Sediment is composed of loose particles of sand, clay, silt, and other substances. Sediment flows into Minnesota lakes, rivers, and streams via runoff in both urban and rural areas.
Much of the sediment in Minnesota waters comes from erosion of bluffs and streambanks, urban stormwater, and runoff from areas of exposed soil such as construction sites and plowed fields. The sources of the problem are numerous and widespread and will require efforts by organizations and individuals throughout the state to reduce sediment pollution.
Human health and environmental concerns
Much of the sediment in Minnesota waters is contaminated by phosphorus and toxic substances, which cling to the particles.
Sediment also contributes to turbidity in lakes and stream, where the water is cloudy or murky from suspended or dissolved particles. Cloudy water prevents sunlight from reaching aquatic plants. Turbidity also can harm fish and other aquatic life by:
- Raising water temperatures
- Decreasing oxygen levels in the water
- Reducing food supplies
- Degrading spawning beds
- Preventing successful development of fish eggs and larvae
- Affecting gill function in fish
In large quantities, sediment can even fill in bodies of water. For instance, the upper seven miles of Lake Pepin on the Mississippi River could be completely filled in with sediment deposits over the next 100 years if nothing is done to remedy the problem.
The strategies for reducing turbidity are focused on slowing the rate at which water runs off land and allowing it to evaporate or soak into soils where possible. Recommended strategies include:
- Building soil health so it can retain more water
- Using reduced tillage, cover crops, and other practices on farmland to slow erosion and run off
- Planting vegetative buffers on the edge of farm fields and next to bodies of water
- Restoring eroded bluffs and streambanks
- Regular street sweeping in urban areas
- Enforcing stormwater controls on construction sites