PRELIMINARY EXPLORATION OF FIRE ACTIVITY RECORDED BY MICROCHARCOAL IN SURFACE SEDIMENTS OF CENTRAL AND WESTERN CHINA
Microcharcoal,a product of the incomplete combustion of plants,serves as an effective wildfire indicator.However,microcharcoal in surface sediments and its relationship with modern wildfires remain poorly understood.Here,35 surface sediments samples were collected for microcharcoal analysis,along a 2950 km transect in the semi-humid,semi-arid and arid regions of central-Western China(34.29°～39.01°N,79.89°～113.16° E)to investigate the spatial distribution of microcharcoal and its relationship with wildfires.In the western region,9 sub-aqueous surface sediment samples were collected from low-lying watercourses,puddles,and reservoirs along the southern margin of the Tarim Basin.In the central region,surface sediment samples were collected from 13 lakes along the northern margin of the Qaidam Basin,from Lake Qinghai westwards.A further 13 surface topsoil samples were collected from the eastern region(from the eastern part of the Loess Plateau,across the Guanzhong Basin,and westwards to the western edge of the Loess Plateau).According to the sediment type and location,the study area was divided into three sub-regions:sub-aqueous surface sediments from the arid region in the west,lacustrine samples from the semi-arid and arid central region,and topsoil samples from the semi-humid and semi-arid region in the east.Microcharcoal was then extracted using standard palynological hydrofluoric acid treatment.Herein,we systematically present the size distribution,concentration,and morphology of the microcharcoal(sub-long and sub-round types with a length/width limit of 2.5),along with the relationship between microcharcoal and fire frequency based on our microcharcoal data and MODIS fire products.Over 80％of the microcharcoal had a particle size＜50μm,and microcharcoal with a particle size＞100 μm accounted for only ca.1％of the total.There was no statistically significant difference in the size distribution of microcharcoal among the three different types of sediments.The microcharcoal concentration ranges in topsoil and lake samples were similar,at 6670～78650 grains/g and 7650～76860 grains/g,respectively,while the sub-aqueous surface sediment samples showed a narrower range(5070～33800 grains/g).Our results suggest that microcharcoal can be effectively extracted from lakes sediments,soils,and sub-aqueous surface catchments(puddles,reservoirs,and waterways).Microcharcoal in lake sediments may overestimate the fire frequency because lakes have a larger watershed.Modern fire activity,as revealed by MODIS fire products,mainly occurs in semi-humid and semi-arid areas with high levels of human activity,high NDVI(normalized difference vegetation index),and a relatively warm and wet climate.A comparison of microcharcoal distribution and modern fire activity suggests that microcharcoal in surface sediments might have been transported up to 50～100 km from the sites;microcharcoal concentration may provide a good indication of fire activity,especially fire frequency.Notably,there was a strong correlation between the microcharcoal morphology ratio(sub-long to sub-round type,i.e.,L/R ratio)and grassland fire events within 50 km(r=0.61,p＜0.05).Hence,the L/R ratio may be used to indicate the type of fuel consumed in wildfires.The findings of this study enhance our understanding of microcharcoal and its relationship with wildfires,and thus provide a modern process on which to base the reconstruction of paleofire history.
microcharcoalmicrocharcoal morphologysedimentsfire activitymodern process
万方数据
维普
