Nitrogen emission and deposition: the European perspective.

Europe has been successful in reducing the emissions of several nitrogenous pollutants over recent decades. This is reflected in concentrations and deposition rates that have decreased for several components. Emissions of nitrogen containing gases are estimated to have decreased in Europe by 10%, 21%, and 14% for NO, NOx, and NH3, respectively, between 1990 and 1998. The main reductions are the result of a decrease in industrial and agricultural activities in the east of Europe as a result of the economic situation, measures in the transport sector, industry and agricultural sector, with only a small part of the reduction due to specific measures designed to reduce emissions. The reduction is significant, but far from the end goal for large areas in Europe in relation to different environmental problems. The Gothenburg Protocol will lead to reductions of 50 and 12% in 2010 relative to 1990 for NOx and NH3, respectively. The N2O emissions are expected to grow between 1998 and 2010 by 9%. Further reductions are necessary to reach critical limits for ecosystem protection, air quality standards and climate change. Emissions of nitrogen compounds result from an overload of reactive nitrogen, which is produced by combustion processes, by synthesis of ammonia or by import from other areas as concentrated animal feeds. Although some improvements can be made by improving the efficiency of combustion processes and agricultural systems, measures to reduce emissions substantially need to be focused on decreasing the production or import of reactive N. Reactive N ceilings for regions based on critical limits for all N-related effects can help to focus such measures. An integrated approach might have advantages over the pollutant specific approach to combat nitrogen pollution. This could provide the future direction for European policy to reduce the impacts of excess nitrogen.

Sulphur and seasalt deposition as reflected by throughfall and runoff chemistry in forested catchments.

At forested catchments at Lake Gårdsjön on the Swedish west coast the deposition and runoff chemistry has been followed during the period 1979-1990 by throughfall and runoff measurements as well as by measurements of atmospheric concentrations. The 10-year means in throughfall and runoff are very similar for sulphur and the main seasalt ions sodium and chloride; for sulphur 26.1 and 27.6 kg ha(-1) yr(-1), for sodium 49 and 52 kg ha(-1) yr(-1) and for chloride 96 kg ha(-1) yr(-1) and 93 kg ha(-1) yr(-1), respectively. The actual flows are 100-200% higher than the wet deposition as collected in open bulk precipitation collectors indicating a very large input by dry deposition. One important question is to what extent the throughfall and runoff values can be used as measures of total deposition. We present results from studies at different experimental catchments illustrating the possibilities of using throughfall and runoff data as measures of atmospheric deposition of sulphur and seasalt.