Benthic metabolism and nitrogen dynamics in a sub-tropical coastal lagoon: microphytobenthos stimulate nitrification and nitrate reduction through photosynthetic oxygen evolution

Dunn, Ryan J.K., Welsh, David T., Jordan, Mark A., Waltham, Nathan J., Lemckert, Charles J., and Teasdale, Peter R. (2012) Benthic metabolism and nitrogen dynamics in a sub-tropical coastal lagoon: microphytobenthos stimulate nitrification and nitrate reduction through photosynthetic oxygen evolution. Estuarine, Coastal and Shelf Science , 113. pp. 272-282.

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Abstract

Benthic oxygen and nutrient fluxes, and rates of nitrate reduction, were determined seasonally under light and dark conditions at four sites within a sub-tropical coastal lagoon (Coombabah Lake, Australia). Sediments at all sites were strongly heterotrophic acting as strong oxygen sinks and sources of dissolved inorganic nitrogen (DIN) in all seasons during both light and dark incubations. Sediment oxygen demand (SOD) and DIN effluxes were greatest during summer, but showed only a relatively small degree of seasonal variation. In contrast, there was a strong spatial trend in SOD and DIN effluxes, which were consistently greater at the sites with fine grained compared to the coarser sediments. Microphytobenthos (MPB) directly influenced SOD and DIN effluxes, with lower SOD and DIN effluxes measured during all light incubations. Strong correlations were found between sediment chlorophyll-a content and light–dark shifts in oxygen and ammonium fluxes (ΔO2 and ΔNH4+), and between ΔO2 and ΔNH4+. Rates of total nitrate reduction were relatively low ranging from 3 to 26 μmol N m−2 h−1 and exhibited only minor seasonal variations. Dissimilatory nitrate reduction to ammonium (DNRA) was the dominant pathway for nitrate reduction, accounting for on average, 65 and 68% of total nitrate reduction during light and dark incubations, respectively. Nitrification was the dominant source of nitrate fuelling nitrate reduction processes, accounting for approximately 90% of total nitrate supply. In contrast to typical MPB colonised sediments, rates of nitrification and, as a consequence, nitrate reduction rates were consistently stimulated in the light, indicating that MPB primarily influenced these processes through photosynthetic oxygen evolution rather than through competition for inorganic N-species.

Item ID: 25425
Item Type: Article (Refereed Research - C1)
Keywords: benthic fluxes, denitrification, dissimilatory nitrate reduction to ammonium (DNRA), microphytobenthos, southern Moreton Bay
Additional Information:

This is a special issue titled: The MIRACLE Project (Mercury Interdisciplinary Research project for Appropriate Clam farming in Lagoon Environment).

ISSN: 1096-0015
Funders: Australian Research Council (ARC)
Date Deposited: 14 Mar 2013 04:17
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050206 Environmental Monitoring @ 70%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050205 Environmental Management @ 30%
SEO Codes: 96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960503 Ecosystem Assessment and Management of Coastal and Estuarine Environments @ 60%
96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960507 Ecosystem Assessment and Management of Marine Environments @ 20%
96 ENVIRONMENT > 9606 Environmental and Natural Resource Evaluation > 960611 Urban Water Evaluation (incl. Water Quality) @ 20%
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