Carbon emission from seasonal frozen ground small ponds on the eastern Tibetan Plateau

Greenhouse gas (GHG) emissions from small ponds are important to the global carbon balance in aquatic ecosystems, but there are large uncertainties due to the scarcity of observational data, particularly in the seasonal frozen ground of the Tibetan Plateau (TP) where small ponds are still not considered. To assess the magnitude of methane (CH 4 ) and carbon dioxide (CO 2 ) fluxes, seasonal variations, and their influences in small ponds in seasonal frozen ground on the TP, surface water CH 4 and CO 2 concentrations, fluxes, and their carbon isotopes were measured utilizing headspace and floating box methods in different months. The results showed that the CH 4 and CO 2 fluxes of seasonal frozen ground small ponds on the TP have obvious seasonal variations, and the average CH 4 diffusive fluxes in April to September obtained based on the headspace method was 3.92±1.85 mmol/(m 2 ·d), and the high concentration of CH 4 and CO 2 accumulated in the winter resulted in high CH 4 and CO 2 fluxes in April and June. The total CH 4 and CO 2 fluxes in June to September obtained based on the floating box method were 2.73±2.39 and −9.29±28.38 mmol/(m 2 ·d), respectively, with the bubble flux contributing 60% of the total CH 4 flux and being the main pathway for methane emissions. Water chemistry parameters (pH, conductivity, dissolved oxygen) and nutrients were the main factors affecting CH 4 and CO 2 fluxes. Despite some variation in the isotopic compositions of δ 13 C–CH 4 and δ 13 C–CO 2 in the studied lakes, Miller-Tans isotope modeling showed a similar pathway of methane production from acetate fermentation in all the studied lakes. As the warming and humidification of the TP intensifies and the permafrost shifts to a seasonal frozen ground, associated with the increasing number and size of small lakes, GHG emissions from similar emerging water bodies need to be incorporated into the regional GHG balance.