River recharge versus O2 supply from the unsaturated zone in shallow riparian groundwater: A case study from the Selke River (Germany).
River recharge versus O2 supply from the unsaturated zone in shallow riparian groundwater: A case study from the Selke River (Germany).
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DOI：
10.1016/j.scitotenv.2018.03.230
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发表时间：
2018-09
期刊：
影响因子：
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通讯作者：
Michael Mader;André M. Roberts;David Porst;C. Schmidt;N. Trauth;R. van Geldern;J. Barth
中科院分区：
文献类型：
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作者：
Michael Mader;André M. Roberts;David Porst;C. Schmidt;N. Trauth;R. van Geldern;J. Barth
除了地表水中的气水交换外，邻近河岸地下水中溶解氧(DO)的呼吸消耗可能会触发来自非饱和带的迄今很少被勘探的来源的增加。这些过程还系统地影响了DO的稳定同位素比值，并与作为保守示踪剂的Cl-−一起研究了近江河岸地下水系统中的水混合。这项研究的重点是位于德国哈尔茨山脉脚下的塞尔克河一段失控的溪流。研究区在2016年4月至2017年5月期间暴露了溪水和河岸地下水之间陡峭的DO梯度。我们的结果表明，微生物群落呼吸的主要影响与观测到的DO浓度梯度有关。这些观察结果可以用河流中的DO来解释，该河流受到微生物呼吸的分馏，典型的分馏系数(αr)为0.982。然而，由于呼吸作用占主导地位，我们预计δ180ODO的同时富集值将比众所周知的大气O2信号+23.9‰相对于维也纳标准平均海水标准(VSMOW)更积极。令人惊讶的是，我们的测量显示，在河流附近的地下水中，δ180D值在+22‰到+18‰之间要低得多。质量平衡计算表明，浅层和非承压含水层中的DO池通过包气带氧的扩散获得了高达80%的贡献，而包气带的同位素值明显低于大气。这一关于来自非饱和带的额外氧源的发现对近河流环境中与氧有关的过程产生了许多影响，包括污染物、营养物质的氧化和生态系统的健康。
Besides gas-water-exchange in surface waters, respiratory consumption of dissolved oxygen (DO) in adjacent riparian groundwater may trigger the addition of so far hardly explored sources from the unsaturated zone. These processes also systematically influence stable isotope ratios of DO and were investigated together with Cl−as a conservative tracer for water mixing in a near-river riparian groundwater system. The study focused on a losing stream section of the Selke River at the foot of the Harz Mountains (Germany). The study area exposed steep DO gradients between the stream water and riparian groundwater between April 2016 and May 2017. Our results indicated dominant influences of microbial community respiration with observed DO concentration gradients. These observations can be explained by DO from the river that is subject to fractionation by microbial respiration with a typical fractionation factor (αr) of 0.982. However, with such respiration dominance, we expected a simultaneous enrichment of δ18ODOtowards values that are more positive than the well-known atmospheric O2signal of +23.9‰ versus the Vienna Standard Mean Ocean Water standard (VSMOW). Surprisingly, our measurements revealed much lower δ18ODOvalues between +22‰ and +18‰ in the near-river groundwater. Mass balance calculations revealed that the DO pool in the shallow and unconfined aquifer receives contributions of up to about 80% by diffusion of oxygen from the vadose zone with a distinctly lower isotope value than the one of the atmosphere. This finding about additional oxygen sources from the unsaturated zone has numerous ramifications for oxygen related processes in near-river environments including the oxidation of pollutants, nutrients and ecosystem health.