Effect of Land Use on Methane Flux from Soil

The precise effects of natural and disturbed terrestrial systems on the atmospheric CH 4 pool are uncertain. This study was conducted to quantify and compare CH 4 fluxes from a variety of ecosystems in central Iowa. We investigated agricultural systems under different management practices, a hardwood forest site, native and restored prairies, and a municipal landfill. Flux measurements were obtained using a closed‐chamber method, and measurements were compiled by sampling over the 1993 and 1994 growing seasons. In 1993, most of the agricultural sites were net CH 4 producers with cumulative CH 4 fluxes ranging from −0.02 to 3.19 g m −2 over the 258‐d sampling season, while the natural ecosystems were net CH 4 consumers, with cumulative seasonal fluxes ranging from −0.27 to −0.07 g m −2 258 d −1 In 1994, only the landfill and the agricultural site treated with broadcast liquid swine manure (LSM) were net CH 4 producers, while the remainder of the natural and agricultural ecosystems were net CH 4 consumers, with mean seasonal flux rates ranging from −0.43 to −0.008 g m −2 271 d −1 We hypothesize that the differences in CH 4 fluxes between the two years are due to differences in rainfall. To illustrate the integration between land use and CH 4 flux, we computed an area‐weighted soil CH 4 flux for the state of Iowa. Our calculations yielded a net average soil CH 4 flux of 139000 Mg CH 4 for 1993 and 1994.