This report synthesizes the views of a diverse group of scientists and resource managers on the impact of chemical contaminants on the Chesapeake Bay. It is the result of a meeting - held at the Belmont Center near Baltimore, Maryland in December, 1995 - designed to reach consensus on the effects that representative contaminants have on the Bay, and to determine what scientific information we still require in order to base on-going restoration efforts on the best available technical knowledge.

Through better understanding of the behavior and, most importantly, the effects of contaminants as they move through the Bay ecosystem, managers can implement more effective prediction-based actions to safeguard the Chesapeake's living resources. Toward such ends, major research to date has focused first on determining the sources and transport of contaminants in the Bay. Much of the Chesapeake Bay Program's management efforts to reduce land-based sources of contaminants have resulted from these studies. While much remains to be learned about sources of contaminants - especially about diffuse inputs - a major research emphasis in recent years has focused on the connection between the movement of contaminants in the estuary and their varying effects on the Bay's ecological health.

Extrapolating the findings of such research can be exceedingly difficult. The dynamic effects of contaminants in an ecosystem like the Bay involve a network of elaborate feedbacks among physical, chemical and biological processes that are themselves mediated by seasonal changes in salinity, temperature, pH, oxygen, winds, tides, precipitation and other factors.

While a single contaminant may have an evident effect - creosote in the Elizabeth River, for example, has caused lesions in fish, and the spilling of Kepone in the James River caused tumors in bottom-feeders - sublethal effects of small concentrations of a contaminant may not be evident at all, at least for some time. The presence of low levels of arsenic, for instance, may have no impact on shellfish or finfish directly; however, it can significantly affect phytoplankton species composition - such changes can cascade through the food web with indirect effects on oysters and striped bass. Together with other environmental stresses, low levels of contaminants such as arsenic could have other unpredictable ecological implications.

Because of the indications of biological impacts, even at relatively low levels of contamination, and because diffuse sources may be more difficult to control than point sources, it is imperative that we further investigate the effects of contaminants, at environmentally realistic levels, on the Bay's food web at key hierarchical levels.

For more information, report problems or provide comments, please contact: webmaster@mdsg.umd.edu