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

Macroinvertebrate faunal assemblages, organic matter availability and instr eam structural complexity were investigated in three systems to determine t he current state of recovery of a post-thermal stream. The abundance and di versity 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 perturba tion. Disparate instream habitat structural components and stream physical changes in the post-thermal and reference systems drive functional differen ces in the macroinvertebrate community. The post-thermal stream is physical ly and biologically structured by high densities of aquatic macrophytes, wh ile the reference system is driven by high concentrations of coarse woody d ebris. Consequently, the abundant, diverse macroinvertebrate communities in both systems illustrate a post-thermal shift in energy source from a relia nce on allochthonous to autochthonous inputs. Biotic indices such as taxa r ichness, 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 succes sful at characterizing divergence in resource utilization and processing. T his distinction between macroinvertebrates' abundance and diversity, and th eir function in the ecosystem is essential in establishing relevant mitigat ion plans and endpoints for stream restoration. (C) 2000 Elsevier Science B .V. All rights reserved.