Photochemical Mineralisation of Dissolved Organic Nitrogen

Kitidis, V; Uher, G

Photochemical Mineralisation of Dissolved Organic Nitrogen

Lookup NU author(s): Dr Vassilis Kitidis, Dr Guenther Uher

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Abstract

Over the last three decades, aquatic photochemical reactions have been shown to be involved in the cycling of climatically active trace gases, metals and nutrients. More recently, these reactions have been shown to release a number of bioavailable nitrogen (N) species, including ammonium, nitrite and low molecular weight dissolved organic substances such as urea, amines and amino acids. In most of the surface ocean, the photic zone is either permanently or seasonally depleted of nutrients and in particular N, which are limiting primary production. Under such conditions, the photochemical mineralisation of dissolved organic nitrogen (DON) may be a significant source of limiting N to primary producers. Extrapolations of local rates of photochemical N release in a diverse range of marine settings suggest that this process may account for up to 50 % of phytoplankton N requirements. However, assessments of the importance of photochemical N release on regional to global scales are hindered by insufficient information on its wavelength dependence and by the lack of robust concepts for the extrapolation of photochemical rates. In this chapter, we synthesise the presently available information on photochemical N release, its environmental controls and wavelength dependence, identify gaps in our understanding of the processes involved and discuss the ecological significance of photochemical DON mineralisation.