Sediment & Erosion Control
Excessive amounts of suspended solids from cropland, urban lands, streambanks
and streambeds is a primary threat to area waters. Working hand-in-hand with stormwater pollution and prevention plans and nutrient management plans, counties in the watershed seek to retain water on the landscape to reduce flooding and subsequent soil erosion, and improve water resources.
Local districts recognize that stormwater runoff volume from impervious surfaces will likely increase as development of the watershed continues. New developments located adjacent to existing cities, near lakeshore or simply placed in a rural setting need to be tightly regulated to prevent the associated nutrient and sediment runoff impacts to our water resources.
The Area’s agricultural dominance, coupled with vast surface water resources has resulted in a “tug of war” between the need for cropping systems and desire for suitable water recreation. To enhance crop production, tiling systems have been improved and wetlands have been drained, causing drainage systems to be inundated with increased volumes of nutrient rich water. These fast flowing systems need to be addressed now - priority issues include potential storage areas, wetland restoration and effective management of the current drainage system program.
Due to the historical draining of much of the areas wetlands and homgenic agricultural practices, priority is given to both wetland preservation and restoration. Wetlands that have been filled and drained retain their characteristic soil and hydrology, often allowing their natural functions to be reclaimed. Restoration is a complex process requiring planning, implementation, monitoring, and management.
Excessive amounts of nutrients, namely phosphorus and nitrogen, contaminate ground and surface waters and create nuisance algae presence in area waters. Major contributors are cropland, urban grasses, municipal wastewater, aging or non-compliant septic systems, and internal cycling.
Feedlot and Animal Waste Management
Managing farms to minimize excess nutrients, pathogens, and odors released into the environment is important to the health of surface and ground water. Agricultural operations need to adequately maintain cropping systems to reduce nonpoint pollution, while feedlot operations need to contain their manure storage areas. Erosion and sedimentation from these operations needs to be closely monitored to reduce the levels of nutrients entering our surface water resources.
State & Regional Management Priorities
Le Sueur River Watershed Management Priorities
Local Government Unit's Management Priorities
“Using multiple lines of evidence, we have demonstrated that under current conditions, the largest sediment sources remain near-channel sources (erosion of bluffs and channel widening and incision) within the incised portion of the “knick zone” of the Le Sueur watershed” (Gran et al, 2011).
The Le Sueur River is one of the heaviest contributors of sediment to the Minnesota River. “The nearly complete transformation of the land surface, vegetation, and hydrology over the past two centuries has increased these already large sediment loadings by a factor of four to five. The average total suspended solids (TSS) load at the mouth of the Le Sueur River during the monitoring seasons from 2000-2010 was 4 to 5 times higher than the amount estimated from pre-settlement valley excavation. The increased delivery of water, sediment, and nutrients to the Minnesota River from the Le Sueur and nearby watersheds now represents an important water quality problem that the State of Minnesota is addressing” (Gran et al, 2011).
What are Total Suspended Solids (TSS)?
The transport of sediment is a natural function of rivers. Modification of the landscape has accelerated the rate of erosion of soil into waterways. Increased runoff has resulted in stream bank erosion. Elevated sediment (suspended soil particles) has many impacts. It makes rivers look muddy, affecting aesthetics and swimming. Sediment carries nutrients, pesticides, and other chemicals into the river that may impact fish and wildlife species. Sedimentation can restrict the areas where fish spawn, limit biological diversity, and keep river water cloudy, reducing the potential for growth of beneficial plant species.
What is Turbidity?
Turbidity refers to how clear the water is. The greater the amount of TSS in the water, the murkier it appears and the higher the measured turbidity.
Why is Elevated TSS a concern?
Excessive amounts of sediment degrade the ecological health and aesthetics of the Le Sueur River and its tributaries. When suspended sediment, measured by TSS, is elevated, turbidity increases, water clarity decreases, and light penetration is reduced. Reduced light penetration shifts stream productivity away from beneficial periphyton (mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems) and favors undesirable suspended algae. An overabundance of algae (phytoplankton) further increases turbidity, compounding the problem. Fine-grained sediments that settle on stream beds cover and degrade the desirable rock and gravel substrates that form essential habitats for invertebrates and fish. During periods of high turbidity, streams take on a murky brownish-green cast, greatly reducing their appeal (State of the Minnesota River, 2009).
The photos above show the dramatic increase in turbidity that often occurs when heavy rains fall on unprotected soils. Upon impact, raindrops dislodge soil particles while runoff waters easily transport fine particles of silt and clay across fields or through drainage systems to ditches and tributary streams throughout the Minnesota River Basin.
Click to see larger map.
What are Nitrates?
Nitrogen exists in the environment in many forms. Nitrate is the oxidized form of Nitrogen that is commonly found in the rivers and streams of the Minnesota River Basin. Because it is highly mobile, and biologically available, it is of special concern for aquatic systems.
In recent decades, there has been a substantial increase in nitrogen fertilizer use. Elevated Nitrate-nitrogen (nitrate-N) in the Minnesota River can pollute aquifers it recharges. Therefore, nitrogen can affect drinking water. At high enough concentrations, nitrate-N can cause
infants who drink the water to become sick and even die (methemoglobinemia).
Why are elevated Nitrates a concern?
Nitrate-nitrogen is important because it is biologically available and is the most abundant form of nitrogen in Minnesota River Basin streams. Like phosphorus, nitrate can stimulate excessive and undesirable levels of algal growth in waterbodies. In recent years, this problem has been particularly severe in the Gulf of Mexico where development of a hypoxia zone (low oxygen) has been linked to excessive amounts of nitrate carried to the Gulf by the Mississippi River. Reduced oxygen levels in the hypoxic zone, brought on by decomposition of algae, have damaged the shellfish industry and threaten the aquatic ecosystem of the Gulf Region. The Minnesota River has been identified as a substantial contributor of excess nitrate to the Mississippi River and the Gulf Region.
MPCA is currently developing a nitrate standard for rivers based on aquatic life toxicity.
Click to see larger map.
What is Phosphorus?
Phosphorus is an important nutrient for plant growth. Total phosphorus is the measure of the total concentration of phosphorus present in a water sample. Excess phosphorus in the river is a concern because it can stimulate the growth of algae. Excessive algae growth, death, and decay can severely deplete the oxygen supply in the river, endangering fish and other forms of aquatic life. Low dissolved oxygen concentrations are a concern particularly during low-flow times or in slow-flowing areas such as reservoirs and the lower reaches of the Minnesota River. Large total phosphorus loads can have major impacts both locally and on downstream receiving waters such as Lake Pepin.
Why are elevated Phosphorus levels a concern?
Phosphorus-enriched streams are commonplace in the Minnesota River Basin. Phosphorus stimulates the growth of algae and elevated phosphorus concentrations often lead to eutrophication which is characterized by undesirably high levels of algal growth. An overabundance of algae and sediment contributes to increased turbidity and reduced light penetration. Water clarity is greatly reduced under these conditions, impairing recreational use and aesthetics of the river environment. Furthermore, algal cells eventually die and their subsequent decomposition consumes in-stream oxygen, as in the lower Minnesota River downstream
reach. This oxygen demand can lower dissolved oxygen in the streams and impair the stream’s ability to support aquatic life. Some outbreaks of highly elevated Blue-green algal growth, termed algal blooms, release toxins into the water. Instances of this have occurred within the Minnesota River Basin and resulted in the death of animals (including pets) that ingested these toxins.
Point-source phosphorus comes mainly from municipal and industrial discharges to surface waters. Nonpoint-source phosphorus comes from runoff from urban areas, construction sites, agricultural lands, manure transported in runoff from feedlots and agricultural fields, and human waste from non-compliant septic systems (State of the Minnesota River, 2009).
Click to see larger map.
The Minnesota Department of Agriculture (MDA) is the lead state agency for most aspects of pesticide and fertilizer regulatory functions. The MDA Monitoring Unit collects pesticide samples from multiple stream locations in the Minnesota River Basin. Pesticide monitoring data indicate the seasonal presence of several chemicals sometimes at levels of concern. The most commonly detected pesticides in the Minnesota River Basin are delineated in the table below. In order to evaluate the presence of commonly used pesticides in the rivers and streams, the MDA conducts an annual statewide survey of selected surface water sites.
What are Pesticides?
A pesticide is any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest. Although often misunderstood to refer only to insecticides, the term pesticide also applies to herbicides, fungicides, and various other substances used to control pests. Under United States law, a pesticide is also any substance or mixture of substances intended for use as a plant regulator.
Most Commonly Detected
Pesticides In the Minnesota River Basin, the following three herbicides are the most commonly detected pesticides:
Acetochlor (Surpass, Harness)
s-Metolachlor (Dual, Brawl)
(State of the Minnesota River, 2009).
Concentrations of acetochlor in the Le Sueur River and the Little Beauford Ditch have violated the MPCA Chronic Water Quality Standard for Acetochlor, resulting in their placement in 2008 on the state’s 303(d) TMDL list of impaired waters. The Chronic Water Quality Standard for Acetochlor is 3.6 μg/L over four days and was established for the protection of aquatic life. Since 2005, neither the Le Sueur River nor the Little Beauford Ditch have violated the surface water standard for acetochlor. The highest acetochlor concentration measured in Le Sueur River since 2005 is 2.05 ppb; in the Little Beauford Ditch is 1.46 ppb.
Acetochlor Impairment Response Plan
A response to the impairments is being developed by the Minnesota Department of Agriculture in collaboration with an advisory committee and the Minnesota Pollution Control Agency. The MPCA and MDA have worked together to develop a proposed “Acetochlor Impairment Response Plan” for the Le Sueur River and Little Beauford Ditch. It outlines specific activities to be completed or evaluated in response to the water quality impairments (Le Sueur River and Little Beauford Ditch Acetochlor Impairment Response Work Plan, 2013).
For More Information:
Le Sueur RIver and Little Beauford Ditch Acetochlor Plan 2013
Click to see larger map illustrating Acetochlor concentrations in MDA monitored waterways.
Click to see larger map illustrating Atrazine
concentrations in MDA monitored waterways.
Click to see larger map illustrating Metolachlor
concentrations in MDA monitored waterways.
The Little Beauford Ditch is a tributary of the Le Sueur River and is located in Blue Earth County south of the city of Mankato. Two streams, the Le Sueur River and the Little Beauford Ditch, violated the Minnesota Pollution Control Agency (MPCA) Chronic Surface Water Quality Standard for Acetochlor and are included on the Minnesota 2008 Impaired waters list (also known as the 303(d) list). These streams violated the Acetochlor surface water standard of an average Acetochlor concentration exceeding 3.6 μg/L over four days (96 hours).
Minnesota's Impaired Waters List
The impaired waters list is comprised of bodies of water that do not meet one or more water quality standards, as defined by Minnesota Rules Chapters 7050 (Waters of the State). Monitoring suggests that about 40% of Minnesota's lakes and streams are impaired for conventional pollutants (i.e. nutrients, bacteria, turbidity, and mercury).
Standards for water quality are required under the federal Clean Water Act, which tells each state to designate beneficial uses for all waters and develop water quality standards to protect each use. Water quality standards are the fundamental benchmarks by which the quality of surface waters are measured and used to determine impairment. Use attainment status is a term describing the degree to which environmental indicators are either above or below criteria specified by Minnesota Water Quality Standards. The Clean Water Act identifies "healthy aquatic life" and "recreation" as beneficial uses, in addition Minnesota rules protect others such as, "drinking water", "industrial and agricultural uses", "wildlife", "navigation", and "aesthetic enjoyment" (Minnesota Rules chapters 7050, Waters of the State).
These standards are developed to protect water resources for uses including, fishing, swimming, and other recreation, and sustaining fish, bugs, plants and other aquatic life. Minnesota is able to measure and identify polluted waters or healthy waters in need of protection. The water quality standards provide a guide to set limits on what regulated facilities can discharge to surface water. The Minnesota Pollution Control Agency is continually developing and adapting Minnesota's water quality standards. The pillars for establishment of water quality standards include:
1. Designated Beneficial Use
These standards can be numeric or narrative in nature and define the concentrations or conditions of surface waters that allow them to meet their designated beneficial uses, such as for fishing (aquatic life), swimming (aquatic recreation) or human consumption (aquatic consumption). All surface waters in Minnesota, including lakes, rivers, streams, and wetlands are protected for aquatic life and recreation where these uses are attainable.
2. Numeric Water Quality Standards
represent concentrations of specific pollutants in water that protect a specific designated use. Ideally, if the standard is not exceeded, the use will be protected. The MPCA uses a variety of tools to fully assess designated uses. Assessment methodologies often differ by parameter and designated use. Furthermore, pollutant concentrations may be expressed in different ways such as chronic value, maximum value, final acute value, magnitude, duration and frequency.
3. Narrative Standards
are statements of conditions in and on the water, such as biological condition,
that protect their designated uses. Interpretations of narrative criteria for aquatic life support in streams are based on multi-metric biological indices including the Fish Index of Biological Integrity (F-IBI), which evaluates the health of the fish community, and the Macroinvertebrate Index of Biological Integrity (M-IBI), which evaluates the health of the aquatic macroinvertebrate community.
This provision achieves and maintains the highest possible quality in surface waters of Minnesota. The existing uses and level of water quality necessary to protect existing uses shall be maintained and protected.
Le Sueur River Watershed Impaired Waters List
The Le Sueur River Watershed was monitored in 2008-2009, where 74 of the 136 stream reaches and 9 of the 52 were assessed as impaired or supporting at least one of their beneficial uses. Details on monitoring results and conditions in the Le Sueur River Watershed, visit the MPCA's Le Sueur River webpage.
Local impaired beneficial uses:
Protection of aquatic life
means the maintenance of healthy, diverse and successfully reproducing populations of aquatic organisms, including fish and invertebrates.
Protection of Recreation
means the maintenance of conditions suitable for swimming and other forms of water recreation.
Protection of consumption
means protecting citizens who eat fish inhabiting Minnesota waters or receive their drinking water from water bodies protected for this use.
Limited Resource Value Waters
Surface waters of the state that have been subject to a use attainability analysis and have been found to have limited value as a water resource.
Protection of Recreation
Is it safe to swim and recreate in the lakes and rivers of the Le Sueur River Watershed?
Disease-causing organisms (pathogens) in water bodies are difficult to measure, so indicators like E. coli bacteria are used to illustrate the likelihood that a water body contains pathogens. Although viruses and protozoa cause many of the illnesses associated with swimming in polluted water, monitoring for E. coli will tend to indicate fecal contamination. Untreated sewage or livestock waste released into the water can expose swimmers to bacteria, viruses, and protozoa.
Children, the elderly, and people with weakened immune systems are most likely to develop illnesses or infections after swimming in polluted water. The most common illness associated with swimming in water polluted by sewage is gastroenteritis.
The illness can have one or more of the following symptoms: nausea, vomiting, stomachache, diarrhea, headache, and fever. Other minor illnesses associated with swimming include ear, eye, nose, and throat infections (State of the Minnesota River, 2009).
How are fish and other aquatic life doing?
MPCA researchers are charged with evaluating the water quality of streams and rivers using the biological communities that live there. The group is divided into two areas of expertise: fisheries, and benthic macroinvertebrates or benthos. Researchers also analyze biological data, dissolved oxygen, turbidity, chloride, pH and NH3 to determine use status.
Only two stream reaches were found to be fully supporting of aquatic life use in the watershed. Most of the streams that were assessed do not meet state water quality standards for aquatic life. Aquatic biological impairments are found throughout the entire watershed where assessments were made (shown in red). Twenty-five (25) new impairments of aquatic life have been added to the Le Sueur River watershed during the 2010 assessment cycle.
Number of assessed streams found to be meeting state water quality standards for aquatic life, based on fish populations sampled.
Number of assessed streams found to be meeting state water quality standards for aquatic life, based on macroinvertebrate populations sampled.
Is it safe to eat fish in the Le Sueur Watershed?
Mercury and Fish Consumption
The primary contaminants of concern in the Le Sueur River Watershed are mercury and polychlorinated biphenyls, or PCBs. In Minnesota, Mercury contamination of fish is a well-documented problem. Mercury is tightly bound to proteins in all fish tissue, including muscle. There is no way to reduce the amount of mercury in a fish through cooking or cleaning it.
Fish Consumption Advisories
The Minnesota Department of Health (MDH) advises people to restrict their fish consumption due to Mercury accumulation in sport fish from lakes and rivers. Large amounts of Mercury in your body may harm your nervous system. The MDH issues fish consumption advisories for lakes and streams in Minnesota where fish have been tested. The advisories contain recommended rates of consumption based on contaminant levels in the fish.
Generally, MDH advises avoiding Minnesota caught walleye longer than 20 inches, northern pike longer than 30 inches, and muskellunge. Nearly all fish and shellfish contain traces of methylmercury. However, larger fish that have lived longer have the highest levels of methylmercury because they’ve had more time to accumulate it. On the other hand, MDH advises that it is safe to eat Minnesota caught: sunfish, crappie, yellow perch, bullheads (one meal per week).
For more information: The Department of Health website is your best resource to learn more about fish caught in particular rivers, streams and lakes.
Minnesota Department of Health’s fish consumption guidelines:
Consumption guidelines are also searchable by lake on the Department of Natural Resources Lake Finder website. www.dnr.state.mn.us/lakefind/index.html
Le Sueur River Watershed Assessment Report Findings
Fish were tested in the lakes and rivers listed below in order to determine the levels of Mercury, Perfluorochemicals (PFCs), and Polychlorinated biphenyls (PCBs). Assessment results are summarized here and more detail can be found in MPCA’s Monitoring and Assessment Report.
Pollutant: Polychlorinated biphenyls (PCBs)
In 2008, the largest carp and the two largest channel catfish collected from the Le Sueur River were analyzed for PCBs. Both channel catfish were below the impairment threshold but the carp was above. Consequently, the fish consumption advice for carp in the Le Sueur River is one meal per month.
Assessed Stream: Le Sueur River
Pollutant: Polyfluorochemicals (PFCs)
In 2009, Madison Lake was sampled for PFCs. Northern pike, walleye and panfish species were sampled and PFOS concentrations in all samples were at or below the laboratory reporting level.
Assessed Lake: Madison Lake
Northern pike, walleye, and yellow perch were collected from Madison Lake, Reeds Lake, and Bass Lake. Walleye in Madison Lake and Northern Pike in Reeds Lake exceeded the threshold for impairment.
Assessed Lake: Madison Lake Reeds Lake Bass Lake
Lake - Status
What is the status of local lakes? Why are local lakes greening?
Le Sueur River Watershed Assessment Report Findings
There are a total of 49 lakes greater than 10 acres in the Le Sueur River Watershed. Eleven of those lakes have been monitored (approximately 22 percent). Nine of the eleven lakes were able to be assessed during the 10-year assessment window. Two of the nine lakes were found to be supporting of Aquatic recreation standards (MPCA, 2012).
Overall, the majority of these lakes possessing assessment level data have been determined to be non-supporting of recreational use. Of the four lakes (Buffalo, Minnesota, Bass, and Rice) that have insufficient data to complete an assessment, only one (Bass Lake) indicates improving water conditions. However, two lakes within the watershed have been determined to be fully supporting of recreational use (MPCA, 2012).
A combination of several factors have degraded lakes in the Le Sueur River Watershed, resulting in poor water quality, abundant algae and lack of wildlife. These impacts can be divided into two general categories:
- External nutrient loading, and
- Internal nutrient loading.
Nutrients flowing into lakes from their watersheds are referred to as external loads. The landscape around these lakes has been transformed with the loss of prairie and drainage of wetlands. The current landscape is intensively cropped. Phosphorus fertilizer is being added to increase/maintain the productivity of the cropped acres. These changes have negatively impacted shallow lakes.
Internal nutrient loading has also caused problems for shallow lakes, and in addition to the extra water flow, and external nutrients. Over the last twenty years, scientists and managers have begun to understand how fish affect internal loading, in particular invasive species like common carp. They stir up the bottom as they feed and move nutrients from the sediments into the water column (Shallow Lakes Brochure).
Reducing levels of Total Phosphorus (TP) will be required in order to reduce the occurrence of algal blooms for lakes within the Le Sueur River watershed. Alternatively, should inlake TP concentrations increase, the potential for nuisance algal blooms will also increase. It is important to limit as much external (watershed) phosphorus loading to the lakes as possible to improve or maintain the current concentrations. Additionally, the watersheds for each of these lakes will need to be addressed through a water quality study to determine the source and extent of pollution problems (MPCA Lake Assessment). The combination of high external phosphorus loads, shallow lake depth, high-P sediments, and bottom feeding fish species makes improving lake quality very challenging.
Decreasing lake water clarity in southern Minnesota
A University of Minnesota study examined lake water clarity using satellite data from 1985-2005. Researchers found strong geographic patterns in Minnesota: lakes in the south and southwest have low clarity, and lakes in the north and northeast tend to have the highest clarity. Over the 20 year period, researchers found mean lake water clarity in central and northern Minnesota stable while decreasing water clarity trends were detected in southern Minnesota (Western Corn Belt Plains and Northern Glaciated Plains Ecoregions).
49 - LAKES > 10 acres in the Le Sueur River Watershed
40 - LAKES NOT ASSESSABLE
9 - LAKES ASSESSABLE
7 - NOT SUPPORTING aquatic recreation standards
2 - SUPPORTING
aquatic recreation standards
Source: Minnesota Pollution Control Agency’s Le Sueur River
Monitoring and Assessment Report, 2012.