Forests play an important role in global mercury (Hg) cycling. A previous study showed that the forest soil in South China is more prone to accumulating Hg than that in North China. Subtropical forests in South China are among the largest terrestrial carbon sinks; however, it is unknown whether high carbon sequestration is associated with high Hg accumulation in the subtropics.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study to explain the high Hg accumulation in subtropical forest ecosystems. They monitored soil Hg storage, carbon (C), nitrogen (N), and sulfur (S) dynamics, and litterfall production for seven years (from 2007-2013) in an old-growth moist evergreen broadleaf (EB) forest and a mossy coppice (MC) forest in the Ailaoshan Station for Subtropical Forest Ecosystem Research Studies (ASSFERS, 24°32′N, 101°01′E,) at 2450–2650 m above sea level.
The researchers collected soil profiles from 6 plot values × 7 years in the evergreen broadleaf (EB) forest and mossy coppice (MC) forest respectively. They observed the variations in soil Hg concentration and found that annual variations in Hg concentration were suggested to be associated with variations in precipitation and litterfall biomass. The EB forest had higher Hg/C ratios than the MC forest mainly because of higher atmospheric/foliar Hg inputs, i.e. higher leaf litter production.
They further found that the soil Hg concentration was significantly associated with the C concentration for the two different soil layers (O- and A-horizons) of the MC forest. However, there was no correlation between the Hg and C concentrations in the O-horizon of the EB forest.
Moreover, they found that Hg/C ratios increased with decreasing C/S ratios, suggesting that the dynamics in soil Hg concentration was closely linked to S concentration.
The results suggested that subtropical forests in South China were accumulating a high amount of Hg because of their high litter production and the interaction between Hg and S in the surface soil.
The study entitled “High mercury accumulation in two subtropical evergreen forests in South China and potential determinants” has been published online in Journal of Environmental Management.
Contact
SHA Liqing Ph.D
Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China
E-mail: shalq@xtbg.ac.cn
