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• This paper provides a new idea for the genesis and evolution of loess tunnels in the Loess Plateau. • There are significant differences in the loess tunnel development density in the different topographic and micro-topographic units. • Spatial statistical modelling was employed to justify and predict the observed spatial distribution tendency of the loess tunnels. • The loess tunnel evolution process can be divided into five stages: the incubation stage, formation stage, development stage, failure stage, and withered stage. Loess tunnels are very common in the Loess Plateau, and they pose unique geological threats. Loess tunnels are often difficult to detect and control due to their concealment and sudden appearance. Thus far, research on the genesis and evolution of loess tunnels remains scarce. In this paper, the genesis and evolution mechanism of the loess tunnels in the Loess Plateau is studied in depth, and the location, shape, and size information are obtained via field investigations. The potential correlations between the loess sediment, the basic physical properties (depth, water content, particle size composition, collapsibility coefficient, and self-weight collapsibility coefficient), and the tunnel density are inferred based on the Pearson's correlation coefficients and tests on the physical and mechanical properties of the loess sediments. In addition, spatial statistical modelling is employed to justify and predict the observed spatial distribution of the loess tunnels assuming Gaussian Markov random fields. The formation of loess tunnels is due to a combination of factors, including the formation thickness, soil properties, joints and fissures, topography, hydrogeology, and climatic conditions. The thickness of the loess, loess sediment properties, and their spatial relationship jointly determine the material basis of the formation of the loess tunnels. The loess tunnels at different depths have different main controlling factors that are hierarchical by depth. The evolution process of loess tunnels can be divided into five stages: the incubation stage, formation stage, development stage, failure stage, and withered stage. The characteristics of each stage are discussed in detail. Our work provides novel insights into subsurface erosion from the aspect of soil tunnels. It improves our understanding of hill slope geomorphological evolution and also provides effective techniques for tunnel erosion control. [ABSTRACT FROM AUTHOR]

• Thermal effects on soil hydraulic and mechanical properties were investigated. • An increasing temperature decreased the soil Ψ in the middle stage of SWRC. • The soil cohesion increased as the power function with increasing soil Ψ. • The soil friction angle increased as the linear function with increasing soil Ψ. • The increase in soil temperature decreased soil matric suction and shear strength. The soil hydrologic and mechanical properties play an important role in the slope stability in the red soil hilly region of southern China. In this study, the red soil layers in a collapsing gully wall were used to investigate the effects of temperature on the soil water retention curve (SWRC) and shear strength. The results showed that the SWRCs of the red soil under different temperatures could be accurately described by the van Genuchten (VG) model (R 2 > 0.95, root mean square error (RMSE) < 0.024). An increasing temperature significantly decreased the soil water holding capacity (WHC), especially in the intermediate range of the SWRCs of the red soil. The soil saturated hydraulic conductivity (Ks) increased linearly with temperature. The soil cohesion and soil friction angle decreased by approximately 44.13% and 30.40% respectively when the soil water content increased from 0.24 cm3 cm−3 to 0.42 cm3 cm−3. The mean soil cohesion and soil friction angle decreased approximately 8.56 kPa and 1.34° respectively when the soil temperature increased from 25 °C to 40 °C. Regression analysis showed that the soil cohesion increased as the power function with increasing matric suction (0–2000 kPa), and friction angle increased as the linear function with increasing matric suction. These results illustrated that an increase in temperature will decrease soil matric suction and shear strength but enhance the soil infiltration rate under certain soil moisture levels. Therefore, the stability of a collapsing gully wall will sharply decrease under the conditions of high temperature and heavy rain in summer. [ABSTRACT FROM AUTHOR]

• A new wetland mapping approach by combing hierarchical classification framework and optimal feature selection. • A coastal wetlands map of Yellow River Delta with 11 detailed wetland types. • Feature selection and separability analysis for accurately extraction of wetland. • Comprehensive analysis of uncertainty assessment for wetland classification. Wetlands play an important role in ecological health and sustainable development, their spatial distribution and explicit thematic information are crucial for developing management and conservation measures. The Yellow River Delta is an important coastal wetland reserve in China, its wetland types are complex and diverse, natural and artificial wetlands are easily confused, making refined classification more difficult. To address this challenge, we proposed a new wetland mapping approach by combing hierarchical classification framework (HCF) and optimal feature selection. First, inheritance-based multiscale segmentation was carried out to obtain object-oriented images, and decision tree classification was used for preliminarily identify wetland and non-wetland. Second, recursive feature elimination and cross-validation (RFECV) was used to select optimal features, which was then utilized for wetland refinement extraction by using random forest (RF) algorithm. The experiments were performed based on Sentinel-1, Sentinel-2 and NASADEM datasets. The results show that effective wetland classification features can be selected by using RFECV. The feature scores are as follows, red edge index > spectral features > vegetation/water body index > backscatter coefficient > topographic features > texture features > location feature > urban index > geometric feature. The overall accuracy and Kappa coefficient of the method in this paper are 92.36 % and 0.915, which are 14.62 % and 6.68 % higher than using only HCF or only RFECV. Compared with the GlobeLand30 and CAS_Wetlands datasets, the refinement of wetland mapping in this paper is higher. This study provides a new idea in methodological selection for wetland information extraction, and the resulting coastal wetland map can be used for sustainable management, ecological assessment and conservation of the Yellow River Delta. [ABSTRACT FROM AUTHOR]

• The elasticity index is adopted to tradeoff the benefits and ecological effects of land consolidation. • Soil erosion of slopes with vegetation is tolerable under climate change. • Slopes below 63° are stable in 6 slope scenarios. • The slope of 53° with Caragana microphylla is the optimal combination scheme. Soil erosion and slope instability restrict the cutting slopes, especially the high and steep slopes of a construction site. It is difficult for present research of observation experiments and investigation to deal with these problems under climate change. Focusing on gully land consolidation in the loess plateau of China, this paper put forward a technical procedure to explore the optimal combination scheme of slope-cutting and vegetation-planting in future climate change. The technical procedure includes scenarios design, model calculation, and scheme optimization. This paper selected a back catchment in Yangjuangou catchment of Yan'an City as a case study and designed 54 combined scenarios consisting of 6 slopes, 3 types of vegetation (including bare land), and 3 climate scenarios. The soil erosion and slope stability under different scenarios were quantified using FLAC/Slope software and Water Erosion Prediction Project (WEPP) model. This paper innovatively designed elasticity indicators to trade off the increase of the flat land area formed by land consolidation and the resulting reduction in slope stability and increase in soil erosion. It is found that the slope of 53° with Caragana microphylla could be the optimal combination scheme considering flat land creating and the safety of slopes. The technical procedure and the resulting parameters could support gully land consolidation in related areas and be referenced by other construction projects. [ABSTRACT FROM AUTHOR]

[Display omitted] • A gully erosion area affected by weathering-related process is focused. • Comprehensive dataset of granite chemical weathering is given. • Applicability of chemical weathering index is critically assessed. • Weathering index is quantitatively corelated to mechanical property. • Various aspects of mechanical property of granite regolith are considered. In most cases, chemical weathering reduces the strength and stability of granite regolith and increases its water sensitivity. When combined with external agents such as climate, these alterations facilitate geomorphological evolution, such as gully erosion in hilly regions. The lack of fundamental understanding about how gully erosion forms have led to an increasing trend of gully erosion in recent years. Because the weathering-controlled properties of granite regolith have a significant effect on gully development, it is vital to assess the chemical weathering degree. However, despite extensive studies on quantifying weathering degree using chemical weathering indices, less is known about how these parameters are correlated with the mechanical properties of granite regolith. To this end, a typical weathering profile is established for granite in Jiangmen, China. This paper investigates the chemical weathering of granite, evaluates the appropriateness of previous chemical weathering indices, and correlates them with the mechanical parameters of granite regolith. Several suitable indices, including CIA, Bases/Al 2 O 3 , Bases/R 2 O 3 , ba 1 , ba 3 , CIW, I mob , and PIA, are selected and correlated with the mechanical parameters. These indices apply well, with some scattering when they are correlated with the internal frictional angle of granite residual soil. This paper provides a comprehensive datset regarding the physical, mineralogical, petrographical, geochemical, and mechanical properties of granite regolith, and enhances the understanding of chemical weathering, especially its correlations with the mechanical properties of regolith. [ABSTRACT FROM AUTHOR]

• River sediments in the eastern and western Fujian have distinct source rock compositions. • Indosinian magmatic rocks predominantly originated from the Proterozoic crust. • Yanshanian magmatic rocks originated from both the DM (Depleted Mantle) and Proterozoic crust. • The middle Zhenghe-Dabu Fault predominantly account for geochemical heterogeneity of river sediments. The Cathaysia Block is featured by intense tectonic activities and magmatic intrusions during the Mesozoic, and its geochemical evolution might greatly imprint the river sediment compositions in southeast China. This paper presents a comprehensive synthesis of data from petrology, U-Pb geochronology, and geochemistry of both river sediments and plutons in Fujian Province, and aims to reveal the constraints of Mesozoic geochemical heterogeneity and geochronology of the Northeast Cathaysia Block on local river sediment geochemistry. The Fujian terrane and relating river systems can be divided into western and eastern parts with the boundary of the Zhenghe-Dabu Fault. The sediments of eastern rivers are characterized by heavy minerals derived from granites and two major U-Pb age groups (90–110 Ma and 120–150 Ma) of detrital zircons. However, the sediments of western rivers are featured by heavy minerals from the Precambrian rocks and have seven zircon U-Pb age groups (from 90 Ma to 3.0 Ga). The Indonesian magmatic rocks predominantly originated from the Proterozoic crust, with less contribution from the depleted mantle, which are much different from the Yanshanian A-type granites and gabbros in the eastern terrane. We infer that the middle part of Zhenghe-Dabu Fault formed in the Jingningian Period primarily caused geochemical and geochronological heterogeneity of the Northeast Cathaysia Block, which further determined the totally different sediment compositions between the western and eastern Fujian rivers. [ABSTRACT FROM AUTHOR]

Soil P, soil fungi change in poplar shelterbelts compared with farmland, and the driving pathway-related mechanism. [Display omitted] • TP in poplar shelterbelts reduced by 27.75% compared with farmlands. • Shelterbelt reduced TP mainly in macroaggregates and HCl-Pi. • Shelterbelt-induced ECM fungi increased and stability of fungal network decreased. • Shelterbelt decreased P in macroaggregates via changes in fungal community structure. • Shelterbelt changed content of leaching fraction-P through soil pH and tree growth. Phosphorus (P) is an indispensable element for all life on Earth, and clarifying soil P components can favor the precise management of soil nutrients. This paper hypothesized that soil total P (TP) and P components in different aggregates and leachable fractions differed between poplar shelterbelts and farmlands. Such changes were strongly associated with fungal variations. Total 24 soil samples were collected from 0 to 40 cm soil layers in 12 pairs of poplar shelterbelts and neighboring farmlands in four sites in Northeast China Plain. The soil P was determined in three soil aggregates (macroaggregates, microaggregates, and silt + clay) and nine sequential leachable fractions (H 2 O-Pi, NaHCO 3 -Pi, NaHCO 3 -Po, NaOH-Pi, NaOH-Po, HCl-Pi, conc. HCl-Pi, conc. HCl-Po, and Re-P), and soil fungi in bulk soils were analyzed by Illumina sequencing. Our data revealed that poplar shelterbelts had 27.75% lower soil TP than neighboring farmlands, mainly occurring in macroaggregates (0.25–2 mm) with no changes in microaggregates and silt + clay. In leachable P fractions, reduced TP was caused by changes in HCl-Pi contributed 47.8%, and NaOH-Pi contributed 34.2% (low or medium plant-available). Poplar shelterbelts decreased the soil fungi diversity and network relations with fewer nodes, edges, and modularity but contained more ectomycorrhizal and less pathogenic fungi than farmlands. The macroaggregates P reduction was mainly driven by fungal community changes, while the fraction-P changes were more closely related to soil pH and tree growth of poplar trees. Our findings highlighted high P depletion from poplars, possible risks for plant availability, and soil fungi roles in the China shelterbelt program, supporting the evaluation and management of soil P-related nutrients in the farmland afforesting system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hoeffding Tree is a promising landslide susceptibility model based on ROC and AUC. • Bayes Network and Logistic Model Tree were applied for comparison. • Correlation analysis of conditioning factors was completed by Frequency Ratio. • Landslide susceptibility maps of Muchuan County and the county town were produced. Landslides, one of the most common hazards around the world, have brought about severe damage to life and property of human. To prevent and mitigate landslides, various models have been introduced to assess landslide susceptibility. In this paper, Hoeffding Tree (HT), a prevailing data stream mining algorithm, was employed to predict landslide susceptibility in Muchuan County, China for the first time. Meanwhile, Logistic Model Tree (LMT) and Bayes Network (BN) were applied to produce landslide susceptibility maps for comparison. The model performances were evaluated by Receiver Operating Characteristic (ROC) curves and areas under the curves (AUC). To obtain landslide inventory map, 279 landslides data was collected, and training and validation datasets were randomly divided with a proportion of 70% to 30%. Furthermore, twelve conditioning factors (altitude, slope angle, profile curvature, plan curvature, slope aspect, distance to roads, distance to rivers, TWI, NDVI, soil, land use and lithology) were selected to construct landslide susceptibility models. Moreover, correlations between conditioning factors and landslides were analyzed using Frequency Ratio (FR). The results showed landslides are prone to occur in areas where human activities concentrate, and all three models exhibited satisfying performances. Concretely, for training dataset, LMT model showed the highest AUC (0.854), followed by HT (0.726) and BN (0.709). However, for validation dataset, LMT and BN models generated similar AUC values (0.761 and 0.764 respectively), and the highest AUC value belonged to HT (0.802). The distributions of landslide susceptibility zones revealed that the interior of county town is mainly seated in low and very low susceptibility zones, whereas regions close to the border suffer high and very high landslide risk. The results acquired in this paper are significant to landslide prevention and urban planning in Muchuan, China. Additionally, this study proved that HT model is a promising classifier for landslide susceptibility modeling. [ABSTRACT FROM AUTHOR]

• Lulao catchment (LLC) is a small, homogeneous watershed on Guizhou Plateau, SW China. • Farmland soil (FS) has higher IRM 300mT /SIRM due to stronger pedogenesis in LLC. • Grassland soil (GS) has low IRM 300mT /SIRM & higher HIRM in LLC where a reservoir lies. • Contribution of FS vs GS to reservoir sediment is inferred with sediment's magnetism. • Changes in erosion is inferred as FS is distant from the reservoir than GS. This paper demonstrates that land use could enhance spatial discrimination of soil magnetism in a homogeneous watershed, and such differences help infer alterations in sediment sources and erosion. One sediment core was sampled from a reservoir built in 1958 and fifteen soil profiles from its catchment on the southern Guizhou Plateau, SW China. The whole watershed was covered by yellow earth developed on limestone. Magnetic measurements and granulometric analysis were performed on the soils and sediments while TOC and TN analysis on two soil profiles and 137Cs analysis on the sediment core. Information of seven years' land-use was derived from remote sensing images. The farmland and grassland soils had different magnetic characteristics while the downwards distributions of TOC and C/N were similar in the two profiles. The grassland soils had higher HIRM, lower χ fd % and IRM 300mT /SIRM. The higher χ fd % and IRM 300mT /SIRM of the farmland soils suggested stronger pedogenesis under cultivation. The average HIRM, χ fd % and IRM 300mT /SIRM were 38 and 334 10-6 A m2 kg−1, 5.7 and 3.6%, and 0.91 and 0.66 for the farmland and grassland soils. The farmland soils were finer probably due to tillage. The reservoir has been closely surrounded mainly by the grassland whereas the farmland, embedded with patches of the grassland, has occurred in the terrains relatively distant from the reservoir. The sediments of 1958–1985 had lower HIRM (156 10-6 A m2 kg−1) and higher IRM 300mT /SIRM (0.79), indicating greater contributions of the remote farmland soils mixed with grassland soils and stronger erosion. HIRM increased (229 10-6 A m2 kg−1) and IRM 300mT /SIRM decreased (0.67) in the sediments of 1985–2019, implying decreased distant-soil contributions and relatively increased input of the grassland soil closely around the reservoir. Erosion thus weakened, as proven by the finer sediments. The declining erosion was mainly due to farmland shrinkage and grassland expansion. [ABSTRACT FROM AUTHOR]

Contrasting landscape and climate settings generate different catenas for alpine steppe grasslands at Maduo (4200 m asl) and alpine meadow grasslands at Maqin (3750 m asl) on the Qinghai-Tibet Plateau. These place-based catenal models can be used as transferable archetypes in environmental management. [Display omitted] • Catenal models are developed for alpine steppe and alpine meadow grasslands on the QTP. • Implications for the generalised use of place-based catenal models are explored. • Research needs and management applications of the catenal models are scoped. Careful development of place-based catenal models and their application as transferable archetypes provides an integrative and generalisable framework for scientifically-informed approaches to environmental management. A workshop and field excursion to the Source Zone of the Yellow River in western China in July 2019 brought together local experts and a team of international researchers to co-develop cross-disciplinary, process-based catenal models that summarise controls on the character and behaviour of grassland environments in alpine meadow (3800 m asl) and alpine steppe (4200 m asl) landscapes. Water, sediment and nutrient fluxes, soil material properties, ground cover (especially percentage bare ground) and the role of small mammals (especially pika) are critical drivers of process linkages in the catenal models. Geologic, climatic and anthropogenic controls on these drivers vary in alpine steppe and alpine meadow settings. While these process interactions have supported grazing adapted ecosystems and sustained biodiversity values in this area for millennia, anthropogenic and climate change disturbances threaten the integrity of these landscapes and their capacity to provide ecosystem services and sustain livelihoods into the future. The place-based catenal models presented in this paper can be used to support applications that appropriately target key attributes, linkages and fluxes that may require conservation, maintenance or treatment in the management of alpine steppe and alpine meadow landscapes. [ABSTRACT FROM AUTHOR]

• Original soil texture and rill flow energy played major roles in sediment sorting. • UDS suffered more severe downcutting erosion than UDQ during rill development. • The rill erodibility parameter of UDS was 1.84 times that of UDQ. • The ω and φ fitted best with the rill erosion rate of UDS and UDQ , respectively. Rill erosion is an important component of soil erosion, however, the process and mechanism of rill erosion on red soil slopes are not clear enough. In this paper, runoff scouring experiments were conducted with five varying inflow rates (8.5, 10, 11.5, 13, 14.5 L min−1 m−1) and one slope (8°) using two typical red soils in subtropical China: Ultisols derived from shale (UDS) and Ultisols derived from quaternary red clay (UDQ). The results showed that for the two red soils, runoff rate, sediment yield rate, and rill erosion amount were all positively correlated with inflow rates in linear relationships (p < 0.05). The high sand and low clay contents in eroded sediments were closely related to the original soil texture (dominated by clay and silt) and rill flow energy. Stream power and unit stream power were the optimal hydraulic parameters to characterize rill erosion mechanisms for UDS and UDQ , respectively. For UDQ with higher clay content and bulk density, the sediment yield process was more stable and the sand content in the eroded sediments was significantly higher than that of UDS , while the silt content was significantly lower. The rill flow of UDQ had slower velocity and larger Darcy–Weisbach resistance coefficient than that of UDS. For UDS with lower clay and higher sand content, the average sediment yield rate and rill depth were 2.26–4.71 and 2.79–6.53 times of UDQ , respectively, and the rill erodibility parameter was 1.84 times that of UDQ. The results are helpful for understanding the rill erosion mechanism and preventing soil loss in subtropical areas. [ABSTRACT FROM AUTHOR]

• Sediment record of paleoflood event was well demonstrated by end-member (EM) model. • Paleoflood magnitude was reconstructed using a one-dimensional (1D) unsteady model. • Flood-frequency distribution curve was greatly improved by the paleoflood data. • An envelope curve for the maximum flood magnitudes along the upper Hanjiang River was first established. This paper provides an important archive of the largest paleoflood event along the Gold Gorge of the upper Hanjiang River, with a review of regional extraordinary flood magnitudes using historical, gauged, and paleoflood datasets. Paleoflood slackwater deposit (SWD) was identified using the sedimentological criteria and high-resolution physicochemical indexes. End-member model demonstrates the paleoflood SWD was dominated by sand component. Optical chronology indicates the paleoflood event was dated to 1000–900 a BP, corresponding to the North Song Dynasty (AD 960–1127). Paleoflood magnitudes derived from one-dimensional unsteady model vary between 23,000 and 34,000 m3/s. The paleoflood data provide a good representation of extraordinary flood event with a 10,000-years return period and greatly improve current flood frequency estimations. Moreover, the envelope curve for extraordinary floods was first established as Q = 50D0.65 and the paleoflood peak discharges are approximately 2–2.5 times of the largest gauged floods within the catchment. These results provide an upper limit of the maximum flood magnitudes along the upper Hanjiang River and also expand our understanding of rare and large magnitude floods in the middle Yangtze River valley. [ABSTRACT FROM AUTHOR]

• A novel approach reveal of the failure mechanism of slopes in tunnel environment. • The failure process is divided into five stages based on failure characteristics. • Tunnel is an important inducement of loess slope failure in tunnel environment. As a unique geological hazard, the occurrence of loess tunnels is closely related to slope failures. However, almost no research on the relationship between loess slope failures and tunnel erosions has been presented, which seriously restricts the deep understanding of the genesis mechanism and evolution process of loess slope failures. This paper focuses on revealing the failure mechanism of loess slopes in tunnel environments via methods including field investigation, exploration, field water injection tests, tracking tests and numerical simulations. The results show that the whole process of permeability coefficient of the soil layer in the test site is divided into three stages: the rapidly decreasing stage, the slowly decreasing stage and then the stable stage; the slope failure process is divided into five stages based on different failure characteristics: the soaking and softening stage, the erosion connecting stage, the slope local failure stage, the slump failure stage and the resting stage. Seepage has a great influence on loess slope failures in the tunnel environment, and it is as an important inducement of failure, while tunnels themselves play an aggravating catalytic role. The soil water interaction is shown to be an important internal cause of slope failure both by field tests and numerical simulations. The existence of tunnels is not conducive to the overall stability of the slope as tunnels expand the influence range of the soil-water interactions. This study re-evaluates the failure mechanism of loess slopes from a novel perspective based on the tunnel erosion environment. [ABSTRACT FROM AUTHOR]

• Delayed channel evolution was revealed at multi-temporal scales. • Retrogressive aggradation migrated upstream beyond the backwater zone. • Conditions in previous ∼4 years cumulatively impact current channel evolution. The delayed response of channel evolution upstream of dams to base-level changes has not yet been thoroughly understood. In this paper, we studied the delayed response of the morphological adjustment at the middle Yellow and lower Wei Rivers upstream of the Sanmenxia Dam, China, based on data of water volume, sediment load, cross-sectional profiles, and erosion/deposition volumes during 1960–2018. Channel evolution upstream of the dam obviously lagged behind the dynamic pool level fluctuation during the first approximately two decades following dam closure, when retrogressive aggradation/erosion phases were identified. The retrogressive aggradation migrated ∼200 km upstream to the tributary of the Yellow River, i.e., the Wei River. The impact of base-level rise may propagate backwards behind the beginning of the backwater reach, reflecting indirect backwater effects. The dam has been operated by the controlled release of "storing the clear water during nonflood seasons and discharging the turbid water during flood seasons" since 1974, and the reservoir has generally been eroded during flood seasons and aggraded during nonflood seasons. The erosion center was defined as the subreach between two adjacent cross-sections with the greatest erosion rate during the flood season, and the aggradation center was defined as that with the greatest aggradation rate during the nonflood season. The results showed that the erosion/deposition centers migrated towards the dam by ∼50–60 km during 1974–2010 and migrated upstream after ∼2010. The location of the erosion/deposition centers was related not only to the water and sediment conditions and backwater length in the current year but also to these conditions in the previous ∼4 years, reflecting the delayed response of channel adjustment or the cumulative impact of pervious conditions on channel morphology. This study helps to inform future reservoir management and the delayed channel response to base level change caused by different natural and anthropogenic disturbances. [ABSTRACT FROM AUTHOR]

• Studies of Holocene soil water content could provide valuable results in water cycle. • The Holocene loess and paleosol in China is the ideal soil water research strata. • The Holocene cultural development in the study area is related to the climate change. In this paper, changes in the Holocene climate, soil water and soil resources in Southern Loess Plateau are studied based on field investigation, grain size and chemical analysis. The purpose is to reveal the impact of the Holocene environmental change on soil water and human activities. The study shows that the mid-Holocene paleosol S 0 in Baoji Region had a CaCO 3 content close to 0, was enriched with Fe 2 O 3 , Al 2 O 3 , was of homogenous dense silty microstructure containing red argillans and had moderate chemical weathering. This shows that the paleosol is luvisol. The mean annual precipitation was about 800 mm at that time. The late-Holocene loess had a high CaCO 3 content, low Fe 2 O 3 and Al 2 O 3 content and of pore-developed crumb microstructure, indicating that the climate was cold and dry. The migration depth of CaCO 3 and Sr in the mid-Holocene paleosol indicates that the distribution depth of gravity water in the soil at that time reached 1.8 m, and the water content in the soil above 1.8 m during the vegetation growing season was higher than 20%. This made it suitable for the development of forest vegetation. The migration depth of CaCO 3 in the Holocene loess was small and the water content in the layers of loess during rainy season was generally lower than 12%; thus, it was not suitable for the development of forest vegetation. In the mid-Holocene soil, water intake was greater than water consumption and soil water was positive balance. Moreover, trace elements, organic matters, water holding capacity and water content in S 0 were higher than those in the early-Holocene and late-Holocene loess, which facilitated agricultural production and human activities. In fact, it is also the primary reason that the mid-Holocene village sites are significantly larger in quantity and greater in scale than the early-Holocene and late-Holocene village sites. [ABSTRACT FROM AUTHOR]

• A typical and common herbaceous plant of Neyraudia reynaudiana roots was selected as the research objective. • The effect of both moisture content and root density to root-soil complex are discussed. • Roots could enhance the soil shear strength mainly reflected in the increase of cohesive force. • Moisture content was introduced into the shear strength model of root-soil complex. The collapse of collapsing walls is a key process during the Benggang development in southeast China and is closely related to the soil shear strength. Plant root reinforcement can effectively improve the soil shear strength. However, there are few studies on the effect of roots on the soil shear strength of collapsing walls. To explore the influence of roots on the soil shear strength of collapsing walls, the roots of Neyraudia reynaudiana was selected as the research object. This paper studies the tensile properties of the roots through root tensile tests and performs a direct shear test to study the influence of the roots on the soil shear strength by setting different mass moisture contents (15%∼30%) and root weight densities (0 ∼ 1.25 g 100 cm−3). Root tensile force is positively correlated with root diameter by a power function, while tensile strength is negatively correlated with diameter by a power function. Roots could increase the soil shear strength, and which was mainly reflected in cohesive force. The shear strength and cohesive force increase first then decrease with the increasing root density, while root density has no effect on the internal friction. The shear strength, cohesive force and internal friction of root-soil complex all decreased with increasing moisture content. The WWM (Wu and Waldron model) greatly overestimated the cohesion of herbaceous roots, and a new prediction model of the shear strength of root-soil composites was obtained by revising the WWM model by introducing the moisture content and root density (NSE = 0.94). In conclusion, Neyraudia reynaudiana roots could improve the soil shear strength, whereas the strengthening effect decreased under the condition of high moisture content. The results provide a basis for the selection and allocation of vegetation restoration measures in Benggang erosion in southern China. [ABSTRACT FROM AUTHOR]

[Display omitted] • FTCs weakened the shear strength and disintegration resistance of the soil. • Increase of water and salt content exacerbated soil erosion due to FTCs. • The effect of FTCs on soil microstructure was investigated. • The underlying micro-mechanism of the change in soil erodibility was explored. Soda-saline loessal soils are distributed extensively in the Songnen Plain of Northeast China. Freeze-thaw effects on soil structure and mechanical properties are becoming more frequent and intense with global warming, which further affects soil erosion in cold regions. Quantifying the effects of freeze-thaw cycles (FTCs) on the erodibility of saline soils is challenging because of the abundant soluble salt content and complex soil mechanical responses. In this study, direct shear tests, disintegration tests, and scanning electron microscopy were conducted to investigate the effects of freeze-thaw action on the erodibility indicators (shear strength and disintegration velocity) of soda-saline loessal soils and their microscopic deterioration mechanisms. Four initial moisture contents (IMCs: 8%, 13%, 18%, 23%), three soluble salt contents (SSCs: 0.5%, 1.0%, 1.5%), and six FTCs (0, 1, 3, 6, 10, 15) were considered. The results showed that successive FTCs continued to degrade the erosion resistance of the soil until it stabilized after approximately 10 FTCs. After 15 FTCs, the shear strength and cohesion decreased by 8.6–19.8% and 24.1–59.2%, respectively, while the angle of internal friction was relatively unaffected. Meanwhile, the soil disintegration velocity increased by 52.3–208.8%. During the freeze-thaw process, the water-ice phase change and the crystallization of soluble salts both led to the continuous adjustment of the microstructure of soda-saline loessal soils. It was found that microcracks within the soil structural units increased significantly, cementation between the structural units weakened continuously, pore connectivity was enhanced, and pore size homogenization increased. Correlation analysis showed that IMC was the fundamental factor affecting the soil mechanical properties, whereas SSC mainly affected the soil's resistance to disintegration. The increase in IMC and SSC exacerbated the deterioration of the soil by freeze-thaw action. This paper presents a new understanding of the erosion characteristics and micromechanisms of soda-saline loessal soils in seasonally frozen regions under freeze-thaw action. [ABSTRACT FROM AUTHOR]

• Monitoring mainland and island coastline variations of the Pearl River Estuary from 1978 to 2018. • Combined Otsu and Canny edge detections to extract coastline from Landsat dataset. • Reclassified coastline as biological, sandy, muddy, estuarine, rocky and artificial via visual interpretation. • Rezoned the study area into Area I-IV and analyzed coastline variations and differences among these areas. • Analyzed natural and anthropogenic factors of coastline variations of the study area. The coastline of the Pearl River Estuary (PRE) experienced significant changes due to the increasing demand for land. Previous studies have focused on coastline changes of the mainland in China; thus changes of island coastlines have not been well investigated. In this study, the coastlines of the continent and islands of the Pearl River Estuary from 1978 to 2018 were extracted and analyzed by integrating Canny edge detection and Otsu methods based on Landsat data, and the coastline was classified into six types including biological, sandy, muddy, estuarine, rocky, and artificial via visual interpretation. The coastline length, coastline change rate and change area were calculated and analyzed for the 40 years period. The precision test showed that the coastline extraction methods presented in this paper meet the accuracy standard. The coastline length of the Pearl River Estuary was found to have increased rapidly from 789 km in 1978 to 979 km in 2018. During the past four decades, a large proportion of natural coastline converted into artificial one (66% in 2018), while 577 km2 land increased in this area. The coastline of the western PRE demonstrates more rapid change rates than that of the eastern part, and more land reclamation has occurred in the western area. Between 1988 and 1997, the coastline length and area of reclamation experienced the most extensive changes. Both natural factors, including sediment transport, sea-level rise, wind, tide, as well as anthropogenic factors, such as land reclamation and dam construction, have impacted coastline variation of the Pearl River Estuary in the past four decades. In general, the western part of the study area showed more remarkable coastline change and experienced the enormous influence of land reclamation, dam construction and sediment transport, compared with the eastern part. [ABSTRACT FROM AUTHOR]

[Display omitted] • FTCs weakened the shear strength and disintegration resistance of the soil. • Increase of water and salt content exacerbated soil erosion due to FTCs. • The effect of FTCs on soil microstructure was investigated. • The underlying micro-mechanism of the change in soil erodibility was explored. Soda-saline loessal soils are distributed extensively in the Songnen Plain of Northeast China. Freeze-thaw effects on soil structure and mechanical properties are becoming more frequent and intense with global warming, which further affects soil erosion in cold regions. Quantifying the effects of freeze-thaw cycles (FTCs) on the erodibility of saline soils is challenging because of the abundant soluble salt content and complex soil mechanical responses. In this study, direct shear tests, disintegration tests, and scanning electron microscopy were conducted to investigate the effects of freeze-thaw action on the erodibility indicators (shear strength and disintegration velocity) of soda-saline loessal soils and their microscopic deterioration mechanisms. Four initial moisture contents (IMCs: 8%, 13%, 18%, 23%), three soluble salt contents (SSCs: 0.5%, 1.0%, 1.5%), and six FTCs (0, 1, 3, 6, 10, 15) were considered. The results showed that successive FTCs continued to degrade the erosion resistance of the soil until it stabilized after approximately 10 FTCs. After 15 FTCs, the shear strength and cohesion decreased by 8.6–19.8% and 24.1–59.2%, respectively, while the angle of internal friction was relatively unaffected. Meanwhile, the soil disintegration velocity increased by 52.3–208.8%. During the freeze-thaw process, the water-ice phase change and the crystallization of soluble salts both led to the continuous adjustment of the microstructure of soda-saline loessal soils. It was found that microcracks within the soil structural units increased significantly, cementation between the structural units weakened continuously, pore connectivity was enhanced, and pore size homogenization increased. Correlation analysis showed that IMC was the fundamental factor affecting the soil mechanical properties, whereas SSC mainly affected the soil's resistance to disintegration. The increase in IMC and SSC exacerbated the deterioration of the soil by freeze-thaw action. This paper presents a new understanding of the erosion characteristics and micromechanisms of soda-saline loessal soils in seasonally frozen regions under freeze-thaw action. [ABSTRACT FROM AUTHOR]

• The near-dam region contributed 10.8% of the total sediment into the reservoir. • Sedimentation mainly occurred in bending, branching and near-dam reaches. • The key factor influencing sedimentation was the incoming sediment load. • New formulas were proposed to calculate sediment trapping efficiency. Sedimentation in the Three Gorges Reservoir (TGR) affects flood control, navigation, power generation and the ecological environment. We present a comprehensive analysis of the characteristics of sedimentation in the TGR from 2003 to 2018. The data set includes field measurements (runoff and sediment) at hydrological stations and estimation for areas where measured data are not available. Based on the data set, the amount of sedimentation in the TGR was calculated with the Sediment Budget Model (SBM) and Section Topography Method (STM). Finally, the variation in sediment Trapping Efficiency (TE) in the TGR was assessed. The results indicate that sediment from smaller tributaries in the TGR region, which has been ignored in most previous studies, constituted approximately 10.8% of the total incoming sediment. The total sedimentation in the TGR was 205478 × 104 t in 2003–2018, and the contribution rates of sediment load flowing into the TGR, the water depth in front of the dam, and runoff discharge flowing into the TGR were 94.4%, 24.5% and −18.9% respectively. The average annual TE was 78.5% in 2003–2018, and it was closely related to the ratio of reservoir storage capacity to flow discharge in the flood season and to sediment concentration in the non-flood season. The results in this paper not only play an important role in the optimal operation of the TGR but also have important reference value for other large reservoirs worldwide. [ABSTRACT FROM AUTHOR]

• Pedodiversity was higher in southern China than northern China. • Analysis unit sizes had little effect on spatial pattern analysis of pedodiversity. • Overall, parent material and topography were major driving factors of pedodiversity. Knowledge of pedodiversity is essential for the protection and management of soil resources. The analysis of regional pedodiversity is typically based on analysis units of different sizes. However, the effect of analysis unit size on regional pedodiversity studies remains unclear. In this paper, the effects of analysis unit size on the studies of spatial distribution characteristics of pedodiversity and its major driving factor in China were studied based on two levels of geomorphological regions. A combined method encompassing the moving window, soil richness, and Shannon index was used to analyze the spatial distribution pattern of pedodiversity in China. A geographical detector was used to determine a major driving factor of pedodiversity in each geomorphological region. The spatial distribution pattern of pedodiversity based on two levels of geomorphological regions both showed that pedodiversity was highest in southern China, followed by northern China, and lowest in the Qinghai-Tibet Plateau, which indicated that analysis unit sizes had little effect on the study on spatial distribution pattern of pedodiversity. The major driving factor analysis of pedodiversity based on first-order geomorphological regions showed that the major driving factor in China, except for the Qinghai-Tibet Plateau, was parent material. However, the results based on second-order geomorphological regions showed that the major driving factors of pedodiversity, except for the Qinghai-Tibet Plateau, were parent material and topography in hilly regions, topography in mountainous regions, and parent material in regions occupied by alluvial landforms, aeolian landforms, or karst landforms. The driving factor analysis of pedodiversity based on the two levels of geomorphological regions suggested that the effect of the analysis unit sizes on the major driving factor study was significant. The results of this study are an important supplement for pedodiversity studies. [ABSTRACT FROM AUTHOR]

• A 150-year environmental change of a populated wetland was reconstructed. • Agriculture and hydrological process variations altered the wetland landscape. • Nutrient and pollution inputs caused negative effects on aquatic plant succession. • Effective protection was helpful to maintain the resilience of wetland ecosystem. Lakes and wetlands in populated areas have become very vulnerable to pollution and habitat degradation, seriously threatening regional ecological security and socio-economic development. Exploring long-term environmental changes in these systems is essential to reveal the interactions of human activities and catchments, and further to provide valuable reference for current restoration. In this paper, we present paleolimnological data from a short sedimentary core from Liangzi Lake, a typical wetland nature reserve in the middle and lower Yangtze River Basin, China. Multiple sedimentary proxies (principally pollen but also geochemistry and grain size data) combined with historical records were used to establish environmental changes of Liangzi Lake, in both terrestrial and lacustrine aspects, over the last 150 years. Despite the influence of hydrological processes to some extent, our results indicate that the anthropogenic effects (negative and positive) are well recorded by the sedimentary records. The landscape changes of the wider Liangzi Lake wetland can be placed into four stages: less disturbed background (before the 1950s), hydrological regulation (1950s–1960s), intensive reclamation (1970s–1990s), and wetland restoration (starting in the late 1990s). Agriculture and hydrological control were the most important factors in transforming the wetland landscapes, as well as the aquatic ecosystem. The changes in the lake itself could be divided into three main stages: low nutrient levels and unstable hydrologic condition with dominant emergent plants (before the 1960s), rising nutrient levels and a stable water environment with increasing submerged plants (1960s–1990s), and high nutrient and pollution levels with the subsequent adjustment and restoration (after the late 1990s). Our study provides a comprehensive history of environmental changes of a typical inland lake and its surrounding wetland, and may contribute to future wetland conservation in similar regions, as well as pollen-based environmental reconstruction studies. [ABSTRACT FROM AUTHOR]

• Distinct slope features of China's cropland conversion were detected. • Cropland conversion in flat areas and steep areas triggered diverse risks. • "Grain for Green project" should be adjusted based on slope features of sub-regions. • Upslope reclamation and downslope loss of cropland indicated develop conflicts. Cropland conversion is a significant theme of the influence of human activities on ecological systems and global food security. Conventionally, cropland conversion in China has been deemed to match the dynamic balance of cropland resources well and to ensure food security for the whole country. However, local studies have presented some conflicting signs that call for an integrated analysis from a national viewpoint. In this paper, by considering the significance of slope in cropland-related natural and socioeconomic issues, we explore the slope features of China's cropland conversion during 2000–2015 and endeavor to identify some potential risks hidden in the process. High-resolution remotely sensed images, digital elevation model and spatial analytical methods are adopted to conduct the analysis. The results show that, the features of cropland conversion in diverse slope division areas are all distinct. Some risks indicated by these conversion features can be identified as follows: (1) unsuitable reclamation of cropland in flat areas causes ecological damage, (2) the invasion of sparsely populated construction land on cropland in steep areas has a dramatic impact on the local area, (3) excessive greening in Northwest and Northeast China, and insufficient greening in Southwest China are not healthy for regional sustainability, (4) cropland's upslope reclamation and downslope loss pose potential risks for food security. In the context of dynamic balance management and other related national policies, cropland conversion in China is not as optimistic as former surveys have indicated, and promoted measures should be elaborately adjusted based on local conditions. [ABSTRACT FROM AUTHOR]

• Identify ancient flood events, which may be the reason for decline of the culture. • Pollen and heavy metals can be used to reflect the strength of human activities. • Pollen and heavy metals revealed the process of culture from prosperity to decline. • This paper defined the chronology from prosperity to decline of Shijiahe culture. • Climate change has been revealed by pollen and heavy metals since 4800 cal. yr BP. The Shijiahe Culture (ca. 4800–4100 yr BP), which originated in the middle Yangtze Basin, was a milestone of prehistoric Chinese civilization. To reveal the interactions between climatic changes and human activities during this time interval, the geochronology and multiple proxies (pollen and heavy metals) of samples from a 220-cm-deep outer wall at the Sanfangwan Site (a typical site of the Shijiahe Culture) were analyzed. Radiocarbon dating indicates that the age range of the Sanfangwan Site is ca. 4800 to 4100 cal. yr BP. From ca. 4800 to 4600 cal. yr BP (the early Shijiahe Culture), pollen assemblages were dominated by Gramineae and an anthropogenic plant community (e.g. Ranunculaceae, Chenopodiaceae, Labiatae, and Cruciferae), indicating an expansion in rice agriculture during this interval. High metal concentrations in the same interval indicate a large flux of metals from smelting and farming activities. Between ca. 4600 and 4100 cal. yr BP (the middle and late Shijiahe Culture), decreases in Gramineae and anthropogenic pollen mirrored the recession of farming. Concurrent decreases in heavy metals may be attributable to a decline in the smelting industry. Three episodes of high pollen concentrations and visible increases in hygrophyte pollen, Pinus pollen, and fern spores at 4600–4550, 4450–4350, and 4200–4100 cal. yr BP probably indicate the occurrence of several flooding events during the middle and late Shijiahe Culture, resulting in the migration of local inhabitants. This study highlights the driving effect of flood events on the collapse of the Shijiahe Culture. [ABSTRACT FROM AUTHOR]

• The induced factors of the Baige landslide are comprehensively investigated. • The Baige landslide is caused by deep-seated gravitational slope deformation. • River downcutting is a prerequisite for the evolution of the Baige landslide. • Earthquake contributes to accelerating the development of the Baige landslide. On October 11 and November 3, 2018, two successive landslides happened at the same location near Baige Village in Tibet of China and dammed the Jinsha River twice. The induced factors and formation mechanism of the Baige landslide are still being questioned. In this paper, high-resolution topographic data, multi-temporal remote sensing images (including the unmanned aerial vehicle (UAV) 3D image, remote sensing, and Geographical Information Systems (GIS) techniques), rainfall data, seismic records, comprehensive field investigations, and numerical simulations are used to identify the main characteristics, the induced factors, and the formation mechanism of the event. The results show that deep-seated gravitational slope deformations play an important role in the evolution process of the Baige landslide; river downcutting is a prerequisite for the progressive evolution of the gravitational slope deformation behavior of the Baige landslide, whereas earthquake plays a catalytic role in the development of the gravitational slope deformation of the Baige landslide. The Baige landslide would be a typical case study for understanding the formation mechanism of large-scale landslides along the Jinsha River. [ABSTRACT FROM AUTHOR]

Schematic figure showing climate driving mechanisms on wetland hydrological and vegetational evolution. The relatively strong East Asian summer monsoon (EASM) with high precipitation tends to generate a higher water-level condition with more hygrophilous herbaceous plants while blocking the deposition of coarse grain-size fractions (a), and vise versa for weak EASM stages (b). [Display omitted] • The late-Holocene hydrological and vegetational regimes were reconstructed. • An ecological lake-to-wetland transition occurred at ~4.5 ka BP. • The wetlands evolution was largely controlled by monsoonal precipitation. The responding mechanism of wetland ecosystem to climate change is currently unclear due to a lack of long-term records incorporating multiple ecological factors. This paper presents a well-dated and multi-proxy cored record from a natural freshwater wetland developed in a paleo-pingo-related depression on the Sanjiang Plain. The study aims to reconstruct the wetland water-level and vegetational regimes during the past ~6.0 ka BP and discuss the wetland evolution response to the East Asian summer monsoon (EASM) circulation. The results show that a shallow-water lake with hygrophilous herbs developed in the depression with a strong EASM during ~6.0–4.5 ka BP. The paleolake was succeeded by a wetland with a lowered mean water level and an increase in tree cover controlled by the weakened EASM during the past 4.5 ka BP. Such an ecological lake-to-wetland transition corresponds well to the sharp decline of the EASM around 4.5 ka BP which has been well documented in various geological records across the EASM domain. During the wetland developing stage over the past 4.5 ka BP, the water-level and vegetational changes in the studied depression were also closely related to the EASM variations. The strengthened EASM usually generated higher water levels with more hygrophilous herbs around 4.0 ka BP, 3.5 ka BP, 3.0 ka BP, 2.0 ka BP, and 1.3 ka BP. Considering the prevalent EASM climate serving as the predominant water supply for the wetlands on the modern Sanjiang Plain, we suggest the EASM circulation has played a critical role in driving the wetland ecological evolution during the mid-to-late Holocene Epoch. The past 0.4 ka BP is an exception as the local Trees/Herbs ratio visibly increased with the declined water level, while the monsoonal precipitation shows no equivalent shift. The wetland evolution at this stage was attributed to human interference. [ABSTRACT FROM AUTHOR]