Suspension-sedimentation of sediment and release amount of internal load in Lake Taihu

Abstract

太湖是一个大型浅水湖泊,湖湾、沿岸及湖心等区域受地形影响,湖流结构及水土界面水力要素均有显著差异.针对目前对不同湖区底泥再悬浮规律差异性研究的缺失,本研究选取了3个具有代表性的点采集太湖底泥,采用矩形水槽开展底泥再悬浮模拟实验,并结合太湖二维水量水质模型及太湖全年实测数据,建立了不同湖区底泥再悬浮通量与风速之间的定量关系;通过室内静沉降实验,得到了静沉降通量与风速的相关关系;最后将底泥再悬浮实验结果参数化应用于太湖二维水量水质模型中,并对底泥悬浮沉降过程进行分解和概化,估算太湖全年内源释放量.结果表明:太湖每日的内源释放量受风速影响显著,和风速变化趋势较为接近,太湖全年进入水体的净底泥量有47.81×10⁴ t,夏季最大,冬季次之;就营养物质释放量而言,COD约为2.06×10⁴ t、总氮约为1149.05 t、总磷约为564.35 t,其中秋季营养物质释放量最小,夏季最大.;As a large shallow lake, Lake Taihu exhibits significant differences in flow structures and hydraulic factor at water-soil interface due to different terrains in lake-bay, coastal and center area. Sediment release under different flow velocities from three sites in Lake Taihu was simulating in a rectangle flume to study sediment resuspension under various hydrodynamic conditions. Combined with the in-situ test and experiment in the laboratory, a 2-D model of water flow and water quality on wind-driven current in Lake Taihu was established. The sediment resuspension flux and settling flux from different lake regions in the four seasons were calculated and the relationships between these fluxes and wind speed were obtained. The experiment result was applied in the numerical model and the suspension-sedimentation process was decomposed and generalized according to the critical wind speed. Annual average release amount of internal load in Lake Taihu during the year 2009 was estimated. The results indicate that daily release amount of internal load in Lake Taihu was significantly influenced by wind and had the same trend of change with wind. Lake Taihu has an annual average release amount of internal load with suspended solid 47.81×10⁴ t, COD 2.06×10⁴ t, total nitrogen 1149.05 t and total phosphorus 564.35 t, of which summer has the markedly higher release amount than other seasons.