Csaba Berta

Duhok Dam is a key multipurpose reservoir in northern Iraq that is increasingly exposed to ecological pressures arising from rapid population growth, climate variability, and localized anthropogenic pollution. In this study, we investigated the seasonal and spatial variability of phytoplankton communities and associated physicochemical variables to evaluate water quality conditions and to assess the reliability of phytoplankton communities as bioindicators of environmental stress. The samples were collected six times over nine months in 2021; 36 samples were collected from six sampling stations representing different pollution sources, across four distinct seasons. Multivariate analyses (PCA) combined with statistical testing revealed pronounced seasonal differentiation in both biological and physicochemical variables (ANOSIM, p < 0.0001). Spring conditions were shaped by precipitation-driven nutrients. This favored mixotrophic phytoplankton, especially Euglena sp. Conversely, summer thermal stratification promoted warm-adapted, pollution-tolerant taxa, such as Oscillatoria sp. and Peridinium cinctum . There was also marked spatial heterogeneity across the reservoir. Sites with untreated domestic wastewater had elevated COD _SMn and NO ₃ -N concentrations and were dominated by pollution-tolerant diatoms like Nitzschia acicularis . Areas impacted by natural sulfur springs hosted distinct phytoplankton assemblages, including Merismopedia sp. and Navicula sp., highlighting the influence of local geochemical conditions. Overall, our results demonstrate that the phytoplankton community structure responds rapidly and sensitively to both anthropogenic and natural stressors, highlighting its value as an integrative bioindicator of reservoir water quality. This study provides a conceptual basis for incorporating phytoplankton-based biological monitoring into sustainable reservoir management and water quality assessment frameworks in semi-arid regions.

Increasing pollution of aquatic ecosystems due to anthropogenic activities underscores the urgent need for effective water quality monitoring. This study evaluates the use of fish scales from chub (Squalius cephalus) and nase (Chondrostoma nasus) as non-invasive bioindicators of trace and macroelement pollution in the Maros/Mureș River. We conducted qualitative and quantitative elemental analyses using X-ray fluorescence (XRF) and inductively coupled plasma optical emission spectrometry (ICP-OES). Scanning electron microscopy (SEM) revealed distinct scale structures among the species studied. Concentrations of Ca, K, Mg, Na, P, S, Al, Ba, Cu, Cr, Fe, Mn, Sr, and Zn were measured by ICP-OES. Our findings indicate significant variability in elemental accumulation in fish scales, supporting their potential use as bioindicators of environmental pollution, with variability depending on the ecological characteristics of the species. This methodology offers promising applications for modern interdisciplinary monitoring programs.

We investigated the effect of land use based on the dominant phytoplankton and physical-chemical variables in the different areas of the Tigris River, within the city of Mosul. Agricultural and urban activities have a significant impact on the water quality of the river. Regardless of physical and chemical variables, phytoplankton act as a bio-indicator of water quality due to their fast and sensitive response to changes in the environment. Our research was conducted in the Tigris River within the city of Mosul by examining the phytoplankton species and the physical-chemical variables at 16 sites during each vegetation period. Point and non-point source pollutants have affected the Tigris River within the city of Mosul, getting into the river from upstream through agricultural activities and by urban activities in the middle section of the city, respectively from both banks. Based on our results, we observed the highest phytoplankton abundance during the October sampling periods, while the lowest occurred during the July sampling period, which was associated with maximum water temperature and absence of rain. According to our study, land use (e.g., agricultural, and urban activities) greatly affected the dominant phytoplankton species and physical-chemical variables of the Tigris River. Oscillatoria sp. dominated all seasons in the agricultural region, while at the same time, we observed an increase in the number of phytoplankton species caused by the nutrient availability upstream on the river. The effects of climate have very significant and characteristic effects in this area, which basically determine the community of organisms and the water quality; the effects resulting from anthropogenic activity significantly modify this. Based on our investigation, in the part of the Tigris River connected to Mosul, we found a clear connection between the pollution caused and the effects of different land uses, through the examination of the algal community and physical-chemical variables in different periods of the year.

Cladocerans are biological indicators of environmental changes. Their remains provide information on past changes in lake environments. We studied the correspondence between contemporary Cladocera assemblages and their subfossil remains from an oxbow lake. We sought to demonstrate that there were differences among the various sites of an oxbow lake with different utilization based on contemporary and subfossil Cladocera assemblages and physical–chemical variables. The oxbow lake’s two sides are used as fishing sites, where angling is the main activity. The middle site of the lake is under nature protection with high macrovegetation coverage. Contemporary and subfossil Cladocera assemblages were sampled from 21 sampling sites along the oxbow lake. Our research showed that the subfossil Cladocera assemblages had higher species richness and densities (36 taxa) than the contemporary species (29 taxa). We found one species of the Polyphemidae family only in the contemporary assemblage. Among the sites, Cladocera assemblages differed in their species composition and density. The highest densities were found in the second fishing site due to the appearance of the small-sized Bosmids. The relationship between Cladocerans and the physical–chemical variables showed that some variables, such as chlorophyll-a, biological oxygen demand, dissolved oxygen, copper, phosphide, and organic matter content, significantly affected Cladocera composition. We found that the subfossil Cladocera assemblage was significantly more diverse and abundant than the contemporary one, indicating that an integrated sampling may be sufficient to provide better results on the total species composition of the water body.

In our work, we sought to answer whether we find differences among the various zones of an oxbow lake with different land uses based on physico-chemical variables and dominant algal plankton species. The two ends of the oxbow lake are bordered by settlements, and near them there are open water areas where fishing is the major utilization form. Between the two open water areas we find a protected area with a large aquatic plant coverage and two transition zones towards the open water areas. The oxbow lake receives periodic water replenishment only at one end from one of the open water areas. During summer—due to the lack of rain—the water of the oxbow lake is used for irrigation in the surrounding arable land, so the water level fluctuation can be significant in the riverbed. Our study was performed within a vegetation period of spring, early summer, mid-summer, and fall. In connection with the ecological classification of a smaller water body, studies on the physical and chemical properties of the water and the composition of the algal plankton are usually carried out in few places and relatively infrequently. The characteristics of a water body are also influenced by seasonal changes, which can be the changes in the extent of vegetation coverage, the way land is used and the possibility of water replenishment, to which the algal community usually responds with changes. Based on our study, it can be said that even in a relatively small water body, we found a large differences based on the chemical and physical properties of the water and the characteristic algal species. Open water zones, areas with large macrovegetation coverage, and the transition zones were separated from each other.

One of the main threats of our time is the increasing water demand not only globally, but also locally. These are often met at the expense of ecological water demand, jeopardizing the structural and operational conditions necessary to maintain good ecological status in aquatic and wetland habitats. This is why it is of great importance to explore possible water retention options. In 2019, based on the long-term data series on the water level of River Tisza, we studied the frequency and extent of flooding in the floodplain between Tiszabercel and Gávavencsellő, where there are valuable wetlands, including a ‘sanctuary’-type backwater. This was necessary because recently the floodplains have undergone negative changes. Their water volume has gradually decreased, their valuable wildlife has become rarer, some of them have completely dried out in the autumn and even one of them has burned out. From the analysis of the examined 48-years data, it could be concluded that flooding was relatively frequent in the sampled area, but the extent of water coverage had no significant effect either in space or time. It was also found that only water levels above 700 cm (based on the water meter of Tiszabercel, 98.36 mBf) could adequately ensure that the water bodies are filled up and flushed out. However, there is little chance of this, because of four reasons: (1) water levels of this height are becoming rare; (2) the duration and height of high water levels are mostly short in time; (3) water levels of several water bodies are artificially decreased; (4) the drainage effect of the River Tisza – which has been significantly incised after the river regulation – prevails in the area. Due to all, in the future, there would be a great need to maintain the water levels in the floodplain wetlands as efficiently as possible after the floods – for which we have made specific proposals for the places and methods to preserve the ecologically necessary amount of water.

Here we report the results of our decades-long study on epiphytic communities from two tributary systems of the Szigetköz section of the Danube River. The main goal of the investigation was to detect changes in the epiphytic communities at structural (core species, changes in the relative abundance of common species) and functional (trait changes) levels as a result of the most important anthropogenic effects on Szigetköz, i.e., hydro-morphological modifications. We also examined the impact of rehabilitation on the tributary systems in terms of ecological potential. We discovered that mainly motile diatom species characterized the epiphyton due to reduced water volume were introduced into the tributary system after the diversion of the Danube. The ecosystem stabilized in the rehabilitated section, while the non-rehabilitated section showed a worsening tendency, mainly in the parapotamic branches. Our long-term data sets may provide a good basis for comparisons of different aquatic ecosystems, to define changes in the abundance of core species and in the structure of community in response to different anthropogenic pressures. It is fundamental to determine adaptive traits in assessing the impact of global warming stressors on biodiversity.

During our work, we investigated the physical and chemical variables of a small surface watercourse to investigate how different anthropogenic effects affect its water quality. Along this small watercourse, there are well-separated areas that are affected by various anthropogenic effects. In addition to its origin and branches, in many places it is surrounded by agricultural land with insufficient buffer zones, which burdens the small watercourse with nitrogen and phosphorus forms. In the lower stages, artificial damming inhibits the natural flow of the Tócó Canal, thereby creating eutrophicated stagnant water areas. This is further strengthened by, in many cases, illegal communal and used water intake that further burdens the small watercourse. Considering the experience of our investigation, it can be stated that the examined small watercourse could barely suffer human impacts, and it could be described with great heterogeneity using physical and chemical variables. We experienced that this heterogeneity caused by anthropogenic effects appeared in all hydrologic states and seasons. Furthermore, our research showed that these small watercourses had such high heterogeneity that their monitoring and examination should be taken just as seriously as when it comes to larger watercourses.

Studying contemporary and subfossil Cladocera (Crustacea) communities, we explored the effect of top-down stressors on the cladoceran communities; we are also interested in the coherence of the contemporary and subfossil communities. The studied Cibakháza oxbow lake is in E Hungary, on the left-floodplain of the River Tisza; it is a large, long, and shallow oxbow lake. Three areas of the oxbow lake were distinguished based on the strength of top-down stress: protected area with low top-down stress, biomanipulated area with high top-down stress, and recreational area with moderate top-down stress. Altogether, we identified 28 taxa in the contemporary and subfossil communities in the oxbow lake. We found that the species number of the contemporary Cladocera communities was lower (protected area: 13; biomanipulated area: 9, and recreational area: 14) than in the subfossil communities (protected area: 20; biomanipulated area: 16, and recreational area: 14). Among the environmental variables, we observed differences between the protected and biomanipulated area, while the recreational area showed a transition. Species number, abundances, and Simpson diversity also showed the effect of the fish introduction. There were no differences in beta-diversity among the contemporary and subfossil Cladocera community. The non-metric multidimensional scaling (NMDS) ordination showed that the biomanipulated area in the case of the contemporary communities was separated from the other areas, while in the case of the subfossil communities, there was no separation according to top-down stress. Our results showed that the number of species of contemporary Cladocera communities was lower in each area (3–10; 3–9; 5–9) compared to the subfossil communities (6–17; 7–12; 8–12). However, the highest abundances were found in the biomanipulated area due to the appearance of small-sized Cladocera species. Our findings suggest that the effect of a short-time fish introduction is restorable when the oxbow lake has a protected part.