Characterization of Dissolved Organic Matter of Sediments in Urban Streams Using EEMs–PARAFAC and Absorption Spectroscopy: A Case Study in Wuhan, China

Abstract

Urbanization has notably changed the characteristics and functions of watershed ecosystems worldwide, influencing the characteristics of chromophoric dissolved organic matter (CDOM) and dissolved organic matter (DOM) of sediments in urban streams. In this study, the biogeochemical characteristics of 42 water samples and the optical absorption and excitation–emission matrix spectra (EEMs) of 14 sediment samples collected from 14 urban streams in Wuhan were systematically examined. In addition, five water samples and one sediment sample were collected in Mulan Lake as a reference for non-urban areas. The a254 values of sediments in urban streams ranged widely (25.7–197.6 m−1), and the mean (116.32 ± 60.5 m−1) was significantly higher than the reference (51.52 m−1), indicating clear individual differences and a higher concentration of CDOM. Two humus-like components and one tryptophan-like component were effectively identified by parallel factor analysis (PARAFAC). The fluorescence index (FI)/biological index (BIX) of DOM of sediments in urban streams was mostly within 1.4–1.7/0.8–1.0, indicating a compound of both allochthonous and autochthonous sources. Compared with the reference, lower FI and BIX and higher humification index (HIX) revealed a higher allochthonous input and humification degree of DOM of sediments in urban streams. Spearman’s correlation analysis and redundancy analysis demonstrated that heavy metals and other water quality parameters had a considerable impact on CDOM concentrations and DOM components. This study could support the use of DOM as an effective tool to monitor the water environment and provide insights into future water pollution management strategies.