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Upper Midwest Environmental Sciences Center

Relationships Among Flow, Water Depth, Sediment Texture, and Fingernail Clams

Fingernail clams (Sphaeriidae) and mayflies (Ephemeroptera) are important food sources for fish and migrating waterfowl in the Upper Mississippi River (UMR). An empirical model is being tested to determine its ability to confidently identify preferred areas for fingernail clams in UMR Pools 7 and 8.

The model was created in 1995 by using calculated water flow and bathymetry to differentiate habitats in Lake Onalaska. As a result, six regions of various flow and depth were created. Flows were calculated using the hydraulic model FastTABS (U.S. Army Corps of Engineers, St. Paul District). Eight sites per region (48 total) per pool were randomly sampled using a standard Ponar. Sampling is conducted primarily during September.

Pool 7 - Reach 1 - Upper Mississippi River

Initial tests are encouraging, as the model indicated that 69% of the variance among fingernail clam population densities is attributed to water flow and depth in Lake Onalaska, UMR Pool 7. To test the robustness of the model, it was then run for lower UMR Pool 8. In the years where fingernail clams were found, the model indicated that only 25% to 40 % of the variance was accounted for.

A Ponar device like the one shown here is used to collect samples of fingernail clams.

Two main variables that may have affected these models' results include increased aquatic vegetation and unionized ammonia. These effects are being investigated.

The intended result of this model is to provide a tool for biologists, researchers, and river managers to map areas conducive for benthic macroinvertebrates and to help design habitat enhancement projects to create improved benthic macroinvertebrate areas.

The project was completed September 30, 2001.

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