Preliminary study on pollen, charcoal records and environmental evolution of Alahake Saline Lake in Xinjiang since 4,700 cal yr BP

Abstract

Human activity can affect the vegetation types and sedimentary records of a region. In this study, we used multiproxy records from a 140-cm sediment profile, including pollen, charcoal, organic carbon, conductivity, and hydrochemical analyses, to reconstruct a vegetation history for Alahake Saline Lake in northern Xinjiang, China. Fossil charcoal pieces (≥100 μm) were used to reconstruct fire history from the sedimentary record. A significant change in the presence of charcoal indicated an increasing occurrence of fire in the Alahake landscape over the past 4730 years. A peak charcoal concentration occurred at a depth of 0–28 cm, indicating intensified human activity since 790 cal. yr BP. For the same period, pollen assemblages revealed some distinct regional vegetation changes; from 4730 to 3600 cal. yr BP, the landscape was relatively rich in tree species and other vegetation types; from 3600–790 cal. yr BP, trees began to decline while the abundance of Chenopodiaceae increased sharply, indicating environmental degradation. The occurrence of Betula spp. (birch) pollen decreased markedly up to 410 cal. yr BP, suggesting the progressive disappearance of birch trees from the landscape, and the salinity of the lake increased (conductivity peaked above 14.16 ms/cm). High lake salinity and increasing anthropogenic activity have been the two most important factors driving historical changes in the abundance of birch in the Alahake Saline Lake region over the past 790 years. The results of this study are of significance for biodiversity conservation planning and wetland protection in semi-arid and arid areas of China.