Trends in Sulfate, Base Cations and H+ Concentrations in Bulk Precipitation and Throughfall at Integrated Monitoring Sites in Finland 1989-1995

Author： Ukonmaanaho L.

Publisher： Springer Publishing Company

ISSN： 0049-6979

Source： Water, Air, and Soil Pollution, Vol.105, Iss.1-2, 1998-07, pp. : 353-363

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Abstract

Temporal trends in sulfate, base cation (Ca2+ + Mg2+ + K+), and H+ 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 °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 $$SO_4^{2-}$$ and H+ ion concentrations in bulk precipitation averaged over the study period and catchments were: 18.7 µmol L-1 and 32.3 µmol L-1. The corresponding values for throughfall were: 37.4 µmol L-1 and 32.4 µmol L-1. Sulfate and H+ 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="" $$so_4^{2-}$$="" slope="" estimates:="" -1.6="" to="" -1.0="" µmol="" l-1="" yr-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="" µmol(+)="" l-1="" in="" bulk="" precipitation="" and="" 83.1="" µmol(+)="" l-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 $$SO_4^{2-}$$ concentration of bulk precipitation, and this reduction has has been reflected in throughfall concentrations. The greatest reduction has taken place in the southern part of the country.