River Ecologist: Missouri Needs Flow of Sediment

The Missouri River needs a flow of sediment, not just water, to stay healthy, and regulatory agencies and scientists need to do a better job of gathering and understanding information about that process.

Jarett Bies Scientists say the Missouri River, shown here near Sioux City, Iowa, needs a flow of sediment as well as water to stay healthy.

A South Dakota State University river ecologist who served on a national panel on Missouri River sediment issues that recently released its findings said that was one important consensus of the group. The panel's report in late September 2010 offered expert advice that can help agencies such as the U.S. Army Corps of Engineers, in particular, to better manage the Missouri River. The study also takes into account the historic role the Missouri has played in supplying sediment to maintain coastal wetlands along the Gulf Coast in Louisiana.

SDSU Distinguished Professor W. Carter Johnson said the problem is that the 20th century dams built along the Missouri River in South Dakota, North Dakota and Montana were designed to manage water, not sediment. Consequently, the Missouri-Mississippi River system that supplied about 400 million metric tons of sediment annually down to the Louisiana coast before 1900 supplied an average of only 145 million metric tons annually from 1987 to 2006.



"The Missouri River was a turbid river. It had a lot of sediment in it. It was called 'the Big Muddy,'" said Johnson, who was one of 13 scientists appointed to the National Research Council's panel on Missouri River Recovery and Associated Sediment Management Issues. "Now, of course, it's not that, it's much clearer water. Sometimes the Environmental Protection Agency standards for how much sediment should be allowed in the river don't match what the historic river was like."

The panel recommended that water quality criteria for the Missouri River should take into consideration the historical sediment conditions in the river.

"Some rivers were naturally clear, and to add sediment would be unnatural. Other rivers were naturally turbid, and to take a clear-water version and add sediment to it would actually be a recovery practice," Johnson said.

The study also tried to evaluate management practices to protect two native bird species, the piping plover and the least tern, and a native fish species, the pallid sturgeon. All are listed under the Federal Endangered Species Act. Recovery practices to help those species include building artificial islands as nesting sites for the birds or adding sediment to the river to create turbid conditions favorable for the pallid sturgeon.



Importantly, the report concluded that although the Corps' projects adding sediment to the river also increase the amount of nutrients such as phosphorus from fertilizer reaching the Gulf of Mexico, such practices do not significantly change the size of the Gulf's "dead zone" - an area of hypoxia that results when nutrients spur algae blooms that in turn deplete oxygen.

Source: Newswise