Reducing CO2 emissions from rivers around bare land contributes to improving the carbon sink function of the Qinghai–Tibetan Plateau

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River CO2 fluxes (FCO2) play an important role in the carbon cycle of the Qinghai‒Tibet Plateau (QTP). However, the carbon budget of river water is ignored in the assessment of the carbon sources and sinks of ecosystems on the QTP, which makes the assessment of the carbon sinks of ecosystems uncertain on the QTP. Here, we selected rivers around alpine steppe, alpine meadow, forestland and bare land areas on the QTP to determine their FCO2 values and control factors during thaw, rainy and freezing periods. The results revealed that river water around the alpine steppe absorbed CO2 during the thaw and freezing periods, making it a carbon sink. The influencing factors of FCO2 around different ecosystems significantly differed across the different periods. The pCO2 was the most direct factor affecting the FCO2 of river water. During the thaw period, the FCO2 of rivers around the alpine steppe and bare land was affected mainly by dissolved organic carbon (DOC) and precipitation, respectively. The FCO2 of rivers around the alpine meadow and forestland was affected by dissolved inorganic carbon (DIC). During the rainy period, the FCO2 of the rivers around the alpine steppe and bare land was affected mainly by total nitrogen (TN) and salinity, respectively. The FCO2 of rivers around the alpine meadow and forestland was affected by dissolved oxygen (DO) and DOC. During the freezing period, the FCO2 of the rivers around the alpine steppe and bare land was affected mainly by TN and pCO2, respectively. The FCO2 of rivers around the forestland and alpine meadow was affected by precipitation, runoff and DIC. The FCO2 in rivers around vegetated areas were affected by rock weathering, aquatic ecosystem biology and hydrological processes to varying degrees at different times. However, rivers around bare ground were less affected by these processes. The FCO2 values around the alpine steppe, alpine meadow, forestland and bare land were 1.40 g C/m2/d, 1.12 g C/m2/d, 2.29 g C/m2/d and 4.20 g C/m2/d, respectively. The river water around bare land released a large amount of CO2. Therefore, to reduce the CO2 emissions of rivers on the QTP, it is urgent that we restore bare-land vegetation and promote the transfer of bare land to steppe, which is an effective way to increase the carbon sink of the ecosystems on the QTP.