United States
Environmental Protection
Agency
Chesapeake Bay
Program
Annapolis MD 21401
Research and Development
EPA-600/S3-83-033 June 1983
Project Summary
Animal-Sediment Relationships
of the Upper and Central
Chesapeake Bay
Eh Reinharz and Arthur O'Connell
Fifty-two bottom sediment box core
samples were taken in fall 1978 and
summer 1979 to investigate the
relationship between benthic biota and
the sedimentary environment of the
upper and central Chesapeake Bay.
Through an examination of the
vertical distribution of the benthos and
a radiographic analysis of the
sediments, the degree of physical and
biological activity and interaction was
determined.
The benthic microfauna were charac-
terized by opportunistic as well as
equilibristic species that inhabit a wide
range of salinity and substrate types.
Many species increased down the
estuary. Greatest species populations
were found in mixed-sediment
environments. The benthos were con-
centrated in the top 10 cm of the
sediment and penetrated to 30 cm.
Most sediments have a deep-dwelling
faunal component, but the number of
deep-penetrating individuals is greatest
in the mixed-sediment environments.
There are deep-dwelling representa-
tives of all taxa except for the arthro-
pods. Many of the deep-dwelling
species are also dominant based on
numerical as well as biomass determi-
nations.
Although biological sediment mixing
(bioturbation) occurs in most areas of
Chesapeake Bay, the degree is
substantially reduced in the upper
region of the Bay because of high sedi-
mentation rates. The prevalence of
physical structures over biological
features in the deep-water channel
regime is due to fluid mudsand periodic
anoxia. The more stable mud
environment is primarily inhabited by a
sedentary tube and relatively
permanent burrow-building commu-
nity. Sands are characterized by a motile
fauna. Most biogenic structures are
produced by polychaetous annelids.
Species population patterns and
previous Pb210 data in Chesapeake Bay
suggest that biological mixing occurs
down to 30 cm and is greatest at the
sediment surface.
This Project Summary was developed
by EPA's Chesapeake Bay Program.
Annapolis. MD. to announce key
findings of the research project that is
fully documented in a separate report of
the same title (see Project Report order-
ing information at back).
Introduction
The benthic community plays a key role
in animal-sediment-chemical inter-
actions within Chesapeake Bay. Benthic
organisms facilitate the exchange of
materials, including toxic compounds,
within the sediments and between the
sediments and water One implication of
this biological activity is the retention of
toxicants within the upper sediment
layers, where such materials may be
incorporated into the biotic system
This project was designed to highlight
the degree to which physical and
biological activities modify the bottom
environment The vertical distribution of
the benthos and sedimentary structures
was examined by using a box core
sampler and X-radiographic techniques
Sampling occurred over a two-year
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period at locations in central (mesohaline
zone) and upper (oligohaline zone)
Chesapeake Bay. Data analysis indicated
that biological processes influenced
sediment texture in most of the study
area. Physical processes dominated in
the uppermost portion of the Bay and in
deeper channels. A unique benthic
community structure was associated
with each sediment type. The extent of
bioturbation in any sediment depended
on the characteristics of the benthos.
Most benthic organisms occupied the
upper 10 cm of the sediment and deep-
burrowing species penetrated to 30 cm.
Results indicate that the sedimentary
environment in Chesapeake Bay is modi-
fied by both physical and biological
forces. This study may serve as a baseline
for research.
Procedure/Methodology
A total of 52 box core samples was
taken in central and upper Chesapeake
Bay between the latitudes 39°35' and
37°55' N. Sampling occurred from
September through November, 1978,
and during June and July, 1979. A
modified spade box corer was used for
this project. Two core samples were
recovered per station, as well as data on
bottom salinity and water temperature.
Both core samples provided information
on sedimentary features and benthic
fauna. This information was illustrated m
three-dimensional diagrams.
One box core was used for quantifying
the benthic community. Increments were
established to determine vertical
population trends. All biological samples
were sieved and organisms were
collected for identification, enumeration,
and biomass determination.
The remaining box core was used for
radiographic processing A 6-cm vertical
slice was sectioned and sealed m a
plexiglass tray for subsequent laboratory
procedures. After refrigeration, the core
sections were trimmed to 2-cm thickness
and photographed with a medical X-ray
unit.
Results and Conclusions
The benthic community of the upper
Chesapeake Bay was characterized by
endemic and colonizing species.
Annelids, arthropods, and molluscs were
the dominant benth c groups,
represented primarily by polychaetes,
crustaceans, and bivalve molluscs,
respectively Most species inhabited a
wide range of salinity and habitat types
Oligochaetous annelids and arthropods
were numerically dominant in the oligo-
haline zone, whereas polychaetous
annelids were most numerous in the
mesohaline zone.
Most benthic organisms were
concentrated in the upper sediment
layers. More than 65 percent of the
benthos were sampled in the upper 5 cm,
and approximately 85 percent of all
benthic organisms were concentrated in
the top 10 cm. However, all habitats
except oligohaline sands contained deep-
dwelling fauna that were found below 10
cm and penetrated to depths of 30 cm.
Annelids were the most successful
deep-dwelling group and penetrated
deeply into the sediment by constructing
long tubes or burrows or by functioning
as free burrowers. Some bivalve molluscs
were deep dwelling by virtue of long
siphons.
Benthic community characteristics
were unique for different sediment types.
Sand environments were inhabited by
motile fauna, primarily free-burrowing,
deep-dwelling species. Mixed-sediment
environments (10 to 85 percent mud)
contained the greatest species diversity
and the highest benthic densities of any
bottom environment. Deep-dwelling
benthos were most abundant in the
mixed sediment regimes. Conditions
favoring the establishment of benthos in
these environments included an
abundance of food and suitable oxygen
concentrations. Stable mud environ-
ments were inhabited by a sedentary tube
and burrow-dwelling fauna. Low oxygen
availability and sediment compaction
were limiting factors in mud substrates,
and the benthic community remained
near the surface or in touch with the
surface-water interface.
Bioturbation, or the modifying of
sediment structure by biological activity,
was observed m nearly all core samples
However, in areas where physica
processes prevailed, biogenii
disturbance was inconsequential, h
coarse to medium sand environment:
found at the head of the Bay, erosion am
sedimentation overwhelmed an'
biogenic effects. Sedimentary features o
channel regions were also shaped b'
physical forces, since fluid muds am
periodic anoxic conditions preventei
long-term establishment of benthos.
In other areas of the Bay, bioturbatioi
had a modifying effect on sedimen
structure. Biogenic structures whict
occurred in Chesapeake Bay sediment!
included dwelling tubes, burrows, an<
feeding traces. Most biological structure
were produced by polychaetes.
Most of the highly bioturbated core:
were located in the meso- and meso
polyhaline regimes, where a greatei
diversity of reworking species exists
Sediments that occurred at depths of less
than 10 m usually supported benthic
populations. Biogenic structure
diversity was greatest in stable muc
environments.
Data indicate that bioturbation of the
sediment occurs in the upper portion o
the substrate. Penetration in the uppei
Bay is greatest in.mixed-sediment envi
ronments and next greatest in the muds
Toxicants are most concentrated in these
regions. Sediment-adsorbed toxicants ir
these substrates are likely to remain ir
the biologically active zone of 20 to 30 err
for up to 100 years.
Results of this biological investigatior
serve as a baseline for research. It is
expected that this information will help tc
explain geochemical profiles and flu>
rates.
Eli Reinharz and Arthur O'Connell are with The Maryland Geological Survey,
Johns Hopkins University, Baltimore, MD 21218.
Duane Wilding is the EPA Project Officer (see below).
The complete report, entitled "Animal-Sediment Relationships of the Upper and
Central Chesapeake Bay." (Order No. PB 83-207 738; Cost: $22.00, 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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