Benthic macroinvertebrate response to hydrogeomorphic fluctuations in a sand bed, prairie river

           Thunderstorm-driven rivers of the Great Plains have flashy hydrologic cycles which have direct consequences for ecosystem structure and function.  Organisms must survive flow variability, continuous bed restructuring, and channel reorganization.  Past research has detailed the importance of rock substrates, woody debris, and aquatic vegetation as important invertebrate habitats.  Since prairie rivers rarely have these habitats, we investigated how zoobenthos coped with hydrogeomorphic fluctuations and determined that geomorphic structures within the riverscape are important to invertebrate dynamics.

            We collected over 500 zoobenthic samples over a 4-month period in summer 2007.  Dominant invertebrate taxa were chironomids, ceratopogonids, and oligochaetes.  Flow pulses significantly changed sandbar shape, altered substrate composition, and changed the number of channels.  Invertebrate richness and community composition were tied to river channel complexity rather than hydrology.  Downstream displacement of organisms was more complete in areas of high hydraulic stress (leading edge of bars), whereas areas of flow relief were more stable.  Additionally, community composition of a side channel alternated between side channel and backwater assemblages when it was repeatedly cut off and reopened.  Understanding roles of hydrogeomorphic fluctuations continues to be important, especially with climate models predicting increased precipitation variability in the Great Plains.