Methane emissions variability from a Welsh patterned raised bog

Abstract

This work investigated the variability of CH4 emissions from a Welsh raised bog Cors Fochno and evaluated the role of ebullition as a mechanism of CH4 flux to the atmosphere. Between 31st March 2008 and 20th March 2009, CH4 fluxes were measured weekly/biweekly from four microform-types - mud-bottomed hollow, hummock, sedge lawn and Sphagnum lawn. CH4 fluxes (measured using flux-chambers) ranged from -8.9 190.1 mg m-2 d-1 (n = 505). The abundance of two key species Rhynchospora alba and Sphagnum moss - was most relevant for describing spatial variation in annual CH4 emissions (best fit model r2 = 0.68, p < 0.001). A combination of air temperature, rainfall, barometric pressure and solar radiation variables produced the best fit model of temporal variation of CH4 flux (r2 = 0.29, p < 0.001). Winter emissions represented 9.4% of the annual CH4 budget of the peat dome. CH4 ebullition fluxes to 28 funnel-traps were measured weekly between 28th May and 12th September 2009. Daily averaged rates of CH4 ebullition ranged from -1.0 784.5 mg CH4 m-2 d-1 (n = 414). Based on assumed rates of methanotrophic processing, CH4 ebullition flux to the water table was entirely consumed before reaching the atmosphere in only one week of the season. In the remaining 15 weeks it was estimated that between 5% and 81% of CH4 ebullition would have escaped to the atmosphere. Ebullition was shown to be an important transport mechanism of CH4 flux from Cors Fochno during the season, accounting for an estimated 7 - 36% of CH4 emissions. Large changes in barometric pressure appeared to be important drivers of ebullition in some microforms. However, air temperature was the most widely-important predictor of temporal variation of ebullition fluxes during the season and during two low pressure events.