Warmer, saltier Chesapeake

Drought conditions: Limited rainfall has both negative and positive results for the bay.

July 14, 1999

THE PROLONGED shortage of rainfall has taken a toll on the Chesapeake Bay, with some exceptionally large fish kills. But it has also had some positive results -- a reminder that the bay system is ever changing and subject to the unpredictable fluctuations of weather.

The drought has been good news for the underwater grasses that are a source of food and habitat for aquatic life. After a recent report that the bay's submerged grasslands had receded over the past year, scientists are finding hopeful signs of renewed growth this summer.

Saltier water in the estuary and its tributaries, caused by a lack of flushing rainfall and accelerated evaporation, should also be good for the blue crab. But catches have been below normal this season, prompting speculation that the number of crabs in the bay is again in decline. Conversely, higher salt levels threaten the oyster population, increasing their vulnerability to diseases such as MSX.

But fish kills have been the most prominent result of the dry spell. The estimated 200,000 dead fish found in the Magothy and Patapsco rivers this month represent the largest fish kill in a decade. The fish (mostly bait fish) died primarily because of warm waters that reduced oxygen levels and because of the excessive salt water that is toxic to many species.

Lack of rain may often lead to cleaner water, reducing the rain-driven flows of pollutants off the land and into the estuary. But state investigators report numerous large algae blooms in upper coves and streams, around urbanized areas lacking natural buffers and filters along the shoreline. The burgeoning blooms impede sunlight from penetrating the water, limiting oxygen-creating photosynthesis of plants. When the blooms die off, they consume large amounts of remaining oxygen.

There's no short term relief in sight. The National Weather Service predicts that net evaporation from land and water will exceed normal summer rainfall, perpetuating the pattern of a warmer, saltier Chesapeake.

Pub Date: 7/14/99

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