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991.
Soil Seed Banks and Forest Succession Direction Reflect Soil Quality in Ziwuling Mountain,Loess Plateau,China 总被引:1,自引:0,他引:1
The paper presents a study by taking the soil seed banks and vegetation successions of the forests in Ziwuling Mountain as indicators to analyze the effects of the ages, and the litter layers and soil depths at growing locations in seven types of forest communities on their seed bank formations and soil quality. The results showed that the seed banks at different growing locations in the communities increased in the order of upper slope, middle slope, and lower slope; the seed storages of the seed banks in the different layers of the communities varied, much more higher in the litter layers than in 0–15 cm, and the seed storages of the seed banks in the seven types of forest communities ranked in the increasing order of Pinus tabulaeformis forest, Pinus shenkaneusis forest, Quercus liaotungensis forest, Populus davidiana forest, Betula platyphylla forest, scrub communities, and grassland communities; in the meantime, the seed storage of seed banks peaked in 30–50 years old P. shenkaneusis forest, 30–40 years old P. tabulaeformis forest, 15–30 years old Q. liaotungensis, and P. davidiana and B. platyphylla forests, and 10–15 years old scrub and grassland communities, and the ages of the communities varied with the seed storages of the seed banks in a significantly correlative manner following a fitted exponential equation. In addition, the soil seed banks of the seven types of communities consisted of rich and diverse species with the herbaceous and shrub species greatly outnumbering the arbor species; in general, the coniferous forests were composed of 31 kinds of plants, the deciduous and broadleaf forests consisted of 20–29 plant species, the shrubs contained 27 plant species, and the herbaceous plants numbered 20 plant species; The various species compositions contained only 4–6 arbor species with most being foreign species. In each of the compositions, Bothriochloa ischemum was the grassland plant with the highest occurrence frequency, Sophora viciifolia and Hippophae reamnoides were the shrub plants with the highest occurrence frequencies, and Q. liaotungensis was the arbor plant with the highest occurrence frequency, and they followed by P. shenkaneusis and P. tabulaeformis. These results showed that soil seed banks and forest successions are better indicators for soil quality from natural successions. 相似文献
992.
993.
哈萨克斯坦滨里海盆地东缘上石炭统KT-Ⅰ油层组主要发育局限海台地-开阔海台地碳酸盐沉积,间夹蒸发岩层。由于区域性白云石化作用,KT-Ⅰ油层组中白云岩广泛分布,为主要油气储集层。研究表明,白云岩中白云石为泥晶、粉晶或细晶,半自形-他形;略富钙,有序度较低(0.336~0.504);δ18OPDB值在-1.06‰~+2.45‰之间,比石炭纪海水(δ18OPDB值介于-1‰~-2‰之间)偏正;δ13CPDB值在+3.36‰~+5.94‰之间,与石炭纪海水(δ13CPDB值介于+3.1‰~+4.7‰之间)接近;锶同位素值接近石炭纪海水(87Sr/86Sr值在0.7082~0.7088之间);微量元素Mn含量平均为92.57 μg/g,Fe含量平均为447.52 μg/g,接近被交代的灰岩含量;Na和K含量的平均值分别为198.80 μg/g 和5.89 μg/g,显示交代流体为蒸发海水。上述岩石学和地球化学资料表明,研究区石炭系KT-Ⅰ油层组白云岩具有渗透-回流机理白云岩的特征。 相似文献
994.
Prediction of streamwise flow-induced vibration of a circular cylinder in the first instability range 总被引:1,自引:0,他引:1
The streamwise flow-induced vibration of a circular cylinder with symmetric vortex shedding in the first instability range is investigated, and a wake oscillator model for the dynamic response prediction is proposed. An approach is applied to calibrate the empirical parameters in the present model; the numerical and experimental results are compared to validate the proposed model. It can be found that the present prediction model is accurate and sufficiently simple to be easily applied in practice. 相似文献
995.
An analytical method is developed to study the sheltering effects on arc-shaped floating perforated breakwaters. In the process of analysis, the floating breakwater is assumed to be rigid, thin, vertical, and immovable and located in water with constant depth. The fluid domain is divided into two regions by imaginary interface. The velocity potential in each region is expanded by eigenfunction in the context of linear theory. By satisfying continuity of pressure and normal velocity across the imaginary fluid interface, a set of linear algebraic equations can be obtained to determine the unknown coefficients for eigenfunction expansions. The accuracy of the present model was verified by a comparison with existing results for the case of arc-shaped floating breakwater. Numerical results, in the form of contour maps of the non-dimensional wave amplitude around the breakwater and diffracted wave amplitude at typical sections, are presented for a range of wave and breakwater parameters. Results show that the sheltering effects on the arc-shaped floating perforated breakwater are closely related to the incident wavelength, the draft and the porosity of the breakwater. 相似文献
996.
Impact of seasonal tide variation on saltwater intrusion in the Changjiang River estuary 总被引:1,自引:0,他引:1
An improved 3-D ECOM-si model was used to study the impact of seasonal tide variation on saltwater intrusion into the Changjiang River estuary, especially at the bifurcation of the North Branch (NB) and the South Branch (SB). The study assumes that the river discharge and wind are constant. The model successfully reproduced the saltwater intrusion. During spring tide, there is water and salt spillover (WSO and SSO) from the NB into the SB, and tidally averaged (net) water and salt fluxes are 985 m3/s and 24.8 ton/s, respectively. During neap tide, the WSO disappears and its net water flux is 122 m3/s. Meanwhile, the SSO continues, with net salt flux of 1.01 ton/s, much smaller than during spring tide. Because the tidal range during spring tide is smaller in June than in March, overall saltwater intrusion is weaker in June than in March during that tidal period. However, the WSO and SSO still exist in June. Net water and salt fluxes in that month are 622 m3/s and 15.35 ton/s, respectively, decreasing by 363 m3/s and 9.45 ton/s over those in March. Because tidal range during neap tide is greater in June than in March, saltwater intrusion in June is stronger than in March during that tidal period. The WSO and SSO appear in June, with net water and salt fluxes of 280 m3/s and 8.55 ton/s, respectively, increasing by 402 m3/s and 7.54 ton/s over those in March. Saltwater intrusion in the estuary is controlled by the river discharge, semi-diurnal flood-ebb tide, semi-monthly spring or neap tide, and seasonal tide variation. 相似文献
997.
???????GPS???????????????泤??????????????????????????????GPS????????????????????GPS???????????辫??????????????????GPS??????衣???????????GPS???????????????????????????????????????????? 相似文献
998.
KRISTEN McDonald 《山地科学学报》2012,9(3):403-413
Qinghai Province is an important component of the Qinghai-Tibet Plateau in China. Scientific evaluation of the suitability of Qinghai’s climate for tourism can contribute to overcoming obstacles posed by climate on sustainable tourism development in Qinghai Province, including disparities between the low and high seasons, high altitude health concerns, and weather events. A tourism climate suitability evaluation model of the Qinghai-Tibet Plateau is constructed (Tourism Climate Suitability Index, or TCSI), and tourism climate suitability is comprehensively evaluated for Qinghai Province from climate data from 1960 to 2009. Results show that: (I) There is clear distributional characteristics of spatial-temporal variability of TCSI values in Qinghai Province. (II) Tourism climate suitability in Qinghai Province has significant seasonal and regional differences. The year is divided into a very suitable period (July and August), suitable tourism periods (from April and October), less suitable periods (From Nov to Mar). June to August is the most suitable tourism period in Qinghai. Qinghai Province is divided into five levels of tourism climate suitability: most suitable regions, very suitable regions, suitable regions, less suitable regions, and unsuitable region. (III) The key factor which influences regional differences in tourism climatic suitability is atmospheric oxygen. And the key factors which chiefly influence seasonal differences of tourism climate suitability are temperature and humidity, the wind chill factor, and barrier weather. 相似文献
999.
Subsurface flow processes in sloping cropland of purple soil 总被引:3,自引:1,他引:2
Subsurface flow is a prominent runoff process in sloping lands of purple soil in the upper Yangtze River basin.However,it remains difficult to identify and quantify.In this study,in situ runoff experimental plots were used to measure soil moisture dynamics using an array of time domain reflectometry(TDR) together with overland flow and subsurface flow using isolated collecting troughs.Frequency of preferential flow during rainfall events and the controls of subsurface flow processes were investigated through combined analysis of soil properties,topography,rainfall intensity,initial wetness,and tillage.Results showed that subsurface flow was ubiquitous in purple soil profiles due to welldeveloped macropores,especially in surface soils while frequency of preferential flow occurrence was very low(only 2 cases in plot C) during all 22 rainfall events.Dry antecedent moisture conditions promoted the occurrence of preferential flow.However,consecutive real-time monitoring of soil moisture at different depths and various slope positions implied the possible occurrence of multiple subsurface lateral flows during intensive storms.Rainfall intensity,tillage operation,and soil properties were recognized as main controls of subsurface flow in the study area,which allows the optimization of management practices for alleviating adverse environmental effects of subsurface flow in the region. 相似文献
1000.
在室内水泥池用淡水和海水培育美洲鲥(Alosa sapidissima)仔鱼,研究两种培育模式下美洲鲥的生长。结果表明,美洲鲥仔稚鱼可较好地适应海水培育环境,经33 d的培育,淡、海水培育模式下美洲鲥平均全长日增长分别为0.965 7 mm和0.922 0 mm,前者略高于后者;成活率分别为70.3%和74.7%,海水培育模式成活率略高于淡水培育模式;仔稚鱼培育期间的生长模型方程分别为Y=9.614 3+0.500 7 X+1.326 6 X2和Y=9.478 3+0.558 4 X+1.038 0 X2(Y为全长,X为日龄)。可见,两种培育模式生长差异不显著,只要生产条件许可,均可采用淡水或海水培育美洲鲥苗种。 相似文献