CRITICAL LOADS FOR NITROGEN DEPOSITION FOR GREAT-BRITAIN

There is currently much interest in mapping critical loads for nitroge n deposition as part of a strategy for controlling nitrogen emissions. While nitrogen deposition may cause acidification and excess nutrient effects, the former were considered previously in studies of sulphur deposition. In the UK, work on developing nutrient nitrogen critical l oads maps has used several methods and databases. Two approaches are d escribed here, one a steady state calculation using a nitrogen saturat ion limit for soil systems, the other an empirical estimate of critica l loads set to prevent changes to vegetation communities. The empirica l method uses national species records and land cover data derived fro m satellite imagery. Maps drawn from the available data are dependent upon a number of factors which reflect the approach used To apply the nutrient critical loads to a strategy for future abatement measures, t he nutrient nitrogen values for soils have been incorporated within a ''critical loads function'' which takes into account both acidity and nutrient effects as related to deposition loads for sulphur and nitrog en. This function may be used with deposition data to identify the nee d for sulphur and nitrogen emission reductions.