Development of an ultra-fast method for continuous and automated analysis of dissolved greenhouse gases in surface waters

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Natural waters such as oceans, lakes, and rivers comprise the largest global reservoirs of numerous greenhouse gases in active exchange with the atmosphere. The diffusive fluxes of these gases between the dissolved aqueous phase and the atmosphere comprise significant fluxes regionally and globally. Previous techniques used to determine surface water concentrations and air-water fluxes primarily focus on collecting discrete samples of surface water in vials or the use of shower-head equilibrators. While collecting discrete samples provides accurate results, the relatively coarse sampling of the natural environment can lead to uncertainties in the true extent of surface water greenhouse gas concentration features. Shower-head equilibrators provide near-continuous data for higher resolution mapping, but the slow response time for gases of low solubility such as methane can render their results inaccurate during rapidly changing dissolved gas concentrations. Interestingly, the over the last few years, several studies have produced data suggesting that the flux of certain dissolved greenhouse gases are emitted to the atmosphere aggressively in extremely localized areas. However, the technology has not been available to quantitatively discover and map the full extent of these features.This project will fully develop a new technique for the continuous analysis of dissolved greenhouse gas concentrations and natural isotopes in surface waters. The main advantage of this new system is an ultra-fast response time to changes in the surface water concentration of dissolved greenhouse gases while still maintaining high accuracy and precision analyses. More specifically, this technique will measure dissolved methane, carbon dioxide, carbon monoxide, and nitrous oxide concentrations and natural stable isotopes. The principle of operation is vacuum gas extraction. Water is continually pumped through a gas-permeable membrane at a rate of 15 liters per minute and a vacuum is applied to the outside of the membrane to extract the dissolved gases from the water stream. The extracted gases are then pumped into an analytical detector for analysis. By comparing the water and extracted gas flow rates with the concentration of a specific greenhouse gas measured in the extracted gases, the dissolved gas concentration can be determined. The main weakness of this system is that the gas extraction efficiency is not 100%. Thus, an integrated and automated calibration system has been developed to quantify the dissolved gas extraction efficiency at predetermined intervals. A prototype of this system has been developed and preliminary tests have been conducted in the laboratory and northern Gulf of Mexico displaying results that are accurate, precise, and able to detect concentration changes on sub-minute timescales. This project will develop this technology to completion with the goal of fully validating the system for a suite of different greenhouse gases, physical and chemical water properties, and extraction membrane types. Laboratory tests and field trials will be conducted with the goal of engineering and validating a system that is user-friendly, portable, and fully automated for use within the scientific community. A graduate student from a group underrepresented in science will be involved in this project as will six undergraduate students. All of these student scientists will be given opportunities to contribute to the entire scientific process from data collection and interpretation to presentation and publication.