天山雪岭云杉树木年轮汞记录对区域大气汞历史演变的重建及其方法验证

Method Validation of the Reconstruction of the Historical Evolution of Regional Atmospheric Mercury by the Tree-Ring Mercury Records of Schrenk Spruce at Mt.Tianshan

树木年轮是一种新兴的重建历史大气汞趋势的自然档案,但其可靠性还需进一步完善。本研究以中国天山雪岭云杉(P.schrenkiana Fischet Mey.)为研究对象,探讨了环境因子和幼龄效应对树轮汞(Hg)浓度的影响,并将树轮汞记录与新疆地区人为汞排放资料和其他研究数据对比,以评估雪岭云杉树轮汞记录的可靠性。结果表明:树轮汞浓度存在一定的个体性差异。相关分析显示新疆乌鲁木齐的年平均日照时数与雪岭云杉树轮汞浓度呈显著性正相关(R^(2)=0.65,P<0.05),说明环境因子可通过影响树木生长进而影响树轮汞记录。受幼龄效应的影响,雪岭云杉树木幼龄期的汞数据不能很好地反映大气汞浓度的变化趋势,但去除这部分数据后可以较好地重建历史大气汞水平。最后,结合新疆地区人为汞排放资料和后向气团轨迹分析,表明新疆地区大气汞浓度的提高主要与近20年来新疆地区人为汞排放的增加,以及与我国西北部相邻的中亚国家排放的大气汞经西风带跨境传输进入新疆有关。经进一步规范和完善,树轮可成为重建大气汞变化趋势可靠的自然档案。

Tree rings have been regarded as an emerging natural archive to reconstruct historical atmospheric mercury(Hg)trends,but its reliability needs to be further improved.In this study,Schrenk Spruce tree rings in the Tianshan Mountains of China were chosen as the research object to explore the influence of environmental factors and tree age effect on tree-ring Hg concentration.The treering Hg records were also compared with anthropogenic Hg emission data in Xinjiang and tree-ring Hg data of other studies to assess the reliability of Schrenk Spruce tree-ring Hg records.Results showed that there are tree-specific variations in the tree-ring Hg concentration of Schrenk Spruce.Correlation analysis showed that the annual average sunshine hours of the study area were significantly positively correlated with the tree-ring Hg concentration(R^(2)=0.65,P<0.05),indicating that environmental factors can affect the growth of trees,thus affect the tree-ring Hg records.Besides,the temporal variation of atmospheric Hg cannot be reflected well by tree-ring Hg data of the young growth period due to the age effect,but it can be better reconstructed after discarding this part of the data.Finally,combined with the anthropogenic Hg emission data in Xinjiang and the analysis of the trajectory of backward air masses,the increase in atmospheric Hg concentration in Xinjiang is mainly related to the increase of anthropogenic Hg emissions of Xinjiang in the past two decades,as well as the cross-border transmission of atmospheric Hg from central Asian countries adjacent to northwest China into Xinjiang through the westerly wind belt.With further standardization and improvement,the tree ring can become a reliable natural archive for reconstructing the historical atmospheric Hg concentration trends.