Résumé
Hydrological signatures are metrics that quantify different aspects of global hydrologicalbehaviour (e.g. magnitude, extremes, timing of flow condition). In the case of karst aquifers,the high degree of variability of their hydrogeological response makes it difficult to generalisea single hydrogeological signature for a given site. Adding physico-chemical variables tohydrological signatures provides thus new opportunities to better understand the variabilityof their responses to rainfall events. The goal of this paper is to provide a methodologyfor characterizing water origin and transfer in karst aquifers at the flood-event timescale,by using an analysis of various high-frequency physico-chemical signatures that describestransfer of dissolved and suspended particulate matters. We computed descriptors of thephysico-chemical time series, including discharge (Q), electrical conductivity (EC), turbidity,and natural fluorescence (NF) of water. The study site is the Fontaine de Nˆımes karstobservatory (southern France), which is located in an urban and Mediterranean environment.On the basis of 27 major flood-events, we propose a flood typology based on hydrologicalconditions. We characterized pre-event and event water using EC changes as they revealwater residence time in karst. EC dilution depends linearly on peak flow (-100 μS/cm for +6m3/s), suggesting that a mixing process by surface waters controls most of the hydrochemicalresponse. Turbidity peak amplitude (0-150 NTU) depends on both peak of first derivativeof Qand flood type. NF peaks are found to be inversely proportional to initial dischargerates, except for summer events. A quantification of the contributions of 3 compartments(surface waters, unsaturated zone, and saturated zone) to spring discharge was performedon each flood-events using an End-member mixing analysis performed using EC and NFsignals. Results showed that the saturated zone is the main contributor for all flood events,but that contributions of the 3 compartments (60-80% for unsaturated zone; 5-20% forsurface waters; and < 5% for unsaturated zone) vary according to flood typology. Wepropose also a framework to identify the origin of water turbidity by means of informationson various signatures: pre-event and event water contributions (EC), intensity of sedimentmobilisation (peak of first derivative of discharge), unsaturated zone contribution (naturalfluorescence peak). The main results show that flood events with the highest turbiditypeaks (> 120 NTU) mobilise pre-event and event waters equally, and are characterizedby relatively ”young” age water during high water levels period. Flood events with lowerturbidity are characterized by pre-event waters of more or less older age according to theseason. Overall, this work highlights the benefit of combining physico-chemical signatures inaddition to hydrogeological ones to better characterize processes in complex aquiferss.