Fig. 3. Modified P Index transport site characteristics included in the modified P Index for watersheds of Minnesota. (a) Potential soil erosion losses (Mg/ha). (b) Observed runoff values interpolated from 327 United States Geological Survey (USGS) long-term gauging stations (cm/yr). (c) Cropland and pastureland area within 91.4 m of drainage ditches and perennial streams normalized by the watershed area.