The structure of phytoplankton of the karst Lake Zadovzhe (Ukraine)

Abstract

The paper presents the results of studies dealing with phytoplankton indicators of Lake Zadovzhe, located in the northwestern part of Rivne region in Volyn Polissia (June–October, 2022). 76 species of algae have been identified in the lake phytoplankton, represented by 77 intraspecific taxa belonging to 62 genera, 39 families, 26 orders, 12 classes and 8 divisions. The floristic spectrum of planktonic algae is formed by the divisions Chlorophyta (32.9% of the total number of species), Bacillariophyta (30.3%) and Cyanobacteria (15.8%). The number of phytoplankton in Lake Zadovzhe varies from 516 thous. cells/dm³ (October) to 5614 thous. cells/dm³ (August), and the biomass varies from 0.3048 mg/dm³ (October) to 0.8246 mg/dm³ (June). The Shannon index varies within 1.52–4.00 bits/mg for biomass and 2.11–3.63 bits/sp for abundance. The saprobity index ranges from 1.49 to 2.27, which corresponds to water quality classes II–III. The leading role at the class level belongs to Bacillariophyceae, Chlorophyceae, Cyanophyceae and Trebouxiophyceae, at the orders level belongs to Sphaeropleales, Naviculales, Chroococcales, Cymbellales and Desmidiales, at the families level belongs to Naviculaceae, Microcystaceae, Scenedesmaceae, Desmidiaceae, Euglenaceae, Hydrodictyaceae, Selenastraceae, Schroederiaceae, Oocystaceae, Cymbellaceae, Ulnariaceae and Aphanizomenonaceae, at the genera level belongs to Schroederia Lemmermann, Staurastrum Meyen ex Ralfs та Navicula Bory. The phytoplankton core of Lake Zadovzhe is formed by planktonic and planktonic-benthic species, indifferent in terms of water saturation with oxygen and rheophilicity, characteristic in relation to water temperature, pH of the environment and halophyte, and mesoeutrophic in terms of trophic level. Among the species-indicators of organic water pollution, saproxenes (according to the Watanabe system) and beta-mesosaprobionts (according to the Pantle-Buk system (modified by Sladechek) predominate. The water quality of Lake Zadovzhe varies from clean to moderately polluted.