Vegetation Type Dominates the Spatial Variability in CH4 Emissions Across Multiple Arctic Tundra Landscapes

Scott J Davidson,Victoria L Sloan,Donatella Zona,Walter C Oechel,James P Fisher,Gareth K Phoenix,Robert Wagner

doi:10.1007/s10021-016-9991-0

Scott J Davidson, Victoria L Sloan + Show 5 more

Open Access

https://doi.org/10.1007/s10021-016-9991-0

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Abstract

Methane (CH4) emissions from Arctic tundra are an important feedback to global climate. Currently, modelling and predicting CH4 fluxes at broader scales are limited by the challenge of upscaling plot-scale measurements in spatially heterogeneous landscapes, and by uncertainties regarding key controls of CH4 emissions. In this study, CH4 and CO2 fluxes were measured together with a range of environmental variables and detailed vegetation analysis at four sites spanning 300 km latitude from Barrow to Ivotuk (Alaska). We used multiple regression modelling to identify drivers of CH4 flux, and to examine relationships between gross primary productivity (GPP), dissolved organic carbon (DOC) and CH4 fluxes. We found that a highly simplified vegetation classification consisting of just three vegetation types (wet sedge, tussock sedge and other) explained 54% of the variation in CH4 fluxes across the entire transect, performing almost as well as a more complex model including water table, sedge height and soil moisture (explaining 58% of the variation in CH4 fluxes). Substantial CH4 emissions were recorded from tussock sedges in locations even when the water table was lower than 40 cm below the surface, demonstrating the importance of plant-mediated transport. We also found no relationship between instantaneous GPP and CH4 fluxes, suggesting that models should be cautious in assuming a direct relationship between primary production and CH4 emissions. Our findings demonstrate the importance of vegetation as an integrator of processes controlling CH4 emissions in Arctic ecosystems, and provide a simplified framework for upscaling plot scale CH4 flux measurements from Arctic ecosystems.

Highlights

The Arctic is warming at nearly double the global rate (IPCC 2013)
We found that a highly simplified vegetation classification consisting of just three vegetation types explained 54% of the variation in CH4 fluxes across the entire transect, performing almost as well as a more complex model including water table, sedge height and soil moisture
We show that vegetation was the dominant variable explaining the spatial heterogeneity of CH4 fluxes across a variety of tundra types across multiple vegetation communities, environmental conditions and geographic locations

Summary

Introduction

The Arctic is warming at nearly double the global rate (IPCC 2013). A temperature increase of approximately 6°C is predicted by the end of the twenty-first century in northern high latitudes (IPCC 2013), leading to major changes in hydrological and thermal regimes, which in turn will heavily influence the direction and magnitude of the Arctic carbon (C) balance (Oechel and others 2000; Chapin and others 2005). One of the greatest concerns is the potential for increases in methane (CH4) emissions from tundra ecosystems to the atmosphere. Arctic tundra ecosystems currently account for approximately 8–30 Tg CH4 y-1 released to the atmosphere (Christensen 1993; McGuire and others 2012; Olefeldt and others 2013). As CH4 has 28.5 times the global warming potential of carbon dioxide (CO2) over 100 years (IPCC 2013), increased emissions are an important positive feedback from the arctic region to global climate (Forster and others 2007; IPCC 2013), further warming the climate system, leading to permafrost degradation and increased emissions

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