United States
Environmental Protection
Agency
Chesapeake Bay
Program
Annapolis MD 21401
Research and Development
EPA-600/S8-79-029 Oct. 1982
Project Summary
Distribution and Abundance of
Submerged Aquatic
Vegetation in the Lower
Chesapeake Bay, Virginia
Robert J. Orth, Kenneth A. Moore, and Hayden H. Gordon
Aerial photography and surface
information were employed to delin-
eate the distribution and abundance of
submerged aquatic vegetation (SAV)
in the lower Chesapeake Bay and its
tributaries. Aerial photographs were
transferred onto 31 topographic
quadrangles which represented over
8500 hectares of SAV. All information
from this 1978 mapping effort was
entered into a computerized data
base.
The areas with the greatest concen-
tration of SAV were located at the
mouths of the largest tidal rivers and
creeks along the Chesapeake Bay
shoreline and to the east of Tangier
and Great Fox Islands. The oligohaline
and freshwater regions were essentially
lacking in large areas of SAV.
Analysis of 40 years of SAV histori-
cal data revealed reduced coverage
and density in the late 1930s, an
increase from 1937 to 1953, followed
by a large loss between 1971 and
1974. Whatever factor or factors
caused the major decline in the 1930s
may also explain the decline of the
1970s. The decline continued through
1978, when the lowest levels of SAV
in 40 years occurred.
This Project Summary was devel-
oped by Linda C. Davidson of EPA's
Chesapeake Bay Program, Annapolis,
MD, to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Submerged aquatic vegetation (SAV)
systems serve many functional roles in
the Chesapeake Bay ecosystem. Among
these are habitat for macroinvertebrates,
protection from predators tor many
species of juvenile fishes and crabs, and
food for herbivores which feed off the
diverse epiphytic growth on SAV blades.
SAV converts an otherwise bare sand or
mud bottom into a complicated vegetated
community that not -only supports a
varied animal population but also serves
as a very efficient "nutrient pump"
moving nutrients from the sediment to
the water column and vice versa. Also,
these grass-beds help reduce shoreline
erosion by absorbing wave energy due
to the binding of the sediment by the
roots and leaves of the plants.
Chesapeake Bay supports extensive
shoal areas that are heavily vegetated
with SAV. Historically, emphasis was
placed on these areas because of their
importance as food for waterfowl.
However, with the recent decline of
SAV in the 1970s, other important roles
of these areas have become apparent.
Because these areas are important to
the well-being of the Bay, they must be
properly managed, recognizing the
importance of the SAV resource, its
location, its abundance, and the dyna-
mics of the SAV systems. The objective
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of this study was to define the current
distribution of SAV in the lower Chesa-
peake Bay and to focus on any trends
related to the dynamics of the system
that might exist in the historical records.
Procedure/Methodology
Aerial photography and field investi-
gations were employed to delineate the
distribution and abundance of sub-
merged aquatic vegetation (SAV) in the
lower Chesapeake Bay. Aerial photo-
graphs were transferred onto topographic
quadrangles (1:24,000). Individual SAV
beds were measured and computed
with an electronic planimeter and
stored in a computer data base. Four
density categories were applied to each
bed: less than 10 percent cover, 10to40
percent cover, 40 to 70 percent cover,
and 70 to 100 percent cover. Field
investigations were done at numerous
sites for species composition, percent
cover, and bottom sediment types
Results/Conclusions
Thirty-one mylar USGS topographic
quadrangles were produced showing
significant areas of SAV. Twenty-seven
of these quadrangles were of mesohaline
and polyhaline areas dominated by a
species mixture of Zostera marina and
Ruppia maritima, the remaining four
depicted significant areas in oligohaline
and freshwater regions of the Potomac,
Chickahommy, and James Rivers.
The oligohaline and freshwater re-
gions were essentially lacking in large
areas of SAV. Field investigations
revealed mostly small areas of SAV
usually adjacent to tidal marshes. The
mesohaline and polyhaline regions of
the largest rivers and creeks along the
Chesapeake Bay shoreline contained
the greatest concentrations of SAV. The
most significant areas were: along the
western shore of the Bay between Back
River and the York River, around the
shoreline of Mobjack Bay; throughout
the shoal areas east of Tangier and
Great Fox Islands; and behind large
protective sand bars located along the
Bay's eastern shoreline near Hungar's
Creek and Cherrystone Creek.
The distribution of SAV species in
tidal waters was classified into three
associations based on their co-occur-
rence: (1) Zostera marina (eelgrass) and
Ruppia maritima (widgeongrass) domi-
nating mesohaline and polyhaline
waters; (2) Potamogeton spp (pond-
weeds) and Zannichellia palustris
(pondweeds) dominating oligohaline
waters; and (3) the freshwater species
Ceratophyllum demersum (coontail).
Species diversity increased in an
upstream direction
Analysis of 40 years of historical SAV
data for six selected areas revealed
changes in grass-bed coverage. All six
sites, Munfort Island and Jenkins Neck
in the York, the East River in Mobjack
Bay, Parrott Island in the Rappahannock
River, Fleets Bay, and Vancluse Shores
at the mouth of Hungar's Creek showed
reduced coverage and density in the late
1930s, an increase from 1937 to 1953,
and then the largest loss between 1971
and 1974. Decreases in SAV continued
through 1978 when the distribution and
abundance was the smallest observed
over the last 40 years
Recommendations
Submerged aquatic vegetation com-
munities are dynamic systems that
change in abundance annually and
seasonally. At present, these systems
are in a reduced state of abundance.
Aerial photography should be takerj
under the constraints of tidal height,
sun angle, wind conditions, etc.; at
altitudes of 3740 meters which allows
direct comparison to the standard
topographic quadrangle (1:24,000); and
during the early summer to record
maximum standing crop of the vegeta-
tion. In addition, because the oligohaline
,and freshwater regions have been
shown to have scattered small beds of
SAV that are not evident from the aerial
photographs, it is recommended that
further field studies be done in these
areas to provide an understanding of the
distribution, abundance, and resource
value of the vegetation.
Robert J. Orth, Kenneth A. Moore, and Hayden H. Gordon are with Virginia
Institute of Marine Science, Gloucester Point, VA 23062.
William A. Cook was the EPA Project Officer (for information, see below).
The complete report, entitled "Distribution and Abundance of Submerged
Aquatic Vegetation in the Lower Chesapeake Bay, Virginia," (Order No. PB
80-140 726; Cost: $18.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
For information contact David Fletner at:
Chesapeake Bay Program
U.S. Environmental Protection Agency
2083 West Street, Suite 5G
Annapolis, MD 21401
« U.8.GOVERNMENTPHINT1NB OFFICE: 1»M-559-017/0850
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