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Optimizing Management Practices to Meet Loading Targets for the Long Island Sound Basin Under Variable Weather
Citation:
Detenbeck, N., S. Ennett, C. Connolly, A. Le, C. Guider, AND H. Parker. Optimizing Management Practices to Meet Loading Targets for the Long Island Sound Basin Under Variable Weather. Overview of dynamic RBEROST tool for Long Island Sound, NA, RI, December 16 - 17, 2025.
Impact/Purpose:
States, tribes, and local stakeholders are faced with a myriad of choices when trying to meet nutrient loading targets for receiving waters, including upgrades to septic systems or wastewater treatment plants, implementation of stormwater best management practices or agricultural conservation practices, and restoration of riparian zones. The Long Island Sound (LIS) 2025-2035 Comprehensive Conservation and Management Plan acknowledges previous successes in meeting nutrient load reduction targets for LIS: summertime hypoxia in the Sound has been reduced by over 50 percent largely due to 70 percent reductions to wastewater discharges, exceeding targets set in the 2015 Comprehensive Conservation and Management Plan (CCMP). However, algal blooms and seasonal hypoxia fueled by nutrient loads from nonpoint sources continue to occur. Moving forward, a key goal for New York state is reducing nitrogen from septic systems by upgrading or removing outdated onsite wastewater treatment systems and connecting more homes to public sewer lines. In Connecticut, the Second-Generation Nitrogen Strategy is identifying nutrient reduction targets for six priority embayments. EPA’s River Basin Export Reduction Optimization Support Tool was initially developed for the Upper Connecticut River in collaboration with Region 1 and stakeholders as a means to identify cost-effective solutions to meeting nutrient load reductions both within the watershed itself (for local TMDLs) and for the downstream waters of the LIS. EPA has expanded the geographic and temporal framework for RBEROST to include the entire LIS basin and to consider temporal variability in nutrient loads over the period 2000-2020. By linking RBEROST to a new dynamic SPARROW loading model under development by USGS, EPA can address potential lags in response to various management practices and evaluate how least cost solutions and chances for success vary with wet versus dry phases.
Description:
US EPA previously released two static versions of the River Basin Export Reduction Optimization Support Tool (RBEROST), one version for the Upper Connecticut River basin (v1s), and one for the Puget Sound Basin (v2s). RBEROST is designed to enable stakeholders to identify the least cost solutions to meet watershed nutrient loading targets, considering potential upgrades to septic systems or wastewater treatment plants, implementation of stormwater best management practices or agricultural conservation practices, and restoration of riparian zones. EPA is preparing to release an expanded version of RBEROST (v1d) that covers the entire Long Island Sound (LIS) basin, and which is coupled with the new USGS dynamic SPARROW loading model for LIS which yields season x year source load estimates for the period 2000-2020. The dynamic version of RBEROST not only allows users to evaluate how least-cost solutions and chances of success in meeting targets may vary between seasons and wet and dry years, but also allows users to evaluate lags in the performance of management practices related to storage of legacy nutrients in the system. This presentation provides an overview of the updates to RBEROST, a description of linkages to source loads from dynamic SPARROW for North Shore watersheds and a groundwater-based model for loads for South Shore watersheds, some preliminary results, items for discussion with stakeholders and next steps.