Geochemical characteristics of the Gacka River karstic springs (Dinaric karst, Croatia) with macroinvertebrate assemblages overview

Three karstic springs of the Gacka River were investigated: Tonkovica vrilo is included in the regional, and Klanac and Majerovo vrilo are included in the local water supply system. The purpose of the research was to investigate geochemical characteristics of the watershed with macroinvertebrate assemblages overview, type and water quality index (WQI) of the groundwater defining hydrochemical facies, presenting one of the most typical Dinaric karst areas in the world. Isotopic investigations were performed measuring the concentration of dissolved radon in the groundwater. The values ranged from 1.00 to 21.88 Bq L-1 which is much lower than the reference level between 100 and 1000 Bq L-1 set by the CD 2013/51/Euratom of 22 October 2013. According to the results of analyses of water from the investigated springs, only the values of microbiological indicators exceed the maximum allowed concentrations laid down by the Ordinance on compliance parameters and methods of analysis of water intended for human consumption [ Official Gazette No. 125 Croatian ordinance on compliance parameters and methods of analysis of water intended for human consumption (OG 125/2013), 2013]. WQI indicates an excellent water status. Hydrochemical facies belongs to the Ca-HCO3 type of water. The results show that the concentrations (mg kg(-1), d.w.) of nickel (80.80) and TN (5900) in the sediment exceed values of the possible toxic effect, while the concentrations of molybdenum (max. 20.30) exceed the value for disposal of dredged sediments. Samples of benthic macroinvertebrates were collected with 38 taxa recorded, dominated by crustaceans and snails. According to investigations, anthropogenic activity still does not affect the quality of groundwater and spring sediments.