Temporal And Spatial Characteristics Of Mercury Cocentration In Environmental Media In Urban Parks And Its Environmental Implications

Mercury?Hg?was the only long-distance gaseous pollutant in heavy metals,which seriously threatened the ecosystem and human health.With the enhancement of human production activities,it is believed mercury emission have changed the global natural cycle of mercury,especially in densely populated urban areas.Parks play an important role in the urban ecosystem,and the Hg concentration characteristics in environmental media can comrehensively reflect the pollution status and distribution characteristics of Hg in urban space.In this study,the spatial and temporal distribution characteristics of Hg concentration in three environmental medias including leaves,topsoil and surface sediments in urban parks were analyzed,and the spatial correlation between mercury concentration in different environmental medias and human activities was discussed.On this basis,an effective environmental index is established to analyze the impact of mercury emissions from human activities on the regional environment.Furthermore,provided scientific basis for mercury circulation mechanism and pollution prevention at the city scale.After this study,the main conclusions were as followed:1.Results showed that total leaf Hg concentrations in camphora?Chinnamomum camphora?L?Presl?,plane?Oriental plane?,metasequoia?Metasequoia glyptostroboides?and prunus serrulata?Cerasus sp?trees were increased from May to November 2019?from emergence to senescence?and showed a strong positive correlation with leaf age?P<0.01?,indicating that leaves accumulate Hg throughout the growing season.Although Hg concentrations in four trees showed a significant interspecies difference?P<0.01?,the daily Hg accumulation rates(?g/kg?d^-1),presented the similar seasonal variation during the growing season,thevalue first rose and then fell from May to September,and showed an upward trend from Spetember to November,suggesting that the uptake dynamics of Hg in leaves could be mostly related to environmental conditions,except for the interspecies difference.2.The leaf Hg concentrations of camphora,plane,metasequoia and prunus serrulata tree were 36.8 4?30.0⁴4.2??g/kg,51.3 8?42.2⁶0.1??g/kg,53.5 8?40.4⁸5.4??g/kg and 66.7 12?46.4⁹6.7??g/kg in 44 parks of Shanghai in november,respectively.There was no significant correlation between the leaf Hg concentrations of the four tree species and the THg concentration in the topsoil,which meant that the contribution of Hg in soil to leaf Hg was negligible.3.The relationship between the maximum and minimum Hg concentration in leaves of the same tree species in November:camphora 1.5,plane 1.4,metasequoia2.1 and prunus serrulata 2.1,which indicated that the spatial distribution gradient differcnce of gaseous element mercury?GEM?in the atmosphere of parks in Shanghai may not be large.Although there was a fine-scale differences in the spatial patterns of senescing leaf Hg concentrations of the four trees in November,the high leaf Hg concentrations of all four trees species occured in Jiading District,Baoshan District,Jinshan District,which was basically consistent with the spatial distribution of industrial in Shanghai.This suggested that leaves may not reflect subtle gradients of atmospheric gaseous elemental mercury?GEM?under regional conditions,but at a relatively large spatial scale,it was an effective method to monitor the concentration of GEM by analysising leaf Hg of various trees.4.The measured biomass of fallen leaves is 810 g/m²·yr^-1,combined reported fallen leaf biomass date to estimate the depositon flux range of fallen leaf Hg was26.6⁴5.3?g/m²·yr^-1 in parks in Shanghai.It was higher than the flux of litterfall Hg in Mt.Damei(16.3²9.1?g/m²·yr^-1),which is close to Shanghai.5.The average concentration?min^max?of total mercury?THg?in topsoil and surface sediments were 186.7±165?37.4⁷5.2?,115±107.4?28.4⁵10.5??g/kg in Shanghai parks,respectively,and exceeded the soil background values of THg concentration?95?g/kg?.There was a significant positive correlation between THg concentration and tatal organic carbon?TOC?concentration in topsoil and surface sediment?P<0.01?.There was a highly similar spatial distribution pattern of THg:TOC ratio between topsoil and surface sediment,which showed that the central urban area was a high value area,and was basically consistent with the spatial distribution pattern of urbanization and industrial layout.Results of our study suggest THg:TOC ratios are a useful normalized indicator of the infuence of anthropogenic Hg releases on Hg enrichment in topsoil and surface sediment.6.The environmental medium were not polluted by Hg in several potential Hg pollution areas were investigated by this research.The high senescing leaf Hg concentrations value point calculated by the judgment model established in this study were all distributed in potential mercury pollution areas,such as coal-fired thermal power plants or metal smelters,which suggested that the calculation result of the model was credible and the model has certain application value.The THg pollution assessment results showed that the THg pollution risk of topsoil is higher than that of surface sediments.The results of Hg concentration in two media indicated that the mercury pollution risk in the central urban area was relatively high,followed by industrial areas or transportation hubs such as Jinshan District,Songjiang District,Baoshan District and Jiading District.The park environment in Qingpu District,Minhang District and Fengxian District is not polluted.