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Soil resources in parts of Tanzania are rapidly being depleted by increased rates of soil erosion and downstream sediment transport, threatening ecosystem health, water and livelihood security in the region. However, incomplete understanding to what effect the dynamics of soil erosion and sediment transport are responding to land‐use changes and climatic variability are hindering the actions needed to future‐proof Tanzanian land‐use practices. Complementary environmental diagnostic tools were applied to reconstruct the rates and sources of sedimentation over time in three Tanzanian river systems that have experienced changing land use and climatic conditions. Detailed historical analysis of sediment deposits revealed drastic changes in sediment yield and source contributions. Quantitative sedimentation reconstruction using radionuclide dating showed a 20‐fold increase in sediment yield over the past 120 years. The observed dramatic increase in sediment yield is most likely driven by increasing land‐use pressures. Deforestation, cropland expansion and increasing grazing pressures resulted into accelerating rates of sheet erosion. A regime shift after years of progressive soil degradation and convergence of surface flows resulted into a highly incised landscape, where high amounts of eroded soil from throughout the catchment are rapidly transported downstream by strongly connected ephemeral drainage networks. By integrating complementary spatial and temporal evidence bases, this study demonstrated links between land‐use change, increased soil erosion and downstream sedimentation. Such evidence can guide stakeholders and policy makers in the design of targeted management interventions to safeguard future soil health and water quality. [ABSTRACT FROM AUTHOR]

Water bodies in Tanzania are experiencing increased siltation, which is threatening water quality, ecosystem health, and livelihood security in the region. This phenomenon is caused by increasing rates of upstream soil erosion and downstream sediment transport. However, a lack of knowledge on the contributions from different catchment zones, land‐use types, and dominant erosion processes, to the transported sediment is undermining the mitigation of soil degradation at the source of the problem. In this context, complementary sediment source tracing techniques were applied in three Tanzanian river systems to further the understanding of the complex dynamics of soil erosion and sediment transport in the region. Analysis of the geochemical and biochemical fingerprints revealed a highly complex and variable soil system that could be grouped in distinct classes. These soil classes were unmixed against riverine sediment fingerprints using the Bayesian MixSIAR model, yielding proportionate source contributions for each catchment. This sediment source tracing indicated that hillslope erosion on the open rangelands and maize croplands in the mid‐zone contributed over 75% of the transported sediment load in all three river systems during the sampling time‐period. By integrating geochemical and biochemical fingerprints in sediment source tracing techniques, this study demonstrated links between land use, soil erosion and downstream sediment transport in Tanzania. This evidence can guide land managers in designing targeted interventions that safeguard both soil health and water quality. [ABSTRACT FROM AUTHOR]

Unsustainable land use and cover changes (LUCC) are driving increased soil erosion and siltation of water bodies in East-Africa, threatening food-, livelihood-, water-, and energy security. Lack of long-term LUCC and sediment flux data in East-Africa's catchments impedes the development of sustainable land- and water management plans to tackle this 'wicked problem'. Using Landsat imagery this study reconstructed almost three decades of LUCC (1988-2016) in the Lake Manyara basin, Tanzania. The effects on the surface water erosion risk were modelled using the Revised Universal Soil Loss Equation (RUSLE), which highlighted notable LUCC in high risk zones, increasing the surface erosion risk substantially in these areas. In parallel, geochemical fingerprinting was applied to attribute sediment contributions from different tributaries to Lake Manyara. By unmixing the fingerprints of lake sediment mixtures against riverine sources, the proportional sediment contributions of the different sub-catchments in Lake Manyara were obtained. Additionally, sediment cores were analysed to investigate the changes in sedimentation rates and tributary sediment contributions under response of LUCC in the tributary sub-catchments. The sediment contributions from different sub-catchments matched closely, but not completely, with those sub-catchments where the model predicted big increases in surface erosion risk. Source-to-sink dynamics in the sub-catchments were explored by soil- and landscape analysis in the potential source areas and composite fingerprinting of the transported sediment. This highlighted the importance of connectivity in the source-to-sink transport of eroded sediment. While surface erosion risk is predicted to be higher in certain sub-catchments, anthropogenic micro-topographic buffers and natural wetlands decrease the connectivity. In contrast, increasing gully formation in other sub-catchments rapidly funnels the sediment to the river systems, increasing connectivity. This study highlights the importance of a multi-technique basin-wide approach to determine areas and dynamics of increased erosion and siltation to assist management authorities for targeted action. [ABSTRACT FROM AUTHOR]