Relative importance of time, land use and lithology on determining aquifer-scale denitrification

Tamara Kolbe (1) , Jean-Raynald De Dreuzy (1) , Benjamin W. Abbott (2) , Jean Marçais (1) , Tristan Babey (1) , Zahra Thomas (3) , Stefan Pfeiffer , Luc Aquilina (1) , Thierry Labasque (1) , Anniet M. Laverman (2) , Jan H. Fleckenstein (4) , Philippe Boulvais (1) , Gilles Pinay (5, 2)

1 GR - Géosciences Rennes
2 ECOBIO - Ecosystèmes, biodiversité, évolution [Rennes]
3 SAS - Sol Agro et hydrosystème Spatialisation
4 Department of Hydrogeology [UFZ Leipzig]
5 OSUR - Observatoire des Sciences de l'Univers de Rennes

Geophysical Research Abstracts Vol. 19, EGU2017-14279, 2017 EGU General Assembly 2017 © Author(s) 2017. CC Attribution 3.0 License. Relative importance of time, land use and lithology on determining aquifer-scale denitrification Tamara Kolbe (1), Jean-Raynald de Dreuzy (1), Benjamin W. Abbott (2,3), Jean Marçais (4,1), Tristan Babey (1), Zahra Thomas (5), Stefan Peiffer (6), Luc Aquilina (1), Thierry Labasque (1), Anniet Laverman (3), Jan Fleckenstein (7,8), Philippe Boulvais (1), and Gilles Pinay (3) (1) OSUR, CNRS, UMR 6118, Géosciences Rennes, Université de Rennes 1, Rennes, France , (2) Michigan State University, Department of Earth and Environmental Sciences, East Lansing, USA, (3) ECOBIO, OSUR, CNRS, Université de Rennes 1, Rennes, France, (4) Agroparistech, 16 rue Claude Bernard, Paris, France, (5) Agrocampus Ouest, Sol Agro et Hydrosystème Spatialisation, Rennes, France, (6) Bayreuth Center of Ecology and Environmental Research, Germany, (7) UFZ-Helmholtz Centre for Environmental Research, Leipzig, Germany, (8) Water and Earth System Science Competence Cluster (WESS), Tübingen, Germany Unconfined shallow aquifers are commonly contaminated by nitrate in agricultural regions, because of excess fertilizer application over the last decades. Watershed studies have indicated that 1) changes in agricultural practices have caused changes in nitrate input over time, 2) denitrification occurs in localized hotspots within the aquifer, and 3) heterogeneous groundwater flow circulation has led to strong nitrate gradients in aquifers that are not yet well understood. In this study we investigated the respective influence of land use, groundwater transit time distribution, and hotspot distribution on groundwater denitrification with a particular interest on how a detailed understanding of transit time distributions could be used to upscale the point denitrification measurements to the aquifer- scale. We measured CFC-based groundwater age, oxygen, nitrate, and dinitrogen gas excess in 16 agricultural wells of an unconfined crystalline aquifer in Brittany, France. Groundwater age data was used to calibrate a mechanistic groundwater flow model of the study site. Historical nitrate inputs were reconstructed by using measured nitrate concentrations, dinitrogen gas excess and transit time distributions of the wells. Field data showed large differences in denitrification activity among wells, strongly associated with differences in transit time distribution. This suggests that knowing groundwater flow dynamics and consequent transit time distri- butions at the catchment-scale could be used to estimate the overall denitrification capacity of agricultural aquifers.

Domains: Sciences of the Universe [physics]; Earth Sciences; Hydrology; Sciences of the Universe [physics]; Earth Sciences; Geochemistry

Tamara Kolbe, Jean-Raynald De Dreuzy, Benjamin W. Abbott, Jean Marçais, Tristan Babey, et al.. Relative importance of time, land use and lithology on determining aquifer-scale denitrification. European Geosciences Union General Assembly 2017, Apr 2017, Vienne, Austria. Geophysical Research Abstracts, 19, pp.EGU2017-14279, 2017. ⟨insu-01534021⟩