Identification of tephra and its pedological significance in Mollisols of Northeast China

Volcanism plays a crucial role in maintaining the stability of Earth’s terrestrial ecosystems through soil rejuvenation. When tephra is incorporated into the soil system, the secondary minerals and micronutrients generated by weathering positively affect soil structure and fertility. Northeast China is home to a vast expanse of highly fertile Mollisols, with numerous volcanoes scattered throughout the region. However, it remains unclear whether volcanic activity and the associated denudation of volcanic materials contribute to the parent material source for Mollisols and thereby alter their physical and chemical properties. This study used mineralogical and geochemical methods to confirm, for the first time, the contribution of tephra to Mollisols and evaluate the effect of tephra addition on soil properties. The TESCAN Integrated Mineral Analyzer (TIMA) identified the presence of volcanic glass, characterized by angular and vesicular shapes, in typical profiles of the northern Songnen Plain. The elemental composition of volcanic glass indicates that it originated from the nearby Wudalianchi and Keluo Volcanic Cluster. The mercury (Hg) content, phosphorus (P) retention, and Al_o+1/2Fe_o jointly indicate that the northern and eastern parts of the study area have been significantly affected by tephra materials, whereas the central and southern areas remain largely unaffected. Tephra proxies are significantly correlated with soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and cation exchange capacity (CEC), indicating the substantial effect of tephra input on key soil properties.