乌鲁木齐市酸雨特征及变化趋势   总被引：2，自引：0，他引：2  

刘新春  何清  艾力·买买提明  梁云  南庆红  LIU Xin-chun  HE Qing  Aili·MAMTIMIN  LIANG Yun  NAN Qing-hong 《沙漠与绿洲气象(新疆气象)》2007,1(5):10-14

通过对乌鲁木齐市1991—2007年降水pH值、K值(电导率)以及相关的天气气候资料的处理,分析了酸雨特征和变化趋势。结果表明:pH平均值有逐年降低的趋势;从2000年开始K平均值呈下降趋势;降水pH平均值和K平均值具有明显的季节变化;供暖对pH平均值和K平均值造成很大的影响,是形成酸雨的重要因素之一。  相似文献   

利用遥感信息研究区域冬小麦气孔导度的时空分布   总被引：5，自引：0，他引：5  

张佳华  符淙斌  王长耀 《气象学报》2000,58(3):347-353

气孔导度是影响作物蒸散和作物的光合速率进而影响作物产量的重要因子。文中通过利用NOAA－AVHRR数据首次对华北平原典型区冬小麦气孔导度分布进行了研究,给出了华北平原典型区冬小麦不同生长季节的气孔导度空间分布状况,为进一步研究田间水分和作物蒸散对产量影响以及建立遥感作物水分胁迫生物量模型和监测不同生育期的农田缺水等提供依据。  相似文献   

毛乌素沙地油蒿群落演替的生理生态学机制   总被引：5，自引：1，他引：4  

张军  黄永梅  焦会景  夏显东 《中国沙漠》2007,27(6):977-983

对毛乌素沙地稀疏阶段、建成阶段和衰老阶段的油蒿群落的野外观测实验结果表明,不同演替阶段的油蒿群落对环境的适应性和生理生态特性表现出明显的差异。随群落盖度的增加,0—20 cm土层中土壤含水量明显增加,而在20—80 cm范围内有所下降。与稀疏阶段和建成阶段的油蒿群落相比,衰老阶段的油蒿群落的平均净光合速率低,光饱合点低,光能及水分利用效率最低,并且日变化过程也表现出受到了明显环境胁迫。在不同的演替阶段,油蒿的气孔导度与植物水势均呈线性相关。随植物水势的降低,处于衰老阶段的油蒿气孔导度降低速率最快。结合气孔导度和水分循环的关系,还初步探讨了毛乌素沙地油蒿群落演替的主要驱动因子。  相似文献   

Photosynthetic responses of Larrea tridentata to a step-increase in atmospheric CO₂at the Nevada Desert FACE Facility     

E. P. Hamerlynck  T. E. Huxman  R. S. Nowak  S. Redar  M. E. Loik  D. N. Jordan  S. F. Zitzer  J. S. Coleman  J. R. Seemann  S. D. Smith   《Journal of Arid Environments》2000,44(4):425

Of all terrestrial ecosystems, the productivity of deserts has been suggested to be the most responsive to increasing atmospheric CO₂. The extent to which this prediction holds will depend in part on plant responses to elevated CO₂under the highly variable conditions characteristic of arid regions. The photosynthetic responses ofLarrea tridentata , an evergreen shrub, to a step-increase in atmospheric CO₂(to 550 μmolmol⁻¹) were examined in the field using Free-Air CO₂Enrichment (FACE) under seasonally varying moisture conditions. Elevated CO₂substantially increased net assimilation rate (A_net) in Larrea during both moist and dry periods of the potential growing season, while stomatal conductance (g_s) did not differ between elevated and ambient CO₂treatments. Seasonal and diurnal gas exchange dynamics in elevated CO₂mirrored patterns in ambient CO₂, indicating that elevated CO₂did not extend photosynthetic activity longer into the dry season or during more stressful times of the day. Net assimilation vs. internal CO₂(A/C_i) responses showed no evidence of photosynthetic down-regulation during the dry season. In contrast, after significant autumn rains, A_max(the CO₂saturated rate of photosynthesis) and CE (carboxylation efficiency) were lower in Larrea under elevated CO₂. In situ chlorophyll fluorescence estimation ofLarrea Photosystem II efficiency (F_v/F_m) responded more to water limitation than to elevated CO₂. These findings suggest that predictions regarding desert plant responses to elevated CO₂should account for seasonal patterns of photosynthetic regulatory responses, which may vary across species and plant functional types.  相似文献   

Quantifying contributions of snowmelt water to streamflow using graphical and chemical hydrograph separation     

Samuel A. Miller  Steve W. Lyon  Scott N. Miller 《水文研究》2020,34(26):5606-5623

In this study, we characterize the snowmelt hydrological response of nine headwater watersheds in southeast Wyoming by separating streamflow into three components using a combination of tracer and graphical approaches. First, continuous 15-min records of specific conductance (SC) from 2016 to 2018 were used to separate streamflow into annual contributions, representing water that contributes to streamflow in a given year that entered the watershed in the same year being considered, and perennial contributions, representing water that contributes to streamflow in a given year that entered the watershed in previous years. Then, diurnal streamflow cycles occurring during the snowmelt season were used to graphically separate annual contributions into rapid diurnal snowmelt contributions, representing water with the relatively fastest hydrological response and shortest residence time, and delayed annual contributions, representing water with relatively longer residence time in the watershed before becoming streamflow. On average, mean annual total streamflow was comprised of between 22% and 46% perennial contributions, 7% and 14% rapid diurnal snowmelt contributions, and 46% and 55% delayed annual contributions across the watersheds. A hysteresis index describing SC-discharge patterns indicated that, annually, most watersheds showed negative, concave, anti-clockwise hysteretic direction suggesting faster flow pathways dominate streamflow on the rising limb of the annual hydrograph relative to the falling limb. At the daily timescale during snowmelt-induced diurnal streamflow cycles, hysteresis was negative, but with a clockwise direction, implying that rapid diurnal snowmelt contributions generated from the concurrent daily snowmelt, with lower SC, arrived after delayed annual contribution peaks and preferentially contributed on the falling limb of diurnal cycles. South-facing watersheds were more susceptible to early season snowmelt at slower rates, resulting in less annual and more perennial contributions. Conversely, north-facing watersheds had longer snow persistence and larger proportions of annual contributions and rapid diurnal snowmelt contributions. Watersheds with surficial geology dominated by glacial deposits had a lower proportion of rapid diurnal snowmelt contributions compared to watersheds with large percentages of bedrock surficial geology.  相似文献   

Variations of crop coefficient and its influencing factors in an arid advective cropland of northwest China          下载免费PDF全文

Risheng Ding  Ling Tong  Fusheng Li  Yanqun Zhang  Xinmei Hao  Shaozhong Kang 《水文研究》2015,29(2):239-249

Understanding the variation and magnitude of crop coefficient (K_c) is important for accurate determination of crop evapotranspiration and water use. In this study, we calculated K_c in an irrigated maize field with ground mulching by eddy covariance evapotranspiration measurements during the whole growing periods in 2009 and 2010 in an arid region of northwest China. A semi‐empirical practical approach for estimating K_c was proposed by introducing the dynamic fraction of canopy cover and incorporating the effect of leaf senescence as a function of days after sowing. The contribution of arid advection of sensible heat resulting from irrigation to K_c and the response of K_c to canopy conductance (G_c) were investigated. The averaged values of daily K_c were lower than typical values obtained previously without mulching due to decreasing effect of mulching on K_c, with 0.82 and 0.80 for the 2 years, respectively. The maximum average K_c occurred at the heading stage, with 1.21 and 1.04 for the 2 years, respectively. The difference of K_c was attributed to the difference of leaf area index. The semi‐empirical practical approach could well estimate the variations of K_c, thus could be a robust and useful tool for the practical users and water managers. The contributions to daily K_c from the arid advection were 4.4–28.0% of the measured K_c. The G_c had stronger control on daily K_c at the early and later stages than at the middle stage. When G_c, leaf area index and relative soil extractable water were lower than the respective threshold values of 20 mm s^?1, 3.0 m² m^?2 and 0.5, the daily K_c increased significantly with the increase of the three factors, and almost remained constant when the three factors were beyond the threshold values. These results are helpful for quantifying contributions of individual factors to K_c, and subsequently improving water management practices according to K_c. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Thermal infrared imaging of the temporal variability in stomatal conductance for fruit trees     

《International Journal of Applied Earth Observation and Geoinformation》2015

Repeated measurements using thermal infrared remote sensing were used to characterize the change in canopy temperature over time and factors that influenced this change on ‘Conference’ pear trees (Pyrus communis L.). Three different types of sensors were used, a leaf porometer to measure leaf stomatal conductance, a thermal infrared camera to measure the canopy temperature and a meteorological sensor to measure weather variables. Stomatal conductance of water stressed pear was significantly lower than in the control group 9 days after stress began. This decrease in stomatal conductance reduced transpiration, reducing evaporative cooling that increased canopy temperature. Using thermal infrared imaging with wavelengths between 7.5 and13 μm, the first significant difference was measured 18 days after stress began. A second order derivative described the average rate of change of the difference between the stress treatment and control group. The average rate of change for stomatal conductance was 0.06 (mmol m⁻² s⁻¹) and for canopy temperature was −0.04 (°C) with respect to days. Thermal infrared remote sensing and data analysis presented in this study demonstrated that the differences in canopy temperatures between the water stress and control treatment due to stomata regulation can be validated.  相似文献   

瞬变电磁视纵向电导成像法在寻找深部隐伏金属矿中的应用     

王文忠  马国林  刘继东 《物探与化探》2011,35(4):473-476

在甘肃北山地区寻找全隐伏深部矿床的勘查中,根据工作区的地质特征,运用V8多功能电法仪,使用瞬变电磁法(TEM)对全区进行了面积扫描,运用视纵向电导成像法进行资料处理和解释,使解释的地下地质体更趋于其赋存特征,从而基本掌握了该区金属矿床赋存的电性特征,为该区的进一步勘查提供了依据。  相似文献   

Temporal and spatial variations of canopy temperature over a C3?C4 mixture grassland     

S. Shimoda  T. Oikawa 《水文研究》2006,20(16):3503-3516

This study discusses the photosynthetic pathway types involved in canopy temperature measurements on a mixed grassland consisting of C₃ and C₄ plants (dominant species in biomass were Solidago altissima (C₃), Miscanthus sinensis (C₄), and Imperata cylindrica (C₄)). In the wet conditions immediately after the rainy season, the mean canopy temperature for S. altissima was the lowest among the dominant species, mainly due to its leaf conductance being twice as large as the other two species. Despite using the same C₄ photosynthetic pathway, M. sinensis had a lower apparent canopy temperature than I. cylindrica due to a smaller proportion of sunlit elements in the field of view. In the dry conditions during late July, the mean canopy temperatures of the three dominant species were within 0·3 °C of one another. These results can be explained by poor water conditions for C₃ species (S. altissima). The simultaneous survey of vegetation and thermal imaging can help clarify characteristics of C₃ and C₄ canopy temperature over complicated grassland. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

利用泉水电导率频率分布辨别岩溶含水系统的水源组分   总被引：1，自引：0，他引：1       下载免费PDF全文

郭芳  姜光辉  刘绍华  汤庆佳 《水科学进展》2018,29(2):245-251

岩溶含水系统中水源组分的识别能帮助认识系统的结构,解决岩溶水文及水化学研究的基础问题。以灵水岩溶大泉为例,分解了4个水文年的电导率频率分布隐藏的峰,并对其所代表的水源组分进行分析。发现灵水泉口的水源组分主要有4种:① 含水系统中岩溶裂隙或管道中释放的重力水,占53%~77%;② 源于泉口附近携带污染物质的水源,占3%~7%;③ 强降雨期间通过覆盖层分散入渗的水源,或先前存贮在管道或裂隙中流动性差的水被带出含水层,占13%~42%;④ 地面径流以及直接降落到湖面的雨水,占2%~3%。将灵水的电导率频率分布与峰丛洼地的两个典型岩溶水系统对比,分析了电导率的频率分布所蕴藏的含义。研究结果为西南3 620个岩溶水系统的进一步归类提供了参考。  相似文献