The Watershed Pollutant Load Monitoring Network is a long-term program designed to measure and compare pollutant load information from Minnesota’s rivers and streams and track water quality trends. WPLMN data are used to assist with assessing impaired waters, watershed modeling, determining pollutant source contributions, developing watershed and water quality reports, and measuring the effectiveness of water quality restoration efforts.
The program utilizes state and federal agencies, Metropolitan Council Environmental Services, state universities, and local partners to collect data on water quality and flow to calculate pollutant loads.
Monitoring sites span three ranges of scale:
- Basin — major river main stem sites along the Mississippi, Minnesota, Rainy, Red, Des Moines, and St. Croix rivers
- Major Watershed — tributaries draining to major rivers with an average drainage area of 1,350 square miles (8 digit HUC scale)
- Subwatershed — major branches or nodes within major watersheds with average drainage areas of approximately 300-500 square miles
Establishment of basin and major watershed monitoring sites began in 2007 following the passage of Minnesota’s Clean Water Legacy Act with subsequent funding from the Clean Water Fund of the Minnesota Clean Water, Land and Legacy Amendment. Establishment of subwatershed monitoring sites began in 2011, with all sites in operation by 2015. There are currently 22 basin, 52 major watershed, and 125 subwatershed sites within the WPLMN; major watersheds contained mostly outside of Minnesota are not included.
Pollutant loads are calculated for total suspended solids, total phosphorus, dissolved orthophosphate (discontinued in 2016), nitrate plus nitrite nitrogen (NO3+NO2-N), and total Kjeldahl nitrogen.