闽江河口湿地土壤对痕量元素吸附⁃解吸特征及其对pH值变化的响应

Adsorption⁃desorption characteristic of micro⁃elements in soils of salt marshes in the Min River estuary and its response to pH variations

选择闽江河口鳝鱼滩的芦苇湿地、短叶茳芏湿地及二者交错带湿地为对象,研究了湿地土壤痕量元素的吸附⁃解吸特征及其对pH值变化的响应.结果表明,3种湿地土壤对Cr^6+、Ni^2+和Cd^2+的吸附能力及其对Cr^6+和Ni^2+的最大缓冲容量均表现为短叶茳芏湿地低于交错带湿地和芦苇湿地;对Cu^2+和Zn^2+的吸附能力和最大缓冲容量在0~30 cm土层均以芦苇湿地较高,而在30~60 cm土层以短叶茳芏湿地较高.导致3种湿地土壤对痕量元素吸附能力差异的原因主要与土壤颗粒组成和pH值的差异有关.Langmuir吸附等温方程可较好地拟合湿地土壤吸附Cr^6+、Ni^2+、Cu^2+、Zn^2+和Cd^2+的热力学过程(R^2≥0.82).3种湿地土壤中Cr^6+、Ni^2+、Cu^2+、Zn^2+和Cd^2+的解吸量均随吸附量的增加而增加,二者呈显著正相关(p<0.05或p<0.01),且其解吸过程均存在滞后现象,说明吸附过程的作用力较解吸过程强.随着pH值的增加,3种湿地土壤对Cr^6+的吸附量均呈波动降低变化,对Ni^2+、Cu^2+、Zn^2+和Cd^2+的吸附量整体均呈增加趋势;而Cr^6+、Cu^2+、Zn^2+和Cd^2+的解吸量对pH值变化的响应与之相反.研究显示,在未来闽江河口硫酸型酸沉降发生频次增加的情况下,相对于短叶茳芏湿地,芦苇湿地和交错带湿地对Ni^2+、Cu^2+、Zn^2+和Cd^2+的吸附量将大幅降低,而解吸量将有所增加,说明Ni^2+、Cu^2+、Zn^2+和Cd^2+将更易游离于这两种湿地的土壤孔隙水中,进而可能增加其对植物或土壤生物的生态毒性风险.

To investigate the adsorption⁃desorption characteristic of micro⁃elements in soils of salt marshes in the Min River estuary and its response to pH variations,the Phragmites australis marsh(PA),Cyperus malaccensis marsh(CM)and ecotonal marsh(P.australis⁃C.malaccensis,PA⁃CM)were studied.Results showed that the adsorption capacities for Cr^6+,Ni^2+and Cd^2+and the maximum buffer capacity(MBC)for Cr6+and Ni2+in soils of CM were lower than those in soils of PA and PA⁃CM.Comparatively,the adsorption capacities and the MBC for Cu^2+and Zn^2+were higher in soils of PA at 0~30 cm depth,while those were higher in soils of CM at 30~60 cm depth.The differences in adsorption capacities for micro⁃elements among the three marsh soils were mainly dependent on their differences in grain composition and pH.The Langmuir adsorption isotherm equation could be used to better describe the adsorption thermodynamics for Cr^6+,Ni^2+,Cu^2+,Zn^2+and Cd^2+(R^2≥0.82).The desorption amounts of Cr^6+,Ni^2+,Cu^2+,Zn^2+and Cd2+in the three marsh soils generally increased with increasing adsorption amounts and significantly positive correlations occurred between them(p<0.05 or p<0.01).There was hysteresis in desorption,indicating that the force of adsorption process was stronger than that of desorption process.With increasing pH,the adsorption amounts of Cr6+generally decreased while those of Ni^2+,Cu^2+,Zn^2+and Cd^2+increased,but the responses of desorption amounts for Cr^6+,Cu^2+,Zn^2+and Cd^2+to pH variations were just in opposite.This paper found that,as the frequency of sulfuric acid precipitation in the Min River estuary increased in future,the adsorption amounts of Ni^2+,Cu^2+,Zn^2+and Cd^2+in soils of PA and PA⁃CM would decrease significantly compared to CM while the desorption amounts would increase greatly,implying that Ni^2+,Cu^2+,Zn^2+and Cd^2+could be more easily desorbed from soils into pore⁃water in PA and PA⁃CM,which might increase their ecotoxicity risk to plants and soil organisms.