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题名: 我国典型森林汞库及土壤-大气汞交换通量研究
作者: 周俊
学位类别: 博士
答辩日期: 2016-04
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 张晓山 ; 王章玮
关键词: Soil mercury distribution ; Forest mercury storage ; Soil-air flux ; Litter decomposition
其他题名: Soil Atmosphere Mercury Fluxes and Mercury Pools in Typical Forest of China
学位专业: 环境科学
英文摘要:        Mercury is a hazardous heavy metal element, which is easily to be bioaccumulated through food chain, leading considerous hazard to human health. Terrestrial ecological system is the main place for biogeochemical cycle of mercury, whereas forest ecosystem is the largest one and always be seen as an active sink of mercury. Therefore, forest ecosystem are the important parts of the global biogeochemical cycle of mercury. Tieshanping subtropical forest in Chongqing and Dongling Mountain temperature forest in Beijing were selected as the study areas, where distributed typical subtropical and temperature forest: mixed evergreen broadleaf-conifer forest and deciduous broad-leaved forest. The characteristics of mercury of typical forest ecosystem was studied by field monitoring to investigate soil/air mecury exchange mechanism and influcing factors as well as mercury dynamics in the inside of the forest ecosystem.
      The results showed that TGM concentrations in Tieshanping and Donglingshan were 3.51 ± 1.39 ng m 2 and 2.47 ± 0.51 ng m 2, suggesting that both areas influenced by anthropogenic resource. The soil-air flux in Tieshanping Forest Park, Southwestern China and in Donglingshan North, were measured about 130 and 90 days to reduce the uncertainty. The result showed that the soil-air flux results showed both emission and deposition and a strong correlation between fluxes and substrate mercury concentrations, with an overall net emission of 2.73 ng m 2 h 1. The fluxes in Pinus tabulaeformis, Quercus liaotungensis, broadleaved mixed and Larix principis-rupprechtii forest in Donglingshan were 0.01 ± 2.60, 0.12 ± 1.28, 3.558 ±6.76, 0.46 ± 1.36 and 1.78 ± 1.48 ng m 2 h 1. The fluxes showed obvious seasonal variations. Fluxes were the highest in evergreen broad-leaf forest in South and evergreen coniferous forest, bare soil in North forest. However, the fluxes of the forest soil in northern deciduous temperatural forest wee highest in leafless period of spring.
In both forest, the lowest fluxes betwwen soil/snow-air were in winter and fluxes in daytime were much higher than that in night, highest in midnoon. For differet plots in each forest, the highest fluxes were in the bare soil plot, lowest in wetland which was annual overall deposition in subtropical forest. For the temperatural forest, the highest fluxes were in the wetland, subsequently in bare soils and fluxes in deciduous forest were higher than that in evergreen forest.
       Using the flux data measured with solar radiation, air TGM concentrations, soil moisture contents and temperatures, and soil mercury concentrations in the five plots,empirical model for estimating soil-air flux were developed. A major implication is that once atmospheric mercury concentrations decreased, it may be likely subjected to renewed TGM re-emission from terrestrial surface to the atmosphere emphasizing the important role of soils in compensating and equilibrium with atmospheric TGM.
      Flushing flow rates significantly affected the calculation of mercury flux and the optimal TOTs was 0.94 min in the forest. TGM in atmosphere was significantly inhibited mercury emission from soils. Initial watering produces a spike in the mercury emissions due to the interstitial soil gas mercury displaced by infiltrating water physically. However, subsequent watering was reducing the fluxes. Soils under the understory had a higher mercury concentrations and deep organic layers. However, the fluxes of soil under the understory significantly were inhibited in daytime because solar radiation was blocked by the understory and the higher litter layer. To further study the mechanism of soil TGM emissions, pore TGM in soil profiles were studied. The highest concentrations consistently occurred in the upper mineral horizons and organic soils in subtropical forest, and in sub-organic layers in temperatural forest.
       Field observation and simulation experiments in showed that subtropical forest showed that TGM in air and water in soils can significantly inhibited mercuy emission from forest soils. Soil mercury content, solar radiation and soil temperaturcan accelerate mercuy emission. Conbined the five parameters and fluxes in each plot, regression equation were developed. The empirical models present in this study demonstrate a promising approach for better estimates of Hg exchange flux between atmosphere and soil.
       Undoubtedly, Air-borne depositions are the main source of mercury in soils. Forest were large nercury pools and sinks. The annual deposition flux of THg was 2 yr 1 in the subtropical forest and Pinus tabulaeformis, Quercus liaotungensis, broadleaved mixed and Larix principis-rupprechtii forest in Donglingshan were 3.96 ± 0.91, 3.53 ± 0.81, 3.22 ± 0.75 and 4.90 ± 0.78 2 yr 1 The concentration and mass of THg and MeHg were forest stand-depended and increased in both the coniferous and broad-leaf litter during the one-year
decomposition. Mercury was mainly resident in residual fraction, which was exceed 90%. Mercury in water soluble and salt soluble fractions were significantly correlated with MeHg concentrations during litter decomposition, which may be the potential fraction that can be methylated by bacterial.THg pool from litter to mineral topsoil was 14.53 mg m 2, which were strongly dependent on the storage of TOM stored: THgpool = 2.4 TOMpool+4.1. THg concentrations in stream waters and soil/air exchange flux of mercury would be increased along with the decrease of the altitude.
      Therefore, elevated mercury concentrations in runoffs and volatilization from soil were identified as the major pathway for increasing THg losses gradually along with the down of the elevation height. Total ecosystem mercury pool in subtropical forest was 103.5 mg m 2, and Pinus tabulaeformis, Quercus liaotungensis, broadleaved mixed and Larix principis-rupprechtii forest in Donglingshan were 7.7 7.6 5.1 and 10.8 mg m 2, while more than 97% mercury was stored in the soil.
      Based on measurement and estimation of atmospheric Hg deposition (67.34 m 2 yr 1) in the subtropical forest. Mercury relesase from runoff and emission from soil-air flux were 2 yr 1 2 yr 1. Thus, the Hg sequestrated in forest soil were 40.02 μg m 2 yr 1, accounting for 62.9% of THg deposition (Zhou et al., 2016). Therefore, it can be deduced that the subtropical forest in TFP is a large sink of atmospheric Hg and soils of forested watershed is a large reservoir of deposited Hg. The consequences of elevated mercury input were ecological stress to humans and animals, and additionally large fluxes of TGM to the global atmospheric
pool during forest fires. Especially for the insects living in the forest soils, mercury concentrations measured in dung beetle were 40 and 283 times higher than that in cicada and longicorn。
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/37060
Appears in Collections:大气环境研究室_学位论文

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Recommended Citation:
周俊. 我国典型森林汞库及土壤-大气汞交换通量研究[D]. 北京. 中国科学院研究生院. 2016.
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