Temporal and spatial/characteristics of mercury concentrations in leaves of common deciduous tree species in parks of Shanghai and its environmental implications

The linear relationships between the concentrations of gaseous element mercury (GEM or Hg0) and Hg concentrations in leaves suggests that leaves can be used as passive monitors of atmospheric Hg.In this study, total leaf Hg concentrations in three common deciduous tree species from 25 parks, including prunus serrulata (Cerasus sp.), metasequoia (Metasequoia glyptostroboides) and plane tree (Oriental plane), were investigated to study the uptake dynamics of GEM in leaves throughout the growing season, and improve an understanding of the spatial distribution of GEM in ambient air in Shanghai city area. Results showed that total leaf Hg concentrations in three trees were increased from May to October 2017 (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 the senescence of leaves among three deciduous species showed a significant interspecies difference (P<0.01), the daily Hg accumulation rates (jjig - kg 1 d 1) presented the similar seasonal variation during the growing season, suggesting that the uptake dynamics of Hg in leaves could be mostly related to environmental conditions, except for the interspecies difference. The senescing leaf Hg concentrations of prunus serrulata, metasequoia and plane tree were (54.2 ±12, 31.8—76.7) jjLg’kg-1, (42.0±9, 23.5— 67.9) ^g’kg 1 and (36.1 ± 11, 21.4—60.3) jJig’kg 1(average, range), in 25 parks of Shanghai, respectively. Furthermore, the senescing leaf Hg concentrations showed no significant differences between the downtown and the suburbs (P > 0. 05). The predicted results of Empirical Bayesian Kriging modeling for senescing leaf Hg concentrations in three deciduous species showed a relatively small gradient difference pattern. However, a different pattern was observed for spatial distribution of leaf Hg concentrations. These results indicated that there could be some uncertainty in using senescing leaf Hg concentrations to reflect the spatial distribution of GEM concentrations in the regional scale levels, which needs a further research.