Will reduced summer UV-B levels affect zooplankton populations of temperate humic and clearwater lakes?* |
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Authors: | TA Clair J Ehrman I Kaczmarska A Locke DW Tarasick KE Day G Maillet |
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Institution: | (1) Environment Canada, Atlantic Region, P.O. Box 6227, Sackville, NB, Canada, E4L 1G6;(2) Dept. of Biology, Mount Allison University, Sackville, NB, Canada, E4L 1G7;(3) Fisheries and Oceans Canada, P.O. Box 5030, Moncton, NB, Canada, E1C 9B6;(4) Meteorological Service of Canada, Environment Canada, 4905 Dufferin Street, Downsview, Ontario, Canada, M3H 5T4;(5) National Water Research Institute, Environment Canada, P.O. Box 5050, Burlington, ON, Canada, L7R 4A6;(6) Dept. Oceanography, Dalhousie University, Halifax, NS, Canada, B3H 4J1 |
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Abstract: | We collected zooplankton samples from 4×4 m enclosures located in two acidified lakes (pH<5) in Nova Scotia from June to August 1996. One lake had mean dissolved organic carbon concentrations greater than 10 mg l–1 (brown water), while the other had values between 2 and 4 mg l–1. In each lake, three enclosures were open to ambient light, while three were covered by Mylar® sheets which removed UVB and UVC wavelengths. Weekly sampling was done at all sites in July and near the end of August. Individuals were identified and the total community weighed. Analysis of results using both t-test and canonical analysis revealed small differences in populations between open and UVB covered clearwater sites in early July, but not later. There was no response of midsummer zooplankton communities in the humic lake which had a 95% extinction depth of 3 cm. In the clearwater lake (95% UVB extinction at 50 cm), the effect of radiation exclusion was relatively weak compared to most other published studies, but nevertheless statistically significant. |
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