Higashino Makoto, Gantzer Charles J, Stefan Heinz G
Department of Civil Engineering, Oita National College of Technology, 1666 Maki, Oita 870-0152, Japan.
Water Res. 2004 Jan;38(1):1-12. doi: 10.1016/j.watres.2003.08.030.
Dissolved oxygen uptake at a sediment/water interface (SOD) is controlled by mass transport and/or biochemical reactions in two adjacent boundary layers: the diffusive boundary layer delta(D) in the water and the penetration depth delta in the sediment. Either one of those boundary layers or both can be controlling. The transition from sediment control to water control is a function of shear velocity at the sediment/water interface (U()) and biochemical activity rate (micro(0)) in the sediment. A model was developed for the unsteady response of SOD and DO profiles near the sediment/water interface. Michaelis-Menten kinetics were used initially, but zero order kinetics work just as well when the half saturation coefficient K(O(2)) is small as was suggested by field data. Beginning with zero DO in the sediments the times required to reach steady state DO profiles and SOD was on the order of minutes to hours, faster where biochemical activity is strong. The values of SOD estimated by the model were compared with experimental data to verify the reliability of the model. The model can reproduce observed penetration depths and diffusive boundary layer thickness. Values of SOD estimated by the model were of same magnitude as observed data. The unsteady DO uptake model can be used to provide guidance for field measurements of SOD. Placing a chamber (with a stirrer) into the sediments disturbs the DO equilibrium at the sediment/water interface. A new equilibrium will be reached within a time that can be measured in terms of cumulative DO consumption in the chamber (SOD exerted). Upper bounds for (SOD exerted) are larger when biochemical activity in the sediments is smaller. Values of SOD exerted are less than 0.1gm(-2) when micro(0) is less than 50mgl(-1)d(-1) and U()>0.1cm/s. In other words, steady state conditions are easier to reach for high SOD values. Actual times required to reach steady state can be from minutes to hours. If flow conditions in the chamber and at the natural sediment/water interface are much different, measured SOD values have to be adjusted. A procedure for the adjustments, which can be substantial, has been developed.
沉积物/水界面处的溶解氧摄取量（SOD）受两个相邻边界层中的传质和/或生化反应控制：水中的扩散边界层δ(D)和沉积物中的穿透深度δ。这两个边界层中的任何一个或两者都可能起控制作用。从沉积物控制到水控制的转变是沉积物/水界面处的剪切速度（U()）和沉积物中的生化活性速率（micro(0)）的函数。开发了一个模型，用于描述沉积物/水界面附近SOD和溶解氧（DO）剖面的非稳态响应。最初使用了米氏动力学，但当半饱和系数K(O(2))如现场数据所示很小时，零级动力学同样适用。从沉积物中的零溶解氧开始，达到稳态溶解氧剖面和SOD所需的时间为几分钟到几小时，在生化活性强的地方更快。将模型估计的SOD值与实验数据进行比较，以验证模型的可靠性。该模型可以再现观测到的穿透深度和扩散边界层厚度。模型估计的SOD值与观测数据的量级相同。非稳态溶解氧摄取模型可用于为SOD的现场测量提供指导。将一个带有搅拌器的腔室放入沉积物中会扰乱沉积物/水界面处的溶解氧平衡。在一个可以根据腔室内累积的溶解氧消耗量（施加的SOD）来测量的时间内将达到新的平衡。当沉积物中的生化活性较小时，（施加的SOD）的上限较大。当micro(0)小于50mgl(-1)d(-1)且U() > 0.1cm/s时，施加的SOD值小于0.1gm(-2)。换句话说，对于高SOD值更容易达到稳态条件。达到稳态所需的实际时间可以从几分钟到几小时。如果腔室内和天然沉积物/水界面处的流动条件差异很大，则必须对测量的SOD值进行调整。已经开发了一种调整程序，这种调整可能很大。
