| Sequential extraction methods for soil sulfur were used to determine δ34S ratios and sulfur contents of total sulfur,organic sulfur,SO2-4 and FeS2 in slope soils of karst areas. In general,FeS2 has the lowest δ34S ratios,ranging from -6.86‰ to -4.22‰,followed in ascending order by SO 2-4(-2.64‰--1.34‰),total sulfur (-3.25‰--1.03‰) and organic sulfur (-1.63‰-0.50‰) in surface soils of profiles,and δ34S ratios in different sulfur forms all show increasing trend with profiles deepening. Covariations of δ34S ratios of SO2-4 and FeS2 with increasing depth are related to SO2-4 dissimilatory reduction,while the increase in parallel of δ34S ratios of total sulfur and organic sulfur could be resulted from organic sulfur cycling. δ34S ratios have been extensively used to indicate sulfur sources,moreover,SO2-4 dissimilatory reduction and organic sulfur mineralization result in significant sulfur isotopic fractionation,and sulfides oxidation and SO2-4 assimilation have no isotopic fractionation occurred,the vertical variations of δ34S ratios in different sulfur forms can therefore be good records for depth-dependant sulfur cycling processes. Furthermore,by comparing depth distributions of sulfur contents and δ34S ratios in different sulfur forms,it is easily to discuss the migration of SO2-4 and organic sulfur fractions in soil profiles. |
