Element diffusion ability in metasomatic agents and its effect on chemical characteristics of metasomatized peridotites

The partial melting and metasomatism are two most important geological processes of changing chemical compositions of mantle. Extracting partial melt from primitive mantle leads residual mantle to deplete in- compatible elements, whereas the metasomatism …     

森林冠层上下湍流谱结构和耗散率

利用新型三维超声风速 /温度仪 ,根据在长白山原始森林冠层上下两个高度上测量的湍流资料 ,采用涡动相关法计算和分析了森林冠层上下湍流谱的结构、局地各向同性和耗散率 .结果表明 ,在惯性副区 ,归一化湍流谱遵从 - 23的指数规律 ;在森林冠层上 ,尽管谱的形状与均匀表面的一致 ,但是 ,大气湍流是非各向同性的 ;而在森林冠层内则是近似各向同性的 ;森林冠层上下湍流能量和热量耗散率比典型草原和牧场的结果大 ,揭示了森林粗糙表面在湍流输送过程中的动力扰动和对大涡的破碎作用     

地球自转长期稳定性的一种解释

古地磁数据显示了在古地磁和热点参照系之间的不到1000km的运动,即100Ma(百万年)期间的真极移,它意味着地球自转轴一直是相当稳定的。这个长期的自转稳定性可以用晚中生代和新生代的大规模板块运动的缓慢变化来解释,只要俯冲带的岩石层是地幔对流导致的地幔密度不均匀性的主要部分。因此,不需要引入其他诸如自转不规则的缓慢再调整之类的机制,就可以解释所观测到的缓慢的真极移。     

CONCENTRATION AND FLUX OF CO_2, TURBULENCE FLUXES AND RADIATION BALANCE IN THE NEAR SURFACE LAYER OVER WHEAT FIELD

The gradient of CO_2 concentration, photosynthetically active radiation (PAR). net radiation.soil heat flux, profiles of wind speed, and air temperature and humidity were measured above awheat field during May and June 1985 at Beijing Agro-Ecosystems Experimental Station. Beijing,China. Fluxes of carbon dioxide, sensible heat, latent heat and momentum were calculated byusing the aerodynamic method. The observation site. equipment, calibration techniques, theerrors associated with the measurement, and the computational procedures are described. Theresults show that the diurnal variations of amplitude of CO_2 concentrations were 103.8 to 27. 0. 86.3 to 22.8 and 69.8 to 11.6 ppm: the average CO_2 concentrations were 331.5. 339.9 and 364.6 ppmfor the photosynthesis type, and 369.6. 364.0 and 375.2 ppm for the respiration type at 1. 2 and10 m above surface, respectively, from May 14 to June 15. In the daytime, transfer direction ofthe CO_2 fluxes and gradients is from air to crop canopy, and at noon (1100 to 1300 BT (BeijingTime)) the transfer rate reaches negative maximum value. At night, transfer of CO_2 fluxes andgradients is in the reversed direction and reaches positive maximum in the early morning (0400 to0600 BT). There are strong negative correlations between CO_2 flux and the net radiation (Rn),available energy (H LE). photosynthetically active radiation (PAR) and momentum flux (τ).     

THE FLOODS AND DROUGHTS OF THE LOWER YANGTZE VALLEY AND THEIR PREDICTIONS

During Ching dynasty from 1644 to 1911, an interval of 268 years, there occurred in the lower Yangtze valley 197 floods and 156 droughts. The most serious droughts came in 1785, 1814, and 1856; and the most disastrous floods in 1680, 1823     

A Comparlson between North Shensi basin&Szechuan basin

One of the most conspicuous feature in Chinese geomorphology is the similardevelopment of some topographic forms such as basins, plateaus etc. betweenthe north and the south China. The basin of North Shensi in the north and     

Modelling of sediment movement in the surf and swash zones

Under the action of marine currents, non-cohesive sediments evolve by bed-load, by saltation or suspension depending on their granulometry. Several authors have considered that the movement of sediment...     

Analysis of karst aquifer spring flows with a gray system decomposition model

There are approximately 470,000 km(2) of karst aquifers that feed many large springs in North China. Turbulent flow often exists in these karst aquifers, which means that the classical ground water model based on Darcy's law cannot be applied here. Ground water data are rare for these aquifers. As a consequence, it is difficult to quantitatively investigate ground water flow in these karst systems. The purpose of this study is to develop a parsimonious model that predicts karst spring discharge using gray system theory. In this theory, a white color denotes a system that is completely characterized and a black color represents a system that is totally unknown. A gray system thus describes a complex system whose characteristics are only partially known or known with uncertainty. Using this theory, we investigated the karst spring discharge time series over different time scales. First, we identified three specific components of spring discharge: the long-term trend, periodic variation, and random fluctuation. We then used the gray system model to simulate the long-term trend and obtain periodic variation and random fluctuation components. Subsequently, we developed a predictive model for karst spring discharge. Application of the model to Liulin Springs, a representative example of karst springs in northern China, shows that the model performs well. The predicted results suggest that the Liulin Springs discharge will likely decrease over time, with small fluctuations.     

Heavy metal contamination in western Xiamen Bay sediments and its vicinity, China

Concentrations of selected heavy metals (Cu, Pb, Zn, Cd, Cr, Ni and Fe) in surface sediments from nine sites in western Xiamen Bay and its vicinity were studied in order to understand current metal contamination due to urbanization and economic development in Xiamen, China. The sediment samples were collected in December 2004 and July 2005 respectively in order to examine temporal variations. In this study, we found that heavy metal concentrations in surface sediments sampled in the western Xiamen Bay and adjacent Maluan Bay and Yuandang Lagoon varied from 19 to 97mg kg(-1) for Cu, 45 to 60mg kg(-1) for Pb, 65 to 223mg kg(-1) for Zn, 0.11 to 1.01mg kg(-1) for Cd, 37 to 134mg kg(-1) for Cr, 25 to 65mg kg(-1) for Ni and 3.08 to 4.81% for Fe. Although all metal concentrations in sediments meets Chinese National Standard Criteria for Marine Sediment Quality, both metal enrichment factors (EF) and geoaccumulation index (I(geo)) show that Pb contamination exists in the entire study area and contamination of other metals are also present in some locations depending on the sources, of which sewage outlets and commercial ports are the main sources of contaminants to the area. This study shows that using the sediment quality standard criteria only to assess sediments cannot properly reflect sediment contamination. A multiple approaches should be applied for the sediment quality assessment.     

Effects of ulvoid (Ulva spp.) accumulation on the structure and function of eelgrass (Zostera marina L.) bed

The objective of this study is to clarify the effect of ulvoid (Ulva spp.) accumulation on the structure and function of an eelgrass bed by the coast of Iwakuni, Seto Inland Sea, Japan. We monitored eelgrass shoot density and volume of ulvoid accumulation in the study site and evaluated effects of the accumulated ulvoid canopy on the percent survival, seedling density, growth rates, photosynthetic photon flux density (PPFD) and carbon contents of eelgrass. Eelgrass shoot density decreased by the accumulation of ulvoid. Also, seedling density decreased by the increase in the ulvoid volumes. Shoot density, seedling density and leaf elongation were negatively correlated with ulvoid volume. Carbon contents in eelgrass decreased by the accumulation of ulvoid (canopy height: 25cm). These results suggest that accumulation of ulvoid bloom has significant negative impacts on the structure and function of eelgrass bed, i.e. decreases in vegetative shoot density, seedling density, shoot height and growth rate.