Continuity and Discreteness of the Communities of Hydrobionts in the Lotic-Lentic Ecosystem of the Danube River Delta: Phytoplankton

Abstract

The paper deals with the patterns of continuity and discreteness of the main abiotic parameters and phytoplankton in the transboundary lotic-lentic aquatic ecosystem, including the branches of the Danube River, the Danube - Sasyk canal, and the Sasyk Reservoir, in autumn and winter periods. Water temperature, dissolved oxygen content, and pH are characterized by spatial continuum, whereas water salinity - by discreteness (fresh water is registered in the branches and canal and brackish water - in the reservoir). Local discreteness conditioned by the difference in the structure of dominant complexes (polydominant complexes - in river branches and oligodominant complexes - in the canal and reservoir) is registered with a spatial continuum of phytoplankton, which manifests itself in a predominance of plankton forms of diatoms, green, and blue-green algae. Phytoplankton cell numbers and biomass are typical of mesotrophic (delta branches) and hypertrophic (the canal and reservoir) ecosystems, whereas oligodominant and polydominant complexes are responsible for high information diversity belonging to essential phytoplankton adaptation characteristics.