Does denitrification occur within porous carbonate sand grains?

Other literature type English OPEN
Cook, Perran L. M. ; Kessler, Adam J. ; Eyre, Bradley D. (2016)

Carbonate sands form a major sediment type in coral reef environments and play a major role in organic matter recycling. It has previously been postulated that porosity of carbonate sand grains may lead to the formation of anoxic microniches that promote denitrification within these sediments. Under this conceptual model, we expect diffusion to exert an influence on process rates, which can be tested by determining their dependence to reactant concentrations. Here, we use two experiments in flow-through reactors to test this hypothesis in carbonate sediments collected from Heron Island, Australia. Denitrification was only observed to commence at substantial rates below 10&thinsp;μM&thinsp;O<sub>2</sub>, suggesting anoxic microniches do not exist. Furthermore, denitrification rates were constant above 18&thinsp;μM nitrate, suggesting no diffusion limitation, as would be expected if significant rates of reaction were occurring within porous grains. Potential rates of denitrification rates relative to respiration were broadly consistent with those previously reported in silicate sands.
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