Fluorescence characteristics and sources of dissolved organic matter in Hulun Lake

Hulun Lake is an important component part of the northern ecological security barrier in China. To study the components and sources of organic matter in Hulun Lake, the three-dimensional excitation-emission matrix spectra (EEMs) and parallel factor (PARAFAC) analysis techniques were used to analyze the fluorescence characteristics of dissolved organic matter (DOM) and its sources. The results showed that three fluorescent components were obtained in DOM using EEM-PARAFAC, namely tryptophan-like substances (C1), humic-like substances (C2) and fulvic-like substances (C3). The total proportion of C2 and C3 fluorescence intensity accounted for about 70%, showing that the humic-like substances were the main part of DOM in the water of Hulun Lake during the normal, wet and dry seasons. The fluorescence intensity of C2 and C3 in the inlet of the ecological supplement channel was higher than that in other regions in different seasons. The average value of the fluorescence index, the biological source index and the humification index of DOM in Hulun Lake were 1.50-1.54, 0.85-1.00 and 4.12-4.68, respectively, during the normal, wet and dry seasons, indicating that DOM of Hulun Lake came from land sources and autogenous sources with autogenous source characteristics. According to the monitoring data, the water quality of Hulun Lake exceeded Class Ⅴ of Environmental Quality Standards of Surface Water (GB 3838-2002) during the normal, wet and dry seasons in 2021. The average concentration of BOD₅ in the normal and wet seasons was higher than that in the dry season in 2021. At the same time, the average concentration of the total organic matter in the normal season was higher than that in the wet and dry seasons. The results of the redundancy analysis showed that C2 was significantly and positively correlated with C3, indicating that the production and source of C2 were consistent with C3 in DOM.