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Investigations of the formation mechanisms of flood peaks in small catchments facilitate flood prediction and disaster prevention under extreme rainstorms. However, there have been few studies on the responses of flood peaks to land use landscape patterns using field surveys during extreme rainstorm events. Based on field data from 17 small catchments near the rainstorm center of Typhoon Lekima, 7 landscape indices were chosen. The flood peak and its sensitivity to the land use landscape were investigated by combining remote sensing interpretation and related analysis. The conclusions are as follows: (1) The peak discharge of the small catchment was 2.36–56.50 m3/s, the peak modulus was 8.00–48.89 m3/(s·km2), and the flood index K ranged from 3.61 to 4.55. (2) Under similar rainfall conditions, the flood peak modulus, K and the proportion of sloping cropland had significantly positive correlations (p

The Loess Plateau is the area with the most serious soil erosion in China, and its control of soil erosion has always been a focus of attention and research. As an important engineering measure of soil and water conservation, the check dam plays an irreplaceable role. However, the effect of connection mode between check dam and downstream channel is not considered in the evaluation of sediment interception efficiency of check dam, which may lead to the high calculation result. In this study, in order to evaluate the sediment interception efficiency of check dam more accurately, the control areas of Caoping hydrological station in Wudinghe River Basin and Ganguyi hydrological station in Yanhe River Basin were taken as study areas, and 24 typical dam-controlled watersheds with different land use types, 4 typical small watersheds with different combinations of check dam were selected, the check dam types and their connection modes between check dam and downstream channel were investigated and analyzed, and the sediment interception efficiency of check dam was estimated. According to the difference of connectivity between check dams and downstream channels, there are 11 types of connection modes between check dam and downstream channel: disconnected, connected with spillway, connected with shaft or horizontal pipe, connected with spillway and shaft or spillway and horizontal pipe, connected with shaft, horizontal pipe and spillway, connected with dam body damaged gap, connected with discharge canal, connected with discharge canal and shaft, connected with discharge canal–spillway, connected with discharge canal–shaft and spillway, connected with discharge canal–dam body damaged gap. Based on the actual control area percentage of dam land, the structure connectivity of sediment between check dam and downstream channel was evaluated. The results show that the structure connectivity of sediment is mainly affected by the discharge canal and its length. The sediment interception efficiency of dam system is greater than the sum of single dams. If there is no drainage channel at the bottom of the key check dam, the sediment interception efficiency of the whole dam system will be greatly increased. The results show that the sediment interception efficiency would be 9.74–18.78% higher if the connection mode is not considered. And extreme rainfall increased the sediment connectivity between check dams and downstream channels, thus greatly reduced the sediment interception efficiency of check dams.

In Lhasa River Basin (LRB), land suitable for settlement or living is experiencing a shortage of resources. Alluvial fans have the potential to alleviate this problem. However, basic information, such as the distribution and land use types of alluvial fans, is rarely studied. In this study, Google Earth, ArcGIS and visual interpretation were used to obtain the outlines, areas, quantities and distribution of alluvial fans. Meanwhile, to show the utilisation potential of alluvial fans, we analysed the land use, their distance from the roads, places (town and village) and rivers. The results showed 826 alluvial fans exist in LRB, with a total area of 1166.03 km2. The number of alluvial fans with areas between 0.1 and 1 km2 is 517, accounting for 62.59% of the total number of alluvial fans. Grassland is the dominant land use type, accounting for 68.70% of the total area of alluvial fans. The cropland area accounted for 2.16% of alluvial fans and accounted for 18.98% of the total cropland area in LRB. Exactly 93.70%, 53.63% and 61.86% of the total number of alluvial fans were located within 5 km from the tertiary road, village, and river, respectively. To sum up, our survey results showed that alluvial fans are important land resources in LRB and may have huge utilisation potential.

A phytogenic mound is a special microtopography that forms under a perennial plant canopy in erosion-affected areas. These mounds result in spatial microenvironmental heterogeneity and thus are imp...

Xiang-lian pill, consisting of Coptis chinensis Franch. coprocessed with Tetradium ruticarpum (A.Juss.) T.G.Hartley (Yu-huang-lian) and Aucklandia lappa DC. (Mu-xiang), is traditionally used to relieve fever, abdominal pain, and gastrointestinal inflammatory symptoms observed in patients with malignancies of the gastrointestinal tract. Each of the three herbs contained in Xiang-lian pill has been indicated to have anticancer effects on a variety of cancers, but its effects on pancreatic cancer remain unexplored. The main extracts of these herbs have anti-pancreatic cancer effects, but the comprehensive mechanism of this compound prescription of Xiang-lian pill in pancreatic cancer remains to be revealed.To explore the main active ingredients, potential anti-pancreatic cancer targets, and related mechanisms of the Xiang-lian pill and to determine its therapeutic value in vivo.Network pharmacology and bioinformatics analysis were applied to screen the potential effective ingredients and key targets. Liquid/gas-mass spectrometry was performed for ingredients validation. Molecular docking and the cellular thermal shift assay were performed to test the binding efficiency between ingredients and targets. A murine pancreatic cancer model was established and administered different doses of the Xiang-lian pill. Hematoxylin-eosin staining was used for histopathological observation. Immunohistochemistry and immunoblotting were conducted for target validation. In vitro studies (cell viability and clonogenicity assays) were conducted to investigate the impact of three main ingredients in Xiang-lian pill on pancreatic cancer cells. PTGS2 overexpression was performed to reversely confirm the antitumor mechanisms of rutaecarpine as a specific PTGS2 inhibitor.Xiang-lian pill suppressed pancreatic cancer growth in the dose range of 0.78-2.34g/kg with no significant toxicity. Sixteen potentially active ingredients and 26 corresponding therapeutic targets for pancreatic cancer were identified. PTGS2, PTGS1, KCNH2, PRSS1, and HSP90AA1 were the top 5 significant genes targeted by the Xiang-lian pill. Evodiamine, rutaecarpine and stigmasterol bound to PTGS2 and PTGS1 with different affinities and inhibited pancreatic cancer cell proliferation. The PTGS2-associated metabolic pathway MEK/ERK was downregulated by rutaecarpine in vitro and the Xiang-lian pill in vivo.Xiang-lian pill mainly regulates inflammation, apoptosis, metastasis, and metabolism to exert an antitumor effect. The main active ingredients in Xiang-lian pill exhibit antitumor roles through directly binding to key targets in pancreatic cancer. PTGS2 mediated MEK/ERK inhibition by rutaecarpine represents a key therapeutic mechanism of Xiang-lian pill.

Check dams play an irreplaceable role in soil and water conservation in the Chinese Loess Plateau region. However, there are few analyses on the connection between check dams and the downstream channel and the impact on structural connectivity and sediment interception efficiency. Based on a field survey, this study classified the connection mode between check dams and the downstream channel, and the actual control area percentage by discharge canal in dam land was used to quantitatively evaluate the degree of the structural connectivity of sediment between the check dam and the downstream channel. The analysis results show that the connection mode can be divided into eleven categories with different structural connectivity. The different connection modes and its combination mode of check dams and downstream channels in dam systems have a large difference, and the structural connectivity of the dam system is less than or equal to that of the sum of single check dams in a watershed. The degree of structural connectivity of a dam system will be greatly reduced if there is a main control check dam with no discharge canal in the lower reaches of the watershed. Compared with a single check dam, the structural connectivity of a dam system is reduced by 0–42.38%, with an average of 11.18%. According to the difference in connection mode and structural connectivity of check dams and dam systems in the four typical small watersheds, the optimization methods for connection mode in series, parallel and hybrid dam systems were proposed. The research results can provide a reference for the impact of a check dam on the sediment connectivity and the sediment interception efficiency in a watershed and can also guide the layout of a dam system and the arrangement of drainage facilities.

Understanding the relationship between water discharge (Q) and suspended sediment concentration (SSC) across the Loess Plateau is a prerequisite for evaluating soil and water conservation measures. Using daily Q and SSC datasets, this study jointly analyzes changes in Q and SSC on the central Loess Plateau, a major sediment producing area of China, during the periods 1971–1987 (P1) and 2008–2016 (P2). The results show that during both P1 and P2, the contribution of the maximum-3-day-per year sediment load to the total annual sediment load (SSL) is almost invariably over 50% (dominant), and in the majority of cases, the size of this contribution increases further between P1 and P2. The contribution of extremely high SSL events plays an overwhelming role in watersheds of area < 10,000 km2 and appears to be almost independent of change in land cover condition. In the Helong section of the Yellow River, there is more evident reduction in SSC than Q between these two periods (streamflow became clearer), while the opposite occurred in the Jing River (streamflow declined). In addition, the range of variation in SSC is large for small Q values, whereas the SSC for flood events tends to be relatively stable in gullied-hilly and flat-surfaced (Yuan) loess areas, which are major sediment producers. Based on scatter plots of SSC versus Q after logarithmic transformation, we find that the lower boundary of the mapped data points for an individual station fits a straight line. This boundary relates to riverbed erosion. Given that soil erosion weakened on gully slopes over time and streamflow in channels during P2 was generally lower, the boundary tended to move downward between P1 and P2 for most watersheds, reflecting a reduction in SSC for a given value of Q in P2 compared to P1.

It is critical to determine soil erosion rates and sediment yields under ecological restoration conditions on the Loess Plateau. Sediments retained in check-dams document the soil erosion history in a small watershed. We selected the check-dam systems to reconstruct the long-term sediment yield in a restored agricultural catchment on the Loess Plateau. The storage capacity curve method was applied to estimate the total sediment deposition of check-dam systems, and 725.82 thousand tons of sediment was trapped in the check-dams systems from 1975 to 2013. Two abrupt change points were detected in 1987 and 2003 using the double mass curve method; the average catchment sediment yields were 5,273.63 t/(km2·a) in Stage-1 (1975–1987), 1,734.09 t/(km2·a) in Stage-2 (1988–2003), and 2,653.10 t/(km2·a) in Stage-3 (2004–2013), represented intense erosion, mild erosion, and moderate erosion, respectively. In Stage-2, the sediment yield variation in the Fangta catchment was mainly affected by human activities, and its contribution reached 97%. According to the hierarchical cluster analysis, the soil erosion intensity changed gradually from mild to moderate and then to intense when the average annual erosive rainfall reached approximately 300, 350, and 400 mm in the Fangta catchment of the loess hilly-gully region. Approximately 6.1–42.6 % of the sediment was deposited along the way since 2003 when the sediments generated by erosion in small watersheds were gradually transported to the downstream river network. Therefore, check-dam systems are important carriers for reconstructing the historical sediment yield in small and ungauged watersheds. The results of this study not only serve as a basis for obtaining reliable information on erosion and sediment yield in small dam-controlled catchments, but also provide a useful reference for implementing sustainable ecological restoration in the future.

The land that is suitable for settlement or live is shortage in Lhasa River Basin (LRB). Alluvial fan is a candidate resource to suitable land in this situation. However, the basic information of alluvial fans, for example its distribution and land-use types, is little known. In this study, Google earth, ArcGIS and visual interpretation were used to get the outlines, areas, quantity and distribution of alluvial fans. Meanwhile, the land use, the distance from alluvial fans to roads, places (town and village) and rivers (including stream) are analyzed. The results show that there are 826 alluvial fans in LRB and the total area is 1166.03 km². The quantity of alluvial fans with area between 0.1 km2 and 1 km2 is 517, which is dominated in all. The quantity of alluvial fans is concentrated in the east of LRB, but that area is mainly distributed in the west. The area of Grassland is the largest in all land use types which is account for 68.70% of alluvial fans. Although cropland area is accounted by 2.16% of alluvial fans, it is accounted by 18.98% of the LRB’s cropland area. The quantity of alluvial fans within in 5km distance to tertiary road, village, and river (including stream) are accounted of 93.70%, 53.63% and 77.38% respectively. Therefore, alluvial fans have played an import role in LRB, and may have huge utilization potential in the future.

Robinia pseudoacacia is regarded as a valuable but problematic plant due to its positive and negative environmental effects. A comprehensive and mechanistic understanding of the effects of R. pseudoacacia afforestation on ecosystems and striking a balance between ecosystem safety and functioning and R. pseudoacacia naturalization are crucially important. To achieve these goals, studying the community functional structure of R. pseudoacacia plantations is an essential prerequisite that remains understudied. Through quantifying and comparing the functional structure of R. pseudoacacia plantations and naturally restored communities relating to soil erosion control and plant ecology strategies along a 10–40-year chronosequence on the hilly and gullied Loess Plateau, China, we assessed the effects of R. pseudoacacia afforestation on plant community structure from a functional perspective. We found significant differences among restoration strategies in all the functional composition indices but only functional divergence (FDiv) indices, suggesting that the afforestation practice had a great impact on functional composition but not on functional diversity. Specifically, the plantations had relatively high community-weighted means (CWMs) of specific leaf area (SLA), plant height (PH), seed production, seed mass, root mean diameter, clonality and resprouting capacity and high FDivs of the leaf-height-seed scheme and persistence traits, partially suggesting that the exotic tree could naturalize and coexist with native plants in the study area. Moreover, the relatively high CWMs of woodiness, PH and SLA and high FDiv of erosion-control-related traits found in the plantations indicate that the plantations might have superiority in soil erosion control. R. pseudoacacia also had a homogenization effect on understory functional composition and divergence. Furthermore, we proposed a trait-based effect-and-response framework to find the balance, thus achieving sustainable coexistence of the exotic species with ecosystems. This study may provide new prospects for management practices of R. pseudoacacia plantations and a robust scaffold to maintain safe, resilient and functioning ecosystems., This study was supported by National Key Research and Development Program of China (No. 2016YFC0501604), National Natural Science Foundation of China (No. 41907044) and Natural Science Research Project of Education Department of Shaanxi Provincial Government, China (No. 19JK0840).

Gully erosion is a major cause of land degradation in many regions worldwide. Recent research shows that the challenges posed by gully erosion are likely to further increase as a result of climate change and increasing land use pressure. Nonetheless, our understanding of this process remains limited in many ways. While numerous studies have focused on the occurrence and morphology of gullies at local (catchment) scale, relatively little research has explored their spatial variations at regional to continental scales. As a result, the factors controlling the density, size and morphology of gullies at such scales remain poorly understood. This is especially the case for the role of climate/weather conditions. Here we aim to advance our understanding on this topic by studying gully densities and gully morphology in the Chinese Loess Plateau (CLP), a region severely affected by gully erosion. We selected five representative catchments in the CLP that are relatively similar in size (7-30 km²), topographic context, soil characteristics and land use but represent a large gradient in rainfall conditions. We mapped 2511 gullies in these catchments, using Pleiades-1B (panchromatic resolution at 0.5 m) and WorldView-3 images (panchromatic resolution at 0.31 m). For each of the gullies, we calculated a range of morphological parameters including the gully length, width, surface area, length-width ratio and shape index. Next, we explored to what extent differences in gully density and morphology are correlated to contrasts in rainfall and other environmental factors.Overall, the gullies showed large variations in gully length (2.1-308 m, average 38.1 m), width (1.3-87 m, average 11.5 m) and density (0-4.8 km/km², average 2.3 km/km²). Gully densities showed a negative correlation with rainfall amounts. This is likely partly attributable to feedbacks between rainfall amounts and vegetation cover. However, also contrasts in rainfall intensity and regime likely play an important role. Also variations in gully width appear strongly correlated with rainfall patterns (with more humid catchments resulting in overall wider gullies). Surprisingly, gully lengths (a first indicator of gully headcut retreat) showed no clear correlation with rainfall patterns. Overall, our results indicate that contrasts in rainfall regime are crucial to understand gully erosion dynamics at regional to continental scales. This is true for their initiation but also for their subsequent expansion (and especially gully widening). These findings have important implications for the development of models aiming to predict gully erosion at regional to continental scales.

The characteristics of soil erosion under extreme rainstorm conditions can reflect the effect of ecological restoration measures and the rationality of land use patterns in the region. 12 dam-controlled catchments was selected after an extreme rainstorm event occurred in the northern Shaanxi Province on 25-26 July 2017 (called “7.26” rainstorm). Soil erosion intensity in the 12 catchments was obtained by digging up the sedimentation profiles and measuring the sedimentation areas. Using digital orthophoto map and digital terrain model by Unmanned Aerial Vehicle to obtain land-use types and their areas, slope gradients and the distance along the flow path to the edge of the downslope and dam-land. Stepwise regression method was used to analyze the main factors affecting catchment erosion intensity. The results showed that the average sedimentation thickness in the 12 damlands ranged from 0.16 m to 1.67 m and the intensity of soil erosion of the 12 catchments varied from 10295 t km-2 to 49227 t km-2. Soil erosion caused by this rainstorm was 10-50 times of the allowable amount of soil erosion in the Loess Plateau region (1000 t km-2.a) issued by Ministry of Water Resource of the People’s Republic of China (MWR). Stepwise regression analysis shows that, the closer the shape of a catchment to the circle is, the larger the area of slope-cropland in inter-gully land is or the closer the distance between slope-cropland and the dam-land is, the larger the erosion modulus in the catchment would be. What’s more, the presence of cement road up the valleys shoulder line reduced the modulus of soil erosion. Theses findings indicated that the existing ecological conditions in the dam-controlled catchments are not able to resist extreme rainstorm erosion effectively. Optimizing the distribution of land use types in catchments should be the focus of soil erosion control.

Determining the soil quality of alluvial fans and its influencing factors is essential for understanding, utilizing, and protecting alluvial fans. In this study, a soil quality index (SQI) was constructed, and the soil of river terrace farmland was used as a control to evaluate the soil quality of alluvial fans in the Lhasa River Basin of the Qinghai-Tibet Plateau. Meanwhile, the influencing factors of soil quality of the alluvial fan were studied using correlation analysis. The results demonstrated that: 1) There is no significant difference in physicochemical indicators between the soil of the alluvial fan and river terrace farmland, namely the total nitrogen, total phosphorus, total potassium, available nitrogen, available phosphorus, available potassium, soil organic matter, pH, electrical conductivity, and soil erodibility; however, the coefficient of variation of each physicochemical indicator of the alluvial fan is greater than that of river terrace farmland. 2) The mean SQI value of alluvial fans and river terrace farmlands are 0.37 and 0.38, respectively. There is no significant difference between the values, demonstrating that the soil quality of alluvial fans is not lower than that of river terrace farmland. 3) The soil quality of alluvial fans has a highly significant positive correlation with vegetation coverage, land use, annual precipitation, altitude, and geomorphic divisions; a significant positive correlation with geomorphic location; and a highly significant negative correlation with annual temperature. Therefore, from the perspective of soil quality, the alluvial fan in the Lhasa River Basin can be used as a reserve arable land resource.

To control the severe soil and water losses on the Loess Plateau, China, a series of vegetation restoration projects were conducted. A better understanding of the effect of vegetation types on the soil infiltration capacity is important for the sustainable development of vegetation restoration. The aim of this study was to establish a soil infiltration capacity index (SIC) and to analyze the mechanism influencing variations in the soil infiltration capacity after vegetation restoration on the Loess Plateau. Eight vegetation types (community dominated by Artemisia scoparia, Stipa bungeana, Artemisia gmelinii + S. bungeana, A. gmelinii + Stipa grandis, A. gmelinii + Artemisia giraldii, Sophora viciifolia, Caragana korshinskii, and Robinia pseudoacacia) and bare land as the control were selected for this study. The SIC was established by a steady infiltration rate (SR, 50–60 min) and stage I average infiltration rate (ARSI, 0–5 min) according to principal component analysis (PCA). Path analysis was used to investigate how the soil properties and plant fine root affected the soil infiltration capacity. The SIC values of the eight vegetation types were all higher than that of the bare land. The R. pseudoacacia community had the highest SIC value (0.43), followed by the A. scoparia community (0.30) while the bare land (− 0.56) had the lowest value. Path analysis showed that the increase in the fractal dimension and non-capillary porosity of soil particles enhanced the SIC directly. Increases in the clay content increased the SIC by affecting the fractal dimension of soil particles, while increases in the fine root density reduced the SIC by affecting the non-capillary porosity. Plant functional groups (grasses and legumes) affected SIC indirectly via non-capillary porosity and plant root. A comprehensive index, the SIC, was established to describe the soil infiltration capacity by the PCA method. Based on a comparison with bare land, vegetation restoration enhanced the soil infiltration capacity. The R. pseudoacacia community was the most effective at improving the soil infiltration capacity. The improvement in infiltration was closely related to direct increases in the soil non-capillary porosity and soil particle fractal dimension.

Phytogenic mounds, a mound-type microtopography, always develop around plants as an interaction of individual plants with erosion, sedimentation, and bioturbation processes in many different ecosystems. In this study, the spatial variation of soil physical, chemical and biological properties was examined in different parts of phytogenic mounds and intercanopy surfaces on different slope gradients on the Loess Plateau of China. The key indicators that affect soil properties were identified. The results revealed that soil properties on mounds underwent a subtle change compared to intercanopy surfaces on α ≤ 46.6% slopes. However, an improvement of soil properties was observed on α > 46.6% slopes. The spatial variability of soil properties did not obviously change among different mound parts on α 46.6% slopes. Soil chemical and biological variables were positively correlated. However, the physical properties correlated negatively with other variables. The soil available nutrient, moisture, and microbial activity were the key indicators that affected soil quality. The findings all indicate that phytogenic mounds play an important role in preventing soil deterioration and influence long-term ecosystem processes on the Loess Plateau of China.

Denitrification is a critical component of soil nitrogen (N) cycling, including its role in the production and loss of nitrous oxide (N2O) from the soil system. However, restoration effects on the contribution of denitrification to soil N2O emissions, the abundance and diversity of denitrifying bacteria, and relationships among N2O emissions, soil properties, and denitrifying bacterial community composition remains poorly known. This is particularly true for fragile semiarid ecosystems. In order to address this knowledge gap, we utilized 42-year chronosequence of Robinia pseudoacacia plantations in the Chinese hilly gullied Loess Plateau. Soil potential N2O emission rates were measured using anaerobic incubation experiments. Quantitative polymerase chain reaction (Q-PCR) and Illumina MiSeq high-throughput sequencing were used to reveal the abundance and community composition of denitrifying bacteria. In this study, the afforestation practices following farmland abandonment had a strong negative effect on soil potential N2O emission rates during the first 33 years. However, potential N2O emission rates steadily increased in 42 years of restoration, leading to enhanced potential risk of greenhouse gas emissions. Furthermore, active afforestation increased the abundance of denitrifying functional genes, and enhanced microbial biomass. Actinobacteria and Proteobacteria were the dominant denitrifying bacterial phyla in the 0 to 33-years old sites, while the 42-years sites were dominated by Planctomycetes and Actinobacteria, implying that the restoration performed at these sites promoted soil microbial succession. Finally, correlation analyses revealed that soil organic carbon concentrations had the strongest relationship with potential N2O emission rates, followed by the abundance of the nosZ functional gene, bulk density, and the abundance of Bradyrhizobium and Variovorax across restoration stages. Taken together, our data suggest above-ground restoration of plant communities results in microbial community succession, improved soil quality, and significantly altered N2O emissions.

Gully erosion is a serious environmental problem worldwide, causing soil loss, land degradation, silting up of reservoirs and even catastrophic flooding. Mapping gully features from remote sensing imagery is crucial for assisting in understanding gully erosion mechanisms, predicting its development processes and assessing its environmental and socio-economic effects over large areas, especially under the increasing global climate extremes and intensive human activities. However, the potential of using increasingly available high-resolution remote sensing imagery to detect and delineate gullies has been less evaluated. Hence, 130 gullies occurred along a transect were selected from a typical watershed in the hilly and gully region of the Chinese Loess Plateau, and visually interpreted from a Pleiades-1B satellite image (panchromatic-sharpened image at 0.5 m resolution fused with 2.0 m multi-spectral bands). The interpreted gullies were compared with their measured data obtained in the field using a differential global positioning system (GPS). Results showed that gullies could generally be accurately interpreted from the image, with an average relative error of gully area and gully perimeter being 11.1% and 8.9%, respectively, and 74.2% and 82.3% of the relative errors for gully area and gully perimeter were within 15%. But involving field measurements of gullies in present imagery-based gully studies is still recommended. To judge whether gullies were mapped accurately further, a standard adopting one-pixel tolerance along the mapped gully edges was proposed and proved to be practical. Correlation analysis indicated that larger gullies could be interpreted more accurately but increasing gully shape complexity would decrease interpreting accuracy. Overall lower vegetation coverage in winter due to the withering and falling of vegetation rarely affected gully interpreting. Furthermore, gully detectability on remote sensing imagery in this region was lower than the other places of the world, due to the overall broken topography in the Loess Plateau, thus images with higher resolution than normally perceived are needed when mapping erosion features here. Taking these influencing factors (gully dimension and shape complexity, vegetation coverage, topography) into account will be favorable to select appropriate imagery and gullies (as study objects) in future imagery-based gully studies. Finally, two linear regression models were built to correct gully area (Aip, m2) and gully perimeter (Pip, m) visually extracted, by connecting them with the measured area (Ams, m2) and perimeter (Pms, m). The correction models were A m s = 1.021 A i p + 0.139 and P m s = 0.949 P i p + &nbsp, 0.722 , respectively. These models could be helpful for improving the accuracy of interpreting results, and further accurately estimating gully development and developing more effective automated gully extraction methods on the Loess Plateau of China.

Vegetation type and topographic characteristics are important factors that affect the amount and spatial distribution of the forest floor and the soil carbon cycling. However, the relationships among vegetation type, topographic characteristics, forest floor properties, soil properties and soil labile organic carbon (LOC) fractions remain to be elucidated. Here, we conducted a field observational study to explore the relationships between the soil LOC fractions (microbial biomass carbon (MBC), extractable organic carbon (EOC) and permanganate oxidizable carbon (Pox-C)) and forest floor characteristics under various vegetation types (forest, forest-steppe and steppe) and topographic features (slope position and aspect). Our results showed that the vegetation type and topography are both important factors that significantly influence the forest floor properties (i.e., stock, thickness and coverage). The soil total nitrogen and phosphorus were significantly increased, and the soil pH and bulk density were decreased, with an increase in litter stock, coverage and thickness. Simultaneously, the SOC and soil LOC fractions were increased significantly with the increase in litter stock, coverage and thickness. Over 50% of the variation in the SOC and soil LOC fractions was jointly explained by environmental factors, litter properties and soil properties. Our results demonstrated that the SOC and soil LOC fractions are directly influenced by soil physical and chemical properties (e.g., pH, bulk density and soil total nitrogen) and indirectly affected by external environmental factors. Changes in vegetation and topography lead to increases in the litter stock, coverage, thickness and water content in the backslope position and northern slope, which could create favorable soil nutrient and environmental conditions (e.g., higher soil moisture and lower bulk density) to further enhance SOC and soil LOC fraction sequestration. The forest floor potentially links environmental factors and soil properties and serves as an important factor for soil C cycling.