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 lack of studies on the regulation of vegetation patterns with respect to soil aggregate loss. In this study, four different vegetation patterns were used to study the loss characteristics of soil aggregates during erosion: no vegetation (pattern A), upslope vegetation (pattern B), middle-slope vegetation (pattern C), and downslope vegetation (pattern D). The results show that the proportions of microaggregates (<0.25 mm) in the sediments during erosion are 65.2%, 72.4%, 77.7%, and 87.7% for patterns A, B, C, and D, respectively. The loss of macroaggregates (>0.25 mm) in the sediment is significantly higher in pattern A than in the other patterns (P < 0.05): A (34.8%) > B (27.6%) > C (22.3%) > D (12.3%). Vegetation on the slope reduces the mean weight diameter (MWD) of aggregates in the sediments by 66.0%–70.0% and the fractal dimension increases by 0.42%–0.96%. The vegetation pattern has different effects on the enrichment rate of aggregates in sediments: the enrichment ratio of macroaggregates decreases by 20.9%–64.7% and the enrichment ratio of microaggregates increases by 11.1%–34.5%. These results indicate that downslope vegetation effectively reduces soil erosion and the loss of soil macroaggregates.