Spoil heaps, resulting from excavation and backfilling at construction sites, are highly susceptible to soil detachment and transport, leading to rill development, while large-scale infrastructure activities continually alter the soil bulk density. However, the mechanisms by which soil bulk density affects rill erosion on spoil heaps remain poorly understood. This study aims to investigate how soil bulk density governs rill morphology and hydraulic parameters on spoil heaps by conducting multiple flume tests under different flow discharges (3, 5, and 7 L min(-1)), slope gradients (10, 20, and 30 degrees), and soil bulk densities (1.2, 1.5, and 1.8 g cm(-3)). Close-range digital photogrammetry was utilized to obtain surface elevation information, which was used for constructing a digital elevation model (DEM). The results showed: 1) soil bulk density significantly affected the soil erosion resistance of spoil heaps: as it increased from 1.2 to 1.8 g cm(-3), soil erodibility decreased, while critical shear stress increased from 4.17 to 6.47 Pa and critical stream power from 1.23 to 2.13 N m(-1) s(-1); 2) soil bulk density significantly suppressed rill development as it increased from 1.2 to 1.8 g cm(-3), reducing the mean rill density by 19.4 %, the mean rill width-depth ratio by 48.2 %, and the mean rill inclination angle by 30.5 %; 3) rill depth was the best morphological predictor of sediment yield (P < 0.01), and among the four derived morphological indicators, the degree of rill dissection was the optimal predictor of rill erosion and morphology, followed by the rill inclination angle, the rill width-depth ratio, and the rill density. This study would enhance understanding of the complicated interactions between soil bulk density and morphological development on spoil heaps, and provides strategic erosion control plans for their management.

This study aimed to quantify the effects of freeze‒thaw on the soil detachment rate (SDR) and soil erosion resistance of alpine meadows with different vegetation cover and develop a prediction model to quantify soil erosion resistance. In this study, alpine meadows with four vegetation coverages (approximately 100

To identify the response of sediment load (SL) to climate change and human activities, the contributions of driving factors should be assessed based on different methods, time series lengths, and reference periods. However, their results are inconsistent, and it is unclear which method is most suitable. Thus, it is crucial to declare the effect of time series division and the application of different methods on outcomes. A database including daily precipitation and temperature from 227 meteorological stations, annual runoff and sediment load from Yichang, Hankou, and Datong hydrological station, storage capacity of dams during 1960-2020, and land use datasets (30 m x 30 m) during 1985-2020, was selected. Five breakpoint analysis methods were chosen to identify reference period, including moving mean difference (MovMean), Pettitt's test, cumulative anomaly, Mann-Kendall test, and sequential cluster methods. Subsequently, three modified empirical models, including double mass curve, slope change ratio of accumulative quantity (SCRAQ), and multi linear regression, were used to quantify why sediment yield changed in upper, middle, lower reaches, and entire basin of Yangtze River. Results indicated that MovMean performed best in the breakpoint analysis. The accurate breakpoints were in 1994 and 2001. Compared to the reference period (1960-1994), SL decreased by 25.16 % during 1995-2001 and 67.97 % during 2002-2020 in the entire basin. The main sand-producing area had changed from upper reach in 1960-2001 to middle and lower reaches in 2002-2020. The SCRAQ method was the most suitable method for comparing contributions of all driving factors to SL. Dam construction was the dominant factor of sediment reduction in the upper reach, cropland area was the important factor of sediment increase in the middle and lower reaches. This study can provide the basic information for selecting appropriate methods to determine the accurate reference period and dominant driving factors of SL variation.

Topographic factor has crucial impacts on the rock weathering and soil development. However, few studies have concerned the influence of topographic features on the spatial distribution of soil properties at the initial soil development stage. To explore this, soil samples were collected from 10 soil profiles on scoria cone, and from 18 quadrats on lava plateau along the NNW-SSE toposequence in Laoheishan volcanic field of 300 years, northeast China. Basic indicators such as soil thickness, mechanical composition, organic carbon and total nitrogen and their mineral-associated fractions were measured, and soil bacterial community were identified by 16S rRNA amplicon sequencing method, and their relationships with topography were determined by Spearman rank correlation and pathway analysis. Compared to lava plateau with weak-weathered binary structure thinner than 13 cm, scoria slopes developed typical soil profiles ranging from 7 to 30 cm, with lower clay and silt fraction (e.g. topsoil: 73.75 % vs. 35.57 %), which positively associated with carbon and nitrogen contents (e.g. topsoil organic carbon: 72.32 vs. 38.59 g kg- 1). Northern slope had finer particles, richer carbon and nutrients than southern slope, with organic carbon peaked around middle slope position with 116.76 and 34.70 g kg- 1, respectively. Northern lava plateau showed distinctive differences from other topographic sites in bacterial phyla structure and functional groups. The total explanation of carbon and nitrogen contents and their stoichiometric ratio values to bacterial phyla structure accounted for 41 %. In conclusion, topography influenced clay fraction gathering, which in turn affected the accumulation of carbon and nutrients. Ultimately, it regulated shifts in bacterial diversity during the initial soil development process. This study will improve understanding of topographic-driven mechanisms of initial soil development and soil characteristics spatial patterns.

Soil erosion causes serious grassland degradation in the Three-River Headwater Region (TRHR) of the Qinghai-Tibet Plateau. Identifying source areas of erosion is important, including understanding the influences of hillslope aspect on soil erosion. However, the effect of hillslope aspect on soil erosion is a much-debated process, wherein contrasting results were previously reported. We hypothesized that aspect-induced differences in environmental variables will be related to differences in erosion magnitude and spatial pattern, and that these differences will impact soil physiochemical characteristics as well. To test this hypothesis, soil samples were collected at conjoined south- and north-facing hillslopes along elevational profiles in a small watershed in Yushu County, with measurements of soil water content (SWC), soil organic carbon (SOC), soil organic matter (SOM), soil particle size distribution, soil total nitrogen (STN) and phosphorus (STP). Soil erosion rate was estimated using 137Cs technology. The results showed that soil erosion rates of the two hillslopes ranged from 0.073 to 10.83 t ha-1 yr-1, and were 3 times greater on the south-facing hillslope. Soil water content ranged from 7.6% to 76.8% on the two hillslopes with lower values on the south-facing hillslope due to the greater solar radiation. By Spearman correlation analysis and path analysis, we concluded that lower soil water content on the south-facing hillslope restricts vegetation growth, and hence resulting in greater soil erosion under the case where vegetation growth is dominantly controlled by water availability. Greater soil erosion on the south-facing hillslope caused greater surficial accumulation of coarser materials and greater loss of soil nutrients, which are expected to complicate the hydrological erosion process. Moreover, the downslope increased soil erosion rate should be fully considered in conservation practices. These results will improve our understanding of the interaction and feedback mechanisms between soil characteristics, vegetation function, and soil erosion in the TRHR.

The deteriorating soil carbon, nutrients, and microbial habitat pose a serious threat to crop production. However, the effects of long-term cultivation with soil erosion on soil carbon, nitrogen, and bacterial communities remain poorly understood. Consequently, this study aims to explore the changes in these soil indicators in the last 110 years and their responses to soil erosion. Luvic Phaeozems in hillslope and Haplic Phaeozems in flat were sampled along 113- and 67-year cultivation chronosequences. The soil organic carbon (SOC), total nitrogen (TN), soil loss rate, the soil bacterial community, and so on were respectively determined using the Walkley-Black, the Kjeldahl, nuclide tracing method, and 16S rRNA amplicon sequencing methods. The comparisons of SOC, TN, and soil bacterial community between Luvic Phaeozems and Haplic Phaeozems were used to differentiate their responses to the soil erosion intensity. The results indicated that SOC and TN decreased negatively and exponentially during long-term cultivation and took longer to regain stability in Luvic Phaeozems than in Haplic Phaeozems (e.g., SOC: from 55.77 to 23.11 g kg-1 after 152 years vs. from 91.83 to 34.24 g kg-1 after 32 years). The bacterial community transitioned into Proteobacteria-dominant communities and the quantity of carbon-fixing and nitrogen-fixing functional groups decreased. These shifts were mainly driven by the SOC and TN contents (40%) and their loss ratios (44%). In conclusion, soil erosion leads to more severe SOC and TN loss on hillslope than flat under long-term improper cultivation, ultimately endangering soil bacterial ecological functions, which has important implications for effective soil erosion control and encouraging conservation tillage in this food-producing region.

Rainfall erosivity is commonly used to estimate the probability of soil erosion caused by rainfall. The accurate detection of temporal changes in rainfall erosivity and the identification of abrupt changes and trends are important for understanding the physical causes of variation. In this study, a detection framework is introduced to identify temporal changes in rainfall erosivity time series as follows: (i) The significance of time series variation of rainfall erosivity is assessed based on the Hurst coefficient and divided into three levels: None, medium, and high. (ii) The detection of abrupt changes (Mann–Kendall, Moving T, and Bayesian tests) and trends (Spearman and Kendall rank correlation tests) of variate series and the correlation coefficient between the variation component and the original series is calculated. (iii) The modified series is obtained by preferentially eliminating the variation component (trend or change point) with larger correlation coefficients. (iv) We substituted the modified series into steps i to iii until the correlation coefficient was not significant. This framework is used to analyze the variation of rainfall erosivity in the Three Gorges Reservoir, China. The results showed that by using traditional methods, both an increasing trend and an upward change point were observed in Zigui station. However, after the upward change point was deducted from the annual rainfall erosivity series R(t), the resultant Rm(t) showed no statistically significant trend. Trend analysis should be performed considering the existence of an abrupt change to assess the long-term changes in rainfall erosivity series; otherwise, it would result in the wrong conclusion. In addition, the change points detected in the Rm(t) varied with the methods. Compared with the single-test method, the proposed framework can effectively reduce uncertainty.

The soil shrink–swell phenomenon produces crack networks and slope instability. However, few studies have involved the continuous shrink–swell process of granite residual soils. The objective of the study is to explore the shrink–swell process of weathered granite soils and its effects on gully development in southern China. The bulk density, soil water content (SWC), shrink–swell ratio (SSR), clay mineral content, and mechanical composition, etc., of soil samples from five soil layers (at depths of 0.3 m, 3.0 m, 7.0 m, 12.0 m, and 16.0 m) along a profile in Yudu County was analyzed. After quantifying the soil properties at different soil depths, we analyzed these data statistically in an effort to identify strong parametric relationships. The results indicated that some properties such as bulk density and shear stress increased with soil depth, while other soil properties, such as plasticity index and liquid limit, were inversely related to depth. Soil cohesion, the angle of internal friction, and shear stress were closely related to the SWC. Every 1% decrease in the SWC resulted in a shear stress reduction of 6.62 kPa. The SSR values exhibited significant variation between the three dry–wet cycles and were closely related to the bulk density values of our kaolin and montmorillonite samples. As an environmental factor, the SWC can trigger changes in internal soil properties such as shear stress and the SSR. Using these data and observations made during our field survey, it can be proposed that continuous shrink–swell variation in deep granite-weathering crust can result in crack formation and gully erosion. It can be inferred that crack development velocity and gully retreat rate may be affected by the soil’s shrink–swell process. Consequently, this information provides insight to understanding the mechanism of gully development in southern China.

Recently, there has been an increase in collapsing gullies in the south of China as one of the most destructive types of soil erosion. Most collapsing gullies are formed on a well-developed granite crust; thus, granite residual soil plays a critical role. However, the extent to which the geotechnical features of residual soil, especially soil disintegration, affects collapsing gully formation is poorly understood. This study performed laboratory disintegration tests on granite residual soil taken from the red soil, sandy soil, and detritus layers of a collapsing gully. The disintegration behaviour was quantified by defining the disintegration ratio, R-d, and three equivalent disintegration rates, v(I), v(II,) and vI(II), corresponding to R-d =10%, 30%, and 50%, respectively. The results revealed that the red soil layer (depth < 1.3 m) and the soil at the shallower depth of the sandy soil layer (depth < 3.0 m) showed similar disintegration behaviours, which were complete (R-d = 100%) and rapid, with vI values in the range of 66.7-266.7%/min. The soil disintegration in the sandy soil layer was characterised by an incremental increase in R-d to 100% within 100 min. The residual soil at the bottom of the sandy soil layer and the top of the detritus layer (depths of 4.0-8.0 m) disintegrated consistently at the first, after which the disintegration rate gradually decreased with v(III) lower than 1%/min. The detritus layer soil at a depth greater than 10.0 m showed incomplete disintegration, and the ultimate R-d was approximately 60%. The formation mechanism for the soil disintegration and gully collapse was also proposed. The weakening of cementation triggered the breakup of soil aggregates and led to soil disintegration and the occurrence of a gully collapse. This study provided new insights on gully erosion.

In most cases, chemical weathering reduces the strength and stability of granite regolith and increases its water sensitivity. When combined with external agents such as climate, these alterations facilitate geomorphological evolution, such as gully erosion in hilly regions. The lack of fundamental understanding about how gully erosion forms have led to an increasing trend of gully erosion in recent years. Because the weathering-controlled properties of granite regolith have a significant effect on gully development, it is vital to assess the chemical weathering degree. However, despite extensive studies on quantifying weathering degree using chemical weathering indices, less is known about how these parameters are correlated with the mechanical properties of granite regolith. To this end, a typical weathering profile is established for granite in Jiangmen, China. This paper investigates the chemical weathering of granite, evaluates the appropriateness of previous chemical weathering indices, and correlates them with the mechanical parameters of granite regolith. Several suitable indices, including CIA, Bases/Al2O3, Bases/R2O3, ba(1), ba(3), CIW, I-mob, and PIA, are selected and correlated with the mechanical parameters. These indices apply well, with some scattering when they are correlated with the internal frictional angle of granite residual soil. This paper provides a comprehensive datset regarding the physical, mineralogical, petrographical, geochemical, and mechanical properties of granite regolith, and enhances the understanding of chemical weathering, especially its correlations with the mechanical properties of regolith.

Ammonia is the simplest molecule for the installation of nitrogen atom in organic compounds. It is abundantly available, economic and highly attractive from the point of atom economy for its use in organic synthesis, however, an highly challenging task for accessing the nitrogenous scaffolds through N−H activation of ammonia. With the advancement of synthetic procedures, scientific community continually developing excellent reactions employing ammonia as a source of nitrogen for various types of amination reactions and accomplishing the synthesis of nitrogenous compounds. This Review provides recent developments in amination reactions employing ammonia as a nitrogen source at a single platform.

Gully erosion is a soil degradation process widely present across the world. Permanent gully erosion has usually soil erosion rates one order of magnitude higher than hillslope water erosion in conventional agriculture, e.g. 2.1 vs 0.6 mm year-1 (Castillo and Gómez, 2016). It remains a major process of soil degradation worldwide. This work attempts to investigate recent trends of published research on gully erosion in relation to gully erosion control since 2000. A review in Web of Science (core collection, 2000-19 by title) reported 401 documents, produced mainly in the European Union (52.1%), China (22.7%), USA (16.0%) and Australia (8.7%). Approximately 17% of all these articles covered restoration or control of gully erosion as their main topic. When screened most of these 68 articles deal with specific situations and techniques with a limited number devoted to a comparative review of effectiveness of different techniques, one of the few exceptions was Liu et al. (2019a). To provide perspective, there were a similar proportion of articles devoted to the study of gully erosion processes, a and a much larger number of articles devoted to the description of gully development and erosion rates in specific situations. It is apparent that the subject of gully erosion control is not a dominant one in the scientific indexed literature. This review was complemented with an analysis in WOCAT (WOCAT, 2019), a comprehensive international databases of soil conservation technologies. It showed with 27 entries of gully erosion restoration techniques over a total of 1098 descriptions (2.5% approximately). This might be explained, partially, because most of the information on gully erosion control appears in documents outside scientific, or technical, international databases, many times in local languages. Overall, two of the major barriers frequently noted by stakeholders, particularly farmers, for effective gully erosion control, their high costs and the complexity of controlling expansion of very large gullies (e.g. Liu et al.2019b) are not major major subjects in the international scientific literature on gullies in the last decades. It is apparent that there is the need for a more comprehensive comparative analysis of the effectiveness and cost of different strategies of gully erosion control techniques, particularly oriented to reduce the investment cost of their implementation, especially in very large gullies where compex slope instability processes might play a dominant role. This communication presents a comprehensive analysis on the available information on international scientific literature on gully erosion research to suggest key lines and strategies for future research. References Castillo, C., Gómez, J.A. 2016 A century of gully erosion research: Urgency, complexity and study approaches Earth-Science Reviews 160: 300–319 Liu, X., et al. 2019a. Gully Erosion Control Practices in Northeast China: A Review. Sustainability 11: 5065, doi:10.3390/su11185065 Liu, H., et al. 2019b. Using 3D scanner to study gully evolution and its hydrological analysis in the deep weathering of southern China. Catena 183. https://doi.org/10.1016/j.catena.2019.104218 WOCAT. 2020. World Overview of Conservation Approaches and Technologies. https://www.wocat.net/en/

Rainfall erosivity (R factor), in the Universal Soil Loss Equation (USLE) , a climate index, is used worldwide to assess and predict the potential of rainfall to cause erosion. The temporal variation in rainfall erosivity, informs of abrupt change and trend, are critical for soil loss prediction. To find a simple and effective method for accurate detection of abrupt change and trend has implication for soil and water conservation planning. In this paper, a four-step framework is proposed to detect abrupt change and trend in rainfall erosivity time series, i.e., evaluate the significance of variation in rainfall erosivity time series at three levels: no, weak and strong, abrupt change and trend detection for rainfall erosivity, estimation of correlation coefficient between the variation component and rainfall erosivity series, remove the variation component with the largest correlation coefficient from the rainfall erosivity series, repeat the above steps for the new series until variance coefficient was insignificance. The first step is based on an index of Hurst coefficient. The trend detection is implemented using both Spearman rank and Kendall rank correlation test. For abrupt change ,three kinds of methods (Mann-Kendall, Moving T and Bayesian test) are employed. This framework is applied to the annual rainfall erosivity series of the Three Gorges Reservoir , China. There was a large uncertainty in detecting variability with a single test method. Application of the proposed framework can reduce uncertainty associated with soil erosion assessment and achieve more accurate regional soil and water management.

The upper reaches of the Hanjiang River Basin (HM-CSNWTP) is the headwater source for the middle route of China?s South-to-North Water Transfer Project (M-CSNWTP), as well as the north-south transitional zone of central China, and is characterized by high precipitation sensitivity and variability. Changes in precipitation patterns can affect the potential runoff generation capacity of the HM-CSNWTP. Therefore, this study was focused on exploring the dynamic precipitation patterns over the HM-CSNWTP and the potential runoff generation capacity of this region at annual and seasonal timescales. Daily precipitation data from 34 meteorological stations for the period 1961?2016 were collected in order to estimate 4 categories of rainfall indices: average daily precipitation on all days (ADP) and on rainy days (ARP), total amount (TP), and rainy days (TD). The nonparametric Mann-Kendall test, LOWESS smoothing, and collaborative kriging method were implemented. The statistical results indicated that: (1) The annual ADP over the basin decreased slightly, at the rate of - 0.22%/10a (-0.002 mm/d/a). Seasonally, summer ADP increased by 1.4%/10a (0.005 mm/d/a), while decreasing ADP values were detected in other seasons. Large increases in annual and summer ARP were found, at rates of 3.73%/ 10a (0.018 mm/d/a) and 3.72%/10a (0.039 mm/d/a), over the HM-CSNWTP, mainly in the southwestern area (Region III), due to the large changes of annual and summer ARP. Annual and summer ARP increased at significant rates of 7.22%/10a (0.034 mm/d/a) and 10.64%/10a (0.083 mm/d/a), respectively. (2) Decreasing light rainfall amounts (TP0-10) and days (TD0-10), and increasing heavy rainfall amounts (TP>25) and days (TD>25) were detected over the HM-CSNWTP, especially for Region III, in which TP>25 and TD>25 increased by 7.00%/10a (1.076 mm/a) and 5.37%/10a (0.023 d/a), respectively. (3) In the wettest assumption scenario, the estimated annual, spring, summer, autumn, and winter runoff depths were 912.9 mm, 183.0 mm, 410.6 mm, 259.0 mm, and 60.3 mm, respectively. In the driest assumption, the estimated annual, spring, summer, autumn, and winter runoff depths were 131.4 mm, 35.6 mm, 65.7 mm, 27.8 mm, and 2.3 mm, respectively, and the planned diversion water accounted for 76.1%, 63.2%, 70.0%, 102.2%, and 156.5% of the annual and seasonal driest assumption runoff depths, respectively. Thus, the water diversion of the M-CSNWTP in the driest assumption may trigger water shortages and environmental disasters in the lower reaches of the Hanjiang River Basin, especially at annual, autumn, and winter timescales. These findings provide some basic information for local water resource management in the HM-CSNWTP.

Global climate change is significant, and the spatiotemporal variations of precipitation associated with it are pronounced. Based on the daily precipitation data from 10 weather stations located from southeast to northwest across China from 1961–2017, the Mann–Kendall trend test was generally applied to analyze the spatiotemporal variations of precipitation. The factors influencing the precipitation changes were investigated. The results revealed that (1) the annual, summer, and winter rainfall amount (RA) exhibited increasing rates of 16.36, 12.31, and 2.49 mm/10 year, respectively. The change rates of annual rainfall days (RD) were 2.68 day/10 year in the northwest region and −1.88 day/10 year in the southeast. The annual and seasonal daily precipitation on rainy days (RP) exhibited an increasing trend. (2) All of the RA, RD, and RP values initially increased, then decreased, and then slightly increased from Southeast to Northwest China. These results proved that the RA increased with the increase of light rain in Northwest China and heavy rain in Southeast China. In addition, changes in the monsoon have altered the rate at which RA, RD, and RP vary with distance from the sea. These findings may help to provide suggestions for the rational spatial utilization of water resources in China.

There are 239,100 gullies in southern China, which cause the degradation of ecological system. However, studies on gully development at the regional scale is relatively lack. The purpose of this study is to analyze the regional gully dynamics and explore how land use and topographic factors affect gully development. Input data consists of land use maps derived from high-resolution images from 2004 to 2014, and topography maps from a digital elevation model with a pixel size of 8 m × 8 m in two 25-km2 study sites of Anxi (AX) and Xingning county (XN). The following results were obtained: (1) AX gullies decreased from 2006 to 2014 while XN first increased from 2004 to 2009, and then decreased from 2009 to 2014. Both AX and XN gully area in percentage of the total area ranged from 1% to 3%, which was higher than the average 0.25% of the whole southern China by the artificial survey in 2005. (2) Most of AX and XN gullies occurred along the ridgeline and had the close relationships with the upstream contributing area and slope gradient. (3) New gullies developed on the exposed land and forestland. The lost gullies were converted into forestland and grassland. In fact, most of these gullies were only covered by vegetation, not real disappearance. These results proved that gully decreased, but construction of roads and buildings intensified gully development. Consequently, these findings reveal that vegetation protection and ecological restoration should be adopted in southern China.

Abstract The Three Gorges Reservoir region suffers from severe soil erosion that leads to serious soil degradation and eutrophication. Interrill erosion models are commonly used in developing soil erosion control measures. Laboratory simulation experiments were conducted to investigate the relationship between interrill erosion rate and three commonly hydraulic parameters (flow velocity V, shear stress τ and stream power W). The slope gradients ranged from 17.6% to 36.4%, and the rainfall intensities varied from 0.6 to 2.54 mm·min−1. The results showed that surface runoff volume and soil loss rates varied greatly with the change of slope and rainfall intensity. Surface runoff accounted for 67.2–85.4% of the precipitation on average. Soil loss rates increased with increases of rainfall intensity and slope gradient, Regression analysis showed that interrill erosion rate could be calculated by a linear function of V and W. Predictions based on V (R2 = 0.843, ME = 0.843) and W (R2 = 0.862, ME = 0.862) were powerful. τ (R2 = 0.721, ME = 0.721) did not seem to be a good predictor for interrill erosion rates. Five ordinarily interrill erosion models were analyzed, the accuracy of the models in predicting soil loss rate was: Model 3 (ME = 0.977) > Model 4 (ME = 0.966) > Model 5 (ME = 0.963) > Model 2 (ME = 0.923) > Model 1 (ME = 0.852). The interrill erodibility used in the model 3 (WEPP) was calculated as 0.332×106 kg·s·m−4. The results can improve the precision of interrill erosion estimation on purple soil slopes in the Three Gorges Reservoir area.

As a large weathered granite soil region in the world, southern China is experiencing severe sheet and rill erosion and gully erosion due to its special geological conditions, inappropriate land use, and high intensity precipitation. However, few studies have been conducted on the long-term dynamics of these two types of soil erosion and the sediment contribution of gully erosion in southern China. To assess this, estimates of soil erosion changes and the contribution ratio of gully erosion to sediment yield in a small catchment in southern China from 1989 to 2015 are quantified. A topographic map and three high-resolution satellite images were interpreted for land use changes to calculate soil erosion modulus of sheet and rill erosion by the Chinese soil loss equation (CSLE) and to estimate the amount of gully erosion by gully volume based on a generalized inverted triangular pyramid model multiplying bulk density. Results indicated that soil erosion modulus started as high as 10,442 t km(-2) in 1989, followed by an initial decrease of 54% before increasing slightly. The total gully volume decreased by 37% overall, as did the cumulative amount of gully erosion. Between 2005 and 2010 positive total soil loss was calculated and the sediment contribution ratio of gully erosion was estimated to be 52.27%. It can be concluded that the combination of remote sensing images, the CSLE, and a new generalized gully model can effectively be used to quantify soil loss from sheet and rill erosion as well as gully erosion. This study provides a new insight to estimate gully erosion and the dynamic evolution of soil loss. Further studies should be performed in combination with field methods to validate this approach. (C) 2020 Elsevier B.V. All rights reserved.

This study integrated 3D scanner measurement techniques with hydrological analysis to study the evolution of gullies developed in the deep weathering (granite) in the subtropical climate of southern China. Two gullies were repeatedly measured using a 3D laser scanner over a 7.5-year period from 2009 to 2016. The measurements with sub-centimeter accuracy indicated that gully head retreat was the dominant process in the gully development, with a mean rate of 0.46 and 1.10 m yr(-1) for gully A and B respectively. To explore the relationship between gully head retreat (GHR) and hydrologic variables, rainfall with three different thresholds, rainfall erosivity and runoff depth were calculated using different methods. Statistical analysis showed a significant correlation between GHR rates and cumulative erosive rainfall depth with a daily rainfall threshold > 25 mm. Hydrological analysis and field observations suggested that gully head retreats mainly result from mass movement triggered by gravity and soil saturation, although water erosion might also play a role in destabilizing the already unstable gully slopes. This study has implications for restoration of gullies in the area, which requires techniques that go beyond a mere reduction of runoff contribution to gully systems. Further studies are needed to gather more data on the evolution and sediment delivery of gullies, to prove the hypothesis of gravity-driven gully headcut development, and to explore more effective gully restoration techniques.