Abstract
The burrow walls created by macrofauna in aquatic sediments are sites of intense chemical mass transfer. Quantitative measurement of their significance is, however, difficult because chemistry in the immediate vicinity of burrow walls is temporally dynamic due to periodic ventilation of burrows by macrofauna. A temporally dynamic, 2D multicomponent diffusion-reaction model was utilized to depict the magnitude and time dependency of chemical mass transfer in the immediate vicinity of burrow walls as well as at the water/sediment interface. The simulation results illustrate that sediment particles, pore water, and microorganisms within a few millimeters of burrow walls experience significant oscillation in pH (as much as two pH units) and dissolved oxygen concentration (between saturation and near anoxia) whereas such oscillation is absent at the water/ sediment interface. The geochemical oscillation is expected to affect the net stability of mineral phases, activities and community structures of microorganisms, and rates and magnitudes of microbial diagenetic reactions.
Highlights
IntroductionBurrowing infauna in aquatic sediments induce temporal fluctuation in concentrations of dissolved species (i.e., geochemical oscillation) through their metabolism and burrow ventilation activities
Burrowing infauna in aquatic sediments induce temporal fluctuation in concentrations of dissolved species through their metabolism and burrow ventilation activities
Determined data on macrofauna burrow geometry, ventilation habits, organic carbon (OC) degradation rates, porosity, and pore water chemistry are necessary in order to properly constrain the model and evaluate the simulation results
Summary
Burrowing infauna in aquatic sediments induce temporal fluctuation in concentrations of dissolved species (i.e., geochemical oscillation) through their metabolism and burrow ventilation activities. They periodically irrigate their burrows to replace metabolite-rich burrow water with fresh overlying water. The immediate vicinity of burrow walls is subject to periodic changes in the concentrations of oxygen, nutrients, and other pore water species.[1,2]. Field and laboratory studies suggest that OC remineralization rates are enhanced by the redox oscillation, even though the anoxic period in each oscillation cycle is typically much longer (y10–100X) than the oxic period for a given sediment microenvironment.[4,5] Temporally averaged redox conditions do not directly correlate to the rates and magnitudes of OC reactions.[3,6] A comprehensive understanding of OC diagenesis in aquatic sediments requires an adequate characterization of the temporal dynamics of redox and other geochemical parameters
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