外源磷在三峡库区典型土壤中的活性演变及形态转化

三峡库区消落带土壤周期性淹水—出露对磷素迁移循环和水体负荷具有重要影响。以三峡库区消落带广泛分布的紫色潮土和灰棕紫泥土为对象,通过室内模拟培养实验,探讨不同饱和度外源磷在两种土壤中的活性变化与形态转化特征。结果表明:(1)外源磷进入土壤后,表征土壤磷活性的有效磷(Olsen-P)含量及磷素释放能力呈指数型衰减,可用指数方程C_t=ae~(-kt)+b拟合,拟合度均在94%左右。(2)外源磷在灰棕紫泥土中较在紫色潮土中能够保持更高的活性,同时也具有更高的渗漏淋失与释放风险。50%Q_m(最大吸附量)是两种土壤Olsen-P与磷素平衡解吸量的突变点,当磷素吸持饱和度≥50%时,土壤磷活性与渗漏淋失风险将明显增大。(3)Olsen-P与磷释放量在p0.01水平上呈显著正相关,两者可用线性方程良好拟合,因此可用Olsen-P含量表征土壤磷素释放潜势。(4)外源磷进入土壤后,主要转化为活性较高的Ca_2-P和Ca_8-P,约占施入量50%~60%;其次是Al-P和Fe-P,约占施入量的30%左右,闭蓄态磷(O-P)和Ca_(10)-P变化不明显。(5)Ca_2-P是决定Olsen-P和磷素解吸能力的主要形态,对两者均起正向直接作用。

Variation of Extraneous Phosphorus in Activity and Morphology in Soils Typical of the Three Gorges Reservoir Area

Eutrophication is the main potential issue threatening the safety of aquatic environment of the Three Gorge Reservoir (TGR) since its full running, and phosphorus is considered as one key restrictive factor of eutrophication. The periodical exposure-inundation of soils in the Hydro-Fluctuation Zone of the TGR produces a significant impact on the circulation and migration of phosphorus, as well as the water loading of phosphorus. Parts of the hydro-fluctuation zone are used for agricultural production during soil drying period, resulting in an excess accumulation of phosphorus adsorbed in the soil, and then the phosphorus absorbed pour into overlying water during flooding period, which enhanced the eutrophication of water body. Therefore, the experimenting on the purple alluvial soil and grey-brown purple soil were widely distributed in Three Gorges Reservoir area. The indoor cultivation experiment was conducted to explore the characteristics of the activity and the morphological transformation of phosphorus with different phosphorus saturation in the soils mentioned above. The results showed as following, (1) As the characterization of soil activity, the releasing ability of phosphorus and Olsen-P content showed exponential decay after the exogenous phosphorus migrated into soil, in addition, which can be described with the equation of Ct = ae-kt b, and both of them had the fitting degree about 94%. In addition, since the exogenous phosphorus migrated into the soil, both Olsen-P content and the phosphorus release content were the largest decline during 15 days. Then they were gradually level off and remain stable. (2) The activity decay, equilibrium concentration and the release potential of exogenous phosphorus in soil were different in various kinds of soils. After the exogenous phosphorus migrated into the soil, the gray-brown purple soil sustained a higher activity and a higher risk of leaching and release than the purple alluvial soil (3) The release potential of soil phosphorus was restricted by the saturation of phosphorus absorption. The 50% of Qm (the maximum adsorption capacity) was the change-point of Olsen-P and the phosphorus equilibrium desorption in purple alluvial soil and gray-brown purple soil. When the phosphorus sorption saturation was higher than 50%, the activity of soil phosphorus and the risk of leaching and release increased rapidly. (4) There was a significant positive correlation between Olsen-P and phosphorus release in p<0.01 level, and these two parameters can be well fitted by linear equation, so the potential of soil phosphorus release could be characterized by Olsen-P content. (5) when exogenous phosphorus were migrated into soil, 50%~60% of exogenous phosphorus transformed to Ca2-P and Ca8-P which had higher activity, while about 30% exogenous phosphorus transformed to Al-P and Fe-P, the content of O-P and Ca10-P did not change significantly. (6) Ca2-P was the main form of IP that determines the ability of Olsen-P and the ability of phosphorus desorption, it had a positive direct effect on both of them.