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Assimilation and regeneration of inorganic nitrogen in a coastal upwelling system: ammonium and nitrate utilization
Assimilation and regeneration of nitrogen off central Chile (36ºS) are influenced by high productivity and seasonal development of subsurface hypoxia. Production and utilization of ammonia results in intense uptake by phytoplankton, even during winter, and oxidation of NH4+ to NO2- and NO3- by nitrifying archaea and bacteria. NH4+ oxidation was coupled with the oxidation of NO2- to NO3- only in near-bottom suboxic waters, while NO3- regeneration in the oxycline resulted from higher levels of NO2- oxidation, compared to NH4+ oxidation. Fernandez and Farias show that NH4+ uptake in this coastal upwelling systems can be in the same range as NO3- assimilation, while its oxidation via nitrification is affected by oxygen concentrations throughout the water column.
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