| Mercury is a global pollutant with serious biological toxicity, and it will cause serious harm to human health after being enriched and enlarged by organism. Greenland in the urban parks is an important part of urban construction and urban ecosystem, also a unique regulator for the urban environment and it responses to environmental pollution sensitively. Plants in the urban parks are important input and output channels for mercury in urban ecosystem. Study on the biogeochemistry of mercury in urban parks can not only reflect the habitat of plants for objective evaluation of the city’s environmental quality, but also help analyze influencing factors on mercury concentration and sources of mercury pollution, according to the relationship between mercury pollution in plants and natural environmental elements, thus providing a scientific basis for the prevention and control of mercury pollution in the city. Camphor leaf, Haplocladium moss and topsoil samples of four seasons were collected along the year as the research object. This research conducts experimental analysis on mercury and heavy metals contents in the samples, using geostatistical and multivariate statistical methods. Thus it compares spatial and temporal variations of mercury content of Camphor leaves directly, explores the relationship between mercury in plants and meteorological environmental factors, as well as the sources of mercury and other heavy metals in Camphor leaves. The conclusions on this research are as follows:1. The mercury content of Camphor leaves in urban parks in Shanghai is in the range of 0.0166-0.1326 μg·g-1 and the average value is 0.0675 μg·g-1, which is high. Nemerow multi-factor index demonstrates that the mercury pollution in the Camphor leaves is middle-polluted level in the studying area reaching 2-3. The order of the level of mercury comprehensive pollution in leaves was:spring> summer>winter>autumn.2. The spatial distribution of mercury in leaves of the four seasons in the studying area was overall similar, showing a pattern that the degree of pollution is higher in the northwestern part than that in the southeastern part. In spring and autumn, the extent and degree of pollution are greater than that in summer. Besides, Jiading District District, Baoshan District, Qingpu and the central urban area are where mercury pollution concentrates, while Pudong District is a low value area of mercury concentration. The mercury content in leaves changes significantly along the seasons with an order of spring> winter> autumn> summer, which demonstrates that the content of mercury in leaves accumulates while growing.3. In temporal and spatial distribution Mercury content in leaves corresponds with the wind speed in Shanghai during the research. For the wind direction, areas with high pollution level mainly are downwind areas in the four seasons especially in summer. For the wind speed, contaminant is widely distributed in autumn, winter and spring season due to the large wind speed while it mainly distributed in the vicinity of typical urban industrial area in summer as the wind speed is relatively small. There is obvious negative correlation between the annual precipitation and mercury content in leaves. Precipitation is concentrated in summer and autumn with large amount while it’s small in winter. On the contrary, mercury content in leaves is lowest in summer and highest in spring. The amount of mercury content is relatively low in areas with larger precipitation and it is relatively high in areas with small precipitation. By correlation analysis between mercury content in leaves of spring in the studying area and regional mean of PM2.5, it indicates that mercury content in leaves is positively and significantly correlated with PM2.5(P<0.01), and is not correlated with dust deposition(P>0.05).4. The total mercury content in topsoil and Haplocladium are respectively between 0.1155～0.3877 μg·g1 and 0.0938-0.2789μg·g-1,with an average of 0.2535 μg·g-1 and 0.1586 μg·g-1. It can be drawn that the absorptive capacity on mercury of moss is superior to that of leaf. Correlation analysis between mercury content in leaves of spring and that of topsoil shows no significant correlation(P>0.05), which indicates that the absorption of mercury from the soil was limited. Besides, the average content of mercury in the moss along the seasons is winter> autumn> spring> summer. Correlation analysis between mercury content in leaves and that of moss shows a significant correlation(P<0.01), which demonstrates that the absorption of mercury of leaves and moss are similar and mercury is mainly absorbed from the atmosphere. The research uses the multiple regression analysis to determine the source of heavy metals like mercury and the result indicates no statistical significance. The reason may be related to the complexity of the atmosphere-soil-leaf system itself and different ways of absorbing and accumulating elements.5. Correlation analysis between mercury and other heavy metals in leaves shows significantly positive correlation with Cr, Fe, Mn, Pb and Zn (P<0.01), positive correlation with Cu (P<0.05), The result of this analysis shows these heavy metals may come from the same source. In addition, cluster analysis on heavy metals in leaves showed that the elements in the leaves can be divided into three classes according to distance, with the first class including Ba, Ca, K and Na elements, the second including Al, Sr and Mg, and the third including Pb、Zn、Cu、Fe、Mn、Hg and Ni. Elements of the first class may be derived from marine aerosols, these of the second class from local dust and these of the third class from industrial activity and transportation like combusting fossil fuels and refining metals. The principal component analysis of heavy metals in leaves showed that four principal components could be extracted. The first principal component (F1) is the source of industrial and traffic pollution, with the contribution rate of 37.328%. The second principal component (F2) is the source of fugitive dust, with the contribution rate of 17.885%. The third principal component (F3) is the source of marine aerosols, with the contribution rate of 13.809%. Each element has a comparatively strong load on its corresponding principal component. |
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