SEMINAR: Recovery of Sudbury lakes from acid and metal contamination: local, not regional, processes regulate community re-assembly

Smelters in Sudbury, Canada, were among the world's largest sources of sulphur dioxide and metal emissions, damaging 7000 lakes over a wide region; however, emissions have fallen by 90%, and the attention of ecotoxicologists has turned to questions of what processes regulate ecological recovery. I will present 35 years of water quality and plankton community composition data from four lakes which differ in residual metal contamination, highlighting the surprising result that Middle and Hannah lakes, the smallest lakes, in the most contaminated urban zone, with the highest residual metal levels, are recovering plankton biodiversity more rapidly than more distant lakes with lower metal levels. This was true even though species accumulation curves in Middle and Hannah lakes prove they are receiving fewer colonists than more distant lakes. I will argue that regional processes, i.e. colonist introduction rates, are not regulating recovery. Instead recovery is regulated by colonist establishment success, a local process. I summarize results from bioassays and biotic ligand modelling which prove that colonists can now survive and reproduce in Middle and Hannah lakes, despite their higher metal total metal concentrations. Comparing species sensitivity to water quality would appear to be critical to predicting recovery of plankton species richness. Understanding the roles of regional processes, Allee effects, and community interactions on recovery would appear to be less important.