Characteristics and significance of nitrogen, phosphorus and oxygen transportation at the sediment-water interface in east Lake Chaohu

Abstract

以东巢湖近城市湖湾沉积物为研究对象，在沉积物氮、磷营养盐分析的基础上，采用沉积物柱状芯样静态释放模拟法定量评估研究区域沉积物-水界面氨氮、溶解性活性磷酸盐营养盐释放潜力，利用微电极非损伤测定技术获得沉积物-水微界面溶解氧（DO）剖面分布及微界面DO消耗和扩散特征.结果表明：东巢湖近城市湖湾沉积物氮、磷污染物蓄积量较高，受TN、TP污染程度较重.沉积物内源氨氮、磷酸盐释放明显，平均释放速率分别达到32.44 mg/（m²·d）和1.25 mg/（m²·d），区域内沉积物已成为水柱中氮、磷营养盐的污染源.研究区域上覆水体处于好氧状态，沉积物-水微界面平均DO穿透深度（OPD）达到5.3 mm，平均DO扩散通量为4.56 mmol/（m²·d），表现出良好的DO扩散能力.沉积物内源氨氮和磷酸盐释放能力与表层沉积物TN/TP物质含量及沉积物-水微界面DO穿透深度有关，在沉积物氮、磷污染较重的情况下，DO穿透深度越低越有利于氮、磷污染物从沉积物向上覆水体释放.;A comprehensive study of transportation features of nitrogen, phosphorous and dissolve oxygen at the sediment-water interface was carried out in near city areas of east Lake Chaohu. Based on the investigation of sediment nutrients analysis and nutrients release incubation experiments, the release potential and release rates of ammonia nitrogen (NH₃-N) and soluble reactive phosphorous (SRP) of different sediments were estimated. The distribution characteristics, diffusion fluxes, and consumption rates of dissolved oxygen (DO) at the sediment-water interface of different sediments were studied by using a non-invasive microelectrode analysis system. The results showed the surface sediments in the near city areas of east Lake Chaohu were in severe nitrogen and phosphorous pollution with high total nitrogen (TN) and total phosphorus (TP) loadings. Typical internal releases of NH₃-N and SRP were observed from all sediments with the average release rates of 32.44 mg/(m²·d) and 1.25 mg/(m²·d), respectively. The sediments play the role of pollution source rather than the sink for NH₃-N and SRP in the study area. Results also showed that all overlying water were at aerobic condition. The average oxygen penetration depth (OPD) and oxygen diffusion flux at sediment-water micro-interfaces reached 5.3 mm and 4.56 mmol/(m²·d) respectively, indicating good DO diffusion ability from the boundary layer to the sediment. The internal release intensity of NH₃-N and SRP are influenced by TN/TP contents of the surface sediment as well as the OPD at the sediment-water interface. The release of NH₃-N and SRP from sediments could be benefited from the high nitrogen and phosphorous loadings and low OPD and contribute to the eutrophication of the lake.