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Citation. Swain, F. M. 1986. Composition of marsh gases in the central and eastern United States. Applied Geochemistry 1:301-305. [1530 CC]
Abstract. Summer samples of marsh gases in Minnesota (fresh-water), Louisiana, and Delaware (fresh-water and brackish-water) yielded 50-85% methane, 3-52% "excess nitrogen", 4-15% carbon dioxide, and small amounts or traces of hydrogen, carbon monoxide, propane, hydrogen sulfide, and C4-C7 hydrocarbons. These types of gas flows were found to decrease drastically in winter periods of sampling, and large amounts of "air" accumulate in some marsh and lake sediments. Carbon dioxide decreases in the winter samples, but carbon monoxide and hydrogen sulfide showed relative increases. Ethan is present in several and butan in one sample from Minnesota in the fall. There is a drop in "excess nitrogen" (non-air N2) in the winter as compared to summer samples. Specimens of marsh plants were place in culture flasks with mud from each collecting locality and allowed to culture for several months. In composition, the cultured gases are predominately methane, carbon dioxide, and "excess nitrogen". Hydrogen, ethane, propane, and hydrogen sulfide are minor components. Carbon monoxide was not detected, in crontrast to marsh gases. Phragmites from industrially polluted Delaware Bay evolved many additional hydrocarbons in culture. pH and Eh were monitored for Typha in culture; pH remained near 7 and Eh near -100 mN after stabilization. Carbohydrate analyses of marsh plants indicate xylans exceed cellulose as a major source of methan in these samples; mannose, galactose, and arabinose are also important potential contributers. Delta carbon-13 values of methane from marsh gases sampled are more negative than those from laboratory-cultured source plants, whereas delta deuterium values of methane from marsh gases are less negative than those of cultured source plants.
Keywords. marsh gases, carbon monoxide, Typha, Phragmites,