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排序方式: 共有1867条查询结果,搜索用时 31 毫秒
941.
942.
Hongjie Xie Xiaobing Zhou Jan M.H. Hendrickx Enrique R. Vivoni Huade Guan Yong Q. Tian Eric E. Small 《Journal of the American Water Resources Association》2006,42(1):237-256
This study examines NEXRAD Stage III product (hourly, cell size 4 km by 4 km) for its ability in estimating precipitation in central New Mexico, a semiarid area. A comparison between Stage III and a network of gauge precipitation estimates during 1995 to 2001 indicates that Stage III (1) overestimates the hourly conditional mean (CM) precipitation by 33 percent in the monsoon season and 55 percent in the nonmonsoon season; (2) overestimates the hourly CM precipitation for concurrent radar‐gauge pairs (nonzero value) by 13 percent in the monsoon season and 6 percent in the nonmonsoon season; (3) overestimates the seasonal precipitation accumulation by 11 to 88 percent in monsoon season and underestimates by 18 to 89 percent in the nonmonsoon season; and (4) either overestimates annual precipitation accumulation up to 28.2 percent or underestimates it up to 11.9 percent. A truncation of 57 to 72 percent of the total rainfall hours is observed in the Stage III data in the nonmonsoon season, which may be the main cause for both the underestimation of the radar rainfall accumulation and the lower conditional probability of radar rainfall detection in the nonmonsoon season. The study results indicate that the truncation caused loss of small rainfall amounts (events) is not effectively corrected by the real‐time rain gauge calibration that can adjust the rainfall rates but cannot recover the truncated small rainfall events. However, the truncation error in the monsoon season may be suppressed due to the larger rainfall rate and/or combined effect of overestimates by bright band and hail contaminations, virga, advection, etc. In general, improvement in NEXRAD performance since the monsoon season in 1998 is observed, which is consistent with the systematic improvement in the NEXRAD network. 相似文献
943.
944.
生态单元制图作为景观生态学研究方法之一,能够提供研究区域内基础详细的、保护或规划定向的、便于使用的生物学和生态学信息,该方法已经成为一些国家自然保护和城乡规划工作的基本工具。论文首先简明介绍了生态单元的定义和功能以及制图的两种主要方法。着重探讨了生态单元制图在国外30多年不同阶段的发展历程,并分析了生态单元制图在自然保护和城乡规划中应用的3个方面:物种和生境保护、土地利用规划和管理以及不同尺度景观规划和管理。另外,论文还对生态单元制图中存在的问题和不足以及深入研究的思路进行探讨。目前生态单元制图研究中存在的问题主要集中在生态单元调查的主观性、制图比例尺和G IS技术等方面。最后分析了生态单元制图在我国的研究现状以及生态单元制图在我国自然保护和城乡规划中应用的前景。 相似文献
945.
Reductions in non-point source pollution through different management practices for an agricultural watershed in the Three Gorges Reservoir Area 总被引:3,自引:0,他引:3
Non-point source water pollution generated by agricultural production is considered a major environmental issue in the Three Gorges Reservoir Area(TGRA) of China.The Annualised Agricultural Non-Point Source Pollution(AnnAGNPS) model was selected to assess the impact of the application of various management treats,including seven crops,five fertilizer levels and three-group management practice scenarios,on water quality from Heigou River Watershed in TGRA.The scenario subsets include conservation tillage practice(CTP),conservation reserve program(CRP) and conversion of cropland into forestland program(CCFP).Results indicated that tea can not be replaced by other crops because comparatively tea resulted in a higher sediment yield.CTP with no-tillage was more effective to reduce sediment yield,but could increased nutrient loss.CRP reduced sediment yield significantly,but slightly benefited on nutrient loss.CCFP reduced not only sediment yield but also the nutrient loss significantly.The conversion of cropland with a slope greater than 10 ° into forestland was found to be the best scenario as the sediment yield export is less than 5 tons/ha and nutrient loss is within the permissible limit. 相似文献
946.
以我国地表水中的河流水质预测评价为例,采用VC++设计开发了适用范围较广具有可操作性的决策系统。结合水环境预测方法和导则标准,对本系统可操作的污染因子进行了选取,设计了持久性污染物、非持久性污染物、酸碱污染物的预测模块;采用综合水质评价方法中的水质质量系数法模型,设计了水质质量系数评价模块;根据最新的农村饮用水安全卫生评价标准,设计了系统的特色模块,感官性状及一般化学指标评价模块和毒理学指标评价模块。利用湖南常德澧县环境监测站所提供的数据,用模块计算值与实测值进行了对比检验,结果表明,本系统功能基本可实现,预测及评价数据可信,为完善环境决策管理软件做了新的研究尝试。 相似文献
947.
948.
两株高效好氧反硝化细菌的分离鉴定及其脱氮效率 总被引:8,自引:0,他引:8
从水稻土和活性污泥中分离到两株可以在好氧条件下进行反硝化作用的细菌ZW23和ZW27.通过对这两株细菌的形态观察和生理生化特征,以及16S rDNA序列测定认为菌株ZW23和ZW27分别是假单胞菌属类产碱杆菌(Pseudomonas pseudoalcaligenes)和假单胞菌属门多萨菌(Pseudomonas mendocina).好氧培养条件下,在初始氮源约为280.00mg·L-1的反应体系中,两株细菌在12h内均引起体系中总氮显著下降,削减率分别达66.43%和65.54%,其余总氮几乎全部转化为内源氮.脱氮速率分别达到约21.72mg·L-1·h-1和22.31 mg·L-1·h-1,比现已分离出的兼性好氧反硝化细菌的脱氮速率要快得多.反应过程中没有检测到亚硝态氮和氨态氮的积累.菌株ZW23和ZW27是两株典型的高效兼性好氧反硝化细菌,具有重要的应用价值. 相似文献
949.
Changes of main secondary metabolites in leaves of Ginkgo biloba in response
to ozone fumigation 总被引:1,自引:0,他引:1
HE Xingyuan HUANG Wei CHEN Wei DONG Tian LIU Changbing CHEN Zhenju XU Sheng RUAN Yanan 《环境科学学报(英文版)》2009,21(2):199-203
To investigate the effect of elevated O3 on the accumulation of main secondary metabolites in leaves of Ginkgo biloba L., four-year-old trees were exposed in open-top chambers with ambient air and the air with twice ambient O3 concentration in Shenyang in 2006.Elevated O3 increased the concentrations of terpenes, but decreased the concentrations of phenolics in G.biloba leaves.The results showed that secondary compounds from G.biloba leaves responded to the elevated O3 exposure in a different way when compared to previous studies which showed elevated O3 increased the concentrations of phenolics but had no effect on the terpenes in leaves of other deciduous trees.Furthermore, reduced synthesis of phenolics may decrease the resistance of G.biloba to O3 and other environmental factors.On the other hand, the induced synthesis of terpenes may enhance the antioxidant abilities in G.biloba leaves at the end of O3 fumigation. 相似文献
950.
The investigation of dissolved organic matter (DOM) on urease, catalase and polyphenol oxidase activity in a phenanthrene (Phe)-
contaminated soil was conducted under laboratory incubation conditions. Values of soil enzymatic activity depended mainly on
incubation time. In the initial 16 days, urease activity increased, and was followed by a decrease. In the initial 8 days, catalase activity
decreased and then increased. Variation of polyphenol oxidase activity was just the reverse of catalase activity. After 30 days of
incubation, no pronounced di erence among treatments with Phe, Phe and DOM, and control were detected in urease, catalase and
polyphenol oxidase activity. Phe might inhibit urease and catalase, and stimulate polyphenol oxidase. DOM could improve inhibition
of Phe in soil urease and catalase activity during the initial period of applying DOM. Nevertheless, DOM had no significant e ect on
polyphenol oxidase activity in the Phe contaminated soil. There was a negative correlation between catalase and polyphenol oxidase
(r = –0.761***), and catalase and urease (r = –0.554**). Additionally, a positive correlation between polyphenol oxidase and urease
was also detected (r = 0.701***). It is implied that the formed DOM after application of organic wastes into soils may counteract the
inhibition of polycyclic aromatic hydrocarbons in soil enzyme activities. 相似文献