Diurnal variations of soil evaporation δ18O and factors affecting it in cropland in North China

doi:10.3724/SP.J.1258.2012.00539

Abstract

Abstract:

Aims The δ¹⁸O of soil evaporation (δ_E) is an important factor controlling the variations of atmospheric δ¹⁸O (δ_v), and it is also one of the key challenges of partitioning evapotranspiration into evaporation and transpiration components. δ_E is mostly simulated by the Craig-Gordon model, which is constrained by the δ_v of water vapor, the relative humidity (h), the equilibrium and kinetic factors and the δ¹⁸O of soil water (δ_s) at the evaporating front. Our objective is to investigate the diurnal variations of δ_E and factors affecting it.
Methods We determined the δ¹⁸O of water vapor in a winter wheat-summer maize cropland based on the in-situ and continuous water vapor isotope ratio measurement system. We sampled soil water at different depths and analyzed it using the cryogenic vacuum distillation technique to acquire the δ¹⁸O of soil water at the evaporating front.
Important findings During the growing period of winter wheat-summer maize, the diurnal variation of δ_E exhibited a bimodal pattern with peaks at 6:00 and 15:00. The h has a significant effect on the diurnal variation of δ_Ein cropland ecosystems, and causes the Craig-Gordon model to be invalid under high humidity condition of h > 95%. The in-situ and high resolution measurement of δ_vovercomes the uncertainty of using the local precipitation equilibrium method to evaluate δ_v, which improves the accuracy of δ_E. Different equilibrium factors have no significant influence on the accuracy of δ_E. Different kinetic factors, especially the canopy scale kinetic factor, influence the accuracy of δ_E significantly. The location of the evaporating front determines the h normalized to soil temperature and the δ¹⁸O of soil water directly and also influences the accuracy of δ_E significantly. Further research is needed to attain direct measurement of δ_E by combining isotope ratio infrared spectroscopy (IRIS) with the static chamber or dynamic chamber.

Key words: Craig-Gordon model, in-situ measurement of atmosphere water vapor δ¹⁸O, kinetic fractionation factors, soil evaporation δ¹⁸O, winter wheat-summer maize

YANG Bin, XIE Fu-Ti, WEN Xue-Fa, SUN Xiao-Min, WANG Jian-Lin. Diurnal variations of soil evaporation δ¹⁸O and factors affecting it in cropland in North China[J]. Chin J Plant Ecol, 2012, 36(6): 539-549.

Add to citation manager EndNote|Ris|BibTeX

URL: https://www.plant-ecology.com/EN/10.3724/SP.J.1258.2012.00539

https://www.plant-ecology.com/EN/Y2012/V36/I6/539

Figures/Tables 8

References 53

[1]	Baldocchi DD (2003). Assessing the eddy covariance technique for evaluating carbon dioxide exchange rates of ecosystems: past, present and future. Global Change Biology, 9, 479-492. DOI URL
[2]	Barnes CJ, Allison GB (1988). Tracing of water movement in the unsaturated zone using stable isotopes of hydrogen and oxygen. Journal of Hydrology, 100, 143-176. DOI URL
[3]	Cappa CD, Hendricks MB, DePaolo DJ, Cohen RC (2003). Isotopic fractionation of water during evaporation. Journal of Geophysical Research-Atmospheres, 108, 4525-4534. DOI URL
[4]	Cermak J, Nadezhdina N (1998). Sapwood as the scaling parameter-defining according to xylem water content or radial pattern of sap flow? Annals of Forest Science, 55, 509-521.
[5]	Craig H, Gordon LI (1965). Deuterium and oxygen 18 variations in the ocean and the marine atmosphere. In: Tongiorgi E ed. Stable Isotopes in Oceanographic Studies and Paleotemperatures. Laboratory of Geology and Nuclear Science, Pisa, Italy. 9-130.
[6]	Farquhar GD, Hubick KT, Condon AG (1989). Carbon isotope discrimination and plant water-use efficiency. In: Rundel PW, Ehleringer JR, Nagy KA eds. Stable Isotope in Ecological Research. Springer-Verlag, New York . 21-40.
[7]	Flanagan LB, Comstock JP, Ehleringer JR (1991). Comparison of modeled and observed environmental influences on the stable oxygen and hydrogen isotope composition of leaf water in Phaseolus vulgaris L. Plant Physiology, 96, 588-596. URL PMID
[8]	Froehlich K (2000). Evaluating the water balance of inland seas using isotopic tracers: the Caspian Sea experience. Hydrological Processes, 14, 1371-1383. DOI URL
[9]	Gat JR (1996). Oxygen and hydrogen isotopes in the hydrologic cycle. Annual Review of Earth and Planetary Sciences, 24, 225-262.
[10]	Gat JR (2008). The isotopic composition of evaporating waters—review of the historical evolution leading up to the Craig-Gordon model. Isotopes in Environmental and Health Studies, 44, 5-9. URL PMID
[11]	Gochis DJ, Cuenca RH (2000). Plant water use and crop curves for hybrid poplars. Journal of Irrigation and Drainage Engineering, 126, 206-214. DOI URL
[12]	Helliker BR, Roden JS, Cook C, Ehleringer JR (2002). A rapid and precise method for sampling and determining the oxygen isotope ratio of atmospheric water vapor. Rapid Communications in Mass Spectrometry, 16, 929-932. URL PMID
[13]	Horita J, Rozanski K, Cohen S (2008). Isotope effects in the evaporation of water: a status report of the Craig-Gordon model. Isotopes in Environmental and Health Studies, 44, 23-49. URL PMID
[14]	Horita J, Wesolowski DJ (1994). Liquid-vapor fractionation of oxygen and hydrogen isotopes of water from the freezing to the critical temperature. Geochimica et Cosmochimica Acta, 58, 3425-3437. DOI URL
[15]	Hu ZM, Yu GR, Zhou YL, Sun XM, Li YN, Shi PL, Wang YF, Song X, Zheng ZM, Zhang L, Li SG (2009). Partitioning of evapotranspiration and its controls in four grassland ecosystems: application of a two-source model. Agricu- ltural and Forest Meteorology, 149, 1410-1420.
[16]	Huxman TE, Wilcox BP, Breshears DD, Scott RL, Snyder KA, Small EE, Hultine K, Pockman WT, Jackson RB (2005). Ecohydrological implications of woody plant encro- achment. Ecology, 86, 308-319. DOI URL
[17]	Jacob H, Sonntag C (1991). An 8-year record of the seasonal variation of ²H and ¹⁸O in atmospheric water vapour and precipitation at Heidelberg, Germany. Tellus Series B- Chemical and Physical Meteorology, 43, 291-300.
[18]	Lai CT, Ehleringer JR, Bond BJ, Paw UKT (2006). Contributions of evaporation, isotopic non-steady state transpiration and atmospheric mixing on the δ ¹⁸O of water vapour in Pacific Northwest coniferous forests. Plant, Cell & Environment, 29, 77-94. DOI URL PMID
[19]	Lee X, Griffis TJ, Baker JM, Billmark KA, Kim K, Welp LR (2009). Canopy-scale kinetic fractionation of atmospheric carbon dioxide and water vapor isotopes. Global Biogeochemical Cycles, 23, GB1002, doi: 10.1029/2008- GB003331.
[20]	Lee XH, Sargent S, Smith R, Tanner B (2005). In situ measurement of the water vapor¹⁸O/¹⁶O isotope ratio for atmospheric and ecological applications. Journal of Atmospheric and Oceanic Technology, 22, 555-565. DOI URL
[21]	Lee XH, Smith R, Williams J (2006). Water vapour ¹⁸O/¹⁶O isotope ratio in surface air in New England, USA. Tellus Series B-Chemical and Physical Meteorology, 58, 293-304. DOI URL
[22]	Majoube M (1971). Fractionnement en oxygene-18 et en deuterium entre l'eau et sa vapeur. Journal De Chimie Physique Et De Physico-Chimie Biologiue, 68, 1423-1436.
[23]	Meiresonne L, Nadezhdin N, Cermak J, Van Slycken J, Ceulemans R (1999). Measured sap flow and simulated transpiration from a poplar stand in Flanders (Belgium). Agricultural and Forest Meteorology, 96, 165-179. DOI URL
[24]	Merlivat L (1978). Molecular diffusivities of H₂¹⁶O, HD¹⁶O, and H₂¹⁸O in gases. The Journal of Chemical Physics, 69, 2864-2871. DOI URL
[25]	Moreira MZ, Sternberg LD, Martinelli LA, Victoria RL, Barbosa EM, Bonates LCM, Nepstad DC (1997). Contribution of transpiration to forest ambient vapour based on isotopic measurements. Global Change Biology, 3, 439-450. DOI URL
[26]	Ripullone F, Matsuo N, Stuart-Williams H, Wong SC, Borghetti M, Tani M, Farquhar GD (2008). Environmental effects on oxygen isotope enrichment of leaf water in cotton leaves. Plant Physiology, 146, 729-736. URL PMID
[27]	Roden JS, Ehleringer JR (1999). Observations of hydrogen and oxygen isotopes in leaf water confirm the Craig-Gordon model under wide-ranging environmental conditions. Plant Physiology, 120, 1165-1174. URL PMID
[28]	Shuttleworth WJ, Wallace JS (1985). Evaporation from sparse crops-an energy combination theory. Quarterly Journal of the Royal Meteorological Society, 111, 839-855. DOI URL
[29]	Sun HY ( 孙宏勇) (2007). Experiments and Simulation of the Dynamic Change of Soil Water in Farmland and the Water-Saving Effect of Irrigations—Case Study on Luancheng National station (农田水分动态与节水灌溉效应实验与模拟——以国家台站栾城为例). PhD dissertation, Institute of Geographic Sciences and Natural Resources Research. Chinese Academy of Sciences, Beijing. 17-21. (in Chinese with English abstract)
[30]	Sun HY ( 孙宏勇), Liu CM ( 刘昌明), Zhang XY ( 张喜英), Zhang YQ ( 张永强), Pei D ( 裴东) (2004). The changing laws of the diurnal evapotranspiration and soil evaporation between plants in the winter wheat field of the North China Plain. Chinese Journal of Eco-Agriculture (中国生态农业学报), 12(3), 62-64. (in Chinese with English abstract)
[31]	Torres EA, Calera A (2010). Bare soil evaporation under high evaporation demand: a proposed modification to the FAO-56 model. Hydrological Sciences Journal, 55, 303-315.
[32]	Tsujimura M, Sasaki L, Yamanaka T, Sugimoto A, Li SG, Matsushima D, Kotani A, Saandar M (2007). Vertical distribution of stable isotopic composition in atmospheric water vapor and subsurface water in grassland and forest sites, eastern Mongolia. Journal of Hydrology, 333, 35-46.
[33]	van de Griend AA, Owe M (1994). Bare soil surface resistance to evaporation by vapor diffusion under semiarid conditions. Water Resources Research, 30, 181.
[34]	Walker CD, Brunel JP (1990). Examining evapotranspiration in a semi-arid region using stable isotopes of hydrogen and oxygen. Journal of Hydrology, 118, 55-75.
[35]	Wang XF, Yakir D (2000). Using stable isotopes of water in evapotranspiration studies. Hydrological Processes, 14, 1407-1421.
[36]	Welp LR, Lee XH, Kim K, Griffis TJ, Billmark KA, Baker JM (2008). δ¹⁸O of water vapor, evapotranspiration and the sites of leaf evaporation in a soybean canopy. Plant, Cell & Environment, 31, 1214-1228. URL PMID
[37]	Wen XF ( 温学发), Zhang SC ( 张世春), Sun XM ( 孙晓敏), Yu GR ( 于贵瑞) (2008). Recent advances in H₂¹⁸O enrichment in leaf water. Chinese Journal of Plant Ecology (植物生态学报), 32, 961-966. (in Chinese with English abstract)
[38]	Wen XF, Lee XH, Sun XM, Wang JL, Hu ZM, Li SG, Yu GR (2012a). Dew water isotopic ratios and their relationships to ecosystem water pools and fluxes in a cropland and a grassland in China. Oecologia, 168, 549-561. URL PMID
[39]	Wen XF, Lee XH, Sun XM, Wang JL, Tang YK, Li SG, Yu GR (2012b). Intercomparison of four commercial analyzers for water vapor isotope measurement. Journal of Atmospheric and Oceanic Technology, 29, 235-247.
[40]	Wen XF, Sun XM, Zhang SC, Yu GR, Sargent SD, Lee XH (2008). Continuous measurement of water vapor D/H and¹⁸O/¹⁶O isotope ratios in the atmosphere. Journal of Hydrology, 349, 489-500. DOI URL
[41]	Wen XF, Zhang SC, Sun XM, Yu GR, Lee XH (2010). Water vapor and precipitation isotope ratios in Beijing, China. Journal of Geophysical Research, 115, D01103, doi: 10.1029/2009JD012408.
[42]	Wilson KB, Hanson PJ, Mulholland PJ, Baldocchi DD, Wullschleger SD (2001). A comparison of methods for determining forest evapotranspiration and its components: sap-flow, soil water budget, eddy covariance and catchment water balance. Agricultural and Forest Meteorology, 106, 153-168. DOI URL
[43]	Wythers KR, Lauenroth WK, Paruelo JM (1999). Bare-soil evaporation under semiarid field conditions. Soil Science Society of America Journal, 63, 1341-1349. DOI URL
[44]	Xiao W, Lee XH, Griffis TJ, Kim K, Welp LR, Yu Q (2010). A modeling investigation of canopy-air oxygen isotopic exchange of water vapor and carbon dioxide in a soybean field. Journal of Geophysical Research, 115, G01004, doi: 10.1029/2009JG001163.
[45]	Xiao W, Lee XH, Wen XF, Sun XM, Zhang SC (2012). Modeling biophysical controls on canopy foliage water¹⁸O enrichment in wheat and corn. Global Change Biology, 18, 1769-1780.
[46]	Xu Z, Yang HB, Liu FD, An SQ, Cui J, Wang ZS, Liu SR (2008). Partitioning evapotranspiration flux components in a subalpine shrubland based on stable isotopic measure- ments. Botanical Studies, 49, 351-361.
[47]	Yakir D, Sternberg LSL (2000). The use of stable isotopes to study ecosystem gas exchange. Oecologia, 123, 297-311. URL PMID
[48]	Yamanaka T, Yonetani T (1999). Dynamics of the evaporation zone in dry sandy soils. Journal of Hydrology, 217, 135-148.
[49]	Yepez EA, Huxman TE, Ignace DD, English NB, Weltzin JF, Castellanos AE, Williams DG (2005). Dynamics of transpiration and evaporation following a moisture pulse in semiarid grassland: a chamber-based isotope method for partitioning flux components. Agricultural and Forest Meteorology, 132, 359-376.
[50]	Yepez EA, Williams DG, Scott RL, Lin GH (2003). Partitioning overstory and understory evapotranspiration in a semiarid savanna woodland from the isotopic comp- osition of water vapor. Agricultural and Forest Meteor- ology, 119, 53-68.
[51]	Yu GR, Wen XF, Sun XM, Tanner BD, Lee XH, Chen JY (2006). Overview of China FLUX and evaluation of its eddy covariance measurement. Agricultural and Forest Meteorology, 137, 125-137.
[52]	Zhang SC, Sun XM, Wang JL, Yu GR, Wen XF (2011). Short-term variations of vapor isotope ratios reveal the influence of atmospheric processes. Journal of Geo- graphical Sciences, 21, 401-416.
[53]	Zhang SC, Wen XF, Wang JL, Yu GR, Sun XM (2010). The use of stable isotopes to partition evapotranspiration fluxes into evaporation and transpiration. Acta Ecologica Sinica, 30, 201-209.

年序日 Day of year	δ_v	δ_s,5cm	δ_s,20cm	T_s,5cm	T_s,20cm	h_5cm	h_20cm
年序日 Day of year	(‰)			(℃)		(%)
冬小麦 Winter wheat
135-137	-(13.1 ± 1.2)	-(5.7 ± 0.1)	-(7.1 ± 0.2)	17.5 ± 1.8	16.4 ± 0.7	79.0 ± 6.5	85.0 ± 9.0
142-144	-(9.0 ± 1.4)	-(3.8 ± 0.5)	-(6.4 ± 0.1)	20.2 ± 2.8	18.3 ± 0.9	76.9 ± 12.5	87.4 ± 20.7
夏玉米 Summer maize
236-237	-(14.3 ± 1.2)	-(8.4 ± 0.3)	-(9.0 ± 0.3)	25.2 ± 2.3	24.5 ± 0.6	74.9 ± 7.2	77.3 ± 10.3
244-246	-(16.1 ± 3.4)	-(6.0 ± 0.5)	-(8.9 ± 0.2)	23.1 ± 2.6	23.1 ± 0.7	56.6 ± 12.8	56.0 ± 10.9

年序日 Day of year	δ_v	δ_s,5cm	δ_s,20cm	T_s,5cm	T_s,20cm	h_5cm	h_20cm
年序日 Day of year	(‰)			(℃)		(%)
冬小麦 Winter wheat
135-137	-(13.1 ± 1.2)	-(5.7 ± 0.1)	-(7.1 ± 0.2)	17.5 ± 1.8	16.4 ± 0.7	79.0 ± 6.5	85.0 ± 9.0
142-144	-(9.0 ± 1.4)	-(3.8 ± 0.5)	-(6.4 ± 0.1)	20.2 ± 2.8	18.3 ± 0.9	76.9 ± 12.5	87.4 ± 20.7
夏玉米 Summer maize
236-237	-(14.3 ± 1.2)	-(8.4 ± 0.3)	-(9.0 ± 0.3)	25.2 ± 2.3	24.5 ± 0.6	74.9 ± 7.2	77.3 ± 10.3
244-246	-(16.1 ± 3.4)	-(6.0 ± 0.5)	-(8.9 ± 0.2)	23.1 ± 2.6	23.1 ± 0.7	56.6 ± 12.8	56.0 ± 10.9

α_e	平衡分馏系数(无量纲) Equilibrium fractionation factor between liquid water and vapor (dimensionless)	d	零平面位移 Displacement height (m)
α_k	动力分馏系数(无量纲) Kinetic fractionation factor (dimensionless)	h	标准化到蒸发前缘温度的空气相对湿度 Relative humidity normalized to soil temperature (%)
δ	相对于标准物质V-SMOW的¹⁸O/¹⁶O或D/H同位素比值 ¹⁸O/¹⁶O or D/H relative to the value of V-SMOW (‰)	h_5cm	标准化到5 cm土壤温度的空气相对湿度 Relative humidity normalized to soil temperature at 5 cm (%)
δ¹⁸O	¹⁸O/¹⁶O的δ值 ¹⁸O/¹⁶O relative to the value of V-SMOW (‰)	h_20cm	标准化到20cm土壤温度的空气相对湿度 Relative humidity normalized to soil temperature at 20 cm (%)
δD	D/H的δ值 D/H relative to the value of V-SMOW (‰)	H	冠层高度 Canopy height (m)
δ_E	土壤蒸发水汽的δ¹⁸O δ¹⁸O of evaporation water (‰)	k	von Karman常数, 等于0.4 von Karman constant, 0.4
δ_E,5cm	0-5 cm土壤水作为蒸发前缘计算的δ_E δ_E calculated with soil water at 0-5 cm (‰)	KH	冠层顶的涡度扩散系数 eddy diffusivity (s²·m^-1)
δ_E,20cm	15-20 cm土壤水作为蒸发前缘计算的δ_E δ_E calculated with soil water at 15-20 cm (‰)	l_w	叶宽 Leaf width (m)
δ_E,Cappa	Cappa等(2003)动力分馏系数计算的δ_E δ_E calculated with kinetic fractionation factor of Cappa et al., (2003) (‰)	L	Monin-Obukhov长度(无量纲) Monin-Obukhov length (dimensionless)
δ_E,_in-situ	采用原位连续观测的大气水汽δ_v计算的δ_E δ_E calculated with calculated with atmosphere water vapor δ¹⁸O acquired by in-situ measurement (‰)	LAI	叶面积指数 Leaf area index (m²·m^-2)
δ_E,Lee	采用Lee等(2009)的动力分馏系数计算的δ_Eδ_E calculated with kinetic fractionation factor of Lee et al.,(Lee et al., 2009) (‰)	r_a	空气动力学阻力 Aerodynamic resistance in the surface layer (s·m^-1)
δ_E,Merlivat	采用Merlivat等(1978)的动力分馏系数计算的δ_E δ_E calculated with kinetic factor of Merlivat (Merlivat, 1978) (‰)	r_a,f	冠层到参考高度之间空气层的空气动力学阻力 Aerodynamic resistance in the air layer between canopy and reference height (s·m^-1)
δ_E,p	采用降水平衡预测的δ_v计算的δ_E δ_E calculated with atmosphere water vapor δ¹⁸O acquired by equilibrium prediction (‰)	r_a,c	土壤表面到冠层高度之间空气层的空气动力学阻力 Aerodynamic resistance in the air layer between soil surface to the canopy height (s·m^-1)
δ_p	降水的δ¹⁸O δ¹⁸O of precipitation (‰)	r_b	土壤边界层对水汽的阻力 Soil boundary layer resistances to water vapor (s·m^-1)
δ_s	土壤蒸发前缘液态水的δ¹⁸O δ¹⁸O of soil water at evaporating front (‰)	r_b^w	冠层对水汽的边界层阻力 Canopy boundary layer resistances to water vapor (s·m^-1)
δ_s,5cm	0-5 cm土壤水的δ¹⁸O δ¹⁸O of soil water at 0-5 cm depth (‰)	r_s	土壤孔隙对水汽的阻力 Soil resistance to water vapor (s·m^-1)
δ_s,20cm	15-20 cm土壤水的δ¹⁸O δ¹⁸O of soil water at 15-20 cm depth (‰)	r_t	参考高度内水汽和热量的总阻力 Total resistance above the foliage surface (s·m^-1)
δ_v	大气水汽的δ¹⁸O δ¹⁸O of atmosphere water vapor (‰)	T_s	土壤温度 Soil temperature at the evaporating front (℃)
δ_v,e	大气水汽δ¹⁸O的降水平衡预测值 δ¹⁸O of atmosphere water vapor acquired by equilibrium prediction (‰)	T_s,5cm	5 cm土壤温度 Soil temperature at 5 cm (℃)
ε_eq	平衡分馏过程引起的同位素富集因子 Equilibrium fractionation factor [ε_eq = 1000(1-1/α_e)] (‰)	T_s,20cm	20 cm土壤温度 Soil temperature at 20 cm (℃)
ε_k	动力分馏过程引起的同位素富集因子 Kinetic fractionation factor [ε_k = 1000(α_k-1)] (‰)	u^*	摩擦风速 Friction wind speed (m·s^-1)
Φ_h	热量的Monin-Obukhov相似函数从地表到参考高度的积分(无量纲) Integral similarity function for heat from soil surface to reference height (dimensionless)	u_c	冠层内平均风速 Mean wind speed in the canopy (m·s^-1)
Φ_h,c	热量的Monin-Obukhov相似函数从地表到冠层高度的积分(无量纲) Integral similarity function for heat from soil surface to canopy height (dimensionless)	u_h	冠层顶风速 Wind speed at the canopy top (m·s^-1)
Φ_m	动量的Monin-Obukhov相似函数从地表到参考高度的积分(无量纲) Integral similar to Monin-Obukhov function for momentum (dimensionless)	u_m	参考高度上风速 Wind speed at the reference height (m·s^-1)
a	风力衰减系数(无量纲) Extinction coefficient of within-canopy wind profile (dimensionless)	w_i	水汽混合比 Mole mixing ratio of vapor in air (μ mol·mol^-1)
b	边界层阻力系数 Boundary layer resistance coefficient (s^0.5·m^-1)	z_m	参考高度 Reference height (m)
B	界面底层Dalton数(无量纲) Dalton number of the interfacial sublayer (dimensionless)	z_o	动量的表面粗糙度 Surface roughness for momentum (m)
CH	动量传导系数(无量纲) Transfer coefficient (dimensionless)	z_oT	温度的表面粗糙度 Surface roughness for temperature (m)

α_e	平衡分馏系数(无量纲) Equilibrium fractionation factor between liquid water and vapor (dimensionless)	d	零平面位移 Displacement height (m)
α_k	动力分馏系数(无量纲) Kinetic fractionation factor (dimensionless)	h	标准化到蒸发前缘温度的空气相对湿度 Relative humidity normalized to soil temperature (%)
δ	相对于标准物质V-SMOW的¹⁸O/¹⁶O或D/H同位素比值 ¹⁸O/¹⁶O or D/H relative to the value of V-SMOW (‰)	h_5cm	标准化到5 cm土壤温度的空气相对湿度 Relative humidity normalized to soil temperature at 5 cm (%)
δ¹⁸O	¹⁸O/¹⁶O的δ值 ¹⁸O/¹⁶O relative to the value of V-SMOW (‰)	h_20cm	标准化到20cm土壤温度的空气相对湿度 Relative humidity normalized to soil temperature at 20 cm (%)
δD	D/H的δ值 D/H relative to the value of V-SMOW (‰)	H	冠层高度 Canopy height (m)
δ_E	土壤蒸发水汽的δ¹⁸O δ¹⁸O of evaporation water (‰)	k	von Karman常数, 等于0.4 von Karman constant, 0.4
δ_E,5cm	0-5 cm土壤水作为蒸发前缘计算的δ_E δ_E calculated with soil water at 0-5 cm (‰)	KH	冠层顶的涡度扩散系数 eddy diffusivity (s²·m^-1)
δ_E,20cm	15-20 cm土壤水作为蒸发前缘计算的δ_E δ_E calculated with soil water at 15-20 cm (‰)	l_w	叶宽 Leaf width (m)
δ_E,Cappa	Cappa等(2003)动力分馏系数计算的δ_E δ_E calculated with kinetic fractionation factor of Cappa et al., (2003) (‰)	L	Monin-Obukhov长度(无量纲) Monin-Obukhov length (dimensionless)
δ_E,_in-situ	采用原位连续观测的大气水汽δ_v计算的δ_E δ_E calculated with calculated with atmosphere water vapor δ¹⁸O acquired by in-situ measurement (‰)	LAI	叶面积指数 Leaf area index (m²·m^-2)
δ_E,Lee	采用Lee等(2009)的动力分馏系数计算的δ_Eδ_E calculated with kinetic fractionation factor of Lee et al.,(Lee et al., 2009) (‰)	r_a	空气动力学阻力 Aerodynamic resistance in the surface layer (s·m^-1)
δ_E,Merlivat	采用Merlivat等(1978)的动力分馏系数计算的δ_E δ_E calculated with kinetic factor of Merlivat (Merlivat, 1978) (‰)	r_a,f	冠层到参考高度之间空气层的空气动力学阻力 Aerodynamic resistance in the air layer between canopy and reference height (s·m^-1)
δ_E,p	采用降水平衡预测的δ_v计算的δ_E δ_E calculated with atmosphere water vapor δ¹⁸O acquired by equilibrium prediction (‰)	r_a,c	土壤表面到冠层高度之间空气层的空气动力学阻力 Aerodynamic resistance in the air layer between soil surface to the canopy height (s·m^-1)
δ_p	降水的δ¹⁸O δ¹⁸O of precipitation (‰)	r_b	土壤边界层对水汽的阻力 Soil boundary layer resistances to water vapor (s·m^-1)
δ_s	土壤蒸发前缘液态水的δ¹⁸O δ¹⁸O of soil water at evaporating front (‰)	r_b^w	冠层对水汽的边界层阻力 Canopy boundary layer resistances to water vapor (s·m^-1)
δ_s,5cm	0-5 cm土壤水的δ¹⁸O δ¹⁸O of soil water at 0-5 cm depth (‰)	r_s	土壤孔隙对水汽的阻力 Soil resistance to water vapor (s·m^-1)
δ_s,20cm	15-20 cm土壤水的δ¹⁸O δ¹⁸O of soil water at 15-20 cm depth (‰)	r_t	参考高度内水汽和热量的总阻力 Total resistance above the foliage surface (s·m^-1)
δ_v	大气水汽的δ¹⁸O δ¹⁸O of atmosphere water vapor (‰)	T_s	土壤温度 Soil temperature at the evaporating front (℃)
δ_v,e	大气水汽δ¹⁸O的降水平衡预测值 δ¹⁸O of atmosphere water vapor acquired by equilibrium prediction (‰)	T_s,5cm	5 cm土壤温度 Soil temperature at 5 cm (℃)
ε_eq	平衡分馏过程引起的同位素富集因子 Equilibrium fractionation factor [ε_eq = 1000(1-1/α_e)] (‰)	T_s,20cm	20 cm土壤温度 Soil temperature at 20 cm (℃)
ε_k	动力分馏过程引起的同位素富集因子 Kinetic fractionation factor [ε_k = 1000(α_k-1)] (‰)	u^*	摩擦风速 Friction wind speed (m·s^-1)
Φ_h	热量的Monin-Obukhov相似函数从地表到参考高度的积分(无量纲) Integral similarity function for heat from soil surface to reference height (dimensionless)	u_c	冠层内平均风速 Mean wind speed in the canopy (m·s^-1)
Φ_h,c	热量的Monin-Obukhov相似函数从地表到冠层高度的积分(无量纲) Integral similarity function for heat from soil surface to canopy height (dimensionless)	u_h	冠层顶风速 Wind speed at the canopy top (m·s^-1)
Φ_m	动量的Monin-Obukhov相似函数从地表到参考高度的积分(无量纲) Integral similar to Monin-Obukhov function for momentum (dimensionless)	u_m	参考高度上风速 Wind speed at the reference height (m·s^-1)
a	风力衰减系数(无量纲) Extinction coefficient of within-canopy wind profile (dimensionless)	w_i	水汽混合比 Mole mixing ratio of vapor in air (μ mol·mol^-1)
b	边界层阻力系数 Boundary layer resistance coefficient (s^0.5·m^-1)	z_m	参考高度 Reference height (m)
B	界面底层Dalton数(无量纲) Dalton number of the interfacial sublayer (dimensionless)	z_o	动量的表面粗糙度 Surface roughness for momentum (m)
CH	动量传导系数(无量纲) Transfer coefficient (dimensionless)	z_oT	温度的表面粗糙度 Surface roughness for temperature (m)

Diurnal variations of soil evaporation δ¹⁸O and factors affecting it in cropland in North China

FullText

PDF (PC)

Knowledge

Cited

Abstract

Cite this article

share this article

Figures/Tables 8

References 53

Related Articles 1

Recommended Articles

Metrics

Comments