Elucidating heterogeneous nitrate contamination in a small basement aquifer. A multidisciplinary approach: NO isotopes, CFCs-SF6, microbiological activity, geophysics and hydrogeology.

Nitrate contamination of groundwater remains a major concern despite all the measures and efforts undertaken over the last decades to protect water resources. We focused on a small catchment in Brittany (France) facing nitrate pollution with concentrations over the European drinking water standard of 50 mg.L.

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

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 NO decreases ranging from 0.3 to 0.

Autotrophic denitrification supported by biotite dissolution in crystalline aquifers: (2) transient mixing and denitrification dynamic during long-term pumping.

We investigated the mixing and dynamic of denitrification processes induced by long-term pumping in the crystalline aquifer of Ploemeur (Brittany, France). Hydrological and geochemical parameters have been continuously recorded over 15 boreholes in 5km on a 25-year period. This extensive spatial and temporal monitoring of conservative as well as reactive compounds is a key opportunity to identify aquifer-scale transport and reactive processes in crystalline aquifers.

Groundwater Isolation Governs Chemistry and Microbial Community Structure along Hydrologic Flowpaths.

This study deals with the effects of hydrodynamic functioning of hard-rock aquifers on microbial communities. In hard-rock aquifers, the heterogeneous hydrologic circulation strongly constrains groundwater residence time, hydrochemistry, and nutrient supply. Here, residence time and a wide range of environmental factors were used to test the influence of groundwater circulation on active microbial community composition, assessed by high throughput sequencing of 16S rRNA.

Impact of climate changes during the last 5 million years on groundwater in basement aquifers.

Climate change is thought to have major effects on groundwater resources. There is however a limited knowledge of the impacts of past climate changes such as warm or glacial periods on groundwater although marine or glacial fluids may have circulated in basements during these periods. Geochemical investigations of groundwater at shallow depth (80-400 m) in the Armorican basement (western France) revealed three major phases of evolution: (1) Mio-Pliocene transgressions led to marine water introduction in the whole rock porosity through density and then diffusion processes, (2) intensive and rapid recharge after the glacial maximum down to several hundred meters depths, (3) a present-day regime of groundwater circulation limited to shallow depth.