Fernandez C, Farías L

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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