流速对太湖河道底泥泥沙、营养盐释放规律影响实验研究

Characteristics of sediments and nutrient release under different flow velocity

河湖中的底泥作为二次污染源,影响河道水环境.太湖河口及调水区河流底泥泥沙、营养盐的释放扩散受水动力条件的影响越来越受到人们的重视.用环形水槽模拟河道的水动力条件的改变,通过实验研究悬浮泥沙、总溶解氮磷(TDN,TDP)和总氮磷(TN,TP)浓度在不同流速条件下在水体中的变化情况,从而掌握底泥泥沙、营养盐在不同流速下的释放特性.本研究按照泥沙的起动标准,把相对应的流速分为"个别动"、"少量动"以及"普遍动"流速,对应不同的泥沙悬浮量以及营养物质的释放量.研究显示高于起动流速下营养盐的动态释放较低于起动流速下的静态释放.泥沙的悬浮量与营养物质的动态释放过程密切相关.TDN、TDP释放量和最终平衡浓度随流速呈对数关系;TN、TP平衡浓度随流速增加呈指数形式增加.整个释放过程为,0~30 min的释放前期为孔隙水释放,营养物质释放量大且速率快;后期为再悬浮颗粒物释放,释放量小且速率减慢,达到平衡之后,营养盐浓度基本稳定.营养物质的空隙水释放与在悬浮颗粒物释放的比例有待进一步的研究.

Contaminated sediments,as a secondary pollution source in rivers and lakes,are of critical importance to water quality.Attention thus has been paid to understand release mechanisms and diffusion characteristics of nutrients from river sediments under different hydrodynamic conditions,especially in Taihu Lake estuary and water transfer areas.In this study,circulated flume experiments were conducted to investigate the release characteristics of sediments,also total dissolved phosphorus（TDP） and nitrogen（TDN） from sediments collected from a river bed near Lake Tai under various flow conditions.In accordance with different sediment starting standard,relative velocity should be divided into ＂individual start＂,＂a few start＂ and ＂universal start＂velocity.These different flow conditions corresponding to different amount of sediment resuspension and nutrient release.It was found that dynamic nutrient release amount with suspended particles is larger than static release with the velocity lower than the threshold.Release amount of TDP,TDN and their equilibrium concentrations in the water column can be described as a Logarithmic relationship;while equilibrium concentrations of total phosphorus（TP） and total nitrogen（TN） are exponentially increased with flow velocity.The whole process has three stages：the nutrient in the pore water was dramatically released in the initial 30 min,then the nutrient adsorbed in the suspended particles started to release to the water column with releasing rate slowed down from 30~60 min,and finally steady state was achieved with equilibrium concentration.The ratio of nutrient release from porewater and re-suspended particles need further study.