The mass balance of molybdenum (Mo) was studied in the Strengbach catchment (eastern France). Monitoring of rainfall, vegetation, and soil characteristics in this 0.8 km2 catchment was started decades ago. We present Mo concentrations and isotopic compositions of about 60 samples including bedrock types, perennial springs, soil profiles, and the roots and leaves of two tree species, and finally the outflowing brook. Both stream waters and bedrocks show Mo concentrations at least an order of magnitude lower than global averages. The Mo isotopic composition of topsoils and organic matter (foliage, litter, and roots) is rather homogeneous. Net biological fractionation is thus subordinate to the differences in the Mo sources. The efficient Mo recycling from organic litter to plants keeps Mo bioavailable. The Mo data, supplemented with new and literature Sr data, are used to identify the source(s) of Mo and Sr and their (transient) storage within the catchment. The resulting best model identifies rock weathering and marine aerosol as the principal Mo sources. Moreover, soil in the Strengbach catchment has reached steady state for Mo (the time constant to achieve soil steady state is calculated as ca. 50 years), i.e., the Mo isotopic compositions of fluxes to and from the catchments soil are identical.
Naegler, T., Pierret, M., Voegelin, A., Pettke, T., Aschwanden, L., Villa, I. (2020). Small catchment scale Mo isotope balance and its implications for global Mo isotope cycling. In K. Dontsova, Z. Balogh-Brunstad, G. Le Roux (a cura di), Biogeochemical Cycles: Ecological Drivers and Environmental Impact (pp. 163-189). John Wiley & Sons Inc [10.1002/9781119413332.ch8].
Small catchment scale Mo isotope balance and its implications for global Mo isotope cycling
Villa I. M.Ultimo
Membro del Collaboration Group
2020
Abstract
The mass balance of molybdenum (Mo) was studied in the Strengbach catchment (eastern France). Monitoring of rainfall, vegetation, and soil characteristics in this 0.8 km2 catchment was started decades ago. We present Mo concentrations and isotopic compositions of about 60 samples including bedrock types, perennial springs, soil profiles, and the roots and leaves of two tree species, and finally the outflowing brook. Both stream waters and bedrocks show Mo concentrations at least an order of magnitude lower than global averages. The Mo isotopic composition of topsoils and organic matter (foliage, litter, and roots) is rather homogeneous. Net biological fractionation is thus subordinate to the differences in the Mo sources. The efficient Mo recycling from organic litter to plants keeps Mo bioavailable. The Mo data, supplemented with new and literature Sr data, are used to identify the source(s) of Mo and Sr and their (transient) storage within the catchment. The resulting best model identifies rock weathering and marine aerosol as the principal Mo sources. Moreover, soil in the Strengbach catchment has reached steady state for Mo (the time constant to achieve soil steady state is calculated as ca. 50 years), i.e., the Mo isotopic compositions of fluxes to and from the catchments soil are identical.
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