MANKATO — Seth Greenwood has watched parts of Seven Mile Creek County Park between Mankato and St.
“ The Minnesota River is eating the bank away,” said the Nicollet County public works director. “It’s really bad on that bend on the river. Five to 15 feet of bank has gone just this year.”
Much of that sediment will likely end up in the Mississippi River and settle to the bottom of Lake Pepin.
While intense efforts to improve the Minnesota River have gone on for 20 years, now there is a major convergence of better data and mounting political pressure that is bringing to a head problems of suspended solids in the river.
The issue is creating growing friction between farmers and environmentalists and residents on Lake Pepin who are suffering from the Minnesota’s pollution.
The millions of tons of sediment getting into the river is emerging as the keystone issue facing the river basin. The impacts on the Mississippi, Lake Pepin and the river basin’s contribution to the Gulf “dead zone” are sweeping and the potential solutions expensive, controversial and complicated, considering the Minnesota watershed covers 16,000 square miles.
Decades of scientific research — bolstered by new techniques such as using radioactive isotopes to trace where dirt particles originated — offer a few major findings:
■ The amount of sediment getting into the river has increased dramatically — tenfold its natural rate by some estimates.
■ Two-thirds or more of the river’s sediment load comes from eroding streambanks and bluffs.
■ Compared to the past, there is much more water flowing into the river more quickly. Part of that comes from more frequent and heavy rains. But more and more, researchers are convinced the high, fast waters tearing into streambanks are largely the result of extensive farm drainage that has changed the hydrology of the landscape.