Abstract
Lakes account for about 10% of the boreal landscape and are responsible for approximately 30% of biogenic methane emissions that have been found to increase under changing climate. However, the quantification of this climate-sensitive methane source is fraught with large uncertainty under warming climate conditions. Only a few studies have addressed the mechanism of climate impact on the increase of northern lake methane emissions. This study uses a large observational dataset of lake methane concentrations in Finland to constrain methane emissions with an extant process-based lake biogeochemical model. We found that the total current diffusive emission from Finnish lakes is 0.12 ± 0.03 Tg CH4 yr−1 and will increase by 26%–59% by the end of this century depending on different warming scenarios. We discover that while warming lake water and sediment temperature plays an important role, the climate impact on ice-on periods is a key indicator of future emissions. We conclude that these boreal lakes remain a significant methane source under the warming climate within this century.
Highlights
Atmospheric methane (CH4) is the second major greenhouse gas after carbon dioxide
We discover that while warming lake water and sediment temperature plays an important role, the climate impact on ice-on periods is a key indicator of future emissions
We estimate that the Finnish lake diffusive methane emission will increase by 25.8% from 0.12 ± 0.04 to 0.16 ± 0.05 Tg CH4 yr−1 under the RCP4.5 scenario while it will increase by about 58.9% from 0.13 ± 0.04 to 0.20 ± 0.06 Tg CH4 yr−1 under the RCP8.5
Summary
Atmospheric methane (CH4) is the second major greenhouse gas after carbon dioxide. It only contributes to about 20% of the warming effect, its global warming potential is 28 times higher than carbon dioxide (Lashof et al 1990, Myhre et al 2013, IPCC 2014). Over the past two decades, surface freshwater including lakes, reservoirs, streams and rivers has been receiving an accumulating attention as important global methane sources (Bastviken et al 2011, Prairie et al 2013, Saunois et al 2016). Studies have shown large uncertainties in the estimation of freshwater methane emissions (Kirschke et al 2013). A better estimation of the present and future lake methane emissions would largely benefit from critical improvement in watercourse mapping and methane flux measurements (Saarnio et al 2009; Kirschke et al 2013). Previous studies mostly focused on quantitative estimation but hardly
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