Abstract
Concentrations of dissolved organic nitrogen and dissolved inorganic nitrogen in the porewater of marine sediment (0-30cm core length) werem easured in various marine environments (Bays, semipelagic sea, pelagic sea). The concentration of total dissolved nitrogen showed regional variations from 40μM in subtropical sediments to 1.3mM, two orders-of-magnitudhe higher, in Tokyo Bay sediments. The ammonium nitrogen concentration also showed regional variations over relatively wider range (three orders-of-magnitude), from 2μM in subarctic pelagic sediments to 1.2mM in Tokyo Bay sedimentsa nd 3-93% of the total dissolved nitrogen. The concentration of dissolved organic nitrogen, however, showed regional variations of relatively narrow range, from 10μM to 180μM and 3-87% of the total dissolved nitrogen. On the other hand, the concentration of nitrate (+nitrite) nitrogen showed regional variations of relatively low values, from 0.3μM in Otsuchi Bay to 49μM in the pelagic sediment and 0.2-70% of the total dissolved nitrogen.
The remarkable regional differences in concentrations and the proportion of respective nitrogen compounds might depend on the outcome in regional differences of diagenesis (ammonification, nitrification and denitrification) in marine sediment. The ammonium nitrogen and dissolved organic nitrogen in the porewater might be an important source for those in overlying seawater in the coastal environment, whereas these nitrogen compounds might not be so important as a source for those in overlying seawater in pelagic environments.
