A Decision Support Framework to Facilitate Nitrogen Load Reductions in Long Island Sound (LIS) Watershed

This feasibility evaluation project was conducted to support the Long Island Sound Study (LISS) Management Committee's objective of estimating and tracking total nitrogen (TN) loads and potential reductions considering both land uses and best management practices (BMPs). A 10% target TN load reduction has been set for the urban and agricultural non-point sources as one component to a larger plan whose goal is to eliminate hypoxia in the western end of LIS. The critical issues identified by the Committee include: (a) minimization of impacts from existing and newer developments, and (b) exploration of region-wide and consistent land use and management practices within the LIS watershed that involves multiple States and local jurisdictions. A decision-support framework was developed and tested, in which the first step was to calibrate and apply an Arc View-based Generalized Watershed Loading Functions (AVGWLF) model to the in-basin drainage areas (all of the State of Connecticut and portions of the New York State). The committee envisioned a simple to use management tool that utilized data generated from the AVGWLF model to assist state and local officials make decisions on pollution control alternatives within municipal and agricultural communities in the watershed. The tool would also enable federal and state managers assess progress toward the target nitrogen reduction goal considering both changes in land cover from new development and the implementation of management practices on existing and new developments. In the second step, an interactive management tool was developed in Microsoft Excel (MSExcel) to identify the potential set of BMPs that could be used to achieve the desired levels of TN reductions. The tool offers significant flexibility to track the current loads, modify the treatment performance of specific BMPs, modify cost information to reflect watershed-specific construction and operation/ maintenance costs of BMPs, and to account for TN reductions resulting from both existing and future BMPs. The tool is aimed at facilitating the LIS TMDL implementation through screening and selection of BMPs and has been distributed to the LISS for the states and local watershed managers' widespread use.