Crawford, S. M. UMCES, Horn Point Laboratory,
Sanford, L. P. UMCES, Horn Point Laboratory,

Diffusion and reaction kinetics both affect fluxes of nutrients and dissolved gasses across solid-water interfaces. Diffusion through the aqueous sublayer above the interface is directly related to boundary layer shear velocity. Reaction kinetics are determined largely by biogeochemical processes at or just below the interface. Determining whether diffusion, reaction, or both control fluxes is important for understanding related ecosystem processes. Previous investigators have studied the extreme cases of pure kinetic control and pure diffusional control, but the intermediate range when both are important remains poorly understood. We developed a model based on Michaelis-Menten kinetics and Fickian diffusion through the aqueous sublayer to look specifically at the intermediate range and to determine thresholds for diffusion-limitation and diffusion-control. Model results show that a single dimensionless number consisting of the boundary layer mass transfer velocity and Michaelis-Menten kinetic parameters determines the extent of diffusional versus kinetic control. According to this criterion, nutrient uptake rates at the wall and bottom boundaries of the MEERC pelagic-benthic mesocosms frequently are diffusion-limited. Nutrient uptake by coral also is predicted to be diffusion-controlled, in agreement with previous coral uptake experiments. In cases such as these, actual maximum uptake rates will be lower than potential maximum uptake rates.
Day: Wednesday, Feb. 3
Time: 08:45 - 09:00am
Location: Eldorado Hotel
Code: SS03WE0845E