Mercury (Hg) is a highly toxic persistent pollutant that poses a threat to health of human and ecosystems. Given that Hg transport and retention on forest floor are often closely linked to natural organic matter (NOM), the stochiometric relations of Hg with carbon (C) and nitrogen (N) have been used as tracers to infer causes and ultimate fates of Hg sequestration in forest ecosystems. However, few studies have displayed the relations among isotopes of C, N and Hg.
In a study published in Environmental Pollution, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and Institute of Geochemistry investigated the C, N and Hg isotopic signatures on evergreen broadleaf (EB) forest floor to verify whether the interplays among isotopes of C and N would provide a new insight in the sequestration and reduction processes of deposited Hg on forest floor.
The researchers measured isotopes at the evergreen broadleaf forest floor at Mt. Ailao (Mountain Ailao) and showed that δ202Hg and Δ199Hg both significantly correlated with δ13C and δ15N in soil profiles.
They identified the microbial Hg reduction as the main cause for the Hg mass-dependent fractionation(MDF) shift and dark abiotic NOM reduction for the Hg mass-independent fractionation (MIF) shift on forest floor by analyzing Hg, C, N and their isotope data.
They also have found that higher N in foliage can lead to greater Hg concentration, and N release and immobility on forest floor was closely linked to the microbial reduction induced Hg0 re-emission.
“We thus suggest that the enhanced N deposition in global forest ecosystems can potentially influence Hg uptake by vegetation and litter Hg sequestration on forest floor,” said LU Zhiyun of XTBG.
Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China
Interplays among isotopes of C and N provide new insight in Hg reduction on forest floor (Image by LU Zhiyun)