Macroinvertebrate Community Response to a Spate Disturbance in a Third Order Ohio Stream

Abstract

A spate, or sudden flood, is a common disturbance in streams and can be an important factor in structuring macroinvertebrate communities. However, the effects of spates are likely mediated by other factors, such as habitat. This study tested whether a spate (22.5 times higher than base flow) influenced macroinvertebrate community composition and abundance in riffles and pools within the Kokosing River in Knox County, Ohio. Five pools and five riffles were sampled before and after a spate for macroinvertebrates and physical parameters during fall 2011. Macroinvertebrate communities and physical parameters differed between riffles and pools. Riffles had higher flow rates, a higher % EPT (Ephemeroptera, Plecoptera and Trichoptera) index and increased Shannon diversity compared to pools. We found that habitat was more influential on macroinvertebrate communities than the occurrence of a single spate. However, this single spate disturbance altered water depth and current velocity, increased diversity in riffles and pools, and homogenized community composition across habitat types. Changes in community structure resulted from decreased abundance for some of the dominant riffle taxa (e.g., Hydropsychidae, Baetidae) and an increased abundance of some taxa in pools after the spate (e.g., Chironomidae). We also found more similarity between riffle and pool communities following the spate. These results suggest that the macroinvertebrate community is relatively resistant and resilient to a spate of this magnitude, but flooding can alter community composition in both riffles and pools in this river.