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Regional Scale Point-Source Nutrient Load Estimation in Support of SPARROW Nutrient Modeling

Gerard McMahon1, Larinda Tervelt2, William Donehoo3

1 U.S. Geological Survey, 3916 Sunset Ridge Road, Raleigh, NC 27607
2 U.S. EPA, 4, 61 Forsyth Street, Atlanta. GA 30303
3 U.S. EPA, Region 4, 61 Forsyth St. SW (WPEB-16), Atlanta, GA 30303

Abstract

One of the greatest challenges in developing regional-scale nutrient water-quality models is the estimation of nutrient inputs. Regional SPARROW (SPAtially Referenced Regressions On Watershed attributes) models require development of either mass-based nutrient input estimates (e.g., total annual nutrient mass associated with fertilizers or point sources) or area-based proxy measures of nutrient inputs (e.g., areas of agricultural or urban land). Researchers at USGS and US EPA, in conjunction with the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program, are estimating annual nitrogen and phosphorus inputs associated with approximately 4,000 point-source dischargers in the southeastern United States, with the intent us using the input estimates in the calibration and application of a regional SPARROW model. The study includes basins draining to the southern Atlantic, Gulf Coast, and the Tennessee River. Site information, including latitude and longitude and monitored effluent data, are compiled into a project database from both state and USEPA databases, including the USEPA Region 4 Permit Compliance System (PCS) database. For sites with a complete effluent monitoring record, flow and effluent concentration data are used to develop estimates of annual point source nitrogen and phosphorus flux. When flow data exist but concentration data are missing or incomplete, typical pollutant concentrations (TPC) of total nitrogen and total phosphorus are used to estimate flux. Dischargers are classified by both the magnitude of discharged flow and type of discharger, indicated by the Standard Industrial Classification (SIC). TPC values are estimated using several approaches, including use of observed distributions of concentrations in the project database, summarized by state, flow classification, and SIC, and a national review of SIC-based discharges conducted by U.S. EPA. Annual point-source nutrient input estimates are allocated to specific river reaches for use in the SPARROW model.

McMahon, Gerard, Tervelt, L., and Donehoo, M., 2006, Regional-scale point source nutrient load estimation in support of SPARROW nutrient modeling: Proceedings of the National Water-Quality Monitoring Council National Monitoring Conference, May 8-12, 2006, San Jose CA.