Linking geochronology and source apportionment of sediments to understand land–lake transfers in the Lake Victoria Basin

Soil erosion is an increasing environmental problem in the Lake Victoria Basin (LVB), resulting in the transfer of sediment, nutrients and contaminants from terrestrial landscapes to aquatic ecosystems. These land-to-lake transfers have implications for soil fertility, water quality, ecosystem functioning and food security, yet the temporal evolution and catchment origins of sediment inputs remain poorly understood. This study combines Pb-210 geochronology, sediment geochemistry and geochemical source apportionment to reconstruct historical sediment delivery to the Winam Gulf of Lake Victoria from the Nyando, Sondu-Miriu, Awach, Luanda and Kisat river catchments. Sediment-core chronologies demonstrate a substantial acceleration in sediment accumulation from the 1960s, with the most rapid increases occurring after 2000. Sedimentation rates increased approximately seven-fold in the Nyando catchment and three-fold in the Sondu-Miriu catchment between the 1960s and 2021. Temporal changes in sediment geochemistry, including phosphorus, sulphur, calcium and organic matter, indicate increasing influence of agricultural expansion, forest clearance and urban development. Using a Frequentist sediment fingerprinting approach, historical sediment contributions were linked to specific sub-catchments, revealing that recent increases in sediment delivery were associated with shifts in sediment provenance driven by land-use change in key source areas. The integration of geochronology and source apportionment provides a multi-decadal reconstruction of land-lake connectivity and identifies priority locations for intervention. From an environmental geochemistry and health perspective, accelerated sediment transfer represents the mobilisation of nutrient-rich topsoil, organic carbon and associated contaminants into aquatic systems, with potential consequences for agricultural productivity, eutrophication, fisheries, water quality and human wellbeing. The approach offers a practical framework for targeting catchment restoration and improving ecosystem resilience across the Lake Victoria Basin and other rapidly changing tropical catchments.