Dernière mise à jour le : 16 décembre 2016

Exposure Time Distributions reveal Denitrification Rates along Groundwater Flow Path of an Agricultural Unconfined Aquifer


Groundwater contamination by nitrate is nearly ubiquitous in agricultural regions. Nitrate is highly mobile in groundwater and though it can be denitrified in the aquifer (reduced to inert N2 gas), this process requires the simultaneous occurrence of anoxia, an electron donor (e.g. organic carbon, pyrite), nitrate, and microorganisms capable of denitrification. In addition to this the ratio of the time groundwater spent in a denitrifying environment (exposure time) to the characteristic denitrification reaction time plays an important role, because denitrification can only occur if the exposure time is longer than the characteristic reaction time. Despite a long history of field studies and numerical models, it remains exceedingly difficult to measure or model exposure times in the subsurface at the catchment scale. To approach this problem, we developed a unified modelling approach combining measured environmental proxies with an exposure time based reactive transport model. We measured groundwater age, nitrogen and sulfur isotopes, and water chemistry from agricultural wells in an unconfined aquifer in Brittany, France, to quantify changes in nitrate concentration due to dilution and denitrification. Field data showed large differences in nitrate concentrations among wells, associated with differences in the exposure time distributions. By constraining a catchment-scale characteristic reaction time for denitrification with water chemistry proxies and exposure times, we were able to assess rates of denitrification along groundwater flow paths. This unified modeling approach is transferable to other catchments and could be further used to investigate how catchment structure and flow dynamics interact with biogeochemical processes such as denitrification.


keyboard_arrow_right Titre : Exposure Time Distributions reveal Denitrification Rates along Groundwater Flow Path of an Agricultural Unconfined Aquifer
keyboard_arrow_right Type de documentation : Actes de colloque/congrès
keyboard_arrow_right Auteur(s) personne(s) : Pinay Gilles, Dreuzy Jean-Raynald De, Peiffer Stefan, Fleckenstein Jan H., Marçais Jean, Babey Tristan, Laverman Aniet, Aquilina Luc, Thomas Zahra, Abbott Benjamin W., Kolbe Tamara
keyboard_arrow_right Date de publication : 16 décembre 2016
keyboard_arrow_right Editeur(s) : American Geophysical Union
keyboard_arrow_right Tags thématiques : aquifère, pollution des eaux souterraines, hydrologie, nitrate, pollution de l'eau
keyboard_arrow_right Mots-clés libres : géochimie
keyboard_arrow_right Langue : Anglais
keyboard_arrow_right Collection : American Geophysical Union Fall Meeting

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