Effect of Stream-Network Resolution and Monitoring-Site Density on the Calibration of a Nutrient SPARROW Model for the Southeastern United States
Anne B. Hoos1 and Gerard C. McMahon2
1 U.S. Geological Survey, 640 Grassmere Park, Suite 100, Nashville, Tennessee 37211
2 U.S. Geological Survey, 3916 Sunset Ridge Road, Raleigh, North Carolina, 27607
Abstract
The U.S. Geological Survey’s National Water-Quality Assessment Program is compiling surface-water quality data and estimates of nutrient sources (agricultural, atmospheric, urban runoff, and wastewater) from Federal, State, and local water-resource agencies throughout the Southeastern United States to estimate rates of nitrogen and phosphorus transport in surface water and to estimate which sources and
watersheds contribute the highest nutrient loads. The SPARROW (SPAtially-Referenced Regression On
Watershed attributes) water-quality model is used to quantify the sources of nutrients and the transport of
these nutrients to downstream water bodies and coastal areas, providing information that can assist water resource managers in selecting nutrient control strategies. The modeling objectives include investigation of the effect of stream-network resolution and monitoring site density on model calibration and performance. Two separate SPARROW models, one built from the RF1 reach network (Reach File Version 1.0, 1:250,000-scale hydrography) and one built from the NHD reach network (National Hydrography Dataset, 1:100,000-scale hydrography), were calibrated. The smaller calibration set for the RF1-based model was developed from the 600-site calibration set for the NHD-based model as the subset (400) of the monitoring sites that intersected the coarser RF1 network. Aspects of model calibration under investigation include sensitivity to network resolution and monitoring-site selection of: (1) prediction accuracy; (2) allocation of nutrient-mass attenuation to overland and instream transport; (3) standard error associated with model estimation of overland and instream nutrient attenuation; and (4) predicted loads and load distribution among stream size classes.
Citation:
Hoos, Anne, and McMahon Gerard, 2006, Effect of stream-network resolution and monitoring-site density on calibration of a nutrient SPARROW model for the Southeastern U.S.: Proceedings of the National Water-Quality Monitoring Council National Monitoring Conference, May 8-12, 2006, San Jose CA.
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