The impact of land use and land cover changes on soil moisture and hydraulic conductivity along the karst hillslopes of southwest China

The understanding of the temporal and spatial dynamics of soil moisture and hydraulic property is crucial to the study of several hydrological and ecological processes. Karst environments are extremely fragile because of thin soil and small soil water holding capacity. A marked intensification of agricultural land use and deforestation due to increase of population and thus expansion of agricultural areas has made the karst environment even more delicate. In this study, the soil moisture contents (SMC) and hydraulic conductivities (K) along four karst hillslopes were measured in situ by time domain reflectometry and the Guelph Permeameter, respectively, at test plots, each of which has a different vegetative cover, landform, land surface slope, soil property and content of rock fragment. The statistical results from the measurements show that land cover changes strongly affect the distribution of soil moisture and hydraulic properties. Compared with SMC in the bare soil areas, SMC values are 30.5, 20.1 and 10.2% greater in the forest, shrub and grass areas, respectively. Vegetation roots significantly increase permeability of low-layer silt soils. Measured K values were 0.8, 0.6 and 0.01 cm/min for the forest, agriculture and bare soil areas, respectively. When the forest was destroyed by fire or cut to become an agricultural area or bare soils, SMC would be reduced by 13.1 and 32.1%, respectively. If deforestation leads to strong rock desertification, SMC was reduced by 70%. Bedrock fractures significantly reduce the SMC in the overlying layer, but increase K values. SMC values of 30–45% would be reduced to 17–30% for the soil layer embedding rocks with and without fractures, respectively. K values could be increased from 1.0 to 8.5 cm/min. SMC are sensitive to terrain. A slope angle increase of 1° would reduce SMC about 0.82%. These changes resulting from land cover and land use alterations offer useful information to further investigate the response of ecosystem evolution to hydrodynamic processes.     

丹江口水库的饵料生物资源及水体营养状态评价

根据1992年12月至1993年9月的调查,丹江口水库的饵料生物资源量为1．845×10~6t．其产鱼潜力为1．615×10~4t．是现有鱼产量（包括捕捞产量和不投饵网箱产量）的5倍左右．就水体营养状态而言,汉江库区为中营养型,丹江库区属贫一中营养型．文中还对丹江口水库的渔业发展和水质保护进行了讨论．     

遂宁市2005年"3.11"寒潮天气分析

通过对遂宁市2005年3月11～12日出现的寒潮天气过程进行分析和总结,得到一些指标特征量,利于今后提高类似的寒潮天气过程的预报水平.     

NUMERICAL SIMULATION STUDY OF HAIL CLOUD—PART Ⅰ:THE NUMERICAL MODEL

In order to study mechanisms of hailstone formation and hail suppression with seeding and toobtain optimum seeding technique for hail cloud,a 3-D compressive numerical seeding model forhail cloud is developed.The water substance in hail cloud is divided into 8 categories,i.e.,watervapor,cloud droplet,raindrop,ice crystal,snow.graupel,frozen drop and hail,and the detailedmicrophysical processes are described in a spectrum with two variable parameters and morereasonable particle number/size distributions.Then,the model is able to predict concentration andwater content of various particles.Especially.it can calculate the number of hailstones whosecores are graupel or frozen drop and apply to study mechanism of hailstone formation.Additionally,a conservative equation of AgI as seeding or glacigenous agent is found andnucleation by condensation of artificial nucleus,and nucleation by freezing of cloud droplet or raindrop which contact with AgI particle are considered.The dynamic energy flux of hail shooting onground is used to verify seeding effect.Therefore the model is also used to study mechanism of hailsuppression with seeding and the seeding technique,     

Climate changes and human activities recorded in the sediments of Lake Estanya (NE Spain) during the Medieval Warm Period and Little Ice Age

A multi-proxy study of short sediment cores recovered in small, karstic Lake Estanya (42°02?? N, 0°32?? E, 670 m.a.s.l.) in the Pre-Pyrenean Ranges (NE Spain) provides a detailed record of the complex environmental, hydrological and anthropogenic interactions occurring in the area since medieval times. The integration of sedimentary facies, elemental and isotopic geochemistry, and biological proxies (diatoms, chironomids and pollen), together with a robust chronological control, provided by AMS radiocarbon dating and ²¹⁰Pb and ¹³⁷Cs radiometric techniques, enabled precise reconstruction of the main phases of environmental change, associated with the Medieval Warm Period (MWP), the Little Ice Age (LIA) and the industrial era. Shallow lake levels and saline conditions with poor development of littoral environments prevailed during medieval times (1150?C1300 AD). Generally higher water levels and more dilute waters occurred during the LIA (1300?C1850 AD), although this period shows a complex internal paleohydrological structure and is contemporaneous with a gradual increase of farming activity. Maximum lake levels and flooding of the current littoral shelf occurred during the nineteenth century, coinciding with the maximum expansion of agriculture in the area and prior to the last cold phase of the LIA. Finally, declining lake levels during the twentieth century, coinciding with a decrease in human pressure, are associated with warmer climate conditions. A strong link with solar irradiance is suggested by the coherence between periods of more positive water balance and phases of reduced solar activity. Changes in winter precipitation and dominance of NAO negative phases would be responsible for wet LIA conditions in western Mediterranean regions. The main environmental stages recorded in Lake Estanya are consistent with Western Mediterranean continental records, and show similarities with both Central and NE Iberian reconstructions, reflecting a strong climatic control of the hydrological and anthropogenic changes during the last 800 years.     

沈阳城区一次暴雨过程的水汽条件分析

利用Micaps实况资料、东北区域中尺度数值模式分析场资料和常规观测资料,对2013年8月16日沈阳城区暴雨的水汽条件进行了分析。结果表明：850 hPa以下城区上空水汽含量占整层的80％以上,地面比湿呈现快速增加后减少的变化,比湿峰值对应的并不是强降水的最强时刻。强降水发生前,城区地面周围的湿度分布不均匀,水汽输送主要以南北向为主。比湿的迅速增加主要是由于降水前风向和风速的快速变化,其中主要是南风分量的贡献。城区上空垂直方向上水汽主要是850 hPa向上输送,850 hPa以下输送强度逐渐减弱。伴随着强降水的开始,水汽的垂直输送转为高度层越低,输送强度越大。强降水发生时,地面U、V方向上水汽通量快速减小。强降水发生后,地面和高空水汽输送均发生了变化。大气可降水量与降水量之间具有一定的对应关系,可降水量的大小主要是取决于水平水汽通量辐合的大小,水汽局地变化对可降水量的贡献较小。水汽通量的辐合、辐散的大小主要取决于水平风场引起的辐合、辐散的大小。     

A statistical approach to disentangle environmental forcings in a lacustrine record: the Lago Chungará case (Chilean Altiplano)

A high resolution multiproxy study (magnetic susceptibility, X-ray diffraction, XRF scanner, gray-colour values, Total Organic Carbon, Total Inorganic Carbon, Total Carbon and Total Biogenic Silica) of the sedimentary infill of Lago Chungará (northern Chilean Altiplano) was undertaken to unravel the environmental forcings controlling its evolution using a number of different multivariate statistical techniques. Redundancy analyses enabled us to identify the main provenance of the studied proxies whereas stratigraphically unconstrained cluster analyses allowed us to distinguish the “outsiders” as result of anomalous XRF scanner acquisitions. Principal Component Analysis (PCA) was employed to identify and isolate the main underlying environmental gradients that characterize the sedimentary infill of Lago Chungará. The first eigenvector of the PCA could be interpreted as an indicator of changes in the input of volcaniclastic material, whereas the second one would indicate changes in water availability. The chronological model of this sedimentary sequence was constructed using 17 AMS ¹⁴C and 1 ²³⁸U/²³⁰Th dates in order to characterize the volcaniclastic input and the changes in water availability in the last 12,300 cal years BP. Comparison of the reconstructed volcaniclastic input of Lago Chungará with the dust particle record from the Nevado Sajama ice core suggested that the Parinacota volcano eruptions were the main source of dust during the mid and Late Holocene rather than the dry out lakes as has previously been pointed out. The comparison of the water availability reconstruction of Lago Chungará with three of the most detailed paleoenvironmental records of the region (Paco Cocha, Lake Titicaca and Salar Uyuni) showed an heterogeneous (and sometimes contradictory) temporal and spatial pattern distribution of moisture. Although the four reconstructions showed a good correlation, each lacustrine ecosystem responded differently to the moisture oscillations that affected this region. The variations in the paleoenvironmental records could be attributed to the dating uncertainities, lake size, lake morphology, catchment size and lacustrine ecosystem responses to the abrupt arid events.     

Consequences of Uncertainties in CO<Subscript>2</Subscript> Density for Estimating Net Ecosystem CO<Subscript>2</Subscript> Exchange by Open-path Eddy Covariance

Errors in the estimation of CO₂ surface exchange by open-path eddy covariance, introduced during the removal of density terms [Webb et al. Quart J Roy Meteorol Soc 106:85–100, (1980) - WPL], can happen both because of errors in energy fluxes [Liu et al. Boundary-Layer Meteorol 120:65–85, (2006)] but also because of inaccuracies in other terms included in the density corrections, most notably due to measurements of absolute CO₂ density (ρ _c ). Equations are derived to examine the propagation of all errors through the WPL algorithm. For an open-path eddy covariance system operating in the Sierra de Gádor in south-east Spain, examples are presented of the inability of an unattended, open-path infrared gas analyzer (IRGA) to reliably report ρ _c and the need for additional instrumentation to determine calibration corrections. A sensitivity analysis shows that relatively large and systematic errors in net ecosystem exchange (NEE) can result from uncertainties in ρ _c in a semi-arid climate with large sensible heat fluxes (H _s ) and (wet) mineral deposition. When ρ_c is underestimated by 5% due to lens contamination, this implies a 13% overestimation of monthly CO₂ uptake.     

四川及邻区地壳垂直形变特征与地震的关系

对四川及邻区五十年代至八十年代的精密水准复测资料进行处理，绘制了四川及邻区的地壳重直形变速率图、垂直形变速率梯度图和垂直形变速率梯度矢量分布图。结合研究区内构造特征，对上述图件进行分析。指出数处呈四象限分布的图像，结合地震活动进行解释，确定了研究区未来的地震危险区。     

溶胶—凝胶工艺制备二氧化钛超微细粉过程中的物相和显微结构的变化

用溶胶—凝胶工艺制备了不同晶型的TiO_2超微细粉,锐钛矿型TiO_2超微细粉呈分散的球形颗粒,平均粒径约为0.03μm;金红石型TiO_2超微细粉呈分散的圆柱状颗粒,平均粒径约为0.07μm。用FT-IR.XRD.DTA/TGA和TEM等手段研究了TiO_2凝胶在煅烧过程中物相和显微结构的变化。发现TiO_2凝胶在200℃以下呈非晶态,在300℃时结晶成锐钛矿,在700℃时,锐钛矿开始转变为金红石,在1000℃时,锐钛矿消失,全部转变为金红石。