草地生态系统碳通量特征及其影响因子研究

该文以内蒙古科尔沁草原为研究对象,利用涡动相关系统观测的2011年生长季(5—9月)的碳通量以及同期常规气象观测数据,分析该生态系统的碳通量的日变化、季节变化及造成碳通量变化的原因,结果表明草地生态系统碳通量日变化呈单峰型;生长季碳通量具有明显的季节变化规律,基本呈"U"型;净辐射和气温是影响草地生态系统碳通量的主要气象因子。     

锦州地区玉米农田生态系统水汽通量变化特征及其调控机制

基于2014年辽宁省锦州地区雨养玉米农田生态系统涡度相关观测数据,分析了锦州地区玉米农田生态系统水汽通量的变化特征,并结合小气候观测数据探讨了水汽通量的调控机制。结果表明:2014年锦州地区玉米农田生态系统各月水汽通量均呈明显的单峰型变化规律,玉米农田生态系统生长季日平均水汽通量可达非生长季的10.31倍。锦州玉米农田生态系统7月水汽通量最大,日最大水汽通量可达0.1202 g·m-2·s-1。玉米农田年蒸散量为417.37 mm,非生长季蒸散总量为49.57 mm,略大于同期降水量;生长季前期5月和6月玉米农田蒸散量占降水量的比例分别为52.0%、71.0%;7月、8月和9月玉米农田的蒸散量大于降水量,其中7月玉米农田的蒸散量为降水量的3.00倍,而此期间正值玉米开花授粉阶段,水分胁迫严重影响玉米产量。玉米农田生长季的水汽通量与净辐射存在显著的正相关关系,同时水汽通量在一定程度上受气温和饱和水汽压差的调控影响。     

全球气候变化对中国森林生态系统的影响

人类活动所引起的温室效应及由此造成的全球气候变化和对全球生态环境的影响正引起人们越来越多的重视.作为全球陆地生态系统一个重要组分,中国的森林生态系统对未来全球气候变化的响应更是人们关注的重点.作者系统地总结了全球气候变化对中国森林生态系统分布、生态系统生产力、森林树种以及森林土壤的影响,指出了现阶段该领域研究中存在的一些问题,并对今后需要加强的一些核心问题与研究重点作了展望.     

珠海凤凰山陆气相互作用观测塔通量数据的质量控制与评价

针对广东省珠海凤凰山森林生态系统2015年的湍流原始数据,分析了各修正过程对通量的影响。结果表明:野点较多,需要考虑去除;频率响应修正对通量结果影响不大;倾斜修正的影响在3%左右;超声虚温修正对感热通量的影响变化幅度达30%;WPL修正对碳通量结果影响可达25%左右。经过对观测数据的质量评价,感热通量约有85%,潜热通量和碳通量约有80%的数据可用于通量分析。感热通量在1年中的变化幅度不大;潜热通量变化显著,尤其在季风后迅速增大;碳通量变化与森林下垫面密切相关,夏季变化幅度大,冬季变化较小。      

玉米农田生态系统CO2通量的动态变化

利用2008年辽宁锦州农田生态系统野外观测站涡动相关系统通量观测资料,分析了玉米农田生态系统生长季(5-10月)及非生长季CO₂通量动态变化。结果表明：玉米农田生态系统的非生长季日动态趋势不明显;生长季日动态明显,呈明显的U型曲线,CO₂通量最大值出现在12:00时,为-1.19 mg·m^-2·s^-1;不同物候期的日动态也呈现U型曲线,各发育期CO₂通量日最大值范围为0.07～-0.23 mg·m^-2·s^-1;玉米农田生长季生态系统净CO₂交换日累积（NEE）为-652.8 g·m^-2,非生长季NEE499.8 g·m^-2,2008年碳收支-153.0 g·m^-2,表现为碳汇。     

台风过程对广西红树林净生态系统碳交换的影响研究

为研究台风过程对广西红树林净生态系统碳交换的影响,利用北海红树林生态观测试验站涡度相关系统观测的红树林碳通量和气象观测数据,分析台风"韦帕"登陆前后红树林净生态系统碳交换变化特征及其与气象因子的响应关系.结果表明:(1)红树林净生态系统碳交换碳汇峰值在台风登陆前递增并达到极值,台风登陆时碳汇峰值迅速降低,而在台风登陆后...     

环境及生态因子对黄土高原典型农田生态系统鲍恩比的影响研究

鲍恩比能够综合反映陆面气候状态的物理特性,是有效刻画生态系统水热分配的关键参数之一.本研究利用安装在定西和庆阳的涡动相关系统开展了黄土高原半干旱和半湿润农田生态系统能量分配特征观测试验,研究了生态环境因子对鲍恩比的影响机理,揭示了干、湿条件下生理生态因子对水热交换的响应规律.结果表明,处于半干旱区的定西年内感热通量是可...     

应用涡动相关法计算水热、CO2通量的国内外进展概况

目前涡动相关法被认为是国内外测定CO2、水热通量的最可靠方法。国外应用此方法解决了均匀下垫面假设下森林和农田等生态系统的CO2、水热通量的计算问题，目前致力于非理想下垫面（真实地形）的CO2、水热通量的计算。而国内应用涡动相关技术起步较晚，用此方法测定水热通量已有一定的知识积累，但测定CO2通量还处于资料收集阶段。我国自然生态系统、环境外交和社会经济可持续发展都要求精确查明我国CO2的时空变化特征和动力学机制，这应是今后研究的重点，并提出了应用该方法存在的主要问题及可能的解决方法，指出值得深入研究的领域。     

不同陆地生态系统碳通量对GEOS-Chem模型模拟全球CO2浓度的影响

大气中CO₂含量的增加速率已经超过了自然界所能吸收的速度,并逐步影响到全球气候变暖。利用模型模拟分析已经成为一个重要的工具用以深入对碳循环的理解。本文使用2008～2010年的生物模型SiB3（Simple Biosphere version 3）与优化后的CT2016（Carbon Tracker 2016）陆地生态系统碳通量驱动GEOS-Chem大气化学传输模型模拟全球CO₂浓度。通过分析模拟CO₂浓度的空间分布与季节变化,加深对全球碳源汇分布特点的理解,探究陆地生态系统碳通量不确定性对模拟结果的影响,进而认识陆地生态系统碳通量反演精度提升的重要性。SiB3与优化后的CT2016陆地生态系统碳通量都具有明显的季节变化,但在欧洲地区碳源汇的表现相反,其全球总量与空间分布也存在极大的不确定性。模拟CO₂浓度结果表明:在人为活动较少地区,陆地生态系统碳通量对近地面CO₂浓度空间分布起主导作用,尤其在南半球和欧洲地区模拟浓度有明显差异,且两种模拟结果的季节差异依赖于陆地生态系统碳通量的季节变化。将模拟结果与9个观测站点资料进行对比,以期选用合适的陆地生态系统碳通量来提升GEOS-Chem模拟CO₂浓度的精度。实验结果表明:两种模拟结果均能较好的模拟CO₂浓度的季节变化及其峰谷值,但CT2016模拟的CO₂浓度在多数站点处更接近观测资料,模拟准确性更高。     

东北雨养玉米田碳交换年际变化及影响因素北大核心CSCD

在气候变化背景下,农田净生态系统生产力变化趋势和影响因素不确定性大,为有效评估农田生态系统的固碳潜力,利用2005-2020年东北雨养春玉米田涡动相关数据分析该区域碳通量年际变化趋势及其气象、土壤和生物影响因素。结果表明:东北雨养春玉米田净生态系统生产力为272±109g·m^(-2)·a^(-1),且无显著变化趋势;与生态系统呼吸相比,净生态系统生产力年际变化主要受总生态系统生产力影响。气象因素的降水量和生物因素的作物水分利用效率是净生态系统生产力年际变化的主要影响因素,影响权重分别为28.4%和31.4%;气象、土壤和生物因素对总生态系统生产力年际变化的影响权重分别为61.0%,43.8%和62.8%;土壤因素和生物因素是生态系统呼吸年际变化的主要影响因素,且土壤因素对生态系统呼吸年际变化的影响权重(39.3%)大于生物因素(29.2%)。在气候变暖背景下,东北雨养春玉米田对水分更为敏感,同时日照和温度通过影响饱和水汽压差和土壤湿度间接影响净生态系统生产力的年际变化。     

Testing of the bandpass eddy covariance method for a long-term measurement of water vapour flux over a forest

The bandpass eddy covariance method has been used to measure the turbulent flux of scalar quantities using a slow-responsescalar sensor. The method issimilar in principle to the traditional eddy correlation method but includes the estimation of high-frequency components of the flux on the basis of cospectral similarity in the atmospheric surface layer. In order to investigate the performance of the method, measurements of the water vapour flux over a forest with the bandpass eddy covariance method and the direct eddy correlation method were compared. The flux obtained by the bandpass eddy covariance method agreed with that by the eddy correlation method within ±20% for most cases, in spite of a rather slow sensor-response of the adopted hygrometer. This result supports its relevance to a long-term continuous operation, since a stable, low-maintenance,general-purpose sensor canbe utilized for scalar quantities. Oneweak point of the method isits difficulty in principle to measure the correct flux when the magnitude of the sensible heat flux is very small, because the method uses the sensible heat flux as a standard reference for the prediction of undetectable high-frequency components of the scalar flux. An advanced method is then presented to increase its robustness. In the new method, output signals from a slow-response sensor are corrected using empirical frequency-responsefunctions for the sensor,thereby extending the width of the bandpass frequency region where components of the flux are directly measured (not predicted). The advanced method produced correct fluxes for all cases including the cases of small sensible heat flux. The advanced bandpass eddy covariance method is thus appropriate for along-term measurement of the scalar fluxes.     

The Spatial Variability of Energy and Carbon Dioxide Fluxes at the Floor of a Deciduous Forest

Fluxes of carbon dioxide, water and sensible heat were measured using three different eddy covariance systems above the forest floor of a closed deciduous forest (leaf area index approx 6). The primary objective was to examine the representativeness of a single eddy covariance system in estimating soil respiration for time scales ranging from one-half hour to more than one week. Experiments were conducted in which the eddy covariance sensors were in one of three configurations: i) collocated, ii) separated horizontally or iii) separated vertically. A measure of the variation between the three systems (CV',related to the coefficient of variation) for half-hour carbon dioxide fluxes was 0.14 (collocated systems), 0.34 (vertically separated systems at 1, 2 and 4 m above the surface), and 0.57 (systems horizontally separated by 30 m). A similar variation was found for other scalar fluxes (sensible and latent heat). Variability between systems decreased as the number of half-hour sampling periods used to obtain mean fluxes was increased. After forty-eight hours (means from ninety-six half-hour samples), CV' values for carbon dioxide fluxes were 0.07, 0.09 and 0.16 in the collocated, vertically separated and horizontally separated experiments, respectively. The time dependence of variability has implications on the appropriateness of using short-term measurements in modelling validation studies. There are also implications concerning the appropriate number of half-hour samples necessary to obtain reliable causal relationships between flux data and environmental parameters. Based on the longer-term measurements, we also discuss the representativeness of a single eddy covariance system in long-term monitoring of soil respiration and evaporation beneath forest canopies using the eddy covariance method.     

非均匀下垫面湍流通量观测的印痕分析

利用2005年在北京昌平区小汤山开展的非均匀下垫面观测实验的观测数据,分别处理了涡旋相关法和大孔径闪烁仪LAS测得的感热通量,并运用印痕模型对数据进行“源区”分析。分析结果表明:在复杂地表上,涡旋相关的测量值由于混杂了其他下垫面的通量信息,不能真实地反映其观测区域的湍流特征,存在着观测误差。而LAS观测出现的低估问题则与掺混高度和“源区”有关。通过用印痕方法进行数据订正后,以上问题均得到很好的改善,订正结果与LAS观测通量的线性关系良好,两者的相关系数达到0.9。实验结果验证了印痕模型在非均匀下垫面的适用性。     

Turbulent variance characteristics of temperature and humidity over a non-uniform land surface for an agricultural ecosystem in China

This paper describes the application of the variance method for flux estimation over a mixed agricultural region in China. Eddy covariance and flux variance measurements were conducted in a near-surface layer over a non-uniform land surface in the central plain of China from 7 June to 20 July 2002. During this period, the mean canopy height was about 0.50 m. The study site consisted of grass (10% of area), beans (15%), corn (15%) and rice (60%). Under unstable conditions, the standard deviations of temperature and water vapor density (normalized by appropriate scaling parameters), observed by a single instrument, followed the Monin-Obukhov similarity theory. The similarity constants for heat (CT ) and water vapor (Cq) were 1.09 and 1.49, respectively. In comparison with direct measurements using eddy covariance techniques, the flux variance method, on average, underestimated sensible heat flux by 21% and latent heat flux by 24%, which may be attributed to the fact that the observed slight deviations (20% or 30% at most) of the similarity “constants” may be within the expected range of variation of a single instrument from the generally-valid relations.     

不同下垫面大孔径闪烁仪观测数据处理与分析

大孔径闪烁仪是近年兴起的测量大尺度（500 m~10 km）地表通量的仪器。北京师范大学等单位分别于2002年、2004年在北京昌平小汤山开展了大孔径闪烁仪短期观测实验, 2006年6月又在北京密云建立了长期观测站。利用这些数据, 对大孔径闪烁仪观测数据进行处理与分析, 结果表明:闪烁仪光径高度和风速是影响观测显热通量的关键因子。当地表粗糙元的高度变化相对于光径高度不可忽略时, 零平面位移需要精确确定。波文比在湿润地表需要准确确定, 而气温、气压和动力学粗糙度则为不敏感因子。计算中所需的大气稳定度可用理查孙数判断, 也可借助日出日落时间或净辐射观测值确定。稳定条件下的普适函数目前无统一表达式, 可采用仪器说明书推荐的函数。通过几个站点闪烁仪观测显热通量与涡动相关仪测量值的比较表明:大孔径闪烁仪在均匀和非均匀地表都能得到合理的显热通量观测值。     

在华北玉米生育期观测的16 m高度CO2浓度及通量特征

利用中国气象局固城农业气象生态试验站2004年玉米生育期通量观测资料,分析了CO2浓度和通量随玉米生长的变化,并估算了玉米生育期陆地与大气CO2净交换量。结果表明:CO2浓度变化对农户活动和作物生长极其敏感;浓度在整个生育期始终有明显的日变化规律,峰值（谷值）出现在日出（日落）前后,通量仅在7月中旬至10月上旬之间出现明显的日变化特点,且位相超前于浓度,开花期通量最大;玉米播种期、苗期和成熟后地面向大气净排放碳, 拔节至成熟前地面从大气净吸收碳;开花期碳吸收最强,其后依次为吐丝－乳熟期和拔节期。比较分析了目前流行的通量计算方法对碳吸收估计的影响,结果显示不同计算方法能产生高达160%的碳吸收估计偏差,应当引起重视。生态系统碳平衡分析结果表明,玉米地在生长季表现为弱碳汇（大约660 kg/hm2）,但这一结果可能低估了实际的碳汇强度,低估程度有待研究。     

基于淮河流域农田生态系统观测资料的通量研究

运用寿县国家气候观象台(代表淮河流域农田生态系统)2007年7月至2008年6月通量观测系统的观测资料,分析研究淮河流域农田生态系统的陆气相互作用,统计梯度和涡度数据缺测率,采用空气动力学(梯度)法和涡度相关法,验证通量观测系统观测数据的可靠性,分析CO2通量、潜热通量、感热通量的季节变化与日变化特征及其与下垫面的关系,计算出地表平均反照率、能量闭合率、动量输送系数等。结果表明:通量观测仪器测得的数据可靠,原始资料具有客观性、可用性;CO2等通量存在明显的季节变化,与下垫面状况有密切的关系,日变化均为单峰型分布,由通量观测系统的观测资料计算得到地表平均反照率为0.18,平均能量闭合率为0.92,平均动量输送系数为0.0092。     

青藏高原东部草甸下垫面涡旋相关观测数据的质量控制及评价研究

目前利用涡旋相关仪观测地表通量的方法已被广泛采用, 但由于涡旋相关法是建立在方程假设简化的基础上, 这对观测数据的质量提出了一定的要求, 所以对观测数据的处理及通量结果的质量状况分析就显得尤为重要。本文以理塘站2006年7月中到8月中的数据为例, 对其进行质量控制, 并将质量控制后的通量计算结果与原始值进行比较。质量控制后感热通量和潜热通量总和有所增长, 动量通量值则受质量控制影响较大。质量评价的结果为:动量通量、感热通量、潜热通量中高质量数据所占比例为68.2%、60.6%、63.3%。     

The HartX-synthesis: An experimental approach to water and carbon exchange of a Scots pine plantation

Summary In May 1992 during the interdisciplinary measurement campaign HartX (Hartheim eXperiment), several independent estimates of stand water vapor flux were compared at a 12-m high Scots pine (Pinus silvestris) plantation on a flat fluvial terrace of the Rhine close to Freiburg, Germany. Weather during the HartX period was characterized by ten consecutive clear days with exceptionally high input of available energy for this time of year and with a slowly shifting diurnal pattern in atmospheric variables like vapor pressure deficit. Methods utilized to quantify components of stand water flux included porometry measurements on understory graminoid leaves and on pine needles and three different techniques for determining individual tree xylem sap flow. Micrometeorological methods included eddy covariance and eddy covariance energy balance techniques with six independent systems on two towers separated by 40 m. Additionally, Bowen ratio energy balance estimates of water flux were conducted and measurements of the gradients in water vapor, CO₂, and trace gases within and above the stand were carried out with an additional, portable 30 m high telescoping mast.Biologically-based estimates of overstory transpiration were obtained by up-scaling tree sap flow rates to stand level via cumulative sapwood area. Tree transpiration contributed between 2.2 and 2.6 mm/day to ET for a tree leaf area index (LAI) of 2.8. The pine stand had an understory dominated by sedge and grass species with overall average LAI of 1.5. Mechanistic canopy gas exchange models that quantify both water vapor and CO₂ exchange were applied to both understory and tree needle ecosystem compartments. Thus, the transpiration by graminoid species was estimated at approximately 20% of total stand ET. The modelled estimates for understory contribution to stand water flux compared well with micrometeorologically-based determinations. Maximum carbon gain was estimated from the canopy models at approximately 425 mmol/(m²day) for the tree needles and at 100 mmol/(m²day) for the understory. Carbon gain was suggested by the modelling analysis to remain relatively constant during the HartX period, while water use efficiency in carbon fixation increased with decreasing vapor pressure deficit. Biologically- and micrometeorologically-based estimates of stand water flux showed good general agreement with variation of up to 20% that reflects both errors due to the inherent assumptions associated with different methods as well as natural spatial variability in fluxes. The various methods support a reliable estimate of average ET from this homogeneous canopy during HartX of about 2.6 mm/day (a maximum of about 3.1 mm/day) with an insignificant decreasing trend in correlation with decreasing vapor pressure deficit and possibly soil moisture.Findings during HartX were embedded in local scale heterogeneity with greater roughness over the forest and much higher ET over the surrounding agricultural fields which results in weak but clearly existant circulation patterns. A variety of measurements were continued after the HartX campaign. They allow us to extend our findings for six months with changing environmental conditions, including shortage of soil moisture. Hydrological estimates of soil water extractions and micrometeorological estimates of ET by the one-propeller eddy covariance (OPEC) system were in very good agreement, supporting the use of this robust eddy covariance energy balance technique for long-term monitoring.With 5 Figures     

Using a One-and-a-Half Order Closure Model of the Atmospheric Boundary Layer for Surface Flux Footprint Estimation

A knowledge of the distribution of the contribution of upwind sources to measurements of vertical scalar flux densities is important for the correct interpretation of eddy covariance data. Several approaches have been developed to estimate this so-called footprint function. Here a new approach based on the ensemble-averaged Navier—Stokes equations is presented. Comparisons of numerical results using this approach with results from other studies under a range of environmental conditions show that the model predictions are robust. Moreover, the approach outlined here has the advantage of a potential wide applicability, due to an ability to take into account the heterogeneous nature of underlying surfaces. For example, the model showed that any variations in surface drag, such as must occur in real life heterogeneous canopies, can exert a marked influence of the shape and extent of flux footprints. Indeed, it seems likely that under such circumstances, estimates of surface fluxes will be weighted towards areas of highest foliage density (and therefore quite likely higher photosynthetic rates) close to the measurement sensor. Three-dimensional footprints during the day and night were also determined for a mixed coniferous forest in european Russia. A marked asymmetry of the footprint in the crosswind direction was observed, this being especially pronounced for non-uniform plant distributions involving vegetation types with different morphological and physiological properties. The model also found that, other things being equal, the footprint peak for forest soil respiration is typically over twice the distance from the above canopy measurement sensor compared to that for canopy photosynthesis. This result has important consequences for the interpretation of annual ecosystem carbon balances by the eddy covariance method.