A New Groundwater Classification for Managing Seawater Intrusion in the Mediterranean Area
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Groundwater salinization in coastal aquifers is primarily driven by seawater intrusion. However, attributing salinization exclusively to seawater intrusion may overlook other potential sources. Understanding whether salinization stems from seawater intrusion and identifying its onset are essential for effective groundwater management, yet there are no universally established threshold values for common indicators like chloride. This study introduces a novel groundwater classification based on 1,662 groundwater samples from five Mediterranean coastal aquifers in Greece, Italy, Turkey, and Tunisia. Despite their differences in size, geological formations, permeability, and salinization sources, these aquifers share common hydrogeochemical challenges. Cumulative probability plots for chloride and total dissolved solids (TDS) were used to establish a threshold for the onset of seawater intrusion. Findings highlight chloride as a reliable non-reactive tracer for seawater intrusion, whereas TDS, being reactive, is less dependable. A chloride concentration of 200 mg/L was identified as the salinization threshold, corroborated by the newly proposed salinization facies classification. The findings also underscore the limitations of using TDS or electrical conductivity (EC) as standalone indicators of salinization. Furthermore, an analysis of nitrate and sulphate concentrations reveals that freshwater in coastal aquifers (Cl < 200 mg/L) are often affected by anthropogenic salinization rather than seawater intrusion. The presence of these pollutants indicates significant contributions from agricultural activities, wastewater infiltration, and other anthropogenic sources. This insight challenges the conventional focus on seawater intrusion as the primary concern for groundwater quality, emphasizing the need for comprehensive assessments that consider multiple sources of salinization. The proposed classification and threshold provide a robust framework for groundwater monitoring and sustainable management across Mediterranean vulnerable coastal aquifers.