Spatial and temporal variations of pCO2, dissolved inorganic carbon and stable isotopes along a temperate karstic watercourse
Spatial and temporal variations of pCO2, dissolved inorganic carbon and stable isotopes along a temperate karstic watercourse
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DOI：
10.1002/hyp.10457
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发表时间：
2015-07
影响因子：
3.2
通讯作者：
R. Geldern;P. Schulte;Michael Mader;Alfons Baier;J. Barth
中科院分区：
文献类型：
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作者：
R. Geldern;P. Schulte;Michael Mader;Alfons Baier;J. Barth
这项研究调查了威森特河的二氧化碳脱气和相关的碳同位素分馏效应，威森特河排出了德国南部弗兰科尼亚阿尔布喀斯特地区的一个集水区。通过对河流源头和河口之间65公里长的下游断面的水和溶解无机碳的物理化学和稳定同位素分析，在整个季节对其进行了调查。计算出污染源的二氧化碳分压为21400±2400µatm。河水中二氧化碳分压迅速下降，并在河口附近降至平均1240±330微米。大约90%的下降发生在河流的前6公里内。在整个过程中，这条河的二氧化碳含量都是过饱和的，一定是作为大气全年持续的二氧化碳来源。用450mmolm−2d−1估算了喀斯特河源的平均CO2通量，其通量最高可达5680mmolm−2d−1。源区δ13CDIC值无季节变化，平均−为14.2±0.2‰。这表明地下水保留了较高的二氧化碳，主要来自土壤二氧化碳。土壤CO2对溶解无机碳的贡献率估计为65%~72%。由于脱气过程中~(12)C同位素的优先损失，下游CO_2的损失使δ~(13)CDIC值在源口之间发生了2‰的正移。考虑到这项研究的结果，以及碳酸盐岩性覆盖地球表面很大一部分的事实，岩溶地区的二氧化碳逃逸可能对全球淡水系统每年释放的二氧化碳有显著贡献。版权所有©2015 John Wiley&Sons，Ltd.
This study investigated CO2 degassing and related carbon isotope fractionation effects in the Wiesent River that drains a catchment in the karst terrain of the Franconian Alb, Southern Germany. The river was investigated by physico‐chemical and stable isotope analyses of water and dissolved inorganic carbon during all seasons along 65‐km long downstream transects between source and mouth. Calculated pCO2 values at the source were 21 400 ± 2400 µatm. The pCO2 rapidly decreased in the river water and dropped to an average of 1240 ± 330 µatm near the mouth. About 90% of this decrease occurred within the first 6 km of the river. The river was supersaturated with respect to CO2 over its entire course and must have acted as a continuous year‐round CO2 source to the atmosphere. The average CO2 flux from the karst river was estimated with 450 mmol m−2 day−1 with higher fluxes up to 5680 mmol m−2 day−1 at the source. At the source, δ13CDIC values showed no seasonal variations with an average of −14.2 ± 0.2‰. This indicated that groundwater retained high pCO2 mainly from soil CO2. The contribution of soil CO2 to dissolved inorganic carbon was estimated at 65% to 72%. The downstream CO2 loss caused a positive shift in δ13CDIC values of 2‰ between source and mouth because of the preferential loss of the 12C isotope during degassing. Considering the findings of this study and the fact that carbonate lithology covers a significant part of the earth's surface, CO2 evasion from karst regions might contribute notably to the annual carbon dioxide release from global freshwater systems. Copyright © 2015 John Wiley & Sons, Ltd.