STABLE SULFUR ISOTOPIC BIOGEOCHEMISTRY OF THE HUBBARD-BROOK-EXPERIMENTAL-FOREST, NEW-HAMPSHIRE

In natural ecosystems, differences often exist in the relative abundan ce of stable S isotopes (delta(34)S) that can provide clues as to the source, nature, and cycling of S. Values of delta(34)S in precipitatio n, throughfall, soils, soil solution, and stream waters were measured at the Hubbard Brook Experimental Forest (HBEF), New Hampshire. Values of delta(34)S in precipitation and throughfall were similar to each o ther but differed seasonally. Precipitation delta(34)S values were hig her in the dormant season [delta(34)S = 5.9+/-0.6 parts per thousand(1 7)] [Mean+SE(N)] than in the growing season [delta(34)S = 5.0+/-0.6 pa rts per thousand (40)] but throughfall growing-season values were high er [delta(34)S = 5.6+/-0.6 parts per thousand (68)] than for the dorma nt season [delta(34)S = 4.9+/-0.7 parts per thousand (9)]. Different t ree species did not affect throughfall delta(34)S values. In soil solu tion, delta(34)S values were higher in the growing season (delta(34)S = 8.9+/-2.8 parts per thousand; 8.8+/-1.7 parts per thousand; and 4.0/-0.6 parts per thousand for Oa, Bh, and Bs horizons, respectively) th an in the dormant season (delta(34)S = 5.6+/-1.5 parts per thousand; 3 .7+/-2.4 parts per thousand; and 3.41+/-1.2 parts per thousand for Oa, Bh, and Bs horizons, respectively). These seasonal differences in del ta(34)S were probably caused by biological isotopic fractionation. The delta(34)S values in streams were generally 2 parts per thousand lowe r and more variable than those in precipitation and throughfall, sugge sting fractionation and/or different isotopic sources in the soil.