CH 4 and CO 2 emissions from Alaskan lakes Methane and carbon dioxide emissions from 40 lakes along a north–south latitudinal transect in Alaska CH 4 and CO 2 emissions from Alaskan lakes BGD CH 4 and CO 2 emissions from Alaskan lakes

Abstract

Uncertainties in the magnitude and seasonality of various gas emission modes, partic-ularly among different lake types, limit our ability to estimate methane (CH 4) and carbon dioxide (CO 2) emissions from northern lakes. Here we assessed the relationship be-tween CH 4 and CO 2 emission modes in 40 lakes along a latitudinal transect in Alaska 5 to physicochemical limnology and geographic characteristics, including permafrost soil type surrounding lakes. Emission modes included Direct Ebullition, Diffusion, Storage flux, and a newly identified Ice-Bubble Storage (IBS) flux. We found that all lakes were net sources of atmospheric CH 4 and CO 2 , but the climate warming impact of lake CH 4 emissions was two times higher than that of CO 2 . Ebullition and Diffusion were the 10 dominant modes of CH 4 and CO 2 emissions respectively. IBS, ∼ 10 % of total annual CH 4 emissions, is the release to the atmosphere of seasonally ice-trapped bubbles when lake ice confining bubbles begins to melt in spring. IBS, which has not been explicitly accounted for in regional studies, increased the estimate of springtime emis-sions from our study lakes by 320 %. Geographically, CH 4 emissions from stratified, 15 dystrophic interior Alaska thermokarst (thaw) lakes formed in icy, organic-rich yedoma permafrost soils were 6-fold higher than from non-yedoma lakes throughout the rest of Alaska. Total CH 4 emission was correlated with concentrations of phosphate and total nitrogen in lake water, Secchi depth and lake area, with yedoma lakes having higher nutrient concentrations, shallower Secchi depth, and smaller lake areas. Our findings 20 suggest that permafrost type plays important roles in determining CH 4 emissions from lakes by both supplying organic matter to methanogenesis directly from thawing per-mafrost and by enhancing nutrient availability to primary production, which can also fuel decomposition and methanogenesis.