ALBERT

Description: 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 (−0.013–0.046 g C-CO2 m−2 d−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 d−1), while all other freshwater systems were minimal emitters of this gas (〈 0.001 g C-CH4 m−2 d−1). Measurements made on terrestrial landscapes in the same watershed between 2008–2012 determined that the near-barren polar semidesert was a very weak consumer of atmospheric CO2 (−0.004 g C-CO2 m−2 d−1), but an important consumer of atmospheric CH4 (−0.001 g C-CH4 m−2 d−1). Alternatively, meadow wetlands were very productive consumers of atmospheric CO2 (−0.96 g C-CO2 m−2 d−1) but relatively weak emitters of CH4 to the atmosphere (0.001 g C-CH4m−2 d−1). When using ecosystem-cover classification mapping, we found that freshwaters were unimportant contributors to total watershed carbon exchange, in part because they covered less than 10 % of total cover in the watershed. High Arctic watersheds are experiencing warmer and wetter climates than in the past, which may have implications for the net uptake of carbon greenhouse gases by currently underproductive polar semidesert and freshwater systems.