The Watershed Pollutant Load Monitoring Network is tied to the goals of the 1972 Clean Water Act for restoring and protecting the multiple beneficial uses and ecological integrity of America's waters.

Primary goals:

  • Measure and compare regional differences in water quality.
  • Determine water quality trends.

Data are used in assessments of impaired waters, watershed and water quality studies and reports, watershed modeling, and measuring effectiveness of major watershed protection and restoration plans.

Monitoring sites

Monitoring sites were first established in 2007. The network has grown to include sampling at basin (22), major watershed (52), and subwatershed (125) sites.

Monitoring strategy and sampling procedures

Approximately 35 water quality samples are collected annually at basin and major watershed sites and 25 samples collected seasonally at subwatershed sites. Water quality data collected include both laboratory and field measurements (see list below). All labs used in the program are certified by the Minnesota Department of Health and are included in the MPCA Sampling and Analytical Services-Environmental Master Contract.

Example: Lac qui Parle River Hydrograph with Sample Collection Dates Plotted Water quality (grab) samples are collected at or near USGS or DNR flow gaging stations at or near the center of the channel. Sample collection frequency is greatest during periods of moderate and high flow when pollutant levels are typically elevated and most dynamic. Low-flow periods are sampled less frequently as concentrations are generally more stable when compared to periods of elevated flow. Despite discharge related differences in sample collection frequency, this staggered approach to sampling generally results in samples being well distributed over the entire range of flows.

WPLMN standard operating procedures (SOP) and guidance

Analytical procedures

A pollutant load is the amount (mass) of a pollutant passing a stream location over a unit of time. Pollutant loads for the WPLMN 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. Pollutant loads are calculated for total suspended solids (TSS), total phosphorus (TP), dissolved orthophosphate phosphorus (DOP), nitrate plus nitrite nitrogen (NO3+NO2-N) and total Kjeldahl nitrogen (TKN).

The monitoring and load calculation period for basin and major watershed sites is January 1 through December 31 (annual) and ice out through October 31 (seasonal) for subwatershed sites.