上海市不同城市化水平区域森林土壤中汞形态特征

Urbanization and plant community play important roles in mercury migration and transformation in soils. To investigate the characteristics of mercury along an urbanization gradient, we analyzed the total mercury (THg), methylmercury (MeHg), and total organic carbon (TOC) concentrations in the soil of three forests, i.e. Cinnamomum camphora forest, Metasequoia glyptostroboides forest and evergreen-deciduous mixed forest, from the outer suburb, inner suburb and central urban district of Shanghai. The speciation of soil mercury was analyzed by thermal analysis method. The results showed that: (1) the THg concentration in the surface soil (0-2 cm) of urban forests varied from 34.01 to 317.98 ng·g^-1, with an obvious spatial pattern of central urban district > inner suburb > outer suburb, indicating that soil mercury was affected by urbanization. Based on the annual data, MeHg concentration of surface soil was correlated with THg concentration (R² = 0.323, P<0.01) instead of soil TOC concentration (P> 0.05). (2) Across the 0-20 cm soil profile, soil MeHg concentration was significantly positively correlated with both THg and TOC concentrations (R²_THg = 0.231, R²_TOC = 0.588, P<0.01). Hg forms affected the formation of mercury methylization. The speciations of adsorbed and organically bound mercury were important factors influencing the methylation of mercury in soil. (3) Compared to Cinnamomum camphora forest, soil MeHg concentration was higher in Metasequoia glyptostroboides forest and mixed forest, indicating that soils under deciduous trees were more methylated.