Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Master → Afrique du Sud → 2019 → Reconstructing the long-term history of water quality and availability using fossil diatoms at an agricultural site in the Cape lowlands

University of Cape Town (2019)

Reconstructing the long-term history of water quality and availability using fossil diatoms at an agricultural site in the Cape lowlands

Hoffenberg, Amy

Titre : Reconstructing the long-term history of water quality and availability using fossil diatoms at an agricultural site in the Cape lowlands

Auteur : Hoffenberg, Amy

Université de soutenance : University of Cape Town.

Grade : Master of Science in Conservation Biology 2019

Résumé
The Berg River is a pivotal source of fresh water for domestic, industrial and agricultural use as well as for in stream ecology, therefore knowledge of what impacts this rivers water quality and assessing whether ecological resilience has been surpassed are of the utmost importance. Since diatom assemblages are inextricably linked to the chemical, physical and biological characteristics of their environment, they were chosen for this study to investigate long-term changes in water quality and availability and suggest potential drivers of such changes at an agricultural site (Rhenostervlei Farm) adjacent the Berg River in the Cape lowlands through fossil diatom analysis of a sediment core (RV3). Diatoms were extracted along the length of the RV3 core, chemically and physically treated to remove unwanted material and then were mounted on a slide to be counted. Twenty abundant diatoms were chosen as environmental indicators for the analysis. Their abundances were plotted against depth and age and changes in water quality and availability were inferred based on their autecological characteristics. The most prominent shift in the indicator diatoms at Rhenostervlei Farm as shown by the stratigraphic diagrams, CONISS analysis and the PCA occurred at the onset of the 20th century CE and was characterised by a shift from a saline, dry and nutrient-poor environment (ca. 1790-1890 CE) to a more turbid, nutrient-rich environment with increased freshwater influence that was prone to periodic flooding (ca. 1890-2011 CE). Through the chronological analysis and the interpretation of the historical record (climate and land-use) as well as other environmental proxies (sediment accumulation rate and macro-charcoal), the causes of the detected change in water availability and quality at the floodplain site were likely related to land-use change in the form of agricultural intensification at Rhenostervlei Farm and potentially in the Berg River catchment as a whole.

Présentation

Version intégrale (3,5 Mb)

Page publiée le 15 janvier 2021