Assessment of eutrophication and water quality in the estuarine area of Lake Wuli, Lake Taihu, China

Water quality assessment in a large plateau lake in China from 2014 to 2021 with machine learning models: Implications for future water quality management

Amid the global surge of eutrophication in lakes, investigating and analyzing water quality and trends of lakes becomes imperative for formulating effective lake management policies. Water quality index (WQI) is one of the most used tools to assess water quality by integrating data from multiple water quality parameters. In this study, we analyzed the spatio-temporal variations of 11 water quality parameters in one of the largest plateau lakes, Erhai Lake, based on surveys from January 2014 to December 2021. Leveraging machine learning models, we gauged the relative importance of different water quality parameters to the WQI and further utilized stepwise multiple linear regression to derive an optimal minimal water quality index (WQImin) that required the minimal number of water quality parameters without compromising the performance. Our results indicated that the water quality of Erhai Lake typically showed a trend towards improvement, as indicated by the positive Mann-Kendall test for WQI performance (Z = 2.89, p < 0.01). Among the five machine learning models, XGBoost emerged as the best performer (coefficient of determination R2 = 0.822, mean squared error = 3.430, and mean absolute error = 1.460). Among the 11 water quality parameters, only four (i.e., dissolved oxygen, ammonia nitrogen, total phosphorus, and total nitrogen) were needed for the optimal WQImin. The establishment of the WQImin helps reduce cost in future water quality monitoring in Erhai Lake, which may also serve as a valuable framework for efficient water quality monitoring in similar waters. In addition, the elucidation of spatio-temporal patterns and trends of Erhai Lake's water quality serves as a compass for authorities, offering insights to bolster lake management strategies in the future.

A national-scale assessment on the spatial and temporal variations in water color for urban lakes in China

Monitoring the variations of lake water quality is essential for urban water security and sustainable eco-environment health. However, it is challenging to investigate the water quality of urban lakes at large scales due to the need for large-amount in situ data with diverse optical properties for developing the remote sensing inversion algorithms. Forel-Ule Index (FUI), a proxy of quantifying water color, whose calculation does not require in situ data of specific properties, can comprehensively reflect water quality conditions. However, the spatial and temporal distribution of water color in Chinese urban lakes is still poorly understood. To fill this research gap, this study investigated the spatial distribution of water color in 523 urban lakes (area > 0.5 km2) in China using the FUI derived from the high-quality Multi-Spectral Instrument (MSI) data onboard Sentinel-2 during the ice-free period (April-October) from 2019 to 2022. The monthly and seasonal variation patterns of water color in urban lakes were also analyzed. Our results show that green domain is the most common color of urban lakes, with about 86 % of urban lakes in China being green, and non-green lakes accounting for only 14 % of the total number of lakes. The monthly variation of FUI in urban lakes across the country and multiple geographic regions is basically the same. The monthly average FUI first increases, then decreases, and then rebounds. We also found that the seasonal variation of water color in most urban lakes in southern and northern China is opposite. This study helps to comprehensively understand the spatial and temporal variation of water color and quality of urban lakes in China, providing key basic information for the protection and governance of urban lakes.

Rainfall seasonality shapes microbial assembly and niche characteristics in Yunnan Plateau lakes, China

Microorganisms are crucial components of freshwater ecosystems. Understanding the microbial community assembly processes and niche characteristics in freshwater ecosystems, which are poorly understood, is crucial for evaluating microbial ecological roles. The Yunnan Plateau lakes in China represent a freshwater ecosystem that is experiencing eutrophication due to anthropogenic activities. Here, variation in the assembly and niche characteristics of both prokaryotic and microeukaryotic communities was explored in Yunnan Plateau lakes across two seasons (dry season and rainy season) to determine the impacts of rainfall and environmental conditions on the microbial community and niche. The results showed that the environmental heterogeneity of the lakes decreased in the rainy season compared to the dry season. The microbial (bacterial and microeukaryotic) α-diversity significantly decreased during the rainy season. Deterministic processes were found to dominate microbial community assembly in both seasons. β-Diversity decomposition analysis revealed that microbial community compositional dissimilarities were dominated by species replacement processes. The co-occurrence networks indicated reduced species complexity for microbes and a destabilized network for prokaryotes prior to rainfall, while the opposite was found for microeukaryotes following rainfall. Microbial niche breadth decreased significantly in the rainy season. In addition, lower prokaryotic niche overlap, but greater microeukaryotic niche overlap, was observed after rainfall. Rainfall and environmental conditions significantly affected the microbial community assembly and niche characteristics. It can be concluded that rainfall and external pollutant input during the seasonal transition alter the lake environment, thereby regulating the microbial community and niche in these lakes. Our findings offer new insight into microbiota assembly and niche patterns in plateau lakes, further deepening the understanding of freshwater ecosystem functioning.

Identify the seasonal differences in water quality and pollution sources between river-connected and gate-controlled lakes in the Yangtze River basin

The river-connected Dongting Lake (DT) and Poyang Lake (PY), and the gate-controlled Taihu Lake (TH) and Chaohu Lake (CH) are the four important lakes in the Yangtze River Basin. The comprehensive Water Quality Index (WQI), the Eutrophication Integrated Index (TLI(Σ)), and the Positive Matrix Factorization (PMF) model were employed to evaluate water quality and the contribution of pollution sources for these lakes. The results show that WQI for all lakes indicated generally good water quality, with DT scoring 73.52-86.18, the highest among them. During the wet season, the eutrophication degree of river-connected lake was medium, and that of gate-controlled lakes was high. The surface runoff and agricultural non-point sources are the main pollution sources for both types of lakes, but their impact is more pronounced in gate-controlled lakes during the wet season. The study provides evidence support for scientific understanding of water quality problems and management strategies in these areas.

Ecological restoration for eutrophication mitigation in urban interconnected water bodies: Evaluation, variability and strategy

Many urban water bodies grapple with low flow flux and weak hydrodynamics. To address these issues, projects have been implemented to form integrated urban water bodies via interconnecting artificial lake or ponds with rivers, but causing pollution accumulation downstream and eutrophication. Despite it is crucial to assess eutrophication, research on this topic in urban interconnected water bodies is limited, particularly regarding variability and feasible strategies for remediation. This study focused on the Loucun river in Shenzhen, comprising an pond, river and artificial lake, evaluating water quality changes pre-(post-)ecological remediation and establishing a new method for evaluating the water quality index (WQI). The underwater forest project, involving basement improvement, vegetation restoration, and aquatic augmentation, in the artificial lake significantly reduced total nitrogen (by 43.58%), total phosphorus (by 79.17%) and algae density (by 36.90%) compared to pre-remediation, effectively controlling algal bloom. Rainfall, acting as a variable factor, exacerbated downstream nutrient accumulation, increasing total phosphorus by 4.56 times and ammonia nitrogen by 1.30 times compared to the dry season, and leading to algal blooms in the non-restoration pond. The improved WQI method effectively assesses water quality status. The interconnected water body exhibits obvious nutrient accumulation in downstream regions. A combined strategy that reducing nutrient and augmenting flux was verified to alleviate accumulation of nutrients downstream. This study provides valuable insights into pollution management strategies for interconnected pond-river-lake water bodies, offering significant reference for nutrient mitigation in such urban water bodies.

Innovative lake pollution profiling: unveiling pollutant sources through advanced multivariate clustering techniques

In many developed and developing nations, lakes are the primary source of drinking water. In the current scenario, due to rapid mobilization in anthropogenic activities, lakes are becoming increasingly contaminated. Such practices not only destroy lake ecosystems but also jeopardize human health through water-borne diseases. This study employs advanced hierarchical clustering through multivariate analysis to establish a novel method for concurrently identifying significantly polluted lakes and critical pollutants. A systematic approach has been devised to generate rotating component matrices, dendrograms, monoplots, and biplots by combining R-mode and Q-mode analyses. This enables the identification of contaminant sources and their grouping. A case study analyzing five lakes in Bengaluru, India, has been conducted to demonstrate the effectiveness of the proposed methodology. Additionally, one pristine lake from Jammu & Kashmir, India, has been included to validate the findings from the aforementioned five lakes. The study explored correlations among various physical, chemical, and biological characteristics such as temperature, pH, dissolved oxygen, conductivity, nitrates, biological oxygen demand (BOD), fecal coliform (FC), and total coliform (TC). Critical contaminants forming clusters included conductivity, nitrates, BOD, TC, and FC. Factor analysis identified four primary components that collectively accounted for 85% of the overall variance. Following identification of pollution hotspots, the study recommends source-based pollution control and integrated watershed management, which could significantly reduce lake pollution levels. Continuous monitoring of lake water quality is essential for identifying actual contaminant sources. These findings provide practical recommendations for maximizing restoration efforts, enforcing regulations on pollutant sources, and improving water quality conditions to ensure sustainable development of lakes.

Quantitative Effects of Anthropogenic and Natural Factors on Heavy Metals Pollution and Spatial Distribution in Surface Drinking Water Sources in the Upper Huaihe River Basin in China

The water quality of sources in the Huaihe River Basin significantly affects the lives and health of approximately 16.7% of China's population. Identifying and quantifying pollution sources and risks is essential for effective water resource management. This study utilized Monte Carlo simulations and Geodetector to assess water quality and eutrophication, as well as to evaluate the sources of heavy metals and the associated health risks for both adults and children. The results showed that eutrophication of water sources in Huaihe River was severe, with an overall EI value of 37.92; 67.8% of the water sources were classified as mesotrophic and 32.2% classified as eutrophic. Water quality and eutrophication levels in the southern mountainous regions were better than those in the densely populated northern areas. Adults were found to have a higher carcinogenic risk than children, whereas children faced a higher noncarcinogenic risk than adults. Cr presented the highest carcinogenic risk, affecting more than 99.8% of both adults and children at levels above 1 × 10-6 but not exceeding 1 × 10-4. The noncarcinogenic risk from metals did not surpass a level of 1, except for Pb. As was primarily influenced by agricultural activities and transportation, whereas Cd, Cr, and Pb were mainly affected by industrial activities, particularly in local textile industries such as knitting and clothing manufacturing. The analysis demonstrated that the influence of anthropogenic factors on heavy metal distribution was significantly enhanced by indirect natural factors. For example, the explanatory power of Precipitation and Road Network Density on As was 0.362 and 0.189, respectively, whereas their interaction had an explanatory power as high as 0.673. This study indicates that the geodetector method is effective in elucidating the factors influencing heavy metal distribution in water, thereby providing valuable insights into pollution sources in global drinking water.

Functional trait-based phytoplankton biomass and assemblage analyses in the pre-growing season for comprehensive algal bloom risk assessment

Algal bloom (AB) risk assessment is critical for maintaining ecosystem health and human sustainability. Previous AB risk assessments have focused on the potential occurrence of ABs and related factors in the growing season, whereas their hazards, especially in the pre-growing season, have attracted less attention. Here, we performed a comprehensive AB risk assessment, including water trophic levels, phytoplankton biomass, functional trait-based assemblages, and related environmental factors, in the pre-growing season in Dongting Lake, China. Although mesotrophic water and low phytoplankton biomass suggested low AB potential, toxic taxa, which constituted 13.28% of the phytoplankton biomass, indicated non-negligible AB hazards. NH4+ and water temperature were key factors affecting phytoplankton motility and toxicity. Our study establishes a new paradigm for quantitative AB risk assessment, including both potential AB occurrence and hazards. We emphasize the importance of phytoplankton functional traits for early AB warning and NH4+ reduction for AB control in the pre-growing season.

Temporal-spatial characteristics and sources of heavy metals in bulk deposition across China

With the rapid development of industries, agriculture, and urbanization (including transportation and population growth), there has been a significant alteration in the emission and atmospheric deposition of heavy metal pollutants. This has consequently given rise to a range of ecological and environmental health issues. In this study, we conducted a comprehensive two-year investigation on the temporal and spatial distribution characteristics of heavy metals in atmospheric deposition across China based on the Nationwide Nitrogen Deposition Monitoring Network (NNDMN). The atmospheric bulk deposition of Lead (Pb), Arsenic (As), Nickel (Ni), Selenium (Se), Chromium (Cr) and Cadmium (Cd) were 6.32 ± 1.59, 4.49 ± 0.57, 1.31 ± 0.21, 1.05 ± 0.16, 0.60 ± 0.06 and 0.21 ± 0.03 mg m-2 yr-1, respectively, with a large variation among the different regions of China. The order for atmospheric deposition flux was Southwest China > Southeast China > North China > Northeast China > Qinghai-Tibet Plateau and rural area > urban area > background area. The concentrations of heavy metals in bulk deposition exhibit seasonal variation with higher levels observed during winter compared to summer and spring, which are closely associated with anthropogenic activities. The Positive Matrix Factorization (PMF) results indicated that combustion, industrial emissions and traffic are the primary contributors to atmospheric deposition of heavy metals. The single factor pollution index (Pi) of heavy metals is consistently below 1, and the composite pollution index (Ni) is 0.16 across China, indicating that atmospheric heavy metal deposition is at a pollution-free level. The comprehensive potential ecological risk index of heavy metals is 11.8, with Cd exhibiting the highest single factor potential ecological risk index at 7.09, suggesting that more attention should be paid to Cd deposition in China. The present study reveals the spatial-temporal distribution pattern of atmospheric heavy metals deposition in China, identifying regional source characteristics and providing a theoretical foundation and strategies for reducing emissions of atmospheric pollutants.

An innovative method based on Gaussian cloud distribution and sample information richness for eutrophication assessment of Yangtze's lakes and reservoirs under uncertainty

The precise assessment of a water body's eutrophication status is essential for making informed decisions in water environment management. However, conventional approaches frequently fail to consider the randomness, fuzziness, and inherent hidden information of water quality indicators. These would result in an unreliable assessment. An enhanced method was proposed for the eutrophication assessment under uncertainty in this study. The multi-dimension gaussian cloud distribution was introduced to capture the randomness and fuzziness. The Shannon entropy based on various sample size and trophic levels was proposed to maximize valuable information hidden in the datasets. Twenty-seven significant lakes and reservoirs located in the Yangtze River Basin were selected to demonstrate the proposed method. The sensitivity and consistency were used to evaluate the accuracy of the proposed method. Results indicate that the proposed method has the capability to effectively assess the eutrophication status of lakes and reservoirs under uncertainty and that it has a better sensitivity since it can identify more than 33-50% trophic levels compared to the traditional methods. Further scenario experiments analysis revealed that the sample information richness, i.e., sample size and the number of trophic levels is of great significance to the accuracy/robustness of the method. Moreover, a sample size of 60 can offer the most favorable balance between accuracy/robustness and the monitoring expenses. These findings are crucial to optimizing the eutrophication assessment.

Assessment of water quality of Netravathi-Gurupur estuary, India through chemometric approach for fisheries sustainability

The present study aimed to assess the water quality dynamics (physicochemical properties, nutrient and chlorophyll-a) in the Netravathi-Gurupur estuary, India across the space and seasons and to simplify the complex water quality dataset through a chemometric approach. The results indicated that pH, EC, temperature, alkalinity, salinity, TDS, hardness, chloride and intense mixing of suspended solids, driven by the semidiurnal tides, are the major factors affecting water quality. Spatial heterogeneity and monsoon have profound impact on nutrient distribution revealing the following values (mg l-1): phosphate-P (0.015-0.105), nitrate-N (0.016-0.094), nitrite-N (0.001-0.012), and silicate (1.83-14.50). The estuary was evaluated for suitability for brackish water fisheries. The results indicated fair water quality during pre- and post-monsoon but marginal quality in monsoon, primarily due to dilution associated with reduced salinity. The outcome of this study can be suitably utilized for the sustainable development of estuaries and their feasibility for brackish water fisheries.

Codisposal of landfill leachate concentrate and antimony mine soils using a one-part geopolymer system for cationic and anionic heavy metals immobilization

Geopolymer solidification/stabilization technology has developed rapidly in the remediation field of heavy metal-contaminated soil. However, geopolymers exhibit low anionic heavy metal immobilization efficiency due to their electronegativity and alkali activation characteristics. This study constructed a one-part blast furnace slag-based geopolymer system using landfill leachate concentrate (LLC) as chlorine and humic acid sources and achieved the solidification/stabilization of cations (Cd, Cu, Hg, and Pb) and anions (Sb and As) in the antimony mine soils (AMS). The LLC addition increased the Sb and As fixation rates from 92%∼94% and 82∼86%, respectively, to over 99%, reducing the leaching concentration of all heavy metal ions to the ppb level. LLC improved the chemical stability and physical encapsulation of Sb/As in three ways: inducing a Friedel's salt (FS) formation, enhancing humic acid complexation/chelation, and promoting geopolymerization. Wet curing was more conducive to FS formation in the geopolymer than dry curing and increased the 28-day compressive strength by 38.5%. Due to the SiO2 skeleton support effect in AMS, a 30 wt% AMS addition was beneficial for geopolymer strength development. Our study provided a harmless method for the codisposal of LLC and AMS and improved the efficiency of geopolymer fixation of complex heavy metal cations and anions.

Dynamics of bacterioplankton communities in the estuary areas of the Taihu Lake: Distinct ecological mechanisms of abundant and rare communities

As the crucial confluences of rivers and lakes, the estuary areas with varied hydrodynamic exchanges intensively affect the bacterioplankton communities, whereas the ecological characteristics of the bacterioplankton in the areas have not been well understood. Here, the distribution patterns and assembly mechanisms of bacterioplankton communities in the estuary areas of the Taihu Lake were investigated using high-throughput sequencing and multivariate statistical analyses. Our results showed obvious seasonal variations in bacterioplankton diversity and community composition, which had significant correlations with water temperature. Neutral and null models together revealed that stochastic processes (especially dispersal limitation) were the major processes in shaping the communities across different seasons. By contrast, heterogeneous selection in deterministic processes exhibited increased impacts on community assembly during summer and autumn, which was significantly related to the comprehensive water quality index (WQI) rather than any single factor. In this study, rare communities displayed more pronounced seasonal dynamics compared to abundant communities, likely due to their sensitivity towards environmental factors. Accordingly, the heterogeneous selection of deterministic processes largely shaped the rare communities. These results enriched our understanding of the assembly mechanisms of bacterioplankton communities in estuary areas and emphasized the specific co-occurrence patterns of abundant and rare communities.

A new approach to quantify chlorophyll-a over inland water targets based on multi-source remote sensing data

Chlorophyll-a (Chl-a) concentration is a reliable indicator of phytoplankton biomass and eutrophication, especially in inland waters. Remote sensing provides a means for large-scale Chl-a estimation by linking the spectral water-leaving signal from the water surface with in situ measured Chl-a concentrations. Single-sensor images cannot meet the practical needs for long-term monitoring of Chl-a concentrations due to cloud cover and satellite operational lifetimes. However, quantifying long-term inland water Chl-a concentrations using multi-source remote sensing data remains a problem, as improper input of satellite reflectance products will affect the accuracy of Chl-a over inland waters, as well as existing models cannot meet the need for multi-source remote sensing data to retrieve high precision Chl-a. To explore these problems towards a solution, four reflectance data derived from Ocean and Land Colour Instrument (OLCI), MultiSpectral Instrument (MSI), and Operational Land Imager (OLI) were evaluated against in situ measurements of Erhai Lake. Reflectance data from these sensors were assessed to determine their consistency. Results indicate that R_rhos products (i.e., surface reflectance, a semi-atmospheric correction reflectance) that controlled for the atmospheric diffuse transmittance were highly correlated with the measured reflectance values. The in situ reflectance also confirmed the higher fidelity of satellite reflectance in the green-red band. Subsequently, a new extreme gradient boosting (XGB) model applied to multi-source remote sensing data is proposed to estimate long-term inland water Chl-a concentrations. Comparative experiments showed the XGB model with R_rhos products outperformed other solutions, providing accurate estimates for daily, monthly, and long-term trends in Erhai Lake. The XGB model was finally processed 3954 R_rhos reflectance data derived from OLCI, ENVISAT Medium Resolution Imaging Spectrometer (MERIS), MSI, and OLI sensors, mapping Chl-a concentrations in Erhai Lake over a 20-year period. This study could serve as a reference for the long-term Chl-a monitoring using multi-source remote sensing data to support inland lake management and future water quality evaluation.

Homogenization of Functional Diversity of Rotifer Communities in Relation to Eutrophication in an Urban River of North China

Rapid urbanization has triggered nutrient loading, which will inevitably lead to the eutrophication of water bodies and further affect the structure of aquatic populations. At present, eutrophication is a significant challenge for urban aquatic ecosystems. However, we still know little about the correlation between eutrophication in urban rivers and the composition of aquatic functional groups. The effects of urban river eutrophication on rotifer communities were investigated using an annual field survey of the Jinan section of the Xiaoqing River, a typical urban river in northern China. Using functional diversity (FD) and beta diversity, the spatiotemporal variation of the aquatic biological functional groups regime along stretches subject to different eutrophication was investigated. The functional evenness (FEve) and functional divergence (FDiv) decreased significantly with the increment of the trophic level index. Functional diversity exhibits an extremely low level across functional groups, with the richness difference (RichDiff) being an important component. The results indicate that eutrophication led to the homogenization of rotifer communities. This can be attributed to the functional homogenization of the rotifer community in the Jinan section of the Xiaoqing River. The observed homogenization may be due to widely distributed species complementing the ecological niche space. Our findings provide valuable information on the conservation of the urban river under the threat of eutrophication caused by high-intensity human activities.

Attribution of lake eutrophication risk to anthropogenic forcing adjacent to the agriculture areas: a case study of Chagan Lake

Lake eutrophication, exacerbated by high-intensity anthropogenic forcing, threatens water ecological security and the sustainable development of fisheries. Accurately evaluating lake eutrophication is the basis for effective management of the water environment. This study aimed to study eutrophication and its anthropogenic forcing in Chagan Lake, which is surrounded by agricultural areas with irrigation discharge as the primary water source. The spatiotemporal evolution characteristics of lake eutrophication and the anthropogenic forcing factors were analyzed based on the long-series multi-source data and modified eutrophication index. The results showed that (1) the average trophic state of Chagan Lake was eutrophic according to the modified eutrophication index (TLI = 58.31) and the nutrient level was higher in summer, reaching hypertrophy (TLI 61.49); (2) the maximum pollution footprint affecting the lake reached 34.7 km2, with a maximum buffer zone radius of 1 km; (3) the gross domestic product of primary industry, total sown area, and rice field area were the main anthropogenic factors leading to the lake eutrophication, with contribution rates of 64.43%, 13.09%, and 10.23%, respectively. Multidimensional management strategies for maximum pollution footprint, buffer zone radius, and contribution of anthropogenic factors were used to improve the water quality of the lake. The findings provided scientific support for the management of water environment of Chagan Lake and guided the formulation of "one lake, one policy."

Supervised machine learning improves general applicability of eDNA metabarcoding for reservoir health monitoring

Effective and standardized monitoring methodologies are vital for successful reservoir restoration and management. Environmental DNA (eDNA) metabarcoding sequencing offers a promising alternative for biomonitoring and can overcome many limitations of traditional morphological bioassessment. Recent attempts have even shown that supervised machine learning (SML) can directly infer biotic indices (BI) from eDNA metabarcoding data, bypassing the cumbersome calculation process of BI regardless of the taxonomic assignment of eDNA sequences. However, questions surrounding the general applicability of this taxonomy-free approach to monitoring reservoir health remain unclear, including model stability, feature selection, algorithm choice, and multi-season biomonitoring. Here, we firstly developed a novel biological integrity index (Me-IBI) that integrates multitrophic interactions and environmental information, based on taxonomy-assigned eDNA metabarcoding data. The Me-IBI can better distinguish the actual health status of the Three Gorges Reservoir (TGR) than physicochemical assessments and have a clear response to human activity. Then, taking this reliable Me-IBI as a supervised label, we compared the impact of selecting different numbers of features and SML algorithms on the stability and predictive performance of the model for predicting ecological conditions in multiple seasons using taxonomy-free eDNA metabarcoding data. We discovered that even with a small number of features, different SML algorithms can establish a stable model and obtain excellent predictive performance. Finally, we proposed a four-step strategy for standardized routine biomonitoring using SML tools. Our study firstly explores the general applicability problem of the taxonomy-free eDNA-SML approach and establishes a solid foundation for the large-scale and standardized biomonitoring application.

The Combined Effects of Toxic Microcystis aeruginosa and Thermal Stress on the Edible Clam (Corbicula fluminea): Insights into Oxidative Stress Responses and Molecular Networks

Cyanobacterial blooms (CYBs) have become a global environmental issue, posing risks to edible bivalves. Toxic cyanobacteria and thermal stress represent the two key co-occurring stressors to bivalves experiencing CYBs. To investigate the combined effects of these stressors on the edible bivalve Corbicula fluminea, the responses to oxidative stress and the molecular mechanisms of physiological adaptations in C. fluminea were examined under co-exposure to toxic Microcystis aeruginosa and thermal stress. The activity of antioxidant enzymes, including GST, SOD, CAT, GPx and GR, was significantly influenced by the interaction between temperature and M. aeruginosa (p < 0.05). A positive correlation was observed between toxic M. aeruginosa exposure and elevated SOD and GPx activities at 30 °C, demonstrating that SOD and GPx may help C. fluminea defend effectively against MCs under thermal stress. Furthermore, significant interactive effects between toxic M. aeruginosa and temperature were also observed in ROS and MDA (p < 0.05). The results of the PCA and IBR index also evidenced the apparent influence of toxic M. aeruginosa and thermal stress on oxidative stress responses of C. fluminea. The eggNOG and GO annotations confirmed that a substantial portion of differentially expressed genes (DEGs) exhibited associations with responses to oxidative stress and transporter activity. Additionally, KEGG analysis revealed that abundant DEGs were involved in pathways related to inflammatory responses, immune functions and metabolic functions. These findings improve our understanding of the mechanism of the physiological adaptation in bivalves in response to cyanotoxins under thermal conditions, potentially enabling the evaluation of the viability of using bivalves as a bioremediation tool to manage CYBs in eutrophic waters.

Water quality pollution assessment and source apportionment of lake wetlands: A case study of Xianghai Lake in the Northeast China Plain

Surface water pollution has always posed a serious challenge to water quality management. Improving water quality management requires figuring out how to comprehend water quality conditions scientifically and effectively as well as quantitatively identify regional pollution sources. In this study, Xianghai Lake, a typical lake-type wetland on the Northeast China Plain, was taken as the research area. Based on a geographic information system (GIS) method and 11 water quality parameters, the single-factor evaluation and comprehensive water quality index (WQI) methods were used to comprehensively evaluate the water quality of the lake-type wetland in the level period. Four key water quality parameters were determined by the principal component analysis (PCA) method, and more convenient comprehensive water quality evaluation models, the minimum WQI considering weights (WQImin-w) and the minimum WQI without considering weights (WQImin-nw) were established. The multiple statistical method and the absolute principal component score-multiple liner regression (APCS-MLR) model were combined to analyse the lake pollution sources based on the spatial changes in pollutants. The findings demonstrated that the WQImin-nw model's water quality evaluation outcome was more accurate when weights were not taken into account. The WQImin-nw model can be used as a simple and convenient way to comprehend the variations in water quality in wetlands of lakes and reservoirs. It was concluded that the comprehensive water quality in the study area was at a "medium" level, and CODMn was the main limiting factor. Nonpoint source pollution (such as agricultural planting and livestock breeding) was the most important factor affecting the water quality of Xianghai Lake (with a comprehensive contribution rate of 31.65%). The comprehensive contribution rates of sediment endogenous and geological sources, phytoplankton and other plants, and water diversion and other hydrodynamic impacts accounted for 25.12%, 19.65%, and 23.58% of the total impact, respectively. This study can provide a scientific method for water quality assessment and management of lake wetlands, and an effective support for migration of migratory birds, habitat protection and grain production security.

Potential of Mie-Fluorescence-Raman Lidar to Profile Chlorophyll a Concentration in Inland Waters

Vertical distribution of phytoplankton is crucial for assessing the trophic status and primary production in inland waters. However, there is sparse information about phytoplankton vertical distribution due to the lack of sufficient measurements. Here, we report, to the best of our knowledge, the first Mie-fluorescence-Raman lidar (MFRL) measurements of continuous chlorophyll a (Chl-a) profiles as well as their parametrization in inland water. The lidar-measured Chl-a during several experiments showed good agreement with the in situ data. A case study verified that MFRL had the potential to profile the Chl-a concentration. The results revealed that the maintenance of subsurface chlorophyll maxima (SCM) was influenced by light and nutrient inputs. Furthermore, inspired by the observations from MFRL, an SCM model built upon surface Chl-a concentration and euphotic layer depth was proposed with root mean square relative difference of 16.5% compared to MFRL observations, providing the possibility to map 3D Chl-a distribution in aquatic ecosystems by integrated active-passive remote sensing technology. Profiling and modeling Chl-a concentration with MFRL are expected to be of paramount importance for monitoring inland water ecosystems and environments.

Macroinvertebrate Response to Internal Nutrient Loading Increases in Shallow Eutrophic Lakes

In eutrophic lakes, even if external loading is controlled, internal nutrient loading delays the recovery of lake eutrophication. When the input of external pollutants is reduced, the dissolved oxygen environment at the sediment interface improves in a season without algal blooms. As an important part of lake ecosystems, macroinvertebrates are sensitive to hypoxia caused by eutrophication; however, how this change affects macroinvertebrates is still unknown. In this study, we analysed the monitoring data of northern Lake Taihu from 2007 to 2019. After 2007, the external loading of Lake Taihu was relatively stable, but eutrophication began to intensify after 2013, and the nutrients in the sediments also began to decline, which was related to the efficient use of nutrients by algal blooms. The community structure and population density of macroinvertebrates showed different responses in different stages. In particular, the density of oligochaetes and the Shannon-Wiener index showed significant differences in their response to different stages, and their sensitivity to eutrophication was significantly reduced. Under eutrophication conditions dominated by internal loading, frequent hypoxia occurs at the sediment interface only when an algal bloom erupts. When there is no bloom, the probability of sediment hypoxia is significantly reduced under the disturbance of wind. Our results indicate that the current method for evaluating lake eutrophication based on oligochaetes and the Shannon-Wiener diversity index may lose its sensitivity.

Synthetic phylogenetically diverse communities promote denitrification and stability

Denitrification is an important process of the global nitrogen cycle as some of its intermediates are environmentally important or related to global warming. However, how the phylogenetic diversity of denitrifying communities affects their denitrification rates and temporal stability remains unclear. Here we selected denitrifiers based on their phylogenetic distance to construct two groups of synthetic denitrifying communities: one closely related (CR) group with all strains from the genus Shewanella and the other distantly related (DR) group with all constituents from different genera. All synthetic denitrifying communities (SDCs) were experimentally evolved for 200 generations. The results showed that high phylogenetic diversity followed by experimental evolution promoted the function and stability of synthetic denitrifying communities. Specifically, the productivity and denitrification rates were significantly (P < 0.05) higher with Paracocus denitrificans as the dominant species (since the 50th generation) in the DR community than those in the CR community. The DR community also showed significantly (t = 7.119, df = 10, P < 0.001) higher stability through overyielding and asynchrony of species fluctuations, and showed more complementarity than the CR group during the experimental evolution. This study has important implications for applying synthetic communities to remediate environmental problems and mitigate greenhouse gas emissions.

Potential linkage between WWTPs-river-integrated area pollution risk assessment and dissolved organic matter spectral index

The direct discharge of wastewater can cause severe damage to the water environment of the surface water. However, the influence of dissolved organic matter (DOM) present in wastewater on the allocation of DOM, nitrogen (N), and phosphorus (P) in rivers remains largely unexplored. Addressing the urgent need to monitor areas affected by direct wastewater discharge in a long-term and systematic manner is crucial. In this paper, the DOM of overlying water and sediment in the WWTPs-river-integrated area was characterized by ultraviolet-visible absorption spectroscopy (UV-vis), three-dimensional excitation-emission matrix combined with parallel factor (PARAFAC) method. The effects of WWTPs on receiving waters were investigated, and the potential link between DOM and N, P pollution was explored. The pollution risk was fitted and predicted using a spectral index. The results indicate that the improved water quality index (IWQI) is more suitable for the WWTPs-river integration zone. The DOM fraction in this region is dominated by humic-like matter, which is mainly influenced by WWTPs drainage as well as microbial activities. The DOM fractions in sediment and overlying water were extremely similar, but fluorescence intensity possessed more significant spatial differences. The increase in humic-like matter facilitates the production and preservation of P and also inhibits nitrification, thus affecting the N cycle. There is a significant correlation between DOM fraction, fluorescence index, and N, P. Fluorescence index (FI) fitting of overlying water DOM predicted IWQI and trophic level index, and a(254) fitting of sediment DOM predicted nitrogen and phosphorus pollution risk (FF) with good results. These results contribute to a better understanding of the impact of WWTPs on receiving waters and the potential link between DOM and N and P pollution and provide new ideas for monitoring the water environment in highly polluted areas.

Spatiotemporal optical properties of dissolved organic matter in a sluice-controlled coastal plain river with both salinity and trophic gradients

Due to the combined effect of sluices and sea tide, the sluice-controlled coastal plain river would be characterized by both trophic state and salinity gradients, affecting the spatiotemporal optical properties of dissolved organic matter (DOM). In this study, we investigated the spatiotemporal variation of water quality parameters and optical properties of DOM in the Haihe River, a representative sluice-controlled coastal plain river in Tianjin, China. A significant salinity gradient and four trophic states were observed in the water body of the Haihe River. Two humic- and one protein-like substances were identified from the DOM by the three-dimensional fluorescence spectra combined with the parallel factor (PARAFAC) analysis. Pearson's correlation analysis and redundancy analysis (RDA) showed that the salinity significantly affected the abundance of chromophoric DOM (CDOM) but did not cause significant changes in the fluorescence optical characteristics. In addition, the effect of Trophic state index (TSI) on the CDOM abundance was greater than that on the fluorescence intensity of fluorescent dissolved organic matter (FDOM). In the water body with both salinity and trophic state gradients, TSI posed a greater influence than salinity on the CDOM abundance. Our results fill the research gap in spatiotemporal DOM characteristics and water quality variation in water bodies with both salinity and trophic state gradients. These results are beneficial for clarifying the joint influence of saline intrusion and sluices on the DOM characteristics and water quality in sluice-controlled coastal plain rivers.

Method for screening water physicochemical parameters to calculate water quality index based on these parameters' correlation with water microbiota

Water quality index (WQI) plays a crucial role in guiding water resource management. However, WQI calculation methods are not uniform, especially the selection of water parameters and the weighting given to each water parameter (P_i). To optimize WQI calculation, 132 water samples from seven rivers and from Chaohu Lake (33 sampling sites in Chaohu Lake Basin) in four seasons were collected, and the water parameters and microbiota composition were analyzed using high-throughput sequencing of 16 S rDNA. The correlation coefficient R² between water parameters and microbiota composition using redundancy analysis with the Monte Carlo method were calculated, and the water parameters that significantly correlated with the microbiota composition were selected to calculate WQI_min. The results showed that TP, COD, DO, and Chl a correlated significantly with water microbiota composition. WQI_b calculated by substituting R² for P_i was more consistent with the similarity between the microbiota compositions. WQI_minb calculated using TP, COD, and DO was consistent with WQI_b. The results of WQI_b and WQI_minb were more consistent than those of WQI and WQI_min. These results imply that using R² instead of P_i could help obtain a more stable WQI_b that could better reflect the biological characteristics of the Chaohu Lake Basin.

A review of the application of the macroinvertebrate-based multimetric indices (MMIs) for water quality monitoring in lakes

The increasing stress on lake ecosystems is affecting their functioning such as providing goods and services to inhabiting organisms and riparian communities. Monitoring of water quality is important for sustainable management and restoration of lake ecosystems. However, the costs associated with traditional approaches have become prohibitive, while not giving reliable early warning signals on resource conditions. Thus, the current shift in the use of bioindicators and multimetric indices (MMIs) in the monitoring of water quality is currently gaining global recognition with more emphasis on its application in lotic ecosystems. Therefore, this paper provides an elaborated insight into the application of macroinvertebrate-based MMIs in lentic ecosystems and the successes achieved so far. The various metrics and indices, the development strategies, application challenges, the use of macroinvertebrates as bioindicators, and the future projection of enhancing MMI usage in lentic environment monitoring, particularly in developing countries, are extensively covered. The use of MMI as a rapid lake biomonitoring tool needs to be adopted for sustainable applications in lake ecosystem management and as an integrated approach to monitoring human-induced stress especially in developing countries where there is a paucity of information.

Microplastic pollution in lakeshore sediments: the first report on abundance and composition of Phewa Lake, Nepal

Microplastic pollution in a freshwater environment has captured the attention of the scientific world in recent years. Microplastic is a new area of research in the freshwater of Nepal. Hence, the present study aims to examine the concentration, distribution, and characteristics of microplastic pollution in the sediments of Phewa Lake. Twenty sediment samples were collected from 10 sites to cover the vast area (5.762 km²) of the lake. The mean abundance of microplastic was 100.5 ± 58.6 items/kg dry weight. The average abundance of microplastics in five sections of the lake showed a significant difference (test statistics = 10.379, p < 0.05). Fibers (78.11%) dominated the sediments of Phewa Lake in all sampling sites. Transparent was the prominent color observed followed by red and altogether 70.65% of the microplastics detected were found at 0.2-1 mm size class. Fourier transform infrared spectroscopy (FTIR) analysis of visible microplastic particles (1-5 mm) confirmed polypropylene (PP) (42.86%) as the dominant polymer type followed by polyethylene (PE). This study can help to bridge the knowledge gap regarding the microplastic pollution in freshwater shoreline sediments of Nepal. Furthermore, these findings would create a new research area to explore the impact of plastic pollution which has been ignored in Phewa Lake.

Unraveling the response of water quality and microbial community to lake water backflowing in one typical estuary of Lake Taihu, China

To investigate the effect of lake water backflowing on the aquatic ecosystem in the estuary, surface water samples in the backflowing and unbackflowing areas were collected from one typical estuary of Lake Taihu, Xitiaoxi River. 16S rRNA sequencing and redundancy analysis were conducted to quantitatively elucidate the correlation between microbial community and water quality parameters. Results indicated lake water backflowing would affect the relative distribution of nitrogen species and increase the concentration of total nitrogen (TN) and nitrate, especially in the outlets of municipal sewage and agricultural drainage. For backflowing areas, more frequent water exchange could lower the seasonal fluctuation of the abundance and diversity of microbial community. RDA results showed crucial water quality parameters that greatly influence bacterial community were total organic carbon (TOC), total dissolved solids (TDS), salinity (SAL), ammonia, nitrate, TN for backflowing areas, and TOC, TDS, SAL, ammonia, TN without nitrate for unbackflowing areas. Verrucomicrobia, Proteobacteria, Microcystis, and Arcobacter were dominant with 27.7%, 15.7%, 30.5%, and 25.7% contribution to the overall water quality in backflowing areas. Chloroflexi, Verrucomicrobia, Flavobacterium, and Nostocaceae were dominant with 25.0%, 18.4%, 22.3%, and 11.4% contribution to the overall water quality in unbackflowing areas. And lake water backflowing might mainly affect the amino acid and carbohydrate metabolism based on the metabolism function prediction. A better understanding of the spatiotemporal changes in water quality parameters and microbial community was obtained from this research to comprehensively assess the effect of lake water backflowing on the estuarine ecosystem.

Pollutant impacts on bacteria in surface water and sediment: Conventional versus emerging pollutants in Taihu Lake, China

Bacteria play a critical role in biogeochemical cycling, self-purification, and food web fueling in surface freshwater ecosystems. However, the comparison between the impacts of conventional and emerging pollutants on the bacteria in surface water and sediment remains unclear and requires for an in-depth understanding to assess ecological risk and select associated bioindicators. Taihu Lake, a typical shallow lake in China, was divided into pollutant impacted and less-impacted zones for sampling. Spatial distributions of conventional pollutants, emerging pharmaceuticals, and bacterial communities were investigated in surface water and sediment. The correlations of pollutants with bacterial communities and the variations in bacterial functions were analyzed to help assess the pollutant influences on bacteria. The results showed that the water quality index and trophic level index across the whole lake were at medium to good, and mesotropher to light eutropher grades, respectively, indicating a relatively good control on conventional pollutants in water. Target pharmaceuticals were at much higher concentrations in water of the impacted zone compared to the less-impacted zone, exhibiting close positive relationships with the bacterial phyla in the impacted water. The ratio of Firmicutes to Proteobacteria in surface water is suggested as a plausible bioindicator to evaluate the level of inflow pharmaceutical contamination and the risk of relevant bacterial resistance in the outflow. In sediment, no significant difference was observed for pharmaceuticals between the two zones, whereas total phosphorus and orthophosphate were substantially higher in the impacted zone. Phosphorus pollutants were tightly associated with the bacterial genera in the impacted sediment, likely relating to the increase in iron- or sulfate-reducing bacteria which implies the potential risk of phosphorus releasing from sediment to water.

The feeding habits of small-bodied fishes mediate the strength of top-down effects on plankton and water quality in shallow subtropical lakes

The proliferation of small-bodied fishes in lakes is often accompanied by deterioration of water quality and ecosystem function. However, the potential impacts of different types of small-bodied fish species (e.g., obligate zooplanktivores and omnivores) on subtropical lake ecosystems in particular have been overlooked mainly due to their small size, shorter life spans and lower economic value. Therefore, we conducted a mesocosm experiment to elucidate how plankton communities and water quality respond to different types of small-bodied fishes, including a common zooplanktivorous fish (thin sharpbelly Toxabramis swinhonis) and other small-bodied omnivorous fishes (bitterling Acheilognathus macropterus, crucian carp Carassius auratus and sharpbelly Hemiculter leucisculus). During the experiment, the mean weekly total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD_Mn), turbidity, chlorophyll-a (Chl.α) and trophic level index (TLI) values were generally higher in treatments where fish were present compared to treatments where fish were absent, but responses varied. At the end of the experiment, phytoplankton abundance and biomass and the relative abundance and biomass of cyanophyta were higher while the abundance and biomass of large-bodied zooplankton were lower in the fish-present treatments. Moreover, the mean weekly TP, COD_Mn, Chl.α and TLI values were generally higher in treatments with the obligate zooplanktivore, thin sharpbelly, when compared to treatments with omnivorous fishes. Also, the ratio of zooplankton to phytoplankton biomass was the lowest, and the ratio of Chl.α to TP was the highest in treatments with thin sharpbelly. Collectively, these general findings indicate that an overabundance of small-bodied fishes can have adverse effects on water quality and plankton communities and that small-bodied zooplanktivorous fishes likely induce stronger top-down effects on plankton and water quality than omnivorous fishes. Our results emphasise that small-bodied fishes should be monitored and controlled if overabundant when managing or restoring shallow subtropical lakes. From the perspective of environmental protection, the combined stocking of different piscivorous fish species that feed in different habitat types could be a way forward to control small-bodied fishes with different feeding habits, but more research is needed to assess the feasibility of this approach.

Using intermittent moving aeration to repair hypereutrophic pond: nutrient removal efficiency and microbial diversity analysis

This study presents a novel perspective on the control of eutrophication by moving aeration through a ten-month pilot field study. Moving aeration significantly reduced the relative abundance of class Cyanobacteria by 14.01%, effectively preventing cyanobacteria from predominating in the overlying water. As a result, the deposition of TOC, N, and P in the surface of the sediment decreased by 90%, 73%, and 93% in comparison to the control group. The analysis of microbial community structure based on 16S rRNA high-throughput sequencing showed that the order Bacillales and Micrococcales contributed to nitrogen removal significantly increased by 19.44% and 3.94%, respectively, while the order Steroidobacterales, Rhizobiales, and Microtrichales involved in the immobilization of carbon and nitrogen were significantly decreased by 4.03%, 2.69%, and 2.3% in the aeration group, respectively. Variation in the number of functional microorganisms based on the MPN method revealed that moving aeration promoted the growth of nitrifying bacteria and denitrifying bacteria. These findings demonstrated that moving aeration is effective in repairing eutrophic water and eliminating endogenous N pollutants.

Quantitative Assessment of Water Quality Improvement by Reducing External Loadings at Lake Erhai, Southwest China

To quantitatively evaluate the effects on water quality improvement caused by reducing external loadings entering Lake Erhai through inflow rivers, a one-dimensional hydrodynamic and ecological model (DYRESM-CAEDYM) was set up to simulate the water quality and water level variations. The calibrated and validated model was used to conduct six scenarios for evaluating the water quality responses to different amounts of external loading reduction at Lake Erhai. The results show (1) the total nitrogen (TN) concentration of Lake Erhai will be higher than 0.5 mg/L without any watershed pollution control during April-November 2025, which cannot meet Grade II standard of the China Surface Water Environmental Quality Standards (GB3838-2002). (2) External loading reductions can significantly reduce the concentrations of nutrients and Chla at Lake Erhai. The effects of water quality improvement will be proportional to the reduction rate of external loading reductions. (3) Internal release might be an important source of pollution It needs to be seriously considered as well as external loading for mitigating the eutrophication at Lake Erhai in the future.

Assessment of Water Eutrophication at Bao'an Lake in the Middle Reaches of the Yangtze River Based on Multiple Methods

Based on the monthly monitoring of Bao'an Lake in Hubei Province from 2018 to 2020, the eutrophication level of Bao'an Lake in the middle reaches of the Yangtze River is investigated using the comprehensive trophic level index (TLI), chromophoric dissolved organic matter (CDOM) absorption coefficient, and the phytoplankton water quality biological method. The influencing factors are then identified. The results demonstrate that the overall water quality of Bao'an Lake remained at levels III-V during 2018-2020. Due to different eutrophication assessment methods, the results are different, but all show that Bao'an Lake is in a eutrophication state as a whole. The eutrophication level of Bao'an Lake is observed to vary with time, exhibiting an increasing then decreasing trend between 2018-2020, while levels are high in summer and autumn, and low in winter and spring. Moreover, the eutrophication level of Bao'an Lake presents an obviously varying spatial distribution. Potamogeton crispus is the dominant species of the Bao'an Lake, the water quality is good in spring when Potamogeton crispus vigorously grows, but poor in summer and autumn. The permanganate index (COD_Mn) and total phosphorous (TP), total nitrogen (TN), and chlorophyll a (Chl-a) contents are identified as the main influencing factors of the eutrophication level of Bao'an Lake, with a significant relationship observed between Chl-a and TP (p < 0.01). The above results provide a solid theoretical basis for the ecological restoration of Bao'an Lake.

Temporal variations and trends prediction of water quality during 2010-2019 in the middle Yangtze River, China

Water quality plays an important role in river habitats. This study revealed the annual and seasonal variations and trend prediction of water quality in the middle Yangtze River after the third impoundment stage of the Three Gorges Reservoir. Multivariate statistical methods including principal component analysis/factor analysis (PCA/FA), Mann-Kendall (M-K) tests, discriminant analysis (DA), rescaled range (R/S) analysis, and the Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI) were used. Herein, eight water quality constituents including pH, electrical conductivity (EC), chloride (Cl), dissolved oxygen (DO), ammonia nitrogen (NH₃N), total phosphorus (TP), water temperature (T), and permanganate index (CODmn) were monthly monitored in the Jiujiang hydrological transaction during 2010-2019. The information of eight water quality constituents, related to salinity, nutrient status, and oxidation reactions efficiency, was extracted. Water quality status remained as fair-good during 2010-2019 based on the results of CCME-WQI, with the seasonal significance ranked as T > DO > Cl > pH > EC > TP > NH₃N > CODmn. In the future decade, annual average T was predicted to continue to increase although it might decrease in the wet season. EC was predicted to continue increasing annually especially in the wet season while Cl might decrease. NH₃N and TP might maintain a significant decreasing trend in the future wet and dry seasons. DO maintained significantly increasing especially in the future dry seasons, whereas CODmn will continue to decrease annually and seasonally. The continued alkalization trend of waterbody was predicted, which is more significant in the wet season. The results provide helpful references for the ecological protection of the middle Yangtze River.

Decomposition of Phosphorus Pollution and Microorganism Analysis Using Novel CW-MFCs under Different Influence Factors

A constructed wetland (CW)-coupled microbial fuel cell (MFC) system was constructed to treat wastewater and generate electricity. The total phosphorus in the simulated domestic sewage was used as the treatment target, and the optimal phosphorus removal effect and electricity generation were determined by comparing the changes in substrates, hydraulic retention times, and microorganisms. The mechanism underlying phosphorus removal was also analyzed. By using magnesia and garnet as substrates, the best removal efficiencies of two CW-MFC systems reached 80.3% and 92.4%. Phosphorus removal by the garnet matrix mainly depends on a complex adsorption process, whereas the magnesia system relies on ion exchange reactions. The maximum output voltage and stabilization voltage of the garnet system were higher than those of the magnesia system. Microorganisms in the wetland sediments and electrode also changed considerably. It indicates that the mechanism of phosphorus removal by the substrate in the CW-MFC system is adsorption and chemical reaction between ions to generate precipitation. The population structure of proteobacteria and other microorganisms has an impact on both power generation and phosphorus removal. Combining the advantages of constructed wetlands and microbial fuel cells also improved phosphorus removal in coupled system. Therefore, when studying a CW-MFC system, the selection of electrode materials, matrix, and system structure should be taken into account to find a method that will improve the power generation capacity of the system and remove phosphorus.

Impact of Textile Industries on Surface Water Contamination by Sb and Other Potential Toxic Elements: A Case Study in Taihu Lake Basin, China

Contamination of industry-derived antimony (Sb) is currently of great concern. This study was conducted to identify the source of Sb together with other potential toxic elements (PTEs) in a typical industrial area in China and emphasize the contribution of Sb to ecological risk in the local aquatic environment. By investigating the distribution of nine PTEs in surface water in Wujiang County in dry and wet seasons, this study revealed that textile wastewater was the main source of Sb. The distribution of Sb (0.48~21.4 μg/L) showed the least seasonal variation among the nine elements. Factor analysis revealed that the factor that controlled Sb distribution is unique. In general, Sb was more concentrated in the southeastern part of the study area where there was a large number of textile industries, and was affected by the specific conductivity and total dissolved solids in water (p < 0.01). Sb concentration in 35.71% of samples collected from the drainage outlet exceeded the standard limit of 10 μg/L. Results from three pollution assessment methods suggested that >5% of the sampling sites were slightly too heavily polluted and Sb contributed the most. Therefore, it is necessary to strengthen the administrative supervision of local textile enterprises and elevate the local standard of textile wastewater emission.

Spatiotemporal heterogeneity of nitrogen transformation potentials in a freshwater estuarine system

Under the influence of water diversion, the microbial community composition of estuarine waters and sediments might have complex spatiotemporal variations. Microbial interactions with N are significant for lake water quality. Therefore, the largest lake receiving seasonal water diversion in the North China Plain was selected as the study area. Based on 16S rRNA high-throughput sequencing and metagenomic sequencing techniques, this study analysed temporal (June-December) and spatial (estuary-pelagic zone) changes in the microbial community and functional gene composition of water and sediment. The results showed that the water microbial community composition had temporality, while sediment microbes had spatiality. The main causes of temporality in the aquatic microbial community were temperature and nitrate-N concentration, while those of sediment were flow velocity and N content. Additionally, there were complex interactions between microbial communities and N. In water, temporal variation in the relative abundance of N-related functional genes might have indirectly contributed to inorganic N composition in June (nitrite-N > ammonia-N > nitrate-N) and August (nitrite-N > nitrate-N > ammonia-N). High nitrate-N concentrations in December influenced the microbial community composition. In sediment, the estuary had higher N functional genes than the pelagic estuary, creating a relatively active N cycle and reducing total N levels in the estuary. This study revealed a potentially overlooked N sink and a flow velocity threshold that has great impacts on microbial community composition. This research contributes to a deeper understanding of the estuarine N cycle under the influence of water diversions, with implications for the calculation of global N balances and the management of lake water environments.

Microbiota assembly patterns and diversity of nine plateau lakes in Yunnan, southwestern China

Microbes serve as important components of ecosystem services and biogeochemical processes in plateau lakes. However, the features of microbiota assembly, abundance and diversity in plateau lakes remain unclear. The microbial communities in surface water from nine plateau lakes in Yunnan Plateau, southwestern China, in the dry and rainy seasons were explored using 16S rRNA gene and 18S rRNA gene sequencing. The results showed that the bacterial community compositions were homogeneous while those of micro-eukaryotes were heterogeneous in plateau lakes. In both seasons, the bacterial phyla of Proteobacteria and Actinobacteriota predominated in oligotrophic lakes. The mesotrophic lakes were dominated by Proteobacteria, Actinobacteriota, Bacteroidota and Cyanobacteria. The eutrophic lakes were mainly dominated by Proteobacteria, Actinobacteriota and Cyanobacteria. The phylum SAR_k_norank had the major micro-eukaryotes in these plateau lakes. The alpha-diversity of bacteria declined in the rainy season, while that of micro-eukaryotes varied from lake to lake. The drivers of microbiotic community assembly in the dry season were identified as nutrient level-related factors. In the rainy season, however, the microbiota in oligotrophic lakes were related to nutrient levels. Microbial communities were driven by precipitation in mesotrophic and eutrophic lakes with large water volumes, while those in lakes with small water volumes were regulated by nutrient level-related factors. Our findings pose first and unique insights into the microbiota of the nine plateau lakes in Yunnan Plateau, providing important ecological knowledge for these lakes with different characteristics.

Spatial effects of urban green infrastructure on instream water quality assessed by chemical and sensory indicators

Urban green infrastructure has been simulated effectively and economically to reduce volume and pollutants of stormwater runoffs but its spatial effects remain unclear. A snap sampling campaign was carried out for surface water quality in the downtown waterway network of a pilot sponge city (Suzhou) in China, dividing into 7 subwatersheds according to the digital elevation map. In total, 144 sampling points were investigated and measured for chemical quality of surface water while 68 out of the sampling points had a sensory evaluation questionnaire interview for water quality with 321 respondents, in whom the native residents scored a significant spatiality of water quality. The downtown waterway network had phosphorus-limited eutrophic surface water with total nitrogen worse than Class V of the national guidelines. Chemical and sensory evaluation indexes of surface water quality had significant spatial consistency (p < 0.001). All types of green spaces (%) in subwatershed, especially along the urban waterway network (waterfront) and roadside, and in the 100 m riparian buffer zone, significantly influenced nutrient loads in surface water. Findings of the present study suggest that the 100 m riparian buffer zone would be priority areas and the waterfront and roadside should be the highly efficient spots for planning strategy on urban green infrastructure implementation to reduce nutrient loads in surface water and to improve urban landscape aesthetics.

Nitrogen and phosphorus spatio-temporal distribution and fluxes intensifying eutrophication in three tropical rivers of Côte d'Ivoire (West Africa)

Nutrient contamination assessments in the three West African tropical Comoé, Bandama, and Bia Rivers (Côte d'Ivoire) were performed from March 2016 to March 2018. Five stations per river were sampled. Nutrients spatio-temporal distributions were mapped and showed nitrogen concentrations (nitrite 0.001 to 0.025 mg/L NO₂^--N, and nitrate 0.26 to 3.60 mg/L NO₃^--N) increased significantly with rainfall contrary to phosphorus (0.01 to 0.12 mg/L P). The Chl-a and TSI_tsr data revealed the hypereutrophic status of rivers. Moreover, N:P mass ratio suggests nitrogen as the main limiting factor of primary production during the low (March) and high flow periods (October-November), while phosphorus is the limiting factor in June, at the high flow beginning. The land uses around watersheds were the main sources of phosphorus and nitrogen enhancing the rivers' eutrophication. Phosphorus and nitrogen fluxes were related to leaching river catchments and were significant sources of nutrients to the Atlantic Ocean.

Changes in the water environment and its major driving factors in Poyang Lake from 2016 to 2019, China

The hydrological exchange process between Poyang Lake (PYL), the largest freshwater lake in China, and the Yangtze River leads to drastic changes in water area (WA) and water level (WL), as well as apparent fluctuations in lake nutrients, algal organisms, and trophic level index. This study investigated the current status of the PYL water environment and the influence of hydrological changes on the nutrient status of the floodplain of the lake. Based on monthly measured data from six hydrological stations from 2016 to 2019, it was hypothesized that WA and WL were the key regulators of the spatial and temporal distribution patterns of lake water quality and algal growth, including water temperature, water clarity (Secchi depth [SD]), and nutrient levels. The results revealed that (1) the spatial and temporal distribution characteristics of major nutrients in PYL were influenced by dynamic changes in hydrological characteristics (SD, total nitrogen [TN], and total phosphorus [TP]); (2) the eutrophication level in PYL has been in a steady state in recent years, while the central area has been more prone to the risk of eutrophication (e.g., the peak eutrophication index during Period 1 [January to April] in the water near the Duchang station reached 70); and (3) there were significant correlations among environmental variables, nutrients, and algal organisms, with different spatial and temporal distribution characteristics (p < 0.05), while the changes in WA and WL considerably influenced the water environment in the PYL.

Seasonal Variation Characteristics and the Factors Affecting Plankton Community Structure in the Yitong River, China

To explore how environmental factors affected the plankton structure in the Yitong River, we surveyed the water environmental factors and plankton population in different seasons. The results showed high total nitrogen concentrations in Yitong River throughout the year, while the total phosphorus, water temperature (WT), and chemical oxygen demand in summer were significantly higher than those in other seasons (p < 0.05), and the dissolved oxygen (DO) concentrations and TN/TP ratio were significantly lower (p < 0.01) than those in other seasons. There was no significant seasonal change in other environmental factors. Cyanophyta, Chlorophyta, and Bacillariophyta were the main phytoplankton phylum, while Protozoa and Rotifera were the main zooplankton phylum. The abundance and biomass of zooplankton and phytoplankton in the summer were higher than those in other seasons. Non-Metric Multidimensional scaling methods demonstrated obvious seasonal variation of phytoplankton in summer compared to spring and winter, while the seasonal variation of the zooplankton community was not obvious. The results of the redundancy analysis showed that WT, DO and nitrate nitrogen were the main environmental factors affecting phytoplankton abundance. In contrast to environmental factors, phytoplankton was the main factor driving the seasonal variation of the zooplankton community structure. Cyanophyta were positively correlated with the changes in the plankton community.

A 16th century artificial reservoir under human pressure: water quality variability assessment in Laguna de Yuriria, central Mexico

This study assesses the variability of physicochemical and biochemical parameters, identifies principal pollutant sources, and characterizes water quality in Yuriria reservoir using water quality indexes in combination with multivariate statistical techniques. In situ parameters were measured in 55 reservoir sites including surface and deep points and in 7 associated channels. Moreover, major compounds and biochemical data were determined. Yuriria reservoir had alkaline, bicarbonate-mixed waters, with total dissolved solids (TDS) of 393.83 ± 3.43 mg L^-1. Water quality index (WQI) indicated a good class for agricultural irrigation but very poor and poor classes for preservation of aquatic life. The nutrient inputs and the internal nitrogen recycling triggered a hypereutrophic status in the reservoir. The decomposition of residual biomass from aquatic macrophytes contributed to reduce dissolved oxygen (DO) in the hypolimnetic waters (mean DO = 3.86 mg L^-1). Statistical analysis revealed that the study area is highly exposed to anthropogenic stress and in a lesser extent to natural processes. Urban and agriculture runoff enhanced the salinization and the generation of solid particles which deteriorated water quality. Chemical oxygen demand (COD), biochemical oxygen demand (BOD), and NO₃^--N presented a common anthropogenic origin by external (point and diffuse) and internal pollution sources, while a diffuse source (agricultural activities) was reveled for phosphorus. This study is important to be used in systematic monitoring and sustainable co-management programs and for formulating the necessary strategies to remediate the Yuriria reservoir water quality and extrapolate to other reservoirs worldwide.

High-resolution circa-2020 map of urban lakes in China

Urban lakes provide important ecological services to local communities, such as flood mitigation, biodiversity, and recreation. With rapid urbanization, urban lakes are significantly affected by socio-economic development and urgently need attention. Yet there is still a lack of datasets that include tiny urban lakes on a global or national scale. This study aims to produce a high-resolution circa-2020 map of urban lakes (≥0.001 km²) in China. The 10-m-resolution Sentinel-2 imagery and a simple but robust water extraction method was used to generate waterbodies. The accuracy of this national-scale dataset was evaluated by comparing it with manually sampled urban units, with the average accuracy of 81.85% in area and 93.35% in count. The database totally inventories 1.11 × 10⁶ urban lakes in China, with a net area of ~2.13 × 10³ km². Overall, the spatial distribution of urban lakes in China showed strongly heterogeneous characteristics. This dataset will enhance our understanding of the distribution pattern of China's urban lakes and contribute to better ecological and environmental management as well as sustainable urban development planning.

Investigating phosphorus loads removed by chemical and biological methods in municipal wastewater treatment plants in Poland

The article presents an analysis of the current methods for phosphorus removal applied in municipal wastewater treatment plants in Poland. Within the study, 131 wastewater treatment plants were investigated, constituting 17 630 500 population equivalent, which is about 1/3 of the overall population equivalent (designed) in Poland. The research was based on a detailed technical questionnaire analysis obtained from wastewater treatment plants operators and calculations of pure metal doses in the applied coagulants and their type per a treated wastewater volume, population equivalent and phosphorus load removed. Moreover, a basic statistical analysis based on Pearson's correlation coefficient was applied to validate the relationship between the consumption of coagulants per the removed P load and the treated wastewater volume in 3 categories of wastewater treatment plants in terms of their population equivalent. The analysis results show that a minimum of 1470 Mg of phosphorus removed by 35 wastewater treatment plants based entirely on biological treatment methods could be used for phosphorus recovery to produce struvite, calcium phosphate or other highly bioavailable alternative fertilizer products. Moreover, 1490 Mg of phosphorus removed by other 17 wastewater treatment plants with a minimal coagulant dose (<1 g of metal per m³ of wastewater), increases the base for phosphorus recovery to approx. 2960 Mg per year using sewage sludge or its dewatering liquors. These results suggest that the implementation of the means mentioned above would significantly increase the possibilities for obtaining phosphorus from secondary sources, especially in wastewater treatment plants without sewage sludge incineration plants.

Extending improvements of eutrophication and water quality via induced natural mixing after artificial mixing in a stratified reservoir

Induced (natural) mixing proposed by our teams can solve a big problem of low-energy water situation improvement of stratified reservoirs by minimizing operating periods of water-lifting aerators (WLAs) to advance a complete natural mixing. Here, the mechanisms influencing water situation via induced mixing were systematically explored using a combination of multi-water-environment assessment methods including trophic level index (TLI), water quality index (WQI), and minimum WQI (WQI_min) based on long-term field data (i.e., non-operational and operational years of WLAs). The results showed that induced mixing after WLA deactivation improved the levels of eutrophication and water quality (into "light-eutrophic" and "good" status) with a decrease in TLI values (56.0-56.2) and increase in WQI (79.0-79.9) and WQI_min (81.5-89.3) values, compared to mixing of the non-operational year (TLI: 69.6, WQI: 73.4, WQI_min: 76.1). Induced mixing was launched by deactivating the WLAs in cooling seasons (i.e., in late September within a subtropical monsoon climate zone), which advanced and prolonged the periods of naturally complete mixing by 2-3 months. Water temperature (WT), Dissolved oxygen (DO), relative water column stability (RWCS) and inflow were primary drivers for the water situation succession in the study years. Induced mixing extended the well-oxygenated and mixed conditions (temperature difference <1.0 °C, DO > 8.5 mg/L, RWCS< 20) following artificial mixing to improve the water status from single index level (improvement of 18.8%-73.7% than mixing before the operational years) to integrated evaluation results by changing WT, DO, and RWCS. This study presents a successful case for energy-saving pollution control using mixing systems.

Combining the multivariate statistics and dual stable isotopes methods for nitrogen source identification in coastal rivers of Hangzhou Bay, China

Coastal rivers contributed the majority of anthropogenic nitrogen (N) loads to coastal waters, often resulting in eutrophication and hypoxia zones. Accurate N source identification is critical for optimizing coastal river N pollution control strategies. Based on a 2-year seasonal record of dual stable isotopes ([Formula: see text] and [Formula: see text]) and water quality parameters, this study combined the dual stable isotope-based MixSIAR model and the absolute principal component score-multiple linear regression (APCS-MLR) model to elucidate N dynamics and sources in two coastal rivers of Hangzhou Bay. Water quality/trophic level indices indicated light-to-moderate eutrophication status for the studied rivers. Spatio-temporal variability of water quality was associated with seasonal agricultural, aquaculture, and domestic activities, as well as the seasonal precipitation pattern. The APCS-MLR model identified soil + domestic wastewater (69.5%) and aquaculture tailwater (22.2%) as the major nitrogen pollution sources. The dual stable isotope-based MixSIAR model identified soil N, aquaculture tailwater, domestic wastewater, and atmospheric deposition N contributions of 35.3 ±21.1%, 29.7 ±17.2%, 27.9 ±14.5%, and 7.2 ±11.4% to riverine [Formula: see text] in the Cao'e River (CER) and 34.4 ±21.3%, 29.5 ±17.2%, 27.4 ±14.7%, and 8.7 ±12.8% in the Jiantang River (JTR), respectively. The APCS-MLR model and the dual stable isotope-based MixSIAR model showed consistent results for riverine N source identification. Combining these two methods for riverine N source identifications effectively distinguished the mix-source components from the APCS-MLR method and alleviated the high cost of stable isotope analysis, thereby providing reliable N source apportionment results with low requirements for water quality sampling and isotope analysis costs. This study highlights the importance of soil N management and aquaculture tailwater treatment in coastal river N pollution control.

Toxicity determination, pollution source delineation, and microbial diversity evaluation of PAHs-contaminated sediments for an urban river

The Feng-Sang River is a metropolitan river in Kaohsiung City, Taiwan. In this study, Feng-Sang River sediments were analyzed to investigate the distributions and sources of polycyclic aromatic hydrocarbons (PAHs). The Sediment Quality Guidelines (SQGs), potentially carcinogenic PAHs (TEQcarc), and toxic equivalence quotient (TEQ) were applied to evaluate influences of PAHs on ecosystems and microbial diversities. Results indicate that PAHs concentrations varied between seasons and locations. The concentrations of ∑16PAHs ranged from 73.6 to 603.8 ng/kg in dry seasons and from 2.3 to 199.3 ng/kg in wet seasons. This could be because of the flushing effect during wet seasons, which caused the movement and dilution of the PAH-contaminated sediments. Diagnostic ratio analysis infers that high PAHs levels were generated by combustion processes and vehicle traffic, and results from multivariate descriptive statistical analysis also demonstrate that the vehicular traffic pollution could be the major emission source of PAHs contamination. Comparisons of PAHs with SQGs indicate that PAHs concentrations in sediment were below the effects range low (ERL) values, and thus, the immediate threat to organisms might not be significant. The diagnostic ratio analyses are effective methods for PAH source appointment. The metagenomic assay results imply that sediments contained essential microbial species with eminent diversity. The detected PAH-degrading bacteria (Desulfatiglans, Dechloromonas, Sphingomonas, Methylobacterium, Rhodobacter, Clostridium, and Exiguobacterium) played a key role in PAHs biotransformation, and Dechloromonas and Rhodobacter had a higher relative abundance. Results of microbial diversity analyses indicate that the contaminated environment induced the changes of governing microbial groups in sediments. PRACTITIONER POINTS: Diagnostic ratio analyses are effective methods for PAHs source appointment. Microbial composition in sediments are highly affected by anthropogenic pollution. Combustion and vehicle traffic contribute to urban river sediments pollution by PAHs. Dechloromonas and Rhodobacter are dominant PAHs-degrading bacteria in sediments.

Denitrification and N2O Emission in Estuarine Sediments in Response to Ocean Acidification: From Process to Mechanism

Global estuarine ecosystems are experiencing severe nitrogen pollution and ocean acidification (OA) simultaneously. Sedimentary denitrification is an important way of reactive nitrogen removal but at the same time leads to the emission of large amounts of nitrous oxide (N₂O), a potent greenhouse gas. It is known that OA in estuarine regions could impact denitrification and N₂O production; however, the underlying mechanism is still underexplored. Here, sediment incubation and pure culture experiments were conducted to explore the OA impacts on microbial denitrification and the associated N₂O emissions in estuarine sediments. Under neutral (in situ) conditions, fungal N₂O emission dominated in the sediment, while the bacterial and fungal sources had a similar role under acidification. This indicated that acidification decreased the sedimentary fungal denitrification and likely inhibited the activity of fungal denitrifiers. To explore molecular mechanisms, a denitrifying fungal strain of Penicillium janthinellum was isolated from the sediments. By using deuterium-labeled single-cell Raman spectroscopy and isobaric tags for relative and absolute quantitation proteomics, we found that acidification inhibited electron transfers in P. janthinellum and downregulated expressions of the proteins related to energy production and conservation. Two collaborative pathways of energy generation in the P. janthinellum were further revealed, that is, aerobic oxidative phosphorylation and TCA cycle and anoxic pyruvate fermentation. This indicated a distinct energy supply strategy from bacterial denitrification. Our study provides insights into fungi-mediated nitrogen cycle in acidifying aquatic ecosystems.