Bowen Ratio Research Articles

Petroleum phase evolution at high temperature: A combined study of oil cracking experiment and deep oil in Dongying Depression, eastern China

Numerous light oil reservoirs have been discovered in the lower part of Mbr 4 of Paleogene Shahejie Fm in the Dongying Depression, Bohai Bay Basin, eastern China. The petroleum phases and reservoir-forming models are crucial to understanding the hydrocarbon accumulation mechanisms in the deep lacustrine layers. The deep formation temperature and pressure, the PVT phase diagrams, as well as the burial-thermal history were simulated and restored based on the results of oil cracking experiments and the analysis of measured data of geological sections in the Dongying Depression. The process and laws of hydrocarbon accumulation were summarized. The cricondentherm envelopes depict a series of variations when the molar percentages of CO2, CH4, C2-5, and C6+ in the fluid composition change. In the process of oil cracking, the cricondenbar increases with the increase in the molar percentage of CH4. With the increase in molar percentage of C2-5 and C6+, the cricondenbar decreases continuously. According to simulations of fluid composition and phase state, the oil reservoirs in this area are primarily oil-rim condensate gas reservoirs and volatile oil reservoirs. Based on burial-thermal history recovered under the constraint of measured vitrinite reflectance (VRo), the homogenization temperature of fluid inclusions suggests two main periods of petroleum charging: in the late deposition of the Mbr 3 of the Paleogene Shahejie Fm and Guantao Fm in the Eocene. In the second charged stage, the oil cracking gas from deep places in the depression was injected into the primary oil and gas reservoirs, causing the changes and differentiation of fluid phases in the reservoirs. The gas invasion and evaporative fractionation caused by late natural gas filling are key factors for the formation of light oil reservoirs.

Evaluation of Selected Empirical Schemes of Calculating Sensible Heat Flux from Routinely-Measured Meteorological Parameters in a Tropical Location

The accurate estimation of sensible heat flux (Hs) is imperative in the exchange of energy and mass between the earth’s systems. However, the process of acquiring the sensible heat flux data is challenging due to the complexity in its direct measurement hence, not readily available. The alternative is to use estimations which are derived from specific models. This study evaluated the performances of five selected schemes of estimating Hs from routinely-measured meteorological parameters using statistical methods such as Mean Bias Error (MBE), Mean Percentage Difference (MPD), Root Mean Square Error (RMSE), Index of Agreement (IA), Correlation Coefficient (R) and Coefficient of Determination (R2). The empirical schemes selected are: Berkowicz and Prahm (BP), Bowen Ratio Energy Balance (BREB), Holstlag and Van Ulden (HU), Smith (ST) and Surface Temperature (ST) schemes. The results obtained revealed that in the dry season, MBE values of 6.9 Wm-2, 7.2 Wm-2, 7.5 Wm-2, 6.3 Wm-2 and -3.8 Wm-2 were obtained for BP, BREB, HU, SMT and ST respectively. In the wet season, BP, BREB, HU, SMT and ST had MBE values of 37.4 Wm-2, 14.2 Wm-2, 4.2 Wm-2, 12.0 Wm-2 and -1.1 Wm-2 respectively. The MBEs, RMSEs and MPDs obtained for the schemes were higher in the wet season (about 70 %) than in the dry season; implying that the schemes performed better in the dry season than in the wet season. The study rated BREB as the best method of estimating the sensible heat flux at the study location having the lowest MBE, lowest MPD, lowest RMSE, high R, high R2 and high IA in both seasons.

Numerical and experimental study of the transient conjugate heat transfer and fluid flow of passive residual heat removal heat exchanger

The transient heat transfer performance of passive residual heat removal heat exchanger (PRHR HX) with C-tube bundle directly influences nuclear reactor safety under accident condition. This paper presents an investigation of transient conjugate heat transfer and fluid flow phenomena and characteristics of scaled-down single C-tube submerged in water tank under atmospheric pressure at the initial period before saturation pool boiling occurs. Empirical calculation model, experimental setup and numerical model were established separately, and both numerical and experimental studies were carried out. The distributions of tube outlet temperature and water temperatures at horizontal and vertical monitoring points in tank were obtained. Detailed comparisons of the results show good agreements. Also, the change tendencies of heat flux, heat transfer coefficients and heat load were analyzed. The fluctuation of heat flux along normalized length from tube inlet firstly increases but finally tends to keep stable with the change of temperature difference and transformation of heat transfer mechanism. The heat transfer coefficient inside tube shows a slight downtrend along normalized length from tube inlet, but the heat transfer coefficient outside tube shows obvious change in the transient process. The total heat load continuously decreases with time. Furthermore, the volume fraction of vapor is relatively low during the subcooled boiling period. The two-phase flow enhances the agitation in water tank and the fluid velocity near tube outside wall is much larger.

Air‐Lake Momentum and Heat Exchange in Very Young Waves Using Energy and Water Budget Closure

AbstractTurbulent momentum and heat exchanges at the air‐water interface of lakes are complex processes due to diverse characteristics such as climate, fetch limitation, and geometry; however, their parameterizations are necessary for hydro‐ and thermodynamic modeling. In this study, we performed comprehensive research on turbulent exchanges of a shallow, large but highly fetch limited lake employing 5 months of simultaneous eddy‐covariance (EC), wave, energy, and water budget measurements. Based on the Monin‐Obukhov similarity theory, wind and wave age‐related drag coefficients and roughness lengths were derived for very young wave ages. The new drag functions showed an increased water surface resistance compared to marine conditions. In terms of water vapor roughness length and transfer coefficients, an apparent intra‐seasonal variation was observed. Turbulent heat fluxes were evaluated by closing the lake's energy budget using the Bowen ratio method. Furthermore, we aimed to close the energy budget by assuring the water balance closure as well through the evaporation (latent heat flux), resulting in significant deviations from the EC‐based results. EC‐based heat fluxes and transfer coefficients were found to be underestimated on average by 29% and 33%, respectively. The water balance closure suggested that the energy residual should not be distributed based on the Bowen ratio, and sensible heat fluxes were more underestimated than latent heat fluxes. In the case of Lake Balaton, atmospheric stability plays a minor role; however, our analysis revealed significant effects caused by the surrounding topography and water side stratification.

Numerical and experimental examinations of free convection condensation of steam in the presence of air over the cooled panel

In this paper, experimental and numerical investigations have been conducted to evaluate the steam condensation in the presence of air over a vertical plate for a small temperature difference between the air and a cold wall. In the paper, we describe the experimental set-up, emphasizing the conditioning and measuring equipment introduced for this research. A numerical model is also described in detail. The estimated condensation quantities agreed well with the experimental data. According to the data, simulated total condensation quantities were higher than measured total condensation amounts in all cases, ranging from 6.8 to 13.4% (average 8.9%). The condensation rate increases by 28% as the sub-cooling temperature rises from 2.1 °C to 4.4 °C. The mass fraction of water vapor in the air also induces condensation. Average condensation flux decreases 41.7% when relative humidity decreases from 74.9 to 65.4% at the same surface temperature. In the last part, an empirical correlation, which is characterized by the partial pressure difference of water vapor at the surface and out of the boundary layer conditions, was proposed to estimate the condensation flux over the vertical plate. This practical correlation is novel and can be used for various engineering applications.

Tree-ring isotopes from Araucaria araucana as useful proxies for climate reconstructions

Tree-ring width (TRW) chronologies have been widely and long-time used to reconstruct past climate variations in the Andes in South America. The use of tree-ring isotopic chronologies is still not widespread in this region although they have proved to be very efficient climate proxies. Araucaria araucana (Molina) K. Koch is a conifer tree species with some multi-century-old individuals that offers an excellent opportunity to measure stable carbon (δ13C) and oxygen (δ18O) isotopes in cellulose from long tree-ring records. Here, we explore whether current or stored carbohydrates are used for A. araucana radial growth and we assess the potential of a tree-ring isotopic record of to study past climate variability. Eleven A. araucana cores from a dry and high-elevation forest at the northern border of Patagonia, Argentina (38°55’S, 70°44’W) were selected for stable isotopes analyses. The strong correlation between the isotopic composition of the first and second parts of the same ring, but also the strong relationships between δ13C and δ18O records with climate parameters of the current growing season such as temperature, show that tree-rings are built mostly with carbohydrates produced during the current growing season with little or no supply from storage or reserves. This finding leads to reconsidering the interpretation of the legacy effect (i.e. ecological memory effects) based on the previously described strong negative correlation between A. araucana TRW chronologies and previous growing season temperature and suggests a dependence of radial tree growth on the level of development of organs. Regarding climate sensitivity, the A. araucana tree-ring δ13C chronology is strongly related to current summer temperature (r = 0.82, p < 0.001), vapour pressure deficit (VPD; r = 0.79, p < 0.001), precipitation (r = −0.53, p < 0.001) and SPEI2 (r = −0.73, p < 0.001). These strong relationships support the use of δ13C of A. araucana tree-ring cellulose to reconstruct past temperature variations at regional scale in relation with large-atmospheric drivers of climate variability such as the Southern Annular Mode. The A. araucana tree-ring δ18O chronology is also correlated with temperature (r = 0.42, p < 0.01) and VPD (r = 0.45, p < 0.01) of the winter preceding the growing season. This suggests that trees are using water from precipitation infiltrated in the soil during the previous recharge period (autumn-winter). The weak correlations of δ18O with current summer atmospheric conditions and the decoupling between δ18O and δ13C, may be due to a high rate of oxygen exchange between sugars and xylem water (Pex) during cellulose synthesis, which dampens evaporative isotopic fractionation.

Analysis of Surface Energy Changes over Different Underlying Surfaces Based on MODIS Land-Use Data and Green Vegetation Fraction over the Tibetan Plateau

To better predict and understand land–atmospheric interactions in the Tibetan Plateau (TP), we used Moderate Resolution Imaging Spectroradiometer (MODIS)-based land-use data and the MODIS-derived green vegetation fraction (GVF) to analyze the variation trend over the TP. The in situ observations from six flux stations (“BJ” (the BJ site of Nagqu Station of Plateau Climate and Environment), “MAWORS” (the Muztagh Ata Westerly Observation and Research Station), “NADORS” (the Ngari Desert Observation and Research Station), “NAMORS” (the Nam Co Monitoring and Research Station for Multisphere Interactions), “QOMS” (the Qomolangma Atmospheric and Environmental Observation and Research Station), and “SETORS” (the Southeast Tibet Observation and Research Station for the Alpine Environment)) at the Chinese TP Scientific Data Center were used to study the surface energy variation characteristics and energy distribution over different underlying surfaces. Finally, we used observation data to verify the applicability of the ERA-5 land reanalysis data to the TP. The results showed that the annual GVF steadily declined from the southeast parts to the northwest parts of the TP, and the vegetation coverage rate was highest from June to September. The sensible heat flux (H), latent heat flux (LE), net surface radiation (Rn), and four-component radiation (solar downward shortwave radiation (Rsd), surface upward shortwave radiation (Rsu), atmospheric downward longwave radiation (Rld), and surface upward longwave radiation (Rlu)) reached their maxima in summer at each station. Rld did not change significantly with time; all other variables increased during the day and decreased at night. The interannual variation in H and LE shows that latent heat exchange was the dominant form of energy transfer in BJ, MAWORS, NAMORS, and SETORS. By contrast, sensible heat exchange was the main form of energy transfer in NADORS and QOMS. The Bowen ratio was generally low in summer, and some sites had a maximum in spring. The surface albedo exhibited a “U” shape, decreasing in spring and summer, and increasing in autumn and winter, and reaching the lowest value at noon. Except for SETORS, ERA-5 Land data and other flux stations had high simulation accuracy and correlation. Regional surface energy changes were mainly observed in the eastern and western parts of the TP, except for the maximum of H in spring; the maximum values of other heat fluxes were concentrated in summer.

Influence Mechanism of Metal Vapor in Plasma Arc Lap Welding

A three-dimensional coupled tungsten electrode–plasma arc–metal vapor– weld pool model was developed to investigate plasma arc and metal vapor characteristics, weld pool convection, and energy transfer in conduction plasma arc lap welding. The arc energy efficiency was also calculated. The numerical results showed that in conduction plasma arc lap welding, the constraint effects of the plasma arc by a small constricting nozzle, plasma gas, and electromagnetic force were strong, and no keyhole was formed inside the weld pool, so the heat flux on the weld pool surface was high as well as the weld pool temperature and mole fraction of Fe vapor above the weld pool surface. The high concentration of Fe vapor in the arc decreased the conduction energy from the plasma arc to the weld pool along with the arc energy efficiency. The calculated arc energy efficiency was only 50.2%. Without considering Fe vapor, the calculated weld pool had complete joint penetration. When considering Fe vapor, the calculated weld geometry agreed well with the experimental result.

A Novel Integrated Design for Heat and Water Recovery from Exhaust Flue Gas of Bandar Abbas Power Plant

This study concerns a theoretical design of a condensing heat exchanger for a 320 MW unit of Bandar Abbas thermal power plant in the south of Iran. A film theory in conjunction with heat and mass transfer analogy is used as the theoretical basis of the design. The condensing unit is used for heat and mass recovery from the natural gas-fired boiler flue gases. The assumed condensing unit includes 4 equal capacity condensing heat exchangers, each of which is supposed to reduce the flue gas temperature from 160 ℃&amp;nbsp;to 53℃. Decreasing the flue gas temperature to below the dew point temperature of its water vapor causes condensation (latent) and sensible heat transfer. The analysis was done for 13%, 15%, and 17% of the water vapor volume fraction in the flue gases, and based on the 17% water vapor fraction, 52.8 tons/hr of water was recovered. This recovered water could be used as the cooling tower makeup, and accordingly, almost 14% of water consumption is saved. The recovered heat by the condensing unit is also being used as the heat source of an ORC cycle, and up to 2.8 MW power is estimated to be generated depending on the evaporation temperature.

Comparison of air and EGR with different water fractions dilutions on the combustion of hydrogen-air mixtures

Lean combustion and exhaust gas recirculation (EGR) are key strategies for controlling NO and heat release process of hydrogen engines. This paper firstly compared these two strategies on combustion behaviors of hydrogen-air mixtures within dilution ratio ranges from 0 to 50%. Then, the water vapor effects in EGR on combustion of hydrogen-air mixtures are further investigated. All tests are conducted in a constant volume combustion vessel at the initial temperature of 373 K and pressure of 1 bar. CHEMKIN PRO is adopted to predict the hydrogen-air mixtures combustion behaviors under different conditions with one-dimensional premixed adiabatic planner flame model. The unburnt hydrogen concentration and the NO mole fraction in the final products were measured. The results show that laminar burning velocity decreases more obviously with the EGR ratio than air dilution ratio. EGR dilution has much obvious influence on reducing NO mole fraction in the final products. However, both dilution strategies adversely cause the increase of incompletely combusted H2. To balance the NO control and unburned H2 emission, 30% EGR rate with 20% water vapor fraction is recommended based on the testing ranges of this study.

Calibration and validation of three evapotranspiration models in a tea field in the humid region of south‐east China

AbstractEvapotranspiration (ETc) is the most important part of agricultural water consumption. Accurate determination of the ETc of tea trees is important in the water management of tea fields. In this study, three models, the Penman–Monteith (PM), Priestley–Taylor (PT) and crop coefficient (KC) models, were applied and calibrated using meteorological data of 2017 in a tea field. The calibrated models were validated using the Bowen ratio energy balance (BREB) method with the data of 2018 and 2019 in the tea field. The canopy resistance of the PM model was calibrated by the inverse method with the BREB‐measured ETc using the Katerji and Perrier (KP) submodel with R2 equal to 0.80. The annual mean value of the coefficient in the PT model (α = 1.03) was determined based on the BREB results and meteorological data. In addition, the crop coefficients of tea trees based on the measured ETc and reference evapotranspiration (ET0) were comprehensively evaluated, with values of 0.86, 1.19 and 0.96 at the three growth stages, showing a cyclical evolution within a year. The PT model performed best, with a root mean square error (RMSE) equal to 0.82 mm day−1 and a Nash–Sutcliffe efficiency (NSE) equal to 0.90. The PM model underestimated ETc with RMSE equal to 0.79 mm day−1 and NSE equal to 0.84, while the KC method overestimated ETc.

Impact of diffuse radiation on evapotranspiration and its coupling to carbon fluxes at global FLUXNET sites

Diffuse radiation is widely known for its higher light use efficiency in ecosystem carbon uptake than direct radiation, which inevitably alters ecosystem evapotranspiration (ET), as plant carbon uptake and water use are closely coupled through leaf stomata. However, although the impact of diffuse radiation on ecosystem carbon uptake has been extensively explored, its impact on ecosystem ET remains unclear on the global scale and across different plant functional types (PFTs). In this study, we explored the impacts of diffuse radiation on ecosystem ET and its coupling to net ecosystem exchange (NEE) based on long-term eddy-covariance observations and the derived diffuse radiation fraction (Kd) at 201 FLUXNET stations. We found that the increase in diffuse radiation results in a net enhancement of ET when Kd was below 0.42-0.48 for most PFTs. Diffuse radiation was more effective in promoting ET than direct radiation because the diffuse fertilization effect (DFE) on NEE tightly regulates ET through stomatal coupling. On average, the efficiency of diffuse radiation (Kd > 0.8) was 1.51 (±0.80) times higher than that of direct radiation (Kd < 0.2) in promoting ET when the PAR level was less than 300 W m−2, which was lower than the ratio of 2.40 (±0.93) for NEE under the same conditions, because the simultaneous reductions in vapor pressure deficit (VPD) in part offset the enhancement of ET. Consequently, the increase in ET results in a higher evaporative fraction under shaded conditions with more diffuse radiation. We emphasized the importance of considering the DFE on ecosystem ET in assessing aerosol-induced perturbations in the water cycle under the current and future climate.

Study on the hydrothermal recovery characteristics of nano-ceramic membranes on regenerative gas

In view of the large energy consumption of the regeneration process in the chemical absorption decarburization process, on the basis of the enrichment classification flow process, the nanoscale ceramic film is used as a new heat exchanger between the enriched liquid and the regeneration gas. The porous ceramic film is capable of coupling thermal-mass transfer to effectively recover part of the water vapor and the heat carried in the regeneration gas, so as to reduce the regenerative energy consumption of the system. The effects of parameters such as regeneration temperature, flow rate, molar fraction of water vapor, and MEA enrichment temperature, flow rate, and MEA concentration of shunt on the hydrothermal recovery effect of ceramic membranes of different pore sizes and lengths were studied by using the heat recovery flux and water recovery rate as the indicators. The results show that the hydrothermal recovery performance of the ceramic membrane increases with the increase of MEA enrichment flow, but decreases significantly with the increase of the enrichment temperature. At the same time, with the increase of regenerative gas velocity and the molar fraction of water vapor in the regenerative gas, the heat recovery flux will increase. The heat recovery performance of the 10 nm ceramic membrane is better than that of the 20 nm ceramic membrane.

Experimental measurements and modelling of vapour−liquid equilibria for four mixtures of 2,3,3,3−tetrafluoropropene (R1234yf) with 1,1,1,2−tetrafluoroethane (R134a) or 1,1−difluoroethane (R152a) or trans−1−chloro−3,3,3−trifluoropropene (R1233zd(E)) or 2−chloro−3,3,3−trifluoropropene (R1233xf)

Isothermal vapour−liquid equilibrium (VLE) for four binary systems involving R1234yf (R1234yf + R134a, R1234yf + R152a, R1234yf + R1233zd(E) and R1234yf + R1233xf) were measured at temperatures from 278.15 to 348.15 K. The experiments were conducted by means of a “static−analytic” apparatus with phase analysis via gas chromatography, with resulting uncertainties of 0.6 K for temperature, 8 kPa for pressure and a maximum of 0.007 for vapour and liquid mole fractions. The main advantage of the equipment is that vapour and liquid samples are taken from vapour and liquid phases by two capillary samplers (ROLSI®). The Peng Robinson Equation of State is considered to represent the experimental data. If possible, comparison between the new experimental data and prediction with REFPROP 10.0 software are realized.

Modified Method of Characteristics for Generating Enhanced Oil Recovery Curves

Summary Gas injection is a frequently used technique for enhanced oil recovery. If the gas injection is carried out at a pressure at or above the minimum miscibility pressure (MMP), it is possible to achieve a recovery that approaches 100%. However, it is not always possible to inject the gas at such a high pressure, which makes it interesting to also know what recoveries can be obtained at pressures below the MMP. The recovery as a function of pressure can be found experimentally by conducting a slimtube experiment or by simulating such an experiment. Jessen et al. (2001) has, as an alternative to a traditional 1D or cell-to-cell slimtube simulation techniques, proposed a very fast simulation method based on the method of characteristics (MoC). It constructs the composition zones developing in a slimtube during gas injection as well as providing gas and oil saturation profiles and compositions throughout the slimtube. From this information, the recovery can readily be calculated. The method in Jessen et al.(2001) relies on volumetric gas and oil saturations evaluated at the tie-line intersections which are molar-based. Molar vapor fractions at the tie-line intersections will be below 0 or above 1 and will therefore represent a fluid located outside the two-phase region. With negative molar fractions, the total volume may become negative or zero. When the total volume becomes zero, the volumetric saturations (volume fractions of each phase) cannot be calculated from the molar phase fractions due to zero-division, and the saturation profile calculation cannot be performed. This paper presents a modified MoC that does not have this weakness and will not encounter a zero-division caused by zero total volume. The paper further presents a scaling method that will ensure that the modified method gives results close to those obtained with the method in Jessen et al. (2001) when the latter does not stop due to a zero-division. The result is a fast, safe, and reliable method for calculating the recovery from an oil field with gas injection conducted at a pressure between the reservoir fluid saturation pressure and the MMP.

Comparison of Fourteen Reference Evapotranspiration Models With Lysimeter Measurements at a Site in the Humid Alpine Meadow, Northeastern Qinghai-Tibetan Plateau.

Evapotranspiration is a key component in the terrestrial water cycle, and accurate evapotranspiration estimates are critical for water irrigation management. Although many applicable evapotranspiration models have been developed, they are largely focused on low-altitude regions, with less attention given to alpine ecosystems. In this study, we evaluated the performance of fourteen reference evapotranspiration (ET0) models by comparison with large weight lysimeter measurements. Specifically, we used the Bowen ratio energy balance method (BREB), three combination models, seven radiation-based models, and three temperature-based models based on data from June 2017 to December 2018 in a humid alpine meadow in the northeastern Qinghai–Tibetan Plateau. The daily actual evapotranspiration (ETa) data were obtained using large weighing lysimeters located in an alpine Kobresia meadow. We found that the performance of the fourteen ET0 models, ranked on the basis of their root mean square error (RMSE), decreased in the following order: BREB > Priestley-Taylor (PT) > DeBruin-Keijman (DK) > 1963 Penman > FAO-24 Penman > FAO-56 Penman–Monteith > IRMAK1 > Makkink (1957) > Makkink (1967) > Makkink > IRMAK2 > Hargreaves (HAR) > Hargreaves1 (HAR1) > Hargreaves2 (HAR2). For the combination models, the FAO-24 Penman model yielded the highest correlation (0.77), followed by 1963 Penman (0.75) and FAO-56 PM (0.76). For radiation-based models, PT and DK obtained the highest correlation (0.80), followed by Makkink (1967) (0.69), Makkink (1957) (0.69), IRMAK1 (0.66), and IRMAK2 (0.62). For temperature-based models, the HAR model yielded the highest correlation (0.62), HAR1, and HAR2 obtained the same correlation (0.59). Overall, the BREB performed best, with RMSEs of 0.98, followed by combination models (ranging from 1.19 to 1.27 mm day−1 and averaging 1.22 mm day−1), radiation-based models (ranging from 1.02 to 1.42 mm day−1 and averaging 1.27 mm day−1), and temperature-based models (ranging from 1.47 to 1.48 mm day−1 and averaging 1.47 mm day−1). Furthermore, all models tended to underestimate the measured ETa during periods of high evaporative demand (i.e., growing season) and overestimated measured ETa during low evaporative demand (i.e., nongrowing season). Our results provide new insights into the accurate assessment of evapotranspiration in humid alpine meadows in the northeastern Qinghai–Tibetan Plateau.

Effective Method of Estimating the Daily Evapotranspiration of Greenhouse Grapes in the Cold Area of Northeast China.

Evapotranspiration (ET) is an important basis and key link for guiding irrigation. One of the key problems to be solved is how to predict the dynamic change in the daily ET and estimate the total amount of ET in greenhouse through limited instantaneous data. In this paper, it is estimated that the daily scale of evapotranspiration by using four methods, including the evaporative fraction method (EF method), the reference evaporative fraction method (EF′ method), the sine method, and the canopy resistance method (rc method), is based on the measured ET data of grapes in a solar greenhouse in Northeast China. The relative root-mean-square pair error (RRMSE) and the efficiency coefficient (ε) are also used to study their applicability in terms of leaf area index, radiation degree, and scale-up time point. In the results, under the condition of different LAI, the simulation accuracies of ET scaled by the four methods ranked as follows (from highest to lowest): the reference evaporative fraction method, the evaporative fraction method, the sine method, and the canopy resistance method. The average RRMSE and ε of the evaporative fraction method with the best simulation accuracy were 7.19–16.46% and 0.61–0.75, respectively. Under different radiation conditions, the simulation accuracies of the four methods ranked as follows (from highest to lowest): the evaporative fraction method, the reference evaporative fraction method, the sine method, and the canopy resistance method. Under different radiation conditions, the RRSME of the four methods ranged from 11.55 to 46.62%, and the maximum of ε was 0.75. The evaporative fraction and reference evaporative fraction methods had the highest simulation accuracy, whereas the reference evaporative fraction method required fewer parameters. We concluded that the reference evaporative fraction method was the best for estimating the daily ET of greenhouse grapes in the cold area of Northeast China.

Surface water isoscapes (δ18O and δ2H) reveal dual effects of damming and drought on the Yangtze River water cycles

The water regimes and biogeochemical cycles are remarkably affected by river damming and drought around the world. However, the dual effects on river water cycles have not yet attracted sufficient attention along the Yangtze River because of the relative consistency of annual water regimes. This study first explored the altered water cycle associated with damming and drought using surface water isoscapes (δ18O and δ2H) of river and lake water along the Yangtze River during the flooding seasons of 2016 and 2018, combined with other historical isotopic data from 2003 to 2013. The results show that river water isotopes are markedly varied on both spatial and temporal scales. The relatively more enriched river water representing δ18O values were observed from 2003 to 2007 compared with those in 2018, which were possibly caused by increased evaporative fractionation under abnormal drought conditions in the Yangtze River. Spatially, river water δ18O values exhibited a positive trend from upstream to the lower reaches because of the contrasting recharged sources, complex mixing, and evaporation from upstream to the lower reaches of the Yangtze River. This trend was related to variations in surface water temperature and water evaporation during the flooding seasons evidenced by a significant correlation between river isotopes and river water temperature. Moreover, the large variability in deuterium-excess (d-excess) and δ18O in the downstream could be inherited from the upstream because of short residence time and incomplete mixing in the Three Gorges Reservoir (TGR) during the initial stage of the Three Gorges Dam (TGD) operation (2003–2007). In contrast, the relatively lower variability of d-excess and δ18O was found in the downstream area due to the complete mixing in the TGR, causing the homogenization of reservoir water during the normal operation stage after 2010 (e.g., 2013 and 2018). Drought stimulates evaporative fractionation on river water and result in more negative d-excess values especially in 2006. The dual effects of river damming and drought remarkably changed the longitudinal hydrological connectivity and water cycle dynamics by prolonging the residence time and enhancing the water mixing, which should be thoroughly considered for water resource management, especially for regions with heavily-regulated rivers.

First use of triply labelled water analysis for energy expenditure measurements in mice

The doubly labelled water (DLW) method is widely used to determine energy expenditure. In this work, we demonstrate the addition of the third stable isotope, 17O, to turn it into triply labelled water (TLW), using the three isotopes measurement of optical spectrometry. We performed TLW (2H, 18O and17O) measurements for the analysis of the CO2 production (rCO2) of mice on different diets for the first time. Triply highly enriched water was injected into mice, and the isotope enrichments of the distilled blood samples of one initial and two finals were measured by an off-axis integrated cavity output spectroscopy instrument. We evaluated the impact of different calculation protocols and the values of evaporative water loss fraction. We found that the dilution space and turnover rates of 17O and 18O were equal for the same mice group, and that values of rCO2 calculated based on 18O–2H, or on 17O–2H agreed very well. This increases the reliability and redundancy of the measurements and it lowers the uncertainty in the calculated rCO2 to 3% when taking the average of two DLW methods. However, the TLW method overestimated the rCO2 compared to the indirect calorimetry measurements that we also performed, much more for the mice on a high-fat diet than for low-fat. We hypothesize an extra loss or exchange mechanism with a high fractionation for 2H to explain this difference.

Environmental and Biophysical Effects of the Bowen Ratio over Typical Farmland Ecosystems in the Loess Plateau

The Bowen ratio (β) comprehensively reflects physical characteristics of the land-surface climate. In this study, eddy covariance systems installed at Dingxi and Qingyang were used to conduct energy distribution measurements and observations characteristic of semi-arid and semi-humid farmland ecosystems on the China Loess Plateau. We studied mechanisms by which eco-environmental factors influence β. Additionally, we investigated responses of physiological and ecological factors to water and heat exchange under seasonally dry and wet conditions within each farmland ecosystem. Our results showed that sensible heat flux in the semi-arid farmland was the main consumer of available energy. In the semi-humid area, latent heat flux in summer had the dominant role in energy distribution (mean β 0.71). The β in the semi-arid region was 1.5 times higher than that in the semi-humid region during the growing season. β increased with an increase in the vapor pressure deficit (VPD) and ground–air temperature difference (Ts − Ta), and decreased significantly with an increase in effective precipitation and soil moisture. The change in β with environmental factors was more clear-cut in semi-arid areas than in semi-humid areas. The Priestley–Taylor coefficient (α) and β satisfied a power function law in the growing season. There was a strong correlation between them, with the coefficients of determination for semi-humid and semi-arid areas being 0.62 and 0.72, respectively. β decreased with an increase in the normalized difference vegetative index (NDVI), with this phenomenon being more obvious in the semi-humid zone (R2 = 0.40). β responded more rapidly to NDVI in the semi-arid area than in the semi-humid area. There was a negative exponential relationship between canopy stomatal conductance (Gs) and β, which displayed a stronger declining trend with the increase in Gs in the semi-arid area than in the semi-humid area. This study provides an important reference for the determination of land-surface characteristics of semi-arid and semi-humid farmland ecosystems on the Loess Plateau and for improving parameterization of land-surface processes.