Hydrogeochemical characterization from historical data of the groundwater flow system in the center of Mexico

The Cuitzeo Groundwater Flow System, located in central Mexico within a volcanic rock region, encompasses two of the largest lakes in the country, Lake Cuitzeo and Lake Pátzcuaro. These lakes are sustained by both surface water and groundwater discharges, playing a critical role in local ecosystems and the surrounding population.
Groundwater is particularly important for maintaining the lakes' existence. However, the behavior of the groundwater flow system in this region has not been described before.
This study compiles data from 170 groundwater sites within the system, collected during the years 1983, 1990, 1997, 1999, 2001, 2002, 2003, 2006, 2007, 2014, and 2015. The compiled parameters include temperature (T°C), pH, Total Dissolved Solids (TDS), and major ions (Ca2+, Mg2+, Na+, K+, SO42-, Cl-, HCO3-, CO32-, and NO3-). The compiled data were analyzed to study the historical behavior of the system, identify recharge and discharge zones, assess water-rock interaction processes, and trace the evolution of groundwater using hydrochemical diagrams such as Piper, Gibbs, and scatter plots.
The results highlight distinct chemical behaviors across the different zones of the study
area, with the most notable being ion exchange consistent with the weathering of volcanic silicates and interaction with lacustrine sediments. A key finding is the identification of a base-level discharge zone near Lake Cuitzeo. Water-rock interactions are the dominant process within the flow system, though some sites are influenced by precipitation and evaporation, and have a relation to the increased Lake Cuitzeo salinity that suggests a natural process of groundwater evolution within endorheic conditions.
This study is crucial as it offers valuable insights into the historical state of the groundwater flow system and highlights areas where additional data is needed to better understand its dynamics. For instance, the lack of data near Lake Pátzcuaro emphasizes the significance of this data compilation and underscores the need for further research in the region.