One aspect of the carbon cycle that is poorly understood in the UK is the type (geological or biological), quantity and quality of carbon stored in the accumulation zones of upland slopes.
Knowledge is required to fill in gaps of the UK soil inventory and to assess potential carbon based greenhouse gas (e.g. CO2, CH4) inputs to the atmosphere. It is therefore important to improve our understanding of how carbon is stored in soils and sediments in the accumulation zones at the base of rapidly eroding upland slopes.
The research is being undertaken within the Ashes Hollow catchment of the Long Mynd, Shropshire. The Long Mynd is an area of outstanding natural beauty (AONB) and is characterised by steep slopes and valleys dominated by heathland.
The geology of the Ashes Hollow consists of Pre-Cambrian siltstone, sandstones and conglomerates. The soils are classified by the Soil Survey of England and Wales as the Withnell 2 series and are well-drained loamy soils over bedrock.
Analysis of soil depth on one slope studied within Ashes Hollow, suggests that soils are < 20 cm thick on the slope divide and > 1 m at the 'accumulation zone' at the base of the slope. Soil erosion is characterised by both debris flows and soil creep.
Building on work started in 2009–10, the rates of soil erosion and accumulation will be used to assess the movement and storage of organic carbon and nitrogen in these upland landscapes. Along with understanding the control of soil depth on carbon and nitrogen storage along transects of the slope, the research aims to provide information about the quality of carbon stored in the soils, particularly in the saturated accumulation zone.
The aims of the project are to determine erosion rates on:
During 2010 we have developed our capacity to use the radionuclide 137Cs as a tool for understanding erosion rates. The use of 137Cs as an environmental tracer to assess soil erosion has been made possible by its release during 1950s nuclear bomb testing and by the Chernybol disaster in 1986.
The second area of our work is determining soil carbon storage and carbon quality, especially in the soil accumulation areas at the foot of slopes. These are often quite moisture saturated. To assess carbon quality in the accumulation zones we will use 12/13C analysis, C:N ratios and thermal analysis of soil carbon. The latter technique will help determine the degree of decomposition and whether there is a geologic component to the soil carbon.