Geochemical and stable isotope studies on natural water in the Taroko Gorge karst area, Taiwan—chemical weathering of carbonate rocks by deep source CO2 and sulfuric acid
Geochemical and stable isotope studies on natural water in the Taroko Gorge karst area, Taiwan—chemical weathering of carbonate rocks by deep source CO2 and sulfuric acid
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DOI：
10.1016/s0009-2541(00)00423-x
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发表时间：
2001-07
期刊：
影响因子：
3.9
通讯作者：
K. Yoshimura;S. Nakao;M. Noto;Y. Inokura;K. Urata;M. Chen;P.-W. Lin
中科院分区：
文献类型：
--
作者：
K. Yoshimura;S. Nakao;M. Noto;Y. Inokura;K. Urata;M. Chen;P.-W. Lin
利用天然水的化学成分数据，以及水和土壤CO2的碳氧稳定同位素比，讨论了台湾太鲁阁喀斯特地区的CO2地球化学循环和水文循环。 1 m 深度土壤 CO2 浓度呈现季节性变化，在 50 至 2000 m asl 的三个不同海拔高度处，最大为 5.2% (v/v)，最小为 0.6% (v/v)。土壤温度是控制该地区土壤CO2浓度的最重要因素。碳酸盐在地下水中的溶解度可以通过封闭系统条件下的演化来解释，具体取决于测量的土壤二氧化碳浓度。出乎意料的是，在一些泉水中观察到地下水中 HCO3− 的 δ13C 值很高。水中Mg2+和Ca2+离子浓度之和与HCO3−和SO42−离子浓度之间也存在等价关系。这两个事实表明，黄铁矿风化产生的一些深源CO2和硫酸可能参与了碳酸盐岩（主要是钙质片岩）以及土壤CO2的化学风化。在对硫酸的贡献进行校正后，一些泉水的HCO3−δ13C值仍然很高，表明存在深源CO2通量。观测到该地区地表水和雨水的海拔同位素效应，可表示为δ18O（‰）=−0.0024h−3.67（h：海拔，m asl）。使用该方程估计的泉水集水盆地的海拔比泉水高1000-2000米以上。高山降下的雨水供给土壤CO2，在封闭系统条件下溶解碳酸盐岩，渗透到地下深处，与深源CO2一起沿断层破碎带再次从泉水中涌出。
The geochemical cycle of CO2and the hydrological cycle in the Taroko Gorge karst area, Taiwan, are discussed using chemical composition data of the natural water, together with stable isotope ratios of carbon and oxygen of the water and soil CO2. The soil CO2concentration at a depth of 1 m showed seasonal variations with a maximum of 5.2% (v/v) and the minimum of 0.6% (v/v) at three different altitudes ranging from 50 to 2000 m asl. The soil temperature is the most important factor controlling the soil CO2concentration in this area. The solubility of carbonates in groundwater can be explained by evolution under closed system conditions depending on the soil CO2concentration measured. Unexpectedly, high δ13C values of HCO3−in groundwater were observed at some springs. There was also an equivalent relationship between the sum of the concentration of Mg2+and Ca2+ions and that of HCO3−and SO42−ions in their waters. These two facts suggest that some deep source CO2and sulfuric acid derived from weathering of pyrite may take part in the chemical weathering of carbonate rocks (mainly calcareous schist) as well as the soil CO2. After the correction for the contribution of sulfuric acid, the δ13C values of HCO3−of groundwater issuing from some springs were still high, suggesting the presence of a deep source CO2flux. Altitude isotope effects were observed for surface water and rainwater in this area and could be expressed as δ18O (‰)=−0.0024h−3.67 (h: altitude, m asl). The estimated altitudes of catchment basins of springs using this equation were over 1000–2000 m higher than those of springs. The rain falling high in the mountains is supplied with soil CO2, dissolves carbonate rocks under closed system conditions, penetrates deep underground, and comes out again from springs together with the deep source CO2along fault crushing belts.