Climate warming accelerates permafrost thaw in northern regions, leading to the breakdown and release of soil carbon (C) in the form of carbon dioxide (CO2) and methane (CH4), both potent greenhouse gases (GHG) (Schuur et al. 2015). Small ponds that develop post-permafrost thaw have been recognized as hotspots for processing recently released permafrost carbon, leading to high dissolved GHG gas concentrations and emissions (Fig 1; Laurion et al. 2010; Wik et al. 2016). Current literature identifies temperature, water depth, and sediment type as the most important drivers of GHG concentrations in ponds (Wik et al. 2016). However, few in-depth pond studies exist, especially so regarding the influence of vegetation, and the impact of fire. Both surrounding and inner vegetation composition may influence GHG gas concentrations in small ponds through the production labile organic carbon root exudates and the uptake of CO2 or CH4 during photosynthesis and metabolic reactions (Knoblauch et al. 2015). In regards to fire, dissolved gas concentrations may be both positively and negatively affected through the combustion of labile organic matter and through accelerated permafrost thaw and land slumping (Liu et al. 2014).
Fig 1. A conceptual diagram outlining carbon dynamics in permafrost ponds. Ponds tend to have extremely high concentrations of dissolved methane and carbon dioxide due a high edge:waterv volume ratio and inputs of both terrestrial carbon and newly released permafrost carbon. Additionally, shallow waters allow sunlight to penetrate and warm the sediments. The diagram also shows the three ways methane can be transported to the atmosphere.
Fig 2. A conceptual diagram outlining the research objectives of this project.
Objectives The specific research objectives of this study are two-fold: First, we hope to identify which physical and chemical variables are commonly associated with increased dissolved GHG concentrations, with an particular interest in CH4, across the three ecosystem types (Level 1). Second, we want to assess the impact of disturbances on commonly studied physical and chemical variables, and, therefore, on dissolved GHG gas concentrations (Level 2). Within the second objective, we looked at two types of disturbances including vegetation communities and fire severity- both of which have never been study within the context of influence on pond chemistry. The ultimate goal of this study is to use multivariate statistical tools to identify the key environmental variables, including physical and chemical characteristics, vegetation communities and wildfire disturbance, that influence GHG gas concentrations in ponds (Fig 2). The results from this study will lead towards a greater understanding of inland water carbon dynamics and the future of GHG emissions with the onset of a changing climate.
Fig. 3 Examples of a moss-dominated pond (a) and a sedge-dominated pond (b).
Expected Results We expect to see water depth, sediment carbon content, and dissolved oxygen concentrations be the common drivers of GHG gas concentrations across all three locations. However, we expect that gas concentrations will differ in the mire ponds based on vegetation communities. For example, we expect ponds covered largely by sedge species to have high methane concentrations than ponds covered by mainly moss species since mosses have been associated with methane consumers (Strom et al. 2012; Leibner et al. 2010; Fig 3). Lastly, we expect GHG gas concentrations in ponds effected by fire will be lower than concentration in ponds unaffected by fire, due to the combustion of organic material surrounding the fire-effected ponds and subsequent changes to physical and chemical characteristics.
References
Knoblauch, Christian, et al. "Regulation of methane production, oxidation, and emission by vascular plants and bryophytes in ponds of the northeast Siberian polygonal tundra." Journal of Geophysical Research: Biogeosciences 120.12 (2015): 2525-2541.
Laurion, Isabelle, et al. "Variability in greenhouse gas emissions from permafrost thaw ponds." Limnology and Oceanography 55.1 (2010): 115-133.
Liebner, Susanne, et al. "Methane oxidation associated with submerged brown mosses reduces methane emissions from Siberian polygonal tundra." Journal of Ecology 99.4 (2011): 914-922.
Liu, Lin, et al. "InSAR detects increase in surface subsidence caused by an Arctic tundra fire." Geophysical Research Letters 41.11 (2014): 3906-3913.
Schuur, E. A. G., et al. "Climate change and the permafrost carbon feedback." Nature 520.7546 (2015): 171-179.
Ström, Lena, et al. "Presence of Eriophorum scheuchzeri enhances substrate availability and methane emission in an Arctic wetland." Soil Biology and Biochemistry 45 (2012): 61-70.
Wik, Martin, et al. "Climate-sensitive northern lakes and ponds are critical components of methane release." Nature Geoscience (2016).