Benthic Diatom Composition in Coastal Zone of Black Sea, Sasyk Reservoir (Ukraine)

Abstract

The Sasyk Reservoir is one of the largest seaside reservoirs in Ukraine, artificially maintained as a freshwater area including various floodplain areas. The Reservoir originated from an estuary to now being an almost freshwater reservoir. The diatoms (Bacillariophyta) in benthos were investigated for analyzing the coastal zone diversity of the Black Sea inside the borders of Ukraine. The indicated diatom composition was formed by 97 species (100 infraspecies taxa). Some rare marine and freshwater taxa were noted, as well as three species reported in Ukrainian territory for the first time (Navicula vandamii Schoeman et R.E.M. Archibald, Sellaphora difficillima (Hustedt) C.E. Wetzel, L. Ector et D.G. Mann, and Mastogloia laterostrata Hustedt). The bioindicative characteristics of the diatom composition testified to the freshwater condition of the reservoir. Changes to the salinity level of the Sasyk Reservoir were exposed due to the composition of benthic diatoms. The presence of mesohalobous species (7 taxa) acknowledges conditions that are typical for estuaries and mouths of rivers and reveals the salinity changes in the Sasyk Reservoir. Likewise, the prevailing number of oligohalobous diatoms (61 taxa) reveal presence of freshwater in the reservoir. The implementation of the Polish phytobenthos lake assessment method for the nearby Ukrainian Reservoir was conducted for the first time. The multimetric Diatom Index for lake values varied from 0.39 to 0.76, and revealed alterations in the status over the Sasyk sites, ranging from good, moderate, to poor. Thus, it may be concluded that the current ecological status relating to the composition of benthic diatoms of the reservoir located in the coastal zone of the Black Sea is evaluated as having a moderate status class with some exceptions.

Indication of Long-Term Changes of Algae Communities in a Hydrologically Transformed Estuary Sasyk, Black Sea, Ukraine

“…Therefore, 17 deep-water sites for phytoplankton sampling and 7 coastal sites for phytobenthos sampling were chosen [11]. To characterize the modern period of the Sasyk's existence, namely stage III, phytoplankton analysis conducted in 2013 and 2014 [19,20] was combined with the phytobenthos analysis conducted in 2018 [8]. For analysis of phytoplankton species composition, the sampling sites were evenly distributed around the Sasyk's surface area.…”

“…For phytobenthos investigations, sampling included seven sites that were mostly located along the shoreline of the water body to evenly cover all of its banks. The obtained lists of species for the modern period of the Sasyk's existence have already been published [8,19,20], and detailed methodological explanations of the sampling strategy and methods used for the collection and analysis of the algal material can be found in these works. In the present study, we focus on the analysis of published data for both the historical and modern periods of the Sasyk's existence.…”

“…At stage III, 278 species (287 ssp.) were found [8,19,20] (Appendix A, Table A1). Thus, we can analyze the created database of phytoplankton and phytobenthos species for tracking changes through a 40-year period covering the three stages of the Sasyk's existence from being an estuary to becoming a reservoir.…”

“…minuta, N. sociabilis, and Planothidium lacustre (Appendix A, Figure A4). Some additional photos of diatoms from the modern period were not included during the preparation of the paper about phytobenthos [8] and are presented in this work (Appendix A, Figures A1-A4).…”

“…The cause of anthropogenic transformation is the formation of a freshwater reservoir. As a result, it became a reservoir with the range of salinity that is common for freshwaters as well as brackish waters (0.49-2.31 g dm −3 ), contrary to an estuary, with salinity about 17 g dm −3 [8]. Nowadays, Sasyk is categorized as being one of the largest "seaside reservoirs" or "shallow lakes" in the world.…”