United States
Environmental Protection
Agency
Chesapeake Bay
Program
Annapolis MD 21401
Research and Development
EPA-600/S3-83-052 Aug. 1983
Project Summary
Stratigraphic Evidence of
Human Disturbance in Some
Chesapeake Bay Tributaries
Grace S. Brush and Frank W. Davis
Response of diatom (algal) and sub-
merged macrophyte (angiospermous)
populations to disturbance in some
Chesapeake Bay tributaries over the
last few centuries is interpreted from
abundance of diatom frustules and
presence of macrophyte seeds pre-
served in dated estuarine sediments.
The historical record of disturbance
during the time period considered in-
cludes land clearance and urbanization
of the watershed resulting from human
activity, as well as from periodic storms.
The stratigraphic record indicates that
both the diatom and submerged macro-
phyte populations were stable prior to
European settlement. With the onset of
land clearance, dramatic changes are
registered that include shifts in total
numbers of cells and seeds as well as in
species composition. The kind of re-
sponse appears to be unique for a
particular type of disturbance.
This Project Summary was developed
by EPA's Chesapeake Bay Program,
Annapolis, MD, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Biostratigraphy is a tool scientists use
to analyze layers of fossil remains of
seeds, pollen grains, and diatoms in order
to gain a long-term perspective of change.
The method used here describes the
changes in submerged aquatic vegetation
(SAV) and diatom populations and corre-
lates these changes with historical rec-
ords of land use as well as with the
stratigraphic record of sediment accumu-
lation. Little historical data are available
concerning the biological and chemical
conditions of Chesapeake Bay. Thus, the
stratigraphic method is important be-
cause sediments contain records of popu-
lations as they occurred both before and
after human occupation of the surround-
ing area. In any stratigraphic study, the
fossils used as indicators must be care-
fully selected with respect to their ability
to preserve and their sensitivity to envi-
ronmental factors. The variability of the
populations in the sediment must be
analyzed for natural factors induced by
competition and predation. Core locations
must be selected in areas of undisturbed
deposition. Though the stratigraphic meth-
od is used in lake and open ocean studies,
it has not been utilized in the estuarine
environment as extensively because it
has been assumed that mixing of sedi-
ments by physical processes and biotur-
bation would have erased or distorted the
records preserved therein.
The stratigraphic method was used in
this study to demonstrate the feasibility of
the approach in identifying trends of SAV
and changes in eutrophication and sedi-
mentation rates in Chesapeake Bay by
developing sampling methods that would
avoid the above-mentioned problems.
Procedure and Methodology
Thirteen sediment cores were gathered
at six locations [Furnace Bay, Patuxent
River (Jug Bay, Eagle Harbor, St. Leonard
Creek), and Ware River] using a piston
corer which extracts samples up to 180
cm long. Cores analyzed for pollen and
diatoms were divided into 2 cm intervals.
Pollen and diatoms were then extracted
from sediment, identified, and counted.
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Cores analyzed for SAV were divided into
4 cm intervals and SAV seeds were
extracted, identified, and recorded as
either present or absent.
Time lines were drawn, based on
changes in the vertical pollen profiles that
reflect major changes in regional vegeta-
tion that can be dated from the historical
record. These changes include land clear-
ance, recognized in the sediments by a
large increase in ragweed pollen; urban-
ization, recognized by an increase in the
density of pollen; and the demise of
chestnut, by the chestnut blight, recog-
nized by the absence of chestnut pollen in
the sediments after the chestnuts had
died.
Results and Conclusions
Prior to human occupation, diatom and
macrophyte populations were fairly uni-
form in Chesapeake Bay estuaries. After
a human settlement, both populations
underwent changes that are correlated
with changes in land and water use.
Presence or absence of seeds from
multiple cores at a location indicates
trends in SAV. One layer void of SAV
seeds has been dated as the time of
Tropical Storm Agnes (1972) when the
SAV population of the upper Bay was
nearly destroyed. The Bay-grass beds
have not yet recovered from the storm.
The rate of sediment accumulation
increases greatly after land clearance
and the accumulation of sediment is
greater in the upper tributaries than at
the mouths.
A change in the number of diatoms
present at a particular level indicates
changes in water turbidity and water
quality. Like sedimentation rates, water
quality is governed by watershed use.
During times of land clearance when
siltation was high, diatom populations
decreased. This may be due to the reduc-
tion of light available for photosynthesis.
The amount of diatoms found may also
indicate changes in water quality; dia-
toms are sensitive to the chemical, phys-
ical, and biological properties of their
environments. With increased human
occupation of the surrounding land (about
1820) came enrichment of the Bay from
inorganic fertilizers and sewage runoff.
Certain species of diatoms that prefer
nutrient rich water were found in sedi-
ment deposited after fertilizers had been
added to the watershed and after sewage
was discharged into the tributaries. Con-
versely, species which are known to
occur only in clear water disappeared at
the time of land clearance and have not
returned. Many benthic species were
replaced by planktonic species.
Recommendations
Historical links exist between changes
in pollen grain types, diatom populations,
the disappearance of SAV seeds, and the
condition of the Bay.
Past regional conditions can be inferred
by careful observation of changes in core
samples. Effects of human activities and
nature on the environmental quality of
the Bay can be analyzed and, where
necessary, corrected. The stratigraphic
method can be useful in defining future
management plans for the preservation
of Chesapeake Bay because it provides a
long-term perspective of the variability of
some populations and allows a compar-
ison of conditions before and after human
occupation of the region.
Grace S. Brush and Frank W. Davis are with The Johns Hopkins University,
Baltimore, MD 21218.
David A. Flemer is the EPA Project Officer (see below).
The complete report, entitled "Stratigraphic Evidence of Human Disturbance in
Some Chesapeake Bay Tributaries," (Order No. PB 83-225 292; Cost: $8.50,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Chesapeake Bay~Program
U.S. Environmental Protection Agency
2083 West Street, Suite 5G
Annapolis, MD 21401
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