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Linking dissolved organic matter sources to greenhouse gas potential in thermokarst lakes of the Qinghai-Tibet Plateau
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DOI：10.1016/j.coldregions.2026.104920.png)
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Abstract
En 中文
Thermokarst lakes (TLs) are major hotspots of carbon emissions in permafrost regions, where the sources and transformation of dissolved organic matter (DOM) strongly regulate greenhouse gas production. On the Qinghai-Tibet Plateau (QTP), however, the coupling between DOM sources and CO2 and CH4 dynamics remains poorly understood. Ultraviolet-visible (UV-Vis) absorption and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy were applied to characterize DOM in TLs and suprapermafrost groundwater (SPGW) across alpine wet meadow, meadow, and steppe ecosystems. The results showed that average dissolved organic carbon (DOC) concentrations were 10.1 f 7.6 mg L-1 in thermokarst lake water (TL water) and 9.1 f 4.7 mg L-1 in SPGW, contributing 19.6% and 7.8% of total carbon (TC), respectively. DOM in TLs exhibited obvious spatial differences in optical properties across alpine ecosystems, with specific ultraviolet absorbance at 254 nm (SUVA254) values ranging from 3.1 to 4.2 L m-1 mg-1 and spectral slope ratios (SR) from 1.4 to 2.2, indicating variations in aromaticity and molecular weight. Fluorescence-PARAFAC analysis showed that the DOM in TLs consisted of both terrestrially derived humic substances (46-52%) and microbially processed components (48-54%), whereas DOM in SPGW was dominated by humic-and fulvic-like material from soils and vegetation. Importantly, DOM composition and optical indices were significantly correlated with dissolved CO2 and CH4 concentrations in TLs, underscoring the regulatory role of DOM quality in greenhouse gas emissions. Elevated dissolved CO2 and CH4 content in SPGW further suggest that lateral inflows are a key pathway fueling TLs carbon emissions. Overall, this study highlights how DOM sources and transformations regulate the greenhouse gas potential of QTP TLs, advancing our understanding of permafrost carbon-climate feedbacks.
Keywords:
Qinghai-Tibet Plateau
Thermokarst lake
Suprapermafrost groundwater
Dissolved organic matter
Greenhouse gas emissions
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