Center for Applied Geoscience, University of Tübingen, Germany; Department of Environmental Systems Science, ETH, Zürich, Switzerland.
Center for Applied Geoscience, University of Tübingen, Germany.
Sci Total Environ. 2019 Mar 10;655:1062-1070. doi: 10.1016/j.scitotenv.2018.11.300. Epub 2018 Nov 22.
The estimation of gas-exchange rates between streams and the atmosphere is of great importance for the fate of volatile compounds in rivers. For dissolved oxygen, this exchange process is called reaeration, and its accurate and precise estimation is essential for the quantification of metabolic rates. A common method for the determination of gas-exchange rates is through artificial gas-tracer tests with a proxy gas. We present the implementation of a portable gas-equilibrium membrane inlet mass spectrometer (GE-MIMS) to record concentrations of krypton and propane injected as tracer compound in the context of a gas-tracer test. The field-compatible GE-MIMS uses signals of atmospheric measurements for concentration standardization, and allows recording the dissolved-gas concentrations at a high temporal resolution, leading to overall low measurement uncertainty. Furthermore, the in-situ approach avoids loss of gas during the steps of sampling, transport, storage, and analysis required for ex-situ gas measurements. We compare obtained gas-exchange rate coefficients, reaeration and derived metabolic rates from the in-situ measurements to results obtained from head-space sampling of propane followed by laboratory analysis, and find much lower uncertainties with the in-situ method.
估算河流中水流与大气之间的气体交换速率对于挥发性化合物的归宿具有重要意义。对于溶解氧，这种交换过程称为复氧，其精确估算对于代谢率的量化至关重要。一种常用的气体交换速率测定方法是通过使用示踪气体的人工气体示踪试验。我们介绍了一种便携式气体平衡膜进样质谱仪（GE-MIMS）的实现，该仪器可记录作为示踪化合物注入的氪和丙烷的浓度，该试验是气体示踪试验的一部分。这种现场兼容的 GE-MIMS 使用大气测量信号进行浓度标准化，并允许以高时间分辨率记录溶解气体浓度，从而总体上降低测量不确定性。此外，该原位方法避免了在采样、运输、储存和分析等步骤中气体的损失，而这些步骤是现场气体测量所必需的。我们将原位测量得到的气体交换速率系数、复氧和推导的代谢率与从顶空采样丙烷并随后进行实验室分析得到的结果进行了比较，发现原位方法的不确定性要低得多。
