China’s rural revitalization and development: Theory,technology and management     

Liu  Yansui  Zang  Yuzhu  Yang  Yuanyuan 《地理学报(英文版)》2020,30(12):1923-1942

Journal of Geographical Sciences - The urban-rural transformation from dichotomy to integration is a gradual process. Like rural areas in many countries, Chinese rural society is experiencing a...  相似文献   

海水温度对衰亡期浒苔释放生源硫影响的模拟研究   总被引：1，自引：0，他引：1  

韩露  邓雪  李培峰  高先池  刘春颖 《海洋学报》2018,40(10):110-118

为研究浒苔释放生源硫的特征，本文对采集于黄海绿潮中期和末期的浒苔进行了实验室模拟培养，探讨了不同温度对衰亡期浒苔释放生源硫化物的影响。实验结果表明，在10~25℃温度范围内，温度升高能够加速浒苔的衰亡。二甲基硫（DMS）的平均释放速率范围为2.79~150.70 nmol/（L·g·d），二甲基硫基丙酸内盐（DMSP）的平均释放速率范围为2.16~113.26 nmol/（L·g·d）。温度升高能够使DMS和DMSP的释放速率加快，释放量增加，DMS最大平均释放速率在25℃条件下比10℃条件下升高了约60%，培养液中DMS浓度升高了2~3倍。采集于绿潮末期的浒苔培养液中的DMS和DMSP和采集于绿潮中期的浒苔相比，浓度有所增加，采集于浒苔绿潮末期浒苔培养液中DMS的最高平均浓度为418.41 nmol/L，约为中期的4倍；DMSP的最高平均浓度为316.14 nmol/L，是中期的3倍。浒苔绿潮的爆发会对水体中的硫体系循环产生影响，进而影响该海域生态环境。  相似文献   

The exponential decline in saturated hydraulic conductivity with depth: a novel method for exploring its effect on water flow paths and transit time distribution          下载免费PDF全文

A. A. Ameli  J. J. McDonnell  K. Bishop 《水文研究》2016,30(14):2438-2450

The strong vertical gradient in soil and subsoil saturated hydraulic conductivity is characteristic feature of the hydrology of catchments. Despite the potential importance of these strong gradients, they have proven difficult to model using robust physically based schemes. This has hampered the testing of hypotheses about the implications of such vertical gradients for subsurface flow paths, residence times and transit time distribution. Here we present a general semi‐analytical solution for the simulation of 2D steady‐state saturated‐unsaturated flow in hillslopes with saturated hydraulic conductivity that declines exponentially with depth. The grid‐free solution satisfies mass balance exactly over the entire saturated and unsaturated zones. The new method provides continuous solutions for head, flow and velocity in both saturated and unsaturated zones without any interpolation process as is common in discrete numerical schemes. This solution efficiently generates flow pathlines and transit time distributions in hillslopes with the assumption of depth‐varying saturated hydraulic conductivity. The model outputs reveal the pronounced effect that changing the strength of the exponential decline in saturated hydraulic conductivity has on the flow pathlines, residence time and transit time distribution. This new steady‐state model may be useful to others for posing hypotheses about how different depth functions for hydraulic conductivity influence catchment hydrological response. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

用一种新滤波函数进行CT图像的局部重建     

徐茂林  邱钧  范惠荣  张兆田  李兴东 《CT理论与应用研究》2004,13(1):54-58

本文阐述了用一种新型滤波函数进行CT图象局部重建的原理,并给出了这种重建的二次误差估计.本文选用一种新的滤波函数,它的旁瓣衰减很快,经证明在可能选取的滤波函数中,它的衰减是最快的.新滤波函数由于空域的迅速衰减性,因此具有良好的局部重建性质.同时保持该滤波函数的其它特性,能够有效地抑制噪声,补偿混迭效应,并缓解Gibbs效应.应用新滤波函数,忽略远离计算点的数据,从而直接用CBP实现图像局部重建.在计算机上对模拟和实测数据进行局部重建的实验结果表明本文建议的图像局部重建算法简便快速,重建图象Gibbs效应减小并与用全部数据的CBP重建图像比较仍具有较高的空间及密度分辨率.  相似文献   

Estimation of groundwater use by crop production simulated by DSSAT‐wheat and DSSAT‐maize models in the piedmont region of the North China Plain     

Yonghui Yang  Masataka Watanabe  Xiying Zhang  Xiaohua Hao  Jiqun Zhang 《水文研究》2006,20(13):2787-2802

Sustainable water use is in serious crisis in the piedmont region of the Taihang Mountains in the North China Plain, owing to rapid groundwater drawdown. Estimating the water requirement for agriculture, the biggest user of groundwater, will be helpful in understanding groundwater decline. Through the use of DSSAT‐3·5 wheat and maize models, we assessed water use in winter wheat and maize, two staple crops in the region, in 1987–2001. Trends between groundwater change and simulated agricultural water use were compared. The results showed that groundwater decline was sensitive to simulated crop water requirement and irrigation requirement. According to regression analysis, 100 mm of water requirement by cultivated land (mainly wheat and maize) resulted in about 0·64 m of groundwater decline. This relationship might be useful in understanding the regional water balance and to help decision‐makers control groundwater decline through controlling crop water use or through long‐distance water transfer. The study demonstrated the usefulness of using the DSSAT model for estimating crop water use and the effectiveness of clarifying the reason for groundwater decline using the simulation results of water use. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Elm bark beetle in Holocene peat deposits and the northwest European elm decline     

Sarah H. E. Clark  Kevin J. Edwards 《第四纪科学杂志》2004,19(6):525-528

The elm decline of 5000 ¹⁴C yr ago has been the most widely discussed phenomenon in post‐glacial vegetation history. This pan‐European reduction of elm populations, echoed in the decimation of elmwoods in Europe during the twentieth century, has attracted a series of interrelated hypotheses involving climate change, human activity, disease and soil deterioration. The elm bark beetle (Scolytus scolytus L.) is an essential component of disease explanations. We present evidence for the presence of the beetle over a prolonged period (ca. 7950–4910 yr BP [8800–5660 cal. yr BP]) from a lowland raised mire deposit in northeast Scotland, with its final appearance at this site, and the first and only appearance in another mire of a single scolytid find, around the time of the elm decline. The subfossil S. scolytus finds are not only the first from Scotland, but they also represent the most comprehensive sequence of finds anywhere. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

论华北地区河口衰亡   总被引：3，自引：0，他引：3  

冯金良  李庆辰 《地理科学》1998,18(2):129-134

河口衰亡是指河口空间形态、河口作用过程及河口功能的衰亡。河口衰亡的主导诱因是人类对河流所实施的水利工程活动。河口衰亡将引起海岸侵蚀、河口淤积、河口环境退化等一系列问题。  相似文献   

Influence of anthropogenic pressure and seasonal upwelling on coral reefs in Nha Trang Bay (Central Vietnam)          下载免费PDF全文

Konstantin S. Tkachenko  Temir A. Britayev  Nguyen H. Huan  Mikhail V. Pereladov  Yuri Y. Latypov 《Marine Ecology》2016,37(5):1131-1146

The growing coastal development, dredging and dumping activities, overfishing and expansion of marine cage culture in Nha Trang Bay (NTB) of Central Vietnam since the beginning of the 2000s have resulted in a dramatic decrease of live coral cover. Surveys conducted in April–May 2013 and the same period in 2014 revealed that with an increase in distance from the outer part of the bay towards the mainland, the rivers’ influxes and dredged areas, coral cover decreased from 75% to 0.6% and species richness from 63 to 5, while the abundance of macroalgae increased from 0% to 56%. These changes correlate with differences in the concentration of suspended sediments on the same gradient. The abundance of the crown‐of‐thorns starfish Acanthaster planci and of the echinoid Diadema setosum significantly increased between the first estimation in 1998 and the survey in 2014, from 0 to 1.7 individuals (ind.) per 100 m^?2 and from 50.8 to 94.5 ind. per 100 m^?2, respectively, contributing to coral loss and intensive bioerosion of the reef framework in the bay. The large sizes of adult colonies of tabulate Acropora on the remote stations with negligible sedimentation and eutrophication loads were inconsistent with the assumptions that temperature‐induced coral bleaching or cyclones could be the major impacts in Nha Trang Bay. Analysis of the 16‐year thermal history of the bay did not reveal any instances in which the coral thermal bleaching threshold had been exceeded up to the present study. Seasonal upwelling, which occurs annually in the vicinity of Central Vietnam, may contribute to mitigation of thermal anomalies within NTB and to the maintenance of healthy coral communities on the remote reefs with relatively low anthropogenic impact.  相似文献   

BOOK REVIEWS     

《The Professional geographer》1982,34(4):458-490

Books reviewed in this article: Aerial Photography and Remote Sensing. Terrain Analysis and Remote Sensing . JOHN R. G. TOWNSHEND , ed. Environmental Data Use in Computer-assisted Data Handling Systems: The Results of a Survey of Applications in the Pacific Northwest States . KENNETH E. GORDON . Applied Land Use: A Spatial Approach . JOHN F. LOUNSBURY , LAWRENCE M. SOMMERS , AND EDWARD A. FERNALD , eds. The Second Battle of New Orleans: A History of the Vieux Carre Riverfront-Expressway Controversy . RICHARD O. BAUMBACH , JR. AND WILLIAM E. BORAH . Cultural Environmental Archaeology . MYRA SHACKLEY . The Immoral landscape: Female Prostitution in Western Societies . RICHARD SYMANSKI . life Among the Poor in Cairo . UNNI WIKAN , translated by Ann Henning. Women, Work and Property in Northwest India . URSULA SHARMA . The Domestication of Women: Discrimination in Developing Societies . BARBARA ROGERS Economic Optimization in Locational and Transport Analysis . A. G. WILSON , J. D. COELHO , S. M. MACGILL , H. C. W. L. WILLIAMS . New Tools for Economic Development: The Enterprise Zone, Development Bank, and RFC . GEORGE STERNLIEB AND DAVID LISTOKIN , eds. Regional Wage Inflation . R. L. MARTIN , ed. Finding A Place For Energy-Siting Coal Conversion Facilities . FRANK J. CALZONETTI WITH MARK S. ECKERT . Environmental Management, Resources, and Systems Environmentalism. Second Edition . T. O'RIORDAN . Countryside Conservation . BRYN GREEN . Medical Spatial Diffusion: An Historical Geography of Epidemics in an Island Community . A. D. CLIFF , P. HAGGETT , J. K. ORD , AND G. R. VERSEY . Philosophy and Geographic Thought Order and Skepticism: Human Geography and the Dialectic of Science . RICHARD SZYMANSKI AND JOHN A. AGNEW . Measurement of Subjective Phenomena . D. F. JOHNSTON , ed. Conceptions of Space in Social Thought: A Geographic Perspective . ROBERT DAVID SACK . The Association of American Geographers: The First Seventy-five Years: 1904-1979 . PRESTON E. JAMES AND GEOFFREY J. MARTIN . The Life and Thought of Isaiah Bowman . GEOFFREY J. MARTIN . Physical River Basin Planning: Theory and Practice . SURANJIT K. SAHA AND CHRISTOPHER J. BARROW , eds. Soils and landforms: An Integration of Ceomorphology and Pedology . A. I. GERRARD Climatic Change and Society. Consequences of Increasing Atmospheric Carbon Dioxide . WILLIAM W. KELLOGG AND ROBERT SCHWARE . Political Political Redistrictings and Geographic Theory . RICHARD L. MORRILL . Population Studies in Spanish American Population History: Dell Plain Latin American Studies NO. 8 . DAVID J. ROBINSON , ed. Population Redistribution in the Midwest . CURTIS C. ROSEMAN , ANDREW J. SOFRANKO , AND JAMES D. WILLIAMS , eds. Geographical Perspectives on the Elderly . A. M. WARNES , ed. Regional Perspective On the American South . MERLE BLACK AND JOHN SHELTON REED , eds. The Prairies and Plains: Prospects for the 80s . JOHN R. ROGGE , ed. Rural Rural Settlement in an Urban World . MICHAEL BUNCE . Social Accident at Three Mile Island: The Human Dimensions . DAVID L. SILLS , C. P. WOLF , AND VIVIEN B. SHELANSKI , eds. The American Small Town: Twentieth-Century Place Images . JOHN JAKLE . Urban A House of My Own . SUSAN LOBO . The City: Patterns and Processes in the Urban Ecosystem . CHRISTOPHER H. EXLINE , GARY L. PETERS , AND ROBERT P. LARKIN . Movement in Cities . P. W. DANIELS AND A. M. WARNES . Urbanization and Urban Planning in Capitalist Society . MICHAEL DEAR AND ALLEN J. SCOT , eds.  相似文献   

Proximate environmental drivers of coral communities at Palmyra Atoll: establishing baselines prior to removing a WWII military causeway     

Williams GJ  Knapp IS  Maragos JE  Davy SK 《Marine pollution bulletin》2011,62(8):1842-1851

A management proposal aims to partly remove a WWII military causeway at Palmyra Atoll to improve lagoon water circulation and alleviate sedimentation stress on the southeast backreef, an area of high coral cover and diversity. This action could result in a shift in sedimentation across reef sites. To provide management advice, we quantified the proximate environmental factors driving scleractinian coral cover and community patterns at Palmyra. The proportion of fine sedimentation was the optimal predictor of coral cover and changes in community structure, explaining 23.7% and 24.7% of the variation between sites, respectively. Scleractinian coral cover was negatively correlated with increases in fine sedimentation. Removing the causeway could negatively affect the Montipora corals that dominate the western reef terrace, as this genus was negatively correlated with levels of fine sedimentation. The tolerance limits of corals, and sediment re-distribution patterns, should be determined prior to complete removal of the causeway.  相似文献