Stable Sulfur Isotopes in Forest Spring Waters from the Fichtelgebirge (Germany)

Abstract

The potential role of processes discriminating S isotopes, for example dissimilatory SO₄ ^2- reduction and mineralization, in determining SO₄ ^2- concentrations was studied in forest spring water. S-isotope composition of sulfate from atmospheric input and forest springs representing a wide range of SO₄ ^2- concentrations was investigated in the Fichtelgebirge (NE Bavaria, Germany). δ³⁴ S values in atmospheric input ranged from +3.7 to - 5.7‰. In spring waters with SO₄ ^2- > 150 μmol 1⁻¹ δ³⁴ S values were between +4 and -5‰. whereas δ³⁴ S values increased up to +7.2‰ below 150 μmol 1⁻¹ SO₄ ^2-. SO₄ ^2- mineralization seemed to have no effect on isotopic composition since all δ³⁴ S values of spring water were higher than input values. Dissimilatory SO₄ ^2- reduction occurred in springs with SO₄ ^2- < 150 μmol1⁻¹. Spatial heterogeneity in forest soils or flow paths has to be invoked to explain increased δ³⁴ S values since NO₃ - concentrations would not allow for SO₄ ^2- reduction to occur.

Key Words:

• Forest hydrochemistry
• natural variations
• spring waters
• sulfate reduction
• sulfur 34