, Volume 53, Issue 1, pp 23-50

Sulfur isotope inventories of atmospheric deposition, spruce forest floor and living Sphagnum along a NW–SE transect across Europe

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Abstract

At five European sites, differing in atmospheric Sinputs by a factor of 6, and differing in S isotope signatures ofthese inputs by up to 14‰ (CDT), we investigated thedirection and magnitude of an assimilation-related δ34S shiftand the relationship between atmospheric deposition and Sretention in selected ecosystem compartments. Bulk precipitationand spruce throughfall were collected between 1994 and 1996 inthe Isle of Mull (Scotland), Connemara (Ireland), Thorne Moors(England), Rybárenská slat' and Oceán (both Czech Republic) andanalyzed for sulfate concentrations and δ34S ratios. Eighteenreplicate samples per site of living Sphagnum collected inunforested peatlands and 18 samples of spruce forest floorcollected near each of the peatlands were also analyzed for Sconcentrations and δ34S ratios. Assimilation of S was associatedwith a negative δ34S shift. Plant tissues systematicallypreferred the light isotope 32S, on average by 2‰. There wasa strong positive correlation between the non-marine portion ofthe atmospheric S input and total S concentration in forest floorand Sphagnum, respectively (R = 0.97 and R = 0.85). Elevated Sinputs lead to higher S retention in these two organic-richcompartments of the ecosystem. It follows that equal emphasismust be placed on organic S as on adsorption/desorption ofinorganic sulfate when studying acidification reversal inecosystems. The sea-shore sites had rainfall enriched in theheavy isotope 34S due to an admixture of sea-spray. The inlandsites had low δ34S reflecting δ34S of sulfur emitted from localcoal-burning power stations. Sphagnum had always lower S contentsand higher δ34S ratios compared to forest floor. The within-siterange of δ34S ratios of Sphagnum and forest floor was wide (upto 12‰) suggesting that at least six replicate samples shouldbe taken when using δ34S as a tracer.