Methane flux dynamics during mire succession

Abstract

Vegetation, temperature and hydrology are major factors controlling wetland methane (CH(4)) dynamics. In order to test their importance, we measured CH(4) emissions and environmental characteristics over 2 years from five mires representing a successional sequence, ranging in age from 178 to 2,520 years. We hypothesized CH(4) emissions to be higher from the sedge-dominated fens than from the older bog stage. The more constant hydrological conditions at later successional stages as a consequence of the thicker peat layer appeared to result in lower temporal variation in CH(4) emissions. Accordingly, the other controls, temperature and vegetation, had an effect on CH(4) emissions only when the water table was sufficiently high. The seasonal variation in CH(4) emissions was controlled by temperature only at the oldest study site, which had the lowest variation in water table. Within-season variation in emissions related to plant phenology was highest at the fen stage, which was dominated by aerenchymatous plants with a strong seasonal pattern, namely sedges and forbs. In contrast to our hypothesis, CH(4) emissions increased with mire age towards the bog stage. However, the trend did not emerge during a rainy growing season, due to a rise in CH(4) emissions at the younger stages. The results may imply two different mechanisms during mire succession: while old mires are able to avoid the perturbation associated with variation in the water table and maintain their function as CH(4) emitters, young mires are exposed to perturbation but are able to recover their function.

Controls for multi-scale temporal variation in ecosystem methane exchange during the growing season of a permanently inundated fen

“…The seasonal variation of CH 4 fluxes is well investigated and mostly water level, temperature and phenology were identified as primary drivers of CH4 exchange (e.g. Hendriks et al, 2010;Leppälä et al, 2011;Wilson et al, 2009). Here, we address the variation of ecosystem CH 4 exchange within the growing season.…”

Sphagnum growth and ecophysiology during mire succession

“…The improved waterholding capacity induced by the development of Sphagnum cover and the peat layer is reflected at the ecosystem level, as the fen-bog transition stage (site SJ 5) is more stable in its functioning than the younger sites (Leppälä et al 2008(Leppälä et al , 2011a. The same site that also has a distinctive surface pattern with minerotrophic hollows had the highest moss diversity.…”

“…This is caused by the lack of a thick peat layer and Sphagnum moss cover, which together induce a high water-holding capacity (Van Breemen 1995). Ecosystem-level measurements show that in favorable years, the production of vegetation and methane emissions at young stages can be high (Leppälä et al 2008;2011a). However, conditions are variable, and change from flooding in spring to drought during summer; in a dry year, the production of young stages may collapse (Leppälä et al 2011b).…”

Methanotrophy induces nitrogen fixation during peatland development

“…The peatlands, 0.5-1.5 ha in size, have developed in depressions between sand dune formations with similar underlying soil (18,37,38). Along the chronosequence, the vegetation changes from flooded Carex nigra and Agrostis canina dominated meadows in the early stages to Carex-dominated mesotrophic and oligotrophic fens and to fen-bog transitions where the bog vegetation is characterized by an increasing cover of dwarf shrubs in hummock surfaces.…”

“…As the hydrological conditions become more stable in the later successional stages with increasing peat depths, CH 4 emissions increase (18). High CH 4 emissions have been linked to minerotrophic fen stages, in which the dense sedge vegetation readily provides substrate for methanogenesis, whereas in ombrotrophic bogs characterized by Sphagnum mosses and dwarf shrubs, the rates of decomposition and substrate supply for the CH 4 production are slow (19).…”