青藏高原东麓贡嘎山东坡土壤中Pb的来源解析

选择青藏高原东麓典型山地——贡嘎山(东坡),根据不同海拔梯度(海拔2 000~4 500 m)差异设置8个采样点,根据土壤发育情况分别采集O层(有机层)、A层(矿物质层)和C层(母质层)样品,分析土壤中w(Pb)的海拔分布特征,并利用FA-MLR(因子回归分析)法、地球化学指标法和Pb同位素三元混合模型定量判识表层土壤中Pb的来源. 结果表明:①各层土壤中w(Pb)表现为O层〔(41.73±4.38)mg/kg〕>A层〔(30.47±2.17)mg/kg〕>C层〔(23.04±1.50)mg/kg〕(P<0.05). 随着海拔的增加,O层和A层中w(Pb)总体呈升高—降低—升高趋势；C层中w(Pb)随着海拔的变化无显著差异,表明贡嘎山东坡土壤中w(Pb)的地球化学背景值基本一致. ②各层土壤中206Pb/207Pb表现为O层208Pb/206Pb表现为O层>A层>C层. ③Pb同位素三元混合模型结果显示,表层(O层和A层)土壤中Pb可能受到化石燃料燃烧和矿物开采及金属冶炼活动的影响；根据FA-MLR法、地球化学指标法和Pb同位素三元混合模型这3种方法,得到O层中污染Pb所占比例分别达到84.9%、66.0%和63.7%,A层中分别为56.6%、27.8%和44.9%；在海拔分布上,Pb的污染在海拔2 770 m以下主要归因于当地化石燃料的燃烧,而在林线(约3 700 m)以上则来自矿物开采及金属冶炼活动. 

Source Identification of Lead in Soils on the Eastern Slope of Gongga Mountain, Eastern Tibetan Plateau

Abstract: Eight sites were selected along a high altitude gradient (2000-4500 m a.s.l.) on the eastern slope of Gongga Mountain, a typical high mountain on the eastern Tibetan Plateau. Soil samples, including organic layer (O-horizon), mineral layer (A-horizon) and parent material layer (C-horizon), were collected according to the soil developed level to investigate the spatial distribution of Pb, and to quantitatively identify its sources using statistical analysis and Pb isotope compositions. The results indicated that the concentrations of Pb (mean±SE) vertically decreased in the order of O-horizon ((41.73±4.38) mg/kg)>A-horizon ((30.47±2.17) mg/kg)>C-horizon ((23.04±1.50) mg/kg) (P<0.05). The concentrations of Pb in the O and A horizons were generally higher in the areas with middle altitude (approximately 3000 m a.s.l.) than at the low or high altitudes. However, the Pb concentrations in the C horizon did not show remarkable difference along with altitude, indicating the homogenous background of Pb in the soil of the eastern slope of Gongga Mountain. The ratios of ²⁰⁶Pb/²⁰⁷Pb increased vertically in the order of O-horizon208Pb/²⁰⁶Pb had an opposite trend. As indicated by isotope composition, Pb in the surface soils (O-horizon and A-horizon) was mainly influenced by fossil fuel combustion and Pb-containing ore smelting. In the O-horizon, Pb pollution reached 84.9%, 66.0% and 63.7%, estimated using factor-regression analysis, geochemical indicators and ternary mixing model respectively, and 56.6%, 27.8% and 44.9% respectively in the A-horizon. At the elevation lower than 2770 m (a.s.l.), the pollution Pb was mainly sourced from fossil fuel combustion, while above the timberline it was mainly from Pb-containing ore smelting.