Some characteristics of the brackish slough Paluda

Abstract

       The hydrographic and biological conditions of the brackish slough Paluda in the vicinity of Rovinj were regularly investigated from 1961 to 1962.

       Communicating with the sea exclusively through underground caverns, the slough reveals considerable fluctuations of some hydrographic factors such as temperature, salinity, and O₂ saturation. In summer, water drains away from a large part of the slough and small quantities of sea water penetrate into it through the underground caverns at high tide. In winter and in early spring, on the contrary, the water level rises in the slough covering an area that is more than six times as large as in summer. This is due to a large supply of surface waters which causes considerable quantities of low salinity water to be discharged into the sea.

       The yearly cycle of many organisms depends on these fluctuating hydro­graphic conditions qualitative changes of plankton were studied in detail, and they were found to be the following (beginning with the winter season): Copepoda-Daphnia-Ostracoda-Oligochaeta-Copepoda. The yearly cycle of some bottom plants and animals is also discussed.