IngentaConnect The humus layer determines SO42 isotope values in the mineral soi...

Abstract:

Biocycling of sulfur (S) has been proposed to play an important role in the recovery of ecosystems following anthropogenic S deposition. Here, we investigated the importance of the humus layer in the biocycling of S in three forested catchments in the Gårdsjön area of southwestern Sweden with differing S inputs and S isotope signature values. These experimental sites consisted of two reference catchments and the Gårdsjön roof experiment catchment (G1), where anthropogenic deposition was intercepted from 1991 until May 2002 by a roof placed over the entire catchment area. Under the roof, controlled levels of deposition were applied, using a sprinkler system, and the only form of S added was marine SO₄^2- with a delta

$${}ˆ{34}\hbox{S}_{\rm {S0}_4} $$ of +19.5 permil

We installed ion exchange resin bags at the interface between the humus layer and mineral soil at each of the catchments to collect SO₄^2- passing through the humus. The resin bags were installed on four occasions, in 1999 and 2000, covering two summer and two winter periods. The ions collected by each bag during these sampling periods were then eluted and their delta

$${}ˆ{34}\hbox{S}_{\rm {S0}_4} $$ values and SO₄^2- concentrations determined. The most striking result is that the average delta

$${}ˆ{34}\hbox{S}_{\rm {S0}_4} $$ value in the resin bags was more than 12 permil

lower compared to that of the sprinkler water in the G1 roof catchment. There was no increasing trend in the isotope value in the resin bag SO₄^2- despite that the roof treatment has been on-going for almost 10 years; the average value for all resin bags was +7.1 permil

. The highest delta

$${}ˆ{34}\hbox{S}_{\rm {S0}_4} $$ values found in the G1 roof catchment were between +11 permil

and +12

. However, these values were all obtained from resin bags installed at a single sampling location. Throughfall and resin bag delta

$${}ˆ{34}\hbox{S}_{\rm {S0}_4} $$ values were more similar in the two reference catchments: about +7.5 permil

in both cases. There was, however, an increase in resin bag delta

$${}ˆ{34}\hbox{S}_{\rm {S0}_4} $$ values during the first winter period, from about +7 permil

to +9

. The resin bag delta

$${}ˆ{34}\hbox{S}_{\rm {S0}_4} $$ value was linearly and positively related (r² = 0.26, p < 0.001) to the amount of SO₄^2- extracted from the resin bags, if relatively high amounts (>50 mmol m^-2) were excluded. High amounts of resin bag SO₄^2- seemed to be related to groundwater inputs, as indicated by the delta

$${}ˆ{34}\hbox{S}_{\rm {S0}_4} $$ value. Our results suggest that rapid immobilization of SO₄^2- into a large organic S pool may alter the S isotope value and affect the delta

$${}ˆ{34}\hbox{S}_{\rm {S0}_4} $$ values measured in the mineral soil and runoff.

Keywords: delta 34S; Anion exchange resin bags; Humus layer; Roof experiment; SO42-; Stable isotopes

Document Type: Research article

DOI: 10.1007/s10533-004-0080-7

Affiliations: 1: Department of Forest Ecology, Swedish University of Agricultural Sciences, S-901 83, Umeå, Sweden, Email: reiner.giesler@sek.slu.se 2: Department of Geology and Geochemistry, Stockholm University, S-106 91, Stockholm, Sweden,

The humus layer determines SO42- isotope values in the mineral soil

The humus layer determines SO₄^2- isotope values in the mineral soil