Chemical and biological studies on some acidic lakes of east Australian sandy coastal lowlands

Abstract

The chemical composition of the water of 16 lakes, three streams and a swamp were investigated. Most of these were located on coastal islands of southern Queensland which consist entirely of siliceous sand. The majority of these lakes apparently originated by the formation of an impermeable organic layer in dune depressions. Complete major ionic analyses are presented together with data on total ionic concentration, optical density, dissolved organic matter and pH. The cationic and anionic order of dominance were unusual, being Na > Mg > Ca > K and Cl > SO₄ > HCO₃, respectively. This is explicable on the basis that atmospheric supply of ions from the sea is of major importance and that supply by land-weathering processes is relatively insignificant. With two exceptions the pH of the waters did not exceed 5.3. It is considered that the acidity of those with pH < 5.0 is due mainly to organic acids. Experiments were carried out on the effect of pH on coloured dissolved organic matter. It is pointed out that the colour of dissolved organic matter depends on pH, only if pH is determined mainly by an inorganic influence.

Biological observations were restricted mainly to Crustacea and to the calanoid copepod Calamoecia tasmanica in particular. It was the observed coastal distribution of this species that prompted the chemical studies. The distribution and abundance of C. tasmanica is discussed in relation to chemical factors.