Quantifying Impacts of River Fragmentation: How Low-Head Dams Alter Geomorphology, Fish Biodiversity, and Habitat in the Neosho River, Kansas

Dams fragment ecological, hydrological, and geomorphological aspects of connectivity, which are fundamental characteristics of riverine ecosystems.  Of the over 2,770 peer-reviewed papers on dams and fish, only about 6% target low-head dams (< 6 m) even though these small dams are a common and ubiquitous type of in-stream barrier.  To increase scientific knowledge about the geomorphic and ecological impacts of low-head dams, we quantified the extent of the dam footprint at five low-head dams in the Neosho River basin, Kansas.  We measured longitudinal patterns in substrate size, using Wolman pebble counts, for all riffles that were within 3 km of dams.  Then we sampled habitat and fish assemblages at 14 transects downstream and nine transects upstream of each dam using a mini-Missouri trawl.  Dams altered geomorphology up to 1,500 m downstream of dams.  Richness (median difference= 4 species) and abundance (median difference = 37 individuals) were significantly higher below dams than above dams.  Below dams, we observed a gradient response in fish biodiversity, the shape of which varied across individual dams.  Our insights about the spatial extent of low-head dam impacts can inform future monitoring and research to help conserve valued aquatic biodiversity in the face of increasing human impacts.