Raman gas spectrometry is introduced as a robust, versatile method for onsite, battery-powered field measurements of gases in the unsaturated and saturated critical zone. In this study, depth-profiles of the concentrations of oxygen and carbon dioxide were simultaneously monitored down to ∼70 meters depth in the subsurface via a transect of drilling holes located in the Hainich Critical Zone Exploratory in central Germany. A special multichannel monitoring system was designed to access and analyze these gases non-consumptively onsite in a closed loop measurement cycle. During the timeframe of six months, seasonal changes in groundwater levels and microbial activity were related to changes observed in gas concentrations. High oxygen concentrations were found in the depths surrounding a karstified aquifer complex, while low oxygen concentrations were found in a fractured aquifer complex. Raman gas depth-profiles complement standard dissolved oxygen measurements as they also deliver oxygen concentrations in the unsaturated zone. The measured depth-profiles of the gas concentrations indicated that regions of anoxia can exist between the aquifer complexes. Lateral transport of O₂ in the deeper aquifer complex provides a local source of O₂ that can influence metabolism. Correlations were found between the observed CO₂ concentrations and pH-values, indicating strong control of carbonate equilibria. The concentrations of O₂ and CO₂ were largely decoupled, thus simultaneous measurements of O₂ soil effluxes give additional insights into biotic and abiotic processes in the Hainich CZE. These results illustrate the versatility of robust onsite Raman multigas measurements of the soil atmosphere and how they can contribute to the analysis of complex processes in previous uncharacterized environments in the critical zone.

中文翻译：

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现场腔增强拉曼光谱仪，用于研究地球关键区域中的气体交换过程

拉曼气相色谱法是一种可靠，通用的方法，可用于在非饱和和饱和临界区中对电池供电的现场气体现场测量。在这项研究中，同时通过地下监测低至约70米深度的氧气和二氧化碳浓度的深度分布图位于德国中部海尼希（Hainich）临界区探索区的钻孔样带。设计了一个特殊的多通道监测系统，可以在闭环测量循环中非消耗性地现场访问和分析这些气体。在六个月的时间范围内，地下水位和微生物活动的季节性变化与气体浓度的变化有关。在岩溶含水层复合体周围的深处发现了高浓度的氧气，而在破裂的含水层复合体中发现了低浓度的氧气。拉曼气体深度剖面补充了标准的溶解氧测量值，因为它们还可以在不饱和区提供氧气浓度。测得的气体浓度深度剖面表明，含水层复合体之间可能存在缺氧区域。更深层含水层中的₂提供了可影响新陈代谢的O ₂的局部来源。发现观察到的CO ₂浓度与pH值之间存在相关性，表明对碳酸盐平衡的强烈控制。O ₂和CO ₂的浓度在很大程度上解耦，因此，同时测量O _2的土壤外排量可以进一步了解Hainich CZE中的生物过程和非生物过程。这些结果说明了对土壤大气进行可靠的现场拉曼多气体测量的多功能性，以及它们如何有助于分析关键区域先前未表征的环境中的复杂过程。