LIMNOLOGICAL CHARACTERISTICS OF 2 COASTAL DUNE LAKES, JERVIS BAY, SOUTH EASTERN AUSTRALIA

Limnological features of two permanent, closed, coastal dune lakes that are separated by only about 400 m are reported. The depth of Lake Windermere fluctuated by about 7 m during this study (1982-1988); however, fluctuations up to 15 m were observed between 1970 and 1988. Lake Windermere is exposed to wind mixing, is transparent and is usually mixed, or only weakly stratified. Lake McKenzie is semi-perched, darkly coloured and strongly stratified with an anoxic hypolimnion during summer. It is about one fifth of the surface area and half the depth of Lake Windermere and protected from wind mixing. Both lakes are acidic and have low salinity, and the dominant ions are sodium and chloride probably from precipitation of marine aerosols. Oxygen depletion in the hypolimnion of both lakes indicates a substantial organic load, the source of which is allochthonous material from the catchment rather than autochthonous material. Lake Windermere had higher densities of zooplankton (mostly Calamoecia tasmanica) than Lake McKenzie, but the latter lake had higher numbers of the predaceous Chaoborus sp. Lake McKenzie had higher invertebrate densities than Lake Windermere and these fluctuated widely between years, corresponding with variation in rainfall. Mayflies and chironomids were numerically dominant in Lake McKenzie, and caddisflies and chironomids were numerically dominant in Lake Windermere. Turtle and odonate predators were more common in Lake McKenzie than in Lake Windermere. It is postulated that biological interactions are more important in shaping the communities in Lake McKenzie and physical factors such as wave action are more important in Lake Windermere.