Nitrogen fixation in the western English Channel (NE Atlantic Ocean)

In temperate Atlantic waters (18.8 to 20.1°C), biological nitrogen fixation has beendemonstrated by 2 independent measurements: 15N-N2 incorporation and nifH identification in theDNA and expressed messenger RNA (mRNA). At 2 stations in the western English Channel, bulkwaters were incubated with 15N-N2. At the high levels of particulate nitrogen (?11.5 ?mol N l–1),absolute fixation rates of 18.9 ± 0.01 and 20.0 nmol N l–1d–1 were determined. While a caveat mustaccompany the magnitude of the rates presented due to the limited number of data, the presence andactivity of diazotrophic organisms in these waters is of ecological significance and may affect currentattitudes to nitrogen and carbon budgets. In particular, our estimate of the rate of N fixation(0.35 mmol N m–2 d–1) is comparable to that of denitrification rates in UK shelf seas. Molecular analysisidentified a diversity of expressed nifH genes, and 21 different prokaryotic nifH transcripts wereidentified