ESTUARIES OF THE POLISH BALTIC COASTAL ZONE

Estuaries are dynamic ecosystems characterized by great and constant variability of physicochemical gra-dients and biological parameters. Considerable fluctuations in salinity levels, temperature, pH, concentra-tions of oxygen, nutrients and organic matter are quite natural in such water bodies. There are many estua-rine forms at the Polish Baltic Coast, including open-sea gulfs (the Gulf of Gdańsk and the Pomeranian Gulf), water bodies connected to the Baltic Sea (Lake Łebsko) and periodically closed water bodies con-nected to the Baltic Sea by channels or through river-mouths (Lake Jamno and Lake Gardno). The mouths of large rivers, like Odra and Vistula, also show features of estuaries. Estuaries perform a very important function of specific natural filters for a variety of chemical compounds contained in waters flowing through this area. In this way they form an effective buffer zone that prevents the penetration of toxic bio-logical substances into seawater. Key words: estuary, estuarine forms at the Polish coast, genesis of estuarie