The sediment delivery ratio in a small catchment in the black soil region of Northeast China   总被引：1，自引：0，他引：1  

Yi-fan DONG  Yong-qiu WU  Tian-yu ZHANG  Wei YANG  Bao-yuan LIU 《国际泥沙研究》2013,28(1):111-117

The black soil region of northeast China,which covers the Provinces of Heilongjiang,Jilin and the Inner Mongolia autonomous region with black soil,chernozem and meadow soil,has experienced soil erosion since intense agricultural reclamation began approximately 100 years ago.However,the sediment delivery ratio,defined as the fraction of gross erosion that is transported from a given area in a given time interval,is still unclear.In this study,we calculated the delivery ratio and analysed changes in erosive processes within Hebei catchment from 1977 to 2007 based on an analysis of sediments of the Liudui reservoir.The original vegetation layer clearly identified the bottom of the reservoir when it was constructed in 1977;thus,the reservoir sediments could be precisely dated.The delivery ratio,calculated by comparing the sediment deposition in the reservoir with the total soil erosion in the upstream catchment,was found to be exponentially correlated（r² = 0.95,P < 0.01） with decreasing grain size,except for the fraction <0.002 mm.The delivery ratio for the clays（<0.002 mm） was low,averaging 0.10 during the study period, which indicated partial removal of clays from the reservoir.The changes in the reservoir deposition rate reflected the temporal changes in the erosion processes.The exceptionally high rainfall in 1998 was confirmed by the distributions of ¹³⁷Cs,²¹⁰Pb,and the grain-size of the sediments.Beginning from the position of the original grass layer,we defined three periods from 1977 to 2007 based on deposition rates:2.40 cm year^-1 from 1977 to 1997,5.60 cm year^-1 in 1998 due to unusually high rainfall,and 1.55 cm year^-1 from 1999 to 2007.The overall average deposition rate for the entire period was 2.26 cm year^-1.Precipitation was found to be the main factor affecting the soil erosion of the study area.  相似文献   

Retrieval algorithm for microwave surface emissivities based on multi-source, remote-sensing data: An assessment on the Qinghai-Tibet Plateau   总被引：1，自引：0，他引：1  

WANG YongQian  SHI JianCheng  LIU ZhiHong  PENG YingJie  LIU WenJuan 《中国科学:地球科学(英文版)》2013,(1):93-101

The Qinghai-Tibet Plateau plays a very important role in studying severe weather in China and around the globe because of its unique characteristics. Moreover, the surface emissivities of the Qinghai-Tibet Plateau are also important for retrieving surface and atmospheric parameters. In the current study, a retrieval algorithm was developed to retrieve the surface emissivities of the Qinghai-Tibet Plateau. The developed algorithm was derived from the radiative transfer model and was first validated using simulated data from a one-dimensional microwave simulator. The simulated results show good precision. Then, the surface emissivities of the Qinghai-Tibet Plateau were retrieved using brightness temperatures from the advanced microwave-scanning radiometer and atmospheric profile data from the moderate resolution imaging spectroradiometer. Finally, the features of the time and space distribution of the retrieved results were analyzed. In terms of spatial characteristics, a spatial distribution con- sistency was found between the retrieved results and surface coverage types of the Qinghai-Tibet Plateau. In terms of time characteristics, the changes in emissivity, which were within 0.01 for every day, were not evident within a one-month time scale. In addition, surface emissivities are sensitive to rainfall. The reasonability of the retrieved results indicates that the algorithm is feasible. A time-series surface emissivity database on the Qinghai-Tibet Plateau can be built using the developed algorithm, and then other surface or atmospheric parameters would have high retrieval precision to support related geological re- search on the Qinghai-Tibet Plateau.  相似文献   

A comparison of two kinds of eastward-moving mesoscale vortices during the mei-yu period of 2010   总被引：2，自引：0，他引：2  

FU ShenMing  YU Fei  WANG DongHai  XIA RuDi 《中国科学:地球科学(英文版)》2013,(2):282-300

During the mei-yu period,the east edge of the Tibetan Plateau and the Dabie Mountain are two main sources of eastward-moving mesoscale vortices along the mei-yu front(MYF).In this study,an eastward-moving southwest vortex(SWV) and an eastward-moving Dabie vortex(DBV) during the mei-yu period of 2010 have been investigated to clarify the main similarities and differences between them.The synoptic analyses reveal that the SWV and DBV were both located at the lower troposphere;however,the SWV developed in a "from top down" trend,whereas the DBV developed in an opposite way.There were obvious surface closed low centers corresponding to the DBV during its life span,whereas for the SWV,the closed low center only appeared at the mature stage.Cold and warm air intersected intensely after the formation of both the vortices,and the cold advection in the SWV case was stronger than that in the DBV case,whereas the warm advection in the DBV case was more intense than that in the SWV case.The Bay of Bengal and the South China Sea were main moisture sources for the SWV,whereas for the DBV,in addition to the above two moisture sources,the East China Sea was also an important moisture source.The vorticity budget indicates that the convergence was the most important common factor conducive to the formation,development,and maintenance of the SWV and DBV,whereas the conversion from the vertical vorticity to the horizontal one(tilting) was the most important common factor caused the dissipation of both of the vortices.The kinetic energy(KE) budget reveals that the KE generation by the rotational wind was the dominant factor for the enhancement of KE associated with the SWV,whereas for the DBV,the KE transport by the rotational wind was more important than the KE generation.The KE associated with the SWV and the DBV weakened with different mechanisms during the decaying stage.Furthermore,the characteristics of baroclinic and barotropic energy conversions during the life spans of both vortices indicate that the SWV and DBV both belong to the kind of subtropical mesoscale vortices.  相似文献   

Numerical analysis for contribution of the Tibetan Plateau to dust aerosols in the atmosphere over the East Asia     

MAO Rui  GONG DaoYi  SHAO YaPing  WU GuangJian  BAO JingDong 《中国科学:地球科学(英文版)》2013,(2):301-310

Although the Tibetan Plateau is widely thought as a potential dust source to the atmosphere over East Asia,little is known about the temporal changes of Tibetan dust activities and Tibetan dust source strength.In this study,we address these two issues by analyzing dust storm frequencies and aerosol index through remote sensing data and by means of numerical simulation.The findings indicate that monthly dust profiles over the Tibetan Plateau vary significantly with time.Near the surface,dust concentration increases from October,reaches its maximum in February March,and then decreases.In the middle to upper troposphere,dust concentration increases from January,reaches its maximum in May June,and decreases thereafter.Although Tibetan dust sources are important contributors to dust in the atmosphere over the Tibetan Plateau,their contribution to dust in the troposphere over eastern China is weaker.The contribution of Tibetan dust sources to dust in the atmosphere over the Tibetan Plateau decreases sharply with height,from 69% at the surface,40% in the lower troposphere,and 5% in the middle troposphere.Furthermore,the contribution shows seasonal changes,with dust sources at the surface at approximately 80% between November and May and 45% between June and September;in the middle and upper troposphere,dust sources are between 21% from February to March and less than 5% in the other months.Overall,dust aerosols originating from the Tibetan Plateau contribute to less than 10% of dust in East Asia.  相似文献   

Changhsingian radiolarian fauna from Anshun of Guizhou,and its relationship to TOC and paleo-productivity     

XIANG Yu  FENG QingLai  SHEN Jun  ZHANG Ning 《中国科学:地球科学(英文版)》2013,(8):1334-1342

Abundant siliceous micro-fossils were found from the Dalong Formation,Xinmin section,Guizhou,which include nine species of radiolarians belonging to seven genera as well as nine types of siliceous spongy spicules.The radiolarian fauna consists of all spherical radiolarians,without any species of Albaillellaria and Latentifistularia,indicating a relative shallow water sedimentary environment.The high relative co-efficient between the radiolarian abundance and total organic carbon(TOC)shows that the radiolarian assemblage represented by Copicyntra and Paracopicyntra can be used as a proxy to the paleo-productivity.However,the relative co-efficient between biogenic silica and the radiolarian and sponge spicule abundances is low.A possible explanation is that an oceanic circulation has changed the biogenic silica content after radiolarian test and siliceous spongy spicule were dissolved.  相似文献   

Paleomagnetic data from the Late Carboniferous-Late Permian rocks in eastern Tibet and their implications for tectonic evolution of the northern Qiangtang-Qamdo block   总被引：1，自引：0，他引：1  

CHENG Xin  WU HanNing  DIAO ZongBao  WANG HaiJun  MA Lun  ZHANG XiaoDong  YANG Gang  HONG JingJing  JI WenHua  LI RongShe  CHEN ShouJian  ZHAO ZhenMing 《中国科学:地球科学(英文版)》2013,(7):1209-1220

We report paleomagnetic results from the Late Carboniferous-Late Permian strata in eastern Tibet (China), and aim to clarify the tectonic and paleogeographic evolution of the northern Qiangtang-Qamdo block, which is the key to the study of plate boundary between the Gondwanaland and the Eurasia during the late Paleozoic. Two hundred and nineteen samples-including limestone, muddy siltstone, basalt, lava, and tuff-were collected at 24 sites in the Upper Carboniferous and Middle-Upper Permian successions. A systematic study of rock magnetism and paleomagnetism yields three reliable paleomagnetic pole positions. Both hematite and magnetite occurred in the Late Carboniferous limestone samples. The demagnetization curve shows a characteristic double-component, with the remanent magnetization (ChRM) exhibiting a positive polarity (negative inclination). In the Late Permian limestone, tuff, and basalt, magnetic information were recorded primarily in magnetite, although a small fraction of them was found in hematite in basalt. The demagnetization curve illustrates a double or single component, with the ChRM showing a negative polarity (positive inclination), which has passed the classic fold test successfully. The single polarity features of the ChRM directions of the Late Carboniferous and Middle-Late Permian rocks are respectively related to the Kiaman positive and reversed polarities under the stratigraphic coordinates. This, in turn, indicates that both ChRMs directions represent the original remanence directions. By comparison with the previously published paleomagnetic results from the late Paleozoic rocks in the northern Qiangtang Range, we suggest that: (1) Qamdo and northern Qiangtang block were independent of each other during the Late Carboniferous to the Early Permian periods. The north Lancangjiang ocean basin between the two blocks may have closed before the Middle Permian and been involved in the continent-continent collision stage in the Late Permian-Early Triassic periods. (2) The northern Qiangtang-Qamdo Block paleogeographically was situated at low to intermediate latitudes in the Southern Hemisphere in the Late Carboniferous-Late Permian periods, and began to displace northward in the Early Triassic, with an amount of more than 5000 km northward transport from its current location.  相似文献   

Blooming of bacteria and algae is a biokiller for mass-extinction of Devonian coral-stromatoporoid reef ecosystems     

WU YiBu  FENG Qi  GONG YiMing 《中国科学:地球科学(英文版)》2013,(7):1221-1232

Studies of rock slices showed that there were many kinds of symbioses between bacteria and algae and corals-stromatoporoids in the coral-stromatoporoid reefs from the Devonian Ganxi section of Sichuan and the Dushan section of Guizhou in South China. They included encrustations, microborings, bioclaustration, etc. In the host corals-stromatoporoids invaded by bacteria and algae were many residues of dead soft issue in the infected parts, where the skeletal structures were injured. Therefore, we considered there were direct interactions between corals-stromatoporoids and bacteria and algae in coral-stromatoporoid reefs, which included that bacteria and algae blocked growth of corals-stromatoporoids and the latter had the ability of self-healing. And the bacteria and algae usually was the active side. In the Middle Devonian with normal seawater condition, corals and stromatoporoids had the ability to resist the invasion of bacteria and algae, and the host coral-stromatoporoids would not be killed; but in the Late Devonian with deterioration of seawater quality, the ability of bacteria and algae infection increased while corals-stromatoporoids’ ability to resist infection declined, and therefore the host corals-stromatoporoids would be dead. Hence we suggested that the invading of bacteria and algae was a possible biokiller for mass-extinction of the Devonian coral-stromatoporoid reefs ecosystem. Beyond that, blooming of bacteria and algae and its triggering cumulative environmental effects played an important role in the reduction and extinction of metazoan in the Late Devonian. Furthermore, it can be used as a useful example to learn the trend and the reasons for the disease and decrease of modern coral reefs.  相似文献   

Insufficient thermalization effects on determining fission-track ages     

PANG JianZhang  ZHENG DeWen  WAN JingLin  LI DaMing  ZHANG PeiZhen  YANG Jing 《中国科学:地球科学(英文版)》2013,(7):1233-1241

Fission-Track Dating (FTD) has been developed as a useful technique for geological studies. Parent elements are measured by counting 235 U tracks induced by thermal neutrons. If insufficient thermalization occurs, fission of 238 U and 232 Th will be induced, and further measurement error will be introduced. Therefore, whether the neutrons are well thermalized or not will affect the FTD results. Due to requirement of safe operation, the 101 reactor was terminated in 2007. By using the 492 reactor as the new thermal neutron reactor, our present paper will attempt to study the feasibility and the potential influence on FTD. By irradiating monitor glass SRM612 and CN5 in pairs, we will study the thermalization situation of the 492 reactor. Irradiated data show that thermal neutrons are not evenly distributed either in horizontal or in vertical dimension. Especially, horizontal heterogeneity is obvious. But we discovered that proper irradiation position in the reactor can meet the requirement of FTD. Under the current irradiation condition, we calculated and assessed the insufficient thermalization effects on determining fission-track ages. We found that the difference between the 232 Th/ 238 U ratios of samples and standards is the main factor to the experiment results. The results will not be affected if the 232 Th/ 238 U value of samples is equal to the standard samples. However, if the 232 Th/ 238 U ratio is larger than that of the standards, the results will be smaller than actual ages. Comparatively, the ages will be more than expected if the 232 Th/ 238 U ratio is less. Therefore, to reduce the irradiation error, we suggest either locating the position of irradiation strictly, or minimizing the influence of lateral heterogeneity by reducing the amount of each sample package. Additionally, accuracy of the experimental results can be improved by increasing standard samples to adjust ζ value and using the monitor of standard glass SRM612 and CN5 together.  相似文献   

基于R树索引的三维场景细节层次自适应控制方法   总被引：1，自引：1，他引：0  

龚俊  朱庆  章汉武  李晓明  周东波 《测绘学报》2011,40(4):531-534

针对大规模三维城市建模需要,介绍一种基于三维R树索引的多细节层次（简称LOD）管理方法,从叶节点层向根节点自动生成LOD场景,并设计实现LOD检索的算法。通过试验分析,证明本文的LOD定义参数能够定量控制三维场景中的渲染目标数目,进而实现三维场景的自适应可视化方法,尤其适合于建筑物和树木类型的地物目标。  相似文献   

自然灾害风险地图中的制图综合研究——以点状承灾体为例   总被引：3，自引：1，他引：2  

潘东华  王静爱  贾慧聪  赵金涛 《武汉大学学报(信息科学版)》2011,(1):51-55

为提高多尺度灾害风险地图表达中高风险区承灾体的准确、有效、快速识别,基于灾害风险理论,运用地理学规律,在GIS等技术支持下,结合数据挖掘和空间分析技术,探讨了在尺度转换过程中点状承灾体的制图综合问题,并结合承灾体自身及在灾害系统中的属性特征,抽象概括了点状承灾体在灾害地图中的制图综合类型,即重要性综合、特殊性综合、邻近性综合、条件性综合、完整性综合、随机性综合。针对每一种综合类型,给出了可能的灾害情景假设及制图综合方法,并进行了技术实现及可视化表达。结果表明,基于上述6种类型的点状承灾体制图综合,不仅有效解决了尺度转换过程中的数据冗余问题,而且还能准确反映出特定孕灾环境下高风险区承灾体的空间分布,同时也为灾害风险地图的制图综合提供一种新的思路。本研究为区域灾害风险识别、风险防范与管理提供理论与技术支持,进而为区域的防灾减灾提供科学依据。  相似文献