About monitoring pollutants

Stream monitoring sites in MinnesotaThe Watershed Pollutant Load Monitoring Network (WPLMN), is a network of state and federal agencies, Metropolitan Council Environmental Services, state universities, and local partners, that collects data on water quality and flow in Minnesota. Since 2007, the network of partners have been collecting data in order to understand long-term trends and observe changes over time.

What is a pollutant load

A pollutant load is the amount a pollutant passes a monitoring station over a period of time. Scientists use this data to calculate pollutant concentrations to track the health of a stream or river. Data are collected for a standard set of key pollutants:

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

Effects of heavy rain on water quality

Shakopee Creek water samplesHeavy rain events can have significant impacts on the water quality of streams. Specifically, heavy rains cause sediment to be transported and/or eroded into streams from the surrounding landscape, decreasing clarity and recreation quality within the stream.

Shakopee Creek illustrates how high-intensity rains contribute significant amounts of sediment to the system. In this example, even a moderate rain event where 2.3” of rain fell over a 21-hour period caused a significant amount of sediment to enter the stream.

Excessive Phosphorus on water quality

Minneopa CreekIncreases in total phosphorus (TP) causes algae to grow within lakes and streams, having a major impact on the health and recreation quality of the water.

Under normal water flow conditions, a majority of the TP in lakes and rivers comes from nonpoint source runoff such as cropland and pastures in addition to point source runoff including wastewater and industrial treatment facilities. Lesser amounts also come from streambank erosion and urban runoff.

In this example, the effects of excess TP can be seen in the green water color of Minneopa Creek caused by the increase of algae.