重金属污染的稻田土中总有机碳和颗粒态碳的变化

Variations of total organic carbon and particulate organic carbon in paddy soils contaminated by heavy metals

从广东大宝山矿区横石河下游受重金属污染的水稻田采集6个土壤剖面样品,研究了土壤中总有机碳(TOC)、颗粒态有机碳(POC)和POC/TOC比率的垂直分布特征,并探讨不同污染程度对土壤有机碳含量及稳定性的影响.结果表明,与轻度污染和中度污染采样点相比,在重度污染的各土层中,TOC含量显著下降,其垂直分布有显著改变.POC含量在不同土层间的变化与TOC表现出相似的规律,但差异更显著.重金属污染会影响土壤有机碳不同组分在土壤剖面上的垂直分布特征及分配比例,从而影响土壤有机碳的稳定性和可利用性.中度重金属污染使POC含量显著增高,土壤有机碳变得易于分解和损失;重度污染使TOC含量显著降低,不利于土壤有机碳的固定和积累.不同重金属对土壤有机碳稳定性的影响不同,Pb表现出与Cu、Cd的拮抗作用,Pb使有机碳稳定性增加;而Cu和Cd则相反.但多种重金属联合效应使土壤有机碳稳定性呈降低趋势.

Six soil profiles were sampled from a paddy field contaminated by heavy metals in the downstream area of Hengshihe River in Dabaoshan Mine in the north of Guangdong Province.Vertical distributions of total organic carbon（TOC）, particulate organic carbon（POC）, and the ratio of POC to TOC in the soil profiles were studied.Soil organic carbon（SOC） content and stability under different levels of heavy metal contamination were discussed.Compared to slightly and moderately contaminated sample plots, TOC decreased drastically in severely contaminated soil profiles, and the vertical distribution of TOC changed obviously due to severe heavy metal contamination.POC varied similarly as TOC among different soil layers.However, the variation of POC was more distinctive than that of TOC.Heavy metal contamination affected the vertical distribution characteristics and allocation proportion of different organic carbon fractions, thus had an effect on soil organic carbon stability and availability.POC increased distinctively in the moderately contaminated soils, leading to acceleration of SOC degradation and loss.TOC decreased distinctively in the severely contaminated soils, reduced fixation and accumulation of SOC.Different heavy metals potentially had different effects on stability of SOC, and there was an antagonism between Pb and Cu, Cd.Pb enhanced stability of SOC, while Cu and Cd had adverse effects.However, the associative effect of multiple heavy metals totally inclined to reduce stability of SOC.