Abstract
This study investigates the different characteristics of dissolved organic matter (DOM) in the Huai River in China (Bengbu section) during wet and dry seasons, using a combination of three-dimensional fluorescence spectroscopy (EEMs) with parallel factor analysis (PARAFAC) and self-organizing map (SOM). Results indicate that the degree levels of humification and the relative molecular weight of DOM in the Huai River are significantly higher during the wet season compared to the dry season (P<0.01). The PARAFAC model resolves three chemical components for both wet and dry seasons: C1 (UVC-like fulvic acid), C2 (humic acid-like), and C3 (tyrosine-like). Humic substances are the main fluorescent components of the Huai River water. During the dry season, the lower rate of water flow leads to an increase in protein-like components due to the slowing of biodegradation rates. The SOM model shows that representative neurons 1 (wet season) and 12 (dry season) are UV-like humic substances, influenced by exogenous inputs and agricultural activities. PCA results show the effects of seasonal variations on dissolved oxygen (DO) and the size of DOM molecules. Organic acids and alkaline functional groups in humic substances buffer the pH value of the water, slowing down its variation. Overall, these results demonstrate dynamic changes of DOM in the Huai River during wet and dry seasons, with terrestrial inputs increasing the level of humification, while also promoting the influence of autochthonous sources in the water.