| Sediment resuspension has been shown to be important for nutrient and contaminant cycling in many previous studies. In order to understand the importance of resuspension and deposition processes on nutrients and contaminants, theoretical/numerical depth and time dependent models were developed and parameterized with realistic approaches. These models incorporated mechanisms linking physical processes (e.g., resuspension and deposition at the sediment-water interface) with their biogeochemical consequences, treating the water column, a floc layer and underlying sediments as a system. Erosion and deposition rates are time-varying rather than at steady state. Particulate organic carbon, pyrene, phosphorus, and ammonium were targeted as example compounds. Two physical environments were chosen: regular tidal resuspension and/or episodic wind-wave induced resuspension. These models were used to explore the responses of both relatively contaminated and relatively clean sediments to different input loadings and hydrodynamic forces. Model outputs include time series of dissolved and particulate concentrations, porewater and particle fluxes, diagenetic rates of organic matter, sorption rates, and nitrification rates. Particle residence time in the floc layer was also calculated in cases with regular tidal resuspension. The results indicate that resuspension at the sediment-water interface has the following impacts: (1) It increases dissolved concentrations in the water column for the cases investigated up to 22% for pyrene in coastal areas with regular tidal resuspension, 40% for phosphorus in shallow lakes with episodic resuspension, and 160% for ammonium in coastal areas with episodic resuspension. (2) It decreases diffusive fluxes but increases advective fluxes in the continuous tidal forcing cases, and enhances both diffusive and advective fluxes in the storm event cases. (3) It decreases accumulation (burial fluxes) and speeds up recycling rates. (4) It accelerates organic matter degradation rates, desorption rates and nitrification rates in the water column. Sensitivity analyses using Monte Carlo simulation techniques indicate that sediment porosity is the most critical parameter for these models. To enhance the prognostic skill of the model, fine tuning in a vast parameter space awaits calibration against a comprehensive data set from laboratory experiments and field measurements. |
