Search Results (203)

The Water Framework Directive (WFD) was designed to protect the quality of all water resources. For reservoirs, the ecological potential classification assesses biological parameters, evaluating only the phytoplankton community. Thus, this study aimed to evaluate the effectiveness of using fish communities to determine water quality in reservoirs. A literature review was conducted to gather information on how fish community data were integrated into reservoir water quality assessment under the WFD. This work includes an exploratory case study of the Aguieira Reservoir (Portugal), evaluating the ichthyofauna community, along with physical, chemical, and biological assessment of the water. The results of the review show that fish abundance and composition (sensitive metrics) should be used to develop ecological indices for assessing water quality in reservoirs. However, the effects of anthropogenic pressures and invasive species are not included in the calculation of most proposed indices. The case study serves as an illustrative example and demonstrates low abundance and composition of the fish community with a high percentage of invasive species, revealing a poor water quality, regarding ichthyofauna biotic index results (F-IBIP). Nevertheless, including these metrics in the classification of ecological potential can help guide restoration strategies to mitigate the effects of anthropogenic pressures. Full article

The effect of periodical heatwaves and related thermal stratification in freshwater aquatic ecosystems has been a hot research issue. A large dataset of samples was generated from samples exposed to temporary thermal stratification in mesocosms mimicking shallow eutrophic freshwater lakes. Temperature regimes were based on IPCC climate warming scenarios, enabling simulation of future warming conditions. Surface oxygen levels reached 19.37 mg/L, while bottom layers dropped to 0.07 mg/L during stratification. Analysis by FlowCAM revealed dominance of Cyanobacteria under ambient conditions (up to 99.2%), while Cryptophyta (up to 98.9%) and Chlorophyta (up to 99.9%) were predominant in the A2 and A2+50% climate scenarios, respectively. We identified temperature changes and shifts in nutrient concentrations, particularly phosphate, as critical factors in microbial community composition. Furthermore, five distinct Microcystis morphospecies identified by FlowCAM-based analysis were associated with different microbial clusters. The combined use of imaging flow cytometry, which differentiates phytoplankton based on morphological parameters, and nanopore long-read sequencing analysis has shed light into the dynamics of microbial communities associated with different Microcystis morphospecies. In our observations, a peak of algicidal bacteria abundance often coincides with or is followed by a decline in the Cyanobacteria. These findings highlight the importance of species-level classification in the analysis of complex ecosystem interactions and the dynamics of algal blooms in freshwater bodies in response to anthropogenic effects and climate change. Full article

Volcanic ash from explosive eruptions can significantly alter lake water chemistry through ash–water interactions, potentially influencing primary productivity. Alkaline (soda) lakes, mostly found in volcanic regions, are particularly sensitive due to their unique geochemical properties. However, the effects of volcanic ash on the biogeochemistry and phytoplankton dynamics of soda lakes remain poorly understood. This study presents the first nutrient release experiments using natural alkaline water from Lake Van (Türkiye) and volcanic ash from four volcanoes (Hekla, Arenal, Sakurajima, Rabaul-Tavurvur) with different compositions. Sixteen abiotic leaching experiments were conducted over contact durations ranging from 1 to 24 h. Results show rapid increases in pH (~0.4–0.5 units), enhanced silica and phosphate concentrations, and elevated levels of Na, K, Ca, Sr, and S. Nitrate and Mg were generally depleted. The low N:P ratio (~0.06) in Lake Van water indicated nitrogen limitation, partially mitigated by ash-derived inputs. Cyanobacteria dominated the phytoplankton community (95%), consistent with nitrogen fixation under low-nitrate conditions. Elevated silica may promote diatom growth, while changes in Mg/Ca ratios suggest possible impacts on carbonate precipitation and microbialite development. These findings highlight the biogeochemical and ecological relevance of volcanic ash inputs to soda lakes. Full article

Conservation units (CUs) play a fundamental role in maintaining and conserving biodiversity, and are important in preserving streams, reducing impacts from human activities and increasing water availability beyond the boundaries of the reserves. However, knowledge about the phytoplankton biodiversity of ecosystems in CUs is scarce. This study evaluated how environmental integrity alters microphytoplankton communities in extractive CUs and their surroundings in the southwestern Brazilian Amazon. Our results demonstrated that the streams exhibited distinct physicochemical and hydrological characteristics, representing spatially heterogeneous environments. Differences in habitat integrity values altered species composition in streams within and outside conservation units. Local beta diversity (LCBD) was negatively influenced by habitat integrity, indicating that sites with greater habitat integrity did not always present a greater number of unique species. The species Trachelomonas hispida, Gyrosigma scalproides and Spirogyra sp. were the ones that contributed the most to beta diversity. However, the phytoplankton species that contributed most to beta diversity were not always associated with streams with greater integrity, indicating that even environments that are less intact play a relevant role in maintaining species richness and beta diversity of microphytoplankton. Factors such as habitat integrity, pH, temperature and dissolved oxygen were the main influencers of microphytoplankton in the streams. Thus, the streams of both CUs and their surroundings, despite their physical–chemical and hydrological differences, effectively contribute to the high richness and beta diversity of regional microphytoplankton. Full article

Land use composition, water level fluctuations (WLFs), and biogeographical factors are recognized as key drivers of phytoplankton dynamics in reservoir ecosystems. This two-year study presents the first assessment of the combined effects of catchment land use, WLFs, and geographical distance on phytoplankton biomass and community composition across twelve Mediterranean reservoirs in Cyprus, which serve primarily for drinking water supply and irrigation. The results show that higher phytoplankton biomass was recorded in reservoirs whose catchments had >30% coverage by developed land (urban and agricultural), suggesting that increased anthropogenic pressures may lead to nutrient enrichment and elevated productivity. However, despite elevated biomass, no consistent spatial patterns were observed in phytoplankton community composition. The geographical distance between reservoirs had only a minor effect on species distribution, implying that other factors—such as water residence time or hydrological variability—play a more prominent role in shaping community structure. Phytoplankton biomass maxima were most often recorded during periods of elevated water levels and were typically dominated by Chlorophyta, Dinoflagellata, Bacillariophyta, and Charophyta. The pronounced temporal variability in species composition across all reservoirs points to a highly dynamic system, where environmental fluctuations strongly influence community assembly. This study provides the first comprehensive data on phytoplankton in Cyprus reservoirs, highlighting the importance of land use and hydrological regulation for water quality management in similar settings. Importantly, this baseline dataset can support the implementation of the Water Framework Directive (WFD) by contributing to the definition of ecological status classes, establishing reference conditions, and guiding future monitoring and assessment efforts. Expanding such datasets through coordinated, basin-wide monitoring initiatives is essential to improve our understanding of phytoplankton dynamics and their role in ecosystem functioning under the pressures of climate change and intensified land use in this Mediterranean “hot spot”. Full article

With rapid economic and social development, eutrophication in coastal areas is currently one of the most severe environmental problems worldwide. However, our understanding of the response of the phytoplankton community structure to the intensification of coastal eutrophication is still relatively limited. Here, seasonal phytoplankton, environmental factors, and nutrients were investigated in 2009 and 2019 in Zhanjiang Bay, where eutrophication has intensified in recent years, to analyze the variation in nutrient structure and its impact on the phytoplankton community. The results revealed that the DIP and DSI concentrations in 2019 were higher than those in 2009. However, dissolved inorganic nitrogen (DIN) has decreased substantially over the past several decades, which is due mainly to the decrease in anthropogenic nitrogen emissions, the substantial increase in the intrusion of high-salinity seawater, and the high-phosphorus wastewater discharged from urban industries. This resulted in a decrease in phytoplankton cell abundance, phytoplankton composition, and species diversity (H′) in 2019 compared with 2009. In addition, the superior N transport, storage, and response strategy to a low N supply of diatoms, especially Skeletonema and Chaetoceros, might benefit the growth of diatoms under low DIN conditions. The lower DIN/DIP ratio in 2019 favored the growth of diatoms, especially Skeletonema and Chaetoceros, leading diatoms to dominate the phytoplankton assemblage. This study demonstrates how changes in nutrient structure alter the community structure of phytoplankton, providing new insights into deepening our understanding of eco-environmental evolution. Full article

As a key component of inherent optical properties (IOPs) in ocean color remote sensing, phytoplankton absorption coefficient ($a_{phy}$), especially in hyperspectral, greatly enhances our understanding of phytoplankton community composition (PCC). The recent launches of NASA’s hyperspectral missions, such as EMIT and PACE, have generated an urgent need for hyperspectral algorithms for studying phytoplankton. Retrieving $a_{phy}$ from ocean color remote sensing in coastal waters has been extremely challenging due to complex optical properties. Traditional methods often fail under these circumstances, while improved machine-learning approaches are hindered by data scarcity, heterogeneity, and noise from data collection. In response, this study introduces a novel machine learning framework for hyperspectral retrievals of $a_{phy}$ based on the mixture-of-experts (MOEs), named PhA-MOE. Various preprocessing methods for hyperspectral training data are explored, with the combination of robust and logarithmic scalers identified as optimal. The proposed PhA-MOE for $a_{phy}$ prediction is tailored to both past and current hyperspectral missions, including EMIT and PACE. Extensive experiments reveal the importance of data preprocessing and improved performance of PhA-MOE in estimating $a_{phy}$ as well as in handling data heterogeneity. Notably, this study marks the first application of a machine learning–based MOE model to real PACE-OCI hyperspectral imagery, validated using match-up field data. This application enables the exploration of spatiotemporal variations in $a_{phy}$ within an optically complex estuarine environment. Full article

Numerous remediation strategies exist for cyanobacterial harmful algal blooms (cyanoHABs); however, most are limited by challenges of scalability and adverse off-target effects on the surrounding ecosystem. Germicidal ultraviolet light (UV-C) has emerged as a promising method for suppressing cyanoHABs in a sustainable, chemical-free manner that is both scalable and results in limited off-target ecological effects in the surrounding area. In this study, the US Army Engineer Research and Development Center’s (ERDC)’s CyanoSTUN^TM (Cyanobacterial Suppression Through Ultraviolet-Light-C Neutralization) vessel was deployed to a cyanoHAB as part of a field trial to determine whether UV-C could effectively suppress cellular growth, degrade associated cyanotoxins, and inhibit harmful phytoplankton species more readily than beneficial species without the addition of chemicals. The cyanoHAB exhibited an average cyanobacteria abundance of 3.75 × 10⁵ cells/mL (n = 5, SD = 6.76 × 10⁴ cells/mL) and average total microcystin concentration of 3.5 µg/L (n = 5; SD = 0.24 µg/L). Pre- and post-treatment samples were collected and re-grown for 9 days in the laboratory to observe differences in microcystin, chlorophyll a, and phycocyanin concentrations, optical density, cell density, and community composition. The results of the field trial showed that the CyanoSTUN UV-C treatment effectively suppressed the growth of the cyanobacteria community for approximately two days at the three tested UV-C doses. The CyanoSTUN UV-C treatment also demonstrated a sustained, dose-dependent effect on microcystin concentration; the average reduction in microcystin concentration for 15, 30, and 45 mJ/cm² treatment doses was 31.6% (n = 10, SD = 20.1%; 1.3 µg/L reduced), 45.7% (n = 10, SD = 10.8%; 1.9 µg/L reduced), and 49.9% (n = 10, SD = 8.2%; 1.7 µg/L reduced), respectively, over the 9-day regrowth period. Non-cyanobacteria were too scarce in this CyanoHAB to conclude whether the CyanoSTUN UV-C inhibits harmful phytoplankton species more readily than beneficial species. Further field studies with the CyanoSTUN^TM are required to validate performance under more severe cyanoHAB conditions, however the results reported herein from the first field trial with the CyanoSTUN^TM suggest that this treatment method may offer water managers confronted with a CyanoHAB the ability to rapidly and safely pause a bloom for multiple days and reduce the risks posed by its associated cyanotoxins without adding chemicals. Full article

Disturbed ecosystems are particularly susceptible to biological invasions. Increasing freshwater salinization, caused by anthropogenic factors, can alter the phytoplankton community and favour newly arrived halotolerant species. This study investigates the halotolerance of four Nostocalean cyanobacterial species—the native to Europe, Aphanizomenon gracile, and alien Chrysosporum bergii, Cuspidothrix issatschenkoi, and Sphaerospermopsis aphanizomenoides—using monoculture experiments under varying NaCl concentrations. Additionally, we performed two microcosm experiments to explore shifts in biodiversity in freshwater phytoplankton communities sourced from artificial reservoirs and assess their susceptibility to cyanobacterial invasion under salinity stress. Results showed that all Nostocalean cyanobacteria were halotolerant under mild salinities (up to 1 g/L NaCl), with Chrysosporum bergii and Sphaerospermopsis aphanizomenoides demonstrating the most salt tolerance. In the microcosm experiment, changes in community composition were driven by the halotolerance of dominant groups. Water body 1, dominated by Bacillariophytina, reduced its biomass of phytoplankton at high salinity (5 g/L NaCl), while water body 2, dominated by Chlorophytina, remained stable regardless of disturbance. Both cyanobacteria successfully invaded both halotolerant and halosensitive communities, increasing their dominance as salinity rose. Our findings suggest that anthropogenic stressors such as freshwater salinization can alter the phytoplankton community and increase a competitive advantage to certain taxa, including widespread alien cyanobacteria, potentially promoting invasions and bloom formation. Full article

This study investigates the feeding behavior and ecological role of Craspedacusta sowerbii in the Danjiangkou Reservoir, a crucial freshwater source in central China. Through in situ cultivation, microscopic examination, and amplicon sequencing analysis, we identified the primary food sources of C. sowerbii within the reservoir’s aquatic food web. Our results indicate that C. sowerbii predominantly consumes zooplankton, specifically rotifers, copepods, and cladocerans, while phytoplankton is ingested less frequently and often remains undigested. Amplicon sequencing data further confirms that the prey composition of C. sowerbii is enriched in zooplanktonic communities compared to phytoplanktonic communities. Our findings suggest that C. sowerbii plays a significant role in regulating plankton populations and shaping the planktonic community structure in the Danjiangkou Reservoir, thereby contributing to the ecosystem’s functions and trophic dynamics. This study enhances our understanding of the feeding ecology of C. sowerbii and highlights its potential as a bioindicator species for assessing freshwater ecosystem health and monitoring water quality. Full article

Olyokma Nature Reserve, where we conducted our research, is in Eastern Siberia in the middle taiga zone in an area characterized by continuous permafrost. This is the only protected area in the region with a complete reserve regime, where there is no human activity. Here, we studied 14 different types of water bodies located along the Olyokma River valley, 13 of which were studied for the first time. For some of the studied water bodies, a high content of biogenic elements was noted, which may be associated with the characteristics of permafrost water bodies, which are under nutrient release from permafrost thaw. The concentration of several biogenic elements, including ammonium, nitrates and phosphates, increases in the water of the lakes toward the bottom of the river valley. In the composition of various communities of these water bodies, including both planktonic and non-planktonic, we identified 246 species and varieties of microalgae. The abundance and biomass of phytoplankton, as well as the number of species, decreased down the river valley. At the same time, at the upper stations there were more diatoms; while at the stations down the valley, green algae came to the fore; and even lower down, cyanobacteria prevailed. At the lower stations, the indicators of microalgae development were minimal. In accordance with the bioindicative properties of microalgae, a decrease in the trophic status of water bodies was noted down the river valley, which, in our opinion, is a characteristic feature of the waters of an undisturbed catchment basin in the permafrost area. This indicates that the studied aquatic ecosystem changes within a set of environmental and biological indicators, that is, it exists in natural conditions for this catchment basin. Research on the territory of Olyokma Nature Reserve allowed us to obtain information on natural transformation and removal of nutrients in permafrost catchments, while excluding the likelihood of anthropogenic impact on these processes. Full article

Different communities of primary producers were surveyed in a series of five river reservoirs on the Sava River in southeast Slovenia. Seasonal differences of phytoplanktonic and phytobenthic communities were studied in the reservoirs of hydroelectric power plants. Macrophytes were surveyed in the summer, while phytoplankton and periphyton were sampled in the winter and summer of 2021. The taxonomic composition of diatoms was studied in greater detail and additionally analysed. The results showed that the species composition of phytoplankton and phytobenthos differed between seasons. The communities were also more similar between the seasons at the same sampling site than between the sampling sites. Temperature was the parameter that had the greatest impact on the taxonomic composition of phytoplanktonic and phytobenthic communities. In total, 51 algal taxa and 81 species of diatoms were recorded, respectively. Furthermore, 15 species of aquatic macrophytes were found. The abundance of phytoplankton was the highest in the lowest reservoir in the series, in Brežice, where the temperature was also the highest. The number of macrophytes also increased downstream, but their abundances were low, mainly due to coarse substrate on the banks consisting of rocks and boulders. Constructing additional reservoirs on this section of the Sava River could increase the probability of the substantial growth of phytoplankton and cyanobacteria within it. On the other hand, providing patches of finer substrates (gravel, pebbles) would support the abundance of macrophyte species, which could control the concentrations of nutrients in the summer and prevent the blooms more efficiently. Full article

Kuibyshev Reservoir, the largest in the Volga basin, is poorly covered by modern molecular studies. The results of a metabarcoding study of pro- and eukaryotic microbial plankton in its lower section during the summer period are presented. Bacterioplankton composition was typical for most temperate freshwater bodies and characterized by the dominance of cyanobacteria, Pseudomonadota, Bacteroidota, Actinomycetota, and PVC superphylum (Verrucomicrobiota and Planctomycetota), with a somewhat increased proportion of the latter. The protist community was dominated by Cryptista, principally phototrophic, and various ciliates. Several picoeukaryotic groups were newly detected in the reservoir. A relationship between the composition of both bacterioplankton and protist communities and the stage of phytoplankton succession, including the cyanobacterial bloom, was observed. Some inconsistency between the cyanobacterial bloom phase and the structure of other parts of the microbial plankton is obviously due to some temporal delay, spatial station position, and inflow from tributaries. Heterotrophic bacterioplankton indicator species of the main bloom stage include OTUs representing both the phycosphere of colonial cyanobacteria and free-living species. Among the protists, sessile ciliates benefit most from plenty of substrates for colonization, while cyanobacterial grazers and parasites were minor. Overall, the cyanobacterial bloom creates new niches for the plankton community and significantly modifies its structure. Full article

This study investigates phytoplankton and zooplankton assemblages and their relationships with environmental factors along trophic gradients in 50 lentic ecosystems across Thailand. Field sampling was conducted at 264 points in April and May 2024. Physical, chemical, and biological parameters were measured both in the field and the laboratory. Plankton samples were identified and quantified to assess species richness, abundance, and community composition. The results revealed that lentic water bodies could be classified into four trophic states: 1 oligotrophic, 6 mesotrophic, 17 eutrophic, and 26 hypereutrophic systems. This study found that phytoplankton density peaked in hypereutrophic waters, while species richness was highest in oligotrophic conditions. Nutrient-rich environments favored Cyanophyta dominance, whereas Dinophyta were more abundant in nutrient-poor systems. Zooplankton assemblages, particularly Rotifers and Copepoda, showed higher abundance in eutrophic and hypereutrophic ecosystems, while diversity was greater in mesotrophic and oligotrophic waters. Statistical analyses indicated that environmental factors, especially nutrient concentrations, played a significant role in shaping plankton assemblages along the trophic gradients. Cyanophyta showed strong positive correlations with total dissolved solid (TDS) (r = 0.383, p < 0.01) and electrical conductivity (EC) (r = 0.403, p < 0.01), while Dinophyta showed a strong positive correlation with dissolved oxygen (r = 0.319, p < 0.05). Zooplankton, particularly Rotifers, exhibited significant correlations with total phosphorus (TP) (r = 0.358, p < 0.05) and TDS (r = 0.387, p < 0.01). Multidimensional Scaling (MDS) analysis and Principal Coordinate Analysis (PCoA) confirmed that water quality variables strongly influenced community structure. This study provides important insights into how environmental factors drive phytoplankton and zooplankton assemblages across trophic gradients in Thai lentic ecosystems, contributing to the improved understanding and management of freshwater bodies and eutrophication. Full article

Artificial reservoirs formed by hydroelectric dams are young ecosystems requiring water quality monitoring, as they often serve local populations. Traditionally, this is performed through hydrochemical and sanitary assessments, alongside phytoplankton composition analysis. This study aimed to assess the seasonal dynamics of microbial communities—both bacterioplankton and microeukaryotes including phytoplankton—in the Irkutsk Reservoir (IR), which is fed by the cold oligotrophic waters of Southern Baikal (SB). Using parallel metabarcoding of 16S and 18S rRNA gene fragments, we analyzed community composition during the open-water season and evaluated the ecological connectivity between these two freshwater systems. We demonstrated that seasonal changes in microeukaryotic communities were closely linked between SB and IR, with the greatest divergence observed in early summer and progressive convergence by autumn. Metabarcoding confirmed microscopy-based observations while providing higher taxonomic resolution and detecting otherwise overlooked groups. Bacterioplankton communities also exhibited seasonal variation and were shaped by environmental gradients and reservoir characteristics. Cyanobacteria peaked in SB in late summer but did not dominate communities, unlike in mesotrophic lowland reservoirs. These findings demonstrate the value of metabarcoding for freshwater monitoring and provide new insights into microbial community dynamics in river–reservoir systems influenced by oligotrophic lake inflow. Full article