Agricultural land occupies only 21% of the Sunrise River watershed but delivers 55% of the phosphorus load from uplands to receiving waters, i.e., streams, lakes, and wetlands (Table 1). Too much phosphorus in these waters can degrade water quality because of excessive algal growth. Estimating agricultural nonpoint loads of phosphorus is complicated by the many factors that affect the runoff response of the watershed to rainfall and snowmelt. These factors include not only soil type, topography, and vegetative cover, but also agricultural practices such as crop rotations, tillage, and applications of manure and inorganic fertilizer. To help account for these factors, a computerized watershed model was constructed for the Sunrise River watershed with the Soil and Water Assessment Tool (SWAT).
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Dr. Jim Almendinger St. Croix Watershed Research Station 16910 152nd St. N Marine on St. Croix, MN 55082
Minnesota Water Research Digital Library