METHANE FLUXES IN A NORTHERN HARDWOOD FOREST ECOSYSTEM IN RELATION TO ACID PRECIPITATION

Methane fluxes were measured periodically in 1990 and 1991 in upland forest and peatland soils of a northern hardwood forest in the Adirondack region of New York State. A portion of the study area received lime (10 Mg CaCO3 ha-1) in October 1989 to mitigate several decades of chronic acid precipitation (H+ deposition in 1981 = 653 eq ha-1 yr-1). Consumption of atmospheric methane by forest soils averaged -0.60 mg CH4 m-2 d-1 and showed no difference between treatments (unlimed versus limed soils). Eliminating root growth and removing leaf litter from the soil seemed to decrease rates of methane consumption. Related responses of soil nitrogen transformations to the lime indicated lower nitrification rates and higher net nitrogen mineralization rates compared to unlimed soils, yet rates of methane consumption were unaffected by these changes in soil nitrogen transformations. Methane efflux from the peatland soils into the atmosphere averaged 12.1 mg CH4 m-2 d-1, with no significant difference in rates between treatments. Laboratory measurements revealed that liming resulted in less consumption of atmospheric methane (measured with atmospheres amended with methane) and potentially more methane production. Overall, methane efflux from these peatland soils is much lower than that for more northern counterparts that currently experience cooler climate but less acid precipitation. This suggests that several decades of acid precipitation may play a role in limiting methane emissions from northern peatlands.