Vegetation patterns affect soil aggregate loss during water erosion

Soil aggregates are important for improving the soil quality and structure. Soil erosion causes the fragmentation and migration of soil aggregates. Vegetation restoration is an effective method for controlling soil erosion, and the vegetation distribution on the slope changes the hydrological processes. However, there is a dearth of studies investigating the regulation of vegetation patterns in relation to soil aggregate loss. This study employed a physical model of a slope gully system to examine the characteristics of soil aggregates loss during erosion processes under four distinct vegetation patterns: no vegetation (pattern A), up-slope vegetation (pattern B), middle-slope vegetation (pattern C), and down-slope vegetation (pattern D), utilizing simulated rainfall experiments. The results showed that under various patterns of vegetation, the loss of soil aggregates is predominantly driven by microaggregates (<0.25 mm), A (65.2%) < B (72.4%) < C (77.7%) < D (87.7%). On the contrary, there is an opposite trend of change observed in macroaggregates(>0.25 mm). The vegetation pattern had different effects on the enrichment rate of aggregates in sediments: the enrichment ratio of macroaggregates decreased by 20.9%-64.7% and the enrichment ratio of microaggregates increased by 11.1%-34.5%. The cumulative loss of soil aggregates and the cumulative runoff volume can be described by a linear equation: y = ax + b, where 'a' denotes the rate of soil aggregate loss. Vegetation patterns had the capacity to decrease the rate of macroaggregate loss. Among these patterns, pattern D exhibits the lowest rate, followed by patterns C, B, and A. These results indicated that down-slope vegetation pattern is effective in reducing the loss of soil aggregates especially macroaggregates.