Abstract
Abstract. Northern peatlands are projected to be crucial in future atmospheric methane (CH4) budgets and have a positive feedback on global warming. Fens receive nutrients from catchments via inflowing water and are more sensitive than bogs to variations in their ecohydrology. Yet, due to a lack of data detailing the impacts of moving water on microhabitats and CH4 fluxes in fens, large uncertainties remain with respect to predicting CH4 emissions from these sites under climate changes. We measured CH4 fluxes with manual chambers over three growing seasons (2017–2019) at a northern boreal fen. To address the spatial variation at the site where a stream flows through the long and narrow valley fen, we established sample plots at varying distances from the stream. To link the variations in CH4 emissions to environmental controls, we quantified water levels, peat temperature, dissolved oxygen concentration, vegetation composition, and leaf area index in combination with flux measurements during the growing season in 2019. We found that due to the flowing water, there was a higher water level, cooler peat temperatures, and more oxygen in the peat close to the stream, which also had the highest total leaf area and gross primary production (GPP) values but the lowest CH4 emissions. CH4 emissions were highest at an intermediate distance from the stream where the oxygen concentration in the surface peat was low but GPP was still high. Further from the stream, the conditions were drier and produced low CH4 emissions. Our results emphasize the key role of ecohydrology in CH4 dynamics in fens and, for the first time, show how a stream controls CH4 emissions in a flow-through fen. As valley fens are common peatland ecosystems from the Arctic to the temperate zones, future projections of global CH4 budgets need to take flowing water features into account.
Highlights
Northern peatlands, which cover approximately 15 % of the boreal and Arctic regions, are long-term sources of the greenhouse gas methane (CH4) (Korhola et al, 2010; MacDonald et al, 2006), partly counteracting the cooling impact of related long-term carbon dioxide (CO2) uptake
The response of northern peatlands to global warming has partly contributed to the recent increase in atmospheric CH4 concentrations (Bousquet et al, 2011; Ciais et al, 2014; Kirschke et al, 2013), and modelling projections have suggested that, globally, wetland CH4 emissions will continue to increase during the 21st century and will have a positive feedback on global warming (Zhang et al, 2017)
non-metric multidimensional scaling ordination (NMDS) was used to explore the linkages between peak season vegetation composition, distance to the stream, biomass production, and flowing water
Summary
Northern peatlands, which cover approximately 15 % of the boreal and Arctic regions, are long-term sources of the greenhouse gas methane (CH4) (Korhola et al, 2010; MacDonald et al, 2006), partly counteracting the cooling impact of related long-term carbon dioxide (CO2) uptake. The response of northern peatlands to global warming has partly contributed to the recent increase in atmospheric CH4 concentrations (Bousquet et al, 2011; Ciais et al, 2014; Kirschke et al, 2013), and modelling projections have suggested that, globally, wetland CH4 emissions will continue to increase during the 21st century and will have a positive feedback on global warming (Zhang et al, 2017). H. Zhang et al.: Water flow controls the spatial variability of CH4 emissions ous environmental drivers that control CH4 fluxes (Riley et al, 2011). To upscale observed CH4 fluxes and produce realistic scenarios for future projections of atmospheric CH4 concentrations, it is crucial to understand and quantify the correlations between peatland CH4 emissions and their environmental drivers
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