Recent trends in sediment and nutrient accumulation rates in coastal, freshwater Lake Sibaya, South Africa

Eutrophication of aquatic systems has emerged as one of the most pressing issues confronted by scientists and environmental managers. In this study, we used two sediment cores from Lake Sibaya, a coastal freshwater lake in South Africa, to infer historical variations in bulk sediment accumulation and nutrient (C, N and P) biogeochemistry. Cores were dated using Pb-210, Cs-137 and C-14, and dates were used to calculate bulk sediment accumulation rates and nutrient concentrations over the last 250 years. In the western section of the lake, stratigraphic variations in total carbon, nitrogen and phosphorus increased abruptly to near-constant levels around the beginning of the 20th century, a trend that appears to be consistent with the onset of human settlement and land clearance in the catchment. In contrast, sedimentation rates have remained relatively constant over this period, despite recent land use change in the catchment. Results of this study suggest that recent increases in development pressure have yet to further influence sedimentation in Lake Sibaya, thus providing values against which future monitoring efforts can be compared. This study represents the first report on recent trends in sedimentation and nutrient biogeochemistry in Lake Sibaya. The results have broad implications for other ecologically sensitive areas within the Maputaland ecoregion of coastal southern Africa.