柴达木盆地北缘湖泊表层沉积物炭屑特征及其环境意义

Characteristics of microcharcoal in the lake surface sediments in the northern margin of Qaidam Basin of China and its environmental significance

沉积物中的炭屑在探讨火(灾)的基本特征及其与植被和人类活动关系方面具有重要意义。采用孢粉学提取方法,对柴达木盆地北缘的湖泊表层沉积物进行了微体炭屑的分析工作,用以探讨其空间分布及其与区域植被和现代人类活动之间的关系。结果表明:不同粒径的炭屑浓度均呈现出自西向东升高的趋势,与区域植被覆盖度自西向东增加的趋势一致。其中,小粒径的炭屑以近圆形占多数,表明区域性火事件中燃烧的木本植被占主导地位;粒径较大的长条形炭屑在盆地东部区域占优势,表明地方性火事件向东增加,草本植物燃烧逐渐增多,与自西向东草本植物的增多相吻合,且燃烧由区域向近源转换。此外,该地区人口数量也有自西向东增加的趋势,推测人类生产生活用火对炭屑浓度有很大的贡献量,与大颗粒炭屑浓度向东升高有较好的对应关系。表层沉积物炭屑的空间变化特征不仅很好地反映了相应地区的火的信息,还对区域植被和人类活动等要素具有较好的指示意义。

Microcharcoal in the surface sediments is of great significance in exploring the basic characteristics of fire and its relationship with vegetation and human activities. Here we analyzed the microcharcoal extracted with the pollen methodology from the surface sediments of lakes in the northern margin of Qaidam Basin to explore its spatial distribution and relationship with regional vegetation and modern human activities. Results showed that the microcharcoal concentration of different grain-size groups has a similarity trend of increasing from northwest to northeast of the basin,which can be coupled with the trend of increasing regional vegetation coverage from west to east. The microcharcoals with the small grain-size(<50 μm)are mostly in the shape of sub-round,which indicates that there is more woody vegetation burning in fires with longer distances. And the sub-long grains microcharcoal with large grain size(>50 μm)is dominant,indicating that the burning of herbaceous plants increased gradually to the east,which consistent with the distribution of herbaceous plants,and the distance from the fire to the sedimentary area of microcharcoal is reduced. Additionally,the population of this area also has a tendency to increase from west to east. Human activities also have a certain impact on the microcharcoal concentration,our analyses show that the microcharcoal concentration has a good correspondence with the population density. Therefore,the spatial variation characteristics of microchacoal in surface sediments not only reflect the fire information of the corresponding areas but also have a good indication for regional vegetation and human activities.