Macroinvertebrate recovery of a post-thermal stream: habitat structure and biotic function

Macroinvertebrate faunal assemblages, organic matter availability and instream structural complexity were investigated in three systems to determine the current state of recovery of a post-thermal stream. The abundance and diversity of the lower foodchain community has recovered substantially since cessation of thermal flows in 1988; however, the biotic communities remain structurally and functionally distinct as a result of past thermal perturbation. Disparate instream habitat structural components and stream physical changes in the post-thermal and reference systems drive functional differences in the macroinvertebrate community. The post-thermal stream is physically and biologically structured by high densities of aquatic macrophytes, while the reference system is driven by high concentrations of coarse woody debris. Consequently, the abundant, diverse macroinvertebrate communities in both systems illustrate a post-thermal shift in energy source from a reliance on allochthonous to autochthonous inputs. Biotic indices such as taxa richness, a family level index and similarity index may not be sufficient to determine functional changes as a result of thermal impacts. However, the distribution of diverse functional feeding groups across streams was successful at characterizing divergence in resource utilization and processing. This distinction between macroinvertebrates' abundance and diversity, and their function in the ecosystem is essential in establishing relevant mitigation plans and endpoints for stream restoration. (C) 2000 Elsevier Science B.V. All rights reserved.