Evaluating the impacts of small impoundments on stream salamanders

Large dams have been repeatedly implicated in declines of riverine species, but the impacts of small dams are largely understudied. The placement of small dams (< 5 m high) on headwater streams, their density, and lack of regulation suggests that these dams may also have significant adverse impacts on headwater biota. The objective of this study was to determine whether small impoundments affect downstream salamander abundance and water quality. Salamanders were identified and counted from 10 paired catchments draining either a small impoundment (< 0.8 ha) or a free-flowing stream. A binomial mixture model was used to estimate abundance after accounting for incomplete detection. Estimated abundance of larval Desmognathus conanti, Eurycea wilderae, and Pseudotriton ruber was 3.9, 19.6, and 9.8 times greater downstream of small impoundments than in unaltered streams. Iron concentrations and pH had positive effects on salamander abundance while conductivity was negatively associated with salamander abundance. Increases in abundance may be due to increased hydrologic stability below dams, different geomorphology, and altered water quality. Despite their small size, small impoundments can have localized, downstream effects on water chemistry and species abundance and may create high quality habitat for some stream species in a heterogeneous landscape.