Sulphur isotope characteristics of two North Bohemian forest catchments

Sulphate concentrations and delta(34)S ratios were monitored in bulk precipitation, spruce throughfall, and soil water (depth of 30 and 90 cm) at Cervena jama (CER) and Nacetin (NAC), two severely polluted sites in the Czech Republic, between December 1992 and September 1994. Throughfall [SO42-], UP to 80 mg L(-1) in winter and as low as 7 mg L(-1) in summer, was higher than [SO42-] in bulk precipitation (annual average 6 mg L(-1)). There was a distinct seasonality in S isotope abundances,with lower delta(34)S(BULK) in summer (+4 per mil CER, +6 per mil NAC) and lower delta(34)S(TF) in winter (+3 per mil CER, +4 per mil NAC). Wintertime delta(34)S(BULK) was around +8 per mil at CER and +10 per mil at NAC, summertime delta(34)S(TF) was close to +7 per mil at both sites. For only a 1-month period in spring, bulk precipitation S became isotopically lighter than throughfall S. Bulk precipitation data from CER were in good agreement with those from the nearby monitoring station Lesna (LES), typically differing by less than 10 mg L(-1) and 2 per mil in [SO42-] and delta(34)S, respectively. Suction lysimeters (soil depth of 30 and 90 cm) yielded higher sulphate concentrations and lower delta(34)S ratios compared to both bulk and throughfall precipitation. Little seasonality was observed in [SO42-] at 30 cm (around 40 mg L(-1)), at 90 cm [SO42-] was higher in winter (70 mg L(-1)) than in summer (45 mg L(-1)). delta(34)S at 90 cm was <+5 per mil in 1993 and up to +7.5 in 1994, lower in the first year and higher in the second year compared to the depth of 30 cm. Sulphur fluxes at CER and NAC are characterized by distinct isotope compositions and can therefore be used to trace I S pathways and transformations in the forest ecosystem.