Dataset on hydrogeochemical characteristics of spring and surface waters in the complex karst catchment area of Southern Dalmatia (Croatia) and Western Herzegovina (Bosnia and Herzegovina).

Large and complex karst catchments, like the one in Southern Dalmatia (Croatia) and Western Herzegovina (Bosnia and Herzegovina), are fragile environments requiring careful protection and sustainable water resources management. Understanding the processes that influence karst aquifer water chemistry is essential for the effective protection of water quality and quantity, ensuring sustainable resource availability and minimizing vulnerability to contamination. A hydrogeochemical dataset comprising over 30 groundwater (springs) and surface water samples, was collected in this cross-border catchment area from September 2013 to September 2020, accounting for seasonal variations. Parameters such as Ca, Mg, Na, K, Cl, NO and SO were analysed using atomic absorption, spectrophotometry and ion chromatography at the Croatian Geological Survey's Hydrochemical Laboratory. Alkalinity was measured through volumetric titration and in-situ pH, electrical conductivity (EC), and temperature (T) were measured using a multi-parameter probe. Additionally, stable sulphur isotope 34 (δS) analysis was conducted on ten samples collected during two hydrological extremes (April and October 2019) using an IRMS analyser at the Jožef Stefan Institute in Slovenia. These data provides a baseline assessment of the hydrogeochemistry of the area, facilitating research on isotope hydrology, particularly δS studies. It could also be used in implementing measures to protect and safeguard groundwater, assess its vulnerability to contamination, and improve existing catchment recharge zones.