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Reaction chain modeling of denitrification reactions during a push-pull test

Abstract : Field quantitative estimation of reaction kinetics is required to predict biogeochemical reactions in aquifers. We extended the analytical solution developed by Haggerty et al. [1] to model an entire 1st order reaction chain and estimate the kinetic parameters for each reaction step. We then evaluated the ability of this solution to model experimental results from a push pull test in a fractured crystalline aquifer (Ploemeur, Brittany). Nitrates were used as the reactive tracer, since denitrification is a sequential reduction of nitrates to nitrogen gas occuring in a chain reaction (NO3 - % NO2 - % NO % N2O % N2) under anaerobic conditions. The kinetics of nitrate consumption and by-products formation (NO2 - and N2O) during autotrophic denitrification were quantified by using a reactive tracer (NO3 -) and a non-reactive tracer (Br-). Comparison of the Br- and NO3 - breakthrough curves showed that 10 % of the injected NO3 - molar mass was transformed during the 12 hour experiment. Similar results, but with slower kinetics, were obtained from laboratory experiments in reactors. The good agreement between the model and the field data shows that the complete denitrification process can be efficiently modeled as a sequence of first order reactions. The variability of biogeochemical reactivity in the field will be also discussed. [1] Haggerty et al. (1998), Ground Water 36 (2), 314-324.
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Submitted on : Thursday, September 26, 2013 - 9:23:35 AM
Last modification on : Thursday, June 2, 2022 - 2:48:11 PM

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Alexandre Boisson, Pietro de Anna, Olivier Bour, Tanguy Le Borgne, Thierry Labasque, et al.. Reaction chain modeling of denitrification reactions during a push-pull test. Goldschmidt Conference 2013, Aug 2013, Florence, Italy. pp.729, ⟨10.1180/minmag.2013.077.5.2⟩. ⟨insu-00866128⟩



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