AME 18:285-292 (1999)  -  doi:10.3354/ame018285

Photochemical formation of biologically available nitrogen from dissolved humic substances in coastal marine systems

Karen L. Bushaw-Newton*, Mary Ann Moran**

Department of Marine Sciences and Institute of Ecology, University of Georgia, Athens, Georgia 30602-3636, USA
*Present address: National Oceanic and Atmospheric Administration, NOS-COP, 1315 East-West Highway, SSMC3 (Room 9700), Silver Spring, Maryland 20910, USA
**Addressee for correspondence. E-mail:

ABSTRACT: The photochemical conversion of the nitrogen fraction of dissolved humic substances into more biologically available compounds was studied in 2 estuarine sites in the southeastern U.S. Marine humic substances were isolated using an XAD-8 resin and used in bacterial bioassays and chemical studies. The bioassays demonstrated that humic substances irradiated with natural sunlight supported enhanced bacterial growth, measured as cell accumulation and protein production, due to increased availability of both the carbon and nitrogen components. Chemical analyses demonstrated the photoproduction of ammonium and dissolved primary amines from the coastal humic substances. The total biologically available nitrogen (ammonium, dissolved primary amines, and other unidentified compounds) formed during a day-long irradiation at natural solar radiation levels accounted for about 6% of the original nitrogen associated with the humic substances. Photochemical modification of marine humic substances may provide a source of labile nitrogen to estuarine and coastal ecosystems that has not previously been considered.


KEY WORDS: Dissolved organic matter · Dissolved organic nitrogen · Humic substances · Photodegradation · Ammonium · Dissolved primary amines · Bacterial secondary production


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