三峡水库澎溪河流域高阳回水区夏季水体CO2分压日变化特性

水柱中CO2分压(pCO2)的时空分布在一定程度上可反映水中碳的环境地化特征.本研究在夏季分层期间对三峡水库澎溪河(小江)流域高阳回水区段进行了昼夜连续观测发现,恒定的温跃层中pCO2随水深增加而显著增大,表层0.5 m处pCO2均值为152±71μatm,而在水深10.0 m处pCO2均值为4568±1089μatm,同水温、pH及DO存在明显的负相关关系,进一步分析认为水温等将影响微生物、浮游植物的代谢过程及水气界面对流传输,进而对pCO2分布产生影响.对水气界面CO2扩散通量的估算结果表明,夏季分层期间高阳水域总体上表现为CO2的汇,其对大气CO2的吸收量最大值于15:00左右,达到-0.33 mmol/(m2.h);最弱在次日凌晨3:00左右,吸收量仅为-0.17 mmol/(m2.h).     

长江中下游湖泊群落水平下沉水植物碳、氮、磷化学计量特征及其影响因素

以长江中下游14个湖泊沉水植物为研究对象,分析群落水平下沉水植物碳(C)、氮(N)、磷(P)的化学计量特征及其影响因素.结果显示,沉水植物群落C含量平均为386.93±25.80 mg/g,范围为315.98~441.97 mg/g,N和P含量的平均值分别为26.10±4.84和2.64±0.99 mg/g,范围分别为13.75~40.89和1.01~5.92 mg/g.与物种水平研究相比,群落水平下沉水植物C、N、P化学计量特征变异系数较小,内稳定性更强.群落C含量与P含量具有显著相关性,而与N含量不相关,这说明C元素与N和P之间的耦合关系并不一致;N∶P比与P含量之间具有极显著的负相关关系,但与N含量不相关,说明沉水植物群落P含量的变异对N∶P比起主导作用.冗余分析表明,环境因子解释了沉水植物群落化学计量特征总变异的30.2%,在P0.01水平下对沉水植物群落化学计量特征具有显著影响的环境因子为底泥总磷、底泥N∶P比、水深和消光系数.变差分解结果表明,底泥和上覆水分别独自解释了化学计量特征总变异的5.21%和10.19%,其交互作用解释了总变异的5.25%.通过该研究结果推测,在恢复湖泊水生植被的实践过程中,相对于底泥,对上覆水光照条件进行控制可能更加迫切.     

Study on Ozone Change over the Tibetan Plateau

This paper reviewed the main results with respect to the discovery of low center of total column ozone (TCO) over the Tibetan Plateau (TP) in summer, and its formation mechanism. Some important advances are summarized as follows: The fact is discovered that there is a TCO low center over the TP in summer, and the features of the background circulation over the TP are analyzed; it is confirmed that the TP is a pathway of mass exchange between the troposphere and stratosphere, and it influences the TCO low center over the TP in summer; models reproduce the TCO low center over the TP in summer, and the formation mechanism is explored; in addition, the analyses and diagnoses of the observation data indicate that not only there is the TCO low center over the TP in summer, but also TCO decrease trend over the TP is one of the strong centers of TCO decrease trend in the same latitude; finally, the model predicts the future TCO change over the TP.     

长江中下游六省大气甲烷柱浓度时空分布

甲烷(CH₄)是造成气候变暖的主要温室气体之一。为了了解长江中下游水稻种植区CH₄浓度的分布情况,本次研究基于温室气体观测卫星(greenhousegasesobservingsatellite,GOSAT)和大气红外探测仪(atmospheric infraredsounder,AIRS)卫星反演的数据产品,对我国长江中下游六省大气CH₄柱浓度的时空分布特征进行了研究。研究结果表明,由GOSAT反演的长江中下游六省大气CH₄浓度呈逐年增长趋势,其年均浓度由2011年的1817×10^-9增长至2018年的1875×10^-9,高于东三省、华北平原和全国平均水平。区域平均年增长量为8.2×10^-9 a^-1。各省年际增长幅度略有差异,纬度偏低的江西、湖南和浙江三省大气CH₄浓度高且增长量偏大,纬度偏高的湖北、安徽和江苏三省大气CH₄浓度略低且增长量偏小。长江中下游六省大气CH...     

Groundwater recharge in arid regions: Review and critique of estimation methods

Arid-site recharge, while generally low, can be highly variable. Recharge under similar climate and soil conditions but with different plant cover and topography can vary from zero to more than the annual precipitation. Simple estimates of recharge based on fixed fractions of annual precipitation are misleading because they do not reflect the plant and soil factors controlling recharge. Detailed water balance models, successful for irrigated agriculture, fail to predict evapotranspiration accurately under conditions where plants suffer seasonal water stress and cover is sparse. Recharge, when estimated as a residual in water balance models, may be in error by as much as an order of magnitude. Similar errors can occur when soil water flow models are used with measured or estimated soil hydraulic conductivities and tension gradients. Lysimetry and tracer tests offer the best hope for evaluating recharge at arid sites, particularly in siting waste disposal facilities, where reliable recharge estimates are needed. Quantification of drainage using lysimetry over several years under a given set of soil, plant, and climate conditions for a specific site can provide a basis for calibrating models for recharge prediction. Tracer tests using such long-lived tracers as ³⁶Cl or perhaps stable isotopes (¹⁸0, deuterium) can provide qualitative estimates of recent recharge at a given site.     

三维地震勘探在晋煤集团成庄矿的应用分析

晋煤集团成庄矿位于沁水煤田南部,区内大部分基岩裸露,少部分黄土覆盖,地形以中、低山、丘陵为主,相对高差436．4m,区内村庄较多,地震测量和野外采集难度较大。区内的黄土覆盖区与坡积物区成孔困难,激发条件差。矿区地层较为平缓,煤系地层较稳定,主采煤层及标志层全区基本上可连续追踪对比。成庄矿共施工三维地震勘探面积51．648km^2,解释陷落柱为165个,断层66条,现已验证4个盘区内9个工作面,验证面积达4．68km^2,准确率平均为50％。通过探采对比,证明勘探边界、陷落柱大小、断距落差及长度以及地形条件等因素都会影响到勘探精度。     

Laboratory Granular Flows generated by Slope Failures

Summary. A series of flume experiments has been set up to analyze the behavior of water sand mixture flows, as a consequence of slope failures induced by water table raising and rainfall. The flows initially accelerated but at a certain stage of the process, unsteady deposition of the sand occurred, preceded by the transformation of the movement from flow to sliding. The comparison of such phenomena with other flume experiments, performed in similar conditions, showed that differences in flow behavior are dependent on a variety of aspects that are difficult to take into account. A numerical modeling of laboratory flows has been performed, using a cellular automata model based on the grain inertia regime. Despite the relatively good agreement between modeled and experimental phenomena, the study shows the difficulties of taking the actual behavior of granular flows into account. Author’s address: Chiara Deangeli, Politecnico di Torino, Ditag, corso Duca degli Abruzzi 24, 10129 Torino, Italy     

Experimental Analysis and Micromechanical Modelling of Dry Granular Flow and Impacts in Laboratory Flume Tests

Summary. The paper presents the results of a numerical analysis, carried out by using the Discrete Element Method (DEM) and aimed at reproducing a series of tests on a small-scale laboratory model of a slope. Particular attention is devoted to the validation of DEM when used for the prediction of the run-out distance and of the impact force on obstacles. The soil used for the small-scale model is a mono-granular medium sand, which revealed to be particularly suitable to simulate flows like debris or rock avalanches. The experimental set-up comprises a flume equipped with a system of differently sized instrumented obstacles. The numerical model of the granular flow has been calibrated on the basis of the displacement measurements, obtained through a photogrammetric technique. Author’s address: Roberto Valentino, Department of Civil, Environmental, Territorial Engineering and Architecture, Università degli Studi di Parma, Parma, Italy     

On the Investigations of Resilient Modulus of Residual Tropical Gravel Lateritic Soils from Senegal (West Africa)

Investigations on the mechanical behavior of compacted gravel lateritic soils have been the subject of several studies. Used as road materials, soils tests were mainly performed using standard tests. Static loads as unconfined compression test (UCT) remain the only engineering approach used. Alternative testing techniques can be chosen as supplementary tests for characterizing pavement materials. These researches were conducted so as to determine the response of these particular and problematic soils in its compacted form with road traffic loads. This paper presents the results of research conducted to investigate the effect of the soil compacity on the resilient modulus of lateritic soils. The influence of the percentage of cement added so as to stabilize each sample at the optimum modified proctor (OPM) State was also determined. Soil big specimens of around 180 mm diameter (with length to diameter aspect ratio of 2:1) were prepared according to the standard procedure described by AASHTO T 307 and then were subjected to repeated load triaxial tests. The models used, analyzed and developed in this paper are mainly the Andrei and the Uzan–Witczak universal model. Test results showed that the specimen compacity has no significant influence on the resilient modulus of the investigated gravel lateritic soils. Soil specimens with variation of the percentage of cement added exhibited the highest resilient modulus values while the specimens with variation of the compacity exhibited the lowest values. The resilient modulus variation seems to be independent of the level of stress.     

Dynamic Response of Machine Foundation on Layered Soil: Cone Model Versus Experiments

This paper presents the experimental validation of analytical solution based on cone model for machine foundation vibration analysis on layered soil. Impedance functions for a rigid massless circular foundation resting on a two layered soil system subjected to vertical harmonic excitation are found using cone model. Linear hysteretic material damping is introduced using correspondence principle. The frequency-amplitude response of a massive foundation is then computed using impedance functions. To verify the solution field experiments are conducted in two different layered soil systems such as gravel layer over in situ soil and gravel layer over concrete slab (rigid base). A total 72 numbers of vertical vibration tests on square model footing were conducted using Lazan type mechanical oscillator, varying the influencing parameters such as depth of top layer, static weight of foundation and dynamic force level. The frequency-amplitude response in general and in particular the resonant frequencies and resonant amplitudes predicted by cone model is compared with the results of experimental investigation, which shows a close agreement. Thus the cone model is reliable in its application to machine foundation vibration on layered soil.