浅水湖泊动力作用下水-土界面底泥起悬驱动力野外观测

The driving force of sediment suspension on sediment-water interface in shallow lakes

动力扰动引起的水-土界面沉积物悬浮是浅水湖泊蓝藻水华控制的难点,本文基于声学高频流速仪、浊度仪、气象、波浪等观测仪器获取的高时空分辨时间序列参量,以太湖为例对动力扰动下的底泥起悬驱动力进行研究.结果表明风速小于3 m/s时,水-土界面处平均悬浮物浓度为59 mg/L,波流综合切应力小于0.015 N/m^2,底泥未起悬或在底床附近极小范围内发生起悬;风速在3~6 m/s时,水-土界面处平均悬浮物浓度为103 mg/L,波浪产生的底切应力大部分情况远大于湖流产生的切应力,波流综合切应力处于0.015~0.25 N/m^2范围内,底泥中等规模起悬;风速大于6 m/s时,水-土界面处平均悬浮物浓度为174 mg/L,波浪产生的底切应力占据绝对的主导地位,波流综合切应力大于0.25 N/m^2,底泥大规模起悬.梅梁湾底泥起悬的临界切应力在0.015 N/m^2左右,临界风速大约为3 m/s.

Sediment suspension on sediment-water interface caused by dynamic disturbance is the difficult issue in shallow lake eutrophication control. To study the driving force of sediment suspension in Meiliang Bay of Lake Taihu, a set of synchronous, highfrequency data of current, turbidity, wind, wave are obtained using the Acoustic Doppler Velocimeter, Optical Backseatter Sensor, PH-II Handheld weather stations, and RBRduo T.D. wave tide gauge. The results show that when the wind speed is less than 3 m/s, the average suspended solid concentration （ SSC ） on sediment-water interface is approximately 59 mg/L. The bottom shear stresses generated by waves is nearly equal to that generated by currents, where no sediment suspension can be found and the comprehensive shear stress generated by wind-induced waves and currents is less than 0.015 N/m2. When the wind speed ranges from 3 to 6 m/s, the average SSC on sediment-water interface is approximately 103 mg/L. The bottom shear stresses generated by waves is greater than that generated by currents in most cases, where a medium amount of sediment is suspended and the comprehensive shear stress generated by wind-induced waves and currents ranges from 0.015 to 0.25 N/m2. When the wind speed exceeds 6 m/s and the average SSC on sediment-water interface is approximately 174 nag/L, the wave-generated shear stress plays an absolute leading role in large amount of sediment suspension and the comprehensive shear stress generated by wind-induced waves and currents is larger than 0.25 N/m2. The critical shear stress of sediment suspension in Meiliang Bay is approximately 0.015 N/m2 while the critical wind speed is 3 m/s.