| With the rapid development of industrialization, air pollution is among the most worrying problems in China. As the by-product of fossil fuels’ combustion, fly ash brings numerous pollutants, such as heavy metals, sulfides and persistent organic pollutants etc. Epikarst system is characterized by the properties of openness and vulnerability and has been exchanging substances and energy with other system all the time. Ground water can be easily contaminated by the pollutants which derive from the surface earth for there are bilayer structure, including surface layer and underground layer, exist in the epikarst system. In view of the importance of karst water,launching the research about the characteristics of fly ash particles and their migration in the epikarst system would play a crucial role in increasing the understanding of how those pollutants disperse and migrate in karst area.Based on the epikarst system, which located on the top of Jinfo Mountain, Chongqing municipality, as the research area, this study has sampled the snowpack on December of 2014 and the rainfall samples in the rainstorm period on June of 2015. Meanwhile, the suspended particles in Fuifang spring have been collected during the snowmelt period and the rainstorm. We employ the technique of scanning electron microscope couples with energy dispersive X-ray spectrometer(SEM- EDS) to analyze the information about morphology and chemical elemental compositions of the fly ash in the samples. We also sampled the soil profiles under the grassland and woodland for obtaining the distribution and movement characteristics of SCP in the soil layer. In addition,high-resolution online tracer technique was applied to acquire hydrogeological parameters of the ground water system in Shuifang spring drainage basin.Results showed that: a great deal of spherical fly ash particles were found in the snow samples,including smooth particles, rough particles and soot particles, which accounted for 80.31%, 14.39%and 5.30% respectively; Average diameter of fly ash particles is 1.64 ?m and the average value of roundness is 1.09. In terms of elemental composition, the fly ash particles counted in this research could be classified into 5 types: Si-dominant particles, C-dominant particles, Fe-dominant particles,Al-dominant particles and Ti-dominant particles, which make up 34.09%, 49.24%, 12.88%, 2.27%and 1.52% respectively. C-dominant particles may come from the resources of contamination around Jinfo Mountain; Si-dominant fly ash particles may result from the plant industry located in west Chingqing, north of Guizhou province, central of Hunan province, Zhejiang province, Jiangxi province and the west of Guangdong province; while the production activities of iron works and rolling mills in the west of Chongqing, the north of Guizhou province and the central of Hunan province may constitute the source of Fe-dominant fly ash particles in the snow.The information of fly ash which exist in rainstorm’ suspended particles was counted. Average diameter of fly ash particles is 1.64 ?m and varied from 0.14 to 14.45?m, the average value of roundness is 1.09. Smooth particles, rough particles and soot, accounted for 87.3%, 15.32% and0.90% respectively. Based on elemental composition, the fly ash particles counted in rainstorm could be classified into 4 types: Si-dominant particles, C-dominant particles, Fe-dominant particles and Ti-dominant particles, which make up 42.34%, 43.24%, 4.51% and 9.91% respectively.Compared with the proportion of various types in the snow, the proportion of C-dominant particles and Fe-particle in the rainstorm decreased, while Si-dominant particles and Ti-dominant particles increased, which may be caused by the discrepancies of air motion and human beings’ activities in different seasons. C-dominant particles may derive from the activities of daily life and industries in Guangxi province, Yunnan province, central of Guizhou and the local area of Jinfo Mountain;Si-dominant particles may originate from the plant industry located in the central of Guangxi province, the southeast of Yunnan province, central and north of Guizhou province; Ti-dominant particles may result from the metal smelting factories in the southeast of Yunnan province, the central of Guangxi province, the central and north of Guizhou province; While the activities of foundries and steel plants in the north of Guizhou province may be the main sources of Fe-dominant fly ash particles in our samples.In both period of snowmelt and rainstorm, fly ash particles, which come from the atmospheric precipitation, were found in Shuifang spring. The characters of fly ash which found in Shuifang spring during the snowmelt period were depicted as follows: average diameter is 0.81 and varied from 0.16 to 2.93?m,the average value of roundness is 1.16 and varied from 1 to 1.63. In terms of elemental composition, those fly ash particles could be classified into 3 types: C-dominant particles,Si-dominant particles and Fe-dominant particles, which make up 80%, 10% and 10% respectively.Nonetheless, the features of fly ash founded in Shuifang spring during the rainstorm could be described as following: average diameter is 1.03μm and varied from 0.24 to 8.39?m,the average roundness is 1.11 and varied from 1.03 to 1.28. Based on elemental composition, the fly ash particles could be classified into 2 types: C-dominant particles and Si-dominant particles, which account for 72.13% and 27.87% respectively. To sum up, the characters of fly ash in Shuifang spring have high similarity with the features of fly ash in their corresponding precipitation;therefore, the properties of fly ash particles inherited the characters of fly ash in precipitation to some extent.The number of SCP in the surface of woodland profile is the maximum, and decreased with the increasing of soil depth, eventually, the SCP vanished at the depth of 50~60cm. At the profile of grassland, SCP changed a little even edge up among 5~20cm and reach to maximum at 15~20cm. It is the same that SCP decreased with the depth increased and then disappeared at 60~70cm. In consequence, the SCP could not reach to the groundwater river as it is hard for SCP to pass the interception of soil layer. The results of high-resolution online tracer test show that: cross-sectional area is 0.96 m2, groundwater pipe surface area is 0.3 m2 and diameter is 1.1 m. Obviously, fly ash,whose diameter is no more than 10?m, would not be blocked in this karst system and would be discharged through epikarst spring or underground river.According to the results of this research listed above, the transportation processes of fly ash in the epikarst system can be summarized to a few steps: To begin with, fly ash particles were produced from all kinds of humans’ activities and released to the atmosphere; secondly, it landed at the surface of the earth, part of it returns to atmosphere via the impact of air motion; Thirdly, part of the fly ash enters into the aquifer systems through sinkholes and other karst fractures, while the other part down into the soil layer and migrates to a certain depth, but could not pass through the whole soil layer. Finally, that fly ash which entered into the underground river would be discharged from the outlets of subterranean river or karst spring. |
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