Autotrophic denitrification supported by biotite dissolution in crystalline aquifers (1): New insights from short-term batch experiments

Abstract : We investigate denitrification mechanisms through batch experiments using crushed rock and groundwater from a granitic aquifer subject to long term pumping (Ploemeur, France). Except for sterilized experiments, extensive denitrification reaction induces NO3 decreases ranging from 0.3 to 0.6 mmol/L. Carbon concentrations, either organic or inorganic, remain relatively stable and do not document potential heterotrophic denitrification. Batch experiments show a clear effect of mineral dissolution which is documented through cation (K, Na, Ca) and Fluoride production. These productions are tightly related to denitrification progress during the experiment. Conversely, limited amounts of SO4, systematically lower than autotrophic denitrification coupled to sulfur oxidation stoichiometry, are produced during the experiments which indicates that sulfur oxidation is not likely even when pyrite is added to the experiments. Analysis of cation ratios, both in isolated minerals of the granite and within water of the batch, allow the mineral dissolution during the experiments to be quantified. Using cation ratios, we show that batch experiments are characterized mainly by biotite dissolution. As biotite contains 21 to 30% of Fe and 0.3 to 1.7% of F, it constitutes a potential source for these two elements. Denitrification could be attributed to the oxidation of Fe(II) contained in biotite. We computed the amount of K and F produced through biotite dissolution when entirely attributing denitrification to biotite dissolution. Computed amounts show that this process may account for the observed K and F produced. We interpret these results as the development of microbial activity which induces mineral dissolution in order to uptake Fe(II) which is used for denitrification. Although pyrite is probably available, SO4 and cation measurements favor a large biotite dissolution reaction which could account for all the observed Fe production. Chemical composition of groundwater produced from the Ploemeur site indicates similar denitrification processes although original composition shows mainly plagioclase dissolution.
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Science of the Total Environment, Elsevier, 2018, 619-620, pp.842-853. 〈10.1016/j.scitotenv.2017.11.079〉
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Contributeur : Isabelle Dubigeon <>
Soumis le : jeudi 30 novembre 2017 - 14:17:45
Dernière modification le : mardi 29 mai 2018 - 12:50:56

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Luc Aquilina, Clément Roques, Alexandre Boisson, Virginie Vergnaud-Ayraud, Thierry Labasque, et al.. Autotrophic denitrification supported by biotite dissolution in crystalline aquifers (1): New insights from short-term batch experiments. Science of the Total Environment, Elsevier, 2018, 619-620, pp.842-853. 〈10.1016/j.scitotenv.2017.11.079〉. 〈insu-01652576〉

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