CH4 emission from a hollow-ridge complex in a raised bog: The role of CH4 production and oxidation

Abstract

The aim of this study was to correlate magnitude andcontrols of CH4 fluxes with the microtopographyand the vegetation in a hollow-ridge complex of araised bog. High CH4 emission rates were measuredfrom hollows and mud-bottom hollows, while hummocksconsumed atmospheric CH4 at a low rate. Thehighest emissions were measured from plots with Eriophorum vaginatum and Scheuchzeriapalustris. CH4 emission ceased after Scheuchzeria had been clipped below the water table,indicating the importance of this aerenchymatic plantas a conduit for CH4. Peat in the upper catotelm of hollows was younger andless decomposed than in hummocks. Potential CH4production in vitro was higher and themethanogenic association was better adapted to highertemperatures in hollow than in hummock peat. Highertemperatures in hollows resulted in a strongerCH4 source in hollows than in hummocks. Negativefluxes from hummocks indicated that even in wetlandsmethanotrophic bacteria exist that are able to oxidizeCH4 at atmospheric mixing ratios, and thatoxidation controls CH4 emission completely. TheCH4 mixing ratio was low in the acrotelm, but itincreased within the catotelm. Comparing fluxesmeasured in static chambers with fluxes calculatedfrom the porewater CH4 profiles it was deducedthat the zone of methane oxidation was located closeto the water table. In hollows, CH4 production at in situtemperature was far higher than emission into theatmosphere, corresponding to an oxidation rate ofnearly 99%. The CH4 flux between the catotelmand the acrotelm of hollows was also higher than theemission, indicating the importance of CH4oxidation in the aerobic acrotelm, too. CH4microprofiles showed that CH4 oxidation inmud-bottom hollows was confined to the topmost 2 mm,and that in Sphagnum-covered hollows CH4oxidation occurred at the lower edge of green Sphagnum-parts.