Abstract
Mercury (Hg) deposition in the forest ecosystem is a significant source of input for methyl Hg (MeHg) and total Hg (THg) to the subtropical forest field and downstream aquatic systems. Wet deposition, litterfall, runoff, and fluxes with forest soil percolate of MeHg and THg were sampled for two years in a watershed forest of southwest China. Results showed that the depositions of THg and MeHg through litterfall and throughfall were 86 µg m−2 yr−1 and 0.8 µg m−2 yr−1 respectively, with litterfall acting as a predominant route for the input of both THg and MeHg. The estimated fluxes of THg and MeHg in the throughfall and litterfall were 3 and 4 times greater than those in the precipitation. Methylmercury in the decomposed litter migrates during its erosion by surface runoff and the concentrations of MeHg were quite consistent with that in the surface runoff. Methylmercury mainly accumulated in the lower layer of the litter and upper layer of the soil (Oi), and its transfer through the soil cross-section was delayed. THg retention was not consistent with MeHg, probably with lower soil layers (Oe and Oa) storing and enriching THg in the forest ecosystem. The forest floor of the lower soil is an effective sink for THg but not for MeHg. Methylmercury accumulated in decomposing litter and upper soil layer might transfer with soil percolate, possessing potential ecological risks for residents living around the downstream aquatic systems.
Highlights
Mercury (Hg) is a worldwide environmental contaminant that leads to the contamination of forest, soil, water, plants, snow, and others [1]
We aimed to investigate whether the differences in the behavior of methyl Hg (MeHg) and total Hg (THg) among different layers of the forest floor support the hypothesis that Hg, especially the MeHg, may be much easier to transport in the forest floor due to the dense canopies under the warm and watery subtropical climate and the regional elevated atmospheric
Mean concentrations of THg in the precipitation ranged than the open precipitation
Summary
Mercury (Hg) is a worldwide environmental contaminant that leads to the contamination of forest, soil, water, plants, snow, and others [1]. It is well accepted that elemental Hg (Hg0 ) can travel long distances in the atmosphere, impacting aquatic systems in remote regions through deposition [2,3,4,5,6]. Wet deposition of Hg in the forest is different with the water surfaces and non-forested areas, being largely dependent on the forest types. Mercury cycling in the forest ecosystem received more attention in the past years because the forest field plays crucial roles in the terrestrial cycling of total Hg (THg) and methylmercury (MeHg), acting as a link between the atmospheric and aquatic ecosystems [10,11]. Atmospheric Hg deposition is promoted in the forest system comparing with other ecosystems due to the large surface areas associated with canopy foliage
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