Evaluation of a method for comparing phosphorus loads from barnyards and croplands in Otter Creek Watershed, Wisconsin

Control of phosphorus from rural nonpoint sources is a major focus of current efforts to improve and protect water resources in Wisconsin and is recommended in almost every priority watershed plan prepared for the State's Nonpoint Source (NFS) Program. Barnyards and crop- lands usually are identified as the primary rural sources of phosphorus. Numerous questions have arisen about which of these two sources to control and about the method currently being used by the NFS program to compare phosphorus loads from barnyards and croplands. To evaluate the method, the U.S. Geological Survey (USGS). in cooperation with the Wisconsin Department of Natural Resources, used phosphorus-load and sediment-load data from streams and phosphorus concentrations in soils from the Otter Creek Watershed (located in the Sheboygan River Basin: fig. 1) in conjunction with two computer-based models.