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83.
青藏高原草地土壤有机碳库及其全球意义 总被引：55，自引：5，他引：50
定量分析了青藏高原各类草地0～0.65m深度范围内有机碳储量,结果表明:青藏高原总面积为1.6027×10hm2的草地有机碳量达到335.1973×108tC,其中以高原草甸土和高原草原土有机碳积累量为主,两者之和达到232.36×108tC,占全国土壤有机碳量的23.44%,是全球土壤碳库的2.4%.在有机碳储量分析的基础上,按土壤碳释放的两种主要途径:土壤呼吸作用和土地利用方式变化与草地退化,对草地土壤碳排放进行了估算,揭示出青藏高原草地土壤通过呼吸每年排放的CO2达到11.7×108tC·a-1,约占中国土壤呼吸总量的2.3%,明显高于全国乃至全球平均值;近30a来,青藏高原草地土壤由于土地利用变化和草地退化所释放的CO2估计约有30.23×108tC.保护青藏高原草地对于全球变化意义重大.定量分析了青藏高原各类草地0～0.65m深度范围内有机碳储量,结果表明:青藏高原总面积为1.6027×10hm2的草地有机碳量达到335.1973×108tC,其中以高原草甸土和高原草原土有机碳积累量为主,两者之和达到232.36×108tC,占全国土壤有机碳量的23.44%,是全球土壤碳库的2.4%.在有机碳储量分析的基础上,按土壤碳释放的两种主要途径:土壤呼吸作用和土地利用方式变化与草地退化,对草地土壤碳排放进行了估算,揭示出青藏高原草地土壤通过呼吸每年排放的CO2达到11.7×108tC·a-1,约占中国土壤呼吸总量的2.3%,明显高于全国乃至全球平均值;近30a来,青藏高原草地土壤由于土地利用变化和草地退化所释放的CO2估计约有30.23×108tC.保护青藏高原草地对于全球变化意义重大. 相似文献
84.
尾矿砂沙害形成机理与工程治理措施的选择 总被引：1，自引：0，他引：1
尾矿砂沙害的形成过程,包含着尾矿砂强烈风蚀、尾矿砂输送搬运与堆积,以及尾矿砂吹扬在大气中的粉沙悬移等3个过程。上述3个过程对土地、大气、水体、道路、建筑物及农作物造成严重危害,甚至影响人身健康。研究结果表明,尾矿砂的治理,需采用固结沙面、切断沙源,即消除灾害源的方法。固结沙面的材料,宜采用坚固耐久、抗风蚀力强、具有较好蓄水保墒性能,以及保温能力高、且廉价的戈壁沙砾石。沙砾石覆盖之后,不仅固结了沙面,切断了沙源,而且为天然植物种子的散落和幼苗发育创造了稳定条件,加快了天然植物衍生。覆盖后的第一年雨季后,植物盖度到达了15%~30%,局部地段高达50%。 相似文献
85.
为探讨粉煤灰污染影响萼花臂尾轮虫(Brachionus calyciflorus)种复合体在灰湖、汀棠湖和凤鸣湖分布的生态学机制,本文研究了曝气自来水(对照)、20％、40％、60％、80％和100％的澄清灰湖水对采自三湖泊中的轮虫姐妹种Ⅰ和汀棠湖中的轮虫姐妹种Ⅱ的种群增长率、混交雌体数/非混交雌体数、携卵雌体数/不携卵雌体数和休眠卵产量的影响.结果显示,无论实验用水中的澄清灰湖水含量如何,来自三湖泊的轮虫姐妹种Ⅰ均具有较高的种群增长率(0.52～0.85 d-1)和休眠卵产量(1.60～12.11ind./(4d·5ml)),这为轮虫的扩散、种群的建立和种群间的基因交流提供了可能.汀棠湖轮虫姐妹种Ⅱ种群中的混交雌体数/非混交雌体数和休眠卵产量均极低,对照组中的混交雌体数/非混交雌体数和休眠卵产量均为0,这是存在于汀棠湖和凤鸣湖中的轮虫姐妹种Ⅱ无法通过扩散而出现在灰湖中的主要原因.澄清灰湖水的含量仅对汀棠湖中两轮虫姐妹种的种群增长率具有显著的影响.各浓度的澄清灰湖水使轮虫姐妹种Ⅰ的种群增长率显著高于对照组,60％、80％和100％的澄清灰湖水使轮虫姐妹种Ⅱ的种群增长率显著高于对照组,这表明粉煤灰污染导致已报道的相关水体中轮虫种群密度的下降并非由于其中所含的污染物(较高浓度的碱性氧化物、硫化物和金属元素等)和水体pH值的改变等对轮虫的直接毒性作用. 相似文献
86.
Seismic wavefield modeling is important for improving seismic data processing and interpretation. Calculations of wavefield propagation are sometimes not stable when forward modeling of seismic wave uses large time steps for long times. Based on the Hamiltonian expression of the acoustic wave equation, we propose a structure-preserving method for seismic wavefield modeling by applying the symplectic finite-difference method on time grids and the Fourier finite-difference method on space grids to solve the acoustic wave equation. The proposed method is called the symplectic Fourier finite-difference (symplectic FFD) method, and offers high computational accuracy and improves the computational stability. Using acoustic approximation, we extend the method to anisotropic media. We discuss the calculations in the symplectic FFD method for seismic wavefield modeling of isotropic and anisotropic media, and use the BP salt model and BP TTI model to test the proposed method. The numerical examples suggest that the proposed method can be used in seismic modeling of strongly variable velocities, offering high computational accuracy and low numerical dispersion. The symplectic FFD method overcomes the residual qSV wave of seismic modeling in anisotropic media and maintains the stability of the wavefield propagation for large time steps. 相似文献
87.
The scattering of plane SH-waves by topographic features in a layered transversely isotropic (TI) half-space is investigated by using an indirect boundary element method (IBEM). Firstly, the anti-plane dynamic stiffness matrix of the layered TI half-space is established and the free fields are solved by using the direct stiffness method. Then, Green’s functions are derived for uniformly distributed loads acting on an inclined line in a layered TI half-space and the scattered fields are constructed with the deduced Green’s functions. Finally, the free fields are added to the scattered ones to obtain the global dynamic responses. The method is verified by comparing results with the published isotropic ones. Both the steady-state and transient dynamic responses are evaluated and discussed. Numerical results in the frequency domain show that surface motions for the TI media can be significantly different from those for the isotropic case, which are strongly dependent on the anisotropy property, incident angle and incident frequency. Results in the time domain show that the material anisotropy has important effects on the maximum duration and maximum amplitudes of the time histories. 相似文献
88.
Hydrologists use the generalized Pareto (GP) distribution in peaks-over-threshold (POT) modelling of extremes. A model with similar uses is the two-parameter kappa (KAP) distribution. KAP has had fewer hydrological applications than GP, but some studies have shown it to merit wider use. The problem of choosing between GP and KAP arises quite often in frequency analyses. This study, by comparing some discrimination methods between these two models, aims to show which method(s) is (are) recommended. Three specific methods are considered: one uses the Anderson-Darling goodness-of-fit (GoF) statistic, another uses the ratio of maximized likelihood (closely related to the Akaike information criterion and the Bayesian information criterion), and the third employs a normality transformation followed by application of the Shapiro-Wilk statistic. We show this last method to be the most recommendable, due to its advantages with sizes typically encountered in hydrology. We apply the simulation results to some flood POT datasets.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR E. Volpi 相似文献
89.
Rock brittleness directly affects reservoir fracturing and its evaluation is essential for establishing fracturing conditions prior to reservoir reforming. Dynamic and static brittleness data were collected from siltstones of the Qingshankou Formation in Songliao Basin. The brittle–plastic transition was investigated based on the stress–strain relation. The results suggest that the brittleness indices calculated by static elastic parameters are negatively correlated with the stress drop coefficient and the brittleness index B2, defined as the average of the normalized Young’s modulus and Poisson’s ratio, is strongly correlated with the stress drop. The brittleness index B2, Young’s modulus, and Poisson’s ratio correlate with the brittle minerals content; that is, quartz, carbonates, and pyrite. We also investigated the correlation between pore fluid and porosity and dynamic brittle characteristic based on index B2. Pore fluid increases the plasticity of rock and reduces brittleness; moreover, with increasing porosity, rock brittleness decreases. The gas-saturated siltstone brittleness index is higher than that in oil- or water-saturated siltstone; the difference in the brittleness indices of oil- and water-saturated siltstone is very small. By comparing the rock mechanics and ultrasonic experiments, we find that the brittleness index obtained from the rock mechanics experiments is smaller than that obtained from the ultrasonic experiments; nevertheless, both decrease with increasing porosity as well as their differences. Ultrasonic waves propagate through the rock specimens without affecting them, whereas rock mechanics experiments are destructive and induce microcracking and porosity increases; consequently, the brittleness of low-porosity rocks is affected by the formation of internal microcrack systems. 相似文献
90.
采用FY-3B/IRAS亮温资料进行广义变分同化研究。广义变分同化结合了经典变分同化和稳健M-估计两者的优点。区别于经典变分同化依赖于先前的质量控制并要求误差服从高斯分布,把M-估计法耦合到经典变分同化框架中,得到广义变分同化,其弱化了同化前的质量控制和误差服从高斯分布这两个条件。目标能量泛函包含M-估计以保证对离群值具有稳健性,从而能够得到较好的同化结果。对比变分同化前后的FNL资料湿度与GDAS湿度相关系数作为同化结果检验评价。具体操作过程在FNL作为背景场的基础上分别采用经典和M-估计不同的权重因子变分同化FY3B/IRAS资料,把得到的分析场与GDAS进行相关性比较,由于湿度具有较强的非高斯性,文中首先评估了安徽省13个站GPS/PWV和积分相关湿度廓线得到大气可降水量(即GDAS/PWV和FNL/PWV资料)的相关性,进一步基于信息熵自由度思想进行了近一个月IRAS 20个通道对分析场的影响贡献率诊断研究。 相似文献