Geochemical analysis of stream responses to changes in land development and seasonal variation, Western Cape, South Africa

[摘要] ENGLISH ABSTRACT: It is generally accepted that poor riparian land-use practices, commonly associated with agricultural, urban and industrial sectors, have a negative effect upon the geochemical state of streams. The Western Cape of South Africa has experienced both a rapid increase in its population, and a severe drought. These factors have highlighted the need to investigate the effect of riparian land-use practices specific to the rivers and estuaries of the Western Cape, which leads to the research question: What is the effect of riparian land-use practices, taking into account seasonal change, upon the Rooiels Estuary, the Eerste River and the Lourens River?A year-long monitoring study was conducted on nutrient and cation fluxes within the Eerste and Lourens River streams. This was done to delineate ion sources and geochemical responses to seasonal change and land-use practices. The anthropogenic influence on these streams was evident from the principal component analysis. Nitrate loading from agricultural land-use practices was highest during the wet season, indicative of a diffusive source. Ammonium and Na loading within the Lourens River wetland were highest during the dry season, indicative of a point source. Urban structure weathering within urban developed sections proved to be a large source of Ca and Mg affecting stream electrical conductivity and carbonate alkalinity. Nutrient retention under base flow conditions was site specific, the highest located in natural stream sections and the lowest in restructured stream segments. Research conducted on nutrient retention was preliminary, thus the need for further research within the field of nutrient retention in sub-Saharan African streams, under fluctuating climatic conditions and differential anthropogenic influences, persists.In conclusion, the freshwater systems of the False Bay region, South Africa, are notably affected by anthropogenic influences. Thus, to maintain the state of freshwater systems, management of the riparian zones, river structures and anthropogenic practices should focus on limiting the anthropogenic impact.

[发布机构] Stellenbosch University