黄土与古土壤中重金属的存在形态及风化成土作用对其影响

DISTRIBUTION AND FRACTIONS OF HEAVY METALS IN LOESS AND PALEOSOL AND THE INFLUENCE OF WEATHERING

本文采用了七步连续萃取方法，研究了洛川黄土剖面黄土与古土壤中Ｆｅ、Ｃｕ、Ｚｎ、Ｃｏ和Ｎｉ五种重金属的存在形态。结果表明：黄土与古土壤中上述元素主要存在于残余态和晶形、无定形氧化铁的结合态中，而且线性回归分析表明Ｃｕ、Ｚｎ、Ｎｉ与晶形氧化铁之间存在正相关；Ｃｎ、Ｃｏ、Ｎｉ与无定形氧化铁之间存在正相关；黄土风化为古土壤后，碳酸盐结合态的重金属几乎全部释放，而晶形、无定形氧化铁结合态的重金属则相对积聚，其它形态变化不大。因而黄土风化为古土壤后，与晶形、无定形氧化铁结合的重金属含量增加是古土壤相对于黄土重金属增加的主要原因。

A seven-step sequential extraction procedure was used to investigate the diseri-bution and fractions of Fe,Cu,Zn,Co and Ni in Luochuan loess-paleosol sequence.Seven fractions i.e. ,exchangeable(EX),carbonates-bound(CARB),Mn-oxidebound(MnOX),alnorphous Fe-oxide-bound(AFeOX),crystalline Fe-oxide-bound(CFeOX),organically bound(OM),and residual(RES)fractions were found through fraction-ation. Tke results indicated that:(1)The above elements mainly existed in RES,CFeOX,and AFeOX fractions.(2)Linear regression analysis indicated that there existed good positive correla-tions between the contents of CFeOX and AFeOX and the Cu,Zn.Co and Ni con- tents in these phases. (3)After loess was weathered into soil,the heavy metals in CARB fractionwould be released completely, but those in AFeOX and CFeOX fractions would inc-rease. The other fractions only showed little variation. So,this study provided anexplanation that the increase of AFeOX and CFeOX fraction might be the lnain ca- use for much higher total content of heavy metals in paleosol than in locss.