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71.
森林被誉为"地球之肺",在防霾治污方面有其独特不可替代的作用,不同树种沉降PM2.5的功能有很大差别.本文选取代表性城市森林——奥林匹克森林公园为研究对象,设置垂直监测塔观测大气PM2.5的浓度垂直分布,以考察不同季节城市森林对PM2.5中各组分的影响.在冬季、春季和夏季各采集PM2.5样品,分析并计算PM2.5中Na+、NH4+、K+、Mg2+、Ca2+、Cl-、NO3-和SO42-等典型水溶性无机离子的浓度.结果表明,PM2.5中水溶性无机离子总浓度呈规律性变化特征:冬季((56.90±27.38)μg·m-3)>春季((46.69±12.24)μg·m-3)>夏季((23.16±8.75)μg·m-3).其中SO42-和NO3-浓度和占PM2.5主要水溶性无机离子总浓度的50%以上.3个季节中,除冬季外,在春季和夏季,8种离子有明显的垂直方向上的沉降,夏季的沉降速率高于春季,但是春季由于大气颗粒物浓度高,沉降通量高于夏季.NO3-和SO42-垂直方向的沉降量在所有可溶性无机离子中最高.植被密度、叶面积指数、气象条件等因素对于PM2.5的沉降特征有明显影响. 相似文献
72.
73.
Effects of Stonewalled Terracing Techniques on Soil-Water Conservation and Wheat Production Under Mediterranean Conditions 总被引:2,自引:0,他引:2
A field plot experiment was conducted in the Palestinian Autonomous Areas to study the effect of stonewalled terracing on soil and water conservation as compared to the nonterraced areas. Effects of the wheat canopy were considered as a second treatment. The experiment was undertaken over a period of two seasons (2000 and 2001). The results of the experiment found that the mean soil erosion was significantly lower (P < 0.05) in the terraced plots than in those that were nonterraced (182 kg/ha and 3525 kg/ha during the first season, 1769 kg/ha and 5057 kg/ha during the second season for terraced and nonterraced plots, respectively). A similar trend was observed with respect to runoff in areas under the same treatments. The wheat canopy showed lower, but not significant runoff and erosion in most of the cases for both seasons. Due to better soil and water conservation, the terraced plots obtained significantly higher total plant dry matter than nonterraced plots (1570 and 630 kg/ha in 2000, 2545 and 889 kg/ha in 2001 for terraced and nonterraced treatment, respectively). The runoff coefficient was 20% and 4% for the nonterraced and terraced plots, respectively. Rainstorms with intensity ≥4 mm/hand rainfall ≥10 mm are more likely to cause runoff and erosion. 相似文献
74.
Fowler D. Sutton M. A. Flechard C. Cape J. N. Storeton-West R. Coyle M. Smith R. I. 《Water, Air, & Soil Pollution: Focus》2001,1(5-6):39-48
Two years of continuous measurements of SO2deposition fluxes to moorland vegetation are reported. The mean flux of 2.8 ng SO2 m-2 s-1 is regulated predominantly by surface resistance (r
c) which, even for wet surfaces, was seldom smaller than 100 s m-1. The control of surface resistance is shown to be regulated by the ratio of NH3SO2 concentrations with an excess of NH3 generating the small surface resistances for SO2. A dynamic surface chemistry model is used to simulate the effects of NH3 on SO2 deposition flux and is able to capture responses to short-term changes in ambient concentrations of SO2, NH3 and meteorological conditions. The coupling between surface resistance and NH3/SO2 concentration ratios shows that the deposition velocity for SO2 is regulated by the regional pollution climate. Recent long-term SO2 flux measurements in a transect over Europe demonstrate the close link between NH3/SO2 concentrations and rc (SO2). The deposition velocity for SO2 is predicted to have increased with time since the 1970s and imply a 40% increase in v
d at a site at which the annual mean ambient SO2 concentrations declined from 47 to 3 g m-3 between 1973 and 1998. 相似文献
75.
Allen S. Hope Ray D. Jackson 《Journal of the American Water Resources Association》1989,25(5):1009-1014
ABSTRACT: Several crop water stress indices were examined to determine their potential for use from a space-based system. These indices were compared using data collected over a wheat crop grown under arid environmental conditions. Indices that required concurrent ground-based measurements were less adaptable than the simple difference between canopy temperatures of a field with unknown stress conditions and a similar crop known to be unstressed. The results indicate that it would be feasible to develop space-based crop water stress techniques that would be useful for scheduling irrigations. 相似文献
76.
文章以河北省兴隆县雾灵山低山地区人工油松林为研究对象,采用植物群落样地调查法,对不同郁闭度的人工油松林样地灌木层和草本层群落的种类组成状况进行了观察和调查,并通过总优势度、Simpson指数、种间相遇概率等指标来探讨不同郁闭度下的油松林植物群落的物种多样性特点,以分析油松林郁闭度对其林下群落结构和物种丰富度的影响。结果表明在油松的郁闭作用下,林下灌木层植物密集,种类丰富,物种多样性高,而草本层植物稀疏,种类贫乏,物种多样性低;随着油松郁闭度的增加,灌木层物种多样性升高,草本层物种多样性有降低的趋势。 相似文献
77.
基于遥感的千烟洲人工林蒸散及其组分模拟研究 总被引:5,自引:0,他引:5
论文通过改进遥感蒸散模型的关键参数,结合遥感数据和气象观测数据,对2003—2008年江西千烟洲人工林生态系统蒸散及其组分进行模拟,并利用涡度相关技术获取的蒸散实测数据对模型模拟结果进行验证和评价。结果表明:①年均蒸散总量模拟值比实测值偏低2.4%,决定系数与均方根误差分别为0.83和0.61 mm·d-1。②土壤蒸发、林冠截留蒸发和植被蒸腾分别占总蒸散量的12%、23%和65%。其中,土壤蒸发季节及年际变化相对稳定;林冠截留蒸发季节变化明显且在不同年份差异较大;植被蒸腾季节变化明显,但年际变异较小。③1—3月植被光合作用较弱,植被蒸腾与蒸散比小于30%。随着植被蒸腾的增强,从4月开始植被蒸腾与蒸散比迅速增加,在生长旺季(7月底)可达到约90%。由于该模型所需数据在区域尺度较易获取,从而为开展区域尺度中亚热带人工林生态系统蒸散及其组分模拟提供方法支撑。 相似文献
78.
H.?Foudhil Y.?BrunetEmail author J.?-P.?Caltagirone 《Environmental Fluid Mechanics》2005,5(3):247-265
A multi-purpose model for small-scale atmospheric flows over heterogeneous landscapes is being developed. The aim of this research is to build a tool able to predict the dynamical (wind, turbulence) and diffusive (gases, particles) fields over landscapes characterised by heterogeneous plant cover. In its present stage of development the model is based on the numerical integration of neutral atmospheric flow equations, using an energy-dissipation closure scheme and over a domain that may include vegetation layers. Three validation cases of the model are presented: (i) response of the airflow to a change in surface roughness; (ii) airflow within and above a horizontally homogeneous plant canopy; (iii) airflow over two complex forest-to-clearing and clearing-to-forest transitions. All simulations provide results in good agreement with the experimental data, except for turbulent kinetic energy just after a clearing-to-forest transition. This result is not surprising for a statistical k– model in a flow region characterised by strong distorsion and intermittent turbulence. However the overall good performance of the model is promising for environmental research at fine scales over heterogeneous landscapes. 相似文献
79.
80.
Wusi Yue Charles Meneveau Marc B. Parlange Weihong Zhu Hyung Suk Kang Joseph Katz 《Environmental Fluid Mechanics》2008,8(1):73-95
A comparative study of turbulence in a wind-tunnel model canopy is performed, using Large eddy simulation (LES) and experimental
data from PIV and hot-wire anemometry measurements. The model canopy is composed of thin cylindrical stalks. In the LES, these
are represented using a plant-scale approach, while the scale-dependent Lagrangian dynamic model is used as subgrid-scale
model. LES predictions of turbulence statistics and energy spectra are found to be in good agreement with the experimental
data. Turbulent kinetic energy (TKE) budgets from the LES simulation are analyzed to provide more information absent in the
measurements. Results confirm that sloshing motions at the low levels of the canopy are mainly driven by pressure fluctuations.
A difference between the energy flux obtained from the energy spectrum and the SGS dissipation rate is observed, consistent
with a spectral bypass mechanism in which the real spectral flux due to cascade is smaller than that implied by the energy-spectrum
level, due to direct drain by the canopy. 相似文献