A global review of sediment source fingerprinting research incorporating fallout radiocesium (137Cs)

Information on the main sources supplying deleterious sediment loads to river systems is needed to improve our understanding of soil erosion processes to better target erosion control measures. In particular. it is important to quantify the respective contributions of surface and subsurface sources to material degrading waterbodies. Radiocesium (Cs-137), emitted during thermonuclear bomb testing (similar to 1950-1980) and nuclear accidents provides significant discrimination between surface material exposed to atmospheric fallout and subsurface material sheltered from it. A systematic worldwide review of research articles (n = 123) that used Cs-137 to trace sediment sources showed that the United Kingdom (n = 24), Australia (n = 23) and the United States (n = 20) had the highest number of publications utilizing Cs-137 in a sediment tracing framework. In contrast, few studies were published for catchments in Africa (n = 9) or South America (n = 2). In the northern hemisphere, positive relationships were evident between Cs-137 activities in surface and subsurface sources and the proportion of thermonuclear bomb fallout. However, given the low proportions of fallout received in regions between 0 and 20 degrees N and 0-20 degrees S, the potential application of Cs-137 tracing techniques may be limited in this area of the world as well as in agricultural regions with severe soil erosion (i.e. Chinese Loess Plateau and South Africa). In total, 94% of the studies researching surface and subsurface sources that analysed Cs-137 as a potential tracing property included this parameter in end-member mixing models. The main challenges for the future of this technique are related to the access to ultra-low background gamma spectrometry facilities and the development of surrogate tracers. Future research should ensure that basic catchment information and details on the sampling design are properly documented to ensure studies are reproducible. Moreover, researchers should provide raw measurement data to help improve our global understanding of Cs-137 dynamics in soil erosion research. (C) 2020 Elsevier B.V. All rights reserved.