In rare good news for the Chesapeake Bay, scientists reported Wednesday that underwater grasses made significant gains last year in the beleaguered estuary, growing thickly enough in the upper bay to visibly clear the water while continuing to rebound in the lower bay.
Aerial surveys found that the grasses had spread across nearly 12,000 additional acres of bottom last year, an increase of 18 percent from 2007, according to the Chesapeake Bay Program, the federal-state partnership working to restore the estuary. The nearly 77,000 acres of bay bottom covered with grasses is the fourth-largest extent of submerged vegetation since scientists started tracking it 25 years ago.
Lee Karrh, a biologist with the Maryland Department of Natural Resources, called the expansion "impressive and encouraging." He noted that grasses in 13 freshwater rivers have exceeded restoration goals set by officials.
Bay grasses play a vital role in the bay, sheltering young fish and crabs, filtering sediment from the water and reducing shoreline erosion. They also are an important barometer of the Chesapeake's health, since they respond to relatively small changes in water quality.
Grass beds in the mouth of the Susquehanna River kept expanding and growing thicker last year, a decade-long trend that scientists attributed to reductions in nitrogen pollution - and to the filtering effects of the grasses themselves.
"These beds are now so big they have a dramatic effect on their own environment," said Robert Orth, a professor at the Virginia Institute of Marine Science and leader of the annual survey. Plumes of clear water can be seen flowing from the flats down the upper bay. Grasses in the upper Potomac River also have increased, a gain researchers attribute to pollution reductions at the Blue Plains wastewater treatment plant in Washington.
Eelgrass, which grows in saltier water in the lower bay, is continuing a comeback after a severe die-off in 2005, the scientists said. The rebound there may stem from milder weather rather than from real improvements in water quality, they caution.
Grasses actually declined, however, in the middle of the bay, particularly in the mouth of the Choptank River and in the lower Potomac. While some grasses hang on in the upper Patuxent, the rest of the river has little or no submerged vegetation. Orth said the problems there stem from continuing high levels of nutrient pollution and declining water clarity.
