Modeling The Variable Effects Of Low-Head Dams On Freshwater Mussel Assemblages

The widespread damming of lotic ecosystems is commonly associated with dramatic ecological effects such as decreased temperature, hypoxia, altered flow regime, physical changes to the structure of the river, and fragmentation of important habitats of stream organisms. However, the majority of the research that describes these negative effects was conducted on large-scale hydroelectric dams on large streams. Contrary to these studies, recent research suggests that the effects of intact low-head dams vary widely across taxa and may improve habitat conditions for some taxa, including native bivalves. The focus of this study was to examine a poorly understood phenomena that results in the formation of high density mussel aggregations in the tailrace of some, but not all, low-head(<10 m) dams. I used mussel survey data from three 150-m reaches (tailrace, upstream, and downstream) for each dam site. These data were compared against a meta-database of dam features - structural height, hydraulic height, year built, length, upstream catchment area, stream order, depth/volume, elevation, forest cover - using a multivariate statistical analysis to determine the parameters most influential to this phenomenon. These results were used to inform the construction of a model meant to predict which low-head dams are likely to harbor high density mussel aggregations. Currently dams are prioritized for removal based on funding and the logistical ease of the project. The results of this study may potentially inform improvements to best management practices for stream restorations with dam removal and benefit the regions’ imperiled mussel populations.