Geochemical characterization of groundwater and submarine discharge in the south-eastern Sicily

The main results of a hydrogeochemical survey carried out during 2002–2003 along the coast of the south-eastern Sicily, which aimed at geochemical characterization of both groundwater chemistry and submarine groundwater discharge (SGD) in the area are presented. A general frame of chemical processes affecting the studied groundwater and SGD point out that most samples fall within the calcite-anhydrite-dolomite field (CAD). The chemical composition of the samples within the CAD triangle is essentially controlled by calcite, dolomite and gypsum dissolution, which are the main minerals of the carbonate rocks hosting the aquifers. An additional process evidenced in this study is a mixing with seawater. Nitrate is the most typical ion significantly disturbed in the groundwater chemistry influenced by agricultural activities. The strong correlation with SO42− indicates that the use of ammonium sulphate fertilisers is widespread in the study area. The K+ vs. NO3− diagram evidences a correlation occurring at lower and higher concentrations, and implies that there is not a common source of both nitrate and potassium, at least on a regional scale. High-phosphate concentration is found in submarine springs along the coast, specifically in the Donnalucata and Avola areas, while its content in inland wells is generally lower. Phosphate is also associated with high-bicarbonate contents in the Donnalucata area, suggesting its possible origin is phosphate-rich carbonate rocks, which are commonly outcropping in the area.