Institute of Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
J Environ Qual. 2010 Feb 19;39(2):734-43. doi: 10.2134/jeq2009.0222. Print 2010 Mar-Apr.
Phosphate (P(i)) release due to Fe(III) oxide dissolution is well documented for soils undergoing reduction. The P(i) sorption properties of soils in anoxic conditions are, however, still under consideration. In this investigation, P(i) sorption to strictly anoxic soils was compared with oxic conditions to assess the potential of lowland soils to function as traps for P(i) when flooded with drainage water. Batch sorption experiments were performed on seven minerogenic soils. Sorption to the anoxic soils was conducted after anoxic incubation, resulting in reduction of 36 to 93% of the dithionite-extractable Fe(III) (Fe(BD)). Langmuir fitted P(i) sorption isotherms showed a P(i) release of up to 1.1 mmol kg(-1) in six soils when P(i) concentrations in the matrix (P(sol)) were lower than 10 microM. Phosphate desorption was attributed to dissolution of amorphous iron oxides, and higher pH under anoxic conditions. The point of zero net sorption (EPC(0)) increased 2- to 10-fold on reduction. Five soils showed higher P(i) sorption capacities in the anoxic than in the oxic state at higher P(sol) concentrations. Solubility calculations indicated that precipitation of vivianite or similar Fe(II) phosphates may have caused the higher sorption capacities. Use of maximum sorption capacity (S(max)) is therefore misleading as a measure of P(i) sorption at low P(sol) concentrations. The results demonstrate that none of the strongly anoxic soils, irrespective of the initial Fe(III) oxide content, the P saturation, and the degree of Fe(III) oxide reduction, could retain P(i) at natural P(sol) concentrations in agricultural drainage water.
由于氧化铁溶解而导致的磷酸盐（P(i)）释放，在进行还原的土壤中已有充分的记录。然而，在缺氧条件下土壤的 P(i)吸附特性仍在考虑之中。在这项研究中，将严格缺氧土壤的 P(i)吸附与好氧条件进行了比较，以评估在被排水淹没时，低地土壤作为 P(i)陷阱的潜力。在 7 种矿物土壤上进行了批吸附实验。在缺氧培养后进行了对缺氧土壤的吸附实验，导致二硫代苏糖醇可提取铁（Fe(BD)）的还原率为 36%至 93%。Langmuir 拟合的 P(i)吸附等温线表明，在 6 种土壤中，当基质中的 P(i)浓度（P(sol)）低于 10 microM 时，会释放高达 1.1 mmol kg(-1)的 P(i)。磷的解吸归因于无定形氧化铁的溶解以及缺氧条件下较高的 pH 值。在还原过程中，零净吸附点（EPC(0)）增加了 2 到 10 倍。在较高的 P(sol)浓度下，5 种土壤在缺氧状态下的 P(i)吸附能力高于好氧状态。溶解度计算表明，可能是蓝铁矿或类似的 Fe(II)磷酸盐的沉淀导致了更高的吸附能力。因此，最大吸附容量（S(max)）的使用作为低 P(sol)浓度下 P(i)吸附的衡量标准是具有误导性的。结果表明，无论初始氧化铁含量、磷饱和度和氧化铁还原程度如何，没有一种强缺氧土壤能够在农业排水中的天然 P(sol)浓度下保留 P(i)。
