Measuring Dissolved Methane in Aquatic Ecosystems Using An Optical Spectroscopy Gas Analyzer

So this research is focused on the use of optical spectroscopy gas analyzers to measure the concentration of greenhouse gases that are dissolved in the sediment of the soil. So we aim to provide a low cost alternative to traditional chromatography for field studies. This could also be particularly useful in remote areas where you don't have access to those types of equipment.

Challenges in measuring greenhouse gas concentrations in various environmental samples, it includes the need for specialized consumables, complex calibration processes, and often difficulties in transporting and operating some traditional analytical platforms in remote locations. So we established that portable optical analyzers can accurately measure methane concentrations within water samples, providing a viable alternative to gas chromatography, showing a strong correlation with an R squared of greater than 0.98 between the two methods. So our findings will enable more accessible and efficient greenhouse gas measurements, particularly in remote and resource limited locations.

And these results paved the way for investigating spatial and temporal dynamics of greenhouse gases in various ecosystems, understanding ecological impacts, and developing mitigation strategies for climate change. So we'll focus on refining our protocol for other greenhouse gases, exploring its applications in diverse ecological settings, and developing automated systems to enhance efficiency and accuracy in field measurements. Begin by performing headspace equilibration of poor water samples in a syringe.

Create headspace gas samples by using a 30 milliliter syringe to draw five milliliters of water from the sample collected in the field. Then add 15 milliliters of nitrogen to create the headspace. Agitate the syringe vigorously and consistently for five minutes, either using a rocking shaker or manually.

To prepare the 10 milliliter vial for gas concentration measurements with the optical analyzer, evacuate the vial by manually pulling the plunger of a 60 milliliter syringe on the closed vial and pumping the air out three times. Next, inject 12 milliliters of headspace gas subsample into the pre evacuated vial. Proceed to manufacture an injection chamber that can accept about one to five milliliters of air into a sealed volume of air connecting to the gas analyzer inflow and outflow to form a closed loop.

The injection chamber and the analyzer form the two main units of the system. To create this chamber, modify the metallic lid of a 365 milliliter mason jar by drilling one 11 millimeter diameter hole to fit one septum as the injection port and two seven millimeter diameter holes to insert stopcock valves that connect with the analyzer. Use epoxy glue to tighten the injection port and fittings and ensure proper chamber sealing.

Connect the jar with the optical analyzers inlet and outlet ports using PFA plastic tubing and account for their added volume. Ensure the tubing follows the instrument manufacturer's recommendation and is clean and dry without condensation. Set the valves that connect the injection chamber to the instrument to open to create a closed loop air circuit.

Wait for gas concentrations to stabilize. When the concentration in the chamber and the signal in the analyzer have stabilized, inject two milliliters of a subsample from the vials containing the headspace sample. Wait for concentrations in the analyzer to stabilize again before injecting the next subsample.

Inject up to 20 subsamples consecutively or less if the concentration gets closer to 100 PPM. Analyze methane check standards for every five samples and evaluate the difference with actual measurements using the relative standard deviation. When done with the set of stacked injections, unplug one of the lines connected to the instrument to reset the chamber to ambient pressure.