Accumulation of sulphur in and on Scots pine needles in the subarctic

Total S concentrations of Scots pine (Pinus sylvestris L.) needles studied in the Finnish subarctic (66-70 degrees N, 24-30 degrees E) in 1990/1992 ranged from 573 to 1153 mu g g(-1). Levels were found to be approximate to 900 mu g g(-1) (i.e. 1.3-1.8 times the 'normal' level of 500-700 mu g g(-1)) in areas where the long-term ambient SO2 concentration was approximate to 2--5 mu g m(-3), particulate SO42- approximate to 2 mu g m(-3) and total S deposition approximate to 0.5 g m(-2). A statistically significant increase in needle total S concentrations was found towards the east, i.e. towards the smelters of the Kola Peninsula in Russia, which emit SO2. The increase in needle total S concentrations to over 900 mu g g(-1) close to the Russian border is thought to result mainly from exposure to high short-term SO2 concentrations. The results also suggest that wintertime S deposition may have an impact on the needle total S content. It is suggested that the UNECE long-term critical level of 15 mu g SO2 m(-3) for forestry in boreal and high mountain climates in Europe is too high for the pine forests in the extreme north, where the proportion of dry-deposited S may be 60-80%.