Net Ecosystem Production of Polar Desert and Wetland Landscapes in the Rapidly Changing Canadian High Arctic

Abstract:

A rapidly warming and wetting Arctic climate is changing the net ecosystem production (NEP) of northern landscapes and subsequent exchange of carbon dioxide (CO2) with the atmosphere. Assessments of northern terrestrial NEP have focused mostly on the rich peatland landscapes of the low Arctic, with far fewer studies from expansive, but sparse, high Arctic polar landscapes. Consequently, how these ecosystems may respond to a warming and wetting climate is still a key gap in our understanding of global carbon feedbacks. We used multi–season eddy covariance measurements to quantify growing season (June to September) NEP on contrasting polar desert and meadow wetland landscapes near Lake Hazen on northern Ellesmere Island (81ºN), in Canada’s high Arctic. We also used variation in contemporary NEP and weather to improve our understanding of potential future carbon cycling in a warmer and wetter high Arctic climate. During a typical growing season, we found that a dry polar desert landscape accumulated only 6.6±1.2 g C m-2 similar to other high Arctic sites and consistent with cold, barren soils with weak plant growth. Desert NEP coincided strongest with landscape moisture, rather than heating, with increased NEP occurring during drier conditions when soil heterotrophic rates were lowest. With a nearly constant but varying supply of water, the productive meadow wetland accumulated 13 times more carbon (86.1±16.9 g C m-2) than the desert during the growing season. NEP at the wetland was similar to comparable landscapes much further south, owing to continuous 24–hour daylight and typically clear–skies surrounding Lake Hazen. Wetland soils showed a consistent strong burst of CO2 to the atmosphere each spring (min. NEP: –2.5 µmol CO2 s-1 m-2) and a well–defined peak in July productivity (3.9–4.4 µmol CO2 s-1 m-2). Wetland NEP associated positively and strongly with both landscape heating and moisture, suggesting that autotrophic limitations other than water or heat controlled ultimate carbon accumulation on the wetland landscape. Because polar desert landscapes comprise the majority of land area in the high Arctic, changes in moisture, rather than heating, will likely continue to strongly affect future net carbon accumulation, at least until plant cover and soil quality changes substantially.