Sarah Roley

Project Title: " Identifying potential physicochemical constraints on survival of the endangered clubshell mussel, Pleurobema clava ."

External Partnership: The Nature Conservancy and Indiana Department of Natural Resources

The once-widespread clubshell mussel, Pleurobema clava, has been eliminated from much of its range and is currently a federally endangered species.  One of the last remaining populations is in the Tippecanoe River in Indiana, but it is declining even there.  P. clava spends its adult life buried beneath coarse, packed sand and relies on percolation of surface water for food and dissolved oxygen for respiration.  In her CAC fellowship, Sarah worked with others to determine whether excess sediments and nutrients associated with agricultural activities are responsible for the decline of P. clava in the Tippecanoe River. 

Excess sediments and nutrients are common in rivers that drain agricultural watersheds.  Field soil is often high in organic matter from crop residue and fertilizers, and is also often highly erodible.   When this soil gets washed downstream, it can cause habitat and water quality problems. 

Because the clubshell remains buried for most of its adult life, it is more vulnerable to water quality problems than surface-dwelling organisms.  Thus even though the Tippecanoe River remains in better condition than most rivers in the region, minor increases in sediment and nutrient export have had a large effect on the mussel. Sedimentation affects the clubshell by filling pore spaces and preventing percolation of dissolved oxygen, and sediment decomposition results in the release of ammonium.  Ammonium is toxic to mussels at high concentrations, and lack of dissolved oxygen results in suffocation.  I will characterize these sub-surface conditions in three habitat types: 1) where clubshell currently exist and reproduce, 2) where clubshell exist but are no longer reproducing, and 3) where clubshell historically existed but are no longer present.  In addition, I will measure nutrient concentrations in the surface water.  If dissolved oxygen is lower and sedimentation and ammonium are higher at sites where mussels no longer exist or no longer reproduce, then these factors likely contribute to the mussel’s decline.  If there is no difference among sites, other stressors (such as industrial contaminants or altered river flow) may be responsible.

Sarah's external partners include The Nature Conservancy (TNC) and the Indiana Department of Natural Resources (IDNR).  TNC is committed to conservation in the Tippecanoe, and the results of this project will help them focus their conservation efforts on specific stressors.  For example, sedimentation may be reduced through the implementation of sediment traps, two-stage ditches, and stream-side buffers.  TNC is providing some funding and field assistance for this project.  IDNR is committed to conserving endangered species, and will provide mussel identification expertise and help with site identification.

Distinctive Outcomes: Sarah is currently working with several agencies to identify potential federal impact on management plan for clubshell mussels.