Limnology of Lake Midmar

Abstract

Lake Midmar is a shallow turbulent lake subject to periodic draw-down. These conditions create considerable instability in the water column and greatly influence the structure and functioing of the system. Analysis of how the lake may be expected to respond to altered nutrient loading illustrates both the inherent limitations of currently available empirical predictive models, and the site specific nature of response. Thus the way in which nutrient load is estimated may alter the prediction from acceptable to unacceptable water quality, yet the lake is not highly productive. Application of general models is constrained by both the specific characteristics of the lake which appear to buffer response against changing nutrient load, and the relative insensitivity of the models. We are now at the stage where we know the limitations of currently available models and have a good idea as to why they exist, but have little alternative to offer. Exciting prospects exist for synthesis and critical analysis of the research on the four lakes (Hartbeespoort, Le Roux, Midmar and Wuras) but if we are to benefit fully, the synthesis must address specific goals.