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201.
Glass-etched micromodel and visualization technology were used to research the removal mechanisms of residual light non-aqueous
phase liquids (LNAPLs) droplets at pore scale. In this research, n-hexadecane was selected as the LNAPL model substance. During the injection of de-ionized water into the pore channel, residual
n-hexadecane droplet was removed quickly at first, then gradually became slow and finally remained nearly invariable; the droplet
size after a definite time depends on its initial value. The relationship between total volume of residual n-hexadecane and time can be described by a logarithmic equation: V = V
0 − 0.0152lnt + 0.0360 (0 < t < 9,420, R
2 = 0.9621). Based on percolation theory, the relationship between fluid percolation velocity in pores and time was determined
through the analysis of residual n-hexadecane droplet size and the flowing characteristics of injected fluid. Gaussian model was used to fit the cumulated dissolved
n-hexadecane, the correlation coefficient R
2 = 0.97269. The removal process of n-hexadecane in network model experiment is similar to that of the sand column flushing experiment, which indicates that the
mass transfer micro-mechanism of network model experiment could be used to interpret the results of column flushing experiment. 相似文献
202.
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204.
Phosphorus biological cycle in the different Suaeda salsa marshes of the Yellow River estuary, China
Zhigao Sun Xiaojie Mou Hanqin Tian Hongli Song Huanhuan Jiang Jinyong Zhao Wanlong Sun Wenguang Sun 《Environmental Earth Sciences》2013,69(8):2595-2608
Much uncertainty exists in the phosphorus (P) cycle in the marshes of the intertidal zone. This study explored the P cycling in the two Suaeda salsa marshes [middle S. salsa marsh (MSM) and low S. salsa marsh (LSM)] of the Yellow River estuary during April 2008 to November 2009. Results showed seasonal fluctuations and vertical distributions of P in different S. salsa marsh soils, and variations in P content in different parts of plants due to water and salinity status. The N/P ratios of the different S. salsa were 9.87 ± 1.23 and 15.73 ± 1.77, respectively, indicating that plant growth in MSM was limited by N, while that in LSM was limited by both N and P. The S. salsa litter in MSM released P to the environment throughout the year, while that in LSM immobilized P from the environment at all times. The P absorption coefficients of S. salsa in MSM and LSM were very low (0.0010 and 0.0001, respectively), while the biological cycle coefficients were high (0.739 and 0.812, respectively). The P turnovers among compartments of MSM and LSM showed that the uptake amounts of roots were 0.4275 and 0.0469 g m?2 year?1 and the values of aboveground parts were 1.1702 and 0.1833 g m?2 year?1, the re-translocation quantities from aboveground parts to roots were 0.8544 and 0.1452 g m?2 year?1, the translocation amounts from roots to soil were 0.0137 and 0.0012 g m?2 year?1, the translocation quantities from aboveground living bodies to litter were 0.3157 and 0.0381 g m?2 year?1, and the annual return quantities from litter to soil were less than 0.0626 and ?0.0728 g m?2 year?1 (minus represented immobilization), respectively. P was an important limiting factor in S. salsa marshes, especially in LSM. S. salsa was seemingly well adapted to the low-nutrient condition and the vulnerable habitat, and the nutrient enrichment due to the import of N and P from the Yellow River estuary would be a potential threat to the S. salsa marshes. 相似文献
205.
黄淮海流域旱涝时空分布及组合特性 总被引：1，自引：0，他引：1
以黄淮海流域及其周边地区204个气象站点1961-2010年逐日降水过程资料、国家1:25万DEM数据和1:20万土地利用数据为基础,在利用降水Z指数对黄淮海流域旱涝进行评价的基础上,采用下垫面数据对结果进行修正,并分析黄淮海流域旱涝面积的时间变化特征,对黄淮海地区的易旱区、易涝区进行了划分,进一步选取集对分析法划分了流域内季节间旱涝交替的易发区。结果表明:黄淮海流域内夏秋两季旱涝问题较为严重,且秋旱面积上升趋势较为明显;黄河和海河流域以干旱居多,淮河则是干旱和雨涝并存,季节间的旱涝交替多集中在淮河流域中上游地区。 相似文献
206.
207.
以干旱易发区海河流域为例,利用流域内及其周边地区58个气象站点1961-2010年逐日气象观测数据,结合累积相对湿润度指数和模糊集对评价法,考虑了干旱的累积效应以及评价标准等级边界的模糊性和评价因子的时程分配,分析了海河流域干旱时空变化特征。结果表明:①近50年来流域主要干旱类型为中旱和重旱,平均面积分别约为7.30万km2和7.78万km2,重旱面积呈现出显著的增加趋势;②近25年来,重旱易发区范围表现出扩张的态势,1985-2010年重旱易发区面积达到14.9万km2,为1961-1985年的1.6倍。 相似文献
208.
首先利用Morlet小波对汉江流域降水进行多时间尺度分析,然后分析主要周期下汉江流域降水与74个环流因子的相关性.结果表明:近50年,汉江流域降水有4,7和18年的主要周期,其中以18年的主要周期最为突出,降水呈现偏少的趋势,同时降水量与西太平洋副高面积指数、冷空气、东太平洋副高北界、北半球极涡中心位置等14个环流因子具有非常强的正相关,而与东亚槽位置、太平洋区极涡强度指数、亚洲区极涡强度指数有非常强的负相关.研究成果将为今后提高汉江流域降水预报水平和有效开展汉江流域及长江中下游防汛抗旱工作提供科学依据. 相似文献
209.
气候变化和人类活动在沙漠化过程中相对作用评价综述(英文) 总被引：2，自引：1，他引：2
Climate change and human activities are the two kinds of driving forces in desertification,and assessing their relative role in desertification is of great significance to deeply understanding the driving mechanisms and preventing desertification expansion.This paper has systematically reviewed the progress of the researches on assessing the relative role of climate change and human activities in desertification from qualitative,semi-quantitative and quantitative aspects respectively.The authors found that there were still some problems in the previous researches.For example,the subjectivity in assessment was obvious,the assessment cannot be easily repeated,and the assessment and its results were always based on administrative regions and less taken and expressed in a continuous space.According to the progress of previous researches and the works conducted by the authors recently,we put forward a quantitative approach by selecting NPP as a common indicator to measure the relative role of climate change and human activities in desertification and dividing the ecological process of "driving force effect-dynamic response of desertified land" into several scenarios.Meanwhile,validation and scale of assessment should be taken into account when quantitative assessment of the relative role of climate change and human activities in desertification are carried out. 相似文献
210.