硫氧同位素解析典型岩溶地下河流域硫酸盐季节变化特征和来源

Seasonal Variation and Sources Identification of Dissolved Sulfate in a Typical Karst Subterranean Stream Basin Using Sulfur and Oxygen Isotopes

全球约1/4的饮用水源为岩溶水,但岩溶含水层极易遭受人类活动污染.以八步地下河为例,利用硫酸盐(SO^(2-)_(4))浓度、硫氧同位素(δ^(34)S-SO_(4)和δ^(18)O-SO_(4))和水中氧同位素(δ^(18)O-H2O)研究岩溶小流域SO^(2-)_(4)的丰、枯水期两个季节变化特征和来源.结果表明:(1)受酸性矿坑水(acid mine drainage,AMD)直接影响的采样点SO^(2-)_(4)浓度较高(≥250 mg·L^(-1)),枯水期>丰水期,其他采样点浓度季节变化相对较弱且浓度低.(2)地表水丰水期δ^(34)S-SO_(4)与δ^(18)O-SO_(4)平均值分别为-10.5‰和4.7‰,枯水期为-11.5‰和1.3‰;地下水丰水期δ^(34)S-SO_(4)与δ^(18)O-SO_(4)平均值分别为-2.9‰和7.1‰,枯水期为-3.2‰和6.2‰.地表水和地下水中δ^(34)S-SO_(4)与δ^(18)O-SO_(4)值都存在丰水期偏重、枯水期偏轻的特征.(3)丰、枯水期流域内地表水和地下水中各采样点δ^(34)S-SO_(4)值变化不明显,表明在特定的采样点SO^(2-)_(4)的来源相对稳定.(4)地表水和地下水中SO^(2-)_(4)主要来源于雨水、硫化物和石膏,地下河出口各来源丰水期所占的比例分别为13%、40%和47%,枯水期为18%、39%和43%.

Karst water,which provides approximately 25% of the world’s drinking water,is especially vulnerable to anthropogenic pollutants. To determine the variations between high and low flow periods and the sources of dissolved sulfate( SO^(2-)_(4)) in small karst basins,SO^(2-)_(4) concentrations,stable sulfur and oxygen isotopes( δ^(34)S-SO_(4) and δ^(18)O-SO_(4)),and oxygen isotopes of water( δ^(18)O-H2 O)were investigated in surface and groundwaters,during the high and low flow seasons,within the Babu subterranean stream basin.Analysis showed that:(1) the water samples that were directly impacted by acid mine drainage exhibited high SO^(2-)_(4) concentrations( ≥250 mg·L^(-1)) and significant seasonal variation,while the seasonal variation of non-AMD-impacted water with low SO^(2-)_(4) concentrations was not significant.(2) During the high flow season,the mean δ^(34)S-SO_(4) and δ^(18)O-SO_(4) values of surface water were -10. 5‰ and 4. 7‰,respectively,and -11. 5‰ and 1. 3‰ during the low flow period;the mean values of δ^(34)S-SO_(4) and δ^(18)O-SO_(4) in groundwater samples were -2. 9‰ and 7. 1‰ during the high flow period,respectively,and-3. 2‰ and 6. 2‰ during the low flow period. Both surface and groundwater samples exhibited higher δ^(34)S-SO_(4) and δ^(18)O-SO_(4) values during the high flow period than during the low flow period.(3) The values of δ^(34)S-SO_(4) in the surface and groundwater samples were relatively stable,indicating that the sources of SO^(2-)_(4) at specific sampling sites were stable.(4) The main sources of SO^(2-)_(4) in surface and groundwaters were rain,sulfide,and gypsum,accounting for 13%,40%,and 47%,respectively,of SO^(2-)_(4) in samples taken from the basin outlet during the high flow season,and 18%,39%,and 43%,respectively,in samples obtained during the low flow season.