Distinct seasonality of river CO2 partial pressure and efflux in permafrost catchments of the Qinghai-Tibet plateau

Riverine CO₂ evasion plays a pivotal role in carbon cycles but is still uncertain, especially for permafrost rivers. Here we investigate the seasonal CO₂ partial pressure (pCO₂) and CO₂ emission flux (FCO₂) of 8 catchments in Yangtze River source region (YRSR), which have high permafrost coverage and seasonally thawed active layer. The YRSR catchments were supersaturated with CO₂ except some sites exhibited CO₂ undersaturation during initial thaw period. Both pCO₂ and FCO₂ peaked in the thawed period under the influence of active layer thaw and hydrological processes. The lower order streams showed significantly higher pCO₂ and FCO₂ than higher order rivers. The YRSR rivers emitted 2.71 TgC of CO₂ annually, corresponding to 75% of terrestrial C that entered the river networks. High emission/export ratio can be attributed to the large proportion of baseflow and steep topography, while in-steam organic carbon mineralization probably played a negligible role. Annually, half of the horizontal C flux and 70% of the CO₂-C emission were transported during the thaw period. The seasonally thawed active layer over QTP played a more crucial role on riverine carbon export than the Arctic. Warming may increase annual CO₂ emission due to deeper flow path and longer emission window.