Spatiotemporal variations of spectral characteristics of dissolved organic matter in river flowing into a key drinking water source in China

The characteristics of dissolved organic matter (DOM) in inflowing river, flowing into drinking water, have profound influences on the quality and safety of water. Here, ultraviolet-visible (UV-vis) spectroscopy and three-dimensional fluorescence (EEM) spectroscopy were combined to investigate the spatiotemporal variations of DOM in Nanfei River flowing into Chaohu Lake in China. 24 water samples and 24 surface sediments samples (including dry-to-wet transition season and wet season in 2018) were collected from different types of outlets. Parallel factor analysis (PARAFAC) model and correlation analysis were conducted to identify the primary sources of DOM. Two humic-like components (C1 235-250 nm/385-430 nm and C3 255-270 nm/455-510 nm) and one tryptophan-like component (C2 270-290 nm/320-350 nm) were effectively identified by PARAFAC model. The results showed DOM concentration presented significant spatiotemporal variations. The concentration was much lower in water than in surface sediments in dry-to-wet transition season, but higher in the wet season. Fluorescence index (FI), biological index (BIX) and humification index (HIX) were used to judge characteristic of DOM origination. These indexes indicated that, DOM in Nanfei River had both the characteristics of humus and autogenous, but neogene autogenic feature was stronger, which was largely due to mixture of water, resuspension and desorption of DOM in sediments and photochemical degradation. In addition, the characteristic parameter of molecular mass of DOM (the values of M) had an obvious linear relationship with the fluorescence intensity ratio of fulvic acid-like to humic acid-like (C1/C3), indicating that macromolecular substances could be removed by adding or improving membrane treatment. These provided technical support for improving quality and comprehensive treatment of drinking water sources.