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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