Influence of groundwater level change on vegetation coverage and their spatial variation in arid regions

Sampling and testing are conducted on groundwater depth and vegetation coverage in the 670 km2 of the Sangong River Basin and semi-variance function analysis is made afterwards on the data obtained by the application of geo-statistics. Results showed that the variance curve of the groundwater depth and vegetation coverage displays an exponential model. Analysis of sampling data in 2003 indicates that the groundwater depth and vegetation coverage change similarly in space in this area. The Sangong River Basin is composed of upper oasis, middle ecotone and lower sand dune. In oasis and ecotone, influenced by irrigation of the adjoining oasis, groundwater level has been raised and soil water content also increased compared with sand dune nearby, vegetation developed well. But in the lower reaches of the Sangong River Basin, because of descending of groundwater level, soil water content decreased and vegetation degenerated. From oasis to abandoned land and desert grassland, vegetation coverage and groundwater level changed greatly with significant difference respectively in spatial variation. Distinct but similar spatial variability exists among the groundwater depth and vegetation coverage in the study area, namely, the vegetation coverage decreasing (increasing) as the groundwater depth increases (decreases). This illustrates the great dependence of vegetation coverage on groundwater depth in arid regions and further implies that among the great number of factors affecting vegetation coverage in arid regions, groundwater depth turns out to be the most determinant one.     

天然气水合物形成条件与含量影响因素的半定量分析

天然气水合物形成条件及其含量的研究是天然气水合物调查研究中最为关心的两个问题.从天然气水合物形成过程的热动力学理论模型出发,半定量地探讨了不同因素（温度、压力、气体组成、孔隙水盐度、沉积物孔隙大小等）对天然气水合物形成作用及含量的影响程度.结果显示,气体组成特别是丙烷的加入对天然气水合物形成的温度和压力条件影响最大,孔隙水盐度也会对天然气水合物形成的温度和压力条件产生重要影响,沉积物孔隙在一定范围内（1×10^-6m～4×10^-8m）对天然气水合物形成的温度和压力条件影响有限.天然气水合物含量受孔隙大小和盐度影响较小,主要只与气体的供应大小有关.     

Precise Seismic Substructural Model of the Eocene Chorgali Limestone in the Turkwal Oil Field,Central Potwar,Pakistan

The precise seismic substructural interpretation of the Turkwal oil field in the Central Potwar region of district Chakwal of Pakistan has been carried out. The research work was confined to the large fore-thrust that serves as an anticlinal structural trap through ten 2D seismic lines. A precise seismic substructural model of the Eocene Chorgali Limestone with precise orientation of thrust and oblique slip faults shows the presence of a huge fracture, which made this deposit a good reservoir. The abrupt surface changes in dip azimuth for the Eocene Chorgali Limestone verifies the structural trends and also the presence of structural traps in the Turkwal field. The logs of three wells (Turkwal deep X-2, Turkwal-01 and Fimkassar-01) were analyzed for petrophysical studies, well synthetic results and generation of an Amplitude Versus Offset (AVO) model for the area. The AVO model of Turkwal deep X-2 shows abrupt changes in amplitude, which depicts the presence of hydrocarbon content. Well correlation technique was used to define the overall stratigraphic setting and the thickness of the reservoir formation in two wells, Turkwal-01 and Turkwal deep X-2. The Eocene Chorgali Limestone in Turkwal-01 is an upward thrusted anticlinal structure and because of the close position of both wells to the faulted anticlinal structure, its lesser thickness differs compared to Turkwal deep X-2. The overall results confirm that the Turkwal field is comparable to several similar thrust-bound oil-bearing structures in the Potwar basin.     

TOPEX/Poseidon and Jason Equatorial Sea Surface Slope Anomaly in the Atlantic in 2002: Comparison with Wind and Current Measurements at 23W

A time series of velocity profile in the upper 150 m of the equatorial Atlantic was gathered at 23W in 2002 within the PIRATA program. It constitutes the first time series of near surface current measurements simultaneous with altimetric data in the equatorial Atlantic. The surface slope anomaly along the equator is computed from satellite altimetry, and, as a proxy for the pressure gradient along the equator, compared with the wind and near surface current data. In a first step, a time series of the surface slope anomaly along the equator in the Atlantic is computed from the 10-year-long TOPEX/Poseidon sea level anomalies. A sensitivity study establishes the robustness of the calculation. Apart from a 15 cm bias, the equatorial sea surface slope anomalies estimated either from TOPEX/Poseidon or from Jason over the 6-month overlap (Feb.–Aug. 2002) do not reveal drastic differences. We produce two sea surface slope anomaly composite time series for 2002 (one with T/P data, the other with Jason data during the commissioning phase) and compare them to the wind and velocity data at 23W. As expected, the near surface velocity and depth of the upper limit of the equatorial undercurrent (EUC) are extremely well correlated with the surface pressure gradient anomaly. 10-year-long time series of altimetry-derived zonal sea surface slope anomaly and ECMWF ERA40 wind stress are also well correlated. They exhibit similar spectral content and similar anomalous years. This is a first step towards a full analysis of the EUC dynamics using altimetry, PIRATA data (near surface current and subsurface thermohaline structure) and model. These initial comparisons reinforce the utility of Jason measurements for continuing the 10-year and highly accurate TOPEX/Poseidon time series for study of equatorial signals.     

基于SAR的拉合尔地面沉降监测与沉降因素评价（英文）

合理开发和管理自然资源对于实现可持续发展至关重要,地面沉降作为目前影响城市可持续发展的最重要地质灾害,其与人类活动有着紧密的关系,如地下水开采,基础设施开发导致的施工超载等。巴基斯坦第二大城市拉合尔出现了显著的地面沉降现象,与此同时,拉合尔也正在经历城市化过程中的人口密度急剧增加、大规模城市建设和地下水开采,通过分析拉合尔地面沉降的不同空间模式与人类活动的对应关系,将有助于合理规划拉合尔城市的发展。本文利用永久散射体合成孔径雷达干涉测量(PSI)技术对拉合尔2018年8月-2019年8月的Sentinel-1数据进行In SAR处理,获取了该城市的地表形变速率为-114-15毫米/年,并结合拉合尔的土地覆盖图、交通网络和水道、土壤类型、人口密度和现场点数据,分析各种因素在地面抬升或沉降发生中的作用。结果显示,沉降与各种参数（如地下水抽取和地下水位降低、土壤类型变化、土地覆盖变化、地表水通道和人口密度）之间建立了很强的相关性,其中拉合尔中部人口密集,地下水开采严重,使其成为该地区沉降最为严重的区域,而在拉维河附近人口较少的农村地区,由于通过运河系统,地下水得到河流补给,观察到了地表抬升。     

Geochemical baselines of major, minor and trace elements in the tropical sediments of the Terengganu River basin, Malaysia

The geochemical baselines and distribution of 31 elements (Al, Fe, K, Na, Mg, Ca, Mn, Ba, Cr, Zr, Ni, Sr, Zn, Y, Li, Cu, Mo, Nb, Th, Co, Ga, W, Ta, Be, Ti, Ge, Se, Bi, Te, Sc and Re) and physico-chemical parameters of the tropical surface sediments of the Terengganu River basin, Malaysia, are reported. Sediments are sandy loam to sand in texture consisting of mostly quartz, low organic matter content (average-2.68%), low CEC (average-2.02 cmol(+)/kg) and mildly acidic pH1:5 (average-5.91). Concentrations of Mn, Fe, Ba, Cr, Ni, Cu, Mo and Se were measured to be above the environmental sediment quality criteria at various locations. Lake sediments registered significantly higher Al, Fe, Ti, Mg, Ca, Mn, Te and Sc concentrations as compared to the river sediments. Most of the elements investigated showed an association with silt size fraction (2-63 μm). Among the investigated metals, Mo and Fe concentrations showed an increasing (5-fold) and decreasing (3-fold) trend, respectively, along the river path from the upstream to the downstream depending on the stream pH-redox conditions. The enrichment factor values (EF 5) of Cr, Ni, Mo and Se indicated enrichment from anthropogenic activities. Alkali and alkali earth metals registered a significant depletion (EF values 0.7) as compared to the Earth's crust. Principal component analysis of the two main components (PC1, 87.4% and PC2, 8.7%) revealed a well-defined group of estuary sediments. Lake and river sediment sampling locations did not form defined groups revealing heterogeneity in the origin of geologic material and the in-stream geochemical processes. However, Cr, Ni, Mo and Se formed a separate group with elevated concentrations (e.g. Cr1,000 mg/kg) indicating contamination of sediments. This work presents the geochemical baselines of the tropical sediments as industrial development and urbanization along the north east coast of Peninsular Malaysia are advancing rapidly.     

青藏高原多年冻土区天然气水合物形成条件模拟研究

基于野外气体地球化学调查研究,以及前人有关冻土表层温度、冻土层内地温梯度、冻土层下地温梯度等的资料,对青藏高原多年冻土区天然气水合物的形成条件开展了模拟研究. 结果显示：研究区冻土条件能够满足天然气水合物形成的基本要求;气体组成、冻土特征（如冻土厚度或冻土表层温度、冻土层内地温梯度、冻土层下地温梯度等）是影响研究区天然气水合物稳定带厚度的最重要因素,其在不同点位上的差异性可能导致天然气水合物分布的不均匀性的主要原因;研究区最可能的天然气水合物为甲烷与重烃（乙烷和丙烷）的混合气体型天然气水合物;在天然气水合物分布的区域,其产出的上临界点深度在几十至一百多米间,下临界点深度在几百至近一千米间,厚度可达到几百米. 与Canadian Mallik三角洲多年冻土区相比,青藏高原多年冻土区除了冻土厚度小些外,其他条件,如冻土层内地温梯度、冻土层下地温梯度、气体组成等条件较为相近,具有一定的可比性,预示着良好的天然气水合物潜力.