SWAT Literature Database for Peer-Reviewed Journal Articles

Title:Watershed-level comparison of predictability and sensitivity of two phosphorus models 
Authors:Sen, S., P. Srivastava, P.A. Vadas, L. Kalin 
Journal:Journal of Environmental Quality 
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URL (non-DOI journals): 
Broad Application Category:hydrologic & pollutant 
Primary Application Category:model comparison 
Secondary Application Category:nutrient cycling and transport 
Watershed Description:336.7 ha Rice Branch in east central Alabama, U.S. 
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Abstract:Buildup of phosphorus (P) in agricultural soils and transport of P to nearby surface waters due to excessive, long-term application of poultry litter is an environmental concern in many poultry producing states. Watershed models are often used to quantify soil and water quality impacts of poultry litter applications. However,depending on how P transport is simulated in watershed models,the anticipated impact could be quite different. The objective of this study was to determine the predictability and sensitivity of the Soil and Water Assessment Tool (SWAT) P model and a newly developed, state-of-the-art manure P model called SurPhos in a poultry litter–applied pasture watershed. A small, predominantly agricultural watershed in Randolph County, Alabama was used for this study. Th e SWAT model, calibrated for surface runoff and total stream fl ows (Nash-Sutcliffe coefficient of 0.70 for both), was used to provide runoff inputs to the SurPhos model. Total dissolved P (TDP) exports simulated by the SWAT P and SurPhos models from the hay hydrological response units of the watershed were compared for different poultry litter application rates and different initial soil Solution P levels. Both models showed sensitivity to poultry litter application rates, with SWAT simulating linear and SurPhos simulating nonlinear increases in TDP exports with increase in poultry litter application rates. SWAT showed greater sensitivity to initial soil Solution P levels, which can lead to overestimation of TDP exports, especially at low poultry litter application rates. As opposed to the SurPhos model simulations and contrary to recent studies, SWAT simulated excessive accumulation of Solution P in the top 10 mm of soil. Because SurPhos appears to simulate P transport and build-up processes from manure-applied areas more accurately, this study suggests that SWAT be replaced by SurPhos to more accurately determine watershed-level effectiveness of P management measures.