Migration mechanism of biogenic elements and their quantification on the sediment-water interface of Lake Taihu:Ⅱ. chemical thermodynamic mechanism of phosphorus release and its source-sink transition

Abstract

室内静态模拟不同温度下太湖15个湖区柱状沉积物磷酸根释放,分析了相应表层沉积物形态磷,以及梅梁湾间隙水中相关离子Al(Ⅲ)、Fe(Ⅱ)、Ca(Ⅱ)和PO^3-₄含量的季节变化.研究表明,受陆源影响较大的泥区通常是太湖内源磷的稳定源;而在开敞度较大的湖区,由于表层沉积物胶体的物化吸附,使得温度对底泥磷释放的影响作用减弱,并易产生磷的“内汇”现象;在梅梁湾区成汇区,还加上春夏季藻类的局部超负荷需磷这一控制因素,从而使得太湖大部分泥区在一年中至少发生一次源-汇转换过程.化学热力学分析揭示,Al-P较之Fe-P和Ca-P更易在界面发生溶解可能是太湖表层沉积物Al-P与PO₄^3--P释放速率呈显著相关(r=0.3858>r_1-0.01,n=45)的内在原因.虽然沉积物中Fe-P有较高的释磷潜力,但浅水湖所营造的沉积物表层氧化层和广泛覆盖的无机胶体及粘土矿物的强吸附介质,可能是抑制沉积物中Fe-P释放成为优势的主要因素.估算太湖沉积物-水界面磷的净通量为899.4±573.6t/a,约占太湖磷入湖量的1/4-1/2,其中成汇通量约为-91.2±42.4t/a.;Phosphate release from the core sediments of fifteen areas in Lake Taihu was simulated at different temperatures，and the phosphorus species in the sediments and seasonal variations of the relative ions，such as A1 (1H ).Fe( II ).Ca( II ) and PO^3-₄ were analyzed. The result shows that the areas affected greatly by terrestrial source are steady internal phosphorus sources in Lake Taihu. In more open areas, the physio-chemical adsorption of deposit colloid makes it weak that temperature have an influence on phosphorus release from sediment so as to produce “internal sink” of phosphorus. At sinking area in the Meiliang Bay, transnormal P demand of the local algae would be one of the most dominating reason of sink formation in addition in spring/summer seasons. There appeared source-sink transition at least once in most of the sediment areas. Chemical thermodynamic analysis reveals that Al-P dissolves more easily than Fe-P and Ca-P on the interface, which perhaps is inherent cause in respect to a marked relationship between Al-P in surface sediment and the phosphate release in Lake Taihu. Although Fe-P is considered to be a potential higher phosphorus release source，the oxidating layer formed on sediment surface and strong adsorbing media in shallow lakes, e. g. inorganic colloid and clay mineral, would be the dominant factors in Fe-P release. The net phosphorus flux, in the whole lake, was estimated about 899. 4±573.6t/a, accounting for about one quarter to half of phosphorus loadings, of which the sinking flux was approximately -91.2±42.4l/a.