Analysis of Hydrogeochemical Processes Regulating Groundwater Quality in a Tropical Agricultural Landscape of Northwestern Mexico

This study assesses the hydrochemical and water quality characteristics of the Mocorito River Aquifer (MRA), located in a tropical region with strong agricultural influence. Water data from seven sites of the aquifer, collected during 2012–2022, were used and evaluated through hydrogeochemical features, water quality index (WQI), and multivariate analysis to identify spatial and seasonal patterns, and anthropogenic effects. The results found low total nitrogen (9.7084 mg/L) but high mineralization and water hardness. High levels of sodium (up to 630.4 mg/L) and fecal coliforms (up to 24196 NMP/100mL) make the water unsuitable for both drinking and irrigation. Spatial and seasonal analyses showed heterogeneity among sites, with the greatest water quality deterioration in agricultural areas resulting from intensive fertilization and the leaching of soluble salts and fertilizer-derived ions (NO₃⁻, Cl⁻, SO₄²⁻, HCO₃⁻, Na⁺, Ca²⁺, Mg²⁺) into the aquifer due to excessive irrigation, and in urban areas from microbiological contamination. Hydrogeochemical assessment indicated that aquifer composition results from the interaction of natural processes (silicate and carbonate dissolution, ion exchange). Piper and USSL diagrams were used to characterize hydrochemical facies and evaluate irrigation suitability, while multivariate analysis demonstrated that groundwater quality in the MRA is controlled by the combined effects of geogenic processes, water–rock interactions, and anthropogenic influences. The MRA aquifer generally maintains good-to-moderate water quality, but localized zones show severe deterioration due to salinity and agricultural pollution, indicating the need for continuous monitoring and sustainable management.