However, in recent years, increasing numbers of dams have been removed owing to failing infrastructure, impounded sediment, danger posed to humans, or general lack of utility (Bednarek 2001 American Rivers 2015).Ĭhannel responses to dam removal vary considerably depending on channel characteristics and sediment regimes (Doyle et al. 2004).Įven relatively small river infrastructure, such as weirs and run-of-river, lowhead dams (< 7.6 m in height) impound water and can cause a general flattening of the channel and fining of streambed substrate, leading to a loss of riffles and gravel substrates upstream of the structure (Doyle et al. Likewise, riffles can support higher densities of benthic macroinvertebrates than pool habitats and are important areas of food production for insectivorous fishes (Scullion et al. 2004) also allows multiple fish species to coexist through spatial partitioning of habitat (Kessler and Thorp 1993). The high substrate heterogeneity typical of riffles (Gordon et al. Riffles increase water turbulence and oxygen concentration and provide important microhabitat variability in depth, velocity, and substrate for aquatic macroinvertebrates (Statzner et al. Riffles-shallow sections of streams or rivers with rapid current-are important habitat units for benthic macroinvertebrate and fish assemblages (Kessler and Thorp 1993 Kessler et al. Our results indicate that riffle habitat development can be an important mechanism related to restoring sensitive species and biological diversity following dam removal. Although hydrogeomorphic characteristics (e.g., streamflow velocity, substrate size) were linked to shifts in macroinvertebrates and fish, chemical water-quality parameters (e.g., dissolved oxygen, nutrient concentrations) were also implicated as potential biotic drivers. Macroinvertebrate, but not fish, assemblage composition was different by time but not riffle. The density and diversity of macroinvertebrates and fish were significantly different over time, largely as a function of season (lowest densities in early spring, greatest in summer). Hydrogeomorphic, water-chemistry, and biotic surveys were conducted at seven study riffles at six time intervals from spring 2014 through summer 2015. We assessed relationships between riffle structure and benthic macroinvertebrate and fish assemblages 2 years after a lowhead dam removal in Ohio, USA. Dam removal is an increasingly common river restoration option, yet some of the mechanisms leading to ecological changes remain unquantified.

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