1a. Objectives (from AD-416):
This project will establish new techniques for validating site assessment indices used in nutrient management using measured and modeled data.
1b. Approach (from AD-416):
The general approach will be to conduct computer simulation modeling in select watersheds to compare edge-of-field phosphorus (P) loss estimates with SWAT (Soil Water Assessment Tool) with predictions of phosphorus loss potential with the P Index. Up to four watersheds (WE-38, PA; St. Joe’s, IN; Riesel, TX; Goodwater Creek, MO) will be included. At each watershed, historical monitoring data will be used to calibrate SWAT so that the model accurately represents local processes controlling P loss at field and watershed scales. Where necessary, activities will include measuring and analyzing P transport under different management systems and across a range of conditions. Activities will involve coordination with Lee Norfleet of NRCS, Doug Smith of ARS, Daren Harmel of ARS, and Andrew Sharpley of University of Arkansas (coordinating SERA-17 590 Standard Task Force).
3. Progress Report:
Two meetings were conducted at the Pasture Systems and Watershed Management Unit (University Park, PA) to train project team members in how to initialize and calibrate the Soil Water Assessment Tool (SWAT). Existing and new hydrologic routines were reviewed. Initial efforts focused upon applying a Variable Source Area (VSA) hydrologic routine to SWAT to improve representation of overland flow processes that are important to the upland regions of the Chesapeake Bay watershed. A manuscript comparing conventional and VSA versions of SWAT is forthcoming. Participated in a meeting in Temple, TX aimed at national coordination of modeling efforts within ARS. To streamline the processes of modeling new watersheds, an online query tool was developed. Most of the watersheds participating in the Chesapeake Bay component of the Conservation Innovation Grant funded P Index project have used this tool. SIGNIFICANT FINDINGS: The VSA version of SWAT significant improves the representation of hydrology at the field scale, consistent with historical monitoring observations in the Mahantango Creek watershed. Specifically, saturation excess runoff processes (i.e., water logging of downslope areas with relatively impervious subsoil features) are better represented than in conventional SWAT.