The new USGS regional models were developed using the SPARROW (SPAtially Referenced Regressions On Watershed attributes) modeling framework. Results detailing nutrient conditions in each region are published in the Journal of American Water Resources Association, and can be accessed with the decision support system online.

Based on the six regional model results, waste-water effluent and urban runoff are significant sources of nutrients in the Northeast and mid-Atlantic, while agricultural sources like farm fertilizers and animal manure contribute heavily to nutrient concentrations in the Midwest and central regions of the na­tion. Atmospheric deposition is the largest contributor of nitrogen in many streams in the eastern United States, and naturally occurring geologic sources are a major source of phosphorus in many areas.

Additionally, the six models used in the decision support system show that the amounts of nutrients transported varies greatly among the regions, because nutrients can be removed in reservoirs or used by plants before they reach downstream waters. Temperature and precipitation variation across the country also affect the rates of nutrient movement and loss on the land and in streams and reservoirs.

The USGS developed the SPARROW water-quality model to assist with the interpretation of available water-resource data and provide predictions of water quality in unmonitored streams. These regional SPARROW models incorporate geospatial data on geology, soils, land use, fertilizer, manure, wastewater treatment facilities, temperature, precipitation and other watershed characteristics, from USGS, NOAA, USDA, and USEPA. These data are then linked to measurements of stream flow from USGS streamgages and water-quality monitoring data from approximately 2,700 sites operated by 73 monitoring agencies. Information on SPARROW modeling applications, data, and documentation can be accessed online.

The model was developed by the USGS National Water Quality Assessment Program, which provides information about water-quality conditions and how natural features and human activities affect those conditions. Federal, regional, and state agencies, including USEPA, USDA, Bureau of Reclamation and others have used the SPARROW model results to inform water-quality management decisions.