||Vast areas of marsh are lost to submergence annually, which threatens critical ecosystem services provided by marshes. Global change factors such as atmospheric elevated CO 2 and nitrogen (N) pollution have strong, direct influences on plants and soil microbes and may impact the soil-forming mechanisms that sustain tidal marshes. To investigate the effects of elevated CO 2 and N pollution on marsh decomposition, I conducted a field experiment in a brackish marsh on the Chesapeake Bay, MD and a companion laboratory incubation study in 2009 and 2010. N addition reduced activity of phenol oxidase (PO) and β-glucosidase (βG), vital enzymes that mediate soil decomposition in marshes, and tended to retard peat decomposition. In contrast, elevated CO 2 tended to increase PO activity probably via plant-mediated effects such as alteration of soil oxygenation and N availability. The incubation study provided direct observation of the N effect on soil decomposition by excluding many in situ variables. Decomposition rate increased with higher PO and βG efficiencies and N addition interacted with soil carbon and O 2 availability to affect decomposition. Decomposition occurs very slowly in marshes; therefore more future effort should be directed towards refining long-term estimates of global change effects on peat decomposition.