SSS2.8

The soil-covered Pisha stone area is the core source area of coarse sediment in the Yellow River and has become the focal point of ecological control of the Yellow River Basin. It is thus vital to study the spatial distribution of erosion coupling between geomorphology, vegetation, and water in the soil-covered Pisha stone area. Some valuable research results have been obtained already by using high-definition remote sensing aerial photographs and-high precision data from unmanned aerial vehicles. In particular, the image resolution obtained by unmanned remote sensing reveals small watershed topographic features and the characteristics of vegetation structure. Thus, the use of remote sensing is vital for research involving the spatial distribution of soil erosion in the slopes of the Pisha stone area and the dynamics of the geomorphic spatial structure of the slopes. In addition, the negative correlation between the spatial structure of the vegetation community and the energy dissipation impedance of erosion requires further study. Research into soil erosion in the Pisha stone area thus represents an urgent scientific need whose outcome will directly affect the theoretical foundation of a comprehensive model for treating soil erosion in this area.

How to cite: shen, Z.: Research progress of soil erosion in Pisha stone area of Yellow River, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3475, https://doi.org/10.5194/egusphere-egu22-3475, 2022.

Terraces are important practice to conserve soil and water in farming systems in mountain areas. Since the mid- 20^th century, marginalization of farmland occurred worldwide in mountainous areas. Farmers reduced investment in terraced fields or even abandoned the fields, and induced negative ecological consequences that are widely concerned. Current studies about marginalization of terraces mainly focus on upland terraces. The understandings of the process of marginalization of paddy terraces and their impacts are limited. Hani Paddy Terraces are one of the Globally Important Agriculture Heritage Systems. However, many of the paddy terraces have changed into upland terraces due to lack of water, labor out-migration ect, which hindered the conservation of the heritage. Taking Amengkong River Basin in Yuanyang County in Southwestern China as the case study area, we explored the changes in terrace structure, productivity of top soil (0~20 cm ) and the water holding capacity soil in 0~70 cm depth in Hani Paddy Terraces since conversion to upland terraces fields by 2~14 years. We found that (1) most ridges disappeared after conversion, the surface of fields were generally maintained in flat conditions, risers of terraces collapsed in varying degrees in more than 70% filed parcels. The degree of damages in terraces structures showed a U-shape curve along with time, as the pattern of drained by 2 years> drained by 3~4 years> drained by 10~14 years > drained by 5~9 years;（2）the soil productivity index increased after converted to upland terraces, and showed a trend of decreasing first and then increasing along with increasing years of conversion. (3) The water holding capacity of 0~70 cm soil dramatically decreased after conversion, and increasingly decreased along with increasing years of conversion. The maximum water holding capacity decreased by 9.16%~21.70% and the capillary volume decreased by 12.09%~24.20%，the decreasing of maximum water holding capacity and capillary volume were most serious in soils of 0~30 cm depth. Our study revealed the impacts of draining on structure of terraces and soil property in Hani Paddy terraces. The findings could enhance the understanding of the biophysical changes in soil during the marginalization in paddy terraces, which would benefit to the conservation and restoration of paddy terraces. 

How to cite: Li, Y., Wang, M., Jiao, Y., Rong, L., and Huang, J.: Changes in Terrace Structures and Soil Properties in Hani Paddy Terraces after Conversion to Upland Terraces, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4391, https://doi.org/10.5194/egusphere-egu22-4391, 2022.

    Subsurface water flow above the weakly permeable soil layer commonly occurs on purple soil slopes. However, it remains difficult to quantify the effect of subsurface water flow on the surface flow velocity. Laboratory experiments were performed to measure the rill flow velocity on purple soil slopes containing a subsurface water flow layer with the electrolyte tracer method considering 3 subsurface water flow depths (SWFDs: 5, 10, and 15 cm), 3 flow rates (FRs: 2, 4, and 8 L min^-1), and 4 slope gradients (SGs: 5°, 10°, 15°, and 20°). As a result, the pulse boundary model fit the electrolyte transport processes very well under the different SWFDs. The measured rill flow velocities were 0.202 to 0.610 m s^-1 under the various SWFDs. Stepwise regression results presented the positive dependence of the flow velocity on FR and SG but a negative dependence on SWFD. SWFD had notable effects on the rill flow velocity. Decreasing the SWFD from 15 to 5 cm increased the flow velocity. Moreover, the flow velocities under the 10- and 15-cm SWFDs were 89% and 86%, respectively, of that under the 5-cm SWFD. The flow velocity under the 5-, 10- and 15-cm SWFDs was decreased to 89%, 80%, and 77%, respectively, of that on saturated soil slopes. The results will enhance the understanding of rill flow hydrological processes under SWFD impact.

How to cite: Tao, T., Chen, S., and Chen, X.: Rill flow velocity affected by the subsurface water flow depth of purple soil in Southwest China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6779, https://doi.org/10.5194/egusphere-egu22-6779, 2022.

Despite soil erosion has a strong impact on crop yield, whether soil erosion depth leads to abrupt or gradual crop yield changes is not well understood. To investigate how crop yields respond to soil erosion depth, we conducted a simulated erosion experiment by adopting the cut-and-fill method from 2012 to 2018 in a typical mountain area in the southeastern China. A completely randomized design with five soil erosion depth (5, 10, 20, 30 and 40 cm soil cut) and a control (0 cm soil cut) were used. Each treatment had three replicates. Maize was planted in these simulated erosion plots and maize yields were monitored from 2012 to 2018. Our results showed that the maize yield decreased with erosion depth and with decreasing remaining A_p horizon depth. Inconsistent with earlier studies, maize yield exhibited a quadratic function rather than linear response to increase in soil erosion depth and decrease in remaining A_p horizon depth. Soil erosion depth led to abrupt changes in maize yield. Compared with control, maize yield did not decrease significantly at 5 cm erosion depth or ＞25 cm remaining A horizon depth, but its reduction rate per 1cm of soil loss (3.36%) increased sharply at 10 cm erosion depth or 20 cm remaining A_p horizon. When remaining A_p horizon left 10 cm, maize yield demonstrated the lowest, which may be irreversible via application of chemical fertilization. Considering high heterogeneity of A_p horizon in the mountain area, soil erosion-crop yield relationship could be expressed well by remaining A_p horizon. We also found remaining A_p depth had a significant direct and indirect (via reduced SOM, soil available water, AP and AK contents) negative effect on maize yield. These results could be useful in identifying allowable soil-loss thickness and highlight the importance of soil nutrient monitoring in different soil erosion levels in designing a fertilization scheme aimed at ensuring food security.

How to cite: Rong, L., Duan, X., Liu, T., and Qin, Y.: The effect of soil erosion depth on maize yields, evidence based on a long-term field simulation experiment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4998, https://doi.org/10.5194/egusphere-egu22-4998, 2022.

Gully erosion was one of the key processes of soil erosion in Hengduan mountain region, which belonged to the eastern part of Qinghai-Tibet Plateau. This dramatic changes in both horizontal and vertical direction has led to a diversity soil groups within the region. The aims of this study were to investigate the gully distribution and density in different soil zones, and find out the key factors that influenced the susceptibility and intensity of gully erosion of Hengduan mountain area. Totally 2300 investigation quadrats were randomly set with the size of 1 km × 1 km to check whether the occurrence and the density by Google Earth images. The ratio of gully occurrence (GR) was 25.5%, and the average gully density (GD) and gully number (GN) was 2.22 km km^-2 and 20.4 of Hengduan mountain area. The annual temperature, vegetation and slope were the key factors that influences the occurrences of gullies in the alpine (>3700 m a.s.l), middle mountain (2000-3700 m a.s.l) and low mountain (<2000 m a.s.l) soil zones, respectively. The intensity of gully erosion showed exponential decreasing relationships with soil property including soil organic matters and silt content, and the average GD in different soil zones showed the same relationships with the R2 higher than 0.7. These results indicating that the distribution of gully erosion were more related to the external environmental factors, and the intensity of gully erosion were determined by soil properties at the regional scales.

How to cite: Dong, Y.: The distribution and intensity of gully erosion in different soil zones of the Hengduan Mountain area, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1947, https://doi.org/10.5194/egusphere-egu22-1947, 2022.

The vegetation cover in China has changed significantly in the past 30 years, however evidence for vegetation cover dynamics in the dry valley region (DVR) is still lacking. This study aimed to detect fractional vegetation cover dynamics in DVR from 2000 to 2020 with MODIS products, and evaluate the effects of precipitation and hydropower construction projects on vegetation cover dynamics. The results showed that: (a) the long-term average annual fractional vegetation cover for the dry valley region, including the dry-hot valleys, dry-warm valleys and dry-temperature valleys were 0.452, 0.426, 0.504 and 0.446, respectively. Significant decreasing trend of annual FVC from 2000 to 2020 was reported for overall dry valley region. Specifically, significant reducing trends were mainly observed in the dry-hot valleys and dry-warm valleys that located in the west-south part of DVR, while significant growing trends in the dry-temperature valleys of the Min and Baishui Rivers; (b) Annual Precipitation and hydropower projects construction are two key factors that contributing to changes in annual FVC for valleys. The present study is probably the first report on vegetation cover dynamics and the effects of influencing factors in DVR of Southwest China, and helpfully for further scientific studies and restoration management practices in DVR, although more detailed studies for the changes of vegetation cover and its mechanism need to be done.

How to cite: Guo, Q., Shan, Z., Zhong, R., and Duan, X.: Fractional Vegetation Cover Dynamics of the dry valleys in Southwest China from 2000 to 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6708, https://doi.org/10.5194/egusphere-egu22-6708, 2022.

Soil erosion in croplands has a strong impact on global carbon (C) cycle. Assessment of erosional effects on soil organic carbon (SOC) dynamics in agricultural soils suffers from the difficulty of distinguishing the erosional effects and complex interaction processes between erosion and C cycling. To simulate the effects of soil erosion, a plots experiment including six erosion levels (0, 5, 10, 20, 30, and 40 cm eroded) was conducted for seven years (2012-2018). The erosion levels were simulated using artificial soil profiles created by mixing soils from different layers in the original soil profile (never eroded) in a certain proportion. Subsequently, based on the field observations during 2012-2018, the SOC dynamics of each experimental plot were simulated by using a process-oriented C cycle model (denitrification-decomposition (DNDC)) to quantify the effects of erosion on SOC dynamics. The measurements at the beginning of the plots experiment showed that simulated erosion resulted in the depletion of SOC with an average reduction rate of 9.7% per 10 cm of soil loss; SOC in eroded soils recovered after seven years of cropping, the declining slope of the SOC measured in 2018 was 3.0% per 10 cm of soil loss, suggesting that dynamic replacement had occurred. Model simulation results indicated that soil erosion could reduce the C inputs from crop residue by lowering soil productivity; soil heterotrophic respiration in eroded soils was restricted due to the lower initial SOC content. As a result, the simulated overall SOC stock in eroded soils was restored after erosion stopped because of the lower C output. These results indicated that SOC loss at eroding sites was caused mainly by lateral transport rather than enhanced decomposition. The fate of the displaced SOC within catchments is key to assess the net impacts of soil erosion on SOC dynamics at a large scale.

How to cite: Lin, H., Duan, X., Li, Y., Zhang, L., Rong, L., and Li, R.: Simulating the effects of erosion on organic carbon dynamics in agricultural soils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6640, https://doi.org/10.5194/egusphere-egu22-6640, 2022.

Abstract: To explore the adaptable plants soil reinforcement effects in the karst region of southwest China. A horizontal pull friction test was performed on the roots and soil by using a three-year-old shrub Pyracantha, and the friction characteristics of root-soil interface were analyzed by scanning electron microscopy and interference method. The results indicated that :(1) the root system of pyracantha showed two failure modes in the pull-out test: the pull-out friction of root-soil interface increases with the increase of root diameter and vertical load. (2) When gravel content is set at 0, 10%, 30% and 50%, the frictional force between root and soil tends to decrease. (3) There was a positive correlation between root surface roughness and root diameter in diameter range of 1-6mm, with correlation coefficient R =0.995. (4) There is an obvious correlation between root-soil friction and roughness. These results are significant to further explore the mechanical mechanism of plant root-soil interaction, and to strengthen the shallow soil and repair the fragile ecological environment.

Key words: Karst; Pyracantha; Root-soil friction; Roughness

How to cite: Guo, H.: Research on the interaction between roots and soil of adaptable plants pyracantha in the karst region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4227, https://doi.org/10.5194/egusphere-egu22-4227, 2022.

Plant litter incorporation into soil is a widespread phenomenon in the natural environment. Accurate estimation of the soil detachment capacity ( Dc ) driven by overland flow under litter incorporation effects is crucial for improving soil erosion prediction. However, the effects of litter incorporation on soil detachment processes are often ignored, and the temporal variation of Dc under litter incorporation effects remains unclear for the Loess Plateau of China. In this study, we conducted flume tests to determine the temporal variation of Dc for soils incorporating two typical plant litters ( Bothriochloa ischaemum (L.) Keng. litter, and Artemisia sacrorum Ledeb. litter) between May 2017 and October 2018 (a 524-day period). Furthermore, the key factors
affecting Dc were identified. Our results showed that the temporal variation in Dc was consistent across the different soil treatments (two litter incorporation treatments and one bare soil control), showing a rapid decline and then fluctuating at a low level, with Dc ranging from 0.115 to 6.876 kg m⁻² s⁻¹ . Incorporation of litter effectively reduced Dc , with the Dc of soil treatments incorporating litter being 15% to 29% lower than that of bare soil (2.110 kg m⁻² s⁻¹ ). Further analysis showed that the temporal variation in Dc was mainly affected by the development of a physical soil crust. Dc can be successfully estimated using a nonlinear equation incorporating flow shear stress and soil cohesion (R² = 0.77, NSE = 0.65), which represent the erosive force and soil erosion resistance, respectively. Our study reveals the important role of plant litter in the soil detachment process and aids the understanding of soil erosion pathways. Further studies are needed to investigate the effects of a physical soil crust on the soil detachment process driven by overland flow.

How to cite: Liu, J.: Effects of Litter Incorporation on Soil Detachment Processes on the Loess Plateau of China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4625, https://doi.org/10.5194/egusphere-egu22-4625, 2022.

How to cite: Li, Y., Duan, X., Li, Y., Li, Y., and Zhang, L.: Interactive effects of land use and soil erosion on soil organic carbon in the dry-hot valley region of southern China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6676, https://doi.org/10.5194/egusphere-egu22-6676, 2022.

The hydrological conditions near the soil surface influence the soil erosion process, as determined by the soil erodibility and critical shear stress. The soil erodibility and critical shear stress of saturated purple soil slopes were computed and compared with those of unsaturated purple soil slopes. The detachment capacities computed through the numerical method (NM), modified numerical method (MNM) and analytical method (AM), from rill erosion experiments on saturated purple soil slopes at different flow rates (2, 4, and 8 L min⁻¹) and slope gradients (5, 10, 15, and 20°), were used to comparatively compute the soil erodibility and critical shear stress. The computed soil erodibilities and critical shear stresses were also compared with those of unsaturated purple soil slopes. At the different slope gradients ranging from 5° to 20°, there were no significant differences in the soil erodibilities of the saturated purple soil and also in those of the unsaturated purple soil. The critical shear stresses slightly varied with the slope gradients. The saturated purple soil was relatively significantly more susceptible to erosion. The NM overestimated the soil erodibility of both saturated and unsaturated soils by 31% and underestimated the critical shear stress. The MNM yielded the same soil erodibility and critical shear stress values as the AM. The results of this study supply parameters for modeling rill erosion of saturated purple soil slope.

How to cite: Li, D., Chen, X., Han, Z., Gu, X., and Li, Y.: Determination of Rill Erodibility and Critical Shear Stress of Saturated Purple Soil Slopes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3290, https://doi.org/10.5194/egusphere-egu22-3290, 2022.

How to use a suitable method to accurately measure gully morphology is very important in the study of gully erosion monitoring and development, and the development of Unmanned Aerial Vehicle (UAV) has made it easy to apply UAV photogrammetry techniques to gully erosion studies. The aim of this study is to evaluate the accuracy of data and the efficiency of data processing by analyzing the errors of different schemes, and to provide suitable plan design ideas for the study of gully by UAV. Gully is the object of study and different flight schemes and Ground Control Point (GCP) placement schemes are used to acquire and process the data, and finally the errors are analyzed by Digital Surface Model (DSM) and orthophoto. Among all the schemes, the one with a flight altitude of 30m, 80%/70% photo overlap and 11 GCPs had the highest accuracy (Mean absolute error of 0.0353m and root mean square error of 0.0525m), but this scheme took more data collection and processing time and was less efficient. The number of GCPs and the placement location also have a significant impact on the accuracy，the position closer to the GCPs has a smaller error，and this study proves that the number of GCPs should not be more than 9 and should be evenly distributed in different parts of the gully.. When the flight altitude is 70m, the overlap is not less than 50%/40%, and the number of control points is 6, both accuracy and measurement efficiency can be taken into account at the same time. In addition, the sources of errors and the distribution locations of checkpoints with high errors were analyzed in four aspects: shadow, slope gradient, slope direction and vegetation. The use of UAVs in gully erosion studies is very convenient to get the later products with centimeter-level accuracy, and based on the results of the study we suggest that the flight altitude and photo overlap can be appropriately reduced when designing the scheme, and the number of GCP can be increased in the areas that need to be focused on and the areas with large elevation changes. At the same time, flight safety, UAV battery power, data collection efficiency and processing efficiency should be considered comprehensively.

How to cite: Yang, J., Dong, Y., and Huang, J.: Assessment of the gully morphology measurement method based on UAV photogrammetry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-828, https://doi.org/10.5194/egusphere-egu22-828, 2022.