Great River News

Mussels Help Scientists Gauge Boone River Health

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Small and sedentary, with little to recommend them to the average person perhaps but their beautiful pearly shells, the mussel is easily overlooked.

But on the Boone River in north central Iowa, these freshwater mollusks with charming names like fat mucket and cylindrical papershell have caught scientists' attention.

Last fall, Nature Conservancy scientists and Ellet Hoke, a mussel expert with Midwest Malacology, Inc., conducted a mussel survey on the Boone River. Hoke had surveyed mussels on the river in 1982, and the Conservancy wanted to replicate his survey methods to get a better idea about qualitative changes in species numbers and abundance over time.

"We were concerned that surveys seemed to show a consistent, steep decline in diversity, abundance and distribution of Boone River mussels over the past 25 years or so," said Kristen Blann, Conservancy freshwater ecologist. "For example, even though 23 mussel species have been recorded in the Boone River at some point in the past, a watershed-wide survey in 2005 only yielded live individuals representing four species."

The results of this year's survey were a little more encouraging, however, yielding 19 different species, five of which are listed as either threatened or endangered in Iowa. In some cases, live individuals were found. But for many of the species only shell material was located.

"Survey conditions can make a big difference in how many mussels you are able to locate," said Eileen Bader, Conservancy freshwater specialist. "We had great conditions for surveying mussels this year. The water was shallow, only six to eight inches deep, and clear. So as we walked in the river and along sandbars, it was easy to spot the mussels sitting on the bottom."

Mussels are "Aquatic Canaries in a Coal Mine"

Because mussels are filter feeders, they are exquisitely sensitive to pollutants that end up in rivers. They are largely immobile for most of their lives and can't easily pick up and move when water quality declines or when they are buried by excessive amounts of sediment, which deprives them of oxygen and other nutrients necessary for survival.

While mussels are long lived, it can sometimes take up to nine years for juveniles to mature into adults and reproduce. And studies have shown that some species of mussels successfully reproduce only once in seven or more years.

For these reasons, mussels are seen as aquatic "canaries in a coal mine," sentinels alerting us that all is not well in our rivers and streams.

Mussel diversity and abundance are two of the measures the Conservancy is using to gauge whether its conservation efforts on the Boone River are having an impact on river health.

Partners Unite to Improve Health of Boone River

The Conservancy has identified the Boone River, a tributary to the Mississippi, as a priority area for conserving native freshwater diversity. The river not only provides important habitat for rare mussels and fish, it eventually drains into the Des Moines River, which serves as a secondary water source for the City of Des Moines.

The Boone flows through a largely agricultural landscape, and excess nutrients from farm fields and sediment from stream bank erosion are contributing to water quality degradation and the loss of habitat for fish, mussels and other wildlife.

With support from The Monsanto Company, the Conservancy and its partners — the Iowa Soybean Association, Prairie Rivers of Iowa Resource Conservation and Development, Prairie Winds of Iowa Resource Conservation and Development and local landowners — are working together to improve the health of the Boone River and its tributary streams.

The partners are in the process of launching a study in three sub-watersheds of the Boone to test the impact of different types of agricultural conservation practices — e.g. planting cover crops after harvest to reduce soil erosion, the use of no-till versus conventional tillage and targeted nutrient management — on water quality.

Data on water quality and on biological indicators of river health such as mussel abundance and diversity is being gathered now and will serve as a baseline to compare against in subsequent years of the study.

"Mussels are fascinating creatures that are vital to healthy, functioning rivers," Blann commented. "We will continue to monitor these little guys in the coming years as one important measure of the progress we are making in improving the health of the Boone River."

You can find more information about Iowa's mussel species on the U.S. Fish and Wildlife Service website.


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