粉尘对祁连山冰川流域微量元素沉降和运移规律的影响

Aeolian (wind-blown) dust is an important source of trace and major elements to snowpack worldwide, as shown in ice core records from polar, mid-latitude, and tropical glaciers. Observation shows that dust contributes both soluble and insoluble mineral particles to precipitation, snowpack and ice, leading to differences in the fate and transport of trace elements during snow melting runoff. In addition to dust, other sources of trace elements loading to snowpack include anthropogenic emissions, sea salt spray, and volcanic tephra. In central Asian region, dust particle has very important effects on regional trace elements transport and deposition in alpine glaciers, and dust-mediated loading of trace elements to the glacier and melt affects the physicochemical properties of meltwater runoff. However, little studies have been carried out on trace element concentrations in snow, ice and meltwater runoff of the glacier basin in central Asia. Furthermore, no previous studies have reported trace element concentrations, and the correlation between trace and major elements with dust particles in the glacier basin in Qilian Mountains, China. This project will be conducted on a typical extreme continental glacial region in the Laohugou area, Qilian Mountains, northwest China. There are many large deserts of central Asia located around the Laohugou glacer basin. Observation shows that glaciers in this region may have been affected by Asian dust greatly. The project has great scientific significances to understand the influences of dust to trace and major elements loading in precipitaion,snowpack and meltwater runoff of the glacier basin in Qilian Mountains. Moreover, this project will provide the basis to understand and evaluate the sources, fate and transport of trace elements, and meltwater chemistry in arid regions of western China.

中亚粉尘及其大气传输过程中运载的许多微量物质对生物地球化学循环产生重要影响。粉尘对北半球冰雪中微量元素和主要化学元素的来源有重要贡献，大量可溶或不可溶粉尘的输入可导致冰雪及融水中微量元素迁移转化规律的变化。一些微量元素作为具有生物抑制作用的营养或有毒金属在流域生态系统中扮演着重要角色；而冰川流域微量元素研究已是目前国际上冰川相关研究的热点之一。本研究拟以中亚粉尘源区的祁连山老虎沟极大陆型冰川区的大气降水、雪冰资料和冰川融水径流资料，开展典型小尺度冰川流域内粉尘对微量元素沉降和运移规律的影响研究。本项研究是我国西北干旱区冰川流域微量元素循环与粉尘相关研究中的薄弱环节，项目的实施无疑会揭示研究区现代和历史时期微量元素来源的谜团和迁移转化规律，为评估祁连山冰川流域水质水环境及形成机制提供依据，为我国在亚洲粉尘与冰雪微量元素方面的研究做出贡献。

高海拔雪冰中沉降的微量元素可以反映区域大气环境污染信息; 而冰川流域雪冰融水微量元素作为下游河流的水质评估亦作用显著，微量元素的浓度和传输模式会影响其在流域下游的生物利用度。由于雪冰融水为下游干旱区人类赖以生存的绿洲和生态系统提供滋养，因此弄清雪冰融水地球化学特征显得十分必要。针对科学问题，本研究开展了整年的祁连山老虎沟冰川区高海拔大气降水观测包括元素组成和浓度(Cr, Ni, Cu, Mn, Cd, Mo, Pb, Sb, Ti, and Zn)， 以便确定区域尺度自由对流层（海拔4300 m）的大气环境组成状况和化学变化过程。结果表明微量元素表现出明显的在冬季(DJF)升高的浓度和富集系数EF。降水中颗粒物的TEM观测显示，主要组成包括粉尘，各种盐类包裹的粉尘、污染来源的黑炭-飞灰-烟尘，以及有机质颗粒物。同时，对比研究了祁连山冰川区和青藏高原唐古拉冬克玛底冰川区积雪中微量元素沉降特征，提供了区域大气环境重金属本底信息。积雪微量元素沉降的浓度和空间分布特征及其影响因素。LHG冰川区主要受西风气团影响，这种传输模式导致了TGL的污染物信号强于LHG冰川区。 基于本项目我们调查了祁连山老虎沟冰川流域融水径流中微量元素的组成和变化。重点针对消融期（6-10月）融水中微量元素的空间变化、季节变换及其日变化特征。融水中主导浓度的元素是Ba, Sr, Cr; 而高富集系数（EF）的元素是Sb, Ni, Mu, Zn; 随着冰川消融期时间变化上，一些元素表现出浓度逐渐升高的趋势(如Sc, Cu, and Rb)，而另一些则表现出降低的趋势(如Ni, Zn, and Pb)。总体上，冰川流域微量元素的浓度变化、pH、EC以及元素组成模式，都与冰川日消融特征和季节性消融增强密切相关。此外，大气粉尘的传输和沉降对冰川融水径流元素化学特征存在一定的影响。粉尘特征在消融期的变化很好地反映了冰川消融过程， 融水中粉尘浓度和粒径众数在冰川强烈消融期的7月份表现为最高。融水中化学离子相对组成及其浓度消融期变化都与粉尘有较好的一致性。因此，中亚大气粉尘的传输和沉降对高海拔冰川区融水径流的理化特征有着重要甚至被低估了的影响作用。上述工作的开展，有助于搞清祁连山冰川流域微量元素沉降和迁移转化规律及受粉尘影响。