湖泛水体沉积物-水界面Fe^2+/ΣS^2-迁移特征及其意义

Effects of Fe^(2+) and ΣS^(2-) transportation at sediment-water interface to the black bloom formation

湖泊水底Fe^(2+)和ΣS^(2-)浓度的快速增加是湖泛暴发最早发生于沉积物-水界面的主要前提,缺氧环境下水底扩散层附近Fe^(2+)和ΣS^(2-)的迁移是其在沉积物-水界面处稳定积累的重要原因.以蓝藻聚积水体沉积物-水界面为研究对象,应用湖泊过程模拟装置及间隙水被动采样等技术,重点研究了间隙水和底层上覆水中Fe^(2+)和ΣS^(2-)的垂向分布特征,并定量估算了二者的扩散通量及迁移方向.结果表明:湖泛样品水体沉积物-水界面处于典型的还原性环境,表层沉积物间隙水中Fe^(2+)和ΣS^(2-)浓度显著高于对照样品,二者在表层沉积物中积累趋势明显.湖泛水体沉积物-水界面处Fe^(2+)释放通量较高,表现出较强烈的自沉积物向上覆水方向的释放能力;而湖泛样品ΣS^(2-)在沉积物-水界面处释放通量为负,迁移方向为自上覆水向沉积物扩散.Fe^(2+)和ΣS^(2-)在湖泛水体沉积物-水界面处不同的迁移特征证明:缺氧/厌氧条件下,湖泊水体表层沉积物间隙水中高浓度Fe^(2+)向上覆水的扩散为湖泛致黑物质的形成提供了重要的物质基础;底层上覆水及界面水中SO^(2-)4在表层沉积物中被还原,为终端还原产物ΣS^(2-)为湖泛致黑物质的形成提供了另一重要物质来源.

The rapid increase of Fe2+ and S S 2- in bottom water layers is a fundamental premise to the outbreak of black blooms at sediment-water interface. Transportation in hypoxi^/anoxic benthic diffusion boundaiy layer is the main cause for the bulk accumulation of Fe2+ and S S 2-. In the present research, the sediment-water interface in the black bloom water system was studied, in which the vertical distribution characteristics of Fe2+ and S S 2- in pore waters were mainly focused. The di^usion fluxes of Fe2+ and S S 2 at the sediment-water interface were also calculated either. Results showed that the sediment-water interface was under typically reduced environment in the black bloom water system. The concentrations of Fe2+ and S S 2 in surface pore waters of the black bloom samples were significantly higher than that of check samples without black blooms. Typical accumulation of Fe2+ and S S 2- in the surface sediment of black bloom system was observed. The Fe2+ release flux at the sediment-water interface in black bloom samples was high' which implied strong Fe2+ release ability from sediments to the overlying water. liowever' unlike the Fe2+ and distinguished from the check samples' the S S 2 release flux at the sediment-water interface in black bloom samples was in minus value' which indicated the S S 2 in the overlying water might be transported into the sediment. The transport characteristics of Fe2+ andS S 2- at the sediment-water interface demonstrated that the release of high concentration Fe2+ from surface pore waters provided important material source to the formation of the black bloom formation' whereas S S 2- — another important material source for the black bloom formation, was the production of reduction SO4- from overlying water at the sediment-water interface.