Local vs. regional regulation of recovery of zooplankton of Sudbury lakes from acidification and metal pollution: lessons for Lake Orta
The largest number of historically acidified and metal-contaminated lakes in the world are near the mining and smelting complexes in Sudbury, Canada. Yan examines the 40 year pattern of recovery of the chemistry and zooplankton in 4 Sudbury lakes, three of which were limed in the 1970s. Zooplankton biodiversity is recovering in these lakes, but the rate of recovery varies by 150% among lakes. The temporal dynamics of species occurrence patterns suggests that recovery is not determined by meta-community processes, i.e. not by propagule pressure. Rather the key processes appear to be local, especially post-colonization persistence and population growth. Biotic ligand model results and toxicity bioassays using natural lake waters suggest that, despite 10 to 100-fold reductions in metal levels, metal toxicity remains the local factor that is regulating recovery of zooplankton. For managers wishing to promote ecological recovery, our work suggests that stocking is not required, a good thing given that historical emissions from smelters damaged about 7000 lakes.
Despite the widespread, historical extirpation of local populations, propagule delivery does not limit recovery. Rather lake managers should focus on in-lake processes, ensuring that waters are not toxic to, and can adequately support colonists.
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