A global review of sediment source fingerprinting research incorporating fallout radiocesium ($^{137}$Cs)

O. Evrard (1, 2) , Pierre-Alexis Chaboche (1) , Rafael Ramon (1, 3) , Anthony Foucher (1) , J. Patrick Patrick Laceby (4)

1 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
2 GEDI - Géochimie Des Impacts
3 UFRGS - Universidade Federal do Rio Grande do Sul [Porto Alegre]
4 EMSD - Environmental Monitoring and Science Division of Alberta

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.

Mots clés: soil erosion; sediment tracing; fallout radionuclides; watersheds

Domaines: Sciences de l'environnement; Planète et Univers [physics]; Interfaces continentales, environnement

O. Evrard, Pierre-Alexis Chaboche, Rafael Ramon, Anthony Foucher, J. Patrick Patrick Laceby. A global review of sediment source fingerprinting research incorporating fallout radiocesium ($^{137}$Cs). Geomorphology, 2020, 362, pp.107103. ⟨10.1016/j.geomorph.2020.107103⟩. ⟨cea-02570827⟩