Researchers from across the country are trying to find out why the Le Sueur River is so dirty.
Along with the Blue Earth River it empties into, the Le Sueur carries more dirt particles into the Minnesota River than any other tributary in the basin.
The research project involves the Minnesota Pollution Control Agency, Minnesota State University, Mankato, the University of Minnesota's St. Anthony Falls Lab and the National Center for Earth Dynamics, part of the National Science Foundation.
With people from universities such as Johns Hopkins, the group is being referred to as a researching "dream team." The team has rented a house in Mankato for use as a base this summer.
Lee Ganske, supervisor of the Minnesota River Basin Watershed unit, based in Mankato, said there are two related projects taking place. One is a biological study, conducted by MPCA staff, of all living creatures in the Le Sueur, from tiny invertebrates to large fish and turtles. The university research teams are trying to pinpoint where sediment in the river is coming from.
"In many cases, biologists will find that sites have poor biological conditions because of the sediment. This will bring to a new level the ability to pinpoint some of those sediment sources," Ganske said.
The impetus for the study lies far from the Le Sueur, which winds from southeast of Mankato to where it empties into the Blue Earth River, which flows into the Minnesota at Sibley Park in Mankato.
It's Lake Pepin, a hundred miles to the northeast, that is in part pushing officials to solve the mystery of the Le Sueur River. Pepin, which is fed by the Mississippi, is loaded with sediment -- almost all of it coming from the Minnesota River. The Minnesota delivers just 25 percent of the water flow to Lake Pepin but carries nearly 90 percent of the sediment filling in the lake.
"There's been a tenfold increase in sediment in Pepin, and the major source is the Minnesota River. That's well documented," said Carrie Jennings, with the Minnesota Geological Survey, is one of the people participating in the study. Jennings said it's not known exactly why the Le Sueur gives up so much soil or if the sediment load coming from the river has increased significantly over time.
The team of scientists will conduct tests and research to find out how much dirt is flowing from the river and where it's coming from.
The Le Sueur and Blue Earth rivers have long poured dirt into the Minnesota River. Early explorers wrote of noticeable muddy water flowing out of the Blue Earth. Modern agriculture and tiling of fields have put more sediment into the rivers.
Jennings said some farmers in the Blue Earth River basin have taken part in best-management practices, such as putting grass buffers around tile intakes and along drainage ditches.
"It's helped, but there may be better ways to do it," Jennings said.
Ganske said the detailed study of the Le Sueur watershed is possible because of funding through the state's Water Legacy Act, passed in 2006. Ganske said it's part of a statewide effort to have a biological assessment done on every major watershed in Minnesota -- about 80 in total.
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