库布齐沙漠两个不同土地利用类型生态系统呼吸比较研究

陆地生态系统的呼吸作用是全球碳循环的一个主要通量和响应全球变化的一个潜在的重要正反馈机制。研究陆地生态系统的呼吸作用特征及其对生物环境因子的响应具有重要意义。本实验利用涡度相关技术对内蒙古库布齐沙漠两个不同土地利用类型的生态系统（人工种植杨树林和天然的油蒿灌丛）2006年生长季（4-10月）的生态系统呼吸特征进行比较研究，并分析了控制生态系统呼吸（Re）的生物与环境因子。结果表明：在这两种生态系统中Re存在着显著的日变化和季节变化，两个生态系统之间Re也存在着显著差异。Re日平均最大值分别2.0 mol CO2 m-2 s-1和1.7 mol CO2 m-2 s-1，都显著低于其他类似生态系统。杨树林和油蒿灌丛的生态系统Re与空气温度都表现出明显的指数相关关系，温度敏感指数Q10分别为1.11和1.12。两个生态系统的Re都与土壤水分含量呈显著的线性正相关关系，表明库布齐沙漠的生态系统的Re受到了土壤水分条件的限制。杨树林和油蒿灌丛生态系统呼吸Re都与叶面积指数的有线性回归关系，说明叶面积指数对生态系统呼吸有很好的指示作用。 本文还选择了两个生态系统内四种常见的土壤覆盖类型（分别是：杨树林生态系统的沙地SL和低洼地BL;油蒿灌丛生态系统的灌丛间BS和灌丛内WS），利用动态密闭气室测定了5-9月土壤呼吸的季节动态以及植株尺度的小尺度空间异质性。结果表明：1）不同土壤覆盖类型的土壤呼吸存在着很大的差异，其中低洼地BL和沙地SL分别有着最大和最小值，灌丛内WS的土壤呼吸要明显高于灌丛外BS。根生物量是导致它们之间差异的主要原因。2）土壤呼吸与土壤含水量之间的线性关系表明，土壤水分是两个生态系统土壤呼吸的限制因子。3）两个生态系统土壤呼吸存在着明显的小尺度差异，在靠近植株（0.5m内）地方的土壤呼吸的值明显高于距植株0.5m外的值，而0.5m外的土壤呼吸没有显著差异。小尺度土壤呼吸与根生物量之间明显的线性关系，说明根生物量是导致小尺度土壤呼吸差异的原因。本实验对沙漠生态系统的土壤呼吸和生态系统呼吸特征及其影响因子的研究，对准确的估计这一地区的碳收支有很大的帮助，为深入的理解干旱半干旱地区的生态系统碳循环提供了有价值的信息。

确定~(137)Cs背景值所需的采样点数与采样面积

137Cs背景值的确定是利用核示踪技术研究土壤侵蚀的前提和根本,直接关系到侵蚀速率计算的准确与否。而大部分研究对137Cs背景值的确定均采取随机采样,没有统一的采样点数与确定的采样面积。本研究利用网格加密采样法,对未扰动地和长期耕种且未平整的农耕地各两块样地的137Cs背景值空间变异进行了分析,结果表明:在未扰动地与农耕地采样地块,137Cs采样点数与背景值空间变异系数都存在指数回归关系;在未扰动地块137Cs背景值存在较大空间变异性,且随着网格面积的扩大137Cs空间变异系数表现为增加趋势,在0.25m2范围内选取最少11个样点才能满足试验精度;在农耕地采样地块,因长期的耕种作用使得137Cs在耕层中混合相对均匀,137Cs背景值空间变异性显著变小,最少选取7个样点就能满足试验精度,且不受采样面积的影响。

黄土高原坡地表层土壤饱和导水率和水分含量空间变异特征

表层土壤水分含量和饱和导水率对深层土壤水分的动态的变化具有重要的决定作用。在黄土高原坡地(50m×360 m)范围内进行网格(10 m×10 m)取样,用地统计学方法研究表层(0~30 cm)土壤饱和导水率和水分含量的空间变异特征。结果表明:1)坡地表层土壤密度变化规律为坡下位大于坡上位,土壤饱和导水率变异系数为0.37,属于中等变异强度;2)饱和导水率和自然对数化的饱和导水率在360 m尺度内均不具备空间结构特征,是纯随机变量,线性有基台模型适用于描述表层土壤水分的分布特征,水分分布存在明显的块金效应,并且随滞后距离的增加半方差变大;3)饱和导水率和水分含量从坡上位到坡下位均呈现波浪式变化,饱和导水率大的采样点土壤水分含量低,反之则高。

黄土丘陵区小流域土壤特性时空动态变化研究

以安塞大南沟为例首次在流域范围内对几项土壤表面特性进行连续定位测定,初步研究了其时空动态变化规律。结果表明,大南沟流域内土壤随机糙度、抗剪力和团粒稳定性具有一定的空间变化规律,不同土地利用方式间有显著差异。不同地貌类型农耕地土壤随机糙度、抗剪力无明显差异,而团粒稳定性则差异显著。年内各测定周期间土壤随机糙度、抗剪力和团粒稳定性随时间变异不显著。

Particle-attached and free-living bacterial communities in a contrasting marine environment: Victoria Harbor, Hong Kong

Diversity of particle-attached and free-living marine bacteria in Victoria Harbor, Hong Kong, and its adjacent coastal and estuarial environments was investigated using DNA fingerprinting and clone library analysis. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA genes showed that bacterial communities in three stations of Victoria Harbor were similar, but differed from those in adjacent coastal and estuarine stations. Particle-attached and free-living bacterial community composition differed in the Victoria Harbor area. DNA sequencing of 28 bands from DGGE gel showed Alphaproteobacteria was the most abundant group, followed by the Bacteroidetes, and other Proteobacteria. Bacterial species richness (number of DGGE bands) differed among stations and populations (particle-attached and free-living; bottom and surface). BIOENV analysis indicated that the concentrations of suspended solids were the major contributing parameter for the spatial variation of total bacterial community structure. Samples from representative stations were selected for clone library (548 clones) construction and their phylogenetic distributions were similar to those of sequences from DGGE. Approximately 80% of clones were affiliated to Proteobacteria, Bacteroidetes and Cyanobacteria. The possible influences of dynamic pollution and hydrological conditions in the Victoria Harbor area on the particle-attached and free-living bacterial community structures were discussed.

Particle-attached and free-living bacterial communities in a contrasting marine environment: Victoria Harbor, Hong Kong

Diversity of particle-attached and free-living marine bacteria in Victoria Harbor, Hong Kong, and its adjacent coastal and estuarial environments was investigated using DNA fingerprinting and clone library analysis. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA genes showed that bacterial communities in three stations of Victoria Harbor were similar, but differed from those in adjacent coastal and estuarine stations. Particle-attached and free-living bacterial community composition differed in the Victoria Harbor area. DNA sequencing of 28 bands from DGGE gel showed Alphaproteobacteria was the most abundant group, followed by the Bacteroidetes, and other Proteobacteria. Bacterial species richness (number of DGGE bands) differed among stations and populations (particle-attached and free-living; bottom and surface). BIOENV analysis indicated that the concentrations of suspended solids were the major contributing parameter for the spatial variation of total bacterial community structure. Samples from representative stations were selected for clone library (548 clones) construction and their phylogenetic distributions were similar to those of sequences from DGGE. Approximately 80% of clones were affiliated to Proteobacteria, Bacteroidetes and Cyanobacteria. The possible influences of dynamic pollution and hydrological conditions in the Victoria Harbor area on the particle-attached and free-living bacterial community structures were discussed.

Generation of internal and surface waves by seafloor movement in a two layer fluid system

Internal and surface waves generated by the deformations of the solid bed in a two layer fluid system of infinite lateral extent and uniform depth are investigated. An integral solution is developed for an arbitrary bed displacement on the basis of a linear approximation of the complete description of wave motion using a transform method (Laplace in time and Fourier in space) analogous to that used to study the generation of tsunamis by many researchers. The theoretical solutions are presented for three interesting specific deformations of the seafloor; the spatial variation of each seafloor displacement consists of a block section of the seafloor moving vertically either up or down while the time-displacement history of the block section is varied. The generation process and the profiles of the internal and surface waves for the case of the exponential bed movement are numerically illustrated, and the effects of the deformation parameters, densities and depths of the two layers on the solutions are discussed. As expected, the solutions derived from the present work include as special cases that obtained by Kervella et al. [Theor Comput Fluid Dyn 21:245-269, 2007] for tsunamis cased by an instantaneous seabed deformation and those presented by Hammack [J Fluid Mech 60:769-799, 1973] for the exponential and the half-sine bed displacements when the density of the upper fluid is taken as zero.

Distribution characteristics of matrix-bound phosphine along the coast of China and possible environmental controls

Matrix-bound phosphine (MBP) concentrations in surface sediments collected from 37 stations along the coast of China in 2006 are reported. MBP was found in all samples and the average concentration was 6.30 ng kg(-1) dry weight (dw). The distribution of MBP showed certain spatial variation characteristics with high MBP concentrations at stations near to the coast. The average concentrations of MBP in the northern Yellow Sea (NYS), the southern Yellow Sea (SYS), the northern area of East China Sea (NECS), the southern area of East China Sea (SECS), and South China Sea (SCS) were 5.57 +/- 3.78, 3.78 +/- 2.81, 5.27 +/- 3.07, 5.48 +/- 4.05 and 13.52 +/- 7.86 ng kg(-1) dw. respectively. The correlations between MBP and influencing factors, such as the sedimentary environmental characteristics (sediment type, the grain size, contents of phosphorous, organic matters and redox potential) and the aquatic environmental characteristics (temperature, salinity, depth and hydrodynamics) were studied. The results indicated that MBP was strongly influenced by various factors, such as total phosphorus (TP), organic phosphorus (OP), organic carbon (OC), the grain size and hydrodynamics, all of which not only offered reasonable interpretations for the distribution characteristics of MBP but also provided evidence to support the viewpoint that phosphine originated from OP decomposition. This work is the first comprehensive study of the distribution of MBP along the coast of China and its relationships with environmental factors which will lead to a better understanding of the phosphorus (P) biogeochemical cycle in the sea. (C) 2008 Elsevier Ltd. All rights reserved.

Diurnal and seasonal variations of UV radiation on the northern edge of the Qinghai-Tibetan Plateau

We monitored UVA, UVB, and solar radiation from August 2001 to 2003 on the northern Qinghai-Tibetan Plateau to characterize the diurnal and seasonal variations of UV radiation on the world's highest plateau. Daily UVB radiation and the ratio of UVB to total solar radiation increased significantly when the atmospheric ozone concentration decreased as estimated by the total ozone mapping spectrometer (TOMS), as well as when cloud coverage decreased. The UVB/UVA ratio also showed a significant increase when the TOMS ozone concentration decreased in the morning. The seasonal variation pattern of UVB, however, was closely correlated with solar elevation but was little affected by the seasonal pattern of the atmospheric ozone amount. Compared to observations from the central plateau, the magnitude of the UVB increase attributed to ozone depletion was smaller at the northern edge. The study suggests that the temporal variation of ground UV radiation is determined by both solar elevation and the ozone amount, but the spatial difference on the plateau is likely to be ascribed mainly to the spatial variation of the ozone amount. (c) 2007 Published by Elsevier B.V.

石油二次运移机理物理模拟研究

Oil and gas migration is very important for theoretical hydrocarbon geology study and exploration practice, but related research is weak. Physical simulation is a main method to study oil migration. Systematic experiments were done to quantitatively describe the migration patterns, path characters and oil saturation by adjusting the possible dynamic factors respectively. The following conclusions were drawn. 1. Darcy velocity and pore throat diameter were calculated according to seepage cross-sectional area and glass beads arrangement. With such normalized Darcy velocity and pore throat diameter, the date from one and two dimensional experiments can be reasonably drawn in two phase diagrams. It is found that the migration pattern can be identified using only one dimensionless number L which is defined as the ration of capillary number and Bond number. 2. Oil saturated in the pores between glass beads was used as calibration and oil saturation in the path was measured by magnetic resonance imaging. The results show that oil saturation in the center of migration path can reach 100%, is higher than oil saturation in the edge of migration path. 3. Percolation backbone during secondary oil migration was identified experimentally using Hele-Shaw cell. The backbone formed mainly because of the spatial variation of the cluster conductivity caused by oil saturation heterogeneity, main resistant force change, and path shrinkage and snap-off. Percolation backbone improves hydrocarbon migration efficiency and is a favorable factor for reservoir forming. 4. In the three dimensional filling models, the thickness of the secondary migration path is mall. It is only 2.5cm even for the piston pattern. Inclination of the model is the main influencing factor of the secondary path width.

喀斯特石漠化区植物水分利用的时空变化研究----以贵州清镇王家寨小流域为例

本研究以西南喀斯特地区的王家寨小流域为研究对象，以植物叶片δ13C值为植物水分利用效率的指示值，结合利用氢氧同位素对植物的水分来源进行确认，通过研究小流域中不同土壤类型石漠化样地、不同季节、不同等级石漠化样地及喀斯特不同小生境中常见植物种水分利用效率及水分来源的差异，旨在从小生境、植物种、植物群落等不同尺度上探讨石漠化发生过程对植物长期水分利用的影响，了解不同水源的利用对植物水分利用效率的影响，了解喀斯特生态系统特有生境中植物对水分的竞争和利用策略，以加深对生态系统水分平衡的认识。通过研究，得出了以下几点认识： 1 喀斯特石漠化区植物叶片δ13C值的时空变化 （1）在本研究区，不同土壤类型区域植物群落δ13C值均随着石漠化的进行趋正，方差分析结果显示黄壤序列植物群落叶片δ13C值存在显著差异（F（3，80）0.01=2.720.05)。整个生长季中，常见种叶片δ13C值与土壤含水量的相关关系研究表明大多数种在大多数时间随土壤水分的减少其WUE提高。 （4）本研究区小生境类型主要有石面、石沟、石缝、及土面。各小生境内植物叶片δ13C值基本上随石漠化进行趋正，即小生境尺度上植物叶片δ13C值随石漠化进行趋正。基于石漠化梯度和小生境类别的双因素方差分析表明，生长于不同石漠化等级及不同小生境的植物叶片δ13C 值总体差异显著。土面上生长的植株叶片δ13C值最负，说明较厚的土层、较多的土量能供给植物较为充足的水分、养分，避免或减小了植物的水分胁迫。对各小生境植物叶片δ13C值与各小生境主要环境因子进行相关分析，结果表明植物叶片δ13C值与小生境土壤厚度、0-10cm土壤平均含水量以及日均大气相对湿度呈显著负相关，而与日均光照强度呈显著正相关。 （5）石漠化过程中常见植物种叶片解剖结构中的栅栏组织厚度、上角质层厚度、下角质层厚度、最大导管直径均呈现逐渐增大的趋势，而海绵组织厚度则呈现逐渐减少的趋势，方差分析结果显示各解剖结构均呈现显著性差异（p<0.05）。另外，对叶片解剖结构指标与叶片δ13C值的相关分析表明，所研究的植物种叶片上述解剖形态结构中除下角质层厚度与叶片δ13C值相关关系不显著（p>0.05）外，其余指标均与其叶片δ13C值呈现显著的正相关关系（p<0.05），说明植物的WUE与植物叶片解剖结构的变化存在着内在的相关关系。 2 喀斯特石漠化区植物水分来源的时空变化 （1）由于07年降雨丰富，其喀斯特皮下水显著低于06年，但是06年喀斯特皮下水的季节变化却不大，这是由于06年为特大欠水年，观测期内降雨仅721mm，为正常年份的60%，“活塞效应”不明显。2006年对各等级石漠化样地植物水分来源研究结果表明：（12月）土壤水及小枝木质部水分的δD及δ18O值明显高于夏季（7、9月）。降雨较多的7月，强、中度石漠化大多数植物主要利用土壤水，轻、无石漠化样地植物则利用土壤水和喀斯特皮下水。9月，由于干旱严重，各石漠化样地大多数植物均不同程度的利用了喀斯特皮下水。 （2）对研究区各小生境植物水分来源的研究表明：各小生境土壤水分δD、δ18O各不相同，石缝小生境土壤水分δD、δ18O最负，石面土壤水分δD、δ18O最正，土面、石沟居中。强度石漠化土壤剖面水分δD、δ18O值>中度石漠化样地>轻度石漠化样地>无石漠化样地，显示随着石漠化的进行，样地蒸发越强烈。整体上，石缝中植物比其他生境更容易利用喀斯特皮下水，无石漠化样地的植物比石漠化样地的植物更容易利用喀斯特皮下水，常绿植物比落叶植物利用更多的喀斯特皮下水，乔木比灌木利用更多的喀斯特皮下水。 3 植物稳定性氢氧同位素与碳同位素耦合 通过对研究区植物叶片δ13C值和不同水源和植物木质部δD、δ18O值的测定，结果表明无石漠化样地植物具有更负的δ13C值，即其水分利用效率（WUE）低于石漠化样地，这是由于无石漠化样地喀斯特水赋存的二元结构，植物除了可以利用浅薄土层的水分，还拥有稳定的浅层地下水即喀斯特皮下水，这已通过植物木质部水分δD、δ18O值的测定得到佐证。落叶种具有比常绿种更正的δ13C值，即其水分利用效率（WUE）高于常绿种，这是由于常绿种比较稳定的利用了浅层地下水，具有稳定的水分来源，使得常绿种的水分利用效率（WUE）较低。土面生境植物具有比其他生境更负的δ13C值，是因为较大的土面面积、较厚的土厚，较多的土量提够给植物较多的水分，养分，土壤水分较充足，避免或减少了植物的水分胁迫，植物WUE较低。

Spatial and Temporal Variation of LURR and Its Implication for the Tendency of Earthquake Occurrence in Southern California

Based on the theory of LURR and its recent development, spatial and temporal variation of Y/Y-c (value of LURR/critical value of LURR) in the Southern California region during the period from 1980 through March, 2001 was studied. According to the previous study on the fault system and stress field in Southern California, we zoned the Southern California region into 11 parts in each of which the stress field is almost uniform. With the time window of one year, time moving step of three months, space window of a circle region with a radius of 100 km and space moving step of 0.25 degree in latitude and longitude direction, the evolution of Y/Y-c were snapshot. The scanning results show that obvious Y/Y-c anomalies occurred before 5/6 of strong earthquakes considered with a magnitude of 6.5 or greater. The critical regions of Y/Y-c are near the epicenters of the strong earthquakes and the Y/Y-c anomalies occur months to years prior to the earthquakes. The tendency of earthquake occurrence in the California region is briefly discussed on the basis of the examination of Y/Y-c.