Functional stability: From soil aggregates to landscape scale in a region severely affected by gully erosion in semi-arid central Mexico
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Soil aggregate stability is a vital indicator of soil structure and potential degradation and is essential to under-stand gully erosion in arid and semi-arid regions. Stability of soil aggregates depends on soil mass properties, local conditions (within the gully), and hillslope conditions. The objectives of this study were 1) to analyze soil aggregate stability at three gully wall positions: headscarps, sidewalls, and gully bottoms, and 2) to explore the relationships between soil aggregate stability and local and landscape conditions to know how stability at different scales is interrelated. Soil macro aggregate stability was estimated from soil samples using the soil aggregate stability kit. Conversely, Cornell infiltrometers were used to evaluate soil microaggregate stability by applying 5-min rainfall events with an intensity of 150 mm-1. Local (within gully) conditions were registered in the field using indicators from the ephemeral drainage line assessment method. Landscape conditions (outside gully), such as terrain attributes, anthropogenic features, and vegetation cover, were computed from topographic maps, digital elevation models, and satellite imagery. Relationships between soil aggregate stability and local and landscape conditions were explored using classification and regression trees. The highest soil macro and micro aggregate stability were found at the gully headscarps, while gully bottoms had the lowest soil aggregate stability. Soil macroaggregate stability was related to terrain attributes, ground cover, and gully dimensions. In contrast, microaggregate stability was associated with ground cover, terrain attributes, gully dimensions, and distance to roads and farm dams. Our study showed that soil aggregate stability differs along gully walls and that soil aggregate stability can be related to different variables at the local and hillslope scales. This knowledge is a valuable indicator for understanding gully erosion and the foundation for restoration strategies in semi-arid regions.
