Nonlinear CO2 degassing dynamics in the Lijiang River Basin of the World Heritage Site

As a core component of the South China Karst World Heritage site, carbon dynamics in the Lijiang River Basin are crucial for ecosystem conservation. This study quantified spatiotemporal variations in CO2 degassing fluxes (FCO2) across Strahler order rivers in June and December 2019. FCO2 exhibited a nonlinear relationship with river order: increasing with order in June but decreasing in December. This shift is likely influenced by respiration and organic carbon degradation (June), as well as photosynthesis and carbonate weathering (December), respectively. Gas transfer velocity and terrestrial carbon input caused FCO2 trends to deviate from expectations at specific orders. In addition, lower-order streams (orders 1–3), covering 34% of the basin area, contributed 38% of total emissions, challenging the hypothesis of disproportionately high emissions from small streams. Linking karst heritage protection to riverine carbon cycling, this study aids carbon emission control, water conservation, and ecosystem stability in the World Heritage site.