Abstract
This study investigated the effects of iron on natural organic matter (NOM) absorbance, fluorescence, and molecular weight. Addition of iron(III) to 5 and 10 mg C/L XAD-8 isolated NOM samples at pH 5.5 caused absorbance of visible light to increase, fluorescence intensity of peaks at excitation/emission wavelengths 230/435 nm and 320/450 nm to decrease, and a small shift from intermediate to higher molecular weight components. Iron(II) had little or no effect on XAD-8 isolate properties. Addition of iron(III) to XAD-4 isolated NOM solutions also caused absorbance of visible light to increase. Iron(III) addition to XAD-4 isolate solutions caused a greater decrease in fluorescence intensity than was observed for the XAD-8 isolate, but little or no change in the molecular weight distribution. Overall, our results suggest that the effects of iron on NOM molecular weight, absorbance, and fluorescence properties depend upon the redox state of iron and the composition of the NOM. These results also suggest that the potential effects of iron should be considered when using fluorescence to infer NOM provenance or structure.
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