Basin Scale Water Quality Model for Coastal Plain Flatwoods

Abstract

ABSTRACT THE BASIN model predicts the total annual nutrient load at the outlet of an agricultural basin, based on estimated delivery of average annual nutrient loads from individual fields/cells defined in the basin. A first-order rate equation is used to attenuate nutrient loads in streamflow and flow through wetlands, with rate coefficients determined from nutrient uptake studies reported in the literature. BASIN also computes nutrient loads from cattle in streams and wetlands, simulates nutrient reductions due to impoundments, and provides background loads for non-agricultural land use. The 464 km2 Taylor CreekNubbin Slough (TCNS) basin in Florida was simulated without calibration using 5 ha grid cells as fields. Parameters were selected from the literature and from knowledge of the area. Predicted long-term average annual nutrient yields compare closely with mean observed values for the TCNS basin and for several sub-basins. The sub-basins range in size from 22 to 270 km2 and encompass a wide range of nutrient loading. At the TCNS basin outlet, predicted average annual loads of 9.0 kg N/ha and 3.3 kg P/ha compare with observed values of 10.0 kg N/ha and 3.6 kg P/ha. Simulation of a hypothetical maximum BMP scenario for the TCNS basin resulted in a predicted reduction of around 50% of the annual nitrogen and phosphorus loads from this basin.