Terrestrial humic substances in Daliao River and its estuary: optical signatures and photoreactivity to UVA light

Abstract

Fluorescent dissolved organic matter (FDOM) components were identified by Parallel Factor Analysis (PARAFAC) in surface water of Daliao River and its estuary with a focus on terrestrial humic substance-(HS)-like FDOM identified under two contrasting hydrological conditions. The hydrological conditions did not have noticeable effect on the spectral features of the terrestrial HS-like FDOM, but did affect the components' intensities and photoreactivity: (1) the intensities of terrestrial HS-like components were higher in the normal flow period than in the high flow period, and (2) a spectrally similar terrestrial HS-like FDOM identified under the two contrasting hydrological conditions showed distinct photoreactivity to the same dose of UVA illumination. The findings indicated that terrestrial HS was generated at lower intensities at the terrestrial sources during the high flow period than during the normal flow period and that the transport of terrestrial HS material through the river-estuary system was affected dominantly by seawater dilution along the salinity gradient while fine-tuned by solar UVA illumination. This study exemplifies the effect of hydrological conditions on optical signatures of terrestrial HS-like FDOM and their photoreactivity towards UVA illumination, improving our understanding of the dynamics of terrestrial HS material in river-estuary systems in the framework of the currently proposed new conceptual model for terrestrial organic matter.

Impact of Hill Fires on Dissolved Organic Matter in Watersheds of Karst Areas Based on Three-Dimensional Fluorescence-Parallel Factor Analysis

“…Tetsuro Kikuchi et al [11] examined the relationship between DOM and trace metals in both natural and sewage water, revealing that dissolved copper and iron concentrations were influenced by DOM concentration and the presence of aromatic DOM. Chen et al [12] investigated the composition of dissolved organic matter in surface waters across various river reaches, elucidating the influence of UV light and hydrological conditions on terrestrial humus content. Moreover, they revealed that DOM exhibits distinct photoresponsive characteristics.…”