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301.
海洋碳循环模式中常使用放射性同位素14C来检验该模式的物理模型是否较好地反映了海洋中的大尺度变化的过程。本工作使用的物理模型是包括太平洋、大西洋和南大洋在内的二维温盐环流模式,在给定的年平均海表强迫下积分4000年后,环流达到准稳态,其定常流场用来驱动14C模式。对14C模式积分5000年以上,可得到14C稳态的分布。使用不同的二氧化碳海气交换系数和垂直湍流扩散系数值进行了7个实验,发现使用Broecker等的交换系数方程和扩散系数值依深度从0.6增加到1.45 cm2/s,模拟的结果较好。使用观测到的大气中14C含量,进一步研究了工业革命后及核试验后的14C在海洋中的穿透,模拟结果与现有的一些资料进行了比较,总体上给出了合理的结果。 相似文献
302.
饱和土地基在既有房屋长期荷载作用下,地基土强度参数值随着地基土的排水固结和压密而提高,地基极限承载力也同时增大,如何估算此提高值而挖掘其潜力,传统方法只是借助于统计回归讨论了设计承载力。本文从土力学基本原理出发,借助Prandtl假定,对既有房屋饱和土地基极限承载力的增长进行了探讨。 相似文献
303.
Organic pollutants associated with macromolecular soil organic matter: Mode of binding 总被引:2,自引:0,他引:2
H. H. Richnow R. Seifert J. Hefter M. Link W. Francke G. Schaefer W. Michaelis 《Organic Geochemistry》1997,26(11-12)
A study of ether-linked moieties in macromolecular bound residues of polycyclic aromatic hydrocarbons (PAH) generated in bioremediation experiments was performed using high temperature hydrolysis degradation with subsequent analysis of the products by GC-MS. This hydrolysis reaction was specifically designed to cleave ether bonds including relatively stable diarylether structures. Among the reaction products, aromatic alcohols representing typical microbiologically derived metabolites of PAH were found in addition to natural compounds. Thus, parts of the bound residues appeared to be linked within the macromolecular material by ether bonds. Model experiments with an oxidoreductase enzyme and aromatic alcohols indicate the formation of these ether bonds to be an enzyme-catalysed process. 相似文献
304.
Javier Castro-Larragoitia Utz Kramar Harald Puchelt 《Journal of Geochemical Exploration》1997,58(1):81-91
The Ag---Pb---Zn---Cu---Au mining district of Santa María de La Paz has been extensively exploited for approximately 200 years. Consequences of these activities are several deposits of tailings with high As and heavy metal concentrations, which are completely unstable. The climate is semiarid and as the dumps have no protective cover, material from the dumps is dispersed by strong winds. It is also washed out during seasonally heavy rainfalls. By these processes approximately 100 km2 of surrounding have been contaminated by dump material. The As and heavy metal content of the soils was determined as well as their level in crops (Zea Maize) from agricultural lands in the vicinity of the dumps. In the direction of prevailing winds concentrations up to 1000 ppm Zn, 400 ppm Pb, 16 ppm Cd, 550 ppm Cu and 300 As have been detected in top soils. Using fuzzy cluster analysis the different contamination sources could be identified. Grains of corn from contaminated sites showed no critical concentrations, but leaves which are also used tor fodder, have As-concentrations up to 20 ppm. 相似文献
305.
我国特殊岩土研究 总被引:1,自引:0,他引:1
顾宝和 《水文地质工程地质》1997,24(2):43-45
本文分析,总结了我国特殊岩土理论与应用研究方面的新进展,内容涉及湿陷性黄土,软土膨胀岩土,红土,软岩和特殊土的结构性,指出需要进一步研究的问题,最后对特殊土的研究方法做了阐述。 相似文献
306.
土壤表面蒸发阻力模型与田间测定方法 总被引:6,自引:0,他引:6
土壤表面蒸发阻力是计算土壤蒸发率的关键参数。本文讨论土壤表面蒸发阻力的概念,一层,二层理论模型与经验模型,并以在澳大利亚进行的田测定为例,说明田间测定与计算方法,并以计算沟中的蒸发率为例,介绍其应用方法。 相似文献
307.
Yitzchak Gutterman 《Journal of Arid Environments》1997,37(4):665-681
About 400 Nubian ibex (Capra ibex nubiana) dig many hundreds of temporary night beds, approximately 80 cm × 110 cm and 15 cm deep, on slopes near the edges of the cliffs bordering the Zin valley. The beds are used according to the wind direction and the size of the ibex group, which depends on the ibex social behaviour during the year.The diggings are gradually abandoned and become important microhabitats for seed accumulation and germination, seedling development and annual plant establishment. These are influenced by soil salinity, slope direction and angle, digging depth, and the time since the diggings were abandoned. A greater variety of plant species and plant density were found in these diggings than upslope from the diggings. 相似文献
308.
I. A. Jaiyeoba 《Journal of Arid Environments》1996,33(4):473-482
Soil was sampled from cropping fields in radial patterns from beneathAcacia albida, Parkia bigloboza(Jacq.) Benth. andEucalyptus camaldulensisDehnh. near Zaria, Nigeria. Results of analysis show a significant coarsening of soil texture and a decrease in organic matter and cation exchange capacity with increasing distance from all three tree species at a depth of 0–15 cm. Concentrations of nitrogen and some exchangeable cations decreased significantly with increasing distance from beneath acacia and parkia, and soil pH decreased with increasing distance from eucalyptus. The implication of the results for land management are discussed in relation to increasing productivity and soil use sustainability. 相似文献
309.
塔克拉玛干沙漠土壤沙化发生条件及对土壤性状影响 总被引:1,自引:0,他引:1
土壤沙化是土壤发育逆向演替恢复母质特性的过程,土壤沙化发生条件可以概括为4个方面:土壤干旱是沙化的根本条件、植被衰败为风沙活动创造了条件、土壤质地轻是沙化物质基础、大风和频繁起沙风是沙化的动力条件。土壤沙化结果使土壤粗粒化、贫瘠化,同时也使土壤含盐量降低。 相似文献
310.
The purpose of this study was to elucidate the floristic and structural characteristics of simple alluvial fan vegetation of southern Sinai and to relate them to environmental variation. The main question addressed was: how does the floristic composition of fan habitats, species richness and life-form vary in relation to environmental change? Thirty-seven alluvial fans, randomly selected in two mainwadis(WadiFeiran andWadiDahab) were analysed quantitively. Two-way Indicator Species Analysis (TWINSPAN) classification and Canonical Correspondence Analysis (CCA) were applied in successive stages of the data analysis to describe vegetational variation in relation to physical gradients. Seven main clusters of fans were defined on the basis of environmental variation. These clusters are divided into three main groups of species richness. Species richness varied along a moisture gradient. The richest fans were the driest habitats, indicating that maximum species richness did not occur at high moisture availability. The moisture gradient is a complex gradient correlated with elevation, slope, climatic aridity, soil texture and the nature of the soil surface. Fine sand, silt plus clay and calcium carbonate showed significant differences between the internal groups and subgroups of the first and second level of the TWINSPAN classification. 相似文献