The micro-scale investigation on the effect of redox condition on the release of the sediment phosphorus in Lake Hongfeng

Abstract

选取贵州红枫湖为研究对象,在实验室条件下模拟了自然、好氧和厌氧条件下沉积物内源磷的释放过程,联合应用微电极技术和沉积物磷形态分析对沉积物水界面开展了微尺度观测与研究.结果表明,厌氧条件下红枫湖沉积物总磷含量显著降低,且主要是NaOH提取态磷(NaOH-P)和残渣态磷(rest-P)含量降低所致,厌氧条件下沉积物孔隙水中磷酸盐浓度明显升高,而好氧条件下沉积物孔隙水磷酸盐浓度显著降低,反映厌氧条件显著促进了红枫湖沉积物磷释放.厌氧条件下沉积物内部溶解氧浓度下降、硫还原活动增强可能是导致NaOH-P释放的主要原因.O₂浓度的降低加速了沉积物还原作用并产生大量H₂S,进而与二价铁离子形成硫化亚铁沉淀,最终导致NaOH-P(Fe-P)释放到孔隙水中.好氧条件向厌氧条件的转换可通过改变沉积物内部pH值分布和微生物活动促使rest-P释放:厌氧条件下,厌氧微生物不仅可以消耗硫酸根产生H₂S,导致pH值降低,还可消耗有机质,将有机磷转变为无机磷.上述研究结果表明,沉积物水界面氧化还原环境可影响沉积物氧渗透深度、pH值分布、微生物活动、硫循环以及有机质降解过程,进而控制沉积物磷的形态转化与释放.联合应用微电极技术和沉积物磷形态分析对湖泊沉积物水界面开展微尺度观测研究是揭示沉积物内源磷释放机制与控制因素的有效途径.;In this paper, Lake Hongfeng, located in Guizhou Province, was chosen to study the release process of the sediment phosphorus under the natural, aerobic and anaerobic conditions. Microscale observation of the physical and chemical properties of sediment-water interface by microelectrode technology was used, together with traditional P-speciation analysis, to explore the P-releasing mechanisms. The results showed that under anaerobic conditions, the total content of phosphorus in the sediment in Lake Hongfeng decreased significantly, which was mainly caused by the reduction of NaOH-P and rest-P, indicating that the aerobic condition promoted the phosphorus release from sediments. The concentration of phosphate in the pore water of sediment increased greatly under anaerobic condition, and the trend was contrary to that under aerobic condition. Under the anaerobic condition, concentration of dissolved oxygen decreased and sulfate reduction was enhanced, which released NaOH-P from the sediment. Decrease of O₂ accelerated the sediment reducing processes and produced a large amount of H₂S, which combined with ferrous icon to form the precipitation-ferrous sulfide, resulting in release of NaOH-P(Fe-P)into the pore water. The conversion of aerobic to anaerobic condition could promote the release of rest-P by changing the distribution of pH value in the sediment as well as microbial activities. Under the anaerobic condition, anaerobic microorganisms could not only contribute to the sulfate reduction and H₂S production, leading to pH decrease, but also consume organic matter and convert organic phosphorus into inorganic phosphorus. The redox environment of sediment-water interface could affect the penetration depth of sediment-oxygen, pH distribution, microbial activity, sulfur cycle as well as organic matter degradation process, which controlled the speciation transformation and release of sediment phosphorus. Microelectrode technology, together with traditional P-speciation analysis, is an effective way to reveal the release mechanisms of sediment phosphorus as well as the control factors.