Effects of Vegetation Cover and Rainfall Intensity on Sediment-Bound Nutrient Loss, Size Composition and Volume Fractal Dimension of Sediment Particles

Vegetation and rainfall are two important factors affecting soil erosion and thus resulting in nutrient loss in the Chinese Loess Plateau. A field experiment was conducted to investigate the effects of rainfall intensities (60, 100 and 140 mm h−1) and vegetation (Caragana korshinskii) coverages (0%, 30% and 80%) on soil loss, nutrient loss, and the composition and volume fractal dimension of eroded sediment particles under simulated rainfall conditions. The results showed that vegetation cover, rainfall intensity and their interaction all had significant effects on sediment transport and the sediment-bound nutrient loss. Higher rainfall intensity and lower coverage led to higher sediment and nutrient losses. Positive linear relationships were observed between soil loss and nutrient loss. The treatments showed more significant effects on the enrichment ratio (ER) of nitrogen (ERN) than organic matter (EROM) and phosphorus (ERp). Compared with the original surface soil, the eroded sediment contained more fine particles. Under the same coverage, the clay content significantly decreased with increasing rainfall intensity. The ER of sediment-bound nutrients was positively correlated with that of clay, suggesting that the clay fraction was preferentially eroded and soil nutrients were mainly adsorbed onto or contained within this fraction. There were increments in the fractal dimension of the sediment particles compared to that of the original surface soil. Moreover, the fractal dimension was positively correlated with clay, silt, and sediment-bound OM, N, and P contents, whereas it was negatively correlated with sand content. This study demonstrated that fractal dimension analysis can be used to characterize differences in particle-size distribution and nutrient loss associated with soil erosion.