Second derivative UV–visible spectroscopy characterizing structural components of dissolved and particulate organic matter in an urbanized river.

Background: Spatio-temporal variations of structural components of the POM–DOM fractions exhibit in urban rivers, which is valuable information to reveal dynamic migration and transformation within and between the organic matter pools, also provide important support for river water quality improvement and management measures. Second derivative UV–visible spectroscopy (SDUVS) was applied to simultaneously characterize structural components and spatial variations of dissolved (DOM: Diameter < 0.2 μm) and particulate (POM1: 0.2 < diameter < 0.7 μm; POM2: diameter > 0.7 μm) organic matters in an urbanized river of northeast China. Results: Thirty-six water samples were collected from mainstream and tributaries along a human impact gradient, i.e., rural, town and urban regions. The DOM was a representative fraction for the natural organic matter pool, which was mostly derived from allochthonous and terrestrial sources. Four components C1 to C4 were identified from the POM–DOM fractions by the SDUVS. The C1 associated with phenolic groups and the C2 related to carboxylic groups were dominant for the organic matter pool. The C3 was composed of the primary humificated materials, and the %C3 was kept relatively consistent in the organic matter pool. The C4 presented deeply humificated organic matter with the increase of aromatic and alkyl structures. The average %C4 of the POM pool was higher than that of the DOM pool, indicating that the humification degree of the POM fractions was higher than that of the DOM fraction. Conclusions: Moreover, the tributaries had a higher average %C4 within the DOM than the mainstream, and trends of the POM pool were similar to the DOM pool. The trophic level of the river water decreased in the order of urban region > town region > rural region, while the molecular sizes of the POM–DOM decreased in the order of rural region > town region > urban region. [ABSTRACT FROM AUTHOR]