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排序方式: 共有313条查询结果,搜索用时 15 毫秒
81.
Yang Yang Jianjun Jia Liang Zhou Jianhua Gao Wenhua Gao Benwei Shi Zhanhai Li Ya Ping Wang Shu Gao 《地球表面变化过程与地形》2020,45(11):2463-2477
Coastal deltaic deposits are the primary locations for sediment storage on Earth, and quantifying their source contributions is a critical prerequisite for delineating S2S patterns in marginal seas. In most cases, quantification for the contribution by fine-grained sediments (i.e. particle size < 63 μm) is considered to be representative to constrain the overall sediment supply. However, this approach may be inappropriate because large differences exist between the two quantities. Here we propose an approach to solve the problem, which is based on the maximum number of tracers from multiple sediment size fractions incorporating the content of all size fractions of sediment. Using this approach, absolute source contributions during the Holocene are reconstructed that provide a first-order model for the S2S pattern of the central Jiangsu coast, China. The Huanghe River is the strongest driver for the Holocene sedimentation, with a mean contribution of ~72 ± 6% (1417 × 108 t). The absolute contributions from the Changjiang and offshore areas were of secondary importance, (i.e. ~17 ± 1% (330 × 108 t) and ~11 ± 5% (217 × 108 t), respectively). The results show that a large difference between the relative and absolute source contributions and the assumption that the relative contribution represents the absolute contribution is invalid in a coastal setting. The impact of the Huanghe is mainly based on episodic events, such as the event of 1128–1855 AD . The model also reveals that the offshore sediments are as important as the Changjiang sediments for the central Jiangsu coast during the Holocene. Thus, the model provides both the time series and overall quantities of sediment supply during the formation and evolution of the Holocene tidal flats on the Jiangsu coast. Our findings shed new light on quantitative analysis of sediment sources applicable to future S2S studies of marginal seas. © 2020 John Wiley & Sons, Ltd. 相似文献
82.
A non‐equilibrium sorption—advection—diffusion model to simulate miscible pollutant transport in saturated–unsaturated soils is presented. The governing phenomena modelled in the present simulation are: convection, molecular diffusion, mechanical dispersion, sorption, immobile water effect and degradation, including both physical and chemical non‐equilibrium processes. A finite element procedure, based on the characteristic Galerkin method with an implicit algorithm is developed to numerically solve the model equations. The implicit algorithm is formulated by means of a combination of both the precise and the traditional numerical integration procedures. The stability analysis of the algorithm shows that the unconditional stability of the present implicit algorithm is enhanced as compared with that of the traditional implicit numerical integration procedure. The numerical results illustrate good performance of the present algorithm in stability and accuracy, and in simulating the effects of all the mentioned phenomena governing the contaminant transport and the concentration distribution. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
83.
����ǿ��ǰ���ϵ��������TEC�쳣�����о� 总被引:2,自引:0,他引:2
???????GPS??TEC???????VTEC???????????15?????????????????ο????????????????????VTEC???? 2006??12??26??????????????7.2???????2008??5??12????8????????????????????????????8???????????????????????????????????????????????????????????????????VTEC????????????????????????????????VTEC?????????????????????????????????????????????????????? 相似文献
84.
85.
江西晚三叠世安源煤系沉积特征及沉积环境探讨 总被引:2,自引:0,他引:2
江西省晚三叠世安源煤系,为江西省主要含煤地层之一,其煤种为烟煤,煤质好且为较好的动力用煤。然而,由于煤矿资源减少,造成我省乃至全国动力用煤的紧张状况,在一定程度上制约了经济的发展。通过对江西晚三叠世安源煤系(组)的沉积特征和沉积环境的分析,指出了研究区安源煤系的分布状况和赋存特征,对寻找后续煤炭资源具有一定的指导意义。 相似文献
86.
河网自动综合中Delaunay三角的应用 总被引:7,自引:0,他引:7
在地图数据处理和GIS分析应用中,河网自动综合是制图综合的一个重要组成部分,其中涉及到从双线河向单线河转化的过程及河间距的研究。本文利用Delaunay三角网中的三角形的边连接具有的空间邻近性特点,介绍了用Delaunay三角网结构的骨架线来提取双线河流中轴线及研究河间距量算的方法。 相似文献
87.
Response of streamflow to climate change and human activity in Xitiaoxi river basin in China 下载免费PDF全文
In recent years, the Xitiaoxi river basin in China has experienced intensified human activity, including city expansion and increased water demand. Climate change also has influenced streamflow. Assessing the impact of climate variability and human activity on hydrological processes is important for water resources planning and management and for the sustainable development of eco‐environmental systems. The non‐parametric Mann–Kendall test was employed to detect the trends of climatic and hydrological variables. The Mann–Kendall–Sneyers test and the moving t‐test were used to locate any abrupt change of annual streamflow. A runoff model, driven by precipitation and potential evapotranspiration, was employed to assess the impact of climate change on streamflow. A significant downward trend was detected for annual streamflow from 1975 to 2009, and an abrupt change occurred in 1999, which was consistent with the change detected by the double mass curve test between streamflow and precipitation. The annual precipitation decreased slightly, but upward trends of annual mean temperature and potential evapotranspiration were significant. The annual streamflow during the period 1999–2009 decreased by 26.19% compared with the reference stage, 1975–1998. Climate change was estimated to be responsible for 42.8% of the total reduction in annual streamflow, and human activity accounted for 57.2%. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
88.
Poyang Lake Migratory Bird Sanctuary includes Bang Lake, Sha Lake, Dahu Lake, and estuaries of the Xiu and Gan Rivers in the Migratory Bird Natural Reserve. Water samples were collected and analyzed to study spatial and temporal water quality variation. Strong seasonal variation of water quality was found. The water quality of Bang Lake was relatively poor compared to Sha and Dahu Lakes in the wet season, but better in the normal season. During the dry season, the water quality of Bang Lake is negatively affected by the activity of migratory birds. According to the correlation analysis of monthly concentrations of each parameter, the concentrations of COD, NH?-4–N, and NO3–N were highly correlated. The correlation index was 0.829 and significance index was0.042 \ 0.05. From north to south within Bang Lake, the concentration of TN decreased; however, the concentration of Chl-a increased. From east to west within Bang Lake,concentrations of COD, NH?4–N, NO-3–N, and Chl-a increased. The Xiu and Gan Rivers influence the water quality of Bang Lake, especially in the northeast area of the lake. The water quality of Bang Lake only reached Chinese water quality standard level IV or V according to a fuzzy comprehensive evaluation. The evaluation factors impacting Bang Lake are TN[TP[NH?4–N[COD, in order of decreasing importance. The waters of Poyang Lake Migratory Bird Sanctuary have been polluted; one of the important contributing factors was migratory birds’ disturbance and feces. 相似文献
89.
Impacts of climate variability and human activities on decrease in streamflow in the Qinhe River,China 总被引:1,自引:0,他引:1
Under the impacts of climate variability and human activities, there are statistically significant decreasing trends for streamflow in the Yellow River basin, China. Therefore, it is crucial to separate the impacts of climate variability and human activities on streamflow decrease for better water resources planning and management. In this study, the Qinhe River basin (QRB), a typical sub-basin in the middle reach of the Yellow River, was chosen as the study area to assess the impacts of climate variability and human activities on streamflow decrease. The trend and breakpoint of observed annual streamflow from 1956 to 2010 were identified by the nonparametric Mann–Kendall test. The results showed that the observed annual streamflow decreased significantly (P?<?0.05) and a breakpoint around 1973 was detected. Therefore, the time series was divided into two periods: “natural period” (before the breakpoint) and “impacted period” (after the breakpoint). The observed annual streamflow decreased by 68.1 mm from 102.3 to 34.2 mm in the two periods. The climate elasticity method and hydrological model were employed to separate the impacts of climate variability and human activities on streamflow decrease. The results indicated that climate variability was responsible for 54.1 % of the streamflow decrease estimated by the climate elasticity method and 59.3 % estimated by the hydrological modeling method. Therefore, the climate variability was the main driving factor for streamflow decrease in the QRB. Among these driving factors of natural and anthropogenic, decrease in precipitation and increase in water diversion were the two major contributions of streamflow reduction. The finding in this study can serve as a reference for regional water resources management and planning. 相似文献
90.
非线性滤波在含“开关”过程的资料同化中的应用研究 总被引:2,自引:0,他引:2
利用一个描述实际数值天气预报模式中比湿在单格线上随时间发展的偏微分方程作为控制方程,研究分析了非线性滤波方法在含开关过程的资料同化中的有效性和可行性。首先在贝叶斯理论框架下,讨论了一般情形的非线性滤波方法,然后对基于粒子滤波(PF)和基于集合卡尔曼滤波(EnKF)的两种同化方法进行对比,由于EnKF是通过对集合成员的统计分析得到的误差分布的一阶矩和二阶矩来近似真实误差分布的,所以当用高斯分布近似真实误差分布所产生的误差较大时,基于EnKF的同化方法得到的结果也会有较大的误差。最后分别从观测算子为线性和非线性、观测误差为高斯型和非高斯型4种情形进行数值试验,结果显示当观测误差为高斯型时,无论观测算子为线性还是非线性,基于PF和基于EnKF的同化方法都能克服由开关过程给资料同化带来的困难,给出满意的同化结果;而当观测误差为非高斯型时,EnKF出现滤波不稳定,产生了非理想的同化结果,但PF方法仍然能够有效地发挥作用,给出满意的同化结果。 相似文献