南海湖沉积物中生物有效态重金属含量及其空间分布

Concentration and Spatial Distribution of Bio-available Fraction of Heavy Metals in the Sediments from the Nanhai Lake

为判识湖泊沉积物中重金属的地球化学行为特征及其控制因素,以包头市南海湖为研究对象,采用连续提取法,系统开展了沉积物中生物有效态重金属的分布研究。结果表明,表层沉积物中重金属生物有效态(前4态之和)的平均比例序列为Cd>Pb>Zn>Cu;Cu的生物有效态占总量的比例为23%,Pb为75%,Zn为42%,Cd为83%。总体而言,表层沉积物中Cd和Pb的潜在危害性最大。湖心区、西南和东北部湖区为表层沉积物中Cu、Pb和Zn的生物有效态含量高值区,Cd仅在西南湖区表现高值。有机物结合态为沉积物柱芯中Cu和Cd生物有效态的主导形态,铁锰氧化物结合态为Pb和Zn生物有效态的主导形态。强还原性条件下,沉积物中以铁锰氧化物结合态为主导形态的Pb、Zn、Cd有一定的潜在风险,Cu的潜在危害较小。与黄河沉积物重金属形态百分比的对比分析表明,南海湖沉积物对重金属的固定能力更强。

The contents of bio-available fractions of Cu, Pb, Zn and Cd in sediments of the Nanhai Lake which was an abandoned channel of the Yellow River were analyzed in this work to study the geochemical behavior of heavy metals in lake sediments and the controlling factors. The resuits showed that the contents of bin-available fractions of Cu, Pb, Zn and Cd in surface sediments were ranked as Zn〉Pb〉Cu〉Cd; The percentages of bio-available fractions in total contents were 23% for Cu, 75% for Pb, 42% for Zn, and 83% for Cd. Therefore, Cd and Pb presented more potential risk than the other two in surface sediments. The bin-available fractions of Cu, Pb and Zn in surface sediments of the central lake, southwest part and northeast part showed higher contents than other parts, while Cd showed higher bio-available fractions at the southwest part. The Cu and Cd in the sediment core were dominated with organic-bound fraction in their bio-available fractions, while Pb and Zn were dominated with Fe, Mn oxides-bound fraction in their bio-available fractions. Under the higher reducibility of the Nanhai Lake, the Pb, Zn and Cd presented potential risk to the water, because they were dominated with Fe, Mn oxides-bound fraction. Compared with the Yellow River, the condition of the Nanhai Lake was more propitious to the transformation of heavy metals into stable fractions.