United States
Environmental Protection
Agency
Chesapeake Bay
Program
Annapolis MD 21401
Research and Development
EPA-600/S3-83-048 Aug. 1983
Project Summary
Baseline Sediment
Characteristics and
Sedimentation Patterns on the
Virginia Portion of the
Chesapeake Bay
R J. Byrne, C. H. Hobbs, III, and M. J. Carron
The distribution patterns of sediment
physical properties, deposition patterns,
and sediment accumulation rates pro-
vide an integrating framework for in-
vestigating the concentration and dis-
tribution of toxic substances. Over
2,000 surface-sediment grab samples
(1.4 km grid) reveal that the bottom of
Chesapeake Bay, Virginia, is signifi-
cantly sandier than previously reported;
about 65 percent of the area is sand.
Nine hundred samples, selected to
avoid the coarser sands, were analyzed
for total carbon, organic carbon, and
sulfur contents. There are strong cor-
relations between these characteris-
tics and sediment type, especially
weight-percent clay. Additionally, there
is a good relationship between the
organic carbon and sulfur contents.
The project includes an attempt at
constructing a sediment budget using
published values for silt and clay es-
tuarine advection and contributions
from shore erosion measured against
the residual accumulations. The re-
sidual accumulation of silt and clay is
an order of magnitude larger than pre-
viously estimated.
This study indicates that the residual
bottom-accumulation of sand may be
greater than the shore erosion con-
tribution by a factor of 40. It is evident
that additional understanding of sed-
iment flux through both the Bay mouth
and the mouths of the flanking tribu-
taries is required.
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
An important reason for the study of the
physical characteristics of the bottom sed-
iments of Chesapeake Bay is that the
sediments are the loci of interaction be-
tween toxic substances that have been
introduced into the Bay system and the
biological communities that use the same
system Whether the biological elements
make permanent use by residing in the
Bay, or temporary use through migration
or seasonal habitation, they all are to some
extent dependent on the sediments and
the sediment-formed strata which form
the physical structure over and through
which the biota are distributed. If, as often
has been postulated, there are discrete
relationships between the substances of
concern and sediment types, knowledge
of the sediments is critical to understand-
ing the problem of toxic substance. Thus,
the first objective of this study was to
discern the sedimentological characteris-
tics of the bottom sediment at a sufficient
sample density so that reasonable inter-
polations could be made from a sample
subset which is analyzed for various toxic
substances and other related parameters.
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A second objective was to supply maps
of the characteristics of the bottom sedi-
ments to support interpretations made in
other phases of the E PA's Chesapeake Bay
Program, specifically those phases deal-
ing with the transportation of materials and
with the history of recent sedimentation.
A third objective of this project was to
provide a comprehensive statement of the
"condition" of the bottom sediments of
the Virginia portion of Chesapeake Bay
against which future sediment samples
and characteristics could be compared.
This study was integrated wth a similar
study in the Maryland portion of the Bay
conducted by the Maryland Geological
Survey (MGS). Thus, compatible Bay-wide
data will be available to those persons
making interpretations and decisions af-
fecting the region.
Procedure and Methodology
The methods used in this study matched,
to the extent possible, those of the Mary-
land Geological Survey's parallel study of
the Maryland portion of the Bay. The two
studies used essentially identical proto-
cols for the analyses of sediment charac-
teristics and chemistry. However, the
treatment of the rates of deposition and
the information derived were somewhat
different due to differences in the avail-
ability of data from bathymetric surveys
and in the formatting for automatic data
processing.
Bottom samples were acquired with a
stainless steel Smith- Maclntyre grab sam-
pler which has a volume of approximately
0.01 m3. When the sampler was on deck,
at least two subsamples were taken from
the sediment surface. Surface samples
were skimmed from the top centimeter for
the carbon and sulfur analyses. These
were placed in labelled plastic vials and
promptly refrigerated or iced. The second
subsamples were several hundred grams
of material from the top 4 to 6 cm. These
were placed in large plastic envelopes with
top fasteners and, although not refrig-
erated, care was taken to avoid long ex-
posure to environmental extremes. The
total field collection was 2,172 sample
sets from 2,018 locations. The smaller
subsamples, for carbon and sulfur anal-
yses, were transported on ice from the
ship and then frozen and held until pre-
treatment for analysis. Upon delivery to
the laboratory, the larger subsamples,
secured for water content and size anal-
yses, were mixed and split into at least
three subsamples.
Because the sediments range in size
from granules to clays, different analytical
techniques were required on different
fractions of the samples. The sand fraction
was analyzed in a Rapid Sediment Analyzer
(settling tube), the granules by conven-
tional sieving, and the fines by Coulter
Counter.
Approximately 900 samples were se-
lected for carbon and sulfur analyses. The
primary interest was in the chemical al-
liances with the finer grained sediments;
therefore, the samples were selected on
the basis of an inferred minimum of 1 5
percent mud by weight. After being dried
and powdered, the samples for sulfur and
total carbon analyses received no further
pretreatment The samples to be analyzed
for organic carbon were digested with 10
percent HCI to remove carbonate. The
analyses were made on LECO equipment
using standard procedures. All were made
in at least duplicate.
Results and Conclusions
The silts and clays are generally con-
fined to the several deep channels within
the system and to the shallower, more pro-
tected areas such as Mobjack Bay. The
deep channel near the southern portion of
the Eastern Shore peninsula is an anomaly
as it contains only sands.
The distribution of the fractional ac-
cumulations of sand, silt, and clay sug-
gests that the principal clay sources are
from the northern Bay followed by the Bay
mouth, that the principal sources of silt are
the Bay mouth followed by the northern
Bay, and that the Bay mouth is the prin-
cipal source of sand.
The estimates of a sediment budget
were constructed for the Virginia portion
of the Bay using measured values for the
contribution from shore erosion and re-
sidual bottom accumulation, and literature
values for silt and clay importation from
Maryland waters. The residual bottom
accumulation of silt and clay exceeds the
values from the estimated sources by a
factor of 1 2. The measured values of the
silt and clay contribution from shore
erosion are an order of magnitude less
than previously estimated. Bottom accum-
ulation of sand exceeds that contributed
from shore erosion by a factor of 40.
Previous attempts at constructing a sed-
iment budget have dealt only with sus-
pended sediments and with shore erosion
as the sole contributor of sand. The
patterns of deposition and the magnitudes
of sand accumulation clearly indicate that
there is a strong advection of nearshore
sands into the Bay mouth and up the Bay
stem.
R. J. Byrne, C. H. Hobbs III. andM. J. Carron are with the Virginia Institue of Marine
Science. Gloucester. MA 23062.
Duane Wilding is the EPA Project Officer (see below}.
The complete report, entitled "Baseline Sediment Characteristics and Sedimenta-
tion Patterns on the Virginia Portion of the Chesapeake Bay," (Order No. PB
83-224 899; Cost: $16.00. 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, MA 21401
ft US. GOVERNMENT PRINTING OFFICE 1983-659-017/7153
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