UK land-use change and its impact on SOC: 1925-2007

[1] The contribution of soil organic carbon (SOC) to atmospheric greenhouse gas (GHG) concentrations could increase due to rising temperatures, agricultural land-management, and land-use change. Here the results of a modeling study are presented, which reviews the changing patterns of UK land-use from 1925 to 2007, and estimates the contribution that these changes have had toward UK GHG emissions. The study uses a large database of SOC concentrations from which SOC stocks are estimated for land-uses typical of the UK, and combines this with literature values of transition times for SOC to adjust to a new concentration following land-use change. The model was designed to be used with limited input data, allowing the impacts of historical land-use change, lacking in site specific soil and vegetation change data to be assessed. This study suggests that from 1925 to 2007 the UK's soils have acted as a net carbon sink as a result of land-use change, sequestering a total of 102 Tg C. This represents a 5% net gain in total SOC stocks, and an average increase of 1.9 Tg C/year (inter-quartile range: 0.19–3.12 Tg C/yr). When the reported losses of SOC due to climate change are compared to the gains resulting from land-use change the UK's soils are a sink of carbon, with the gains from land-use change offsetting those due to climate change. This overall sink is the result of an increase in the area of woodland, and conversion of arable land to permanent grassland. The greatest sequestration in any one year occurred in 1993 and coincides with the introduction of set-aside. The largest SOC flux to the atmosphere occurred in 1942 following arable expansion, emitting 12.3 Tg C in one year. This flux is equivalent to almost 10% of the UK's current total GHG emissions, indicating that such land-use change should be avoided in the future if targets to reduce GHG emissions are to be met.