An investigation of base cation deposition in Finland

The deposition of the base cations Na+, K+, Ca2+ and Mg2+ in 1998 was estimated for Finland using measurement data for precipitation and air quality. The highest deposition for all compounds was measured near the southern coast, and it decreased gradually northwards. Deposition of sodium and magnesium increased again in the far north in the vicinity of the Arctic Ocean. The estimated ranges for the annual deposition of sodium, magnesium, potassium and calcium in Finland were 90–610 mg m–2, 10–80 mg m–2, 30–160 mg m–2 and 30–210 mg m–2, respectively. Similar values have been published for large areas of Sweden and Norway. During the last decade the sum of the base cation concentration in bulk precipitation decreased by 15%–35% in all areas in Finland. The non-sea-salt fraction declined in bulk precipitation approximately as much. An especially large reduction occurred in the southeastern part of Finland, where the wet deposition of base cations decreased almost as much as the wet deposition of sulphur.