TUFA DEPOSITION IN A KARST STREAM AS AN INDICATOR OF WATER QUALITY (PAPUK NATURE PARK, CROATIA)

Tufa deposition and accompanying periphyton community were studied on artificial substrates, in karst Jankovac Stream (Papuk Nature Park, Croatia). Influence of environmental parameters on protozoans and metazoans in periphyton were assessed in two microhabitats, differed in flow velocity (fast 1.28 0.61 m s-1, medium 0.56 0.50 m s-1), and across different exposure period (one and two months). Measured environmental parameters indicated oligotrophic water condition. Samples collected in fast flow velocity reached significantly higher tufa deposition (0.26 0.04 mg cm-2 d-1) contrary to those in medium flow velocity (0.09 0.01 mg cm-2 d-1). Results of our study suggested that tufa deposition increased with temperature, flow velocity, amount of organic matter and algal biomass. In total, 26 taxa were identified on artificial substrate, among them 16 ciliate and 5 rotifer taxa. Most taxa recorded low abundance in periphyton, < 10 ind cm-2. Just few taxa achieved higher maximum abundances, i.e., ciliates: Chilodonella cucullulus (28 ind cm-2), Vorticella similis (68 ind cm-2) and rotifers: bdelloids (55 ind cm-2) and Dicranophorus forcipatus (64 ind cm-2). Periphyton community achieved statistically significant higher abundance in fast than in medium flow velocity microhabitats, with increasing effect through the longer exposure. We presume that oligotrophic conditions in karst running water facilitate tufa deposition. In this study we revealed microscopic freshwater organisms, often neglected in investigation, but very important in food webs as link to gastropods, crustaceans, insect larvae, juvenile and adult fish.