Abstract
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.
Highlights
Freshwater ecosystems cover less than 10 % of global icefree land area (Lehner and Doll, 2004) and have been typically overlooked as substantial contributors to, or sinks of, atmospheric carbon greenhouse gases (GHGs; Bastviken et al, 2011)
Four distinct types of freshwater systems were evident from our sampling in the Lake Hazen watershed (Table 3; Fig. S1 in the Supplement; hierarchical cluster analysis; see Methods)
“Evaporative” ponds occurred in the upland of the Lake Hazen catchment and were hydrologically isolated from their surrounding basins post-snowmelt. These ponds were relatively high in concentrations of total dissolved solids, most measured ions, dissolved inorganic carbon (DIC), DOC, organic particles, TDP, and chl a
Summary
Freshwater ecosystems cover less than 10 % of global icefree land area (Lehner and Doll, 2004) and have been typically overlooked as substantial contributors to, or sinks of, atmospheric carbon greenhouse gases (GHGs; Bastviken et al, 2011). Between approximately 45 and 75◦ N, contain the highest abundance of lakes, ponds, and wetlands on the planet (Lehner and Doll, 2004) due to historical glaciations and moderate annual precipitation. These regions contain the world’s largest belowground stores of organic carbon (Tarnocai et al, 2009). These carbon- and lake-rich northern ecosystems, have been critically important sinks historically and will potentially be strong emitters of this legacy carbon moving forward (ACIA, 2004). Heterotrophic respiration by microbes continues perennially in most lake waters and sediments, continuously releasing CO2 to the water
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