Multi-regression analysis between stable isotope composition and hydrochemical parameters in karst springs to provide insights into groundwater origin and subsurface processes: regional application to Lebanon

Abstract

Joint applications of isotope characterization using δ2H, δ18O and geochemical analyses have allowed for a better conceptualization of hydrological systems and helped in the evaluation and management of water resources. Processes of infiltration, and evapotranspiration (ETP), as well as mixing in the unsaturated zone, incur changes in the meteoric δ2H-δ18O signal that is transferred to groundwater during recharge. Previous studies on the isotopic composition of atmospheric precipitation highlight the importance of rainwater differentiation in terms of chemical composition and isotopic signature as a function of topographical and orographic variations as well as natural and anthropogenic impacts and identified altitude gradients for both δ2H and δ18O. In this work, a comparative correlative analysis of stable oxygen and deuterium isotopes was conducted on selected Lebanese springs. At the first stage, a hydrochemical analysis allowed the characterization of the springs and their clustering according to their predominant ionic content and aquifer units. Additionally, a multi-regression analysis reveals a relationship between hydrogen and oxygen isotopes and other easily measured parameters at the spring such as temperature, electrical conductivity, elevation, and easting and northing. The obtained relationship validated on a second campaign was attributed qualitatively to the extent and elevation of the spring catchment, the depth of flow, mixing, the snow effect, and residence time. Moreover, outliers characterized by a very large catchment area or allochthonous recharge could be outlined in the set of investigated springs. The results show that the stable isotopic signature indicative of recharge areas can be inferred based on easily measured spring parameters and can, therefore, help in the identification of protection zones and direct areas of spring recharge from a regional dataset. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.