Recharge processes and vertical transfer investigated through long-term monitoring of dissolved gases in shallow groundwater

JOURNAL OF HYDROLOGY

卷:560

Article

de Montety, V.¹  Aquilina, L.²  Labasque, T.²  Chatton, E.²  Fovet, O.³  Ruiz, L.³  Fourre, E.⁴  de Dreuzy, J. R.² 

[1] Univ Montpellier, CNRS, HSM, IRD, Montpellier, France

[2] Univ Rennes 1, OSUR Geosci Rennes, CNRS, F-35042 Rennes, France

[3] INRA, Agrocampus Ouest, Sol Agro & Hydrosyst Spatialisat UMR1069, F-35000 Rennes, France

[4] UVSQ, CNRS, IPSL CEA, LSCE,UMR8212, Saclay, France

关键词: CFCs;    SF6;    Noble gases;    Residence time;    Groundwater recharge processes;    Flow model;    Agricultural catchment;    Vadose zone;   

DOI  :  10.1016/j.jhydrol.2018.02.077

来源: Elsevier

【 摘 要 】

We investigated temporal variations and vertical evolution of dissolved gaseous tracers (CFC-11, CFC-12, SF6, and noble gases), as well as H-3/He-3 ratio to determine groundwater recharge processes of a shallow unconfined, hard-rock aquifer in an agricultural catchment. We sampled dissolved gas concentration at 4 locations along the hillslope of a small experimental watershed, over 6 hydrological years, between 2 and 6 times per years, for a total of 20 field campaigns. We collected groundwater samples in the fluctuation zone and the permanently saturated zone using piezometers from 5 to 20 m deep. The purpose of this work is i) to assess the benefits of using gaseous tracers like CFCs and SF6 to study very young groundwater with flows suspected to be heterogeneous and variable in time, ii) to characterize the processes that control dissolved gas concentrations in groundwater during the recharge of the aquifer, and iii) to understand the evolution of recharge flow processes by repeated measurement campaigns, taking advantage of a long monitoring in a site devoted to recharge processes investigation. Gas tracer profiles are compared at different location of the catchment and for different hydrologic conditions. In addition, we compare results from CFCs and H-3/He-3 analysis to define the flow model that best explains tracer concentrations. Then we discuss the influence of recharge events on tracer concentrations and residence time and propose a temporal evolution of residence times for the unsaturated zone and the permanently saturated zone. These results are used to gain a better understanding of the conceptual model of the catchment and flow processes especially during recharge events. (C) 2018 Elsevier B.V. All rights reserved.

【 授权许可】

Free