summary and conclusions：总结和结论..pdf

8 Don Monteith & Chris Evans n Atmospheric deposition and the impact on UKAWMN sites (1988-1998) The ultimate aim of emissions reduction policy is to achieve improvements in target environments damaged by the effects of atmospheric deposition. Emission reductions on a national and international level have resulted in a major decline in SO 2 concentration and S deposition in urban and rural areas in central and south England. However, the target environments of concern for the UKAWMN are the acidified freshwaters which are mostly located in more remote parts of the UK. In order to test whether these ecosystems have benefited from implemented policy, a series of functional links, from emissions reduction, through deposition reduction, to the recovery of water chemistry and finally aquatic biota, must be demonstrated. Each link has been discussed in the course of this report, and is summarised below. Have reductions in anthropogenic emissions led to a reduction in acid deposition in the UK over the past decade? Undoubtedly yes. Over the period 1986-1997, sulphur emissions reductions of 55% have almost been matched by a 50% reduction in sulphur deposition for the UK as a whole. However, smaller declines in emissions of NO x are not reflected in deposition trends. In some remote regions NO 3 deposition appears to have increased slightly. Do we observe reductions in sulphur deposition in the regions with acid sensitive freshwaters? Nationally, there has been a disproportionate decline in dry, relative to wet, deposition. Substantial reductions in both wet and dry xSO 4 and H + concentrations have occurred at sites within 100 km of major emissions sources, and particularly those in the east Midlands and Yorkshire. This has had a major effect in the Pennines area where freshwaters are believed to be some of the most impacted in the entire UK. Sensitive areas at intermediate distances from sources, including mid-Wales and the Lake District have experienced smaller, bu