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

Abstract

AbstractCO2and CH4exchange are strongly affected by hydrology in landscapes underlain by permafrost. Hypotheses for these effects in the modelecosyswere tested by comparing modeled CO2and CH4exchange with CO2fluxes measured by eddy covariance from 2006 to 2009, and with CH4fluxes measured with surface chambers in 2008, along a topographic gradient at Daring Lake, NWT. In an upland tundra, rises in net CO2uptake in warmer years were constrained by declines in CO2influxes when vapor pressure deficits (D) exceeded 1.5 kPa and by rises in CO2effluxes with greater active layer depth. Consequently, net CO2uptake rose little with warming. In a lowland fen, CO2influxes declined less withDand CO2effluxes rose less with warming, so that rises in net CO2uptake were greater than those in the tundra. Greater declines in CO2influxes with warming in the tundra were modeled from greater soil‐plant‐atmosphere water potential gradients that developed under higherDin drained upland soil, and smaller rises in CO2effluxes with warming in the fen were modeled from O2constraints to heterotrophic and belowground autotrophic respiration from a shallow water table in poorly drained lowland soil. CH4exchange 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 CH4modeled from degassing during soil freezing in October–November contributed about one third of the annual total.