National Park Service

Great Lakes Network (GLKN)

Large River Water Quality Monitoring

St. Croix National Scenic River
St. Croix National Scenic River

GLKN Large River Water Quality Monitoring Briefs

GLKN Large River Water Quality Monitoring Reports

GLKN Large River Water Quality Monitoring Protocol

For more information contact:
David VanderMeulen


Large rivers around the world have been historically affected by human activities and face an uncertain future in which water quality may be further threatened by climate change, expansion of urban areas, agriculture, transportation uses, exotic species, and recreation. The preservation of water quality and quantity is of utmost importance to park managers, researchers, and the general public.

The National Park units in the Network that are based on large, non-wadeable rivers are the Mississippi National River and Recreation Area (MISS) and the St. Croix National Scenic Riverway (SACN). Water quality is generally good throughout SACN but the last 25 miles of the river (Lake St. Croix) is being impacted by excessive nutrients (phosphorus). Although water quality at MISS has improved greatly over the past 50 years it is still impacted by excess sediment and nutrients, especially below the confluence with the Minnesota River. Both large rivers are highly vulnerable to invasion exotic Asian carp, which are spreading northward via the Mississippi River.

Because conditions can change quickly, it is important to detect change as early as possible, in order to maximize the potential for effective management actions. These rivers are used extensively by visitors for commercial transportation, fishing, boating, swimming, and other recreational activities.

Long-term Monitoring

The Great Lakes Network monitors water quality at five sites at MISS on the Mississippi River and 13 sites at SACN on the St. Croix and Namekagon Rivers. Sites at MISS were selected to fill spatial monitoring gaps by other monitoring agencies. At SACN, six sites were randomly selected to represent the entire stretch within park boundaries, and seven additional sites were selected to integrate inputs from important river reach areas and river tributaries not currently monitored by other organizations.

Sites at each park are sampled monthly during the ice-free season, in alternating years. A multiprobe sonde is used to measure temperature, specific conductance, pH, and dissolved oxygen from the surface to the bottom at 1-m intervals. Clarity is measured with a Secchi disk or transparency tube. Water samples are collected with a 2-m integrating tube for laboratory analysis of alkalinity, dissolved organic carbon, calcium, potassium, sodium, magnesium, chloride, sulfate, total nitrogen, total phosphorus, nitrate+nitrite-nitrogen, ammonium-nitrogen, dissolved silica, total suspended solids, and chlorophyll-a.  At select sites water level is recorded from a staff gage or measured from a bridge deck.  Data on flow are obtained from U.S. Geological Survey and U.S. Army Corp of Engineers gage stations located near each monitoring site.

This monitoring is integrated with a protocol to monitor diatom remains in bottom sediments. Diatoms are a class of algae with silica-based cell walls. When a diatom dies, the remains are preserved in sediments. Diatoms make excellent bioindicators because they are generally abundant in aquatic systems and respond rapidly to changes in their environment. Through monitoring water quality and diatoms together, we expect to be able to determine trends sooner and more accurately than by monitoring water quality alone.

Through sharing our data with other agencies active in monitoring water quality in the two parks, the Great Lakes Network is contributing to a better understanding of water quality trends in these important rivers.

Parks Monitored

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Last Updated: December 30, 2016 Contact Webmaster