Diatom paleoecology of Laguna Zoncho,Costa Rica

We analyzed diatoms in a sediment profile from Laguna Zoncho in southern Pacific Costa Rica (lake elevation 1190 m asl, depth 2.6 m, area 0.75 ha) spanning some 3240 cal yr. Diatoms are common in the profile, which we subdivide into three zones. Zone C (3240–1020 cal yr B.P.) is dominated by Staurosira construens var. venter and Aulacoseira spp.; during this time, the lake was dilute and circumneutral. Benthic and acidophilous taxa increase gradually in the upper section of this zone. Zone B (1020–460 cal yr B.P.) almost totally lacks Aulacoseira, and instead is dominated by combinations of Eunotia minor, Encyonema lunatum, Gomphonema gracile, and Pinnularia braunii. Previous pollen and charcoal analysis indicates that this zone falls within the peak of prehistoric agricultural activity at the lake, but diatoms may also reflect climate change. During this period, the lake was likely shallower and more acidic, but not eutrophic. Finally, Zone A (460 cal yr B.P. to AD 1997) begins near a 1.5-cm tephra layer from nearby Volcán Barú; diatom assemblages are dominated by Aulacoseira spp., and suggest deepening of the lake and return to conditions similar to Zone C. This was a time of indigenous population decline and forest recovery in the Zoncho region, probably reflecting the impact of European diseases on the native population, although climate change and impacts of the tephra deposition cannot be wholly discounted.     

BOOK REVIEWS

Book Reviewed in this article: Geography and the Third World. International Seminar, 14–18 May 1980, Kuala Lumpur, Malaysia . Ishmail Ahmad and Jamaluddin Md Jahi, eds. The Growth Dilemma: Residents' Views and Local Population Change in the United States . Mark Baldassare. Sport and Place: A Geography of Sport in England, Scotland & Wales . John Bale. The Deindustrialization of America: Plant Closings, Community Abandonment, and the Dismantling of Basic Industry . Barry Bluestone and Bennett Harrison. Selected Essays 1963–1975: Carl O. Sauer . Bob Callahen, ed. Housing and Planning in the Countryside . G. Clark. Conflict, Politics and the Urban Scene . Kevin R. Cox and R. J. Johnston, eds. Thematic Maps: Their Design and Production . David J. Cuff and Mark T. Mattson. Wine: A Geographic Appreciation . Harm Jan de Blij. USSR in Maps . J. C. Dewdney. Political Geography: A Contemporary Perspective . Ramesh D. Dikshit. Rethinking Human Adaptation . Rada Dyson-Hudson and Michael A. Little, eds. Sacred Sands: The Struggle for Community in the indiana Dunes . J. Ronald Engel. Geography of the Biosphere . A. Furley and Walter W. Newey. Disaster and Reconstruction . Robert Geipel. Glasgow: The Making of a City . Andrew Gibb. Design for Arid Regions . Giden S. Golany, ed. Urbanization and Cancer Mortality: The United States Experience, 1950–1975 . Michael R. Greenberg. Geology in the Nineteenth Century: Changing Views of a Changing World . Mott T. Greene. Colonización y Destrucción de Bosques en Panamá . Stanley Heckadon Moreno and Alberto McKay, eds. Urban Geography: A First Approach . David T. Herbert and Colin J. Thomas. The Visual and Spatial Structure of Landscapes . Tadahiko Higuchi. Climate from Tree Rings . M. K. Hughes, P. M. Kelly, J. R. Pilcher, and V. C. LaMarche, Jr., eds. The structure of Nineteenth Century Cities . James H. Johnson and Colin G. Pooley, eds. The American Planner: Biographies and Recollections . Donald A. Krueckeberg, ed. Urban Land Policy For the 1980s, the Message for State and Local Government . George Lefcoe, ed. Regional Planning: Evolution, Crisis and Prospects . Gill C. Lim, ed. Relevance and Ethics In Geography . Bruce Mitchell and Dianne Draper. China: The Geography of Development and Modernization . Clifton W. Pannell and Laurence J. C. MA. The Urban Retailing System . Robert B. Potter. Hants. Nonconventional Energy Resources . Philip R. Pryde. Caribbean Migrants: Environment and Human Survival on St. Kitts and Nevis . Bonham C. Richardson. Population and Resources . Harry Robinson. East Los Angeles: History of A Barrio . Ricardo Romo. Integrated Impact Assessment . Frederick A. Rossini and Alan L. Porter, eds. Environmental Aesthetics: Essays in Interpretation . Barry Sadler and Allen Carlson, eds. Earthwatch . Charles Sheffield. Field Techniques and Research Methods in Geography . Robert H. Stoddard. Haiti: Land of Poverty . Robert J. Tata. Weathering and Erosion: Sources and Methods in Geography . Stephen T. Trudgill. Once Beneath the Forest. Prehistoric Terracing in the Río Bec Region of the Maya Lowlands . B. L. Turner, II. The Historical Geography of Scotland since 1707 . David Turnock.     

An assessment of the risk associated with urban development in the Thiaroye area (Senegal)

Water quality data from 56 wells, aquifer characteristics, soil types and land use in the city suburb of Dakar were compared to assess the effects of land use on the Thiaroye groundwater quality. The study area encompassed an unsewered densely populated zone, agricultural land, low density villages, and undeveloped land located in the sand dunes. A method similar to GIS technologies was applied to evaluate the degree of vulnerability of the different parts of the aquifer in relation to urban development, land use and aquifer characteristics. The aquifer parameters (hydraulic conductivity, groundwater level depth, recharge, soil type) were re-evaluated qualitatively into three class rankings (high, moderate and low), depending on the likelihood for contaminants reaching the water table, then combined using the two matrix Boolean logic based approaches to identify the nine classes of vulnerability assessed in the aquifer domain. An attempt was made to explain the distribution of nitrate concentration with the assessed vulnerability. In the area assessed, in the densely populated zone running from Pikine, to Thiaroye and Yeumbeul, very high nitrate concentrations correspond with the highest vulnerability index (H1). Nitrate contamination in this area is a consequence of point-source seepage from individual septic systems improperly built in this area. In the eastern part of the aquifer, high nitrate concentrations at Deni B. Ndao, Mbawane and Golam localities coincide with a moderate vulnerability assessment. The major source of nitrate in these areas is induced by agricultural activities.     

Impact of Mining Activities upon Environment in Panzhihua Region, Southwestern China

Mining activities have left huge uncovered slopes, large areas of gangue ground and extensive railings dams. In this paper, we studied some impacts of mining activities upon environment in Panzhihua region, southwestern China. The environmental impacts include ecological destruction, geological disasters, environmental pollution, land damage, solid waste and occupational health effect in study area. The author suggested that local government should take some measure to reduce environmental impact in Panzhihua City. First, the countermeasure of reducing environmental impact is to set up ecological rehabilitation and environmental management system, which ensure the sustainable development of resources, environment, economy and society in this region. Second, the area needs to be monitored regularly for trace metal and other pollutants to forewarn urban eco-environmental safety.     

An automated image-based technique for tracking sequential surface wave profiles

Fast-deforming steep surface wave profiles are of particular interests to the design of marine structures and validation of numerical models. In this paper, an improved active contour model, gradient vector flow (GVF) snake, is adapted to automatically track sequential wave profiles taken by a non-intrusive high-speed imager. The robustness and efficiency of the adapted GVF snake is demonstrated through accurately delineating temporal and spatial wave profiles of three examples, including a spiller, a plunger, and a plunging breaker striking a vertical cylinder. Detailed characterizations to these breaking surface wave profiles are given. Overall, the automated adapted GVF snake imaged-based technique is shown to be a power tool for measuring surface wave motions and interfacial flows.     

Vibrating-Sliding Motion of Caisson Breakwaters Under Various Breaking Wave Impact Forces

Sliding is one of the principal failure types of caisson breakwaters and is an essential content of stability examination in caisson breakwater design. Herein, the mass-spring-dashpot model of caisson-base system is used to simulate the vi-brating-sliding motion of the caisson under various types of breaking wave impact forces, i.e., single peak impact force, double peak impact force, and shock-damping oscillation impact force. The effects of various breaking wave impacts and the sliding motion on the dynamic response behaviors of caisson breakwaters are investigated and the calculation of relevant system parameters is discussed. It is shown that the dynamic responses of the caisson are significantly different under different types of breaking wave impact forces even when the amplitudes of impact forces are equal. The amplitude of dynamic response of the caisson is lower under single peak impact excitation than that under double peak impact or shock-damping oscillation impact excitation. Though the disp     

Analysis of Collision Protection for Ocean and Offshore Structures

1 .Introduction Many accidents of ocean and offshore structuresinvolve impact loadings .Some famous ship colli-sion cases arethe Tj rn Bridge (Sweden) ,the West Bridge of the Great Belt Link (Denmark) andtheMaracaibo Bridge (Venezuela) . Most studies usedthe Hertzian contact law(Zukaset al .,1982) tocalculate the impact force and analyze structures subjectedtoimpact loadings .Other alternative meth-ods such as the spring-dashpot and momentumbalance methods utilizedthe coefficient of rest…     

9914号台风对厦门岛东南部岸滩的环境效应

1999年14号台风于10月9日正面袭击厦门，最大风力达12级以上（47．1m/s），台风中心在厦门滞留5－6h，全市经济损失十几亿元.本文依据台风前后对厦门岛东南部海岸、沙滩的第一手调查资料以5条固定沙滩剖面多次测量比较进行综合分析。结果表明：人工护岸毁坏1／10以上、岸线后退，沙滩冲淤剧烈、沙源流失严重，海岸与沙滩环境恶化。文中还进一步探讨各种影响因素，提出今后该区域开发利用时应注意事项及防灾措施。     

Control and Recovery of Environment after the Construction

The Taiwan Strait Tunnel Project will bring very deep, far, and long lasting influence on the environment inevitably. This article focuses on what shall be done considering environmental issues after the construction. Herein an environmental protection program with a four-step procedure is particularly illustrated, including setting environmental objectives, formulation of environment protection program, plan of environmental survey, and management of environmental event. This procedure based on the outcome of environmental impact assessment formulates an environment protection program to control and recover environmental problems after the project completed. Two case studies will illustrate the special design and considerations adopted that make the project coexist with the environment successfully, peacefully, and friendly.     

开敞大河口滩槽冲淤对台风的响应及其动力泥沙机制探讨——以长江口南汇边滩—南槽—九段沙系统为例

台风期间 ,潮间带和潮下带岸坡总体上遭受侵蚀 ,而向岸一侧的沼泽和向海一侧的深槽则趋于淤积。台风期间的冲淤强度比正常天气的高 1- 2个数量级。台风期间裸滩的侵蚀机制是风将高能传递给水体使水体挟沙能力剧增 ,沼泽迅速淤积的机制与植被的消能捕沙功能、涨潮水体的高含沙量和明显的增水有关 ,而深槽的骤淤则是由于深水区底层相对较弱的动力条件与浅滩侵蚀所致的高含沙量不相适应。受径流和潮流对泥沙扩散作用的影响 ,台风所致的滩槽冲淤不一定达成平衡