Modelling spatial variations in dissolved oxygen in fine-grained streams under uncertainty

Abstract

This paper presents a novel triple-layer model, called VART DO-3L, for simulation of spatial variations in dissolved oxygen (DO) in fine-grained streams, characterized by a fluid mud (fluff or flocculent) layer (an advection-dominated storage zone) as the interface between overlying stream water and relatively consolidated streambed sediment (a diffusion-dominated storage zone). A global sensitivity analysis is conducted to investigate the sensitivity of VART DO-3L model input parameters. Results of the sensitivity analysis indicate that the most sensitive parameter is the relative size of the advection-dominated storage zones (As/A), followed by a lumped reaction term (R) for the flocculent layer, biological reaction rate (μo) in diffusive layer and biochemical oxygen demand concentration (L) in water column. In order to address uncertainty in model input parameters, Monte Carlo simulations are performed to sample parameter values and to produce various parameter combinations or cases. The VART DO-3L model is applied to the Lower Amite River in Louisiana, USA, to simulate vertical and longitudinal variations in DO under the cases. In terms of longitudinal variation, the DO level decreases from 7.9 mg l at the Denham Springs station to about 2.89 mg l−1 at the Port Vincent station. In terms of vertical variation, the DO level drops rapidly from the overlying water column to the advection-dominated storage zone and further to the diffusive layer. The DO level (CF) in the advective layer (flocculent layer) can reach as high as 40% of DO concentration (C) in the water column. The VART DO-3L model may be applied to similar rivers for simulation of spatial variations in DO level. Copyright © 2014 John Wiley & Sons, Ltd.