Abstract

 In order to better understand the effects of tidal resuspension on contaminant cycling in coastal waters, a 1-D theoretical/numerical time and depth dependent model was developed and parameterized with more realistic approaches including advection, diffusion, organic carbon biodegradation, and linear-reversible sorption of contaminants. The model simulates interactions between a water column, a resuspendable floc layer, and the underlying sediments through multiple resuspension and deposition cycles induced by regular tides. Pyrene and particulate organic carbon (POC) cycling were simulated at the same time in this study. The model was used to explore the responses of both relatively contaminated and relatively clean sediments to different input loadings and hydrodynamic forces. Model results confirm the influences of resuspension found in previous field and model studies, and show some unexpected effects on porewater fluxes. The results indicate that tidal resuspension: 1. accelerates the organic carbon degradation rate in the water column. 2. affects porewater fluxes by increasing mass transport, but decreasing the concentration difference between the water column and sediments, with unexpected results. 3. decreases accumulation (burial fluxes) in the sediments. 4. prolongs particle residence time in the water column and allows greater diagenesis and sorption/desorption to take place. In addition, resuspension may influence the sites and rates of organic matter mineralization in shallow environments and therefore affect distributions of particulate organic matter.
  Sensitivity analyses using Monte Carlo simulation technique indicate that sediment porosity is the most critical parameter for the model, which means sediment porosity should be investigated in future application of the model. Enhancing the prognostic skill of the model will require comparison to specific data sets from laboratory experiments and field measurements. Experiments in specially designed mesocosms at the Chesapeake Biological Laboratory are planned.