Mathematical Modelling of Arctic Polygonal Tundra with <i>Ecosys:</i> 2. Microtopography Determines How CO₂ and CH₄ Exchange Responds to Changes in Temperature and Precipitation

Abstract

Abstract Differences of surface elevation in arctic polygonal landforms cause spatial variation in soil water contents ( θ ), active layer depths (ALD), and thereby in CO 2 and CH 4 exchange. Here we test hypotheses in ecosys for topographic controls on CO 2 and CH 4 exchange in trough, rim, and center features of low‐ and flat‐centered polygons (LCP and FCP) against chamber and eddy covariance (EC) measurements during 2013 at Barrow, Alaska. Larger CO 2 influxes and CH 4 effluxes were measured with chambers and modeled with ecosys in LCPs than in FCPs and in lower features (troughs) than in higher (rims) within LCPs and FCPs. Spatially aggregated CO 2 and CH 4 fluxes from ecosys were significantly correlated with EC flux measurements. Lower features were modeled as C sinks (52–56 g C m −2 yr −1 ) and CH 4 sources (4–6 g C m −2 yr −1 ), and higher features as near C neutral (−2–15 g C m −2 yr −1 ) and CH 4 neutral (0.0–0.1 g C m −2 yr −1 ). Much of the spatial and temporal variations in CO 2 and CH 4 fluxes were modeled from topographic effects on water and snow movement and thereby on θ , ALD, and soil O 2 concentrations. Model results forced with meteorological data from 1981 to 2015 indicated increasing net primary productivity in higher features and CH 4 emissions in some lower and higher features since 2008, attributed mostly to recent rises in precipitation. Small‐scale variation in surface elevation causes large spatial variation of greenhouse gas (GHG) exchanges and therefore should be considered in estimates of GHG exchange in polygonal landscapes.