Chesapeake Bay
Underwater Grasses Increase 10 Percent in 2007, But Remain Well Short of
Restoration Goal
Largest gains seen in
Susquehanna Flats, while grasses in lower Bay continue to recover from
2005 losses
ANNAPOLIS, MD – Underwater bay grasses covered nearly 65,000
acres of the Chesapeake Bay and its tidal rivers in 2007, about 35
percent of the 185,000-acre baywide restoration goal, according to data
from scientists with the Chesapeake Bay Program. Though a 10 percent
increase from 59,000 acres in 2006, bay grasses have not yet recovered
to the recent high of 90,000 acres in 2002.
Bay grasses -- also called submerged aquatic vegetation or SAV -- are
critical to the Bay ecosystem because they provide habitat and nursery
grounds for fish and blue crabs, trap sediments, absorb excess nutrients
and reduce shoreline erosion. Bay grasses are also an excellent measure
of the Bay’s overall condition because they are not under harvest
pressure and their health is closely linked to water quality.
“While we saw a slight increase in SAV baywide in 2007 -- due in part
to increases in the very large and dense beds in the upper Bay and upper
Potomac River -- overall there is concern about SAV in many areas
because of declining water clarity,” said Bob Orth, scientist with the
Virginia Institute of Marine Science and leader of the SAV baywide
annual survey.
In the upper Bay zone (from the Chesapeake Bay Bridge north), bay
grasses covered about 19,000 acres, 80 percent of the 23,630-acre goal
and an increase from about 15,500 acres in 2006. The massive grass bed
on the Susquehanna Flats, which is now visible on satellite images,
dominated this zone. Bay grasses in the Flats increased from 8,743 acres
in 2006 to 11,726 acres in 2007, 97 percent of the restoration goal for
that segment. However, much of the rest of the upper Bay zone had little
grasses, particularly on the Eastern Shore from the Sassafras River to
the Chester River.
In the middle Bay zone (from the Chesapeake Bay Bridge to the Potomac
River), bay grass acreage decreased slightly to about 30,000 acres, 26
percent of the 115,229-acre restoration goal. Grass beds remained
reasonably robust in the Severn, upper Patuxent and upper Potomac
rivers. Bay grasses in the upper Potomac River increased from 4,234
acres in 2006 to 6,246 acres in 2007, exceeding Maryland and Virginia’s
restoration goals for that area. However, grasses in the lower central
Bay in Virginia decreased from 2,017 acres in 2006 to 1,342 acres in
2007.
Unusually high salinities due to dry conditions during summer 2007
may have contributed to declines in the Chester and Magothy rivers and
in Eastern Bay, where bay grass acreage fell from 565 acres in 2006 to
80 acres in 2007. Low river flows during drought conditions allow
saltier waters to move up from the Atlantic, negatively impacting
certain bay grass species that are adapted to growing in fresher waters.
In the lower Bay zone (from the Potomac River south), researchers
mapped about 16,000 acres of grasses -- an increase from a record low of
13,000 acres in 2006 and 35 percent of the 46,030-acre restoration goal.
Many beds dominated by eelgrass, which dramatically died back during the
hot summer of 2005, showed some modest recovery in 2007. Grass beds in
the eastern lower Bay, for example, increased from 3,740 acres in 2006
to 5,134 acres in 2007 -- still far short of the 15,107-acre goal for
this segment.
“The overall picture for eelgrass -- one of the two dominant SAV
species in the lower Bay zone -- remains bleak due to multiple
stressors, including declining water clarity, warmer summertime
temperatures and cownose rays,” said Orth.
Bay grasses continue to show a strong presence in many of the
low-salinity and freshwater areas in the lower Bay zone, such as the
Mattaponi, Pamunkey and Chickahominy rivers and creeks off the upper
mainstem James River. These tributary segments are far enough from the
Bay that the drought did not raise their salinity enough to cause
diebacks of the low-salinity grass species that grow there.
“Over the past five to 10 years we have witnessed large increases of
SAV in many of the freshwater tributaries and segments of the Bay,” said
Lee Karrh, scientist with the Maryland Department of Natural Resources
and chair of the Bay Program’s SAV Workgroup. “However, middle- and
high-salinity areas, such as Eastern Bay and Tangier Sound, are well
below their peaks.”
Because of their importance to the Bay ecosystem, in 2003 Bay Program
partners committed to protect and restore 185,000 acres of bay grasses
by 2010.
Annual bay grass acreage estimates are an indication of the Bay's
response to pollution control efforts, such as implementation of
agricultural best management practices (BMPs) and upgrades to wastewater
treatment plants. Bay watershed residents can do their part to help bay
grasses by reducing their use of lawn fertilizers, which contribute
excess nutrients to local waterways and the Bay, and participating with
their local tributary teams or watershed organizations.
Bay managers are supplementing pollution reduction efforts with
experimental bay grass plantings where predicted improvements in water
quality would support bay grasses where none currently exist. These
newly planted grasses act as seed sources which, in turn, produce more
grass beds as water quality improves.
Bay grasses acreage is estimated through an aerial survey, which is
flown from late spring to early fall. For additional information about
the aerial survey and survey results, go to
www.vims.edu/bio/sav/.
Click here for individual river SAV progress.
