Deposition and leaching of sulphate and base cations in a mixed boreal forest in eastern Finland

Monthly fluxes of sulphate (SO42-) and base cations (Ca2+, Mg2+, K+) were studied from 1993 to 1996 as precipitation passed through forest vegetation and surface soil layers in an area receiving low and declining levels of atmospheric sulphate pollution. The canopy was dominated by mature Norway spruce (Picea abies Karsten) and the soil was a podzol developed on glacial till material. The mean annual bulk deposition of SO42- collected in the open was 136 mol(c) ha(-1) and that of Ca2+, Mg2+ and K+ was 44, 11 and 25 mol(c) ha(-1), respectively. The annual total throughfall deposition of SO42- was 318 mol(c) ha(-1) and that of Ca2+, Mg2+ and K+ was 151, 64 and 181 mol(c) ha(-1), respectively. Sulphate was the dominant anion accompanying the base cations leached from the canopy. More than half (58%) of the annual total throughfall deposition of SO42- was retained by the O-horizon and only 15% leached from below the B-horizon. The annual leaching of Ca2+, Mg2+ and K+ from below the B-horizon was 14, 25 and 9% of the annual total throughfall deposition, respectively. The transport of base cations through the soil was predominantely countered by SO42- anions.