Sediment resuspension

Assuming most PAH are stable in the atmosphere, which we feel is an excellent assumption, we ask what happens to these compounds after they are released from combustion systems throughout the world. We suggest that PAH are transported to a-quatic sediments either by direct airborne transport or by sediment resuspension and redeposition. 

The flux resulting from sediment resuspension is assumed to be proportional to the difference between the concentration on the resuspended sediment particles, Cssc, and the sorbed concentration, Csop, which the particles would have in equilibrium with the aqueous concentration in the water column, Cpp ... 

In Part 2 of the PCB story, we introduced the exchange between the water column and the surface sediments in exactly the same way as we describe air/water exchange. That is, we used an exchange velocity, vsedex, or the corresponding exchange rate, ksedex (Table 23.6). Since at this stage the sediment concentration was treated as an external parameter (like the concentration in the air, Ca), this model refinement is not meant to produce new concentrations. Rather we wanted to find out how much the sediment-water interaction would contribute to the total elimination rate of the PCBs from the lake and how it would affect the time to steady-state of the system. As shown in Table 23.6, the contribution of sedex to the total rate is about 20% for both congeners. Furthermore, it turned out that diffusion between the lake and the sediment pore water was much more important than sediment resuspension and reequilibration, at least for the specific assumptions made to describe the physics and sorption equilibria at the sediment surface. 

In Box 23.2 it is shown that the combined exchange of a chemical at the sediment-water interface due to sediment resuspension and to diffusion, respectively, can be expressed by a single exchange velocity. Explain why this result is a direct consequence of the assumption that the lake model can be formulated in terms of linear differential equations. 

Miller SM (2003) The effects of large-scale episodic sediment resuspension on persistent organic pollutants in Southern Lake Michigan. PhD Dissertation, Civil and Environmental Engineering, University of Iowa, Iowa City, IA... 

Figure 6.6 A conceptual diagram showing that while the ETM roughly tracks the limit of salt, it is often decoupled from the salt front (defined here at the isohaline with a salinity of 1), due to a lag of ETM sediment resuspension/transport from rapid meteorologically driven movement of the salt front. (From Sanford et al., 2001, with permission.)...

Chang, G. C., Dickey, T. D., and Williams, A. J. (2001). Sediment resuspension over a continental shelf during Hurricanes Edouard and Hortense. J. Geophys. Res. 106, 9517—9531. 

Fanning, K. A., Carder, K. L., and Betzer, P. R. (1982). Sediment resuspension by coastal waters A potential mechanism for nutrient re-cycling on the ocean s margins. Deep Sea Res. 29,1223—1229. 

Sloth, N. P., Riemann, B., Nielsen, L. P., and Blackburn, T. H. (1996). Resilience of pelagic and benthic microbial communities to sediment resuspension in a coastal ecosystem, Knebel Vig, Denmark. Estuar. Coast. Shelf Sd. 42, 405—415. 

Churchill J., Wirick C., Flagg C., and Pietrafesa L. (1994) Sediments resuspension over the continental shelf east of the Delmarva Peninsula. Deep-Sea Res. II41, 341-363. 

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