The diffusive boundary layer of sediments: oxygen microgradients over a microbial mat

Area of Science:

• Geochemistry
• Microbiology
• Environmental Science

Background:

• The diffusive boundary layer (DBL) at the sediment-water interface critically influences biogeochemical processes.
• Microbial mats in saline ponds exhibit high oxygen consumption and complex surface structures.

Purpose of the Study:

• To analyze diffusive boundary layer (DBL) distribution in relation to surface topography and flow velocity.
• To quantify the impact of DBL on oxygen uptake by sediments.

Main Methods:

• Oxygen microelectrodes were used to measure DBL thickness and oxygen uptake rates.
• Three-dimensional mapping at 0.1-mm resolution characterized sediment-water interface topography.
• Flow velocity was varied to assess its effect on DBL and oxygen flux.

Main Results:

• DBL thickness decreased from 0.59 to 0.16 mm with increasing flow velocity (0.3 to 7.7 cm s-1).
• Oxygen uptake rate increased from 3.9 to 9.4 nmol cm-2 min-1 with higher flow.
• Surface topography increased effective surface area and oxygen flux by 49% compared to a flat surface.

Conclusions:

• Diffusion through the DBL is a significant rate limitation for sediment oxygen uptake.
• Flow velocity and surface topography are key factors controlling DBL dynamics and oxygen availability.
• Complex sediment topography enhances oxygen flux, impacting benthic microbial communities.