Throughout the world, river basins are directly or indirectly affected by human activities, reducing local and global biodiversity and preventing the ecosystem from properly functioning. Our research focused on the Irpin River basin (Ukraine), whose water bodies have experienced various impacts due to human activities, including the unexpected extremes caused by military operations in the catchment area: long-term flooding, disturbance of free flow, significant water level fluctuations, etc. The study hypothesized that the primary factors determining the structural and spatial distribution of quantitative indicators of microalgae and aquatic macrophytes are the result of various hydromorphological changes, that lead to changes in the physical and chemical parameters of the aquatic environment. Very high values of chlorophyll a in the water column (59–106 µg · L⁻¹), an increase in the abundance (number of cells) and biomass of algae (due to the predominance of certain groups in the transformed sections), as well as saprobic index were recorded in the sections of the Irpin River basin that underwent significant hydromorphological changes. Our results revealed a strong correlation between phytoplanktonic (in the water column) chlorophyll a levels and water temperature (r = 0.76, p < 0.001), as well as organic phosphorus and polyphosphate concentrations (r = 0.61, p < 0.01). ANOVA and Monte Carlo permutation tests in a Canonical Correspondence Analysis (CCA) showed that the abundance of different divisions of phytoplankton and phytobenthos were significantly and similarly related to several environmental variables. We observed a positive correlation between the number of cyanobacteria and the concentration of ammonium nitrogen, nitrites, and phosphorus compounds. An increase in dissolved organic matter in the water can explain the increase in the biomass of Dinoflagellata and Euglenophyta. Species richness and the cover values of the macrophytes also clearly reflected changes in vegetation activity in sections of the Irpin River caused by hydromorphological changes. The results indicated that long-term flooding had the most negative impact on macrophyte communities. At some sites, the impact was so severe that the number of macrophyte species was very low. The total number of macrophyte species showed a significant negative correlation with total suspended solids (r = −0.51, p < 0.05) and phytoplankton chlorophyll a concentration (r = −0.73, p < 0.001). Our results provide a scientific basis for predicting changes in riverine microalgal and aquatic macrophyte communities due to extreme hydrological events.

The river basin of Siversky Donets is of great scientific interest since this river runs through a territory with heavy industry (in particular, coal mining, chemical processing and metal industries). Within the basin, rivers of different sizes were explored (small, medium, large and extra-large) that flow through siliceous and calcareous rocks on the same elevation (lowland—below 200 m a.s.l.). Phytoplankton, as one of the Biological Quality Element, was used to perform the assessment of ecological status of the water bodies within the Siversky Donets river basin in 2019. The state monitoring program based on the updated approaches has been implemented in the river basin for the first time. The composition of phytoplankton species in the basin comprised 167 species (168 intraspecies taxa), mainly Bacillariophyta (63%) and Chlorophyta (22%) with the presence of other species (Cyanobacteria, Charophyta, Chrysophyta, Dinophyta and Euglenophyta). High species diversity and divisions amount are a distinctive property of the smaller rivers, while the bigger rivers show lower number of divisions. The “bloom” events, which are important ecological factors, were not detected in the Siversky Donets river basin. Algal species composition in plankton samples of the basin was identified and series of ecological parameters, such as habitat preferences, temperature, pH, salinity, oxygenation and organic water pollution according to Watanabe and Sládeček’s index of saprobity (S) trophic state and nitrogen uptake metabolism were analyzed. The ecological conclusions were also verified by a canonical correspondence analysis (CCA). The significance of the Canonical Correspondence Analysis (CCA) results was estimated of by a Monte-Carlo permutation test. The high concentrations of inorganic phosphorus compounds (permanganate index (CODMn)) and nitrite ions favored the diversity of Chlorophyta and Cyanobacteria diversity correlated with the levels of bicarbonate and CODMn. High diversity of diatoms was facilitated by the total amount of dissolved solids and chemical oxygen demand (COD). It was found that low water quality could be associated with conditions leading to predominant growth of the mentioned groups of algae. According to the analysis, the highest water quality was characterized by balanced phytoplankton composition and optimal values of the environmental variables. The sites with reference conditions are proposed for future monitoring.

The study aimed to conduct a hydromorphological assessment of the main types of surface water bodies (SWB) in the Irpin River basin and to determine the degree of change in the hydromorphological characteristics of water bodies in the areas affected by the war. The assessment was carried out based on the analysis of the results of expeditionary research in 2023–2024 using stock, literary, cartographic data, and space photographs according to the “Methodology of hydromorphological monitoring of surface water bodies of the categories ‘Rivers’ and ‘Lake’ adopted in Ukraine” (2019) and from considering the practice of conducting similar studies on other river basins in Ukraine and the EU. It was established that the studied areas belong to the I–IV class of hydromorphological condition; in particular, the II–III class prevails on small rivers, both I–II and IV classes are observed on medium ones, and large ones (the Irpin River in the lower and middle reaches) I–IV class with a slight predominance of II class. The main factors affecting the deterioration of the hydromorphological state are the regulation of flow by ponds and reservoirs, morphological changes in the riverbed and coastal zone, reclamation of hydrotechnical structures, and using floodplains for economic needs. Hydromorphological indicators before and after the impact of military operations were determined to assess the degree of impact of military operations. Changes in the HM condition were established in the destruction and subsequent restoration of bridges and hydraulic structures. The estuary of the Irpin River, where the HM class changed from II to IV, suffered the greatest military impact. Based on cluster analysis, groups of sites with similar hydromorphological conditions and the degree of military influence were selected. Differences in the HM condition in the main morphological zones of rivers—riverbed, coastal zone, and floodplain were evaluated.

This paper considers the changes in the structural characteristics and macrophyte underwood species diversity of the Kiliya Danube Delta as a detection of the edge effect when the environmental conditions are changing. A total of 27 species of water vascular plants were identified. Moreover, filamentous algae were found but their species and genus were not determined. Biodiversity changes were evaluated using the Shannon Index which integrates species richness and their uniformity in the group. The significance of the results was assessed by testing the null hypothesis which is to verify the absence of changes in the average values of the sample using the Student's t test. Transitional watercourses (channels) have the highest indicators of information diversity where the manifestation of the edge effect is more distinct. There were statistically significant differences between the Shannon index in the end of the branch and the channel, as well as between the channel and the beginning of the water body, at the level of p = 0.05 which indicates the strength of the edge effect in the sample. It is established that the edge effect is reliably displayed in the transition from lotic (delta branches) to lentic conditions (non-flowing reservoirs – "corners"). It is displayed in the form of increasing biological diversity, decreasing in the role of monodominant groups and also in increasing floating pleistophytes quantity. Also in the channels which connect a flowing stream and waterbody is the highest species diversity and the highest Shannon index. Under lotic conditions even in the places of branch ramification and at different distances from such branches, the manifestation of the edge effect is not statistically proven. Therefore, we cannot prove the existence of edge effect in these objects despite the fact that we observe a tendency to increase species diversity at the beginning and end of the watercourse. The ecological structure of macrophyte groups is practically unchanged within each individual watercourse along its entire length. The Ochakivsky branch is dominated by groups of high-grass helophytes and floating pleistophytes, in Starostambulsky by groups of high-grass helophytes and rooted gidatophytes, and in the Vodtochny by low-grass gelophytes and floating pleistophytes.