Methane ebullition fluxes and temperature sensitivity in a shallow lake

Inland waters are important sources of atmospheric methane (CH4), with a major contribution from the CH4 ebullition pathway. However, there is still a lack of CH4 ebullition flux (eFCH4) and their temperature sensitivity (Q10) in shallow lakes, which might lead to large uncertainties in CH4 emission response from aquatic to climate and environmental change. Herein, the magnitude and regulatory of two CH4 pathways (ebullition and diffusion) were studied in subtropical Lake Chaohu, China, using the real-time portable greenhouse gas (GHG) analyzer-floating chamber method at 18 sites over four seasons. eFCH4 (12.06 ± 4.10 nmol m−2 s−1) was the dominant contributing pathway (73.0 %) to the two CH4 emission pathways in Lake Chaohu. The whole-lake mass balance calculation demonstrated that 56.6 % of the CH4 emitted from the sediment escaped through the ebullition pathway. eFCH4 was significantly higher in the western (WL: 16.54 ± 22.22 nmol m−2 s−1) and eastern lake zones (EL: 11.89 ± 15.43 nmol m−2 s−1) than in the middle lake zone (ML: 8.86 ± 13.78 nmol m−2 s−1; p < 0.05) and were significantly higher in the nearshore lake zone (NL: 15.94 ± 19.58 nmol m−2 s−1) than in the pelagic lake zone (PL: 6.64 ± 12.37 nmol m−2 s−1; p < 0.05). eFCH4 was significantly higher in summer (32.12 ± 13.82 nmol m−2 s−1) than in other seasons (p < 0.05). eFCH4 had a strong temperature dependence. Sediment total organic carbon (STOC) is an important ecosystem level Q10 driver of eFCH4. The meta-analysis also verified that across ecosystems the ecosystem-level Q10 of eFCH4 was significantly positively correlated with STOC and latitude (p < 0.05). This study suggests that eFCH4 will become increasingly crucial in shallow lake ecosystems as climate change and human activities increase. The potential increase in ebullition fluxes in high-latitude lakes is of great importance.