被动微波反演裸露区土壤水分综述

被动微波具有全天候、穿透性以及不受云的影响等特征,使其在反演土壤水分时具有很大的优势。通过研究发现,被动微波遥感是反演土壤水分的各种技术中最有效的方法之一。概括了主要的被动微波传感器并从被动微波遥感的原理出发,针对被动微波遥感裸露区地表随机粗糙面的模型以及土壤水分反演算法作了简要介绍。     

用ERS风散射计数据估算土壤水分方法的研究

欧空局ERS1/2卫星上的风散射计(WSC),分辨率是50km,4天内能覆盖全球超过80%的范围,并可在多角度下对地物目标进行观测。本文研究利用该散射计数据估算土壤水分的方法。首先,利用基于ERS散射计数据建立的全球C波段雷达后向散射系数数据库,根据传统的几何光学模型(GOM),反演得到与土壤含水量密切相关的法线方向Fresnel反射率,并与两个采样点(安多和那曲)上的实测降雨量及土壤水分相对比,证明了ERS散射计数据与土壤水分的高相关性;第二步,以水云模型为基础,结合AIEM模型,发展了一种简化模型来估算土壤水分绝对值,分别利用气象站实测点数据和同时期的Basist湿度指数(BWI)进行验证,表明反演结果能较好反映土壤水分的空间分布状况。     

Analysis of the impact of conservation measures on stream flow regime in catchments of the Loess Plateau,China

Catchments in the Loess Plateau have been under the influence of human activities for centuries. In the last four decades, soil conservation measures have accelerated and intensified. These measures were designed to reduce soil erosion, improve agricultural productivity, and enhance environmental quality. It is important to evaluate the effects of these measures on hydrology in order to develop sustainable catchment management plans in the region. This study evaluated changes in stream flow data for four selected catchments in the Loess Plateau following large‐scale soil conservation measures. The non‐parametric Mann–Kendall test was used to identify trends in annual stream flow and the results showed significant downward trends in three of the four catchments. The Pettitt test indicated that a change point occurred in 1978 in these three catchments. Annual precipitation in all the catchments showed no significant trend during the period of record. Comparison of daily flow duration curves for two 20‐year periods (1957–1978) and (1979–2003) showed significant changes in stream flow regime. Reduction in most percentile flows varied between 20 and 45%, and the reduction in low flows was greatest. Overall, the reductions in daily flow were increasing with time, with significant changes occurring in the 1990s. However, it is not clear whether these catchments have seen the full effects of the soil conservation measures, so the results of this study might underestimate the final impact of soil conservation on stream flow regime. Copyright © 2007 John Wiley & Sons, Ltd.     

Heterogeneous mantle melting and magmatic processes at the East Pacific Rise (2.6–3.1°S): Evidence from mid-ocean ridge basalt geochemistry and Sr–Nd–Pb isotopes

ABSTRACT

We present the major and trace elements and Sr, Nd, and Pb isotopes in mid-ocean ridge basalts (MORB) from the East Pacific Rise (EPR) at 2.6–3.1°S. These samples are low-K tholeiites and show significant variation in their major element compositions (e.g. 4.60–8.18 wt% MgO, 8.34–12.12 wt% CaO, 9.78–14.25 wt% Fe₂O₃, and 0.06–0.34 K₂O wt%). Trace element abundances of the 2.6–3.1°S MORB are variably depleted (e.g. (La/Sm), _N = 0.51–0.78, Zr/Y = 2.35–3.42, Th/La = 0.035–0.056, and Ce/Yb = 2.38–3.96) but closely resemble the average N-MORB. In the compatible elements (Ni and Cr) against incompatible element Zr plots, the 2.6–3.1°S MORB show well-defined negative correlations, together with a liquid line of descent (LLD) modelling and petrographic observations, implying a significant role of olivine, plagioclase and clinopyroxene fractionation during magma evolution. When compared to global MORB and peridotites, the 2.6–3.1°S MORB and most of the other axial lavas from the South EPR show similar Zn/Fe, Zn/Mn, and Fe/Mn ratios, attesting to a peridotite-dominated mantle lithology. However, the relationships between incompatible trace element ratios, such as Zr/Rb and Nb/Sm, and the negative correlation between Zr/Nb and ⁸⁷Sr/⁸⁶Sr indicate a geochemically heterogeneous mantle source. The mantle beneath the South EPR likely consists of two components, with the enriched component residing as physically distinct domains (e.g. veins or dikes) in the depleted peridotite matrix. In the Sr–Nd–Pb isotope space, the South EPR MORB lie along the mixing lines between the depleted MORB mantle (DMM) and the ‘C’-like Pukapuka endmember. We infer that low-F melts derived from these enriched materials may cause localized mantle heterogeneity (veins or dikes) via an infiltration process. Subsequent melting of the refertilized mantle may impart an isotopically distinct characteristic to South EPR MORB.     

Geo-engineering properties of expansive soil treated with xanthan gum biopolymer

ABSTRACT

This paper presents the effectiveness of xanthan gum (XG) biopolymer in stabilising the expansive soil. The XG biopolymer is mixed with expansive soil in different proportions such as 0%, 0.2%, 0.5%, 0.8% and 1.0% by weight of the dry soil mass. The plasticity, compaction, swelling, compressibility, hydraulic conductivity, strength and durability characteristics of the treated and un-treated expansive soil are examined. Results show that the plasticity index of the treated soil mass initially increases but beyond 0.5% biopolymer addition it decreases sharply. The optimum moisture content and maximum dry density of treated soil, found out from light and heavy compaction tests, do not follow any definite trend. It is also found that increasing XG content increases compressibility slightly but, it reduces swelling pressure, differential free swelling value and hydraulic conductivity remarkably. On the other hand, time-dependent compressive strength and resistance to mass loss increases with increasing XG content. Microscopic examination confirms the formation of gel-like linkage, which brings about the modifications in the treated expansive soil.     

青海省都兰县丘吉东沟金矿地球化学特征及找矿潜力分析

丘吉东沟金矿是近年来在青海省都兰县境内的东昆仑山系中部新发现的金矿床之一，但其研究工作程度较低。本文基于区内1∶5000土壤地球化学测量工作，对20种土壤地球化学特征元素进行研究，通过相关分析、聚类分析后发现，本区Sb、Hg、Au、As等元素具有较好的异常，这些异常多分布于成矿的有利部位，并且套合较好，具有良好的找矿前景；综合考虑地球化学异常元素的组合特征及区域成矿地质特征，圈定2个找矿靶区。     

辽宁东平金矿床地质特征及找矿方向

东平金矿位于辽西凌源-阜新金成矿带上，金矿（化）体主要赋存在硅化构造角砾岩、硅化流纹岩和硅化流纹质角砾熔岩中.矿石以自然金和银金矿为主，其中自然金约占80%，银金矿约占20%.激电中梯及钻探结果显示矿体主要受北北西向构造控制，金矿（化）体主要位于高阻低极化率的F2构造蚀变带内.土壤地球化学测量圈定综合异常22处，Ⅰ-4异常区经钻探验证发现多个隐伏金矿（化）体.在详细研究矿床地质特征的基础上，通过对比邻区赵家沟金矿，初步推断其成因类型为低温热液型金矿.同时认为区内北北西向构造蚀变带内具有的黄铁矿化、强硅化和碳酸盐化是主要的矿化蚀变信息，高阻低极化率及Au土壤地球化学综合异常带是重要的找矿方向.     

昆明机场红土地层地下结构抗震模拟研究

昆明机场残积红土既是区域内重要的土地资源,更是各类工程建设的建筑地基,由于机场及临近区域内小江地震活动断裂带和普渡河断裂带地震活动频繁,使研究区处于较不稳定状态。本文采用MIDAS GTS有限元数值分析软件,利用动三轴试验所得出的结果,分别对昆明长水国际机场玄武岩残积红土、砂页岩残积红土地层下典型的地下结构进行了抗震模拟研究。所获得的研究成果,对红土分布区城市及村镇房屋建筑地基和地下空间结构抗震安全稳定性评价具有一定的指导意义和实用价值。     

Survey on PCDDs and PCDFs in sediments and soils in Ya-Er Lake area, China

INTRODUCTIONOverthepastseveralycars,considerableinteffethasbocenteIdontheenvir0nmentalbehaviouroftoxicandpersistritcomP0undssuchashalogenatalaromat-ies,inparticularthepolychiorinataldibopdioxins(PCDDe)andpolydil0rinateddi~fUtansrpCDFs).ManyofthesecomPounds,espedllythosewithahighdegere0fchiorinesubstitution,arehighlylipophiliccontawhnantSwithlowWhtersolubility,highre-sistancet0chdricaltransformationsandlowwhcrobiologhaldegradatfonpeatnnann,l988,Bromanetal.,l989,Hites,l990)whichexplain…     

利用地基土应力分布原理确定砂垫层厚度

软弱土层场地若采用天然地基不能满足建筑物所需强度与沉降要求,采用换土撼砂法就可以提高地基的承载力。运用应力分布原理合理确定撼砂层厚度不仅可保证工程稳固性,并可节约投资和缩短工期。