荔波板寨小流域水体硫同位素特征及其对流域风化的指示意义

Water Chemistry and Sulfur Isotope of Ground / River Water in Banzhai Small Watershed of Libo and Their Significances for Weathering

在生态脆弱的喀斯特地区,硫酸的参与加快了碳酸盐岩的风化速率,改变了区域碳循环过程。选择位于西南喀斯特森林地区的板寨小流域为研究区域,结合地表、地下水化学及其SO_4^(2-)的δ^(34)S同位素特征,分析了水体主要溶解物的来源,验证硫酸参与区域碳酸盐的风化过程。研究结果显示:所有水样均表现出明显的岩溶水化学特征,其主要阴离子为HCO_3^-,占总阴离子的57.4%~93.8%,流域内小学附近采样点的泉水中含有较多的SO_4^(2-);流域水体主要阳离子为Ca^(2+)、Mg^(2+),二者分别占总阳离子当量的61.4%~90.8%和7.64%~37.6%,其中板寨河水中含有较多的Mg2+,平均可占总阳离子当量的33.0,表明板寨河水可能受石灰岩和白云岩风化的共同作用。小学样点的SO_4^(2-)含量远高于其余各个样点。而δ^(34)S同位素结果显示小学和黎明关两个样点地下水SO_4^(2-)的平均δ^(34)S同位素值分别为-11.1‰和-9.12‰,接近贵州煤的δ^(34)S同位素统计值,表明其可能受到地下煤层中硫化物氧化的影响。瑶寨地下水和板寨河水的δ^(34)S同位素与西南喀斯特地区大气降水SO_4^(2-)的δ^(34)S同位素值相近,可能主要来源于大气降水。

In the ecologically fragile areas of Karst region,the participation of sulfuric acid accelerates the weathering rate of carbonate rocks,and changes the regional carbon cycle process. In this study,the characteristics of hydrochemical and sulfur isotopic of the surface and ground water samples in Banzhai small watershed were measured for revealing the main sources of the water dissolved and proving the process that sulfuric acid is involved in the weathering of carbonate. Results showed that all samples indicated a clear characteristic of carbonate water chemistry from karst region. The main anion is HCO3-,which takes 57. 4% 93. 8% of total anions. SO42-concentrations of ground water samples near a primary school are higher than those of other sites. Main cations of the water are Ca2＋and Mg2＋,which take the total cation equivalent of 61. 4% 90. 8% and 7. 64% 37. 6%,respectively. There is more Mg2＋in river water of Banzhai; the average can take 33% of the total cation equivalent,showing that river water of Banzhai may be jointly affected by the weathering of limestone and dolomite. SO42-contents of the school sample site are much higher than the rest sample sites. The averagedδ34S isotope values were-11. 1‰ and-9. 12‰ in ground water of school and Limingguan,respectively,which are close to the coalδ34S isotope values in Guizhou. This suggests that it may affected by the oxidation sulfide in local subterranean coal; while the δ34S isotope values of ground water of Yaozhai and river water of Banzhai are close to the values of rain water of southwest Karst area in China,indicating the SO42-of two sites are mainly from the rain.