Trends in sulfate, base cations and H super(+) concentrations in bulk precipitation and throughfall at integrated monitoring sites in Finland 1989-1995

• Published in: Water, air, and soil pollution Vol. 105; no. 1-2; pp. 353 - 363
• Main Authors: Ukonmaanaho, L, Starr, M, Ruoho-Airola, T
• Format: Journal Article
• Language: English
• Published: 01.07.1998
• Subjects: Finland
• ISSN: 0049-6979

Temporal trends in sulfate, base cation (Ca super(2+) + Mg super(2+) + K super(+)), and H super(+) ion concentrations in bulk precipitation and throughfall samples collected over a seven year period (1989-95) in four forested catchments in Finland are presented. The catchments are in remote locations and span the boreal zone (61-69 degree N). The stands represent old, undisturbed forests, and are composed of varying proportions of Scots pine, Norway spruce and deciduous species (mainly Betula spp.). Monthly SO sub(4) super(2-)-S and H super(+) ion concentrations in bulk precipitation averaged over the study period and catchments were: 18.7 mu mol L super(-1) and 32.3 mu mol L super(-1). The corresponding values for throughfall were: 37.4 mu mol L super(-1) and 32.4 mu mol L super(-1). Sulfate and H super(+) ion concentrations in bulk precipitation and throughfall both showed negative linear trends, which were significant (p < 0.05) for the three southernmost catchments. Concentrations and trend slope decreased northwards (e.g., bulk precipitation SO sub(4) super(2-)-S slope estimates: -1.6 to -1.0 mu mol L super(-1) yr super(-1)). The decline was greater for throughfall than for bulk precipitation, indicating a proportionally greater reduction in dry deposition than wet. The sum of base cation concentrations averaged 12.1 mu mol sub((+)) L super(-1) in bulk precipitation and 83.1 mu mol sub((+)) L super(-1) in throughfall. There were no significant trends in the sum of base cations (p > 0.05). It is concluded that the reported reduction in S emissions over the study period has resulted in a significant reduction in the acidity and SO sub(4) super(2-) concentration of bulk precipitation, and this reduction has been reflected in throughfall concentrations. The greatest reduction has taken place in the southern part of the country.