Ecosystem CO₂and CH₄exchange in a mixed tundra and a fen within a hydrologically diverse Arctic landscape: 1. Modeling versus measurements

Abstract

CO 2 and CH 4 exchange are strongly affected by hydrology in landscapes underlain by permafrost.Hypotheses for these effects in the model ecosys were tested by comparing modeled CO 2 and CH 4 exchange with CO 2 fluxes measured by eddy covariance from 2006 to 2009, and with CH 4 fluxes measured with surface chambers in 2008, along a topographic gradient at Daring Lake, NWT. In an upland tundra, rises in net CO 2 uptake in warmer years were constrained by declines in CO 2 influxes when vapor pressure deficits (D) exceeded 1.5 kPa and by rises in CO 2 effluxes with greater active layer depth. Consequently, net CO 2 uptake rose little with warming. In a lowland fen, CO 2 influxes declined less with D and CO 2 effluxes rose less with warming, so that rises in net CO 2 uptake were greater than those in the tundra. Greater declines in CO 2 influxes with warming in the tundra were modeled from greater soil-plant-atmosphere water potential gradients that developed under higher D in drained upland soil, and smaller rises in CO 2 effluxes with warming in the fen were modeled from O 2 constraints to heterotrophic and belowground autotrophic respiration from a shallow water table in poorly drained lowland soil. CH 4 exchange modeled during July and August indicated very small influxes in the tundra and larger effluxes characterized by afternoon emission events caused by degassing of warming soil in the fen. Emissions of CH 4 modeled from degassing during soil freezing in October-November contributed about one third of the annual total.

Impacts of microtopographic snow redistribution and lateral subsurface processes on hydrologic and thermal states in an Arctic polygonal ground ecosystem: a case study using ELM-3D v1.0

“…Our use of the satellite phenology mode, which imposes transient LAI profiles on each plant functional type in the domain, ignores the likely influence of nutrient constraints (Zhu et al, 2016) on photosynthesis and therefore the surface energy budget. Other model simplifications, e.g., the simplified treatment of radiation competition, may also be important, especially as simulations are extended over periods where vegetation change may occur (e.g., Grant et al, 2015).…”

HIMMELI v1.0: HelsinkI Model of MEthane buiLd-up and emIssion for peatlands

“…In order to upscale observed CH 4 fluxes and to produce realistic scenarios for the future atmospheric greenhouse gas concentrations, it is essential to know how wetland CH 4 emissions respond to climatic variables. Modeling these responses has been active in recent years (e.g., Wania et al, 2010;Riley et al, 2011;Melton et al, 2013;Schuldt et al, 2013;Grant et al, 2015).…”

“…Some of the models also simulate the O 2 transport and the simulated O 2 concentrations affect the CH 4 processes. These models have been used in multiple studies (e.g., van Huissteden, 2009, 2011;Khvorostianov et al, 2008;Ringeval et al, 2011;Melton et al, 2013;Budishchev et al, 2014;Cresto Aleina et al, 2015;Grant et al, 2015), and some are referred to in the assessment report of the Intergovernmental Panel on Climate Change (IPCC; Ciais et al, 2013). These models have different approaches in simulating the production of CH 4 , ranging from separating distinct heterotrophic microbial communities (Grant and Roulet, 2002) to taking a constant fraction of the simulated heterotrophic soil respiration (Riley et al, 2011).…”

Arctic permafrost landscapes in transition: towards an integrated Earth system approach

“…Atmospheric carbon exchange may vary over short length scales, depending on the landscape type as in in a wet fen environment (Grant et al 2015). Large quantities of particulate and organic carbon released by degrading permafrost are transported by streams and rivers to coastal seas, where they may be sequestered by sedimentation and burial, or converted to CO 2 by bacterial and photochemical processes (Vonk et al 2015).…”