During the last 50 years, nutrient enrichment has reduced the size of sea grass beds and lowered dissolved oxygen concentrations, both contributing to the degradation of bottom habitats. Excess nutrients can cause large algae blooms which cloud the water. When the algae bloom dies it sinks to the bottom and decays through bacterial processes that rapidly deplete dissolved oxygen. Significant increases in the organic content of 200 year-old sediment suggest stimulation of algae blooms during pre-industrial times. Lead author Dr. W. Michael Kemp, of the University of Maryland Center for Environmental Science, said "By studying long-term effects of nutrient enrichment and detailed processes by which coastal ecosystems have been altered, we will be far better positioned to effect restoration of the estuary's valuable resources."
These trends have been made even worse by declines in oyster beds, caused by overfishing and disease. The oyster was considered one of the Bay's dominant bottom feeders consuming vast amounts of algae. Extensive tidal marshes, which serve as effective nutrient buffers, are now being lost due to rising sea levels thus making the problems of nutrient loading even worse.
While the total fish production in the Bay is not believed to have declined, the type of fish have changed. Fish populations have shifted from species living near the seabed to those living in the upper waters. This shift may lead to food chain inefficiencies that favor production of bacteria and small invertebrates.
Even in some Chesapeake Bay tributaries such as the Potomac and Patuxent Rivers, where significant nutrient pollut
Contact: David Nemazie
University of Maryland Center for Environmental Science