PHYSICAL CHARACTERISTICS AND ISOTOPES OF SEDIMENTS FROM TWO LAKE SYSTEMS IN KWAZULU-NATAL, SOUTH AFRICA

The sedimentary records of lake and river systems have long provided information about paleoclimatic change. Additionally, %C and %N and isotopic C and N changes in the sediments can reflect changes in the system inputs. Sociopolitical change continues in southern Africa and with it comes population increases and movement, as well as increased agriculture and industry. It is therefore important to assess large scale and regional environmental change in the recent past (within the Holocene) so as to provide insight into ecosystem change for informed management decisions in the future. Further, information from southern Africa is severely lacking in the global climate change database. In an effort to study change recorded in the sediments, this region is specifically selected on the basis of its location with respect to known climatic influences and variability in the ITCZ and the Walker Cell circulation. The sites used in this study, Lake Sibaya and the Kosi Lake system in northeastern KwaZulu-Natal in South Africa, were selected as they are fairly remote, not heavily influenced by anthropogenic activities and are closely situated to the coast with the assumption being that their sediment record should reflect extreme tropical cyclone events. Sediment samples were taken from the sites via coring to depths of up to two meters in length to assess what signals of climate influence and change, if any, can be found in the sediments. Samples from the two Sibaya cores (2 & 3) had isotopic values for d¹³C that ranged from –27.9 to -18.7‰ and from 0 to 6.8‰ for d¹⁵N. The Kosi core (11) values for d¹³C that ranged from –24.0 to -16.7‰ and from 0 to 4.9‰ for d¹⁵N. Elemental (C/N ratio) compositions ranged from 11.8 to 95.5 in the Sibaya cores and 12.7 to 56.1 in the Kosi core. Statistical parameters obtained from grain size analyses of the three cores via sieving, reveal changes with depth in cores 3 and 11, as well as differences in the characteristics of the sediments between the cores. This multi-proxy approach enables an investigation into different trends exhibited in the sediment record of these sites and reveals much about the environmental changes in this area of southern Africa.