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231.
Groundwater of the coastal plain of the Rio de La Plata, Argentina,contains up to 17 g L-1 SO4 and 37 gL-1 TDS. Some of this SO4 is from paleo-seawater intrusion; however, SO4 : Cl ratios can be>2 : 1, and most of the SO4 must, therefore, have another source. Three possible sources were investigated: gypsum, organic matter,and iron sulphides. Dissolved SO4 showed δ34S valuesfrom -7 to 0‰, typical values for S from iron sulphides or organicmatter, but distinct from that of seawater (+22‰). To test whetherthe SO4 was derived from oxidation of reduced S, four 4-mcores were taken from marine sediments of the coastal plain. Two were takenfrom higher, drier areas where the highest dissolved SO4values were encountered, and two were taken from lower, wetter areas thathad much lower SO4 concentrations. Pore waterSO4, Cl and alkalinity were determined; solids were analyzedfor SO4, sulphide-S and organic-S. Sulphide-S was the dominant form of reduced S, averaging about0.5% S in the lower interval (2.5–4 m) of the cores. Sulphidewas absent in the upper 2.5 m in both topographically higher and lowerareas. Sulphate was present in the entire unit in the higher, drier areas,but almost absent in lower areas. Organic-S was insignificant. Our model for the origin of dissolved SO4 is: fine-grainedpyrite was oxidized during hotter or drier periods. Some resulting dissolvedSO4 was precipitated as gypsum. Iron from the pyriteprecipitated as FeOOH. Lower, wetter areas formed over time where recharginggroundwater dissolved most of the gypsum. In higher areas with low hydraulicgradients and high net evapotranspiration, SO4 remained asgypsum and in the dissolved phase. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
232.
天津滨海新区区域发展过程研究   总被引:6,自引:1,他引:6  
贾艳杰 《地理科学》2002,22(4):408-412
以天津经济新区-滨海新区为例,以1993-2000年相关统计资料为基础,通过其发展过程和影响因素分析,探讨区域发展特点,滨海新区的研究表明,在我国由计划经济向市场经济体制转型时期,小区域发展是一个相当复杂的过程,政府在滨海新区的发展过程中始终扮演重要角色,中央政府通过经济政策创造宏观发展环境,影响区域发展,地方政府是地方发展战略的决策者,通过促进经济增长引导区域发展方向,形成区域特色,地方开发条件是影响区域发展的基本因素,其在开发的初期阶段尤为重要,它是政府发展战略形成和外商投资选择的基础,环渤海城市间的竞争与联合对天津滨海新区的发展亦产生重大影响。  相似文献   
233.
ABSTRACT. Meltwater contributes to watershed hydrology by increasing summer discharge, delaying the peak spring runoff, and decreasing variability in runoff. High‐elevation snowshed meltwater, including glacier‐derived input, provides an estimated 26.9 percent of summer streamflow (ranging annually from 16 to 40 percent) in the Nooksack River Basin above the town of Deming, Washington, in the North Cascades Range. The Nooksack is a major spawning river for salmon and once was important for commercial, recreational, and tribal fishing, and in the past its flow met the demands of both human and aquatic ecosystems. But the river is already legally overallocated, and demand is rising in response to the rapidly growing human population. Variability in snowshed contributions to the watershed is considerable but has increased from an average of 25.2 percent in the 1940s to an average of 30.8 percent in the 1990s. Overall stream discharge shows no significant increase, suggesting that the glaciers are melting, and/or precipitation levels (or other hydrologic factors) are decreasing at about the same rate. If glaciers continue to recede, they may disappear permanently from the Cascades. If that occurs, their summer contribution to surface‐water supplies will cease, and water‐management policies will need drastic revision.  相似文献   
234.
马彬  张勃  贾艳青  唐敏 《气象学报》2017,75(4):661-671
利用中国内陆1961年以来734个气象台站0 cm地表最低温度作为初、终霜日的参考指标,运用概率密度函数方法定义了不同等级的霜冻指数,重点分析了全球气候状态转变后中国农业区初、终霜日稳定性,异常初、终霜日时空变化特征,以及环流因子变化对初、终霜日的影响。结果显示:(1)青藏高原地区在20世纪90年代之后初霜日明显推后、终霜日明显提前,无霜期明显延长;四川盆地东部、华南地区南部部分站点在20世纪90年代之后霜期缩短明显,出现低频率无霜年份,无霜日站点相对有所增多,出现向北扩展趋势,20世纪90年代之后扩展趋势明显。(2)20世纪80年代初、终霜日相对于其他时段稳定性最强,20世纪90年代稳定性最低,气候状态转变之后青藏高原和新疆南部地区初、终霜日稳定性较强区域面积明显增大;空间上四川盆地东部和华南区初、终霜日稳定性最低,其他区域初、终霜日稳定性相对较低,华南区霜日不稳定区分布范围在21世纪最初10年之后有所减小,稳定区北移明显。(3)异常初、终霜日发生频率:偏早初霜日>偏晚终霜日>特早初霜日>特晚终霜日,气候状态转变前后异常初、终霜日发生频率较高,20世纪90年代偏早初霜日高频率覆盖地区范围最大,其次是20世纪70年代偏早初霜日,气候状态的转变对异常初、终霜日的发生影响较大。(4)各农业区初霜日的推迟、终霜日的提前与极涡缩小、副热带高压北移有直接关系;极涡与副热带高压的位置、强度、面积变化对中国农业区初、终霜日多年气候状态的转变有一定的驱动作用。   相似文献   
235.
Eric D. Carter 《Geoforum》2008,39(1):278-293
Recently, geographers and other scholars have reappraised the state’s spatial properties, roles, and strategies. According to these interpretations, modern states seek to control their subjects and coordinate economic development through various “rational” and “scientific” strategies that involve the standardization, transformation, and bureaucratization of space, territory, and landscape. Through this process social relations are increasingly configured through state discourses and institutions. The role of public health institutions in the development of state spatialities has been relatively underappreciated. This paper explores the establishment and early action of a malaria control campaign in Northwest Argentina, in the early twentieth century. I make three arguments: first, in creating a malaria control program, the Argentine state did not merely respond to a given “social fact” but rather was the key participant in constructing the “malaria problem”. Second, in response to this problem the Argentine state created a new technical-administrative territory, “the malarious zone”, which encompassed several provinces and defined the federal government’s jurisdiction for public health action. Finally, state actors came to understand the malaria problem, and potential solutions to it, through specific “rational” practices of the modern state: surveying, mapping, measurement, and statistical compilation. In its early years, the malaria campaign did not so much control the disease itself, as much as establish control over the “malaria question”, making it indisputably a state project.  相似文献   
236.
A low-angle thrust fault places high-PT granulites (hangingwall) of the Internal Zone of the Neoproterozoic Brasília Belt (Tocantins Province, central Brazil) in contact with a lower-grade footwall (External Zone) comprised of nappes of distal passive margin- and back-arc basin-related supracrustals. The footwall units were emplaced at  750 Ma onto proximal sedimentary rocks (Paranoá Group) of the São Francisco paleo-continent passive margin. The high-PT belt is comprised of 645–630 Ma granulite-facies paragneiss and orthogneiss, and mafic–ultramafic complexes that include three major layered intrusions and metavolcanic rocks granulitized at  750 Ma. These complexes occur within lower-grade metasedimentary rocks in the hangingwall of the Maranhão River Thrust, which forms the Internal Zone–External Zone boundary fault to the north of the Pirineus Zone of High Strain. Detailed lithostructural studies carried out in Maranhão River Thrust hangingwall and footwall metasedimentary rocks between the Niquelândia and Barro Alto complexes, and also to the east of these, indicate the same lithotypes and Sm–Nd isotopic signatures, and the same D1D2 progressive deformation and greenschist-facies metamorphism. Additionally, footwall metasedimentary rocks exclusively display a post-D2 deformation indicating that the Maranhão River Thrust propagated through upper crustal rocks of the Paranoá Group relatively late during the tectonic evolution of the belt. Fault propagation was a consequence of intraplate underthrusting during granulite exhumation. The results allow for a better tectonic understanding of the Brasília Belt and the Tocantins Province, as well as explaining the presence of the Pirineus Zone of High Strain.  相似文献   
237.
热带纬向平均臭氧层动力学系统的重建   总被引:3,自引:2,他引:1  
将TOMS测量的5°N纬向平均O3总量逐日序列作相空间拓展,使O3层的行为特征可用相轨迹刻划。首先计算O3层系统吸引子的分数维,而后把相点作为动力学系统的离散特解集合,反演出描述系统状态随时间演化的数学模型中的客观控制参数值,建立起反映热带O3层短期演化特征的非线性动力学系统。  相似文献   
238.
1INTRODUCTIONWaterqualitytrends,orlackthereof,canreflecttherelationbetwenwaterqualityandhumanactivities-changesinconcentrati...  相似文献   
239.
R. Lee Lyman   《Quaternary Research》2008,70(3):426-432
For more than fifty years it has been known that mammalian faunas of late-Pleistocene age are taxonomically unique and lack modern analogs. It has long been thought that nonanalog mammalian faunas are limited in North America to areas east of the Rocky Mountains and that late-Pleistocene mammalian faunas in the west were modern in taxonomic composition. A late-Pleistocene fauna from Marmes Rockshelter in southeastern Washington State has no modern analog and defines an area of maximum sympatry that indicates significantly cooler summers than are found in the area today. An earliest Holocene fauna from Marmes Rockshelter defines an area of maximum sympatry, including the site area, but contains a single tentatively identified taxon that may indicate slightly cooler than modern summers.  相似文献   
240.
理论气候学中的几个基本问题   总被引:2,自引:1,他引:2  
探讨了当前理论气候学中存在的几个基本问题,并初步阐述了开拓理论气候学研究的一些新方法和新手段。  相似文献   
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