Sediment dynamics and provenance of hydrologic and vegetation signals of the Mzimvubu Catchment, Eastern Cape, South Africa.

Abstract

Southern Africa has a high vulnerability to future climate change, therefore realiable and comprehensive information on local hydrological, vegetation and sediment processes are crucial for future mitigation and management practices. Marine sediments can provide valuable, continuous and long-term data about climatic, vegetation and sediment dynamics of the adjacent continent. To accurately interpret these records, the question of terrestrial organic and inorganic material provenance and their contribution to marine archives is essential. Provenance studies however, have mostly been conducted along the western shoreline, very few studies exist along the eastern shoreline. This study presents an investigation of inorganic and organic signals transported within the Mzimvubu Catchment, Eastern Cape.To investigate proxy provenance, plantleaf-wax derived long-chain n-alkanes, pollen grains and element compositions of 32 River Bed Sediment (RBS) and Suspended Particulate Matter (SPM) samples of the five major tributaries were compared over three different seasons. The δ13C composition of river sediment yielded depleted values indicating input from predominantly C3vegetation. δD of RBS changed with increasing altitude and distance from the ocean and rainfall amount. Enriched δ13C values, depleted δD values, reduced norm31 and low CPI values indicate input from arborealvegetation with elevated sediment erosion rates originating from the northern tributaries. Depleted δ13C values, enriched δDvalues, elevated norm31 and high CPI values indicate reduced sediment erosion rates and input from adjacent grasslands in the southern tributaries. XRF Fe/K, Ti/Al and Al/Si ratios revealed areas of high erosion of fine grained particles due to anthropogenic pressures and aeolian dust input from south easterly trade winds in the northern tributaries, compared to the fluvial input of coarse grained particles in the southern tributaries and river mouth. Proxy signals were influenced by various environmental,physiological and taphonomic processes. These findings present the first comprehensive multiproxy overview of vegetation, sediment and hydrologic provenance based on palynomorph abundance, n-alkane isotopic distributions and elemental compound dynamics within the Mzimvubu Catchment, which can aid the interpretation of marine cores extracted from the Indian Ocean for future palaeoclimatological and palaeoenvironmental research.