渭河流域全新世土壤剖面木炭屑记录及其古环境意义

Charcoal records of Holocene loess-soil sequences and its palaeoenvironmental significance in Weihe River Drainage

通过野外采样及其磁化率、总有机碳(TOC)、木炭屑的分析,探讨全新世野火活动与生态环境演变的关系。研究结果表明:TOC并不能完全指示野火活动,木炭屑是指示野火活动的理想指标,木炭屑对生态环境演变特征具有环境指示意义。末次冰期11500aB.P.之前,渭河流域气候干旱,植被为半荒漠草原,自然野火频繁发生;全新世早期(11500～8500aB.P.)野火发生频率大大降低;全新世气候适宜期(8500～3100aB.P.),气候比较湿润,生物风化成壤作用强烈,自然野火发生几率明显下降,但不同地点人类活动引发的野火活动存在区域差异;全新世晚期近3100年以来,气候向干旱化发展,加之人类利用土地活动加剧,生物量燃烧的规模大幅度增加;1500aB.P.以后,木炭屑浓度大幅度减少,野火发生频率大大降低。可能由于渭河流域土地利用方式发生重大改变,人工自然复合生态景观基本形成,因而不再大规模放火烧荒。此外,木炭屑对人类活动的遗迹具有指示作用。

Analysis （of samples collected through field investigation） of total organic carbon,magnetic susceptibility of Holocene loess-soil charcoal sequences in Weihe River Drainage have revealed the relationship between Holocene wildfire occurrence changes and ecological environment.The current study shows that total organic carbon （TOC） does not fully indicate the occurrence of wildfire in an ecological environment.However,charcoal is regarded as a direct and reliable indicator of wildfire occurrence.Indications of changes in Holocene and charcoal environment have great environmental significance.Before 11 500 a B.P.,the climate was arid and wildfire frequently occurred in semi-desert grasslands.Conversely,the incidence of wildfires decreased during the early Holocene epoch.During the optimum Holocene climatic between 8 500 a B.P.and 3 100 a B.P.,natural wildfires occurrence fell sharply.Pathogenic alterations in dust accumulation processes were so active that forest-grasslands formed under humid warmer Holocene Mega thermal climate.However,with regional distinction,localized wildfires in connection with human activity occasionally occurred.Levels of burnt biomass were very high during the Late Holocene epoch when the climate was drier and historical land-use more intensive in the study area.After 1 500 a B.P.,the amount of charcoal sharply decreased and wildfire occurrence slowly disappeared.It may had resulted from a significant change in land use pattern.The artificial-natural ecological landscape had been established and large-scale burning of land did not occured.Charcoal could therefore be used as a vital indicator for human activity in geological time.