Advection Drives Nitrate Past the Microphytobenthos in Intertidal Sands, Fueling Deeper Denitrification.

Nitrification rates are low in permeable intertidal sand flats such that the water column is the primary source of nitrate to the sediment. During tidal inundation, nitrate is supplied to the pore space by advection rather than diffusion, relieving the microorganisms that reside in the sand from nitrate limitation and supporting higher denitrification rates than those observed under diffusive transport. Sand flats are also home to an abundant community of benthic photosynthetic microorganisms, the microphytobenthos (MPB).