Methane and carbon dioxide emissions from 40 lakes along a north–south latitudinal transect in Alaska

Abstract

Abstract. Uncertainties in the magnitude and seasonality of various gas emission modes, particularly among different lake types, limit our ability to estimate methane (CH4) and carbon dioxide (CO2) emissions from northern lakes. Here we assessed the relationship between CH4 and CO2 emission modes in 40 lakes along a latitudinal transect in Alaska 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 CH4 and CO2, but the climate warming impact of lake CH4 emissions was two times higher than that of CO2. Ebullition and Diffusion were the dominant modes of CH4 and CO2 emissions respectively. IBS, ~ 10% of total annual CH4 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 emissions from our study lakes by 320%. Geographically, CH4 emissions from stratified, 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 CH4 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 suggest that permafrost type plays important roles in determining CH4 emissions from lakes by both supplying organic matter to methanogenesis directly from thawing permafrost and by enhancing nutrient availability to primary production, which can also fuel decomposition and methanogenesis.

Clumped Isotopes Link Older Carbon Substrates With Slower Rates of Methanogenesis in Northern Lakes

“…Further study will be needed to assess whether the patterns observed here for ebullition CH 4 also apply to diffusive CH 4 fluxes. However, for the studied lakes, ebullition fluxes are estimated to be the dominant source of CH 4 emissions in the ice-free season (Jansen et al, 2019;Sepulveda-Jauregui et al, 2015).…”

Inland waters and their role in the carbon cycle of Alaska

“…, Sepulveda‐Jauregui et al. ). Erosion along thermokarst lake margins delivers this labile organic matter into anerobic lake bottoms, which promotes high rates of methane production and emission (Walter et al.…”

“…, Sepulveda‐Jauregui et al. ). Previous studies also highlight the importance of regional differences in hydrology and C chemistry across high latitude systems (McClelland et al.…”

Modeling the impediment of methane ebullition bubbles by seasonal lake ice

“…To increase the sample size, we also compared modeled concentrations to measurements of 30 encapsulated bubbles from four other thermokarst lakes in interior Alaska, the northern Seward Peninsula in Alaska, and northern Siberia (Walter et al, 2008;Sepulveda-Jauregui et al, 2014b). It was often impossible to classify ebullition sites beneath white ice during the spring ice-melt period as A, B, or C, so measurements from all ebullition classes were pooled and adjusted to account for observed differences in fresh bubble CH 4 concentrations among lakes (SepulvedaJauregui et al, 2014b).…”