H2O Fluxes Research Articles

Constraining input and output fluxes of the southern-central Chile subduction zone: water, chlorine and sulfur

In this paper, we constrain the input and output fluxes of H2O, Cl and S into the southern-central Chilean subduction zone (31°S–46°S). We determine the input flux by calculating the amounts of water, chlorine and sulfur that are carried into the subduction zone in subducted sediments, igneous crust and hydrated lithospheric mantle. The applied models take into account that latitudinal variations in the subducting Nazca plate impact the crustal porosity and the degree of upper mantle serpentinization and thus water storage in the crust and mantle. In another step, we constrain the output fluxes of the subduction zone both to the subcontinental lithospheric mantle and to the atmosphere–geosphere–ocean by the combined use of gas flux determinations at the volcanic arc, volume calculations of volcanic rocks and the combination of mineralogical and geothermal models of the subduction zone. The calculations indicate that about 68 Tg/m/Ma of water enters the subduction zone, as averaged over its total length of 1,480 km. The volcanic output on the other hand accounts for 2 Tg/m/Ma or 3 % of that input. We presume that a large fraction of the volatiles that are captured within the subducting sediments (which accounts for roughly one-third of the input) are cycled back into the ocean through the forearc. This assumption is however questioned by the present lack of evidence for major venting systems of the submarine forearc. The largest part of the water that is carried into the subduction zone in the crust and hydrated mantle (accounting for two-thirds of the input) appears to be transported beyond the volcanic arc.

The peaked response of transpiration rate to vapour pressure deficit in field conditions can be explained by the temperature optimum of photosynthesis

Leaf transpiration rate (E) frequently shows a peaked response to increasing vapour pressure deficit (D). The mechanisms for the decrease in E at high D, known as the ‘apparent feed-forward response’, are strongly debated but explanations to date have exclusively focused on hydraulic processes. However, stomata also respond to signals related to photosynthesis. We investigated whether the apparent feed-forward response of E to D in the field can be explained by the response of photosynthesis to temperature (T), which normally co-varies with D in field conditions. As photosynthesis decreases with increasing T past its optimum, it may drive a decrease in stomatal conductance (gs) that is additional to the response of gs to increasing D alone. If this additional decrease is sufficiently steep and coupling between A and gs occurs, it could cause an overall decrease in E with increasing D. We tested this mechanism using a gas exchange model applied to leaf-scale and whole-tree CO2 and H2O fluxes measured on Eucalyptus saligna growing in whole-tree chambers. A peaked response of E to D was observed at both leaf and whole-tree scales. We found that this peaked response was matched by a gas exchange model only when T effects on photosynthesis were incorporated. We conclude that field-based studies of the relationship between E and D need to consider signals related to changing photosynthetic rates in addition to purely hydraulic mechanisms.

The response of the18O/16O composition of atmospheric CO2to changes in environmental conditions

[1] This study investigates the response of the global mean and spatial variations of the δ18O value of atmospheric CO2 (δCa) to changes in soil CO2 hydration rates, relative humidity, the δ18O value of precipitation and water vapor, visible radiation, temperature, and ecosystem flux partitioning. A three-dimensional global transport model was coupled to a mechanistic land surface model and was used to calculate isotopic fluxes of CO2 and H2O and the resulting δCa. The model reproduced the observed global mean and north-south gradient in δCa. The simulated seasonal amplitude and phases of CO2 and δCa agreed well at some but not all locations. Sensitivity tests with relative humidity increased by 3.2% from its original value decreased δCa by 0.21‰. Similarly, a global 3.3‰ decrease in the isotopic composition of both precipitation and water vapor (δWP and δWAV, respectively) caused a 2.6‰ decrease in δCa. A 1 K increase in atmospheric temperatures also affected δCa, but there was a very small δCa response to realistic changes in light levels. Experiments where leaf and soil CO2 fluxes were repartitioned revealed a nontrivial change to δCa. The predicted north-south δCa gradient increased in response to an increase in soil CO2 hydration rates. However, the δCa gradient also had a large response to global changes in δWP and δWAV. This result is particularly important since most models fail to deplete δWP enough at middle and high latitudes, where the influence of δWP and δWAV on the δCa gradient is strongest.

Herschel SPIRE and PACS observations of the red supergiant VY CMa: analysis of the molecular line spectra★

We present an analysis of the far-infrared and submillimetre molecular emission line spectrum of the luminous M-supergiant VY CMa, observed with the SPIRE and PACS spectrometers aboard the Herschel Space Observatory. Over 260 emission lines were detected in the 190-650-micron SPIRE FTS spectra, with one-third of the observed lines being attributable to H2O. Other detected species include CO, 13CO, H2^18O, SiO, HCN, SO, SO2, CS, H2S, and NH3. Our model fits to the observed 12CO and 13CO line intensities yield a 12C/13C ratio of 5.6+-1.8, consistent with measurements of this ratio for other M supergiants, but significantly lower than previously estimated for VY CMa from observations of lower-J lines. The spectral line energy distribution for twenty SiO rotational lines shows two temperature components: a hot component at 1000 K, which we attribute to the stellar atmosphere and inner wind, plus a cooler ~200 K component, which we attribute to an origin in the outer circumstellar envelope. We fit the line fluxes of 12CO, 13CO, H2O and SiO, using the SMMOL non-LTE line transfer code, with a mass-loss rate of 1.85x10^-4 Msun yr^-1 between 9 R* and 350 R*. To fit the observed line fluxes of 12CO, 13CO, H2O and SiO with SMMOL non-LTE line radiative transfer code, along with a mass-loss rate of 1.85x10^-4 Msun yr^-1. To fit the high rotational lines of CO and H2O, the model required a rather flat temperature distribution inside the dust condensation radius, attributed to the high H2O opacity. Beyond the dust condensation radius the gas temperature is fitted best by an r^-0.5 radial dependence, consistent with the coolant lines becoming optically thin. Our H2O emission line fits are consistent with an ortho:para ratio of 3 in the outflow.

Analysis of carbon dioxide, water vapour and energy fluxes over an Indian teak mixed deciduous forest for winter and summer months using eddy covariance technique

In the present study, we report initial results on analysis of carbon dioxide (CO2), water vapour (H2O), and energy fluxes (sensible and latent heat flux) over teak mixed deciduous forests of Madhya Pradesh, central India, during winter (November 2011 and January 2012) and summer (February–May 2012) seasons using eddy covariance flux tower datasets. During the study period, continuous fast response measurements of CO2, H2O and heat fluxes above the canopy were carried out at 10 Hz and averaged for 30 minutes. Concurrently, slow response measurements of meteorological parameters are also being carried out. Diurnal and seasonal variations of CO2, H2O and heat fluxes were analysed and correlated with the meteorological variables. The study showed strong influence of leaf off and on scenario on the CO2, H2O and energy fluxes due to prevalence of deciduous vegetation type in the study area. Maximum amount of CO2 was sequestered for photosynthesis during winter (monthly mean of $-25~\upmu $ mol/m2/s) compared to summer (monthly mean of $-2~\upmu $ mol/m2/s). Energy flux analysis (weekly mean) showed more energy being portioned into latent heat during winter (668 W/m2) and sensible heat during summer (718 W/m2).

Simulation of canopy CO2/H2O fluxes for a rubber (Hevea brasiliensis) plantation in central Cambodia: The effect of the regular spacing of planted trees

We developed a soil-vegetation-atmosphere transfer (SVAT) model applicable to simulating CO2 and H2O fluxes from the canopies of rubber plantations, which are characterized by distinct canopy clumping produced by regular spacing of plantation trees. Rubber (Hevea brasiliensis Müll. Arg.) plantations, which are rapidly expanding into both climatically optimal and sub-optimal environments throughout mainland Southeast Asia, potentially change the partitioning of water, energy, and carbon at multiple scales, compared with traditional land covers that are being replaced. Describing the biosphere–atmosphere exchange in rubber plantations via SVAT modeling is, therefore, important to understanding the impacts on environmental processes. The regular spacing of plantation trees creates a peculiar canopy structure that is not well represented in most SVAT models, which generally assume a non-uniform spacing of vegetation. Herein we develop a SVAT model applicable to a rubber plantation and an evaluation method for its canopy structure, and examine how the peculiar canopy structure of rubber plantations affects canopy CO2 and H2O exchanges. Model results are compared with measurements collected at a field site in central Cambodia. Our findings suggest that it is crucial to account for intensive canopy clumping in order to reproduce observed rubber plantation fluxes. These results suggest a potentially optimal spacing of rubber trees to produce high primary productivity and water use efficiency.

Measuring H2O and CO2 fluxes at field scales with scintillometry: Part II – Validation and application of 1-min flux estimates

This paper evaluates four methods to obtain accurate averaged flux estimates under conditions of non-stationary turbulence. In Part I (Van Kesteren et al., 2012), we introduced and evaluated these four combined methods for 30-min averaging intervals, notably the flux-variance method, the Bowen-variance method, the structure-parameter method, and the energy-balance method. The aim of this paper, Part II, is to validate the accuracy of the 1-min flux estimates of the CO2 flux, FCO2, and the evapotranspiration/latent-heat flux, LvE. Furthermore, we use the 1-min fluxes to investigate flux and vegetation responses under conditions of non-stationary turbulence. Using several validation methods, we show that both the eddy-covariance method and the energy-balance method are unsuitable for estimating fluxes over 1-min averaging intervals. The three other combined methods are more successful in determining 1-min fluxes. The random error is approximately half that of the eddy-covariance method, but still some issues limit the success. The Bowen-variance method has a +0.09 systematic error and moreover, 30% of the data had to be omitted, because the method requires more stringent conditions. Furthermore, the flux-variance method has a −0.15 systematic error. The structure-parameter method performs best of all methods and accurately resolves 1-min fluxes. With this method, we do a final validation with a different data set and show that also under dry conditions the method accurately resolves FCO2, although LvE was more difficult to resolve. In the last part, the structure-parameter method is successfully applied under conditions of non-stationary turbulence. We show that LvE and FCO2 have a different step response upon abrupt changes in solar radiation, because different processes drive these fluxes. Also, we observe a 2-min time lag between solar radiation and 1-min fluxes and show the relevance of taking this into account for determining light–response curves of the plants for both 1-min and 30-min averaging intervals. Furthermore, we show the relevance of 1-min fluxes for studying the light–response curves of plants for conditions with different temperature and humidity. Finally, we show that accurate estimates of 1-min averaged canopy resistances can be determined via the resistance expressions for sensible heat and LvE. As such, we show that vegetation can indeed modify its canopy resistance significantly within several minutes.

Partitioning ozone fluxes between canopy and forest floor by measurements and a multi-layer model

Ozone uptake by plant leaves is essential to studies investigating atmospheric air pollution and plant injury. A major challenge to these investigations is the up-scaling of leaf-level stomatal processes to the ecosystem level, the accounting for forest floor ozone removal mechanics, and resolving the numerous pathways responsible for non-stomatal ozone removal within the canopy sublayer. To progress on the first two and offer constraints on the third, the O3 fluxes above and within a boreal Scots pine forest in Southern Finland are explored using a combination of two-level eddy covariance fluxes and detailed within-canopy concentration profiles. The interpretation of the results is aided by a multi-layer canopy model (MLM), which couples radiation attenuation and turbulent transport within the canopy volume with leaf-level gas exchange, photosynthesis, and stomatal conductance. Validation of the MLM against measured turbulent CO2 and H2O fluxes within and above the canopy, as well as their concomitant mean concentration profiles suggest that the stomatal pathway is reasonably quantified via the proposed MLM approach. The results show that the stomatal pathway alone can explain some 80% of the daytime dry-canopy ecosystem uptake of O3. The non-stomatal O3 uptake is largest during nighttime and early morning hours when between one third and half of it seems to originate from below the overstory canopy. During daytime, almost all the non-stomatal uptake occurs in the sub-canopy region. Sub-canopy and/or understory processes contribute between 25–30% (nighttime) and 35–45% (daytime) ecosystem O3 uptake. In sub-canopy, the non-stomatal component exceeds the stomatal by a factor of 2–4 during daytime. Finally, the MLM was used to study some of the potential non-stomatal pathways, including cuticular and soil uptake, forest floor uptake and disequilibrium between photochemical O3 production and a first-order kinetic chemical destruction mechanism. The results indicate that the likely location of the non-stomatal sink is in the lower trunk-space close the forest floor but the soil surface uptake is insignificant. According to the results, a bulk gas-phase disequilibrium between O3 production (assumed to vary linearly with light at a given level inside the canopy) and destruction (assumed to vary exponentially with mean air temperature) is a plausible explanation for non-stomatal O3 removal inside the canopy.

Dynamic modelling and analysis of an amine-based post-combustion CO2 capture absorption column

A dynamic, non-equilibrium model of a packed column for the chemisorption of CO2 from dilute gas streams using a monoethanolamine solvent has been proposed. The model uses the SAFT-VR equation of state to describe the thermophysical properties and fluid-phase behaviour of this process. The SAFT-VR equation-of-state is used to account for all of the inter-species interactions in the fluid, including the reactions. In this way, we avoid the use of enhancement factors. Further it is not necessary to include a detailed description of the reaction mechanisms or the reaction products. Steady state validation of the proposed model is performed using pilot plant data. The position and extent of the mass transfer zone is found to be a function of competing interphase fluxes of H2O and CO2. We evaluate through dynamic simulation the effect of changing the lean solvent flowrate and thermodynamic state on column behaviour. The influence of flue gas humidity on the position and shape of the mass transfer zone is also highlighted and discussed.

Balancing heat, water and nutrients under environmental change: a thermodynamic niche framework

Summary Models of the regulatory behaviour of organisms are fundamental to a strong physiologically‐based understanding of species' responses to global environmental change. Biophysical models of heat and water exchange in organisms (biophysical ecology) and nutritionally‐explicit models for understanding feeding behaviour and its fitness consequences (the Geometric Framework of nutrition, GF) are providing such an underpinning. However, temperature, water and nutrition interact in fundamental ways in influencing the responses of the organism to their environment, and a priority is to develop an integrated approach for conceptualising and measuring these interactions. Ideally, such an approach would be based on a thermodynamically‐formalized energy and mass budgeting approach that is sparsely parameterised and sufficiently general to apply across a range of situations and organisms. Here we illustrate how mass‐balance aspects of Dynamic Energy Budget theory can be applied to obtain first‐principles estimates of fluxes of O2, CO2, H2O and nitrogenous waste. Then, using an herbivorous lizard (Egernia cunninghami) as a case study, we demonstrate how these estimates can be integrated with heat/water exchange models and environmental data to provide a holistic understanding of how foraging strategy, food availability, habitat and weather interact with heat, water and nutrient/energy budgets across the life‐cycle. The analysis shows the potential importance of the water balance in affecting the energy budgets of ‘ dry skinned’ ectotherms, especially early in ontogeny, and highlights a significant gap in our knowledge of the physiological and behavioural traits that affect water balance when compared with our knowledge of thermal traits. In general, the modelling approach we describe can provide the thermodynamically‐constrained stage on which other evolutionary and ecological interactions play out; the ‘thermodynamic niche’. This in turn provides a solid foundation from which to tackle key questions about organismal responses to environmental change.

Constraints on magma processes, subsurface conditions, and total volatile flux at Bezymianny Volcano in 2007–2010 from direct and remote volcanic gas measurements

Direct and remote measurements of volcanic gas composition, SO2 flux, and eruptive SO2 mass from Bezymianny Volcano were acquired between July 2007 and July 2010. Chemical composition of fumarolic gases, plume SO2 flux from ground and air-based ultraviolet remote sensing (FLYSPEC), and eruptive SO2 mass from Ozone Monitoring Instrument (OMI) satellite observations were used along with eruption timing to elucidate magma processes and subsurface conditions, and to constrain total volatile flux. Bezymianny Volcano had five explosive magmatic eruptions between May 2007 and June 2010. The most complete volcanic gas datasets were acquired for the October 2007, December 2009, and May 2010 eruptions. Gas measurements collected prior to the October 2007 eruption have a relatively high ratio of H2O/CO2 (81.2), a moderate ratio of CO2/S (5.47), and a low ratio of S/HCl (0.338), along with moderate SO2 and CO2 fluxes of 280 and 980t/d, respectively, and high H2O and HCl fluxes of ~45,000 and ~440t/d, respectively. These results suggest degassing of shallow magma (consistent with observations of lava extrusion) along with potential minor degassing of a deeper magma source. Gas measurements collected prior to the December 2009 eruption are characterized by relatively low H2O/CO2 (4.13), moderate CO2/S (6.84), and high S/HCl (18.7) ratios, along with moderate SO2 and CO2 fluxes of ~220 and ~1000t/d, respectively, and low H2O and HCl fluxes of ~1700 and ~7t/d, respectively. These trends are consistent with degassing of a deeper magma source. Fumarole samples collected ~1.5months following the May 2010 eruption are characterized by high H2O/CO2 (63.0), low CO2/S (0.986), and moderate S/HCl (6.09) ratios. These data are consistent with degassing of a shallow, volatile-rich magma source, likely related to the May eruption. Passive and eruptive SO2 measurements are used to calculate a total annual SO2 mass of 109kt emitted in 2007, with passive emissions comprising ~87–95% of the total. Total annual volatile masses for the study period are estimated to range from 1.1×106 to 18×106t/year. Annual CO2 masses are ~8 to 40 times larger than can be explained by degassing of dissolved CO2 within eruptive magma, suggesting that the eruptive magma contained a significant quantity of exsolved volatiles sourced either from the eruptive melt or unerupted magma at depth. Variable total volatile fluxes ranging from ~3000t/d in 2009 to ~49,000t/d in 2007 are attributed to variations in the depth of gas exsolution and separation from the melt under open-system degassing conditions. We propose that exsolved volatiles are quickly transported to the surface from ascending magma via permeable flow through a bubble and/or fracture network within the conduit and thus retain their equilibrium composition at the time of segregation from melt. The composition of surface CO2 and H2O emissions from 2007 to 2009 are compared with modeled exsolved fluid compositions for a magma body ascending from entrapment depths to estimate depth of fluid exsolution and separation from the melt. We find that at the time of sample collection magma had already begun ascent from the mid-crustal storage region and was located at maximum depths of ~3.7km in August 2007, approximately 2months prior to the next magmatic eruption, and ~4.6km in July of 2009 approximately five months prior to the next magmatic eruption. These findings suggest that the exsolved gas composition at Bezymianny Volcano may be used to detect magma ascent prior to eruption.

Measuring H2O and CO2 fluxes at field scales with scintillometry: Part I – Introduction and validation of four methods

This study introduces four methods for determining turbulent water vapour and carbon dioxide flux densities, the evapotranspiration and CO2 flux respectively. These methods combine scintillometer measurements with point-sampling measurements of scalar quantities and consequently have a faster statistical convergence than the eddy-covariance method. The scintillometer measures the friction velocity and stability averaged over space, allowing the time averaging to be a minute or less in homogenous conditions. This paper aims to thoroughly test the methods by analysing their sensitivity to the variables that go into the method and validate the methods with 30-min eddy-covariance data. Introduced are: the Bowen-variance method, the flux-variance method, the structure-parameter method, and the energy-balance method. Sensitivity analysis shows that each method is sensitive to the turbulence measurements of the scalar quantities that are specific to the method, as well as to the friction velocity. This demonstrates that the accuracy of the flux results from a correct representation of the turbulence variables used by the methods. Furthermore, a 30-min flux validation shows that the methods compare well to the independent eddy-covariance fluxes. We found that the structure-parameter method performs best – a low scatter (the correlation coefficient, r=0.99) and a 5% underestimation were observed. Also the other methods perform well, although the energy-balance did not close, because storage terms and CO2 flux were neglected. Furthermore, during the night the variance methods were influenced by non-stationarity in the measurement signal. Finally, we suggest using the correlation coefficients between temperature and scalar quantities to acquire the sign of the fluxes. Data for this study were gathered in May–June 2009 over a wheat field near Merken, Germany, in the framework of the TransRegio32 program.

Growing season variability in evapotranspiration, ecosystem water use efficiency, and energy partitioning in switchgrass

ABSTRACTEvapotranspiration (ET), ecosystem water use efficiency (EWUE), and energy partitioning in switchgrass (Panicum virgatum L.) ecosystems are crucial to understand its water and energy balances since switchgrass acreage is expanding for cellulosic biofuels. We measured CO2, H2O, and energy fluxes over a switchgrass field in Chickasha, OK, USA, using eddy covariance method. The objective of this study was to quantify seasonal variations in ET, EWUE, and seasonal distributions of energy partitioning in response to controlling factors. Seasonal (May to mid‐November) cumulative ET (450 mm) was similar to cumulative rainfall (432 mm). During June to September, ET was 1·92 times of rainfall, indicating that the crop experienced severe drought during the mid‐growing season. ET showed clear seasonality with 3–4 mm day−1 during the active growing season (late May and June) to low rates of about 0·5 mm day−1 during the late growing season (November). The ET rate decreased during dry periods. On seasonal scale, more energy was partitioned to sensible heat flux (H) than latent heat (LE) because of drought. Estimation of EWUE by dividing time integrals of gross ecosystem photosynthesis (GEP) by respective H2O fluxes (ET) at monthly time scale provided EWUE from 10·46 (August) to 14·08 g CO2 mm−1 ET (October) with a seasonal average of 12·01 g CO2 mm−1 ET. Seasonal patterns in EWUE were observed with smaller values during drought because of more rapid reduction in carbon assimilation (GEP) than ET. These findings confirm the major role of precipitation in determining water and energy balances in switchgrass. Copyright © 2012 John Wiley & Sons, Ltd.

Analyzing transient closed chamber effects on canopy gas exchange for optimizing flux calculation timing

Transient type canopy chambers are still the only currently available practical solution for rapid screening of gas-exchange in agricultural fields. The technique has been criticized for its effect on canopy microclimate during measurement which affects the transport regime and regulation of plant gas-exchange. Field studies in which the technique has been compared against independent methods are still fragmentary. The aims of this study were to quantify the changes of the physical environment during chamber placement, to determine optimum flux measuring windows, to compare three flux-calculation procedures, and to test the performance of the method against independent measurements of sap-flow. Two wheat experiments were conducted for these purposes under German temperate climate conditions.Leaf transpiration and sap-flow remained relatively constant during the first 120s after chamber deployment, but changed considerably afterwards. Canopy H2O fluxes could thus be inferred from concentration measurement series during this interval. A saturation function, previously not mentioned in the literature, was compared against the commonly used constant and quadratic regression methods and identified as the most suitable method for calculating vapor fluxes. The study reconfirmed that small proportional changes of CO2 concentrations during the calculation interval facilitate the application of the frequently applied quadratic regression method for calculating CO2 fluxes. Sap-flow, leaf and canopy gas-exchange were severely perturbed after chamber removal. Revisiting times of same sample locations need to be planned accordingly. The study confirms that the transient chamber technique can be applied for determining canopy gas-exchange, provided that characteristic time intervals within concentration measuring series are determined and their non-linearity tested to establish appropriate flux calculation procedures.

ECOSYSTEM WATER USE EFFICIENCY OF NORWAY SPRUCE MONOCULTURE FROM EDDY-COVARIANCE AND ECOPHYSIOLOGICAL MEASUREMENTS

Water release and biomass production of young Norway spruce stand were investigated by different approaches during 2004-2009. Closed-path eddy-covariance system (LI-7000) was found to be suitable for accurate net ecosystem production evaluation (NEP). NEP was in a good correspondence with the biomass inventory data. In contrary, water vapour eddy-covariance fluxes were found underestimating a real water release of the stand. Global radiation and air water vapour pressure deficit at 75% of the stand height were main micrometeorological control drivers for stand transpiration (T) and evapotranspiration (ET). Thus, missing or bad quality data of eddy-covariance ET can be simulated according to these parameters. Water use efficiency (WUE) values calculated from net and gross primary production data highly differed in absolute values as well as in seasonal course mainly due to respiration. Annual WUE values from eddy-covariance and from ecophysiological measurements of T and stand biomass increment were unfortunately incomparable. Therefore, precise research of eddy-covariance H2O fluxes and WUE evaluation need to continue.

Quantification of the Mass Flux of H2O Gas (Steam) at Three Active Volcanoes Using Thermal Infrared Imagery

We apply a measurement technique that utilizes thermal video of vapor-dominated volcanic plumes to estimate the H2O gas flux at three degassing volcanoes. Results are compared with H2O flux measurements obtained using other methods to verify the thermal camera-derived values. Our estimation of the H2O emission rate is based on the mass and energy conservation equations. H2O flux is quantified by extracting the temperature and width of the gas plume from the thermal images, calculating the transit velocity of the gas plume from the thermal video, and combining these results with atmospheric parameters measured on-site. These data are then input into the equations for conservation of mass and energy. Selected volcanoes for this study were Villarrica in Chile, Stromboli in Italy, and Santa Ana in El Salvador. H2O fluxes estimated from the thermal imagery were 38–250 kg s−1 at Villarrica, 4.5–14 kg s−1 for Stromboli’s Central Crater, and 168–219 kg s−1 at Santa Ana. These compare with H2O flux values estimated by other methods of 73–220, 3–70 and 266 kg s−1, at the three volcanoes, respectively. The good agreement between thermal image-derived results and those estimated by other methods seem to validate this method.

EX Lupi FROM QUIESCENCE TO OUTBURST: EXPLORING THE LTE APPROACH IN MODELING BLENDED H2O AND OH MID-INFRARED EMISSION

We present a comparison of archival Spitzer spectra of the strongly variable T Tauri EX Lupi, observed before and during its 2008 outburst. We analyze the mid-infrared emission from gas-phase molecules thought to originate in a circumstellar disk. In quiescence the emission shows a forest of H2O lines, highly excited OH lines, and the Q branches of the organics C2H2, HCN, and CO2, similar to the emission observed toward several T Tauri systems. The outburst emission shows instead remarkable changes: H2O and OH line fluxes increase, new OH, H2, and HI transitions are detected, and organics are no longer seen. We adopt a simple model of a single-temperature slab of gas in local thermal equilibrium, a common approach for molecular analyses of Spitzer spectra, and derive the excitation temperature, column density, and emitting area of H2O and OH. We show how model results strongly depend on the selection of emission lines fitted, and that spectrally-resolved observations are essential for a correct interpretation of the molecular emission from disks, particularly in the case of water. Using H2O lines that can be approximated as thermalized to a single temperature, our results are consistent with a column density decrease in outburst while the emitting area of warm gas increases. A rotation diagram analysis suggests that the OH emission can be explained with two temperature components, which remarkably increase in column density in outburst. The relative change of H2O and OH emission suggests a key role for UV radiation in the disk surface chemistry.

温带混交林碳水通量模拟及其对冠层分层方式的响应——耦合的气孔导度-光合作用-能量平衡模型

A stomatal conductance-photosynthesis-energy balance model developed by Leuning is used to estimate CO2 and H2O fluxes of temperate mixed forests.The canopy is divided into multiple layers,using both Gaussian integration and average-layer method.The fluxes are calculated layer by layer and then accumulated for the whole canopy.The model calculates CO2 and H2O exchange between atmosphere and canopy based on the input of meteorological variables.We compare the modeled fluxes with those measured by eddy covariance system,and analyze the influence of different layer-methods on the modeled fluxes.The energy balance ratios(EBR) of CBS,GDK and MMF sites are 0.76,0.66 and 1.07,respectively,which is reasonable according to the international reported range(0.34—1.2).The results of the Gaussian integration method agree well with the eddy covariance fluxes,showing the diurnal CO2 fluxes as bell shaped.The CO2 flux(Fc) is negative and stable during the night,which suggests that forest ecosystems release CO2 to the atmosphere.After sunrise,Fc increases gradually to positive values,peaking at noon,and decreases in the afternoon to the negative night values.The diurnal cycle of H2O fluxes(LE) is similar to that of Fc,and the modeled LE agree well with the measured LE.The estimated fluxes are influenced by the different layer-methods.We compared CO2 and H2O fluxes from dividing the canopy into 2,5,10 and 20 layers averagely with the fluxes from Gaussian integration method.Larger numbers of layers produce lower LE and higher Fc.The fluxes from different layer-methods are sensitive to the vertical profiles of absorbed radiation,temperature,humidity and wind speed.Furthermore,the leaf photosynthesis responds nonlinearly to the radiation.

Carbonyl sulfide (COS) as a tracer for canopy photosynthesis, transpiration and stomatal conductance: potential and limitations.

The theoretical basis for the link between the leaf exchange of carbonyl sulfide (COS), carbon dioxide (CO2) and water vapour (H2O) and the assumptions that need to be made in order to use COS as a tracer for canopy net photosynthesis, transpiration and stomatal conductance, are reviewed. The ratios of COS to CO2 and H2O deposition velocities used to this end are shown to vary with the ratio of the internal to ambient CO2 and H2O mole fractions and the relative limitations by boundary layer, stomatal and internal conductance for COS. It is suggested that these deposition velocity ratios exhibit considerable variability, a finding that challenges current parameterizations, which treat these as vegetation-specific constants. COS is shown to represent a better tracer for CO2 than H2O. Using COS as a tracer for stomatal conductance is hampered by our present poor understanding of the leaf internal conductance to COS. Estimating canopy level CO2 and H2O fluxes requires disentangling leaf COS exchange from other ecosystem sources/sinks of COS. We conclude that future priorities for COS research should be to improve the quantitative understanding of the variability in the ratios of COS to CO2 and H2O deposition velocities and the controlling factors, and to develop operational methods for disentangling ecosystem COS exchange into contributions by leaves and other sources/sinks. To this end, integrated studies, which concurrently quantify the ecosystem-scale CO2, H2O and COS exchange and the corresponding component fluxes, are urgently needed.We investigate the potential of carbonyl sulfide (COS) for being used as a tracer for canopy net photosynthesis, transpiration and stomatal conductance by examining the theoretical basis of the link between leaf COS, carbon dioxide (CO2) and water vapour (H2O) exchange. Our analysis identifies several limitations that need to be overcome to this end, however at present we lack appropriate ecosystem-scale field measurements for assessing their practical significance. It however appears that COS represents a better tracer for CO2 than H2O. Concurrent measurements of ecosystem scale COS, CO2 and H2O exchange are advocated.

Calculating CO2 and H2O eddy covariance fluxes from an enclosed gas analyzer using an instantaneous mixing ratio

AbstractEddy covariance flux research has relied on open‐ or closed‐path gas analyzers for producing estimates of net ecosystem exchange of carbon dioxide (CO2) and water vapor (H2O). The two instruments have had different challenges that have led to development of an enclosed design that is intended to maximize strengths and minimize weaknesses of both traditional designs. Similar to the closed‐path analyzer, the enclosed design leads to minimal data loss during precipitation events and icing, and it does not have surface heating issues. Similar to the open‐path design, the enclosed design has good frequency response due to small flux attenuation loss in the short intake tube, does not need frequent calibration, has minimal maintenance requirements, and can be used in a very low power configuration. Another important feature of such a design is the ability to output instantaneous mixing ratio, or dry mole fraction, so that instantaneous thermal and pressure‐related expansion and contraction, and water dilution of the sampled air have been accounted for. Thus, no density corrections should be required to compute fluxes during postprocessing. Calculations of CO2 and H2O fluxes via instantaneous mixing ratio from the new enclosed CO2/H2O gas analyzer were tested in nine field experiments during 2009–2010 in a wide range of ecosystems and setups. Fluxes computed via a mixing ratio output from the instrument without applying density corrections were compared to those computed the traditional way using density corrections. The results suggest that with proper temperature, water vapor, and pressure measurements in the cell, gas fluxes can be computed confidently from raw covariance of mixing ratio and vertical wind speed, multiplied by a frequency response correction. This has important implications for future flux measurements, because avoiding hourly density corrections could have the advantages of increasing flux measurement quality and temporal resolution, reducing the magnitude of minimum detectable flux, unifying data processing steps, and assuring better intercomparison between different sites and networks.