Advances in understanding phosphorus cycling in inland waters - Their significance for South African limnology

Abstract

The definitions of the different phosphorus compound fractions present in inland waters are reviewed and the limitations of the definitions discussed. The development of models of phosphorus cycling is summarized. Attempts to establish their applicability to South African inland waters have been unsuccessful. The exchange processes involved in the phosphorus cycle are influenced by the biota, by phosphorus enzymes and by the presence or absence of littoral vegetation. These processes are poorly understood, however. It is not known to what extent phosphorus exchange between sediment and water takes place in South African inland waters, but these exchange processes are influenced by the presence of a variety of soluble phosphorus fractions, dissolved oxygen and other chemical constituents in the water and by the nature of the sediments and sedimentation processes. The influence of external loading on phosphorus cycling and its significance in the prediction of algal growth is discussed. It is concluded that in South Africa factors such as shallowness, mixing and silt-loading make it desirable to study phosphorus cycling in local impoundments; existing knowledge is based primarily on deep, stratified and clear north temperate lakes. In addition, there is a need to standardize terminology and analytical techniques.