Robert Lončarić

Influence of submarine groundwater discharge on seawater properties in Rovanjska-Modrič karst region (Croatia)

Coastal karst aquifers are dynamic hydrogeological systems with substantial hydrological, geomorphological and ecological impacts on the marine and coastal karst ecosystems, mostly induced by the submarine groundwater discharge (SGD). This paper presents complex hydrogeological settings of the Rovanjska-Modrič coastal karst region on the eastern Adriatic coast characterized by: (1) high temporal and spatial variations in seawater properties; (2) significantly reshaped coastal bottom morphology, and (3) plethora of associated biocenoses from fresh water, brackish, marine and cave assemblages. With the aim of resolving spatiotemporal interconnections of SGD and marine environment changes, we conducted field prospection and seasonal measurements of different water properties on- and off-shore. Obtained results pointed to: (1) the composite recharge system consisting of numerous sinking rivers in the distant hinterland (with different climate settings) and local precipitation input; (2) specific discharge settings highly governed by a complicated karst conduits network, the hydrological situation in the hinterland and local meteorological conditions, i.e. one system that permanently feeds coastal and probably submarine springs, while the other operates periodically; (3) disturbed winter isothermy and three-layered summer stratification of the seawater column, and (4) slightly changed trophic settings. All of that is the consequence of extreme heterogeneity of the coastal karst aquifer, characteristic for the eastern Adriatic coast.

Groundwater quality in selected caves in Ravni kotari (Croatia)

Complex mechanisms of pollution transport in karst underground and the fact that contaminated cave water can be a health hazard if used for human consumption, imposes the need for monitoring the cave water quality. In order to determine groundwater quality, water samples were collected in four caves in Ravni kotari (Croatia) and analyzed for microbiological and chemical indicators of pollution. Microbiological analyses showed increased concentration of various coliform bacteria at all four locations. Probable sources of pollution are inadequately built septic tanks in nearby villages and bat guano in caves with bat colonies. Chemical analyses indicated values of possible pollutants to be much lower than the permitted values, which reflects the fact that agriculture, as a frequent source of chemical pollution in rural regions, is not as developed as it used to be, thus posing no serious threat to the groundwater quality.