| Tory Lake, a small eutrophic kettle lake, was hypolimnetically aerated for two summers. Distinct increases in dissolved oxygen concentration to more than 4 mg/l were observed in both summers, and conductivity, colour, turbidity, total alkalinity and phosphorus concentrations in the hypolimnion decreased. An estimated 1900 kg of CaCO;The development of an hypoxic metalimnion appeared to be an effective barrier to vertical movements (both diel and seasonal) of both zooplankton and fish species and proved toxic to fish which were kept in the metalimnion. One rotifer population (Filinia longiseta) became established in the hypolimnion and was isolated from a similar one which was confined to the epilimnion. The development of such a barrier suggests that hypolinmetic aeration and subsequent stocking of cold water fishes may not be successful, as zooplankton prey species are unable to migrate into or invade the hypolimnion, and may be subjected to intense fish predation within the confines of the epilimnion. (Abstract shortened by UMI.). |
