CHLORIDE BUDGET FOR THE GREAT LAKES:
A CURRENT ASSESSMENT
OOOR81004
By:
William C. Sonzogni
William Richardson
Paul Rodgers
Timothy J. Monteith
Great Lakes Environmental Planning Study (GLEPS)
Great Lakes Basin Commission, Ann Arbor, Michigan 48106
Contribution No. 39
June, 1981
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CHLORIDE BUDGET FOR THE GREAT LAKES:
A CURRENT ASSESSMENT
By:
William C. Sonzogni1
William Richardson2
Paul Rodgers^
Timothy J. Monteith3
Great Lakes Environmental Planning Study (GLEPS)
Great Lakes Basin Commission, Ann Arbor, Michigan 48106
Contribution No. 39
June, 1981
^Great Lakes Environmental Research Laboratory
National Oceanic and Atmospheric Administration
Ann Arbor, MI 48104
(GLERL Contribution No. 272)
2Large Lakes Research Station
'U.S. Environmental Protection Agency
Grosse Isle, MI 48138
Lakes Basin Commission
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ABSTRACT
*
Concentrations of chloride and other conservative ions in the Great
Lakes are of interest, not only as indicators of pollution, but also because
these ions may affect species diversity of algae and other aquatic orga-
nisms. As part of an evaluation of the current status of conservative ion;
in the lakes, a current cl ioride budget was developed and its implications
assessed. Chloride inputs to the lakes (in 106 MT/YR) increase in the order
of Superior (0.3), Michigan (0.9), Huron (1.1), Erie (3.7), and Ontario
(6.3). The Oswego River, draining into Lake Ontario, contributes more
chloride than any other U.S. tributary. Regarding specific sources,
discharges from industrial processes are probably the most significant.
Road salt contributes an important, but not necessarily predominant, portion
of the anthropogenic load to the lakes. Overall, chloride inputs-, espe-
cially industrial discharges, appear to have decreased in recent years.
Lake Erie in-lake chloride concentrations have, in fact, decreased
measurably compared to those in the early 1960's.
Based on a chloride model that treats the lakes as five completely
mixed systems in series, it is estimated that, if current loads are main-
tained, the average chloride concentrations in Lake Michigan should increase
over the long term from less than 8 mg/L to nearly 20 mg/L. Chloride con-
centrations in the other Great Lakes are predicted to remain relatively
stable. Based on analogies to other lakes where chloride levels have
increased, it is uncertain whether the expected rise in the chloride con-
centrations in Lake Michigan will result in a shift in phytoplankton toward
more nuisance species. It may well be that increased conservative ion
levels are a factor ecologically, but of less importance than other factors,
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such as nutrients. The response of the Great Lakes to the massive
phosphorus reduction program of the 1970's should provide further insight
into the relative importance of chloride and other conservative ions as
pollutants.
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INTRODUCTION
Chloride has long been used as a tracer of pollution (Beeton, 1965;
Upchurch, 1976), but has only recently been implicated as a pollutant itself
in the Great Lakes, the worlds largest freshwater resource. The concern
over chloride (and other conservative ions) stems from its possible role in
changing the species diversity ar J distribution of algae and other organisms
in the Great Lakes.
Concern over chloride is exemplified by a recent conference held to
help develop a five year federal plan for research and development in the
Great Lakes. Chloride discharges, which have increased markedly over the
last century, were identified as one of several major problems worthy of
special attention (Beeton et al., 1980).
In response to renewed interest in chloride, this paper summarizes
current information on chloride inputs to the Great Lakes from various sour-
ces. Chloride trends in the lakes are then evaluated with the aid of two
mathematical models. Finally, management implications of current and future
chloride inputs to the lakes are discussed. Particular attention is given
to Lake Michigan, especially with regard to modeling the response of lakes
to chloride inputs.
Chloride Sources
Chloride sources include land runoff, base flow (i.e., ground water
inputs), municipal and industrial effluents, the atmosphere and several
minor contributers. In the developed portion of the Great Lakes basin,
point sources and runoff from agricultural and urban land dominate chloride
sources, while in the undeveloped portion, which includes most of the
Superior and Huron watersheds and part of Michigan's basin, chloride inputs
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are mostly derived from natural weathering of chloride containing
minerals.
Because of its local availability (large underground deposits withir>
the basin provide an abundant supply of salt), sodium chloride is commonly
used for road deicing in the Great Lakes basin. Salt use has proliferated
in recent years as a "bare pavement policy" has been in force in many urban
areas. Highway runoff may enter tributaries directly or may enter tribu-
taries via storm sewers (separate or combined) and can result in chloride
concentrations as high as 10,000 mg/L (Schraufnagel, 1965).
One portion of the Great Lakes that has been acutely affected by road
salt runoff is Irondequoit Bay, a small embayment near Rochester, N.Y., that
is separated from Lake Ontario by a sandbar. Over the past 20 years road-
salt runoff to the bay has resulted in an increase in _the chloride level to
the point that the drinking water standard of 250 mg/L has been exceeded
(Bubeck et al., 1971). Further, a vertical density gradient has formed
which has impeded mixing of the bay, particularly during spring and fall
turnover. It is speculated that continued road salt buildup may eventually
cause the bay to become meromictic (Bannister and Bubeck, 1978). Although
Irondequoit Bay is a dramatic example of road salt pollution of a Great
Lakes embayment, it is perhaps a unique case due to the very limited mixing
between the bay and Lake Ontario proper.
The Pollution from Land Use Activities Reference Group (PLUARG, 1977)
estimated that about 2.8 x 10° metric tons of chloride are currently applied
to roads in the Great Lakes basin annually. However, due to (1) increasing
salt prices, (2) concern over salt induced corrosion, (3) local water quality
problems caused by salt runoff and (4) damage to terrestrial vegetation,
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the rate of salt application will probably decline (PLUARG 1977, 1978).
Importantly, the Pollution from Land Use Activities Reference Group Study
(PLUARG, 1978) concluded that, given the current and expected future use of
chloride for deicing, road salt pollution was more of a local problem than .1
Great Lakes problem.
Base Flow L
Ground water inputs to streams (i.e., base flow) are also a source of
chloride in tributaries. In some areas groundwater chloride concentrations
can be high, particularly in deeper bedrock deposits. Cummings (1980)
reported the results of a survey of the chemical characteristics of ground-
water deposits within Michigan and found that bedrock deposits had a mean
concentration of 71 mg/L while glacial (surface) deposits had a mean con-
centration of 11 mg/L. Ground water contributions to streams would likely
be from surface deposits, and thus high chloride levels in streams are not
generally the result of groundwater inputs (Sonzogni et al., 1978).
Point Sources
Municipal sewage effluent contains substantial amounts of chloride.
Conventional treatment processes do not remove chloride to an appreciable
extent. Typical chloride concentrations in municipal effluents of plants
draining into the Great Lakes range from 50 mg/L or less to over 160 mg/L.
Major sources of chloride received by treatment plants include human wastes,
garbage disposal wastes, water softening by-products, urban runoff (for com-
bined sewer systems) and industrial contributions. Humans contribute about
6 g of chloride per person per day to sewage (Metcalf and Eddy, 1972). Home
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water softening systems, where numerous, can be responsible for large
chloride inputs to wastewater (Schraufnagel, 1965).
Whereas most municipal waste treatment processes do not remove chloride,
chemical treatment practices may actually add chloride to effluents. Over
the last ten years phosphorus removal processes, largely in the form of
chemical precipitation have been implemente at a large number of municipal
J
sewage treatment plants in the Great Lakes basin. Of the chemicals added to
wastewater for phosphorus removal, ferric chloride is most frequently used
(Monteith et al., 1980). Since chloride is a by-product of ferric chloride
use, this phosphorus removal practice appears to be adding to the chloride
content of discharge water. For example, Kenaga (1978) noted that the
chloride concentration in Lansing, Michigan, wastewater effluent increased
about 10 mg/L as a result of phosphorus removal. Consequently, phosphorus
removal may be contributing measurably to chloride inputs.
Discharges from industrial processes are probably the most significant
of all chloride sources to the Great Lakes. Chemical, steel and food
packaging industries are major sources. A number of industries have located
in the basin not only because of the abundance of water, but also because of
the large salt deposits found in different parts of the basin. For example,
Ownbey and Kee (1967) reported that, at the time of their work, over half of
the chloride load to 'the Detroit River could be attributed to industrial
sources. Many chemical firms are, in fact, situated in the Detroit-Windsor
area in order to use the inexpensive salt brine for the production of soda
ash and other alkali products (Ownbey and Kee, 1967). In fact, Ownbey and
Kee noted that Lake Erie's chloride level first began to increase at the
turn of the century when these industries became established.
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The influence of industrial sources of chloride is further illustrated
by discharges to Onondaga Lake, a lake which drains into Lake Ontario via
the Oswego River. Onondaga Lake has extremely high chloride concentrations
(seasonal averages have exceeded 1500 mg/L), largely as a result of
discharges from a chlor-alkali manufacturer (Effler et al., 1981). As will
be discussed, the outflow from Onondaga Lake is a ' ajor reason for the
extremely high chloride load to Lake Ontario from "the Oswego River.
Atmospheric Sources
Chloride also enters the Great Lakes via rainfall. Atmospheric
chloride inputs can be an appreciable part of the total load, particularly
for Lakes Superior and Michigan which have large surface areas. The salt
content of rainfall is largely derived from sea spray (Tiffany et al., 1969).
Other means by which chloride could enter the atmosphere are by wind erosion
9
of soil and industrial emissions. The significance of these sources is
not known, however.
Minor Sources
Some minor sources of chloride to the Great Lakes include direct
groundwater inputs, shoreline erosion and vessel discharges. The quantity
of groundwater which directly flows into the lakes is not known, but is
believed to be a small part of the water budget (Quinn, 1978).
Consequently, chloride load from this source is assumed to be negligible.
Regarding shoreline erosion, which can contribute a large amount of
particulate material to the Great Lakes (Monteith and Sonzogni, 1976),
little information exists on chloride inputs. The Upper Lakes Reference
Group (1977) did estimate a chloride load of about 800 metric tons per year
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from shoreline erosion, however. Since this is a small part of the total
load (as will be shown), it will be ignored as a source.
Finally, the Upper Lakes Reference Group (1977) estimated that Lake
Superior received a surprisingly high chloride load, about 11,000 metric tons
per year, from vessel discharges (mostly salt water ballast). However, this
source is likely only to be significant relative ts other sources in Lake
j
Superior, Lake Superior having the lowest total chloride load of any of the
lakes. Vessel discharges are not considered further here as an important
source.
Chloride Loads
Total Loads
Chloride loads to each of the Great Lakes are summarized in Table 1.
These loads represent data primarily from the mid to late 1970's.
U.S. total tributary (river mouth) loads are the average annual load
over the water years 1975 through 1978, except for Lake Erie, where data
were not available for 1978. and Lake Michigan, where the 1975 load was
excluded as a major shift in industrial chloride discharges occurred during
this year. Calculations of chloride from gaged tributaries were made using
the ratio estimator method (Great Lakes Water Quality Board, 1976; Sonzogni
et al., 1978). This method accounts for the importance of flow variability
in estimating annual loads. Chloride loads from ungaged and/or unmonitored
tributaries were estimated as reported in Sonzogni et al. (1978). Primary
sources of data included state surveillance programs, reports of the U.S.
Geological Survey, the Upper Lakes Reference Group Study of the Inter-
national Joint Commission, the U.S. Army Corps of Engineers Lake Erie
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Table 1
Summary of Estimated
Chloride Loads to the Great Lakes
During the 1970's (mt/yr)
Lake
Superior
U.S.
Canada
Lake
Michigan
Lake
Huron
U.S.
Canada
Lake
Erie
U.S.
Canada
Lake
Ontario
U.S.
Canada
Total
Tributary
195,900
89,500
106,400
598,000
583,400
315,800
267,600
741,100
598,100
143,000
1,725,300
1,365,800
359,500
Direct
Point
Sources
32,600
3,200
29,400
220,400
23,200
15,000
8,200
170,000
168,000
2,000
104,700
23,300
81,400
Input
jj from Upstream
Atmospheric Lake(s)
55,000
82,900
48,700 477,700
20,100 2,759,000
14,000 4,448,100
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Wastewater Management Study and other university studies and special state
or federal projects. A more detailed description of the load calculation
methodology and sources of data may be found in Sonzogni et al. (1978) and
Sullivan et al. (1980).
U.S. direct point sources inputs were obtained or calculated from
various sources. Direct inputs to Lake Superior and Lake luron were based
»*?
on data presented by the Upper Lakes Reference Group (1977). While this
data represents information from the early to mid 1970's and thus may not
reflect current conditions, inputs (with the possible exception of the
direct point source chloride input to Lake Superior from Canada) are rela-
tively small. Direct point source inputs to Lake Michigan were based on
recent industrial loads supplied by the U.S. Environmental Protection
Agency's Great Lakes National Program Office (H. Zar, U.S. EPA Region V,
personal communication, 1980) and direct municipal inputs calculated from
the total annual flow (average of 1975 and 1976 flows) discharged from all
direct municipal dischargers and an assumed chloride effluent concentration
of 160 mg/L. The use of 160 mg/L was based on the average effluent chloride
concentration for Lake Erie basin municipal treatment plants as determined
by the U.S. Army Corps of Engineer's Lake Erie Wastewater Management Study
(reported in Sonzogni et al., 1978). Municipal direct point source inputs
to Lake Michigan turned out to be about equal to industrial direct inputs.
U.S. direct point source loads to Lakes Erie and Ontario were estimated
similarly, except that no data on direct industrial chloride inputs were
available. While these industrial inputs are not likely to be a major com-
ponent of the total chloride budget to these lakes, there are a few indus-
trial operations (e.g., steel plants) on the lake that could contribute
substantial amounts of chloride and thus should be considered in future work.
10
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Canadian tributary and direct point source loads to Lakes Superior and
Huron are based on 1973 through 1975 data as reported by the Upper Lakes
Reference Group (1977). Canadian total tributary and direct point source
loads to Erie and Ontario are from Fraser and Wilson (1981) and Casey and
Salbach (1974), respectively.
Atmospheric chloride inputs to each of the lakes were "* ised on Andren
* /
s»
et al. (1977). Inputs to Lake Huron from upstream lakes (Lalces Michigan and
Superior) are from the Upper Lakes Reference Group (1977). The upstream lake
contribution to Lake Erie is based on the average annual Detroit River load
over the period 1975 through 1978 as supplied by the Michigan Department of
Natural Resources (J. Hartig, Michigan Dept. of Natural Resources, personal
.communication, 1981). The upstream (Niagara River) input to Lake Ontario is
the average of the 1975, 1976 and 1977 annual mean load reported by Chan
(1979).
Inputs from Individual U.S. Tributaries
Chloride loads to each of the Great Lakes from selected major tribu-
taries are presented in Table 2 for water years 1975 through 1978. Also
included in these tables are the river mouth tributary flows. These data
illustrate that large changes in year-to-year chloride loads are often clo-
sely related to changes in flow. Finally, the tables contain extrapolated
total loads and flows for the whole basins. The methodology used for the
load determinations were previously described. Similar information on other
U.S. tributaries can be found in Sullivan et al. (1980).
Lake Superior. The largest U.S. contributor is the St. Louis River,
which also has the largest flow. However, the load is high relative to the
flow, indicating the likelihood of major industrial and municipal chloride
11
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Table 2
Annual Mean Chloride Loads and Flows of Selected U.S. Great Lakes
Tributaries for Water Years 1975 through 1976
Chloride Load (mt/yr) Flow at Mouth (nrVs)
River 1975 1976 1977 1978 1975 1976 1977 >) 1978
Superior
St. Louis
Nemadji
Ontonagon
Carp
Mineral
Total,
Tributary3
25468
812
3697
1362
21243
92680
14351
486
3381
1764
81600
15617
810
2435
922
80220
25044
1125
4075
-
104060
84.5
12.9
40.5
3.6
450.3
47.7
10.3
40.4
4.0
379.5
29.9
7.7
29.0
2.3
271.9
112.7
15.1
41.9
-
566.4
Michigan
Me nominee
Fox
Menomonee
St. Joseph
Kalamazoo
Grand
Manistee
Manistique
Total
Tributary3
3210
51200
10300
78300
60200
171000
163000
4070
775000
3970
55700
10800
86800
57000
150000
85700
3900
711600
5250
36100
5250
68300
48600
95600
74900
2980
490200
7800
53200
-
73100
57000
116000
71800
4200
590300
100.8
118.4
3.3
123.0
68.4
162.4
60.8
61.2
1190.7
95.6
124.2
3.0
143.4
67.1
185.4
66.2
58.3
1276.0
58.8
58.1
1.3
96.1
44.1
73.2
53.3
48.0
732.0
94.6
121.6
3.9
135.9
52.8
102.5
55.5
76.0
1108.4
Huron
Pine
Au Sable
Au Gres
Saginaw
Total
Tributary3
1100 467 510 689
9926 10047 6900 7839
2974 3797 2465 3960
295140 320890 156433 202946
377400 422100 200600 263800 444.6 530.3 232.1 333.6
11.5
59.4
3.5
165.5
9.5
59.5
5.1
216.4
7.7
46.3
1.8
63.0
10.5
48.8
4.3
109.2
12
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Table 2 (Continued)
Chloride Load (mt/yr) Flow at Mouth (m^/s)
River 1975 1976 1977 1978 1975 1976 1977 1978
Erie
Clinton
Rouge
Maumee
Sandusky
Vermillion
Cuyahoga
Chagrin
Total
Tributary3
Ontario
Genesee
Oswego
Black
Oswagatchie
Raquette
Total
Tributary3
17724
273018
46846
4715
110964
21672
44549
161000
25800
16149
132639
20944
56100
73700
123000
29400
5400
71000
15900
17.6
157.0
39.8
8.8
50.5
14.4
26.7
165.6
29.8
7.1
39.2
855600 696900 592200
13.
12,
100,
24,
7.2
28.3
12.5 10.1
608.3 615.0 422.9
129819 129359 141060 213370 95.1 114.2 94.1
1057788 1386606 965441 1160764 215.7 312.4 214.5
7548 8606 10050 8537 137.0 194.1 161.9
4834 7348 5739 5382 75.2 125.5 100.1
2481 3308 3106 4660 62.8 95.0 75.4
126.6
305.3
168.8
112.6
91.1
1197900 1607800 1166000 1489200 616.8 873.0 673.4 843.5
alncludea contributions from all U.S. tributaries, not just those listed;
see Sonzogni et al. (1978) and Sullivan et al. (1980) for details.
13
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contributions. The Carp River, which drains a portion of the upper penin-
sula of Michigan, also delivers a high chloride load relative to its flow.
The Carp River receives considerable municipal inputs. Finally, the aptly
named Mineral River delivers an extremely large chloride load relative to
its flow. The large chloride load is apparently caused by the discharge of
brine to the river from local mining operations (Sonzogni et al., 1978).
i
*t'
Lake Michigan. The largest single contributer of chloride was the **
Grand River, which drains into the eastern part of the lake. The Grand is
also the largest (in terms of flow) of the Lake Michigan tributaries. Note
that the Menomonee River, which drains a highly urbanized area within
metropolitan Milwaukee, contributes a large load relative to its flow (Table
2). Road salt may have been a major contributer to this load. The Manistee
River, which drains into eastern Lake Michigan, also contributes a large
amount of chloride relative to its flow. Discharges to the river from salt
mining operations account for the high load. The 1975 chloride load from
the Manistee was particularly high relative to 1976, 1977 and 1978.
Apparently, the reduced annual loads following 1975 reflect abatement of
some industrial chloride discharges to the river. Notice that the major
tributaries draining into the lower two-third of Michigan's eastern basin
namely, the St. Joseph, Kalamazoo, Grand, Muskegon and Manistee Rivers
contribute a large proportion of the total tributary chloride load to the
lake.
Lake Huron. Most of the U.S. tributary inputs to Lake Huron is deli-
vered to Saginaw Bay. The Saginaw River is the principal contributor to
Saginaw Bay. The Au Gres River (which also drains into Saginaw Bay) also
contributes a large load relative to its flow. High chloride loads to
14
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Saginaw Bay reflect the influence of municipal and industrial sources. Most
(over 90 percent) of the total U.S. wastewater flow to Lake Huron tribu-
taries is delivered to streams draining into Saginaw Bay. Chemical
industries and brine wells are also important sources of chloride to Sagint.,
Bay.
Lake Erie. In almost all cases, U.S. tributary chloride loads to Lake
Erie tend to be high relative to flows (compared to tributaries with less
developed watersheds). The Mauraee River, the second largest U.S. tributary
to the Great Lakes, ranks second behind Lake Ontario's Oswego River as the
largest contributer (among tributaries) of chloride to the Great Lakes.
Steel and manufacturing, as well as chemical industries, contribute to high
chloride loads to streams draining the Detroit metropolitan area, such as
the Clinton and Rouge Rivers. The Cuyahoga River, which drains the
Cleveland.area, also contributes a high chloride load relative to its flow.
Overall, however, the largest input to Lake Erie, as seen from Table 1, is
the input from the channel connecting it with Lake Huron, i.e., the Detroit
River.
Lake Ontario. The tributary chloride load to Lake Ontario is dominated
by the Oswego River (Table 2), the largest contributer of chloride of all
the U.S. tributaries. While the Oswego has the largest historical annual
mean flow of any U.S. tributary, its chloride load is also high relative to
its flow. As discussed previously, a chlor-alkali plant on Onondaga Lake,
which drains into the Oswego, is a major source of chloride to the Oswego.
Overall, about 50 percent of the Oswego's chloride load has been attributed
to point sources (Sonzogni et al., 1978). Despite the importance of the
15
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Oswego as a chloride source, the largest overall input to Lake Ontario is
the flow from the upper lakes through the Niagara River.
Deicing Salt Useage Versus Loads
While it is not possible to directly assess the amount of road salt
that reaches the Great Lakes, some insight on the important of road salts
can be obtained by comparing application rates with the total chloride loads
given in Table 3. Based on PLUARG (1977), the amount of road salt applied
annually to basins of Superior, Michigan, Huron, Erie and Ontario total
88,000, 595,000, 370,000, 696,000, and 1,046,000 metric tons, respectively.
Accordingly, even if all applied reached the lakes (which is not the case),
road salt would account- for less than 35 percent of the load for all lakes
except Michigan. In the case of Lake Michigan, the higher ratio of road
salt applied to total load is perhaps the result of an overestimate of the
road salt applied. Apparently, in determining salt useage for Lake
Michigan, PLUARG (1977) estimates were made on a county basis. However,
because large portions of counties adjacent to southern Lake Michigan (these
counties are heavily populated and presumedly have high salt useage) do not
drain into the lake, salt useage in the Michigan drainage basin may have
been overestimated.
Thus, it appears that road salt contributes a significant, but not
necessarily a predominant, portion of the anthropogenic chloride load to
Great Lakes. This conclusion is consistent with the results of a study of
chloride inputs from the City of Buffalo (Meredith and Rumer, 1976), which
indicated that road salts were the source of 36 percent of the chloride
leaving Buffalo's combined sewer system.
16
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Table 3
Comparison of Estimates of Chloride Loads (metric tons/year)
to the Great Lakes
Lake
Estimated Load for 1960
(O'Connor & Mueller, 1970)
Estimated Load for
the mid to late 1970'i
(Present Study)
Superior
Michigan
Huron
Erie
Ontario
230,000
927,000
1,417,000
4,619,000
5,944,000
283,500
901,300
1,133,000
3,690,200
6,292,100
17
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Comparison of Present Chloride Load Estimates With Previous Estimates
In their now classic water quality modeling paper, O'Connor and Mueller
(1970) estimated 1960 chloride loads for the entire Great Lakes system.
Their estimated chloride loads .to each of the Great Lakes are compared with
the loads from this study (mid to late 1970's) in Table 3. O'Connor and
Mueller's chloride load includes an "other sources" category, which was
determined by difference (so that inputs balanced storage and outputs).
These "other sources" comprised 22, 23, 48, 17 and 21 percent of O'Connor
and Mueller's loads presented in Table 3 for Lakes Superior, Michigan,
Huron, Erie and Ontario, respectively. Thus, were it not__£or_ their "other
sources," O'Connor and Mueller's loads would be considerably less than those
of this study for all lakes except Erie.
Ownbey and Kee (1976) presented an assessment of chloride loads from
individual tributaries to Lake Erie. Their results are compared to estima-
tes from this study in Table 4. Note that in most cases current estimates
are greater than Ownbey and Kee's.
The estimates of both O'Connor and Muller (1970) and Ownbey and Kee
(1967) were necessarily based on scant data. In many cases, loads were
derived from unit area loads or per capita inputs rather than actual
measurements. Loads from the present study are based on better information
and likely are more accurate. For example, loads to Lake Erie were based on
extensive monitoring of streams, especially during the high flow events when
a large portion of the total load may enter the lakes, as part of the Lake
Erie Wastewater Management Study (U.S. Army Corps of Engineers, 1979).
18
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Table 4
of
to Lake Erie
_ ""
'-
^^^^^
Detroit River
Hur on
Raisin
Moumee
Portage
Sandusky
Black
Rocky
Cuyahoga
Chagrin
Grant " «>hio>
Ash tabula
Conneant
U.S. Direct Municipal
__
__
Ownbey and Kee (1967)
._ .
2,996,400
14,982
20,884
118,040
5,448
29,510
7,264
19,068
72,640
4,540
635,600
9,080
2,724
Discharges 49,940
__
Present Study*
^
2,759,000
25,650
29,687
185,673
11,542
34,015
16,737
10,800
104,701
19,339
4,553
4,498
143,000
centration of 160 mg/L chloride.
19
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Long-Tenn Trends in Chloride Loads and In-Lake Concentrations
While not obvious from the comparison of current loads with 1960 loads
(Table 3), there is evidence that some chloride inputs have decreased, espe-
cially industrial inputs. As early as 1972, considerable progress was made
in controlling certain Michigan point sources of chloride. For instance,
the U.S. Environmental Protection Agency (1972) reported that a 40 percent
reduction in the chloride discharge of several major industries would occur
between 1971 and January 1973. As mentioned previously, a significant
decrease in the chloride load of Michigan's Manistee River, which received
chloride from major salt producers, is attributed to abatement measures
(Little, G., Michigan Department of Natural Resources, personal
communication). Perhaps the best example of decreasing chloride loads is
the Detroit River contribution to Lake Erie. Figure 1 shows how the
chloride load has steadily decreased since the late 1960's. This decrease
is most likely the result of reduced industrial chloride discharges.
Further, comparing the concentration of chlorides at the head of the Detroit
River with those at the mouth (Table 5) suggests that the reduced Detroit
River load is the result of decreased inputs from the Detroit-Windsor
complex. While the concentration of chloride at the head of the Detroit
River has changed little over the period of record, the concentration at
the Detroit River mouth has progressively decreased. This indicates that
the observed decrease is probably the result of reduced chloride discharges,
most likely from industrial sources from the Detroit-Windsor area.
Table 6 shows typical average concentrations (open lake) that were
measured during the early 1900's, the 1960's and 1970's. While con-
centrations have apparently increased significantly since 1900, the changes
20
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Table 5
Comparison of Annual Mean Chloride Concentrations (mg/L)
at the Head and Mouth of the Detroit River3
Water
Year
1967
1968
1969
1970
1971
1972
1973
1974
1975
Head
9
10
11
10
9
9
. 9
9
9
Mouth
-
23
18
18
15
17
14
16
15
aData from Great Lakes Water Quality Board (1976)
21
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Table 6
Changes in Great Lakes Chloride Concentrations (mg/L)
(values from Beeton, 1969, except as noted)
Lake Superior
Lake Michigan
Lake Huron
Lake Erie
Lake Ontario
1900' s
1.2
3
5
11
10
1960 's CurrcuL
1 la
6-7 7.7b
7 5.5a
26C 20d
27xr~ 27. 7e
aUpper Lakes Reference Group (1977)
bRockwell et al (1981)
and Chawla (1969)
^Rockwell, D.C., U.S. EPA, Great Lakes National Program Office, Chicago
personal communication, 1981)
eSimons (1979)
22
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between the 1960's, when chloride inputs from industrial sources were likely
at their peak, and the present are not as obvious. In fact, current con-
centrations of chloride in Lake Erie appear to be less than reported for the
I960's. This may be an indication of decreased chloride loads to Lake Erie.
Further, because Lake Erie is much shallower than the other lakes it flushes
more quickly. Hence, a decrease in chloride concentration as a result of
decreased chloride loads would be noticed in Lake Erie much faster than in
the other Great Lakes.
Accordingly, it would appear that, at least in some locations,
industrial chloride inputs are decreasing. On the other hand, new
industrial operations, such as new plants or new treatment technologies,
could increase inputs. For example, a new wastewater treatment plant for
the steel industry, located near Gary, Indiana, is expected to increase its
chloride input to Lake Michigan by 49,800 metric tons per year (University
of Michigan Research News, 1978). Further, as mentioned previously, munici-
palities may be discharging more chloride than previously with the use of
metal salts for phosphorus removal. More information is needed on indivi-
dual point source contributions to evaluate overall trends of chloride
inputs to the Great Lakes.
Chloride Model of the Great Lakes
Several investigators have presented models relating chloride inputs to
chloride concentrations in the Great Lakes. The chloride model of O'Connor
and Mueller (1970) is particularly noteworthy, as it considered the Great
Lakes as an integrated system. Snow (1974) applied O'Connor and Mueller's
approach specifically to Lake Michigan. Meredith et al. (1974) and
23
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Richardson (1974) applied the same basic model approach to Lake Erie and
Saginaw Bay, respectively. Other modeling attempts similar to O'Connor and
Mueller's include those of Rainy (1967), Dingman and Johnson (1971), and
Butler et al. (1974).
A chloride simulation (CS) model similar to that developed by O'Connor
and Mueller (1970) is used here to reevaluate predictions of future chloride
concentrations using current loading information. Importantly, the model
considers the effect of changes to one lake on another by treating the lakes
as five completely mixed systems in series. The model is used to examine
Lake Michigan in detail because of current concern over the effects of
chlorides and other dissolved solids in the lake.
Model Formulation
The CS model is based on a simple chloride mass balance which reflects
the conservative behavior of chloride. The change in chloride concentration
as a function of time is thus represented as the sum of inputs minus the
outputs, expressed mathematically as:
V -j| - ZW - QC (1)
where,
C « in-lake chloride concentration
V » lake volume
EW » sum of all chloride loads, including those from upstream
lakes
Q » flow out of the lake
t - time
24
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Equation 1 can be solved analytically, yielding:
-St.
C(r) - SL (l-e M
^^t; " TT ^i e ;
where,
C(t) « Chloride concentration at time t
Co Initial chloride concentration, when t = 0
Equation (2) also shows that following a change in the chloride loading,
equilibrium or steady state conditions are approached exponentially. At
EW
steady-state (t * <»), C - ^ . That is, at steady-state the in-lake con-
centration equals the average concentration of the inflow. Approximately
95% of the steady-state concentration is obtained within three hydraulic
V
residence "times, the hydraulic residence time defined as Q- For detail on
basic model formulation, including elaboration on treating the lakes in
series, see O'Connor and Mueller (1970) and Chapra and Sonzogni (1979).
Model Inputs
Chloride inputs for the CS model were those summarized in Table 3. For
lake volumes and flows, values reported in O'Connor and Mueller (1970) were
used except in the case of Lake Michigan where data summarized in Rodgers
and Salisbury (1981) was used. Lake Michigan hydrology is complicated by
the difficulty of measuring flows out through the Straits of Mackinac.
Consequently, outflows from Lake Michigan must be calculated indirectly
using a water budget procedure (Quinn, 1977).
Table 7.compares water budgets from three sources, including the Rodgers
and Salisbury (1981) budget used here. The tributary discharge in Rodgers
25
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Table 7
Water Budgets for Lake Michigan
(m3/7r)
Tributary Discharge
Net Precipitation
(Preceiptation-Evaporation)
Infiltration
Storage
0' Conner
and
Mueller
(1970) Quinn (1977)a
34.8 x 109 33.0 x 109
14.3 x 109 6.3 x 109
_
0 0.4 x 109
Rodgers
and
Salisbury
(1981)
32.3 x 109
12.5 x 109
0.4 x lo'
0
Outflow through Chicago 2.8 x 10'
Diversion Canal
c
Outflow through 46.3 x 10"
Straits of -Mackinaw
Volume (km3) 4877
Water Residence Time (yrs) 99
2.9 x ID'
2.9 x 10'
36.0 x 109(70.8xl09b) 42.3 x 109
4915
126 (67°)
4976
110
aAverage over 1950-1966
"Assumes return flow during stratified period
26
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and Salisbury is based on long-term historical flows recently reported by
Sonzogni et al. (1979) and Sullivan et al. (1980).
Note in Table 7 that Quinn (1977) reports two possible hydraulic resi-
dence times. The shorter estimate, 67 years, incorporates a return flow
through the straits during summer stratification (based on limited measure
ments of currents in the straits). The inclusion of the deep layer return
flow when calculating the hydraulic residence time or as a source of loading
presupposes that these waters are completely mixed throughout Lake Michigan.
There is some evidence that this is not case, and that the return flow
creates only a localized cell of mixing. For instance, Moll et al. (1976),
using cluster analysis of chemical and biological parameters, were able to
identify Lake Michigan waters in a plume extending into Lake Huron, but Lake
Huron waters could not be located west of Bois Blanc Island (Lake Huron).
Chloride data from Lake Michigan during 1962-63 and 1976, as reported in
Rockwell et al. (1980), indicates a sharp gradient in the area adjacent to
the straits as compared to the rest of Lake Michigan. Consequently,
%
hydraulic residence times on the order of 100 years appear to be most repre-
sentative for chloride modeling purposes.
Model Results
Figure 2 depicts the chloride concentrations changes in each of the
Great Lakes will change over time given that current loads to the Great
Lakes System (Table 1) remain the same. Projected long-term steady-state
concentrations range from about 4 mg/L in Lake Superior to about 30 mg/L in
Lake Ontario. The greatest chloride concentration change is expected to
occur in Lake Michigan, where the current level of 7.7 mg/L is projected to
rise to nearly 20 mg/L over the next 300 years.
27
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Figure 2 also indicates a relatively small rise of chloride in Lake
Erie. This increase is mostly in response to the gradual build-up of
chloride in the upper lakes, which drain into Lake Erie. The initial dip in
concentration in Lake Ontario in Figure 2 reflects a lagged response to
changes in chloride concentrations in Lake Erie. Both Lakes Erie and
Ontario are presently close to being in equilibrium with their loads, and in
fact the present Lake Ontario chloride concentration appears to still be
equilibrating to decreasing Lake Erie chloride concentrations during the
recent past. Thus, assuming current loads to the system remain the same,
chloride in the lower lakes will increase slightly as a result of the
buildup of chloride in the upper lakes according to the CS model.
Table 8 shows the reductions in external chloride loads that would be"
needed to maintain current chloride levels in the lakes (initial,conditions
in Figure 2). Reductions assume that upstream lakes maintain current con-
ditions. For instance, to maintain a concentration of 5.5 mg/L, Lake Huron
would require a 32 percent reduction in its external chloride load provided
Lake Michigan and Lake Superior remained at their present concentrations of
1.0 and 7.7 mg/L, respectively. Note that to maintain present levels in
Lake Michigan, a large reduction in the current load will be required.
Also, while Table 8 shows a large percent reduction in the chloride load to
Lake Superior would be required to maintain the very low current chloride
concentration of 1 mg/L, the actual load reduction required is relatively
small.
Examining Lake Michigan in more detail, Figure 3 illustrates a range of
possible equilibrium chloride concentrations bounded by upper and lower esti-
mates of the current chloride load and hydraulic residence times. A + 25
28
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Table 8
Reduction in External Chloride Load Required
to Maintain Current Concentrations
% of present MT/YR
Lake External Load Reduction
Superior 77 218,400
Michigan 60 540,800
Huron 32 209,700
Erie 8 226,200
Ontario 0 0
29
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percent range for the chloride load was chosen, reflecting an approximate
error bounds in chloride loading estimates. Ranges in hydraulic residence
times were deduced from Table 7, and reflect the uncertainty in outflow from
Lake Michigan.
Notice in Figure 3 that to achieve an equilibrium concentration belov?
the current concentration, the current load to Lake Michigan would have to
be reduced by a factor of 2 or more even under the most optimistic
(shortest) hydraulic residence time. From a Lake Michigan management
perspective, then, it is clear that Lake Michigan chloride concentrations
are likely to continue to build-up, even under conservative estimates of
current loading and hydraulic residence times. Subsequently, Lake
Michigan's chloride build-up will affect Lakes Huron, Erie and Ontario.
A relevant question is whether the response time to a Lake Michigan
load reduction could be shortened. For example, what chloride load reduc-
tion to Lake Michigan could achieve a desired in-lake chloride concentration
in 30 years as opposed to the normal response time of 300 years. In order
to reduce the time required to reach a target concentration, it can be shown
from a reformulation of equation 2 that the chloride load would have to be
reduced to a greater extent than if the time of response was not a cri-
terion. In other words, to achieve a 50 percent reduction in the chloride
concentration of Lake Michigan at an accelerated pace, the load reduction
would necessarily have to be greater than 50 percent until the target con-
centration was obtained. Accordingly, in lakes with long hydraulic resi-
dence times such as the Great Lakes, the long-term consequence of allowing
conservative substances to exceed prudent limits should be realized in
advance and long-term planning made accordingly. Managers should therefore
30
-------
realize that recovery periods for conservative ions will be more prolonged
or require accentuated levels of treatment as compared to nutrients which
are subject to losses other than natural flushing (i.e., sedimentation).
Management Considerations
The CS model results (Figure 2) indicate that the chloride con-
centration in Lake Michigan, and to a lesser extent Lake Huron, may be
expected to increase most dramatically in the future. For Lake Michigan,
concentrations are expected to increase to about 20 mg/L, an increase of
greater than 6 fold compared to concentrations at the turn of the century.
A salient management question, then, is whether the Lake Michigan ecosystem
will be seriously degraded by the chloride change.
Storemer (1978) provides evidence that the less desirable phytoplankton
species that have invaded the Great Lakes tend to come, virtually exclusi-
vely, from saline waters. The filamentous blue green alga, Stephanodiscus,
which has been known to decrease filtration time at water treatment plants
as well as cause taste and odor problems, has already been observed to be
increasingly more prevalent in southern Lake Michigan (where industrial
chloride discharges are high). The rapid spread through the Great Lakes of
the marine alga, Bangia atropurpurea, is believed to be linked to increased
chloride levels or increases in dissolved solids. Eureytemora affinis, a
brackish water copepod, is also now established in the Great Lakes.
Stoermer (as noted in Great Lakes Water Quality Board, 1977) has further
hypothesized that a biological breakpoint between 7.5 and 10 mg/L chloride
may exist for Lake Michigan. Beyond this concentration, a major shift in
phytoplankton toward nuisance taste and odor causing blue green algae could
occur.
31
-------
There is also some evidence that, in general, productivity increases
with increases in chloride or total dissolved solids (Rawson, 1951, 1960;
Northcote and Larkin, 1956; Kerekes and Nursall, 1966; Seenayga, 1973).
Robertson and Powers (1967) reported that total organic matter in the Great
Lakes increased in the order of Superior, Huron, Michigan, Erie and Ontario*
Average chloride concentrations also increase in the same order. Stoermer
(1978) has thus questioned whether nutrient control alone will provide
desired improvements (less eutrophic) in Great Lakes water quality, which is
often measured in terms of the assembleges of organisms. However, as
discussed by Sorrenson et al. (1978) and Stoermer (1978), the effects of
chlorides or other dissolved solids are subtle, are often confounded by
other factors (e.g., nutrient enrichment) and are difficult to directly eva-
luate experimentally.
Despite the difficulty in directly assessing whether increasing
chloride levels will seriously impair Lake Michigan, some inferences may be
obtained from other lakes with higher chloride levels. For example, Lake
Ontario's average chloride concentration currently is about four times
higher than found in Lake Michigan. Lake Ontario's Irondequoit Bay has
chloride concentrations several times Lake Ontario's and Onondaga Lake has
even higher chloride levels.
Undoubtedly, the Lake Ontario ecosystem has been severely disturbed.
Stoermer et al. (1975) reported that Lake Ontario's phytoplankton assemblage
is dominated by species indicative of degraded water quality, including spe-
cies of blue-green algae that are potential nuisances. They note that many
of the taxa commonly found in the offshore waters of the more oligotrophic
upper Great Lakes are absent or rare in Lake Ontario. Finally, they report
32
-------
a shrinking abundance of halophilic species in the lake, such that the domi-
nant and sub-dominant taxa are more commonly found in brackish and saline
inland waters.
Although these changes indicate degraded water quality, it is not clear
what impact this has had on uses of the lake. Little information exists =» *,
the economic impacts of these changes or how human perception of the quality
of water has changes. Lake Ontario is supporting a growing sport fishery
and is still a major source or drinking water. Thus, while Lake Ontario
has undergone extensive ecological changes, the ecosystem still serves many
uses. Accordingly, it is difficult to quantify the practical impact that
would result should some of the changes observed in Lake Ontario become
manifested in Lake Michigan.
If an effect of chloride or increased dissolved solids were to be
obvious, it should be so in Onondaga Lake and Irondequoit Bay, where
chloride levels have gotten "extremely high. Interestingly, the high sali-
nity of Onondaga Lake has not resulted in significant amounts of non-fresh
water organisms at any trophic level (Effler et al., 1981). Irondequoit Bay
was reported to have phytoplankton species and numbers similar to Onondaga
Lake. Both of these waters are productive, however, and receive large
nutrient inputs.
In summary, analogies to other lakes where chloride levels have
increased provides conflicting inferences as to the future of Lake Michigan.
It may well be that the influence of conservative ions is secondary to
nutrient enrichment. For example, while higher conservative ion levels
may provide a competitive advantage for halophilic species, they may not
flourish without abundant nutrient supplies. In other words, increased
33
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conservative ion levels may be a factor ecologically, but of lesser impor-
tance than other factors such as nutrients.
The occurrence of halophilic organisms in the Great Lakes as opposed to
other inland lakes with high chloride levels may also be related to the
direct linkage of the Great Lakes with the sea. With the construction of
St. Lawrence Seaway system, salt water organisms have had access to all the
Great Lakes. The invasion of non-native fish in this manner (for example,
the sea lamprey and alewife) is well documented. Further, ocean going
vessels using the Great Lakes often dump salt water ballast into the lakes.
The uncertainty of the effect of conservative ions exemplifies the
need to carefully monitor how the Great Lakes respond to the massive munici-
pal point source phosphorus control program enacted during the 1970's. As
discussed in Heidtke et al. (1979), future phosphorus loads to the Great
Lakes from municipal point sources should be reduced over 50 percent (750
metric tons/year) compared to mid-1970 levels. The extent to which the
lakes actually respond to this reduction should provide valuable insight
into the importance of conservative ions as a pollutant and the potential
need for controlling chloride inputs to the Great Lakes, especially Lake
Michigan.
34
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42
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List of Figures
Figure 1. Annual mean chloride loads (and their standard deviation) to
Lake Erie from the Detroit River.
Figure 2. Projections of chloride concentrations over time in response
to current external loads.
Figure 3. Lake Michigan chloride load versus equilibrium chloride
concentration for a range of possible hydraulic detention
times.
43
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Figure 2. Projections of'Chloride Concentration Over Time in
Response to Current External Loads.
0 50 100 150 200 250 300 350 400 450 500
(1975) (2075) (2175) (2275) (2375) (2475)
Time (years)
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