Impact of Holocene dust aggradation on A horizon characteristics and carbon storage in loess-derived Mollisols of the Great Plains, USA

Abstract

The amount and vertical distribution of soil organic carbon (SOC) storage is primarily a function of vegetation type and climate, with influence from soil and landscape properties and human activities. The influence of dust aggradation on landscapes during the Holocene has largely been ignored as a factor in long-term SOC storage. Dust aggradation is important to soil horizonation and C sequestration since the dust deposit buries the landscape and increases solum thickness. Mollisols on loess-covered upland tables in central Nebraska have aggraded throughout the Holocene as Bignell Loess accumulated above the late Pleistocene Brady Soil. In the loess tablelands, the thickness of mollic colors, A horizon properties, and SOC storage all decrease with distance from the source of Bignell Loess, which is along a gradient of increasing precipitation. For example, along a 140-km transect of decreasing Bignell Loess thickness and increasing rainfall, total thickness of A horizons decreases by 70 cm and the thickness of mollic colors decreases by 93 cm. Total SOC storage decreases from 17.5 to 7.7 kg/m 2. A portion of the SOC in subsurface horizons of modern soils was likely inherited from the Brady Soil, which probably formed in a climate different than the present, suggesting that SOC storage is probably not in equilibrium with modern climatic conditions. Dust aggradation on a biologically active surface in a steppe environment has affected horizonation, pigmentation and SOC storage in central Great Plains loess-derived Mollisols.