[Seasonal Variation in DOM Spectral Characteristics and Sources in Different Types of Lakes]

To study the spatio-temporal distribution characteristics and sources of dissolved organic matter （DOM） in different types of lakes, water samples were collected from the Wuliangsuhai Lake, Daihai Lake, and Nanhai Lake in Inner Mongolia in April and July 2023. The spectral characteristics and composition of DOM in the three lakes were analyzed using UV-vis spectroscopy, 3D fluorescence spectroscopy, and parallel factor analysis. Additionally, the response of DOM to water quality factors was explored. The results showed that the Daihai Lake had the highest DOM content among the three lakes. Compared to that during spring, the average concentration of dissolved organic carbon （DOC） during summer in the Wuliangsuhai Lake, Daihai Lake, and Nanhai Lake increased by 69.57%, 14.68%, and 85.88%, respectively. Additionally, the highest concentration of DOC in the Wuliangsuhai Lake increased from 15.32 mg·L^-1 in the northern region during spring to 25.73 mg·L^-1 in the central region during summer. The highest DOM concentration in the Daihai Lake was in the central region during spring with 56.12 mg·L^-1 DOC but in the western region during summer with 64.12 mg·L^-1 DOC. In the Nanhai Lake, the DOM in the inlet area was higher during spring, whereas it doubled in the outlet area during summer. Moreover, DOM in the Wuliangsuhai Lake showed the highest aromaticity and hydrophobicity, but lowest values were found in the Nanhai Lake. In addition, the humus of the three lakes mainly comprised fulvic acid. As for source, DOM was mainly endogenous during spring and exogenous during summer in the Wuliangsuhai Lake, while it was endogenous in the Daihai Lake and Nanhai Lake. Furthermore, the exogenous characteristics of DOM in the Daihai Lake were enhanced, while the endogenous characteristics of DOM in the Nanhai Lake were enhanced from spring to summer. Significant correlations were observed between DOM and TN, TP, and DO in the three lakes. The increase in TN, TP, and Chl-a in the Wuliangsuhai Lake and TN, TP, and COD in the Daihai Lake weakened the endogenous characteristics of DOM, whereas the increase in TN, Chl-a, DO, and COD in the Nanhai Lake enhanced the endogenous characteristics of DOM. The seasonal variation of spatial distribution and sources of DOM in different types of lakes were markedly influenced by hydrological conditions, external water input, biological activities, and human impacts.