期刊
GEOCHIMICA ET COSMOCHIMICA ACTA
卷 141, 期 -, 页码 440-453出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.gca.2014.06.028
关键词
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资金
- Australian Research Council [LP0991254, DP1096457, DE140101733]
- Melbourne Water Corporation
- Environment Protection Authority Victoria
- Monash University Sir James McNeill Foundation
- US National Science Foundation [EAR-0955750]
- Directorate For Geosciences
- Division Of Earth Sciences [0955750] Funding Source: National Science Foundation
- Australian Research Council [LP0991254, DP1096457] Funding Source: Australian Research Council
It has recently been hypothesized that bulk denitrification rates in carbonate sands may be enhanced by reactions occurring in the intra-granular pores, cracks and crevices. We tested this hypothesis using a series of flow and reactive transport models spanning from the pore-scale (similar to mm) to the continuum scales (similar to 10 cm bedforms). Pore-scale simulations solved the coupled Navier-Stokes and Brinkman equations and represented flow-through reactor experiments previously performed on coral reef sands. The results revealed that intra-granular transport and reactions can explain over-all denitrification enhancement. A sensitivity study with a single grain diffusive transport model showed that in the majority of cases, the resultant increase in denitrification was not coupled to nitrification within a single grain. Only for large grain diameters of 2 and 4 mm was coupled nitrification-denitrification important. In most cases, coupled nitrification-denitrification instead arose as conditions became more reducing along a flow path, as is the case in quartz sands without intragranular pores. An intra-granular reaction rate based on a single grain model was incorporated into a continuum-scale Darcy flow and reactive transport model for a rippled sand bed, where porewater flow is driven by the turbulent current over the ripple. The results of the Darcy-scale model suggest that intra-granular pores increase the amount of slow-flowing areas within which coupled nitrification-denitrification can occur. We conclude that the complex advective flow field does not strongly inhibit denitrification enhancement by carbonate sand grains, as it does in silica sands. Thus, intra-granular reactions may enhance bulk denitrification in carbonate sediment with porous grains under natural advective conditions. (C) 2014 Elsevier Ltd. All rights reserved.
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