Emissions of methane and other biogenic volatile organic compounds from boreal peatlands

Abstract

This study aims to 1) quantify the spatial and temporal variation in diffusive and ebullitive methane fluxes, and to 2) assess the quantity and quality of BVOC emissions and how they are controlled by vegetation composition and environmental factors in boreal peatlands. Methane fluxes were measured with static chambers and bubble traps from a boreal ombrotrophic bog and compared to eddy covariance measurements on the ecosystem level. BVOC emissions were measured with dynamic chambers from the same boreal bog and a nearby boreal fen. Vegetation removal treatments were applied to differentiate BVOC emissions from intact vegetation, mosses, and peat. Both methane and BVOC emissions showed strong seasonality linked to temperature and vegetation phenology. While diffusive methane fluxes did not differ between three years or different plant community types, methane ebullition was highest during the wettest of the three years studied and varied spatially being greater from open water pools than from wet bare peat surfaces. Decrease in water table led to higher ebullition, but so did also increase in air pressure. In total, ebullition contributed only 2 % – 8 % to the methane emission on the ecosystem level, which supports the general paradigm that diffusion through peat and aerenchymatous plants are the main pathways for methane from peat to the atmosphere. Isoprene was the most emitted BVOC from both peatlands. Isoprene emission was strongly linked to sedges, and thus isoprene and total BVOC emission rates were higher in the sedge-dominated fen than the shrub-dominated bog. Moreover, total BVOC and isoprene emissions were highest from intact vegetation. However, organic halide emissions had stronger link with water level as they were absent during exceptional drought in the summer 2018. Therefore, warming climate and associated drougths and shrubification are likely to alter the quality and quantity of BVOCs emitted from boreal peatlands.