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Planktonic archaea and bacteria play important roles in biogeochemical cycling, but their biogeographical patterns and underlying ecological processes remain poorly understood, particularly in large‐scale rivers.We collected 43 water samples covering a 2279 km reach of the Jinsha River, one of the largest rivers in southwest China, and performed high‐throughput sequencing analysis on planktonic archaeal and bacterial communities. Partial Mantel analysis and neutral model were used to assess the factors influencing microbial distributions. The associations among different microbial species and their geographical distribution patterns were linked through co‐occurrence networks, and the putative key taxa in the archaeal and bacterial networks were analysed.The Shannon index of both archaeal and bacterial communities was highest in the midstream reach. The Pielou's evenness of archaea did not vary among the three reaches, whereas those of bacteria increased from upstream to downstream. The archaeal and bacterial community compositions were significantly different in the three reaches, but the differences among the bacterial communities were greater than among the archaeal communities.Both dispersal limitation and environmental selection affected the community compositions of the archaea and bacteria, but dispersal limitation was the most influential factor. Compared to archaea, bacteria were less affected by dispersal limitation and more by environmental selection.The co‐occurrence network analysis demonstrated that, compared with the bacterial network of all sites, the archaeal network with larger graph density had higher connectivity and complexity, but a lower proportion of negative correlations. The putative key taxa belonged to Nitrososphaeraceae and Candidatus_Nitrocosmicus from the archaeal community, and Hydrogenophaga and Sphingorhabdus from the bacterial community.Taken together, these findings demonstrated that the planktonic archaea were more dispersal‐limited and showed more network connectivity than the planktonic bacteria in the Jinsha River. This study enhances our understanding of the biogeographical distribution patterns and underlying ecological processes of planktonic microorganisms over large‐scale freshwater systems. [ABSTRACT FROM AUTHOR]

Sediment, consisting of different aggregation fractions, is a hotspot site for transport and transformation of various pollutants including antibiotics. However, the fate of different antibiotics in aquatic sediments mediated by sediment aggregation fraction adsorption and the mechanism behinds are still unclear. In this study, we investigated the adsorption behavior of two fluoroquinolone antibiotics (ciprofloxacin and ofloxacin) on four aggregation fractions separated from the sediment of Taihu Lake, a typical lake contaminated by antibiotics in China. The results showed that the adsorption of ciprofloxacin and ofloxacin fitted the Freundlich model, irrespective of sediment aggregation size. The adsorption of ciprofloxacin and ofloxacin was depended on the size of sediment aggregation fractions, and the macroaggregation (> 200 μm) exhibited the strongest capacity, followed by large microaggregation (63–200 μm), medium microaggregation (20–63 μm), and small and primary microaggregation (< 20 μm). This fraction size-dependent effects of sediment aggregations on antibiotic adsorption might be closely related to the differences in their specific surface areas, organic matter contents, and surface functional groups. The adsorption of ciprofloxacin and ofloxacin by sediment aggregation fractions was characterized by a combination of chemical and physical adsorptions, with the former being the dominant process. Compared with ofloxacin, ciprofloxacin could be more rapidly and easily absorbed by four sediment aggregation fractions, and more readily complexed with carboxyl groups on macroaggregation surface. The adsorption of two antibiotics by extracellular polymeric substance showed that tryptophan and tyrosine protein-like, humic-like substance on the surface of sediment could bind to both antibiotics through a complexation reaction. The π-π electron donor–acceptor interaction and hydrogen bonds were responsible for the antibiotic adsorption by sediment aggregation. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive application of the probabilistic risk assessment methodology for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), which are two types of perfluoroalkyl acids frequently studied in recent years. The exposure characteristics of PFOA and PFOS in Chinese surface water on a nationwide scale were summarized. Individual predicted no-effect concentration (PNEC) and the sensitivities for taxonomic groups of primary producers, invertebrates, and vertebrates were derived by the species sensitivity distributions method. Both hazard quotients (HQs) and joint probability curves were calculated to assess the risks to aquatic organisms. Among seven Chinese river basins, the mean concentrations of PFOA and PFOS in the Yangtze River Basin were the highest (58 ng/L and 22 ng/L, respectively), while the lowest concentrations (< 1 ng/L) were in the Songhua River Basin. The acute PNEC value was 2.43 mg/L for PFOA and 0.96 mg/L for PFOS, and the chronic PNEC value was 0.0067 mg/L for PFOA and 0.0012 mg/L for PFOS, respectively. The sensitivities of different taxonomic groups revealed higher sensitivity of primary producers for PFOA and higher sensitivity of invertebrates for PFOS. The acute HQs of PFOA and PFOS were less than 1. The probabilities of exposure concentrations exceeding 5th percentile toxicity value of the chronic data for all aquatic organisms were 1.65% for PFOA and 1.23% for PFOS, respectively, suggesting a low probability of effects to aquatic organisms. Compared with the risk scenarios worldwide, the ecological risks for chronic effects decreased in the order of PFOS (worldwide) > PFOA (China) > PFOS (China) > PFOA (worldwide). [ABSTRACT FROM AUTHOR]

Bacterial communities play critical roles in biogeochemical cycles and serve as sensitive indicators of environmental fluctuation. However, the influence of mineral resource exploitation on shaping the bacterial communities in the urban river is still ambiguous. In this study, high-throughput sequencing was used to determine the spatial distribution of the sediment bacterial communities along an urban river in the famous mining city Panzhihua of China. The results showed that mineral resource exploitation had a significant impact on the urban river bacterial community structure but not on the bacterial ecological functions. Distinct families of bacteria often associated with nutrients (i.e., Comamonadaceae and Sphingomonadaceae) and metal contaminants (i.e., Rhodobacteraceae) were more predominant in the residential and mining area, respectively. Relative to dispersal dynamics, environmentally induced species sorting may primarily influence bacterial community structure. Heavy metals and sediment physicochemical properties had both similar and significant influence on shaping bacterial community structure. Among heavy metals, essential metal elements explained more rates of bacterial variation than toxic metals at moderate contaminant levels. Moreover, the bacteria with multiple metal resistances identified in culture-dependent experiments were probably not suitable for indicating heavy metal contamination in field research. Thus, several sensitive bacterial genera such as Rhodobacter, Hylemonella, and Dechloromonas were identified as potential bioindicators to monitor metals (iron and titanium) and nutrients (phosphorus and organic carbon) in the river ecosystem of the Panzhihua region. Together, these results profiled the coupling effect of urbanization and mineral resource utilization on shaping sediment bacterial communities in urban rivers. [ABSTRACT FROM AUTHOR]

Microeukaryotes are considered critical for biogeochemical cycles and material transformation in river ecosystems, but their biogeography and underlying mechanisms of their assemblages remain poorly understood.We collected 35 water samples and 26 sediment samples covering an 1,148 km reach of the Lancang River, a highly regulated large river in south‐western China. The planktonic and sedimentary microeukaryotic communities were analysed by sequencing the V4 region of eukaryotic 18S rRNA gene. Factors associated with patterns in microeukaryotic communities were assessed by canonical correlation analysis and neutral models. Species interactions and keystone species in microeukaryotic communities were investigated by co‐occurrence network analysis.The results showed that community composition was distinct between planktonic and sedimentary microeukaryotes, as well as between upstream natural sites and regulated sites downstream. Similar environmental (pH, nutrient concentrations) and spatial (altitude, distance) variables were associated with patterns in community composition of planktonic and sedimentary microeukaryote communities, except that turbidity and water temperature were associated only with patterns in planktonic communities.Neutral models were an excellent fit to the distributions of both planktonic (r2 = 0.67) and sedimentary (r2 = 0.50) microeukaryotic communities. The estimated immigration rate (m) from planktonic communities (m = 0.032) was higher than from sedimentary communities (m = 0.022).Co‐occurrence pattern analysis showed that planktonic microeukaryotic networks had more connectivity but a lower proportion of positive interactions than sedimentary microeukaryotic networks. Keystone species, in particular those belonging to phylum Ascomycota, played essential roles in maintaining stability of both planktonic and sedimentary microeukaryotic communities.Our results showed that the composition of planktonic and sedimentary microeukaryote communities differ, and that diversity in both communities was influenced by river regulation. Given the important roles played by microeukaryotes in nutrient cycling and food webs, such impacts may alter other ecosystem processes in rivers. [ABSTRACT FROM AUTHOR]

Agricultural drainage ditches (ADDs) are ubiquitous and regarded as active zones for biogeochemical reactions and microbe-mediated pollutant removal. However, little is known about the microbial distribution and community assembly in ADDs. Here, a typical large-scale irrigation district, including five orders of farmland drainage systems (namely field, sublateral, head, branch, and trunk ditches that could efficiently remove excess water from paddy fields to downstream water bodies), was selected to investigate the ecological processes of microbial communities and N- and P-transformation processes in multistage ditches. We found that scale effects drove distinct environmental gradients and microbial community dissimilarities and that the five ordered ditches were grouped into three clusters (field vs. sublateral vs. head, branch, and trunk ditches). Specifically, the microbial communities in the field ditches located adjacent to the paddy fields were strongly selected by agricultural fertilization and irrigation drainage, enriching salt-tolerant microbes with high nitrification and inorganic P solubilization capabilities. In comparison, the sublateral ditches showed the highest removal performance for total nitrogen (13.28–55.80%) and total phosphorus (9.06–65.07%) during the growth of rice, which was mainly attributed to the enrichment of versatile microbiota (e.g., C39 , Nitrospira, and Novosphingobium) as a result of the increased stochastic processes driven by the low redox potential. Notably, the specific gene (i.e., hzsB) for anaerobic ammonium oxidation in sublateral ditches was 1–2 orders of magnitude higher than in adjacent ditches, further contributing to N loss. As field water was discharged into the large-sized head, branch, and trunk ditches, the nutrient levels decreased sharply. At the same time, deterministic processes gained more importance (∼82%), leading to the flourishing of Synechococcus and increasing the potential risk of eutrophication. Overall, the microbial communities in multistage ADDs were co-shaped by agricultural practices and ditch size, which further governed the N and P removal performance. These results provide unique insights into microbiota assembly patterns and dynamics in multistage ADDs and important ecological knowledge for controlling agricultural non-point source pollutants by managing of small-sized ditches. [Display omitted] • Microbial dynamics and their contributions to N and P removal were investigated. • Microbial communities in multistage drainage ditches were scale dependent. • Agricultural practices and ditch size co-shape the microbial communities in ditches. • Local heterogeneity enhanced stochastic process and enriched functional microbiota. • Multistage drainage ditches were efficient to control non-point source pollutants. [ABSTRACT FROM AUTHOR]

Summary: Despite the essential functions of sedimentary bacterial and fungal communities in biogeochemical cycling, little is known about their biogeographic patterns and driving processes in large rivers. Here we investigated the biogeographic assemblies and co‐occurrence patterns of sedimentary bacterial and fungal communities in the Jinsha River, one of the largest rivers in southwestern China. The mainstream of river was divided into upstream, midstream and downstream. The results showed that both bacterial and fungal communities differed significantly among three sections. For both communities, their composition variations in all sites or each river section were controlled by the combination of dispersal limitation and environmental selection, and dispersal limitation was the dominant factor. Compared with bacteria, fungi had stronger dispersal limitation. Co‐occurrence network analyses revealed higher network connectivity but a lower proportion of positive interaction in the bacterial than fungal network at all sites. In particular, the keystone species belonging to bacterial phyla Proteobacteria and Firmicutes and fungal phyla Ascomycota and Chytridiomycota may play critical roles in maintaining community function. Together, these observations indicate that fungi have a stronger dispersal limitation influence and less network connectivity than bacteria, implying different community assembly mechanisms and ecological functions between bacteria and fungi in large rivers. [ABSTRACT FROM AUTHOR]

Bacterioplankton communities commonly consist of few highly abundant species and a large number of rare species that play key roles in biogeochemical cycles of aquatic ecosystems. However, little is known about the biogeographic assemblies of these communities, especially in large rivers suffering from cascade dam regulation. Here, we used a 16S rRNA gene amplicon sequencing approach to investigate the biogeographic patterns and underlying assembly mechanisms of abundant and rare bacterioplankton taxa in cascade reservoirs of the Jinsha River in China. The results revealed species loss of bacterioplankton due to dam construction, which was more significant for rare taxa than for abundant ones. The distributions of abundant and rare taxa exhibited similar spatial and temporal patterns, which were significantly distinct between winter and summer and between upstream and downstream reservoirs. Both spatial (dispersal-related process) and environmental (selection process) factors seemed to together govern the assembly and biogeography of abundant and rare taxa, although both factors explained only a small fraction of variation in the rare taxa. More importantly, environmental factors explained more community variation in abundant sub-community than that in rare sub-community. Co-occurrence network analysis revealed that abundant species with closer interactions were more often located in a central position of the network compared with rare species. Nevertheless, half of the keystone species were rare species and may play important roles in maintaining the network stability. Overall, these findings indicate that distinct assembly mechanisms underlie the similar biogeography of rare and abundant bacteria in cascade reservoirs of a large river. [ABSTRACT FROM AUTHOR]

• DOP is highly bioavailable in Lake Taihu, China, especially in Meiliang Bay. • DOP utilization is vital in shaping phytoplankton community in P-deficient waters. • High APA expression is not equal to the high capacities of DOP utilization. • Low algal APA implies the restriction of other factors under P-deficient conditions. • APA can be used to optimize the prediction of algal blooms in P-deficient lakes. Dissolved organic phosphorus (DOP) could be transformed to dissolved inorganic phosphorus (DIP) under phosphorus (P) deficient conditions by various enzymes, among which alkaline phosphatase activity (APA) is regarded as the most important one. To better understand the different response of phytoplankton to DOP and the role of alkaline phosphatase activity (APA) in phytoplankton growth in natural waters, the distribution of P, APA, and phytoplankton density were measured at 12 sites in Lake Taihu, China, in summer, autumn, and winter of 2016. In this study, 34.12% of DOP could be hydrolyzed, indicative of the high bioavailability of DOP in Lake Taihu, especially in Meiliang Bay. More than 70% of enzymatically hydrolyzed DOP came from alkaline phosphatase-hydrolyzed DOP, verifying that APA had a major role in hydrolyzing DOP to fulfill the DIP requirements of phytoplankton, and that phosphomonoesters were the main form of bioavailable DOP in Lake Taihu. Redundancy analysis implied a high capacity of DOP use may be important for species dominance under P-deficient conditions, but high APA expression is not equal to the high capacities of DOP utilization. In this study, phytoplankton density was significantly positive with bulk APA, algal APA and bacteria APA. APA, despite of its complex contributors, is able to increase the amount of bioavailable P for phytoplankton growth. Moreover, algal APA reflects the actual response of phytoplankton to available P under P-deficient conditions. Low algal APA means that other factors limit phytoplankton growth. Increased algal APA means that other limitations get alleviated and algae are in anxious demand for P. Therefore, this paper suggests that monitoring APA can be used as a supplementary indicator to reflect the actual demand for P of algal, thus to optimize the prediction of algal blooms. [ABSTRACT FROM AUTHOR]

Pharmaceuticals are increasingly detected in environmental matrices, but information on their trophic transfer in aquatic food webs is insufficient. This study investigated the bioaccumulation and trophic transfer of 23 pharmaceuticals in Taihu Lake, China. Pharmaceutical concentrations were analyzed in surface water, sediments and 14 aquatic species, including plankton, invertebrates and fish collected from the lake. The median concentrations of the detected pharmaceuticals ranged from not detected (ND) to 49 ng/L in water, ND to 49 ng/g dry weight (dw) in sediments, and from ND to 130 ng/g dw in biota. Higher concentrations of pharmaceuticals were found in zoobenthos relative to plankton, shrimp and fish muscle. In fish tissues, the observed pharmaceutical contents in the liver and brain were generally higher than those in the gills and muscle. Both bioaccumulation factors (median BAFs: 19–2008 L/kg) and biota−sediment accumulation factors (median BSAFs: 0.0010–0.037) indicated a low bioaccumulation potential for the target pharmaceuticals. For eight of the most frequently detected pharmaceuticals in food webs, the trophic magnification factors (TMFs) were analyzed from two different regions of Taihu Lake. The TMFs for roxithromycin, propranolol, diclofenac, ibuprofen, ofloxacin, norfloxacin, ciprofloxacin and tetracycline in the two food webs ranged from 0.28 to 1.25, suggesting that none of these pharmaceuticals experienced trophic magnification. In addition, the pharmaceutical TMFs did not differ significantly between the two regions in Taihu Lake. [ABSTRACT FROM AUTHOR]

Fungi are important contributors to the various functions of activated sludge wastewater treatment plants (WWTPs); however, the diversity and geographic characteristics of fungal populations have remained vastly unexplored. Here, quantitative polymerase chain reaction and 454 pyrosequencing were combined to investigate the abundance and diversity of the activated sludge fungal communities from 18 full-scale municipal WWTPs in China. Phylogenetic taxonomy revealed that the members of the fungal communities were assigned to 7 phyla and 195 genera. Ascomycota and Basidiomycota were the most abundant phyla, dominated by Pluteus, Wickerhamiella, and Penicillium. Twenty-three fungal genera, accounting for 50.1 % of the total reads, were shared by 18 WWTPs and constituted a core fungal community. The fungal communities presented similar community diversity but different community structures across the WWTPs. Significant distance decay relationships were observed for the dissimilarity in fungal community structure and altitudinal distance between WWTPs. Additionally, the community evenness increased from 0.25 to 0.7 as the altitude increased. Dissolved oxygen and the C/N ratio were determined to be the most dominant contributors to the variation in fungal community structure via redundancy analysis. The observed data demonstrated the diverse occurrence of fungal species and gave a marked view of fungal community characteristics based on the previously unexplored fungal communities in activated sludge WWTPs. [ABSTRACT FROM AUTHOR]

Metal resistance genes (MRGs) are potential bio-indicators to diagnose contamination stress on riverine ecosystems. Within reservoir systems, river damming weakens hydrodynamic condition and enriches metal contaminants. But, little is known about the synergic impacts of geographic variation and anthropogenic pollution on MRGs. In this study, the abundance, composition and microbes of MRGs in four cascade reservoirs along the Jinsha River, southwestern China were investigated via high-throughput metagenomics. The results showed significant enrichment of chromium, cadmium and lead in Ludila and Xiluodu reservoirs with moderate ecological risks based on the criteria of drinking water quality and aquatic life protection. Nevertheless, at watershed scale, these metals played little role in up-regulating MRGs abundance owing to the limited toxic stress on microbes. Accordingly, geographic variation showed stronger impacts on MRGs composition than metals as revealed by the distance-decay relationship (Pearson correlation, r geo = 0.24–0.57, r metal = 0.10–0.41) and co-occurrence network (Node degree to MRGs subtype, n geo = 180, n metal = 6). River damming, as an artificial isolation of geographic space, significantly affected MRGs composition. The longer operation history, smaller storage capacity and higher regulation frequency caused the higher dissimilarity of MRGs composition between the reservoir's upstream and downstream areas. In conclusion, the metal pollution level is a prerequisite regulating MRGs; while under the lowly-polluted conditions, geographic variation had stronger impacts on MRGs than metal pollution via altered assembly of microbial communities. This study provides an important guidance for the future environmental management and ecological protection of river-reservoir ecosystems. • Metal pollution level is a prerequisite regulating MRGs abundance in reservoir water. • Geographic variation had stronger impact on MRGs composition than metal pollution. • Reservoir operation time, storage size and regulation mode affected MRGs abundance. • Reservoir MRGs distribution was internally affected by relevant microbial community. [ABSTRACT FROM AUTHOR]

Perfluorinated compounds (PFCs) can pose adverse effect on aquatic species and community structure. However, little is known about how the characteristics of molecules of PFCs affect their chronic toxic potencies to aquatic species, and the species sensitivity distributions (SSDs) and ecological risk assessments of PFCs are hampered by limited available data of chronic toxicity. In the present study, a novel procedure is proposed to obtain the ecological risk of PFCs using existing exposure concentrations of PFCs and SSDs integrated with the chronic toxicity prediction through robust QSAR models. The results showed that the energy of the lowest unoccupied molecular orbital (E LUMO) exhibited the strongest correlation with the chronic toxicities of 15 PFCs (R 2 > 0.844, F > 16.206, p < 0.05). SSDs of 15 PFCs on eight species were first constructed, and the SSD fitting parameters were significantly correlated with E LUMO (R 2 > 0.610, F > 19.471, p < 0.05). The QSAR-SSDs support the evaluation of hazardous criteria of PFCs for which data are lacking. Given environmental exposure distributions (EEDs) of the national presence of PFCs in aquatic systems in China, the QSAR-SSDs models allow the development of the ecological risk assessment for PFCs. This way, it was concluded that negligible environmental risk (defined as 5% of the species being potentially exposed to concentrations able to cause effects in < 5% of the case) could be expected from exposure to PFCs in surface waters in China. This method may be helpful for providing an evidence-based approach to guide the risk management for PFCs in aquatic environment. • Molecular descriptor, E LUMO showed the strongest correlation with log-NOEC/LOEC. • HC 5 and its 95% confidence intervals of 15 PFCs were predicted by QSAR-SSD. • Molecular descriptors can be directly used to estimate SSD parameters for PFCs. • Acceptable environmental risk expected from exposure to PFCs. [ABSTRACT FROM AUTHOR]

Sediment bacterial communities are sensitive to water conditions in river ecosystems. The objective of this study was to compare the influences of different pollution sources, including urban areas, wastewater treatment plants (WWTPs), suburban areas, and agricultural areas, on sediment bacterial communities along a typical tributary of Taihu Lake, China. The dominant composition of the sediment bacterial community was determined using a combination of terminal restriction fragment length polymorphism (T-RFLP) and a 16S rRNA clone library. The results showed that the sediment bacterial communities were distinctly affected by the four pollution sources. Alphaproteobacteria, Betaproteobacteria, and Actinobacteria (>50 % in total) were the predominant bacterial taxa across the sediment samples. Apart from those, the sediment bacterial community composition (BCC) affected by WWTP effluent was subsequently dominated by Nitrospira (12.4 %) and Bacteroidetes (11.5 %), agriculture was dominated by Firmicutes (13.2 %) and Deltaproteobacteria (7.2 %), while urban and suburban were dominated by Bacteroidetes (7.6 and 7.9 %, respectively) and Deltaproteobacteria (7.9 and 7.6 %, respectively). Cluster analysis indicated that the BCC affected by WWTP effluent was distinct from the BCC in urban, suburban, and agricultural areas. In addition, the bacterial community richness and evenness affected by WWTP effluent were much less than those by the other pollution sources. Redundancy analysis (RDA) indicated that the variation in BCC across the sediment samples was significantly associated with ammonium (17 %), organic matter (12 %), and cadmium (3 %) ( p < 0.01). Overall, the results indicated that the four different pollution sources (WWTP, urban, suburban, and agriculture) have dissimilar impacts on the sediment BCC in the tributary of Taihu Lake, while WWTPs exhibited the greatest potential to lead to biotic homogenization in river sediments. [ABSTRACT FROM AUTHOR]

Dam construction causes phosphorus (P) accumulation in reservoir sediments and significantly affects the generation of available P. However, the effect of dam construction on the activity of sediment alkaline phosphatase (ALP), which is encoded by the bacterial phoD gene and participates in P mineralization, in river sediments remains unclear. Here, we investigated the ALP activities in 78 sediment samples collected from the cascade reservoir regions located in the Lancang River and the Jinsha River, two highly regulated rivers in southwestern China. The abundance and community composition of phoD -harboring bacteria were determined based on the phoD gene using quantitative real-time PCR and MiSeq sequencing, respectively. Comparison of control and affected sites indicated that dam construction significantly increased sediment ALP activity in both rivers. The abundances of phoD -harboring bacteria increased and their community compositions varied in response to dam construction; the relative abundances of the dominant genera Methylobacterium and Bradyrhizobium were particularly higher in affected site than control site. Co-occurrence network analyses revealed much higher network connectivity and relative abundances of keystone species in affected sites. Some microbial factors including phoD -harboring bacterial abundances, network clustering coefficients, and relative abundance of keystone species were positively correlated with ALP activity. The relative abundance of keystone species was identified as the most important microbial factor contributing to variation in ALP activity based on structural equation modeling analysis. These findings enhance our understanding of how dam construction affects the functions of phoD -harboring bacteria and their role in the P biogeochemical cycle in highly regulated rivers. • Sediment alkaline phosphatase activity was markedly enhanced by dam construction. • Damming altered the abundance and community composition of phoD -harboring bacteria. • Damming enhanced connectivity and cooperation in phoD -harboring bacterial network. • Keystone species of phoD -harboring bacteria were enriched in reservoir sediments. [ABSTRACT FROM AUTHOR]

Purpose: Sediments are significant methane (CH) sources of the atmosphere. However, the mechanisms of CH generation remain unclear in sediments of shallow urban lakes. The aims of this investigation were to study the characterization of environmental parameters, CH generation, and methanogen populations in Wulongtan Lake, China, which is affected solely by nonpoint pollution. Materials and methods: The concentrations of CH in the atmosphere and of vertical sediment profiles and the methane flux at the air-water interface were monitored in the summer of 2012. Environmental parameters in the water column and in the vertical sediment profiles were assayed. The activities of cellulose, saccharase, polyphenol oxidase, and urease enzyme and 16S rRNA gene copy numbers of Archaea (ARC), Methanobacteriales (MBT), Methanococcales (MCC), Methanomicrobiales (MMB), Methanosarcinales (MSL), Methanosarcinaceae (MSC), and Methanosaetaceae (MST) were determined in the vertical sediment profiles. The abundance of methyl-coenzyme A reductase (ME) gene was also determined to evaluate the total activities of methanogens. Results and discussion: High CH concentrations were detected in the atmosphere above the lake, and the mean CH flux at the air-water interface was 6.21 mM m h. Dissolved oxygen decreased with an increase of water depth. Eh values and CH contents increased, but total nitrogen, water content, and total organic carbon (TOC) decreased with an increase of sediment depth. Cellulose, saccharase, polyphenol oxidase, and urease activities were detected in all sedimentary layers. The copy number of 16S rRNA gene (wet weight) for Archaea reached the highest value in the surface sediment. Copy numbers of ME were higher at 12-33 cm than at 0-6 cm. In general, abundances of MMB, MBT, and MSL were higher than that of MCC in the same sedimentary layer. 16S rRNA gene copy numbers of MST decreased with increasing depth, while MSC was higher at 18-27 cm than that at other sections. These indicate that hydrogenotrophic, aceticlastic, and methylotrophic pathways coexisted in these sediments. Principal component analysis revealed that in the sediments, the level of CH was closely related with several parameters including saccharase, urease, ME, and MBT, while TOC content was related to CEL, MST, ARC, water content, and Eh. Conclusions: High CH release potential was detected in this shallow urban lake and can be ascribed to the anaerobic aquatic environment, bacterial enzyme activities, and methanogens. The orders MMB, MBT, and MSL were dominant in sediments for CH production. The presence of orders or families of methanogens might be determined by the types of available substrates in lake sediments. [ABSTRACT FROM AUTHOR]

Abstract: In this study, surface sediment from Zhushan Bay in Taihu Lake was subjected to resuspension under 6 different wind forces using a pneumatic annular flume. Water samples were taken at specific intervals, and the physicochemical parameters of the water column were monitored throughout the experiment. Concentrations of heavy metals (Cd, Pb, Cr, Ni, Cu, and Zn) in the sediment, water, and suspended particulate matter (SPM) were determined following standard methods. Total metal concentrations in overlying water increase with wind speed and the duration of the experiment. According to the principal component analysis (PCA), physicochemical factors, pH, dissolved oxygen (DO), and SPM all showed a close relationship with total metal content. Dissolved metal concentrations did not show significant variation. In contrast, a remarkable increase in the concentrations of metals was noted in the SPM in response to increases in wind speed and duration time of the study. Distribution coefficients (K ds) of metals between particulate and dissolved fractions generally appeared in the following order: Pb > Cr > Zn > Cu > Cd > Ni under six different disturbance conditions. However, the enrichment factors (EFs) of particulate metals generally appeared in the following pattern with respect to concentration: Zn > Pb > Cr > Cd > Cu > Ni. In general, the values of both indicators were directly proportional with as water turbulence. The results of this study may serve as a reference for distribution rules of heavy metals in water columns and SPM during sediment resuspension processes. [Copyright &y& Elsevier]

The speciation and distribution of the nutrients nitrogen and phosphorus in riverbed sediment play an important role in river water quality and are the primary product for the river ecosystem. Previous research on river nutrients has not considered the relationship between nitrogen and phosphorus and their mobility effects. To investigate the role of nitrogen and phosphorus in water quality and their interactions between sediments and water, sediment and water samples were taken from 10 sites along the middle main stream of the Huai River in China from Linhuaigang to Fengtai County on December 12, 2008. Nitrogen and phosphorus concentrations in water, organic matter (OM), and different forms and contents of the elements in sediment were investigated. Results showed a positive correlation between total nitrogen in sampled sediments, primarily occupied by organic nitrogen and chlorophyll concentrations in water (). Total phosphorus in sediments was primarily represented as inorganic phosphorus, accounting for 80.9-96.1% of total phosphorus. The concentrations of non-apatite inorganic phosphorus in sediment ranged from . Results from statistical correlation analyses showed that the non-apatite inorganic phosphorus content in sediment was obviously negatively correlated with total nitrogen concentration in water (, ); inorganic nitrogen and non-apatite inorganic phosphorus contents in sediment were positively correlated with total phosphorus and resolvable phosphorus concentrations in water, respectively. Furthermore, data of May 2008 were added and analyzed. The same principles were observed between total nitrogen and non-apatite inorganic phosphorus, total phosphorus and inorganic nitrogen, but a positive correlation was found between (1) total nitrogen in water and (2) exchangeable nitrogen () and inorganic nitrogen () in sediments. [ABSTRACT FROM AUTHOR]

The riparian vegetation zone plays an important role in river ecosystems, flow resistance, water velocity distribution, and water level variation. In this paper, the impacts of riparian reed zones on river flow and water level were studied by comparing measurements in river reaches with or without riparian reed zones in the Chaodongweigang River of Taihu Lake Basin, China. The effects of the density, stem diameter, and rigidity of reeds on flow regime, water velocity, and water level were investigated. Subsequently, flow resistance on the river’s longitudinal water level caused by the riparian reed zone was studied. The results showed three water velocity zones in the river reach where there were riparian reeds, including the slack water zone, the transition zone of flow velocity, and the river’s main flow zone. The water velocities in the three zones were related to reed density, diameter, and rigidity. The water-surface slope in the river reach with a riparian reed zone was larger than that without a reed zone. It showed that the riparian reed zone influenced the river flood discharge to some degree and resulted in increased water level upstream. Additionally, the water level of the river cross section exhibited a concave shape that the water level was higher in the riparian reed zone than in the center of river midstream, section with a riparian reed zone exhibited a concave shape; the water level was higher in the riparian reed zone than in midstream, and the water level difference was influenced mainly by the reed density. [ABSTRACT FROM AUTHOR]

Understanding the characteristics of domestic sewage discharge in different rural areas is an important prerequisite for effective sewage treatment. Here, we revealed the spatial variation in the water quantity and quality of rural domestic sewage and its influencing factors in 31 provinces and cities of China, based on a multi-factorial analysis. The results showed that the water quantity of rural domestic sewage discharge generally increased from Northwest to Southeast in China and the water quality had opposite pattern. The water quantity was positively correlated with water resources, gross domestic product, rainfall, and temperature, but negatively correlated with altitude. Water resources, with an influence weight of 25.04% by principal component analysis, had the greatest impact on the spatial variation in water quantity. Differently, gross domestic product, which was directly negatively correlated with ammonium-nitrogen and total phosphorus in structural equation model, was a dominant factor influencing water quality. These findings will help us to better understand the factors of controlling rural domestic sewage discharge at a national scale and to optimize the treatment technology of rural domestic sewage. [Display omitted] [ABSTRACT FROM AUTHOR]

• Alkaline copper mine drainage caused elevated sulfur and metal(loid) pollution. • Metals (Cu, Zn, and Cr) and TOC notably affected sediment bacterial communities. • Bacterial functional groups at polluted sites were involved in S and Cu cycles. • Significant variation of indicator species can reveal alkaline copper mine pollution. • Co-occurrence network showed more positive bacterial interactions at polluted sites. Contamination of alkaline copper mine drainage (AlkCuMD) causes serious damages to riverine ecosystem. Sediment bacterial community, as the fundamental component of biogeochemical processes, has been applied as an effective ecological indicator for various pollutants, but little is known about its relation to AlkCuMD. In this study, the composition variation, indicator species, and co-occurrence pattern of sediment bacterial community were studied in the Jinsha River, a typical AlkCuMD polluted large river in southwestern China. Results showed that significant sulfur (TS max , 84.06 g/kg) and copper (Cu max , 1.63 g/kg) contamination from AlkCuMD decreased the richness and diversity of bacterial community, and the composition of bacterial community was significantly altered by copper, zinc, chromium, and total organic carbon. Moreover, the indicator species identified in the polluted sediments, including Thiovirga and Symbiobacterium , exhibited the functional traits of sulfur oxidation and metal(loid) cycling; while the indicator species in the unpolluted sediments were mainly associated with the nitrogen and phosphorus biotransformation. In addition, the bacterial co-occurrence pattern showed higher positive interactions and network connectivity at polluted sites, suggesting the potential enhancement of bacterial interspecific mutualistic relationships against AlkCuMD contamination. Therefore, this study provides an important evaluation of AlkCuMD influence on sediment bacterial community, and proposes the potential ecological indicators for evaluating AlkCuMD pollution in river sediments. [ABSTRACT FROM AUTHOR]

Metals and metalloids contamination has become a significant global environmental issue. The Jinsha River Basin (JRB) in China, an important water resource for the Yangtze River, has become increasingly subject to anthropogenic disturbances. We analyzed ten metal(loid) concentrations (Hg, As, Cu, Zn, Ni, Cr, Cd, Pb, Fe, and Al) in riverbed sediments, following a multivariate analysis approach, which includes source apportionment and ecological risk assessment. The metal(loid) spatial distribution revealed significantly high concentrations of Cr in the upper reaches, Ni in the midstream, Cu and Fe in the lower reaches, and Cd in the entire river. The positive matrix factorization and correlation analysis indicated that Hg, Cd, Pb, and Zn originated mainly from atmospheric deposition and agricultural discharge, and Cu and Fe originated primarily from mining and industrial wastes. The main source of Cr, Ni, As, and Al was natural disturbances, such as rock weathering, hydraulic souring, and geological processes. The ecological risk assessment indicated that the entire JRB posed a low to moderate ecological risk, and the mobility and biotoxicity of metal(loid)s showed an increasing trend along the river. Notably, Cd had the highest mobility and ecological risk. Overall, the risk to the locals and aquatic organisms of the JRB due to metal(loid) pollution was significant, with contamination from mining and agriculture being of particular concern. • The first evaluation of the metal(loid) pollution of the Jinsha River Basin in China • Four metal(loid) assessment models were employed (PERI , m RAC , m HQ , and ECI). • Contamination from mining and agriculture is a potential cause for concern. • Metal(loid) mobility and biotoxicity trend similar to anthropogenic pollution trend [ABSTRACT FROM AUTHOR]

The development of microbial community-based biological indicators for assessing aquatic ecological status is urgently needed in heavily impaired regions, due to the local extinction of traditional indicator macroorganisms. The aim of this study was to develop and validate a microbial community-based index of biotic integrity (MC-IBI) for the assessment of rivers in the Taihu Basin, China. MC-IBI was developed based on sediment samples collected from 55 sites of 42 rivers, with least disturbed sites as reference sites. High-throughput sequencing and real-time PCR methods were employed to measure the microbial diversity and abundance of the samples. A total of 341 candidate metrics related to microbial diversity, composition, pollution tolerance and function categories were established based on microbial data. Five core metrics, including% FCA (percentage of Firmicutes, Chloroflexi and Acidobacteria), log 16S rRNA /ARG (log the ratio of 16S rRNA gene to antibiotic resistance gene), log AOB/AOA (log the ratio of ammonium oxidizing bacteria to ammonium oxidizing archaea), nirK / nirS (ratio of nirK gene to nirS gene) and BFG/A (ratio of Bacteroidetes, Firmicutes and Gammaproteobacteria to Alphaproteobacteria), were identified to develop a MC-IBI. The developed MC-IBI was demonstrated to be robust using a validation dataset. Further, the MC-IBI showed a significantly negative association with the index of water quality. The river ecological conditions of the 55 sampled sites in the Taihu Basin were defined as excellent (9.1%), good (14.5%), moderate (25.5%), poor (23.6%) and bad (27.3%) separately based on the MC-IBI scores. Overall, the MC-IBI provides a novel assessment tool for the ecological health status of freshwater rivers. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, many methods have been proposed to cope with eutrophication, a serious ecological problem in estuaries. Many of these problems have resulted from the new production of non-siliceous algae. In this paper, a runoff optimized regulation model for eutrophication control was developed to limit the potential of new non-siliceous algae production, which, in this paper, is defined as eutrophication potential. At the beginning of the model, a formula of silicon flux was modified by adding a dam retention coefficient and a turbidity maximum zone (TMZ) retention coefficient. Afterwards, the formula was used to improve the expression of the ICEP (indicator of coastal eutrophication potential) for a more exact result. The ICEP (treated as an ecology objective to limit the potential of sustaining new production of non-siliceous algae), harmonious index, and cost function were then integrated into the optimization model, at which point the ICOA (immune clone optimization algorithm) was proposed to solve this model. We then chose the Yangtze Estuary as a case study to verify the performance of the optimization model, and used an uncertainty analysis, a comparative analysis, and a sensitivity analysis to assess the model''s performance. The results show the best combination of weight factors for integrating objectives is λ 1 =0.48, λ 2 =0.32, λ 3 =0.2. The optimized runoff performs well at keeping the value of the ICEP within reasonable limits while at the same time meeting the goal of economy and society in the Yangtze Estuary. Finally, we discuss transfer rates in different exceedance probabilities, illustrating that the optimized runoff is feasible for this study area, and the results can then be used as a point of reference regarding water transfer decisions. [Copyright &y& Elsevier]

In this research, a new approach has been suggested for providing an optimization bidding strategy in the day-ahead market for case research in China. This research uses a newly developed version of Emperor Penguin Optimizer (CEPO) to govern the fitness function of all individuals based on the Market Clearing Price (MCP) probability function. The resemblance amounts between each day and the next day are used for clustering. The clustering is performed based on the well-known subtractive clustering methodology. A simulation model using the probability function in MCP estimates the fitness function of the generated strategies. The results indicate that this method proposed is a statistically effective bidding design in China's day-ahead market related to two other plans from the literature. • An optimized method for bidding strategy in the day-ahead market in China. • Converged Emperor Penguin Optimizer (CEPO) for problem optimization. • The problem is to minimize the Market Clearing Price (MCP) probability function. • Subtractive clustering for data clustering between each day and the next day. [ABSTRACT FROM AUTHOR]

Pharmaceuticals and personal care products (PPCPs) are recognized as a group of emerging contaminants closely related to anthropogenic activities, which capture increasing attention worldwide. To evaluate the anthropogenic disturbances on PPCP distribution and sources, this study investigated the distribution and sources of 50 PPCPs along the 2300 km long Jinsha River and revealed different anthropogenic disturbances on PPCPs. Results showed that 40 out of the 50 PPCPs were ubiquitously detected among these river water samples, with the concentrations varied from less than 1 ng/L to more than 500 ng/L. Although most PPCPs concentrations were much lower in the Jinsha River than in highly developed rivers, the prevalence of PPCPs suggested the widespread use and improper disposal of PPCPs in the Jinsha River. The risk assessment also revealed that some PPCPs posed risks to aquatic organisms in the Jinsha River. Anthropogenic activities including human habitation and dam construction had different influence on PPCPs. PPCP distribution varied significantly across the "Hu Huanyong line", indicating human habitation significantly influenced PPCP distribution. Dam construction was insignificant in altering PPCP distribution throughout the Jinsha River. Moreover, the land use index indicated degradation level of multiple lands related to anthropogenic activities and represented the major sources of PPCPs in the Jinsha River. Most PPCPs were correlated with anthropogenic lands, for example, antibiotics, analgesics, and endocrine disrupting chemicals mainly originated from artificial surfaces, whereas other PPCPs mainly originated from cultivated lands. Together, this study indicates the disturbances of multiple anthropogenic activities on PPCP distribution and sources along the Jinsha River, which contributes to PPCP management in rural areas. • Complex sources and distribution of PPCPs were studied along large-scale rural river. • PPCPs were ubiquitous but present at relative low levels in the Jinsha River. • Due to human habitation, PPCP distribution varied across the "Hu Huanyong" line. • Land use index reflected major PPCP sources in less urbanized area. • This study has implications for the PPCP management in rural areas worldwide. [ABSTRACT FROM AUTHOR]

With the increasing human disturbance to urban rivers, the extinction and biodiversity losses of some macroorganism species decreased the accuracy of bioassessment. In this study, a novel index of biotic integrity based on bacteria (Ba-IBI) was first developed for Qinhuai River in Nanjing city, China. Thirty-two biofilm samples were collected along the river bank and the bacterial communities were identified by high-throughput sequencing. By the range, responsive, and redundancy tests, four core metrics were selected from the dataset of 78 candidate metrics, including Pielou's evenness index, proportion of Paenibacillus , proportion of OTUs tolerant to organic pollution and proportion of Nitrosomonas. The results showed that the Ba-IBI was able to effectively discriminate different impaired site groups, and had a good correlation with the index of water quality (r = 0.79, p < 0.01) and the qualitative habitat evaluation index (r = 0.51, p < 0.01). Moreover, the Ba-IBI was negatively correlated with the number of population within a 1 km buffer (r = −0.71, p < 0.01). Application of the index showed that most of the sites were in the poor or bad class in the river. Our study revealed that the Ba-IBI is an effective and reliable approach for assessing the ecological status of Qinhuai River basin, which can complement the existing ecological assessment approaches for urban rivers. Meanwhile, repeted surveys and field validations are still needed to further improve the applicability of the index in future studies. [ABSTRACT FROM AUTHOR]

To alleviate the water shortage in northern China, the Chinese government launched the world's largest water diversion project, the South-to-North Water Diversion Project (SNWDP), which delivers water from water-sufficient southern China to water-deficient northern China. However, an up-to-date study has not been conducted to determine whether the project is a favorable option to augment the water supply from an environmental perspective. The life cycle assessment (LCA) methodology integrated with a freshwater withdrawal category (FWI) was adopted to compare water supply alternatives in the water-receiving areas of the SNWDP, i.e., water diversion, wastewater reclamation and seawater desalination. Beijing, Tianjin, Jinan and Qingdao were studied as representative cities because they are the primary water-receiving areas of the SNWDP. The results revealed that the operation phase played the dominant role in all but one of the life cycle impact categories considered and contributed to more than 70% of their scores. For Beijing and Tianjin, receiving water through the SNWDP is the most sustainable option to augment the water supply. The result can be drawn in all of the water-receiving areas of the middle route of the SNWDP. For Jinan and Qingdao, the most sustainable option is the wastewater reclamation system. The seawater desalination system obtains the highest score of the standard impact indicators in all of the study areas, whereas it is the most favorable water supply option when considering the freshwater withdrawal impact. Although the most sustainable water supply alternative was recommended through an LCA analysis, multi-water resources should be integrated into the region's water supply from the perspective of water sustainability. The results of this study provide a useful recommendation on the management of water resources for China. [ABSTRACT FROM AUTHOR]

• A novel bio-assessment framework combined Ba-IBI and path model was established. • The bio-assessment was used to assess ecological effect of fluvial inputs on lake. • Water nutrients were the controlling fluvial inputs for Ba-IBI of Dongting Lake. • Hydrological parameters had a highest indirect effect on Ba-IBI of Dongting Lake. Rivers bring large amounts of water, sediment, and other abundant materials (nitrogen, phosphorus, carbons, etc.) into lakes, which places great pressure on lake ecosystems. In this study, a novel bio-assessment framework integrating the bacteria-based index of biotic integrity (Ba-IBI) and path model was established to determine the direct and indirect effects of fluvial inputs on the ecological status of Dongting Lake, China. Twenty-two sampling sites were selected in Dongting Lake basin during two days in August 2017. After range, responsive, and redundancy tests, four core metrics were selected from the dataset of 130 candidate metrics to develop the Ba-IBI, including the proportions of Flavobacteriia, Burkholderiales, phototrophs, and streptomycin producers. The Ba-IBI value, which was the sum of each individual metric value, was ranged from 1.37 to 3.66. Based on the 25th and 75th percentiles of the Ba-IBI, three levels were classified to show the influence degree of fluvial inputs on the ecological status. The Ba-IBI showed a gradient distribution for the distance from estuaries to the major lake regions. To further investigate the relative contributions of each individual fluvial input to the Ba-IBI, a path model was established and validated. The results showed that water nutrients (r = −0.658, p < 0.1) was the controlling group of factors for the Ba-IBI, including direct (r = −0.538, p = 0.002) and indirect effect (r = −0.12, p < 0.1). Water organics and sediment characteristics groups exerted direct effects, with coefficients of −0.324 (p = 0.015) and 0.271 (p = 0.089). The hydrological parameters group (r = −0.3, p < 0.1) had an indirect effect on the Ba-IBI mediated through water nutrients, water physicochemical properties, and sediment characteristics groups. The bio-assessment framework can provide a new insight for the management and protection of lake ecosystems. [ABSTRACT FROM AUTHOR]

Emerging organic pollutants (EOPs) in urban rivers have raised concerns regarding their eco-toxicological effects. However, the bacterioplankton community disturbances caused by EOPs in urban rivers and the associated ecological mechanisms remain unclear. This study provided profiles of the spatial distribution of a bacterioplankton community disturbed by human activity along an urban river. The results showed that EOP concentration and composition were differently distributed in residential and industrial areas, which significantly influenced bacterioplankton community structure. Based on redundancy analysis, parabens (methylparaben and propylparaben) were the major factors driving bacterioplankton community changes. Parabens inhibited gram-positive bacteria and promoted oxidative stress-tolerant bacteria in the river ecosystem. Parabens also disturbed ecological processes of bacterioplankton community assembly, shifting from a homogeneous selection (consistent selection pressure under similar environmental condition) to stochastic processes (random changes due to birth, death, immigration, and emigration) with changing in paraben concentrations. Heterogeneous selection was predicted to dominate microbial community assembly with paraben concentration changes exceeding 61.6 ng/L, which could deteriorate the river ecosystem. Furthermore, specific bacterial genera were identified as potential bioindicators to assess the condition of EOP contaminants in the river. Overall, this study highlights significant disturbances in bacterioplankton communities by EOPs at environmental concentrations, and our results could facilitate generation of appropriate management strategies aimed at EOPs in urban rivers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Riverine bacterioplankton are highly responsive to river alterations and their abundant and rare sub-communities may have different roles in biogeochemical cycling. However, with the rapid development of dam constructions, our knowledge on adaptation mechanism of these sub-communities in regulated river ecosystem was still limited, especially with regard to their functional traits. Here, our study was conducted in the 2800 km Yarlung Tsangpo River on the Tibetan Plateau to address the question of how abundant and rare bacterioplankton would respond taxonomically and functionally to river damming using 16S rRNA gene sequencing combined with Geochip microarray technique. Our results showed that abundant sub-community dominated taxonomic composition while rare sub-community largely determined functional composition. It is also observed that taxonomic diversity of abundant sub-community was significantly stimulated in the reservoir while that of rare sub-community was markedly inhibited. Moreover, abundant sub-community exhibited functional redundancy under damming disturbances since altered taxonomic composition and unaltered functional composition co-occurred simultaneously. Meanwhile, due to portfolio effect, rare sub-community maintained a greater stability under damming disturbances with little variation in taxonomic and functional compositions. In addition, the Stegen null model analysis revealed that stochastic process governed community assembly in both abundant and rare sub-communities. However, according to source tracking analysis, the taxonomic dispersion of abundant sub-community was less significantly impeded by the dam while the functional dispersion of rare sub-community was less strongly interrupted, indicating that the dispersal process in the dominated sub-community was less susceptible to damming. Therefore, by considering bacterioplankton functional traits, our study provided comprehensive evidences for the distinct strategies of abundant and rare sub-communities in response to damming., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The widespread use of polybrominated diphenyl ethers inevitably results in their increased release into natural waters and subsequent deposition in sediments. However, their long-term effects on the bacteria participating in each step of denitrification in eutrophic lake sediments are still unknown. Here, we conducted a one-year microcosm experiment to determine the long-term effects of decabromodiphenyl ether (BDE-209), at low (2 mg kg -1 dry weight) and high (20 mg kg -1 dry weight) contamination levels, on six-type denitrifying bacteria and their activities in sediments collected from Taihu Lake, a typical eutrophic lake in China. At the end of the experiment, sediment denitrifying reductase activities were inhibited by BDE-209 at both levels, with the greatest inhibition seen for nitric oxide reductase activity. The higher nitrate concentration in the contaminated sediments was attributed to the inhibition of nitrate reductase activities. The abundances of six-type denitrifying genes (narG, napA, nirK, nirS, norB, and nosZ) significantly decreased under high BDE-209 treatment, and narG and napA genes were more sensitive to the toxicity of BDE-209. The results from pyrosequencing showed that BDE-209, at either treatment concentration, decreased the six-type denitrifying bacterial diversities and altered their community composition. This shift of six-type denitrifying bacterial communities might also be driven by the debrominated products concentrations of BDE-209 and variations in sediment inorganic nitrogen concentrations. In particular, some genera from phylum Proteobacteria such as Pseudomonas, Cupriavidus, and Azoarcus were decreased significantly because of BDE-209 and its debrominated products., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Plants are vital components of the nitrogen (N) cycling in the riparian zones. Understanding of N uptake strategies of riparian plants, including N sources and preference in N forms (ammonium (NH 4 + ) vs. nitrate (NO 3 - )), is essential to advance our knowledge on the role that plants play in regulating nutrient biogeochemical cyclings in the riparian areas. In this study, stable N isotopes (δ 15 N) of three riparian plants, including Acorus calamus, Canna indica and Phragmites australis, and the δ 15 N of NH 4 + and NO 3 - in different sources were measured during the plant growing season (June-September) in the Taihu Lake Basin. The dissolved inorganic N (DIN) from river water, groundwater, rainwater and soil were considered as the major N sources for plants in the riparian ecosystem. Our results indicated that soil was the largest source for plant N nutrition, with significantly different (P < 0.05) contributions from soil observed among plant species (80.5 ± 4.1, 73.9 ± 2.8 and 58.7 ± 6.1% for A. calamus, C. indica, and P. australis, respectively). Meanwhile, complex water networks, shallow water tables, and high DIN content in rainwater lead to nonignorable N contributions from river water, groundwater and rainwater to plants. Groundwater contributed more percentage of N to P. australis (12.8 ± 3.2%) than A. calamus (6.1 ± 1.9%) and C. indica (8.0 ± 1.5%), which is likely attributed to the deeper roots of P. australis. All plants showed similar N preference for NO 3 - during the growing season. External environmental conditions and plant characteristics and adaption to more abundant soil NO 3 - content are possible explanations. Our research could provide important information for vegetation selections during the process of riparian ecological restoration. Reasonable choice of vegetation is essential to plant growth and water quality management, especially in agricultural watersheds where N concentrations are relatively high in agricultural runoff due to the wide uses of N fertilizers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

River damming has raised controversial concerns as it simultaneously contributes to socioeconomic development but may jeopardize aquatic ecology. Since bacterioplankton catalyze vital biogeochemical reactions and play important roles in aquatic ecosystems, more attention has been paid to their responses in dammed rivers. Here, a comparative study was conducted between single-dammed (the Yarlung Tsangpo River) and cascade-dammed (the Lancang River) rivers in Southwest China to investigate whether bacterioplankton respond equally to different river regulations. Our results showed that the decreased bacterioplankton abundance and the increased α-diversity always co-occurred in reservoirs of the Yarlung Tsangpo River and the Lancang River. However, the impact of damming on bacterioplankton abundance and α-diversity were resilient in the Lancang River, which can be attributed to the repeated alterations of environmental heterogeneity in cascade damming reaches. Meanwhile, a generalized additive model (GAM) was applied to identify the important drivers affecting bacterioplankton variation. The abundance was influenced by trophic conditions, such as dissolved silicon, while α-diversity was closely related to the microbial dispersal process, such as elevation and distance-from source. And it is also noted that the bacterioplankton dispersal process was interrupted in cascade damming reaches. In addition, based on their important drivers, variations in abundance and α-diversity were also predicted by GAM. As revealed by the quantitative mutual validation between the two rivers, abundance and α-diversity in the cascade-dammed river can be predicted by their response to single-dammed river, suggesting that the impact of cascade damming on bacterioplankton can be pre-assessed by referring to the single stage damming effect. Therefore, our study provides the first trial of quantitative evidence that bacterioplankton do not respond equally to different river regulations, and the impact of cascade damming on bacterioplankton can be predicted based on single stage damming effect, which can contribute to the protection of aquatic ecology in the cascade hydropower development., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The effect of rising atmospheric CO 2 on freshwater lakes is a subject of considerable debate. However, it is not clear how rising CO 2 concentration affects cyanobacterial bloom development under potential nutrient limitation conditions and if CO 2 should be taken into account in making nutrient reduction strategy. To fill the knowledge gaps, this study investigated the spatiotemporal variability in aquatic CO 2 concentration (pCO 2 ) from 2006 to 2016 in Lake Taihu, where cyanobacterial blooms often occurred from late spring to the early fall. Lake Taihu is an atmospheric CO 2 source in May and November, with only 18% and 11% pCO 2 -undersaturated areas, respectively. During cyanobacterial bloom in August, 81% of the lake areas are pCO 2 -undersaturated, absorbing ~ 0.53 t C/h of atmospheric CO 2 . The results demonstrated that CO 2 transfer across air-water interface was important in supporting cyanobacterial bloom development. Besides, Field investigation showed that the chlorophyll a level is significantly positively correlated with supersaturated pCO 2 (>13.56 µmol/L) in May, but pCO 2 decreases with high chlorophyll a levels in August, suggesting that cyanobacterial growth would be promoted by high pCO 2 over a threshold. These observations suggested that the effect of rising atmospheric CO 2 on freshwater lakes and cyanobacterial blooms should be paid attention to. Further, when the N- and P-levels are >0.3 mg/L and >0.02 mg/L, respectively, high-pCO 2 conditions allow a more rapid growth rate of cyanobacteria via improved nutrient-use efficiency. Moreover, cyanobacteria afford maximum N- or P-use efficiency at lower N- or P-concentrations with high CO 2 concentration. This improvement would result in an earlier bloom-maintenance phase and higher cyanobacterial biomass. In this case, nutrient reduction is more imperative under future high CO 2 conditions., Competing Interests: Declaration of Competing Interest There are no conflicts of interest to declare., (Copyright © 2020. Published by Elsevier Ltd.)

Phytoplankton-derived particulate matter (PPM) is the active component of the solid particles in eutrophic shallow lakes. To date, understanding of the degradation characteristics of PPM and the effect of degradation products on nutrient cycling in water are limited. In this study, field observations and simulation experiments were carried out to elaborate the nutrient transformation during phytoplankton-derived particulate matter deposition in the cyanobacterial blooming area of Lake Taihu. Results showed that the deposition of the PPM was strongly facilitated by the cyanobacterial bloom and the sediment resuspension. The main variation characteristics of phosphorus (P) species in PPM are shown in the increase of Ortho-P and the decrease of biodegradable phosphorus (Poly-P, DNA-P) during the deposition of PPM. The degradation of the PPM resulted in the release of dissolved nitrogen (N) and P to the water body. The conversion of easily degradable particulate N and P in the PPM to ammonium nitrogen (NH 3 -N) and soluble reactive phosphorus were believed to be responsible for this phenomenon. The cycling of nutrients and the cyanobacterial bloom status might therefore be altered because of the deposition and degradation of PPM. More considerations should be given on this process in future works.

Polybrominated diphenyl ethers (PBDEs) are typical persistent organic pollutants (POPs) in the environment. However, little is known about their effects on phosphorus mineralizing bacteria (PMB) in eutrophic lake sediments, despite the critical role of PMB in phosphorus (P) biogeochemical cycling. In this study, we carried out a 60-day microcosm experiment to understand the effects of 2 and 20 mg kg -1 dry weight decabromodiphenyl ether (BDE-209) on the activity, abundance, diversity, and community composition of PMB in the sediment of Taihu Lake, a typical eutrophic lake in China. The results showed that BDE-209 contamination, regardless of the contamination levels, significantly increased the orthophosphate concentration in overlying water and available phosphorus concentration in sediments on day 60. Such increases may be explained by the stimulatory effects of BDE-209 on alkaline phosphatase (ALP) activity and PMB abundance. Moreover, based on Miseq sequencing of the phoD gene encoding ALP, Actinobacteria was the dominant PMB phylum in all treatments, and BDE-209 significantly increased the diversity of PMB and altered their community composition. In particular, the relative abundances of some PMB genera such as Bradyrhizobium were increased significantly after 60 days of the High treatment. A co-occurrence network analysis further revealed that the high level of BDE-209 contamination strengthened the connectivity and interspecific co-operative relationships in the PMB community. These results will help us to understand the effects of POPs on P biogeochemical cycling in eutrophic lakes and the associated microbial mechanisms., (Copyright © 2019 Elsevier B.V. All rights reserved.)

To investigate the relationship between cyanobacteria decomposition and the remobilization of heavy metals in Taihu Lake, the indoor simulation experiments were conducted. The areas of Taihu Lake that undergo harmful algal blooms mostly caused by excessive cyanobacteria have serious problems of heavy metal pollution. The results showed that cyanobacteria decomposition can release heavy metals into the water and change the total contents and chemical speciation of Cr, Ni, Cu, Zn, As, Cd, Hg, and Pb in sediment due to the change of physical and chemical properties in overlying water and sediment. The decomposition rate of cyanobacteria with sediment was clearly faster than that without sediment, and decomposition changed the pH and dissolved oxygen (DO) concentrations in overlying water. The cyanobacteria decomposition reduced the oxidation-reduction potential (ORP), and increased organic matter (OM) and total organic carbon (TOC) in the surface sediment. According to ecological risk assessment, the cyanobacteria decomposition increased the degree of heavy metal pollution and the potential ecological risk in sediment.

Deep-water reservoir sediment is a unique habitat sheltering indispensable microorganisms and facilitating their biogeochemical functions; however, the assembly processes of the microbial community therein remain elusive. This study focuses on the assembly processes in the Three Gorges Reservoir Area (TGRA). A total of 42 sediment samples were collected from the TGRA, both in the mainstream and the tributaries, and in different seasons. Metagenomic analyses of 16S rRNA using Exact Sequence Variants revealed the spatiotemporal distribution patterns of the microbial communities. Linear regressions between dissimilarity of microbial communities, geographic and environmental distance showed that environmental, rather than geographic factors, impacted the microbial community. However, the environmental differences explained little variations (14.14%) in community structure, implying the homogeneity of environmental conditions across the TGRA. From the quantification of ecological processes, homogeneous selection was shown to be a dominating factor (51.34%) in the assembly of the microbial communities. The co-occurrence network showed that keystone species were more important than prevalent abundant species in interspecies interactions. Overall, the assembly of microbial community in the deep-water reservoir sediment is mediated by both deterministic and stochastic processes, and homogeneous selection plays a leading role., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Identifying vertical and horizontal assemblage drivers of bacterial community is important for improving the efficacies of ecological evaluation and remediation for a huge contaminated river (e.g. black-odor urban river). However, little is known about the effect of stochastic vs. deterministic processes on the reliability of the identification processes. Here, a comprehensive analysis was performed to reveal vertical and horizontal assemblage drivers of bacterial community in a heavily polluted urban river (total area of 4.23 km 2 and total length of 9.3 km), considering the relative importance of stochastic and deterministic processes. Heterogeneous bacterial community assemblages were observed in both vertical and horizontal profiles and the differences in the bacterial community between depths were relatively significant at genus level. The higher values for the Simpson dissimilarity index (horizontal β SIM  = 0.59 ± 0.02; vertical β SIM  = 0.48 ± 0.03) compared to the nestedness-resultant dissimilarity index (horizontal β NES  = 0.05 ± 0.02; vertical β NES  = 0.05 ± 0.05) showed that species replacement explained both the vertical and horizontal beta-diversity patterns. Comparison of horizontal and vertical Sørensen dissimilarity indices further indicated that the biodiversity of vertical community deserved more attention due to the shorter geographical distance with similar beta-diversity patterns compared to horizontal assemblages. Various traditional analysis without consideration for phylogenetic turnover revealed that TN, TP, NH 4 + -N, DO, ORP, Conductivity and COD Mn were all the related environmental factors that influenced bacterial community. However, after taking stochastic vs. deterministic processes into account, only NH 4 + -N and ORP were identified as the main driving forces of trends in the vertical and in the horizontal assembly of bacterial community in the polluted urban river, respectively. This study is helpful for improving ecological assessment methodology and remediation strategy for contaminated urban rivers., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The world famous South-to-North Water Transfer Project was built to alleviate serious water shortages in northern China. Considering that lake Hongze is an important freshwater lake in this region, analyzing the influence of water diversion on typical contaminant bioavailability and microbial abundance could aid in achieving a good overall understanding of hydrodynamic variation. Accordingly, in situ high-resolution measurements of diffusive gradients in thin films (DGT) and next-generation high-throughput sequencing were combined in order to survey Lake Hongze and determine the relationship between environmental factors and microbial communities. The DGT method effectively obtained more than the 85% of bioavailable concentrations of the corresponding contaminants; the results showed that labile P, S, Fe, As, and Hg concentrations were higher in areas influenced by water transfer. Moreover, the relative abundance and alpha diversity of the sampling sites distributed in the water transfer area differed significantly from other sites. The pH, conductivity, and labile Mn, As, and P were shown to be the primary environmental factors affecting the abundance and diversity of microbes. With the exception of bioturbation-affected sites controlled by labile Mn and pH, sites distributed in the water diversion area were most affected by As and conductivity, with little spatial discrepancy. Furthermore, site 2, with higher bioturbation abundance, and site 10, with stronger hydrodynamics, had low alpha diversity compared to the other sites. Consequently, the bioavailability of typical contaminants such as P, S, As, Hg, Fe, Mg, Cd, Pb, and Mn, as well as the diversity and abundance of microbial in the sites influenced by the water diversion, were significantly different to the other sites. Thus, the impacts of the South-to-North Water Transfer Project on participant lakes were non-negligible overall in the investigation.

A growing awareness of the wider environmental significance of diffuse sediment pollution in interconnected river-lake systems has generated the need for reliable provenance information. Owing to their insufficient ability to distinguish between multiple sources, common sediment source apportionment methods would rarely be a practical solution. On the basis of the inseparable relationships between sediment and adsorbed microorganisms, community-based microbial source tracking may be a novel method of identifying dominant sediment sources in the era of high-throughput sequencing. Dongting Lake was selected as a study area as it receives considerable sediment import from its inflowing rivers during the flood season. This study was conducted to characterize the bacterial community composition of sediment samples from the inflow-river estuaries and quantify their sediment microbe contributions to the central lake. Metagenomic analysis revealed that the community compositions of source sediment samples were significantly different, allowing specific sources to be identified with the machine learning classification program SourceTracker. A modified analysis using SourceTracker found that the major contributors to three major lake districts were the Songzi, Zishui, and Xinqiang Rivers. The impacts of hydrodynamic conditions on source apportionment were further verified and suggested the practicability of this method to offer a systematic and comprehensive understanding of sediment sources, pathways, and transport dynamics. Finally, a novel framework for sediment source-tracking was established to develop effective sediment management and control strategies in river-lake systems.

Black-odor phenomenon in highly urbanized river is increasingly recognized as a global ecological risk. Biotransformation associated with sulfur cycle is a major contributor to the blank-odor phenomenon. The vertical geochemical gradient in black-odor rivers is likely to alter microbial community assemblages and functions in the sulfur cycle. However, the interactions between geochemical gradients and microbial communities, as well as the changes in the process of sulfur biotransformation under different environmental conditions remain largely unknown. The vertical community assembly patterns and the impacts of microbial communities and genes on the biotransformation in the sulfur cycle were revealed in our study for the first time in a typical urban black-odor river, Jinchuan River, in China. Vertical beta-diversity patterns of microbial communities mainly resulted from species replacement that was largely driven by spatial turnover (β SIM  = 0.43) but also influenced by nestedness (β NES  = 0.08). MiSeq sequencing and GeoChip 5.0 microarray chip approaches were applied and identify 41 bacterial genera, 8 archaeal genera, and 26 genes involved in the sulfur cycle in Jinchuan River. The vertical beta-diversity patterns of microbial profile mainly resulted from species replacement. Those sulfur-related bacterial and archaeal genera, accounting for 23.15% and 42.65% of the total bacteria and archaea respectively in analysed samples, were mainly responsible for sulfur reduction. According to redundancy analysis, oxidation-reduction potential (r = -0.8662, P < 0.05), S 2- concentration (r = -0.6288, P < 0.05), and total nitrogen concentration (r = -0.6782, P < 0.05) were identified as factors that significantly affect sulfur-related microbial communities. The highest reaction potential was detected in the dissimilated sulfate reduction action and experienced an increase with depth increasing in the river system. The results indicated that the sulfur biotransformation in a deeper layer in river sediment could make more contribution to the black-odor phenomenon in urban rivers., (Copyright © 2019. Published by Elsevier Ltd.)

In order to accurately monitor the changes in a freshwater ecosystem in response to anthropogenic stressors, microbe-environment correlations and microbe-microbe interactions were combined to determine crucial indicator taxa in contaminated sediments. The diversity, composition, and co-occurrence pattern of bacterial communities in 23 sediment samples collected from Lake Taihu were explored using 16S rRNA amplicon sequencing analysis. Fisher's exact test showed that the cluster analyses of samples could show a direct correlation between the relative abundance of bacterial communities and the physicochemical properties of the sediment (P < 0.0001), suggesting that bacterial communities can be used to monitor contamination gradients in freshwater sediments. According to the microbe-environment correlation, 24 orders and 60 families were initially identified via indicator species analysis as indicator taxa of different pollution levels. The co-occurrence network further showed that topological features of bacterial communities were clearly different at different pollution levels, although the diversity and composition of bacterial communities displayed similarities between minimally and moderately polluted sites. Indicator taxa were then screened for keystone species, which co-occurrence relationships showed the high degree and low betweenness centrality values (i.e. degree >5, betweenness centrality <1000) of the network. Nine orders and 13 families were finally extracted as crucial indicator taxa of the different pollution levels in eutrophic Lake Taihu. Obtaining crucial indicator taxa from environmental sequences allows to trace increasing levels of pollution in aquatic ecosystems and provides a novel mean to monitor watersheds sensitive to anthropic influences., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Microbial biodegradation plays a key role in determining the fate of estrogens and can be affected by the background nutrients in natural environments. However, information on how microbial community and nutrient conditions influence estrogen biodegradation is very limited. In this study, 13 C-17β-estradiol ( 13 C-E2) was supplied to sediments from the Central Area (CA), Gonghu (GH), Meiliang (ML), and Zhushan (ZS) Bays of Taihu Lake to investigate shifts in bacterial community structure associated with 13 C-E2 mineralization over a 30-day incubation period, and the relationships between the background nutrients and cumulative 13 C-E2 mineralization rates. The cumulative 13 C-E2 mineralization rate for ZS Bay was 87.40% on Day 30, which was significantly greater (P < 0.05) than the rates for ML Bay (67.74%), GH Bay (62.79%), and the CA (52.60%). A correlation analysis suggested that the cumulative 13 C-E2 mineralization rate was significantly and positively related to the concentrations of total organic carbon (P < 0.01), nitrate-nitrogen (P < 0.05), ammonia-nitrogen (P < 0.001), and dissolved phosphorus (P < 0.001) in the sediments. Although the highest relative abundances of Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes (contain most estrogen-degrading bacteria) were not initially in the ZS Bay sediment, the addition of 13 C-E2 stimulated their growth in all sediments, with the greatest increases observed for ZS Bay. At the genus level, the cumulative increases of seven genera (Nitrosomonas, Bacillus, Pseudomonas, Sphingomonas, Novosphingobium, Alcaligenes and Mycobacterium) considered to be associated with E2 degradation were also highest for ZS Bay (80.2 times), followed by ML Bay (39.8 times), GH Bay (28.1 times), and CA (19.0 times). Besides the higher nutrient concentrations, the responses of bacteria to 13 C-E2 addition in ZS Bay could also explain it having the highest cumulative 13 C-E2 mineralization rate. These results indicate both the background nutrients and bacterial community evolution in the sediments determined the 13 C-E2 mineralization rates., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Biofilms are often observed at the solid-water interface. The leaves of many floating macrophytes have characteristics of both terrestrial plants and submerged macrophytes, because, in general, their upper and lower surfaces are exposed to air and water, respectively. However, little is known about the biofilms attached to floating plants. We investigated biofilms attached to the leaves, stems and roots of the floating plants Nymphoides peltata (in summer and winter) and Trapa natans (in summer) in the Gonghu Bay of Lake Taihu. Bacteria and algae were major components of the biofilm on the leaves of the two species of plants. In addition, 454 pyrosequencing analysis of bacterial 16S rRNA genes revealed that Proteobacteria was the dominant phylum, followed by Bacteroidetes, Firmicutes, Chloroflexi, Acidobacteria, and Verrucomicrobia. Cluster analysis showed that bacterial communities from the same plant source were clustered into the same group. A total of 677 genera were detected, and 47 genera were shared by all samples. Nitrifiers, including Nitrosomonas, Nitrosococcus and Nitrospira were detected in this study. Seven denitrifying genes (napA, napG, nirS, nirK, cnorB, qnorB and nosZ) were used to detect the abundance of denitrifiers. Genes nirK, nirS cnorB and nosZ were the four most abundant genes in all samples. Our results demonstrated that cultivation of floating plants in water column could enlarge the area for biofilm growth, and biofilms might play an important role in denitrification in eutrophic water., Competing Interests: The authors have declared that no competing interests exist.

Rivers make vital contributions to the transport of water, sediment and nutrients from terrestrial to marine ecosystems. However, many large rivers worldwide are suffering from dam regulation. Increasing attention has been paid to bacterioplankton communities since they are highly responsive to river alterations and may influence biogeochemical processes. Here, a comprehensive study was conducted in the highly regulated Lancang-Mekong River Basin to address the question of how bacterioplankton communities respond to cascade damming. The results showed that dam constructions increased nutrient concentrations and threatened water quality in cascade reservoirs. Bacterioplankton cell abundance was reduced by damming, and α-diversity was inhibited in cascade reservoirs. Fortunately, however, river ecosystems were resilient after the remarkable disturbance caused by damming. Moreover, bacterioplankton community composition was significantly altered by cascade dams, including a shift in the dominant phylum from r-strategists to k-strategists. Meanwhile, according to GeoChip analysis, the functional composition of bacterioplankton was less affected than taxonomic composition. In addition, geographic and environmental features both followed a distance-decay relationship with community and functional composition, but the local environment condition was the dominant driver in the Lancang River. Therefore, the impoundments of cascade dams had significant impacts on bacterioplankton communities and more attention should be paid to the potential ecological consequences of river regulation., (© 2018 John Wiley & Sons Ltd.)

Spatial and seasonal variations of particulate phosphorus (PP) in a large shallow, eutrophic Lake Taihu with different ecotypes (including a phytoplankton-dominated zone, lake center zone, estuary zone and macrophyte-dominated zone) were investigated. The results showed that particulate organic phosphorus (POP) was the dominant form of PP (>88.0%). The concentration of POP showed higher levels in the bloom-sensitive northwestern zone (phytoplankton-dominated zone and estuary zone) during warm seasons, phytoplankton blooms and input of exogenous particulate matter were the main sources of POP in the lake water. Based on 31 P nuclear magnetic resonance ( 31 P NMR) analysis, orthophosphate (Ortho-P) was the dominant molecular species of PP and positively correlated with soluble reactive phosphorus (SRP) ( p < 0.01). This suggested that the release of Ortho-P from suspended particulate matter (SPM) was the main source of SRP in the lake water. Pyrophosphate (Pyro-P), which is regarded as a highly labile species of P compounds, represented a large fraction of PP, and its significant positive correlations with chlorophyll a (Chl a ), indicated that the concentration of Pyro-P could be used as an important indicator for the degree of eutrophication of Lake Taihu. These results proved that PP in lake water was a significant factor supporting lake eutrophication and must be controlled.

With the rapid development of CeO 2 nanoparticles (NPs), the released CeO 2 NPs entering into wastewater treatment plants might bring the challenges for sludge pumping and mixing. In this study, we firstly elucidated the rheological behavior of 4.0 wt% sludge at various concentrations of CeO 2 NPs. With the increase of CeO 2 NPs to 5 mg/L, the shear stress at any given shear rate was reduced and the limiting viscosity was also decreased, indicating the sludge became more flowability. The dynamic sweep tests further demonstrated the decreased elastic behavior and weakened internal structure in response to low concentrations of CeO 2 NPs (≤ 5 mg/L). However, 20 mg/L CeO 2 NPs had negative effects on the rheological evolution of sludge, namely, better solid-like property and higher elastic structure. These results were mainly attributed to the combination of the decreased β-D-glucopyranose polysaccharides which support the rigid structure of sludge and the dramatically increased protein content (especially in 20 mg/L CeO 2 NPs). These results can potentially provide novel information for the efficient design of sludge treatment when coped with CeO 2 NPs. Graphical abstract ᅟ.