Response of phytoplankton and periphyton to the physical and chemical parameters in lotic area of a karstic River Krka

Net phytoplankton and periphyton from artificial substrate (plexy slides) were investigated on a vertical profile of travertine barrage lotic area of the River Krka, located in karstic region of the NW Dinarid Mountains (Croatia). Net phytoplankton samples were collected monthly during a year, at six depths. Periphyton samples were carried out after 30, 60, and 90 days of exposition during summer period at three depths. Plexy slides were placed parallel and perpendicular to the current velocity. The physical and chemical parameters were measured simultaneously. Seasonal distribution of net phytoplankton abundance showed two peaks, in June and March. The highest abundance was observed at depths of 5 and 10 meters. In periphyton community the highest cells density was observed after 60 days of exposition on horizontally placed surface, in epilimnion. During the research period 42 and 88 species were identified in phytoplankton and periphyton community, respectively. Main abundance constitution corresponded to the diatoms, in phytoplankton same as in periphyton. The canonical correspondence analysis (CCA) of the full data set indicated some separation of the data in ordination space based on seasons for plankton and days of exposition for periphyton. First three axes for plankton data explained 17.0 % and for periphyton data explained 25.9 % of the species variance. The most influential parameters associated with the first axis were: temperature, total phosphorus and dissolved oxygen for plankton, and total phosphorus, orthophosphates and conductivity for periphyton. Parameters that correlated with the second axis were nitrites and nitrates for plankton, and temperature and total nitrogen for periphyton.