Effect of Soil Aggregate on Preferential Path in Gully Systemof Dry-hot Valley

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    [Objective] To investigate the impact of soil aggregate structure on the formation of preferential pathways in the gully system of the dry-hot valley of the Jinsha River to enhance our understanding of soil moisture and solute transport in the gully system. [Methods] We selected different sections (i.e., catchment area, gully head, gully bed, and gully bottom) of both active and stable gullies in the dry-hot valley of the Jinsha River as our research subjects. We used staining tracers and morphometric image analysis techniques to extract the preferential pathways from the soil level profile. RDA (Redundancy Analysis), gray correlation, and coupled coordination were used to explore the relationship between soil aggregate structure and preferential pathways. [Results] (1) The stability of soil aggregates in stable gullies were higher than those in active gullies. Except for specific soil layers, the contents of mechanically stable aggregates (>0.25 mm, [QX(Y12#]DR[QX)]0.25), water-stable aggregates (>0.25 mm, [QX(Y12#]WR[QX)]0.25) and average mass diameter (MWD) in active gully were significantly lower than those in the stable gully ([QX(Y12#]p[QX)]<0.05). The aggregate destruction rate (PAD) and unstable aggregate index ([QX(Y12#]E[QX)]LT) showed the opposite trend. As the gully system extends from the catchment towards the gully bottom, the fraction of large soil and the stability of aggregates all decreased. (2) The number and connectivity of preferential pathways in active gullies were higher than those in stable gullies. However, the connectivity of the preferential pathways in the gully system deteriorated as it extended from the catchment to the bottom of the gully. The preferential pathways with a diameter>10 mm served as primary channel. The Simpson index of active gullies exhibited an increase by 3.12% compared to stable gullies, indicating a higher richness of preferential pathways across different diameter classes. (3) The formation and distribution of preferential pathways were affected by the stability of soil aggregates, and MWD and WR0.25 were strongly correlated with the number of preferential pathways and had the most significant influence ([QX(Y12#]p[QX)]<0.01). (4) As the gully system extended from the catchment to the bottom of the gully, the coupling coordination between the soil aggregate structure and the preferential pathways decreased. Overall, the order of performance was as follows: gully head>catchment area>gully bottom>gully bed. [Conclusion] Soil aggregate structure is an of the important driving factors for the formation of preferential paths, and the distribution of preferential paths has significant impact on the development of gully systems in dry-hot valleys.

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  • Received:July 04,2023
  • Revised:September 10,2023
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  • Online: May 20,2024
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