EXECUTIVE SUMMARY 



A conceptual model for the Chesapeake Bay ecosystem (wetlands, tributaries, and bay- 

 proper) has been developed as an interrelated series of diagrams showing carbon and nutri- 

 ent pathways. Information was based on an analysis of local literature and discussions with 

 scientists who are studying the Bay. The ecological functions that produce the resources of 

 commercial and recreational fisheries, habitat for migratory birds and other wildlife, waste 

 disposal, and aesthetic water quality are indicated. Physical (light, turbidity, mixing, trans- 

 port, sedimentation) and chemical (sediment-water interactions, presence of pollutants) 

 aspects of the environment modify the rates of biological processes (primary production, 

 nutrient regeneration, larval survival). 



Marshes and other wetlands export carbon as detritus into the Bay system. They also trap 

 nutrients, and release them gradually. Their natural buffering capacity can be, at times, ex- 

 ceeded by excessive nutrient loading from sewage or fertilizers. 



Natural nutrients and detritus as well as pollutants such as trace metals, refined hydro- 

 carbons, herbicides, and pesticides enter the Bay system through river flow and overland 

 runoff. 



In the Bay and tributaries, primary producers are phytoplankton, seagrasses, and benthic 

 algae. Plankton dynamics facilitate nutrient regeneration, as do sediment chemistry and 

 benthic organisms. Plankton, benthos, and marsh organisms provide food for fin- and shell- 

 fishes of commercial importance. 



A detailed ecosystem model combining the wetlands, plankton, seagrasses, other ben- 

 thos, and fish trophic dynamics submodels shows the importance of material transfer and 

 interactions between subsystems. In hierarchical research designs, there is a tendency to 

 focus on interactions within subsystems. Exchanges between subsystems should also be 

 studied. Quantitative data and estimates of flows on a Bay-wide, annual basis are needed. 



In relating observed changes in the system, such as the decline of submerged aquatic 

 vegetation or reduction in oyster spatfall, to water quality, the ecosystem context is useful 

 in indicating possible causal mechanics and pathways. Potential indicators of water quality 

 and ecosystem health are distribution and abundance of seagrasses, chlorophyll a, dissolved 

 oxygen, water transparency, blue crab abundance, larval setting, and concentrations of pol- 

 lutants in the tissues of commercial fin- and shellfishes, plankton, and forage fishes. 



To provide information on the relative importance of various biological processes for 

 water-quality maintenance, and the relative magnitude of different pollutant impacts on the 

 Bay, quantitative estimates of the flows in the conceptual models should be made. 



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