Effects of land disturbance on runoff and sediment yield after natural rainfall events in southwestern China

Severe soil erosion occurs in southwestern China owing to the large expanses of urbanization and sloping land. This field monitoring study was conducted to record the rainfall events, runoff, and sediment yield in 20-, 40-, and 60-m plots under conditions of artificial disturbance or natural restoration in the purple soil area of southwestern China. The study took place during the rainy season, and the plots were situated on a 15 degrees slope. The results showed that rainstorms and heavy rainstorms generated runoff and sediment yield. Rainfall intensity had a significantly positive power relationship with runoff rate and sediment yield rate in artificially disturbed plots but not in naturally restored plots. Plot length had a significant effect on runoff rate under artificial disturbance but not natural restoration. Within the same land disturbance category, there was no significant effect of plot length on sediment yield rate but there was a significant effect on sediment concentration. Overall, runoff rate, sediment yield rate, and sediment concentration showed remarkable effects of land disturbance across all plot lengths: naturally restored plots had 62.8-77.5% less runoff, 95.1-96.3% less sediment yield, and 63.1-73.5% lower sediment concentration than artificially disturbed plots. The relationship between runoff rate and sediment rate under the different land disturbances could be described by an exponential function. The results not only demonstrate the effectiveness of natural restoration for controlling runoff and sediment yield but also provide useful information for the design of field studies, taking into consideration the complexity of terrestrial systems.