Characterizing Aquifers - Hydrogeology: Objectives, Methods, Applications - page 139

Figure 74 Discharge and chloride content after rainfall.
6.1.2 Effective rainfall signature. Example of the Fontaine de
Vaucluse (Mudry, 1987; Emblanch, 1997)
Infi ltration following a precipitation event has characteristic meteoric
tracers (chlorides) or pedogenic tracers (nitrates, organic carbon), and a
characteristic lack of tracers due to a long residence time (silica, magnesium).
The Fontaine de Vaucluse clearly shows magnesium dilution concomitant
with increasing chloride concentrations (Figure 75). Dissolved organic
carbon, or DOC (humic and fulvic acids), is another tracer leached from
soil, but one with a non-conservative behavior: it becomes mineralized over
time by transforming into CO 2 , then into bicarbonates. Its presence at the
outlets of a hydrosystem indicates a very brief transit time between soil and
emergence. Figure 75 shows the October discharge peak, which includes a
series of peaks with very brief residence times (a few days), separated by
water having undergone a decrease in its DOC content.