Blog: Mineral Soils: A Future Methane Sink? Scientific Evidence and Policy Considerations

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By Katie Lim. 21st June 2011.

Methane is a potent greenhouse gas with rising emissions attributed to anthropogenic activity. Whilst current mitigation policies focus primarily on decreasing emissions, the implications of climate change on current methane sinks are largely ignored. This article examines the potential consequences of increased precipitation caused by climate change on methane production in mineral soils within the UK, and the adaption measures which should be considered in the future.

Mineral Soils as Methane Sinks

Soils are vital as they are the sole methane sink potentially managed or manipulated by man. The methane flux emitted from a soil is a delicate balance of the simultaneously occurring production and oxidation processes occurring within. In most soils, the high-affinity methanotrophic bacteria controlling methane oxidation exist in abundance concurrent with negligible internal production. Hence, mineral soils are generally classed as sinks for budget calculations, as any methane produced may be oxidized in situ before reaching the atmosphere.

Future UK Climate and Impacts of Methane Production

Progressive climatic changes are predicted to impact the UK. The UK Climate Projections (UKCP09) describe probabilistic projections of future changes in climate in the UK over the 21st century based on observed trends and climate models, with the intention to provide a basis for impact studies and adaption measures. Observed data indicates that although the annual mean precipitation has not significantly changed since 1766, it is evident nevertheless that the rainfall pattern is changing. On average, precipitation has increased in winter and decreased in summer, in addition to heavy precipitation events becoming much more frequent [1].

Frequent or seasonal water saturation promotes anoxic conditions in the soil, which favours conditions for microbially-mediated methanogenesis. Mineral soils undergoing such water saturation have even been shown to act as a net source of methane [2]. 43% of UK soils have impeded drainage and consequently the predicted rise in heavy precipitation events may induce an increase in methane production or potentially change the capability of such UK soils to act as a methane source rather than a sink.

Current Policies and Implications for Adaption Measures

Methane is one of the six greenhouse gases targeted in the Kyoto Protocol [3], which requires that collective greenhouse gas emissions within the EU must be reduced 8% below 1990 levels by 2012. The EU has further committed to reducing emissions by 2020 by 20% [4]; moreover the UK has set an additional target of 80% below 1990 baseline by 2080 [5]. In an effort to both mitigate emissions and consider future climate impacts, the European Commission published a White Paper [6] in 2009 presenting the framework for adaptation measures. Among its aims was a commitment to improve knowledge and availability of potential climatic effects, and to consider such plausible adaptation measures in relevant policies. The scientific evidence suggesting that anthropogenic climate change does not solely impact methane sources argues that future challenges lie in predicting other potential indirect consequences, of which increased knowledge are required. Furthermore adaptation policies should not only account for reducing greenhouse gas emissions, but also consider other relevant implications with future climatic change including the subsequent effects of climate change on methane sinks.

Our research focuses on investigating the microbial influences on methane flux in such water-saturated mineral soils using a combination of novel biomolecular proxies and stable isotope probing methods. For more information on this and other projects being carried out in the Organic Geochemistry Unit please see http://www.chm.bris.ac.uk/ogu/ or contact k.lim@bristol.ac.uk.


References

[1] Jenkins, G. J., et al, 2009, UK Climate Projections: Briefing report. Met Office Hadley Centre, Exeter, UK. [2] Teh, Y. A., et al, 2005, Global Change Biology 11 (8), 1283-1297. [3] http://unfccc.int/resource/docs/convkp/kpeng.pdf [4] http://ec.europa.eu/clima/news/index_en.htm [5] http://www.legislation.gov.uk/ukpga/2008/27/contents [6] European Commission, 2009, White paper – Adapting to climate change: towards a European framework for action, Brussels.

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