| Summary: | Dissolved organic matter (DOM) degradation in freshwaters plays an important role in the global carbon cycle, yet there is limited understanding of how the origin and composi- tion of DOM regulate the production of riverine greenhouse gases. We investigated the molecular composition of DOM using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and measured the potential carbon dioxide (CO2) production in pristine subarctic rivers of Finnish Lapland. During 21-day incubations, dissolved organic carbon (DOC) was effectively mineralized into CO2 in the clearwater river associated with mineral soils. The high degradability of mineral soil-derived DOM was supported by a high presence of aliphatic and peptide-like compounds. Significantly lower CO2 produc- tion per DOC was observed in the brown-water river, likely due to a large number of less biodegradable, vascular plant-derived compounds from surrounding peatlands. These find- ings highlight the significance of biolabile molecular compounds in the DOM degradation dynamics of subarctic catchments. published version peerReviewed
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