Location: Watershed Physical Processes ResearchTitle: Three-dimensional numerical modeling of water quality and sediment-associated processes in natural lakes Author
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 7/5/2012
Publication Date: 6/5/2013
Citation: Chao, X., Jia, Y. 2013. Three-dimensional numerical modeling of water quality and sediment-associated processes in natural lakes. IN: Water Quality: Indicators, Human Impact, and Environmental Health, You-Gan Wang (ed.). ebook novapublishers.com. ISBN: 978-1-62417-112-3. Chapter 3, pp. 63-97. Interpretive Summary: A three-dimensional numerical model (CCHE3D_WQ) was developed to simulate the concentration of water quality constituents in shallow natural lakes where sediment-associate processes are important. Four biochemical cycles were simulated, and eight state variables were involved in the interacting systems. Sediment-associated water quality processes were studied. A formula was obtained based on field measurements to calculate the light attenuation coefficient by considering the effects of suspended sediment and chlorophyll. The concentrations of particulate and dissolved nutrients due to adsorption-desorption were calculated using two formulas derived based on the Langmuir Equation. The release rates of nutrients from the bed sediment were calculated by considering the effects of the concentration gradient across the water-sediment interface, pH, temperature and dissolved oxygen concentration. The sediment-associated processes were integrated into CCHE3D_WQ to study the concentration of water quality constituents in Deep Hollow Lake in Mississippi Delta. Realistic trends and magnitudes of nutrient and phytoplankton concentrations obtained from the numerical model generally agreed with field observations. The effects of sediment-associated processes are quite important in water quality processes. Without considering the sediment-associated processes, the model overestimated ortho-phosphorus concentration and underestimated organic phosphorus. After considering those processes, the numerical results produced better agreements with field observations. The model was also used to conduct analyses of the sensitivities of lake chlorophyll concentration to SS concentration and nutrient loadings. Lake primary productivity is mainly limited by suspended sediment concentration, which limits light penetration. After the reduction of SS in the lake, there is significant increase in chlorophyll concentration. The numerical results also show that the concentration of chlorophyll is much more sensitive to the inorganic nitrogen than that to the inorganic phosphorus in Deep Hollow Lake. This model provides a useful tool for predicting water quality constituents in natural lakes. It helps us understand the interaction processes between water quality and sediment in natural lakes. It is also useful for the decision makers to evaluate BMPs established in the lake watersheds.
Technical Abstract: This chapter presents the development and application of a three-dimensional water quality model for predicting the distributions of nutrients, phytoplankton, dissolved oxygen, etc., in natural lakes. In this model, the computational domain was divided into two parts: the water column and the bed sediment layer, and the water quality processes in these two domains were considered. Three major sediment-associated water quality processes were simulated, including the effect of sediment on the light intensity for the growth of phytoplankton, the adsorption-desorption of nutrients by sediment and the release of nutrients from bed sediment layer. This model was first verified using analytical solutions for the transport of non-conservative substances in open channel flow, and then calibrated and validated by the field measurements conducted in a natural oxbow lake in Mississippi. The simulated concentrations of water quality constituents were generally in good agreement with field observations. This study shows that there are strong interactions between sediment and water quality constituents.