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

Southwest Forestry University

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National Science Fund Projects(42067005). Agricultural Joint Special Project in Yunnan Province(202101BD070001-075). Basic Research Project of Yunnan Province(202001AT070136). Yunnan Young Talents Project(YNWR-QNBJ-2019-215;YNWR-QNBJ-2019-226). Yunnan Natural Ecological Monitoring Network Project(2022-YN-13)

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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 and enhance our understanding of soil moisture and solute transport in the gully system. [Method] We selected different sections (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 morphological image analysis techniques to extract the preferential pathways of the soil level profile. Moreover, we employed RDA, gray correlation, and coupled coordination analysis to explore the relationship between soil aggregate structure and preferential pathways. [Result] (1) Soil aggregates in stable gullies were more stable than those in active gullies. Except for specific soil layers, the contents of mechanically stable aggregates (>0.25 mm, DR0.25) and water-stable aggregates (>0.25 mm, WR0.25) and average mass diameter (MWD) in the four parts of the active gully were significantly lower than those in the stable gully (p < 0.05). The aggregate destruction rate (PAD) and unstable aggregate index (ELT) showed the opposite trend. As the gully system extends from the catchment to the bottom of the gully, the fraction of large soil, and the stability of aggregates all decreased. (2) The number and connectivity of preferential pathways in active gullies exceeded 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 the primary channel. The Simpson index of active gullies exhibited an increase of 3.12% compared to stable gullies, indicating a higher richness of preferential pathways across different diameter classes. (3) The stability of soil aggregates affected the formation and distribution of preferential pathways. Remarkably, there is a strong correlation between soil aggregate structure and the number of preferential pathways, with MWD and WR0.25 of showing the most substantial effect on the number of preferential pathways (p < 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 one of the important driving factors for the formation of preferential paths, and the distribution of preferential paths has a significant impact on the development of gully systems in dry-hot valleys.

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  • Received:July 04,2023
  • Revised:September 10,2023
  • Adopted:September 11,2023
  • Online: January 27,2024
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