Xia Jicheng, Wang Jianxu, Zhang Leiming, Wang Xun, Yuan Wei, Peng Tao, Zheng Lirong, Tian Weijun, Feng Xinbin
State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.
Water Res. 2022 Nov 1;226:119271. doi: 10.1016/j.watres.2022.119271. Epub 2022 Oct 19.
Guizhou Province is located in the heart of a karst zone in southwest China, which is one of the largest karst areas in the world. Given the fragile surface ecosystem and highly developed underground karst structure, the migration and transformation of soil Hg may impact groundwater quality in karst environments with high Hg background concentrations. This study examines the vertical migration and transformation of soil mercury (Hg) in two karst catchments, Huilong and Chenqi, with the former containing high Hg contents associated with mineralization and the latter representing regional background Hg. The results show that the soil Hg pool in the Huilong catchment was as high as 44.4 ± 4.2 g m, whereas in the Chenqi catchment was only 0.17±0.02 g m. Compared with farmland soil, forest soil showed a significant loss of Hg. The results of L X-ray absorption near edge structure of Hg indicated that α-HgS, the primary mineral of Hg ore, gradually changed to other mineral types during soil formation. In Huilong catchment, the proportion of organic bound Hg(SR) out of total Hg decreased from 44.0% to 20.3% when soil depth increased from 10 cm to 160 cm in farmland soil profile and from 39.3% to 34.5% in forest soil profile, while the proportion of ionic Hg increased with soil depth, from 4.2% to 10.7% in the farmland soil profile and from 6.7% to 11.6% in the forestland soil profile. Results from the triple-mixing isotope model show that soil Hg accounts for more than 80% Hg in groundwater in the two catchments. Results from this study indicate potential risks of soil Hg entering into groundwater in this karst area.
贵州省位于中国西南部喀斯特地区的中心地带，该地区是世界上最大的喀斯特地区之一。鉴于地表生态系统脆弱且地下喀斯特结构高度发育，土壤汞（Hg）的迁移和转化可能会影响汞背景浓度较高的喀斯特环境中的地下水质量。本研究考察了回龙和陈旗两个喀斯特流域土壤汞（Hg）的垂直迁移和转化情况，前者汞含量高与矿化作用有关，后者代表区域汞背景。结果表明，回龙流域的土壤汞库高达44.4±4.2 g/m，而陈旗流域仅为0.17±0.02 g/m。与农田土壤相比，森林土壤汞有显著损失。汞的L边X射线吸收近边结构结果表明，汞矿石的主要矿物α-HgS在土壤形成过程中逐渐转变为其他矿物类型。在回龙流域，农田土壤剖面中，当土壤深度从10厘米增加到160厘米时，有机结合汞（SR）占总汞的比例从44.0%降至20.3%，森林土壤剖面中从39.3%降至34.5%，而离子汞的比例随土壤深度增加，在农田土壤剖面中从4.2%增至10.7%，在林地土壤剖面中从6.7%增至11.6%。三混合同位素模型结果表明，两个流域地下水中80%以上的汞来自土壤汞。本研究结果表明该喀斯特地区土壤汞进入地下水存在潜在风险。
