The Role and Control of Nutrients in Chesapeake Bay

The results of a workshop conducted by scientists who participated in a 6-year, multidisciplinary study of hypoxia on the Chesapeake Bay suggest that although an exact quantification of the management target for nutrient reduction is difficult to make, at least a 40% reduction in total inputs is needed to reduce hypoxia and restore a trophic structure that maximizes mctazoan food chains and minimizes microbial processes. Nutrient enrichment contributes to the formation of hypoxia in the Bay's main stem and lower tributaries by over-stimulating the growth of phytoplankton that ultimately decompose and consume oxygen in deep water. Enrichment effects can be traced in the sedimentary record to colonial times, but are not as easily discerned in water quality parameters from monitoring in the last 50 years. Initially, agricultural land-use practices that decreased forest coverage and increased erosion accounted for most nutrient inputs, but in this century, point and non-point sources, that result from demographic change and impact in the watershed, predominate.