Bay grasses expand 6% in '96 survey Results reverse declines recorded in previous two years

'It's really fascinating'

Increase was surprise to scientists after major spring flooding

April 15, 1997|By Timothy B. Wheeler | Timothy B. Wheeler,SUN STAFF

The underwater grasses that sustain fish and crabs in the Chesapeake Bay expanded by 6 percent last year, reversing a two-year decline in one of the key indicators of the bay's health.

The 3,500-acre growth of bay grasses, reported yesterday by the Environmental Protection Agency's bay program office, was a welcome surprise because it occurred despite storms that flooded the Chesapeake with record flows of fresh water.

Biologists had blamed spring flooding in 1994 and 1995 for declines in underwater grasses during those years. Experts said the "freshets" had killed off grasses by pumping more sediment and nutrient pollution into the bay.

"It's really fascinating that bay grasses held their own in 1996 despite the record freshwater flow," said Robert Orth, a biologist at the Virginia Institute of Marine Science.

In 1996, a blizzard in January and a hurricane in September helped flood the bay with 87.5 billion gallons of fresh water daily, the highest flow ever recorded. The second highest occurred in 1972 after the region was hit by Tropical Storm Agnes, an event that many scientists say triggered long-term declines in the bay's grass beds and fish.

Orth, who coordinates the annual baywide aerial survey, said the timing of last year's storms probably made the difference. The blizzard flooded the bay before underwater grasses sprout, and the hurricane hit after the growing season was over.

However, experts caution that the mud and nutrient pollution dumped in the bay in September still may hurt the growth of underwater grasses this spring.

"We're still trying to figure out whether there are delayed impacts," said Peter Bergstrom, a biologist with the U.S. Fish and Wildlife Service in Annapolis.

Most of the growth occurred in Maryland, where state officials attributed the 13 percent increase in grasses to improved water quality because of pollution control efforts.

But Orth said scientists lack the data to link grass resurgence firmly to improved water quality in all areas of the bay.

The improvement last year is the first since 1993, when federal and state officials working to restore the Chesapeake Bay made restoration of the estuary's grass beds one of their top priorities.

Underwater grasses provide vital nurseries for fish and crabs in the bay, and they improve water quality by absorbing nutrients and settling out sediments clouding the water. They also can help control shoreline erosion.

But the grasses die if excessive sediment blocks out sunlight, or if too many nutrients get in the water.

Once thought to cover nearly 600,000 acres of bay bottom, underwater grasses dwindled after Tropical Storm Agnes struck in June 1972. The low point came in 1984, just before the bay restoration effort began, when an aerial survey found only 29,800 acres of submerged vegetation.

Grasses recovered steadily as the bay cleanup progressed, peaking in 1993 at 73,100 acres.

With last year's recovery, grasses rebounded to 63,400 acres, which represents an expansion of 70 percent overall since the mid-1980s.

Federal and state officials hope to restore grasses to 114,000 acres by 2005.

One-year increases of more than 20 percent were recorded in some upper bay rivers, such as the Bush, Gunpowder, Middle, Patapsco, Severn and South. Parts of the Patuxent and Magothy, where scientists have noted improved water quality, also saw big increases.

Some areas lost grasses, which experts attributed to localized water quality problems, such as high levels of sediment or algae. Declining areas included the Northeast, Elk, Bohemia, Sassafras, Chester, Manokin and Big Annemessex rivers.

Grasses grew by 17 percent overall on the Potomac River, but lost vegetation in some areas around Washington.

Pub Date: 4/15/97

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