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991.
David?L.?DettmanEmail author Manuel?R.?Palacios-Fest Hudson?H.?Nkotagu Andrew?S.?Cohen 《Journal of Paleolimnology》2005,34(1):93-105
Evaporation dominates the removal of water from Lake Tanganyika, and therefore the oxygen isotope composition of lake water has become very positive in comparison to the waters entering the lake. The surface water in Lake Tanganyika has remained relatively unchanged over the last 30 years with a seasonal range of +3.2 to +3.5 VSMOW. Water from small rivers entering the lake seems to have a 18O value between –3.5 and –4.0, based on scattered measurements. The two largest catchments emptying into the lake deliver water that has a 18O value between these two extremes. This large contrast is the basis of a model presented here that attempts to reconstruct the history of runoff intensity based on the 18O of carbonate shells from Lake Tanganyika cores. In order to use biogenic carbonates to monitor changes in the 18O of mixing-zone water, however, the oxygen isotope fractionation between water and shell carbonate must be well understood. The relatively invariant environmental conditions of the lake allow us to constrain the fractionation of both oxygen and carbon isotope ratios. Although molluskan aragonitic shell 18O values are in agreement with published mineral-water fractionations, ostracode calcite is 1.2 more positive than that of inorganic calcite precipitated under similar conditions. Ostracode shell 18O data from two cores from central Lake Tanganyika suggest that runoff decreased in the first half of this millennium and has increased in the last century. This conclusion is poorly constrained, however, and much more work needs to be done on stable isotope variation in both the waters and carbonates of Lake Tanganyika. We also compared the 13C of shells against predicted values based solely on the 13C of lake water dissolved inorganic carbon (DIC). The ostracode Mecynocypria opaca is the only ostracode or mollusk that falls within the predicted range. This suggests that M. opaca has potential for reconstructing the carbon isotope ratio of DIC in Lake Tanganyika, and may be a useful tool in the study of the history of the lakes productivity and carbon cycle. 相似文献
992.
993.
玉龙喀什河是昆仑山北坡最大的河流——和田河的主要支流。玉龙喀什河同古孜洛克水文站夏洪严重。因此预测最大洪峰出现日期是十分有意义的。用灰色系统理论来预测最大洪峰出现日期,是以原始数据为基础,按累加生成,建立GM(1,1)模型,并通过模型求出平滑度,进而作相对误差检验,合格后再作预测。经过检验,预测基本上符合实际。 相似文献
994.
THE RESEARCH ON THE DISTRIBUTION AND FORMS OF HEAVY METALS IN THE XIANGJIANG RIVER SEDIMENTS 总被引:1,自引:0,他引:1
In this paper, the contents and various forms of Cd, Cu, Zn and Pb in the sediments of the Xiangjiang River have been investigated. The presentation of this paper focuses on the various forms and characteristics of the heavy metals in the column sediments at Xiawan Port of Zhuzhou, which has been severely polluted by a metallurgical plant.The forms of the heavy metals discussed in this paper are: The concentration of the exchangeable forms of Cd, Cu, Zn and Pb, in the forms of carbonates and Fe/ Mn oxide in water, the combination of Cu with organic matter and form, and the proportion of the residue form at each section have been studied. 相似文献
995.
Geospatial-temporal analysis of land-use changes in the Yellow River Delta during the last 40 years 总被引:5,自引:0,他引:5
Qinghua?YeEmail author Gaohuan?Liu Guoliang?Tian Shenliang?Chen Chong?Huang Shupeng?Chen Qingshen?Liu Jun?Chang Yanan?Shi 《中国科学D辑(英文版)》2004,47(11):1008-1024
Research on land use/land cover changes (LUCC)has been the core project of the Global EnvironmentalChanges since the 1990s[1—6]. Scientists at home andabroad have been laying emphasis on integrationstudies on land-use change by “space and process”features[7—10] as researches on LUCC are in a greatdeal. It is of paramount important for us to studyLUCC at various spatial-temporal scales and build aquantitative assessment of land-use conversion by in-tegrated spatial-temporal features. … 相似文献
996.
The Sample Catchment Basin (SCB) mapping technique extends the representativeness of the geochemical features of stream sediments to the surface of the whole upstream drainage basin. SCB boundaries clash with the water divides traced from each sampling point and are limited upstream by the presence of further SCBs. They are also assumed to represent the elementary map unit. The rank of SCBs can be defined counting the number of upstream SCBs along the branches of a fluvial network. The presence of low rank SCBs minimizes the statistical redundancy of measures. The SCB technique is particularly suitable for the geochemical mapping of mountainous or hilly areas and to correctly display the information into a morphological context. This approach can be also valuable in the case of low sampling density, inhomogeneous sampling schemes, and especially when very accurate evaluations of the spatial distribution of chemicals (with natural or anthropogenic origin) are required. 相似文献
997.
太行山前平原非河道条件下地下调蓄功能实验研究--以滹沱河冲洪积平原为例 总被引:5,自引:0,他引:5
摘要:通过实验研究探讨了太行山前平原地下调蓄能力,实验研究表明,在汇水坑渗、井灌和引水渠渗条件下,太行山前冲洪积平原地下调蓄功能不仅与地表积水深度、入渗时间有关,而且还与汇水总量的多少有关。单位时间渗漏量的大小与地表蓄水深度呈正相关关系。地表蓄水深度愈大,单位时间渗漏量愈大;累计渗漏量随着入渗时间的延长而增加,渗漏速率随着累计渗漏量的增加而减小。采用井灌方式进行地下调蓄的关键,是选择具有强渗透性的层位。 相似文献
998.
Granulometric and chemical composition of the Sava River sediments upstream and downstream of the Krsko nuclear power plant 总被引:2,自引:2,他引:0
Visnja?OrescaninEmail author Stipe?Lulic Gordana?Pavlovic Luka?Mikelic 《Environmental Geology》2004,46(5):605-614
Total concentrations of 13 elements (K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, Rb, Sr, Y, Zr, Pb) in the size-fractionated Sava River sediments upstream and downstream of the Krsko nuclear power plant together with metal speciation within bulk sediment have been investigated. Trace metals generally increase with decreasing particle size, however, because of entrapment of organic matter in the 0.63–1 mm fraction, concentrations in the coarser sediment fraction are higher than expected. Exchangeable Pb, Zn, Cu, Mn, Cr and Fe are generally found to represent a negligible fraction of the total metal concentration of the bulk sediment. Seasonal variations of the Pb, Zn and Cu concentrations in the <0.5 mm fraction reflect decreased values during the spring period. Heavy metal concentrations in the 2003 waste water discharges from the Krsko nuclear power plant released into the Sava River were much lower than their maximum allowed values. Combined rubidium and organic matter normalization of the Zn, Pb and Cu concentrations, which was applied on the minus 0.063 mm fraction, indicated three potential sources of contaminants. 相似文献
999.
1000.
文章利用金沙江河谷地貌调查与水利工程选址勘察地质资料,根据河槽纵剖面与18个河谷横剖面的资料以及攀枝花金江河段、会理鱼鲊河段、元谋龙街河段、禄劝凹嘎河段的阶地调查结果,对金沙江下段河槽地貌进行了初步分析,金沙江下段的河谷为典型的深切"V"形河谷,在虎跳峡、乌东德、白鹤滩峡谷段河槽比降发生明显变化。根据河谷阶地下切幅度与形成时代,以T3阶地计算金沙江下段河槽平均下切速率达到0.71~1.18m/ka,以T2阶地计算金沙江下段河槽平均下切速率为0.75~1.36m/ka,因此,近十几万年来,金沙江下段河谷平均下切速率达到0.9~1.0m/ka。现代金沙江河槽底部均堆积了一定厚度的冲积-崩积物覆盖层,最厚的石鼓剖面河床底部冲积物盖层达到173m,一般河段堆积物盖层均达10m以上。金沙江河槽的迁移是河槽下切过程与岸坡崩塌过程综合作用的结果,形成原河槽崩塌阻塞,河槽被动迁移或原河槽改道下切,形成古河槽-离堆山-新河槽的地貌组合,以及河槽侧向迁移3种模式。 相似文献