Units: keq ha-1 yr-1
Resolution: 1 km
Year: 2004
Data provided by: Centre for Ecology and Hydrology, Bangor
CLmaxS - Maximum critical load of sulphur
CLmaxS is the critical load for acidity assuming sulphur only contributes to acidification, ie when nitrogen deposition is zero. It is based upon the acidity critical load values but takes into account net base cation deposition to the soil system and base cation removal from the system:
CLmaxS = CL(A) + BCdep - BCu
- where CL(A) = critical load of acidity (empirical or SMB)
- BCdep = non-marine base cation deposition less non-marine chloride deposition
- BCu = base cation uptake by vegetation
CLminN - Minimum critical loads of nitrogen
CLminN is the deposition independent critical load of acidity solely due to nitrogen removal processes in the soil (nitrogen uptake and immobilisation):
CLminN = Nu + Ni
- where Nu = nitrogen uptake
- Ni = nitrogen immobilisation
CLmaxN - Maximum critical loads of nitrogen (CL max (N)) CLmaxN is the critical load of acidity assuming only nitrogen contributes to acidification, ie when sulphur deposition is zero. It is therefore equivalent to the CLmaxS but also allows for nitrogen removal processes.
CLmaxN is defined by CLminN and CLmaxS :
CLmaxN = CLminN + CLmaxS
More detailed information on these values can be found at the UK National Focal Centre critical loads website.
Additional Info:
Acidity critical loads for the non-woodland terrestrial ecosystems are based on the empirical map of critical loads of acidity for soils (Hornung et al., 1995; Hall et al., 1998; Hall et al., 2001, Hall et al, 2003). Critical loads were assigned to the dominant soil in each 1 km grid square of the UK. Critical loads for mineral soils are based on the soil mineralogy and chemistry, while the critical loads for peat soils are based on an updated method that sets the critical load to the amount of acid deposition that would give rise to an effective rain pH of 4.4 (Hall et al, 2003).
Critical loads for managed coniferous woodland, managed broadleaved woodland and unmanaged coniferous and broadleaved woodland are calculated using the Simple Mass Balance (SMB) equation. The equation is parameterised according to the appropriate critical chemical criteria and critical limits that will protect the receptor from the adverse effects of acidification; different chemical criteria are used for calculating critical loads for woodland on mineral soils and woodland on organic soils. It should also be noted that the "weathering rate" inputs to the SMB equation are derived from the empirical critical loads of acidity for soils described above, hence the SMB critical loads for woodlands also relate to the dominant soil type in each 1 km grid square. For areas of woodland in 1km grid squares dominated by peat soils, the above mentioned peat critical loads are applied, since the SMB is inappropriate for these soil types.
For further details on the calculation of critical loads and habitat mapping at the national scale, please refer to Hall et al (2003) and the UK National Focal Centre web site: http://critloads.ceh.ac.uk
References:
FC. 2001. National inventory of woodland and trees: England. Inventory Report. Forestry Commission, Edinburgh.
FC. 2002a. National inventory of woodland and trees: Scotland. Inventory Report. Forestry Commission, Edinburgh.
FC. 2002b. National inventory of woodland and trees: Wales. Inventory Report.
Fuller, R.M., Smith, G.M., Sanderson, J.M., Hill, R.A. & Thomson, A.G. 2002a. The UK Land Cover Map 2000: construction of a parcel-based vector map from satellite images. Cartographic Journal, 39, 15-25.
Fuller, R.M., Smith, G.M., Sanderson, J.M, Hill, R.A., Thomson, A.G., Cox, R., Brown, N.J. & Gerard, F.F. 2002b. Countryside Survey 2000 Module 7: Land Cover Map 2000. Final Report, CSLCM/Final. Unpublished CEH report to Defra.
Hall, J., Bull, K., Bradley, I., Curtis, C., Freer-Smith, P., Hornung, M., Howard, D., Langan, S., Loveland, P., Reynolds, B., Ullyett, J. and Warr, T. (1998) Status of UK Critical Loads and Exceedances (January 1998). Part 1: Critical Loads and Critical Loads Maps. Report to the Department of Environment, Transport and the Regions. DETR/NERC Contract EPG1/3/116. Available in online and downloadable versions from: http://critloads.ceh.ac.uk
Hall, J., Ullyett, J., Hornung, M., Kennedy, F., Reynolds, B., Curtis, C., Langan, S. and Fowler, D. (2001) Status of UK Critical Loads and Exceedances. Part 1: Critical Loads and Critical Loads Maps. Update to January 1998 report: February 2001. Report to Department for Environment, Food and Rural Affairs. DETR/NERC Contract EPG1/3/185. . Available in online and downloadable versions from: http://critloads.ceh.ac.uk
Hall, J., Ullyett, J., Heywood, E., Broughton, R., Fawehinmi, J. & 31 UK experts. (2003). Status of UK Critical Loads: Critical Loads Methods, Data & Maps. February 2003. Available in online and downloadable versions from: http://critloads.ceh.ac.uk
Hornung, M., Bull, K.R., Cresser, M., Hall, J., Langan, S., Loveland, P. and Smith, C. (1995) An empirical map of critical loads of acidity for soils in Great Britain. Environmental Pollution 90, 301-310.