377 - Sources and properties of fluorescent dissolved organic matter affecting mercury photoreduction rates

The formation of dissolved gaseous mercury in lake water is mainly attributed to the photochemical reactions mediated by dissolved organic matter (DOM). In this study, we explored how different DOM components influence the Hg(II) photoreduction rate constant (kr) in lake surface water. For this purpose, the kr and the fluorescence properties of DOM were obtained from the three Korean lakes with different trophic states. Three major fluorophores were identified by excitation-emission matrix fluorescence spectroscopy combined with a parallel factor analysis: plant-derived terrigenous humic-like DOM (C1), autochthonous DOM (C2), and soil fulvic-like DOM (C3). The principal component analysis loading matrix substantiated that kr increases when bulk DOM has high flavin-like and soil-derived fulvic-like fractions. The results of the Pearson’s correlation analysis agreed with the outcome of the principal component analysis: kr showed a strong positive correlation with the soil fulvic-like DOM component (r = 0.92) and the redox index (r = 0.92). This was further confirmed by a partial least squares regression model that predicted kr (r = 0.99) using multiple DOM components. Overall results suggest that kr can be modeled using fluorescence intensities of diverse DOM components, which in turn has the potential to be incorporated into Hg biogeochemical models to better predict the variability of Hg redox rates across lake systems.