## 3 Results
### Phytoplankton  
The peculiarities of phytoplankton in 2018 and 2019 are described in our previous papers [16; 55], and here is the integrated picture for all the periods of our study (2018-2020). During the period of study, we found 264 taxa of microalgae, belonging to 11 classes: Bacillariophyceae (111), Chlorophyceae (58), Trebouxiophyceae (21), Ulvophyceae (1), Conjugatophyceae (1), Eugelenoidea (20), Chrysophyceae (4), Cyanophyceae (34), Dinophyceae (12), and Imbricatea (1), and an uncertain taxon of flagellate (1). The contribution of different classes in the total phytoplankton diversity is shown in (Supplementary Materials Figure S4). The basis of taxonomic diversity was formed by diatoms, green algae, and cyanobacteria, which is usual for freshwater phytoplankton. The basis of phytoplankton biomass during the study period belongs to Bacillariophyta. There was no significant correlation between phytoplankton biomass and any of the measured hydrophonical or hydrochemical parameters (Supplementary Materials Figure S5). The regression analysis for the pairs of the key factors of phytoplankton development and biomass of microalgae also gives low values of correlation. Multiple regression coefficients are 0.367 for temperature and pH, 0.377 for temperature and DIP, 0.320 for temperature and DIN, 0.435 for temperature and silicates, 0.441 for pH and DIP, 0.356 for pH and DIN, 0.468 for pH and silicates, 0.326 for DIP and DIN, 0.368 for DIP and silicates, and 0.230 for DIN and silicates. For multiple factors of temperature, pH, DIP, DIN, and silicates, multiple regression coefficients figured as 0.406. The highest multiple regression coefficient of 0.494 is observed for a combination of three factors: DIP, silicates, and pH. The addition of temperature to these three factors did not change the value of multiple regression coefficients within three significant digits and replacing any of these factors with temperature makes the value of multiple regression coefficients lower.  
In 2020, we have also compared the parameters of the phytoplankton community in two sites of the Lower Driester-Palanca and Maialky (after the confluence of the Driester  
Figure 5: The ratio of the average concentrations of heavy metals and metalloids to their environmental quality standards (EQS) in bottom sediments in the lower reaches of Palanca and Maialky of the Driester River.  
with its arm Turunchuk). At Palanca, the average biomass was lower than at Maiaky (550 \(\pm\) 262 and 621 \(\pm\) 243 mg m\({}^{-3}\), respectively). For almost all the samples, the biomass in Maiaky was higher than in Palanca (Figure 6), but this difference did not exceed the standard deviation.  
The comparison of the taxonomic structure of the phytoplankton community at these two sites (Figure 7) shows the higher contribution of green algae to the total biomass at Maiaky station, especially in the spring and early summer period. The analysis of vertical distribution of phytoplankton shows no consistent difference in quantitative characteristics between surface and bottom layers (Supplementary Materials Figure S6), but in the summer period, the share of diatoms in the bottom layer was higher. Nevertheless, the data were not sufficient for detailed analysis.