Abstract
Natural water bodies, such as lakes, rivers, and oceans, are important sources of atmospheric methane (CH4). Therefore, quantitative and accurate determination of the dissolved CH4 concentration in water is of great significance for studying CH4 emissions and providing an in-depth understanding of the carbon cycle. Headspace gas chromatography (HGC) is the traditional method for measuring CH4 in water. Despite its long success, it has a lot of problems in use, such as complex pretreatment and a long measurement time, and it is not suitable for the CH4 determination of a large number of samples. In view of these shortcomings, a more convenient and efficient method based on membrane inlet mass spectrometry (MIMS) for quantitative measurements of the dissolved CH4 concentration in water was established. In our study, the standard curves showed that the method had high accuracy, both at low and high CH4 concentrations. After a laboratory test, to evaluate the sensitivity of this method, samples were collected from a large shallow lake (Lake Taihu). Both the HGC method and MIMS method were used to determine the dissolved CH4 to compare these two methods. The small difference in CH4 concentration obtained from the MIMS and HGC methods and the significant correlation between the CH4 concentrations derived from the MIMS method with those derived from the HGC method showed that the MIMS method could replace the HGC method in the determination of dissolved CH4 in natural waters. In addition, we also measured the sediment CH4 production rates in three different areas of Lake Taihu using a laboratory incubation experiment. During the experiment, significant CH4 accumulations were observed, indicating that sediment CH4 production was an important source of dissolved CH4 in the water column. Our study concluded that the MIMS method was sufficient and a better alternative than the HGC method owing to its capacity to measure a broad range of values plus the fact that it was relatively easy to use with less manipulation of the samples.
Highlights
Greenhouse gases mainly include methane (CH4 ), carbon dioxide, and nitrous oxide, which can lead to the greenhouse effect, which is having a significant impact on the natural ecosystem, such as climate anomalies, melting glaciers, and increasing sea levels [1,2,3,4]
We introduced a novel method based upon the membrane inlet mass spectrometry (MIMS) method to determine the dissolved CH4 concentrations in natural waters
This method was tested in the laboratory and further applied to a large shallow lake, namely, Lake Taihu
Summary
Greenhouse gases mainly include methane (CH4 ), carbon dioxide, and nitrous oxide, which can lead to the greenhouse effect, which is having a significant impact on the natural ecosystem, such as climate anomalies, melting glaciers, and increasing sea levels [1,2,3,4]. the CH4 concentration in the atmosphere is very low compared with carbon dioxide, the greenhouse effect of CH4 is more than 21–23 times that of carbon dioxide [5].As important sources of CH4 , natural water bodies, such as lakes, oceans, and reservoirs, have attracted much attention [6,7]. Greenhouse gases mainly include methane (CH4 ), carbon dioxide, and nitrous oxide, which can lead to the greenhouse effect, which is having a significant impact on the natural ecosystem, such as climate anomalies, melting glaciers, and increasing sea levels [1,2,3,4]. The CH4 concentration in the atmosphere is very low compared with carbon dioxide, the greenhouse effect of CH4 is more than 21–23 times that of carbon dioxide [5]. There is a great demand for determining the dissolved CH4 concentrations in waters. The CH4 diffusive flux can be calculated through Fick’s first law if we know the dissolved CH4 concentration, corresponding water temperature, salinity, and wind speed [7,8], which indicates that if we can quickly and accurately determine the concentration of the dissolved
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