Production of Methane and Nitrous Oxide by Organic Soils within a Northern Hardwood Forest Ecosystem

Abstract

Methane and nitrous oxide fluxes and the processes governing these fluxes were measured in a well-drained, upland forest soil (Spodosol) and a water-logged, organic soil (Histosol) in the northern hardwood forest at the Hubbard Brook Experimental Forest in New Hampshire, USA, to determine the extent to which fluxes and processes varied between soil types. Field measurements were carried out between April and November 1990 and indicated that methane fluxes were mostly negative (net consumption of atmospheric methane) for the forest soil and positive (net emission into the atmosphere) for the organic soil. The rate of methane consumption by the forest soil was highest when the soil was relatively dry. Methane production by the organic soil seemed to be controlled by sulfate deposition in rain which may have stimulated sulfate reduction at the expense of methane production. Nitrous oxide fluxes were negligible for the forest soil and relatively high for the organic soil. Interactions of several processes seemed to control nitrous oxide production by the soils and nitrous oxide fluxes observed in situ. When fluxes were weighted by the areal extent of these soil types in the forest, the ecosystem became a net source of atmospheric methane, with a mean daily flux of 0.5 mg m^-2 d^-1, rather than a methane sink as commonly thought and a slightly larger nitrous oxide source than expected.