Research Division
The University of Michigan
Ann Arbor, Michigan 48109
10. PROGRAM ELEMENT NO.
1BA769
11. CONTRACT/GRANT NO.
Grant R 803086
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Research Laboratory-Duluth
Office of Research and Development
U.S. Environmental Protection Agency
Duluth, Minnesota 55804
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/03
15. SUPPLEMENTARY NOTES
Project Officer:
Michael D. Mullin, ERL-Duluth, Grosse He, MI 48138
16. ABSTRACT
It is widely recognized that most metal contaminants in lakes are primarily
associated with particulate matter and are conveyed to underlying deposits in
association with fine-grained materials such as organic debris, hydroxides of iron,
and manganese or clay minerals. In the Great Lakes the fine-grained sediments and
associated contaminants are not deposited uniformly over the bottom but are
confined to "pockets" or depositional basins which are of more limited extent and
generally found in deeper areas of each lake. This report describes the composition
and rates of accumulation of metal contaminants in the depositional basins of
southern Lake Huron.
Results of this study include: (1) recognition of the role of sediment
mixing by benthic organisms in modifying metal contaminant and radioactivity
profiles, (2) estimates of the rates of accumulation of metal contaminants in these
depositional basins, (3) identification of which metals are contaminants and their
degree of surface enrichment, and (4) limited comparisons of accumulation rates
with lake loadings.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. cos AT I Field/Group
Sediments
Benthos
Metals
Lake Huron
Particulate matter
Depositional basins
Accumulation rates
Loading rates
08/H
18. DISTRIBUTION STATEMENT
Release to the public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
330
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
310
U.S. GOVERNMENT PRINTING OFFICE: 1980--657-165/0083
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