Evaluation of management strategies for reducing nitrogen loadings to four US estuaries.

In this study we used the Watershed Assessment Tool for Evaluating Reduction Strategies for Nitrogen (WATERSN) model to evaluate a variety of management strategies for reducing nitrogen (N) loads to four US east coast estuaries: Casco Bay, Long Island Sound, Chesapeake Bay and Pamlico Sound. These management strategies encompass reductions in atmospheric emissions and deposition of N from sources including, fossil fuel burning utility emissions and mobile NO(x) emissions, N treatment in wastewater and controls on agricultural N inputs. We find that in primarily urban watersheds biological removal of N in wastewater treatment produces the greatest reduction in N loading (32-57% reductions), while in less urban watersheds, reductions in agricultural loading are more effective (5-56% reductions) in decreasing N loads to coastal ecosystems. Because anthropogenic N inputs are derived from a variety of sources, we also examined an integrated scenario targeting all major N sources; this resulted in 35-58% reductions in N loading. Nitrogen pollution originates from multiple sources and is transported through several media (air, soil, water); a major challenge of the development of N management strategies will be the control of multiple sources to effectively reduce N loads to estuaries.