Program

With growing input of anthropogenic nitrogen to the coastal ocean, the structure of nitrogen species composition has been significantly changed. Thus the primordial nitrogen cycle should be reconstructed in the coastal ocean which significantly perturbed by human activities and the relative importance of nitrogen transformations is not well known. Among these processes, N₂O may be produced as a byproduct or intermediate product, which is a strong greenhouse gas and its yield in associated nitrogen processes in also not clear. In September 2013, we conducted a study in a coastal bay, by adding 15N labelled NH₄⁺, NO₂^- and NO₃^- under dark incubation. NH4+ concentration, NO2-, NO3-, PN and N2O concentrations and nitrogen isotope were measured. Our results showed that ammonium uptake and ammonium oxidation rates were 137.3 nmolL^-1h^-1 and 34.1 nmolL^-1h^-1, respectively. N₂O emission rate was 0.002 nmolL^-1h^-1 and the yield ratio is 0.06‰ during NH₄⁺ consumption. Meanwhile, both NO₂^- and NO₃^- assimilations by phytoplankton were much less than ammonium uptake in dark incubation. Thus, we suggest that NH₄⁺ is the major substrate for primary producer in coasts, leaving NO₂^- and NO₃^- utilized by denitrification and anammox before exporting offshore.