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Local and regional-scale assessment of zooplankton recovery from acidification.
Arnott, Shelley*,1, Keller, Bill2, Holt, Carrie3, Yan, Norman4, 1 Queen's University, Kingston, Ontario, Canada2 Cooperative Freshwater Ecology Unit, Sudbury, Ontario, Canada3 Simon Fraser University, Burnaby, British Columbia, Canada4 York University, Toronto, Ontario, Canada
ABSTRACT- There is overwhelming evidence that many of the world's ecosystems have been damaged by human activities. This has prompted international agreements to alter human activities and reduce their impact on ecosystems (e.g., Kyoto Protocol, Great Lakes Water Quality Agreement, Clean Air Act). Now, some of the most pressing challenges facing scientists involve understanding the process by which damaged ecosystems recover. Lakes in Killarney Wilderness Park, Canada, provide a rare opportunity to study mechanisms associated with the recovery of aquatic communities after a prolonged period of acidification. Since the 1970s, local sulphur emissions have been reduced an order of magnitude, resulting in widespread chemical recovery of many damaged lakes. Limited evidence of biological recovery associated with improvements in water quality, suggests that biotic communities may not be as resilient as water chemistry. We analysed data from three years (1972, 1990, and 2000) for zooplankton communities in 44 Killarney Park lakes to examine biological recovery trajectories at both local and regional scales. Twenty-two reference lakes in south-central Ontario, an area less influenced by acid deposition, were compared with Killarney Lakes. Regional richness for lakes in Killarney Park was higher than in the reference area, primarily resulting from the presence of rare species. Mean individual lake richness, however, tended to be lower in the recovering lakes than in the reference lakes. Species turnover rates were high in recovering lakes, reflecting community changes associated with recovery. High regional diversity and species turnover rates suggest that colonists have access to lakes and that zooplankton recovery is probably limited primarily by local conditions. Assessing diversity at both local and regional scales provides additional insights into factors that limit biological recovery in stressed ecosystems.
Key words: acidification, biodiversity, recovery, zooplankton