Influence of urban tributaries on freshwater mussel populations in a biologically diverse piedmont (USA) stream

Abstract

The Southeastern USA is currently experiencing a period of rapid growth of human populations that is likely having profound effects on the region’s unique aquatic biota. Using both survey data and experimental protocols, we assessed the influences of water and habitat quality on freshwater mussel populations in a small Piedmont stream. Chewacla Creek is a high-quality stream located near the rapidly growing towns of Auburn and Opelika in east-central Alabama. From 1999 to 2007 we monitored freshwater mussel populations and measured substrate and water chemistry variables in Chewacla Creek. Surveys revealed that mussel abundance decreased substantially concomitant with degraded habitat and water quality downstream of three highly urbanized tributaries. We conducted sentinel trials using adult mussels (Villosa lienosa) in Chewacla Creek and a tributary (Parkerson Mill Creek) that receives wastewater discharge. Sentinel mussels were placed in cages at three locations downstream of the effluent discharge point and at one upstream site (control). Sentinel mussels exposed to wastewater discharge exhibited lower survival rates compared to control animals. Together, survey and experimental data suggest that degraded tributary sub-catchments may fragment mussel populations in high-quality streams. Moreover, our data indicate that protection of sensitive aquatic taxa necessitates effective management of water quality across large spatial scales.