The importance of freshwater systems to the net atmospheric exchange of carbon dioxide and methane with a rapidly changing high Arctic watershed

Abstract. A warming climate is rapidly changing the distribution and exchanges of carbon within high Arctic ecosystems. Few data exist, however, which quantify exchange of both carbon dioxide (CO₂) and methane (CH₄) between the atmosphere and freshwater systems, or estimate freshwater contributions to total catchment exchange of these gases, in the high Arctic. During the summers of 2005 and 2007–2012, we quantified CO₂ and CH₄ concentrations in, and atmospheric exchange with, common freshwater systems in the high Arctic watershed of Lake Hazen, Nunavut, Canada. We identified four types of biogeochemically distinct freshwater systems in the watershed; however mean CO₂ concentrations (21–28 µmol L⁻¹) and atmospheric exchange (−0.013 to +0.046 g C–CO₂ m⁻² day⁻¹) were similar between these systems. Seasonal flooding of ponds bordering Lake Hazen generated considerable CH₄ emissions to the atmosphere (+0.008 g C–CH₄ m⁻² day⁻¹), while all other freshwater systems were minimal emitters of this gas (< +0.001 g C–CH₄ m⁻² day⁻¹). When using ecosystem-cover classification mapping and data from previous studies, we found that freshwaters were unimportant contributors to total watershed carbon exchange, in part because they covered less than 10 % of total area in the watershed. High Arctic watersheds are experiencing warmer and wetter climates than in the past, which may have implications for moisture availability, landscape cover, and the exchange of CO₂ and CH₄ of underproductive but expansive polar semidesert ecosystems.