Methane and carbon dioxide emissions from thermokarst lakes on mineral soils

Alex Matveev,Isabelle Laurion,Warwick F Vincent

doi:10.1139/as-2017-0047

Abstract

Thermokarst lakes are known to emit methane (CH4) and carbon dioxide (CO2), but little attention has been given to those formed from the thawing and collapse of lithalsas, ice-rich mineral soil mounds that occur in permafrost landscapes. The present study was undertaken to assess greenhouse gas stocks and fluxes in eight lithalsa lakes across a 200 km gradient of permafrost degradation in subarctic Québec. The northernmost lakes varied in their surface-water CO2 content from below to above saturation, but the southern lakes in this gradient had much higher surface concentrations that were well above air-equilibrium. Surface-water CH4 concentrations were at least an order of magnitude above air-equilibrium values at all sites, and the diffusive fluxes of both gases increased from north to south. Methane oxidation in the surface waters from a northern lake was only 10% of the emission rate, but at the southern end it was around 60% of the efflux to the atmosphere, indicating that methanotrophy can play a substantive role in reducing net emissions. Overall, our observations show that lithalsa lakes can begin emitting CH4 and CO2 soon after they form, with effluxes of both gases that persist and increase as the permafrost continues to warm and erode.

Highlights

Lakes and ponds in permafrost landscapes are known to be emission sources of greenhouse gases (GHG) to the atmosphere (Tan and Zhuang 2015; Holgerson and Raymond2016), with potentially large feedback effects on global climate (Grosse et al 2016; Kokelj and Jorgenson 2013)
Zimov et al (1997) drew attention to the strong output of CH4 from lakes in Siberia formed by thawing and collapse of ice-rich permafrost, and concluded that the CH4 was largely derived from ancient organic carbon that had been previously stored in the frozen soils
We evaluated this hypothesis by making measurements at a series of lithalsa lakes across a gradient of permafrost conditions in subarctic Québec, including at the southern limit of current permafrost extent where thermokarst lakes have formed and persisted for at least many decades

Summary

Introduction

Lakes and ponds in permafrost landscapes are known to be emission sources of greenhouse gases (GHG) to the atmosphere (Tan and Zhuang 2015; Holgerson and Raymond2016), with potentially large feedback effects on global climate (Grosse et al 2016; Kokelj and Jorgenson 2013). A constraint in defining the error in such estimates, is the poorly known extent of local and regional variability in GHG fluxes, with large variations among thermokarst lakes (Laurion et al 2010; Sepulveda-Jauregui et al 2015; Vonk et al 2015). Another major source of variability in GHG emissions from thermokarst lakes is that associated with landscape evolution (Allan et al 2014; Grosse et al 2016; He et al 2012; Lipson et al 2015). The exact trajectory of geomorphological change and the associated biogeochemical effects remain uncertain in many regions of permafrost thaw and degradation

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