Kalmar "Gas ɗin Marsh" yawanci tana nufin iskar methane da ake samarwa ta hanyar bazuwar kwayoyin halitta a yankunan dausayi, kamar marshes. Methane gas ne mara launi, mara wari, mai ƙonewa wanda shine babban ɓangaren iskar gas. A cikin mahallin dausayi, ana iya samar da iskar gas ta hanyar rushewar kayan shuka, sharar dabbobi, da sauran kwayoyin halitta ta kwayoyin cuta a cikin yanayi mara kyau na oxygen. Kalmar “Marsh gas” kuma tana iya komawa ga sauran iskar gas da ake samarwa a muhallin dausayi, kamar carbon dioxide da hydrogen sulfide, amma methane shine mafi yawan iskar gas a wannan mahallin.