Poring over old photographs at the National Archives, a Maryland researcher has found proof that the Chesapeake Bay's aquatic grasses have declined extensively in the past 50 years, depriving bay creatures of vitally important shelter.
The grasses surrounding one small island in Tangier Sound have fallen from 6,000 acres in 1952 to 83 acres in 1997, said Michael Naylor, a biologist with the Maryland Department of Natural Resources.
"When you look at it historically, it's almost a complete obliteration of what used to be there," Naylor said yesterday.
In a speech to Maryland environmentalists and public officials in Annapolis, Gov. Parris N. Glendening yesterday called Naylor's early findings "troubling" and said governments need to do more to tackle the onshore pollution that trickles down to damage bay grasses.
"It is time to fight for the protection of our green infrastructure," Glendening said.
Experts think most of the bay was once a lush underwater meadow, where young fish, crabs and clams hid from hungry predators while vast flocks of water birds nibbled on the grasses' blades, roots and seeds. But the grasses began disappearing as pollutants clouded bay waters, blocking sunlight from the bottom.
Scientists estimate that perhaps 600,000 acres of bay bottom were covered with grasses when European explorers arrived here in the 1600s. University of Virginia expert Robert Orth found only about 69,000 acres remained in 1997 -- an improvement over previous years, but still far from the restoration goal of 114,000 acres.
The scientists' estimate of the original acreage is a guess, based on their belief that the grasses probably can't grow in water much deeper than six feet. No one is sure exactly how widespread the grasses once were or when the decline began. Naylor's research could help find some answers.
With the help of Chesapeake Bay Program biologist Kent Mountford, Naylor tracked down a series of aerial photographs taken by the U.S. Department of Agriculture in 1952. "It was part of an effort after World War II to evaluate cropland and the potential productivity of America's soils nationwide," he said.
Using modern techniques that allow the use of satellite data to pinpoint the photographs' precise locations and computer imagery to analyze the vegetation patterns they show, Naylor compared the USDA photos with Orth's most recent aerial survey, the 1997 study.
The results showed grasses had declined by 98 percent around South Marsh Island, a low, grassy spit that is a nesting ground for pelicans and other birds just north of Smith Island in Somerset County.
Naylor said much of the decline is probably due to Hurricane Agnes, which dumped tremendous amounts of silt into the bay in 1972, smothering bay grasses. A postwar building boom also added silt and brought seepage from septic tanks, runoff from farm fields and other contaminants that have clouded bay waters.
Naylor will spend much of the next year comparing the old and new images of Tangier Sound, the mouth of the Potomac, Eastern Bay near Kent Island and other once-grassy areas.
While underwater grasses have expanded by about 10 percent overall in recent years, Orth's survey shows Tangier Sound is rapidly becoming denuded. Its grass beds have fallen from 18,000 acres in 1992 to 9,000 acres last year.
That's especially worrisome, Naylor and many other experts say, because the Tangier Sound area is vital to the blue crab fishery.
Female blue crabs lay their eggs at the bay's mouth, relying on currents to carry the tiny youngsters back into the bay. "When the blue crabs are being flushed back into the bay, Tangier Sound is the first place they settle, and they require those [grasses] for survival," Naylor said.
Pub Date: 1/19/99