The influence of ocean acidification on nitrogen regeneration and nitrous oxide production in the northwest European shelf sea

• Published in: Biogeosciences
• Main Authors: D. R. Clark, I. J. Brown, A. P. Rees, P. J. Somerfield, P. I. Miller
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2014
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Ocean acidification
• Online Access: https://doi.org/10.5194/bg-11-4985-2014; https://doaj.org/article/bf8f9113e0924915a6fb2e9701966b4a

The assimilation and regeneration of dissolved inorganic nitrogen, and the concentration of N 2 O, was investigated at stations located in the NW European shelf sea during June/July 2011. These observational measurements within the photic zone demonstrated the simultaneous regeneration and assimilation of NH 4 + , NO 2 − and NO 3 − . NH 4 + was assimilated at 1.82–49.12 nmol N L −1 h −1 and regenerated at 3.46–14.60 nmol N L −1 h −1 NO 2 - was assimilated at 0–2.08 nmol N L −1 h −1 and regenerated at 0.01–1.85 nmol N L −1 h −1 NO 3 − was assimilated at 0.67–18.75 nmol N L −1 h −1 and regenerated at 0.05–28.97 nmol N L −1 h −1 . Observations implied that these processes were closely coupled at the regional scale and that nitrogen recycling played an important role in sustaining phytoplankton growth during the summer. The [N 2 O], measured in water column profiles, was 10.13 ± 1.11 nmol L −1 and did not strongly diverge from atmospheric equilibrium indicating that sampled marine regions were neither a strong source nor sink of N 2 O to the atmosphere. Multivariate analysis of data describing water column biogeochemistry and its links to N-cycling activity failed to explain the observed variance in rates of N-regeneration and N-assimilation, possibly due to the limited number of process rate observations. In the surface waters of five further stations, ocean acidification (OA) bioassay experiments were conducted to investigate the response of NH 4 + oxidising and regenerating organisms to simulated OA conditions, including the implications for [N 2 O]. Multivariate analysis was undertaken which considered the complete bioassay data set of measured variables describing changes in N-regeneration rate, [N 2 O] and the biogeochemical composition of seawater. While anticipating biogeochemical differences between locations, we aimed to test the hypothesis that the underlying mechanism through which pelagic N-regeneration responded to simulated OA conditions was independent of location. Our objective was to develop a ...