Modification and implementation of a new method for methane analysis in lake sediments

Lake sediments are recognized today as a significant source of methane, which itself is a strong and a quickly increasing greenhouse gas in the atmosphere. Different techniques have been used to measure methane in lake sediments, but many drawbacks were identified, such as the possible loss of gas and contamination during sampling and measurement. In order to optimize the measurement of methane concentration in lake sediment, we modified and implemented a new measurement technique that was initially developed for noble gas analysis in sediment pore water. This technique is advantageous as it minimizes sample loss or contamination. However, during our investigation of the technique on CH4-saturated artificial water samples, we found that reproducible results were not possible with the low pressure generated by the samples during methane analysis using gas chromatography. Before optimization, dissolved methane was more than 6 times lower in samples analysed according to the new technique than in samples analysed according to the standard method. Therefore, we optimized the new technique, extending the headspace and adding N2. The new results, after optimization, agreed between the optimized technique and the standard method. The new technique was applied to samples taken from Lake Lungern, Switzerland. These samples were taken from oversaturated sediment, which produces methane bubbles that occasionally reached the water surface. The new technique was proven to be efficient even in case of methane-oversaturated sediments