Spatial-Temporal Patterns of Litterfall Mercury Concentration and Flux in Typical Vegetation in China

Mercury is one of the most toxic heavy metal pollutants, and mercury absorbed by plant leaves accumulates in forests in the form of litterfall. Therefore, in this study, leaf mercury concentrations and mercury fluxes were analyzed in typical sample plots of each vegetation type, which were selected from 7 geographic regions in China. The results showed that the amount of litterfall of each component varied among different vegetation types, with leaves accounting for the largest proportion (51.12% to 80.54%). The annual amount of leaf litter ranged from 3.35 to 5.50 t/(hm2<middle dot>year). On the seasonal scale, the litterfall amount peaked in the autumn for most vegetation types. On a spatial scale, the litterfall amount displayed a decreasing trend with increasing latitude, with the highest of 8.16 +/- 4.61 t/(hm2<middle dot>year) in the southwestern China, and the lowest was 2.98 +/- 0.89 t/(hm2<middle dot>year) in north China. Moreover, leaf litter mercury concentrations ranged from 2.11 to 236.70 ng/g, with a mean value of 57.92 +/- 33.07 ng/g. Leaf mercury concentrations of most tree species increased gradually with the growing period and showed a pattern of higher in the south and lower in the north on the spatial scale. Furthermore, leaf mercury fluxes of the 5 vegetation types ranged from 177.58 to 410.50 mg/(hm2<middle dot>year), and the accumulation of mercury mainly occurred in autumn. The comprehensive quantification of mercury fluxes in this paper provides data support for the long-term monitoring of litterfall and fundamental information to potentially solve the problem of mercury pollution in China.