H2O Fluxes Research Articles

Temporal patterns of carbon-water coupling of a subalpine peatland in subtropics: Insights from a seven-year eddy covariance monitoring

Study regionA well-preserved subalpine peatland in the subtropics, the Dajiuhu peatland, in Shennongjia, Hubei Province, China. Study focusOver a seven-year period, constant in-situ carbon flux monitoring was conducted using the eddy covariance method. The patterns of CO2 and H2O fluxes were analyzed, encompassing both daytime and nocturnal period observations, spanning both growing and non-growing seasons, and the interconnection between carbon and water within the Dajiuhu peatland. Furthermore, this investigation identified meteorological parameters shaping these flux dynamics. New hydrological insights for the regionThe water source function was more resilient to the effects of extreme weather events and showed higher stability when compared to the carbon sink function. Daytime carbon-water coupling presented a pronounced negative correlation during the growing season, contrasting with a more complex trinomial relationship evident during the non-growing season; however, nocturnal periods did not reveal any apparent correlation. Relative humidity (RH), water table depth (WTD), and evapotranspiration (ET) emerged as key variables impacting jointly on both CO2 and H2O fluxes. Furthermore, net radiation (Rn) magnifies the hysteresis loops associated with net ecosystem exchanges of CO2 (NEE) during the growing season, with WTD being the prime determinant influencing seasonal fluctuations in hysteresis related to H2O fluxes. These findings exemplify the complexities inherent in the management of carbon and water resources within subalpine peatlands, underscored by their intricately intertwined and inseparable relationship.

Seasonal precipitation distribution determines ecosystem CO2 and H2O exchange by regulating spring soil water–salt dynamics in a brackish wetland

Abstract The intensification of the global hydrological cycle is anticipated to increase the variability of precipitation patterns. Brackish wetlands respond to changes in precipitation patterns by regulating the absorption and release of CO2 and H2O to maintain the stability of ecosystem functions. However, there is limited understanding of how the inter‐seasonal precipitation distribution (SPD) affects ecosystem CO2 and H2O exchange compared with annual precipitation totals. Here, we conducted four consecutive years of field experiments in a brackish wetland, manipulating the proportion of precipitation across different seasons while maintaining a constant annual precipitation total. We utilized five inter‐SPD proportions (+73%, +56%, control (CK), −56%, −73%) to examine the effects of SPD on ecosystem CO2 and H2O exchange. Our findings revealed that the annual ecosystem CO2 and H2O fluxes showed a trend of decreasing with the decrease in spring precipitation distribution. Among them, the annual net ecosystem CO2 exchange, evapotranspiration, carbon use efficiency and water use efficiency were shown to be more sensitive to decrease in spring precipitation distribution and increase in summer and autumn precipitation distribution. This negative asymmetric response pattern suggests that annual ecosystem CO2 and H2O exchange is primarily governed by seasonal precipitation variability, with spring soil water–salt dynamics identified as the key driver. Therefore, this association can be explained by the fact that drought of the early growth stage exacerbates soil salinization and inhibits vegetation colonization and growth, thereby greatly impairing the annual CO2–H2O exchange capacity of brackish wetlands. Our results emphasized that the spring extreme precipitation‐induced soil water–salt conditions will greatly influence CO2 and H2O exchange in brackish wetlands in the future. These findings are crucial for improving predictions of the carbon sequestration and water‐holding capacity of brackish wetlands. Read the free Plain Language Summary for this article on the Journal blog.

Jasmonic acid and heat stress induce high volatile organic compound emissions in Picea abies from needles, but not from roots.

Plants emit diverse volatile organic compounds (VOCs) from their leaves and roots for protection against biotic and abiotic stress. An important signaling cascade activated by aboveground herbivory is the jasmonic acid (JA) pathway that stimulates the production of VOCs. So far it remains unclear if the activation of this pathway also leads to enhanced VOC emissions from conifer roots, and how the interplay of above- and belowground defenses in plants are affected by multiple stressors. Therefore, we simultaneously analyzed needle and root VOC emissions of Picea abies saplings, as well as CO2 and H2O fluxes in response to aboveground JA treatment, heat stress and their interaction in a controlled climate chamber experiment. Continuous online VOC measurements by PTR-TOF-MS showed an inverse pattern of total needle and root VOC emissions, when plants were treated with JA and heat. While needle sesquiterpene emissions increased nine-fold one day after JA application, total root VOC emissions decreased. This was mainly due to reduced emissions of acetone and monoterpenes by roots. In response to aboveground JA treatment, root total carbon emitted as VOCs decreased from 31% to only 4%. While VOC emissions aboveground increased, net CO2 assimilation strongly declined due to JA treatment, resulting in net respiration during the day. Interestingly, root respiration was not affected by aboveground JA application. Under heat the effect of JA on VOC emissions of needles and roots was less pronounced. The buffering effect of heat on VOC emissions following JA treatment points towards an impaired defense reaction of the plants under multiple stress. Our results indicate efficient resource allocation within the plant to protect threatened tissues by a rather local VOC release. Roots may only be affected indirectly by reduced belowground carbon allocation, but are not involved directly in the JA-induced stress response.

Dynamics of carbon and water vapor fluxes in three typical ecosystems of Heihe River Basin, Northwestern China

Understanding the dynamics of carbon and water vapor fluxes in arid inland river basin ecosystems is essential for predicting and assessing the regional carbon-water budget amid climate change. However, studies aiming to unravel the mechanisms driving the variations and coupling process of regional carbon-water budget in a changing environment in arid regions are limited. Here, we used the eddy covariance technique to analyze the relationship between CO2 and H2O fluxes in three typical ecosystems across the upper, middle, and lower reaches of an arid inland river basin in Northwestern China. Our results showed that all ecosystems acted as carbon sinks, with the alpine swamp meadow, cropland, and desert shrubland sequestrating −300.2 ± 0.01, −644.8 ± 2.9, and − 203.7 ± 22.5 g C m−2 yr−1, respectively. Air temperature (Ta) primarily controlled daily gross primary productivity (GPP) and net ecosystem CO2 exchange (NEE) in the irrigated cropland during the growing season, while soil temperature (Ts) and vapor pressure deficit (VPD) regulated these parameters in the alpine swamp meadow and desert shrubland. Additionally, Ta and net radiation (Rn) controlled daily evapotranspiration (ET) in cropland, while Ts and Rn regulated ET at other sites. Consequently, carbon and water vapor fluxes of all three ecosystems tended to be energy-limited during the growing season. The differential responses of carbon and water vapor fluxes in the upper, middle, and lower reaches of these ecosystems to biophysical factors determined their distinct coupling and variations in water use efficiency. Notably, the desert shrub ecosystem in the lower reach of the basin maintained a stable balance between carbon gain and water loss, indicating adaptation to aridity. This study provides valuable insights into the underlying mechanisms behind the changes in carbon and water vapor fluxes and water-use efficiency in arid river basin ecosystems.

Cover crop inclusion and residue retention improves soybean production and physiology in drought conditions

Soybean (Glycine max (L.) Merr.) planting has increased in central and western North Dakota despite frequent drought occurrences that limit productivity. Soybean plants need high photosynthetic and transpiration rates to be productive, but they also need high water use efficiency when water is limited. Crop residues and cover crops in crop rotations may improve soybean drought tolerance in northern Great Plains. We aimed to examine how a management practice that included cover crops and residue retention impacts agronomic, ecosystem water and carbon dioxide flux, and canopy-scale physiological attributes of soybeans in the northern Great Plains under drought conditions. The experiment consisted of two soybean fields over two years with business-as-usual (no-cover crops and spring wheat residue removal) and aspirational management (cover crops and spring wheat residue retention) during a drought year. We compared yield; aboveground biomass; green chromatic coordinates, and CO2 and H2O fluxes from eddy covariance, Phenocam images, and ancillary micrometeorological measurements. These measurements were used to derive ecosystem-scale physical, and physiological attributes with the ‘big leaf’ framework to diagnose underlying processes. Soybean yields were 29 % higher under drought conditions in the field managed in a system that included cover crops and residue retention. This yield increase was associated with a 5 day increase in the green-chromatic-coordinate defined maturity phenophase, increasing agronomic and intrinsic water use efficiency by 27 % and 33 %, respectively, increasing water uptake, and increasing the rubisco-limited photosynthetic capacity (Vcmax25) by 42 %. The inclusion of cover crops and residue retention into a cropping system improved soybean productivity because of differences in water use, phenology timing, and photosynthetic capacity. These results suggest that farmers can improve soybean productivity and yield stability by incorporating cover crops and residue retention into their management suite because these practices to facilitate more aggressive water uptake.

Impact Analysis of H2O Fluxes and High-Frequency Meteorology–Water Quality: Multivariate Constrained Evaporation Modelling in Lake Wuliangsuhai, China

It is imperative to elucidate the process of evaporation in lakes, particularly those that are freshwater and are situated in middle and high latitudes. Based on one-year evaporation and high-frequency meteorological–water quality data of Lake Wuliangsuhai, this study analyzed the applicability and driving mechanism of the evaporation model. These dynamics are elucidated by the vorticity covariance method combined with the multivariate constrained evaporation Modelling method. The findings of this study revealed that (1) Lake evaporation (ET) is affected by multiple meteorological–water quality constraints, and the water quality indicators significantly related to ET are also affected by lake stratification. The coupled meteorological–water quality evaporation model can explain 93% of the evaporation change, which is 20% higher than the traditional meteorological Modelling evaporation model. (2) The nighttime ET is mainly affected by the thermal inertia lag, and the nighttime ET loss in Lake Wuliangsuhai accounts for 37.34% of the total evaporation, which cannot be ignored. (3) The actual water surface evaporation of the lake is much smaller than that measured by the pan conversion method and the regional empirical C formula method. The cumulative evaporation of Lake Wuliangsuhai from the non-freezing period to the early glacial period converted from meteorological station data is 1333.5 mm. The total evaporation in the non-freezing period is 2.77~3.68 × 108 m3, calculated by the lake area of 325 km2, while the evaporation calculated by the eddy station is 1.91 × 108 m3. In addition, the ET value measured by the cumulative C formula method was 424.2% higher than that of the model method and exceeded the storage capacity. Low-frequency and limited environmental index observations may lead to an overestimation of the real lake evaporation. Therefore, in situ, high-frequency meteorological–water quality monitoring and the eddy method deserve more consideration in future research on lake evaporation.

Mid-infrared spectra of T Tauri disks: Modeling the effects of a small inner cavity on CO2 and H2O emission

Context. The inner few AU of disks around young stars, where terrestrial planets are thought to form, are best probed in the infrared. The James Webb Space Telescope is now starting to characterize the chemistry of these regions in unprecedented detail, building on earlier results of the Spitzer Space Telescope that the planet-forming zone of disks contain a rich chemistry. One peculiar subset of sources characterized by Spitzer are the so-called CO2-only sources, in which only a strong 15 μm CO2 feature was detected in the spectrum. Aims. One scenario that could explain the weak or even non-detections of molecular emission from H2O is the presence of a small, inner cavity in the disk. If this cavity were to extend past the H2O snowline, but not past the CO2 snowline, this could strongly suppress the H2O line flux with respect to that of CO2. For this work, we aimed to test the validity of this statement. Methods. Using the thermo-chemical code Dust And LInes (DALI), we created a grid of T Tauri disk models with an inner cavity, meaning we fully depleted the inner region of the disk in gas and dust starting from the dust sublimation radius and ranging until a certain cavity radius. Cavity radii varying in size from 0.1 to 10 AU were explored for this work. We extended this analysis to test the influence of cooling through H2O ro-vibrational lines and the luminosity of the central star on the CO2 /H2O flux ratio. Results. We present the evolution of the CO2 and H2O spectra of a disk with inner cavity size. The line fluxes show an initial increase as a result of an increasing emitting area, followed by a sharp decrease. As such, when a large-enough cavity is introduced, a spectrum that was initially dominated by H2O lines can become CO2-dominated instead. However, the cavity size needed for this is around 4–5 AU, exceeding the nominal position of the CO2 snowline in a full disk, which is located at 2 AU in our fiducial, L* = 1.4 L⊙ model. The cause of this is most likely the alteration of the thermal structure by the cavity, which pushes the snowlines outward. In contrast, our models show that global temperature fluctuations, for example due to changes in stellar luminosity, impact the fluxes of H2O and CO2 roughly equally, thus not impacting their ratio much. Alternative explanations for bright CO2 emission are also briefly discussed. Conclusions. Our modeling work shows that it is possible for the presence of a small inner cavity to explain strong CO2 emission in a spectrum. However, the cavity needed to do so is larger than what was initially expected. As such, this scenario will be easier to test with sufficiently high angular resolution (millimeter) observations.

Measuring Turbulent Water Vapor Fluxes Using a Tunable Diode Laser-Based Open-Path Gas Analyzer

The reliable observation and accurate estimates of land–atmosphere water vapor (H2O) flux is essential for ecosystem management and the development of Earth system models. Currently, the most direct measurement method for H2O flux is eddy covariance (EC), which depends on the development of fast-response H2O sensors. In this study, we presented a cost-efficient open-path H2O analyzer (model: HT1800) based on the tunable diode laser absorption spectroscopy (TDLAS) technique, and investigated its applicability for measuring atmospheric turbulent flux of H2O using the EC method. We prepared two HT1800 analyzers with lasers that operate at wavelengths of 1392 nm and 1877 nm, respectively. The field performance of the two analyzers was evaluated through inter-comparative experiments with LI-7500RS and IRGASON, two of the most commonly used H2O analyzers in the EC community. Water vapor densities measured by the three types of analyzers had high overall agreement with the reference sensor; however, they all experienced drift. The mean density drifts of HT1800, LI-7500 and IRGASON were 3.7–5.2%, 4.0% and 3.8%, respectively. Even so, the half-hourly H2O fluxes measured by HT1800 were highly consistent with those by LI-7500RS and IRGASON (with a difference of less than 2%), suggesting that HT1800 can obtain H2O fluxes with high confidence. The HT1800 was also proved to be suitable for EC application in terms of data availability, flux detection limit and response to the high-frequency turbulent variation. Furthermore, we investigated how the spectroscopic effect influences the measurements of H2O density and flux. Despite the fact that the 1392 nm laser was much more susceptible to the spectroscopic effect, the fluxes after correcting for this bias showed excellent agreement with the IRGASON fluxes. Considering the cost advantage in laser and photodetector, the HT1800 analyzer using a 1392 nm infrared laser is a promising and economical solution for EC measurement studies of water vapor.

Measuring Canopy Gas Exchange Using CAnopy Photosynthesis and Transpiration Systems (CAPTS).

Canopy photosynthesis (Ac), rather than leaf photosynthesis, is critical to gaining higher biomass production in the field because the daily or seasonal integrals of Ac correlate with the daily or seasonal integrals of biomass production. The canopy photosynthesis and transpiration measurement system (CAPTS) was developed to enable measurement of canopy photosynthetic CO2 uptake, transpiration, and respiration rates. CAPTS continuously records the CO2 concentration, water vapor concentration, air temperature, air pressure, air relative humidity, and photosynthetic photon flux density (PPFD) inside the chamber, which can be used to derive CO2 and H2O fluxes of a canopy covered by the chamber. This system can also be used to measure the fluxes of greenhouse gases when integrating with CH4 and N2O analyzers. Here, we describe the protocol for using CAPTS to perform experiments on rice (Oryza sativa L.) in paddy field, wheat (Triticum aestivum L.) in upland field, and tobacco (Nicotiana tabacum L.) in pots.

Earthworms do not increase greenhouse gas emissions (CO2 and N2O) in an ecotron experiment simulating a three-crop rotation system

Earthworms are known to stimulate soil greenhouse gas (GHG) emissions, but the majority of previous studies have used simplified model systems or lacked continuous high-frequency measurements. To address this, we conducted a 2-year study using large lysimeters (5 m2 area and 1.5 m soil depth) in an ecotron facility, continuously measuring ecosystem-level CO2, N2O, and H2O fluxes. We investigated the impact of endogeic and anecic earthworms on GHG emissions and ecosystem water use efficiency (WUE) in a simulated agricultural setting. Although we observed transient stimulations of carbon fluxes in the presence of earthworms, cumulative fluxes over the study indicated no significant increase in CO2 emissions. Endogeic earthworms reduced N2O emissions during the wheat culture (− 44.6%), but this effect was not sustained throughout the experiment. No consistent effects on ecosystem evapotranspiration or WUE were found. Our study suggests that earthworms do not significantly contribute to GHG emissions over a two-year period in experimental conditions that mimic an agricultural setting. These findings highlight the need for realistic experiments and continuous GHG measurements.

Data treatment and corrections for estimating H2O and CO2 isotope fluxes from high-frequency observations

Abstract. Current understanding of land–atmosphere exchange fluxes is limited by the fact that available observational techniques mainly quantify net fluxes, which are the sum of generally larger, bidirectional fluxes that partially cancel out. As a consequence, validation of gas exchange fluxes applied in models is challenging due to the lack of ecosystem-scale exchange flux measurements partitioned into soil, plant, and atmospheric components. One promising experimental method to partition measured turbulent fluxes uses the exchange-process-dependent isotopic fractionation of molecules like CO2 and H2O. When applying this method at a field scale, an isotope flux (δ flux) needs to be measured. Here, we present and discuss observations made during the LIAISE (Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment) 2021 field campaign using an eddy covariance (EC) system coupled to two laser spectrometers for high-frequency measurement of the isotopic composition of H2O and CO2. This campaign took place in the summer of 2021 in the irrigated Ebro River basin near Mollerussa, Spain, embedded in a semi-arid region. We present a systematic procedure to scrutinise and analyse measurements of the δ-flux variable, which plays a central role in flux partitioning. Our experimental data indicated a larger relative signal loss in the δ fluxes of H2O compared to the net ecosystem flux of H2O, while this was not true for CO2. Furthermore, we find that mole fractions and isotope ratios measured with the same instrument can be offset in time by more than a minute for the H2O isotopologues due to the isotopic memory effect. We discuss how such artefacts can be detected and how they impact flux partitioning. We argue that these effects are likely due to condensation of water on a cellulose filter in our inlet system. Furthermore, we show that these artefacts can be resolved using physically sound corrections for inlet delays and high-frequency loss. Only after such corrections and verifications are made can ecosystem-scale fluxes be partitioned using isotopic fluxes as constraints, which in turn allows for conceptual land–atmosphere exchange models to be validated.

Water stress changes the relationship between photosynthesis and stomatal conductance

Understanding the relationship between stomatal conductance (gs) and photosynthesis (An) under water stress conditions can improve the accuracy of land surface models for estimating the gas exchange of crop canopies with the atmosphere. However, little is known about the effect of water stress on this relationship in crops. A glasshouse experiment was, therefore, conducted to investigate changes in the linear relationship between gs and An owing to water stress in rice and the association with soil moisture content. Severe (SWS), mild (MWS), and no water stress (NWS) conditions were applied from flowering onwards and the gas exchange in fully developed flag leaves was assessed weekly. The Ball-Woodrow-Berry linear model was used to assess the relationship between gs and An under different treatments. SWS had a significant effect and reduced the slope of the linear relationship between gs and An by 30 % compared with NWS. Only in SWS were An and gs strongly correlated with soil water content. Our study revealed that changes in the linear relationship through a reduction in the slope imply a conservative water-use strategy for rice under intense water stress. We propose that crop models that use the linear relationship should consider the impact of water stress conditions when simulating yields and estimating CO2 and H2O fluxes from crop canopies.

Eddy correlation measurements to visualize CO2 and water vapor concentrations and fluxes

Eddy correlation measures gas exchange between canopy and the overlying atmosphere by evaluating the correlation between fluctuations in the gas-of-interest’s mixing ratio and the vertical wind velocity and considered the most accurate approach for measuring gas fluxes, mostly carbon dioxide and water vapor under ideal homogeneous conditions. It has been used in micrometeorology for decades to quantify mass and energy transfer between urban, natural and agricultural ecosystems and the atmosphere. We assessed its application under various—homogeneous and non-homogeneous—conditions. Our study indicates that fluxes of CO2 and H2O correlate well with plants activity only when turbulent conditions are present, in open fields. At such conditions, direct measurements of concentration of those gases are not an accurate indicator for plants activity. On the other hand, in closed systems (e.g. greenhouses)- fluxes as measured by an eddy correlation system can't accurately be related to the state of the vegetation, but the fluctuations in the concentrations of CO2 and H2O directly correlate to the actual plants activity. Adapting conditions in greenhouses to limiting factors as temperature, increases CO2 sequestration by plants, and may increase productivity

A study of the role of seven historically significant fast-response hygrometers and sensor calibration on eddy covariance H2O fluxes and surface energy balance closure

Water vapor fluxes are a major component of the surface energy balance, hydrological cycle, and ecosystem processes. As newer sensors are developed for eddy covariance measurements, the role of different technologies and calibration uncertainties on H2O fluxes and surface energy balance closure should be assessed. Here, a field intercomparison is described testing historically significant fast-response hygrometers: Lyman-α, KH2O, LI-7000, LI-7500, LI-7200, EC155, and EC150. This study occurred in southeastern Wyoming in September 2015. Three methods of calibration are investigated: standard calibration with a dew point generator and zero-air gas, referencing to a first principles slow-response hygrometer, and piecewise calibration between fast-response hygrometers based on blocks of time with consistent relationships between 5-minute data. Differences in fluxes among the infrared gas analyzers were largest when using the standard calibration (maximum difference of 15.9%, standard deviations of differences between 4.1–6.0%) with differences reduced by 0.3–0.6 × when the calibrations were referenced to a first principles hygrometer. The smallest differences occurred using the piecewise calibration, which emphasizes the intrinsic differences among the sensor technologies, where differences were further reduced by 0.04–0.09 × (maximum difference of 8.2%, standard deviations of differences between 2.3–3.0%). The Lyman-α and KH2O experienced severe drifts, though their piecewise calibrations were generally within the range of the others. The two most influential factors beyond calibration uncertainty were the oxygen correction for the ultraviolet absorption sensors, especially the KH2O, and the tube attenuation spectral correction for closed-path analyzers, mostly with the lower flow EC155. The effect of hygrometers on the energy balance closure was minor with some uncertainty associated with the standard calibration, though this was less than the change in closure associated with the choice of sonic anemometer. These results focus attention on the need to further develop accurate calibration methodologies that are suitable for all flux tower sites.

Implications of seasonal changes in photosynthetic traits and leaf area index for canopy CO2 and H2O fluxes in a Japanese cedar (Cryptomeria japonica D. Don) plantation

Recently, requests for forest management to conserve water resources and sequester carbon have increased in Japan, where approximately 27% and 12% of the total land area are covered by forest plantations and Japanese cedar (Cryptomeria japonica D. Don). To formulate better forest management practices that maximize forest functions by maintaining water and carbon cycles, an understanding of how leaf-level ecophysiological traits influence canopy-level CO2 and H2O exchanges in Japanese cedar plantations is required. In this study, observations of eddy covariance flux and leaf ecophysiology in a Japanese cedar plantation in southern Japan indicate that significantly greater productivity and seasonal variations tend to occur in canopy CO2 and H2O fluxes, with seasonal patterns of photosynthetic traits (maximum carboxylation rate normalized at 25 °C, Vcmax,25) and leaf area index (LAI). We also examined how biotic (e.g., Vcmax,25 and LAI) and abiotic (e.g., meteorological variables) factors govern canopy fluxes using a multi-layer soil–vegetation–atmosphere transfer (SVAT) model. The model validation suggests that seasonal variations in Vcmax,25 and LAI must be included to reproduce the fluxes observed in the plantation. Quantitative experiments using the validated SVAT model indicate that considering cold acclimation during the winter improved the reproducibility of the model with regard to the measured fluxes, constant high intra-annual LAI had the least impact on forest productivity, and a consistently high Vcmax,25 value increased forest productivity but considerably decreased the nitrogen use efficiency and required a larger nitrogen supply from the ecosystem during the winter. These findings highlight the necessity of decreasing photosynthetic ability during the winter, which safeguards the ecosystem's nitrogen resources to sustain the productivity of the Japanese cedar plantation throughout the year.

A dataset of carbon and water fluxes and micrometerological elements in Danzhou rubber plantation (2010-2018)

Rubber plantation is one of the main artificial vegetation types in Hainan Island. As an important forest ecosystem in China’s tropical regions, rubber plantation plays an important role in the regional carbon and water cycle. Measuring the carbon and water fluxes is critical for estimating the carbon and water balance and energy exchange of rubber plantation. Since November 2009, near-surface CO2 and H2O fluxes observation have been carried out in Danzhou rubber plantation, including eddy covariance system and meteorological observation system. Up to now, it has accumulated flux and meteorological observation data for 12 years. This dataset organizes the rubber plantation flux and conventional meteorological data in Danzhou from 2010 to 2018, including net ecosystem productivity, ecosystem respiration, gross ecosystem productivity, latent heat flux, sensible heat flux, evapotranspiration, air temperature, air relative humidity, vapor pressure, wind speed, wind direction, atmospheric pressure, total radiation, net radiation, photosynthetically active radiation, soil temperature, soil water content and precipitation. This dataset can provide basis and reference for ecosystem evaluation and sustainable development planning in economic and social.

Simulating canopy carbonyl sulfide uptake of two forest stands through an improved ecosystem model and parameter optimization using an ensemble Kalman filter

The uptake of carbonyl sulfide (COS) by plant canopy closely correlated with photosynthetic CO2 uptake as they share the same diffusion pathway. Process-based ecosystem models have been used to simulate the CO2, H2O and COS fluxes between terrestrial ecosystems and atmosphere. Some model parameters often vary seasonally and interannually. In this study, the hourly Boreal Ecosystem Productivity Simulator (BEPS) was first improved to simulate the canopy COS uptake rate. Then, an ensemble Kalman filter was designed to optimize the key parameters of the hourly BEPS model, considering the errors in the input, parameters and measurements. The optimized parameters include leaf maximum carboxylation rate at 25 °C at top of canopy (Vcmax250) and a calibration term (α) used to scale the apparent conductance for COS uptake from the intercellular airspace (gcos) to Vcmax. The fluxes of gross primary productivity (GPP), latent heat (LE) and COS uptake by canopy (Fcos_veg) measured using eddy covariance method at a temperate deciduous forest during 2012–2013 and a boreal conifer forest during 2013–2017 were used for data assimilation. Parameters were optimized daily and presented as 10-day averages. It was found that the parameters showed considerable seasonally and interannually variations. With parameter optimization using EnKF, the improved hourly BEPS model could explain 86%, 68% and 55% of variations in measured daily GPP, LE and Fcos_veg at US-Ha1 site during 2012 and 2013 and captured 90%, 74% and 69% of variations in the measured GPP, LE and Fcos_veg at FI-Hyy site during 2013–2017, respectively. The simulated daily Fcos_veg with the parameters optimized using EnKF could capture the day-to-day variations of Fcos_veg at the two studied sites and performed better than the simulations with calibrated parameter values. Further efforts were required to investigate the impacts of model structure and different parameter optimization methods on the optimized parameter values.

Open-path anti-pollution multi-pass cell-based TDLAS sensor for the online measurement of atmospheric H2O and CO2 fluxes.

We report an open-path and anti-pollution multi-pass cell based tunable diode laser absorption spectroscopy (TDLAS) sensor, which was designed for online measurement of atmospheric H2O and CO2 fluxes. It is mainly composed of two plano-convex mirrors coated on a convex surface, which makes it different from traditional multi-pass cells. This design does not allow a direct contact between the coating layer of the lens and air, thereby realizing the anti-pollution effect of the coating layer. Two DFB lasers operating at 1392 nm and 2004 nm were employed to target H2O and CO2 absorption lines, respectively. Allan analysis of variance indicated that detection limits of H2O and CO2 were 5.98 ppm and 0.68 ppm, respectively, at an average time of 0.1 s. The sensor performance was demonstrated by measuring CO2 and H2O flux emissions at Jiangdu Agricultural Monitoring Station in Jiangsu Province. The results were compared with those obtained using the commercial instrument LI-7500, which is based on non-dispersive infrared technology. The developed gas analysis instrument exhibited good consistency with commercial instruments, and its accuracy was comparable; thus, it has strong application prospects for flux measurements in any ecosystem.

Accuracies of field CO2–H2O data from open-path eddy-covariance flux systems: assessment based on atmospheric physics and biological environment

Abstract. Ecosystem CO2–H2O data measured by infrared gas analyzers in open-path eddy-covariance (OPEC) systems have numerous applications, such as estimations of CO2 and H2O fluxes in the atmospheric boundary layer. To assess the applicability of the data for these estimations, data uncertainties from analyzer measurements are needed. The uncertainties are sourced from the analyzers in zero drift, gain drift, cross-sensitivity, and precision variability. These four uncertainty sources are individually specified for analyzer performance, but so far no methodology exists yet to combine these individual sources into a composite uncertainty for the specification of an overall accuracy, which is ultimately needed. Using the methodology for closed-path eddy-covariance systems, this overall accuracy for OPEC systems is determined from all individual uncertainties via an accuracy model and further formulated into CO2 and H2O accuracy equations. Based on atmospheric physics and the biological environment, for EC150 infrared CO2–H2O analyzers, these equations are used to evaluate CO2 accuracy (±1.22 mgCO2 m−3, relatively ±0.19 %) and H2O accuracy (±0.10 gH2O m−3, relatively ±0.18 % in saturated air at 35 ∘C and 101.325 kPa). Both accuracies are applied to conceptual models addressing their roles in uncertainty analyses for CO2 and H2O fluxes. For the high-frequency air temperature derived from H2O density along with sonic temperature and atmospheric pressure, the role of H2O accuracy in its uncertainty is similarly addressed. Among the four uncertainty sources, cross-sensitivity and precision variability are minor, although unavoidable, uncertainties, whereas zero drift and gain drift are major uncertainties but are minimizable via corresponding zero and span procedures during field maintenance. The accuracy equations provide rationales to assess and guide the procedures. For the atmospheric background CO2 concentration, CO2 zero and CO2 span procedures can narrow the CO2 accuracy range by 40 %, from ±1.22 to ±0.72 mgCO2 m−3. In hot and humid weather, H2O gain drift potentially adds more to the H2O measurement uncertainty, which requires more attention. If H2O zero and H2O span procedures can be performed practically from 5 to 35 ∘C, the H2O accuracy can be improved by at least 30 %: from ±0.10 to ±0.07 gH2O m−3. Under freezing conditions, the H2O span procedure is impractical but can be neglected because of its trivial contributions to the overall uncertainty. However, the zero procedure for H2O, along with CO2, is imperative as an operational and efficient option under these conditions to minimize H2O measurement uncertainty.

Modeling Gas Flow Velocities in Soils Induced by Variations in Surface Pressure, Heat, and Moisture Dynamics

AbstractChanges in atmospheric pressure continuously ventilate soils and snowpacks. This physical process, known as pressure pumping, is a major factor in the exchange fluxes of H2O, CO2, and other trace gases between the soil and atmosphere. Thus models of pressure pumping are relevant to many areas of critical importance. This study compares the three principal models used to describe pressure pumping. Beginning with the fundamental physical principles and whether the flow field is compressible or incompressible, these models are categorized as linear parabolic (one model—compressible) or nonlinear hyperbolic (two models—incompressible). Using observed soil surface pressure data, measured vertical profiles of soil permeability and standard linear analysis and numerical methods, this study shows that nonlinear models produce advective velocities that are one to two orders of magnitude greater than those associated with the linear model. Incorporating soil temperature and moisture dynamics made very little difference to the linear model, but a significant difference in the nonlinear models suggesting that advective velocities induced by pressure changes associated with soil heating and moisture dynamics may not always be small enough to ignore. All numerical results are sensitive to the frequency of the pressure forcing, which was band‐pass filtered into low, mid and high frequencies with the greatest model differences at low frequencies. Partitioning the pressure forcing and model responses helped to establish that mid‐frequency weather‐related phenomena (empirically identified as inertia gravity waves and solitons) are important drivers of gas exchange between the soil and the atmosphere.