Spatial variations of DOM in a diverse range of lakes across various frozen ground zones in China: Insights into molecular composition

• Published in: Water research (Oxford) 2024-03, Vol.252, p.121204-121204, Article 121204
• Main Authors: Wen, Zhidan, Han, Jiarui, Shang, Yingxin, Tao, Hui, Fang, Chong, Lyu, Lili, Li, Sijia, Hou, Junbin, Liu, Ge, Song, Kaishan
• Format: Article
• Language: English
• Subjects: Carbon; carbon cycle; China; Chinese lakes; climate; cold; dissolved organic carbon; Dissolved Organic Matter; Frozen ground; FT-ICR MS; lakes; Lakes - chemistry; Mass Spectrometry; mineralization; Molecular composition; molecular weight; Permafrost; polyphenols; temperature; water
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2024.121204

•Lakes in cold regions retained more organic carbon than in warmer regions.•In-lake DOM in permafrost zone had lower molecular weight and higher lability.•Lakes in the permafrost zone serve as significant hubs for carbon processing.•CHO% exhibited a gradual decline trend along the warming ground.•CHON% exhibited an increasing trend along the warming ground. Dissolved organic matter (DOM) plays a significant role in aquatic biogeochemical processes and the carbon cycle. As global climate warming continues, it is anticipated that the composition of DOM in lakes will be altered. This could have significant ecological and environmental implications, particularly in frozen ground zones. However, there is limited knowledge regarding the spatial variations and molecular composition of DOM in lakes within various frozen ground zones. In this study, we examined the spatial variations of in-lake DOM both quantitatively, focusing on dissolved organic carbon (DOC), and qualitatively, by evaluating optical properties and conducting molecular characterization using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Lakes in cold regions retained more organic carbon compared to those in warmer regions, the comparison of the mean value of DOC concentration of all sampling sites in the same frozen ground zone showed that the highest mean lake DOC concentration found in the permafrost zone at 21.4 ± 19.3 mg/L. We observed decreasing trends in E2:E3 and MLBL, along with increasing trends in SUVA254 and AImod, along the gradually warming ground. These trends suggest lower molecular weight, reduced aromaticity, and increased molecular lability of in-lake DOM in the permafrost zone compared to other frozen ground zones. Further FT-ICR MS characterization revealed significant molecular-level heterogeneity of DOM, with the lowest abundance of assigned DOM molecular formulas found in lakes within permafrost zones. In all studied zones, the predominant molecular formulas in-lake DOM were compounds consisted by CHO elements, accounting for 40.1 % to 63.1 % of the total. Interestingly, the percentage of CHO exhibited a gradual decline along the warming ground, while there was an increasing trend in nitrogen-containing compounds (CHON%). Meanwhile, a substantial number of polyphenols were identified, likely due to the higher rates of DOM mineralization and the transport of terrestrial DOM derived from vascular plants under the elevated temperature and precipitati