Historical Records of Mercury Stable Isotopes in Sediments of Tibetan Lakes.

Runsheng Yin,Handong Yang,Shichang Kang,Ryan F Lepak,James P Hurley,Xiangdong Li,David P Krabbenhoft,Xinbin Feng

doi:10.1038/srep23332

Abstract

The Tibetan Plateau (TP), known as the “Third Pole”, is a critical zone for atmospheric mercury (Hg) deposition. Increasing anthropogenic activities in the globe leads to environmental changes, which may affect the loading, transport and deposition of Hg in the environment. However, the deposition history and geochemical cycling of Hg in the TP is still uncertain. Our records of Hg and Hg isotopes in sediment profiles of the two largest lakes in the TP, Lake Qinghai and Nam Co, show increased Hg influx since last century, with the maximum Hg influx enrichment ratios of 5.4 and 3.5 in Lake Qinghai and Nam Co, respectively. Shifts in negative δ 202Hg in Lake Qinghai (−4.55 to −3.15‰) and Nam Co (−5.04 to −2.16‰) indicate increased atmospheric Hg deposition through rainfall, vegetation and runoff of soils. Mass independent fractionation of both even-Hg (∆ 200Hg: +0.05 to +0.10‰) and odd-Hg (∆ 199Hg: +0.12 to +0.31‰) isotopes were observed. Positive Δ 200Hg suggest high proportion of precipitation-derived Hg in the TP, whereas the positive Δ 199Hg results from Hg(II) photo-reduction. Both lakes show increasing Δ 199Hg since the 1900 s, and we conclude that with the decrease of ice duration, Hg(II) photo-reduction may have been accelerated in these TP lakes.

Highlights

The Tibetan Plateau (TP), known as the “Third Pole”, is a critical zone for atmospheric mercury (Hg) deposition
Large variations of both Hg-mass dependent fractionation (MDF) and -mass independent fractionation (MIF) signatures have been documented in different environmental compartments[16], and can provide multi-dimensional information to identify the sources and better understand biogeochemical Hg cycling[15]
Historical sediment profiles from both Lake Qinghai and Nam Co show a general trend of increasing total Hg concentration (THg) over the past century (Fig. 2A)

Summary

OPEN Historical Records of Mercury

Stable Isotopes in Sediments of Tibetan Lakes received: 13 October 2015 accepted: 29 February 2016. The TP has warmed over the past several decades at twice the global average rate[13] This has resulted other dependent changes such as cryospheric systems and hydrological regimes12–14, 1State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China. Sediment profiles collected from two of the largest lakes in the TP (Lake Qinghai and Nam Co) were age-dated and analyzed for total Hg concentration (THg) and Hg isotopic composition. Based on the measured THg concentration [Table S1 of Supplementary Information (SI)], samples and certified reference materials (NIST 2711 and MESS-2) were digested and diluted prior to isotopic measurement on a Neptune Plus MC-ICP-MS housed at the University of Wisconsin-Madison’s State Laboratory of Hygiene. Where β is the independent isotope-specific scaling factor determined by the laws of MDF, which 0.2520 for 199Hg, 0.5024 for 200Hg, and 0.7520 for 201Hg

Results and Discussion

Author Contributions

Additional Information