title: Management effects on greenhouse gas dynamics in fen ditches.
abstract: Globally, large areas of peatland have been drained through the digging of ditches, generally to increase agricultural production. By lowering the water table it is often assumed that drainage reduces landscape-scale emissions of methane (CH4) into the atmosphere to negligible levels. However, drainage ditches themselves are known to be sources of CH4and other greenhouse gases (GHGs), but emissions data are scarce, particularly for carbon dioxide (CO2) and nitrous oxide (N2O), and show high spatial and temporal variability. Here, we report dissolved GHGs and diffusive fluxes of CH4and CO2from ditches at three UK lowland fens under different management; semi-natural fen, cropland, and cropland restored to low-intensity grassland. Ditches at all three fens emitted GHGs to the atmosphere, but both fluxes and dissolved GHGs showed extensive variation both seasonally and within-site. CH4fluxes were particularly large, with medians peaking at all three sites in August at 120-230mgm-2d-1. Significant between site differences were detected between the cropland and the other two sites for CO2flux and all three dissolved GHGs, suggesting that intensive agriculture has major effects on ditch biogeochemistry. Multiple regression models using environmental and water chemistry data were able to explain 29-59% of observed variation in dissolved GHGs. Annual CH4fluxes from the ditches were 37.8, 18.3 and 27.2gCH4m-2yr-1for the semi-natural, grassland and cropland, and annual CO2fluxes were similar (1100 to 1440gCO2m-2yr-1) among sites. We suggest that fen ditches are important contributors to landscape-scale GHG emissions, particularly for CH4. Ditch emissions should be included in GHG budgets of human modified fens, particularly where drainage has removed the original terrestrial CH4source, e.g. agricultural peatlands.
authors.affiliation: School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom. Electronic address: michael.peacock@open.ac.uk.
authors.forename: Mike
authors.initials: M
authors.lastname: Peacock
authors.affiliation: School of Environment, Natural Resources and Geography, Bangor University, Bangor, Gwynedd, LL57 2UW, United Kingdom; School of Geographical Sciences, Bristol University, Bristol, BS8 1SS, United Kingdom.
authors.forename: Luke M
authors.initials: LM
authors.lastname: Ridley
authors.affiliation: Centre for Ecology and Hydrology, Bangor, Gwynedd, LL57 2UW, United Kingdom.
authors.forename: Chris D
authors.initials: CD
authors.lastname: Evans
authors.affiliation: School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom.
authors.forename: Vincent
authors.initials: V
authors.lastname: Gauci
keywords: Carbon dioxide; Ditch flux; Methane; Nitrous oxide; Peatland; Restoration