Plants, microorganisms, and soil temperatures contribute to a decrease in methane fluxes on a drained Arctic floodplain

Abstract

As surface temperatures are expected to rise in the future, ice-rich permafrost may thaw, altering soil topography and hydrology and creating a mosaic of wet and dry soil surfaces in the Arctic. Arctic wetlands are large sources of CH , and investigating effects of soil hydrology on CH fluxes is of great importance for predicting ecosystem feedback in response to climate change. In this study, we investigate how a decade-long drying manipulation on an Arctic floodplain influences CH -associated microorganisms, soil thermal regimes, and plant communities. Moreover, we examine how these drainage-induced changes may then modify CH fluxes in the growing and nongrowing seasons. This study shows that drainage substantially lowered the abundance of methanogens along with methanotrophic bacteria, which may have reduced CH cycling. Soil temperatures of the drained areas were lower in deep, anoxic soil layers (below 30 cm), but higher in oxic topsoil layers (0-15 cm) compared to the control wet areas. This pattern of soil temperatures may have reduced the rates of methanogenesis while elevating those of CH oxidation, thereby decreasing net CH fluxes. The abundance of Eriophorum angustifolium, an aerenchymatous plant species, diminished significantly in the drained areas. Due to this decrease, a higher fraction of CH was alternatively emitted to the atmosphere by diffusion, possibly increasing the potential for CH oxidation and leading to a decrease in net CH fluxes compared to a control site. Drainage lowered CH fluxes by a factor of 20 during the growing season, with postdrainage changes in microbial communities, soil temperatures, and plant communities also contributing to this reduction. In contrast, we observed CH emissions increased by 10% in the drained areas during the nongrowing season, although this difference was insignificant given the small magnitudes of fluxes. This study showed that long-term drainage considerably reduced CH fluxes through modified ecosystem properties.

Shifted energy fluxes, increased Bowen ratios, and reduced thaw depths linked with drainage-induced changes in permafrost ecosystem structure

“…The long-term changes in soil water conditions, vegetation coverage, radiation, and snow cover listed above have increased both carbon content and bulk density (see Kwon et al, 2017, for details), and also trigger profound shifts in the soil thermal regime within this tundra ecosystem. These effects are summarized in Fig.…”

Year-round simulated methane emissions from a permafrost ecosystem in Northeast Siberia

“…During the spring snowmelt (May and June), 170 large sections of the Kolyma floodplain usually become inundated, and during summer, the extent of surface water recedes due to evapotranspiration and drainage to the river channels located nearby. However, most areas remain inundated throughout the year (Kwon et al, 2016 shrubs, Sphagnum mosses, and lichens, but few trees (Dutta et al, 2006;Merbold et al, 2009). Loess soil deposits originating from the accumulation of aeolian and alluvial sediments characterize the soil in this region.…”

“…At the Kolyma River floodplain, the soil profile has a top 165 layer of organic material (~15 cm) that is located above alluvial mineral soils, i.e. silty loam (Kittler et al, 2016;Kwon et al, 2016). In this area, the vegetation is heterogeneous and representative of wet tussock tundra.…”

“…These changes will therefore also propagate to the magnitude of future emissions of CO 2 and CH 4 into the atmosphere from Arctic terrestrial ecosys-60 tems (Hugelius et al, 2014;Lawrence et al, 2015;Schuur et al, 2008). Drier soil columns will enhance methane oxidation and increase CO 2 emissions (Kittler et al, 2016;Kwon et al, 2016;Lawrence et al, 2015;Liljedahl et al, 2016;Sturtevant et al, 2012), also leading to changes in plant community structure (Christensen et al, 2004;Kutzbach et al, 2004;Kwon et al, 2016). Thus, it is imperative to improve our understanding of the effects of climate 65 change in permafrost wetlands, specifically their contribution to greenhouse gases into the atmosphere.…”

“…In this area, the vegetation is heterogeneous and representative of wet tussock tundra. There, the water-logged areas are covered by the tussockforming sedges, such as Carex appendiculata and Carex lugens, and cotton grasses like Eriophorium angunstifolium (Kwon et al, 2016). During the spring snowmelt (May and June), 170 large sections of the Kolyma floodplain usually become inundated, and during summer, the extent of surface water recedes due to evapotranspiration and drainage to the river channels located nearby.…”