Seven millennia of Lead(Pb)and mercury(Hg)accumulation in a peat profile,Hani peat land,Jilin,China.

【摘要】：A peat core of 10 m length was collected from the Hani peatland,Jilin Province,northeast China(42°43'N,126°31'E)which is close to the Northern Peatlands region.The peat land consisted of scattered humps with a sphagnum composition,which is anindicator that the peat land is continuously evolving from mineratrophic(groundwaterfed)to ombrotrophic nature(rain water fed).The average dry bulk density and the ashcontent were 0.1g/cm3 and 20%with both closely following trends in the profile.The14C age dating of the top 550 cm showed that the peat accumulation for the last sevenmillennia with peat accumulation rate of approx.12 cm/yr.Taking Titanium(Ti)as anindicator of mineral input,the average concentration was about 0.2%with two peaksat ca.550 cm and 50 cm.The increment of Ti and density at ca.550 cm indicates thechanges in either source area of the minerals or the changes in depositional flux orboth.At ca.50 cm,the absence of Ti peak coinciding with the increment of densitymay reflect the changes in plant composition and thus the humification of the peat.For mercury(Hg)the average concentration was 150 ng/g,and showed few elevatedpeaks.Similarly,for Pb,the concentration remained fairly stable between 50 and 550cm.Above 50 cm,the concentration increased by more than six times.Combiningwith the Ti profile,two things could be interpreted:1)Pb is predominantly ofatmospheric origin,and 2)above 50 cm,anthropogenic input may be responsible forincrease in Pb.This is also supported by another lithogenic element such as Zr.However,for the precise timing of increment for the last ca.100 years,age datingother than 14C is required.