Watershed pollutant load monitoring overview

The Watershed Pollutant Load Monitoring Network (WPLMN), which includes state and federal agencies, Metropolitan Council Environmental Services, state universities, and local partners, collects data on water quality and flow in Minnesota to calculate pollutant loads in rivers and streams. Pollutant loads are the amount of a pollutant that passes a monitoring station over a period of time. Data is collected at 199 sites around the state.

Pollutant loads are calculated for five substances: 

  • Total suspended solids
  • Total phosphorus
  • Nitrate plus nitrite nitrogen
  • Total Kjeldahl nitrogen
  • Dissolved orthophosphate

WPLMN data assist in watershed modeling, determining pollutant source contributions, developing reports, and measuring water quality restoration efforts.

Sampling procedures

Each year, approximately 25 - 35 water quality samples are collected at each monitoring site, either year-round or seasonally depending on the site. Water quality samples are collected near gaging stations, at or near the center of the channel. Samples are collected more frequently when water flow is moderate and high, when pollutant levels are typically elevated and most changeable. Pollutant concentrations are generally more stable when water flows are low, and fewer samples are taken in those conditions. This staggered approach generally results in samples collected over the entire range of flows. Learn more about WPLMN standard operating procedures and sampling protocols on the Water monitoring: Standard operating procedures page.

Analytical procedures

WPLMN pollutant loads are calculated by coupling water quality and discharge data from U.S. Geological Survey and Minnesota Department of Natural Resources flow gaging stations to create mathematical relationships (using the FLUX32 model) to estimate pollutant concentrations on days when samples are not collected. Primary output includes annual/seasonal loads and flow weighted mean concentrations (pollutant load/total flow volume) and daily loads and concentrations.

Partner organizations

Tracking the health of streams in Minnesota is a big job, and one that the MPCA can’t do alone. The agency depends on local partners for help and provides funding to local organizations to assist with intensive water quality monitoring. The agency also provides field training to ensure consistent sampling procedures. Partners must submit extensive data to the MPCA:

  • Quality assurance project plan
  • Stream water quality data
  • Field meter calibration log and field notes
  • Digital photos taken during site visits
  • Pollutant loading data
  • Interim progress report and final report

The organizations that participate in the WPLMN:

  • Chippewa River Watershed Project
  • Crow River Organization of Water
  • Fillmore Soil and Water Conservation District
  • Hawk Creek Watershed Project
  • International Water Institute
  • Itasca County Soil and Water Conservation District
  • Koochiching County Soil and Water Conservation District
  • Lake of the Woods Soil and Water Conservation District
  • Metropolitan Council Environmental Services
  • Middle Fork Crow River Watershed District
  • Mille Lacs Soil and Water Conservation District
  • Minnesota State University—Mankato, Water Resources Center
  • Mississippi Headwaters Board
  • North Fork Crow River Watershed District
  • Olmsted Soil and Water Conservation District
  • Rainy River Community College
  • Redwood Cottonwood Rivers Control Area
  • Sherburne Soil and Water Conservation District
  • Sibley Soil and Water Conservation District
  • University of Minnesota  Natural Resources Research Institute
  • Vermilion Community College
  • Widseth Smith Nolting