base of urban and other surface runoff samples collected during this program for use in nonpoint source water quality analyses and modeling. Additional effort should be devoted to characterization and statistical analysis of such data.

Managerial concern with the impacts of nutrient over-enrichment often is concerned with the perceived effects that nutrient loading will have on higher trophic levels in the system (e.g., the loss of commercial and recreational fisheries). These linkages are not always clearly demonstrable, and modeling of such cause and effect relationships is in its infancy. To further complicate the situation, the phytoplankton appear to be readily modeled as a continuum, while higher trophic levels often are characterized using individual models. The European regional seas ecosystem model (Baretta et al. 1995) is a suite of interconnected models that attempt to model the entire North Sea ecosystem up through the fish communities and including the benthos and the microbial loop. The present lack of knowledge concerning the connections among nutrient loadings, phytoplankton community response, and higher trophic levels implies a disconnection between the estimates used to evaluate management scenarios and the goals for which management is taking place. Therefore, the development of heuristic models using comparative ecosystem approaches is needed to identify and better understand key processes and their controls in estuaries.