Ammonia concentrations generally were greatest at sites located in the TCMA downstream of Minnesota River and the major wastewater discharge points. Stream load is the total amount of a constituent that is carried past a point on a stream during a given period of time, usually one year. The nitrogen load in the Mississippi River changes from predominantly organic and ammonia nitrogen upstream of the Minnesota River to predominantly nitrate downstream of the confluence with the Minnesota River. Concentrations of nitrate were least in the Namekagon and Kettle Rivers, which drain forested areas. In the Minnesota, Straight, and Cannon Rivers, concentrations of nitrate generally were greatest during the spring and summer.
Yield is the load divided by the stream's drainage area.
Nitrate yields were least at sites on the St. Croix and Kettle Rivers, which drain predominantly forested land. Organic and ammonia nitrogen was the predominant form of nitrogen load in tributaries draining these areas. During low-flow, total phosphorus concentrations increased substantially downstream of the TCMA's major wastewater discharge point. Under average and high-flow, the greatest increases in total phosphorus concentrations were downstream of the confluence with the Minnesota River. Total phosphorus concentrations generally peaked during the spring and summer at most sites in the study area.