子牙新河下游湿地土壤重金属垂直分布及形态特征

Vertical distribution and speciation characteristics of heavy metals in wetlands soils of Ziyaxin River downstream

2014年秋季在子牙新河下游湿地采集柱状土壤样品,分析了Cd、Zn、Cu、Pb的垂向分布特征,利用Tessier连续浸提法,分析了典型湿地N1、N3、B3的重金属形态.研究结果表明,Cd、Zn、Cu、Pb含量垂向分布差异性比较大,波动幅度比较大,多数点位Cd、Cu、Zn在11—19 cm深度处出现峰值,可能与过去金属的输入和周期性淹水有关.Zn、Cu、Pb形态分布为残渣态>铁锰氧化物结合态>有机物结合态>可交换态>碳酸盐结合态,Cd形态分布为铁锰氧化物结合态>可交换态>残渣态>有机物结合态>碳酸盐结合态,Cd的生物有效性较高.湿地淹水条件影响到湿地重金属Cd的交换态和铁锰氧化物结合态的垂直分布.Cd主要以铁锰氧化物结合态的形式存在于湿地土壤中,其百分含量占53.2%,而重金属Zn、Cu、Pb主要以残渣态的形式存在于湿地土壤中,其百分含量均高于60%.根据风险评价编码法(RAC)对重金属的化学形态进行风险评价,风险顺序为:Cd>Zn>Cu>Pb,因此重金属Cd应引起足够的重视.

Soil samples were collected from wetlands of Ziyaxin River downstream in the fall of 2014. The vertical distribution characteristics of heavy metals （Cd, Zn, Cu, Pb ） were analyzed. Speciation of Cd, Zn, Cu and Pb of typical wetland were analyzed using the method of Tessier sequential extraction. Wave variances of heavy metal concentration were observed in vertical direction, which implied the difference of metals input in different periods. Peak values of Cu, Cd and Zn in depth 11-19 cm showed that the concentration was affected by historical input of metals to wetlands and vertical transport caused by water level. The order of form distribution of Zn, Cu and Pb was residual fraction〉Fe-Mn oxide-bound fraction〉organio-bound fraction〉exchangeable fraction 〉carbonate-bound fraction. However, the order of form distribution of Cd was Fe-Mn oxide-bound fraction〉exchangeable fraction〉residual fraction〉organio-bound fraction〉carbonate-bound fraction.Therefore, the bioavailability of Cd was high. The vertical distributions of exchangeable and Fe-Mn oxide-bound fraction Cd were affected by the waterflooding environment. Fe-Mn oxide-bound Cd accounted for 53.2%, and residual Zn, Cu and Pb accounted for more than 60% in wetland soil. According to risk assessment of coding method （RAC）, the risk order of heavy metal, speciation was Cd〉Zn〉Cu〉Pb. Therefore more attention should be paid to the risk of Cd in this area.