Geochemical models help to understand the influence of climate change and intensive groundwater extraction in the chemical composition of a tropical, maar lake in Central Mexico

The tropical maar Lake Alchichica lays in the high altitude (> 2,000 m a.s.l). The orographic shadow of the Sierra Madre Oriental generates a semiarid climate with a negative water budget (1 to 3) so the lake's water balance depends on groundwater. Nonetheless, the decreasing trend of the water level from 1959 on suggests a combined effect of climate change and increasing groundwater extraction (agriculture, urban). Applying geochemical models to explore the interaction between groundwater and surface water allow to identify the geochemical source of the reported increase in sulfate, magnesium, and chloride concentration in the lake water and its relation to climate change and intensive extraction of groundwater. Thirty-five groundwater samples were obtained from wells surrounding Lake Alchichica. Samples were analyzed for major ionic composition and trace elements. We generated a conceptual model of groundwater-surface water interaction and conducted inverse and evaporation geochemical models using the PHREEQC code. Geochemical models explore the water-rock processes between groundwater and geologic materials, understanding the chemical evolution of the groundwater flow system, and understanding the influence of groundwater chemical characteristics in the chemical composition of the lake. This investigation unravels how climate change and intensive groundwater extraction define the way in which: 1) groundwater influences the chemistry of the lake, and 2) to understand the chemical changes that have been reported in the lake.