Confounding forecasts that the Chesapeake Bay would fare relatively well this summer, scientists report now that the bay's fish-stressing "dead zone" has grown to its usual size.
Sampling conducted by the University of Maryland Center for Environmental Science found that the volume of water in the bay where oxygen levels are too low to sustain fish and shellfish is typical for this time of year, its scientists said.
Last month, Maryland and other scientists had predicted that the Chesapeake's 'dead zone' this summer would be one of the smallest in years because of relatively low rainfall this spring in those portions of Pennsylvania and New York that drain into the Susquehanna River.
The Susquehanna normally produces half of all the fresh water entering the bay from rivers along its 190-mile length.
UM marine scientist William C. Dennison said it appears that heavy rains in Maryland and Virginia offset the reduced flow from the Susquehanna, producing higher-than-normal runoff of nutrient pollution from farms, lawns and roads in the bay's other rivers.
Based on water sampling conducted every two weeks, scientists have found that the stretch of bay with little or no oxygen in it expanded from below average in late May to larger than normal in June.
It has continued to grow since last month and remains about average size for this time of year, even though rainfall subsided for a time.
"We're not going to have a terrible year - but not the great year we would have expected," Dennison said.
The bay's dead zone is produced when sewage, air pollution and runoff of farm and lawn fertilizer spur algae growth in the water. The algae die and sink to the bottom, sucking oxygen from the water as they decompose.