Chemical and biological recovery of Killarney Park, Ontario Lakes (1972-2005) from historical acidification
Shead, Justin A.
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Forty-five lakes in Killarney Provincial Park and the surrounding area in south-central Ontario, Canada, were sampled for crustacean zooplankton and water chemistry in the summer of 2005. For each of the lakes, we had historic data from peak-acidification in the 1970s and post-acidification periods in 1990 and 2000. Situated among the orthoquartzite ridges of the La Cloche Mountains in and near Killarney Provincial Park, many of these lakes were acidified during the mid-1900s owing to extensive mining and smelting activities in nearby (40-60 km) Sudbury, Ontario. There is large variation in the geochemistry of the soils and the bedrock within the park. As a result, these freshwater lakes have varying degrees of acidification, ranging from being heavily acidified (pH < 4.5) to others that were buffered from the effects of acidic deposition. With over 90% reductions in sulphur dioxide smelter emissions over the past 30 years and the present, many lakes in the Sudbury region are starting to show strong evidence of chemical recovery. Despite significant increases in lake water pH, there is limited evidence of biological recovery. A variety of univariate and multivariate metrics, as well as variation partitioning, were used to examine recovery on a lake-by-lake basis and on a regional scale. Our results revealed only moderate recovery of crustacean zooplankton communities despite improvements in water quality. Some lakes increased in zooplankton richness while others decreased compared to richness during peak acidification. Shifts in community composition from a damaged state toward those typical of circum-neutral lakes were observed for lakes that have chemically recovered. The lack of chemical recovery is believed to be impeding biological recovery of many lakes. Biological resistance and dispersal limitation do not appear to be hindering biological recovery. Other stressors such as the invasion by the predatory zooplankton Bythotrephes and climate change may delay biological recovery in the coming years. Future recovery of Killarney Park lakes will require further chemical recovery for biological recovery to become complete.