Mussel Community Response to Wastewater Effluent in a Midwestern River

Proper treatment of wastewater is essential to preserving freshwater ecosystems.  Treated sanitary effluent dumped into rivers can release nutrients and chemicals harmful to biotic communities.  Mussel communities have shown sensitivity to chemicals and other abiotic factors, but their response to sanitary effluent has not been fully investigated.  We studied the impact of sanitary effluent on mussel species composition.  Four sites were chosen above and below an effluent.  Habitat was assessed using the Qualitative Habitat Evaluation Index.  Water chemistry was conducted monthly.  We performed mussel surveys with four man-hour hand searches and 20 scoops of the substrate at each site.  Physical habitat increased in quality downstream of the effluent.  A significant increase in nutrients, temperature, and conductivity occurred below the effluent.   Catch per unit effort (CPUE) upstream at 14.38/hour and 0.28/scoop was greater than CPUE downstream at 0.17/hour and 0.0/scoop.  Species richness upstream (13) was greater than species richness downstream (2).  Upstream Simpson’s Diversity Index (0.29) was less than downstream (0.50). Mussels were absent directly below the effluent.  The most common species were Amblema plicata, Leptodea fragilis, Potamilus ohiensis, and Truncilla truncata.  Further investigation is required to determine what aspect of the effluent is responsible for the mussel local extinction event.