STRATIGRAPHIC EVIDENCE OF HUMAN DISTURBANCE
IN SOME CHESAPEAKE BAY TRIBUTARIES
Final Report
by
Grace S. Brush and Frank W, Davis
Department of Geography and Environmental Engineering
The Johns Hopkins University
Baltimore, Maryland 21218
Grant Numbers R 805 962 and
806 680 01
Project Officer
Dr. David Flemer
Chesapeake Bay Program
U. S. Environmental Protection Agency
2083 West Street
Annapolis, Maryland 21401
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STRATIGRAPHIC EVIDENCE OF HUMAN DISTURBANCE
IN SOME CHESAPEAKE BAY TRIBUTARIES
Final Report
by
Grace S. Brush and Frank W. Davis
Department of Geography and Environmental Engineering
The Johns Hopkins University
Baltimore> Maryland 21218 iQO-/
Grant Numbers R 805 962 and
806 680 01
Project Officer
Dr. David Flemer
Chesapeake Bay Program
U. S. Environmental Protection Agency
2083 West Street
Annapolis, Maryland 21401
-------
CONTENTS
Summary . i
Figures iii
Acknowledgements iv
1. Introduction 1
2. Methods 4
3. Results 7
Furnace Bay 7
Patuxent River 10
Ware River 19
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SUMMARY
The stratigraphic record indicates that for centuries prior to European
settlement, diatom and macrophyte populations were fairly uniform in the
Chesapeake Bay estuaries studied. Waters in tributaries draining Piedmont
watersheds underlain for the most part by thick saprolites appear to have
been clear with sufficient nutrients to support diverse and abundant sub-
merged macrophyte .and benthic diatom populations. In the tributary draining
sandy Coastal Plain sediments, habitats were extremely oligotrophic capable
only of supporting a very sparse diatom population. After initial defores-
tation, macrophytes and diatoms showed significant changes, many of which
were coincident with historically documented changes in land and water use.
Today, forests comprise about 40% of the land; sediment yield is 5 to 10 :
times and nutrient loading 2 to 6 times greater in agricultural than in
forested watersheds (Lystrom et al. 1978) . The rate of application of high-
nitrate chemical fertilizers, applied to cultivated land since the roid-19th
century, has quadrupled since 1900. Since the mid-20th century, sewage has
increased phosphorus-loading of some estuarine tributaries by 5 to 15 times.
At oligohaline locations, strong correlations between macrophyte seed
and diatom stratigraphy are coincident with land clearance and nutrient load-
ing. At Jug Bay, in the Upper Patuxent River, the appearance of Potamogeton '.
epihydrus and Zannichellia palustris along with an increase in flux of peri-
phytic diatoms occurred at about the time fertilizers were added to the
watershed. At Furnace Bay, in the Upper Chesapeake Bay, low diatom fluxes
accompanied by the first major discontinuities in the macrophyte record fol-
lowed early European land clearance. A large increase in diatom flux, domi-
nated by the eutrophic planktonic Fragilaria crotonensis, around 1930, was
associated with the first appearance of the eutrophic adventive macrophyte
Myriophyllum spicatum. These population changes were coincident with the
initial discharge of sewage effluent into Furnace Bay. At both locations,
the proportion of planktonic diatoms has increased in recent years. At the
same time, seed stratigraphy (particularly at Furnace Bay) and field surveys
have documented severe declines in macrophyte populations. At mesohaline
locations, the stratigraphic record shows that the effect of human disturb- :
ance is much less obvious and suggests that the greatest alteration of estua-
rine habitats is mainly a result of local disturbance.
Causal links between eutrophication and epiphytic diatom and macrophyte (
populations have been studied in lakes by Phillips et al. (1978) and summa- ;
rized for Chesapeake Bay by Valentine and Stevenson (1981). Based on obser-
vations in lakes in England, Phillips et al. (1978) postulated that increased
nutrient loading stimulates the growth of epiphytic and filamentous algae
-------
which normally are suppressed by macrophyte-secreted chemicals and law
nutrients. The accelerated algal growth decreases the light available to
the macrophytes. If nutrient levels continue to increase, phytoplankton
growth also increases thus further shading the macrophytes and resulting
eventually in the elimination of both the macrophytes and associated epi-
phytes. In the sediments of Jug Bay and Furnace Bay, increasing flux of
epiphytic diatoms with fertilizers, large increases in both epiphytic and
planktonic diatoms with sewage, and a rise in planktonic species in recent
years concurrent with the decline of macrophytes support the hypothesis of
Phillips et al. (1978). The epiphytic diatoms do not decline as sharply as
might be expected especially as the macrophytes were essentially eliminated
from both areas. However, only a few epiphytic diatoms occur only on macro-
phytes; many can also use filamentous algae and nearby emergent vegetation
as a substrate. It should be noted also that factors other than eutrophica-
tion, including a catastrophic flood in 1972 (Bayley et al. 1978) and re-
gional increases in herbicide use since 1970 (Kemp et al. 1981) also could
have played a role in the recent decline of macrophytes in the Chesapeake
Bay.
ii
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. FIGURES
Number.
1. Map of Chesapeake Bay showing locations of areas cored:
1. Furnace Bay, 2. Jug Bay, 3. Eagle Harbor, 4. St.
Leonard Creek, 5. Ware River - midstream, 6. Ware River
downstream 2
2. Pollen profile at Furnace Bay. TP - total pollen; O:R
- the ratio of oak to ragweed pollen. Similar abbrevi-
ations are used in all pollen profiles.. 8
3. Diatom and macrophyte profile at Furnace Bay. Ecolog-
ical groupings based on Patrick and Reimer (1966,1975);
Hustedt (reprinted 1977); Lowe (1974); Schoeman (1973);
and Davis and Brinson (1980). In all figures, profiles
of.eutrophic diatoms are colored black, and fluxes
< IxlO1* are shown as a black dot 9
4. Pollen profile at Jug Bay in the upper Patuxent River... 11
5. Diatom and macrophyte profile at Jug Bay, upper Patux-
ent River 13
6. Pollen profile at Eagle Harbor in the middle Patuxent
River 15
7. Diatom profile at Eagle Harbor in the middle Patuxent
River 16
8. Pollen profile at St. Leonard's Creek in the lower
Patuxent River 17
9. Diatom and macrophyte profile at St. Leonard's Creek
in the lower Patuxent River 18
10. Pollen profile at the midstream location in Ware River.. 20
11. Diatom profile at the midstream in Ware River 21
12. Pollen profile at the downstream location in Ware River. 23
13. Diatom profile at downstream in Ware River 24
111
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ACKNOWLEDGEMENTS
We express our appreciation to the following individuals: to R.
Summers for helping in core collecting; J. Stasz and S. Rumer for diatom
counts; C. Stenger for assisting with pollen counts and historical research;
R. Patrick and F. Uhler for lending their expertise in providing identifi-
cations and ecological requirements of diatom and macrophyte species; W.
Boynton, J. P. Bradbury, O. Bricker, D. Flemer, K. Mountford, J. Sanders
and M. G. Wolman for reviewing the manuscript.
IV
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SECTION 1
INTRODUCTION
Organisms and parts of organisms preserved in estuarine sediments provide
a quantitative record of changes in populations that can be compared with the
historical and stratigraphic records of environmental change. Stratigraphic
records of biological populations in recent sediments are particularly valu-
able for evaluating effects of environmental change because the historical
records are often meagre, seldom quantitative, and do not allow comparisons
between pre-historic and historic conditions. We investigated the history of
diatom and submerged macrophyte populations preserved in sediments deposited
over several centuries in 3 areas of Chesapeake Bay in order to assess the
effect of human disturbance on estuarine habitats. The disturbances investi-
gated, which have altered parts of estuaries, include sediment loading from
land clearance, nutrient loading from fertilization of the cultivated land-
scape and the discharge of sewage effluent into estuarine waters, thermal
loading from cooling water discharged by a power plant, and toxic loading
from herbicide application to the farmed land and chlorination of both sewage
treatment and power plants.
Fifteen sediment cores, 1 to 2 m long and 5.4 cm in diameter were col-
lected with a piston corer at 6 locations in the upper, middle and lower
Chesapeake Bay (Figure 1).
Furnace Bay is a shallow (1-2 m), oligohaline (0.5-1.0 °/oo) erobayment
at the head of Chesapeake Bay. It drains a watershed of 68 km2, underlain by
unconsolidated Cretaceous sediments and saprolite derived from Piedmont crys-
talline rocks. Four ..cores were taken at this locality. Locally, major human
activities since European settlement of the watershed include agriculture
since 1730, fertilization of cultivated land since 'V 1845, charcoal produc-
tion from 1720 to 1900, sewage disposal.presently 1 mgd (U. S. Army Corps of
Engineers 1977) since 1918, sand and gravel mining since 1950 and the use of
herbicides since the mid-19601s.
The Patuxent River at approximately the mid-section of Chesapeake Bay,
is 285 km long and drains an area of 'V 2400 km2 underlain by Piedmont sapro-
lite and unconsolidated Coastal Plain sediments. Nine cores were taken at 3
locations. Jug Bay, 84 km upstream from the mouth, is a shallow, oligohaline
'(0.1-1.3 °/oo).embayment, always turbid and eutrophic. Eagle Harbor at river
km 44 in the mesohaline stretch (3-9 °/oo salinity) is located at the end of ;
the discharge canal of Chalk Point Power Plant (^ 900 MW) and is within the
turbidity maximum (Roberts and Pierce 1976). St. Leonard Creek at river km
15, is the most saline site (9-16 °/oo) and is outside both the turbidity ;
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ESAPEAKE BAY
i'i 0 ^ 0 'JiL:ciL MILES
Figure 1. Map of Chesapeake Bay showing locations of areas cored:
1. Furnace Bay, 2. Jug Bay, 3. Eagle Harbor, 4. St.
Leonard Creek, 5. Ware River - midstream, 6 Ware River
downstream.
2
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maximum and the thermal plume of the power plant. The entire Patuxent water-
shed was farmed primarily for tobacco from 1650 to 1840 and also for grain
from 1840 to the present (Craven 1925). Chemical fertilizers have been ap-
plied to cultivated land since the mid-to-late 1800's and herbicides since
the mid-19601s. Intense urbanization of the upper watershed since the early
1960's has resulted in a present discharge of 35 mgd of effluent from 29 sew-
age treatment plants into the Upper Patuxent River (U. S. Army Corps of Engi-
neers 1977). During the past 20 years, nutrient and suspended solid concen-
trations have increased throughout the estuary, with highest concentrations
in the upper estuary, lower in the vicinity of Eagle Harbor and lowest at the
mouth (Roberts and Pierce 1976). The Chalk Point Power Plant went into
operation in 1965; since that time water temperature within the thermal plume
has been raised ah average of 5 to 8°C. However, the temperature increase ;
affects primarily surface water, except at the discharge canal (1.5 km long),
where mixing ensures a more or less uniform vertical temperature profile
(Carter 1968). ~
The Ware River in the Lower Chesapeake Bay is 12 km long. Its rural
watershed of 58 km2 is underlain by sandy Coastal Plain sediments. Salini-
ties range from 5-13 °/oo at the head to 17-20 °/oo at the mouth. Two cores
were analyzed from 2 locations. The watershed was initially farmed for
tobacco and since the mid-19th century primarily for grain. Chemical ferti-
lizers have been used since the mid-to-late 19th century and herbicides since
the mid-1960's. A secondary sewage treatment plant with an average discharge
of 0.13 mgd. was built near the head of the estuary in 1936 (U. S. Army Corps
of Engineers 1977); its effects are restricted to a small area immediately
downstream from the plant (VIMS, unpublished data).
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SECTION 2
METHODS
Cores were extruded and split lengthwise. Splits analyzed for pollen
and diatoms were divided into 1 and 2 cm intervals. The procedure for ex-
tracting pollen from the sediments follows that outlined by Faegri and
Iversen (1964). Diatoms were extracted using a modified version of the
method described by Funkhouser and Evitt (1959). Pollen and diatoms were
each extracted from 1 cm3 of sediment from each interval analyzed. Identifi-
cations and counts were made from several aliquots from each sample. Diatom
fluxes (number of frustules deposited cm" y~ were calculated by multiplying
the total number of frustules per cm3 of sediment by the appropriate sedimen-
tation rate (cm y"1). Because of the large number of species enumerated from
these cores, most of which occurred < 0.5%, we included in our analyses only
those species that comprised >. 3% of the population at a level. Complete
vertical distributions of fluxes of all species comprising >. 3% of the popu-
lation arranged into major ecological groups were plotted against time axes
(Figures 3, 5, 7, 9, 11 and 13).
Splits analyzed for seeds were divided into 4 cm intervals (40-50 ml).
Seeds were extracted from all samples by first disaggregating the sediment in
dilute nitric acid (Godwin 1956) and then washing the sample through 20-mesh
and 60-mesh sieves (0.8 mm and 0.25 mm apertures). All macrophyte seeds were
identified and counted, and seed identifications confirmed using the seed
reference collection at the Patuxent Migratory Bird Habitat Research Labora-
. tory in Laurel, Maryland. The presence of seeds from continuous samples in
several cores 50-100 m apart at a location was plotted against the time axis.
We measured the effect of environmental change on diatom populations by
analyzing one core at each location. This was considered representative of
the local population because calculated settling velocities of diatom frus-
tules are in the range of 15 m/day and observed settling velocities range
from 1 to 30 m/day (Smayda 1971). These rates indicate that diatoms are not
transported far in shallow estuaries. A comparison of pollen distributions
in surface sediments of the Potomac estuary with tree and shrub distributions
in a broad band along the estuary show that the local patchiness of the vege-
tation is erased in the pollen distributions due to estuarine transport, but
the regional gradients are maintained (Brush and DeFries 1981). Pollen
grains are similar in size to diatom frustules, but they have a lower speci-
fic gravity and hence are likely to be transported farther than diatoms be-
fore being deposited. Thus, we expect that estuarine transport erases local
variations in diatom distributions but does not result in regional mixing
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We measured the effect of habitat alteration on submerged macrophytes
by analyzing several cores at a location, because unlike diatoms which range
from ^ 20-150P, the larger macrophyte seeds (1-2 mm) are not transported far
from the original grass beds thus resulting in localized and patchy distri-
butions of seeds in the sediments (Davis 1982).
Selective preservation of macrophyte seeds (Stark 1971) and dissolution
of diatom frustules (Parker et al. 1977; Hecky and Kilham 1973) have been
documented in some sedimentary environments. We selected for study cores
with relatively intact stratigraphy and good fossil, preservation. Except
for poor preservation of Potamogeton fruits, seeds were well preserved at 3
locations. Diatoms were consistently well preserved in all cores analyzed.
In order to construct chronologic profiles of diatom fluxes and seed :
occurrences, sediments in the cores were dated based on changes in the verti-
cal pollen profiles reflecting historically dated changes in regional vegeta-
tion caused by deforestation and disease (Davis 1968; Anderson 1974). In all
cores, initial European settlement is recorded in the sedimentary record by
an increase in percent of ragweed pollen and a corresponding decrease in the
rates of oak to ragweed. During modern intensive agriculture, the percent
of land cleared for agriculture increased from < 20 to 40 to 60. This is
reflected in the pollen profiles by a dramatic increase in ragweed generally
to between 20 to 30% of total pollen. The ratio of oak to ragweed is almost
always < 1. Dates assigned to the stratigraphic horizons representing these
2 phases of land clearance (initial or early European settlement and inten-
sive agriculture) are different for different watersheds (Figures 2, 4, 6, 8,
10 and 12) . The demise of American chestnut about 1930 is reflected in pol-
len profiles from Furnace Bay either by the absence of chestnut or a decrease
to < 1%.
Proportions of ragweed and chestnut of total pollen and the ratio of oak
to ragweed pollen were plotted against depth for each core. Time lines were
drawn where the changes described above occurred in the pollen profiles.
Sedimentation rates were averaged between dated horizons by dividing the
length of the core between dated horizons by the time between the horizons.
Uncertainties in sedimentation rates, resulting from the size of the
sampling intervals, distance between sampled intervals and the error in-
volved in assigning a precise date for an event which may have occurred over
several years were calculated using the first order propagation of error
(Benjamin and Cornell 1970 ; Brush et al. 1982) and are recorded in the pol-
len profiles (Figures 2, 4, 6, 8, 10 and 12).
Although it is necessary to use average sedimentation rates between j
dated horizons, we recognize that sediment accumulation was probably not uni-:
form at all localities over the time periods studied. This can also lead to
error in the calculation of population fluxes. As of now, we have no means ]
for estimating this error. j
We have assumed a 0.1 cm y~ sedimentation rate for the period of time '
" prior to European settlement. This rate is based on an average of rates
-------
ranging between 0.05 and 0.18 cm y~l derived from ltfC dated sediments from
some Chesapeake Bay tributaries. The 14C dated sediments were selected from
cores where sedimentation is believed to have been continuous since the time
llfC dated sediment was deposited (Kraft and Brush unpublished data; Wilke
et al. 1981).
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SECTION 3
RESULTS
FURNACE BAY
The pollen profile (Figure 2) shows the early settlement Cv 1730) hori-
zon at 92 cm where percent ragweed increases from 4 to 13 and the ratio of
oak to ragweed decreases from 8 to 2; the intensive agricultural horizon
C^ 1780) at 83 cm where percent ragweed increases to > 20 and the oak-rag-
weed ratio becomes < 1; and the demise of chestnut (^ 1930) horizon at 28 cm
where percent chestnut pollen decreases to < 1. Based on these horizons,
average rates of sediment accumulation were 0.16 ± 0.04 cm y"1 during early
settlement, 0.37 ± 0.02 cm y"1 during intensive agriculture when percent
land cleared reached 60, and 0.58 ± 0.06 cm y"1 from 1930 to 1978, when the
cores were collected.
Out of a total of 246 diatom species identified and enumerated from this
core, 23 occurred in percentages >_ 3 (Figure 3). Prior to European settle-
ment, an essentially periphytic flora was dominated by Cocconeis placentula.
Some of the species present at that time, such as Gomphonema parvulum,
Navicula peregrina and Synedra pulchella are often found today in high-
nutrient waters (Lowe 1974; Schoemari 1973). Planktonic species were extreme-
ly rare except for Synedra pulchella which can be either periphytic or plank-
tonic. As Europeans cleared the land for agriculture, sediment accumulation
increased at Furnace Bay. Total diatom flux was reduced to one-half its
original size. Most of the original species were still present following
early land clearance except Gomphonema parvulum and Synedra pulchella. Both
of these species disappeared almost completely during this period. Epithemia
adnata minor was also greatly reduced. The planktonic Synedra rumpens ap-
peared and was present more or less continuously from that time on. Navicula
rhyncocephala alsa made its first appearance following early settlement.
Coincident with the addition of chemical fertilizers to the cultivated land,
around the middle 19th century (Davis 1982), total diatom flux increased.
This increase was accompanied by an increase in many species existing at
that time. Cocconeis placentula remained dominant. Some new species, such
as Achnanthes minutissima and the pollution-tolerant Navicula cryptocephala
(Lowe 1974) appeared. Gomphonema parvulum which favors high-nutrient water
reappeared. Early in this century and coincident with the discharge of sew-
age effluent into Furnace Bay, diatom flux increased dramatically from ^ 1
;to > 5 million. The planktonic Fragilaria crotonensis, considered an indica-
tor of eutrophication (Lowe 1974; Brugam 1978) comprised 30% of the flora at
that time. Kilham (1982) has shown experimentally that this species is a
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00
Depth Sediment
(cm)
40-
80-
130
TP
(no/g
sed)
Ragweed 0:R Chest- Dated
nut Horizon
Dark
Gray
Silt
and
Clay
Light gray
silt and
clay
1978 -1
1930 n
1x10
Sedimentation
Rate
(cm y-1)
0.58±0.06
0.37+0.02
0.16±0.04
assumed
0.10
Figure 2. 'Pollen profile at Furnace Bay. TP - total
pollen; 0:R - the ratio of oak to ragweed
pollen. Similar abbreviations are used in
all profiles.
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DIATOMS
1
PERIPHYTIC/
PLANKTONIC
1 1 1
PLANK-
TONIC
1 1
HACROPHYTES
1400
0 -H -O
I 8 I
kT
si
All scales 1x10*
No. frustules deposited cm"2 y"1
.1 a
Increasing >
turbidity tolerance
5"t CJ -H
-I tJ -1
u
seeds present
(data from 4 cores)
Figure 3.
Diatom and macrophyte profile at Furnace Bay. Ecological group-
ings based on Patrick and Reimer (1966,1975), Hustedt (reprinted
1977), Lowe (1974), Schoeman (1973) and Davis and Brinson (1980).
In all figures, profiles of eutrophic diatoms are colored black,
and fluxes < 1x10** are shown as a black dot.
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good competitor for phosphorous, present in large quantities in sewage. The
periphyte, Cymbella lunata present in small numbers but continuously until
the early 19th century, when it disappeared, reappeared in large numbers in
the early 20th century. The eutrophic periphyte Synedra pulchella also re-
appeared at this time and Epithemia adnata minor disappeared and did not
return. In the early 1950's, Fragilaria crotonensis crashed, contributing
to a decrease in total flux. It was succeeded by species of Coscinodiscus
which can be either periphytic or planktonic and by the planktonic Melosira
granulata. Among the eutrophic periphytes, Navicula peregrina disappeared
and Gomphonema angustatum appeared.
Among the submerged macrophytes, Vallisneria americana, Najas gracillima
and Elodea canadensis occurred continuously prior to European settlement,
while Najas flexilis and N. guadalupensis were present most of the time.
During early settlement (1730-1780), Najas flexilis and Elodea canadensis be-
came sporadic. After 1780, as sediment accumulation doubled, Najas gracil-
lima disappeared and until 1930 all of the species except Vallisneria ameri-
cana, considered the most turbidity-tolerant of the macrophyte species (Davis
and Brunson 1980), occurred infrequently. The infrequency of occurrence was
particularly evident for Najas guadalupensis and Elodea canadensis. Najas
flexilis occurred continuously from 1930 to the early 1970's. Myriophyllum
spicatum, introduced into Eastern North America in the late 19th century,
first appeared in Furnace Bay between 1930 and 1940, reappeared after 1950,
and dominated aquatic macrophyte communities in this area between 1960 and
1967 (Bayley et al. 1978). The species thrives in alkaline eutrophic lakes
(Seddon 1967; Lind and Cottam 1969) and can grow in moderately low light
(Davis and Brinson 1980; Wentz and Stuckey 1971) in a broad range of salini-
ties (Rawls 1964). After 1972, all native species of macrophytes disappeared
from the seed record, including Vallisneria americana which was present con-
tinuously up~to this time. .
The stratigraphic record of diatoms and macrophytes suggests that prior
to deforestation and cultivation of the watershed for agriculture, Furnace
Bay was a shallow, clear-water embayment supporting an abundant and diverse
macrophyte and periphytic diatom population. Following land clearance, the
waters became turbid with increased sedimentation and populations of both
macrophytes and diatoms were reduced. With the introduction of fertilizers,
populations increased and included more eutrophic periphytes.and free-float-
ing diatoms. After the introduction of sewage, the embayment was transformed
into a more highly eutrophic system supporting a much larger planktonic dia-
tom population, and eventually the macrophyte populations disappeared com-
pletely from the area.
PATUXENT RIVER
Jug Bay
The pollen profile from the core at Jug Bay in the upper Patuxent River
(Figure 4) shows the early settlement Cv> 1650) horizon at 99 cm, where per-
cent ragweed changes from 2 to > 5 and the ratio of oak to ragweed changes
from 20 to < 10. The beginning of intensive agriculture about 1840 occurs
10
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Depth Sediment
(cm)
40-i
80
118
Brown-
Gray
Silt
and
Clay
Gray-
Yellow
Dark
Gray-
Brown
TP
(no/g
sed)
Ragweed 0:R
Dated Sedimentation
Horizon Rate
(cm y'1)
- 1980 -i
1840 n
1650 q
0.41+0.03
0.16±0.02
assumed
0.10
1x10* 5% 5.
Figure 4. Pollen profile at tfug Bay in the
upper Patuxent River.
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at 56 cin where percent ragweed increases to > 20 and the oak-ragweed ratio
is ^ 1. Based on these horizons, the average rate of sediment accumulation
which was 0.16±0.02 cm y"1 during the era of tobacco agriculture more than
doubled to 0.4110.03 cm y"1 when at least 40% of the watershed was cleared
for farming.
Twenty-three of the 190 diatom species enumerated from this core oc-
curred 2. 3% (Figure 5). Total diatom flux remained fairly uniform before and
after European settlement until the beginning of the 20th century when it
more than doubled. The pre-settlement flora was a diverse assemblage con-
sisting mainly of periphytes and including Cyclotella memenghiniana and the
planktonic Melosira granulata angustissima. Both of these species are con-
sidered eutrophic (Schoeman 1973; Lowe 1974). Prior to settlement eutrophic
periphytes were extremely rare. With the onset of European agriculture, a
number of species appeared including the eutrophic periphyte Navicula rhyn-
cocephala (Lowe 1974) and some species disappeared including Cyclotella
memenghiniana and Melosira granulata angustissima, also eutrophic. Coinci-
dent with the application of chemical fertilizers to the watershed, total
diatom flux began to increase. This increase was accompanied by increases
in species that prefer high nutrient waters, such as Gomphonema parvulum,
Navicula rhyncocephala and W. viridula, all periphytes. Cocconeis placen-
tula, unimportant prior to the middle 19th century, became a dominant part
of the flora, as did Achnanthes lanceolata. With the introduction of sewage
effluent into the Upper Patuxent River in the 1950"s, diatom flux tripled,
accompanied by the appearance in large numbers of species which had not been
present prior to this time or were present in very small numbers such as
Cyclotella menenghiana, C. kutzingiana, O.K. planetophora, and Nitzschia
parvula. Species of Cyclotella can occur as periphytes or plankton. The
eutrophic planktonic Melosira granulata angustissima also reappeared at this
time, and the eutrophic periphyte Navicula rhyncocephala, was present in
large numbers. At the same time, populations of previously important peri-
phytes, such as Cocconeis placentula, Eunotia pectinalis and Navicula radi-
osa tenella were greatly reduced.
Pre-settlement sediments contain seeds of 6 macrophyte species (Figure
5), the most common of which were Najas guadalupensis, W. flexilisf and
Elodea canadensis. The seed record of the 18th and early.19th centuries is
poorly preserved. Najas flexilis dropped out of the record and Elodea cana-
densis became sporadic during this time interval. By the mid-19th century,
at about the time chemical fertilizers were applied to the cultivated water-
shed, Potamogeton epihydrus, which grows in mesotrophic to mildly eutrophic
alkaline waters, (Hellquist 1975) appeared along with Zannichellia palustris.
The latter is a shallow-water pioneer species in Chesapeake Bay, that tole-
rates very high nutrient levels (Stevenson and Confer 1978). Between 1940
and 1960, when diatom flux increased enormously, Potamogeton epihydrus dis-
appeared. Field surveys show that since the late 1960's beds of submerged
macrophytes declined greatly in the Upper Patuxent River (Stevenson and
Confer 1978) and this is reflected in the sediments by a decrease in macro-
phyte seeds since 1960 (Brush et al. 1981).
The large increase in diatom flux, dominated by species of Cyclotella
12
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DIATOMS
MACROPHYTES
PERTPHYTIC
||
PLANK-
PERTPHYTIC-PLAHKTOMIC TON 7 1 1
Increasing
pollution t
tolerance
I || | | || 1 | 1
U)
1600-
1400-
1x10
All scales 1x10*
Number of frustules deposited cm"S y"1
Seeds Present
(data front 4 cores)
Figure 5. Diatom and macrophyte profile at Jug Bay, upper
Patuxent River.
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and the disappearance of submerged macrophytes are coincident with the period"
of intensive urbanization of the watershed and increasing discharge of sewage
effluent into the river.
Eagle Harbor
The pollen profile (Figure 6) shows an early settlement (^ 1650) horizon
at 115 cm, where percent ragweed changes from < 1 to > 2 and the oak-ragweed
ratio from > 35 to < 10. The horizon representing intensive clearing Cv
1840) occurs at 60 cm, where percent ragweed increases to > 20 and the oak-
ragweed ratio decreases to < 1. Sediment accumulated at a rate of 0.22±
0.02 cm y"1 during early settlement and like the upper part of the river more
than doubled to 0.51±0.06 cm y"1 as a greater proportion of land was fanned.
Of the 129 diatom species identified, 23 were present at >. 3% (Figure
7). There is little change in total diatom flux throughout the entire core,
except in the very top part, where it doubles. Nor are there any dramatic
.changes in -the species composition throughout the core. Essentially the
flora consists of a mixture of periphytes and species that can be either
periphytic or planktonic and includes eutrophic species at all levels. The
increase in flux in the early to mid-1970"s is due mostly to a relatively
large increase in Cyclotella kutzingiana. There are no changes in the diatom
flora strictly coincident with the discharge of cooling water in the river at
this location (the core was taken at the end of the Chalk Point Power Plant
discharge canal).
Seed stratigraphy was not analyzed at this location because of low seed
concentrations in the sediment.
St Leonard Greeks
The pollen profile (Figure 8) from the core in the downstream part of
the Patuxent River indicates that the overall sedimentation rate was lower
than at either up-or midstream. The early settlement horizon is at 69 cm,
where percent ragweed changes from 1 to > 5 and the oak-ragweed ratio from
30 to < 5. The intensive land clearance horizon is located at 48 cm, indi-
cated by an increase in percent ragweed to > 10 and a < 2.decrease in the
oak-ragweed ratio. Thus, sediment accumulated at an average rate of 0.1±
0.009 cm y"1 during early settlement and was probably not very different from
the pre-settlement rate. After land clearance reached ^40%, sediment accu-
mulation tripled, averaging 0.3410.03 cm y"1.
Total diatom flux is fairly uniform throughout the core (Figure 9). A .
total of 110 species were identified, of which 17 comprise ^ 3% of the total
population. The population consists of a mixture of periphytes and species
that can be either periphytic or planktonic and includes a few species that
prefer high nutrient habitats, such as Nitzschia amphibia, Cyclotella bo-
danica, Meridion spp., and Synedra fasiculata. The only major change in
species composition in the core was the disappearance of the eutrophic peri-
phyte Rhopalodia gibberula (Lowe 1974) with the onset of agriculture, and
Cyclotella bodanica became sporadic in the late 19th century.
14
-------
Depth Sediment
(cm)
TP Ragweed O:R
(no/g
sed)
40-,
80-
128'
Uniform
Gray
Silt
and
Clay
1x10"
5%
Dated
Horizon
1980 -i
Sedimentation
Rate
(cm y-1)
1840 =i
1650 n
0.51±0.06
0.2210.02
Figure 6. Pollen profile at Eagle Harbor in
the middle Patuxent River.
-------
PERIPHYTIC i PERIPHYTIC/PLWJKTON1C
r ii 1 r
!
W HI
g"*H N ffi
-i m « q
*d -H OlQU q> E
*H'H iJ Id -H 41 0 IQQ«££
H T1 * « « *> cmmu B 3 o -
Id MO -H3 Id IQC'^Q) oi?Q)E
0 DiaioSfl 4J SSpSa^S
0 Mum H3E: -H*H O'HU ti! '^S1^ ^cq4J>H -Hit
B 4J ji -q
a ° 8 " ' ,
1980 "
1950-
1900-
1800-
1600-
non -
o
o
r
(U
u
1
r-4
1
2
0)
N
H
r-l
3
QJ
T
14
V
fl
3
o
s
n)
V
X
Pre-
Europoan
1
s
k
U
) Q« >.£
Q o! q fe a a
s
t
1
1
r
h'
I
1
1
a
i
t
i
t
\*
=
)
s
j t
i
<
j I
1
b
C
-I
! ,
3s
1x10'
All scales Ixlfl'
No. frustulcs deposited cm y
Figure 7. Diatom profile at Eagle Harbor in
the middle Patuxent River.
-------
Depth Sediment TP Rag- O:R
(cm) (no/g weed
sed)
0-
40-
80-
112
Gray sand
silt and
clay
Dk. gray
sand, silt
and clay
Yellow-
Gray
Silt
and
Clay
1x10
Dated Sedimentation
Horizon Rate
(cm y"1)
* 1980 -i
1840 S
1650 J
0.34±0.03
0.1010.009
assumed
0.10
Figure 8. Pollen profile at St. Leonard's
Creek in the lower Patuxent River
-------
DIATOMS
MACROPIIYTES
00
PERIPIIYTIC- |
1
ID
H ;H
£ D*
10 q
3 §
Q 3
(0 i 1
M 1 |
H -H
*H *M
3 3 t!
ID i fl KJ
PLANKTONIC
1
U
'3
1
q
q
. f! .. S
?
~T1
q.75
*H -Q
Q m
3 ** ffl
*o o
ry o
>,
1980 "
1900-
1800-
.1600-
1400-
1200-
X
o
TJ «
§<
U
O
§_
iH
*
1
H
S
S.
1
a
0*
U W
o o
H H
°> Q
H 7
o 1
N \
r~t '
M
& ;
i
H ^
ti
S
i
Q,Q,C4JVi
mco
-i-o-c!
Cl,<~lQ,
Q.4I
-
, ^
1x10'
All scales 1x105
No. frustulos deposited cm y
cou
3qw
CCON
5-14J
o -1
"t
|seeds present
(data, .from 3 cores)
Figure 9.
Diatom and macrophyte profile at
St. Leonard's Creek in the lower
Patuxent River.
-------
The macrophyte seed record at St. Leonard Creek is scant, consisting of
Zannichellia palustris, Ruppia maritima, Potamogeton perfoliatus v. bupleu-
roidis (not shown) and Zostera marina (riot shown). Profiles from 3 cores
suggest that Ruppia maritima and Zannichellia palustris grew locally for at
least 3 centuries (Figure 9). Aerial photographs and field surveys document
the decline of marcophytes in this section of the estuary since the late
1960's (Stevenson and Confer 1978; Anderson and Macomber 1979).
Diatom and macrophyte populations preserved in recent sediments indi-
cate that the Upper Patuxent River, like Furnace Bay, was a shallow, probably
clear, mesotrophic embayment supporting a diverse macrophyte and predomi-
nantly periphytic diatom population prior to European settlement. Gradually,
as agriculture was succeeded by urbanization, Jug Bay changed into a highly
eutrophic system dominated by species of Cyclotella, which can occur as
plankton. At the same time, the macrophyte population was greatly reduced.
The record also-indicates that the deeper mesohaline part of the river was
affected only slightly by human activity, principally by an increase in
Cyclotella kutzingiana coincident with the deterioration of water quality in
the late 1960's and early 1970's (Roberts and Pierce 1976). Downstream,
where there has been little change in water quality, there is no detectable
change in diatom and macrophyte populations over several centuries. :
WARE RIVER
Midstream
The pollen profile (Figure 10) shows the early settlement horizon (^
1650) at 63 cm where ragweed increases from < 1 to > 1 but < 5 and the ratio
of oak to ragweed changes from > 10 to ^ 5. The 1840 horizon is at 52 cm
based on an increase in percent ragweed to > 5 and a decrease in the oak-
ragweed ratio to < 3. Based on these horizons, the sedimentation rate be-
tween mid-17th and mid-19th century was 0.0610.009 cm y"1. Because it is
unlikely that the pre-settlement sedimentation rate would have been higher
at least in the decades immediately preceding settlement, we assumed a 0.06
cm y"1 rate for pre-settlement sediments. The average rate since the mid-
19th century to the present is 0.36±0.03 cm y""1.
Ninety-seven diatom species were identified in this core, of which 18 ;
occurred >. 3% (Figure 11). Total flux was never high here, but prior to
European settlement, the flora was extremely sparse; however, most species
which occurred later were also represented in these early sediments. After
settlement, there was a slight increase in most species. The eutrophic
periphyte, Opephora martyrii (Lowe 1974) appeared in the late 1800's at about
the time fertilizers were added to the watershed. Cocconeis placentula also
appeared about the same time. An increase in flux since 1950 is represented '
mainly by increases in Achnanthes temperii and Cocconeis fluviatilis. :
19
-------
NJ
O
Sediment TP Rag- Dated Sedimentation
Depth (no/g weed O:R Horizon Rate
(cm) sed) ;
n
40-
80-
120-
Dark gray
silt, clay
and sand
Gray-
Brown
Silt
and .
Clay
I
1
(
\
\
/
^^
^>
^^
>
\
\
/
{
\
}
1
1
.
t.
(cm y-1)
i oor\
\
I
/
/
L
^ . * 1840 -
\
-i 1650 -
?v.
\
\
*
0.36±0.03
0.06±0.009
assumed
0.06
IxlO1*
5%
Figure 10. Pollen profile at the midstream
location in Ware River.
-------
to
(-1
PERIPHYTIC
H ID
10
0)
1900-
o
f
>.f
C
*
-------
Downstream
The pollen profile (Figure 12) at this location of the river shows the
1650 horizon at 88 cm based on a first appearance of ragweed. The 1840 hori-
zon is located at 55 cm based on an increase in percent ragweed to between
5 and 15 and a decrease in the oak-ragweed ratio to < 2. These dated hori-
zons yield sediment rates of. 0.1710.01 cm y"1 during early settlement and
0.39±0.03 cm y"1 during intensive agriculture.
As in the core taken at midstream, total diatom flux is extremely low
prior to settlement (Figure 13). Ninety-seven species were enumerated; 15
occurred in percentages k 3. The flora consists of several species of peri-
phytes and 5 species of Cyclotella. Most of the species were present prior
to European settlement. Then the flora was dominated by Cyclotella bodanica
which is mesotrophic to eutrophic, Diploneis smithii and Cyclotella kutzingi-
ana. The increase of flux with settlement was represented by an increase in
most species and by the first appearance of Achnanthes perpusilla. At the
time fertilizers were added to the land, Cyclotella chaetoceios and Fragilar-
ia virescens appeared, and again flux increased with an increase in most
species. Since 1950, flux has tripled due largely to increases in Cyclotella
chaetoceros, C. kutzingiana, C.k. planetophora, and Fragilaria virescens.
Water quality and available historical data do not provide an explanation for
this sudden large increase in species that are not necessarily periphytic but
may also be planktpnic. Records from the other cores studied suggest that a
local source of nutrients probably stimulated the growth.
The poor seed record in all cores collected in the Ware River did not
allow a reconstruction of macrophyte populations in the southern region of
the Chesapeake Bay.
The stratigraphic record of diatoms indicates that the Ware River,
prior to European settlement, was a highly oligotrophic 'estuary draining a
watershed underlain entirely by nutrient-poor Coastal Plain sediments. After
land clearance, abundance increased particularly as chemical fertilizers were
added to the watershed.
22
-------
00 >
Depth
(cm)
0
Sediment
TP i
(no/g sed)
Rag-
weed
O:R
40-
80-
110-
Dark gray
silt and
clay
Gray-
Brown
Silt
and
Clay
Gray
Silt
and
Clay
1x10"
5%
"1
1
Dated
Horizon
1980 -i
Sedimentation
Rate
(cm y'1)
1840 =^
1650 n
0.3910.03
0.17±0.01
assumed
0.1
Figure 12. Pollen profile at the downstream
location in Ware River.
-------
PERIPIIYTlfc
PERIPHYTIC/PLANKTONIC
NJ
1400-
1200-
I T
:* a
u
-------
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28
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