Long-Terra Changes in the Limnology and Macrozooplankton of a Large British Columbia Lake

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Abstract
Macrozooplankton distribution and abundance as well as limnological conditions were compared during 1949 and 1964 in Kootenay Lake, a large oligotrophic lake in southeastern British Columbia. The standing crop of macrozooplankton increased two- to threefold over 15 years. Changes in physical–chemical limnological conditions, such as a decrease in depth of light penetration, and increases in pH, specific conductivity, dissolved nutrients, and phosphates also occurred, indicating an increase in productivity.The most noticeable change in macrozooplankton was a shift in cladoceran species composition in the north arm of the lake, formerly dominated by Daphnia but now by Diaphanosoma. Size-selective predation, differences in food availability, and competition for food with Diaphanosoma and Mysis relicta are suggested to be responsible for changes in the spatial distribution of Daphnia since 1949.Examination of changes in midsummer zooplankton abundance between successive years (1964–66) indicated that total zooplankton was least abundant in 1964. Differences in abundance during this period were small when compared with those between 1949 and 1964.

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