Acidification of the natural environment by anthropogenic sources of sulphur and nitrogen in many parts of Europe is well documented (Last & Watling 1991). In Britain at present point sources account for approximately 70% of the total load (RGAR 1990). Acidification leads to a number of adverse impacts on the nature conservation resources of Britain (Woodin & Farmer 1993, Farmer 1995) and it is important that emissions are reduced to a level which is sustainable (DoE 1994).

There has, however, been little attempt to quantify the relative contribution of different sources of sulphur to impacts on nature conservation. Such information would be particularly important in formulating national pollution reduction strategies and inform individual regulatory decisions. This report presents results from one approach to this problem. The nature conservation impact is assessed by reference to Sites of Special Scientific Interest (SSSIs). However, it is important to note that whilst these statutorily designation sites do contain the most important habitats and species of nature conservation importance in Britain, important conservation resources also occur in other areas. The analysis is based on assessments using the critical loads approach. The impact is quantified by an examination of sulphur deposition which is greater than the critical load for soils on each SSSI. The critical loads approach (Bull 1991, CLAG 1994) has been used extensively to define thresholds for effects and is a central component of the UK government’s policy development for controlling acid emissions (DoE 1991, DoE 1994). In this study exceedence of a critical load leading to soil acidification on an SSSI is considered to constitute an adverse impact on that site.