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601.
通过对反向传播人工神经网络的算法和网络结构的研究,发现拟牛顿算法训练速度较快,能够较好地接近误差目标值,同时建立了包括输入层、隐含层、输出层的人工神经网络三层拓扑结构。通过对街道峡谷人工神经网络的训练,模拟计算了街道峡谷NOx浓度分布值。结果显示,训练误差和测试误差比为1.11,训练样本的模拟值与实测值的相关系数为0.93,测试样本的模拟值与实测值的相关系数为0.87,模拟值与实测值的相关系数均高于显著水平为α=0.05与α=0.01所对应检验性表的相关系数临界值。该模型能够用于街道峡谷污染物浓度的模拟计算,具有较好的泛化能力。 相似文献
602.
603.
Quantifying Terrestrial Ecosystem Carbon Dynamics in the Jinsha Watershed, Upper Yangtze, China from 1975 to 2000 总被引:1,自引:0,他引:1
Shuqing Zhao Shuguang Liu Runsheng Yin Zhengpeng Li Yulin Deng Kun Tan Xiangzheng Deng David Rothstein Jiaguo Qi 《Environmental management》2010,45(3):466-475
Quantifying the spatial and temporal dynamics of carbon stocks in terrestrial ecosystems and carbon fluxes between the terrestrial
biosphere and the atmosphere is critical to our understanding of regional patterns of carbon budgets. Here we use the General
Ensemble biogeochemical Modeling System to simulate the terrestrial ecosystem carbon dynamics in the Jinsha watershed of China’s
upper Yangtze basin from 1975 to 2000, based on unique combinations of spatial and temporal dynamics of major driving forces,
such as climate, soil properties, nitrogen deposition, and land use and land cover changes. Our analysis demonstrates that
the Jinsha watershed ecosystems acted as a carbon sink during the period of 1975–2000, with an average rate of 0.36 Mg/ha/yr,
primarily resulting from regional climate variation and local land use and land cover change. Vegetation biomass accumulation
accounted for 90.6% of the sink, while soil organic carbon loss before 1992 led to a lower net gain of carbon in the watershed,
and after that soils became a small sink. Ecosystem carbon sink/source patterns showed a high degree of spatial heterogeneity.
Carbon sinks were associated with forest areas without disturbances, whereas carbon sources were primarily caused by stand-replacing
disturbances. It is critical to adequately represent the detailed fast-changing dynamics of land use activities in regional
biogeochemical models to determine the spatial and temporal evolution of regional carbon sink/source patterns. 相似文献
604.
China’s Primary Programs of Terrestrial Ecosystem Restoration: Initiation, Implementation, and Challenges 总被引:5,自引:0,他引:5
China has undertaken several major programs of terrestrial ecosystem restoration (ERPs) in recent years, including the Natural
Forest Protection Program (NFPP) and the Sloping Land Conversion Program (SLCP). There have been reports on the implementation
of these programs, their preliminary impacts, and the problems encountered in carrying them out; a great deal has been learned
from these studies. Nonetheless, China’s ERPs are not limited to the NFPP and the SLCP. Because a complete documentation and
a timely update of these major efforts are still missing from the literature, it is difficult to gauge the scope of these
programs and the scale of their impacts. In addition, a more thorough and critical analysis of both the general ERP policy
and the specific technical measures used in implementing the ERPs remains urgently needed. The purpose of this article is
to tackle these tasks. Overall, with the huge government investments in the ERPs, tremendous progress has been made in implementing
them. To complete them successfully and to fundamentally improve the targeted ecosystems, however, it is essential for China
to have a more balanced and comprehensive approach to ecological restoration. This approach must include: adopting better
planning and management practices; strengthening the governance of program implementation; emphasizing the active engagement
of local people; establishing an independent, competent monitoring network; and conducting adequate assessments of program
effectiveness and impact. 相似文献
605.
Quantifying the Effect of Ecological Restoration on Soil Erosion in China’s Loess Plateau Region: An Application of the MMF Approach 总被引:5,自引:0,他引:5
Changbin Li Jiaguo Qi Zhaodong Feng Runsheng Yin Biyun Guo Feng Zhang Songbing Zou 《Environmental management》2010,45(3):476-487
Land degradation due to erosion is one of the most serious environmental problems in China. To reduce land degradation, the
government has taken a number of conservation and restoration measures, including the Sloping Land Conversion Program (SLCP),
which was launched in 1999. A logical question is whether these measures have reduced soil erosion at the regional level.
The objective of this article is to answer this question by assessing soil erosion dynamics in the Zuli River basin in the
Loess Plateau of China from 1999 to 2006. The MMF (Morgan, Morgan and Finney) model was used to simulate changes in runoff
and soil erosion over the period of time during which ecological restoration projects were implemented. Some model variables
were derived from remotely sensed images to provide improved land surface representation. With an overall accuracy rate of
0.67, our simulations show that increased ground vegetation cover, especially in forestlands and grasslands, has reduced soil
erosion by 38.8% on average from 1999 to 2006. During the same time period, however, the change in rainfall pattern has caused
a 13.1% ± 4.3% increase in soil erosion, resulting in a net 25.7% ± 8.5% reduction in soil erosion. This suggests that China’s
various ecological restoration efforts have been effective in reducing soil loss. 相似文献
606.
607.
608.
Cai M Xie Z Möller A Yin Z Huang P Cai M Yang H Sturm R He J Ebinghaus R 《Chemosphere》2012,87(9):989-997
Neutral polyfluorinated alkyl substances (PFASs) were measured in high-volume air samples collected on board the research vessel Snow Dragon during the 4th Chinese National Arctic Expedition from the Japan Sea to the Arctic Ocean in 2010. Four volatile and semi-volatile PFASs (fluorotelomer alcohols (FTOHs), fluorotelomer acids (FTAs), perfluoroalkyl sulfonamides (FASAs), and sulfonamidoethanols (FASEs)) were analyzed respectively in the gas and particle phases. FTOHs were the dominant PFASs in the gas phase (61-358 pg m−3), followed by FTAs (5.2-47.9 pg m−3), FASEs (1.9-15.0 pg m−3), and FASAs (0.5-2.1 pg m−3). In the particle phase, the dominant PFAS class was FTOHs (1.0-9.9 pg m−3). The particle-associated fraction followed the general trend of FASEs > FASAs > FTOHs. Compared with other atmospheric PFAS measurements, the ranges of concentrations of ∑FTOH in this study were similar to those reported from Toronto, north America (urban), the northeast Atlantic Ocean, and northern Germany. Significant correlations between FASEs in the gas phase and ambient air temperature indicate that cold surfaces such as sea-ice, snowpack, and surface seawater influence atmospheric FASEs. 相似文献
609.
8种植物床人工湿地脱氮除磷的研究 总被引:2,自引:0,他引:2
分别以水葫芦、西洋芹、空心菜、水芹、混合种(黄菖蒲、千屈菜、再力花)、千屈菜、再力花、黄菖蒲等植物床构建潜流人工湿地,研究其对生活污水氮、磷的净化功能及其去除率与水力停留时间(HRT)的变化规律。结果表明,各种植物床对TN、TP的去除率随HRT的延长而增加,不同植物床的脱氮除磷效果是不同的。千屈菜植物床对TN的去除效果最好,HRT为3d时,TN去除率为56%;HRT为6d时,TN去除率达77%。再力花植物床对TP的去除效果最好,HRT为3d时,TP去除率达78%;HRT为6d时,TP去除率达96%。其他植物床也有较好的脱氮除磷效果。各种植物床处理后出水TN、TP均较低,HRT为3d时,出水TN均低于《城镇污水处理厂污染物排放标准》(GB 18918—2002)一级A标准规定的限值(15mg/L),出水TP均低于GB 18918—2002二级标准规定的限值(3mg/L);7种植物床构建的潜流人工湿地(水葫芦的数据丢失)对TN、TP的去除均满足一级反应动力学方程,且相关性显著。 相似文献
610.
南苕溪支流锦溪水质时空变化特征分析 总被引:2,自引:1,他引:1
综合运用灰色聚类法、综合污染指数法、等级聚类法就南苕溪支流锦溪近年水质时空变化特征进行分析。结果表明,锦溪入青山水库断面水质2005—2009年逐年改善,2007年后达到灰色聚类等级Ⅲ类水质要求;2009年秋季至2010年夏季期间秋、冬两季的污染程度高于春、夏季节;枯水期综合污染指数最高,但TN、TP污染分指数在丰水期最高,表明污染源中面源污染已占相当比例。空间变化方面从玲珑桥到江桥锦溪水质的综合污染指数不断提升,到江桥时达到极值13.25,锦溪末端三眼桥断面水质较江桥断面有所改善;SPSS空间聚类分析可分为轻污染区(从玲珑桥到冬韵桥)、重污染区(从群利桥到江桥)和中度污染区(从江桥到三眼桥)。锦溪上游农业区对河水中的COD、TN和TP的贡献率分别为66%、54%和49%,农业面源污染已成为制约锦溪水质改善的主要因素。 相似文献