What can we learn about hydrochemical dynamics of streamwater during flood events in a forested karstic catchment from the Pyrenees Mountains (Southwestern France)?
Résumé
Hydrological variations hold a significant influence over the water chemistry in the karst systems within the critical zone. In this context, the Baget Catchment (BC) was monitored at highresolution over two hydrological years. The high-frequency survey at the outlet of BC displayed multiple hydrochemical patterns in response to hydrological variations, mixing water sources, and biogeochemical processes. Among the major elements, sulfate exhibited the widest relative variation during flooding and showed a significant dilution, whereas calcium and bicarbonate revealed a chemostatic behavior as a result of carbonate dissolution in the karst. Hysteretic analysis evidenced the control of different hydrological reservoirs over the stream transport processes of dissolved elements. The concentration of dissolved organic carbon increased during the hydrograph rising limb and was controlled by surface runoff. The relationships between Ca 2+ and HCO3concentrations and stream-discharge exhibited hysteresis patterns with counterclockwise loops, unlike all other elements, due to the carbonate weathering by biogenic CO2-rich water. Finally, highfrequency sampling during storm events improved the understanding of the factors controlling the hydrochemical dynamic of the Baget stream water. The relative contributions of the karst and epikarst zones, of rainwater, as well as the role of different biogeochemical processes and the hydrological conditions were highlighted.
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