The large-scale production of high-Ti steels is limited by the formation of Ti-containing oxides or nitrides in steel-slag reactions during continuous casting.These processes degrade mold flux properties,clog submerge...The large-scale production of high-Ti steels is limited by the formation of Ti-containing oxides or nitrides in steel-slag reactions during continuous casting.These processes degrade mold flux properties,clog submerged entry nozzles,form floaters in the molds,and produce various surface defects on the cast slabs.This review summarizes the effects of nonmetallic inclusions on traditional CaO-SiO_(2)-based(CS)mold fluxes and novel CaO-Al_(2)O_(3)-based(CA)low-or non-reactive fluxes containing TiO_(2),BaO,and B_(2)O_(3)additives to avoid undesirable steel,slag,and inclusion reactions,with the aim of providing a new perspective for research and practice related to balancing the lubrication and heat transfer of mold fluxes to promote smooth operation and reduce surface defects on cast slabs.For traditional CS mold flux,although the addition of solvents such as Na_(2)O,Li_(2)O,and B_(2)O_(3)can enhance flowability,steel-slag reactions persist,limiting the effectiveness of CS mold fluxes in high-Ti steel casting.Low-or non-reactive CA mold fluxes with reduced SiO_(2)content are a research focus,where adding other components can significantly change flux characteristics.Replacing CaO with BaO can lower the melting point and inhibit crystallization,allowing the flux to maintain good flowability at low temperatures.Replacing SiO_(2)with TiO_(2)can stabilize the viscosity and enhance heat transfer.To reduce the environmental impact,fluorides are replaced with components such as TiO_(2),B_(2)O_(3),BaO,Li_(2)O,and Na_(2)O for F-frce mold fluxes with similar lubrication,crystallization,and heat-transfer effects.When TiO_(2)replaces CaF_(2),it stabilizes the viscosity and enhances the heat conductivity,forming CaTiO_(3)and CaSiTiO_(5)phases instead of cuspidine to control crystallization.B_(2)O_(3)lowers the melting point and suppresses crystallization,forming phases such as Ca_(3)B_(2)O_(6)and Ca_(11)Si_(4)B_(2)O_(22).BaO introduces non-bridging oxygen to reduce viscosity and ensure flux flowability at low temperatures.However,further studies are required to determine the optimal mold flux compositions corresponding to the steel grades and the interactions between the various components of the mold flux.In the future,the practical application of new mold fluxes for high-Ti steel will become the focus of further verification to achieve a balance between lubrication and heat transfer,which is expected to minimize the occurrence of casting problems and slab defects.展开更多
The consequences of climate change continue to threaten European forests,particularly for species located at the edges of their latitudinal and altitudinal ranges.While extensively studied in Central Europe,European b...The consequences of climate change continue to threaten European forests,particularly for species located at the edges of their latitudinal and altitudinal ranges.While extensively studied in Central Europe,European beech forests require further investigation to understand how climate change will affect these ecosystems in Mediterranean areas.Proposed silvicultural options increasingly aim at sustainable management to reduce biotic and abiotic stresses and enhance these forest ecosystems'resistance and resilience mechanisms.Process-based models(PBMs)can help us to simulate such phenomena and capture early stress signals while considering the effect of different management approaches.In this study,we focus on estimating sensitivity of two state-of-the-art PBMs forest models by simulating carbon and water fluxes at the stand level to assess productivity changes and feedback resulting from different climatic forcings as well as different management regimes.We applied the 3D-CMCC-FEM and MEDFATE forest models for carbon(C)and water(H_(2)O)fluxes in two sites of the Italian peninsula,Cansiglio in the north and Mongiana in the south,under managed vs.unmanaged scenarios and under current climate and different climatic scenarios(RCP4.5 and RCP8.5).To ensure confidence in the models’results,we preliminary evaluated their performance in simulating C and H_(2)O flux in three additional beech forests of the FLUXNET network along a latitudinal gradient spanning from Denmark to central Italy.The 3D-CMCC-FEM model achieved R^(2)values of 0.83 and 0.86 with RMSEs of 2.53 and 2.05 for C and H_(2)O fluxes,respectively.MEDFATE showed R^(2)values of 0.76 and 0.69 with RMSEs of 2.54 and 3.01.At the Cansiglio site in northern Italy,both models simulated a general increase in C and H_(2)O fluxes under the RCP8.5 climate scenario compared to the current climate.Still,no benefit in managed plots compared to unmanaged ones,as the site does not have water availability limitations,and thus,competition for water is low.At the Mongiana site in southern Italy,both models predict a decrease in C and H_(2)O fluxes and sensitivity to the different climatic forcing compared to the current climate;and an increase in C and H_(2)O fluxes when considering specific management regimes compared to unmanaged scenarios.Conversely,under unmanaged scenarios plots are simulated to experience first signals of mortality prematurely due to water stress(MEDFATE)and carbon starvation(3D-CMCC-FEM)scenarios.In conclusion,while management interventions may be considered a viable solution for the conservation of beech forests under future climate conditions at moister sites like Cansiglio,in drier sites like Mongiana conservation may not lie in management interventions alone.展开更多
Continental crust is the long-term achievements of Earth's evolution across billions of years.The continental rocks could have been modified by various types of geological processes,such as metamorphism,weathering...Continental crust is the long-term achievements of Earth's evolution across billions of years.The continental rocks could have been modified by various types of geological processes,such as metamorphism,weathering,and reworking.Therefore,physical or chemical properties of rocks through time record the composite effects of geological,biological,hydrological,and climatological processes.Temporal variations in these time series datasets could provide important clues for understanding the co-evolution of different layers on Earth.However,deciphering Earth's evolution in deep time is challenged by incompleteness,singularity,and intermittence of geological records associated with extreme geological events,hindering a rigorous assessment of the underlying coupling mechanisms.Here,we applied the recently developed local singularity analysis and wavelet analysis method to deep-time U-Pb age spectra and sedimentary abundance record across the past 3.5 Gyrs.Standard cross-correlation analysis suggests that the singularity records of marine sediment accumulations and magmatism intensity at continental margin are correlated negatively(R^(2)=0.8),with a delay of~100 Myr.Specifically,wavelet coherence analysis suggests a~500-800 Myr cycle of correlation between two records,implying a coupling between the major downward processes(subduction and recycling sediments)and upward processes(magmatic events)related to the aggregation and segregation of supercontinents.The results clearly reveal the long-term cyclic feedback mechanism between sediment accumulation and magmatism intensity through aggregation of supercontinents.展开更多
The melting of seasonal sea ice in Antarctica plays a pivotal role in the region’s carbon cycle,influencing global carbon storage and the exchange of carbon between the atmosphere and the ocean.However,the impact of ...The melting of seasonal sea ice in Antarctica plays a pivotal role in the region’s carbon cycle,influencing global carbon storage and the exchange of carbon between the atmosphere and the ocean.However,the impact of variability in the timing of seasonal sea ice retreat on the flux and composition of sinking particulate matter remains to be elucidated.In this study,we deployed sediment traps in Prydz Bay during the austral summers of 2019/2020 and 2020/2021,noting that sea ice melting occurred approximately one and a half months earlier in the former summer compared to the latter.We analyzed sediment trap data,which included total mass flux(TMF),particulate organic carbon(POC),biogenic silica(BSi),particulate inorganic carbon,and lithogenic particle(Litho)fluxes,as well as the stable isotopesδ^(13)C andδ^(15)N of particulate organic matter(POM).Additionally,we incorporated remote sensing data on sea ice concentration and chlorophyll a.This dramatic delay in sea ice melting timing could result in a significant increase in TMF,BSi and POC fluxes in the summer of 2020/2021 compared to 2019/2020.Elevated BSi fluxes and more ^(13)C-depleted POC in the austral summer of 2020/2021 suggest that the delayed melting of sea ice may have stimulated the productivity of centric diatoms.Furthermore,the higher BSi/POC ratio and more negativeδ^(15)N values of POM,along with a reduced presence of krill in the traps,indicate a diminished grazing pressure from zooplankton,which collectively enhanced the sedimentation efficiency of POC during the austral summer of 2020/2021.These findings highlight the critical role of sea ice melting timing in regulating productivity,flux and composition of sinking particulate matter in the Prydz Bay ecosystem,with significant implications for carbon cycling in polar oceans.展开更多
Carbon fluxes are essential indicators assessing vegetation carbon cycle functions.However,the extent and mechanisms by which climate change and human activities influence the spatiotemporal dynamics of carbon fluxes ...Carbon fluxes are essential indicators assessing vegetation carbon cycle functions.However,the extent and mechanisms by which climate change and human activities influence the spatiotemporal dynamics of carbon fluxes in arid oasis and non-oasis area remains unclear.Here,we assessed and predicted the future effects of climate change and human activities on carbon fluxes in the Hexi Corridor.The results showed that the annual average gross primary productivity(GPP),net ecosystem productivity(NEP),and ecosystem respiration(Reco)in the Hexi Corridor oasis increased by 263.91 g C·m^(-2)·yr^(-1),118.45 g C·m^(-2)·yr^(-1)and 122.46 g C·m^(-2)·yr^(-1),respectively,due to the expansion of the oasis area by 3424.84 km^(2) caused by human activities from 2000 to 2022.Both oasis and non-oasis arid ecosystems in the Hexi Corridor acted as carbon sinks.Compared to the non-oasis area,the carbon fluxes contributions of oasis area increased,ranging from 10.21%to 13.99%for GPP,8.50%to11.68%for NEP,and 13.34%to 17.13%for Reco.The contribution of the carbon flux from the oasis expansion area to the total carbon flux change in the Hexi Corridor was 30.96%(7.09 Tg C yr^(-1))for GPP,29.57%(3.39 Tg C yr^(-1))for NEP and 32.40%(3.58 Tg C yr^(-1))for Reco.The changes in carbon fluxes in the oasis area were mainly attributed to human activities(oasis expansion)and temperature,whereas non-oasis area was mainly due to climate factors.Moreover,the future increasing trends were observed for GPP(64.99%),NEP(66.29%)and Reco(82.08%)in the Hexi Corridor.This study provides new insights into the regulatory mechanisms of carbon cycle in the arid oasis and non-oasis area.展开更多
Microplastics(MPs)pollution has emerged as a critical global environmental issue,for which rivers serve as key conduits for the transport of MPs from land to ocean.There remained a lack of clarity regarding the charac...Microplastics(MPs)pollution has emerged as a critical global environmental issue,for which rivers serve as key conduits for the transport of MPs from land to ocean.There remained a lack of clarity regarding the characteristics and transport patterns of MPs pollution in diverse environmental media and seasons within a river basin.The Jiulong River basin in Fujian,southeast China was studied as case,whose spatial-temporal distribution,pollution characteristics,and transport dynamics of MPs in both surface water and groundwater were analyzed.Additionally,the features of MPs in different land use types during the dry season were examined.Results show that in wet season,the abundance of MPs in river water varied from 840 to 12300 p/m^(3),with an average of 3920 p/m^(3);in groundwater,the range was 740-1820 p/m^(3),averaging 1107 p/m^(3);and from 68 to 951 p/kg,with an average value of 265 p/kg in the soil(dry weight).In dry season,levels of MPs in river water ranged from 580 to 8880 p/m^(3),with an average of 4034 p/m^(3);groundwater exhibited a range of 860-14980 p/m^(3),averaging 3453 p/m^(3).Fibers consistently dominated the morphology of MPs,of which polyethylene terephthalate was identified as the predominant composition in each environmental medium.Our findings underscore the spatial and temporal variability in distribution and contamination characteristics of MPs across different media.Notably,MPs abundance in river water and groundwater exhibited a seasonal pattern,being higher in levels in dry season than in wet season.The downstream transport of MPs was facilitated by surface runoff,in which MPs in groundwater and surface water could complement to each other.Furthermore,population density and human activities were identified as influential factors on the distribution and abundance of MPs.This study revealed the order of magnitude of difference in annual estimates of MPs entering the sea among different models.Additionally,the interception volume by mangrove forest in the Jiulong River estuary was estimated approximately 1.51×10^(10)MPs particles per year.Ecological interception shall be considered when estimating the fluxes of MPs into the sea.展开更多
The North Water Polynya(NOW)is one of the largest and most productive polynyas in the Arctic.Compared to the surrounding sea ice,the combination of high winds and cold air,together with the thin ice or open water surf...The North Water Polynya(NOW)is one of the largest and most productive polynyas in the Arctic.Compared to the surrounding sea ice,the combination of high winds and cold air,together with the thin ice or open water surface of the NOW,produces large turbulent heat fluxes(THFs).The accurate estimation of these parameters requires high-resolution atmospheric data,which can be provided by the reanalysis products from different sources.In this study,we calculated the winter latent heat flux(LHF)and sensible heat flux(SHF)over the NOW and its surrounding sea ice area from 2005/2006 to 2015/2016 using high-resolution(15 km)Arctic System Reanalysis version 2(ASRv2)data and low-resolution(30 km)European Centre for Medium-Range Weather Forecasts ERA5 data.Results show that the LHF/SHF over the surrounding sea ice is about 82%/88%lower than over the NOW,as estimated using either dataset.Furthermore,within each area,the difference in the THFs estimated from the two datasets is small.The spatial distribution of the LHF/SHF estimated from both data sources is similar to that of sea ice concentration.The average LHF/SHF in the polynya obtained using ASRv2 data is only 5%/7%higher than that from the values obtained using ERA5 data.This is because the wind speed and air temperature from the ASRv2 data are higher than those of ERA5,and their effects on the THFs can cancel each other out.Furthermore,the estimated THFs do not necessarily improve with the refined resolution of ASRv2.展开更多
Global warming and nitrogen(N)deposition have a profound impact on greenhouse gas(GHG)fluxes and consequently,they also affect climate change.However,the global combined effects of warming and N addition on GHG fluxes...Global warming and nitrogen(N)deposition have a profound impact on greenhouse gas(GHG)fluxes and consequently,they also affect climate change.However,the global combined effects of warming and N addition on GHG fluxes remain to be fully understood.To address this knowledge gap,a globalmeta-analysis of 197 datasets was performed to assess the response of GHG fluxes to warming and N addition and their interactions under various climate and experimental conditions.The results indicate that warming significantly increased CO_(2)emissions,while N addition and the combined warming and N addition treatments had no impact on CO_(2)emissions.Moreover,both warming and N addition and their interactions exhibited positive effects on N_(2)O emissions.Under the combined warming and N addition treatments,warming was observed to exert a positive main effect on CO_(2)emissions,while N addition had a positive main effect on N_(2)O emissions.The interactive effects of warming and N addition exhibited antagonistic effects on CO_(2),N_(2)O,and CH_(4)emissions,with CH_(4)uptake dominated by additive effects.Furthermore,we identified biome and climate factors as the two treatments.These findings indicate that both warming and N addition substantially impact soil GHG fluxes and highlight the urgent need to investigate the influence of the combination of warming and N addition on terrestrial carbon and N cycling under ongoing global change.展开更多
The Antarctic Slope Current(ASC)links the processes occurring in the coast area with the global ocean by modulating the flow across the continental slope,which influences global overturning circulation and the mass ba...The Antarctic Slope Current(ASC)links the processes occurring in the coast area with the global ocean by modulating the flow across the continental slope,which influences global overturning circulation and the mass balance of the Antarctic ice shelves.This paper aims to explore the effects of wind and buoyancy fluxes on the long-term changes in the ASC using observation and reanalysis datasets.From 1993 to 2022,the ASC accelerated in all seasons,particularly in austral autumn,and was accompanied with the advancement of the strong flow.The positive buoyancy flux anomaly generates a low-density anomaly,which is accumulated by the prevailing surface easterly,maintaining a sharp density front along the continental slope.The heat flux intensifies the positive trend of buoyancy flux in summer and autumn,increasing the input of the lighter density anomaly into the ocean and advancing the strong flow of ASC.Compared with the annual mean,the additional acceleration of the ASC in autumn is mainly due to the contribution of the barotropic component,which could be explained by the local momentum input from the weakly enhanced local surface wind.The acceleration of the ASC is primarily driven by the positive trend of the buoyancy flux,while the influence of the wind on its seasonal variability becomes more significant due to the contribution of the local surface wind in autumn.展开更多
Peng et al.in[Phys.Rev.Research,2020,2(3):033089,11 pp.]formulated one-way fluxes for a general chemical reaction far from equilibrium,with arbitrary complex mechanisms,multiple intermediates,and internal kinetic cycl...Peng et al.in[Phys.Rev.Research,2020,2(3):033089,11 pp.]formulated one-way fluxes for a general chemical reaction far from equilibrium,with arbitrary complex mechanisms,multiple intermediates,and internal kinetic cycles.They defined the limit of the ratio of mesoscopic one-way fluxes and the volume of the tank reactor when the volume tends to infinity as macroscopic one-way fluxes,but a rigorous proof of existence of the limit is still awaiting.In this article,we fill this gap under a mild hypothesis:the Markov chain associated with the chemical master equation has finite states and any two columns in the stoichiometric matrices are not identical.In fact,an explicit expression of the limit is obtained.展开更多
Accurate quantification of carbon and water fluxes dynamics in arid and semi-arid ecosystems is a critical scientific challenge for regional carbon neutrality assessments and sustainable water resource management.In t...Accurate quantification of carbon and water fluxes dynamics in arid and semi-arid ecosystems is a critical scientific challenge for regional carbon neutrality assessments and sustainable water resource management.In this study,we developed a multi-flux global sensitivity discriminant index(D_(sen))by integrating the Biome-BGCMuSo model with eddy covariance flux observations.This index was combined with a Bayesian optimization algorithm to conduct parameter optimization.The results demonstrated that:(1)Sensitivity analysis identified 13 highly sensitive parameters affecting carbon and water fluxes.Among these,the canopy light extinction coefficient(k)and the fraction of leaf N in Rubisco(FLNR)exhibited significantly higher sensitivity to carbon fluxes(GPP,NEE,Reco;D_(sen)>10%)compared to water flux(ET).This highlights the strong dependence of carbon cycle simulations on vegetation physiological parameters.(2)The Bayesian optimization framework efficiently converged 30 parameter spaces within 50 iterations,markedly improving carbon fluxes simulation accuracy.The Kling-Gupta efficiency(KGE)values for Gross Primary Production(GPP),Net Ecosystem Exchange(NEE),and Total Respiration(Reco)increased by 44.94%,69.23%and 123%,respectively.The optimization prioritized highly sensitive parameters,underscoring the necessity of parameter sensitivity stratification.(3)The optimized model effectively reproduced carbon sink characteristics in mountain meadows during the growing season(cumulative NEE=-375 g C/m^(2)).It revealed synergistic carbon-water fluxes interactions governed by coupled photosynthesis-stomatal pathways and identified substrate supply limitations on heterotrophic respiration.This study proposes a novel multi-flux sensitivity index and an efficient optimization framework,elucidating the coupling mechanisms between vegetation physiological regulation(k,FLNR)and environmental stressors(VPD,SWD)in carbonwater cycles.The methodology offers a practical approach for arid ecosystem model optimization and provides theoretical insights for grassland management through canopy structure regulation and water-use efficiency enhancement.展开更多
Understanding the characteristics and variations of heat exchange and evaporation of lakes is important for regional water resource management and sustainable development.Based on eddy covariance measurements over Lak...Understanding the characteristics and variations of heat exchange and evaporation of lakes is important for regional water resource management and sustainable development.Based on eddy covariance measurements over Lake Vanajavesi in southern Finland,characteristics of energy fluxes and cold frontal effects on energy exchange were investigated.The lake acted as a heat sink in spring and summer and a heat source in winter.The latent heat flux reached its minimum value in the morning and peaked in the afternoon.The diurnal variation of sensible heat flux was opposite to that of latent heat flux.Impact factors for the sensible heat flux were mainly the lake-air temperature difference and the product of lake-air temperature difference and wind speed.The latent heat flux was mainly affected by the vapor pressure deficit and the product of vapor pressure deficit and wind speed.The annual mean values of bulk transfer coefficients for momentum,heat,and water vapor were 1.98×10^(-3),1.62×10^(-3),and 1.31×10^(-3),respectively.Bulk transfer coefficients for heat and water vapor were not equal,indicating that the parameterization of energy exchange in numerical models,where the assumption that the heat coefficient equals the water vapor coefficient needs improvement.During the ice-free season,cold fronts resulted in 28 sensible heat pulses and 17 latent heat pulses,contributing to 50.59%and 34.89%of sensible and latent heat exchange in Lake Vanajavesi.These results indicate that cold fronts significantly impact the surface energy budget and evaporation over lakes.展开更多
The noise feature of a single-mode class-A laser amplifier is investigated by solving the Maxwell–Bloch equations of motion in the presence of the fluctuation force of cavity Langevin.The aim is to calculate the simu...The noise feature of a single-mode class-A laser amplifier is investigated by solving the Maxwell–Bloch equations of motion in the presence of the fluctuation force of cavity Langevin.The aim is to calculate the simultaneous fluctuations that are superimposed on the amplitude and phase of the cavity electric field, as well as the atomic population inversion. The correlation function of these fluctuations yields the amplitude, phase, and spontaneous emission noise fluxes, respectively. The amplitude and spontaneous emission noise fluxes exhibit the Lorentzian profiles in both the below-threshold state and the injection-locking region of the above-threshold state. While noise is typically viewed negatively in science and engineering, this research highlights its positive role as a valuable tool for measuring the optical properties of a laser amplifier. For instance, the degree of first-order temporal coherence(DFOTC) is derived by taking the Fourier transform of the amplitude noise flux. The damping rate of DFOTC is associated with the coherence time of the light emitted by the laser amplifier. Furthermore, the uncertainty relation between noise bandwidth and coherence time is confirmed. Finally, it is demonstrated that the input pumping noise flux, together with the output amplitude and spontaneous emission noise fluxes, satisfy the principle of flux conservation.展开更多
Steel–flux reactions involving the high aluminum(0.75–3.85 wt.%Al)low manganese(2.2 wt.%Mn)steel and the 18 wt.%SiO_(2)–18 wt.%Al2O3 mold flux were investigated.The results indicated that the reaction rate increase...Steel–flux reactions involving the high aluminum(0.75–3.85 wt.%Al)low manganese(2.2 wt.%Mn)steel and the 18 wt.%SiO_(2)–18 wt.%Al2O3 mold flux were investigated.The results indicated that the reaction rate increased when the initial aluminum content increased from 0.76 to 3.85 wt.%.Utilizing the two-film theory,a steel–flux reaction kinetic model controlled by mass transfer was established,which considered the influence of the initial composition on the density of liquid steel and flux.The mass transfer of aluminum in the steel phase was the reaction rate-determining step.It was confirmed that the mass transfer coefficient of Al was 1.87×10^(−4).The predicted results of the kinetic model were consistent and reliable with the experimental results.Thermodynamic equilibrium calculation was performed using FactSage 8.2,which was compared with the steel and flux final composition after 30 min.The content of initial aluminum in the liquid steel played a critical role in the SiO_(2)equilibrium content of the mold flux.In addition,the steel–flux reaction between[Al]and(SiO_(2))occurred with the initial SiO_(2)content in the mold flux lower than 3 wt.%.展开更多
The flux of dissolved inorganic nitrogen(DIN),predominantly nitrate(NO_(3)^(-))and ammonium(NH_(4)^(+)),from land to coastal waters via rivers is commonly estimated simply by multiplying water flux with nitrogen conce...The flux of dissolved inorganic nitrogen(DIN),predominantly nitrate(NO_(3)^(-))and ammonium(NH_(4)^(+)),from land to coastal waters via rivers is commonly estimated simply by multiplying water flux with nitrogen concentration.Understanding DIN fluxes in gated estuaries is critical as these systems often serve as hotspots for nutrient transformations,influencing coastal water quality and ecosystem health.However,the subsequent interactions involving NO_(3)^(-)and NH_(4)^(+)adsorption or desorption on suspended sediments are often overlooked.To better understand the impact of these interactions on the overall NO_(3)^(-)and NH_(4)^(+)sorption or desorption and subsequently,the mobility and transport to the coastal zone,we conducted a series of NO_(3)^(-)and NH_(4)^(+)adsorption and desorption experiments.These experiments involved varying suspended sediment concentrations,particle sizes,salinities,and sea-salt ions to assess their potential effects.Results indicate that desorption of NO_(3)^(-)and NH_(4)^(+)from suspended sediments is more prominent than adsorption,with NH_(4)^(+)desorption being particularly significant.Notably,at low suspended particle concentrations and high salinity,NH_(4)^(+)desorption from sediments increased markedly,which further amplified in polyhaline conditions.This effect could result from ion pairing between NH_(4)^(+)and seawater anions,along with competition from seawater cations for sediment cation exchange sites,enhancing NH_(4)^(+)diffusion from estuarine sediments,and the elevated NH_(4)^(+)release could promote DIN transport to nearshore waters,especially in gated estuaries where sediment resuspension occurs.Given the critical role of NH_(4)^(+)in estuarine nitrogen cycling,ignoring these dynamics could lead to underestimations of DIN transport in river-estuary systems.Therefore,incorporating sediment dynamics into DIN flux estimations is crucial for accurately assessing nitrogen transport in gated estuaries.展开更多
Vorticity is locally generated on a boundary at a rate measured by the boundary vorticity flux(BVF),which can be further decomposed into the sum of the orbital rotation and the generalized spin(specifically,the sum of...Vorticity is locally generated on a boundary at a rate measured by the boundary vorticity flux(BVF),which can be further decomposed into the sum of the orbital rotation and the generalized spin(specifically,the sum of shear and streaming vorticity)under the field description.For an incompressible viscous flow interacting with a stationary wall,the full expressions of the boundary fluxes of the orbital rotation and the spin are derived,for the first time,to elucidate their boundary creation mechanisms.Then,these new findings are successfully extended to the study of the boundary enstrophy dynamics,as well as the Lyman vorticity dynamics as an alternative interpretation to the boundary vorticity dynamics.Interestingly,it is found that the boundary coupling of the longitudinal and transverse processes is only embodied in the boundary spin flux,which is definitely not responsible for the generation of the boundary orbital-rotation flux.In addition,the boundary fluxes of enstrophy are directly associated with the boundary source of the second principal invariant of the velocity gradient tensor(VGT)and the two quadratic forms representing the spin-geometry interaction.The present exposition provides a new perspective and an additional dimension for understanding the vorticity dynamics on boundaries,which could be valuable in clarifying the formation mechanisms of near-wall coherent structures and flow noise at the fundamental level.展开更多
Surface-latent heat(LE)and sensible heat(SH)fluxes play a pivotal role in governing hydrological,biological,geochemical,and ecological processes on the land surface in the Tibetan Plateau.However,to accurately assess ...Surface-latent heat(LE)and sensible heat(SH)fluxes play a pivotal role in governing hydrological,biological,geochemical,and ecological processes on the land surface in the Tibetan Plateau.However,to accurately assess and understand the spatial distribution of LE and SH fluxes across different underlying surfaces,it is crucial to verify the validity and reliability of ERA-5,GLDAS,and MODIS data against ground measurements obtained from the Flux Net micrometeorological tower network.This study analyzed the spatial patterns of LE and SH over the Tibetan Plateau using data from ERA-5,GLDAS,and MODIS.The results were compared with ground measurements from Flux Net tower observations on different underlying surfaces,and five statistical parameters(Pearson's r,LR slope,RMSE,MBE,and MAE)were used to validate the data.The results showed that:(1)MODIS LE data and ERA-5 SH data exhibited the closest agreement with ground observations,as indicated by their lowest root mean square error and mean bias area values.(2)The accuracy of ERA-5 SH was the highest in meadows and steppes,while GLDAS SH performed optimally in shrublands.Notably,MODIS LE consistently outperformed the other datasets across all vegetation types.(3)The spatial distribution of LE and SH displayed considerable heterogeneity,contingent upon the specific data sources and underlying surfaces.Notably,there was a contrasting trend between GLDAS and ERA-5,as well as MODIS,in terms of SH distribution in the shrubland.In shrublands and meadows,MODIS SH and LE exhibited more pronounced changes than ERA-5 and GLDAS.Additionally,ERA-5 SH demonstrated the opposite variation in meadow and steppe regions compared to GLDAS and MODIS.展开更多
Gaseous nitrous acid(HONO)is a critical contributor to daytime hydroxyl radical in the troposphere.Livestock farming has been recognized as an overlooked HONO source,but the lack of detailed flux measurements from liv...Gaseous nitrous acid(HONO)is a critical contributor to daytime hydroxyl radical in the troposphere.Livestock farming has been recognized as an overlooked HONO source,but the lack of detailed flux measurements from livestock and poultry wastes would cause uncertainties in modeling its environmental impacts.Here,based on field flux measurements and laboratory experiments,we observed substantial HONO emissions from the composting of swine feces and chicken manure in the warm season,which might be mainly attributed to nitrification process in livestock and poultry wastes.The HONO emission from chicken manure was found to bemuch higher than that from swine feces,and the higher NH3 emission but lower N2O and NO emissions fromchicken manurewere also observed.Considering that the interaction among these nitrogen species during nitrification process,the obviously lower HONO emission from swine feces was likely to be explained by the lack of the total ammonia nitrogen and H+donors in swine feces.Temperature is also a key factor that influences the HONO emission from livestock wastes.In addition,the total HONO emission from swine feces in Chinawas estimated to be approximately 107.7 Gg-N/yr according to the national swine amounts,which is comparable to the national soil HONO emissions,underscoring its non-negligible contribution to regional air quality.Therefore,effective emission control of HONO fromlivestock and poultry wastes should be carried out to further improve air quality in China.展开更多
A growing global demand exists to formulate plans to lessen the greenhouse gas emissions produced by agricultural activities.The purpose of this study was to uncovered the changes in soil CO_(2)fluxes under varying sc...A growing global demand exists to formulate plans to lessen the greenhouse gas emissions produced by agricultural activities.The purpose of this study was to uncovered the changes in soil CO_(2)fluxes under varying scenarios including nitrogen fertilization rates,irrigation rates,and air temperatures in the Hetao Irrigation District(HID)over the 38-year period.DAYCENT model was used to predict carbon dioxide(CO_(2))fluxes from cultivated soils in the HID,Inner Mongolia from^(2)023 to 2060(the year of achieving the"carbon neutrality"goal)in this study.Results showed that mean soil CO_(2)fluxes in the sunflower field[1035.13 g/(m^(2).yr)]were significantly lower than those in the maize field[1405.54 g/(m^(2).yr)].An increase in nitrogen fertilization rate led to a significant escalation in soil CO_(2)fluxes.Moreover,elevating irrigation rates for washing salts by irrigation(WSBI)diminished soil CO_(2)fluxes in the sunflower field while amplifying them in the maize field.A rise in air temperature resulted in an increase in soil CO_(2)fluxes from the maize field,with annual increases observed,but a reduction in soil CO_(2)fluxes from the sunflower field.The sunflower fields in the HID have a more substantial advantage than the corn fields in mitigating soil CO_(2)emissions.展开更多
CH4 is one of the most important greenhouse gases, and mainly comes from soils in forest ecosystems. The objective of this study was to determine the effects of forest management practices such as understory removal a...CH4 is one of the most important greenhouse gases, and mainly comes from soils in forest ecosystems. The objective of this study was to determine the effects of forest management practices such as understory removal and N-fixing species （Cassia alata） addition, on soil CH4 fluxes in four forest plantations in southern China. Fluxes of CH4 were measured in Eucalyptus urophylla plantation （B1）, Acacia crassi-carpa plantation （B2）, 10-native-species-mixed plantation （B3）, and 30-native-species-mixed plantation （B4） stands using the static chamber method in Southern China. Four forest management treatments, includ-ing （1） understory removal and replacement with C. alata （UR＋CA）; （2） understory removal only （UR）; （3） C. alata addition only （CA）; and （4） control without any disturbances （CK）, were applied in the four forest plantations. The results showed that plantation types had a significant effect on soil CH4 fluxes. B1 and B2 tended to be CH4 consumers, while B3 and B4 inclined to be CH4 producers. UR decreased CH4 fluxes by providing a more optimal soil temperature and moisture regime for mi-croorganism community and increasing substrate mineralization. How-ever, CA enhanced CH4 fluxes in B1 and B2 for N-fixing function of C. alata while lowered CH4 fluxes in B3 and B4. Soil CH4 flux rate was significantly related to soil temperature and moisture conditions in the top 10-cm soil layer. Furthermore, the quality of substrates, such as Soil Organic Carbon （SOC） and mineral N might also be important driving factors for CH4 fluxes. This study improved our understanding on CH4 fluxes in plantations under different management practices such as UR and CA.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52204345 and 52474361)the Scientific Research Innovation Projects of Graduate Student of Jiangsu province,China(No.KYCX24_4184)。
文摘The large-scale production of high-Ti steels is limited by the formation of Ti-containing oxides or nitrides in steel-slag reactions during continuous casting.These processes degrade mold flux properties,clog submerged entry nozzles,form floaters in the molds,and produce various surface defects on the cast slabs.This review summarizes the effects of nonmetallic inclusions on traditional CaO-SiO_(2)-based(CS)mold fluxes and novel CaO-Al_(2)O_(3)-based(CA)low-or non-reactive fluxes containing TiO_(2),BaO,and B_(2)O_(3)additives to avoid undesirable steel,slag,and inclusion reactions,with the aim of providing a new perspective for research and practice related to balancing the lubrication and heat transfer of mold fluxes to promote smooth operation and reduce surface defects on cast slabs.For traditional CS mold flux,although the addition of solvents such as Na_(2)O,Li_(2)O,and B_(2)O_(3)can enhance flowability,steel-slag reactions persist,limiting the effectiveness of CS mold fluxes in high-Ti steel casting.Low-or non-reactive CA mold fluxes with reduced SiO_(2)content are a research focus,where adding other components can significantly change flux characteristics.Replacing CaO with BaO can lower the melting point and inhibit crystallization,allowing the flux to maintain good flowability at low temperatures.Replacing SiO_(2)with TiO_(2)can stabilize the viscosity and enhance heat transfer.To reduce the environmental impact,fluorides are replaced with components such as TiO_(2),B_(2)O_(3),BaO,Li_(2)O,and Na_(2)O for F-frce mold fluxes with similar lubrication,crystallization,and heat-transfer effects.When TiO_(2)replaces CaF_(2),it stabilizes the viscosity and enhances the heat conductivity,forming CaTiO_(3)and CaSiTiO_(5)phases instead of cuspidine to control crystallization.B_(2)O_(3)lowers the melting point and suppresses crystallization,forming phases such as Ca_(3)B_(2)O_(6)and Ca_(11)Si_(4)B_(2)O_(22).BaO introduces non-bridging oxygen to reduce viscosity and ensure flux flowability at low temperatures.However,further studies are required to determine the optimal mold flux compositions corresponding to the steel grades and the interactions between the various components of the mold flux.In the future,the practical application of new mold fluxes for high-Ti steel will become the focus of further verification to achieve a balance between lubrication and heat transfer,which is expected to minimize the occurrence of casting problems and slab defects.
基金the Institute Research Centre for Ecological and Forestry Applications (CREAF) of Barcelona that supported the research by the Spanish “Ministerio de Ciencia e Innovacio'n”(MCIN/AEI/ 10.13039/501100011033) (grant agreement No. PID 2021-126679OBI00)partially supported by MIUR Project (PRIN 2020) between WATER and carbon cycles during droug“Unraveling interactionsht and their impact on water resources and forest and grassland ecosySTEMs in the Mediterranean climate (WATERSTEM)”(Project number: 20202WF53Z),“WAFER”at CNR (Consiglio Nazionale delle Ricerche)+3 种基金Priwitzer et al. (2014) (cod. 2020E52THS)-Research Projects of National Relevance funded by the Italian Ministry of University and Research entitled: “Multi-scale observations to predict Forest response to pollution and climate change”(MULTIFOR, project number: 2020E52THS)funding by the project OptForEU Horizon Europe research and innovation programme under grant agreement No. 101060554the project funded under the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.4-Call for tender No. 3138 of December 16, 2021, rectified by Decree n.3175 of December 18, 2021 of Italian Ministry of UniversityResearch funded by the European UnionationEU under award Number: Project code CN_00000033–Next Gener, Concession Decree No. 1034 of June 17, 2022 adopted by the Italian Ministry of University and Research, CUP B83C22002930006, Project title“National Biodiversity Future Centre-NBFC”
文摘The consequences of climate change continue to threaten European forests,particularly for species located at the edges of their latitudinal and altitudinal ranges.While extensively studied in Central Europe,European beech forests require further investigation to understand how climate change will affect these ecosystems in Mediterranean areas.Proposed silvicultural options increasingly aim at sustainable management to reduce biotic and abiotic stresses and enhance these forest ecosystems'resistance and resilience mechanisms.Process-based models(PBMs)can help us to simulate such phenomena and capture early stress signals while considering the effect of different management approaches.In this study,we focus on estimating sensitivity of two state-of-the-art PBMs forest models by simulating carbon and water fluxes at the stand level to assess productivity changes and feedback resulting from different climatic forcings as well as different management regimes.We applied the 3D-CMCC-FEM and MEDFATE forest models for carbon(C)and water(H_(2)O)fluxes in two sites of the Italian peninsula,Cansiglio in the north and Mongiana in the south,under managed vs.unmanaged scenarios and under current climate and different climatic scenarios(RCP4.5 and RCP8.5).To ensure confidence in the models’results,we preliminary evaluated their performance in simulating C and H_(2)O flux in three additional beech forests of the FLUXNET network along a latitudinal gradient spanning from Denmark to central Italy.The 3D-CMCC-FEM model achieved R^(2)values of 0.83 and 0.86 with RMSEs of 2.53 and 2.05 for C and H_(2)O fluxes,respectively.MEDFATE showed R^(2)values of 0.76 and 0.69 with RMSEs of 2.54 and 3.01.At the Cansiglio site in northern Italy,both models simulated a general increase in C and H_(2)O fluxes under the RCP8.5 climate scenario compared to the current climate.Still,no benefit in managed plots compared to unmanaged ones,as the site does not have water availability limitations,and thus,competition for water is low.At the Mongiana site in southern Italy,both models predict a decrease in C and H_(2)O fluxes and sensitivity to the different climatic forcing compared to the current climate;and an increase in C and H_(2)O fluxes when considering specific management regimes compared to unmanaged scenarios.Conversely,under unmanaged scenarios plots are simulated to experience first signals of mortality prematurely due to water stress(MEDFATE)and carbon starvation(3D-CMCC-FEM)scenarios.In conclusion,while management interventions may be considered a viable solution for the conservation of beech forests under future climate conditions at moister sites like Cansiglio,in drier sites like Mongiana conservation may not lie in management interventions alone.
基金supported by the National Natural Science Foundation of China(No.42050103)。
文摘Continental crust is the long-term achievements of Earth's evolution across billions of years.The continental rocks could have been modified by various types of geological processes,such as metamorphism,weathering,and reworking.Therefore,physical or chemical properties of rocks through time record the composite effects of geological,biological,hydrological,and climatological processes.Temporal variations in these time series datasets could provide important clues for understanding the co-evolution of different layers on Earth.However,deciphering Earth's evolution in deep time is challenged by incompleteness,singularity,and intermittence of geological records associated with extreme geological events,hindering a rigorous assessment of the underlying coupling mechanisms.Here,we applied the recently developed local singularity analysis and wavelet analysis method to deep-time U-Pb age spectra and sedimentary abundance record across the past 3.5 Gyrs.Standard cross-correlation analysis suggests that the singularity records of marine sediment accumulations and magmatism intensity at continental margin are correlated negatively(R^(2)=0.8),with a delay of~100 Myr.Specifically,wavelet coherence analysis suggests a~500-800 Myr cycle of correlation between two records,implying a coupling between the major downward processes(subduction and recycling sediments)and upward processes(magmatic events)related to the aggregation and segregation of supercontinents.The results clearly reveal the long-term cyclic feedback mechanism between sediment accumulation and magmatism intensity through aggregation of supercontinents.
基金The National Key Research and Development Program of China under contract No.2022YFE0136500the Scientific Research Fund of the Second Institute of Oceanography,Ministry of Natural Resources,under contract Nos JG2212 and JG2211+2 种基金the National Natural Science Foundation of China under contract Nos 42276255,41976228,and 42176227the National Polar Special Program“Impact and Response of Antarctic Seas to Climate Change”under contract Nos IRASCC 01-01-02 and IRASCC 02-02the China Scholarship Council under contract No.201704180017.
文摘The melting of seasonal sea ice in Antarctica plays a pivotal role in the region’s carbon cycle,influencing global carbon storage and the exchange of carbon between the atmosphere and the ocean.However,the impact of variability in the timing of seasonal sea ice retreat on the flux and composition of sinking particulate matter remains to be elucidated.In this study,we deployed sediment traps in Prydz Bay during the austral summers of 2019/2020 and 2020/2021,noting that sea ice melting occurred approximately one and a half months earlier in the former summer compared to the latter.We analyzed sediment trap data,which included total mass flux(TMF),particulate organic carbon(POC),biogenic silica(BSi),particulate inorganic carbon,and lithogenic particle(Litho)fluxes,as well as the stable isotopesδ^(13)C andδ^(15)N of particulate organic matter(POM).Additionally,we incorporated remote sensing data on sea ice concentration and chlorophyll a.This dramatic delay in sea ice melting timing could result in a significant increase in TMF,BSi and POC fluxes in the summer of 2020/2021 compared to 2019/2020.Elevated BSi fluxes and more ^(13)C-depleted POC in the austral summer of 2020/2021 suggest that the delayed melting of sea ice may have stimulated the productivity of centric diatoms.Furthermore,the higher BSi/POC ratio and more negativeδ^(15)N values of POM,along with a reduced presence of krill in the traps,indicate a diminished grazing pressure from zooplankton,which collectively enhanced the sedimentation efficiency of POC during the austral summer of 2020/2021.These findings highlight the critical role of sea ice melting timing in regulating productivity,flux and composition of sinking particulate matter in the Prydz Bay ecosystem,with significant implications for carbon cycling in polar oceans.
基金The Foundation for Distinguished Young Scholars of Gansu Province,No.22JR5RA046Key Research Program of Gansu Province,No.23ZDKA0004+2 种基金The Joint Funds of the National Natural Science Foundation of China,No.U22A202690Interdisciplinary Youth Team Project from the Key Laboratory of Cryospheric Science and Frozen Soil Engineering,No.CSFSE-ZQ-2408The Youth Innovation Promotion Association CAS to X.W.,No.2020422。
文摘Carbon fluxes are essential indicators assessing vegetation carbon cycle functions.However,the extent and mechanisms by which climate change and human activities influence the spatiotemporal dynamics of carbon fluxes in arid oasis and non-oasis area remains unclear.Here,we assessed and predicted the future effects of climate change and human activities on carbon fluxes in the Hexi Corridor.The results showed that the annual average gross primary productivity(GPP),net ecosystem productivity(NEP),and ecosystem respiration(Reco)in the Hexi Corridor oasis increased by 263.91 g C·m^(-2)·yr^(-1),118.45 g C·m^(-2)·yr^(-1)and 122.46 g C·m^(-2)·yr^(-1),respectively,due to the expansion of the oasis area by 3424.84 km^(2) caused by human activities from 2000 to 2022.Both oasis and non-oasis arid ecosystems in the Hexi Corridor acted as carbon sinks.Compared to the non-oasis area,the carbon fluxes contributions of oasis area increased,ranging from 10.21%to 13.99%for GPP,8.50%to11.68%for NEP,and 13.34%to 17.13%for Reco.The contribution of the carbon flux from the oasis expansion area to the total carbon flux change in the Hexi Corridor was 30.96%(7.09 Tg C yr^(-1))for GPP,29.57%(3.39 Tg C yr^(-1))for NEP and 32.40%(3.58 Tg C yr^(-1))for Reco.The changes in carbon fluxes in the oasis area were mainly attributed to human activities(oasis expansion)and temperature,whereas non-oasis area was mainly due to climate factors.Moreover,the future increasing trends were observed for GPP(64.99%),NEP(66.29%)and Reco(82.08%)in the Hexi Corridor.This study provides new insights into the regulatory mechanisms of carbon cycle in the arid oasis and non-oasis area.
基金Supported by the National Natural Science Foundation of China(No.41961144011)。
文摘Microplastics(MPs)pollution has emerged as a critical global environmental issue,for which rivers serve as key conduits for the transport of MPs from land to ocean.There remained a lack of clarity regarding the characteristics and transport patterns of MPs pollution in diverse environmental media and seasons within a river basin.The Jiulong River basin in Fujian,southeast China was studied as case,whose spatial-temporal distribution,pollution characteristics,and transport dynamics of MPs in both surface water and groundwater were analyzed.Additionally,the features of MPs in different land use types during the dry season were examined.Results show that in wet season,the abundance of MPs in river water varied from 840 to 12300 p/m^(3),with an average of 3920 p/m^(3);in groundwater,the range was 740-1820 p/m^(3),averaging 1107 p/m^(3);and from 68 to 951 p/kg,with an average value of 265 p/kg in the soil(dry weight).In dry season,levels of MPs in river water ranged from 580 to 8880 p/m^(3),with an average of 4034 p/m^(3);groundwater exhibited a range of 860-14980 p/m^(3),averaging 3453 p/m^(3).Fibers consistently dominated the morphology of MPs,of which polyethylene terephthalate was identified as the predominant composition in each environmental medium.Our findings underscore the spatial and temporal variability in distribution and contamination characteristics of MPs across different media.Notably,MPs abundance in river water and groundwater exhibited a seasonal pattern,being higher in levels in dry season than in wet season.The downstream transport of MPs was facilitated by surface runoff,in which MPs in groundwater and surface water could complement to each other.Furthermore,population density and human activities were identified as influential factors on the distribution and abundance of MPs.This study revealed the order of magnitude of difference in annual estimates of MPs entering the sea among different models.Additionally,the interception volume by mangrove forest in the Jiulong River estuary was estimated approximately 1.51×10^(10)MPs particles per year.Ecological interception shall be considered when estimating the fluxes of MPs into the sea.
基金supported by the National Key Research and Development Program of China(Grant no.2024YFB3908004).
文摘The North Water Polynya(NOW)is one of the largest and most productive polynyas in the Arctic.Compared to the surrounding sea ice,the combination of high winds and cold air,together with the thin ice or open water surface of the NOW,produces large turbulent heat fluxes(THFs).The accurate estimation of these parameters requires high-resolution atmospheric data,which can be provided by the reanalysis products from different sources.In this study,we calculated the winter latent heat flux(LHF)and sensible heat flux(SHF)over the NOW and its surrounding sea ice area from 2005/2006 to 2015/2016 using high-resolution(15 km)Arctic System Reanalysis version 2(ASRv2)data and low-resolution(30 km)European Centre for Medium-Range Weather Forecasts ERA5 data.Results show that the LHF/SHF over the surrounding sea ice is about 82%/88%lower than over the NOW,as estimated using either dataset.Furthermore,within each area,the difference in the THFs estimated from the two datasets is small.The spatial distribution of the LHF/SHF estimated from both data sources is similar to that of sea ice concentration.The average LHF/SHF in the polynya obtained using ASRv2 data is only 5%/7%higher than that from the values obtained using ERA5 data.This is because the wind speed and air temperature from the ASRv2 data are higher than those of ERA5,and their effects on the THFs can cancel each other out.Furthermore,the estimated THFs do not necessarily improve with the refined resolution of ASRv2.
基金supported by Ningxia Key Research and Development Fund Project of China(No.2023BCF01048)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2023-JC-YB-182).
文摘Global warming and nitrogen(N)deposition have a profound impact on greenhouse gas(GHG)fluxes and consequently,they also affect climate change.However,the global combined effects of warming and N addition on GHG fluxes remain to be fully understood.To address this knowledge gap,a globalmeta-analysis of 197 datasets was performed to assess the response of GHG fluxes to warming and N addition and their interactions under various climate and experimental conditions.The results indicate that warming significantly increased CO_(2)emissions,while N addition and the combined warming and N addition treatments had no impact on CO_(2)emissions.Moreover,both warming and N addition and their interactions exhibited positive effects on N_(2)O emissions.Under the combined warming and N addition treatments,warming was observed to exert a positive main effect on CO_(2)emissions,while N addition had a positive main effect on N_(2)O emissions.The interactive effects of warming and N addition exhibited antagonistic effects on CO_(2),N_(2)O,and CH_(4)emissions,with CH_(4)uptake dominated by additive effects.Furthermore,we identified biome and climate factors as the two treatments.These findings indicate that both warming and N addition substantially impact soil GHG fluxes and highlight the urgent need to investigate the influence of the combination of warming and N addition on terrestrial carbon and N cycling under ongoing global change.
基金The National Natural Science Foundation of China under contract Nos 42376256,42230405,and 41576020.
文摘The Antarctic Slope Current(ASC)links the processes occurring in the coast area with the global ocean by modulating the flow across the continental slope,which influences global overturning circulation and the mass balance of the Antarctic ice shelves.This paper aims to explore the effects of wind and buoyancy fluxes on the long-term changes in the ASC using observation and reanalysis datasets.From 1993 to 2022,the ASC accelerated in all seasons,particularly in austral autumn,and was accompanied with the advancement of the strong flow.The positive buoyancy flux anomaly generates a low-density anomaly,which is accumulated by the prevailing surface easterly,maintaining a sharp density front along the continental slope.The heat flux intensifies the positive trend of buoyancy flux in summer and autumn,increasing the input of the lighter density anomaly into the ocean and advancing the strong flow of ASC.Compared with the annual mean,the additional acceleration of the ASC in autumn is mainly due to the contribution of the barotropic component,which could be explained by the local momentum input from the weakly enhanced local surface wind.The acceleration of the ASC is primarily driven by the positive trend of the buoyancy flux,while the influence of the wind on its seasonal variability becomes more significant due to the contribution of the local surface wind in autumn.
基金partially supported by NSFC(Nos.11701265,11961033).
文摘Peng et al.in[Phys.Rev.Research,2020,2(3):033089,11 pp.]formulated one-way fluxes for a general chemical reaction far from equilibrium,with arbitrary complex mechanisms,multiple intermediates,and internal kinetic cycles.They defined the limit of the ratio of mesoscopic one-way fluxes and the volume of the tank reactor when the volume tends to infinity as macroscopic one-way fluxes,but a rigorous proof of existence of the limit is still awaiting.In this article,we fill this gap under a mild hypothesis:the Markov chain associated with the chemical master equation has finite states and any two columns in the stoichiometric matrices are not identical.In fact,an explicit expression of the limit is obtained.
基金jointly funded by the National Natural Science Foundation of China(Grant No.42161024)the Central Financial Forestry and Grassland Science and Technology Extension Demonstration Project(2025)(Grant No.Xin[2025]TG 09)。
文摘Accurate quantification of carbon and water fluxes dynamics in arid and semi-arid ecosystems is a critical scientific challenge for regional carbon neutrality assessments and sustainable water resource management.In this study,we developed a multi-flux global sensitivity discriminant index(D_(sen))by integrating the Biome-BGCMuSo model with eddy covariance flux observations.This index was combined with a Bayesian optimization algorithm to conduct parameter optimization.The results demonstrated that:(1)Sensitivity analysis identified 13 highly sensitive parameters affecting carbon and water fluxes.Among these,the canopy light extinction coefficient(k)and the fraction of leaf N in Rubisco(FLNR)exhibited significantly higher sensitivity to carbon fluxes(GPP,NEE,Reco;D_(sen)>10%)compared to water flux(ET).This highlights the strong dependence of carbon cycle simulations on vegetation physiological parameters.(2)The Bayesian optimization framework efficiently converged 30 parameter spaces within 50 iterations,markedly improving carbon fluxes simulation accuracy.The Kling-Gupta efficiency(KGE)values for Gross Primary Production(GPP),Net Ecosystem Exchange(NEE),and Total Respiration(Reco)increased by 44.94%,69.23%and 123%,respectively.The optimization prioritized highly sensitive parameters,underscoring the necessity of parameter sensitivity stratification.(3)The optimized model effectively reproduced carbon sink characteristics in mountain meadows during the growing season(cumulative NEE=-375 g C/m^(2)).It revealed synergistic carbon-water fluxes interactions governed by coupled photosynthesis-stomatal pathways and identified substrate supply limitations on heterotrophic respiration.This study proposes a novel multi-flux sensitivity index and an efficient optimization framework,elucidating the coupling mechanisms between vegetation physiological regulation(k,FLNR)and environmental stressors(VPD,SWD)in carbonwater cycles.The methodology offers a practical approach for arid ecosystem model optimization and provides theoretical insights for grassland management through canopy structure regulation and water-use efficiency enhancement.
基金supported by funds from the National Natural Science Foundation of China(Grant Nos:42275079,41975017,42411530052,and 42161144010)the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(Grant No.2019QZKK0105)。
文摘Understanding the characteristics and variations of heat exchange and evaporation of lakes is important for regional water resource management and sustainable development.Based on eddy covariance measurements over Lake Vanajavesi in southern Finland,characteristics of energy fluxes and cold frontal effects on energy exchange were investigated.The lake acted as a heat sink in spring and summer and a heat source in winter.The latent heat flux reached its minimum value in the morning and peaked in the afternoon.The diurnal variation of sensible heat flux was opposite to that of latent heat flux.Impact factors for the sensible heat flux were mainly the lake-air temperature difference and the product of lake-air temperature difference and wind speed.The latent heat flux was mainly affected by the vapor pressure deficit and the product of vapor pressure deficit and wind speed.The annual mean values of bulk transfer coefficients for momentum,heat,and water vapor were 1.98×10^(-3),1.62×10^(-3),and 1.31×10^(-3),respectively.Bulk transfer coefficients for heat and water vapor were not equal,indicating that the parameterization of energy exchange in numerical models,where the assumption that the heat coefficient equals the water vapor coefficient needs improvement.During the ice-free season,cold fronts resulted in 28 sensible heat pulses and 17 latent heat pulses,contributing to 50.59%and 34.89%of sensible and latent heat exchange in Lake Vanajavesi.These results indicate that cold fronts significantly impact the surface energy budget and evaporation over lakes.
文摘The noise feature of a single-mode class-A laser amplifier is investigated by solving the Maxwell–Bloch equations of motion in the presence of the fluctuation force of cavity Langevin.The aim is to calculate the simultaneous fluctuations that are superimposed on the amplitude and phase of the cavity electric field, as well as the atomic population inversion. The correlation function of these fluctuations yields the amplitude, phase, and spontaneous emission noise fluxes, respectively. The amplitude and spontaneous emission noise fluxes exhibit the Lorentzian profiles in both the below-threshold state and the injection-locking region of the above-threshold state. While noise is typically viewed negatively in science and engineering, this research highlights its positive role as a valuable tool for measuring the optical properties of a laser amplifier. For instance, the degree of first-order temporal coherence(DFOTC) is derived by taking the Fourier transform of the amplitude noise flux. The damping rate of DFOTC is associated with the coherence time of the light emitted by the laser amplifier. Furthermore, the uncertainty relation between noise bandwidth and coherence time is confirmed. Finally, it is demonstrated that the input pumping noise flux, together with the output amplitude and spontaneous emission noise fluxes, satisfy the principle of flux conservation.
基金support from the National Key R&D Program of China(No.2023YFB3709900)the National Natural Science Foundation of China(Grant No.U22A20171).
文摘Steel–flux reactions involving the high aluminum(0.75–3.85 wt.%Al)low manganese(2.2 wt.%Mn)steel and the 18 wt.%SiO_(2)–18 wt.%Al2O3 mold flux were investigated.The results indicated that the reaction rate increased when the initial aluminum content increased from 0.76 to 3.85 wt.%.Utilizing the two-film theory,a steel–flux reaction kinetic model controlled by mass transfer was established,which considered the influence of the initial composition on the density of liquid steel and flux.The mass transfer of aluminum in the steel phase was the reaction rate-determining step.It was confirmed that the mass transfer coefficient of Al was 1.87×10^(−4).The predicted results of the kinetic model were consistent and reliable with the experimental results.Thermodynamic equilibrium calculation was performed using FactSage 8.2,which was compared with the steel and flux final composition after 30 min.The content of initial aluminum in the liquid steel played a critical role in the SiO_(2)equilibrium content of the mold flux.In addition,the steel–flux reaction between[Al]and(SiO_(2))occurred with the initial SiO_(2)content in the mold flux lower than 3 wt.%.
基金Supported by the Tianjin Key R&D Program(No.21YFSNSN00220)。
文摘The flux of dissolved inorganic nitrogen(DIN),predominantly nitrate(NO_(3)^(-))and ammonium(NH_(4)^(+)),from land to coastal waters via rivers is commonly estimated simply by multiplying water flux with nitrogen concentration.Understanding DIN fluxes in gated estuaries is critical as these systems often serve as hotspots for nutrient transformations,influencing coastal water quality and ecosystem health.However,the subsequent interactions involving NO_(3)^(-)and NH_(4)^(+)adsorption or desorption on suspended sediments are often overlooked.To better understand the impact of these interactions on the overall NO_(3)^(-)and NH_(4)^(+)sorption or desorption and subsequently,the mobility and transport to the coastal zone,we conducted a series of NO_(3)^(-)and NH_(4)^(+)adsorption and desorption experiments.These experiments involved varying suspended sediment concentrations,particle sizes,salinities,and sea-salt ions to assess their potential effects.Results indicate that desorption of NO_(3)^(-)and NH_(4)^(+)from suspended sediments is more prominent than adsorption,with NH_(4)^(+)desorption being particularly significant.Notably,at low suspended particle concentrations and high salinity,NH_(4)^(+)desorption from sediments increased markedly,which further amplified in polyhaline conditions.This effect could result from ion pairing between NH_(4)^(+)and seawater anions,along with competition from seawater cations for sediment cation exchange sites,enhancing NH_(4)^(+)diffusion from estuarine sediments,and the elevated NH_(4)^(+)release could promote DIN transport to nearshore waters,especially in gated estuaries where sediment resuspension occurs.Given the critical role of NH_(4)^(+)in estuarine nitrogen cycling,ignoring these dynamics could lead to underestimations of DIN transport in river-estuary systems.Therefore,incorporating sediment dynamics into DIN flux estimations is crucial for accurately assessing nitrogen transport in gated estuaries.
基金Project supported by the National Natural Science Foundation of China(No.12402262)。
文摘Vorticity is locally generated on a boundary at a rate measured by the boundary vorticity flux(BVF),which can be further decomposed into the sum of the orbital rotation and the generalized spin(specifically,the sum of shear and streaming vorticity)under the field description.For an incompressible viscous flow interacting with a stationary wall,the full expressions of the boundary fluxes of the orbital rotation and the spin are derived,for the first time,to elucidate their boundary creation mechanisms.Then,these new findings are successfully extended to the study of the boundary enstrophy dynamics,as well as the Lyman vorticity dynamics as an alternative interpretation to the boundary vorticity dynamics.Interestingly,it is found that the boundary coupling of the longitudinal and transverse processes is only embodied in the boundary spin flux,which is definitely not responsible for the generation of the boundary orbital-rotation flux.In addition,the boundary fluxes of enstrophy are directly associated with the boundary source of the second principal invariant of the velocity gradient tensor(VGT)and the two quadratic forms representing the spin-geometry interaction.The present exposition provides a new perspective and an additional dimension for understanding the vorticity dynamics on boundaries,which could be valuable in clarifying the formation mechanisms of near-wall coherent structures and flow noise at the fundamental level.
基金funded by the West Light Scholar of the Chinese Academy of Sciences(xbzg-zdsys-202202)the Natural Science Foundation of Henan(Grant No.232300420165)Integrated Scientific Investigation of the North-South Transitional Zone of China(2017FY100900)。
文摘Surface-latent heat(LE)and sensible heat(SH)fluxes play a pivotal role in governing hydrological,biological,geochemical,and ecological processes on the land surface in the Tibetan Plateau.However,to accurately assess and understand the spatial distribution of LE and SH fluxes across different underlying surfaces,it is crucial to verify the validity and reliability of ERA-5,GLDAS,and MODIS data against ground measurements obtained from the Flux Net micrometeorological tower network.This study analyzed the spatial patterns of LE and SH over the Tibetan Plateau using data from ERA-5,GLDAS,and MODIS.The results were compared with ground measurements from Flux Net tower observations on different underlying surfaces,and five statistical parameters(Pearson's r,LR slope,RMSE,MBE,and MAE)were used to validate the data.The results showed that:(1)MODIS LE data and ERA-5 SH data exhibited the closest agreement with ground observations,as indicated by their lowest root mean square error and mean bias area values.(2)The accuracy of ERA-5 SH was the highest in meadows and steppes,while GLDAS SH performed optimally in shrublands.Notably,MODIS LE consistently outperformed the other datasets across all vegetation types.(3)The spatial distribution of LE and SH displayed considerable heterogeneity,contingent upon the specific data sources and underlying surfaces.Notably,there was a contrasting trend between GLDAS and ERA-5,as well as MODIS,in terms of SH distribution in the shrubland.In shrublands and meadows,MODIS SH and LE exhibited more pronounced changes than ERA-5 and GLDAS.Additionally,ERA-5 SH demonstrated the opposite variation in meadow and steppe regions compared to GLDAS and MODIS.
基金supported by the National Key Research and Development Program(No.2022YFC3701102)the National Natural Science Foundation of China(Nos.41905109,42405114,and 42105105).
文摘Gaseous nitrous acid(HONO)is a critical contributor to daytime hydroxyl radical in the troposphere.Livestock farming has been recognized as an overlooked HONO source,but the lack of detailed flux measurements from livestock and poultry wastes would cause uncertainties in modeling its environmental impacts.Here,based on field flux measurements and laboratory experiments,we observed substantial HONO emissions from the composting of swine feces and chicken manure in the warm season,which might be mainly attributed to nitrification process in livestock and poultry wastes.The HONO emission from chicken manure was found to bemuch higher than that from swine feces,and the higher NH3 emission but lower N2O and NO emissions fromchicken manurewere also observed.Considering that the interaction among these nitrogen species during nitrification process,the obviously lower HONO emission from swine feces was likely to be explained by the lack of the total ammonia nitrogen and H+donors in swine feces.Temperature is also a key factor that influences the HONO emission from livestock wastes.In addition,the total HONO emission from swine feces in Chinawas estimated to be approximately 107.7 Gg-N/yr according to the national swine amounts,which is comparable to the national soil HONO emissions,underscoring its non-negligible contribution to regional air quality.Therefore,effective emission control of HONO fromlivestock and poultry wastes should be carried out to further improve air quality in China.
基金Supported by Natural Science Foundation of the Inner Mongolia Autonomous Region(2020MS04001)Inner Mongolia Autonomous Region Science and Technology Program Project+1 种基金Hetao College Science and Technology Research Project(HYYB202303)Hetao College Science and Technology Innovation Team.
文摘A growing global demand exists to formulate plans to lessen the greenhouse gas emissions produced by agricultural activities.The purpose of this study was to uncovered the changes in soil CO_(2)fluxes under varying scenarios including nitrogen fertilization rates,irrigation rates,and air temperatures in the Hetao Irrigation District(HID)over the 38-year period.DAYCENT model was used to predict carbon dioxide(CO_(2))fluxes from cultivated soils in the HID,Inner Mongolia from^(2)023 to 2060(the year of achieving the"carbon neutrality"goal)in this study.Results showed that mean soil CO_(2)fluxes in the sunflower field[1035.13 g/(m^(2).yr)]were significantly lower than those in the maize field[1405.54 g/(m^(2).yr)].An increase in nitrogen fertilization rate led to a significant escalation in soil CO_(2)fluxes.Moreover,elevating irrigation rates for washing salts by irrigation(WSBI)diminished soil CO_(2)fluxes in the sunflower field while amplifying them in the maize field.A rise in air temperature resulted in an increase in soil CO_(2)fluxes from the maize field,with annual increases observed,but a reduction in soil CO_(2)fluxes from the sunflower field.The sunflower fields in the HID have a more substantial advantage than the corn fields in mitigating soil CO_(2)emissions.
基金This research was supported by the Natural Science Foundation of China (30630015, 30771704)
文摘CH4 is one of the most important greenhouse gases, and mainly comes from soils in forest ecosystems. The objective of this study was to determine the effects of forest management practices such as understory removal and N-fixing species （Cassia alata） addition, on soil CH4 fluxes in four forest plantations in southern China. Fluxes of CH4 were measured in Eucalyptus urophylla plantation （B1）, Acacia crassi-carpa plantation （B2）, 10-native-species-mixed plantation （B3）, and 30-native-species-mixed plantation （B4） stands using the static chamber method in Southern China. Four forest management treatments, includ-ing （1） understory removal and replacement with C. alata （UR＋CA）; （2） understory removal only （UR）; （3） C. alata addition only （CA）; and （4） control without any disturbances （CK）, were applied in the four forest plantations. The results showed that plantation types had a significant effect on soil CH4 fluxes. B1 and B2 tended to be CH4 consumers, while B3 and B4 inclined to be CH4 producers. UR decreased CH4 fluxes by providing a more optimal soil temperature and moisture regime for mi-croorganism community and increasing substrate mineralization. How-ever, CA enhanced CH4 fluxes in B1 and B2 for N-fixing function of C. alata while lowered CH4 fluxes in B3 and B4. Soil CH4 flux rate was significantly related to soil temperature and moisture conditions in the top 10-cm soil layer. Furthermore, the quality of substrates, such as Soil Organic Carbon （SOC） and mineral N might also be important driving factors for CH4 fluxes. This study improved our understanding on CH4 fluxes in plantations under different management practices such as UR and CA.
