Nutrients and suspended sediment in snowmelt runoff from part of the Upper Mississippi River Basin, Minnesota and Wisconsin, 1997

The U.S. Geological Survey sampled snowmelt runoff from 42 stream sites during March and April 1997 in part of the Upper Mississippi River Basin, Minnesota and Wisconsin, to characterize nutrient and suspended-sediment concentrations, yields, and loads. Ancillary data from 12 sites provided data to estimate constituent loads delivered during snowmelt and 1997. The snowmelt period contributed from 1 to 50 percent of 1997 annual loads of total nitrogen, total phosphorus, and suspended sediment at small stream sites, and 17 to 70 percent of annual loads at mainstem river sites. Small streams in agricultural areas transported the greatest proportions of annual loads during snowmelt. Snowmelt from urban streams transported the least proportions of annual loads. Agricultural streams had significantly greater median yields (p < 0.025) of dissolved nitrite, nitrate, phosphorus, orthophosphate, total nitrogen, and total phosphorus than forested sites, and significantly greater median yields (p < 0.025) of dissolved nitrate and orthophosphate than all other land uses. In forested areas, yields of suspended sediment and all nutrient forms were significantly greater (p < 0.05) for streams draining impermeable deposits than permeable deposits.