Macroinvertebrate responses to in-stream restoration structures in a midwestern river

Riffles constructed over a multiyear period in the upper Cache River in southern Illinois provided an opportunity to examine macroinvertebrate responses to in-stream restoration activities.  These riffles were designed to control channel incision in the restored stream section, improve in-stream habitat, and to protect ecologically important riparian wetlands as part of an extensive watershed-level restoration project.  We hypothesized that macroinvertebrates would respond positively to the rough, stable substrate and hydraulic heterogeneity of the riffles, and thus diversity and biomass would be highest in these habitats.  We compared macroinvertebrate assemblages on previously constructed riffles and newly constructed riffles to those on snags and scoured clay streambed, the two dominant substrates in the unrestored reaches of the river, during 2003 and 2004.  Taxa richness, Shannon diversity, and total biomass did not differ among habitats.  However, biomass of Ephemeroptera, Plecoptera, and Trichoptera (EPT) and total insect biomass were significantly higher on constructed riffles than the streambed for most sample periods.  Snags usually supported intermediate EPT and insect biomass compared to constructed riffles and the streambed.  Non-metric multidimensional scaling ordinations (NMDS) revealed distinct assemblages on constructed riffles, snags, and the streambed.  Analysis of similarity supported visual interpretation of NMDS plots.  Assemblages on recently constructed riffles were very similar to older riffles.  All other pair-wise comparisons showed significant differences between habitats.  Our results reflect positive responses by macroinvertebrate assemblages to in-stream restoration in the Cache River.  Moreover, these responses were not evident with more standard measures of diversity and total biomass.