The Badlands of Britain

The uplands of northwest England are dominated by the presence of blanket peat deposits, forming due to the accumulation of organic matter over time (Bragg and Tallis, 2001). British blanket peat accounts for approximately 15% of the global total blanket peat (Evans and Lindsay, 2010). The peatlands of the South Pennines are considered to be extensively degraded and have been referred to as "the badlands of Britain" (Tallis, 1997).

This degradation occurs in the form of extensive gully networks, incising deep into the peat surface (Evans et al., 2006). Evans et al. (2006) calculated that sediment lost from some South Pennine catchments via gullying was as much as 267 tonnes per kilometre2 per year (t km-2 a-1). This released sediment is being carried via gullies to reservoirs and water courses.

It is thought that changes in the vegetation cover of blanket mires have led to the initiation of gullying (Yeloff et al., 2005). These changes can come in the form of vegetation removal or subtle changes in species distribution.

With the South Pennines being situated directly between two major cities in the Industrial Revolution (Manchester and Sheffield), It is thought that these vegetation changes are the result of heavy metal pollution emanating from chimney stacks, metal smelting and more recently, auto-mobile emissions (Rothwell et al., 2007). It is thought that vegetation on blanket mires is particularly susceptible to lead pollution.

Over grazing in these areas can cause trampling of vegetation and the removal via feeding of excessive livestock numbers (Smith et al., 2007), which could lead to gullying. However, Smith et al. (2007) concede that present livestock density in the South Pennines are relatively low and are not likely to cause a notable change in vegetation cover.

Peat is rich in organic matter and therefore carbon. Gullying and removal of the peat in the South Pennines has the potential for blanket mires to make the transition from carbon sink to carbon source. Once again it seems that there is another significant positive feedback loop in the climate change model.

Note: Maybe I should rename this blog Feedback loops in Atmospheric Carbon!

See also this brilliant blog and resource: www.peatbog.org

  References

Bragg, O.M., Tallis, J.H., 2001. The sensitivity of peat-covered upland landscapes. Catena, Vol 42 p345-360.

Evans, M., Lindsay, J., 2010. High resolution quantification of gully erosion in upland peatlands at the landscape scale. Earth Surface Processes and Landforms, Vol 35 p876-886.

Evans, M., Warburton, J., Yang, J., 2006. Eroding blanket peat catchments: global and local implications of upland organic sediment budgets. Geomorphology, Vol 79 p45-57.

Rothwell, J.J., Evans, M.G., Allott, T.E.H., 2007b. Lead contamination of fluvial sediments in an eroding blanket peat catchment. Applied Geochemistry, Vol 22 p446-459.

Smith, R.S., Charman, D., Rushton, S.P., Sanderson, R.A., Simkin, J.M. and Shiel, R.S., 2007. Vegetation change in an ombrotrophic mire in northern England after excluding sheep. Applied Vegetation Science, Vol 6 p261-270.

Tallis, J.H., 1997. Peat erosion in the Pennines: the badlands of Britain. Biologist, Vol 44 p277-279.

Yeloff, D.E., Labadz, J.C, Hunt, C.O., Higgitt, L., Foster, I.D.L., 2005. Blanket peat erosion and sediment yield in an upland reservoir catchment in the southern Pennines, UK. Earth Surface Processes and Landforms, Vol 30 p717-733.

Land Degradation in Drylands

Drylands across the globe are dominated by the presence of biological soil crusts (Belnap and Lange, 2003). They form a surface layer consisting of an assemblage of cyanobacteria, lichens, fungi, algae sediment and organic matter (Belnap et al., 2003). Biological soil crusts are an important factor in stabilising soil in drylands from erosion where organic matter in soil is characteristically low. Cyanobacteria are particularly influential in the stabilising of the soil surface, their filament form entangles sediment grains, reducing the susceptibility of soil to the effects of wind erosion (Thomas and Dougill, 2007).

The notable "Dust Bowl" period that occurred across 1930s USA saw how poor land management resulted in elevated dust release to the atmosphere, reducing precipitation in a positive feedback mechanism (Worster, 1979). Land management is becoming increasingly significant in dryland systems as a means of stabilising sediments and reducing the risk of land degradation (Ravi et al., 2010). Despite this, in African countries such as Botswana, grazing intensities- and with it, soil crust destruction- are more dependent upon socio-economic factors rather than long term landscape stability.

Over-grazing of rangelands in African dryland areas directly causes vegetation change (Ravi et al., 2010). As the more palatable grasses are grazed at a rate greater than they can re-grow, woody shrub encroachment over the cleared grassland occurs (Eldridge et al., 2011). Field et al. (2011) found that enhanced levels of trampling from cattle can cause destruction of biological soil crusts, leaving loose soil vulnerable to removal by aeolian and fluvial processes.

  References

Belnap, J., Lange, O.L., 2003. Structure and functioning of biological soil crusts: a synthesis. In: Belnap, J., Lange, O.L. (Eds.), Biological Soil Crusts: Structure, Function and Management. Springer-Verlag, Berlin, pp. 471–479.

Belnap, J., Büdel, B., Lange, O.L., 2003. Biological soil crusts: characteristics and distribution. In: Belnap, J., Lange, O.L. (Eds.), Biological Soil Crusts: Structure, Function and Management. Springer-Verlag, Berlin, pp. 3–30.

Eldridge, D. J., Bowker, M. A., Maestre, F. T., Roger, E., Reynolds, J. F., Whitford, W. G., 2011. Impacts of shrub encroachment on ecosystem structure and functioning: towards a global synthesis. Ecology Letters. Vol 14 (p709-722).

Field, J. P., Breshears, D. D., Whicker, J. J., Zou, C. B., 2010. Interactive effects of grazing and burning on wind- and water- driven sediment fluxes: rangeland management implications. Ecological Applications. Vol X, (pX-X).

Ravi, S., Breshears, D. D., Huxman, T. E., D'Odorico, P., 2010. Land degradation in drylands: Interactions among hydrologic-aeolian erosion and vegetation dynamics. Geomorphology. Vol 116, (p236-245).

Thomas, A. D., Dougill, A. J., 2007. Spatial and temporal distribution of cyanobacterial soil crusts in the Kalahari: Implications for soil surface properties. Geomorphology. Vol 85, (p17-29).

Worster, D., 1979. Dust bowl: the Southern Plains of 1930s. Oxford University Press, New York.