State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.
State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; CAS Centre for Excellence in Quaternary Science and Global Change, Xi'an 710061, China.
Sci Total Environ. 2021 May 15;769:144892. doi: 10.1016/j.scitotenv.2020.144892. Epub 2021 Jan 14.
Karst regions have long been recognised as landscapes of ecological vulnerability, however the mass balance and fate of mercury (Hg) in karst regions have not been well documented. This study focused on the largest contiguous karst area in China and investigated Hg mass balance in two catchments, one with high geological Hg (Huilong) and the other representative of regional background Hg (Chenqi). The mass balance of Hg was calculated separately for the two catchments by considering Hg in throughfall, open field precipitation, total suspended particulate matter (TSP), litterfall, fertilizer, crop harvesting, air-surface Hg exchange, surface runoff and underground runoff. Results show that litterfall Hg deposition is the largest loading (from atmosphere) of Hg in both catchments, accounting for 61.5% and 38.5% of the total Hg input at Huilong and Chenqi, respectively. Air-surface Hg exchange is the largest efflux, accounting for 71.7% and 44.6% of the total Hg output from Huilong and Chenqi, respectively. Because both catchments are subject to farm and forest land use, cultivation plays an important role in shaping Hg fate. Mercury loading through fertilizer was ranked as the second largest input (28.5%) in Chenqi catchment and Hg efflux through crop harvest was ranked as the second largest output pathway in both Huilong (27.0%) and Chenqi (52.9%). The net Hg fluxes from the catchments are estimated to be 1498 ± 1504 μg m yr and 4.8 ± 98.2 μg m yr. The significantly greater magnitude of net Hg source in Huilong is attributed to higher air-surface Hg exchange. The output/input ratio of Hg in this study was much greater than has been reported for other forest or agricultural ecosystems and indicates that the karst region of Southwest China is a significant source of atmospheric Hg. The results of this study should be considered in the development of pollution control policies which seek to conserve fragile karst ecosystems characterised by high geological background of Hg.
岩溶地区长期以来一直被认为是生态脆弱的景观，然而，岩溶地区汞的质量平衡和归宿尚未得到很好的记录。本研究集中在中国最大的连续岩溶区，调查了两个集水区的汞质量平衡，一个集水区具有高地质汞（回龙），另一个代表区域背景汞（陈旗）。通过考虑穿透雨、开阔场降水、总悬浮颗粒物（TSP）、凋落物、肥料、作物收获、空气-表面汞交换、地表径流和地下径流中的汞，分别为两个集水区计算了汞的质量平衡。结果表明，凋落物汞沉积是两个集水区最大的汞负荷（来自大气），分别占回龙和陈旗总汞输入的 61.5%和 38.5%。空气-表面汞交换是最大的流出量，分别占回龙和陈旗总汞输出的 71.7%和 44.6%。由于两个集水区都受到农田和林地的利用，耕作在塑造汞归宿方面起着重要作用。通过肥料输入的汞负荷被列为陈旗集水区的第二大输入（28.5%），通过作物收获的汞流出被列为回龙（27.0%）和陈旗（52.9%）的第二大输出途径。集水区的净汞通量估计为 1498±1504μg m yr 和 4.8±98.2μg m yr。回龙净汞源的显著较大幅度归因于更高的空气-表面汞交换。本研究中汞的输出/输入比值远高于其他森林或农业生态系统的报道，表明中国西南岩溶地区是大气汞的重要来源。在制定旨在保护以高地质背景汞为特征的脆弱岩溶生态系统的污染控制政策时，应考虑本研究的结果。
