Small-scale spatial and temporal variability in coastal benthic O ₂ dynamics: Effects of fauna activity

In situ measurements in a shallow water sediment were performed using three different modules - a microprofiling unit, a transparent benthic chamber, and a planar optode periscope. The combined data set revealed an extremely patchy and variable benthic O₂ distribution primarily due to temporal variations in fauna activity and photosynthesis. A distinct diel pattern in the fauna activity, dominated by Hediste diversicolor, resulted in strongly elevated O₂ uptake rates of ∼5.3 mmol m^-2 h^-1 at the onset of darkness. The activity gradually diminished during the night, and the O₂ uptake decreased to less than half the maximum rate just before sunrise. The volume of oxic sediment around burrow structures was influenced by changing environmental conditions (benthic photosynthesis and fauna activity) but grossly exceeded that below the primary sediment surface. The volume specific respiration rate around burrows was more than seven times higher than the equivalent value at the sediment surface. A budget of the O ₂ consumption revealed that the O₂ uptake through the burrow walls just after sunset accounted for the major part of the total O ₂ uptake on a diel scale. The study demonstrates that light-driven variations in fauna activity can have great effects on the total benthic O ₂ consumption rate with large implications for estimated benthic mineralization rates.