The Chesapeake Bay usually makes headlines for the sorry state of its ecosystem — chronically beset by pollution, everything from its famous crabs to fish stocks seem to always be teetering on the brink of calamity. It's nice to have some good news for a change.
According to a 17 year-long study, vegetation in the Potomac River, one of the bay's largest tributaries, has made a dramatic comeback. Native aquatic species are elbowing out invaders, and excess nutrients from sewage and other pollutants are on a long-term decline.
Henry Ruhl of the University of Southampton in the United Kingdom and Nancy Rybicki of the United States Geological Survey charted the growth of submerged vegetation in the Potomac from 1990 trough 2007. Plants that grow in less than about six feet of water are crucial habitat for fish, birds, and a host of tiny aquatic creatures that form the base of the ecosystem.
Farming around the Chesapeake watershed and the arrival of sewage treatment plants like the Blue Plains Wastewater Treatment Plant in Washington, D.C. spewed huge amounts of nitrogen and phosphorous into the water for decades. The excess nutrients triggered blooms of microorganisms that lowered oxygen levels and clouded the water, making it tough for plants to survive. By the late 1970s, previously thriving areas of the river were devoid of vegetation.
Over the last two decades, Ruhl and Rybicki found that vegetation increased by a factor of ten through much of the Potomac (see figure from the paper, where SAV stands for "submerged aquatic vegetation"). Much of this improvement came from Blue Plains cleaning up its act.
"Upgrades to the wastewater treatment plant have benefited SAV habitats 50 miles downstream. These findings underscore the benefits of nutrient reduction efforts on a major tributary to the Chesapeake Bay," Rybicki said.
Ruhl and Rybicki published their results in a recent issue of the journal Proceedings of the National Academy of Sciences.
"People want to know that money spent on ecosystem restoration is having tangible results, but many feel that efforts to clean up Chesapeake Bay have so far had limited success," Ruhl said.
To a large extent, that remains the case — the Chesapeake has made relatively small gains in recovering its lost vegetation. But the researchers are hopeful that the Potomac's success story can be used as a guide for restoration throughout the bay. By minimizing pollution from waste treatment plants and farmland, one of the country's great waterways could soon see a great resurgence of green.
Image: USGS/Curtis Dalpra, Interstate Commission on the Potomac River Basin