In April and May 2024, unprecedented rainfall pounded the southern Brazilian state of Rio Grande do Sul, leaving 95% of its municipalities affected by the largest and most destructive floods in its history. Porto Alegre, the state capital and largest city, is bordered by Lake Guaíba and was severely affected by the flood. Floodwaters resulting from extreme weather events may contain high concentrations of fecal bacteria and other contaminants, including metals. This study aimed to assess contamination levels in Lake Guaíba following the flood event. Surface water samples were collected at two locations: Site 1, situated in the urban area of Porto Alegre, and Site 2, located in a more preserved area. The samplings were performed during pre-flood periods (December 2023 and March 2024) and post-flood period (June 2024). The following water quality parameters were analyzed: total coliforms, Escherichia coli, Al, Cd, Cu, Fe, Pb, Mn, Hg, Ni, Cr, and Zn. In the post-flood period, total coliforms and E. coli concentrations increased respectively by factors of 20.2 and 2.3 at Site 1 and 6.2 and 7.5 at Site 2, compared to the average for the pre-flood periods. Among the metals analyzed, Cd, Pb, Cu, Cr, Hg, and Ni were not detected during any sampling period. Among the quantified metals, Zn was only detected in the post-flood period at both sampling sites. These findings indicate that the flood event was associated with substantial increases in fecal contamination, whereas no clear and consistent pattern was observed for metal contamination.
The creation of riverine reservoirs may alter the nature and distribution of dissolved organic matter (DOM) in water quality and sediments. However, the characterization of water quality and DOM in the water body and its response to the ecological environment are not clear. In this study, we collected water and sediment samples from Yanxi Lake, and analyzed the optical properties and compositions of water quality and DOM using fluorescence indices (FI, BIX, and HIX) and three-dimensional fluorescence spectroscopy combined with parallel factor analysis (EEM-PARAFAC). The results showed that DOM in both water and sediment was dominated by autochthonous sources, with relatively small contributions from heterogenic inputs. In sediments, the establishment of riverine-type reservoirs led to significant changes in FI, BIX and HIX values. The PARAFAC model identified six fluorescent fractions in DOM, including terrestrial humic-like substances (C1, C2), humic-like fractions (C3), and proteinaceous substances (C4, C5, C6, of which C6 is tyrosine-like). The fluorescence intensity of humus-like fractions in the water column was enhanced by the expansion of the inundated area and the increase of inputs from land-based sources after the establishment of riverine-type reservoirs. In sediments, spatial differences in fluorescence intensity were reduced and microbial activity was enhanced. Correlation analysis revealed a close link between water quality and DOM properties. Water temperature, pH, dissolved oxygen (DO), and nutrients (TP, NH4+-N), were closely correlated with DOM dynamics. These findings reveal the influence of the establishment of riverine-type reservoirs on the spatial and temporal variations of water quality and DOM, and provide a theoretical basis for assessing the ecological cycle of rivers and optimizing ecological management strategies.
Climate change is intensifying hydrological variability in streams, but organism groups may respond to different environmental pathways associated with low-flow and high-flow conditions. We assessed how hydrologically relevant environmental gradients were associated with five biological response groups (diatoms, macrophytes, herbaceous riparian vegetation, macroinvertebrates and cotton-strip decomposition) in perennial lowland streams in Germany. Predictors included shear stress, nutrient concentrations (total N, total P, DOC), water temperature, solar radiation, shading and elevation above water level. Community composition and functional metrics were analysed using Canonical Correspondence Analyses and regression models. Predictor associations varied among groups, with macrophytes showing the highest explained variance (42%) and riparian vegetation the lowest (10.1%). Macrophyte composition was mainly associated with shear stress and total N, while diatom assemblages were most strongly associated with solar radiation. Riparian vegetation reflected local light and moisture gradients, with shading and elevation above water level correlated with Ellenberg indicator values. Macroinvertebrate metrics were associated with shear stress, total P and temperature, while cotton-strip decomposition increased with DOC and maximum temperature. Overall, our results indicate organism-specific sensitivity pathways rather than uniform responses to hydrological variability. Multi-taxa assessments can therefore help identify which environmental gradients and ecosystem components are most relevant for anticipating ecological responses to climate-driven hydrological change.
Zebra mussels (Dreissena polymorpha) can colonize mobile hard substrates, including crayfish exoskeletons, yet the host-related and environmental factors associated with this interaction remain insufficiently documented in many freshwater reservoirs. To our knowledge, this study provides the first report of zebra mussel colonization on narrow-clawed crayfish (Pontastacus leptodactylus) in Atikhisar Reservoir, & Ccedil;anakkale, T & uuml;rkiye. A total of 6634 crayfish were examined monthly from July 2020 to June 2021 to evaluate colonization prevalence, host-related correlates, attachment-frequency patterns across crayfish body regions, and associations with selected environmental variables. Zebra mussels were recorded on 321 crayfish, corresponding to an overall colonization prevalence of 4.84%. Colonization prevalence was higher in males (5.43%) than females (3.94%). Colonized crayfish had greater mean carapace length and body weight than non-colonized individuals, and colonized individuals were mainly concentrated in the 40.0-69.9 mm carapace length classes. A total of 2227 attached zebra mussels were recorded, most of which belonged to Class I (<= 12.9mm), indicating that colonization was mainly associated with small individuals. Attachment was recorded across seven crayfish body regions, with the dorsal carapace showing the highest attachment frequency, followed by the dorsal and ventral abdomen. Because body-region surface areas were not measured, these patterns were interpreted as attachment-frequency differences rather than evidence of active substrate preference or selectivity. Logistic regression indicated that crayfish carapace length, body weight, sex, water temperature, reservoir water level, and dissolved oxygen were associated with zebra mussel presence/absence, although model explanatory power was weak. These findings show that zebra mussel colonization on crayfish in Atikhisar Reservoir is associated with both host traits and environmental conditions, and they highlight the broader value of considering mobile benthic hosts when monitoring zebra mussel interactions in invaded freshwater systems. Future studies should incorporate zebra mussel density, larval availability, molting history, and body-region surface area to better evaluate the mechanisms underlying host-associated colonization.
Aquatic communities play a fundamental role in freshwater ecosystems, acting in energy transfer and nutrient cycling in the food chain. Among these communities, Cladocera often stand out due to their high abundance and ecological importance. This study evaluated the spatiotemporal variation of the Cladocera community along a channel located in the subtropical coastal plain (São Gonçalo Channel, southern Brazil), integrating taxonomic and functional approaches. This ecosystem connects two large water bodies in Brazil: Lagoa Mirim to the south and Lagoa dos Patos to the northeast. Sampling was conducted between 2018 and 2019 along a 42-km transect. A total of 133 sites were sampled across four annual periods in three zones of the channel, testing the following hypotheses: (i) the southern region of the channel presents higher taxonomic and functional diversity; (ii) the taxonomic and functional diversity metrics of the community are influenced more strongly by temporal variation than by spatial variation. Taxonomic diversity was measured using metrics of abundance, richness, taxon frequency, diversity, dominance, and evenness, while functional diversity was assessed through trait categorization and indices of functional richness, divergence, and evenness. A total of 2307 individuals of Cladocera were recorded, distributed across 16 genera, with Moina and Bosmina being the most frequent. The results showed that temporal variation was the main structuring factor of the functional and taxonomic composition of the Cladocera community. The findings of this study reinforce the importance of integrated approaches to understand the ecological processes structuring aquatic communities in subtropical water bodies.
Decomposition process of aquatic plants is regulated by dissolved organic matter (DOM), which serves as a nutrient pool. However, the priming effects (PE) on nutrient release during decomposition, induced by input DOM of different sources in lakes, and their underlying microbial mechanisms, remain unclear. In this study, microcosm incubations were conducted to simulate the effects of DOM from different sources (algal, sewage, and soil) on nutrient release, microbial community structure, key taxa, and assembly processes during the decomposition of Phragmites australis. Results indicate that algal- and sewage-derived DOM enhanced decomposition, as evidenced by positive PE, with increases of 1.51-12.54% in the release of dissolved organic carbon, nitrogen, and phosphorus compared to theoretical values. Conversely, soil-derived DOM suppressed decomposition, showing negative PE with reduced release (6.87-16.82%). Partial least squares path model revealed that DOM significantly influenced microbial community structure by altering environmental factors. Key taxa such as Nitrospira, Sphingopyxis, and Microvirga exhibited significant correlations with nitrogen and phosphorus fluxes, indicating possible involvement in mediating the PE. Community assembly analysis revealed that algal-derived DOM mainly enriched microorganisms via stochastic dispersal limitation, sewage-derived DOM may induce positive PE through deterministic homogeneous selection, and soil-derived DOM exerted strong dispersal limitation, thereby filtering for specialist taxa. Overall, DOM-induced shifts in microbial communities are closely coupled with the PE observed during decomposition, implying their role as potential drivers. These findings provide critical insights into the potential ecological risks posed by PE during litter decomposition in aquatic ecosystems.
Zenarchopterus clarus (Hemiramphidae), commonly known as a halfbeak fish, is a small estuarine species distributed in mangrove and coastal ecosystems of Southeast Asia. This study investigated its feeding ecology in a mangrove estuary in Ca Mau Province, Vietnam, using relative gut length (RGL), the Clark index, and diet composition analyses of 892 individuals collected monthly from August 2024 to July 2025 at two sites. Of the 892 examined individuals, 35 stomachs were empty and excluded from diet analyses. Gut contents were analyzed using frequency of occurrence, gravimetric proportion, and a points index, while differences among sex, site, and season were tested using PERMANOVA and non-parametric analyses. The mean RGL (0.37 +/- 0.08) indicated a carnivorous feeding strategy. Diet composition was strongly dominated by terrestrial ants, followed by crustaceans, insects, and small fishes. PERMANOVA indicated no significant main effects of sex, site, or season on overall diet composition, although significant interaction effects involving season were detected. Ant contribution was significantly higher during the wet season. The mean Clark index was 0.34 and varied significantly with sex, sampling site, and size class (p < 0.05), with males and individuals from Vinh Phuoc showing slightly higher values. These findings demonstrate that Z. clarus is a surface-feeding carnivore strongly dependent on terrestrial insect subsidies, with seasonal variation mainly reflected by increased ant consumption in the wet season. The study provides baseline ecological information to understand trophic dynamics and to support future ecological research and resource management in the Mekong Delta.
Hoa Binh Reservoir (Vietnam) is a key water-supply system that is increasingly vulnerable to eutrophication, as indicated by elevated chlorophyll a (Chla) concentrations. This study quantified spatiotemporal Chla dynamics, identified dominant environmental drivers, and developed an uncertainty-aware machine-learning (ML) framework for early warning. Generalized linear mixed models indicated that temporal variation outweighed spatial effects. Temperature, conductivity, dissolved oxygen, and pH emerged as dominant drivers, while nutrients contributed little. The best ML model, including phytoplankton, achieved high accuracy (normalized error: 8.7%, R2 = 0.91 [95% CI: 0.76-0.92]); excluding phytoplankton reduced performance (normalized error: 11.7%, R2 = 0.82 [95% CI: 0.67-0.84]). Prediction uncertainty was assessed with 1000 bootstrapped models, and a web-based interface was deployed for real-time Chla prediction. These results enhance understanding of phytoplankton dynamics and provide a robust framework for eutrophication risk assessment in tropical reservoirs.
The prevalence of nitrogen limitation and nitrogen-phosphorus co-limitation (henceforth referred to as nitrogenrelated limitation) in Norwegian lakes and their relationships with atmospheric nitrogen deposition, climate, dissolved organic matter (DOM), and catchment characteristics were assessed across space and time. Routine monitoring data from 1529 lakes in the national Vannmilj & oslash; database were analyzed for two multi-year periods (1995-2009 and 2010-2025). Limitation was inferred using the molar NO3--N/TP ratio as an indicator of dissolved inorganic nitrogen availability. Nitrogen-related limitation was widespread in both periods and exhibited strong regional structure, with highest prevalence in northern regions and lowest prevalence in southern and western regions. Overall prevalence increased from 31% to 38% between periods, with significant increases in western regions. Regional-scale models identified climate, forest cover, DOM, agriculture, and atmospheric nitrogen deposition as predictors of limitation probability, whereas study period per se and bog/peatland cover were not significant. At the local scale, atmospheric nitrogen deposition and DOM were the only consistent predictors, with substantially lower explanatory power than at the regional scale. These results indicate that large-scale environmental gradients play a major role in shaping nutrient stoichiometry in Norwegian lakes. Because the monitoring dataset primarily represents lakes affected by human activities, the findings are particularly relevant for water management. The widespread occurrence of nitrogen-related limitation suggests that nitrogen availability may influence phytoplankton growth in many systems and that dual-nutrient management strategies addressing both nitrogen and phosphorus may be required in many regions.
Urban wetlands regulate sediment and nutrient fluxes in urban catchments, where stormwater delivers elevated loads. This study examined four South African urban wetlands, measuring sediment, total phosphorus, and total nitrogen at inlet and outlet sites, with internal sampling in two of the wetlands. All wetlands were net sediment sinks (27-84% efficiency), but nutrient dynamics varied, with some exporting phosphorus and nitrogen. Internal sampling revealed spatial variability, including deposition, resuspension, and release, highlighting the complex functioning of wetlands beyond inlet-outlet assessments.
River ecosystems and their plant communities are a critical component to the landscape of Mississippi and invasion represents a substantial threat to these systems. This study focused on the Pascagoula River, the Pearl River, and the Tennessee-Tombigbee Waterway, whose hydrology range from largely unaltered to highly altered. The rivers’ aquatic and riverine communities were measured using point surveys and site community compositions were assessed using nonmetric multidimensional scaling (NMDS). We found that sites on the Pascagoula and Pearl rivers were similar to each other while being dissimilar to the TTW sites, and that coastal systems on the Pascagoula and Pearl Rivers separated from the noncoastal sites. The effects of latitude and river system on species sample richness (s) were assessed using a linear mixed-effects model. The effects of latitude and native species richness (sn) on the presence/absence of introduced species (pai) were assessed using a generalized linear model. Results showed that across all river systems, decreasing latitude increased s. These results suggest that although these rivers have differences in their community composition, the effect of latitude on s is strong enough to be exhibited consistently in all three rivers. Additionally, we found that sn (positive) and latitude (negative) had substantial effects on pai with sn being the stronger predictor. These findings are consistent with the well-supported “rich get richer” hypothesis that posits a positive relationship between native plant richness and introduced plant richness. This pattern describes the broad and indirect association between native species richness and susceptibility to invasion.
Beta diversity provides important insights into the deterministic and stochastic processes that shape biological communities. Gerromorpha, semiaquatic insects commonly found in Amazonian streams and rivers, are particularly well suited for investigating these mechanisms because they respond to both environmental gradients and constraints imposed by hydrological connectivity. In this study, we evaluated how environmental and spatial variables structure Gerromorpha beta diversity in streams of the Central Amazon. We sampled communities across four Amazonian sub-basins and collected environmental, spatial, and biological data. Beta diversity was quantified using local contributions to beta diversity (LCBD) based on abundance data (LCBDab), presence-absence data (LCBDpa), and species contributions to beta diversity (SCBD). We then assessed the relationships between LCBDab and LCBDpa and local environmental and spatial characteristics, as well as between SCBD and species attributes, including abundance, occupancy, niche breadth, and niche position. LCBDab was mainly explained by spatial structure, represented by multiple spatial axes, whereas LCBDpa was primarily related to environmental variation, especially the Habitat Integrity Index (HII). Species with high abundance but low occupancy contributed more strongly to SCBD, as did generalist species with non-marginal niche positions. Overall, our results indicate that beta diversity in Gerromorpha metacommunities is jointly shaped by environmental filtering and dispersal limitation, with these processes influencing species abundances and occurrences in distinct ways. Maintaining environmental integrity and connectivity among sites is therefore crucial for preserving regional compositional variation and preventing biotic homogenization in Gerromorpha metacommunities.
This study characterized the phytoplankton communities of 65 lakes across a large heterogeneous landscape classified by ecoregion in Ontario, Canada. Although phytoplankton communities were anticipated to vary according to ecoregion type based on their unique edaphic and water quality characteristics, there was no statistically significant difference (ANOVA, p>0.05) in taxonomic division, functional traits, size class, or size spectra across ecoregions. Taxonomic composition also did not vary across ecoregions, but redundancy analysis showed a separation of edible and inedible functional groups according to two ecoregion groupings. Additionally, cell-size spectra across the study lakes were significantly different across trophic status (oligotrophic, mesotrophic, and eutrophic) and recreational fishing pressure (high vs. low). Cyanophyta emerged as the dominant division across all lakes based on biomass, but also distinct from other algal groups with respect to environmental drivers. Total nitrogen and dissolved organic carbon were identified as significant positive explanatory variables of Cyanophyta biomass. The positive relationship with dissolved organic carbon may be related to Cyanophyta’s superior ability to grow in low-light conditions such as browning lake waters. Overall, our results indicate that ecosystem-scale factors such as trophic status and fishing pressure may play a role in phytoplankton community structure based on functional traits (i.e., edibility and metabolism) rather than taxonomic classification.
Protozoans are globally distributed across aquatic environments and play key roles in ecosystem functioning. This study assessed how environmental filters associated with urbanization shape the spatial and temporal variation of protozoan assemblages in shallow urban lakes and evaluated their predictive capacity for trophic status and water quality assessment. Four urban ponds located in Santa Fe and Santo Tome cities (Argentina) were sampled over one year. Several environmental relevant variables were measured, including inorganic nutrient concentrations and indicators of organic matter contamination. With Generalized Linear Models and partial Canonical Correspondence Analysis, we first focused on total protozoan density and evaluated the influence of the environment, time, and spatial predictors on the distribution of the most abundant groups. Multiple regression models and Principal Coordinates Analysis (PCoA) were applied to estimate the bioindicator value of dominant protozoans' groups. Protozoans showed significantly higher total densities during warmer months and differed among ponds. Eight of sixteen recorded groups were dominant and displayed non-uniform distributions. Nutrient availability, temperature, pH, and organic matter contamination were identified as key predictors of the assemblage's structure. Moreover, multiple regression models indicated that at least four groups (Choreotrichia, Haptoria, Arcellinida and Hypotrichia) responded significantly to eutrophication, organic contamination, and pH variation. Overall, protozoan assemblages responded to environmental, spatial, and temporal drivers. These results suggest that taxonomic levels such as class or family can function as sensitive and operational indicators of water quality in urban ponds, particularly in monitoring programs requiring rapid, costeffective, and feasible assessment tools.
Bacterial growth efficiency (BGE), the proportion of organic carbon transferred to higher trophic levels in aquatic systems, is generally considered to be controlled by substrate availability. However, the role of top-down forces such as viruses and heterotrophic nanoflagellates (HNF) remains poorly understood. We conducted a year-long study (2023-2024) in the pelagic zone of a shallow temperate eutrophic Lake Chambon (France) to assess viral lysis and HNF grazing effects on bacterial-mediated carbon flux. BGE, calculated from bacterial production (BP) and respiration (BR), ranged from 10% to 39% (mean: 25.5 +/- 8.3%). BR was consistently about five times higher than BP, producing substantially lower BGE than values commonly reported for many eutrophic systems. Weak temporal coupling between BP and BR contributed to this variability. Flow cytometry showed that high-nucleicacid (HNA) bacteria were primarily associated with biosynthesis (BP), whereas low-nucleic-acid (LNA) bacteria were more closely linked to carbon mineralization (BR). BGE showed little relationship with abiotic factors, including nutrient concentrations and stoichiometry, suggesting limited bottom-up control. Viral abundances were high (0.8-7.0 & times; 108 VLP mL-1) and dominated (81%) by the low-fluorescence V1 subgroup, representing bacteriophages that reduced BGE via host-specific lysis. HNF grazing selectively removed larger HNA cells, further constraining BGE. Mechanistically, viral lysis redirects bacterial production toward dissolved organic carbon via the viral shunt, while HNF grazing increases bacterial turnover and maintenance costs, jointly lowering BGE. This study highlights top-down control as a key driver of bacterial carbon processing in eutrophic freshwater ecosystems.
Monsoon-driven estuaries experience strong and recurrent environmental forcing, yet it remains unclear whether zooplankton functional structure follows a simple seasonal cycle or undergoes directional reorganisation across monsoon transitions. Understanding how functional traits reorganise under predictable disturbance is central to interpreting ecosystem processes in dynamic aquatic systems. We examined zooplankton functional feeding-mode (FFM) organisation in the Pasur River estuary (south-western Bangladesh) using monthly sampling at 12 stations from June 2024 to May 2025, covering pre-monsoon, monsoon, and post-monsoon periods. All physicochemical variables differed significantly among seasons (p < 0.001), with salinity and alkalinity highest in pre-monsoon, total suspended solids peaking during monsoon, and dissolved oxygen highest post-monsoon. FFM composition shifted markedly: medium copepod and cladoceran filter feeders, primarily very small microzooplankton (protozoans; PF group), dominated pre-monsoon (28.7%), particle feeders dominated monsoon (37.2%), and post-monsoon assemblages were more even. Seasonal differences in FFM structure were not statistically significant after accounting for spatial variation among sampling stations (PERMANOVA, p = 0.192), while dispersion did not differ among seasons. Functional diversity and evenness declined during monsoon, indicating disturbance-driven compression of functional roles, accompanied by increased dominance and highest turnover across the pre-monsoon-monsoon transition. Redundancy analysis identified salinity, pH, and dissolved oxygen as key drivers of FFM organisation. These results indicate that recurrent hydrological disturbance restructures trophic organisation through functional filtering rather than symmetric seasonal cycling. Overall, monsoon onset emerged as a critical phase of directional functional reorganisation rather than cyclic recovery, highlighting the importance of transitional functional states in disturbance-regulated plankton ecosystems.
Periphyton plays a crucial role in nitrogen (N) and phosphorus (P) retention and assimilation in urban streams. From 2024-2025, we conducted seasonal daytime in situ microcosm experiments using epilithic periphyton naturally colonized on cobbles across three geomorphic habitats-deep pool (DP), shallow riffle (SR), and stagnant zone (SZ)-in a suburban headwater stream in Hefei, Anhui, China, to investigate ambient and elevated nutrient concentrations on N and P uptake rates and kinetics. Results revealed that across seasons, nitratenitrogen (NN) and soluble reactive phosphorus (SRP) uptake rates and accumulation exhibited a pattern of DP > SR > SZ, whereas ammonium-nitrogen (AN) uptake was highest in SZ. Nevertheless, no statistically significant differences were detected among the three habitats for any nutrient species. Under elevated nutrient conditions, NN uptake capacity in SR ranked: phosphate-enriched group (Elevated P + Ambient N) > control (Ambient P + Ambient N) > ammonium-enriched group (Ambient P + Elevated N) > combined N and P enriched group (Elevated P + Elevated N). AN uptake ranked Elevated P + Elevated N > Ambient P + Elevated N > Ambient P + Ambient N > Elevated P + Ambient N; and SRP uptake ranked Elevated P + Ambient N > Ambient P + Ambient N > Elevated P + Elevated N > Ambient P + Elevated N. Correlation heatmap and Partial least squares path modeling (PLS-PM) indicated that under ambient conditions, NN and AN uptake in DP were closely associated with periphyton physicochemical properties, but not in SR or SZ. Under elevated nutrient conditions, a stronger correlation between nutrient uptake rates and environmental factors was evident only in Elevated P + Ambient N. These findings enhance the mechanistic understanding of how geomorphic heterogeneity and water column nutrient dynamics influence periphyton-mediated nutrient retention, providing deeper insights into N and P cycling in urbanized headwater stream ecosystems.
