Impacts of landform evolution on the pedosphere carbon dynamics (Case study: Aladagh hillslope, northeasternIran)

Alluvial fans can be known as non-equilibrium landform resulting from the spatial-temporal variability erosional and depositional processes, weathering processes, and drainage patterns on them. Formation and evolution of the alluvial fans is effectively affected by climate changes. These landforms play an important role in the exchange of carbon between the atmosphere and pedosphere. The aim of this study was to evaluate how the evolution of alluvial fan ages can affect soil carbon dynamics. The present study measured factors controlling the C mineralization ratio and carbon dioxide flux within the soil environments belonging to different alluvial fan ages (including young fan, intermediate fan, and old fan) located at the base of the Aladagh Mountain hillslope. The intermediate alluvial fans exhibited more stable environment compared with other fans. Furthermore, the position of the intermediate fans on lowlands of the old fans increased the organic carbon concentration, exchangable cattions, and fine fraction. On the other hand, the lower transport capacity of the erosion processes decreased lower micro-aggregate losses compared with other fans. As a result, the organic carbon contained in the micro-aggregates is inaccessible to microbial decomposition over long-term timescale. The old fans exhibited a significant decrease of clay fraction, which could be due to their positions on uplands and their susceptibility to gully erosion processes, causing the transportation of a larger amount of OC-rich topsoil. This condition degrades soil structure and weakens aggregate stability within the old fans, encouraging more vulnerability of organic carbon to microbial decomposition. The geomorphological differences of the alluvial fan surfaces in different ages stimulated the variation of soil carbon dynamics. This conceptual approach of combining our field survey data with an empirical model aids in a better understanding of the biochemical mechanisms controlling the C dynamics under the evolution of geomorphic landforms.