Data

The national critical loads data sets are available free of charge under a standard CEH data licence agreement. 
Full details on the methods and data used for mapping the broad habitats and for the calculation of critical loads and their exceedances in the UK can be found in the 2015 UK Status Report.  Maps of the data can be found here.

The last major update to the acidity critical loads database was made in 2004, with further minor updates made in 2008 and 2009.  Empirical critical loads of nutrient nitrogen, applied to UK natural and semi-natural habitats, were updated in March 2011.  Mass balance nitrogen critical loads for managed (productive) forest ecosystems remain unchanged from the 2004 calculations.

For acidity or nitrogen deposition (CBED) data please follow this link.

The critical loads data are available in two different formats:

• MS Access database
• ArcGIS grid export files (.e00 format)

To obtain the data in either format please email us specifying the format you require, a brief outline of what you intend to use the data for, and your full address.  We will then send you a licence agreement to sign and upon receipt of this (digital scanned copy is fine) we will make the data available to you using a “File Catalyst” system.
Please read the use and interpretation of maps and data before using these data.
The critical loads of acidity for soils are based on the mineralogy and weathering rate of the dominant soil type in each 1x1 km grid square, with the exception of squares dominated by peat soils where a different method is applied.  Where squares are dominated by peat soils and arable land, they are considered to be less sensitive to acidification and the critical load is set to 4.0 keq ha^-1 year^-1.
In addition, critical loads of acidity (CLmaxS, CLminN, CLmaxN) and of nutrient nitrogen (CLnutN), together with the habitat areas to which they apply, are available for the habitats listed in the table below:

(1) Unmanaged woodland is mapped in four separate classes for nutrient nitrogen: acidophilous oak-dominated woodland (oak), beech woodland (fgw), Scots pine woodland (spw), other areas of unmanaged woodland (umw), ie, areas of unmanaged woodland not included in the other three classes.
(2) For acidity all unmanaged woodland is treated the same and included within the “cdw” unmanaged woodland data set.
(3) Acidity critical loads have only been calculated for 1752 selected freshwater sites across the UK; the data cannot be extrapolated to apply to other areas.  Critical loads of nutrient nitrogen have not been applied to these sites.

It should be noted that the terrestrial habitat area data are based on the habitat distribution maps generated for UK critical loads (acidity, nitrogen) research and (a) only include areas where data exist for the calculation or derivation of critical loads; (b) may differ from other national habitat distribution maps or estimates of habitat areas.

There are some differences in the area of habitats mapped for acidity and for nutrient nitrogen as the distributions are restricted to areas for which data exist to calculate critical loads nationally for each habitat type.  Please refer to the UK Status Reports for further information