Environmental Change and Depositional Evolution of the Neretva River Delta (Croatia): A Multiproxy Sediment-Core Study

Karstic deltas preserve complex sedimentary records in which changes in element concentrations may reflect depositional conditions rather than contamination. This study investigated sedimentological and geochemical variability in surface sediments, four shallow cores, and the approximately 5 m long NER7 core from the Neretva River Delta (Croatia) to reconstruct changes in the depositional environment and assess possible anthropogenic influence. Sediment pH, organic matter content, grain size distribution, and total concentrations of 26 elements were determined, and element associations were evaluated using Spearman rank correlations and Al normalisation. Recent sediments ranged from coarse-grained, organic-poor coastal deposits to finer-grained, organic-rich marsh sediments. Core NER7 contained two compositionally distinct units separated by a transition zone at approximately 245–300 cm. The deeper unit was alkaline, organic-poor, and enriched in Ca and Mg, whereas the upper unit contained more organic matter and higher concentrations of Al-associated elements. These coordinated changes indicate a transition from an estuarine or lagoonal environment to a marsh and delta-plain setting during delta infilling. Most trace element variability was controlled by changes in aluminosilicate, carbonate, and organic matter components. Localised Cu and Pb enrichment may indicate limited anthropogenic inputs, but the available data cannot quantify anthropogenic contributions independently of natural sediment variability.