ECOSSE: Estimating Carbon in Organic Soils - Sequestration and Emissions: Final Report

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Executive Summary

Organic soils include deep peats, which are composed almost entirely of a deep layer of organic material, and organo-mineral soils, which have a thinner layer of organic material overlying mineral soil layers or rock. They are important soil types in Scotland and Wales.

New calculations undertaken as part of this project show that organic soils in Scotland and Wales contain 2735 Mt carbon and 196 Mt carbon respectively. These estimates omit the carbon content in the mineral soils and are greater than all the carbon held in surface vegetation in the UK (114 Mt carbon).

The data derived as part of this project, and other experiments on organic soils worldwide, have been used to develop a model for organic soils - ECOSSE. ECOSSE can simulate and predict greenhouse gas fluxes under various climatic and land use scenarios.

Rationale

  • Climate change is one of the most serious threats facing our planet, and is of concern at both UK and devolved administration levels. Accurate predictions for the effects of changes in climate and land use on GHG emissions are vital for informing land use policy.
  • Land use change and climate change can cause emissions of GHGs; for example, land use change on organic soils is estimated to be responsible for 15% of Scotland's total greenhouse gas emissions.
  • Organic soils are abundant in Scotland and Wales. They contain by far the majority of the soil carbon stocks in the UK - combined they contain 3000 Mt carbon. Stock estimates were particularly uncertain below 1 m depth and the project has reduced this uncertainty for the organic soils of Scotland and Wales.
  • When carbon is lost from organic soils (as carbon dioxide, the main greenhouse gas responsible for climate change) there are serious consequences for the emissions of greenhouse gases. In addition, methane (an even more potent greenhouse gas), can be emitted from wet organic soils.
  • Organic soils behave very differently from mineral soils. This is primarily due to the properties of organic matter and the conditions which favour the accumulation of plant debris. These soils are subject to significant land use changes and the carbon they contain can be affected by these changes.
  • Despite the importance of organic soils, prior to this project there were no models able to adequately simulate greenhouse gas emissions from the organic soils of Scotland and Wales.
  • In this project, a model - ECOSSE - was developed to predict the impacts of changes in land use and climate change on greenhouse gas emissions from organic soils. ECOSSE stands for Estimating Carbon in Organic Soils - Sequestration and Emissions.

Key Findings

  • New estimates have been derived for the amount of carbon stored in organic soils in Scotland and Wales. The data illustrate the huge pool of carbon in the organic soils of Scotland and Wales. Stock estimates have increased by over 30% for Scotland and 20% for Wales with the inclusion of organic material below 1 m depth and the improved estimates of bulk density.
  • Some uncertainty remains over soil C stocks and further validation is required to reduce this uncertainty. Remote sensing techniques may potentially be useful to update our knowledge of soil C stocks, particularly in the uplands of Scotland and Wales. It is important to have a reliable estimate for the carbon held in soils in order to be able to monitor and predict the consequences of global change on GHG emissions.
  • Measurements of greenhouse gases fluxes from organic soils (carbon dioxide, methane and nitrous oxide) at three sites in Scotland and Wales over the course of the project have provided invaluable data for developing the ECOSSE model, as well as revealing some of the key factors controlling greenhouse gas emissions at each site. New data suggests that emissions from soils will increase when X conditions apply
  • Experimental work, albeit on a very limited sample of three sites, has shown for the first time a statistically significant overall loss (13%) in carbon following 25 years of birch growth on heather moorland. Further investigation is merited.
  • New land use change matrices for Scotland and Wales for 1950s to 2000s have been derived. This has provided improved land use change information for modelling greenhouse gas ( GHG) emissions from land use change.
  • A resurvey of the Welsh Bronydd Mawr grassland experiment showed that carbon stocks in the brown earth soil were unaffected by 12 years of pasture de-intensification. The stock of carbon in standing litter and vegetation increased after liming stopped, even under continued grazing.
  • New evidence from this project suggests that changes in soil acidity have had a significant influence on the upland carbon cycle. The clearest effect appears to be the doubling of concentrations of dissolved organic carbon in runoff waters since the 1980s. Radiocarbon analysis shows this to be relatively new carbon

Practical Applications

  • A review of the effects of forest and woodland planting on the carbon pools and fluxes of upland organo-mineral soils under semi-natural/grazed vegetation has been undertaken. The overall conclusion (as assumed by UK carbon balance models) is that afforestation probably has little net effect on soil organic carbon stores in organo-mineral soils, but this statement is very uncertain. The review findings suggest that these soils are likely to be vulnerable to carbon losses during the tree establishment phase and through erosion losses during ground preparation. A second period of vulnerability may be associated with forest harvesting both through physical disturbance and accelerated leaching losses of dissolved organic carbon. The effect of current forestry best-practice at these vulnerable times has yet to be quantified.
  • Suggested guidance for management of new forests and woodlands include minimising ground disturbance, maintaining as much vegetation cover during establishment as possible and encouraging rapid re-vegetation after felling. Evidence from the National Soil Inventory in England and Wales, together with limited evidence from international studies suggests that broadleaved trees maybe more beneficial for soil carbon than conifers. This appears to contradict the results of experimental work undertaken as part of this project. Further research is required before guidance on species choice can be recommended.
  • Based on outputs achieved as part of this study an evidence base is provided for the development of guidance on the management of organic soils in Scotland and Wales. Modelled estimates of the consequences of different land management practices will help to choose those management practices that protect organic soils and reduce GHG emissions from organic soils. For example having the ability to predict the effecting of liming and increased stock densities can be useful for decision making

The legacy of ECOSSE

  • The funding for this project from the Scottish Executive and the National Assembly for Wales has enabled the development of a model that can simulate and predict GHG emissions from organic soils.
  • The project has generated interest from researchers internationally who intend to use the ECOSSE model for application to organic soils outside the UK.
  • The UK Meteorological Office (Hadley Centre) and the Natural Environment Research Council ( NERC) QUEST programme have recognised the necessity for the ECOSSE model and the importance of GHG emissions from organic soils. Outputs from this project are already being used to understand better the role of organic soils in the global carbon cycle within those ongoing programmes.
  • The ECOSSE model will form a central plank in assessing GHG emissions from soils in future UK, Scottish and Welsh inventories. Funding has been secured to develop ECOSSE further for use in future GHG inventories, which are reported to the United Nations under the Framework Convention on Climate Change for the UK.