Hydrological development of the Eilandvlei system, southern Cape coast, South Africa during the Holocene

The Wilderness embayment on the southern Cape coast of South Africa lies in the year-round rainfall zone and experiences climatic phenomena associated with the polar westerlies and the tropical easterlies. Bounded by the Outeniqua Mountains in the north and the Indian Ocean in the south, the embayment contains several coastal lakes lying in an east-west orientation. Eilandvlei, the most westerly lake in the complex, currently receives freshwater from the Duiwe River as well as groundwater throughflow, local surface runoff, and direct precipitation, while backflow along the Serpentine Channel brings in brackish and marine waters. The retrieval of sediment cores along a northwest-–southeast transect has provided long, continuous records for a high-resolution study into the development of the system during the Holocene epoch. The combination of the records presents a complimentary account of environmental conditions and climatic fluctuations over the last ca. 10000 cal yrs BP. Preliminary results of diatom analysis suggest the primary controlling mechanism for the system is salinity with strong and rapid biological responses to changes in source waters, revealing periods of marine inundation and dynamic water level fluctuations. However, anthropogenic forcing during the last few centuries has resulted in considerable modifications in the natural functioning of the lake system, altering dynamics and nutrient influx. The Wilderness lakes show great potential as natural geoarchives for Holocene environmental changes, and ongoing multi-proxy analyses on Eilandvlei, Swartvlei, Groenvlei, Rondevlei and Bo-Langvlei are expected to reveal further insights into the relative influences of climate variability, sea-level change and human impact.