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)
Résumé
For 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.