The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa
1Department of Environmental and Geographical Sciences, University of Northampton, Northampton, NN2 6JD, UK
2Department of Geography, Rhodes University, Grahamstown 6140, Eastern Cape, South Africa
3Environmental Change Institute, Oxford Centre for the Environment, University of Oxford, Oxford OX1 3QY, UK
4Department of Environmental and Geographical Science, University of Cape Town, Rondebosch 7701, South Africa
5Sustainable Soils and Grassland Systems Department, Rothamsted Research, Okehampton, EX20 2SB, UK
6Department of Environmental Sciences, University of Basel, Klingelbergstr. 27, 4056 Basel, Switzerland
7Department of Geography & Environment, School of Geosciences, University of Aberdeen, Aberdeen, AB24 3UF, UK
Abstract. Several research projects undertaken by the authors and others over the last 14 years have used fallout and geogenic radionuclides for understanding erosion processes and sediment yield dynamics in South Africa over the last 100–200 years as European settlers colonised the interior plains and plateaux of the country and imported new livestock and farming techniques to the region. These projects have used two fallout radionuclides (210Pb and 137Cs) to date sediments accumulating in reservoirs, farm dams, wetlands, alluvial fans and floodouts and have used other fallout nuclides (7Be) and long-lived geogenic radionuclides (e.g. 40K, 235U) as part of a composite fingerprint exploring contemporary sediment sources and changes to sources through time. While successful in many parts of the world, applying these techniques in Southern Africa has posed a number of challenges often not encountered elsewhere. Here we explore some of the benefits and challenges in using gamma-emitting radionuclides, especially 137Cs, in these landscapes. Benefits include the potential for discriminating gully sidewall from topsoil sources, which has helped to identify contemporary gully systems as sediment conduits, rather than sources, and for providing a time-synchronous marker horizon in a range of sedimentary environments that has helped to develop robust chronologies. Challenges include the spatial variability in soil cover on steep rocky hillslopes, which is likely to challenge assumptions about the uniformity of initial fallout nuclide distribution, the paucity of stable (non-eroding) sites in order to estimate atmospheric fallout inventories, and the limited success of 210Pb dating in some rapidly accumulating high altitude catchments where sediments often comprise significant amounts of sand and gravel. Despite these challenges we present evidence suggesting that the use of gamma-emitting radionuclides can make a significant contribution to our understanding of erosion processes and sediment yield dynamics. Future research highlighted in the conclusion will try to address current challenges and outline new projects established to address them more fully.
Foster, I. D. L., Boardman, J., Collins, A. L., Copeland-Phillips, R., Kuhn, N. J., Mighall, T. M., Pulley, S., and Rowntree, K. M.: The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa, Proc. IAHS, 375, 29-34, doi:10.5194/piahs-375-29-2017, 2017.