Periodic flooding enhances the function of soil Fe/Al oxides in stabilizing particulate organic carbon in a water level drawdown zone

The stabilization of soil organic carbon is closely linked to edaphic properties and environmental variables. Despite this, the mechanism of soil organic carbon stabilization, as well as the primary factor controlling soil organic carbon in riparian ecosystems, remains unclear. To address this gap, our study investigated the impact of flooding regimes on soil organic carbon fractions and other chemical properties in the riparian zone, focusing on the dominant intrinsic factors controlling soil organic carbon content within the three soil types (Anthrosols, Luvisols, and Regosols). Our results demonstrated that flooding regimes significantly affect soil chemical properties in the riparian zone, with varying effects among the three soil types. Specifically, Regosols showed an increase in the particulate organic carbon with flooding intensity. Organic carbon fractions in Anthrosols and Luvisols are found to respond similarly to flooding regimes. The effects of soil chemical properties on organic carbon fractions varied across the three soil types. The variations in POCc, POCf, and MOC for Anthrosols were explained by path models by 43 %, 95 %, and 33 %, respectively. Similarly, for Luvisols, the path models accounted for 66 %, 90 %, and 29 % of the variations, whereas for Regosols, the variations were explained by 43 %, 93 %, and 21 %. Overall, for all tested soils combined, the path models explained 36 %, 89 %, and 12 %, respectively. Therefrom, under flooding regimes, soil oxides played a more significant role in stabilizing soil organic carbon for the three soil types than clay, silt, and cations. Specifically, in Anthrosols, Luvisols, and Regosols, the path coefficient for soil oxides was 0.90, 0.95, and 0.97, respectively, for POCf; while it was 0.30, 0.21, and 0.22 for POCc. In conclusion, we revealed that flooding regimes enhance the role of soil oxides in stabilizing organic carbon. Therefore, we recommend that soil oxides shall be included in organic carbon saturation models for riparian zones subjected to flooding regimes.