Methane production and oxidation in oil sands tailings ponds: Controlling factors and effects on fugitive greenhouse gas emissions

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Total annual fugitive methane emissions from oil sands tailings ponds in Alberta are estimated at >2.3 Mt of CO2e. Canada's total methane emission budget is 92 Mt CO2e/yr., meaning that tailings ponds produce a hugely disproportionate amount of this total compared to their tiny surface area of 110 km2. There is a large range in the methane efflux rates estimated from different tailings ponds, over three orders of magnitude. This variability may be ultimately due to different management decisions, such as the use of particular extraction chemicals, addition of minerals like gypsum as flocculants, water recycling management, and pond age, which all affect the development of methane-cycling microorganisms. The highest methane fluxes have been measured from the oldest active ponds. These data suggest that ponds may become more methanogenic as they age, but that particular management decisions may allow us to limit emissions of methane by bioengineering the methane-cycling microbial communities present. The aim of this study is to examine methane fluxes in various oilsands tailings ponds, and understand what factors control the linked microbial processes of methane production and methane oxidation. Specifically we will: 1. Estimate the effectiveness of methanotrophy in removing methane from different tailings ponds 2. Determine whether anaerobic methane oxidation occurs in tailings ponds, and determine the microbes responsible for both aerobic and anaerobic methane oxidation3. Compare methane production and oxidation rates in diverse oil sands tailings ponds and assess management factors that potentially affect methanogenesis and methanotrophy 4. Estimate the effectiveness of adding redox-active iron oxide minerals as a strategy for inhibiting methanogens and stimulating anaerobic methanotrophsThe Canadian Oil Sands Innovation Alliance will provide field samples and laboratory analyses for the research. The results will inform management of tailings ponds to minimize methane emissions.