Effect of land use change on methane oxidation in temperate forest and grassland soils

Abstract

Evidence is accumulating that land use changes and other human activity during the past 100 to 200 years have contributed to decreased CH 4 oxidation in the soil. Recent studies have documented the effect of land use change on CH 4 oxidation in a variety of ecosystems. Increased N additions to temperate forest soils in the northeastern United States decreased CH 4 uptake by 30 to 60%, and increased N fertilization and conversion to cropland in temperate grasslands decreased CH 4 uptake by 30 to 75%. Using these data, we made a series of calculations to estimate the impact of land use and management changes which have altered soil the CH 4 sink in temperate forest and grassland ecosystems. Our study indicates that as the atmospheric mixing ratio of CH 4 has increased during the past 150 y, the temperate CH 4 sink has risen from approximately 8 Tg y −1 to 27 Tg y −1, assuming no loss of land cover to cropland conversion. The net effect of intensive land cover changes and extensive chronic disturbance (i.e., increased atmospheric N deposition) to these ecosystems have resulted in about 30% reduction in the CH 4 sink relative to the soil sink assuming no disturbance to any of the temperate ecosystems. This will impact the global CH 4 budget even more as atmospheric CH 4 concentrations increase and as a result of further disturbance to other biomes. Determining the reasons for the decreased CH 4 uptake due to land disturbance is necessary to understand the role of CH 4 uptake in conjunction with the increasing atmospheric CH 4 concentrations. Without accounting for this approximately 20 Tg y −1 temperate soil sink, the atmospheric CH 4 concentration would be increasing about 1.5 times the current rate.