What is the source of sediment in streams?

It can come from upland fields, from the stream channel itself or from stream banks and bluffs, says Greg McIsaac,a retired University of Illinois associate professor of natural resources and a soil-erosion expert with Decatur-based Agricultural Watershed Institute, a conservation group.

“Stream-bank and -bed erosion are natural processes,” he says, but they can be accelerated by land-use changes, such as row-crop production and urbanization, that increase runoff.

“More intense rainfalls also contribute to more erosion in fields and stream banks.”


Why is sediment in surface waters harmful?

High sediment loadsimpair water clarity, disrupt aquatic plant growth and destroy fish and wildlife habitat, McIsaac says. Sediment deposition also reduces the capacity of stream channels to convey water, contributing to more frequent flooding. Phosphorus (P) and other pollutants can move along with soil, too, further degrading water quality.


What factors influence field erosion?

Field erosion is determined by the slope of the land, the amount of vegetation or residue covering the soil and rainfall intensity, McIsaac says. Soil moisture content, hydraulic conductivity and subsurface drainage also affect erosion.