Isotope Systematics of Sulfate-oxygen and Sulfate-sulfur in Six European Peatlands

Abstract

Oxygen (O) and sulfur (S) isotope systematics in bog water sulfates were determined for six Sphagnum dominated wetlands located in the British Isles and the Czech Republic, Central Europe. Comparison of a polluted and unpolluted site showed that 4 times higher atmospheric S inputs led to 3 times higher bog water sulfate concentrations and substrate S concentrations, 3 times increased ranges of substrate S concentrations, and 3 times increased ranges of d 34 S values. Sites with elevated atmospheric S inputs exhibited greater geochemical variability in wetland S species. Sulfate O-S isotope composition of bog pore water at a depth of 40 cm below surface differed from that of surface bog water, indicating that dissimilatory bacterial sulfate reduction, a process known to discriminate against the heavier isotopes 18 O and 34 S, occurred in surface peat layers. While bacterial sulfate reduction remained to be one of the main isotope-selective processes for sulfate in peat, it could not fully explain the O-S isotope systematics of peat waters. The 'residual' sulfate was not simultaneously enriched in the heavier isotopes 18 O and 34 S. Mixing of residual sulfate following bacterial sulfate reduction with the product of S 2À reoxidation, cleavage of esters, and isotope exchange reactions may have contributed to the decoupling of the d 34 S SO4 and d 18 O SO4 values. Large within-site differences in d 18 O SO4 and d 34 S SO4 (up to 13 and 15&, respectively) indicated little communication between the 0 and 40 cm peat depth at some sites. Extremely high d 18 O SO4 and d 34 S SO4 values found in several peat bog water samples from Connemara (Ireland), Thorne Moors (England) and Ocean (Czech Republic) were not seen in streams draining the wetlands. Direct runoff of atmogenic sulfate constituted a significant portion of the bog outflow. At the wetland scale, zones of dissimilatory bacterial sulfate reduction form pockets whose lateral hydrological fluxes are small.

Lithological controls on biological activity and groundwater chemistry in Quaternary sediments

“…Sulfate in rainfall in this area has υ 34 S of C4Ð7‰ (Novak et al, 2001) and υ 18 O of C11Ð4‰ (Novak et al, 2005). However, with a sulfate concentration of 8 mg/l in rain, inputs from this source will account for a maximum of 25% of the 74 mg/l sulfate in the groundwater, after concentration by evapotranspiration.…”

Atmospheric deposition and isotope biogeochemistry of zinc in ombrotrophic peat

“…Multiple isotopic fractionation during diagenetic or biogeochemical cycling has been proposed before for iron (Zhu et al, 2002), sulphur (Canfield and Teske, 1996) or nitrogen (Novák et al, 2005).…”

The effect of geochemical processes on groundwater in the Velenje coal basin, Slovenia: insights from mineralogy, trace elements and isotopes signatures

“…The stable carbon isotope composition of dissolved inorganic carbon (DIC) in groundwater (δ 13 C DIC ) is often dependent on vegetation and lithology. For example, groundwater in aquifers containing non-carbonated minerals typically has δ 13 C DIC values reflecting soil CO 2 . Chemical reactions in non-carbonate-bearing aquifers such as silicate hydrolysis and ionic exchange do not significantly shift δ 13 C DIC values.…”