Jennifer Gilbert, Plant and Soil Sciences, University of Delaware, 152 Townsend Hall, Newark, DE 19716, James Thomas Sims, 531 S. College Avenue, University of Delaware, University of Delaware, Department of Plant & Soil Sciences, Newark, DE 19717-1303, R. Richard Lowrance, 2379 Rainwater Rd., USDA-ARS, USDA-ARS, S.E. Watershed Research Laboratory, Tifton, GA 31793, and Randall G. Williams, Southeast Watershed Research Lab, USDA-ARS, 2375 Rainwater Rd., P.O. Box 748, Tifton, GA 31793.
The Riparian Ecosystem Management Model was designed to quantify the water quality benefits of riparian buffers through nutrient and sediment attenuation. The processes simulated in REMM include surface and subsurface hydrology, sediment transport and deposition, vegetation growth, and nitrogen (N), phosphorus (P) and carbon(C) cycling. Organic P in REMM is associated with the soil C, residue C and dissolved C pools; inorganic P is divided into three pools, stable, active, and labile, based on the EPIC model. Labile P is further partitioned into dissolved and adsorbed forms which are transported in surface runoff. Phosphorus desorption from soil was not previously considered in REMM. Laboratory experiments were conducted using soils from Mid Atlantic Coastal Plain (MACP) vegetated filter strips (VFS) to determine what factors most strongly influence soil P sorption and desorption. Data showed that REMM equations were under predicting soil P sorption, and can be improved by basing sorption equations on Mehlich-3 P, Al, and the P saturation ratio (PSR). Many MACP soils are saturated with respect to P and may act as a source instead of a sink of P to subsurface flow. For this reason a new equation has also be added to the model to simulate P desorption from soil, based on labile P, rainfall, and season. In REMM, modeling P transport through a VFS is accomplished by setting all three zones of the riparian buffer to herbaceous vegetation. A simulation of 2 fields with VFS from the University of Delaware Research and Education Center farm will be run with both the original and revised P sorption and desorption equations. Output from the simulations will be compared to field data to quantify the impact of tailoring model equations to MACP soils.
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