Search

• A novel model integrating hillslope and in-stream sediment processes is developed. • We quantified the effects of soil-water conservation (SWC) on the Loess Plateau. • SWC contributes to 54.4% and 91.9% of the decline in discharge and sediment load. • Sediment reduction effect of hillslope SWC is more lasting compared to that of check dams. Soil erosion and sediment transport processes, which are intimately connected with hydrological processes, strongly affect land surface morphology and earth system dynamics. Over the past 60 years, intensive Soil-Water Conservation (SWC) measures implemented on the Loess Plateau have significantly reduced sediment load and concurrently exacerbated runoff declines, while the quantitative evaluation of the effects of SWC measures remains challenging. This study develops a sediment module which simulates the hillslope and in-stream sediment processes, and then incorporates the module into a Geomorphology-Based Ecohydrological Model (GBEHM). Besides, the model also couples with an explicit representation of different types of SWC measures, including both Hillslope SWC (HSWC) and River-network SWC (RSWC) measures. The newly developed hydro-sediment model is then applied to the Kuye River basin, a typical river basin on the Loess Plateau, and used for quantifying the effects of SWC measures on river discharge and sediment load during 1982–2019. Compared with Period 1 (1982–2000), the river discharge decreased by 48.7% in Period 2 (2001–2019), while the sediment load experienced a more substantial decrease of 95.3% between the two periods. Based on the numerical experiment results, HSWC and RSWC contributed to 25.4% (58 million m3/yr) and 28.9% (66 million m3/yr) of the annual runoff decline, as well as 58.1% (36 million t/yr) and 33.9% (21 million t/yr) of the annual sediment load reduction between the two periods, respectively. Besides, HSWC plays an increasingly important role in sediment reduction in recent years due to check dam silting. The model developed in this research is useful to evaluate the multi-faceted effects of existing SWC measures and to help with future SWC planning and policymaking. [ABSTRACT FROM AUTHOR]

• Hillslope erosion dynamic model integrating vegetation effect was established. • Unified baseline parameters were obtained across different land uses. • Effect of vegetation on soil detachment and sediment transport was revealed. • Contribution rates of vegetation to sediment reduction along slopes were quantified. Developing a process-based soil erosion model that comprehensively considers the effects of vegetation is complex but crucial for evaluating sediment reduction during vegetation restoration. Current understanding of the effect of vegetation on sediment reduction along hillslopes across different land uses is limited. In this paper, we developed a dynamic model of hillslope erosion that integrates the effects of vegetation on soil detachability and hydrodynamics (VED) based on the feedback mechanism between soil detachment and sediment transport. The VED was calibrated and validated with runoff plot data for woodland, grassland, and farmland in the Wuding, Yan, Jing and Wei Rivers of the Loess Plateau in China. Unified baseline parameters and decay coefficients of vegetation were obtained. The model validation results indicated that the coefficient of determination, Nash–Sutcliffe simulation efficiency and relative error ranged from 0.59 to 0.99, 0.56 to 0.90, and −45.99 % to 46.36 %, respectively. The decay coefficients for soil detachment capacity (Φ), sediment transport capacity (T c), and the sediment reduction effect of vegetation exhibited the following order: woodland > grassland > farmland. Compared with VED, existing process-based soil erosion models failed to effectively characterize the influence of vegetation on Φ and T c on the Loess Plateau, with differences of several orders of magnitude. The individual contributions of runoff, soil detachability, and hydrodynamics with vegetation impact on sediment yield were quantified by VED. The contribution rates of vegetation to sediment reduction decreased gradually with increasing slope length because the soil detachment capacity of bare slopes exceeded that of vegetated slopes, resulting in a faster increase in sediment yield. The contribution rates of vegetation to sediment reduction for woodland, grassland, and farmland with 20 %–60 % vegetation covers were 66.75 %–99.95 %, 57.43 %–99.63 %, and 27.91 %–88.63 % in the boundary conditions of this study, respectively. The results reveal the potential for integrating VED into other distributed watershed hydrological and sediment models to assess the effects of vegetation restoration on sediment reduction at a watershed scale. [ABSTRACT FROM AUTHOR]

• Sediment sources prediction accuracy is high for no particle sorting. • Particle sorting caused low conservatism and prediction accuracy of five tracers. • Adding SOM correction factor could negatively affect model results. • Reliable result if source and sediment have consistent and narrow particle sizes. Sediment fingerprinting has proven highly efficient and rapid in identifying the sources and hotspots of sediment, thereby facilitating the targeted implementation of control measures. However, the unpredictable effect of particle sorting during sediment transport on source identification has increased the uncertainty associated with this method. Here, laboratory sieving experiments were carried out to simulate particle sorting during sediment transport. The conservatism of the five widely used tracers (geochemical elements, mid-infrared, near-infrared, visible, and color properties) and the accuracy of sediment source fingerprinting were investigated in the process of sorting. The results highlight that selected tracers exhibited high source contribution prediction accuracy (mean MAE 6.6 %) without particle sorting, with the exception of the color tracer. In contrast, the predictive ability of all tracers significantly reduced (mean MAE 16.2 %) in simulated particle sorting groups (especially for 125–31 μm) due to the enrichment of fine particles. Moreover, the correction factor failed to improve the accuracy of source contribution prediction in this study. The uncertainty caused by particle sorting can be effectively resolved by narrowing the source and sediment particle sizes to <63 μm (for all five tracers) or <31 μm (except for color tracer). This study contributes a deeper understanding of the role of particle size in sediment source fingerprinting, providing valuable insights to guide future tracer selection and associated particle size criteria. [ABSTRACT FROM AUTHOR]

• A novel framework for prediction and early-warning of bank erosion is proposed. • The proposed framework captures major bank erosion sites in the MYR. • A model ensemble is better to improve the accuracy of bank erosion prediction. Bank erosion can cause serious damage to flood control infrastructures in alluvial rivers, and thus threaten the safety of riparian residents and industry in heavily populated river systems, such as the Middle Yangtze River (MYR), China. The current study proposes a novel framework for the prediction and early-warning of bank erosion. The prediction of bank erosion is implemented by coupling a dynamic model with a data-driven random forest model. To determine the early-warning level, four indices are proposed corresponding to bank erosion intensity and dangerous degree, respectively. These indices are combined into a final early-warning level of bank erosion. The proposed framework is applied to the MYR, with its performance being evaluated by the corresponding flow, sediment, and topographic measurements. The results show that: (1) the dynamic model reproduces the flow and sediment transport process well in the MYR, with relative errors being less than 6%, 33%, and 4% for the water discharge, sediment discharge, and river stage, respectively. The model is also able to capture the major bank erosion sites well; (2) The performance of the data-driven model is increased when the input data groups are balanced, with a recall rate of 0.67 and an precision of 0.80 being obtained; (3) the calculated distributions of early-warning sites are generally in accordance with the observations in 2020, and the dangerous areas locate close to the outlet of the Jingjiang Reach of MYR. Besides, a model ensemble is probably a better way to improve the prediction of bank erosion, as compared with solely relying on the refinement of a dynamic model. However, some major gaps are also identified in the current framework. [ABSTRACT FROM AUTHOR]

• SWAT-Twn 2.0: Enhanced model with adaptable landslide triggers improves sediment simulation. • Dual triggers (PCP: rainfall and FSW: fraction of soil water content) in SWAT-Twn 2.0 show superior performance. • PCP trigger significantly affects landslide identification accuracy. • Lack of particle size leads to channel deposition overestimation. • Incorporate landslide characteristics into HRU (Hydrologic Response Unit) classification to address limitations. Landslides, caused by heavy rainfall, earthquakes, or human development, are likely occur in steeper slopes, while some occur in moderate slopes (15°– 35°). Although landslides can contribute a significant amount of sediment transport in a watershed, landslides are rarely considered in hydrological models. To conduct a thorough investigation into the influence of landslides on sediment transport within rivers, a detailed analysis of landslide characteristics was performed. Subsequently, a dedicated landslide module was integrated into a hydrological model, known as SWAT-Twn 2.0 – an enhanced version of SWAT-Twn, originally developed by Chiang et al. (2021). This integration allowed for the simulation of sediment transport at the hydrologic response units (HRUs) within the Xiuguluan River Basin, a mountainous watershed located in Taiwan. The study explores multiple threshold values for landslide-triggering factors (PCP: rainfall and FSW: fraction of soil water content), emphasizing the influence of the number and locations of rainfall stations on landslide identification. In comparative scenario simulations (S1: no trigger, S2: single trigger, S3: dual trigger), the integration of dual triggers (PCP + FSW) significantly improves sediment simulation results, particularly for peak total load (S3: R2 = 0.83, NSE = 0.74, PBIAS = 23.69 %). It also emphasizes the importance of specifying the particle size distribution of landslides for accurate sediment deposition calculations. In summary, it is necessary to consider landslide-triggering factors in hydrological models to enhance accuracy in sediment yield simulations. To further improve landslide identification and sediment transport modeling, the study recommends incorporating additional triggering factors into HRU classification (i.e., elevation and aspect). [ABSTRACT FROM AUTHOR]

• SY and Sr of the SL was the largest, but the sediment MWD was the smallest. • Change in the flow discharge did not affect the distribution pattern of sediment particles. • Dynamic coupling of runoff hydraulics and EG morphology drove soil loss. • SDR was the most direct influencing factor on the Sr in EGs. Ephemeral gully (EG) erosion represents the early stage of large-scale gully (locally named as "Benggang") development on Ultisols in the granite hilly area. However, the EG erosion process and the mechanism underlying sediment production have not been fully elucidated. In this study, a series of field scouring experiments were conducted under different flow discharge levels (10, 15, 20, 25, and 30 L·min−1), and the primary EGs in three typical soil layers with different weathering degrees (red soil layer (RL), transition layer (TL), and sandy layer (SL)) was dynamically monitored. The results indicated that the ratio of width to depth of the EGs rapidly decreased as the flow discharge increased. At 30 L·min−1, the average sediment yield and transport rate (Sr) of the SL were 4.85 and 5.39 times, greater than those of the RL, respectively. The sediment particles were concentrated within the 1–2 mm particle size range, accounting for over 35 %. In addition, the mean weight diameter of the sediment particles in the RL was the largest. The sediment distribution characteristics did not respond to flow changes but were affected by EG morphological changes. With increasing flow discharge, the flow shear stress and stream power increased. Further analysis revealed that the coupling effect of flow hydraulic characteristics and EG morphological evolution drove the EG erosion sediment production process, and the Sr of the SL was highly sensitive to flow discharge changes. The soil disintegration rate was an internal factor that directly affected soil loss in the EGs, with a path coefficient of 0.71. The bulk density, organic matter content, and sand content were all indirect influencing factors. The RL exhibited greater anti-erodibility than the other layers and could serve as an effective protective layer for granite hilly areas. These findings provide a theoretical basis for improving soil loss management systems. [ABSTRACT FROM AUTHOR]

• It is essential to utilize diverse sources of observational data for the validation of long-term morphological simulations. • The multiple underlayer settings of the Delft3D model enable its acquisition of decadal bed layer stratigraphy. • Wind and waves sort sediment based on grain size, smoothing out morphological changes induced by tides. • Sea level rise significantly influences regions characterized by intricate morphological features. • Radial sand ridges form under a radial regime with low tidal ellipticity, abundant sand, and minor cohesive sediment. The tidal sand ridges in the southwestern Yellow Sea are unique in the world characterized by radial morphology, significantly higher elevation above low water level, and fine-grained sediment deposits. Using a numerical model, we examined the morphological evolution of the radial sand ridge system from 1979 to 2059. The model was calibrated and validated using hydrodynamic and sediment transport data, seabed topography, and grain size distributions from sediment cores. Our findings reveal that tidal force is the primary driver of the ridges' evolution, and they will continue to expand in response to sediment supply from the abandoned Yellow River delta and the Yangtze delta, with the latter contributing more. The ridges are mainly composed of fine sand and mud, with finer sediment dominating in the north and coarser sediment dominating in the south. Wind and waves sort sediment, depositing sand on ridges and fine sediment in channels, leading to erosion of higher elevated lands and filling of deep channels. Sea-level rise increases regional erosion, which has a large impact on areas with complex morphology. The 500-year morphological evolution of sand ridge systems, simulated through an idealized model, illustrated that the formation of radial sand ridges is dependent upon specific conditions such as the radial tidal regime, sufficient sediment sand, and the presence of cohesive sediment. This study deepens our understanding of the long-term prediction of coastal morphology and interpretation of seabed stratigraphy, and offers insights for effective coastal management. [ABSTRACT FROM AUTHOR]

• We model the sediment response to Tropical Cyclones (TCs) of a catchment in Fiji. • We use remote sensing data to set up the model and validate results. • Most of the sediment remains in the catchment due to limited transport capacity. • The contribution of TCs to the annual sediment export is about 25%. • TCs events produce six times more sediment than non-TC events. Coastal areas in the tropics are remarkably vulnerable to extreme weather-related events (e.g. floods, storm surge, erosion), which are expected to intensify in the future. Erosion of catchments is affected by changes in climate and vegetation, which alters the production of sediment transported into coastal areas and can lead to the loss of important ecosystem services. In many areas in the tropics, cyclones and depressions (TCs) produce the largest floods and massive discharges of sediment, which can affect coastal habitats in wetlands, lagoons and reefs. Here we focus on the Pacific Islands, but the methodology can be used in any tropical catchment affected by cyclones. A hydro-sedimentological model was used to analyse the sediment outputs of the Dreketi River (Fiji) and their relationship with cyclone activity over the last 45 years. The model was developed based on satellite and ground information on topography, soils, land use, and climatic data. The sediment export was related to TCs in the area, which were identified using the Southwest Pacific Enhanced Archive of Tropical Cyclones (SPEArTC) database. TC-related precipitation events were found to be three times more intense than non-TC events, and the average annual contribution of TCs to sediment export was about 25 %, with years contributing more than 50 %. TC-related events produced six times the sediment export of non-TC events, indicating a strong relation with precipitation intensity. Relations between precipitation rate and sediment export were developed for both TC and non-TC events, which can be used to predict the effects of increase of cyclone activity in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • The new anicut reoperation enhanced upstream impoundment by 16%/year. • The reoperation redoubled flow regime shifts within five years. • It deviated two-third of water level between upstream and downstream. • Multi-fold expansion of upstream channel contracted half of the downstream channel. • Reoperation sequestered 82 % sediment that stopped infilling 0.64 km2 mining pits. In the last century, more than 58,000 large dams were constructed worldwide. Meanwhile, some of these older dams were renovated/reconstructed and started reoperation with enhanced regulation capacity to meet the rising water demand. However, the impact of dam reoperation on rivers is not thoroughly understood. This study aimed to examine the impact of dam reoperation on the Kangsabati River's flow regime, sediment transport and planform adjustments in upstream and downstream of the reconstructed anicut (like a dam/barrage) in the lower Ganga plains. The anicut structure was built by the British in 1866. It was demolished, underwent further reconstruction, and recommenced operation in 2016. While the Kangsabati reservoir (KR), with 1135 million-m3 (MCM) capacity in 80 km anicut's upstream, has been functional since 1974. Together, these regulation structures enable irrigation across 0.4 million hectare cropland in dry regions. Meanwhile, the KR operation reduced 34 % (1974–2010) and 70 % (2010–2015) flow before the new anicut's reoperation. Likewise, within five years, the reoperation reduced 35 % mean annual flow and two-thirds of the non-monsoon flow, despite the anicut's small 6-MCM storage capacity that redoubled the flow regime shift. After the reoperation (16 %/year), the enhanced water impoundment reduced fluvial landform diversity by submerging upstream channel area and abandoning/exposing downstream landforms, as effectively captured with the non-water/water index (NWI). It led to significant channel planform alterations, with 85 % expansion of the upstream channel, 44 % contraction of the downstream channel, and 72 % variation in both upstream and downstream water levels, unlike before the reoperation. Reoperation disrupted sediment infilling of 1.3 MCM downstream sand mining pits. This deprived the downstream communities, relying on mining activities for their livelihoods. Thereby, the reoperation-induced regulations have ignored upstream and downstream ecological connectivity and ecosystem services, resembling the impacts of any large dam. This requires urgent attention and strategies aimed at restoring river ecology and associated benefits. [ABSTRACT FROM AUTHOR]

• Drag coefficient ratio (β) can be used as a parameter reflecting plant shape. • Sand transport rate (Q) and aerodynamic entrainment rate (E) decrease with β. • Models of Q and E are established by introducing attenuation function of wind speed. • Attenuation function of effective wind speed decays linearly with β. Plant shape is an important factor affecting sand transport rate and aerodynamic particle entrainment rate. Two different types of flexible plant models (one is slender and the other has a large upper part and a small lower part) and a rigid tree-like plant model are selected with approximately zero basal-to-frontal area ratio. The sand transport rate, aerodynamic entrainment rate and shear stress partitioning on vegetated surfaces were measured under different plant densities and incoming wind speeds in a wind tunnel. The results show that the sand transport rate and aerodynamic entrainment rate on vegetated surfaces decrease with an increase in lateral cover and form drag of plant models. The relationship between sand transport rate, aerodynamic entrainment rate and drag parameter β (defined as the drag coefficient ratio of a plant model to the bare surface) is established by introducing the attenuation function of effective wind speed, which decays exponentially with an increase in lateral cover and linearly with an increase in drag coefficient ratio β. The present findings contribute to our understanding of how different vegetation types affect sediment transport rate and aerodynamic entrainment rate. [ABSTRACT FROM AUTHOR]

• Microtextures of quartz grains in the Bay of Bengal shoreline sediments in Bangladesh are investigated. • Microtextures are grouped as mechanical, chemical, and both mechanical/chemical origin. • V-shaped marks are abundant, indicating a high-energy storm event. • The solution and precipitation features suggested a silica-saturated subaqueous marine environment. • Well-rounded grains suggested aeolian origin, and angular to sub-angular grains support a local source. SEM and SEM-EDS studies of quartz grains in the shoreline sediments of the Bay of Bengal, Bangladesh were carried out to evaluate the mode of origin, paleoclimate, and depositional environment. A total of 38 microtexture types were identified, which were grouped into mechanical (23 features), mechanical/chemical (6 features), and chemical (9 features) origins. The morphology of quartz grains in the shorelines was dominantly sub-angular to sub-rounded in shape, which represents robust energy conditions, short residence time, low weathering, and nearby sediment provenance. The microtextures of mechanical origin such as straight and curved scratches, pits, broken edges, and crescent-shaped features were relatively abundant in the eastern site samples (Section-I) indicating high-energy, fluvial, and beach environments. The abundance of V-shaped marks and smooth surfaces of quartz grains indicate high-velocity storm conditions and/or high-energy impact events. The well-rounded outline, low relief with dish-shaped depressions, mechanically upturned plates, and arcuate steps were also observed on quartz grain surfaces. These features suggest that they were developed during an aeolian process in the beach berm environment. Etching, solution/irregular pits, and differential relief on quartz grains were somewhat elevated in the western site samples (Section-III), reflecting that these microtextures were associated with a subaqueous collision and humid climates in the fluvial and nearshore environments. Quartz grains in all sections represented microtextures of high energetic subaqueous environment as well as wind events. However, the absence of corrosion channels and high density of voids in the quartz grains revealed low degree of weathering. [ABSTRACT FROM AUTHOR]

• Natural radionuclides trace sediment transport from the coastline to the deeper bay. • In the submerged part of the beach 226Ra, 228Ra and 40K trace erosion/accumulation. • 226Ra, 228Ra and 40K are influenced by the mineral composition of samples. • 210Pb ex is correlated to the smaller grain size samples. • 210Pb ex as a tracer of the seabed areas where the accumulation sedimentation occurs. Erosion and accumulation of coastal areas have become an increasing concern in recent years since they can result in important social and economic problems. In this framework, natural radionuclides have emerged as an alternative tool to study coastal sediment transport and help with the management of the littoral zone. However, there is still a lack of knowledge on how these radionuclides can be applied as tracers of coastal sediment dynamics and how the sediment characteristics can influence this use. Thus, a methodology is presented in this work to use natural radionuclides as tracers of coastal erosion, transport and accumulation of sediments. For this purpose, the spatial distributions of 226Ra, 228Ra, 40K and unsupported 210Pb (210Pb ex) in two periods of time were analysed and compared in a coastal area with diverse marine dynamics. The results showed that 226Ra, 228Ra and 40K identified the different sediment erosion, transport and accumulation occurring in the study region. In addition, it was found that changes in the activity concentrations of the samples were mostly related to variations in their mineralogical composition. Finally, the activity concentration values of 210Pb ex made it possible to trace the areas where accumulation due to the sedimentation of aerosol particles in the seabed is favoured. These results highlight the suitability of natural radionuclides to study coastal sediment transport. [ABSTRACT FROM AUTHOR]

• The height of sediment traces is used as an alternative indicator to the functional connectivity. • The frequency and magnitude of sediment connectivity are not necessarily synchronized. • The response of sediment connectivity to rainfall is nonlinear in watersheds. • The spatial inhomogeneity and amount of rainfall are important factors influencing sediment connectivity. Sediment connectivity is a fundamental concept for understanding sediment dynamics within watersheds, serving as a crucial component in watershed management and soil and water conservation. However, quantifying sediment connectivity remains a challenging task due to its complexity and the difficulties associated with direct measurements of sediment flux at multiple temporal and spatial scales. Our research aims to address this challenge by monitoring functional sediment connectivity at various scales using two key indicators: sediment yield and sediment marks. Sediment yield is monitored at slope plots, slope-channel cascades, and watershed outlets, while sediment marks provide additional insight into functional sediment connectivity along the sediment transport path, particularly in slope-channel cascades and channels following rainfall events. To record sediment marks, we used wooden sticks wrapped with clean gauze as an alternative to assessing functional connectivity. Our results revealed that the activation of sediment connectivity was influenced by rainfall amount, intensity, and type, with the highest activation observed at the slope plot, followed by the outlet of the slope-channel cascade and the watershed outlet. Notably, strong sediment connectivity at slope plots, slope-channel cascades, and main channels exhibits a weak correlation with sediment connectivity at the watershed outlet. In upper contribution areas with lower vegetation coverage and higher human disturbance, rainfall amount and I 60 values associated with sediment connectivity activation tend to be lower. Furthermore, our research indicates that medium-duration and moderate-intensity rainfall events have a more significant impact on sediment connectivity at slope plots, while rainfall types characterized by longer durations, lower intensity, and larger amounts have a more pronounced effect on sediment transport paths. This suggests that the identification of sediment connectivity switch nodes can be achieved by considering both rainfall characteristics and underlying surface features. Looking ahead, future research can leverage long-term observations and data-driven models to explore rainfall thresholds for sediment connectivity at various scales, ultimately improving sediment transport prediction within watersheds. [ABSTRACT FROM AUTHOR]

• Hydro operations led to 56.8% decrease in sediment load in upper Yangtze River. • The construction of cascade hydropower reduced the sediment concentration by 56.6%. • Changes in sediment transport and high flow pulses reduce spawning abundance. • The effect of flooding processes on spawning abundance was not significant. • Novel methodology analysed the effects of cascade hydropower on fish spawning. The upper reaches of the Yangtze River (YR) constitute the largest group of hydropower cascade projects in the world. The construction of cascade hydropower systems has a significant impact on the flow regimes and sediment transport in rivers, ultimately affecting fish spawning. Previous studies have examined the effects of fluctuating flow and water temperature on spawning; however, insufficient attention has been paid to their effects on sediment transport. This study analysed changes in runoff and sediment load (SL) at the Xiangjiaba hydrologic station (XJB) and Zhutuo hydrologic station (ZT) in the upper reaches of the YR over the past 60 years. Based on the indicators of hydrological regimes and sediment transport, we used the generalized additive models (GAM) to investigate the effects of cascade hydropower operations from 2009 to 2018 on the spawning abundance of Coreius heterodon (C. H) in the upper YR Fish Reserve. Following the operation of cascade hydropower, the SL and sediment concentration decreased by 56.8% and 56.6%, respectively, while the median size of the bed-material load demonstrated an initial thinning trend followed by subsequent coarsening. In addition, the frequency of the high-flow pulse increased by 32.1%, whereas the peak flow and duration of the high-flow pulse decreased by 41.2% and 62.6%, respectively. However, no significant changes were noted in the indicators of the flooding process. The decrease in sediment transport and changes in the flow regime led to a reduction in the spawning abundance of C. H. Reductions in sediment transport and changes in high-flow pulses caused by cascade hydropower can negatively affect C. H spawning, and SL is the most important indicator of impacts on spawning abundance (contribution of 77.7%). These findings are critical for evaluating the long-term impacts of cascade hydropower on fish habitats. [ABSTRACT FROM AUTHOR]

• The meteorological Lepage test effectively anlyzed the temporal variation of the water and sediment discharge for the first time. • The increase in sediment transport within tributaries and during short-term flood events has become a key characteristic of the upper Yangtze River in recent years. • The reduction in sediment entering the Three Gorges Reservoir decreased its downstream sediment reduction effect. After the construction of the cascade reservoirs in the lower Jinsha River, it has become necessary to clarify the spatial and temporal variability of the volume of sediment entering the Three Gorges Reservoir in order to manage sediment within the basin considering the new situation of rapid sediment reduction. Previous studies were affected by the inaccurate analyses of transition points and associated causes and were unable to identify clear changes in the spatial and temporal characteristics. Therefore, the impact that the Three Gorges Reservoir has on sediment reduction in the upper Yangtze River needs to be reassessed. The Lepage test and sediment identity factor method were applied to reveal that the sediment transported by the Jinsha River has significantly decreased since 2013 due to the reservoir construction, while the sediment transported by the Min River and Jialing River has slightly increased since 2014 and 2015 due to heavy rainfall. However, this has ultimately led to a significant reduction in sediment entering the Three Gorges Reservoir since 2013. Accordingly, the spatial composition of sediment sources in the Three Gorges region has been dominated by tributaries in recent years, with the Jialing River accounting for 38.98 % of the total and the Jinsha River accounting for only 1.74 %. Under these new conditions, sediment transported during short-term floods becomes more important, with sediment entering the Three Gorges Reservoir during 7 day flood events accounting for up to 47.16 % of the total transport in a year. As a result of sediment trapping by the upstream reservoirs, the Three Gorges Reservoir is responsible for only 7.5 % to 22.75 % of the sediment reduction observed at Yichang Station. Understanding the weakened impact that the Three Gorges Reservoir has on the sediment reduction phenomenon in the upper Yangtze River is important for managing the schedules of the reservoirs in the upper Yangtze River. [ABSTRACT FROM AUTHOR]

• Mass movement is an important erosion mode and sediment source in gully network. • Mass movement increased sediment concentration and led to peak sediment concentration. • Mass movement was prone to be triggered by rainfall with a medium-duration and moderate-intensity. • Rainfall amount and slope gradiet determined the trigger and total volume of mass movement. Mass movement erosion on the gully sidewalls is recognized as an important erosion mode and sediment source in hilly and gully watersheds. However, the trigger of mass movement erosion and transport of gravity-detached material remain poorly understood. A series of rainfall simulation experiments were conducted on six loess gully sidewall models, with a height (1 m), three rainfall (60 mm, 48 mm and 24 mm) and two slope gradients (70° and 80°), to quantitatively explore the sensitivity factor and transport mechanisms of mass movement. Results revealed that the accumulation volume and initiation of the mass failure were significantly influenced by rainfall amount. The accumulative volume of failure events was observed to increase in a linear pattern with increasing rainfall amount. The minimum cumulative rainfalls for the initiation of mass failure on the loess gully sidewalls were approximately 43.6, 28.2 and 65.6 mm for short-duration and high-intensity, medium-duration and moderate-intensity and short-duration and moderate-intensity rainfalls, respectively. This implied that the initiation of mass failure was more prone to rainfall events with a medium-duration and moderate-intensity than those with a high intensity and short duration. Rainfall amount and initial slope gradient were the most sensitive elements driving the number and volume of the mass movement erosion. Mass movement erosion raised sediment concentration, but the eroded material was unable to be transported by runoff in a timely manner. Average sediment concentrations at the model outlet increased by 1.9–11.9 times following the occurrence of mass failures compared to those before. A low instantaneous sediment delivery ratio of 0.032 for the mass movement erosion. The experimental findings help comprehend the influence of mass movement erosion on sediment supply on the gully sidewall in the hilly and gully network, i.e. the Loess Plateau. [ABSTRACT FROM AUTHOR]

• Lateral sediment flux from hillslopes is directly connected to the curve number. • The curve number summarized the resistance from the soil-group complex. • The lateral sedimentologic connectivity was well represented by the curve number. • The soil-cover complex in a watershed is closely related to watershed erodibility. The flux of suspended sediment and bedload in a watershed is closely linked to the resistance of soil, known as erodibility. However, the relation between the resistance generated by soil to sediment transport from the hillslope to the river flow is still a challenge. Typically, the bedload flux is related to the shear stress of the main channel. However, the link between lateral sediment flux from hillslopes to suspended sediment flux of the main channel and the relation between bedload and suspended sediment flux to soil erodibility need to be developed. For three Brazilian watersheds, suspended sediment and bedload transport, soils, and hydrological data were obtained to determine watershed soil erodibility. The landscape connectivity expressed by hydrological-sediment connectivity was applied to determine the lateral sediment transport to the primary watershed channel. The flow resistance and lateral suspended sediment discharge were represented by the curve number, which summarized the resistance from the soil-group complex leading to soil erodibility. The curve number addressed the lateral flow and suspended sediment transport to represent the lateral connectivity on the landscape. Sediment transport (sand and suspended sediment) from hillslopes was added to the bedload transport along the longitudinal axis of the watershed, and the watershed soil erodibility (K W) was, thus, obtained for each of the three evaluated watersheds. [ABSTRACT FROM AUTHOR]

[Display omitted] • We estimated SOC and TN transport rates due to landslides during 64 years. • Mean SOC and TN transport rates were 5.8–9.3 MgC km−2 yr−1 and 0.5–0.9 MgN km−2 yr−1. • SOC and TN transports in young forests (<20 yr) accounted for 87% of the total. • Forest harvesting increased landslide frequency, and SOC and TN transport rates. • Our results are useful for optimizing forestry practice to sequestrate more carbon. Landslides considerably affect soil organic carbon (SOC) and total nitrogen (TN) transports. However, the quantitative assessment of these effects remain limited. Furthermore, it is unresolved how forestry practices, especially clearcutting and subsequent planting, affect the SOC and TN transports by facilitating landslides. Therefore, we quantified the SOC and TN transports attributable to landslides from 1948 to 2012 in a steep mountainous area in Japan and examined the impacts of forest clearcutting on SOC and TN transports through landslides. We used 12 aerial photographs and two LiDAR DEMs to identify the landslide areas and to estimate their scar depths. In addition, we sampled soil at 17 points to examine the relationship between SOC and TN and soil depth. Subsequently, we estimated the temporal changes in SOC and TN transports due to landslides and examined the relationships between forest age and rates of SOC or TN transport due to landslides. During the 64 years, the average annual rate of landslide was 3.7 × 10−2 ha km−2 yr−1. Large temporal variability existed in rates of landslide, and the maximum rate of landslide was around 11.0 × 10−2 ha km−2 yr−1, while almost no landslide occurred in some periods. The average annual SOC and TN transport rates were 5.8–9.3 MgC km−2 yr−1 and 0.5–0.9 MgN km−2 yr−1, respectively. Many landslides occurred at places where trees were 15 years old or less in plated forests. The amount of SOC and TN transports in landslide areas with < 20 forest age accounted for 87% of the total amounts moved owing to landslides. That is, our results clearly showed that forest harvesting increased landslide frequency and SOC and TN transport rates. We expect our results to be useful for predicting carbon stock in forest ecosystems and optimizing forestry practices in steep mountainous regions. [ABSTRACT FROM AUTHOR]

• Relatively small changes in rainfall at the event scale were observed. • Anthropogenic activities play a leading role in hydro-erosive responses variation. • Saturation-excess overland flow is increasingly occurring. • Reduced sediment connectivity resulted from the increasing disconnected areas. China's Loess Plateau remains one of the most serious water erosion areas on Earth, while runoff and sediments of the Yellow River continue to decrease due to soil and water conservation (SWC) measures. Besides, climate conditions are dynamic. A total of 197 rainfall-runoff events from 1965 to 2020 in the Huangfuchuan catchment, which were divided into 3 sub-periods (P0: 1965 – 1982 limited measures; P1: 1983–1998 only dams and P2: 1999–2020 dams and revegetation), were selected to reveal the differences and mechanisms of runoff generation and sediment dynamics. The results show that: 1) anthropogenic activities played a leading role in water and sediment reduction; 2) infiltration-excess overland flow during the first two periods was dominant mechanism, but the results imply a potential shift towards saturation-excess overland flow occurring more often during P2; 3) the studied system, in a highly erodible region, is transport-limited; 4) sediment connectivity is reduced noticeably at the catchment scale, in which the decrease in index of connectivity (IC) values mainly resulted from the increase in proportion of the most disconnected areas of the catchment, especially in P2. These findings can help towards a better understanding of the mechanisms behind the changes in sediment dynamics, which can be applied to develop and implement sustainable water and soil conservation planning in the local or other similar areas. Besides this knowledge is very important for improving hydrological and sedimentological models in order to forecast the effects of human induced changes. [ABSTRACT FROM AUTHOR]

• Ridge slope erosion included inter-rill erosion, headward erosion, and rill erosion process. • Erosion rate reached the maximum during headward erosion process. • The dominated erosion process was detachment-limited after headward erosion occurring. • Re-detachment, transport, and deposition simultaneously occurred with the appearance of headward erosion. Extreme rainfall is becoming more frequent and intense, which no doubt increases the risks and uncertainty of water erosion in widely-used contour ridge systems. Ridge slope erosion can increase the probability of contour failure occurrence and then induce contour ridge losing anti-erosion properties. However, there is little understanding of ridge slope erosive process controlled by contour ridge system responding to extreme rainfall. In this study, five rare earth elements were applied in different ridge segments and soil layers to monitor the successive development of ridge slope erosion process under extreme rainfall in contour ridge system. Simulated rainfall experiments at high rainfall intensity (100 mm h−1) lasting for 60 min were conducted in runoff plots with ridge tillage practices characterized by microtopography indices and ridge geometry indices. Results showed that three sub-processes were observed for ridge slope erosion, including inter-rill erosion, headward erosion, and rill erosion. Headward erosion mainly resulted from the break-point at ridge surface and sidewall collapse at ridge toe, and the pouring of ponding water in furrow greatly promoted rill development. Erosion rate was the largest during headward erosion process, and rill erosion contributed the most to eroded source. The dominated erosion process was transport-limited during inter-rill erosion process, and detachment-limited during headward and rill erosion processes. Sediment transport and deposition processes as well as their transformation occurred simultaneously after the development of headward erosion. Eroded sediment was mainly from the low part of ridge, which was transported by raindrop-impacted sheet flow or overflow. These findings provide better responding of agricultural tillage to global climate change and references for the development of physically-based erosion models. [ABSTRACT FROM AUTHOR]

[Display omitted] • Longitudinal influences of low-water crossing on sedimentological connectivity. • Sedimentologic and morphologic modifications due to different rainfall patterns. • Destruction and deposition of sediments and the channel morphology were analyzed. • Low-water crossings mainly interrupt coarser sediments. • Low-water crossings function similarly to check dams, weirs, and sand dams. This study evaluated the longitudinal influences of low-water crossing on the river system and sedimentological connectivity in a Brazilian semiarid basin. The Lower Piancó River basin was chosen as the study area, and four low-water crossings along the catchment were identified and selected for analysis and diagnosis. The effective catchment areas of each structure were delimited, and their impacts assessed over time. Rainfall data from three gauges were used to analyze precipitation events capable of causing significant sedimentological and morphological modifications. These events were classified into three types according to their magnitudes: high, moderate, and low. Sediment samples were collected at each low-water crossing, and lateral profiles were drawn upstream and downstream of the structures to analyze the destruction and deposition of sediments and channel morphology. The analysis showed that the low-water crossings could act as barriers to sediment flow, especially for coarser sediments, and favor the incision of the downstream channel. However, during exceptional flows, the low-water crossings allowed the transmission of sediments due to the clogging of the upstream channel riverbed. This highlighted a unique interaction between the river system and the low-water crossings over time. The results of the connectivity analyses revealed that low-water crossings have a unique impact on the fluvial system compared to other structures, particularly due to their role in the sedimentological connectivity of coarse sediments. Specifically, sediment transport downstream of the crossing emerged as a significant factor in understanding its influence on the surrounding environment. Compared to other types of small longitudinal fluvial interventions, the stage model and low-water crossings displayed structural and aesthetic similarities with floodways and fords. However, functionally, the low-water crossings had strong similarities with check dams, weirs, and sand dams due to their roles in retaining sediments and altering the morphology of the channels in which they are installed. [ABSTRACT FROM AUTHOR]

• The sediment transport capacity was developed for loessal slopes. • Two-dimensional erosion numerical model was developed for loessal slopes. • Erosion numerical model could accurately simulate slope runoff and sediment process. Simulated slope erosion sediment yield and its development process have great significance for quantitative evaluation of erosion and its sources. In this study, a loess slope erosion experiment was implemented indoors to establish a sediment transport capacity formula suitable for loess slope erosion. A two-dimensional slope erosion numerical model was developed with corrected sediment transport capacity formula, and the model was verified by a simulated indoor slope rainfall erosion experiment. The results showed that the corrected slope sediment transport capacity formula is suitable for loess slopes. The proposed two-dimensional slope erosion numerical model could simulate runoff and sediment processes in a relatively more accurate. The most severely eroded areas were the middle and lower parts on erosion spatial contribution based on the simulation erosion results. Good agreements between the simulated and observed results were found for erosion and its spatial distribution. The research results can further improve loessal slope erosion process simulation and prediction. [ABSTRACT FROM AUTHOR]

• A mathematical model considering the operation of 24 mega reservoirs was proposed. • The sedimentation mainly occurs in the mainstream during the flood season. • The cascade reservoirs operation leads to easier and prolonged sedimentation. The intensive construction of large dams in the upper Yangtze River Basin (UYRB) has formed large-scale cascade reservoirs and obviously altered the flow regime and sediment transport of the basin. However, few studies have quantitatively described the cumulative impact of these reservoirs on sediment interception. In this study, a flow and sediment transport model that fully considers the operation processes of 24 mega reservoirs in the UYRB was established, and the spatial and temporal variations in sedimentation from 2011 to 2080 were elucidated, assuming repeated series of daily input flow discharge and sediment concentration during 2011–2020 and monthly water operation levels of 24 reservoirs during 2018–2021 as boundary conditions. The results showed an annual average sedimentation of more than 300 Mt in the UYRB during 2011–2060, which falls to 270 Mt in the period 2061–2080, and more than 80% of the sedimentation occurs in the flood season. Nearly 80% of the total sedimentation during 2010–2080 was observed in the mainstream reservoirs, especially the four mega reservoirs in the lower Jinsha River and the Three Gorges Reservoir (TGR), which accounted for 31.9% and 22.7% of the total sedimentation, respectively. The proportion of sedimentation in mainstream reservoirs will further increase with increasing operation periods. Most reservoirs in the UYRB will not reach sedimentation equilibrium by 2080, except for reservoirs in the Min River Basin. The ratio of siltation capacity to average annual sediment yield determines the percentage of residual siltation capacity of each reservoir. The operation of the cascade reservoirs in 2013–2020 had no more immediate impact on the middle and lower Yangtze River than that in 2003–2012, when the TGR started impoundment. However, the joint operation of these cascade reservoirs has changed the spatial distribution of sedimentation in the UYRB, and will lead to prolonged impacts on downstream channel erosion. [ABSTRACT FROM AUTHOR]

• Distribution and sorting of sediments from gentle slope land were investigated. • The migration of fine particle sediments was more pronounced on gentle slope land. • Aggregation behaviour of particles controls the selective transport of sediment. • Sediments were predominantly transported as aggregates besides 2–20 μm particles. During water erosion, selective transport of eroded sediments reduces the fertility of surface soil and exacerbates the risk of waterbody pollution. At present, sloping farmland >10° (SFL 10), which easily causes soil erosion, is the main research object. However, there has been relatively little focus on gentle slope lands (GSL). GSL refers to large fields with slope gradients of <6° divided by ditches, roads, and ridges, which can meet the requirements of mechanized production and intensive land management. In this study, to clarify the distribution and selectivity characteristics of the eroded sediment on GSL, natural rainfall experiments were conducted on GSL of 2° (S1), GSL of 5° (S2), and SFL of 12° (S3), where S3 was set as the control. Our results have demonstrated that although fine particles (<20 μm) were the main component of the eroded sediment on the GSL and SFL 10 , accounting for approximately 70–90%, there were differences in the enrichment ratio (ER) of fine particles. The ERs of <2 and 2–20 μm particles from S1 were significantly higher than those from S3 (P < 0.05). The <2 μm particles were predominantly transported as aggregates, and 2–20 μm particles were predominantly transported as single particles. Furthermore, the ERs of <2 and 2–20 μm particles from S2 were significantly lower than those from S1 owing to the influence of sediment particles undergoing flocculation. This demonstrates that selective transportation of fine particles controlled by particle flocculation is a key feature of soil erosion on GSL. When sediment is flocculated to a low degree, selective transportation of fine particles is more pronounced. Even on farmland with a slope of 2°, water erosion also results in the loss of many fine particles. [ABSTRACT FROM AUTHOR]

• Flow frequency distribution and sediment-transport rate were influenced by floodplain lake. • Frequency distribution of medium-high flow agreed well with broken power law. • Sediment-transport rating curve deviated from power law at high flow. • Effective discharges decreased by 10%–20% indicating flood channel shrinkage. In natural quasi-equilibrium rivers or anthropogenically-influenced nonequilibrium rivers, the occurrence frequency and sediment transport capacity of different flow levels are greatly important to understanding the linkage between forms and processes. However, our knowledge of the controlling factors on flow frequency and sediment-transport magnitude in large river systems remains limited. In this paper, the hydrological and sediment-transport characteristics of the middle and lower Yangtze River (MLYR) were systematically examined before and after impoundment of the Three Georges Reservoir (TGR). More than 30 years of daily discharge and suspended sediment concentration data were collected from six hydrological stations. The results showed that in the pre-TGR period, the flow frequency distributions (FFDs) and sediment-transport rating curves had segmentation characteristics. Generally, the FFDs of medium-high flow agreed well with the broken power law, and the sediment-transport rating curves deviated from the power law at high flow. This was because the floodplains, especially the Dongting Lake, had significant effects on flood attenuation and sediment storage. Compared the inflection points of the FFD and the sediment-transport rating curve, as well as the effective discharge and bankfull discharge, these four values were of the same order of magnitude. This suggested that the local river system had a dominant effect on the hydrological and sediment-transport characteristics. In the post-TGR period, the overall characteristics of the FFDs were preserved, but the segmental characteristics of the sediment-transport rating curves at higher discharges disappeared. Through analysis, the effective discharge was largely determined by the inflection value (a 1) of the FFD. The reduced a 1 induced a 10%–20% decrease in effective discharge, which indicated flood channel shrinkage in the long run. These findings not only further the understanding of water-sediment regimes in a large alluvial river with an extensive floodplain system but also offer guidance for improving dam operation schemes for river restoration. [ABSTRACT FROM AUTHOR]

• Rainfall and runoff explained 70–85% of sediment yield variability in two karst watersheds. • Specific rainfall and runoff variables affecting sediment yield the most were identified. • The PLSR model provides a convenient way of solving variable collinearity. As one of the largest and most typical continuous karst distribution belts in the world, Southwest China is vulnerable to soil erosion and rocky desertification because of its unique geological conditions and heterogeneous landscapes. Understanding the rainfall-runoff-sediment transport relationships is critical to effectively controlling soil erosion in karst watersheds. This study aims to evaluate the sediment yield variability at different temporal scales (daily, monthly/seasonal, and annual) from 2014 to 2019 and to further identify the rainfall and runoff variables most associated with sediment yield in the selected Mahuangtian (2.26 km2) and Muzhaihe (0.09 km2) karst watersheds. Since rainfall and runoff variables were highly codependent, the partial least squares regression (PLSR) model was used to quantify the relative importance of rainfall and runoff variables to sediment yield. The variable importance of the projection (VIP) scores>1 was considered to be the most influential predictor of the PLSR model. Results showed that sediment yield was greatly influenced by rainfall and runoff, which can explain 70% and 85% of the variation of sediment yield in the Mahuangtian and Muzhaihe watersheds, respectively. For rainfall variables, three-day antecedent precipitation (VIP = 1.41) and five-day antecedent precipitation (VIP = 1.28) were the main first-order factors controlling sediment yield in the Mahuangtian watershed. In contrast, the rainfall amount (VIP = 1.35) was the dominant factor influencing sediment yield in the Muzhaihe watershed. For runoff variables, runoff amount, runoff coefficient, and maximum discharge were the primary variables controlling the sediment yield in these two karst watersheds. By partially eliminating the co-dependency of the variables, the PLSR approach can conveniently determine the dominant factors controlling sediment yield in heterogeneous karst watersheds. [ABSTRACT FROM AUTHOR]

• The density and spatial distribution of keystones exert a minor control on the bed surface grain-size distribution (GSD). • Keystones tend towards a random spatial distribution regardless of their initial configuration. • Sediment transport has a positive correlation to the proportion of dislodged keystones. Large particles strongly influence flow resistance, energy dissipation, bed stability, and channel morphology in mountain streams. We conducted flume experiments to evaluate effects of the density and spatial distribution of coarse particles (i.e., keystones) on bed stability, surface texture and sediment transport in steep channels. Keystones were placed on the channel bed surface at the beginning of each experiment, both in clustered and in uniformly spaced (i.e., anti-clustered) configurations and in different numbers (i.e., for different values of keystone density). The flow rate was increased by 20 % every hour and each experiment continued until the bed was completely scoured. Sediment transport was measured with a sediment trap located at the flume outlet. Topographic data from high-resolution surface imagery and second-order structure functions (SSF) of bed elevations, were used to characterize bed surface structuring while the Ripley's K function was used to assess the degree of clustering of keystones relative to random spatial distributions. Our results indicate that (1) the density and spatial distribution of keystones exert a minor control on the bed surface grain-size distribution (GSD), (2) for increasing flow rates, the spatial distribution of keystones naturally evolves towards a random distribution, regardless of the initial spatial arrangment, and (3) sediment transport has a higher correlation with the proportion of dislodged keystones than with flow discharge. [ABSTRACT FROM AUTHOR]

• Anticlockwise hysteresis type was the dominating hysteresis type. • Complex hysteresis type generated more sediment than either of three other types. • Antecedent rainfall dominated clockwise type, along with time lag for complex type. • Intraday rainfall and sediment separately dominated clockwise and anti-clock types. • Largest patch index and grassland separately dominated complex and other types. This study aims to quantitatively evaluate the effects of hydrological and landscape characteristics on suspended sediment concentration and discharge (SSC-Q) hysteresis. Runoff and sediment data of 405 flood events were collected from 10 basins in Wudinghe River basin on the Loess Plateau of China. Hysteresis analysis is a key tool for the interrogation of transport of sediment, which have been shown to be important within catchments. It can provide insight into catchment function, allowing the development and testing of process-based hypotheses. The principal components and corresponding explanatory power were extracted quantitatively from hydrological and landscape characteristics via principal component analysis (PCA) and redundancy analysis (RDA), respectively. The most common hysteresis type was anticlockwise. The proportions of the total event sediment loads for different hysteresis types were not always generally correlated to the frequency of the corresponding events. Furthermore, the composition and explanatory power of controlling principal components varied among clockwise, anticlockwise, figure-of-eight, and complex hysteresis types. For hydrological principal components, the antecedent precipitation, intraday precipitation, and sediment principal components controlled clockwise, anticlockwise, and figure-of-eight hysteresis types, which had explained 47.03%, 58.82% and 52.05% of the variation of hysteresis index, respectively; the antecedent precipitation and time lag principal component controlled complex hysteresis type and accounted for 28.22% and 34.65% of the variation of hysteresis index, respectively. For landscape principal components, grassland principal component dominated clockwise, anticlockwise, and figure-of-eight hysteresis types, and accounted for 95.00%, 69.70%, and 92.00% of the variation of hysteresis index, respectively. Largest patch index principal component controlled complex hysteresis type and accounted for 100% of the variation of hysteresis index. Therefore, within this catchment, whereas hysteresis patterns varied due to all of the hydrological and landscape variables to some extent, precipitation, suspended sediment, area of grassland, and the largest patch area had stronger impact on hysteresis dynamics. [ABSTRACT FROM AUTHOR]

• Effective sediment sizes were determined along a gradient of soil structural stability. • Sediment average size exhibited a unimodal variation with soil structural stability. • Suspension-saltation dominated sediment transport for low and high stable soils. • Suspension-saltation and rolling jointly dominated erosion for medium stable soils. • Soil structural stability determined rainfall intensity effect on sediment transport. Sediment transport patterns (suspension, saltation and rolling) not only depend on flow hydrodynamic characteristics, but also on sediment properties, both of which are largely influenced by soil structural stability. However, how sediment sizes and transport patterns response to original soils over a wide range of structural stability remains unclear. Herein, field plot rainfall simulation experiments on five soils along an increased gradient of structural stability were conducted at two rainfall intensities of 45 and 90 mm h−1 to investigate effective sediment size characteristics and associated transport patterns in sheet erosion. Differing from runoff and sediment yield, sediment sizes were most influenced by soil structural stability (F = 386.9) rather than rainfall intensity (F = 246.7, p < 0.001). Mean weight diameter of sediment (0.16–0.84 mm) and the proportion of coarse particles (>0.25 mm) exhibited a unimodal variation with increased soil structural stability. The effective sediment size distribution shifted from unimodal with the peak at < 0.10 mm for low and high stable soils to bimodal with two peaks at < 0.10 mm and 0.5–1 mm for medium stable soils. Correspondingly, suspension-saltation (>74 %) dominated sediment transport for low and high stable soils, which was determined by fine sized fragments from aggregate breakdown and small flow transport capacity, respectively; while both suspension-saltation (<0.10 mm) and rolling (>0.25 mm) jointly contributed to sediment transport for medium stable soils, which was controlled by the interaction between fragment size and flow transport capacity. Moreover, the positive effect of rainfall intensity on sediment sizes was more remarkable for the medium than for the low and high stable soils. A conceptual model of sediment transport mechanisms in response to soil structural stability is firstly proposed, which merits consideration in the future development of erosion modeling and soil conservation techniques. [ABSTRACT FROM AUTHOR]

• Models can account for effects of conservation measures on soil erosion dynamics in tramlines. • Contouring efficiency of tramlines captures variations in slope and sowing directions. • Increased contouring efficiencies of tramlines indicate lower runoff and soil erosion rates. • Reduced tillage indicates significantly lower runoff and soil erosion rates in tramlines. To reduce water erosion, one of the most severe land degradation processes on arable soils, conservation measures such as contour farming or reduced tillage practices can be applied. The general effectiveness of these measures on reducing soil erosion is well understood, however, little is known about the influence on tramline tracks, which have considerable impact on the transport of sediment and runoff. This study assesses the impact of reduced and conventional tillage and slope-related tramline directions on runoff and soil erosion rates at catchment level. For this purpose, a published and freely available dataset was used consisting of soil loss and runoff data modelled for a single soil erosion event considering courses and structural properties of tramlines (cf. Saggau et al., 2022). The orientation of tramlines against the slope direction was defined as contouring efficiency (Cef) and calculated by an approach that relates slope and tramline directions. Finally, results of the statistical analyses are compared with mapped soil erosion data. Results show that i) high-resolution derivation of Cef, based on tramlines, shows reasonable results in capturing variations in slope curvatures within the fields, ii) increased Cefs can significantly reduce runoff and soil erosion in tramlines and, iii) reduced tillage indicates significantly lower runoff and soil erosion rates in tramlines and cultivated areas. The results reveal that tramlines have strong interrelations with surface runoff, water connectivity and soil erosion. The consideration of tramlines in process-based models should be employed in other model approaches as it improves assessments of soil erosion risk and efficiencies of conservation measures, which are necessary in taking appropriate actions in support of soil and water conservation. [ABSTRACT FROM AUTHOR]

• Demonstration of rise and fall of carbon discharge with time. • Demonstration of enrichment of sand in loose layer above soil. • Demonstration of no carbon enrichment is sediment at the steady state. Soil carbon losses from sheet and interrill erosion areas have an impact on the global carbon cycle. Sediment discharged in many experiments where artificial rainfall has been applied to sloping soil surfaces show greater proportions of carbon in the sediment than found in the cohesive soil source. In many cases, conclusions drawn from these experiments fail to recognise that the enrichment of carbon in the sediment discharge is a result of unsteady conditions that occur before the steady state develops. It is known that particles of sand of different sizes move at different rates when raindrop induced salation occurs with the result that initially the particle size distribution is finer than the source but tends towards that of the source as time progresses. The presence of carbon in aggregates influences the density of aggregates. Here a qualitative model of sediment transport of sand and coal particles by raindrop induced saltation is used to demonstrate time varying enrichment of coal resulting from the effect of carbon on particle settling velocity. The model also demonstrates how the layer of loose particles that develops on top of the cohesive soil surface influences the relative amounts of carbon and sand in the sediment discharges. The steady state is not achieved until the slowest moving particle detached at the farthest distance from the downslope boundary is discharged. That may not be achieved in many of the experiments reported in the literature. [ABSTRACT FROM AUTHOR]

[Display omitted] • Temporal evolution of fine sediment deposits on a gravel bar during a two-year period. • Simple physical-based models introduced to better understand fine sediment dynamics. • Flow-related events can yield thick deposits or erosion depending on the discharge-concentration time-series. • Strong wind-related events disperse fine sediments and yield erosion. • Limitation of the image-analysis due to the seasonal variability of the image quality. In this study, the temporal evolution of fine sediment deposits on a gravel bar is analysed during a two-year period. The time-series of fine deposit surface area is obtained using the methodology proposed in Part 1 of this work. By combining the hydro-meteorological data, the main evolutions of the fine deposits observed on the bar surface are found to be triggered by events such as natural floods, dam flushes, and strong wind valley breezes, and are quantified for each of these events. A simple processed-based flow model is proposed to investigate the sediment dynamics during the flood events, which balances the erosional/depositional processes of fine sediments. Variability in the fine deposit evolution after floods is mainly due to the different flow and sediment concentration conditions. For small events for which the gravel bar is not totally submerged, a slight erosion generally occurs. For larger events for which the gravel bar is totally submerged, a large net deposition is often observed. The fine deposit surface area time-series also shows sharp decreases of the surface deposit coverage after some strong valley breeze events, with an evolution of the same order of magnitude than floods. The application of a wind transport model shows that strong wind valley breezes can transport fine particles from the bar surface to the river channel, thus leading to a loss of fine deposits on the bar surface. Also, the deposit initial moisture is a crucial element having impact on the fine sediment transport on the bar surface. Dry deposits are much more likely to be transported than wet deposits. A discussion is also provided on the potential impact of wind and vegetation on the long-term dynamics of fine sediment deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Different delivery pathways have variable impacts on local plant and soil communities. • Bulk density and plant diversity varied significantly downward the pathways. • Slope and contributing area are the main external driver determining gully occurrence. • Erosion resistance determines the development of pathways from partial to full gully. • We established critical thresholds for initiation and development of gully pathways. Road erosion is a global environmental issue. The transport of eroded sediment from road to stream can devastatingly impact water quality. Research efforts to combat this issue have prioritized maintaining roads and preventing erosion. Little research has explored the fate of eroded road materials in their transport from road to stream. Therefore, taking the Xiangchagou watershed in the Dabie Mountains of China as a case, this study investigated how local geography determines the formation and thresholds of different delivery pathways (gullied, partially gullied, and diffuse pathways) for road-eroded sediment through runoff, based on the binary logistic regression analysis, random forest model, and the lowest point data fitting methods. It explored how these different pathways have variable impacts on local plant and soil communities. Our results showed that soil D 50 , bulk density, shrub-grass coverage, and local plant diversity varied significantly (p < 0.05) between different delivery pathways. In particular, soil bulk density and local plant diversity varied significantly (p < 0.05) among different position of these delivery pathways. Specifically, the diffuse pathways are characterized by lower soil bulk density, looser soil structure, and higher species diversity, likely explained by the deposition of sediment-loaded runoff. Gullied pathways, conversely, had significantly more compacted surface soil and lower local plant diversity, likely as a result of scouring by sediment-loaded runoff. Slope gradient of upslope catchment (U s), road segment (R s), and lower hillslope (D s) and effective contributing area (E ca), which determine the intensity and kinetic energy of sediment-loaded runoff, are the main external drivers that determine the occurrence of gullied pathways. By contrast, the soil median particle size, surface roughness, and shrub-grass cover of lower hillslope, which contribute to erosion resistance of hillslope, are the primary intrinsic drivers promoting development of pathways from partial to full gully. Furthermore, we found that the critical topographic thresholds for the initiation of the gully pathways and the continued development of gully from partial to complete gully pathways could be expressed as D s = 0.35E ca −0.13 and D s = 0.41E ca −0.17, respectively. These results are expected to provide basis for understanding the formation and development mechanism of sediment delivery pathways from road to stream. [ABSTRACT FROM AUTHOR]

[Display omitted] • The movement of the bedload and suspended load simultaneously existed. • Sediment transport capacity (T c) equations derived with large particle-size soils underestimated the T c of small particle-size soils. • A more accurate sediment transport capacity equation was developed for small particle-size soils. Sediment transport capacity (T c) is a relevant component in physical-process-based soil erosion models. At present, the sediment transport capacity prediction model for soils with a low median grain diameter is not fully understood. In this study, the T c values of three different soils (median grain diameter d 50 = 0.015, 0.040, and 0.095 mm) were investigated by conducting indoor experiments at unit flow discharges of 0.19 – 1.89 × 10-3 m2·s−1 and slopes of 0.07–0.21. In addition, data describing the overland flow sediment transport capacity of black soil (d 50 = 0.01 mm) were obtained from Yu et al. (2018). First, the performance of seven shear stress, unit stream power, stream power, and mean flow velocity concept-based T c equations were evaluated based on the measurements. The results confirmed that none of the existing formulas performed well over the entire experimental range. T c equations derived using soils with a large particle size generally underestimate the T c of soils containing small particles. The Zhang equation, when calibrated based on the data in this study, can predict overland flow T c with a PoP of 66 % (PoP refers to the percentage of predictions in which the discrepancy ratio falls between 0.5 and 2.0, whilst the discrepancy ratio is the ratio of the predicted and measured T c). Based on the general flow parameter concept, a more accurate T c equation was developed for the four types of soils, which was characterized by a PoP of 83 %. When these equations are beyond the scope of their development conditions, they should be verified further. [ABSTRACT FROM AUTHOR]

• Mudstone deposits behave like noncohesive sediments in terms of erosion resistance. • High erosion resistance of laterites cannot be predicted merely by particle size. • Shields' parameter predicted by water content, clay content, and plasticity index. Soil erosion and sedimentation are major factors in landscape evolution and river morphology. The erosion resistance of sediments plays an important role in landscape evolution processes because it determines the threshold of an acting force at the initiative sediment motion, and the amount of sediment transports. This study examined the sediment properties and their correlations to the erosion resistance of mudstone deposits and laterites, which are two representative natural cohesive soils in hill and terrace topography in Taiwan. Soil physical properties and pore water chemical properties, and the erosion resistance were investigated and determined using laboratory tests and hydraulic flume experiments, respectively. Investigations of sediment properties showed that the mudstone deposits and laterites had significant differences in median particle size, soil texture, level of plasticity, internal structure, and pH value and electrical conductivity of their aqueous slurry. Results from the hydraulic flume experiments showed that the laterites had stronger erosion resistance, indicating by larger values of critical shear stress and the Shields' parameter, than the mudstone deposits. Through the stepwise multiple regression analysis, a quantitative equation was proposed to estimate the Shields' parameter using fine sediment properties including water content, clay content, and the plasticity index expressed in decimal fractions, of the two soils. Despite more experiments of the two natural soils with different ranges of the sediment properties are needed to validate the empirical equation for predicting the Shields' parameter, the proposed methodology provides an essential reference in which erosion resistance is an important parameter. [ABSTRACT FROM AUTHOR]

[Display omitted] • Total volume and peak discharge are the most important drivers of sediment transport. • Antecedent moisture condition is correlated only with the initial discharge of floods. • Hysteresis loops between SSC and Q are analyzed with the hysteresis index (HI). • Negative HI are predominant indicating delayed SS transport and distant SS sources. • In the catchment soil erosion from hillslopes is the dominant process. This study aimed to evaluate the drivers of suspended sediment (SS) transport by analyzing the flood events recorded from July 2010 to June 2011 in the Celone River basin (Apulia, S-E Italy). High-resolution data of rainfall, streamflow (Q), and measurements of suspended sediment concentrations (SSC) were used to carry out the multivariate analysis. Among the initial 18 variables, the Principal Component Analysis revealed that total volume (m3), peak discharge (Qmax, m3/s), and the flood duration were the most important factors influencing SS transport. Total rainfall and total kinetic energy recorded in the gauging station located in the lowland were also important factors, whereas the same rainfall variables recorded in the remote mountainous area of the basin had a minor influence on SS transport. Antecedent moisture conditions were significantly correlated only with the initial discharge of the flood. Hysteresis loops between SSC and Q were analyzed for each flood event by using the hysteresis index (HI). Results showed that this catchment was dominated by anticlockwise loops (negative values of HI) representative of delayed SS transport and of distant SS source areas in terms of the gauging station. These results also suggested that soil erosion from hillslopes was the dominant process compared with channel and bank erosion and that there was no exhaustion of sediment availability in the basin. [ABSTRACT FROM AUTHOR]

[Display omitted] • The SWAT model supports better management of erosion processes. • Computational models can be used with methods of visual recording erosion. • Simple statistical models aligned to SWAT is adequate to analyze erosive processes. • The spatially distributed erosion identifies the susceptible areas to water erosion. Water-driven erosion associated with the transport and deposition of sediments in watersheds may lead to contamination problems causing significant damage to land and infrastructure. The key factors that influence erosive processes are well known and include the precipitation rate, terrain topography, soil type, and vegetation cover. The soil and water assessment tool (SWAT) considers these factors and may be used to identify areas susceptible to soil erosion and to estimate soil loss and sediment transport and deposition. To corroborate this assumption, real data on rill erosion and sediment transport from the Mogi Guaçu River Basin in southeastern Brazil were used to validate SWAT estimates. The study shows that the model is able to identify soil-eroded areas and replicate the scale and variation patterns of sediment production, although not with great precision. Hence, it can successfully be used for prioritizing areas that require action and for evaluating alternative soil management and conservation practices to mitigate erosive processes. [ABSTRACT FROM AUTHOR]

• Factors contribution to runoff, sediment in different seasons and spatial scales. • Contribution of precipitation and underlying surface to runoff and sediment. • Assess the group relationships between different types of influencing factors. The changes in runoff and sediment are the most active parts of river systems. Identifying the effect of precipitation, vegetation coverage (VC), landscape metrics, land-use and land-cover changes (LUCC) on runoff and sediment variations is essential for understanding hydrological processes and the environmental evolution mechanisms of watersheds. This study selected four watersheds located in the Qinling Mountains in China to quantify the effects of different driving forces on runoff and sediment variations at different scales. The results showed that VC increased significantly in the study watersheds (p < 0.05) by more than 16 % since 1990. Obvious increases in forest area were the main features of land use change after 2000. The annual sediment transport and sediment concentration in the wet season showed downward trends. The change of underlying surface contributed more than 58 % to reductions in runoff and sediment concentration in controlled watersheds in Xiangjiaping and Jingziguan. The factors influencing runoff and sediment variations displayed obvious spatial and temporal differences. The 2000 m buffer scale could better explain the runoff and sediment variations than other spatial scales. Rainfall and VC were the main factors affecting runoff and sediment variations at different spatial scales during the wet season, while the aggregation index at the watershed-scale and VC were the main influencing factors in the dry season. Moreover, the intersections between precipitation and landscape pattern, between precipitation and LUCC & VC, and between landscape pattern and LUCC & VC in the dry season and wet season were −31.9 %, −27.6 %, −29.0 % and −18.7 %, −11.1 % and −2.3 %, respectively. Therefore, multi-scale differences in the impact of driving factors and the group relationships between measures should be considered for effective runoff and sediment regulation. [ABSTRACT FROM AUTHOR]

• Length dependent rill erosion processes seemed to be different on gentle slopes. • Equilibrium sediment transport was reached on the rills >7 m length under Q L. • Rolling of coarse particles affected by flow rates and rill length was evidenced. • Continuous head-cuts formation along long rills was an important affecting process. • Steady C and Dr of the 1-m-rill deviated from the Foster-Meyer conceptual model. Understanding the dynamic mechanisms of rill erosion is vital for accurately modeling of soil erosion. In this research, rill erosion was experimentally studied using different rill lengths. A flume, 11 m long and 0.2 m wide adjusted to 3% slope, was used for constructing rectangular rills of 0.05 m width and six different lengths (1 to 12 m). The experiments were carried out on a clayey calcareous soil from a semiarid region under two flow rates of Q L = 0.025 and Q H = 0.045 L s−1. Temporal sediment concentrations (C) were measured at the rill outlet for 40 min and the sediment size distribution (PSD) was recorded twice during each test. The common decreasing trend of C was affected by both flow rate and rill length. The formation of head-cuts along the bed of long rills was an important erosion process affecting C and PSD. The compiled data were used to determine the exponential models' parameters of both C and soil detachment rate based on the steady, unsteady, and event-average values. While, the equilibrium sediment transport occurred by increasing rill length beyond 7 m under Q L , the tested rills under Q H were not sufficiently long for the flow to reach its maximum transport capacity at the gentle slope used and for the calcareous soil tested. Based on the sediment PSD, the selective transport of coarse particles was evidenced. Selectivity transport was affected by rill length reached its maximum at the rill length of 7 m. The findings provides better understanding of rill erosion processes for calcareous soils on gentle slopes in semiarid regions. Further research is needed for better understanding of the rill erosion processes on short gentle slopes to provide experimentally supports for the existing theoretical concepts of rill erosion models. [ABSTRACT FROM AUTHOR]

• MEMD revealed scale-specific daily suspended sediment load (SSL) variation. • SSL dynamics were dominated by short time intervals of approximately 4–23 days. • Runoff was the principal driver of daily SSL at both short and long timescales. • Measurements at a single timescale cannot capture sufficient information on daily SSL dynamics. • MEMD can enhance daily SSL predictions. Temporal variation in sediment load is generally scale dependent and affected by many factors operating at different timescales. Due to the complexity of sediment transportation mechanisms and the nonlinear behavior of hydrological processes, identifying multi-timescale effects of variables on daily suspended sediment load (SSL) is challenging. Using multivariate empirical mode decomposition (MEMD), the aims of this study were to investigate scale-dependent relationships between daily SSL and associated variables and to predict daily SSL based on these relationships. Data on daily SSL in four typical karst catchments of southwest China and five potential variables affecting daily SSL (i.e., runoff, precipitation, air temperature, potential evapotranspiration, and Normalized Differential Vegetation Index) were collected during 2009–2012. The results indicated that MEMD decomposed temporal patterns of daily SSL and five potential variables affecting daily SSL into eight or nine intrinsic mode functions (IMFs) and a residue. Short timescale oscillations of IMF1 to IMF4 contributed more than 72 % of the total variance in daily SSL in the four catchments, indicating that temporal variation in SSL was dominated by short intervals of 4–23 days. Runoff was the dominant explanatory variable for the overall daily suspended sediment load prediction at the observation scale. The predictions of daily SSL based on the IMFs and their residuals greatly outperformed those based on the original time series data. This result implies that a single scale (e.g., observation scale) is not sufficient to capture the complex relationships that exist between daily SSL and associated variables at all timescales. The results demonstrate the superiority of MEMD in characterizing scale-specific relationships between daily SSL and associated variables and improving daily SSL predictions. Given the complexity, nonlinearity, and nonstationarity inherent in many hydrological and sediment transport processes, MEMD is recommended for identifying scale-specific variation in daily SSL in future studies. [ABSTRACT FROM AUTHOR]

• Proglacial areas show complex dynamics of sediment transport. • Today proglacial areas act as both sediment storage and sediment source areas. • Positive temperature anomalies lead to changes in sediment connectivity. • Extreme precipitation and snow-melt events enhance functional connectivity. Proglacial areas in high-mountain environments are among the most dynamic landscape zones in terms of morphological, sedimentological, and hydrological changes. In fact, in such areas both glacial and paraglacial dynamics exert a strong control on water fluxes (and thus on bedload transport capacity) and on sediment supply. Because of the rapid changes undergoing in these environments, the understanding of the dynamics of sediment transfer and the prediction of how this will change in future still remain a challenge. In this study, we used four different high-resolution topographic surveys to quantitatively analyse the spatio-temporal patterns of sediment transport that occurred in the proglacial area of the Sulden glacier (South Tirol, Italy). The topographic surveys covered the period 2013–2019 and – by building DEMs of difference (DoDs) – we calculated the volumes of erosion and deposition occurring at the glacier terminus and along its outflow channels. Our results indicate that, within the analysed time-period and for different areas, erosion and deposition generally show similar values, suggesting that the analysed proglacial areas has been acting both as a sediment trap and as a sediment source for the downstream river reaches. In addition, the results indicate a complex morphological dynamics, which have strongly impacted coarse sediment connectivity in the upper catchment. In particular, high temperatures and the recent and rapid glacier melt, have promoted a direct control on the structural connectivity within the proglacial area. Morphological changes have increased or decreased sediment connectivity depending on pre-existing morphological features. In contrast, extreme precipitation events, both in term of rainfall and snowfall, have locally and temporally increased the functional connectivity, sometimes leading to long-term modifications in the proglacial area. Overall, in the analysed time-period sediment transfer has been extremely dynamic, suggesting that sediment in the downstream river channel may have been supplied with irregular pulses associated with the morphological changes taking place in the proglacial area. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coherent dataset on specific sediment yield for 30-year' period (1990–2019) • Strong variation in sediment yield along the Peruvian western Andes. • River discharge and river channel steepness explain 55% of the variance in sediment yield. • Spurious correlation between land cover, river discharge and topography. • Empirical data on sediment yield during extreme events are needed. The tropical Andes has been less studied in terms of erosion processes in comparison to other major mountain ranges in the world. Environmental gradients are steepest along the western flank of the Andes that is characterized by marked differences in vegetation, rough topography with deeply incised canyons, and highly variable and extreme precipitation patterns. Previous efforts mostly focused on sediment fluxes in large rivers draining to e.g. the Amazon basin while small to medium-sized rivers such as the ones flowing towards the Pacific Ocean have been relegated. They highlighted the link between sediment yield, anthropogenic and natural factors, e.g. climate, topography, river runoff, lithology and vegetation cover. In this study, we identified the spatial patterns of specific sediment yield along the western slopes of the Peruvian Andes between 3° and 13° S latitude for 21 catchments. We collected and analysed data from 22 environmental factors to elucidate their importance on spatially varying sediment yield. The sediment load was derived from gauging stations, reservoir sedimentation and water turbidity over a 30-yr period. The specific sediment yield varies strongly along the Peruvian western Andes as a consequence of the spatial variation in climate, topography and land cover controlling sediment production and transport. We reported higher-than-average specific sediment yields for the central part (6°-11°S) with values of 2130 and 2300 t km−2 yr−1 and low and uniform yields of 39 to 551 t km−2 yr−1 in the southern part (11° − 14.5° S). Given the scarcity of data on sediment yield, we included an uncertainty assessment based on bootstrapping approaches as to get a better grasp on the potential range of specific sediment yields in the study region. Using statistical techniques including Spearman correlation rank, univariate and multivariate regression analyses, we were able to determine the importance of the 22 environmental variables on the specific sediment yield. About 55 % of the observed variance can be explained by river discharge (Q 90) and river steepness index (ks 50). By adding an anthropogenic variable based on land cover, the explained variance in SSY increases up to 63 %, however, the effects of land cover on specific sediment yield are not clear because of spurious correlation between land cover, river discharge and topography. Our study therefore provides important new insights in the ongoing scientific debate on sediment yield variability in the western Andes. [ABSTRACT FROM AUTHOR]

• Landslide connectivity has a significant negative relationship with the area and location. • The connectivity evolution of landslides has a positive effect on the supply capacity from landslides to debris flows. • An integrated method is proposed to estimate the debris-flow magnitude. • The average error of magnitude estimation is<20% when considering landslide connectivity. In an earthquake disturbed basin, the earthquake-induced landslides' connectivity with debris-flow channels determines the landslide sediment volume that is transported into debris flows, and the debris-flow magnitude as well. In this study, the index of sediment connectivity (IC) was used to analyze the evolution of landslide sediment transport capacity. A normalized IC was developed to quantify the movable volume of the landslide sediment available for debris flows. Combined with a landslide empirical relationship, sediment connectivity calculation, particle model, and numerical algorithm, two debris-flow events after the 2008 Wenchuan earthquake were simulated for the Qipan catchment. The results show good agreement between the simulated and observed debris-flow magnitudes of peak discharges, inundated areas, and depths with approximately 9% average error, which indicates that the normalized landslide connectivity index is suitable for estimating the movable volume. Moreover, the IC and landslide characteristics (area and location) showed significant negative correlations, indicating that the spatial connectivity of landslide sediment generally decayed over time, with a corresponding reduction in debris-flow magnitude. [ABSTRACT FROM AUTHOR]

• Land use experienced reclamation during 1938–1958 and vegetation restoration 1958–2020. • Sediment yields varied consistently with land use changes. • High spatial heterogeneity of landscapes reduce sediment yield and transport. Understanding the response of soil erosion to the changes of land use and landscape pattern is valuable for the optimization of soil and water conservation measures in a watershed. This study selected a typical hilly-gully watershed of the Chinese Loess Plateau, the Zhifanggou watershed, to assess its long-term land use changes from 1938 to 2020 and their impacts on sediment yield by using the spatially distributed soil erosion model WaTEM/SEDEM with an average annual rainfall erosivity of 2000–2010. The results indicated that the main land use types in the Zhifanggou watershed were cropland, forest and grassland, and experienced two changing periods: rapid agricultural reclamation during 1938–1958 and vegetation restoration during 1958–2020. The average annual sediment yields varied consistently with land use changes, showing evident changes from 51.84 t ha−1 y−1 in 1938 to 254.1 t ha−1 y−1 in 1958 and then to 4.27 t ha−1 y−1 in 2020. Correlation analysis suggested that sediment yield was closely related to the landscape indices of interspersion and juxtaposition index and Perimeter-area fractal dimension. The results indicated that increased vegetation cover and high spatial heterogeneity of landscapes could alter sediment transport pathways, reduce sediment connectivity, and induce less sediment discharged into the river. Our findings could provide a good reference for optimizing soil and water conservation measures in the watershed. [ABSTRACT FROM AUTHOR]

• • Thorough analysis of WSRS-induced impacts on the river channel and delta. • • The natural hydrological cycle process has been altered by the artificial floods. • • Reservoirs regulation scheme altered the erosion–deposition regime of the riverbed. • • New light is shed on saving the global sinking deltas. The water and sediment regulation schemes (WSRS) orientated by dams have profoundly adjusted the hydrological process and geomorphological evolution of the lower Yellow River and delta. Two decades since the implementation of WSRS, the observed multidisciplinary datasets allowed us to systematically evaluate the impacts of this unprecedented engineering effort on the river-coastal system. The sediment fluxes transported to the sea showed a notable rebounded and coarsened process due to the erosion of the riverbed during the WSRS periods. The average median grain size of suspended sediment increased from 17.7 μm in the 1990 s to 26 μm in 2002–2009. The natural rhythm of hydrological process is fundamentally altered by WSRS, about 50% and 30% of annual sediments and water delivered to the sea for only 20 days. The water discharge system is more temporally dynamic and complex with higher dimensionality after the operation of WSRS. The erosion pattern has been a dominant feature in all the channel segments downstream the Xiaolangdi Reservoir, with an average total erosion volume of 1.02 × 108 m3/a after the WSRS. However, the erosion efficiency of the lower river showed a decreased trend, due to the riverbed had formed a coarse armored substrate for the continued scouring since 2002. The YRD has changed from the pattern of erosion to progradation for the increase of sediment supply, and the average growth rate of subaerial delta was about 6.89 km2/a during 2003–2014. The lessons learned from the operation of WSRS may provide a valuable reference for the management of global large river systems. [ABSTRACT FROM AUTHOR]

• Quantitative reconstruction of soil erosion, sediment transport and delta deposition. • Soil erosion intensity was weak before the late Holocene, and increased afterwards. • The sediment deposition and soil erosion intensity were synchronous. • Soil erosion was dominated by climate as natural process before the middle Holocene. • Soil erosion was accelerated by human activities in the late Holocene. The Yellow River Basin is ideal for studying fluvial landscape evolution under climate change and human activities. Quantitative reconstruction of soil erosion, sediment transport, and delta deposition in the basin enhances understanding of the dynamic mechanisms of fluvial surface processes. This study reconstructs the spatial and temporal distribution of precipitation and vegetation cover based on geological profile records, paleoclimatic datasets, and historical documentation in the Yellow River basin during the Holocene. A landscape evolution model (Landlab) is introduced to simulate soil erosion and sediment deposition processes. Modeling results show that soil erosion intensity in the middle reaches of the Yellow River was weak during the early and middle Holocene. Since the late Holocene, soil erosion has increased due to vegetation degradation, as the climate became drier, but with more fluctuations. Since 2.0 ka (1 ka = 1,000 calibrated a B.P.), and especially since 1.0 ka, soil erosion in the middle reaches of the Yellow River increased rapidly due to strong human activity, with the intensity-six times higher than the average level before the late Holocene. Average sediment deposition thickness in the lower reach of the Yellow River (North China Plain) was about 2.4 m, and sediment volume was about 3.6 × 1011 m3. The deposition rate and soil erosion intensity showed synchronous changes during the Holocene. Since 2.0 ka, the sediment load and deposition rate have increased rapidly, to 6–10 times higher than in the early and middle Holocene. On this basis, the effects of climate change and human activities on the evolution of the fluvial landscape are discussed. [ABSTRACT FROM AUTHOR]

• An inventory of rock glaciers in the Gangdise Mountains was made. • Rock glacier metrics were calculated and analysed. • A comparison with rock glaciers on the Tibetan Plateau and surrounding regions was made. • Increasing temperature and precipitation increase rock glacier occurrence. Rock glaciers are linked to palaeoenvironment, water storage, sediment transport, and natural hazards. Previous rock glacier studies have been conducted in many places globally, but detailed studies have not been done in the Gangdise Mountains of the southern Tibetan Plateau (TP). In this study, 132 rock glaciers were mapped in the western, central, and eastern sectors of the Gangdise Mountains and their metrics calculated. The smallest rock glacier length in the east and the increasing trends of rock glacier density and specific area eastward reflect the effect of temperature and precipitation. The decreasing trend of mean altitude and minimum altitude of the rock glacier front towards east highlight the role of precipitation. Rock glaciers with altitudes of 5143–5651 m above sea level (asl) tend to face N, but their vector strength values decrease with altitude. Rising above 5651 m asl, rock glaciers tend to face SE. These results imply the ability of high altitude to promote rock glacier development on climatically unfavourable slopes. Bedrocks that mainly produce finer or platy debris are rarely sources of rock glacier materials. High altitude may diminish this effect. Aspect does not affect rock glacier size and shape, but rock glaciers on northern slopes have lower altitudes than those on southern slopes due to the effect of solar radiation. Welch's test shows that rock glacier size is mainly controlled by non-lithological factors. By comparing with the previous results of the TP, it is found that increasing temperature and precipitation increase rock glacier occurrence but limit its size. [ABSTRACT FROM AUTHOR]

• Soil erosion process on frozen-stony slope is experimentally investigated. • Sediment concentration on frozen-stony slope follows linear-exponent curves. • The impacts of thawed soil depth and rock fragment content on sediment transport process are quantified. Rill erosion on frozen-stony slope in high-altitude or high-latitude areas commonly undergo freeze–thaw cycle, which is significantly influenced by partially thawed soil with rock fragment. This research aims to investigate the influences of thawed soil depth (TSD) and rock fragment content (RFC) on rill erosion and quantifying the mathematical relationships among them. The laboratory experiment is conducted to evaluate the influences of TSD (1, 2, 5, and 10 cm) and RFC (0%, 10%, 20%, and 50%) on sediment delivery processes by concentrated meltwater flow under three slope gradients of 5°, 10°, and 15°, and three flow rates of 1, 2, and 4 L min−1 at nine rill lengths from 0.5 m to 8.0 m. Five runoff samples are obtained from each experiment run and used to calculate sediment concentration (SC). The SC increases linearly and then exponentially with rill length to approximate the extremum and fits well with piecewise functions. Restrictive effect of TSD and RFC on sediment supply is evident during linear stage induced by shallow TSD, which keeps a long distance under shallow TSD and low RFC to collect sufficient sediment for exponential period. However, TSD and RFC impacts become apparent during the exponential period and lead to higher sediment yield with RFC of 10% and 20% than that on totally thawed soil without rock fragment. In this research, the positive effect on sediment yield increases with RFC increases from 10% to 20%, which may need to be eliminated for efficiency in erosion control. In contrast to low RFC, the protection impact of rock fragment always exerts with RFC of 50%. The experimental data and the functional relationship can provide the basic knowledge for evaluating the model parameters such as soil detachment rate and erodibility of rill erosion on frozen-stony slope. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dominant sediment source in the MYR changed from upstream input to fluvial erosion and tributary input. • Sediment supply amount accounted for 21% of sediment transport capacity in the MYR. • Bank erosion contributed to 9–18% of the sediment amount transported in the MYR. Sediment transport in alluvial rivers is critical to reshape channel morphology and to the global geochemical cycle. This study reports a detailed investigation into the contributions of different sources to sediment transport in the Middle Yangtze River (MYR). It is found that: (i) after the operation of the Three Gorges Project (TGP), the dominant sediment source in the MYR changed from the upstream input to the fluvial erosion and tributary input, with the upstream input providing 38% of the outlet sediment amount in the MYR and the fluvial erosion and tributary input providing around 39% and 23%, respectively; (ii) river bed erosion contributed to 21% of the transported sediment after the TGP, whereas bank erosion contributed to around 18%, which was estimated to be 2 times larger if bank protection works were not constructed after the TGP; (iii) in terms of the sediment transport processes of different fractions after the TGP, the fraction of fine sediment (diameter d ≤ 0.31 mm) in the MYR mainly came from the upstream and tributary input, and the fraction of medium sediment (0.31 mm < d ≤ 0.125 mm) almost equally came from each source, whereas the fraction of coarse sediment (d > 0.125 mm) was primarily eroded from the bed and banks. Besides, the MYR was transformed from a transport-limited river system into a supply-limited one after the TGP operation, with the total amount of sediment supply accounting for 21% of its transport capacity under current flow and boundary conditions. The development of bed armoring in the main stream and the construction of various river regulation works, would result in a further decrease in the sediment supply rate of the MYR in the future. [ABSTRACT FROM AUTHOR]

• Pedodiversity can increase soil retention services, but decreases water yield services. • Pedodiversity can increase the stability of soil retention services over time. • Environmental factors have both direct and indirect effects on ecosystem services. • Total effect of pedodiversity and environmental factor on ecosystem service is similar. Pedodiversity has an important influence on soil water movement, sediment transport, plant growth, biodiversity maintenance, and many other ecological processes related to ecosystem services. However, the influence of pedodiversity on ecosystem services is still unknown, especially in mountainous areas. In this study, the relationships between the pedodiversity and two essential ecosystem services, soil retention (SR) and water yield (WY) services, were analyzed, and the influences of pedodiversity on the temporal changes in the SR (DSR) and WY (DWY) during 2000 and 2015 were determined. The results showed that pedodiversity was generally positively correlated with the SR, but it was negatively correlated with the WY. This indicates that a higher pedodiversity is favorable to soil and water conservation. Both the SR and WY decreased during the study period. The Shannon index was significantly negatively correlated with the DSR, indicating that pedodiversity was conducive to maintaining the temporal stability of the SR. However, a positive correlation was found between pedodiversity and the DWY, indicating that the higher pedodiversity area exhibited a more significant decreasing trend in the WY. This in turn suggests that pedodiversity helps improve the water retention capacity. The influence of pedodiversity on ecosystem services is mainly a direct effect. However, the influences of the environmental factors had both direct and indirect effects. The results of this quantitative analysis of the influence of pedodiversity on ecosystem services provide evidence that protecting pedodiversity is necessary, and they also provide a new direction for pedodiversity research. [ABSTRACT FROM AUTHOR]