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University of Iowa News Release

Nov. 11, 2003

Photo: Scott Carpenter collecting a water sample from the Iowa River.

Researchers Study Decline Of Iowa Freshwater Mussels

Two researchers, one from the University of Iowa and the other from Iowa State University, have received a $20,000 seed grant from the UI Center for Global and Regional Environmental Research (CGRER) to examine the geochemical reasons for the decline of freshwater mussels in Iowa's rivers over the past 125 years.

The project, which will examine freshwater mussels on the Iowa, Cedar, Skunk and Des Moines rivers, will be conducted by Donna M. Surge, assistant professor in the ISU department of geological and atmospheric sciences, ecology and evolutionary biology, and Scott J. Carpenter, CGRER associate research scientist, associate director of the Paul H. Nelson Stable Isotope Laboratory and adjunct associate professor in the UI College of Liberal Arts and Sciences' department of geoscience.

The project will document the chemical changes recorded in modern mussel shells and those collected over the past 125 years to provide a glimpse of the historical changes of Iowa's rivers. Carpenter and Surge plan to collect and analyze freshwater clams from the same areas where population declines have been documented over the past 20 years and where famed Iowa naturalist Bohumil Shimek collected similar samples from the late 1870s to the early 1930s. Selected specimens from Shimek's collection, now housed at the Smithsonian Institution in Washington, D.C. will be analyzed.

Although Iowa freshwater mussels were a mainstay of the U.S. button industry during the early 20th century, today they are in rapid decline and many species are endangered -- with the causes of decline not well understood. As freshwater mussels filter the water in which they live, they are generally considered good water quality indicators.

Carpenter notes that mussel shells serve as historical archives, with incremental growth bands in shells -- like tree rings -- recording information about life history and local environmental conditions. In particular, Carpenter and Surge plan to tap the information contained by the shells by measuring the amounts of nitrogen isotopes present as indicators of agricultural activity. Along with the 2003-2004 mussels they plan to collect, the researchers have access to shells gathered in 1984-1985 and 1998-1999 as well as the Shimek collection. Carpenter says that the study will provide information about regional climate change over the last century, however the primary study focus remains to learn about the geochemical impact of agricultural practices on Iowa mussels.

"The cause of mussel decline is not well understood," Carpenter says. "Some possible causes include the damming of rivers and various agricultural factors, such as the application of pesticides and the increase in river silt resulting from cultivation. As no quantitative examination of the causal mechanisms of this decline has been conducted, our proposed study will be the first to examine this topic."

Carpenter's research interests also include: characterizing near recent and ancient climate change by examining various materials such as clam shells, fish ear bones (otoliths), and stalagmites.

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