Stable sulfur isotopic biogeochemistry of the Hubbard Brook Experimental Forest, New Hampshire

In natural ecosystems, differences often exist in the relative abundanceof stable S isotopes (°³⁴S) that can provide clues as tothe source, nature, and cycling of S. Values of °³⁴S inprecipitation, throughfall, soils, soil solution, and stream waters weremeasured at the Hubbard Brook Experimental Forest (HBEF), New Hampshire.Values of °³⁴S in precipitation and throughfall weresimilar to each other but differed seasonally. Precipitation°³⁴S values were higher in the dormant season°³⁴S = 5.9±0.6 (17)]Mean + SE(N)]than in the growing season °³⁴S = 5.0±0.6(40)] but throughfall growing-season values were higher°³⁴S = 5.6±0.6(68)] than for the dormantseason °³⁴S = 4.9±0.7 (9)]. Different treespecies did not affect throughfall °³⁴S values. In soilsolution, °³⁴S values were higher in the growing season(°³⁴S = 8.9±2.8; 8.8±1.7;and 4.0±0.6 for Oa, Bh, and Bs horizons, respectively) thanin the dormant season (°³⁴S = 5.6±1.5;3.7±2.4; and 3.4±1.2 for Oa, Bh, and Bshorizons, respectively). These seasonal differences in°³⁴S were probably caused by biological isotopicfractionation. The °³⁴S values in streams were generally2 lower and more variable than those in precipitation andthroughfall, suggesting fractionation and/or different isotopic sources inthe soil.