Models that have been developed to quantify the oxygen flux at the sediment-water interface (SWI) generally do not explicitly consider the influence of bioroughness (mounds and burrows) and bioirrigation. We performed a numerical study of the influence of overlying water velocity, bioroughness, and bioirrigation on the oxygen flux across the SWI. We found that compared with a flat bed, bioroughness significantly increases O2 transport at the SWI as a result of enhanced turbulence and pressure differences across the roughness. Bioirrigation can also enhance O2 transport across the SWI by a factor of up to 10 when the roughness Reynolds number (Re*) is low, but the influence of bioirrigation decreases with increasing Re*. Burrows increase O2 penetration depth, and bioirrigation causes asymmetric distributions of O2 along burrows. Despite the complexity of O2 distribution in sediments, the net exchange across the SWI can be described by the relationship of O'Connor and Harvey (2008, https://doi.org/10.1029/2008WR007160) (Formula presented.) when the shape is two-dimensional or when the burrow density is low. When the burrow density is large, flow is three-dimensional and flow interactions between burrows become important. Under these conditions the net exchange across the SWI increases by up to a factor of 4. A burrow number is introduced, Bu = [burrow density]1/2 [burrow height], to correct the coefficient in O'Connor and Harvey's relationship, that is, a = 0.005 for Bu < 0.05 and a = 0.02 for Bu ≫ 0.1.
- hyporheic exchange