NOVELTY - Aquatic method for producing methane, carbon dioxide, and plant nutrients involves collecting gases generated in excess of their equilibrium concentration at top of first container and pass upwards through second container; passing the water in first container downward through third container, where water exiting third container contains respective third, equilibrium concentration of dissolved methane and a fourth concentration of dissolved carbon dioxide, where third/fourth concentrations of methane/carbon dioxide, are lower than first/second concentrations of methane and carbon dioxide.    USE - As an aquatic method for producing methane, carbon dioxide, and plant nutrients comprising microbial anaerobic digestion of feedstock (claimed); for off-shore energy production, particularly for generating large amounts of methane via anaerobic digestion, producing purifying the methane, and sequestering environmentally deleterious by-products such as carbon dioxide.    ADVANTAGE - The method can potentially produce up to 60% of world energy demand while requiring only 6% of Earth's water surface area to grow plankton; can captures atmospheric carbon dioxide and store it within a tiny fraction of Earth's seafloor sediments where it can remain safely sequestered for many millennia, typically without expending much energy in the process relative to typical sequestration technologies. The off-shore energy production facilities supported by water bodies can offer many advantages over land-based digesters, including without limitation large, available open water bodies as an alternative means of support, access to a wide range of pressure and suitable temperatures with good heat transfer and specific heat properties, and the potential for locating the facilities at sites that already contain, or can be easily modified to generate, sufficient amounts of feedstock onsite.    DETAILED DESCRIPTION - An aquatic method for producing methane, carbon dioxide, and plant nutrients involving microbial anaerobic digestion of a feedstock by bacterium where the feedstock comprises water and at least one plant or animal material, involve digesting the feedstock within first, flexible container where first container is supported by and submerged in a water body, thus producing a methane gas and a carbon dioxide gas where a first concentration of the methane gas dissolved in the first container is in excess of its equilibrium concentration and a second concentration of the carbon dioxide gas dissolved in the container is below its equilibrium concentration, collecting gases generated in excess of their equilibrium concentration at the top of the first container and pass upwards through second container; passing the water in the first container downward through third container; the water exiting the third container contains at least one respective third, equilibrium concentration of dissolved methane and a fourth concentration of dissolved carbon dioxide, where the third and fourth concentrations of methane and carbon dioxide, respectively are lower than the first and second concentrations of methane and carbon dioxide, respectively; and capturing the carbon dioxide dissolved in the water exiting the third container.    DESCRIPTION OF DRAWING(S) - The figure shows schematic transverse cross sectional view of a water supported anaerobic digester with secondary liquid carbon dioxide capture chamber and mixing gas generator.