Calcium chemistry of Blue Lake, Mt Gambier, Australia, and relevance to remarkable seasonal colour changes

Calcium speciation and other water quality variables in the Blue Lake, Mt Gambier, Australia, were monitored between August 1999 and August 2000 in order to test previously proposed mechanisms for the seasonal colour changes of this lake. The concentration of calcite was found to be highest in winter when the lake appears grey, and lowest in summer when the lake appears blue. A potential component of the colour change mechanism is therefore identified in which the lake is grey in winter because of non-selective scattering of light by calcite particles, and blue in summer because of the absence of absorbing or scattering impurities.