What is the status of phosphorus in the Minnesota River Basin?
Low dissolved oxygen rates are of concern particularly during low-flow times or in slow-flowing areas such as reservoirs and the lower reaches of the Minnesota River. Large total phosphorus loads can have major impacts on downstream receiving waters such as Lake Pepin. The map and chart at right illustrate the total phosphorus levels in 2002 for selected Minnesota River Basin watersheds. The illustrations show flow-weighted mean concentrations (FWMC) of total phosphorus. This is equivalent to routing all of the flow that passed a monitoring site during a specific timeframe into a big, well-mixed pool, and collecting and analyzing one sample from the pool to give the average concentration. Total phosphorus is an issue in all major tributaries. During 2002, the bulk of total phosphorus loading from tributaries occurred in the watersheds located in the middle and lower Minnesota River Basin (i.e. downstream of Morton). Total phosphorus FWMC values in the Minnesota River mainstem, six majo
