典型冰川退缩区铅的来源、累积及历史沉降——以青藏高原海螺沟冰川退缩区为例

为探究青藏高原东部陆地生态系统中铅的来源、累积分配过程及百年来大气铅的沉降状况，以贡嘎山海螺沟冰川退缩区为对象，利用冰川退缩区样地年龄可确定的优势，对160年来完整的植被演替序列进行了系统研究.采用电感耦合等离子体质谱法（ICP-MS）测定了土壤和植物样品中的铅以及其他微量元素的含量，明确了铅在该地区生态系统中的含量和储量变化格局，并采用主成分分析（PCA）解析了土壤铅的潜在来源，评估了历史沉降铅的累积速率.结果表明，森林有机土壤是大气铅的重要汇集区域.大气沉降的铅主要累积于O层中，而C层土壤铅含量相对较低；植物地上部以树枝和树皮铅含量最高，树干铅含量最低.植被序列中不同树种的铅储量变化趋势和植被演替趋势成正相关.在植被生长期，铅储量因生物量增加而不断升高，而随着演替过程中植被的死亡而降低.整个演替系统铅的储量随冰川退缩时间显著增加，至1936年样地的云冷杉顶极群落达到最大值.PCA源解析表明有机土壤中57%左右的铅来自于人为来源铅的大气沉降过程，即外源污染的大气沉降是贡嘎山中铅的主要来源.进一步分析表明，中国西南地区和南亚地区（印度、孟加拉国等）是主要的污染潜在源区.在百年尺度上，大气来源沉降铅在冰川退缩区的平均累积速率为（8.87±3.55） mg/（m²·a）.此研究为探究铅在陆地生态系统中的来源、分配及累积，理解未来全球变化对铅的环境地球化学过程影响提供了经典范例与数据依据.

Lead sources,accumulation and historical deposition in typical glacial retreat area: A case study of Hailuogou glacial retreat area,Qinghai-Tibet Plateau

Given the advantage of the timing of glacial retreated regions, we systematically studied centennial trends of lead (Pb) to demonstrate the sources, accumulation, distribution, and atmospheric deposition in the terrestrial ecosystem of glacial retreated regions, eastern Qinghai-Tibet Plateau. We comprehensively determined the concentration of lead and other trace elements in soil and vegetation of glacier retreated regions by inductively coupled plasma mass spectrometry (ICP-MS), and quantified the temporal patterns of lead concentration and storage, and then analyzed the potential sources by principal component analysis (PCA), and finally estimated the accumulation rate of historical lead deposition in soils. The results showed that the atmospheric deposition of lead mainly accumulated in O-horizon, and both lead concentration and storage in O-horizon increased with the time of glacier retreated. This suggests that forest soils act as an important atmospheric lead sink in the terrestrial ecosystems. For the aboveground component of vegetations, the lead concentration in branches and barks were the highest, while the lead concentration in trunk was the lowest. The Pb pool size of vegetation showed a positive correlation with the vegetation biomass production. More in detail, the vegetation had the higher uptake rate of lead during the growth period, while decreased distinctly during the old period time. Briefly, the Pb mass in the whole ecosystems increased with the increasing retreated time, and reached the plateau in 1936spruce top community sampling site. The PCA results displayed that 57% of lead in organic soil was derived from the atmospheric deposition of anthropogenic Pb. Further back trajectories analysis suggested that Southwest China and South Asia (India, Bangladesh, etc.) are the main potential sources of lead in Gongga Mountain. Finally, we estimated the centennial average of accumulative rate of lead deposition from atmospheric sources in the glacial retreat area was (8.87±3.55) mg/(m²·a), significantly lower than values in the economically developed regions of China. Overall, our study provides a typical example and data basis for exploring the source, distribution, and accumulation of lead in terrestrial ecosystems, and contributes to understand the impact of future global changes on Pb biogeochemical cycling.