|Shields Jr, Fletcher|
Submitted to: Journal of Environmental Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2006
Publication Date: 11/1/2006
Citation: Chao, X., Jia, Y., Cooper, C.M., Shields Jr, F.D., Wang, S. 2006. Development and application of a phosphorus model for a shallow oxbow lake. Journal of Environmental Engineering 132:(11)1498-1507. DOI: 10.1061(ASCE)0733-9372(2006)132:11(1498). Interpretive Summary: Lakes in agricultural watersheds sometimes have water quality problems triggered by elevated concentrations of key nutrients (nitrogen and phosphorus) that lead to rapid growth of algae. Predicting lake phosphorus changes in response to changing watershed land use or inflow water quality is complicated due to the large number of physical, chemical, and biological influences on lake nutrient concentrations. A computer program to simulate lake phosphorus concentrations was developed, tested using hypothetical conditions, and then adjusted to match actual conditions in Deep Hollow Lake, an oxbow lake surrounded by fields in the Mississippi Delta. The computer program reproduced observed levels of chlorophyll with reasonable accuracy, showing that reduction of fine sediment entering the lake triggered more desirable conditions. These results provide a foundation for developing better tools for predicting the benefits of agricultural best management practices.
Technical Abstract: A three-dimensional numerical model was developed for simulating the phosphorus concentration in a shallow oxbow lake. In this model, the computational domain was divided into two parts: the water column and the bed sediment layer. The processes of mineralization, settling, adsorption, desorption, bed release (diffusion), growth and death of phytoplankton were considered, and the concentration of organic phosphorus, orthophosphate and related water quality constituents were simulated. The concentrations of particulate and dissolved phosphorus due to adsorption-desorption were calculated using two formulas derived based on the Langmuir Equation. The release rate of phosphorus from the bed sediment layer was calculated by considering the effects of the concentration gradient across the water-sediment interface, pH, temperature, dissolved oxygen concentration, and flow conditions. The adsorption and desorption of phosphorus from sediment particles, as well as its release from bed sediment were verified using results obtained from laboratory experiments. The model was calibrated and applied to Deep Hollow Lake in the alluvial plain of northwestern Mississippi. The simulated trends and magnitudes of phosphorus concentration were compared with field observations.