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Autumnal and over-winter limnology of three small eutrophic lakes with particular reference to experimental circulation and trout mortality Halsey, Thomas Gordon

Abstract

Autumnal and over-winter limnological conditions in Marquette, Corbett and Courtney Lakes in British Columbia were followed monthly from autumn, 1961, to spring, 1964, and some additional data were collected in winter, 1965. Indices of productivity for summer and winter conditions suggest that Courtney Lake is most productive, Marquette Lake least productive and Corbett Lake intermediate. Although over-winter mortality of fishes would be, expected to occur in Courtney Lake it has not been observed there whereas in Marquette and Corbett Lakes it frequently occurs. Marquette and Corbett Lakes were sharply stratified in summer because local topography provided protection from wind action whereas stratification in the more exposed Courtney Lake was ill-defined. Average wind velocities on Courtney Lake were 4.3 times greater and more unidirectional than those on Corbett Lake. Marquette Lake was subject to wind action similar to that of Corbett Lake. To test the hypothesis that winter limnological differences between Courtney and Corbett Lakes were due to insufficient autumnal circulation, Corbett Lake was experimentally circulated. Autumnal circulation in Courtney Lake was complete and resulted in over-winter survival of Salmo gairdneri and Richardsonius balteatus. Incomplete autumnal circulation and oxygenation in Corbett and Marquette Lakes resulted in over-winter mortality of Salmo gairdneri and Salvelinus fontinalis. In order to experimentally examine causes for the limnological differences between the lakes, Corbett Lake was artificially circulated. A compressed air "bubbler system" comprised of a submerged circles(circumference = 726 m) of plastic pipe and an air compressor was used to circulate Corbett Lake in the autumn of 1962 and 1963. The results of the experimental circulation of Corbett Lake compared to the limnological conditions in the "control" lakes, confirmed the original hypothesis. Below average snow fall in 1962-63 resulted indirectly in anomalous dissolved oxygen values (supersaturation). Consequently the expected over-winter mortalities of fishes in Marquette Lake did not occur whereas the expected winter mortalities did occur in 1961-62 and 1963-64. Winter light penetration and intensity in Corbett Lake was correlated with differences in snowfall between years. Light penetration and intensity differed considerably between lakes when snow and ice conditions were about equal (1965) because of differences in water quality.

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