For the second year in a row, underwater grasses in the Chesapeake Bay declined in 2011 -– dropping by 21 percent from 2010, following a 7 percent decline the previous year, in part because of heavy rainfall and runoff pollution, according to the U.S. EPA Chesapeake Bay Program.
Hurricane Irene and Tropical Storm Lee turned the Bay into a muddy mess that looked like chocolate milk in satellite photos, and this muck smothered the grasses.
Aquatic vegetation is important to the Bay, because it filters silt out of the waterways and adds oxygen to water. Grasses also serve as vital shelter for young blue crabs, striped bass, and other forms of life. The extent of grasses in the Chesapeake Bay, however, are now at their lowest levels since 2006.
The amount of grass is now “much more typical of what was observed prior to 1991 when grass acreages were at the lowest levels recorded” by aerial surveys, according to the Chesapeake Bay Program, which announced the results this morning. Contributing to the decline were hot weather and heavy rains in 2010 and 2011, which washed large amounts of sediment down the Susquehanna River and other waterways.
The long-term trend is that underwater grasses in the Bay remain at less than half the levels they were in the early to mid 20th century, before Hurricane Agnes in 1972 smothered many grass beds with muddy runoff.
Bay grasses have gradually expanded since that low point in the 1970s, and in 2010 were at 79,675 acres, or roughly double the roughly 35,000 acres of a quarter century ago, according to figures from EPA's Chesapeake Bay Program. In 2011, however, the total extend fell to an estimated Bay-wide total of 63,074 acres, according to the Bay Program.
The Bay Program website gave this explanation for the decrease in grasses in 2011:
"According to Bob Orth, scientist with the Virginia Institute of Marine Science (VIMS) and coordinator of the annual bay grass survey:
1) Summer 2010 was unusually hot, causing severe eelgrass die offs in the lower Bay. These beds had already been measured for the 2010 acreage survey, so these eelgrass losses were not officially recorded until 2011.
2) In Spring 2011, heavy rains and resulting runoff created very muddy conditions in the upper Bay and its rivers during the bay grass growing season.
3) Last September, Hurricane Irene and Tropical Storm Lee brought even more rain and mud to the Bay’s waters."
By Tom Pelton
Chesapeake Bay Foundation
(Photo at top from Chesapeake Bay Program)