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

Lazarus, Louis Reuben (2018-11-19)

Thesis (MSc)--Stellenbosch University, 2018.

Thesis

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.

AFRIKAANSE OPSOMMING: Daar word algemeen aanvaar dat swak oewere-grondgebruikspraktyke, wat algemeen verband hou met landbou-, stedelike en nywerheidsektore, 'n negatiewe uitwerking het op die geochemiese toestand van strome. Die Wes-Kaap van Suid-Afrika het beide 'n vinnige toename in sy bevolking ervaar en terselde tyd 'n ernstige droogte. Hierdie faktore het die behoefte beklemtoon om die effek van oewerlandgebruikspraktyke, wat spesifiek vir die riviere en riviermondings van die Wes-Kaap is, te ondersoek, wat lei tot die navorsingsvraag: Wat is die effek van oewerlandgebruikspraktyke, met inagneming van seisoenale verandering , op die Rooiels-riviermonding, die Eersterivier en die Lourensrivier? 'N Jaarlange moniteringsstudie is uitgevoer oor voedingstowwe en katione in die Eerste en Lourensrivierstrome. Dit is gedoen om ioonbronne en geochemiese reaksies op seisoensverandering en grondgebruikspraktyke te definieer. Die antropogene invloed op hierdie strome was duidelik geidentifiseer uit die hoofkomponent-analise. Nitraat van landbougrondgebruikspraktyke was die hoogste gedurende die nat seisoen, wat aandui dat dit 'n diffuse bron is. Ammoniumkosentrasies en natriumkonsentrasies binne die Lourensrivier-vleiland was die hoogste gedurende die droë seisoen, wat aandui dat dit 'n puntbron is. Stedelike struktuur verwering binne stedelike ontwikkelde afdelings was 'n groot bron van Ca en Mg wat elektriese geleidingsvermoë en karbonaat alkaliniteit beïnvloed. Nutriëntretensie onder basisvloei toestande was plekspesifieke, die hoogste in natuurlike stroomafdelings en die laagste in herstruktureerde stroomsegmente. Navorsing oor nutriëntretensie was voorlopig, en die behoefte aan verdere navorsing op die gebied van nutriëntretensie in Suid Afrika, onder fluktuerende klimaatstoestande en differensiële antropogene invloede, bly voort. Ten slotte word die varswaterstelsels van die Valsbaai-streek, Suid-Afrika, veral beïnvloed deur menslike invloede. Om die toestand van varswaterstelsels te handhaaf, moet die bestuur van die oewersones, rivierstrukture en menslike praktyke dus fokus op die beperking van die menslike impak.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/104932
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