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Water Quality Concerns

The Minnesota River Basin (Fig. 1) encompasses a large area in the state of Minnesota covering roughly 10 million acres, with approximately 700,000 rural, municipal, and urban residents. It drains 12 major watersheds. The predominant land use in the basin is agricultural.

Like many Minnesotans, you may be concerned about water quality in the Minnesota River Basin. You may have heard that it is ranked as one of twenty rivers in America that is seriously threatened by pollution.

During spring and summer especially, water quality in the Minnesota River can be severely impacted by:

• Pathogens (bacteria and viruses)that cause disease. If people, especially children come in contact with pathogens, they may get sick.

  Figure 1. Minnesota River Basin major watersheds

• Sediment (suspended soil particles) that makes rivers look muddy and turbid, restricts the ability of fish to spawn, limits biological diversity, and carries phosphorus into the river.

• Phosphorus that stimulates the growth of algae. As algae die and decompose, oxygen levels in the water are lowered, which may kill fish and other aquatic organisms.

• Nitrogen that can affect drinking water. At high enough concentrations, nitrate-nitrogen can cause infants who drink the water to become sick.

  Concerted efforts are needed by town dwellers, farmers, municipalities, and industries to reduce pollution of the river and its tributaries. Degraded water quality in the Minnesota River has a significant impact locally, as well as regionally and nationally.

• Local effects can include waterborne health hazards, reduced fish populations, and impaired recreational opportunities.

• Regional effects include eutrophication or lowered oxygen levels caused by large algal populations that consume dissolved oxygen.

Regional effects are common during summer when the river is low, in both Lake Pepin and the Minnesota River between St. Peter and Ft. Snelling. Further downstream, there is growing concern that the hypoxic zone (an area of very low dissolved oxygen levels in water) in the Gulf of Mexico is caused by nitrate-nitrogen from the Upper Mississippi Basin, including the Minnesota River Basin. Low oxygen levels in water, whether fresh or sea water, cause fish and other organisms to die.

Historic Perspective

While the public has a right to expect improved water quality in the Minnesota River, goals need to be realistic. The Minnesota River never will be a crystal clear running stream. Serious degradation in water quality has, however, occurred in the Minnesota River over the last 150 years due to significant changes in land use. The Minnesota River Basin once was a prairie and wetland landscape that supported a thriving population of birds and bison. As European-Americans moved in, they established many towns and cities, plowed the prairie, and drained the wetlands.

The Minnesota River Basin is now dominated by two major features. First is the vast agricultural landscape that contributes billions of dollars to the economy of Minnesota. Second is the large urban population center of the Twin Cities at the mouth of the Minnesota River (where it enters the Mississippi River). Approximately 700,000 people live in the Minnesota River Basin. These two features help explain the poor water quality and loss of wildlife habitat in the Minnesota River Basin.

Local Water Quality Goals

Goals for the river cleanup are often driven by local water quality concerns. The day-to-day concerns of people for the river could include:

• Are the fish safe to eat?
• Are opportunities for fishing and boating limited by pollution or by flooding?
• Is it safe to swim in the river?

These concerns have less to do with water quality standards and more to do with quality of life. People want to use and enjoy the rivers. People are also concerned about specific areas within the broader watershed. For instance, there may be strong local concern about an individual lake or small stream.

These concerns can be used to develop local water quality goals. Citizens and landowners develop local organizations that work cooperatively through individual county water plans and watershed management projects. To enhance this effort, the Minnesota River Basin Joint Powers Board has endorsed a strategy known as “Watershed Implementation from the Local Level” (WILL), designed to build on the framework of individual county water plans. After a WILL watershed management plan is developed in each of the major watersheds of the Minnesota River Basin, its goals and objectives will become part of individual county water plans. Together these 12 WILL plans will become the “road map” for cleanup of the Minnesota River Basin.

Water Quality Standards

While local perceptions about the river are important, the state and federal governments have developed specific water quality standards for rivers that indicate the extent of pollution. Water quality in the Minnesota River and its tributaries has been monitored by state and federal agencies for the last 30 or so years. The key water quality standards for rivers are given below, along with a listing for the percent of water quality monitoring samples which violate these standards (Table 1):

• Monthly average fecal coliform concentrations must not exceed 200 organisms/100 mL. This standard is frequently violated in the Minnesota River between Morton and Ft. Snelling (Table 1), and in tributaries throughout the basin.

• Turbidity levels, affecting cloudiness of the water (primarily caused by suspended sediment at high flows or by algae at low flows), must not exceed 25 nephelometric turbidity units (NTUs). This standard is frequently violated in the Minnesota River between Courtland and Ft. Snelling (Table 1).

• Nitrate-nitrogen levels in ground and surface water must not rise above 10 mg/L in order to meet state and federal drinking water standards. There are often violations of the nitrate-N water standard in the Minnesota River between St. Peter and Jordan (Table 1).

• Dissolved oxygen levels in water must not drop below 5 mg/L if the river is to support healthy aquatic life. This standard is sometimes violated in the Minnesota River between Shakopee and Ft.Snelling, and at Milan (Table 1).

• High levels of phosphorus can cause low levels of dissolved oxygen by stimulating the growth and decay of algae. There are currently no statewide water quality standards for phosphorus levels in rivers. Streams and rivers in the Minnesota River Basin have an average phosphorus concentration of 0.25 mg/L, and this level is frequently exceeded in the Minnesota River near Ft. Snelling and between Courtland and St. Peter (Table 1).

Table 1 shows the percent of water quality samples that violate standards. According to Table 1, water quality standards in the Minnesota River downstream of Morton are frequently violated, causing local concerns for human health, and affecting fish and other aquatic life. Major reductions in pollution from all sources will be required to protect human and aquatic health, to meet water quality standards, and address local concerns for pollution. To help achieve these pollution reductions, an interim target for a 40% reduction in sediment and phosphorus loads entering the Minnesota River and its tributaries has been recommended by state and federal agencies, and endorsed by the Minnesota River Basin Joint Powers Board. Specific goals for other pollutants will be established in the future.

Regional Patterns in Pollution

Water quality standards are frequently violated in the Minnesota River from Morton downstream to Ft. Snelling, as well as in the tributaries to the river. Thus every one of the 12 major watersheds in the Minnesota River has local effects on water quality. There are, however, differences in the regional effects of each watershed on pollution in the Gulf of Mexico, Lake Pepin, or the stretch of the Minnesota River near the Twin Cities. The primary parameters of concern at the regional level are sediment, phosphorus, and nitrogen.

Figure 2. Comparison of total suspended solids loads in major watersheds of the Minnesota River Basin

Water quality monitoring data collected by various state and federal agencies from 1968 to 1994 provide a comprehensive framework for understanding which watersheds have the largest regional effects. Sampling locations for this analysis were mostly at the mouth of major tributaries near the point where they enter the Minnesota River.

Sediment

The loads of total suspended solids (TSS) in the Minnesota River at Ft. Snelling are controlled primarily by three watersheds. These are the Blue Earth and Le Sueur watersheds, and the Lower Minnesota watershed, which includes contributions from Rush River, and from High Island, Sand, and Bevens Creeks. Combined, the Blue Earth, Le Sueur, and Lower Minnesota watersheds drain an area which represents roughly 25% of the total area in the Minnesota portion of the basin. This relatively small area generates two-thirds of the TSS load in the Minnesota River upstream of Ft. Snelling. The rough breakdown for TSS loads generated (Fig. 2) is:

• the Lower Minnesota watershed generates 26% of the basin-wide TSS load
• the Le Sueur watershed generates 21% of the basin-wide TSS load
• the Blue Earth watershed generates 19% of the basin-wide TSS load

Sediment loads from the other nine watersheds generate one-third of the basin-wide load. This is an important load, and causes significant impacts on local water quality. The sediment loads from these nine watersheds cannot be overlooked in efforts to clean up the Minnesota River Basin.

Figure 3. Comparison of total phosphorus loads in major watersheds of the Minnesota River Basin.

Phosphorus

Roughly 65% of the total phosphorus load at Ft. Snelling comes from the Lower Minnesota, Le Sueur, and Blue Earth watersheds.

The distribution of phosphorus loads in these three watersheds (Fig. 3) is:

• the Lower Minnesota watershed generates 33% of all the phosphorus in the basin
• the Le Sueur watershed generates 17% of all the phosphorus in the basin
• the Blue Earth watershed generates 15% of all the phosphorus in the basin

From 1968 to 1994 about one-third of the phosphorus generated in the Lower Minnesota watershed was produced by the Blue Lake and Seneca wastewater treatment plants. Recently, biological phosphorus removal procedures have been adopted at these plants, which has reduced phosphorus loads from wastewater effluent by 60-70%.

The other nine watersheds in the basin drain three-fourths of the total basin, and generate one-third of the total sediment and phosphorus loads. Again, loads from these nine watersheds have important local water quality effects, and cannot be overlooked in efforts to clean up the Minnesota River Basin.

Nitrogen

Roughly 64% of the nitrate-nitrogen load at Ft. Snelling comes from the Blue Earth, Le Sueur, and Watonwan watersheds. The distribution of nitrogen loads in these three watersheds (Fig. 4) is:

• the Blue Earth watershed generates 26% of all the nitrate-N in the basin
• the Le Sueur watershed generates 26% of all the nitrate-N in the basin
• the Watonwan watershed generates 12% of all the nitrate-N in the basin

Three other watersheds—the Lower Minnesota, Middle Minnesota, and Cottonwood watersheds—generate another 31% of the nitrate-N load.

Figure 4. Comparison of nitrate-N loads in major watersheds of the Minnesota River basin.

Reasons for Watershed Differences

Results of the sediment and phosphorus evaluation for the Minnesota River Basin show significant increases in both loads and yields going from the western to eastern portion of the basin. The three primary reasons for this increase are:

• Mean annual precipitation increases from 22" on the western side to 32" on the eastern side of the basin (Fig. 5). As a result, mean annual runoff depths increase from less than 2" on the western side to 8" on the eastern side of the basin.

• Due to a steeper landscape (Fig. 6) and wetter climate, soils in the eastern part of the basin are more erodible than in the western part.

• The major population centers of the basin are located on the eastern side of the basin. About 60% of the population resides in six of the 37 counties in the basin, namely, Hennepin, Scott, Blue Earth, Carver, Dakota, and Nicollet counties.

Figure 5. Minnesota River Basin mean annual precipitation.

Figure 6. Minnesota River Basin slope steepness groups.

Sources of Pollution

Pollutants of concern in the Minnesota River Basin include bacteria and other disease-causing organisms, suspended sediments, excess nutrients, and decaying organic matter responsible for low levels of oxygen. These pollutants come from a variety of sources including runoff and erosion from agricultural fields, stream banks and stream channel scouring, city streets, construction sites, feedlots, and the effluent from wastewater treatment plants and septic systems.

There are significant agricultural and nonagricultural sources of pollution that degrade water quality in the Minnesota River Basin. To the best of our knowledge, municipal and industrial wastewater discharges account for about 10% of the loading during high flow years, and for at least 90% of the total phosphorus loading in the Minnesota River during low flow years.

Indirect measurements suggest that nonagricultural sources of sediment (stream bank erosion, erosion from construction sites) account for about 25% of the total sediment loading in the Minnesota River. These estimates are subject to refinement as better information becomes available. These data show that both point and nonpoint source efforts are going to be required to clean up the Minnesota River.

Implementation Strategy

A cleanup strategy must target the locations in the basin which have the greatest impact on water quality, as well as the most important sources of water quality degradation. The most important sources of pollution are:

• sediment and nutrients from agricultural cropland
• phosphorus and bacteria from municipal waste water treatment plants
• bacteria and other pathogens from septic systems
• sediment from stream bank erosion
• nutrients and bacteria from animal manure runoff

There are about 179 municipal wastewater treatment plants and 103 industries in the Minnesota River Basin that, taken together, discharge significant quantities of phosphorus. Occasionally, these plants may malfunction, discharging bacteria into surface water. It is estimated that there are also 30,000 septic systems in the basin that illegally discharge bacteria and pathogens directly to tile drains, ditches, and streams. Minnesota spends millions of dollars every year to reduce pollutants in the effluent from municipal wastewater treatment plants and from septic systems.

Minnesota agricultural producers also spend millions of dollars every year on a wide array of Best Management Practices (BMPs) for agricultural land. Since agricultural production contributes several billion dollars annually to Minnesota’s economy, any changes in agricultural management practices made for the sake of improving water quality in the Minnesota River must be economically feasible and reasonable. Some of the BMPs most effective at protecting water quality include:

• conservation tillage on erodible well-drained lands
• sediment basins and animal waste management facilities
• grassed waterways, filter strips, and riparian buffer strips
• soil testing prior to fertilizer or manure applications
• following University of Minnesota guidelines for application of fertilizer or manure

The BMP selected will depend on site-specific characteristics, as well as individual attitudes and financial or labor constraints. Assistance in selecting among the various BMPs can be obtained from the University of Minnesota Extension Service, Soil and Water Conservation Districts (SWCD), Minnesota Department of Agriculture (MDA), the Natural Resources Conservation Service (NRCS), or the Minnesota Pollution Control Agency (MPCA).

Effects of BMPs on Water Quality

There are reasons to be optimistic about improving water quality in the Minnesota River and its tributaries. Recent studies by the University of Minnesota and the MPCA found a significant reduction in sediment and phosphorus loads in the Minnesota River during the last twenty years. This improvement was due to a combination of factors including accelerated adoption of BMPs by farmers (including conservation tillage), improved manure management, the installation and upgrading of wastewater treatment plants, and septic system improvements. Just in the last year, there have also been significant reductions in phosphorus concentrations of effluent from the Blue Lake and Seneca wastewater treatment plants. These results show that it is possible to clean up the Minnesota River by adoption of BMPs and by improved waste management and wastewater processing. Additional efforts are needed so that Minnesotans can regain their pride in a Minnesota River that is swimmable, fishable, and unpolluted.

Edited by D. J. Mulla, Professor
Data processing and graphics by A. P. Mallawatantri,
    Post-Doctoral Associate
Department of Soil, Water, and Climate, University of
    Minnesota

Produced by Communication and Educational Technology Services, University of Minnesota Extension.

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