Anthropocene environmental change in an overlooked South African lake: Mountain Lake, Matatiele, Eastern Cape

Abstract

Very little is known about the impacts of Anthropocene environmental change on aquatic systems in the mountains of southern Africa. The Maloti-Drakensberg region forming the border between South Africa and Lesotho is not generally associated with natural, permanent lakes, but there are dammed wetland lakes with evidence that natural water bodies were present before lake levels were raised, including Mountain Lake in the Eastern Cape in South Africa. In order to address a regional lack of long-term monitoring data, here we present evidence from lake sediment records spanning over 50 years from Mountain Lake that industrial signals of contamination associated with distant coal fired power stations are transported across the region, including trace metals, mercury (reaching 95 ng·g⁻¹) and spheroidal carbonaceous particles. In addition, high concentrations of the organochlorine pesticides DDT (ΣDDT = 166.3 ng·g⁻¹) and methoxychlor (39.3 ng·g⁻¹), most likely from catchment sources, are recorded in recent sediments. Finally, the diatom record indicates shifts in assemblages within the last 20 years indicative of possible nutrient enrichment, which is consistent with known intensification of agricultural and other human activity within the catchment, shown by increasing sediment enrichment of P, Mn, Fe, As and Co. Hence there are multiple lines of evidence for increasing environmental pressures on the ecosystems of Mountain Lake and its catchment over the period of the proposed Anthropocene. Further studies are required to assess the magnitude of threats to the unique but largely unstudied biodiversity associated with lakes in the region, including those in protected areas.

Keywords:

• Palaeolimnology
• nutrients
• trace metals
• mercury
• diatoms
• organochlorine pesticides

ACKNOWLEDGMENTS

The authors are extremely grateful to David Rawlins of Resthaven Guest House in Matatiele for inspiring this study with his extensive knowledge of the site and guiding assistance during fieldwork. Jennifer Fitchett of the University of the Witwatersrand and Alice Milner of Royal Holloway, University of London also assisted with coring fieldwork. We thank Prof Pieter van Zyl and Jan-Stefan Swartz for major ion analysis at NWU. Finally, we thank Bradley Robinson for the rigorous bathymetric survey of the lake during his Geography Honours project at the University of the Witwatersrand.