Simulating nonequilibrium transport of atrazine through saturated soil

Atrazine, an herbicide widely used for selective control of grassy weeds in the fields where maize is grown, is a potential ground water contaminant in China and, consequently, there is interest in predicting its mobility in agricultural soils. In this study, we determined the nonequilibrium transport characteristics of atrazine in Shahe soil (Beijing sandy loam) using the advection-dispersion equation, and using a sensitivity analysis, we evaluated the contribution of the uncertainty in a given input parameter to the overall uncertainty in model results. The asymmetrical shape and tailing of the atrazine breakthrough curve (BTC) showed that atrazine was subject to nonequilibrium transport. The observed atrazine BTC was best fitted by the chemical nonequilibrium model with a nonlinear least-squares optimization approach. Results from the sensitivity analysis indicated that the retardation factor was the most sensitive parameter. Considering the reliability of the estimated parameters, the best fit to the atrazine BTC was obtained by fixing the retardation factor based on the linear distribution coefficient, and by calculating the dispersion coefficient from the bromide BTC and the average pore water velocity from the measured data; nonequilibrium parameters were the only unknown parameters that were optimized. Model verification procedures were based on best-fit parameters optimized from one soil column experiment and applied to simulate the transport of atrazine in the duplicate experiment. The results showed there was good agreement between measured and simulated concentrations for atrazine leaching in the soil column.     

A semi-empirical formula for evaluating residual strain of soils under earthquake loading

A new semi-empirical formula for evaluating the residual strain of soils under earthquake loading is presented in this paper based on the incremental method and the increment model proposed by the authors. When the incident loading is uniform, the results calculated by the new formula are nearly the same as those by the existing formula. For excitation of the random earthquake loading, the results calculated by the new formula are compared to the results obtained by dynamic triaxial tests. The dynamic triaxial tests had been performed considering different seismic waves, confining stresses,consolidation ratios, and types of cohesive soils. The comparison between the calculated and tested results indicate that the presented formula can efficiently and practically describe the time-dependent process of the soil residual strains under actual seismic loads.     

Seismic waves in a layered half-space from an arbitrary buried source

In this paper, a transfer matrix and a three-dimensional dynamic response of a layered half-space to an arbitrary buried source are derived with the aid of a technique which combines the Laplace and two-dimensional Fourier transforms in a rectangular coordinate system. This method is clear in concept, and the corresponding formulas given in the paper are simple and convenient for marine seismic prospecting and other fields' applications. An example is presented and the calculated results are in good agreement with those of the finite element method (FEM).     

北京市大气细粒子的质量浓度特征研究

大气能见度的降低是当今国际上比较突出的城市环境问题。北京近年的监测结果表明 ,大气中通过消光作用使大气能见度下降的气溶胶细粒子的污染程度呈现上升趋势。从 2 0 0 1年对北京市气溶胶细粒子 (空气动力学直径小于 2 .5μm的粒子 ) 4个季节的采样监测结果分析 (有效采样天数为 50d)得出 ,北京市细粒子质量浓度年平均值已超过美国国家标准的 7倍以上。研究发现细粒子的质量浓度不仅与环境条件有关 ,而且与气象条件也有着密切的关系。文中以细粒子的观测数据为基础 ,结合当时的气象条件进行细粒子浓度与气象条件定量关系的研究     

新藏公路新疆段多年冻土特征及其灾害初探

新藏公路新疆段沿线海拔高，气候干冷，第四纪松散堆积层厚，在高山区和山原河谷盆地区发育了多年冻土。勘查研究表明：多年冻土分布于K306 000～K310 000和K515 000～K705 00间191．6km路段上，属高原片状连续多年冻土。沿线个别路段含冰量较高，为多冰-富冰冻土，中冻胀中融沉；绝大部分路段以少冰多年冻土为主，弱冻胀弱融沉。现有公路主要冻土灾害有涎流冰、路基融沉、路面翻浆、冻胀破坏、冻融滑塌和冻融泥流等。随着整治改建工程的实施，多年冻土原有的水热平衡的破坏，冻土灾害将趋于严重。根据沿线多年冻土的特征，提出施工和运营中应采取保护冻土的设计原则，通过改线避绕、抬高路基、提高路基强度及完善截排水系统等5条措施以减少公路工程对多年冻土的扰动和破坏。     

安徽铜陵矿集区与块状硫化物矿床有关的热水沉积岩

通过对铜陵地区系统的填图观察和室内研究 ,初步确定了铜陵地区海西期的热水沉积岩。它们是 :石炭系黄龙组 ,由下而上、由内到外的层序包括含硫化物滑石蛇纹石岩 (由原岩为含水富镁碳酸盐岩 +二氧化硅的热水沉积岩变质而成 )→块状、层状 (含铜金 )黄铁矿±铁碧玉±硬石膏±菱铁矿±菱锰矿±硅质岩→含炭质粘土→白云岩 ;二叠系为栖霞组 (含铅锌金 )硅质岩、孤峰组 (含锰 )硅质岩和大隆组 (含钼 )硅质岩。这些热水沉积岩总体构成铜陵地区晚古生代多期热水活动的格局。常量元素、微量元素和稀土元素的分析结果表明 ,本区的硅质岩具有热水沉积岩的特征。氧同位素估算的热水硅质岩古温度在 4 9℃以上。铜陵地区的热水沉积岩对层控矿床的勘查和隐伏矿床的预测评价具有重要的理论和实际意义 ,尤其是黄龙组底部的热水沉积岩是铜陵地区找矿的重要标志 ,对于指导长江中下游地区 ,如宁芜等地 ,寻找该层位的矿床有着不可替代的指示意义。     

安徽铜陵朝山金矿床稳定同位素、稀土元素地球化学研究

朝山金矿床位于安徽铜陵狮子山矿田，属于矽卡岩型金矿床，侵入岩体为白芒山辉石二长闪长岩体。成矿过程包括矽卡岩阶段、石英-硫化物阶段和碳酸盐阶段3个主要成矿阶段。文章通过对朝山金矿床的氢、氧、碳、硫、硅同位素组成和稀土元素地球化学特征的研究，探讨成矿溶液中水、碳、硅和硫的来源以及成矿溶液的演化问题。研究表明，成矿热液早期以岩浆热液为主，随着成矿过程的进行，加入的大气降水比重越来越大，到晚期可能主要以大气降水为主。该矿床矿石中方解石的碳、氧同位素组成与矿区大理岩的碳、氧同位素组成明显不同，其δ^13 Cv-PDB、δ^18OV-SMOW值分别为-4．5～-5．3‰、13．9～14．0‰，与岩浆作用形成的CO2的碳、氧同位素组成一致，表明矿石中方解石的碳、氧来源于岩浆作用。硅和硫具深部岩浆或岩浆热液来源的特点。     

Eclogitic metapelites in the western segment of the north Qaidam Mountains: Evidence on “in situ” relationship between eclogite and its country rock

Science China Earth Sciences - In Yuka-Luofengpo area of the north Qaidam Mountains, eclogitic metapelites are recognized. The metapelites enclosed lenses of eclogites, and locally intercalated...     

柴达木盆地北缘鱼卡河岩群的地质特征和时代

柴达木盆地北缘的鱼卡河岩群是在最近几年区域地质调查和研究的基础上新建立的构造岩石单位，主要分布于绿梁山—锡铁山—沙柳河—带，由石榴白云石英片岩、石榴(蓝晶)白云片岩、二云片岩、黑云变粒岩、黑云角闪片岩、榴辉岩、石榴斜长角闪岩及大理岩等组成，以含馏辉岩为特征。在绿梁山地区，鱼卡河岩群呈不同规模的残块产于花岗闪长质—二长花岗质片麻岩之中。野外观察和变质作用特点显示，至少有一部分榴辉岩的原岩是鱼卡河岩群表壳岩的组成部分，在早占生代遭受了高压变质再造。根据从鱼卡河岩群及花岗片麻岩中获得的同位素年龄，结合两者的野外地质关系，初步确定鱼卡河岩群形成于中元古代。     

合肥—潢川盆地南缘中生代冲积沉积及其构造意义

合肥—潢川盆地南缘中生代地层被划分为4个年代体（Chronsome）。年代体Ⅰ包括早侏罗世防虎山组和中晚侏罗世圆筒山组下部，由辫状河、曲流河以及滨一浅湖沉积体系组成，局限于盆地东端；年代体Ⅱ包括中晚侏罗世三尖铺组、朱集组和圆筒山组上部，下部为冲积扇沉积，中、上部为辫状河沉积，早期属于横向水流系统（南北方向），晚期是纵向水流系统（东西方向），近EW向的信阳—金寨—舒城断裂是其南部边界；年代体Ⅲ包括早白垩世早期凤凰台组、段集组、周公山组，前两组为冲积扇沉积，后者为辫状河和越岸沉积，粗碎屑明显向盆进积达数公里，南部边缘发育横向水流，而往盆地方向发育纵向水流。年代体Ⅳ为早白垩世晚期黑石渡组和陈棚组，南部边界是磨子潭晓天断裂和桐柏-商城断裂，断裂以伸展走滑为主，东段早期为冲积扇-扇三角洲沉积，晚期为深湖浊积岩沉积。晚白垩世沉积仅发育在西段局部地区，其余处于隆升状态。平行于大别山造山带的近EW向纵向断裂控制着年代体的南部边界，NE向郯城庐江断裂和商城麻城断裂控制着年代体侧向相的变化。合肥潢川盆地南缘沉积从东往西逐渐超覆，揭示大别造山带折返具有自东而西的递进特征。郯城—庐江断裂和商城—麻城断裂对年代体的发育有明显影响，郯城—庐江断裂控制着早侏罗世沉积，表明构造活动至少始于早侏罗世。