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Journal Articles ACS Earth and Space Chemistry Year : 2023

Geochemical Controls on the Uranium Cycle in a Lake Watershed


Understanding the uranium (U) cycle – reservoirs and processes – at the watershed scale is key to manage contaminated areas, to elucidate ore formation processes as well as to implement paleoenvironmental research. Here, we investigated the different steps of the U cycle, from sources to sinks, and the relative roles of redox processes and organic matter in the control of U mobility in the naturally U-rich small mountainous watershed of Lake Nègre (France). We interpret the U repartition in U reservoirs through chemical, isotopic (δ238U and (234U/238U)) and speciation analyses, in the light of anterior studies of the site. We show that U(VI) originates from the leaching of U-rich rock fractures and is transported in dissolved forms. Wetlands and meadow soils then act as intermediary sinks where U(VI) is complexed by organic matter (up to > 5000 µg/g) and subsequently partly reduced to U(IV). Dissolved U is also supplied to the lake, in addition to particulate and colloidal U resulting from soil physical erosion. After entering the lake, most U(VI)-bearing organic particles settle in the sediments and U(VI) is reduced to U(IV), resulting in high sedimentary U concentrations (up to > 1000 µg/g), while a fraction of U is potentially desorbed from particles. Remaining dissolved U is exported from the watershed through the lake outlet stream. In this high-mountain lake catchment, the U cycle is mainly controlled by organic matter complexation and particulate transport, though U reduction in the lake sediments may help to its long-term immobilization.
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hal-04117087 , version 1 (05-06-2023)





Pierre Lefebvre, Arnaud Mangeret, Alkiviadis Gourgiotis, Pascale Louvat, Pierre Le Pape, et al.. Geochemical Controls on the Uranium Cycle in a Lake Watershed. ACS Earth and Space Chemistry, 2023, 7 (5), pp.972-985. ⟨10.1021/acsearthspacechem.2c00348⟩. ⟨hal-04117087⟩
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