喀斯特小流域黄壤硫同位素组成特征——对环境过程和效应的指示

用连续提取方法分析了黄壤中总硫、SO₄^2-、总还原态硫（TRS）和有机硫的硫同位素组成，探讨黄壤中硫的迁移转化过程及其环境效应.有机硫是主要的硫形态，SO₄^2-是主要的无机硫形态.TRS具有最低的δ³⁴S值，同时SO₄^2-和TRS的δ³⁴S值随剖面加深而平行地增大指示黄壤中存在SO₄^2-异化还原过程.黄壤剖面中总硫和有机硫的δ³⁴S值先增大后降低与有机硫矿化及有机硫组分的迁移和底层吸附有关.生物滞留后剩余SO₄^2-的吸附、解吸、淋溶迁移及深层吸附与累积导致剖面中SO₄^2-的δ³⁴S值先增大后明显降低.酸沉降下剖面中SO₄^2-的吸附、解吸和淋溶迁移可引起黄壤酸化.值得关注的是，酸沉降输入的SO₄^2-主要以有机硫和吸附态SO₄^2-滞留在黄壤中，则在硫的年沉降速率大幅降低后，在较长时期内，黄壤中有机硫矿化和吸附态SO₄^2-解吸可能释放大量SO₄^2-进入地表和地下水体，与之相关的土壤理化性质变化和水体化学组成改变等方面的环境效应值得关注.

Sulfur isotopic compositions in yellow soil of karst small catchment-Implications for environmental processes and effects

Sequential extraction method for soil sulfur was used to determine δ³⁴S values of total sulfur, SO₄^2-, total reduced sulfur (TRS) and organic sulfur in yellow soil, aiming to discuss the transportation and transformation of sulfur and its environmental processes and effects in yellow soil. Organic sulfur was the major sulfur form in yellow soil. SO₄^2- was the major inorganic sulfur form in yellow soil. Total reduced sulfur (TRS) had the lowest δ³⁴S values; meanwhile the parallel increasing δ³⁴S values of TRS and SO₄^2- indicated the occurrence of a bacterial reduction process of sulfate in yellow soil. The δ³⁴S values of total sulfur and organic sulfur firstly increased and then decreased with deepening of soil profiles, which can be explained by mineralization of organic sulfur and the subsequent transportation and adsorption at bottom layers of organic sulfur fractions in yellow soil profiles. The residual SO₄^2- after biological S retention was firstly adsorbed and then desorbed; this desorbed SO₄^2- can transport downward and was subsequently re-adsorbed and accumulated at deep soil layers. This explained the increasing δ³⁴S values of SO₄^2- from surface layers to middle layers and the decreasing δ³⁴S values of SO₄^2- from middle layers to bottom layers in yellow soil profiles. Under acid deposition, the adsorption, desorption and transportation of SO₄^2- can result in soil acidification of yellow soil. It is noted that the deposited SO₄^2- was retained as organic sulfur and adsorbed SO₄^2- in yellow soil, then yellow soil may release more S into rivers by organic sulfur mineralization and desorption of the adsorbed SO₄^2- in a long period after a large decrease in annual sulfur deposition rate. The environmental implications such as changes of soil properties and chemical compositions of river water in southwest China should be investigated in the future.