LONG ISLAND SOUND (LIS) DYNAMIC SPATIALLY REFERENCED REGRESSION ON WATERSHED ATTRIBUTES (SPARROW) MODEL

Dynamic SPARROW models for watersheds draining into Long Island Sound (LIS) are being developed cooperatively by the U.S. Geological Survey (USGS) and the U.S. Environmental Protection Agency (EPA). Both point and nonpoint sources are being modeled with a seasonal storage component that varies throughout the 21-year model period, 2000-2020. Predictor variable datasets, seasonally discretized wherever possible, include atmospheric deposition, land use such as urban land, waste-water-treatment plant discharges, snow cover, vegetation index, precipitation, temperature, and streamflow. A new variable, baseflow groundwater nitrogen loads, is being evaluated for inclusion in the nitrogen model.

The models use an enhanced version of the 1:100,000-scale stream network and catchments of the National Hydrography Dataset Plus Version 2.1 (E2NHDPlusV2) as its hydrologic framework. NHDPlusV2-based estimates of both mean annual and mean monthly stream flows account for excess evapotranspiration, major flow additions and removals, and gaged flow adjustments.

Dependent variables to be modeled include loads of nitrogen, phosphorus, and suspended sediment at monitoring sites where sufficient data are available. Loads and source components will be simulated for each NHDPlusV2 flowline (river network or coastal reach) within the watershed. Each estimated load and source component for each flowline, for each seasonal time step, will be accompanied by an estimate of the portion of the load delivered to LIS. Once calibrated, the models can be used to test best management scenario conditions as currently planned by EPA and other stakeholders using EPA’s River Basin Export Reduction Optimization Support Tool (RBEROST).