Ecosystem CO2 and CH4 Exchange in a Mixed Tundra and a Fen Within an Arctic Landscape: Modeled Impacts of Climate Change

Abstract:

Climate change will have important effects on arctic productivity and greenhouse gas exchange. These changes were projected by the model ecosys under an SRES A2 scenario over the 21^st century for a landscape including an upland tundra and a lowland fen at Daring Lake, NWT. Rising temperatures and precipitation caused increases in active layer depths (ALD) and eventual formation of taliks, particularly in the fen, which were attributed to heat advection from warmer and more intense precipitation and downslope flow. These changes raised net primary productivity from more rapid N mineralization and uptake, driven by more rapid heterotrophic respiration and increasing deciduous vs. evergreen plant functional types. Consequently gains in net ecosystem productivity (NEP) of 29 and 10 g C m^-2 y^-1 were modelled in the tundra and fen after 90 years. However CH₄ emissions modelled from the fen rose sharply from direct effects of increasing soil temperatures and greater ALD on fermenter and methanogenic populations, and from indirect effects of increasing sedge growth which hastened transfer of CH₄ through porous roots to the atmosphere. After 90 years, landscape CH₄ emissions increased from 1.1 to 5.2 g C m^-2 y^-1 while landscape NEP increased from 34 to 46 g C m^-2 y^-1. Positive feedback to radiative forcing from increases in CH₄ emissions more than offset negative feedback from increases in NEP. This feedback was largely attributed to rises in CH₄ emission caused by heat advection from increasing precipitation, the impacts of which require greater attention in arctic climate change studies.