Abstract
Abstract. Biogenic greenhouse gas emissions, e.g., of methane (CH4) and carbon dioxide (CO2) from inland waters, contribute substantially to global warming. In aquatic systems, dissolved greenhouse gases are highly heterogeneous in both space and time. To better understand the biological and physical processes that affect sources and sinks of both CH4 and CO2, their dissolved concentrations need to be measured with high spatial and temporal resolution. To achieve this goal, we developed the Fast-Response Automated Gas Equilibrator (FaRAGE) for real-time in situ measurement of dissolved CH4 and CO2 concentrations at the water surface and in the water column. FaRAGE can achieve an exceptionally short response time (t95 %=12 s when including the response time of the gas analyzer) while retaining an equilibration ratio of 62.6 % and a measurement accuracy of 0.5 % for CH4. A similar performance was observed for dissolved CO2 (t95 %=10 s, equilibration ratio 67.1 %). An equilibration ratio as high as 91.8 % can be reached at the cost of a slightly increased response time (16 s). The FaRAGE is capable of continuously measuring dissolved CO2 and CH4 concentrations in the nM-to-sub mM (10−9–10−3 mol L−1) range with a detection limit of sub-nM (10−10 mol L−1), when coupling with a cavity ring-down greenhouse gas analyzer (Picarro GasScouter). FaRAGE allows for the possibility of mapping dissolved concentration in a “quasi” three-dimensional manner in lakes and provides an inexpensive alternative to other commercial gas equilibrators. It is simple to operate and suitable for continuous monitoring with a strong tolerance for suspended particles. While the FaRAGE is developed for inland waters, it can be also applied to ocean waters by tuning the gas–water mixing ratio. The FaRAGE is easily adapted to suit other gas analyzers expanding the range of potential applications, including nitrous oxide and isotopic composition of the gases.
Highlights
Despite the well-established perception of inland waters as a substantial source of atmospheric methane (CH4) and carbon dioxide (CO2) (Bastviken et al, 2011; Cole et al, 2007; Tranvik et al, 2009), the magnitude of these greenhouse gases remains uncertain owing to the fact that some key processes affecting CH4 and CO2 budget are still poorly constrained (Saunois et al, 2019)
Applications are provided exemplarily to demonstrate the potential of the Fast-Response Automated Gas Equilibrator (FaRAGE) for improving our understanding of the spatial distribution and temporal dynamics of dissolved CH4 and CO2 in inland waters
The effect of tube length on the performance of the device was examined by adapting 1, 2, 4.4, 8.4 and 13 m Tygon tubes onto the gas–water mixing unit. For all these tests, triplicated measurements of the equilibration ratio and response time were performed corresponding to different mixing ratios, and the mean values were used for analysis
Summary
Despite the well-established perception of inland waters as a substantial source of atmospheric methane (CH4) and carbon dioxide (CO2) (Bastviken et al, 2011; Cole et al, 2007; Tranvik et al, 2009), the magnitude of these greenhouse gases remains uncertain owing to the fact that some key processes affecting CH4 (e.g., bubbling) and CO2 budget are still poorly constrained (Saunois et al, 2019). Resolving the spatio-temporal dynamics of both dissolved CH4 and CO2 is a prerequisite for a better understanding of the production and loss processes of these gases in freshwater lakes. Storms can act as another driver for short-term dissolved gas dynamics in the lake because they often contribute to higher evasion rates caused by strong vertical turbulent mixing (Zimmermann et al, 2019) and enhanced horizontal transport (Fernández et al, 2016). Driven by the need to resolve temporal and spatial variability of dissolved CH4 and CO2 in inland waters with sufficient precision, we developed a novel, low-cost equilibrator to achieve fast gas–water equilibration. Applications are provided exemplarily to demonstrate the potential of the FaRAGE for improving our understanding of the spatial distribution and temporal dynamics of dissolved CH4 and CO2 in inland waters
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