Sulfur isotope dynamics in two Central European watersheds affected by high atmospheric deposition of SOx

M. Novak et al., Sulfur isotope dynamics in two Central European watersheds affected by high atmospheric deposition of SOx, GEOCH COS A, 64(3), 2000, pp. 367-383
Citations number
Categorie Soggetti
Earth Sciences
Journal title
ISSN journal
0016-7037 → ACNP
Year of publication
367 - 383
SICI code
Sulfur fluxes and delta(34)S values were determined in two acidified small watersheds located near the Czech-German border, Central Europe. Sulfur of sulfate aerosol in the broader region (mean delta(34)S of 7.5 parts per tho usand CDT) was isotopically heavier than sulfur of airborne SO2 (mean delta (34)S Of 4.7 parts per thousand). The annual atmospheric S deposition to th e Jezeri watershed decreased markedly in 1993, 1994, and 1995 (40, 33, and 29 kg/ ha.yr), reflecting reductions in industrial S emissions. Sulfur expo rt from Jezeri via surface discharge was twice atmospheric inputs, and incr eased from 52 to 58 to 85 kg/ha.yr over the same three-year period. The del ta(34)S value of Jezeri streamflow was 4.5 +/- 0.3 parts per thousand, inte rmediate between the average atmospheric deposition (5.4 +/- 0.2 parts per thousand) and soil S (4.0 +/- 0.5 parts per thousand, suggesting that the e xcess sulfate in runoff comes from release of S from the soil. Bedrock is n ot a plausible source of the excess S, because its S concentration is very low (<0.003 wt.%) and because its delta(34)S value is too high (5.8 parts p er thousand) to be consistent with the delta(34)S of runoff. A sulfur isoto pe mixing model indicated that release of soil S accounted for 64 +/- 33% o f sulfate S in Jezeri discharge. Approximately 30% of total sulfate S in th e discharge were organically cycled. At Nacetin, the same sequence of delta (34)S(IN) > delta(34)S(OUT) > delta(34)S(SOIL) was observed. The seasonalit y found in atmospheric input (higher delta(34)S in summer, lower delta(34)S in winter) was preserved in shallow (<10 cm) soil water, but not in deeper soil water. delta(34)S values of deeper (> 10 cm) soil water (4.8 +/- 0.2 parts per thousand) were intermediate between those of atmospheric input (5 .9 +/- 0.3 parts per thousand) and Nacetin soils (2.4 +/- 0.1 parts per tho usand), again suggesting that remobilization of soil S accounts for a signi ficant fraction (roughly 40 +/- 10%) of the S in soil water at Nacetin. The inventories of soil S at both of these sites are legacies of more intense atmospheric pollution during previous decades, and are large enough (740 an d 1500 kg S/ha at Jezeri and Nacetin, respectively) to supply significant s ulfur fluxes to runoff for several more decades. The ongoing release of thi s stored soil S may significantly delay the recovery of water quality under declining atmospheric S deposition. Analysis of possible scenarios that wo uld result in different S isotope composition of rainfall, runoff and soil suggested that biologic S isotope fractionation must be involved. Mineraliz ation of organic soil S was recorded in two opposite but complementary vert ical isotope trends: while soil water had lower delta(34)S values in deeper horizons, bulk soil had higher delta(34)S values in deeper horizons. Copyr ight (C) 2000 Elsevier Science Ltd.