Author(s): Chen Li; Wei Wu; Hang Chen; Lei Ren; Xiao Kang
Linked Author(s): Lei Ren, Wei Wu
Keywords: CO2 and CH4 emissions freeze‒thaw seasonal variations environmental controls inland waters upper Yellow River Tibetan Plateau
Abstract: Inland waters are significant sources of atmospheric carbon greenhouse gas (carbon dioxide [CO2] and methane [CH4]) emissions. The dynamic characteristics, regulatory processes, and overall contributions of carbon emissions from various regions and types of inland waters exhibit considerable variability globally, particularly in areas that are characterized by notable environmental specificity and sensitivity. The Tibetan Plateau exemplifies a region that is highly sensitive to global climate change and possesses a fragile ecological environment. This study investigated the seasonal emission patterns of CO2 and CH4 from water bodies during the soil freeze‒thaw stage (i. e., freezing and thawing periods), along with the associated environmental controls, in the Longyangxia to Liujiaxia section of the upper Yellow River, a region of significant concern on the Tibetan Plateau. The results indicated that the seasonal emissions of CO2 and CH4 from Longyangxia to Liujiaxia were significantly greater during the thawing period than during the freezing period, with values of 239.32±94.43 and 201.12±366.57 mmol m-2 d-1 during the thawing period and 134.69±82.76 and 46.77±33.56 mmol m-2 d-1 during the freezing period, respectively. This finding suggested that the thawing period represented a critical window for CO2 and CH4 emissions. The seasonal emissions of these gases from inland waters during the freeze‒thaw stage was driven by two distinct metabolic behaviours: photodegradation of organic carbon predominated during the freezing period, whereas anaerobic respiration by microorganisms was the primary process during the thawing period, supplemented by photodegradation. Additionally, the seasonal emissions of CO2 and CH4 from water bodies during the freeze‒thaw stage are controlled by multiple synergistic environmental factors, including the physicochemical properties and productivity of the water bodies, as well as the natural geographic conditions. CO2 emissions are driven primarily by natural environmental pressures, particularly the unique climate and geography of the plateau region. Precipitation and altitude were the main factors influencing the carbon input from terrestrial sources, whereas dissolved oxygen and chlorophyll-a predominantly governed the metabolism of carbon from endogenous sources. Notably, the contribution of land sources to carbon inputs was significantly greater than that of endogenous sources. CH4 emissions are influenced primarily by anthropogenic environmental pressures, including reservoir siltation and the confluence of tributaries characterized by high pollutant loads. Ammonia nitrogen serves as a critical limiting factor for CH4 emissions, which, along with dissolved oxygen, pH, and oxidation‒reduction potential, collectively affect CH4 releases. These findings enhance the understanding of the balance of greenhouse gas carbon emissions in rivers on the Tibetan Plateau and provide a scientific basis and theoretical support for greenhouse gas emission reduction and protection of the fragile ecological environment in this region.
Year: 2025