Stable sulfur isotope ratios as a tool for interpreting ecosystem sulfur dynamics

Stable S isotope ratios (σ³⁴S) were evaluated in soil solution leachates, soluble plus adsorbed soil SO_inf4^sup2-, soil organic S, precipitation, and in stream solutions along an elevational gradient at the Hubbard Brook Experimental Forest in the White Mts. of New Hampshire, U.S.A. The σ³⁴S of soil organic S varied with soil horizon and vegetation type, but was generally more negative than adsorbed or soil solution SO_inf4^sup2-. In the Bh horizon, σ³⁴S of organic S was typically more negative than the Oa horizon or lower mineral soil (Bsl). The patterns suggest a combination of plant and microbial fractionation processes. Stream σ³⁴S values decreased with decreasing elevation and were correlated with decreases in SO_inf4^sup2-concentration, suggesting an additional S source in higher elevation coniferous sites with a unique σ³⁴S.