Extensive research has taken place, and is ongoing, to better understand the specific causes and contributing factors for Lake Pepin’s dramatic sedimentation increase, and possible strategies for mitigating and managing and addressing this threat.
Mitigation refers to actions that reduce sediment and nutrients transport near their source and before they can enter entering waterways. Given the substantial complexity and steep challenge of the South Metro Mississippi impairments and cleanup goals, as well as the need to undertake major pollution reductions in the Minnesota River Basin, the MPCA in 2015 released a report,The Sediment Reduction Strategy for the Minnesota River Basin and South Metro Mississippi River, which sets forth an interim goal of 25% sediment reduction in the Minnesota River by 2020. It also provides general water quality protection strategies for local watershed managers to consider in their ongoing planning efforts, recognizing that significant pollution reductions will require a combination of traditional conservation practices that reduce soil erosion from cropland and urban development areas, along with efforts to control near-channel erosion.The Sediment Reduction Strategy organizes Best Management Practices, or BMPs into several categories based on sediment and nutrient sources. Key BMP categories include:
- Improve Riparian Buffers
- Increase Water Storage
- Limit Soil Erosion
- Nutrient Management
The Lake Pepin Legacy Alliance has created its Minnesota River Basin county scorecard mapping tool to help interested people visualize and track the implementation and impacts of BMPs in these categories throughout the MRB landscape.
Riparian zones, the ecosystems that occur along watercourses or water bodies, are critically important areas for protecting water quality throughout the Minnesota River Basin. Riparian zones that are planted in perennial vegetation act as protective “buffers” for the river and its tributaries. They trap and remove pollutants, such as sediment and nitrogen that are often contained in surface runoff waters, before those pollutants can enter the adjacent waterways. Perennially vegetative riparian areas also tend to be much less vulnerable to erosion because the root systems of vegetation act to hold soil in place. They also function to reduce water velocities, further lessening the likelihood that sediment and nutrient-rich organic materials will reenter waterways. Vegetative riparian areas also provide other important ecological benefits through creating habitat for highly valued wildlife; shading, and thus maintaining cool temperatures in waterways; and maintaining high-quality in-stream habitat for fish and invertebrates. Conversely, riparian areas planted in annual row crops have a greater potential for supplying excess nutrients and sediment to adjacent and downstream water bodies both because of their vulnerability to erosion and because they present no barrier to the overland flow of surface runoff. Riparian BMPs include: riparian herbaceous cover, riparian forest buffer, streambank and shoreline protection, and stream channel stabilization.
Water storage alleviates erosive forces acting on upland and near-channel sediment sources. It also encourages water filtration to reduce pollutants. Water storage BMPs include: sediment basins, ponds, water control structures, water and sediment control basins and maintenance, wetland restoration/creation, stormwater retention basins, public drainage management, push-up ponds, and pond maintenance.
Soil Loss Protection
Soil loss protection helps maintain the integrity of the soil and limit its movement from upland fields. Conservation Tillage is a key BMP that keeps the previous harvest residues on fields to stabilize soil and reduce surface flows. Government incentive programs are another BMP option that financially compensates landowners for protecting environmentally sensitive areas, often as an alternative to cultivation. Other soil erosion BMPs include: conservation cover, conservation crop rotation, residue and tillage management, contour farming, contour buffer strips, cover crop, critical area planting, no tillage, reduced tillage, ridge tillage, strip tillage, mulch tillage, windbreak establishment, windbreak management, filter strip, grade stabilization structure, grassed waterway, stormwater runoff control, and erosion control.
Nutrient management addresses the application and absorption of nutrients on agricultural fields. BMPs include: comprehensive nutrient management plan, nutrient management plan, waste water and feedlot runoff control.
In 2012, The Minnesota Department of Agriculture released the Ag BMP Handbook to provide a comprehensive inventory of agricultural Best Management Practices (BMPs) that address water quality impairments for Minnesota specifically. The goal is to ensure that BMPs are placed in areas of the landscape where they will have the greatest environmental benefit. This Handbook includes the following information:
- A definition of Ag-BMPs that affect water quality
- An estimate of the effectiveness of each Ag-BMP
- An estimate for the cost of design, installation and maintenance
- A list of the potential barriers to adoption
- A list of knowledge gaps
In coordination with the Ag BMP Handbook, The Minnesota Department of Agriculture developed this tool to provide a comprehensive database of information related to agricultural BMPs and in easily accessible formats to individuals across the state of Minnesota. The Ag BMP Assessment and Tracking Tool attempts to answer the following questions:
- What are the pros and cons of different practices?
- What is the cost of each practice?
- Are certain practices better suited for particular areas of the landscape?
- Which practices are eligible for grant dollars or other financial assistance?
- What are the economic considerations of individual practices?
- How long does it take for a practice to deliver the desired pollutant load reduction?
- Are there case studies that highlight the impact of a specific practice? Can successes be replicated?
- What are barriers for adoption for individual BMPs?
Management refers to actions that restore water systems that are already being impacted by sediment and excess nutrients. Mitigating the problem at the source is crucial, especially for long-term sustainability, but waterways that are already experiencing impacts need ongoing management to ensure ecological health and human use in the meantime. Management strategies vary depending on the impacts being experienced. Physical and/or chemical removal of algae and invasive species is common practice in many lakes throughout Minnesota. Managing sediment is slightly more difficult and often involves expensive equipment and complex permitting for dredging, often done to maintain transportation systems. Island construction and other restoration projects that use natural materials to strategically alter and improve sedimentation patterns are also expensive, but effective sediment management approaches. Strategic draw-downs in certain locations so as to promote the growth of rooted vegetation.
To learn more about management using island construction, check out and support the Lake Pepin Restoration Project.