Combining hydrodynamics, hydrochemistry, and environmental isotopes to understand the hydrogeological functioning of evaporite-karst springs. An example from southern Spain

摘要

This work adopts a multicriteria approach, combining diverse karst hydrogeology techniques, to investigate the functioning of evaporite-karst systems, which are normally less studied due to the poor quality of their water resources. The applicability of using several methods was also verified. In view of previous experience at a pilot site within southern Spain, the natural responses of the main discharge point of the system of study (Lower Anzur spring) were controlled by continuous monitoring of the discharge rate, water temperature, and electrical conductivity. Water samples were collected for chemical analysis and for the determination of intrinsic fluorescence, water stable isotopes (delta O-18, delta H-2) and tritium (H-3) concentrations. Physico-chemical data were statistically examined applying principal component analysis (PCA) and trend analysis tests (Mann-Kendall and Sen's slope). The system shows a clear karstic functioning, highly dependent on concentrated recharge, and influenced by a limited drainage capacity of the conduit network. The piston-flow effects at the beginning of floods indicate a contribution to the drainage of deep ascending flows through the saturated zone. Subsequent drops in temperature and mineralization values in the water drained by the spring, as well as a recent infiltration deduced from the signature of intrinsic fluorescence and stable isotopes, point to a good hydrogeological connection from the recharge areas to the spring. Later restoration of the initial values of mineralization -in a much shorter time than those of temperature- reveals a faster geochemical evolution of the recently infiltrated groundwater, which may be a distinctive trait of evaporite karst aquifers. Lastly, the high solute content of the spring water in depletion conditions, with ascending trends of mineralization and temperature observed during several dry years as a consequence of lower recharge contribution, together with the tritium activity of sele