Freshwater flows into the Chesapeake Bay this year averaged 84 billion gallons a day through September, almost 1.6 times higher than average, according to the latest figures from the U.S. Geological Survey.
The only higher year was 1972, when flows averaged 85 billion gallons a day, largely as the result of floods resulting from Hurricane Agnes.
The high flows have dramatically increased the amount of sediment and nutrients flushed into the Bay, according to the USGS.
About 263 million pounds of nitrogen and 18 million pounds of phosphorus have accompanied the high flows that have dominated the Chesapeake from the January floods through Hurricane Fran in September.
"The amount of nitrogen is about 50 percent higher and phosphorus is about twice the normal amount that usually enters the Bay," said Scott Phillips, coordinator of the USGS Chesapeake Bay Science Program in Towson, Md.
The huge amounts of nutrients that this year's rains have washed off the land are likely to reverse the Bay's nutrient trends, which had been improving until a series of wetter than normal years. Besides this year, flows in 1993 and 1994 were also significantly higher than normal.
The Bay Program goal is to reduce the amount of the phosphorus and nitrogen entering the Bay 40 percent - during an average flow year - by the turn of the century. Excessive amounts of those nutrients spur algae blooms in the Bay which, along with increased sediment loads, can decrease the amount of light that is available for underwater grasses that provide habitat for crabs and fish and food for waterfowl.
Also, when the algae dies, it sinks to the bottom and decays in a process that depletes the water of oxygen needed by other organisms.
Because of this year's high nutrient flows, scientists have observed some of the highest concentrations of algae and lowest oxygen conditions reported in portions of the Bay.
Noting that nutrient concentrations in many rivers feeding the Bay had been declining prior to 1986, Phillips said this year's situation could have been worse.
Preliminary estimates made by the USGS, in cooperation with the Maryland Department of Natural Resources and the Virginia Department of Environmental Quality indicate that nutrient loads to the Bay would have been higher if not for sewage treatment plant upgrades and other actions taken to reduce reduce nutrient pollution.
"The Potomac River, for example, has transported about 87 million pounds of nitrogen and 7 million pounds of phosphorus to the Bay during 1996," Phillips said. "If nutrient reduction methods had not been implemented within the Potomac River basin, we estimate that more than 100 million pounds of nitrogen and 10 million pounds of phosphorus could have entered the Bay."
"That's quite a reduction," Phillips said. "And when you take into account reductions in nutrients from all of the rivers monitored, it is clear that some of the efforts to clean up the Bay are working."
Still, the high flows may pose some problems for the Bay. The amount of Bay grasses in the Chesapeake have declined the last two years after having increased for nearly a decade.
Bay grasses are considered a key indicator of water quality, and their recent decline is thought to have resulted from the high flows of 1993 and 1994. Thus, a continued decline is possible next year as a result of this year's high flow.