Origin, transport, and retention of fluvial sedimentary organic matter in South Africa's largest freshwater wetland, Mkhuze Wetland System

Abstract. Sedimentary organic matter (OM) analyses along a 130 km long transect of the Mkhuze River from Lebombo Mountains to its outlet into Lake St Lucia, Africa's most extensive estuarine system, revealed present active trapping function terminal freshwater wetland. Combining bulk OM analyses, such as Rock-Eval®, and source-specific biomarker plant-wax n-alkanes their stable carbon (δ13C) hydrogen (δD) isotopic composition showed that fluvial sedimentary originating inland areas is mainly deposited in floodplain swamp area wetland system but not downstream lake area. A distinctly less degraded signature, i.e., considerably lower degree transformation unstable components (higher I index) contribution refractory persistent fractions (lower R well recognizably higher δD values compared samples upstream sub-environments, characterizes surface sediments Lucia. The offset indicates contributing vegetation, although similar vegetation inputs terms photosynthetic pathway alkane distribution pattern, experienced different hydrological growth conditions. results suggest under current conditions hinterland throughout up Swamps, which ultimately captures transported OM. Consequently, located Lucia show locally derived signals instead integrated encompassing river catchment. This finding raises important constraints for future environmental studies assumption watershed-integrated archives retrieved lakes or offshore might hold true certain settings.