大九湖泥炭地距今16000年以来Hg沉积记录及影响因子

摘要

神农架大九湖盆地距今16000年以来的泥炭沉积被用来分析Hg含量变化及其主要影响因子.基于剖面Ti、Al、Sc、Rb、Sr、Pb、Zn等元素含量和δ13C、腐殖化度等指标,主成分分析和逐步回归分析揭示泥炭剖面Hg含量变化主要受大气降尘、地表径流作用下的矿物质输入、大气降水、泥炭分解程度等因子影响.根据各因子影响Hg含量的强度随年代(深度)变化以及剖面Hg含量变化,距今16000年以来大九湖泥炭剖面的Hg记录可以分为6个阶段.在阶段Ⅰ(16.0~15.6cal kyr BP),Hg含量低值源于大气降尘减少和泥炭分解程度降低;第Ⅱ阶段(15.6~14.2cal kyr BP)大气降水增加以及陆地生物量增多、陆源有机物输入增多,导致Hg含量升高;阶段Ⅲ(14.2~11.3cal kyr BP)Younger Dryas时期(YD,12.3~11.3cal kyr BP),因大气降尘增多,泥炭分解程度增加,Hg含量较YD之前升高;第Ⅳ阶段(11.3~4.3cal kyr BP),各因子作用波动明显,Hg含量整体处于高值段;在第Ⅴ阶段(4.3~3.1cal kyr BP)气候转干,大气降尘也较低,Hg含量出现明显的降低.第Ⅵ阶段(3.1cal kyr BP以来)表现出大气降尘的逐渐增加和整体减少的矿物质输入,反映降水减少以及逐渐增强的人类活动影响,Hg含量则持续升高.%In the present study, a peat core sampled in Dajiuhu montane mire, Hubei province, extending back to 16,000yr BP was analyzed for Hg accumulation and main environmental processes involved in the control of Hg concentrations. Based on Ti, Al, Sc, Rb, Sr, Pb and Zn contents as well as humification and δ13C of the core, principal component analysis (PCA) and stepwise regression analysis revealed that main processes controlling Hg concentrations included the mineral input by precipitation and runoff (PC1), dust deposition (PC2), wet deposition (PC3) and peat decomposition (PC4). On the basis of the relative importance of each factor on Hg concentrations, the 16,000yr record of the Dajiuhu peat core could be divided into six main phases. During phaseⅠ(16.0~15.6cal kyr BP), reduced regional dustfall and peat decomposition resulted in decreased Hg concentrations. In PhaseⅡ(15.6~14.2cal kyr BP) ,significantly increased atmospheric wet deposition and fluxes of particulate and dissolved terrestrial organic matter from soils under enhanced terrestrial productivity after the last glacial period were probably responsible for higher Hg concentrations. In phaseⅢ(14.2~11.3cal kyr BP), Hg concentrations were enhanced later during the Younger Dryas(12.3~11.3cal kyr BP) by increased regional dustfall and peat decomposition. During phaseⅣ(11.3~4.3cal kyr BP), although significant volatility of the four factors, Hg concentrations were higher as a whole. Lower Hg concentration in phaseⅤ(4.3~3.1cal kyr BP) were mainly resulted from apparent decrease in atmospheric wet and dry deposition. In phaseⅥ(3.1cal kyr BP to present), the Hg concentration increased with decreasing depth, albeit with evident volatility. This phase was characterized by reduced input of mineral matter into the mire and gradual increase in regional dustfall, indicating precipitation reduction and progressively increasing influence of anthropogenic activities on Hg accumulation in the peat.