Spectroscopic properties of dissolved organic matter during the wet season in the Huma River Basin, China

Abstract Dissolved organic matter (DOM) is the largest organic matter pool in natural waters, which is critical for ecological and societal values. The Huma River Basin (HRB) in China during the wet season presented a high background value, owning to the unusually high COD Mn concentrations. To explain the phenomenon, the spectroscopic properties of DOM were studied using spectroscopic techniques combined with statistical analysis. The variations of several UV-visible parameters showed that DOM predominantly consisted of aromatic and high-molecular-weight natural organic matter. Fluorescence excitation-emission matrixes (EEMs) spectroscopy-parallel factor analysis (PARAFAC) recognized four characteristic components representing humic-like substances (C1, C2 and C3) and protein-like substances (C4). Fluorescence parameters showed that the allochthonous terrestrially-derived DOM had important humic character. Fourier transform infrared (FT-IR) spectra characterized the structure of DOM, containing aromatic, aliphatic, carbohydrate and protein compounds. Principal component analysis (PCA) revealed that humic-like components explained approximately 93.8% of the total variance. Correlation coefficient matrix analysis indicated that DOC and COD Mn were mainly derived from humic-like substances. The results demonstrated that the background value in the HRB during the wet season was mainly attributed to terrestrial humic-like substances. Such knowledge could assist in monitoring and managing the river with a high background value.