Analyzing spatial and temporal evolution of groundwater salinization through multivariate statistical analysis and hydrogeochemical facies evolution-diagram

The growing groundwater withdrawal rates in coastal aquifers in arid/semi-arid regions exacerbate seawater intrusion and saltwater upconing by causing groundwater salinization and potential adverse and cascading effects to related groundwater-depending systems. This study aims to highlight the dynamics of groundwater salinization in time and space by comparing the efficacy of statistical (hierarchical cluster and factor analyses) and hydrogeochemical (hydrogeochemical facies evolution) methods. Multi-temporal groundwater samples collected from the monitoring well network in the study area (Salento Aquifer, Puglia region, Southern Italy) have been considered to recognize such dynamics. By comparing the spatial and temporal evolution of water clusters, factor scores, and hydrogeochemical facies, the proposed methodological approach enables the identification of zones characterized by the low dynamics of freshening and intrusion processes (with invariant features during the investigated period), which correspond to groundwater recharge areas and zones subject to groundwater salinization respectively. On the contrary, a high spatial and temporal variability of salinization dynamics typifies the zones subject to alternation of groundwater characteristics. These results allow outlining of a preliminary hazard map related to groundwater salinization processes, which might be a useful tool for policymakers and stakeholders involved in groundwater management of coastal aquifers. Results suggest that generally, a thoughtful understanding of limitations concerning the aquifer heterogeneity and anisotropy, distribution and density of control points, and depth of sampling is crucial for handling the study outcomes, especially for the aims of management.