Increased CO 2 loss from vegetated drained lake tundra ecosystems due to flooding Donatella Zona, 1,2 David A. Lipson, 2 Kyaw T. Paw U, 3 Steve F. Oberbauer, 4 Paulo Olivas, 4 Beniamino Gioli, 5 and Walter C. Oechel 2 Received 7 January 2011; revised 8 February 2012; accepted 11 March 2012; published 21 April 2012. [1] Tundra ecosystems are especially sensitive to climate change, which is particularly rapid in high northern latitudes resulting in significant alterations in temperature and soil moisture. Numerous studies have demonstrated that soil drying increases the respiration loss from wet Arctic tundra. And, warming and drying of tundra soils are assumed to increase CO 2 emissions from the Arctic. However, in this water table manipulation experiment (i.e., flooding experiment), we show that flooding of wet tundra can also lead to increased CO 2 loss. Standing water increased heat conduction into the soil, leading to higher soil temperature, deeper thaw and, surprisingly, to higher CO 2 loss in the most anaerobic of the experimental areas. The study site is located in a drained lake basin, and the soils are characterized by wetter conditions than upland tundra. In experimentally flooded areas, high wind speeds (greater than 4ms 1 ) increased CO 2 emission rates, sometimes overwhelming the photosynthetic uptake, even during daytime. This suggests that CO 2 efflux from C rich soils and surface waters can be limited by surface exchange processes. The comparison of the CO 2 and CH 4 emission in an anaerobic soil incubation experiment showed that in this ecosystem, CO 2 production is an order of magnitude higher than CH 4 production. Future increases in surface water ponding, linked to surface subsidence and thermokarst erosion, and concomitant increases in soil warming, can increase net C efflux from these arctic ecosystems. Citation: Zona, D., D. A. Lipson, K. T. Paw U, S. F. Oberbauer, P. Olivas, B. Gioli, and W. C. Oechel (2012), Increased CO 2 loss from vegetated drained lake tundra ecosystems due to flooding, Global Biogeochem. Cycles, 26, GB2004, doi:10.1029/2011GB004037. 1. Introduction [2] Recent estimates indicate that the total organic carbon in the upper 3 m of northern circumpolar permafrost-affected soils is 1024 Pg C, and 1672 Pg C if yedoma and deltaic deposits are included [Schuur et al., 2008; Tarnocai et al., 2009]. This is much greater than previously reported and corresponds to 30–50% of the global belowground organic carbon pool [Schuur et al., 2008; Kuhry et al., 2009; Tarnocai et al., 2009]. Of this 1672 Pg C, 277 Pg C are present in northern circumpolar peatlands [Schuur et al., 2008]. There is significant potential for this soil carbon to be released into the atmosphere as CO 2 or CH 4 in response to changes in hydrology and soil temperature [Billings et al., 1982; Peterson et al., 1984; Oechel et al., 1998; Schuur et al., 2008; Frank et al., 2010; Hayes et al., 2011]. [3] Drying of wet anaerobic areas of northern peatlands increases rates of soil respiration and is therefore thought to increase net CO 2 emissions [Billings et al., 1982; Peterson et al., 1984; Oechel et al., 1998; Olivas et al., 2010; Flanagan and Syed, 2011]. A decrease in the water table generally increases oxygen diffusion into soils, leading to more aerobic conditions, and consequently increases decomposition, peat degradation, and CO 2 loss to the atmosphere [Billings et al., 1982; Peterson et al., 1984; Oechel et al., 1998]. Conversely, a rise in the water table generally slows the diffusion of oxygen into the peat, limits aerobic microbial activity and decomposition rates, consequently decreasing CO 2 loss or increasing CO 2 sink [Billings et al., 1982; Peterson et al., 1984; Oechel et al., 1998; Chivers et al., 2009]. [4] As a result of predicted and observed decrease of soil moisture in large part of the Arctic [Oechel et al., 2000; Hinzman et al., 2005], the majority of the carbon flux studies in the Arctic have mostly focused on the impacts of decreased soil moisture [Billings et al., 1982; Peterson et al., 1984; Oechel et al., 1998; Merbold et al., 2009]. However, the impact of climate change over the Arctic is very complex, and increasing wetness in extensive tundra regions overlying 1 Research Group of Plant and Vegetation Ecology, Department of Biology, University of Antwerp, Antwerp, Belgium. 2 Global Change Research Group, Department of Biology, San Diego State University, San Diego, California, USA. 3 Department of Land, Air, and Water Resources, University of California, Davis, California, USA. 4 Department of Biological Sciences, Florida International University, Miami, Florida, USA. 5 Institute for Biometeorology, National Research Council, Florence, Italy. Copyright 2012 by the American Geophysical Union. 0886-6236/12/2011GB004037 GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 26, GB2004, doi:10.1029/2011GB004037, 2012 GB2004 1 of 16