As the primary component of harmful algal blooms, cyanobacteria exhibit unique adaptation strategies under environmental stress. The impact of erythromycin (ETM), a common macrolide antibiotic in aquatic environments, on colonial cyanobacteria remains unclear. This study examined the chronic toxic effects of different ETM concentrations (0.01, 0.1, 1, 10, 20 and 100 μg/L) on colonial Microcystis aeruginosa (M. aeruginosa) under varying nutrient conditions. Results showed that at 0.01–1 μg/L, ETM could promote the growth of M. aeruginosa, while high concentrations of ETM (≥10 μg/L) significantly inhibited growth (p < 0.05). Low-level ETM exposure accelerates M. aeruginosa growth by boosting PSII efficiency, extracellular polymeric substance (EPS) production, and the activities of superoxide dismutase (SOD) and catalase (CAT). Metatranscriptomic and metabolomic analyses further reveal that this stimulation is underpinned by enhanced trace-element uptake, reinforced carbon cycling, and increased biosynthesis of proteins, polysaccharides, and chlorophyll precursors. High-level ETM exposure inhibited the growth of M. aeruginosa, as evidenced by decreased photosynthesis, damaged membranes and suppressed metabolic activity. Metatranscriptomic and metabolomic analyses showed the upregulation of photosynthesis andpathways, metabolic pathways, and the accumulation of potent allelochemicals in P-limited cells exposed to 10 µg/L ETM relative to 10 µg/L ETM in nutrient-replete BG11 medium. Furthermore, phosphorus deficiency may enhance the potential of net methane formation. These findings underscore the complex interactions between antibiotic exposure and nutrient stress in cyanobacteria, with significant implications for environmental management of antibiotic contamination.

The eutrophication and algal blooms caused by human activities significantly change the structure of lake microbial communities. Yet whether this process can also cause changes in the dissemination of antibiotic resistance genes (ARGs), metal resistance genes (MRGs), and mobile genetic elements (MGEs) urgently needs to be investigated. In this study, metagenomic approaches were employed to investigate the abundance, diversity, relationships and hosts of ARGs, MRGs, MGEs and virulence factors (VFs) in free-living (FL) and particle-associated (PA) fractions during cyanobacterial blooms. The diversities of resistance genes were significantly higher in the FL fraction, while the abundance of MRGs and MGEs were greater in the PA fraction. Large-sized cyanobacterial aggregates may alter the bacterial community structure and modulate the diversity and abundance of resistance genes across distinct fractions. These aggregates enhanced topological complexity and multidimensional connectivity of microbial networks, while harboring elevated transposon abundance. Metagenomic assembly results demonstrated a high-frequency co-occurrence of transposons with MRGs, particularly in cyanobacteria-derived assembled sequences. This suggests that cyanobacterial aggregates, which are enriched with transposases, may facilitate the dissemination of MRGs in the environment. Furthermore, we identified potential pathogenic bacteria harboring multiple resistance genes and VFs. This work provides a systematic profile of resistance genes across fractions during cyanobacterial blooms, revealing distinct trends between ARGs and MRGs. These findings offer critical insights for developing effective lake management strategies to curb the dissemination of resistance genes.

Steroids in the aquatic environment, including extremely important natural hormones and numerous synthetic hormones, have garnered significant attention due to their endocrine disrupting effects. This study conducted a comprehensive investigation of steroid pollutants in Lake Chao and its inflows. In summer, 9 steroids were detected in surface water at total concentrations ranging from 1.3 to 6 ng/L, while 8 steroids were identified in winter with higher total concentrations (2.86-15.09 ng/L). In winter, total concentrations of all steroids were significantly higher than those in summer (p < 0.05). Natural steroids dominated in surface water in summer, whereas steroid metabolites prevailed in winter. Untreated wastewater was identified as the primary source of steroid inputs in both summer and winter, accounting for 56 % and 75 % of the total inputs, respectively. Ecological risk assessments and hazard indices indicated that steroids in Lake Chao pose an overall moderate risk level in both seasons. Progesterone (P) and 17α-trenbolone (17α-TBL) were identified as the highest-priority contaminants in summer, while 4-Androstene-3,17-dione (AED) was determined as the highest-priority contaminant in winter. This research represents the first systematic investigation of steroids and their metabolites in the surface water of Lake Chao, including their spatiotemporal distribution patterns, primary sources, and ecological risks. By employing a multi-criteria assessment approach, the study further identifies priority control pollutants across different seasons, providing critical scientific evidence to support steroid management strategies and precise pollution control measures.

The effects of antibiotics and antibiotic resistance genes (ARGs) on endogenous nitrogen (N) biogeochemistry, particularly in relation to cyanobacterial bloom dynamics, remain poorly understood. Therefore, laboratory microcosms simulating the full life cycle of cyanobacteria were established to investigate the effects of clindamycin (CLIN), tetracycline (TC), sulfamethoxazole (SMX), and their mixture (MIX) on N cycling across the sediment-water interface. Antibiotics accelerated ammonia oxidation and thus nitrification in overlying water during cyanobacterial bloom and decline. ARGs may influence N-cycling functional microbiota and the associated N transformation processes indirectly through mechanisms such as MGEs-mediated horizontal gene transfer or modulation of microbial community structure. Antibiotics increased the ammonia supply in overlying water, thereby supporting cyanobacterial blooms, by increasing N-fixing genes and cyanobacteria and associated N fixation. In sediments, N-cycling genes and ARGs were core regulators of NO2--N and NH3-N, suppressing organic N mineralization while promoting denitrification. At low ambient concentrations, CLIN and MIX stimulated cyanobacterial growth and bloom formation by increasing photosynthesis, strengthening N fixation capacity, and alleviating pressure from competing bacteria. By contrast, high concentrations caused toxic, inhibitory effects. Tetracycline increased cyanobacterial growth by reducing nutrient competition and increasing NH3-N uptake at all concentrations. Sulfamethoxazole at 1000 ng/L sustained a longer duration of cyanobacterial bloom, possibly because it alleviates bacterial competition via folate synthesis inhibition. Therefore, by mediating bacterial communities and functional genes, antibiotics and their ARGs regulate endogenous N cycling and consequently influence cyanobacterial blooms. These findings provide novel insights into the mechanisms behind cyanobacterial bloom outbreaks in eutrophic lakes and thus have important implications for managing endogenous pollution.

Tire additives, classified as high-production-volume chemicals, are released onto road surfaces through tire-road abrasion and subsequently transported into various environments such as rivers, lakes, and soils via surface runoff. Both tire additives and their transformation products (TATPs) have been demonstrated to exert adverse effects on aquatic ecosystems. However, their contamination profiles in large urban lakes remain unclear. To address this gap, 16 TATPs were profiled in the surface waters of Chao Lake during summer and winter. Pronounced seasonal differences were observed in the occurrence of TATPs. Nine compounds were detected in summer and 12 in winter. The total concentrations of detected TATPs ranged from 5551 to 25,201 ng/L in summer and from 2834 to 15,235 ng/L in winter, with significantly higher levels observed in summer (p < 0.01). Although the compositional profiles of TATPs varied seasonally, 1H-benzotriazole (BT) and benzothiazole (BTH) consistently dominated as the primary contaminants. Ecological risk quotient (RQ) assessment showed that the overall potential ecological risk, expressed as the hazard index (HI), exceeded 1 at 55.6% of the sampling sites in summer and 74.1% in winter, with N,N′-diphenylurea (DPU) identified as the primary contributor. Using a multi-criteria prioritization framework, four compounds including 2-methylthio-benzothiazole (2-Me-S-BTH), DPU, BTH, and N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q) and three compounds including 2-Me-S-BTH, BTH, and DPU were identified as high-priority contaminants in summer and winter, respectively. These findings highlight the necessity of temporally resolved monitoring of TATPs in freshwater lakes and underscore the need for increased attention to ubiquitous and environmentally hazardous TATPs in future investigations.

Accelerating anthropogenic activity in watersheds is reshaping reservoir ecosystems and threatening their ecological integrity and services, yet the scarcity of long-term records limits our understanding of how ecosystems respond to cumulative watershed disturbance. Here we used microeukaryotic sedimentary DNA (sedDNA) to reconstruct four decades (1981-2019) of watershed disturbance and ecological change in Duihekou Reservoir. Consistent with a concurrent shift in watershed disturbance, microeukaryotic communities underwent a clear state shift around 2000, from a moderately disturbed, low-nutrient state to a human-impacted, nutrient-enriched mesotrophic regime. This shift favoured mixotrophic and phagotrophic taxa as "winners", potentially threatening water quality and higher trophic levels. At the same time, co-occurrence networks reorganized from a fungus-centered web into a denser, multi-core architecture with higher robustness metrics, motivating the hypothesis that recovery may face a higher barrier once the mesotrophic state is established. Community assembly also became increasingly deterministic, with watershed human activities emerging as the strongest correlates of succession and the regime shift. Using random forest algorithms, we developed microeukaryotic sedDNA indicator models to reconstruct watershed disturbance and clarified their applicability and limitations for hindcasting past watershed conditions. Together, these findings demonstrate that microeukaryotic sedDNA archives can serve as sensitive, integrative sentinels of cumulative watershed disturbance and reservoir regime shifts, providing a basis for applying sedDNA-based indicator models in long-term monitoring and adaptive management.

Despite the pivotal role of fungi in regulating algal blooms and ecosystem health, community-level fungal dynamics in natural cyanobacterial bloom events, and their correlation with changes in algal communities, remain poorly understood. Through a year-long survey in eutrophic Lake Chaohu, China, we analyzed the planktonic fungal and phytoplankton community changes. The results showed that Chytridiomycota dominated the fungal community throughout the year, whereas Ascomycota and Basidiomycota increased markedly during late-bloom and post-bloom periods, suggesting a functional shift from potential parasitism to saprotrophy. Algal and fungal communities showed significant concordance at the community level, as indicated by the positive relationship between their Bray-Curtis distances (P < 0.001). Separate fitting of dominant algal taxa onto the fungal ordination space showed that Microcystis was primarily associated with the bloom-period fungal assemblage, whereas Chlorella and others were more closely associated with non-bloom fungal community variation. The strength of algal-fungal associations also increased significantly with the relative dominance of algal taxa (P < 0.05), supporting a dominance-dependent interaction pattern. Together, these results indicate that planktonic fungal communities were closely associated with algal community dynamics through both host-abundance- and host-dominance-related patterns, and highlight the importance of considering fungal processes in ecological frameworks for understanding phytoplankton succession and cyanobacterial bloom dynamics.

Submerged macrophytes influence sediment microbial communities in shallow lakes; however, the ecological roles of their community-level characteristics remain underexplored. In this study, we examined the relationships between macrophyte community coverage and diversity and the composition of sediment bacterial communities in Dongshan Bay, Lake Taihu. We combined high-throughput sequencing, functional prediction, and multivariate statistical modelling to analyse sediment bacterial composition, potential metabolic functions, community assembly proceses, and their associations with macrophyte communities and environmental factors. Macrophyte community structure explained more variation in sediment bacterial community structure than seasonal dynamics. Higher coverage and diversity were related to improved water clarity, elevated sediment nutrient concentrations, and enhanced bacterial metabolic potential. In macrophyte-dominated zones, bacterial communities were primarily structured by homogeneous selection, and microbial co-occurrence networks became less complex. Our results indicate that species richness, diversity, and coverage most effectively capture the ecological functions of submerged macrophyte communities, and collectively influence sediment bacterial communities through multiple pathways, including habitat modification and altered selection pressures. This study underscores the ecological role of macrophyte diversity and coverage in shaping sediment microbiota, offering insights for lake restoration strategies.

Pollution source identification is the key foundation of urban river water quality management. In this study, fluorescence fingerprinting was employed to analyze changes in dissolved organic matter (DOM) sources in urban river outfalls P1-P3 in Hefei City, China, before and during a rainfall event. The water quality of the outfalls varied before and during rainfall, with an apparent dilution in P2 and a combined effect of urban nonpoint runoff and dilution in P3. The fluorescent components of the DOM in the outfall water were fulvic acid-like substances C1, terrestrial humic-like substances C2, and tryptophan-like substances C3. The dominant C1 in P1 was diluted by rainfall runoff, decreasing the total fluorescence intensity (FT) of the DOM. The increased FT and proportion of C1 + C2 in P2 during early rainfall indicated runoff inputs, whereas those in P3 increased and decreased thereafter, suggesting that rainfall led to an influx of domestic sewage. Fluorescence fingerprinting analysis indicated that the DOM in P1 originated primarily from rainwater and domestic wastewater treatment plant (WWTP) effluent. The DOM in P2 originated from domestic WWTP effluent pre-rainfall, rainwater, and domestic WWTP effluent during early rainfall and urban non-point runoff during later rainfall, whereas that in P3 originated from domestic sewage before and during early rainfall and urban non-point runoff during later rainfall. Identifying sources of pollution provides a basis for urban outfall and river water quality management before and during rainfall events.

Understanding the coupling relationships among lake physicochemical properties, internal nutrient recycling, and related microbes is key for the control of freshwater eutrophication. In this study, seasonal variations in microorganisms at the sediment–water interface (SWI) of the eutrophic Lake Chaohu in China were analyzed, in order to reveal changes in phosphorus (P)-cycling-related microbes in the sediments and its association with internal P release during the cyanobacterial life cycle. The identified P-cycling-related microbes include phosphorus-solubilizing bacteria (PSB) (dominant of Bacillus, Thiobacillus and Acinetobacter), sulfate-reducing bacteria (SRB) (dominant of Sva0081_ sediment_ group, norank_ c__ Thermodesulfovibrionia and Desulfatiglans) and iron-reducing bacteria (FeRB) (dominant of Geothermobacter, Anaeromyxobacter, Thermoanaerobaculum and Clostridium_sensu_stricto_1). Increased PSB and reduced proportions of iron-aluminum–bound P (Fe/Al-P) and calcium–bound P (Ca-P) from the benthic stage to initial cyanobacterial growth indicated that internal phosphorus was released through the solubilization of Fe/Al-P and Ca-P by PSB. Growth of cyanobacteria was accompanied by cyanobacteria death, deposition, and degradation during early algal blooms, which increased SRB caused by high organic matter and the net deposition of phosphorus in the western lake. Conversely, phosphorus release in eastern lake was observed because of organic phosphorus mineralization. High linear discriminant analysis effect size of SRB and FeRB and the decreased Fe/Al-P in sediments indicated sulfide-mediated chemical iron reduction (SCIR) and FeRB-mediated microbial iron reduction mechanisms for internal phosphorus release during late algal blooms. The observed seasonal pattern of P-cycling-related microbes and its mediation on internal phosphorus release provides a foundation for internal P management in Lake Chaohu.

Biocides, including fungicides and paraben preservatives, are widely used in medicine, agriculture and food industries, and are ubiquitous in aquatic environments, which will have adverse impacts on aquatic organisms. This study investigated the occurrence, distribution, ecological risks, and human health risks of 7 target biocides in Chao Lake, a large eutrophic urban lake, and its tributaries. Four biocides were detected, with total concentrations ranging from 186 ng/L to 853 ng/L. Carbendazim (CBD), fluconazole (FCZ), and methylparaben (MP) had detection frequencies of 100%, with mean concentrations of 234 ng/L, 35.3 ng/L, and 26.8 ng/L, respectively. Significant spatial heterogeneity was observed, with obviously elevated levels in the western region compared with the central and eastern regions. Strong correlations (p ≤ 0.01) were found between these three biocides, CBD, FCZ, and climbazole (CLI), and the following two environmental factors: total nitrogen and dissolved total nitrogen. Based on the risk quotient (RQ) evaluation, CBD was identified as a high-risk compound for aquatic organisms, particularly Daphnia magna, with RQ values exceeding 1 and reaching up to 7.42. CLI showed moderate risks at some sampling sites, while FCZ and MP posed no risk. Human health risk quotient (RQh) analysis revealed no significant health risks to different age groups, with the RQh values of biocides at all sampling sites in Chao Lake below 0.1. The ecological risks of CBD warrant even greater attention.

Understanding size-dependent grazing dynamics is critical for elucidating trophic interactions in eutrophic lakes. This study employed a dual-zone (littoral vs. pelagic) framework in Lake Chaohu to quantify zooplankton grazing on size-classified phytoplankton from April 2023 to March 2024 via dilution experiments. Our results reveal inedible cyanobacteria colonies (>200 μm) dominated phytoplankton biomass (86% -96%) during peak-blooms, accumulating in littoral zones. Edible phytoplankton (<200 μm), predominantly in the 40-200 μm (56%) and 3-20 μm (28%) size fractions, sustained zooplankton feeding in pre- and post-bloom periods. Zooplankton consumed 19.4% of phytoplankton biomass during non-bloom periods compared to only 8.3% during blooms. Meso-zooplankton filter feeders (dominant in littoral zones) exerted strong grazing pressure on S-sized phytoplankton (3-20 μm), contributing to clear-water phases (May-Jun). Cyanobacterial proliferation suppressed meso‑zooplankton grazing and shifted the primary grazing pressure to micro-zooplankton filter feeders, which exhibited significant consumption of L-sized cyanobacteria (40-200 μm) during peak-bloom. However, this micro-zooplankton grazing on bloom-forming cyanobacteria was constrained by predation from meso‑zooplankton carnivores in pelagic zones. These results underscore the interplay of phytoplankton size structure, zooplankton functional traits, and trophic cascades in mediating bloom dynamics and energy flow pathways in eutrophic lakes.

Understanding the interactions between dissolved organic matter (DOM) and nutrient behavior during cyanobacterial events has important implications for water management. Therefore, we constructed a simulated cyanobacterial growth and decline experiment, measured the changes in the DOM and the nitrogen and phosphorus fluxes at the sediment–water interface (SWI), and examined the effects of cyanobacterial growth and decline on DOM components and nitrogen and phosphorus release. Results of 3D fluorescence spectroscopy showed that the fluorescent components of DOM in the sediment and overlying water comprised microbially derived humic-like C1, terrestrially derived humic-like C2, tyrosine-like C3, and tryptophan-like C4. From initial cyanobacterial growth to the blooms phase, C3 and C4 in overlying water increased due to the formation and release of extracellular algal-derived organic matter. During the cyanobacterial growth and decline, protein-like C3 and C4 in sediment increased from the settling of algae. The rapid increase in phosphorus fluxes during the blooms stage indicated that cyanobacterial growth promoted the release of phosphorus from sediments through organic phosphorus mineralization and Fe/Al-P transformation. High ammonium fluxes occurred at the initial cyanobacterial growth mainly due to the mineralization of organic matter in sediments. Redundancy analysis showed that changes in the sediment DOM were primarily associated with the loss on ignition and cyanobacterial blooms promoted the release of DOM into the water. This study provides fresh perspectives on the associations between DOM and nutrient behavior during cyanobacterial growth and decline and has strong implications for internal pollution management. Graphical Abstract

Antibiotic resistance genes (ARGs) represent an emerging pollutant of increasing concern. In this study, we analyzed the composition and spatiotemporal variation of ARGs in the sediments of eutrophic Chaohu Lake, China, using a metagenomic method. A total of 22 ARGs and 199 ARGs subtypes were detected, with the most prevalent subtypes being multidrug (57.720 %) and rifamycin (21.781 %). A higher abundance of ARGs in Chaohu Lake was observed (p < 0.05) during winter and spring owing to multiple factors, including variations in seasonal inputs and hydraulic conditions, occurrence of cyanobacterial blooms, and changes in ARGs host bacterial communities. Spatially, a higher abundance of multidrug was observed in sediments near the Nanfei River outlet, which flows through urban areas; whereas higher levels of bacitracin were observed in sediments near the Zhao River outlet, which flows through agricultural areas. Cyanobacterial blooms and declines change the sediment physicochemical properties, endogenous phosphorus contents, microbial communities, and seasonal ARGs distribution. Correlation and collinearity analyses indicated that ARGs were transferred horizontally via mobile genetic elements (MGEs). High-risk ARGs in Chaohu Lake were observed at a very low proportion, although certain ARGs presented health risks in the western lake during spring. In this study, we highlight the interactions between cyanobacterial blooms and variations in ARGs in Chaohu Lake and provide novel insights into ARGs dynamics in eutrophic freshwater ecosystems.

Submersed macrophytes are an integral component of shallow lake ecosystems,and their distribution patterns are influ-enced by environmental factors,particularly water depth.Key factors affecting the growth of submersed macrophyte vary across dif-ferent water depth gradients,and they interact synergistically with water depth conditions to influence submersed macrophyte com-munities.Dongshan Bay,a typical macrophyte-dominated lake area in the eastern part of Lake Taihu,was selected as research area in this study.From October 2020 to June 2021,three surveys were conducted on water physicochemical indicators and the species richness and abundance of submersed macrophyte at 31 sampling sites with varying water depths.The relationship between sub-mersed macrophyte and environmental factors at different water depths were analysed using one-way ANOVA,Spearman correlation analysis,and redundancy analysis,to identify key environmental factors influencing submersed plant community composition in dif-ferent water depth zones.The results indicated:1)physicochemical parameters of the water exhibited significant spatiotemporal differences.The average chlorophyll-a(Chl.a)content and the ratio of Secchi depth to water depth(SD/WD)in the nearshore waters of shallow areas in the Dongshan Bay of Lake Taihu were significantly higher than those in deeper near-lake center area.To-tal nitrogen(TN),nitrate nitrogen,total phosphorus(TP),phosphate and suspended solids concentrations were significantly higher in spring than in autumn and summer.2)This study recorded 12 species of submersed macrophyte in Dongshan Bay,with higher frequency of submersed macrophyte in the middle waters.The submersed macrophyte communities in different water depth areas showed differences in species composition,with species like Potamogeton wrightii/Potamogenton malaianus,Vallisneria na-tans and Hydrilla verticillata exhibiting higher frequency and abundance in the near-lake center area.3)Key water environmental factors influencing the submersed macrophyte community in the Dongshan Bay include water depth,TN,TP,SD/WD and Chl.a,and the composition of submersed macrophyte communities in different water depth areas is regulated by different water environmen-tal factors.The key environmental factors affecting submersed macrophyte growth in shallow nearshore areas include water depth and Chl.a;submersed macrophytes in the midwater area are mainly influenced by water TN and TP;while submerged macrophytes in deeper areas near the lake center are significantly correlated with water depth,TN and TP.The results of this study provide impor-tant theoretical basis for shallow lake water level management and submersed macrophyte restoration under different water depth en-vironments.

The seasonal fluctuation of phosphorus in shallow water lakes is a crucial process in the response of lake ecosystems to environmental changes. Unravelling the seasonal fluctuation pattern of phosphorus and its influencing factors in lakes is key to scientific and effective lake management. This study utilized 12 years of continuous monthly monitoring data from Lake Chaohu to analyze the seasonal variation pattern of phosphorus and its driving factors. The results indicated that phosphorus in Lake Chaohu exhibited a distinct intra-annual fluctuation pattern. The period from February to April represented the low values of phosphorus, which gradually increased thereafter, with the peak phosphorus concentration occurring from August to October, reaching the annual high. During the high phosphorus period, the total phosphorus concentration was 0.058 mg/L higher on average than the low phosphorus period, representing an average increase of 84%. Moreover, this fluctuation amplitude increased gradually from east to west. The intra-annual variation patterns of phytoplankton biomass and chlorophyll- a did not precisely align with the phosphorus fluctuation pattern. The peak values of phytoplankton biomass occurred earlier in the year than the peak phosphorus values, and there was a period of substantial phytoplankton distribution even in winter when phosphorus concentrations were relatively low. The explanatory power of algal intra-annual fluctuation amplitude on phosphorus fluctuation amplitude was less than 10%, indicating a limited influence of phytoplankton's intra-annual changes on the seasonal phosphorus fluctuation in Lake Chaohu. The intra-annual fluctuation pattern of phosphorus in Lake Chaohu was likely primarily driven by the natural release of internal phosphorus, with limited evidence of the regulatory effects of algal pump suction and external pollution entering the lake. This study enhanced our understanding of the seasonal variation of phosphorus in shallow lakes and held significant scientific implications for formulating strategies to control internal pollution in lakes.

Community structure and diversity of fish exhibit a strong correlation with environmental variables.We studied the spatial and temporal patterns of the fish community structure and diversity in both the small and main lake regions of Lake Hengshui throughout 2021.The relationships between fish community structure and environmental factors were analyzed.A total of 29 fish species across 15 families and 27 genera were recorded in Lake Hengshui.Cyprinid species contributed 98％to the total catch by weight.The dominant fish species in Lake Hengshui were Hemiculter leucisculus,Carassius carassius,Hypophthalmus molitrix and Pseudobrama simoni.There were no seasonal and spatial variations in Shannon-Wiener diversity index,Pielou's evenness index and Margalefs species richness index of fishes in the main region of the lake.However,permutational multivariate analysis highlighted significant temporal variations in fish community structure in the main lake region.Similarity percentage analysis revealed an aver-age seasonal difference over 40％in fish communities of the main lake,the spatial difference of fish community structure between the main lake and small lake regions was 41％.The abundance-biomass curve indicated that fish communities in the main lake re-gion was largely disturbed in all sampling seasons.In the small lake region,these disturbances were only observed in spring and summer,while not in autumn.Redundancy analysis indicated that the epilimnetic total phosphorus of the main lake explained most of fish community changes(36％).Total phosphorus,nitrite,secchi depth and total nitrogen were also the main contributors which influencing the fish community structure of the main lake.The fish community structure of Lake Hengshui is dominated by small omnivorous fish,such as H.leucisculus,C.carassius and P.simoni,while the abundance of piscivorous fish is relatively low.Therefore,in the context of enhancing water quality and ecological restoration,after the reduction of external nutrient loads,it is important to manipulate the fish community structure of Lake Hengshui.This involves strengthening the top-down effect by carnivo-rous fish,mitigating the potential adverse impacts of omnivorous fish and planktivorous fish on water quality,ultimately working to-wards the objective of improving water quality.

Global warming has caused an increase in the frequency and duration of droughts worldwide. Droughts could trigger large changes in physico-chemical conditions and phytoplankton community in waterbodies, resulting in a shift in the phytoplankton community. Spring diatom blooms in reservoirs have been increasingly observed in the past decade in the Taihu Lake basin. The aim of the present study is to elucidate the impacts of droughts on aquatic environment and to determine the driving factors for the succession of the phytoplankton functional groups based on the analysis of data collected during spring from 2009 to 2020 in the Daxi Reservoir. The unimodal relationship between 1-month aggregated precipitation index and phytoplankton species richness indicated the competitive exclusion occurred in extremely drought period. The structural equation modeling indicated that drought-related low water level conditions intensified sediment resuspension, and increased the phosphorus-enriched nonalgal turbidity in the Daxi Reservoir. Concurrently, a steady shift in the Reynolds phytoplankton functional groups from L0, TD, J, X2, and A (phytoplankton taxa preferring low turbidity and nutrient conditions) to TB (pennate diatoms being adapt to turbid and nutrient-rich conditions) was observed. The increased TP and non-algal turbidity in addition to the lowered disturbance contribute to the prevalence of Group TB. Considering the difficulties in nutrient control, timely water replenishment is often a feasible method of controlling the dominance of harmful algae for reservoir management. Finally, alternative water sources are in high demand for ensuring ecological safety and water availability when dealing with drought.

Understanding the response of the phytoplankton community to climate change is essential for reservoir management. We analyzed a long-term data series (2009–2020) on the phytoplankton community in a large mesotrophic reservoir in the wet season to investigate the impacts of temperature and precipitation increases caused by climate change on the functioning and trait composition of the phytoplankton community. Over the last twelve years, the 3-month accumulative precipitation increased from 291.03 mm to 590.91 mm, and the surface water temperature increased from 25.06 °C to 26.49 °C in wet season, respectively. These changes caused a higher water level, stronger thermal stratification and lower nitrogen concentration in Daxi Reservoir. The dynamic equilibrium model indicated that the increased precipitation and water temperature-related environmental changes would result in a more diverse and productive phytoplankton community. The effects of increasing water temperature and precipitation on the niche complementarity and selection effects within the phytoplankton community were analyzed using structural equation model by means of the functional divergence index and functional evenness index, respectively, elucidating the reasons for the increase in cyanobacteria in the absence of a significant increase in nutrient levels. Based on these results, it is advisable that more stringent phosphorus control standards might be conducted to reduce the risks of cyanobacteria proliferation in the context of global warming.