河北宁晋泊地区2600年来古气候变化研究

今年宁晋泊南王庄剖面的孢粉,粘土矿物,粒度等数据和Ｐｏｒｔｅｒ等的粒度年龄模型建立时间标尺,划分出２６００年来的气候冷暖变化阶段。基本特征如下：孢粉Ⅰ带,大约２００ａＢＰ－６３０ａＢＰ,气候冷干;Ⅱ带,大约６３０ａＢＰ－１０１０ａＢＰ,气候温暖,上部偏干,下部潮湿;Ⅲ带,大约１０１０ａＢＰ－１１６５ａＢＰ,气候稍冷较湿;Ⅳ大约１１６５ａＢＰ－１３５０ａＢＰ,气候温暖潮湿;Ⅴ带,大约１３５０ａＢＰ－     

Plain strain problem of poroelasticity using eigenvalue approach

A plain strain problem of an isotropic elastic liquid-saturated porous medium in poroelasticity has been studied. The eigenvalue approach using the Laplace and Fourier transforms has been employed and these transforms have been inverted by using a numerical technique. An application of infinite space with concentrated force at the origin has been presented to illustrate the utility of the approach. The displacement and stress components in the physical domain are obtained numerically. The results are shown graphically and can be used for a broad class of problems related to liquid-saturated porous media.     

松辽平原西部水文地质空间数据库工作方法

松辽平原西部地下水资源调查评价水文地质空间数据库采用Office Access 2000为数据录入操作平台,应用MapGIS软件作为图形工具平台.在建库过程中,遵循统一的建库格式标准和工作指南;制定符合调查评价项目建库的作业指导手册;建立统一的子图库系统,采用统一比例尺的地理底图作为数据库建库的基础图件;在内部属性录入和挂接之前,各区片之间的成果图件要进行拼接,使接缝间的线和图元接好后无误.     

江汉平原土地利用的时空变化及其驱动因素分析

采用遥感、GIS一体化技术,利用1989～1990、1995～1996和1999～2000年获取的三期陆地资源卫星图像,对江汉平原土地利用10年变化和以1995～1996年为界的前后两个5年变化的时空特征进行了分析,并探讨了变化的驱动因素。结果表明,该区的土地利用在不同的时间及空间尺度上有明显不同的特点。10年间,耕地减少近5万hm²,其中,前5年的减少量占多数,达6783%。各类建设用地总计增加了156万hm²,其中,前5年的增加量是后5年的2倍。水域面积在10年间增加了达到354万hm²,后5年的增幅不到前期的1/2。土地利用变化最快的区域均处于工业经济较发达、城市化较快的地区如武汉、仙桃,变化最慢的区域在监利、松滋、天门等地。政策、社会经济与科技因素对土地利用随时间尺度的变化有决定性的影响。     

渤海湾海陆交互相沉积的磁性地层学

渤海湾的海陆交互相沉积对研究海陆环境变化、新构造活动及华北平原的演化历史等均有重要意义,而建立可靠的年代地层框架是上述研究的前提。对取自渤海湾西岸天津市深度为203.57 m的BZ2钻孔进行了详细的磁性地层学研究,结果表明,钻孔岩心包含4个正极性段,分别可与标准极性柱中布容(Brunhes)、贾拉米洛(Jaramillo)、奥尔都维(Olduvai)和高斯(Gauss)正极性世对比;获得的3个负极性段则与松山(Matuyama)和凯纳(Kaena)事件对应,从而获得钻孔岩心底部年龄约为3.18 MaBP。磁性界限之间平均沉积速率的相对一致性,指示了渤海湾在晚上新世以来总体稳定的下沉趋势。     

Measurement of evapotranspiration in a winter wheat field

Daily evapotranspiration from a winter wheat field on the North China Plain measured by large‐scale weighing lysimeter was linearly related to that measured by the Bowen ratio energy balance (BREB) technique. Soil evaporation averaged about 23·6% of evapotranspiration from the post‐winter dormancy revival stage to the grain ripening stage in 1999. On clear days during winter dormancy, about half of the net radiation flux R_n was used to warm soil. During the revival stage, conductive heat flux G also used most of the incoming R_n, but the ratio of latent heat flux λE to R_n increased. During the stem‐extension stage, λE was about 50% of R_n; thereafter, λE/R_n increased continually, but G remained less than 10% of R_n. During the ripening stage, λE was almost 90% of R_n. Evaporative fraction (EF) can be expressed as a function of plant status and atmospheric boundary layer conditions. The relationship between EF and available energy under moderate air temperature and vapour pressure deficit conditions was examined for five combinations of aerodynamic and canopy conductance. Although the theoretical relationship indicates that EF should be highly correlated to soil water content, the correlation has been difficult to identify under field conditions. However, we observed that there exists a threshold value of R_n ? G, above which EF is less than 1·0, and that the threshold value is lower under soil‐water deficit conditions than under abundant soil‐water conditions. Copyright © 2002 John Wiley & Sons, Ltd.     

松嫩平原农业水资源优化管理模型

松嫩平原是我国重要的商品粮生产基地，水资源短缺和不合理利用严重制约着农业的可持续发展。研究中选择国家“九五”农业重点科技攻关吉林省大安试验作为研究区，针对农业发展状况和目标、次生盐碱化形成机理和水资源开发利用现状及其存在的问题等多种自然和人为条件，建立区域农业水资源优化管理模型，确定水资源最优利用方案，为农业发展规划提供理论依据和科学指导。同时，拟把此套模型技术推广和应用到整个松嫩平原地区，保证农业安全生产，促进生态环境稳定健康发展。     

华北平原缺水盐渍区浅层地下水位动态分析

本文以国家农业科技攻关南皮试区为例,分析了华北缺水盐渍区地下水水位动态及其与降水量的关系,应用灰色系统理论的GM(1,1)预测方法,建立了地下水位动态的模拟、预测模型。结果表明,在目前供水、用水和水文地质条件下,未来地下水水位呈缓慢下降趋势,年均下降速度为0.12～0.14m/年。单靠平水年甚或丰水年降水难以维持地下水采补平衡,必须进行多年径流调节或跨流域调水,以丰补歉,互济余缺,并实施农田综合节水技术,防止区域水环境的恶化。     

三江平原和横断山区的泥炭资源及其合理开发利用

三江平原和横断山区是我国泥炭资源两大丰富区，作者详细论述了三江平原和横断山区的泥炭资源分布、泥炭资源评价和开发利用与保护问题。泥炭的形成和积累是各种自然因素综合作用的结果。不同地区由于地貌、地质、气候以及各种成矿作用组合的差异，不仅造成泥炭分布的时空不平衡性，而且也影响着泥炭性质、质量，左右着泥炭开发利用的方向。泥炭质量评价以泥炭的性质为依据，是泥炭合理开发利用的基础，决定着泥炭利用的方向和效益。     

Establishment of wetlands on the southeastern Atlantic Coastal Plain: Paleolimnological evidence of a mid-Holocene hydrologic threshold from a South Carolina pond

The series of climatic events affecting landscapes on the southeastern Atlantic Coastal Plain over the past several thousand years is poorly understood. This is due, in part, to the paucity of depositional basins in this region containing adequately preserved microfossils for paleoecological analyses. This research reconstructs past hydrologic environments from the microfossil record of Peat Bay, a small, peat-filled pond in south-central South Carolina. We cored the deepest location in the pond and retrieved 120 cm of sediment representing 5200 yr of deposition. Fine clays at the base of the core resembled sediments deposited in abandoned channels of the nearby Savannah River, suggesting the basin may have functioned as an oxbow wetland prone to periodic flooding and drying. Overlying peats containing planktonic diatom assemblages mark the onset of persistent open-water conditions ca. 4600 B.P. These data, in conjunction with a small body of paleoecological evidence from other southeastern wetlands, suggest that a hydrologic 'threshold' was surpassed during the mid-Holocene that resulted in flooding and expansion of low-lying depressions that characterize the regional landscape. This is likely the culmination of long-term hydrologic trends related to glacial retreat, including increased precipitation and a rise in ground water levels corresponding to a global rise in sea level. In Peat Bay, lake-like conditions persisted until about 3800 B.P., after which time aerophilic diatoms and remains of other temporary pond organisms dominated the fossil record. Episodic drying of pond sediments during the late-Holocene may have been a response to decreased precipitation, stabilization of the water table and infilling of the pond by decaying vegetation and terrigenous clastics. The microfossil record indicates that temporary pond conditions persisted until recent years (ca. 1985) when the basin returned to a permanently flooded state due to groundwater connection to a large reservoir constructed nearby.