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Subtropical Forests Act as Mercury Sinks but as Net Sources of Gaseous Elemental Mercury in South China
journal contribution
posted on 2020-02-21, 20:11 authored by Qian Yu, Yao Luo, Guangyi Xu, Qingru Wu, Shuxiao Wang, Jiming Hao, Lei DuanComprehensive
mercury (Hg) budgets were constructed in two typical
subtropical forests in southern China in 2014 to quantify Hg (gaseous
elemental Hg, Hg0, and reactive Hg, HgII) input
and output fluxes and Hg retention in forests, consequently exploring
the roles of subtropical forests in the global Hg cycle. At site Qianyanzhou,
representing a background region with an enhanced atmospheric Hg0 concentration, the total HgII deposition (67.7
μg·m–2·year–1,
73% as dry HgII deposition) was found to be slightly higher
than the Hg0 emission above the canopy (58.5 μg·m–2·year–1), indicating that the
forest is a minor Hg sink but a significant net Hg0 source
on a yearly basis. In contrast, the forest in the moderately polluted
region (site Huitong) acted as a significant Hg sink but a minor net
Hg0 source with a higher HgII deposition (73.7
μg·m–2·year–1)
and relatively negligible Hg0 emission (2.65 μg·m–2·year–1). The decreasing atmospheric
Hg0 concentrations declined the total Hg sink based on
the Hg budgets synthesized of this and previous studies and may promote
forest Hg0 emissions. Consequently, it was expected that
the re-emission of historically deposited Hg may be enhanced from
subtropical forests by recent decreases in atmospheric Hg0 concentrations throughout China.