猪粪源DOM对三峡消落带土壤吸附Cd的影响

Effects of pig manure-derived dissolved organic matter on the adsorption of cadmium to soils in the Three Gorges Reservoir region,China

由于周期性的淹水-排干交替作用导致三峡库区消落带土壤理化性质和孔隙性质产生较大空间差异进而影响重金属的吸附和迁移行为。本研究以库区非消落带(177 m)和消落带(160、151 m)不同淹水时长土壤为对象,通过吸附动力学试验和等温吸附平衡试验研究猪粪源溶解性有机质(DOM)添加对库区土壤吸附Cd的影响。结果表明,Elovich方程能较好地描述库区土壤对Cd的动态吸附(R2>0.886),而Langmuir和Freundlich模型均能较好地拟合Cd的吸附等温线。库区土壤对Cd的吸附为化学吸附且表现出强烈的非线性(1/n≤0.45)。在梯度上,库区土壤对Cd的吸附强度(Qe、Qm及Kf):消落带160 m>非消落带177 m>消落带151m,土壤pH是最关键的内在影响因素。猪粪DOM的添加能有效抑制库区土壤对Cd的吸附,尤其对消落带下部(151 m)土壤Cd吸附的抑制效果最明显。库区土壤对Cd的吸附量对猪粪DOM初始添加浓度梯度的响应呈现先快速降低(DOM添加浓度<30 mg C·L^-1)再平稳缓慢增加的特点。在"后三峡"时代消落带管理过程中应特别注意消落带下部土壤中外源DOM输入对Cd动态的影响。

The periodical flooding-drainage effect results in spatial variations in the soil physicochemical properties in the water level fluctuation zone(WLFZ)in the Three Gorges Reservoir region.This affects the sorption and transport behavior of heavy metals.Soils beyond(177 m)and within(160 m and 151 m)the WLFZ were investigated via batch sorption experiments.The results showed that the kinetic sorption of Cd fit the Elovich equation(R2>0.886)well,whereas sorption isotherms fit Langmuir and Freundlich equations well.Chemical sorption was the dominant sorption mechanism for Cd and strong non-linearity was observed(1/n≤0.45).The sorption intensities(implied by Qe,Qm,and Kf)of Cd to the soils followed the altitude order of 160 m>177 m>151 m.Soil pH was the critical factor that determined the sorption intensity of Cd to the soils.The addition of pig manure-derived dissolved organic matter(DOM)decreased the sorption of Cd effectively,especially to the soils at the lower end(151 m)of the WLFZ.The sorption of Cd to soil rapidly decreased in the presence of DOM when the concentration of DOM added was lower than 30 mg CžL-1,whereas a slow increase of sorption occurred when the concentration was higher.Consequently,attentions should be given to the soils at the lower end of the WLFZ regarding the potential effects of exogenous DOM on the fate of Cd in the"Post Three Gorges"region.