MEPS 451:1-14 (2012)  -  DOI: https://doi.org/10.3354/meps09683

ABSTRACT: The main processes involved in nitrogen cycling (as NO₃⁻ and NH₄⁺ assimilation and their regeneration) were studied using N-tracer experiments in the coastal upwelling system off central Chile (36°S). The study area shows seasonal surface fertilization and the development of subsurface hypoxia in austral spring and summer. The rates of NO₃⁻ uptake during active upwelling were 5 times higher than in non-upwelling seasons. Uptake of NH₄⁺ was almost half that of NO₃⁻ uptake rates during upwelling periods, and similar to NO₃⁻ uptake rates in the absence of upwelling. Nitrification experiments showed higher rates during active, compared to non-active, upwelling seasons. NH₄⁺ oxidation was coupled with NO₂⁻ oxidation in near bottom (suboxic) waters, while in the oxycline (hypoxic water), total fluxes of NO₃⁻ regeneration via nitrification resulted from higher activity of NO₂⁻ oxidation compared to NH₄⁺ oxidation. On the other hand, archaeal NH₄⁺ oxidation had the potential for processing a large fraction of NH₄⁺ and could therefore co-occur with bacterial NO₂⁻ oxidation. NH₄⁺ utilization in this coastal upwelling is thus in the same range as NO₃⁻ assimilation. NH₄⁺ oxidation is affected by oxygen concentration in the water column, leading to occasional decoupling of NH₄⁺ and NO₂⁻ oxidation, particularly at the oxycline. This study gives preliminary evidence of the importance of archaeal–bacterial interactions in the nitrification process and highlights the role of ammonium in fueling annual primary production in coastal upwelling systems.

KEY WORDS: Coastal upwelling · Nitrogen uptake · Ammonium oxidation · Archaea

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Cite this article as: Fernandez C, Farías L (2012) Assimilation and regeneration of inorganic nitrogen in a coastal upwelling system: ammonium and nitrate utilization. Mar Ecol Prog Ser 451:1-14. https://doi.org/10.3354/meps09683 Export citation Share:    Facebook - - linkedIn