Evaluation of surface and groundwater quality and identification of saltwater sources by hydrogeochemical analysis in river Neretva coastal aquifer system

The river Neretva coastal aquifer system is the largest agricultural area along Croatia's Adriatic Sea coast. With the construction of an embankment, pumping stations, and melioration channels, a once-marshy area has been transformed into an area with favourable agricultural conditions.  Due to its proximity to the sea, numerous anthropogenic impacts in the region, and climate change, groundwater and surface water in the study area are presently significantly influenced by the salinization process. 
Multiple times per year, groundwater and surface water samples are collected to fully comprehend saltwater processes and the origin of saltwater in the study area. Within each sample, the concentration of major ions (K+, Na+, Ca+, Mg2+, Cl-, HCO3- and SO42-) is determined under laboratory conditions.
The analysis of major ions indicates that seawater intrusion is the primary source of salinization in both unconfined and confined aquifers. In contrast to unconfined aquifer, confined aquifer is minimally affected by precipitation and surface water regimes. In addition, samples of groundwater from unconfined aquifer are categorized into three groups based on their degree of contamination with seawater. The samples from the Diga area that are closest to the Adriatic Sea are most significantly influenced by the seawater. The groundwater quality in the Jasenska area varied significantly between dry and rain periods, whereas groundwater samples from the area of Vidrice revealed the lowest level of seawater contamination.   Neretva river surface water samples reveal the presence of a salt wedge, while river Mala Neretva samples indicate that river Mala Neretva is the primary source of freshwater in the study area during dry season.