Assessing the role of artificially drained agricultural land for climate change mitigation in Ireland

• Published in: Environmental science & policy 2018-02, Vol.80, p.95-104
• Main Authors: Paul, Carsten, Fealy, Réamonn, Fenton, Owen, Lanigan, Gary, O’Sullivan, Lilian, Schulte, Rogier P.O.
• Format: Article
• Language: English
• Subjects: Greenhouse gas; Histosol; IWMS; LULUCF; Organic soil; Peatland
• ISSN: 1462-9011; 1873-6416
• DOI: 10.1016/j.envsci.2017.11.004

•IPCC Wetlands Supplement strongly increased default EF of drained organic soils.•This makes their rewetting more attractive as a climate change mitigation measure.•Drainage emissions and mitigation potential were analysed for Irish agriculture.•We calculated annual emissions from histic and humic soils as 8.7 and 1.8Tg CO2e.•Rewetting 50% of histic soils could generate annual GHG savings of 3.2Tg CO2e. In 2014 temperate zone emission factor revisions were published in the IPCC Wetlands Supplement. Default values for direct CO2 emissions of artificially drained organic soils were increased by a factor of 1.6 for cropland sites and by factors ranging from 14 to 24 for grassland sites. This highlights the role of drained organic soils as emission hotspots and makes their rewetting more attractive as climate change mitigation measures. Drainage emissions of humic soils are lower on a per hectare basis and not covered by IPCC default values. However, drainage of great areas can turn them into nationally relevant emission sources. National policy making that recognizes the importance of preserving organic and humic soils’ carbon stock requires data that is not readily available. Taking Ireland as a case study, this article demonstrates how a dataset of policy relevant information can be generated. Total area of histic and humic soils drained for agriculture, resulting greenhouse gas emissions and climate change mitigation potential were assessed. For emissions from histic soils, calculations were based on IPCC emission factors, for humic soils, a modified version of the ECOSSE model was used. Results indicated 370,000ha of histic and 426,000ha of humic soils under drained agricultural land use in Ireland (8% and 9% of total farmed area). Calculated annual drainage emissions were 8.7Tg CO2e from histic and 1.8Tg CO2e from humic soils (equal to 56% of Ireland’s agricultural emissions in 2014, excluding emissions from land use). If half the area of drained histic soils was rewetted, annual saving would amount to 3.2Tg CO2e. If on half of the deep drained, nutrient rich grasslands drainage spacing was decreased to control the average water table at −25cm or higher, annual savings would amount to 0.4Tg CO2e.