三峡水库主要支流沉积物的磷吸附／释放特性

Adsorption and release of phosphorus from sediments from the main branches of the Three-Gorges Reservoir

以三峡水库主要支流寸滩、小江、大宁和香溪表层沉积物为对象,通过连续提取法分析4种沉积物磷的赋存形态,模拟研究了pH和温度对不同沉积物磷吸附/释放的影响.结果表明,寸滩、小江、大宁和香溪表层沉积物磷赋存形态均以无机磷为主(占总磷含量的59.29%～78.82%),其中钙结合态磷(Ca-P)含量大于铁/铝结合态磷(Fe/Al-P).上覆水pH值对沉积物磷释放有明显的影响,中性条件下磷释放量最低,酸性条件下由于占优势的Ca-P大量溶解导致磷释放量大于碱性条件,因此,水体酸化易增加三峡主要支流(寸滩、小江、大宁和香溪)的磷释放风险.pH值变化亦明显影响沉积物对于磷的吸附,pH在6～8范围内,4种沉积物对于磷的吸附量保持在较高的水平,吸附量从大到小的顺序为:小江>大宁>寸滩>香溪.偏酸性条件(pH<6)下过多的H+与固体表面竞争溶解态活性磷(SRP);偏碱性条件(pH>8)下大量的OH-与SRP竞争沉积物表面的吸附位,故这一pH值范围内(pH<6或pH>8)磷的吸附量明显减少.磷在4种沉积物上的吸附为吸热过程,不同温度下(278K、293K、303K)沉积物对P的吸附均符合修正后的Langmuir模型,标准吸附热为18.92～46.63kJ·mol-1,其中,磷从水体分配到大宁河沉积物中的标准吸附热最大.

The effects of pH and temperature on adsorption and release of phosphorus （P） from sediments from the main branches （Cuntan, Xiaojiang, Daning and Xiangxi） of the Three-Gorges Reservoir （China） were investigated. The contents and fractions of P in the sediments were analyzed by sequential chemical extraction. The results showed that inorganic P was the major fraction of total P （accounting for 59.29% - 78.82 % of total P） for all the samples in this study. The content of calcium-bound P （Ca-P） was higher than that of Fe/Al oxides-bound P （Fe/Al-P）. The pH of the overlying water influenced P release from the sediments. The least amount of P was released under neutral conditions. Higher P release was observed in acid than in alkaline conditions due to the dissolution of Ca-P at lower pH, Thus acidification of the overlying water increases the risk of eutrophication in the main branches of the Three-Gorges Reservoir, Adsorption of P on the sediments also varied with the pH. The maximum P adsorption capacity of various sediments occurred at pH values between 6 and 8. The adsorption capacity followed the order： Xiaojiang 〉 Darting 〉 Cuntan 〉 Xiangxi. At pH 〈6, the sediment surfaces compete with H · to trap soluble reactive P （ SRP）, whereas at pH 〉 8, high concentrations of free OH - could prevent adsorption of SRP onto sediment surfaces. So the adsorption of P decreased rapidly when pH 〈 6 or pH 〉 8. Moreover, the adsorption of P on the sediments was endothermic. A modified Langmuir model may describe the P adsorption well for all the samples at different temperatures （278K,293K,303K）. The standard heat ofadsorption （△H^θ） of P on the sediments ranged from 18.92 to 46.63 kJ-mol ^-1, and the highest value was observed in the Daning sediment.