Hydrologically driven seasonal changes in the sources and production mechanisms of dissolved organic carbon in a small lowland catchment

Authors

  • Thibault Lambert,

    1. Observatoire des Sciences de l'Univers de Rennes, CNRS, UMR 6118 Géosciences Rennes, Université de Rennes 1, Rennes, France
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  • Anne-Catherine Pierson-Wickmann,

    1. Observatoire des Sciences de l'Univers de Rennes, CNRS, UMR 6118 Géosciences Rennes, Université de Rennes 1, Rennes, France
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  • Gérard Gruau,

    1. Observatoire des Sciences de l'Univers de Rennes, CNRS, UMR 6118 Géosciences Rennes, Université de Rennes 1, Rennes, France
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  • Anne Jaffrezic,

    1. Observatoire des Sciences de l'Univers de Rennes, CNRS, UMR 6118 Géosciences Rennes, Université de Rennes 1, Rennes, France
    2. UMR INRA–Agrocampus Ouest Sol, Agrohydrosystème, Spatialisation, Route de Saint-Brieuc, Rennes, France
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  • Patrice Petitjean,

    1. Observatoire des Sciences de l'Univers de Rennes, CNRS, UMR 6118 Géosciences Rennes, Université de Rennes 1, Rennes, France
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  • Jean-Noël Thibault,

    1. UMR INRA–Agrocampus Ouest PEGASE, Domaine de la Prise, Saint-Gilles, France
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  • Laurent Jeanneau

    Corresponding author
    1. Observatoire des Sciences de l'Univers de Rennes, CNRS, UMR 6118 Géosciences Rennes, Université de Rennes 1, Rennes, France
    • Corresponding author: T. Lambert, Observatoire des Sciences de l'Univers de Rennes, CNRS, UMR 6118 Géosciences Rennes, Université de Rennes 1, Campus de Beaulieu, FR-35042 Rennes CEDEX, France. (tibo.lambert@gmail.com)

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Abstract

[1] To obtain better constraints on the control of seasonal hydrological variations on dissolved organic carbon (DOC) dynamics in headwater catchments, we combined hydrometric monitoring with high-frequency analyses of DOC concentration and DOC chemical composition (specific UV adsorption, δ13C) in soil and stream waters during one complete hydrological cycle in a small lowland catchment of western France. We observed a succession of four hydrological periods, each corresponding to specific DOC signatures. In particular, the rise of the upland water table at the end of the rewetting period yielded to a strong increase of the specific UV absorbance (from 2.5 to 4.0 L mg C−1 m−1) and of the δ13C values (from −29 to −27‰) of the soil DOC. Another striking feature was the release of large amounts of DOC during reduction of soil Fe-oxyhydroxides at the end of the high-flow period. Comparison of hydrometric data with DOC composition metrics showed that soils from the upland domains were rapidly DOC depleted after the rise of the water table in these domains, whereas wetland soils acted as quasi-infinite DOC sources. Results from this study showed that the composition and ultimate source of the DOC exported to the stream will depend on the period within the annual hydrological cycle. However, we found that the aromatic DOC component identified during the high-flow period will likely represent the dominant DOC component in stream waters on an annual basis, because most of the annual stream DOC flux is exported during such periods.

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