Journal article
Benthic fluxes of nitrogen in the tidal reaches of a turbid, high nitrate subtropical river
Estuarine, Coastal and Shelf Science, Vol.59(4), pp.675-685
2004
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Abstract
<p>Benthic fluxes of dissolved inorganic nitrogen (NO<sub>3</sub><sup>-</sup> and NH<sub>4</sub><sup>+</sup>), dissolved organic nitrogen (DON), N<sub>2</sub> (denitrification), O<sub>2</sub> and TCO<sub>2</sub> were measured in the tidal reaches of the Bremer River, south east Queensland, Australia. Measurements were made at three sites during summer and winter. Fluxes of NO<sub>3</sub><sup>-</sup> were generally directed into the sediments at rates of up to -225 µmol N m<sup>-2</sup> h<sup>-1</sup>. NH<sub>4</sub><sup>+</sup> was mostly taken up by the sediments at rates of up to -52 µmol N m<sup>-2</sup> h<sup>-1</sup>, its ultimate fate probably being denitrification. DON fluxes were not significant during winter. During summer, fluxes of DON were observed both into (-105 µmol m<sup>-2</sup> h<sup>-1</sup>) and out of (39 µmol m<sup>-2</sup> h<sup>-1</sup>) the sediments. Average N<sub>2</sub> fluxes at all sampling sites were similar during summer (162 µmolN m<sup>-2</sup> h<sup>-1</sup>) and winter (153 µmolN m<sup>-2</sup> h<sup>-1</sup>). Denitrification was fed both by nitrification within the sediment and NO<sub>3</sub><sup>-</sup> from the water column. Sediment respiration rates played an important role in the dynamics of nitrification and denitrification. NO<sub>3</sub><sup>-</sup> fluxes were significantly related to TCO<sub>2</sub> fluxes (p<0:01), with a release of NO<sub>3</sub><sup>-</sup> from the sediment only occurring at respiration rates below 1000 µmol C m<sup>-2</sup> h<sup>-1</sup>. Rates of denitrification increased with respiration up to TCO<sub>2</sub> fluxes of 1000 µmol C m<sup>-2</sup> h<sup>-1</sup>. At sediment respiration rates above 1000 µmol C m<sup>-2</sup> h<sup>-1</sup>, denitrification rates increased less rapidly with respiration in winter and declined during summer. On a monthly basis denitrification removed about 9% of the total nitrogen and 16% of NO<sub>3</sub><sup>-</sup> entering the Bremer River system from known point sources. This is a similar magnitude to that estimated in other tidal river systems and estuaries receiving similar nitrogen loads. During flood events the amount of NO<sub>3</sub><sup>-</sup> denitrified dropped to about 6% of the total river NO<sub>3</sub><sup>-</sup>load.</p>
Details
- Title
- Benthic fluxes of nitrogen in the tidal reaches of a turbid, high nitrate subtropical river
- Creators
- Perran LM Cook - University of TasmaniaBradley D Eyre - Southern Cross UniversityRhys LeemingEdward CV Butler
- Publication Details
- Estuarine, Coastal and Shelf Science, Vol.59(4), pp.675-685
- Identifiers
- 1213; 991012820638302368
- Academic Unit
- Centre for Coastal Biogeochemistry; School of Environment, Science and Engineering; Science; Faculty of Science and Engineering
- Resource Type
- Journal article