Use of littoral benthic invertebrates to assess factors affecting biological recovery of acid and metal damaged lakes

Biological recovery of aquatic ecosystems from acidification damage is proving to be a slow process.  In lakes near the massive copper and nickel smelters in Sudbury, Canada, the delays are possibly because of residual metals, habitat damage, altered predator—prey interactions or other persistent ecological stressors.  Assessments of benthic invertebrate communities in 24 Sudbury lakes were conducted to assess the relative importance of these delaying factors.  At the time of sampling, all lakes had chemically recovered to a pH > 6.0 threshold, but varied widely in the duration of time above this threshold as well as in current metal concentrations, watershed contributions of organic matter, littoral habitat conditions, and fish community composition.  A model developed using partial redundancy analyses (RDA) with four environmental variable groups (water chemistry, fish communities, physical lake descriptors, and littoral habitat) was able to account for 78.8% of the variance in benthic invertebrate community metrics across these environmental gradients.  The duration of pH recovery, fish species richness, and lake area were the most significant variables, explaining 38.0%, 16.0%, and 6.0% of the benthic invertebrate community metric variance, respectively.  Damaged systems clearly need sufficient time to recover from severe disturbances, however, this study also suggests that remediation techniques such as manipulation of predator—prey interactions through fish introductions may speed the recovery of benthic invertebrate communities.