Photochemical transformation of dissolved organic matter (DOM) has been well recognized as an important process impacting carbon cycling and nutrient dynamics across aquatic environments. Photo-degradation of DOM can induce photo-flocculation. In this study, DOM-rich blackwater samples were subjected to photo-irradiation in a solar simulator system in the laboratory, and flocculation was observed within a week. Bulk analysis of carbon, nitrogen, and nutrients were conducted at multiple time points to track their dynamic changes in both dissolved and particulate matter during photo-irradiation. We have applied an array of advanced analytical techniques to examine the molecule evolution of DOM and photo-flocculated particulate organic matter (POM) through ultra-high resolution mass spectrometry, NMR, and x-ray adsorption spectroscopy. Meanwhile, ammonium was released continuously, and appears to become incorporated into the DOM and POM. We observed neoformation of nitrogen-containing molecules that are associated with both aliphatic proteinaceous organic compounds (e.g., amide, peptides) and aromatic compounds. It is suggested that the photo-product ammonium and the intermediate products, e.g., small peptides, may promote the incorporation of nitrogen to DOM. We will propose the underlying pathways for phototransformation and N incorporation, which have important biogeochemical implications to the fate of organic carbon and nitrogen in aquatic environments.

Phototransformation and flocculation of dissolved organic matter to new organic compounds: the biogeochemical implications

2019 Spring National Meeting

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