Freshwater flows bode ill for bay life Freshet could cause major algae bloom

April 12, 1993|By Timothy B. Wheeler | Timothy B. Wheeler,Staff Writer

Spring showers may bring flowers, but last month's blizzard and downpour are likely to yield blooms of a different sort in Chesapeake Bay this summer.

Melting snow and heavy rains in March produced near-record flows of fresh water into the bay from its tributaries, according to the U.S. Geological Survey. The Susquehanna River, which crested April 3, is still running much higher than normal.

That bodes well for swimmers in bay country, since a wet spring may delay the summer onslaught of stinging sea nettles.

But the surge of muddy, fresh water also seems likely to spawn unusually intense "blooms" of algae, the microscopic floating plants whose death and decay produce a vast "dead zone" of oxygen-starved water on the estuary's bottom every summer.

Scientists say the spring freshet could spell trouble for the bay's slowly recovering underwater grasses, and for clams, crabs, oysters and some finfish.

"It may give an unwanted jolt, ecologically [to the bay]," said Dr. William C. Boicourt, an oceanographer at the University of Maryland's Horn Point Environmental Laboratory.

What a difference a year makes. Last fall, state and federal officials declared that the bay's waters were the healthiest they have been since 1984.

One reason: Last spring was abnormally dry, and the reduced flow of fresh water into the Chesapeake delayed and weakened algae growth. As a result, the bay's deep waters had unusually high concentrations of dissolved oxygen, which fish and shellfish need to breathe.

The bay suffers every year from an oversupply of nutrients, nitrogen and phosphorus from sewage, from fertilizer washing off farmland and suburban lawns and from air pollution raining down on the 64,000-square-mile watershed.

Those nutrients feed massive algae growths in the spring, which eventually die and sink to the bottom.

As bacteria feeding on the dead plants consume the dissolved oxygen, a zone of lifeless water forms on the bottom and #F stretches down the middle of the Chesapeake, from the Bay Bridge to the mouth of the Rappahannock River in Virginia.

Heavy freshwater flows aggravate the problem by preventing oxygen from working its way down into deeper water. Salt water pushing up the bay from the Atlantic Ocean is heavier than fresh water, and the two layers do not mix well when fresh water surges in from the bay's tributaries.

And heavy spring runoff of rain and melting snow also muddies the water with sediment and delivers an extra dose of nutrients.

Last month's "storm of the century" dumped 10 to 50 inches of snow on the East Coast, then chased it with more than an inch of rain.

The amount of fresh water flowing into the bay from its tributaries averaged 149 billion gallons per day, said Robert James at the Geological Survey's Towson office.

That is the third highest flow in more than 40 years, and more than 50 percent above average, he said.

The flow of the Susquehanna, the bay's largest tributary, over Conowingo Dam has not been this high for 15 years, said Michael Wood, a spokesman for Philadelphia Electric Co., the utility that operates the hydropower dam.

On April 3, half the dam's 53 spillways were opened to release what Mr. Wood said was a "spectacular" peak flow of 445,000 cubic feet of water each second -- nearly three times last year's high.

Dr. Boicourt predicts that this pulse of fresh water will create the largest zone of oxygen-starved water in years, starting in June. The zone could even extend northward beyond the Bay Bridge.

Fish kills could increase this spring and summer, said William J. Goldsborough, fisheries scientist for the Chesapeake Bay Foundation.

Moreover, watermen may find more dead crabs in their traps, he said, and people may see more crab "jubilees" -- the eerie phenomenon where crabs seem to fight to get out of the water, perhaps because they are suffocating.

The bay's underwater grasses, which provide food and shelter for crabs, fish and waterfowl, also could suffer from the spring flood.

Badly depleted in the 1970s and early 1980s, the grass beds have been recovering slowly. But they cannot grow in water made too murky -- by sediment or algae -- for sunlight to penetrate.

In the Susquehanna-fed upper bay, the water is "pretty much chocolate milk," said Dr. J. Court Stevenson, a University of Maryland ecologist at the Horn Point lab.

"Right now, it doesn't look good at all for submerged grasses this year, at least north of the Bay Bridge," he said.

And if spring rains continue, the fresh water might deal a death blow to more of the bay's disease-ravaged oysters.

Dermo and MSX, the parasitic diseases that are killing oysters, cannot tolerate fresher water, and many scientists had hoped that a wet winter and spring might flush the microscopic organisms down the bay.

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