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491.
492.
Though polychlorinated biphenyls (PCBs) have distributed as threats in the environment to human beings for several decades, monitoring of trace level PCBs in-field is still a challenge. As a potential method for monitoring PCBs at trace levels, Raman spectroscopy has been used to detect several PCBs in the laboratory. To facilitate the development of rapid detection of PCBs by Raman spectroscopy, it is essential to investigate the Raman spectra of all PCB congeners. Herein, the stable configurations and vibrational spectra of all the PCB congeners were calculated by Gaussian 03 program package. Based on molecular symmetry, PCBs are classified into seven groups. The structural features and the normal vibration modes for each group are discussed. Taking the C(2)-2 group as an example, the wavenumber ranges of the various normal vibration modes in the Raman spectra of PCBs were analyzed. The accuracy of calculated results was verified by experimental Raman spectra of PCB77 standard. This study can elucidate further information to promote the development of Raman spectroscopy in environmental monitoring. 相似文献
493.
A sensitivity study was performed to investigate the responses of potential natural vegetation distribution in China to the
separate and combined effects of temperature, precipitation and [CO2], using the process-based equilibrium terrestrial biosphere model BIOME4. The model shows a generally good agreement with
a map of the potential natural vegetation distribution based on a numerical comparison using the ΔV statistic (ΔV = 0.25). Mean temperature of each month was increased uniformly by 0–5 K, in 0.5- or 1-K intervals. Mean precipitation of
each month was increased and decreased uniformly by 0–30%, in 10% intervals. The analyses were run at fixed CO2 concentrations of 360 and 720 ppm. Temperature increases shifted most forest boundaries northward and westward, expanded
the distribution of xeric biomes, and confined the tundra to progressively higher elevations. Precipitation increases led
to a greater area occupied by mesic biomes at the expense of xeric biomes. Most vegetation types in the temperate regions,
and on the Tibetan Plateau, expanded westward into the dry continental interior with increasing precipitation. Precipitation
decreases had opposite effects. The modelled effect of CO2 doubling was to partially compensate for the negative effect of drought on the mesic biomes and to increase potential ecosystem
carbon storage by about 40%. Warming tended to counteract this effect, by reducing soil carbon storage. Forest biomes showed
substantial resilience to climate change, especially when the effects of increasing [CO2] were taken into account. Savannas, dry woodland and tundra biomes proved sensitive to temperature increases. The transition
region of grassland and forest, and the Tibetan plateau, was the most vulnerable region. 相似文献
494.
Impacts of climate change on Chinese ecosystems: key vulnerable regions and potential thresholds 总被引:1,自引:0,他引:1
Jian Ni 《Regional Environmental Change》2011,11(1):49-64
China is a key vulnerable region of climate change in the world. Climate warming and general increase in precipitation with strong temporal and spatial variations have happened in China during the past century. Such changes in climate associated with the human disturbances have influenced natural ecosystems of China, leading to the advanced plant phenology in spring, lengthened growing season of vegetation, modified composition and geographical pattern of vegetation, especially in ecotone and tree-lines, and the increases in vegetation cover, vegetation activity and net primary productivity. Increases in temperature, changes in precipitation regime and CO2 concentration enrichment will happen in the future in China according to climate model simulations. The projected climate scenarios (associated with land use changes again) will significantly influence Chinese ecosystems, resulting in a northward shift of all forests, disappearance of boreal forest from northeastern China, new tropical forests and woodlands move into the tropics, an eastward shift of grasslands (expansion) and deserts (shrinkage), a reduction in alpine vegetation and an increase in net primary productivity of most vegetation types. Ecosystems in northern and western parts of China are more vulnerable to climate changes than those in eastern China, while ecosystems in the east are more vulnerable to land use changes other than climate changes. Such assessment could be helpful to address the ultimate objective of the United Nations Framework Convention on Climate Change (UNFCCC Article 2). 相似文献
495.
496.
Yuanxin Zhang Fei Li Chaoqiong Ni Song Gao Shuwei Zhang Jin Xue Zhukai Ning Chuanming Wei Fang Fang Yongyou Nie Zheng Jiao 《Frontiers of Environmental Science & Engineering》2023,17(2):21
497.
Guorong Zhu Guilan Di Meng Zhang Te Cao Leyi Ni Rongting Fang Gongliang Yu 《Environmental science and pollution research international》2018,25(34):34027-34045
Few studies have focused on the biomechanical responses of submerged, rosette-forming macrophytes to wave action, water depth, or their co-occurrence in naturally eutrophic systems. The plant architecture, root anchorage strength-related traits, leaf morphology, and biomechanics of Vallisneria natans inhabiting a range of water depths were examined along three transects (T1, T2, and T3) in a eutrophic lake, Lake Erhai, in Yunnan Province, China. These transects were exposed to weak wave action and hyper-eutrophication (T1), moderate wave action and eutrophication (T2), or strong wave action and eutrophication (T3). The results showed that V. natans was mainly distributed at intermediate depths, with the widest colonization depth in T1. The values of plant architecture, root anchorage strength-related traits, leaf morphology, and biomechanics were generally highest in T3 and smallest in T2. Along the depth gradient, these values were generally highest at 3.5, 2.5, and 2.5 m for the plants growing in T1, T2, and T3, respectively. These findings suggest that V. natans adopts a “tolerance” strategy to cope with the effects of strong wave action in eutrophic habitats and an “avoidance” strategy when exposed to moderate wave action in eutrophic areas. Since the absence of an avoidance strategy increases the resistance to low-light stress at the expense of increased drag forces, there is a limit to the wave action that V. natans can withstand. This study indicates that biomechanics could be important when determining the distribution pattern of V. natans in Lake Erhai. 相似文献
498.
Source identification of PCDD/Fs in agricultural soils near to a Chinese MSWI plant through isomer-specific data analysis 总被引:4,自引:0,他引:4
Isomer-specific data were investigated in order to identify the sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in agricultural soils, including Fluvo-aquic and paddy soils, in the vicinity of a Chinese municipal solid waste incineration (MSWI) plant. Homologue and isomer profiles of PCDD/Fs in soils were compared with those of potential sources, including combustion sources, i.e., MSWI flue gas and fly ash; and the impurities in agrochemicals, such as the pentachlorophenol (PCP), sodium pentachlorophenate (PCP-Na) and 1,3,5-trichloro-2-(4-nitrophenoxy) benzene (CNP). The results showed that the PCDD/F isomer profiles of combustion sources and agricultural soils were very similar, especially for PCDFs, although their homologue profiles varied, indicating that all the isomers within each homologue behave identically in the air and soil. Moreover, factor analysis of the isomer compositions among 33 soil samples revealed that the contamination of PCDD/Fs in agricultural soils near the MSWI plant were primarily influenced by the combustion sources, followed by the PCP/PCP-Na and CNP sources. This implication is consistent with our previous findings based on chemometric analysis of homologue profiles of soil and flue gas samples, and identifies PCP/PCP-Na as an additional important source of PCDD/Fs in the local area. This makes the similarities and differences of isomer profiles between Fluvo-aquic and paddy soils more explainable. It is, therefore, advisable to use isomer-specific data for PCDD/F source identifications where possible. 相似文献
499.
Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F) were analyzed in surface sediments and top soils collected from 30 sites in Daliao River Basin. The concentrations of PCDD/F ranged from 0.28 to 29.01 ng TEQ kg(-1) dw (mean value, 7.45 ng TEQ kg(-1)dw) in sediments, and from 0.31 to 53.05 ng TEQ kg(-1)dw (mean value, 7.00 ng TEQ kg(-1)dw) in soils. PCDD/F pollution in sediments from the mid- and downstream sections of Hun River was found to be relatively heavy, and the levels of PCDD/F contamination in paddy soils were generally higher than those of upland soils. Using multivariate statistical analysis, the PCDD/F homologue and congener profiles of all soil and sediment samples were compared with those of suspected PCDD/F sources. The results showed that, PCDD/F contamination in most sediments of Hun River should mainly originated from the production of organochlorine chemicals, while metal smelting was the important potential source of PCDD/F in the drainage area of Taizi River. PCDD/F contamination in paddy soils should be simultaneously attributed to the polluted water irrigation and the organochlorine pesticide application. 相似文献
500.
光助Fenton氧化法降解水中六氯苯的研究 总被引:7,自引:2,他引:5
采用光助Fenton氧化法处理六氯苯模拟废水,考察了反应时间、Fe3 与H2O2摩尔比、Fenton试剂用量、初始pH、六氯苯初始浓度、光强对六氯苯降解效果的影响,并初步探讨了六氯苯的降解动力学规律.结果表明.光助Fenton法降解六氯苯的最佳工艺条件为:紫外灯功率为300 W、Fe3 投加量为1.0 mmol/L、H2O2投加量为5.0 mmol/L、反应时间为60 min、初始pH为3,在此条件下,浓度为500μg/L的HCB的去除率可达91.3%.UV辐射与Fenton氧化对HCB的降解具有协同效应.光助Fenton法对HCB的降解符合一级反应动力学方程,表观速率常数为0.04 min-1,与Fenton法相比,提高了近9倍. 相似文献