The Role of Dissolved Organic Nitrogen in the
Eutrophication of Chesapeake Bay
For more than a decade, scientists have been detailing the impacts of heavy nutrient inputs to the Chesapeake Bay–among those impacts are massive algal growth, poor water quality, loss of underwater vegetation and an altered food web that may promote extensive bacterial production. A key element of the Bay cleanup aims at slashing nutrient loadings by 40 percent, to levels comparable to the 1950s. The aim is to significantly curtail the abundance of algae (also called phytoplankton). The major targets for nutrient reduction are river inflow, sewage and land runoff–all are sources of dissolved inorganic nitrogen. But inorganic nitrogen accounts for only about 50 percent of the Bay's total dissolved nitrogen; 20 to 50 percent take the form of dissolved organic nitrogen, such as urea, amino acids and nitrogen released from plankton and other sources.
While organic nitrogen was once thought to be relatively unavailable to algae, studies by Patricia Glibert and others have shown that this is not the case. Glibert hypothesizes that certain forms of algae may be efficient at assimilating organic nitrogen; together with bacterial uptake of organic nitrogen, subtle shifts in the food web could occur that may ultimately affect the yield of commercially important fish species in the Chesapeake. In continuing field studies, Glibert and Paul del Giorgio will characterize how the composition of dissolved organic nitrogen changes seasonally along the length of the Bay; in laboratory studies, they will detail how microbial populations drawn from the Choptank River make use of different sources of dissolved organic nitrogen. In collaboration with ongoing research by other scientists on the east coast, these findings will provide vital information on the role that dissolved organic nitrogen has in regulating the Bay's food web.
|
Patricia M. Glibert and Paul A. del Giorgio
Horn Point Laboratory
University of Maryland Center for Environmental Science
|
|
|
