Baltimore Sun

Study: Cleaner Potomac boosts underwater grasses

Is all the money and effort we've put into cleaning up the Chesapeake Bay doing any good?  In one spot, the Potomac, the answer appears to be yes. 

A study by the U.S. Geological Survey and England's National Oceanography Centre has found that reducing nutrient pollution in the Potomac River and improving its water clarity have helped restore a rich fish habitat there of underwater grasses. Analyzing 18 years of data,  US and British scientists found that as nutrient levels in the river declined, the extent of submerged aquatic vegetation, or underwater grasses, has doubled since 1990.

What's more the area covered by native grasses has increased 10-fold researchers say, eclipsing the exotic hydrilla that once represented about the only vegetation there.


"Improvements to plant communities living at the bottom of the river have occurred nearly in lock step with decreases in nutrients and sediment in the water and incremental reductions in nitrogen effluent entering the river from the wastewater treatment plant for the Washington DC area," USGS scientist Dr. Nancy Rybicki said in a news release reporting the study results.

Underwater grasses had virtually disappeared from the Potomac by the 1980s, when the bay restoration effort began.  Submerged vegetation coverage in the river has grown from 4,207 acres in 1990 to 8,441 acres in 207.  The growth has occurred up to 50 miles downstream from Washington, where the Blue Plains sewage treatment plant is the biggest single discharger of wastewater in the entire six-state Chesapeake watershed.  Most of the underwater grass restoration goal has been met for that stretch, almost reaching the Harry Nice (US 301) bridge.  See the graph here.

The lower river, however, remains seriously deficient in underwater grasses.  That portion is heavily influenced by tidal influx from the bay, where nutrient levels have not declined as much.  But scientists said the improvements in the upper river offer hope for restoring the rest of the bay, if nutrient and sediment pollution throughout the watershed can be reduced.


"Our results suggest that widespread recovery of submerged vegetation abundance and diversity can be achievable if restoration efforts are enhanced across the bay," said Henry Ruhl of the National Oceanography Centre.

(Photo of underwater grasses by Curtis Dalpra, Interstate Commission on the Potomac River Basin; photo wild celery by Nancy Rybicki, USGS)