State of the Minnesota River 2000 Surface Water Quality Monitoring



Access the full 2000 State of the Minnesota River Report
Basin Overview
Precipitation & Runoff
For More Information

Water quality monitoring This executive summary provides an overview of the more detailed report entitled: “State of the Minnesota River: Summary of Surface Water Quality Monitoring 2000.” The full report can be accessed on the Minnesota River Basin Data Center website at: The Minnesota River has been cited as one of the nation’s and state’s most polluted rivers. In response to these pronouncements, considerable attention and support has been given to clean up efforts. In order to determine whether these efforts have been successful, it is necessary to measure their effect on the river’s health. This report, a cooperative venture of multiple state and local organizations, begins the task of assembling water quality data and creating a foundation for gauging progress toward a cleaner Minnesota River. A list of contributors is included on the back page.
Basin overview map
The Minnesota River flows more than 335 miles from its source at Big Stone Lake to its confluence with the Mississippi River at Fort Snelling. It winds through diverse landscapes and drains nearly 20 percent of Minnesota (roughly 15,000 square miles). The landscape around the upper reaches is partly forested. As it moves downstream, the river drains primarily agricultural land—some of the state’s richest. The lower reaches are characterized by more densely settled urban landscapes. The basin is subdivided into 13 major watersheds and includes 37 counties. Many water quality challenges relate to land uses—including agricultural runoff and urban point-source discharges. While promising strides have been made to reduce point-source pollutants (like industrial and wastewater treatment plants), managing the array of nonpoint-source inputs marks the challenge ahead.

Over the past thirty years, state and federal agencies have collected water quality data at various locations and at various times throughout the Minnesota River Basin. In 1994, the most comprehensive study of water quality in the Minnesota River Basin, the Minnesota River Assessment Project (MRAP), examined the effect of pollution on the river’s physical, chemical, and biological systems. MRAP research concluded that the Minnesota River is impaired by excessive amounts of nutrients, sediment, bacteria, and oxygen-demanding materials. Particularly in spring and summer, water quality often is impacted by elevated levels of suspended sediments, nitrate-nitrogen, and phosphorus. Previous studies found that the Minnesota River violated standards for bacteria, turbidity, dissolved oxygen, and ammonia.

Monitoring Stations

The map shows the locations of the monitoring stations included in this report. Eight are located near the mouths of major tributaries, and two are located on the Minnesota River main stem. This allows us to assess the contributions of major tributaries and in some instances, the resulting impact to the main stem. Noticeably lacking are data from tributaries on the lower Minnesota River between St. Peter and the confluence with the Mississippi River. Data from this area were not finalized at the time this report was prepared. The report also does not include data from many of the smaller tributaries and field-scale evaluations occurring within the basin. The 2001 summary report is expected to include data from some of these missing watersheds or stations.

Monitoring Season
Growing season monitoring data were gathered by Clean Water Partnership Projects (administered by the Minnesota Pollution Control Agency), Metropolitan Council Environmental Services, and the Minnesota Department of Agriculture. Most monitoring occurred from early April until mid to late October, the period when the vast majority of flow in the basin occurs.

The task of collecting water quality data is difficult and complex, and lends itself to a number of different methodologies. Organizations involved in the preparation of this report are moving toward a standard set of methods, a step that will further improve the accuracy of water quality comparisons across the basin. Data analysis involves a number of calculations, all of which are included in the full report. This executive summary uses only one of these calculations, flow weighted mean concentration (FWMC), to describe water quality during the study period. FWMC refers to the concentration (mg/L) of a particular pollutant (e.g. total phosphorus) taking into account the volume of water passing a sampling station over the entire sampling season. It is calculated by dividing the total load (mass) by the total flow. In other words, if all the water passing a monitoring site was put in a large pool, mixed well, and a sample collected, this sample would represent the FWMC. The full report provides a more complete assessment of sediment and nutrient transport including descriptions of loads and yields as well as concentrations.
Precipitation and runoff
Water quality for many pollutants is often linked to precipitation patterns. Due to geographical differences, precipitation patterns vary across the basin (see map). Generally, the precipitation pattern can be characterized as increasing from the western portion of the basin eastward—higher precipitation in the east than west.

Typically, the more precipitation that occurs in a watershed, the more runoff there will be. However, factors such as soil type, slope, and land use can affect runoff. Evaluating runoff enables a comparison of the relative amount of water coming out of the individual watersheds. This is relevant because studies have shown a relationship between runoff and the concentration of chemicals of interest.

2000 Runoff Findings

There is a strong correlation between runoff and water quality.

Total suspended solids, nitrate-nitrogen, and total phosphorus yields are positively correlated with runoff.

Trends indicate an increase in runoff volume throughout the 1900s. However, the 2000 monitoring season runoff values were almost all below the 15-year average except the Le Sueur River, which had comparatively higher runoff. The chart at left illustrates these values.
TSS findings
Suspended sediment is a major water quality concern (see box below). Sediment concentration, loads, and yields can increase substantially during runoff periods causing wide fluctuations in annual delivery. The amount of sediment that enters and is transported through the streams and rivers of the Minnesota River Basin varies greatly from year to year. For example, the average sediment transport of the Minnesota River at Mankato is about one million tons per year, but it can range from 200,000 to 3.5 million tons per year.

It is difficult to find a single agreed-upon value indicating a desirable or acceptable TSS concentration for streams and rivers in the Minnesota River Basin. In part, this is due to wide fluctuations in seasonal concentrations. Standards define water quality goals for a particular waterbody. The state of Minnesota has not established a standard for TSS, but one has been established for turbidity which is an indicator of water clarity. To meet water quality standards, turbidity levels must be no greater than 25 NTUs (25 NTUs equates to an approximate TSS concentration of 46 mg/L). Ecoregion values provide another basis of comparison. Throughout most of the Minnesota River Basin, minimally impacted waterbodies would be expected to exhibit TSS concentrations ranging between 26 and 75.5 mg/L.

2000 TSS Findings
Like runoff rates, there appears to be a general west to east trend in TSS concentrations, with eastern watersheds having higher concentrations.

All monitored sites exceed the turbidity standard.

As shown on the chart at right, the Le Sueur and Cottonwood Rivers exhibited the highest TSS concentrations.

Even though the Le Sueur River Watershed is considerably smaller than several of the other watersheds, it had a much larger TSS concentration.

The Le Sueur (1,483 lbs/acre), Redwood (756 lbs/acre), Blue Earth (236 lbs/acre), and Cottonwood (181 lbs/acre) Rivers exhibited the highest TSS yields.

Nitrate-N Findings
Nitrate-nitrogen in the Minnesota River has the potential to impact water quality downstream, particularly contributing to the hypoxia problem in the Gulf of Mexico. Elevated nitrate concentrations in river systems also have the potential to impact water supply wells (see box).

Nitrate-nitrogen concentrations in drinking water supplies are a public health issue. The standard for drinking water is 10 mg/L. Nitrate-nitrogen in surface water (non-drinking) poses a threat by contributing to the zone of hypoxia in the Gulf of Mexico. For minimally impacted streams in the Minnesota River Basin, the nitrate-nitrogen range is 0.9 to 6.5 mg/L.

2000 Nitrate-N Findings
Most watersheds exceeded the ecoregion value for minimally impacted stream sites.

Seven Mile Creek subwatershed had the highest nitrate FWMC of any of the tributary or main stem sites, followed by the Watonwan, Blue Earth, Middle Minnesota, and Le Sueur River Watersheds.

Phosphorus findings
Phosphorus has been identified as a major pollutant of the Minnesota River (see box). Elevated phosphorus levels is one of the main reasons the Minnesota River is considered one of the most polluted rivers in the state. Controlling phosphorus is an important part of protecting the river.

There is growing interest in the establishment of phosphorus standards for rivers and streams across the nation. In the Minnesota River Basin, this interest is due to phosphorus-induced algal blooms that can lead to turbidity and dissolved oxygen depletion. Until standards are developed, the concentration of phosphorus in minimally impacted streams in the basin can be used as a benchmark for attainable water quality conditions. Average ecoregion values for minimally impacted rivers in the Minnesota River Basin range from 0.21 - 0.35 mg/L.

2000 Phosphorus Findings
TP concentration, like TSS, is positively correlated with runoff.

The largest portion of phosphorus loads were tied to organic and inorganic particles, rather than dissolved phosphorus.

As indicated on the chart at left, many watersheds were above the 0.35 mg/L threshold.

Little Cottonwood River, Chippewa River, Seven Mile Creek, Watonwan River, and the Minnesota River at Judson were below the 0.35 mg/L ecoregion value.

When normalized for runoff, the Redwood River point source contributions were high.


Brown-Nicollet-Cottonwood Clean Water Project
Chippewa River Watershed Project
High Island Creek Watershed Assessment Project
Martin County Environmental Services
Metropolitan Council Environmental Services Program
Minnesota Department of Agriculture Surface Water Monitoring Program
Minnesota Pollution Control Agency, Mankato Office
Redwood-Cottonwood Rivers Control Area
Watonwan River Clean Water Parnership Project
Water Resources Center: Minnesota State University, Mankato

Contact Information
Minnesota River Basin Data Center:
Water Resources Center,
Minnesota State University, Mankato
Phone: 507-389-5492

Minnesota Pollution Control Agency

Metropolitan Council Environmental Services

Minnesota Department of Agriculture

University of Minnesota:
Department of Soil, Water, and Climate


This page was last updated 12/12/02