Long-Term Gully Erosion and Its Response to Human Intervention in the Tableland Region of the Chinese Loess Plateau

Abstract

The gully erosion process is influenced by both natural conditions and human activities on the tableland region, the Chinese Loess Plateau, which is a densely populated agricultural area with unique topography. For the purpose of assessing long-term gully growth rates, the influencing factors and potential of gully growth, KH-4B satellite images, Quickbird-2 images, and unmanned aerial vehicle (UAV) images were used to assess gully erosion from 1969 to 2019. The effects of runoff, topography and human activities were analyzed with information derived from historical and present images. Ninety-five investigated gullies were classified into four types: 45 growing, 25 stable, 21 infilled and four excavated gullies. The rates (RA) of 45 growing gullies ranged from 0.50 to 20.94 m2·yr−1, with an average of 5.66 m2·yr−1 from 1969 to 2010. The present drainage area, local slope, average drainage slope, annual runoff, and ratio of the terraced area were all significantly different between the stable and growing gullies. The long-term gully growth rate could be estimated using a nonlinear regression model with annual runoff (Qa) and the slope of the drainage area (Sd) as predictors (RA = 0.301Qa0.562Sd, R2 = 0.530). Based on the Sg-A and Sg-Qa relationship that was used to reveal the threshold conditions for gully growth, all growing gullies still have the potential to keep growing, but soil and water conservation measures, including terraces, could change the threshold condition by reducing the effective drainage area. The results of this study could be helpful for preventing further gully erosion by dealing with gullies far above the threshold line.

Root Distribution and Soil Properties of Gully Heads and Their Effects on Headcut Migration in the Mollisols Region of Northeast China

“…Guo et al [32] reported that the SDR, SHC, SOM and MWD of gully heads significantly related to root diameter, RLD and root surface area density in the gullied region of the Loess Plateau. Furthermore, we found that some studies considered several soil properties including SHC, SDR, MWD, clay ratio, soil cohesion, and soil penetration resistance as indicators of soil erosion resistance [23,27,29,31,39,[50][51][52]. Therefore, the positive effects of vegetation roots on soil properties of gully heads fully manifested that the soil resistance of gully heads to erosion was closely affected by root distribution.…”

“…For example, Frankl et al [56] found that the linear, areal, and volumetric retreat rate were 0.34 m yr −1 , 1.70 m 2 yr −1 and 5.20 m 3 yr −1 over the rainy reason of 2010, respectively, while larger rates were found during medium to long time periods (1-47 years), with averages of 3.8 m yr −1 , 31.5 m 2 yr −1 and 47.7 m 3 yr −1 in northern Ethiopia, respectively. Wang et al [23] reported the lower linear and areal retreat rate of 0.30 m yr −1 and 5.66 m 2 yr −1 from 1969 to 2010 in the tableland region of the Chinese Loess Plateau. The above comparison indicated that the gully headcut migration rate in the Mollisols area of northeast China is relatively higher than that in other areas of the world.…”

“…The high soil bulk density represents high soil compactness and has a positive effect on soil erosion reduction [24]. The soil aggregate stability and shear strength reflect soil erodibility of gully heads [22,23,31,33], and thus their improvement would restrain gully headcut retreat. However, we found that gully headcut retreat was positively related to organic matter content and root density, which was different from previous studies that have confirmed that the vegetation effect on reducing gully erosion mainly depended on the root characteristics [6,16,[20][21][22]32,33,59].…”

“…In addition, many studies have documented that the root system had a positive effect on the improvement of soil properties [21][22][23]. For example, root and its exudates can improve soil infiltration capacity, strengthen aggregate stability, and soil cohesion [24][25][26].…”

“…The presence of roots is mainly dependent on the root binding effect, bonding effect and the biochemical effect [27,28]. Some soil property parameters, such as saturated hydraulic conductivity, soil aggregate stability, soil shear stress and soil disintegration rate, are regarded as being representative of soil erodibility [23,[29][30][31]. Moreover, Guo et al [16,[31][32][33] have proved the positive effect of roots on soil properties of gully heads and further significantly decreased soil erodibility of gully heads in the Chinese Loess Plateau.…”