| Hydrodynamic processes (turbulent mixing, wave action, circulation, etc.) and sediment transport processes (settling, resuspension, deposition, flocculation, etc.) can significantly affect the nutrient dynamics in lakes and estuaries. Previous water quality models (e.g., WASP model) did not use sophisticated models for hydrodynamics and sediment dynamics and therefore lack the ability of quantitatively modeling the complex nutrient dynamics in lakes and estuaries. In addition, most of the previous water quality models used very large grid (box) size and time step (much larger than the time and length scales of hydrodynamics and sediment transport processes) which could result in totally incorrect model predictions.;Because of the dependence of nutrient dynamics on hydrodynamics and sediment dynamics, it is essential that a water quality model should be able to quantify hydrodynamic and sediment transport quantities in lakes and estuaries and that the grid size and the time step in model applications should be smaller than the length and time scales of hydrodynamics and sediment transport. This study developed 1-D and 3-D nutrient models and aggregated these nutrient models with models for hydrodynamics and sediment transport originally developed by Sheng et al. to study effects of hydrodynamics and sediment transport processes on nutrient cycles in shallow lakes and estuaries. The integrated 1-D and 3-D models for hydrodynamics, sediment transport, and nutrient dynamics were applied to Lake Okeechobee and Tampa Bay. From field data and model applications, this study obtained four major conclusions: (1) resuspensions of sediments and nutrients in Lake Okeechobee and Tampa Bay were mainly caused by wind-induced waves, (2) the resuspension flux of nutrients is about 2 to 3 orders of magnitude larger than the diffusive flux, (3) the release of nutrients from suspended sediments is affected by pH and dissolved oxygen levels in Lake Okeechobee and Tampa Bay, and (4) because the time step of a real-time simulation (10-15 min.) is generally much smaller than the time scale of desorption-adsorption reactions of nutrients, equilibrium models for desorption-adsorption reactions often overpredict the release of nutrients from resuspended sediments. |
