No abstract

Information on the main sources supplying deleterious sediment loads to river systems is needed to improve our understanding of soil erosion processes. In particular, it is important to quantify the respective contributions of surface and subsurface sources to material degrading waterbodies. Radiocesium (137 Cs), emitted during thermonuclear bomb testing (~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 137 Cs 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 137 Cs 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 137 Cs activities in surface and subsurface sources and the proportion of thermonuclear bomb fallout. However, given the low proportions of fallout received in regions between 0-20°N and 0-20°S, the potential application of 137 Cs 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 analyzed 137 Cs as a potential tracing property included this parameter in end-member mixing models. The main challenges for the future of this technique are mainly 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 137 Cs dynamics in soil erosion research.