Effect of water table on greenhouse gas emissions from peatland mesocosms

Abstract

This version available at http://nora.nerc.ac.uk/5459/ NERC has developed NORA to enable users to access research outputs wholly or partially funded by NERC. Copyright and other rights for material on this site are retained by the authors and/or other rights owners. Users should read the terms and conditions of use of this material at http://nora.nerc.ac.uk/policies.html#access This document is the author's final manuscript version of the journal article, incorporating any revisions agreed during the peer review process. Some differences between this and the publisher's version remain. You are advised to consult the publisher's version if you wish to cite from this article. Peatland landscapes typically exhibit large variations in greenhouse gas (GHG) emissions due to microtopographic and vegetation heterogeneity. As many peatland budgets are extrapolated from small-scale chamber measurements it is important to both quantify and understand the processes underlying this spatial variability. Here we carried out a mesocosm study which allowed a comparison to be made between different microtopographic features and vegetation communities, in response to conditions of both static and changing water table. Three mesocosm types (hummocks + Juncus effusus, hummocks + Eriophorum vaginatum, and hollows dominated by moss) were subjected to 2 water table treatments (0-5 cm and 30-35 cm depth). Measurements were made of soil-atmosphere GHG exchange, GHG concentration within the peat profile and soil water solute concentrations. After 14 weeks the high water table group was drained and the low water table group flooded. Measurement intensity was then increased to examine the immediate response to change in water table position.Mean CO 2 , CH 4 and N 2 O exchange across all chambers was 39.8 µg m -2 s -1 , 54.7 µg m -2 h -1 and -2.9 µg m -2 h -1 , respectively. Hence the GHG budget was dominated in this case by CO 2 exchange. CO 2 and N 2 O emissions were highest in the low water table treatment group; CH 4 emissions were highest in the saturated mesocosms. We observed a strong interaction between mesocosm type and water table for CH 4 emissions. In contrast to many previous studies, we found that the presence of aerenchyma-containing vegetation reduced CH 4 emissions. A significant pulse in both CH 4 and N 2 O emissions occurred within 1-2 days of switching the water table treatments. This pulsing could potentially lead to significant underestimation of landscape annual GHG budgets when widely spaced chamber measurements are upscaled. Introduction:Northern peatlands are estimated to contain 455 Gt of carbon (Gorham 1991), representing approximately a third of the estimated total global soil carbon pool.They are considered to be net sinks of CO 2 and net sources of CH 4 (Bartlett and Harriss 1993;Gorham 1991;Huttunen et al. 2003) , though annual and inter-annual variation can be extremely high. Peatlands also represent an important source of dissolved organic carbon to drainage waters (Urban et al. 1989;Billett et al. 2004;Daw...

Short-Term Effects of Drying and Rewetting on CO2 and CH4 Emissions from High-Altitude Peatlands on the Tibetan Plateau

“…This finding contradicts previous research on peatlands [16], but is consistent with the findings of Bubier et al [21]. Currently, no study has reached a clear conclusion about how rewetting affects CH 4 emissions.…”

“…The drop in the water Researchers have drawn different conclusions about the effects of alternate drying and rewetting on CO2 release from the soil in wetlands. Some studies suggested that alternate drying and rewetting can stimulate CO2 release from peatlands as a result of increased substrate availability to microbes from the release of osmolytes accumulated during the drying phase, as well as cell lysis and the breakdown of aggregates that release previously protected organic matter [4,16]. In our study, alternate drying and rewetting had little impact on CO2 release.…”

Effects of soil warming, rainfall reduction and water table level on CH 4 emissions from the Zoige peatland in China

“…Mesocosms are considered as an effective system for measuring the effects of climate change on carbon emissions, especially when simulating changes in water table levels and temperature (Dinsmore et al, 2009a;Strack and Waddington, 2007;Updegraff et al, 2001). Although mesocosms allow easy control of water table levels, this experimental system can also give biased estimates of carbon emission.…”

“…Higher environmental temperatures may accelerate decomposition and oxidize the surrounding peat in the cylinder, thereby releasing more carbon. Second, the death of plant roots cut during mesocosm collection may accelerate mineralization (Dinsmore et al, 2009a), leading in turn to higher carbon emissions during early stages of experiments. Third, a decrease in water content in surface peat and an increase in soil aeration may stimulate decomposition in the short term (Strakova, 2010).…”

“…Changes in water table level, precipitation and temperature all affect CH 4 emissions from peatlands by influencing organic matter decomposition and carbon mineralization (Taggart, 2010;van Winden et al, 2012b;Ward et al, 2013). More specifically, the water table level influences the aerobic/anoxic boundary and redox level of the soil (Dinsmore et al, 2009a). The aerobic environment caused by water table drawdown decreases CH 4 emissions due to limited methanogen activity (Fenner and Freeman, 2011).…”