Methane and carbon dioxide fluxes from open and blocked ditches in a blanket bog

Abstract

Background and aims: There is growing interest in how the rewetting of drained peatlands can restart their carbon (C) sink function. However, there are few studies on the effect of ditch blocking on the within-ditch C balance. For a UK blanket bog we assessed how methane (CH 4 ) emissions, net ecosystem exchange (NEE), and the overall greenhouse gas (GHG) balance expressed as carbon dioxide equivalents (CO 2 -e) responded to ditch blocking. Methods: We conducted a fully replicated field trial on a blanket bog in the Upper Conwy catchment, North Wales, UK. Twelve parallel ditches, that ran approximately downslope, were investigated. Four were left open, four had peat dams installed at intervals of a few metres along their length, and four were partially infilled with peat (reprofiled) and dammed. For a period of four years after blocking, we measured peatland-atmosphere fluxes of CH 4 and CO 2 within the ditches. Results: CH 4 fluxes, NEE and overall GHG balance (expressed in terms of CO 2 -e) in the experimental area showed no evidence of varying systematically between the different types of ditch treatment (open, dammed, and reprofiled). In addition, there was little evidence that CH 4 fluxes or CO 2 -e balance changed systematically with time since blocking. Conclusions: We found no evidence of consistent differences between blocking treatments in terms of CH 4 emissions or overall CO 2 -e balance. There was high spatial and temporal variability in CO 2 and CH 4 fluxes within each treatment. We did not observe a post-blocking ‘spike’ in CH 4 fluxes.