Zhang Y.,Nangjing University |
Xue Y.,Nangjing University |
Wu J.,Nangjing University |
Wang H.,Nangjing University |
He J.,Nangjing University
Engineering Geology | Year: 2012
Long-term excessive groundwater withdrawal causes severe land subsidence and considerable economic loss. During the period of land subsidence, aquifer sands present complex deformation characteristics. Field data in the Southern Yangtse Delta, China have shown that the deformation characteristics of aquifer sands are closely related to the changing patterns of groundwater level the aquifer units have experienced. When the groundwater level fluctuates yearly within a certain range, the aquifer unit behaves primarily as an elastic material. When the groundwater level rises and falls alternatively with the average decreasing but higher than the previous lowest value the unit has experienced, the aquifer unit behaves primarily as a visco-elastic and elasto-plastic material. However, when the average level decreases and is lower than the previous lowest value the unit has experienced, the aquifer unit behaves primarily as a visco-elastic, elasto-plastic, and visco-plastic material. The plastic and creep deformation of aquifer sands is also proved through laboratory tests. With the increasing cycle number of loading, the creep and plastic deformation decreases and the expansion under unloading is closer to the compression under loading in a single cycle. On the basis of field and laboratory data, a new mechanical model is constructed, which can describe various kinds of deformation characteristics under different changing patterns of groundwater level, including elastic, visco-elastic, plastic, and visco-plastic deformation. The model includes two yielding stresses and six parameters. When the appropriate field data are available, the six parameters of the model can be determined through graphic methods. Then the deformation of aquifer units can be calculated if the changing groundwater level is known. © 2011 Elsevier B.V.
Tang D.,Nangjing University |
Zou X.,Nangjing University |
Liu X.,CAS South China Sea Institute of Oceanology
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2013
Ecosystem health assessment is a fundamental issue in ecosystem protection and monitoring studies. Maintaining a healthy ecosystem is regarded as the key management objective for more and more environmental sectors. Therefore, a comprehensive and accurate index to indicate the ecosystem status is urgently needed. In previous researches, both exergy and biodiversity indicators are effectively and commonly used in assessing ecosystem health. But the difference between them is not reported. This paper provides a case study in Jiangsu coastal zone. Starting from Xiuzhen estuary in north and stretching down to the north shore of Yangtze estuary in south, Jiangsu coastal zone lasts for 954km. This research focuses on the nektonic and benthic communities in three different geographical areas (the Haizhou Bay-in the north, radiative sand ridges-in the middle, and the north shore of Yangtze estuary-in the south). 15 samples were collected in the marine survey conducted during July-Aug. 2006. After analyzing the exergy and bio-diversity values at these 15 locations, the spatial distribution structure of exergy and bio-diversity values were revealed. Further analysis was conducted based on Arcgis and SPSS software. Following results are obtained: Both exergy and structure exergy values in radiative sand ridges area are consistent. They are smaller than those in Haizhou Bay and Yangtze estuary region. In Haizhou Bay, the exergy value is lower than that in Yangtze estuary region, while the structure exergy values distribute oppositely. As one kind of biodiversity index, Margalef index value in south area is slightly larger than that in the north, while the value in the middle is the least. The distribution patterns of both Shannon Wiener and Simpson index values are south > middle > north. In mature ecosystem, both exergy and biodiversity can indicate the similar health status. But when they are used in valuing less mature ecosystems, significant difference occurs. This is because exergy measures ecosystem from cells'level, while biodiversity more focuses at species level. Further analysis also indicates that 15 samples can be divided into four categories: site 14 is healthy, 8, 11, 12 are sub-healthy, 1, 6, 7, 10, 13 are poor, others are uncertainty. The differences between exergy and the biodiversity indicators can be concluded as follows: (1) The theoratical base of exergy is thermodynamics, from which ecosystem's organism structure and genetic information can be reflected in relatively microcosmic perspective, while biodiversity indicators are based on population size and species abundance, which illustrate the stability of ecosystem in macro perspective. (2) Exergy can directly reflect the status and the changes of ecosystem, while biodiversity indicators indicate the ecological health status in an indirect way. (3) Exergy and structure exergy are complementary, while biodiversity indicators are parallel. (4) Exergy calculation is more or less restricted by gene measurement techniques, while, the ecological changes in diversity cannot be distinguished whether from species distribution or the quantity change of species.