Abstract:

This study took the complete and continuous primary succession sequence in the Hailuogou Glacier Retreat area as a case example to explore the cumulative distribution process of lead (Pb) in high mountain area ecosystems in middle and low latitudes and pollution records on a time scale of 100 years. In accompaniment with an investigation of vegetation biomass, soil bulk density, and soil thickness, the concentrations of Pb in vegetation and soil were determined, the storage change and distribution pattern of Pb in this primary succession ecosystem from 1890 to 2017 were studied systematically, and the pollution history of Pb in this period was retrieved. The results show that: (1) the concentration of Pb in the soil was higher than the background value and showed obvious surface enrichment during the retreat of glaciers, and the enrichment coefficient of the surface soil showed that the change of Pb concentration in the soil O horizon was affected mainly by exogenous factors rather than the parent material. (2) The Pb concentrations in different parts of each dominant tree were higher in the belowground part than that in the aboveground part. The migration capacity of the aboveground part was low, and the degree of enrichment of the belowground part was higher than that of the aboveground part, which caused the Pb concentration in fine roots to be significantly higher than the concentration in other parts. (3) In the undergrowth vegetation, the Pb concentration was significantly higher in ground cover (moss), which has a strong Pb enrichment capacity, than in the shrub or herb layer. (4) As the biomass of the tree layer accounted for the highest proportion of the vegetation, it was the largest Pb storage unit among the living vegetation. However, although the biomass of the ground cover (moss) contributed less than 5% to the total biomass, its maximum contribution to the accumulation of Pb in the vegetation could reach 36%, potentially causing Pb pollution in the ecosystems in alpine regions. (5) Pb storage in the primary succession ecosystem of the Hailuogou Glacier Retreat area experienced a process of accumulation, from an initial value of 64.64 kg?hm^?2 to 227.16 kg?hm^?2, and soil was the main storage unit of Pb in the ecosystem. (6) The Pb accumulation rate in the ecosystem was relatively fast from 1958 to 1970 and from 1980 to 2000, which corresponded to the Pb concentration change in tree rings on the eastern slope of Gongga Mountain. It indicated that the Pb accumulation process in the ecosystem of the primary succession sequence in the Hailuogou Glacier Retreat area reflected the pollution history of Pb in the past 100 years.

Key words: primary succession, ecosystem, heavy metal of Pb, accumulation process, pollution history, glacier retreat area

摘要：

为探究铅在中低纬高山地区生态系统中的累积分配过程及百年时间尺度上的污染记录，以海螺沟冰川退缩区形成的完整且连续的原生演替序列为载体，通过调查植被生物量、土壤容重和厚度，测定铅在植被和土壤中的含量，系统地研究1890—2017年来铅在该原生演替序列生态系统中的贮量变化及分配格局并反演该时期铅的污染历史。结果表明：（1）各冰川退缩时期土壤中铅的含量高于背景值并表现出明显的表层富集，且表层土壤的富集系数表明土壤O层中铅含量的变化主要受外源性因素的影响而非成土母质；（2）各优势乔木不同部位铅的含量均表现为地下部分>地上部分，且地上部分的运移能力较低，而地下部分的富集程度均高于地上部分，使得根系所吸收的铅可能大部分被存留在根系组织中，导致细根中铅的含量明显高于其他部位；（3）在林下植被中，地被层（苔藓）的铅含量明显高于灌木层和草本层，具有较强的铅富集能力；（4）乔木层生物量在植被中占比最高，使其成为活体植被中最大的铅贮存单元，但地被层（苔藓）的生物量对总生物量贡献不足5%，其对植被铅的积累贡献最大可达36%，这对高山高寒地区的生态系统可能造成潜在的铅污染；（5）海螺沟冰川退缩区原生演替生态系统铅的贮量经历了从无到有的积累过程，从64.64 kg?hm^?2增长到227.16 kg?hm^?2，且土壤是生态系统铅的主要贮存单元；（6）生态系统铅的积累速率在1958—1970年和1980—2000年较快，并与贡嘎山东坡树轮中铅含量的变化相对应，说明海螺沟冰川退缩区原生演替序列生态系统铅的积累过程能反演近百年来铅的污染历史。

关键词: 原生演替, 生态系统, 重金属铅, 积累过程, 污染历史记录, 冰川退缩区