Seasonal benthic nitrogen cycling in a temperate shelf sea: the Celtic Sea

Kitidis, V; Tait, K; Nunes, J; Brown, IJ; Woodward, EMS; Harris, C; Sabadel, AJM; Sivyer, DB; Silburn, B; Kröger, S. 2017 Seasonal benthic nitrogen cycling in a temperate shelf sea: the Celtic Sea. Biogeochemistry. 10.1007/s10533-017-0311-3

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Abstract/Summary

We undertook a seasonal study of benthic N-cycling on the Celtic Sea continental shelf in 2015, augmented by an earlier cruise in 2014. Two cruises in 2015 were centred before and after the Spring phytoplankton bloom and a further cruise was carried out in late summer. Five sites covering the mud to sand continuum were visited on all cruises, where we determined ammonium-oxidation, anammox and denitrification rates, expression of anammox and denitrification genes, N-nutrient fluxes and sediment porewater profiles of N-nutrients. Highest process rates were found during the post-bloom and late summer periods. The Celtic Sea was overwhelmingly a source of inorganic-N to the overlying water column. The efflux of nitrate was controlled by the magnitude of ammonium-oxidation. The latter accounted for 10–16% of total Oxygen consumption in cohesive sediments and 35–56% in sandy sediments. Ammonium oxidation rates in the range of 0.001–2.288 mmol m−2 days−1 were inversely correlated with sediment porosity and positively correlated with organic matter content (OM) which together explained 66% of the variance in rates. N-removal was dominated by anammox (0.003–0.636 mmol m−2 days−1), rather than denitrification (0.000–0.034 mmol m−2 days−1). This finding was supported by the corresponding gene expression data. The expression of hydrazine oxidoreductase (anammox) was significantly correlated with anammox and total N-removal rates. Anammox was positively correlated with porosity and OM, whilst denitrification was correlated with OM. The N-requirement of these processes was largely met through nitrification (ammonium-oxidation) rather than influx from the overlying water column. We estimated that N-removal via denitrification and anammox removed 6–9% of the organic-N deposited at the sea-floor from the overlying water column. The Celtic Sea system was thereby losing N which must be replenished on an annual basis in order to sustain productivity.

Item Type: Publication - Article
Subjects: Chemistry
Marine Sciences
Oceanography
Divisions: Plymouth Marine Laboratory > Science Areas > Marine Biochemistry and Observations
Depositing User: Malcolm Woodward
Date made live: 13 Mar 2017 14:23
Last Modified: 06 Jun 2017 16:18
URI: http://plymsea.ac.uk/id/eprint/7418

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