4.3 Ephemeral gully erosion rate
The world is under serious threat of soil erosion. The ephemeral gully
erosion rate in Europe and America is 90–6,490 t
km–2 y–1 (Capra et al., 2009; Li
et al., 2016; Maetens et al., 2012; Panagos et al., 2015; Valcárcel et
al., 2003). On the Loess Plateau, the ephemeral gully erosion rate
without vegetation coverage is about 1,000–12,000 t
km–2 y–1, and with vegetation
coverage is 215 t km–2 y–1 in the
Loess Plateau (Zhang et al., 2017; Zheng, 2006). This study estimated an
ephemeral gully erosion rate of 22.12 m3km–2 y–1 or 28.75 t
km–2 y–1 (average soil bulk
density is 1.3 g cm–3) based on high-resolution
remote sensing images in the watershed from 2009 to 2021, considerably
lower than previous results but attributed to the improved vegetation
coverage in the watershed since the Chinese government implemented the
‘Grain for Green Project’ in 1999.
The increased vegetation coverage and biomass results in a dense
vegetation canopy that can intercept and redistribute rainwater and
reduce the kinetic energy of raindrops, and the grassland cover and
plant litter can reduce runoff erosion by avoiding the direct impact of
raindrops on soil, increasing soil infiltration capacity and runoff
resistance and decreasing runoff velocity (Hayas et al., 2017; Mukai,
2017; Sun et al., 2016; Vanmaercke et al., 2016). In addition, the
well-developed root systems have great physical and chemical binding
effects for combining soil particles and soil aggregates to improve soil
cohesion and the shear strength and tensile strength of the soil–root
matrix, significantly enhancing soil resistance to erosion (Allen et
al., 2018; Barthès and Roose, 2002; De Baets and Poesen, 2015; Guo et
al., 2019; Khan and Lateh, 2015; Wang et al., 2021c; Zegeye et al.,
2018; Zhao et al., 2013). In summary, vegetation restoration has
improved soil erosion conditions and enhanced regional water and soil
conservation benefits.