重金属胁迫下四种红树植物幼苗生理响应特征

研究了四种红树植物红海榄、秋茄、木榄、角果木幼苗在不同浓度重金属水溶液胁迫28天后的生理生化指标变化特征,包括可溶性蛋白含量、超氧化物歧化酶（superoxide dismutase, SOD）、过氧化物酶（peroxidase, POD）活性和氧化损伤标志物丙二醛（malondialdehyde, MDA）含量。研究结果表明四种植物叶片内的SOD、POD活性均呈现出先升高后下降趋势,10倍重金属水溶液中的红海榄,5倍重金属水溶液中的秋茄和木榄,以及1倍重金属水溶液中的角果木具有较好的抗氧化酶活性,能有效清除活性氧,减小氧化损伤。在同等浓度重金属水溶液处理下,MDA含量结果显示红海榄受损程度最轻,秋茄、木榄受损程度居中,角果木受损程度最重。红海榄抗重金属胁迫能力强于秋茄、木榄,角果木抗重金属能力最弱。上述四种红树植物对重金属的抗性结果说明红树科植物具有较强的抗污染能力,这对于我国红树林生态修复与保护具有重要的指导意义。     

Physiological acclimation strategies of riparian plants to environment change in the delta of the Tarim River,China

The occurrence and development of riparian forests, which were mainly dominated by mesophytes species related closely with surface water. Since there was no water discharged to the lower reaches of Tarim River in the past three decade years, the riparian forests degrade severely. The groundwater table, the saline content of the groundwater, as well as the content of free proline, soluble sugars, plant endogenous hormones (abscisic acid (ABA), and cytokinins (CTK)) of the leaves and relative rates of sap flow of the Populus euphratica Oliv. (arbor species), Tamarix ramosissima Ldb. (bush species), and Apocynum venetum L. (herb species) were monitored and analyzed at the lower reaches of the Tarim River in the study area where five positions on a transect were fixed at 100 m intervals along a sampling direction from riverbank to the sand dunes before and after water release. The physiological responses and acclimation strategies of three species to variations in water and salinity stress were discussed. It was found that A. venetum population recovered to groundwater table ranging from −1.73 to −3.56 m, and when exposed to saline content of the groundwater ranging from 36.59 to 93.48 m mol/L; P. euphratica appeared to be more sensitive to the elevation of groundwater table than the A. venetum and T. ramosissima at groundwater table ranging from −5.08 to −5.80 m, and when exposed to saline content of the groundwater ranging from 42.17 to 49.55 m mol/L. T. ramosissima tended to be the best candidate species for reclamation in this hyper-arid area because it responded to groundwater table ranging from −1.73 to −7.05 m, and when exposed to saline content of the groundwater ranging from 36.59 to 93.48 m mol/L. These results explained the distribution patterns of desert vegetation in the lower reaches of the Tarim River. Understanding the relationships among ecological factors variables, physiological response and acclimation strategies of plant individuals could provide guidance to sustainable management, reclamation and development of this and similar regions.     

构造环境应力场在确定新疆地震危险区中的应用

基于断裂力学的研究成果和位错论,提出了断裂力学地震破裂模式,进而推导出了几个从地震波观测资料直接计算震源处构造环境剪力场量值ｒ０的公式。根据这些公式计算了中国地区中小地震的构造环境剪应力值。结果表明：ｒ０值的大小与分布和大震发生的地点有密切关系,即剪应力水平较高的地区将容易发生大地震,而剪应力水平较低的地区通常只发生小地震。据此,从１９９２年开始,根据环境应力场进行寻找地震危险区的尝试总有效北达７     

Projection of future world water resources under SRES scenarios: an integrated assessment

Abstract

Changes in water resources availability, as affected by global climate warming, together with changes in water withdrawal, could influence the world water resources stress situation. In this study, we investigate how the world water resources situation will likely change under the Special Report on Emissions Scenarios (SRES) by integrating water withdrawal projections. First, the potential changes in water resources availability are investigated by a multi-model analysis of the ensemble outputs of six general circulation models (GCMs) from organizations worldwide. The analysis suggests that, while climate warming might increase water resources availability to human society, there is a large discrepancy in the size of the water resource depending on the GCM used. Secondly, the changes in water-stressed basins and the number of people living in them are evaluated by two indices at the basin scale. The numbers were projected to increase in the future and possibly to be doubled in the 2050s for the three SRES scenarios A1b, A2 and B1. Finally, the relative impacts of population growth, water use change and climate warming on world water resources are investigated using the global highly water-stressed population as an overall indicator. The results suggest that population and socio-economic development are the major drivers of growing world water resources stress. Even though water availability was projected to increase under different warming scenarios, the reduction of world water stress is very limited. The principal alternative to sustainable governance of world water resources is to improve water-use efficiency globally by effectively reducing net water withdrawal.

Editor Z.W. Kundzewicz; Associate editor D. Gerten     

Intrinsic and attenuative dispersion characteristics of direct P-waves in and near the source area of the 1999 MW7.6 Chi-Chi,Taiwan, earthquake before and after the mainshock

Based on the measurement of the arrival time of maxima magnitude from band-pass filtering signals which were determined using a new Morlet wavelet multiple-filter method, we develop a method for measuring intrinsic and attenuative dispersion of the first cycle direct P-wave. We determine relative group delays of spectral components of direct P-waves for 984 ray paths from SML and ALS stations of the Taiwan Central Weather Bureau Seismic Network (CWBSN). Using continuous relaxation model, we deduce a new transfer function that relates intrinsic dispersion to attenuation. Based on the genetic algorithm (GA), we put forward a new inversion procedure for determining which is defined the flat part of quality factor Q(ω) spectrum, τ₁ and τ₂ parameters. The results indicate that ① The distribution of Q_m values versus epicentral distance and depth show that Q_m values linearly increase with increasing of epicentral distance and depth, and Q_m values is clearly independent of earthquakes magnitude; ② In the different depth ranges, Q_m residual show no correlation with variations in epicentral distance. Some significant changes of Q_m residual with time is likely caused by pre-seismic stress accumulation, and associated with fluid-filled higher density fractures rock volume in the source area of 1999 Chi-Chi Taiwan earthquake. We confirm that Q_m residual with time anomaly appears about 2.5 years before the Chi-Chi earthquake; ③ A comparison of Q_m residual for different depth range between SML and ALS stations show that the level of stress has vertical and lateral difference; ④ The area near observation station with both anomalously increasing and decreasing averaged Q_m residual is likely an unstable environment for future strong earthquake occurrence. This study demonstrates the capability of direct P-waves dispersion for monitoring attenuation characteristics and its state changes of anelastic medium of the Earth at short propagation distance using seismograms recorded from very small events.

     

宁夏及邻区地震震源衰减模型及震源参数研究

选取2003年1月至2011年12月宁夏及邻区发生的201个M_L2.0以上地震事件进行反演, 用经验格林函数计算得到本区地震震源谱衰减模型。 在已知非弹性衰减系数和场地响应的条件下, 计算得到震源谱并研究了近震震级与拐角频率、 地震矩、 震源破裂半径及应力降之间的关系。 详细分析了震源参数误差大小及各种误差影响因素。 对剩余应力降时空演化特征分析研究结果表明: 高剩余应力降集中分布在宁夏北部宁蒙交界地区、 低剩余应力降分布在宁夏中部同心、 中卫一带, 银川盆地中南部的吴灵地区和宁夏南部海原断裂带中东段剩余应力降变化较为明显, 在时间分布上这两个区域剩余应力降在中强地震前均有降低—增强的趋势。     

软岩隧道中双层初期支护的应力情况分析

两水隧道穿越的地层主要岩性为炭质千枚岩,地质情况较差,围岩破碎度高,节理发育。自2009年两水隧道开工建设以来,隧道工程问题层出不穷,出现了初期支护开裂、破坏,甚至出现二衬开裂、掉块,仰拱隆起等严重的隧道结构破坏现象,施工进度缓慢。在进口桩号为DK359+712～ DK359+742段采用双层初期支护和单层二次衬砌的支护方式,取得了良好的效果。通过应力情况分析为炭质千枚岩隧道的支护选型提供了依据。     

苍山地震库仑破裂应力变化与地震活动相关性探讨

本文收集了苍山地震周围断层的几何参数和运动学参数, 选择不同的接受断层, 研究了苍山地震库仑应力变化对余震及周边断层活动的影响。 结果表明, 苍山地震正的库仑应力变化对余震活动有促进作用, 大部分苍山余震分布于库仑应力变化增加区域, 应力增加量值为0.003~0.005 MPa。 通过对比该地区苍山地震前后16年的地震资料, 发现苍山地震正的库仑应力变化对苍山断裂附近地震活动增强亦有一定的促进作用, 而对于周边其他断层, 由于距离较远, 库仑应力变化量较小, 苍山地震库仑应力变化的影响可以忽略。     

A smoothed cap model for variably saturated soils and its robust numerical implementation

This paper deals with the numerical implementation of a cap model for unsaturated soils. It provides a brief review of existing cap model approaches, based on which an improved model formulated in terms of generalised effective stress and matric suction is derived and described in detail. Although the proposed model is a multisurface plasticity model, it can efficiently be implemented using only single‐surface projections because of the smoothness of the model, which is obtained by construction. Numerical algorithms are provided for these single‐surface stress projections, using a single‐equation approach whenever possible. The robustness of the utilised single‐equation approaches is enhanced by proposing problem‐fitted start‐up procedures based on investigations of the nonlinear projection equations. A comparison of the model response with extensive material test data is used to validate the model and to demonstrate the robust application of the approach to silty sands and low to medium plasticity clays. Copyright © 2015 John Wiley & Sons, Ltd.