Gush of rainfall called harmful to bay

Runoff after long drought threatens oxygen supply in water, scientist says

April 24, 2003|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

A leading Chesapeake Bay scientist says a three-year drought, followed by the winter's heavy snow and rain have combined to create the worst possible conditions for the bay's health and could lead to the worst crab harvest ever.

Since October, almost 30 inches of precipitation have fallen, and researchers say so much sediment has washed into the nation's largest estuary that it threatens the supply of oxygen for crabs and other organisms.

"It's the worst of all possible conditions," said J. Charles Fox, a former Maryland Department of Natural Resources secretary and federal environmental official who is now a vice president of the Chesapeake Bay Foundation.

Watermen also say that more oysters are dying than ever before, which they see as an worrisome sign for the crabbing season that began April 1.

"If things are this bad this early in the year, it's going to get even worse," said Larry Simns, president of the Maryland Watermen's Association.

Fox, who surveyed a popular oyster bar off Hackett's Point near Annapolis yesterday, agreed that the large number of dead oysters dredged up are a warning signal for this year's crab harvest.

He added that runoff poses a particularly serious threat this year because the three-year drought built up sediment on fields and farms that is now washing into the bay over a relatively short time.

"With the recent rains, we're in effect flushing two or three years of pollution into the bay," Fox said.

Although they concede that Fox may be correct, other scientists argue that it is too early to say whether oxygen levels are higher than average or will hurt this year's crabbing.

"Oyster mortality happens in the spring, and if there's no hard data, it's going to be hard to say what actually caused it," said Chris Judy, director of the Maryland Department of Natural Resources' shellfish division.

The return of the rainfall that started in October -- with nearly 11 inches falling in February and March -- made this the 10th wettest winter on record.

During March, 144 billion gallons of water flowed into the Chesapeake Bay each day, 49 percent above average, according to the U.S. Geological Survey.

Fox said the phosphorus and nitrogen in the runoff will stimulate algae blooms when the bay's temperatures warm up this summer, blocking sunlight and choking off the bay grasses that serve as habitat for crabs and other aquatic life.

When the algae formed by the nutrients die and settle on the bottom of the bay, their decomposition will remove more oxygen from the water, he said.

But other scientists say it is hard to pinpoint what killed the oysters dredged up in Fox's survey, or whether oxygen levels were lower than normal in the waters where they were found.

DNR's Judy said he had heard watermen's concerns about oyster mortality and indeed found a number of dead oysters and mussels during a survey he conducted last month.

But he and others say it is unclear whether low oxygen levels or parasites killed the shellfish. They note that the bay's oyster population has been reduced significantly since the mid-1980s by two parasitic diseases, MSX and Dermo.

"We've heard reports from around the bay that winter mortality is higher than normal. It could be low oxygen, but it could be something else," Judy said.

Oysters have become so scarce that this year's harvest is the smallest since Maryland began keeping records in 1870. Preliminary reports show that 51,145 bushels were harvested during the six-month oyster season that ended April 1, compared with 148,000 bushels last season.

Michael Fritz, an ecologist and coordinator for the Environmental Protection Agency's Chesapeake Bay Program, said heavy rainfalls could also produce a less salty bay and healthier oysters this year since the parasites thrive in salt water.

"What [Fox] is talking about are manifestations of a nutrient overloaded system, and nutrient overloads are always worse when we have a high flow year that follows extremely dry years," he said.

Fritz said it is too early to predict summer oxygen levels and their effect on the crab harvest.

"How bad it will be, that's hard to say. We have to wait and see," he said.

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