In Virginia, the extent of oyster damage caused by the freshet will not be known until an October survey, said Jim Wesson, the oyster management specialist with the Virginia Marine Resources Commission. Strong fresh water flows on the surface creates a barrier between it and the more dense salt water on the bottom. June, July and August flows were much below normal. This June and July, we've had a tremendous amount of rain, which has kept salinity depressed, resulting in greater stratification. The greater the difference between the top and bottom salinities, the greater the stratification between the two.
Stronger stratification means that little oxygen is exchanged between the two layers.
The Bay cleanup effort has been focused on reducing the amount of nutrients reaching the Bay as the key to restoring water quality. Excess amounts of phosphorus and nitrogen feed large blooms of algae which then die and sink to the bottom. On the bottom, the algae is decomposed in a process that depletes the water of oxygen. This year, the nutrients flushed down the Bay fueled typically large algae blooms, but they generally occurred 20 to 30 miles south of where they normally would be observed, said Richard Lacouture of the Academy of Natural Sciences' Benedict Lab. Brackish algae species were causing blooms 20 miles below the Bay Bridge, where salt water species normally dominate.