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Forum: What is the Future of the Chesapeake?

Heavy Rains Likely to Cause Large "Dead Zones" This Summer

Waterimage Rain, rain, go away. Don’t give us a murky Bay.

All the heavy rains and snows over the last few months will likely mean that the Chesapeake Bay will have severe low-oxygen “dead zones” in the Chesapeake Bay during the summer of 2010, some scientists are predicting.

Rain and melting snow flushes fertilizers and other sources of nitrogen and phosphorus pollution off of fields, yards and streets. These nutrients spur the growth of algal blooms that die and rot, sucking oxygen out of the water.

Dr. Bill Dennison, a professor of the University of Maryland Center for Environmental Science, said this morning that he expects the "dead zones" in the Chesapeake Bay will be widespread this summer.  He and colleagues in the Chesapeake Bay Program this spring will crunch the numbers and release an official projection of low-oxygen zones in the bay for summer of 2010. So far, he said, it's not looking good.

Dr. Beth McGee, senior scientist at the Chesapeake Bay Foundation, also said that the heavy rainfall is likely to have an impact on the Bay's health. “I would expect with all this rain and runoff from melting snow that it could be a bad year,” Dr. McGee said.

She added that this projection could change if the rest of March and April turn out to be significantly drier than 2010 has been so far.

It is raining hard again today (Monday, March 22), and it has been unusually wet for the last several months across the Chesapeake Bay watershed.

Up north, in Chester County, Pennsylvania, for example, the equivalent of 27 inches of rain have fallen over the last six months, which is about 29 percent more than normal, according to the National Weather Service.  (That includes melting snow calculated as a rain equivalent).  

In Anne Arundel County, Maryland, 33 inches of precipitation have fallen over the last six months, which is about 54 percent more than normal.

And in Hampton County, Virginia, 32 inches have fallen over this period, which is roughly 59 percent more than normal.

The record-breaking snowfalls added even more water to the Bay. For example, at Baltimore-Washington International Airport, a record-breaking 15.5 inches of rain fell on February 10, shattering the record of 9.8 inches set in 1926, according to the National Weather Service. Records at BWI were also set on February 5-6, when 24.8 inches of snow fell over a two-day period, surpassing the 24.4 inches that fell on Feb. 16-17 2003.

Rain and snow themselves are not the main problem, of course -- it's all the pollution that humans spread across the land, which gets picked up by the water.  This is why imposing stronger storm water control regulations is so important, because requiring developers to build retention ponds and filtration systems, among other steps, helps to clean the rain water before it can pour into the Bay.

All this additional fresh water from rain also has another effect on the Bay, said Dr. Dennison.  The fresh water forms a layer on top of heavier salt water from the Atlantic ocean. And these separate layers in the Bay create a barrier that makes it hard for oxygen to circulate.

“If you have a have a strong fresh water sitting on top of the salt water, then the stratification is very hard to break up,” making the circulation of oxygen difficult, Dr. Dennison explained.


Article by Tom Pelton.  Photo by Philip and Karen Smith.





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