Spatiotemporal Distribution Characteristics of Dissolved Organic Matter Spectrum in the Agricultural Watershed of Dianbu River

The agricultural watershed of Dianbu River is the largest tributary of Nanfeihe River, so it is important to explore the temporal and spatial evolution mechanism of dissolved organic matter (DOM) in this watershed to understand its aquatic ecosystem. In this study, we comprehensively utilized the 3-D fluorescence spectrum and UV-visible spectrum of water bodies to track the DOM characteristics of this watershed. PARAFAC method was adopted to extract DOM components from the measured 3-D fluorescence spectral matrix. Moreover, we analyzed the DOM fluorescence components and the proportion of water bodies in a specific period. DOM's temporal and spatial characteristics in Dianbu River agricultural watershed were analyzed by combining the fluorescence parameters (FI, autobiogenic index BIX and humification index HIX) and UV-visible absorption characteristic parameters (a(254), E-2/E-3). The results show that the watershed water DOM in the specific period (September 2020 April 2021) contains two effective components of fluorescence, one kind of humus (fulcrum acid-like component) and one kind of protein ( Low excitation tryptophan-like component), the proportion of two components were 53. 9% and 46. 1% respectively; The fluorescence parameters of the three water bodies (FI, BIX and HIX) showed significant seasonal variations in different seasons (autumn in September, winter in January and spring in April), indicating that DOM was generally influenced by terrigenous and endogenous substances, but had strong humification and weak authigenic characteristics. The characteristic absorption parameters of the UV-visible spectrum (a(254) E-2/E-3) indicated that the relative concentration and molecular weight of DOM in winter water in January were lower than those in the other two seasons (autumn in September and spring in April), while the molecular weight and relative concentration of DOM at each sampling point showed no obvious regional variation trend from upstream to downstream in the watershed. In this study, the three-dimensional fluorescence spectral characteristics and UV-visible spectral absorption characteristics of water bodies in the watershed were combined to trace the component sources of DOM in the Dianbu River in a specific period and its spatiotemporal distribution characteristics were analyzed to provide a reliable theoretical basis for the comprehensive management of the ecological environment in the watershed.