Origin and hydrogeochemical processes in the salinization of a coastal aquifer in the Colombian Caribbean

ABSTRACT Coastal aquifers are affected by various processes that control the complex dynamics of salinization, such as the case of the coastal unconfined aquifer of the deltaic zone of the Sinú River, located around the Lower Sinú Coastal Zone in the Colombian Caribbean. In this fluvial-marine plain system, soil and groundwater salinization seriously limit the economic development supported by agriculture and ecosystem services. This study aims to characterize the origin of the hydrogeochemical processes and the major ions that control salinization in the local shallow alluvial aquifer. Using a combined approach of hydrogeochemical techniques and multivariate statistical analysis, 388 samples were collected from a monitoring database, between 2002 and 2008, and analyzed. Major ion concentrations (Cl⁻, HCO₃⁻, SO₄2⁻, Na⁺, K⁺, Mg2⁺, Ca2⁺), total dissolved solids (TDS), electrical conductivity (EC), pH, and distance to the coastline were evaluated. The results reveal two distinct groups of groundwater flows, differentiated by ion concentrations, salinity levels, and statistical correlations between the ions. A total of twenty five hydrochemical facies were identified, with Na-Cl, MixNa-Cl, MixMg-Cl, and Mg-Cl being the most dominant. The spatial distribution of these facies suggests a strong influence of both natural and anthropogenic factors. The origin of the ions varies among marine, lithological, and meteoric sources. The main hydrogeochemical processes responsible for mineralization include seawater intrusion and ion exchange reactions. These findings are essential for improving groundwater management strategies and mitigating salinization in vulnerable coastal environments.