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981.
为研究太湖的流场结构,更好实施引清调水方案改善太湖水质。在确定太湖四季主导风向及其平均风速的基础上,采用有限体积Godunov型通量差分裂(FDS)格式构建太湖水动力模型,并得到了实测流场的良好验证。并进一步研究各季节各湖区的流动规律,确定太湖风生流水动力时空差异特征。结果表明:太湖风生流流态特征主要与风向、风速有关;不同季节平均流速由大到小分别为:冬季、春季、秋季、夏季;从不同的湖区看,湖岸区最大、湖湾区次之、湖心区最小。由此可选择冬季、湖岸区实施调水方案改善太湖水质。 相似文献
982.
983.
984.
Spatial variations of macrozoobenthos and sediment nutrients in Lake Yangcheng: Emphasis on effect of pen culture of Chinese mitten crab 总被引:2,自引:0,他引:2
Liping Chen Ying Zhang Qigen LiuZhongjun Hu Yuejuan SunZiran Peng Lijing Chen 《环境科学学报(英文版)》2015,37(11):118-129
We determined the effect of Chinese mitten crab (CMC) pen culture on the quantified spatial distribution of the macrozoobenthic community and sediment nutrients in Lake Yangcheng. Redundancy analysis indicated that water temperature, macrophyte occurrence, sediment type, and crab culture were the main environmental factors that influence the spatiotemporal macrozoobenthic distribution. Macrozoobenthic assemblages in the lake were characterized by eutrophic indicator species. In the most polluted estuaries, the abundance and diversity indices of the whole community and abundance of chironomids and oligochaetes were significantly depressed, and sediment carbon (C) and phosphorus (P) were significantly enhanced compared with those in the western, middle (MB), and eastern basin (EB). Crab culture in this lake had significant effects on the species composition of the macrozoobenthic community in one of three CMC culture pens (CP), and generally depressed the abundance of most chironomid and oligochaete species. Significantly increased diversity, evenness, sediment carbon and nitrogen content, and sediment C:P ratio in the CP were found compared with those in the three basins. However, no conspicuous difference in sediment P content between the CP and the two basins of MB and EB was detected. Our results showed that the enhanced diversity and evenness of macrozoobenthos might be associated with the joint effect of macrophyte planting and crab predation, and macrophyte planting may modify the effects of CMC culture by leading to disproportional accumulation of C and N in the sediment relative to P in the CP of the lake. 相似文献
985.
Chunmei Gong Jiajia Wang Congxia Hu Junhui Wang Pengbo Ning Juan Bai 《环境科学学报(英文版)》2015,27(8):184-196
C4 plants possess better drought tolerance than C3 plants. However, Hedysarum scoparium, a C3 species, is dominant and widely distributed in the desert areas of northwestern China due to its strong drought tolerance. This study compared it with Haloxylon ammodendron, a C4 species, regarding the interactive effects of drought stress and different leaf–air vapor pressure deficits. Variables of interest included gas exchange, the activity levels of key C4 photosynthetic enzymes, and cellular anatomy. In both species, gas exchange parameters were more sensitive to high vapor pressure deficit than to strong water stress, and the net CO2 assimilation rate (An) was enhanced as vapor pressure deficits increased. A close relationship between An and stomatal conductance (gs) suggested that the species shared a similar response mechanism. In H. ammodendron, the activity levels of key C4 enzymes were higher, including those of phosphoenolpyruvate carboxylase (PEPC) and nicotinamide adenine dinucleotide phosphate-malate enzyme (NADP-ME), whereas in H. scoparium, the activity level of nicotinamide adenine dinucleotide-malate enzyme (NAD-ME) was higher. Meanwhile, H. scoparium utilized adaptive structural features, including a larger relative vessel area and a shorter distance from vein to stomata, which facilitated the movement of water. These findings implied that some C4 biochemical pathways were present in H. scoparium to respond to environmental challenges. 相似文献
986.
987.
Carbonyl compounds are important intermediates in atmospheric photochemistry, but their primary sources are still not understood well. In this work, carbonyls, hydrocarbons, and alkyl nitrates were continuously measured during November 2011 at a rural site in the Yangtze River Delta region of China. Mixing ratios of carbonyls and hydrocarbons showed large fluctuations during the entire measurement. The average level for total measured volatile organic compounds during the pollution episode from 25th to 27th November, 2011 was 91.6 ppb, about 7 times the value for the clean period of 7th–8th, November, 2011. To preliminarily identify toluene sources at this site, the emission ratio of toluene to benzene (T/B) during the pollution episode was determined based on photochemical ages derived from the relationship of alkyl nitrates to their parent alkanes. The calculated T/B was 5.8 ppb/ppb, significantly higher than the values of 0.2–1.7 ppb/ppb for vehicular exhaust and other combustion sources, indicating the dominant influence of industrial emissions on ambient toluene. The contributions of industrial sources to ambient carbonyls were then calculated using a multiple linear regression fit model that used toluene and alkyl nitrates as respective tracers for industrial emission and secondary production. During the pollution episode, 18.5%, 69.0%, and 52.9% of measured formaldehyde, acetaldehyde, and acetone were considered to be attributable to industrial emissions. The emission ratios relative to toluene for formaldehyde, acetaldehyde, and acetone were determined to be 0.10, 0.20 and 0.40 ppb/ppb, respectively. More research on industrial carbonyl emission characteristics is needed to understand carbonyl sources better. 相似文献
988.
989.
Tingting Han Xingang Liu Yuanhang Zhang Yu Qu Limin Zeng Min Hu Tong Zhu 《环境科学学报(英文版)》2015,27(5):51-60
A field experiment from 18 August to 8 September 2006 in Beijing, China, was carried out. A hazy day was defined as visibility 10 km and RH(relative humidity) 90%. Four haze episodes, which accounted for ~ 60% of the time during the whole campaign, were characterized by increases of SNA(sulfate, nitrate, and ammonium) and SOA(secondary organic aerosol) concentrations. The average values with standard deviation of SO2-+4, NO-3, NH4 and SOA were 49.8(± 31.6), 31.4(±22.3), 25.8(±16.6) and 8.9(±4.1) μg/m3, respectively, during the haze episodes, which were 4.3, 3.4, 4.1, and 1.7 times those in the non-haze days. The SO2-4,NO-3, NH+4, and SOA accounted for 15.8%, 8.8%, 7.3%, and 6.0% of the total mass concentration of PM10 during the non-haze days. The respective contributions of SNA species to PM10 rose to about27.2%, 15.9%, and 13.9% during the haze days, while the contributions of SOA maintained the same level with a slight decrease to about 4.9%. The observed mass concentrations of SNA and SOA increased with the increase of PM10 mass concentration, however, the rate of increase of SNA was much faster than that of the SOA. The SOR(sulfur oxidation ratio) and NOR(nitrogen oxidation ratio) increased from non-haze days to hazy days, and increased with the increase of RH. High concentrations of aerosols and water vapor favored the conversion of SO2 to SO2-4and NO2 to NO-3, which accelerated the accumulation of the aerosols and resulted in the formation of haze in Beijing. 相似文献
990.
Chemical characterization of size-resolved aerosols in four seasons and hazy days in the megacity Beijing of China 总被引:2,自引:0,他引:2
Kang Sun Xingang Liu Jianwei Gu Yunpeng Li Yu Qu Junling An Jingli Wang Yuanhang Zhang Min Hu Fang Zhang 《环境科学学报(英文版)》2015,27(6):155-167
Size-resolved aerosol samples were collected by MOUDI in four seasons in 2007 in Beijing. The PM10 and PM1.8mass concentrations were 166.0 ± 120.5 and 91.6 ± 69.7 μg/m~3, respectively,throughout the measurement, with seasonal variation: nearly two times higher in autumn than in summer and spring. Serious fine particle pollution occurred in winter with the PM1.8/PM10 ratio of 0.63, which was higher than other seasons. The size distribution of PM showed obvious seasonal and diurnal variation, with a smaller fine mode peak in spring and in the daytime. OM(organic matter = 1.6 × OC(organic carbon)) and SIA(secondary inorganic aerosol) were major components of fine particles, while OM, SIA and Ca_2+were major components in coarse particles. Moreover, secondary components, mainly SOA(secondary organic aerosol) and SIA,accounted for 46%–96% of each size bin in fine particles, which meant that secondary pollution existed all year. Sulfates and nitrates, primarily in the form of(NH_4)_2SO_4, NH_4NO_3, Ca SO_4, Na_2SO_4 and K_2SO_4, calculated by the model ISORROPIA II, were major components of the solid phase in fine particles. The PM concentration and size distribution were similar in the four seasons on non-haze days, while large differences occurred on haze days, which indicated seasonal variation of PM concentration and size distribution were dominated by haze days. The SIA concentrations and fractions of nearly all size bins were higher on haze days than on non-haze days, which was attributed to heterogeneous aqueous reactions on haze days in the four seasons. 相似文献