Limnology of Perched Lake, south-west Tasmania

Abstract

Perched Lake is one of the few lakes of lowland parts of south-west Tasmania. It is a warm monomictic lake, stratifying for 7-8 months each summer and, unlike most other bodies of standing water in the south-west, is only moderately dystrophic. Oxygen concentrations of the hypolimnion decline late in the stratification period but do not fall below 20% saturation, indicating low areal productivity. Though only moderately dystrophic, there is sufficient organic colour to cause marked attenuation of photosynthetically active radiation, particularly in the blue wavelengths. Its water chemistry is that of dilute seawater. Certain thermal and chemical anomalies are possibly explained by subsurface inflows of artesian water. The plankton of Perched Lake is dominated by chrysophytes and chlorophytes, with no well-defined seasonal change of biomass or species composition. An unusual dinoflagellate with marine affinities. probably Phalacroma sp., occurs in the lake.