Comparison of retention and output of sulfur in limestone soil and yellow soil and their responses to acid deposition in a small karst catchment of Guizhou Province, Southwest China.

Investigating the responses of retention and output of sulfur (S) is significant to understand the impact of atmospheric S deposition on the S cycling in soils and its environmental effects in the karst catchments of Southwest China. This study analyzed the contents and δ34S values of different S forms (total S, carbon-bonded S, ester-bonded SO42-, SO42-, and total reduced inorganic sulfur [TRIS]), the δ34S values of stream SO42-, the δ13C values of soil organic carbon, and sulfate-reducing bacteria (SRB) quantity in limestone soil and yellow soil profiles in a typical small karst catchment of Southwest China. The results showed that under the same acid deposition level, the limestone soil and yellow soil profiles are significantly different from the distribution of contents and δ34S values of different S forms and the number of SRB. At the same time, more than 70% of the SO42- in the stream water draining the sampling slopes came from soils at different depths in limestone soil and yellow soil profiles. These results indicate the different response of retention and output of S in the limestone soil and yellow soil to S deposition input. The organic S formation and dissimilatory SO42- reduction (DSR) to form TRIS are S retention processes that exist in both limestone soil and yellow soil profiles. There are processes of transport and accumulation of SO42- at the bottom layer in yellow soil profile; therefore, retaining S as absorbed SO42- is also a main S retention process in yellow soil. At present, the output of SO42- through stream water mainly comes from the deposited SO42- which undergoes DSR reaction driven by SRB, not from organic S mineralization and desorption of adsorbed SO42- in the limestone soil and yellow soil profiles. However, organic S is the main S form in limestone soil and yellow soil. After the annual S deposition flux is significantly reduced, organic S mineralization in limestone soil and yellow soil profiles may release a large amount of SO42- into the surface water.