Recovery of copepod, but not cladoceran, zooplankton from severe and chronic effects of multiple stressors

Authors

  • Norman D. Yan,

    Corresponding author
    1. Department of Biology, 4700 Keele Street, York University, Toronto, Ontario M3J 1P3, Canada
    2. Dorset Environmental Science Centre, Ontario Ministry of Environment, Box 39, Dorset, Ontario P0A 1E0, Canada
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  • Robert Girard,

    1. Dorset Environmental Science Centre, Ontario Ministry of Environment, Box 39, Dorset, Ontario P0A 1E0, Canada
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  • Jocelyne H. Heneberry,

    1. Ontario Ministry of Environment, Co-operative Freshwater Ecology Unit, Laurentian University, Ramsay Lake Road, Sudbury, Ontario P3E 2C6, Canada
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  • W. Bill Keller,

    1. Ontario Ministry of Environment, Co-operative Freshwater Ecology Unit, Laurentian University, Ramsay Lake Road, Sudbury, Ontario P3E 2C6, Canada
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  • John M. Gunn,

    1. Biology Department, and Co-operative Freshwater Ecology Unit, Ramsay Lake Road, Sudbury, Laurentian University, Sudbury, Ontario P3E 2C6, Canada
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  • Peter J. Dillon

    1. Environmental and Resources Studies, Trent University, Peterborough, Ontario K9J 7B8, Canada
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* E-mail: nyan@yorku.ca and yanno@ene.gov.on.ca

Abstract

In the mid-twentieth century, many lakes near Sudbury, Canada, were severely contaminated by acid and metal emissions from local smelters. For example, in the early 1970s, Middle Lake had pH of 4.2, and Cu and Ni levels both >0.5 mg L−1 . To determine if crustacean zooplankton could recover from such severe and chronic damage, Middle Lake was neutralized in 1973. A comparison of its zooplankton with that of 22 reference (pH > 6) lakes indicates that the planktonic Copepoda completely recovered by 2001. In contrast, the cladoceran assemblage improved but did not recover. Colonist sources existed – Cladocera and Copepoda occurred with equal frequency in area lakes – but six separate colonizations by cladoceran species failed. We argue that local factors, metal toxicity and predation by yellow perch, have, to date, prevented cladoceran recovery. Nonetheless, the complete copepod recovery is encouraging, given the severity and duration of pre-neutralization stress.

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