TropSOC - Tropical soil organic carbon dynamics along erosional disturbance gradients in relation to variability in soil geochemistry and land use
Physical Geography
Final Report Abstract
The African Tropics are hotspots of modern-day land-use change and are, at the same time, of great relevance for the cycling of carbon (C) and nutrients between plants, soils and the atmosphere. In particular, the African continent is facing huge environmental and societal challenges with a projected population growth of 400% by the end of this century (Gerland et al., 2014), much of it happening in (sub-)tropical sub-Saharan Africa. In consequence, forested landscapes in tropical Africa are currently facing unprecedented levels of land conversion. As a result, deforestation and soil degradation have accelerated greatly since the second half of the 20th century with soil erosion and decrease in soil fertility, in particular, emerging as the main driver of soil degradation. The response of soils to disturbance by erosion is also one of the great uncertainties in predicting greenhouse gas fluxes from soils to the atmosphere and, hence, future earth system dynamics. This is largely due to a lack of data in remote areas but also due to an inadequate transfer of knowledge from smaller to larger scales. The focus of project TropSOC was to shed light how the dramatic changes in land use and soil properties will shape future biogeochemical cycles in soils across landforms, geologies, and soil types in tropical Africa. TropSOC’s results demonstrate that even in deeply weathered tropical soils, parent material has a long-lasting effect on soil chemistry that can influence and control microbial activity, the size of subsoil C stocks, and the turnover of C in soil. Soil parent material and the resulting soil chemistry need to be taken into account in understanding and predicting C stabilization and turnover in tropical forest soils. Given the investigated rates of erosion on cropland, our findings confirm the threat of large losses or organic matter leading to sharp decline in soil fertility with little potential of soils to recover from nutrient losses naturally on decadal or centennial timescales. TropSOC highlights that considering feedbacks between geochemistry and topography to understand the development of soil fertility in the Afrcan Great Lakes Region regions can significantly improve our insights into the role of tropical soils for reaching several key sustainable development goals such as climate mitigation and zero hunger and help to raise awareness for the need to maintain limited soil resources for future generations. TROPSOC made a significant contribution to improving our understanding of the factors that give rise to the spatial distribution and fate of C of tropical soil systems. TROPSOC produced benchmark data products that help now to bridge the gap between plot scale process understanding and large scale modelling of tropical C cycling. Ultimately, this will reduce the uncertainty associated with terrestrial C fluxes and the response of soils to disturbance, which are among greatest uncertainties in current global assessments (Todd-Brown et al. 2013). While TROPSOC focuses on investigating differences in biogeochemical cycling between stable and eroding landforms, sampling valley bottoms yielded valuable information on C storage in depositional landforms of tropical (agro-)ecosystems. This information is essential in helping us to determine whether eroding tropical landscapes act as a sink or source of C, since the deposition and burial of presumably labile and poorly stabilized C in young sediments may contribute to C sequestration in soils, at least in the short run, and must therefore be considered together with any C losses or gains at eroding sites. TROPSOC’s data, gathered along complete geomorphic transects, is also the fundament for follow-up research aimed at upscaling the results to larger spatial scales and determining, finally, whether eroding tropical landscapes will act as a sink or source of C in a changing world.
Publications
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2020. Environmental research in the heart of Africa: The Congo Biogeochemistry Observatory: The role of the changing Tropics for future global carbon dynamics. Editorial, Open Access Government. Vol. 25: 328-329
Doetterl S., Drake T., Bauters M., Van Oost K., Barthel M., Hoyt A.
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2021. Assessing soil erosion of forest and cropland sites in wet tropical Africa using 239+240Pu fallout radionuclides. Soil 7:399-414
Wilken F., Fiener P., Ketterer M., Meusburger K., Muhindo D.I., Van Oost K., Doetterl S.
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2021. Filling a key gap: a soil infrared library for central Africa. SOIL Discussion (pre-print)
Summerauer L., Baumann P., Ramirez-Lopez L., Barthel M., Bauters M., Bukombe B., Reichenbach M., Boeckx P., Kearsley E., Van Oost K., Vanlauwe B., Chiragaga D., Heri-Kazi A.B., Moonen P., Sila A., Shepherd K., Bazirake Mujinya B., Van Ranst E., Baert G., Doetterl S., Six J.
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2021. Organic matter cycling along geochemical, geomorphic and disturbance gradients in forests and cropland of the African Tropics - Project TropSOC DATABASE_v1.0. Earth System Science Data 13, 4133–4153
Doetterl, S., Asifiwe, R.K., Baert, G., Bamba, F., Bauters, M., Bukombe, B., Cadisch, G, Cizungu, L., Cooper, M., Hoyt, A., Kabaske, C., Kalbitz, K., Kidinda, K.L., Maier, A., Mainka, M., Mayrock, J., Muhindo, D., Mujinya, B., Mukotanyi, S.M., Nabahungu, L., Reichenbach, M., Rewald, B., Six, J., Stegmann, A., Summerauer, L., Unseld, R., van Oost, K., Verheyen, K., Vogel, C., Wilken, F., Fiener, P.
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2021. Sorption and desorption of organic matter in soils as affected by phosphate. Geoderma 405: 115377
Spohn M., Diáková K., Aburto F., Doetterl S., Borovec J.
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2021. Spatial and temporal patterns of rainfall erosivity in the Lake Kivu region: insights from a meteorological observatory network. Progress in Physical Geography 1-19
Bagalwa R.M., Chartin C., Baumgartner S., Mercier S., Syauswa M., Samba V.C., Zabona M.T.,Karume, Cizungu N.L., Barthel, M., Doetterl S., Six, J., Boeckx, P., Van Oost, K.
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2021. The role of geochemistry in organic carbon stabilization in tropical rainforest soils. Soil 7: 453-475
Reichenbach M., Fiener P., Garland G., Griepentrog M., Six J., Doetterl S.
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Heterotrophic soil respiration and carbon cycling in geochemically distinct African tropical forest soils. SOIL 7, 639-659
Bukombe B., Fiener P., Hoyt A., Doetterl S.
