Effect of breakdown and dispersion of soil aggregates by erosion on soil CO2 emission

Abstract

Soil erosion is a serious problem around the world, in addition to soil loss, erosion is also considered to have a significant impact on SOC dynamics and CO2 release to the atmosphere. There is disagreement on the overall effect of soil erosion on CO2 emission at the landscape level. We measured the proportion of various aggregate size fractions at different slope positions which were affected by erosion. The cumulative CO2 emitted from bulk soil samples and different aggregate sizes fractions from five slope positions in a landscape was examined in a 128-d incubation study to estimate how the breakdown and dispersion of soil aggregates by erosion affect C loss to the atmosphere via CO2 emission. The proportion of coarse size aggregate fractions (>0.25mm) at eroded slope positions was greater than that at depositional positions. Bulk soil samples at the summit emitted the greatest cumulative CO2-C (0.49±0.04gCkg−1soil) among all the slope positions. During the initial 22days of incubation, the CO2 emission rate from coarse size aggregate fractions (0.024±0.009gCkg−1soild−1) was six times higher than that from small size aggregate fractions (0.0038±0.0011gCkg−1soild−1) at the depositional toe-slope position. The CO2 emission rate from coarse size aggregate fractions at depositional slope positions (toe-slope and foot-slope) was significantly greater than that at eroded slope positions (summit, shoulder-slope and back-slope). We concluded that the breakdown and dispersion of aggregates by erosion impacts both aggregate size distribution and CO2 emission from the aggregates at different slope positions, thus, affects the C loss to the atmosphere.