4.3. Particle size distribution and composition of eroded
sediment
Regarding the particle size distribution of eroded sediments, Dx (10),
Dx (50), and Dx (90) were mainly made up of silt, coarse powder grains
and very fine sand, and very fine sand and fine sand, respectively, with
the main enriched particle size increasing. Under the influence of
overland runoff, the structurally unstable fine particles were most
easily eroded, leading to different levels of fine particle enrichment
(Berger et al., 2010). Moreover, the erosion sediment gradually showed a
trend of coarse particles with longer scouring time (Schiettecatte et
al., 2008). These results were similar to those obtained by Jiang et al.
(2014). The enriched sediment of different particle sizes showed a trend
of first increasing and then decreasing with increasing slope gradient,
consistent with the results of
Zhang et al. (2015). Under different vegetation covers, the difference
of sediment particle size was obvious on slopes less than 15° but not
slopes greater than 15°, suggesting
that
the
flow velocity, which was influenced by slope gradient, can affect the
movement of soil particles differently. When the slope was less than
15°, the larger sediment particles were not easily eroded and
transported, meanwhile vegetation patches acted as sinks of sediment
(Cantón et al., 2012; Muñoz-Robles et al., 2013), to effectively
intercept and restrain sediment, thus the coarse particles were reduced
and the average particle size became smaller (Schiettecatte et al.,
2008; Zhu et al., 2016). However, when slope was greater than 15°,
the runoff eroding power was
increased, and soil corrosion resistance and anti-scourability were
reduced (Berger et al., 2010; Zhu et al., 2016). Meanwhile, the effect
of vegetation on interception and sorting of eroded sediment particles
was gradually decreased, thus Dx (10), Dx (50), and Dx (90) gradually
stabilized under different vegetation covers.