Rivers play a crucial role in connecting terrestrial and fluvial systems. Over the recent decades, the world’s rivers are exposed to unprecedented climatic and anthropogenic perturbations and are becoming significant sources of the atmospheric greenhouse gas (GHG) emissions. The cold temperate zones across the world, which are increasingly sensitive to temperature variations, experience notable changes in the riverine GHG emissions. However, until recently, there has been very little understanding of the GHG emissions where river system is interacted tundra forests. The GHG emissions emanating from the Changbai Mountain (CBM) area in the temperate China, are predominantly concentrated within the forest soil and tundra ecosystems. We investigated the GHG emissions from the Erdao River system in CBM using in situ gas flux monitoring technique at the water-gas interface at eight sampling sites between July and September (2022). The results indicate that GHG fluxes peaked in August, with CO 2 emissions in the CBM region were lower than in other cold-temperate areas (-1234.19~1073.60 mg·m −2·d −1) due to concentrated precipitation and high altitudinal gradients. CH 4 emissions are concentrated in nature reserves and floodplains, whereas rivers near urban areas at the foothills of CBM exhibit elevated N 2O emissions (2.49~3.31mg·m −2·d −1) because of urbanization. The heterogeneity in GHG emissions across the sites is correlated with water quality parameters, with temperature significantly affecting the N 2O emissions, which are the primary contributor to global warming potential (80.25%) in the river system. Organic matter sources in CBM river system are predominantly terrestrial, with a minor contribution from sea ice reservoirs. The intensified precipitation during the summer season increased the influx of terrestrial organic matter, thereby affecting GHG discharges. This study provides empirical evidence for precise quantification of GHG emissions in the cold temperate zone of China. Identifying emission patterns across various river systems in the CBM region, fills a significant gap in the existing literature. This studyestablishes a scientific framework essential for understanding and projecting carbon fluxes from fluvial systems in the temperate region.

The availability of electron acceptors (EAs) in peatlands determines the potential of methene (CH 4) formation under anaerobic conditions. Previous studies suggested that EAs can suppress CH 4 production based on Gibbs free energy under the Redox Ladder Theory. However, there is a growing body of evidence that challenges this theory, raising the question of how the coupling of soil substrates with EAs influences CH 4 emissions. To answer this key question, peat soils were collected across different climatic zones with different degrees of soil degradation. Anoxic incubation experiments were set up, and continuous addition of SO 4 2-, Fe 3+ and humic acid (HA) at different levels of concentrations followed by characterization of dissolved organic matter (DOM) using fluorescence spectroscopy. Results suggest that low concentrations of SO 4 2- (1000 μmol L -1), Fe 3+ (100 μmol L -1), and HA (30 mgC L -1) promoted CH 4 production in most of the peat soils. With the addition of SO 4 2- and HA, increased CH 4 emissions were contributed to the facilitation of dissolved organic carbon and reduced quinone-like component C1, which increased the substrate availability for methanogenesis. Furthermore, strengthened microbial activity as indicated by fluorescence component C2 led to higher CH 4 production under Fe 3+ treatments. On the other hand, at high concentrations of SO 4 2- (5000 μmol L -1), Fe 3+ (500 μmol L -1) and HA (50 mgC L -1), CH 4 emissions rapidly decreased by 70.65 ± 1.57% to 96.25 ± 0.45% compared to control group without EAs addition, accompanied by increased δ 13C-CH 4 signatures indicating the outweighed CH 4 production under anaerobic oxidation of methane (AOM) when coupling with reduced EAs. The effect of EAs on CH 4 emissions in peat soils could also be related to natural organic substrates. Our results suggest that the CH 4 production in peatlands could be facilitated by regulating organic substrates at low EAs concentrations, but excessive EAs will reduce net CH 4 emissions through AOM.