What is the origin of phosphorus contributions to Wisconsin’s waterways? That persistent question led a team from the Wisconsin Department of Natural Resources (WDNR) to develop the Pollutant-load Ratio Estimation Tool (PRESTO), a screening-level tool that quantifies the dominant phosphorus source (diffuse, nonpoint sources versus end-of-pipe, point sources) within a user-defined watershed, such as the watershed to a point source outfall.
PRESTO,a statewide GIS-based tool, compares the average annual phosphorus load originating from point and nonpoint sources using three unique functions: watershed delineation, effluent aggregation for all point sources in the watershed, and nonpoint source estimation using land use-based multiple regression models. WDNR provided PRESTO calculated phosphorus loads and load ratio results for 606 permitted municipal and industrial outfalls in Wisconsin. The point to nonpoint ratio helps industrial and municipal dischargers and WDNR determine whether the discharger iseligible for watershed adaptive management as part of Wisconsin administrative code NR 217. Adaptive management allows a point source to control phosphorus discharges from other point and/or nonpoint sources to achieve compliance with applicable phosphorus water quality criteria in s. NR 102.06 in more economically efficient manner.
Customizable GIS tools such as PRESTO provide a visual, efficient, and transparent method for determining regulatory compliance. In addition, PRESTO has provided water resource professionals with both a consistent approach to watershed delineation and basin characteristics such as area, stream density, and land use composition.
Results to Date:
Since the release of PRESTO in December 2011, WDNR has provided model results and training is use of the model to the municipal and industrial permittees as well as the consulting firms that support them. The tool provides a reliable and agreeable answer for municipalities and businesses, generally eliminating the need for additional analysis by the permittee, thus saving precious compliance dollars. The results will also save WDNR permit staff hundreds of hours each year. The PRESTO tool and associated documentation is located at: http://dnr.wi.gov/org/water/wm/ww/presto/
Director, Water Quality Bureau
Wisconsin Department of Natural Resources