Hydrodynamical changes and their consequences on groundwater hydrochemistry induced by three decades of intense exploitation in a Mediterranean Karst system

International audienc

Punctual and continuous estimation of transit time from dissolved organic matter fluorescence properties in karst aquifers, application to groundwaters of 'Fontaine de Vaucluse' experimental basin (SE France)

For about 10 years, environmental tracing development using dissolved organic matter (DOM) has been the subject of several studies. Particularly, the use of characterization techniques, like fluorescence emission-excitation matrices has enabled the identification of DOM sources and monitoring them within mainland or marine hydrosystems. Moreover, hydrogeologists have shown the significance of total organic carbon content used as a fast seepage tracer in karstic aquifers. The aim of this study consists in using DOM fluorescence signals to develop a transit time semi-quantitative tracer in heterogeneous hydrosystems. The Low-Noise Underground Laboratory (Vaucluse, France) cuts the network of Fontaine de Vaucluse (FV) karstic vadose zone randomly, and offers a special access to different unstructured dripwaters, with different hydrodynamic behaviour, inside its galleries, i.e. not hierarchical as in natural caves. Previous long-term hydrodynamic and hydrochemical studies allowed the understanding of their hydrogeological behaviour and the estimation of mean transit times. That is why this site is adequate to develop new transit time tracers. After identification of the different DOM sources (i.e. lithic and rendzic leptosols), fluorescence intensities monitoring from soil leachates and dripwaters, for certain excitation-emission wavelength pairs, allowed the development of punctual transit time tracing, by spotting infiltration periods of fluorescent compounds, and monitoring their transfer within a hydrosystem. A fluorescence index (humification index) and the mean transit time of each gallery groundwater, stemmed from previous hydrodynamic and hydrochemical studies, allowed the calibration of a logarithmic relationship. This one allows the development of a continuous transit time tracing method that estimates transit times without long-term studies. It has been tested on two springs of FV catchment basin, providing transit time estimations for karstic hydrosystems that do not present a mixture between recent and pluriannual waters

Evidence of an Early Phreatic and Confined Karst Phase in Minervois, South of France

International audienc

Monitoramento in situ de teste de traçadores: como distinguir a recuperação do traçador da composição natural

International audienceHydrogeological tracer tests are primarily conducted with fluorescent tracers. Field fluorometers make it possible to monitor tracers at very low concentrations (<1 ppb) and at high frequency. However, changes in natural fluorescence at a site resulting from variations of dissolved and suspended inorganic and organic material may compromise the measurement of useful signals, thereby limiting the chances of identifying or quantifying the real tracer recovery. An elevated natural signal can mask small concentrations of the tracer while its variability can give the impression of a false recovery. This article shows how the use of a combination of several continuous measurements at different wavelengths allows a better extraction of the natural signal. Field multispectral fluorometers were installed at two Mediterranean karst outlets; both drain carbonate systems but have different environmental conditions. The fluorometers functioned over several hydrologic cycles, in periods affected or not by artificial tracers, making it possible to observe natural signal variations at these sites. The optical properties of this type of field fluorometer were used to calculate the spectral response of the different optics of the measuring probe. These responses, superimposed on three-dimensional excitation/emission matrices produced from laboratory fluorescence measurements, allowed an understanding of what the fluorometer sees under natural flow conditions. The result is an innovative method for correcting artificial tracer results. This type of correction makes it possible to fine-tune the effect of natural background variation on tracer recovery curves for a clear identification of the tracer presence and a more precise quantification of its recovery

Carbon 13 of TDIC to quantify the role of the unsaturated zone: the example of the Vaucluse karst systems (Southeastern France)

International audienc

Geochemical evidence of water source characterization and hydrodynamic responses in a karst aquifer

International audienc

Transit Time Environmental Tracing from Dissolved Organic Matter Fluorescence Properties in Karstic Aquifers. Application to Different Flows of Fontaine de Vaucluse Experimental Basin (SE France)

International audienceFor about ten years, environmental tracing development using Dissolved Organic Matter (DOM) has been the subject of several studies. Particularly, the use of characterization techniques, like fluorescence Emission-Excitation Matrices (EEM), has enabled identification and monitoring of DOM sources within mainland or marine hydrosystems. Hydrogeologists have already shown the significance of Total Organic Carbon (TOC) used as fast seepage tracer in karstic aquifers. The aim of this study consists in using DOM fluorescence signals to develop a transit time quantitative tracer in heterogeneous hydrosystems. The Low-Noise Underground Laboratory of 'Rustrel - Pays d'Apt' (France) offers a special access to different kinds of unstructured karstic flows, cutting randomly through the fault network of 'Fontaine de Vaucluse' vadose zone. The hydrochemical monitoring of these flows since 2002 has allowed their behaviour to be well known, and therefore to calibrate a relationship between a fluorescence index (Humification IndeX) and their mean transit time. Finally, this relationship has been tested on two springs of 'Vaucluse' plateaus, giving good transit time estimations for hydrosystems which do not present mixture between recent and pluriannual waters