Abstract
Abstract. Vegetation and hydrology are important controlling factors in peatland methane dynamics. This study aimed at investigating the role of vegetation components, sedges, dwarf shrubs, and Sphagnum mosses, in methane fluxes of a boreal fen under natural and experimental water level drawdown conditions. We measured the fluxes during growing seasons 2001–2004 using the static chamber technique in a field experiment where the role of the ecosystem components was assessed via plant removal treatments. The first year was a calibration year after which the water level drawdown and vegetation removal treatments were applied. Under natural water level conditions, plant-mediated fluxes comprised 68 %–78 % of the mean growing season flux (1.73±0.17 g CH4 m−2 month−1 from June to September), of which Sphagnum mosses and sedges accounted for one-fourth and three-fourths, respectively. The presence of dwarf shrubs, on the other hand, had a slightly attenuating effect on the fluxes. In water level drawdown conditions, the mean flux was close to zero (0.03±0.03 g CH4 m−2 month−1) and the presence and absence of the plant groups had a negligible effect. In conclusion, water level acted as a switch; only in natural water level conditions did vegetation regulate the net fluxes. The results are relevant for assessing the response of fen peatland fluxes to changing climatic conditions, as water level drawdown and the consequent vegetation succession are the major projected impacts of climate change on northern peatlands.
Highlights
One-third of all terrestrial carbon is stored in boreal and subarctic peatlands (e.g., Yu, 2012) that generally act as CO2 sinks in current climatic conditions
We studied the contribution of the ecosystem components to the net CH4 fluxes in wet and dry conditions by means of plant removal treatments
Potential new predictors were sequentially added and after each addition the significance of all predictors was tested. We reported both models separately for the year 2004: one including plant removal and water level drawdown (WLD) treatments as fixed predictors for CH4 flux and another including the response of CH4 flux to leaf area and cover of plant groups and environmental variables
Summary
One-third of all terrestrial carbon is stored in boreal and subarctic peatlands (e.g., Yu, 2012) that generally act as CO2 sinks in current climatic conditions. The carbon sink function of peatlands is mostly due to the slow decomposition rate resulting from waterlogged, anaerobic conditions sustained by a high water level, which simultaneously favor CH4 production. CH4 is the end product of anaerobic decomposition by strictly anaerobic methanogenic archaea. It is released from the peat into the atmosphere via diffusion through the peat column, ebullition or plant-mediated transport (Lai, 2009). A considerable part, from 20 % to up to 90 % (Le Mer and Roger, 2001; Pearce and Clymo, 2001; Whalen, 2005) of the CH4 diffusing through the upper, aerobic part of the peat layer is oxidized to CO2 by methanotrophic bacteria (MOB) before reaching the atmosphere
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