Land Use and upland soil erosion dynamics along climatic and human disturbance gradients in the Kasai Basin (DR Congo)

The Kasai basin (DRCongo), southwest part of the Congo Basin, displays a unique array of climatic conditions, mineralogical compositions and land use trajectories. It is currently experiencing an explosive demographic expansion, which leads to drastic land use and land cover changes (LULCC) such as deforestation and cropland expansion. The net terrestrial C exchange from both vegetation and soils accompanying land use change is relatively well constrained. In contrast, C exchange associated with accelerated soil erosion following the degradation of natural habitats is an uncertain component of the carbon budgeta,b,c, particularly in tropical settingsd,e,f.To remedy this lack of knowledge, we used remote sensing techniques in conjunction with field observations and preexisting datasets describing potential drivers such as Worldpopg, global Human Modificationh, etc. We analyzed the temporal evolution of LULCC and its drivers within the Kasai Basin at high spatial resolutions. Preliminary results show a discernable surge in deforestation rates, varying across the different sub-basins, alongside expansions in cropland cultivation and artisanal mining activities, all recognized as contributors to heightened soil erosion. Using estimated time series of suspended sediment yield derived from in-situ measurements and remote sensing products as an indicator for upland soil erosion, we compared observed changes in sediment yield to LULCC trajectories. We also conducted a robust sampling campaign and collected over 5000 soil samples from 15 hillslopes transects alongside the Kasai River. Multiple soil organic carbon (SOC) analyses were realized to investigate C dynamics in tropical eroding uplands: carbon and nitrogen content and stable isotopes, soil texture, clay mineralogy and fallout radionuclide inventory of a selection of samples, and MIR spectroscopy to have high depth resolution results.The results of our study will provide insights into the environmental drivers responsible for the heightened soil erosion and lateral carbon fluxes observed within the Kasai Basin. The forthcoming study of these fluxes will improve the knowledge of the tropical C budget in eroding upland soils. REFERENCESa Stallard, R. F. (1998). Global Biogeochemical Cycles, 12(2), 231257. https://doi.org/10.1029/98GB00741 b Berhe, A. A. et al. (2007). Bioscience, 57, 337346, https://doi.org/10.1641/B570408 cVan Oost, K. et al. (2007). Science, 318(5850), 626629. https://doi.org/10.1126/science.1145724 d Don, A. et al. (2011). Global Change Biology, 17(4), 16581670. https://doi.org/10.1111/j.1365-2486.2010.02336.x e Reichenbach, M. et al. (2023). Global Change Biology, 00, 117. https://doi.org/10.1111/gcb.16622 f Wilken, F. et al. (2020). Soil, 122. https://doi.org/10.5194/SOIL-7-399-2021 g Lloyd, C. T. et al. (2017). Scientific Data, 4(1), 170001. https://doi.org/10.1038/sdata.2017.1 h Kennedy, C.M. et al. (2019). Global Change Biology, 25(3), 811826. doi:10.1111/gcb.14549