Ag drainage and erosion: New research confirms primary cause of river pollution

A new study by a team of researchers at the Science Museum of Minnesota and several major universities, published in the journal Hydrological Processes, has shown that the extensive network of agricultural drainage ditches and underground drainage pipes is responsible for increasing river-channel erosion and sediment loads to the Mississippi River.

Many rivers in Minnesota, including the South Metro Mississippi and many of its heavily cropped tributaries, are impaired by high concentrations of suspended sediment. Sediment, which is tiny particles of soil and organic matter suspended in the water, degrades aquatic habitat and harms fish and wildlife.

Excess sediment is perhaps most visible at the confluence of the St. Croix and Mississippi Rivers, where the dark, clear St. Croix mixes with the heavily polluted Mississippi River. This sediment, mostly from the heavily agricultural Minnesota River, is also rapidly filling in Lake Pepin, a natural lake on the Mississippi south of the Twin Cities.

According to the study, Minnesotas rivers are eroding at unnatural and increased rate. The research concludes that agricultural drainage, more so than excess rainfall, caused the erosion of our riverbanks. By quickly routing water out of the soil and into ditches and streams, water that would normally evaporate or be taken up by plants is flushed quickly into surface waters. The subsequent increase in river flow results in more erosive rivers that can carry greater quantities of pollution downstream the Mississippi River and beyond.