Characteristics of spatio-temporal distribution and source differences of DOM in urban watersheds of Xi'an during the dry, normal and wet periods

Abstract

The spatio-temporal distribution characteristics of the fluorescence components, molecular properties, source of DOM in water bodies of Xi'an during dry, normal and wet period were investigated by using three-dimensional fluorescence spectroscopy combined with parallel factor analysis, and UV spectroscopy. The results showed that the order of the mean DOC values of water bodies was: normal period > dry period > wet period, and the mean values of UV254 and α355 of DOM were the highest in wet period, with the mean values of 0.137 ± 0.043 cm− 1 and 7.69 ± 2.62 m− 1, respectively, indicating the content of aromatic compounds and the relative content of CDOM were higher. The DOM in wet and dry periods was humus-like dominant, while the proportion of humus-like and protein-like substances in normal period was close. The sources of DOM were mainly dominated by endogenous sources in dry period, and the proportion of exogenous sources in the DOM increased in normal and wet period. COD, IMn, DOC, UV254, α355, fluorescence intensity of peak D and fluorescence intensity of peak E exhibited significantly positive correlations with each other(r = 0.594–0.975, P < 0.01). The humification degree of the Zaohe River DOM increased along the water flow direction, while the humification degree of the Juehe River DOM decreased and its autogenous characteristics enhanced. The Heihe River was the least biologically active during dry and normal period, and more humified than other water bodies in normal and wet period. The composition, molecular properties and sources of DOM show spatio-temporal heterogeneity. In each period, the DOM contained at least two types of humus-like substances with fulvic acid being dominated. UV254, α355, fluorescence intensity of peak D, fluorescence intensity of peak E could indirectly represent the relative content of DOM, and COD, IMn in the water bodies, which could provide basis for the protection and restoration of the water ecology of urban watersheds.