by Alicia Pimental
April 29, 2009
Underwater bay grasses increased by 18 percent in 2008 to cover 76,861 acres throughout the Chesapeake Bay and its tidal rivers, according to data collected by scientists with the Bay Program. This is the fourth largest total amount of bay grasses recorded since surveying began in 1984.
Bay grasses are vital to the Bay because they filter pollutants, produce oxygen, prevent erosion, shelter fish and blue crabs and provide food for waterfowl. They are 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.
The 11,943-acre increase from 2007 was driven by the continued expansion of grasses on the Susquehanna Flats in the upper Bay and the steady recovery of eelgrass and widgeon grass in the middle and lower Bay.
- Susquehanna Flats grass beds increased by 2,642 acres, accounting for 22 percent of the baywide increase.
- Growth of eelgrass and widgeon grass accounted for about 60 percent of the baywide increase.
Another positive sign for bay grasses is that about 60 percent of bay grass beds were considered “high-density,” the highest percentage since 1984. High-density grass beds are better at removing pollution, producing oxygen and providing shelter for fish and shellfish.
The 2008 bay grass acreage of 76,861 brings the Bay Program to 42 percent of its goal to restore 185,000 acres of grasses.
For the first time since 2001, bay grasses increased in all three geographic zones of the Bay.
In the upper Bay (from the mouth of the Susquehanna River to the Bay Bridge), bay grasses increased 21 percent to 22,954 acres. This is 97 percent of the upper Bay goal of 23,630 acres.
Bay grass increases in the upper Bay are due in part to lower amounts of nitrogen entering the Bay from the Susquehanna River. The Susquehanna Flats, which includes three of the five largest grass beds in the Bay, now filter water so well that plumes of clear water are visible flowing down the Bay.
“Thirteen of the Bay’s fresh water rivers have exceeded their bay grass restoration goals, with another four on the verge of passing benchmarks,” said Lee Karrh, a biologist with the Maryland Department of Natural Resources and chair of the Bay Program’s Submerged Aquatic Vegetation Workgroup.”
In the middle Bay (from the Bay Bridge to the Potomac River), bay grasses increased 15 percent to 34,521 acres. This is 30 percent of the middle Bay goal of 115,229 acres.
One middle Bay segment that continues to show increases is the upper Potomac. At 6,517 acres of bay grasses, the upper Potomac has exceeded its restoration goal by 41 percent. This increase is due in part to improvements in wastewater treatment at the Blue Plains facility in Washington, D.C. in 2000.
However, 21 of the 44 middle Bay segments had no bay grasses in 2008. Additionally, many middle Bay segments saw decreases in bay grass acreage, including:
- The mouth of the Choptank River (decreased by 798 acres, or 63 percent)
- The lower Potomac River (decreased by 282 acres, or 42 percent)
In the lower Bay (from the Potomac River to the mouth of the Bay), bay grasses increased 21 percent to 19,386 acres. This is 42 percent of the lower Bay goal of 46,030 acres.
Eelgrass, a species only found in the Bay’s saltier waters, continued its comeback from a 2005 baywide die-off. Notable segments include:
- The eastern lower Chesapeake Bay (21 percent increase to 6,230 acres)
- The lower Rappahannock River (44 percent increase to 610 acres)
- Mobjack Bay (29 percent increase to 7,977 acres)
“The continuing recovery of eelgrass in the lower portions of the Bay is an extremely positive sign, particularly in light of the dramatic losses in 2005,” said Bob Orth, a professor at the Virginia Institute of Marine Science and leader of the annual survey.
Despite the overall increase, 11 of the 28 lower Bay segments had no bay grasses in 2008, and the Chickahominy River lost 25 percent of its grasses.
Annual bay grass acreage estimates are an indication of the Bay's response to pollution control efforts, such as implementation of agricultural conservation practices 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.
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/.