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Rivers and streams contribute significant quantities of methane (CH4) to the atmosphere. However, there is a lack of CH4 flux and ebullitive (bubble) emission data from urban rivers, which might lead to large underestimations of global aquatic CH4 emissions. Here, we conducted high-frequency surveys using the boundary layer model (BLM) supplemented with floating chambers (FCs) and bubble traps to investigate the seasonal and diurnal variability in CH4 emissions in a eutrophic urban river and to evaluate whether the contribution of bubbles is important. We found that ebullition contributed nearly 99% of CH4 emissions and varied on hourly to seasonal time scales, ranging from 0.83 to 230 mmol m-2 d-1, although diffusive emissions and CH4 concentrations in bubbles did not exhibit temporal variability. Ebullitive CH4 emissions presented high temperature sensitivity (r = 0.6 and p < 0.01) in this urban river, and eutrophication might have triggered this high temperature sensitivity. The ebullitive CH4 flux is more likely to be underestimated at low temperatures because capturing the bubble flux is more difficult, given the low frequency of ebullition events. This study suggests that future ebullition measurements on longer time scales are needed to accurately quantify the CH4 budgets of eutrophic urban rivers.

Ordered macroporous materials with rapid mass transport and enhanced active site accessibility are essential for achieving improved catalytic activity. In this study, boron phosphate crystals with a three-dimensionally interconnected ordered macroporous structure and a robust framework were fabricated and used as stable and selective catalysts in the oxidative dehydrogenation (ODH) of propane. Due to the improved mass diffusion and higher number of exposed active sites in the ordered macroporous structure, the catalyst exhibited a remarkable olefin productivity of ~16 golefin gcat−1 h−1, which is up to 2–100 times higher than that of ODH catalysts reported to date. The selectivity for olefins was 91.5% (propene: 82.5%, ethene: 9.0%) at 515 °C, with a propane conversion of 14.3%. At the same time, the selectivity for the unwanted deep-oxidized CO2 product remained less than 1.0%. The tri-coordinated surface boron species were identified as the active catalytic sites for the ODH of propane. This study provides a route for preparing a new type of metal-free catalyst with stable structure against oxidation and remarkable catalytic activity, which may represent a potential candidate to promote the industrialization of the ODH process.

Community detection is one of the most popular researches in a variety of complex systems, ranging from biology to sociology. In recent years, there’s an increasing focus on the rapid development of more complicated networks, namely multilayer networks. Communities in a single-layer network are groups of nodes that are more strongly connected among themselves than the others, while in multilayer networks, a group of well-connected nodes are shared in multiple layers. Most traditional algorithms can rarely perform well on a multilayer network without modifications. Thus, in this paper, we offer overall comparisons of existing works and analyze several representative algorithms, providing a comprehensive understanding of community detection methods in multilayer networks. The comparison results indicate that the promoting of algorithm efficiency and the extending for general multilayer networks are also expected in the forthcoming studies.

Microemulsion flooding is a effective enhanced oil recovery for low permeability. In this paper, combined the advantage of sulphobetaine surfactant and gemini surfactant, a kind of gemini sulphobetaine surfactant (DPSB) was used to prepared microemulsion. The oil–water interfacial tension and adsorption for different concentration surfactant was measured to evaluate the DPSB property. The stability of microemulsion, the microemulsion volume percentage, solubilisation parameter and relative phase volume, microemulsion viscosity was also measured. The performance of this surfactant was further optimized by adding the additives. The relative permeability was determined to analyze the fluid flow characteristics, and the recovery efficiency was studied through natural core and visual core displacement experiment. The results show that the oil–water interfacial tension is 9.1 × 10−4 mN/m when DPSB concentration is 0.5%, and it can still maintain low interfacial tension after adsorption. The interfacial tension can be further decreased by adding n-butyl alcoholy. When the DPSB concentration is 1.5% and n-butyl alcohol concentration is 1.5%, the microemulsion volume percentage is 31%, and the viscosity is 4.37 mPa∙s. It can reduce the flow velocity of displacing fluid, and expand sweep volume. Compared with water flooding, the residual oil saturation reduces by about 30% in microemulsion flooding. The recovery efficiency is increased by about 4% compared with the low concentration of surfactant flooding.

Pore structure characteristics of ultra-low permeability reservoirs are studied in this paper. The impact of pore structure characteristics on permeability and reservoir development effect is analyzed by conventional and constant-rate mercury penetration experiments. The results show that the frequency curve of pore radius distribution of ultra-low permeability reservoirs has little change with permeability. The average pore radius in ultra-low permeability reservoirs with different permeability levels had little difference, and its distribution ranges from 98.5 to 110.1 μm. With decrease of permeability, the frequency distribution curves of throat radius and pore-throat ratio change significantly. The peak value of throat radius curve moves to the left and increases significantly, and the average throat-radius distribution decreases from 2.33 to 0.91 μm. However, the impact of pore-throat ratio on permeability is contrary to that of throat radius. Both throat radius and pore-throat ratio has strong correlation with permeability, and they are in exponential relationship. With the in-depth study, it is found that seepage capacity of reservoirs is restricted mainly by throat radius and pore-throat ratio. When throat radius decreases to less than 1 μm and pore-throat ratio increases more than 130, permeability decreases sharply and obviously. When permeability is less than 2 × 10−3μm2, the proportion of fine throats and medium throats under the condition of effective water injection is significantly lower, and the production of single well and the recovery efficiency by water flooding in ultra-low permeability reservoirs are low. The study explains effectively the fundamental reason for the poor efficiency of production and recovery of ultra-low permeability reservoirs from the mechanism.

The purposes of this study were to analyse the spatiotemporal variations in greenhouse gas diffusive fluxes at the sediment–water interface of sewage-draining rivers and natural rivers, and investigate the factors responsible for the changes in greenhouse gas diffusive fluxes. Greenhouse gas diffusive fluxes at the sediment–water interface of rivers in Tianjin city (Haihe watershed) were investigated during July and October 2014, and January and April 2015 by laboratory incubation experiments. The influence of environmental variables on greenhouse gas diffusive fluxes was evaluated by Spearman’s correlation analysis and a multiple stepwise regression analysis. Sewage-draining rivers were more seriously polluted by human sewage discharge than natural rivers. The greenhouse gas diffusive fluxes at the sediment–water interface exhibited obvious spatiotemporal variations. The mean absolute value of the CO2 diffusive fluxes was seasonally variable with spring>winter>fall>summer, while the mean absolute values of the CH4 and N2O diffusive fluxes were both higher in summer and winter, and lower in fall and spring. The annual mean values of the CO2, CH4 and N2O diffusive fluxes at the sewage-draining river sediment–water interface were − 123.26 ± 233.78 μmol m−2 h−1, 1.88 ± 6.89 μmol m−2 h−1 and 1505.03 ± 2388.46 nmol m−2 h−1, respectively, which were 1.22, 4.37 and 134.50 times those at the natural river sediment–water interface, respectively. The spatial variation of the N2O diffusive fluxes in the sewage-draining rivers and the natural rivers was the most significant. As a general rule, the more serious the river pollution was, the greater the diffusive fluxes of the greenhouse gases were. On average for the whole year, the river sediment was the sink of CO2 and the source of CH4 and N2O. There were positive correlations among the CO2, CH4 and N2O diffusive fluxes. The main influencing factor for CO2 and N2O diffusive fluxes was the water temperature of the overlying water; however, the key factors for CH4 diffusive fluxes were the Eh of the sediment and the NH4+-N of the overlying water. River sediment can be either a sink or a source of greenhouse gases, which varies in different levels of pollution and different seasons. Human sewage discharge has greatly affected the carbon and nitrogen cycling of urban rivers.

This work concerned the oxo exchange of americyl(VI) ([AmO2]2+) in alkaline solution by means of B3LYP calculations. Four possible reaction pathways were investigated and compared, which covered the direct intramolecular proton transfer pathway (Path 1 and 2), the pathway via a T-shape [AmO3](aq) intermediate (Path 3), and the binuclear pathway (Path 4). The Path 3 was predicted as the most probable pathway in view of the energetics, the activation energy (∆G≠) to which was calculated to be 55.7 kJ/mol. The evolution of the Mayer bond order of key bonds were analyzed to assist the understanding of the mechanism.

The functionalization of CO2 mediated by a series of U(IV) mixed-sandwich compounds, (COTTIPS2)Cp*UR (R = −CH3, −CH2Ph, −CH2TMS, −CH(TMS)2, −NHPh, −OPh, −SPh, −SePh; COTTIPS2 = C8H6(SiiPr3-1,4)2; C...

While nitrogen (N2) fixation is an important process in nitrogen (N) biogeochemical cycling, supplying a significant portion of the N in natural ecosystems, few quantitative constraints exist concerning its contribution to the N enrichment and export from river ecosystems. This study estimates the N2 fixation rates of urban rivers in the Yangtze Estuary area using acetylene reduction. The results demonstrate that the prominent spatiotemporal variability of river N2 fixation rates is driven by various environmental factors. River N2 fixation rates are significantly higher in the summer (90.57 ± 14.60 ngN·L−1·h−1) than in the winter (57.98 ± 15.73 ngN·L−1·h−1). Spatially, rivers draining urban and suburban areas have higher N2 fixation rates than those draining rural areas. The N2 fixation rates are positively correlated with the N2 fixing cyanobacteria density, water temperature, light, and the water phosphorus (P) concentration, but they are negatively correlated with the dissolved N concentration (NH4+-N and NO3−-N). The N2 fixation rates annually range from 53.20 to 89.24 ngN·L−1·h−1 for all of the sampling rivers, which is equivalent to a depth integrated (0–0.6 m) N input of 0.163–0.274 gN·m−2·a−1. The determined annual N input via N2 fixation is generally higher than that of marine systems, but it is lower than that of eutrophic lakes. This study provides robust evidence that N2 fixation can supply a substantial portion of the N input to human-impacted river ecosystems, which has not been sufficiently accounted for when determining the N mass balance of riverine ecosystems. A high N2 fixation rate may increase the ratio of N to P input to river systems, and therefore render P the limiting factor in aquatic eutrophication.

Sidestream EBPR (S2EBPR) is an emerging alternative process to address common challenges in EBPR related to weak wastewater influent and may improve EBPR process stability. A systematic evaluation and comparison of the process performance and microbial community structure was conducted between conventional and S2EBPR facilities in North America. The statistical analysis suggested higher performance stability in S2EBPR than conventional EBPR, although possible bias associated with other plant-specific factors might have affected the comparison. Variations in stoichiometric values related to EBPR activity and discrepancies between the observed values and current model predictions suggested a varying degree of metabolic versatility of PAOs in S2EBPR systems that warrant further investigation. Microbial community analysis using various techniques suggested comparable known candidate PAO relative abundances in S2EBPR and conventional EBPR systems, whereas the relative abundance of known candidate GAOs seemed to be consistently lower in S2EBPR facilities than conventional EBPR facilities. 16S rRNA gene sequencing analysis revealed differences in the community phylogenetic fingerprints between S2EBPR and conventional facilities and indicated statistically higher microbial diversity index values in S2EBPR facilities than those in conventional EBPRs. PRACTITIONER POINTS: Sidestream EBPR (S2EBPR) can be implemented with varying and flexible configurations, and they offer advantages over conventional configurations for addressing the common challenges in EBPR related to weak wastewater influent and may improve EBPR process stability. Survey of S2EBPR plants in North America suggested statistically more stable phosphorus removal performance in S2EBPR plants than conventional EBPRs, although possible bias might affect the comparison due to other plant-specific factors. The EBPR kinetics and stoichiometry of the S2EBPR facilities seemed to vary and are associated with metabolic versatility of PAOs in S2EBPR systems that warrant further investigation. The abundance of known candidate PAOs in S2EBPR plants was similar to those in conventional EBPRs, and the abundance of known candidate GAOs was generally lower in S2EBPR than conventional EBPR facilities. Further finer-resolution analysis of PAOs and GAOs, as well as identification of other unknown PAOs and GAOs, is needed. Microbial diversity is higher in S2EBPR facilities compared with conventional ones, implying that S2EBPR microbial communities could show better resilience to perturbations due to potential functional redundancy.

Oxidative dehydrogenation (ODH) of light alkanes catalyzed by metal oxides is considered to be a thermodynamically favorable process for olefin production. The strong interaction between the unoccu...

Molecular dynamics (MD) simulations were performed to investigate the influence of curvature and backbone rigidity of an oxygenated surface, here graphene oxide (GO), on its adsorption of uranyl in collaboration with humic acid (HA). The planar curvature of GO was found to be beneficial in impeding the folding of HA. This, together with its rigidity that helps stabilize the extended conformation of HA, offered rich binding sites to interact with uranyl with only marginal loss of binding strength. According to our simulations, the interaction between uranyl and GO was mainly driven by electrostatic interactions. The presence of HA not only provided multiple sites to compete/cooperate with GO for adsorption of free uranyl but also interacted with GO acting as a "bridge" to connect uranyl and GO. The potential of mean force (PMF) profiles implied that HA significantly enhanced the interaction strength between uranyl and GO and stabilized the uranyl-GO complex. Meanwhile, GO could reduce the diffusion coefficients of uranyl and HA and retard their migrations in aqueous solution. This work provides theoretical hints on the GO-based remediation strategies for the sites contaminated by uranium or other heavy metal ions and oxygenated organic pollutants.

In this paper, the influence of humic acid (HA) and fulvic acid (FA) on biomineralization behaviour was evaluated. The results showed HA and FA did not obviously inhabit or promote the precipitation of U-phosphate minerals. The data from molecular dynamic simulation indicated that the free energy for the dissociation of uranyl the PO43− -uranyl was 202.49 kJ/mol, which was much larger than that form HA-uranyl (88.3 kJ/mol). These simulated results revealed the less competitiveness of HA and FA with PO43− for uranyl and explained why HA and FA had less impacted on the formation of U-phosphate minerals. However, the influence of HA/FA on the morphology was obvious, the microstructure of the bio-minerals changed from small particles to lamellar stacking structure with the addition of HA or FA. The findings of this study are helpful for us to gain a better understanding natural U-phosphate biomineralization behaviour.

Polycyclic aromatic hydrocarbons (PAHs) are key organic pollutants in the environment that pose threats to the ecosystem and human health. The degradation of high molecular weight (HMW) PAHs by enriched bacterial consortia has been previously studied, while the involved metabolisms and microbial communities are still unclear and warrant further investigations. In this study, five bacterial consortia capable of utilizing different PAHs (naphthalene, anthracene, and pyrene) as the sole carbon and energy sources were enriched from PAH-contaminated soil samples. Among the five consortia, consortium TC exhibited the highest pyrene degradation efficiency (91%) after 19 d of incubation. The degradation efficiency was further enhanced up to 99% by supplementing yeast extract. Besides, consortium TC showed tolerances to high concentrations of pyrene (up to 1000 mg/L) and different heavy metal stresses (including Zn2+, Cd2+, and Pb2+). The dominant genus in consortium TC, GS, and PL showing relatively higher degradation efficiency for anthracene and pyrene was Pseudomonas, whereas consortium PG and GD were predominated by genus Achromobacter and class Enterobacteriaceae, respectively. Consortium TC, as a highly efficient HMW PAH-degrading consortium, could be applied for synergistic biodegradation of HMW PAHs and in situ bioremediation of the sites contaminated with both PAHs and heavy metals.

Non-autoregressive Transformer is a promising text generation model. However, current non-autoregressive models still fall behind their autoregressive counterparts in translation quality. We attribute this accuracy gap to the lack of dependency modeling among decoder inputs. In this paper, we propose CNAT, which learns implicitly categorical codes as latent variables into the non-autoregressive decoding. The interaction among these categorical codes remedies the missing dependencies and improves the model capacity. Experiment results show that our model achieves comparable or better performance in machine translation tasks, compared with several strong baselines., 11 pages, 3 figures, 7 tables. Accepted by NAACL-2021

Bisphenol A diglycidyl ether (BADGE)-based epoxy resin is one of the most widely used epoxy resins with an annual production amount of several million tons. Compared with all other legacy or emerging organic compounds, BADGE is special due to its toxicity and high reactivity in the environment. More and more studies are available on its analytical methods, occurrence, transformation and toxicity. Here, we provided a comprehensive review of the current BADGE-related studies, with focus on its production, application, available analytical methods, occurrences in the environment and human specimen, abiotic and biotic transformation, as well as the in vitro and in vivo toxicities. The available data show that BADGE and its derivatives are ubiquitous environmental chemicals and often well detected in human specimens. For their analysis, a water-free sample pretreatment should be considered to avoid hydrolysis. Additionally, their complex reactions with endogenous metabolites are areas of great interest. To date, the monitoring and further understanding of their transport and fate in the environment are still quite lacking, comparing with its analogues bisphenol A (BPA) and bisphenol S (BPS). In terms of toxicity, the summary of its current studies and Environmental Protection Agency (EPA) ToxCast toxicity database suggests BADGE might be an endocrine disruptor, though more detailed evidence is still needed to confirm this hypothesis in in vivo animal models. Future study of BADGE should focus on its metabolic transformation, reaction with protein and validation of its role as an endocrine disruptor. We believe that the elucidation of BADGEs can greatly enhance our understandings of those reactive compounds in the environment and human. National Environmental Agency (NEA) Published version This work was funded by Singapore National Environmental Agency (Grant No. 04SBS000714N025), the National Natural Science Foundation of China (Grant No. 52070156 and 31600421) and Visiting Researcher Fund Program of the State Key Laboratory of Eco-hydraulics in Northwest Arid Region, Xi’an University of Technology (Grant No. 2019KFKT-10).

Streams and rivers, especially in urban areas, are substantial sinks of bioavailable nitrogen owing to their hydrological connections with terrestrial systems and the intensity of inputs mediated by human activities. Denitrification can account for nitrogen removal in rivers, but its importance in urban rivers has been scarcely studied. This study chose 8 representative rivers in Shanghai, under different level of urbanization, and measured denitrification rates of sediments across a year. The results showed significant differences in temporal, spatial and vertical distributions (p

The de novo drug design plays an important role in the drug discovery. Recently deep learning based method has been popular as a promising approach for the design of novel drugs with desirable properties. However, conventional target-specific generative models mainly concentrate on the known inhibitors and thus produce similar molecules. And these derivatives of known inhibitors are probably negative against the same target. Considering the cost of chemical synthesis and experimental validation, the low false positive rate of generative molecules is very important. In this paper, we propose an efficient pipeline to generate novel SARS-CoV-2 3C-like protease inhibitors. Based on the GPT2 generator and the well performing multi-task predictor which achieves high precision on the highly imbalanced 3CL in vitro screening dataset (650 positive of 297,467 molecules), we acquired a number of novel 3CL-target compounds and analyzed their molecular properties. Moreover, we applied randomized SMILES for data augmentation of positive molecules to create larger chemical space for the generator. Finally, the selected positive compounds with desirable properties are exhibited, as well as their nearest neighbors of 3CL inhibitors which have already been verified in vitro.

The identification of protein-drug interaction plays an important role in the early stage of drug discovery. Recently, deep learning has been introduced into this area and gained excellent results, which mainly benefits from effective representations of protein and drug. However, the sparseness of raw input data builds the fundamental barrier for protein and drug representation learning. In this paper, we propose an end-to-end model representing better the characteristics of protein and drug to estimate binding affinity between protein and drug. By incorporating protein sequence, protein contact map and drug SMILES, our model achieves better results on PDBbind dataset as compared to 3D structure based classical deep model Pafnucy. Moreover, we explore the effects of different parts of our model with ablation study and find that by combining all the modules of our model we can get the best predictive results.

Identifying vital nodes in complex networks is of paramount importance in understanding and controlling the spreading dynamics. Currently, this study is facing great challenges in dealing with big data in many real-life applications. With the deepening of the research, scholars began to realize that the analysis on traditional graph model is insufficient because many nodes in a multilayer network share connections among different layers. To address this problem both efficiently and effectively, a novel algorithm for identifying vital nodes in both monolayer and multilayer networks is proposed in this paper. Firstly, a node influence measure is employed to determine the initial leader of a local community. Subsequently, the community structures are revealed via the Maximum Influential Neighbors Expansion (MINE) strategy. Afterward, the communities are regarded as super-nodes for an iteratively folding process till convergence, in order to identify influencers hierarchically. Numerical experiments on 32 real-world datasets are conducted to verify the performance of the proposed algorithm, which shows superiority to the competitors. Furthermore, we apply the proposed algorithm in the graph of adjacencies derived from the maps of China and USA. The comparison and analysis of the identified provinces (or states) suggest that the proposed algorithm is feasible and reasonable on real-life applications.

The influence maximization problem (IMP) in complex networks is to address finding a set of key nodes that play vital roles in the information diffusion process, and when these nodes are employed as &rdquo, seed nodes&rdquo, the diffusion effect is maximized. First, this paper presents a refined network centrality measure, a refined shell (RS) index for node ranking, and then proposes an algorithm for identifying key node sets, namely the reject neighbors algorithm (RNA), which consists of two main sequential parts, i.e., node ranking and node selection. The RNA refuses to select multiple-order neighbors of the seed nodes, scatters the selected nodes from each other, and results in the maximum influence of the identified node set on the whole network. Experimental results on real-world network datasets show that the key node set identified by the RNA exhibits significant propagation capability.

The nine-membered ring-bearing bicyclo[5.2.2]tetrahydrooxonines frameworks have enantioselectively been constructed via a tandem [3 + 2] cycloaddition/Cope rearrangement reaction of vinylethylene carbonates (VECs) with coumalates or pyrones. Under mild conditions, palladium-catalyzed asymmetric tandem reaction of various substituted VECs and coumalates or pyrones proceeds smoothly to produce the corresponding medium-sized heterocyclic compounds in high yields with very high enantioselectivities. Moreover, the reaction on the gram scale and further diverse transformations of the products were workable. The reaction mechanism was investigated through control experiments and DFT calculations, which show the reaction proceeds via a tandem [3 + 2] cycloaddition/Cope rearrangement pathway rather than via a [5 + 4] cycloaddition pathway.

A new class of tantalum-based peroxocarbonate ionic liquid ([P4,4,4,4]3[Ta(η2-O2)3(CO4)]) has been generated through the reaction of pressurized CO2 with [P4,4,4,4]3[Ta(O)3(η2-O2)] in the presence of H2O2 during the reaction process. The newly formed species has been verified by NMR, FT-IR, HRMS and density functional theory (DFT) calculations. The CO2-induced monomeric peroxocarbonate anion-based ionic liquid is more advantageous than the monomeric peroxotantalate analogue for the epoxidation of olefins under very mild conditions. Interestingly, the transformation between peroxotantalate and peroxocarbonate species is completely reversible, and CO2 can actually act as a trigger agent for epoxidation reaction. The further mechanism studies by DFT calculation reveal that peroxo η2-O2 (site a) affords higher reactivity towards the CC bond than that of peroxocarbonate–CO4 (site b). These quantitative illustrations of the relationship between structural properties and kinetic consequences enable rational design for an efficient and environmental IL catalyst for the epoxidation of olefins.

Enterobactin (Ent) is a typical siderophore with strong iron affinity. Its dynamics in its intact form and holo state remains to be studied to understand its role in the in vivo behavior of metal ions and to facilitate its potential application in drug design and environmental remediation. Here, we report molecular dynamics simulations of both Ent enantiomers and their complexes with key actinides (Am3+, Cm3+, Th4+, U4+, Np4+ and Pu4+) to study the folding equilibria of Ent enantiomers and their binding affinity with actinides. For comparison, the ferric cation was also considered. In their neutral state, both enantiomers may exist in their folded and extended states in the aqueous phase with the former more stable owing to the favorable cation-π, π-π, and H-bond interactions. A helicity preference was observed in the folded states of Ent enantiomers, which was solidified when binding with Fe3+ while disrupted when binding with actinides. Upon binding with metal ions, the dynamics of Ent enantiomers exhibited dependence on the metal ions, and appeared to be more flexible in An3+/4+-Ent complexes than in Fe3+-Ent complexes. The conformational analysis and the energy decomposition of M3+/4+-Ent complexes indicated that their distinct conformational variations and dynamic fluxionality are enthalpy driven behaviors and dependent on the nature of the loaded metal ions. The Fe3+-Ent complexes had a more compact conformation, while the relatively loosely bound An3+/4+-Ent complexes allowed solvent water molecules to access the first coordination shell of An3+/4+ and weaken the interaction between An3+/4+ and Ent. This work is expected to enrich our knowledge of the folding equilibria of Ent enantiomers and their An3+/4+-Ent complexes, and contribute to communities that concern the in vivo and in vitro behaviors of Ent enantiomers and actinides.

In this manuscript, phosphine-dependent [3 + 3] and [4 + 3] annulation reactions of allenoate with aziridines were disclosed. The alkyldiphenylphosphine-promoted [4 + 3] annulation of allenoate with aziridines has been achieved under mild conditions, providing biologically interesting functionalized tetrahydroazepines in moderate to excellent yield with moderate to excellent regioselectivity and diastereoselectivity.

Social network analysis is a multidisciplinary research covering informatics, mathematics, sociology, management, psychology, etc. In the last decade, the development of online social media has provided individuals with a fascinating platform of sharing knowledge and interests. The emergence of various social networks has greatly enriched our daily life, and simultaneously, it brings a challenging task to identify influencers among multiple social networks. The key problem lies in the various interactions among individuals and huge data scale. Aiming at solving the problem, this paper employs a general multilayer network model to represent the multiple social networks, and then proposes the node influence indicator merely based on the local neighboring information. Extensive experiments on 21 real-world datasets are conducted to verify the performance of the proposed method, which shows superiority to the competitors. It is of remarkable significance in revealing the evolutions in social networks and we hope this work will shed light for more and more forthcoming researchers to further explore the uncharted part of this promising field.

A DFT mechanistic study is undertaken on the functionalization of CO2 to form C-C, C-N, C-S, and C-O bonds promoted by trivalent uranium complexes (Tp*)(2)UR [Tp*=hydrotris(3,5-dimethylpyrazolyl)-borate ligand, R= -C equivalent to CPh (Cpda-CC), -C equivalent to CSiMe3 (Cpda-CSi), -NHPh (Cpda-N), -SPh (Cpda-S), and -OPh (Cpda-O)]. These model systems are similar in view of their two-step reaction mechanisms, that is, the insertion of CO2 into the U-E (E=C, N, O, S) bond to form a [U-kappa(1)-O2C] intermediate, followed by the reorientation of the carboxylate group to coordinate with the U atom in the kappa(2) manner (Cpdb-X, X=CC, CSi, N, S, O). However, the free energy barriers to the rate-determining steps are substantially different, increasing in the order Cpda-S

Coastal wetlands can serve as a considerable sink for carbon (C) gases. However, the capacity for wetlands to serve as more permanent C and N sinks over the long term is less clear given the time dependence of sediment deposition, organic matter decomposition, and anthropogenic land use change. In this study, we compare the short-term (decadal scale) and long-term (millennial scale) C and N accumulation rates estimated using 137Cs and radiocarbon dating of vibracores collected from a freshwater coastal wetland in the Louisiana Mississippi River deltaic plain (Atchafalaya River delta). The mean short-term (60 yrs) sediment accumulation rate was 1.4 cm/yr while the mean rate of long-term (100–1000 yrs) sediment accumulation was an order of magnitude lower at 0.12 cm/yr. Annual rates of C and N accumulated over the past several thousand years were approximately 10% of that over the past 60 years after correcting for bulk density. These results are similar to other coastal wetlands and suggest that time scale must be considered in determining the relative permanence of C and N storage in coastal wetland soils. This difference is especially important for assessing the role of C cycling in relation to global change models and N cycling related to water quality in accurately quantifying the role of coastal deltaic fresh water wetlands in regulating these biogeochemical cycles.

Although there have been numerous studies focusing on plants' roles in methane (CH4) emissions, the influencing mechanism of wetland plants on nitrous oxide (N2O) emissions has rarely been studied. Here, we test whether wetland plants also play an important role in N2O emissions. Gas fluxes were determined using the in situ static flux chamber technique. We also carried out pore-water extractions, sedge removal experiments and tests of N2O transportation. The brackish marsh acted as a net source of both CH4 and N2O. However, sedge plants played the opposite role in CH4 and N2O emissions. The removal of the sedges led to reduced CH4 emissions and increased accumulation of CH4 inside the sediment. Apart from being a conduit for CH4 transport, the sedges made a greater contribution to CH4 oxidation than CH4 production. The sedges exerted inhibitory effects on the release of N2O. The N2O was barely detectable inside the sediment in both vegetated and vegetation-removed plots. The denitrification measurements and nitrogen addition (the addition rates were equal to 0.028, 0.056 and 0.112 g m−2) experiments suggest that denitrification associated with N2O production occurred mainly in the surface sediment layer. The vascular sedge could transport atmospheric N2O downward into the rhizosphere. The rhizospheric sediment, together with the vascular sedge, became an effective sink of atmospheric N2O.

Oxidative dehydrogenation of light alkanes to alkenes is an attractive alternative route for industrial direct dehydrogenation because of favorable thermodynamic and kinetic characteristics, but encounters difficulties in selectivity control for alkenes because of over-oxidation reactions that produce a substantial amount of undesired carbon oxides. Recent progress has revealed that boron nitride is a highly promising catalyst in the oxidative dehydrogenation of light alkanes because of its superior selectivity for and high productivity of light alkenes, negligible formation of CO2, and remarkable catalyst stability. From this viewpoint, recent works on boron nitride in the oxidative dehydrogenations of ethane, propane, butane, and ethylbenzene are reviewed, and the emphasis of this viewpoint is placed on discussing the catalytic origin of boron nitride in oxidative dehydrogenation reactions. After analyzing recent progress in the use of boron nitride for oxidative dehydrogenation reactions and finding much new evidence, we conclude that pure boron nitride is catalytically inert, and an activation period is required under the reaction conditions; this process is accompanied by an oxygen functionalization at the edge of boron nitride; the B-O species themselves have no catalytic activity in C-H cleavage, and the B-OH groups, with the assistance of molecular oxygen, play the key role in triggering the oxidative dehydrogenation of propane; the dissociative adsorption of molecular oxygen is involved in the reaction process; and a straightforward strategy for preparing an active boron nitride catalyst with hydroxyl groups at the edges can efficiently enhance the catalytic efficacy. A new redox reaction cycle based on the B-OH sites is also proposed. Furthermore, as this is a novel catalytic system, there is an urgent need to develop new methods to optimize the catalytic performances, clarify the catalytic function of boron species in the alkane ODH reactions, and disclose the reaction mechanism under realistic reaction conditions.

Perchlorate (ClO4−), a persistent inorganic compound, has harmful effects on human health. Natural ClO4− is formed in the atmosphere and enters into the surface environment through deposition. However, the knowledge on the occurrence, spatial variability and sinks of natural ClO4− in different environments remains limited, especially in the polar regions. Here, we investigate the sources and sinks of ClO4− in soil collected in three ice-free areas in coastal Antarctica, where the research stations and wildlife colonies are mainly distributed. No statistically significant difference in ClO4− concentrations between sites near and away from the stations suggests that local human presence is not a significant source of ClO4− in soil. Concentrations of ClO4− in soil from wildlife colonies are not significantly higher than those from sites with no intense wildlife activities, indicating that wildlife activities have no significant influences on ClO4− in soil. Thus, atmospherically formed ClO4− is the main source for soil in Antarctica. In general, ClO4− concentrations (0.1–5.1 μg kg−1) in soil in this study are much lower than those in the arid environments and comparable to those in the unsaturated zones. Leaching by snow meltwater may be the main sink for ClO4− in soil, and deeper depths for aqueous migration may contribute to the lower ClO4− concentrations in Antarctic surface soil compared to the values in the arid areas with low precipitation amount. Due to the biological origin of NO3−, no correlation between NO3− and ClO4− in soil is observed in this study, different from the observations in arid areas. In addition, no significant correlation is observed between organic matter contents and ClO4− concentrations in soil, suggesting that biological reduction is not an important sink for ClO4− in Antarctic soil.

Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) concentration, saturation and fluxes in rivers (Beitang drainage river, Dagu drainage rive, Duliujianhe river, Yongdingxinhe river and Nanyunhe river) of Tianjin city (Haihe watershed) were investigated during July and October in 2014, and January and April in 2015 by static headspace gas chromatography method and the two-layer model of diffusive gas exchange. The influence of environmental variables on greenhouse gases (GHGs) concentration under the disturbance of anthropogenic activities was discussed by Spearman correlative analysis and multiple stepwise regression analysis. The results showed that the concentration and fluxes of CO2, CH4 and N2O were seasonally variable with >winter>fall>summer, spring>summer>winter>fall and summer>spring>winter>fall for concentrations and spring>summer>fall>winter, spring>summer>winter>fall and summer>spring>fall>winter for fluxes respectively. The GHGs concentration and saturation were higher in comprehensively polluted river sites and lower in lightly polluted river sites. The three GHGs emission fluxes in two sewage draining rivers of Tianjin were clearly higher than those of other rivers (natural rivers) and the spatial variation of CH4 was more obvious than the others. CO2 and N2O air-water interface emission fluxes of the sewage draining rivers in four seasons were about 1.20-2.41 times and 1.13-3.12 times of those in the natural rivers. The CH4 emission fluxes of the sewage draining rivers were 3.09 times in fall to 10.87 times in spring of those in the natural rivers in different season. The wind speed, water temperature and air temperature were related to GHGs concentrations. Nitrate and nitrite (NO3-+NO2--N) and ammonia (NH4+-N) were positively correlated with CO2 concentration and CH4 concentration; and dissolved oxygen (DO) concentration was negatively correlated with CH4 concentration and N2O concentration. The effect of human activities on carbon and nitrogen cycling in river is great.

Although carbon nanotubes can be described as a seamlessly curled graphene nanosheet, two-dimensional graphene oxide (GO) and one-dimensional oxidized carbon nanotubes (OCNTs) have different fates and environmental risks, such as deposition, degradation and cytotoxicity. In particular, coexisting heavy metal ions (HMs) trigger distinct morphological transformations of both of these carbon derivatives. In addition, these morphological transformations can change the interface behaviors of HMs on both of these materials. In this study, the differences in the morphological changes of GO and OCNTs and the interface behaviors of Ni(II) were explored via the intrinsically microscopic structural changes of both of these typical carbon materials. Batch experiments revealed that Ni(II) sorption on GO drastically decreased with increasing ionic strength, while it was almost independent of ionic strength on the OCNTs. This phenomenon is attributed to the aggregation and wrinkling of GO sheets at higher Na+ concentrations, resulting in a decrease in the GO surface area and number of sorption sites. Meanwhile, the intertwining aggregations of OCNTs still ensured that the sorption sites were naked. For the first time, Ni2+ ions were observed to persist as inner-sphere complexes on GO even under alkaline conditions, where the Ni(OH)2(s) phase was determined on the OCNTs. This could be attributed to the fact that the fast aggregation of GO, which fixed Ni2+ ions into the interlayers, inhibited the nucleation of Ni(OH)2. Stable layered structures of GO aggregations were difficult to exfoliate, leading to a decreased release of Ni(II) from GO with increasing Ni(II) loading. For the OCNTs, naked Ni2+ ions could be easily and effectively released. These findings are critical to assess the mobility, transformation and cytotoxicity of nanomaterials and HMs in aquatic environments.

Although there have been a lot of studies on the adsorption of trivalent actinides on clay minerals, the gaps between surface complexation model (SCM) for the description and prediction of macroscopic adsorption and the coordination structures and configurations of the surface complexes are still not completely bridged. Aiming at a multi-scale description of Am(III) adsorption on bentonite, density functional theory (DFT) calculations and surface complexation modeling were carried out. The results showed that the SCM considering cation exchange reactions and the formation of surface complexes, i.e., ≡SSOAm2+, ≡SSOAm(OH)+ and ≡SSOAm(OH)2 could reproduce all batch experimental data for Am(III) adsorption on Gaomiaozi bentonite, a potential buffer material for China's Beishan high-level radioactive waste repository. The stoichiometric coefficients of 1 in the SCM are deduced, while the surface complexes at the sites of ≡Al(OH)2 on (010) surface and those of ≡AlO(OH) on (110) surface are bidentate according to DFT calculations. The detailed calculations of electronic structures indicated that both covalent bond and electrostatic interaction account for Am(III) coordinating with the surface hydroxyl groups. In addition, it was found that the structures and energy properties of Am(III) complexes on (010) surface are similar to those on (110) surface. Hydrogen bonds between binding waters of Am(III) and the surface hydroxyl groups are formed in all cases, contributing to additional stability of Am(III) surface complexes. Overall, this study provides an improved understanding of Am(III) adsorption on the edge surfaces of bentonite/montmorillonite.

In recent years, various kinds of nanomaterials based invasive or non-invasive deep neural stimulation tools are developed for modulating neural system and illuminating the relationship between neural circuits and specific behaviors. For better modulation of neural system and clinical application, the neural stimulation nanotools should be optimized. In this work, we demonstrated a novel non-invasive neural modulation approach relying on magnetic field, which is realized by modifying magnetic nanoparticles (MNPs) with anti-His antibody and inserting His-tag at specific position of TRPV4 to target the activation of TRPV4 ion channel. The activated TRPV4 ion channel could induce the calcium influx by in vitro calcium imaging assay in cultured neurons. This study showed that this approach can improve the calcium transient compared with unmodified MNPs. Furthermore, this approach was confirmed in freely moving mice presenting valid magnetic control of rotation around the body-axis and freezing of gait. This work demonstrates that TRPV4 ion channel can be activated by MNPs based nanotool, which provides a new alternative way for achieving magnetic stimulation in deep-brain circuits. This work also can serve as a useful validation study for magnetogenetics.

O-Phospho-l-serine is one of the naturally occurring phosphorylated amino acids, having important pharmacological activity and bioactivity. The protonation constants of O-phospho-l-serine were determined by means of potentiometric titrations at 25 °C and ionic strength of 0.5 mol·L−1 (NaCl). The heat effects of the protonation reaction of the O-phospho-l-serine were measured by direct calorimetry. NMR spectroscopy has demonstrated that the first protonation site occurs at the nitrogen atom in the amino group, followed by one of the oxygen atoms in the phosphono group, and finally the carboxyl oxygen atom. This trend is in good agreement with the enthalpy of protonation and quantum chemical calculations. These data will help to predict the speciation of O-phospho-l-serine in physiological systems.

Solvent extraction studies of UO22+ were carried out using N,N′-dimethyl-N,N′-dibutylmalonamide (DMDBMA), N,N,N′,N′-tetrabutylmalonamide (TBMA), and N,N,N′,N′-tetraoctylmalonamide (TOMA) dissolved in three room temperature ionic liquids (RTILs) of 1-alkyl-3-methylimidazolium bis(trifluoromethane)sulfonamide ([Cnmim][Tf2N], n = 4,6,8). At lower acidity, the extraction of UO22+ carried out in RTIL was found to be much more efficient than in the conventional molecular diluents, while this advantage diminishes at higher acidity. The alkyl chain length of the RTILs plays an important role on the extraction performance. The effect of concentration of three diamides and nitric acid on extraction performance was also investigated. The extraction mechanism using RTILs as the diluent was deduced by the slope analysis and extraction experiment, and a cation-exchange mechanism at lower acidity and a neutral solvation mechanism at higher acidity were proposed. Density functional theory method was used to characterize ...

A novel metal-organic frameworks (MOFs) UiO-66-Schiff base was successfully synthesized by post-synthetic modification to investigate the cobalt sorption behaviour in simulated wastewater. The thermodynamic and kinetic parameters demonstrated the sorption process to be spontaneous, endothermic and pseudo-second-order chemisorption. The maximum cobalt sorption capacity of the synthetic MOFs was approximately 256 mg g −1 , and the stable and porous Schiff base-derived material displayed excellent regenerated availability with at least five recycle applications. Moreover, density functional theory (DFT) calculations have been performed to explore the coordination modes between cobalt ions and ligands in UiO-66-Schiff base, which revealed that the Schiff base group could take cobalt (II) from cobalt ions hydrates [Co(H 2 O) 6 ] 2+ and Co-CHES (Co-2-(cyclohexylamino)-ethane sulfonic acid) complex [Co(CHES)(H 2 O) 5 ] + to form [CoL N (H 2 O) 5 ] 2+ or [CoL O (H 2 O) 4 ] + . This study offers a facile approach for developing Schiff base modification MOF sorption of cobalt (II) ions from aqueous solutions and provides theoretical and practical guidance on new MOF designs for selective removal of radionuclides.

Silicon carbide fiber-reinforced silicon carbide matrix composites have been investigated for their use as structural materials for advanced nuclear reactor. Although quite a number of researches have been devoted to probe the effects of irradiation on various properties of the composites, there is little known about the atomistic mechanism for irradiation resistance. In this study, a two-temperature model has been used to investigate the irradiation damage of SiC/Gra/SiC composites, which includes three parts and two SiC/C interfaces, two single crystal cubic silicon carbide on two sides and a few graphene sheets in the middle part. By simulating 100 keV displacement cascades, we find that the number of defects in the reinforcement is larger than that in the matrix, which indicates the damage in the reinforcement is more serious than that in the matrix. Moreover, we explicitly investigate the damage behavior of the interphase graphene layers and find that some atoms in one graphene sheet form many new chemical bonds with atoms in another one, which leads to the transition from sp 2 to sp 3 hybridization. The newly formed chemical bonds link the different graphene layers and make graphene-like electronic structure more “diamond-like”, enhancing the irradiation resistance of the matrix.

Evasion of carbon dioxide (CO2) and methane (CH4) in streams and rivers play a critical role in global carbon (C) cycle, offsetting the C uptake by terrestrial ecosystems. However, little is known about CO2 and CH4 dynamics in lowland coastal rivers profoundly modified by anthropogenic perturbations. Here, we report results from a long-term, large-scale study of CO2 and CH4 partial pressures (pCO2 and pCH4) and evasion rates in the Shanghai river network. The spatiotemporal variability of pCO2 and pCH4 were examined along a land-use gradient and the annual CO2 and CH4 evasion were estimated to assess its role in regional C budget. During the study period (August 2009 – October 2011), the overall mean pCO2 and median pCH4 from 87 surveyed rivers were 5846±2773 μatm and 241 μatm, respectively. Internal metabolic CO2 production and DIC input via upstream runoff were the major sources sustaining the widespread CO2 supersaturation, coupling pCO2 to biogeochemical and hydrological controls, respectively. While CH4 was oversaturated throughout the river network, CH4 hotpots were concentrated in the small urban rivers and highly discharge-dependent. The Shanghai river network played a disproportionately important role in regional C budget, offsetting up to 40% of the regional terrestrial net ecosystem production (NEP) and 10% of net C uptake in the river-dominated East China Sea fueled by anthropogenic nutrient input. Given the rapid urbanization in global coastal areas, more research is needed to quantify the role of lowland coastal rivers as a major landscape C source in global C budget.

N-(phosphonomethyl)-l-proline is an analogue of glyphosate. The protonation for N-(phosphonomethyl)-l-proline was studied by potentiometry, calorimetry, 31P NMR spectroscopy and quantum chemical calculations to further understand the protonation process of glyphosate. The results confirmed that the order of successive protonation sites of totally deprotonated N-(phosphonomethyl)-l-proline are a phosphonate oxygen, amino nitrogen, and finally the carboxylate oxygen. The results can improve the understanding of the biological activity of these types of molecules in solution.

Oxidative dehydrogenation of propane to olefins is a promising alternative route to industrialized direct dehydrogenation, but encounters the difficulty in selectivity control for olefins because of the overoxidation reactions that produce a substantial amount of undesired CO2. Here we report edge-hydroxylated boron nitride, a metal-free catalyst, that efficiently catalyzed dehydrogenation of propane to propylene with superior selectivity (80.2 %) but with only negligible CO2 formation (0.5 %) at a given propane conversion of 20.6 %. Remarkable stability was evidenced by the operation of a 300 h test with steady conversion and product selectivity. The active BNO. site, generated dynamically through hydrogen abstraction of B−OH groups by molecular oxygen, triggered propane dehydrogenation by selectively breaking the C−H bond but simultaneously shut off the pathway of propylene overoxidation towards CO2.

Boron nitride containing hydroxyl groups efficiently catalysed oxidative dehydrogenation of ethane to ethylene, offering rather high selectivity (95%) but only small amount of CO2 formation (0.4%) at a given ethane conversion of 11%. Even at high conversion level of 63%, the selectivity of ethylene retained at 80%, which is competitive with the energy-demanding industrialized steam cracking route. A long-term test for 200 h resulted in stable conversion and product selectivity, showing the excellent catalytic stability. Both experimental and computational studies have identified that the hydrogen abstraction of B-OH groups by molecular oxygen dynamically generated the active sites and triggered ethane dehydrogenation.

The increasing sophistication of single cell Raman spectroscopy (SCRS) via its integrations with other advanced analytical techniques and modern data analytics, enable unprecedented exploration of complex biological and environmental samples with significantly improved specificity, sensitivity, and resolution. Because of the merits of being high-resolution, label-free, non-invasive, molecular-specific, culture-independent, and suitable for in situ, in vitro or in vivo analysis, the SCRS-derived techniques offer abilities superior to conventional bulk measurements for environmental and biological studies. Here, we provide a comprehensive and critical review of the most recent advances in the development and application of SCRS-enabled technologies, with focus on those biomolecular and cellular high-resolution applications in environmental and biological fields. The basic principles, unique advantages, and suitable applications, as well as recognized limitations for each technology are recapitulated. The remaining challenges, research needs and future outlook are discussed. We predict that SCRS-enabled technologies are earning its place as a routine and powerful tool in many and rapidly expanding applications across disciplines.

The pandemic of COVID-19 has posed an urgent need to learn the dynamics of the virus and the mechanism of its contagion of host cells. By means of molecular dynamics simulations, this work addressed the behavior of 2019-nCoV in two aspects: the binding affinity of its receptor binding domain (RBD) with ACE2, and its potential conformation preferences in its unbound state. The results showed that the RBD of 2019-nCov bound much stronger with ACE2 than that of SARS-CoV due to a better organized hydrogen bond network between the former pair with most of the residues at the contact interface sharing the responsibility to hold the pair tightly. This is in contrast to the case of SARS-CoV, which strongly relied on the residues at the ends of the cleft. In its unbound state, the RBD of 2019-nCoV was found to fold part of its receptor binding motif (RBM) into a helical conformation and flip into a concave to minimize its contact with the external environment. This has the biological implication that the virus may achieve higher translational motion in the condensed phase and have a higher chance of survival by avoiding capture by the immune system before reaching its target receptor.

Organochlorine pesticides (OCPs) have been restricted for application for about 30 years in China. Intertidal zone is a sink for anthropogenic pollutants, and to better understand the current pollution status of OCPs in China, 324 surface sediment samples collected from 14 typical intertidal zones of China were analyzed for 22 OCPs. The total concentrations of OCPs ranged from 0.051 to 4141.711 ng/g, with DDTs and HCHs being the dominant components. Seasonal variations were not significant for most intertidal zones (p > 0.05), while significant spatial variations (p

To address the common challenges in enhanced biological phosphorus removal (EBPR) related to stability and unfavorable influent carbon to phosphorus ratio, a side-stream EBPR (S2EBPR) process that involves a side-stream anaerobic biological sludge hydrolysis and fermentation reactor was proposed as an emerging alternative. In this study, a full-scale pilot testing was performed with side-by-side operation of a conventional anaerobic-anoxic-aerobic (A2O) process versus a S2EBPR process. A comparison of the performance, activity and microbial community between the two configurations was performed. The results demonstrated that, with the same influent wastewater characteristics, S2EBPR configuration showed improved P removal performance and stability than the conventional A2O configuration, especially when the mixers in the side-stream anaerobic reactor were operated intermittently. Mass balance analysis illustrated that both denitrification and EBPR were enhanced in S2EBPR configuration, where return activated sludge was diverted into the anaerobic zone to promote fermentation and enrichment of polyphosphate accumulating organisms (PAOs), and the influent was bypassed to the anoxic zone for enhancing denitrification. A relatively higher PAO activity and total PAO abundance were observed in S2EBPR than in A2O configuration, accompanied by a higher degree of dependence on glycolysis pathway than tricarboxylic acid cycle. No significant difference in the relative abundances of putative PAOs, including Ca. Accumulibacter and Tetrasphaera, were observed between the two configurations. However, higher microbial community diversity indices were observed in S2EBPR configuration than in conventional one. In addition, consistently lower relative abundance of known glycogen accumulating organisms (GAOs) was observed in S2EBPR system. Extended anaerobic retention time and conditions that generate continuous and more complex volatile fatty acids in the side-stream anaerobic reactor of S2EBPR process likely give more competitive advantage for PAOs over GAOs. PAOs exhibited sustained EBPR activity and delayed decay under extended anaerobic condition, likely due to their versatile metabolic pathways depending on the availability and utilization of multiple intracellular polymers. This study provided new insights into the effects of implementing side-stream EBPR configuration on microbial populations, EBPR activity profiles and resulted system performance.

Methane (CH4) emissions are low in the coastal zone due to a higher redox poise, related to sulfate reduction. However, river deltas are a potential source of CH4 flux in coastal zones globally, due to fresh condition and high primary production. The goal of this study was to seasonally measure CH4flux at three different geomorphic settings (newly forming island, river channel bottom and established freshwater marsh) within the Wax Lake Delta, Louisiana, USA. CH4 flux rates were 386 ± 327 mg C m−2 d−1 in March and 2859 ± 1286 mg C m−2 d−1 in June at the freshwater marsh site. At the island site, CH4 flux was significantly smaller at 7.94 ± 3.57 mg C m−2 d−1 in March and 215 ± 153 mg C m−2 d−1 in June while at adjacent river channel bottom site, CH4 flux was lowest at 2.49 ± 3.38 mg C m−2 d−1 in March and 19.5 ± 1.12 mg C m−2 d−1 in June at the air-water interface. CH4 emission rates show significant spatial heterogeneity with rates up to two orders of magnitude greater at the marsh site at the periphery of the delta, related to greater soil total C. Therefore regions within the active delta do not provide a significant source of methane, due to a lack of soil C, despite freshwater conditions. However, marshes at the periphery within the halo of fresh water, populated with established plant communities can be significant hotspots of CH4 emissions, despite their location within the coastal zone.

Static floating chambers (FCs) are the conventional method to measure CH4 fluxes across the water-air interface in ponds, while thin boundary layer (TBL) modelling is increasingly used to estimate CH4 fluxes. In this study, both FCs measurements and TBL models of gas transfer velocity were used to determine CH4 evasion from aquaculture ponds in southeastern China. The surface water CH4 concentrations ranged from 0.4 to 9.1 μmol L-1 with an average of 4.8 ± 0.8 μmol L-1. CH4 flux was always positive, indicating the ponds as a persistent CH4 source to air. Mean CH4 flux based on different TBL models showed large variations, ranging between 19 and 316 μmol m−2 h−1. Compared against the direct measurement FCs, three TBL models developed for the open sea, flowing estuarine system and lentic ecosystem (TBLW92a, TBLRC01, and TBLCL98, respectively) overestimated CH4 emission by 40–200%, while the wind tunnel-based TBL model (TBLLM86) underestimated CH4 emission. Two TBL models developed for lakes (TBLW92b and TBLCW03) gave estimates similar to FCs.