Long-neglected contribution of nitrification to N2O emissions in the Yellow River.

Rivers play a significant role in the global nitrous oxide (N2O) budget. However, the microbial sources and sinks of N2O in river systems are not well understood or quantified, resulting in the prolonged neglect of nitrification. This study investigated the isotopic signatures of N2O, thereby quantifying the microbial source of N2O production and the degree of N2O reduction in the Yellow River. Although denitrification has long been considered to be the dominant pathway of N2O production in rivers, our findings indicated that denitrification only accounted for 18.3% (8.2%-43.0%) of the total contribution to N2O production in the Yellow River, with 50.2%-80.2% being concurrently reduced. The denitrification contribution to N2O production (R2 = 0.44, p < 0.01) and N2O reduction degree (R2 = 0.70, p < 0.01) were positively related to the dissolved organic carbon (DOC) content. Similar to urban rivers and eutrophic lakes, denitrification was the primary process responsible for N2O production (43.0%) in certain reaches with high organic content (DOC = 5.29 mg/L). Nevertheless, the denitrification activity was generally constrained by the availability of electron donors (average DOC = 2.51 mg/L) throughout the Yellow River basin. Consequently, nitrification emerged as the primary contributor in the well-oxygenated Yellow River. Additionally, our findings further distinguished the respective contribution of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to N2O emissions. Although AOB dominated the N2O production in the Yellow River, the AOA specie abundance (AOA/(AOA + AOB)) contributed up to 32.6%, which resulted in 25.6% of the total nitrifier-produced N2O, suggesting a significant occurrence of AOA in the oligotrophic Yellow River. Overall, this study provided a non-invasive approach for quantifying the microbial sources and sinks to N2O emissions, and demonstrated the substantial role of nitrification in the large oligotrophic rivers.

Effect of low temperature on contributions of ammonia oxidizing archaea and bacteria to nitrous oxide in constructed wetlands.

Constructed wetlands (CWs) have been widely used for ecological remediation of micro-polluted source water. Nitrous oxide (N2O) from CWs has caused great concern as a greenhouse gas. However, the contribution of ammonia oxidation driven by ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) to N2O emission, especially at low temperature, was unknown. This study aimed to quantify the contributions of AOA and AOB to N2O through lab-scale subsurface CWs. The N2O emission flux of CW at 8 °C was 1.23 mg m-2·h-1, significantly lower than that at 25 °C (1.92 mg m-2·h-1). The contribution of ammonia oxidation to N2O at 8 °C (33.04%) was significantly higher than that at 25 °C (24.17%). The N2O production from AOA increased from 1.91 ng N·g-1 at 25 °C to 4.11 ng N·g-1 soil at 8 °C and its contribution increased from 23.38% to 30.18% (P < 0.05). Low temperature impaired functional gene groups and inhibited the activity of AOB, resulting in its declined contribution. Based on the transcriptional analysis, AOA was less affected by low temperature, thus stably contributing to N2O. Moreover, community diversity and relationships of AOA were enhanced at 8 °C, while AOB declined. The results confirmed the significant contribution of AOA and demonstrated molecular mechanisms (higher activity and community stability) of the increased contribution of AOA to N2O at low temperature.

Distinct oxygen isotope fractionations driven by different electron donors during microbial nitrate reduction in lake sediments.

Microbial nitrate reduction can be driven by organic carbon oxidation, as well as by inorganic electron donors, such as reduced forms of sulfur and iron. An apparent inverse oxygen isotope fractionation effect was observed during nitrate reduction in sediment incubations from five sampling sites of a freshwater lake, Hongze Lake, China. Incubations with organic and inorganic electron donor additions were performed. Especially, the inverse oxygen isotope effect was intensified after glucose addition, whereas the incubations with sulfide and Fe2+ showed normal fractionation factors. Nitrate reductase encoding genes, napA and narG, were analysed with metagenomics. Higher napA/narG ratios were associated with higher oxygen fractionation factors. The most abundant clade (59%) of NapA in the incubation with glucose was affiliated with Rhodocyclales. In contrast, it only accounted for 8%-9% of NapA in the incubations with sulfide and Fe2+ . Differences in nitrate reductases might explain different oxygen isotope effects. Our findings also suggested that large variance of O-nitrate isotope fractionations might have to be considered in the interpretation of natural isotope records.

Archaeal and bacterial ecological strategies in sediment denitrification under the influence of graphene oxide and different temperatures.

As an emerging material, graphene oxide (GO) has been widely used in recent years and will inevitably enter into natural water bodies, and it may have an impact on lake microbial communities owing to its potential toxicity and denitrification-enhancing ability. This study simulated the effect of 0.1 g/L GO on denitrification in lake sediments under summer (28 °C) and winter temperatures (8 °C). GO promoted carbon source metabolism and denitrification. Phylogenetic bin-based null model analysis suggested that GO significantly altered the contribution of heterogeneous selection in bacterial and archaeal community assembly. The co-occurrence network indicated that bacterial communities responded to the enhancement of heterogeneous selection by strategies of enhancing positive correlation and shared niche, whereas archaeal communities adopted strategies of enhancing negative correlation and competition. Bacterial networks also emerged with more non-hub connector species that could drive changes in community structure. Our study contributed to the understanding of different ecological strategies adopted by bacterial and archaeal communities in response to changes in ecological selection driven by GO.

Using hierarchical stable isotope to reveal microbial food web structure and trophic transfer efficiency differences during lake melt season.

The microbial food web (MFW) is a material and energy source in lake water ecosystems. Although it is crucial to determine its structure and function for water ecological health, MFW changes during lake melt period have not been well studied. In this study, the MFW was divided into three categories by analyzing its structure and trophic transfer efficiency using hierarchical C/N stable isotopes and eDNA sequencing techniques, including the detrital food web (DFC, 15 %), classical grazing food web (CFC, 60 %), and mixed trophic food web (MFC, 25 %). The trophic structure and type of MFW in ice-melting lakes are always in the process of succession and adaptation, which is in a relatively low trophic transfer efficiency stage under stable conditions (i.e. CFC), whereas the input of exogenous debris and organic pollutants may lead to an increase in MFW trophic transfer efficiency (i.e. MFC, DFC). The trophic transfer efficiency from the previous trophic level to protozoa and micrometazoa was 16.32 % and 20.77 % in DFC and 10.20 % and 29.43 % in MFC, respectively. Both are obviously higher than those of the CFC (11.69 % and 9.45 %, respectively). In terms of trophic structure, the community interaction and trophic cascade effect of DFC and MFC were enhanced but easily changed with environmental factors. In contrast, the core species and cascading effects of the CFC were clearer, and the MFW structure was relatively stable. Overall, this study reveals that the explosive increase in MFW trophic transfer efficiency induced by exogenous input during the lake melt period may subsequently lead to the destabilization of the microbial community structure and cause potential ecological risks. These are manifested in the absence of ecological trophic processes, the decrease in trophic structure complexity and stability, and the weakening of microecology self-adaptive regulation ability.

Electron beam-induced athermal nanowelding of crossing SiO x amorphous nanowires.

Nanowelding of two crossing amorphous SiO x nanowires induced by uniform electron beam irradiation at room temperature was demonstrated in an in situ transmission electron microscope. It was observed that, under the electron beam irradiation, the amorphous nanowires became unstable driven by nanocurvature non-uniformly distributed over the nanowire surface centered around the crossing site of the nanowires. Such an instability of the nanowires could give rise to an athermal fast and massive migration of atoms nearby the surface centered around the crossing site, and thus the two crossing nanowires become gradually welded. The existing knock-on mechanism and molecular dynamics simulations seem inadequate to explain the observed athermal migration of the surface atoms and the resulting structural change at the nanoscale. To elucidate the observed phenomena of nanowelding, a mechanism of athermal atomic diffusion driven by the effects of the nanocurvature as well as the athermal activation of the electron beam was proposed and simulated. The simulation revealed the detailed process of the nanowelding and corresponding effects of the nanocurvature and athermal activation of the electron beam. In doing so, the nanowelding parameters became predictable, controllable, and tunable to a desired welding effect.

The promotion and inhibition effect of graphene oxide on the process of microbial denitrification at low temperature.

This study found that graphene oxide (GO) improved microbial denitrification at low temperatures (~12 °C), and the optimal concentration was 10 mg/L as the removal rate of NO3-N increased by 17%. At the optimal concentration, GO improved the electron transport system activity of the microbes and enhanced the activity of nitrate reductase and nitrite reductase while exhibited low microbial toxicity. The addition of GO increased the content of tightly bound extracellular polymeric substances (EPS). The results of fluorescence spectrometer indicated that GO accelerated the renewal of bound EPS (B-EPS). Fourier Transform infrared spectroscopy (FTIR) results showed that GO affected the secondary structure of the protein in B-EPS, making B-EPS more hydrophobic and promoting microbial aggregation. B-EPS affected by GO can promote the electron transfer process of microorganisms. However, high concentration (>25 mg/L) of GO may inhibit denitrification by competing for electrons, which was not conducive to denitrification thermodynamically.

Microbial coupling mechanisms of nitrogen removal in constructed wetlands: A review.

Nitrogen removal through microorganisms is the most important pathway in constructed wetlands (CWs). In this review, we summarize the microbial coupling mechanisms of nitrogen removal, which are the common methods of nitrogen transformation. The electron pathways are shortened and consumption of oxygen and energy is reduced during the coupling of nitrogen transformation functional microorganisms. The highly efficient nitrogen removal mechanisms are cultivated from the design conditions in CWs, such as intermittent aeration and tidal flow. The coupling of microorganisms and substrates enhances nitrogen removal mainly by supplying electrons, and plants affect nitrogen transformation functional microorganisms by the release of oxygen and exudates from root systems as well as providing carriers for microbial attachment. In addition, inorganic elements such as Fe, S and H act as electron donors to drive the autotrophic denitrification process in CWs.

Nanoinstabilities of Cu2O porous nanostructured films as driven by nanocurvature effect and thermal activation effect.

In this work, the instabilities at the nanoscale (i.e. nanoinstabilities) of triangular pyramids-like Cu2O porous nanostructured films (PNFs) are studied by heating treatments under different atmosphere and temperature. It is found that the nanoscale building triangular pyramids turn round preferentially at the sharp angles and/or coalesce with their contacting ones by directional diffusion and plastic flow of atoms, which are driven by the nonuniformly-distributed surface nanocurvature. As a result, the triangular pyramids become quasi-sphere shape and the PNF evolves into a big, dense particles film. It is also observed that the heating or thermal activation effect efficiently promotes the reduction or oxidation of Cu2O pyramids and the crystallization or growth of the as-achieved Cu or CuO grains. The above physical and chemical instabilities or changes at the nanoscale of Cu2O PNFs can be well accounted for by the combined mechanism of nanocurvature effect and thermal activation effect. The nanocurvature effect can lower the energy barrier for the atom diffusion or plastic flow and lower the activation energy for the chemical reactions, while the thermal activation effect can supply the required kinetic energy or activation energy and make the atomic transportations and reactions kinetically possible. The findings reveal the evolution laws of morphology, crystal structure and composition of triangular pyramids-like Cu2O PNF during heating treatments, which can further be extended to other types of Cu2O PNFs. Also, the findings have important implications for the nanoinstabilities of Cu2O PNFs-based devices, especially those working at a high temperature.

Quantitative analysis of genetic associations in the biodegradative pathway of PAHs in wetland sediments of the Bohai coast region.

The present study characterized the distribution and sources of polycyclic aromatic hydrocarbons (PAHs) in 57 sediment cores collected from estuary and tidal flat wetlands in the Bohai coast region and investigated the molecular degradation mechanism of PAHs. The results showed that the PAH concentrations in estuary sediments were significantly higher than in tidal flat sediments. PAH patterns and pollutant sources were more complicated in estuary sediments. Quantitative response relationships showed that in estuary sediments, the key factors affecting PAH degradation changed from initial dioxygenase genes and C23O to salicylate hydroxylase genes and C23O with an increase in the PAH ring number. In contrast, for tidal flat sediments, the initial dioxygenase genes remained the key factors (nidA and nahAc/nagAc, except only nidA for 5-ring PAHs) related to PAHs with different ring numbers. Non-metric multidimensional scaling (NMDS) analysis revealed that the lower catechol dioxygenase pathway coupled with the upper pyrene dioxygenase pathway. The total polycyclic aromatic hydrocarbon (TPAH) level across the Bohai coast region was most affected by catechol dioxygenation (catA + C23O). Catechol dioxygenation was directly affected by naphthalene dioxygenation/nahG ((nahAc + nagAc)/nahG), indicating that the interaction within the upper pathway coupled with the lower pathway. In addition, TOC had direct positive effects on catechol dioxygenation and nidA. This study improves our understanding of the biodegradative pathway of PAHs with different ring numbers and the response of PAHs to biotic and abiotic factors.

Cu2O porous nanostructured films fabricated by positive bias sputtering deposition.

In this work, the authors fabricated Cu2O porous nanostructured films (PNFs) on glass slide substrates by the newly developed positive bias deposition approach in a balanced magnetron sputtering (MS) system. It was found that the surface morphology, crystal structure and optical property of the as-deposited products were greatly dependent on the applied positive substrate bias. In particular, when the substrate was biased at +50 and +150 V, both of the as-prepared Cu2O PNFs exhibited a unique triangular pyramids-like structure with obvious edges and corners and little gluing, a preferred orientation of (111) and a blue shift of energy band gap at 2.35 eV. Quantitative calculation results indicated that the traditional bombardment effects of electrons and sputtering argon ions were both negligible during the bias deposition in the balanced MS system. Instead, a new model of tip charging effect was further proposed to account for the controllable formation of PNFs by the balanced bias sputtering deposition.

Preparation and specific recognition of protein macromolecularly imprinted polyampholyte hydrogel.

Bovine serum albumin (BSA) imprinted polyampholyte hydrogels (PAHs) were prepared by free radical polymerization using acrylamide (Am) as structural monomer, N-isopropylacrylamide (NIPAm), [2-(methacryloyloxy)ethyl]trimethylammonium chloride (DMC) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as functional monomers and N,N'-methylenebisacrylamide (MBA) as crosslinker in aqueous solution. The morphology of imprinted hydrogels and non-imprinted hydrogels were characterized by scanning electron microscope (SEM). The adsorption and recognition properties were evaluated as functions of Am monomer concentration, NIPAm/Am molar ratio, crosslinking structure and charge density ratio etc. The adsorption capacity and association constant of specific interaction between hydrogel and template protein were analyzed by Langmuir isotherm model and Freundlich model. The fitting experimental data suggested that this adsorption was better described as a monolayer adsorption. The specific adsorption on hydrogel with different crosslinking structure was investigated by selective binding BSA from single solution and binary mixture solution. The charge density ratio in molecular imprinting hydrogel had obvious influence for protein adsorption and recognition. The resultant of regeneration tests showed that elution had large impact on deterioration of the imprinting structure.

In situ TEM observation of preferential amorphization in single crystal Si nanowire.

The nanoinstability of a single crystal Si nanowire under electron beam irradiation was in situ investigated at room temperature by the transmission electron microscopy technique. It was observed that the Si nanowire amorphized preferentially from the surface towards the center, with the increasing of the electron dose. In contrast, in the center of the Si nanowire the amorphization seemed much more difficult, being accompanied by the rotation of crystal grains and the compression of d-spacing. Such a preferential amorphization, which is athermally induced by the electron beam irradiation, can be well accounted for by our proposed concepts of the nanocurvature effect and the energetic beam-induced athermal activation effect, while the classical knock-on mechanism and the electron beam heating effect seem inadequate to explain these processes. Furthermore, the findings revealed the difference of amorphization between a Si nanowire and a Si film under electron beam irradiation. Also, the findings have important implications for the nanoinstability and nanoprocessing of future Si nanowire-based devices.

Coalescence between Au nanoparticles as induced by nanocurvature effect and electron beam athermal activation effect.

The coalescence of two single-crystalline Au nanoparticles on surface of amorphous SiOx nanowire, as induced by electron beam irradiation, was in situ studied at room temperature in a transmission electron microscope. It was observed that along with shrinkage of the SiOx nanowire during irradiation, adjacent Au nanoparticles moved around and migrated close to each other. Once the two nanoparticles contacted with each other, a fast, massive atom transportation took place along their contact surface, where a neck region was created. With a further irradiation, the two nanoparticles rotated, aligning their crystal orientations, and gradually coalesced into a larger single-crystalline nanoparticle. The above coalescence process demonstrated an intriguing surface nanowetting ability and nanograin boundary dislocation climb and slip of Au NPs at room temperature as driven by the non-uniformly distributed nanocurvature over the surface of the two contacting nanoparticles as well as the beam-induced instability and soft mode of atomic vibration, which have been underestimated or neglected in the existing theoretical descriptions or simulations.

Atom Diffusion and Evaporation of Free-Ended Amorphous SiOx Nanowires: Nanocurvature Effect and Beam-Induced Athermal Activation Effect.

Arresting effects of nanocurvature and electron beam-induced athermal activation on the structure changes at nanoscale of free-ended amorphous SiOx nanowire were demonstrated. It was observed that under in situ uniform electron beam irradiation in transmission electron microscope, the near surface atoms at the most curved free end of the nanowire preferentially vaporized or diffused to the less curved wire sidewall. The processing resulted in an intriguing axial shrinkage and an abnormal radial expansion of the wire. It was also observed that with the beam energy deposition rate being lowered, although both the diffusion and the evaporation slowed down, the processing transferred from an evaporation-dominated status to a diffusion-dominated status. These results are crucial not only to the fundamental understanding but also to the technical controlling of the electron beam-induced structure change at nanoscale or nanoprocessing of low dimensional nanostructures.

Removal of Cu(II) and Ni(II) ions from an aqueous solution using α-Fe2O3nanoparticle-coated volcanic rocks.

An adsorbent, volcanic rocks coated with α-Fe2O3nanoparticles, was prepared and utilized for the removal of Cu(II) and Ni(II) ions from an aqueous solution. Characterization of the coated volcanic rocks indicated that the α-Fe2O3nanoparticles were successfully and homogeneously distributed on the volcanic rocks, including penetration into rock pores. Batch experiments were conducted to investigate adsorption performance. The adsorption behavior of both ions was found to best fit a pseudo second-order model and Langmuir isotherm. The maximum adsorption capacities of Cu(II) and Ni(II) ions were 58.14 mg g⁻¹ and 56.50 mg g⁻¹ at 293 K, respectively, and increased with rising temperature. The loaded α-Fe2O3nanoparticles onto volcanic rock significantly increased removal of Cu(II) and Ni(II) ions. The adsorption process was combined control of film diffusion and intra-particle diffusion. Adsorption thermodynamics indicated the adsorption process was spontaneous and occurred mainly through chemisorption. The results confirmed that the volcanic rocks coated with α-Fe2O3nanoparticles acted as a high-efficiency and low-cost absorbent, and effectively removed Cu(II) and Ni(II) from wastewater.

Intriguing surface-extruded plastic flow of SiOx amorphous nanowire as athermally induced by electron beam irradiation.

Nanoinstability and nanoprocessing of a SiOx amorphous nanowire at room temperature as induced by in situ electron beam irradiation in transmission electron microscopy are systematically investigated. It is demonstrated that in contrast to the crystalline nanowires where only the beam-induced ablation of atoms was observed, the amorphous nanowire herein can give rise to an arresting beam-induced surface-extruded plastic flow of massive atoms and surface migration of atoms in addition to the beam-induced ablation of atoms. Via the plastic flow and ablation, a new S-type deformed wire and the thinnest amorphous nanowire are elaborately created locally at nanoscale precision with a highly controllable manner depending on the beam current density, beam spot size, and beam position. The existing knock-on mechanism and simulation seem inadequate to explain these processes. However, it is indicated that a much higher nanocurved surface energy of nanowires and an enhanced beam-induced soft mode and instability of atomic vibration control the processes.

Assessment and sources of heavy metals in surface sediments of Miyun Reservoir, Beijing.

Heavy metals concentrations in surface sediments from Miyun Reservoir were determined to evaluate the pollution and identify the sources. The average content of metals in sediments from Miyun Reservoir followed the order Al>Fe>Ti>Mn>V>Zn>Cr>Ni>Cu>Pb>As>Cd>Hg, and the most mean values were lower than the globe average shale. Heavy metals concentrations at the inflow area of Baihe were higher than those at the inflow area of Chaohe. Heavy metals pollution assessment was carried out by factor enrichment (EF), geoaccumulation index (I(geo)), and potential ecological risk (RI). The EF values for all heavy metals except Hg, Cd, and Cr at several sites were lower than 3, suggesting low anthropogenic impact on the metals level. The I(geo) values of Pb indicated that half of the sites were unpolluted to moderately polluted and mainly located in the Baihe area of the reservoir. The RI showed that heavy metals of Miyun Reservoir were low potential risk, however, Hg approached or belonged to moderate ecological risk at sites of M5, M7, and M13. Correlation analysis and principal component suggested that Ni, Cu, V, Zn, Mn, Cr, Ti, and Pb were derived from soil erosion in upper reaches of the reservoir, while Fe, Cd, Hg, As, and partial Pb originated from anthropogenic sources, particularly industrial mining and gold tailings.

Controllable fabrication of PS/Ag core-shell-shaped nanostructures.

In this paper, based on the previous steps, a facile in situ reduction method was developed to controllably prepare polystyrene/Ag (PS/Ag) core-shell-shaped nanostructures. The crucial procedure includes surface treatment of polystyrene core particles by cationic polyelectrolyte polyethyleneimine, in situ formation of Ag nanoparticles, and immobilization of the Ag nanoparticles onto the surface of the polystyrene colloids via functional group NH from the polyethyleneimine. The experimental parameters, such as the reaction temperature, the reaction time, and the silver precursors were optimized for improvement of dispersion and Ag coat coverage of the core-shell-shaped nanostructures. Ultimately, the optimum parameters were obtained through a series of experiments, and well-dispersed, uniformly coated PS/Ag core-shell-shaped nanostructures were successfully fabricated. The formation mechanism of the PS/Ag core-shell-shaped nanostructures was also explained.