Groundwater recharge by high-salinity lake water in a density-driven flow dominated system: an isotopic approach

Petrola Lake is a terminal lake located in the discharge zone of an endorheic basin. Terminal lakes may be responsible for a significant amount of recharge from evaporated saline water, increasing the salinity of the shallow groundwater. The purpose of this paper is to evaluate the interaction between groundwater and saline water from Petrola Lake in order to improve the knowledge of groundwater recharge processes by density-driven flow (DDF) in terminal lakes. To achieve this goal, hydrochemical (chloride concentration) and stable isotope (δ18 O and δDH2O ) data were used. The isotopic composition of 190 groundwater and surface water samples collected between September 2008 and July 2015 provide a regression line (δDH2O = 5.0·δ18 O – 14.3‰, R2 = 0.95) consistent with dominant evaporation processes. In the basin, groundwater recharge is mainly produced by Atlantic-derived precipitation. In the lake, isotope data suggested that the loss of water occurred at humidity values between 60% and 75%. The saline boundary layer is formed at elevated salt concentrations. Leakage from the lake to the underlying aquifer would take place with salinities from 1.24 g/cm3 by means of the DDF. This study contributes to better understand the role of DDF in terminal lakes.