The chemical characterization of the reactive components of dissolved organic matter relies on developing new fractionation techniques for this highly complex mixture of organic compounds. DOM in natural waters contributes to the global carbon cycle through its photochemical degradation and the generation of bioavailable, low molecular weight compounds and carbon dioxide. The concentration and composition of the allochthonous DOM in natural waters depends on the source organic material, precipitation, and hydrological conditions. Rising global temperatures will result in changes in DOM composition and concentration. In this study we fractionate DOM from the Black River, NC using a stepwise gradient of solid-phase extracted DOM to generate three main fractions based on hydrophobicity. Spectroscopic characterization of the fractions included UV-visible spectroscopy, excitation-emission matrix fluorescence spectroscopy and <sup>1</sup>H NMR. A solar simulator was used to determine differences in the extent of photochemical degradation of the three fractions over a 55 hour time period. The more hydrophobic fractions were more photochemically labile and the general trend was a modest increase (approx. 20%) in UV absorbance (A<sub>254nm</sub>) and fluorescence up to two hours followed by a decrease ranging from 28% for the more hydrophilic fraction to 46% for the most hydrophobic fraction. A fraction desorbed from particulates in Black River water (PdOM) was also photo-degraded (37%) over the same time period. A new reversed-phase separation profiled the different elution characteristics of the three SPE fractions (Figure 1).

Photochemical degradation of dissolved organic matter in natural waters: Characterizing the more labile constituents using gradient solid phase extraction

251st National Meeting (2016)

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