| Shanghai Green Belt is the largest cross-century ecological engineering in Shanghai. As the most significant aspect of environmental pollution, the heavy metal contamination on road not only affects the surrounding soil, plants and atmosphere environment, but affect human health through food chain. The heavy metal contamination on road has attracted high attention so far. In this study, based on the field survey data in Shanghai Green Belt, which contained 13 segments and 37 plots, through the investigation on the plant community structure and the soil chemical properties, Cu, Zn, Pb, Cd content and these four heavy metals content and magnetism characteristic in tree rings, we assessed the pattern of heavy metal distribution in soil, evaluated the soil pollution condition and explored the formation mechanism of heavy metals in soil and tree rings and heavy metal enrichment effect. Main findings were:(1) Generally, the soil was in alkaline condition. The total nitrogen, total phosphorus and organic matter content in soil were low.(2) Shanghai Green Belt was in slight degree of soil heavy metal pollution. The variance of four heavy metal content were different (Pb>Cd>Cu>Zn). The single heavy metal pollution index, index of four kinds of heavy metal pollution ranked as Cd>Pb>Zn>Cu. The slightly polluted level held most area for Cu, Zn and Cd, while security level held most area for Pb.Nemerow pollution index method showed that the soil overall remained slightly polluted. Through potential ecological risk index evaluation, the heavy metal Cd was under moderate ecological risk, while heavy metal Cu, Zn and Pb were under slightly ecological risk. Samples under different ecological risk ranked as slightly ecological risk> moderate ecological risk = ecological risk> strong ecological risk= extremely strong ecological risk. Through geo-accumulation index assessment, in addition to some plots under slight polluted, partial moderate polluted, moderate polluted and heavily polluted, the rest was under clean. Cu’s, Zn’s content decreased with the increase of soil depth.(3) Cu’s content was positively correlated to the age of constructive species leaves; Zn’s content was not correlated to all six factors; Pb’s content was positively correlated to the height of plant and the age of green belt; Cd’s content was positively correlated to the height of plant and the age of green belt, while negatively correlated to the distance from plots to outer ring. The heavy metal content was positively correlated to the vertical structure of community, i.e. heavy metal content ranked with the vertical structure of community as arbor-shrub-grass compound land>arbor-shrub compound land>arbor-grass compound land>arbor land. And positively correlated to leaf properties of constructive species, that is, under the broad-leaf forest soil’s heavy metal enrichment ability was higher than condition of the coniferous forest. Four heavy metal element had no correlation with pH, total nitrogen and total phosphorus, while Zn and Cd were positively correlated with organic matter content. The heavy metal content in soil was influenced by multi-factors, including the average height of plants,the age of green belt, the distance to outer ring road, vertical structure of community, characteristics and ages of build group’s leaves, and soil physical and chemical properties.(4) Cu’s, Zn’s content increased from 2005 to 2014, no significant change in the content of Pb and Cd. The content of heavy metals in 10-year ring section, five-year ringsection and Cd’s content in soil showed significant positive correlation. Camphor rings enriched the four kinds of heavy metal with ranking order Cu> Cd≈Zn>Pb.Camphor rings’ enrichment capacity for the four heavy metal had no correlation with soil chemical properties. Cu, Zn and SIRM showed significant positive correlation, while Pb, Cd and SIRM has no correlation. |
PDF Full Text Request