Evaluating effects of land management on greenhouse gas fluxes and carbon balances in boreo-temperate lowland peatland systems

Peatlands cover 2 to 5 percent of the global land area, while storing between 30 and 50 percent of all global soil carbon (C). Peatlands constitute a substantial sink of atmospheric carbon dioxide (CO2) via photosynthesis and organic matter accumulation, but also release methane (CH4), nitrous oxide (N2O), and CO2 through respiration, all of which are powerful greenhouse gases (GHGs). Lowland peats in boreo-temperate regions may store substantial amounts of C and are subject to disproportionately high land-use pressure. Whilst evidence on the impacts of different land management practices on C cycling and GHG fluxes in lowland peats does exist, these data have yet to be synthesised. Here we report on the results of a Collaboration for Environmental Evidence (CEE) systematic review of this evidence. Evidence was collated through searches of literature databases, search engines, and organisational websites using tested search strings. Screening was performed on titles, abstracts and full texts using established inclusion criteria for population, intervention/exposure, comparator, and outcome key elements. Remaining relevant full texts were critically appraised and data extracted according to pre-defined strategies. Meta-analysis was performed where sufficient data were reported. Over 26,000 articles were identified from searches, and screening of obtainable full texts resulted in the inclusion of 93 relevant articles (110 independent studies). Critical appraisal excluded 39 studies, leaving 71 to proceed to synthesis. Results indicate that drainage increases N2O emission and the ecosystem respiration of CO2, but decreases CH4 emission. Secondly, naturally drier peats release more N2O than wetter soils. Finally, restoration increases CH4 release. Insufficient studies reported C cycling, preventing quantitative synthesis. No significant effect was identified in meta-analyses of the impact of drainage and restoration on DOC concentration. Consistent patterns in C concentration and GHG release across the evidence-base may exist for certain land management practices: drainage increases N2O production and CO2 from respiration; drier peats release more N2O than wetter counterparts; and restoration increases CH4 emission. We identify several problems with the evidence-base; experimental design is often inconsistent between intervention and control samples, pseudoreplication is common, and variability measures are often unreported.