Methane Emissions From the Qinghai-Tibet Plateau Ponds and Lakes: Roles of Ice Thaw and Vegetation Zone

Abstract

Comprehensive seasonal observation is essential for accurately quantifying methane (CH₄) emissions from ponds and lakes in permafrost regions. Although CH₄ emissions during ice thaw are important and highly variable in high-latitude freshwater ponds and lakes (north of ∼50°N), their contribution is seldom included in estimates of aquatic-atmospheric CH₄ exchange across different alpine ecosystems. Here, we characterized annual CH₄ emissions, including emissions during ice thaw, from ponds and lakes across four alpine vegetation zones in the Qinghai-Tibet Plateau (QTP) permafrost region. We observed significant spatial variability in annual CH₄ emission rates (8.44−421.05 mmol m⁻² yr⁻¹), CH₄ emission rates during ice thaw (0.26−144.39 mmol m⁻² yr⁻¹), and the contribution of CH₄ emissions during ice thaw to annual emissions (3−33%) across different vegetation zones. Dissolved oxygen concentration under ice, along with substrate availability and water salinity, played critical roles in influencing CH₄ flux during ice thaw. We estimated annual CH₄ emissions from ponds and lakes in the QTP permafrost region as 0.04 (0.03−0.05) Tg CH₄ yr⁻¹ (median (first quartile−third quartile)), with approximately 20% occurring during ice thaw. Notably, the average areal CH₄ emission rate from ponds and lakes in the QTP permafrost region amounts to only 8% of that from high-latitude waterbodies, primarily due to the dominance of large saline lakes with lower CH₄ emission rates in the alpine permafrost region. Our findings emphasize the significance of incorporating comprehensive seasonal observation of CH₄ emissions across different vegetation zones in better predicting CH₄ emissions from alpine ponds and lakes.