Loess Plateau Research Articles

The Impact of Soil Dry–Wet Cycles on the Mineralization of Soil Organic Carbon and Total Nitrogen in Check Dams of the Loess Plateau

Frequent soil drying and wetting cycles significantly affect the mineralization processes of soil organic carbon (SOC) and total nitrogen (STN), impacting soil quality and contributing to nutrient loss. However, the effects of these dry–wet cycles on SOC and STN mineralization in dam soil are not well understood. This study simulated four consecutive wet–dry cycles under five soil moisture gradients of 0% (CK), 5%, 10%, 15%, and 100%, and 100%, across four cycles of 7, 14, 21, and 28 days, to investigate the effects on soil aggregates, enzyme activities, and the mineralization of SOC and STN. The results indicated that soil enzyme activity peaked after two dry–wet cycles and then began to decline. The dry–wet cycles reduced the proportion of soil macro-aggregates while also decreasing the proportions of small and micro-aggregates. In contrast, the 100% treatment conditions exhibited the opposite effect. Dry–wet cycles enhanced the mineralization rates of SOC and STN, with the average mineralization rates under the 10% soil moisture content being the highest—1.78 and 2.38 times greater than the CK treatment for SOC and STN, respectively. The impact of dry–wet cycles on SOC and STN mineralization through the enzyme pathway was greater than through the aggregate pathway. These research findings provide theoretical insights and scientific references for the efficient operation and ecological protection of sedimentation dams in the Loess Plateau.

Evolutionary characteristics and influencing factors of agricultural regional system in the Loess Plateau of China under rapid urbanization

Evolutionary characteristics and influencing factors of agricultural regional system in the Loess Plateau of China under rapid urbanization

Reconstructing the late Quaternary soil erosion and dust deposition dynamics in the southern Loess Plateau: Insights from Lake Luyanghu sedimentary records

Investigating the history of wind-dust deposition and soil erosion is crucial for understanding the relationship between geomorphologic formation, monsoon evolution and the current state of soil erosion on the Loess Plateau. This study utilizes a 50-m sedimentary record from Lake Luyanghu (LYH) in the southern Loess Plateau. We developed a chronological framework using optically stimulated luminescence (OSL) dating and stratigraphic comparisons. By applying end-member modeling of grain size, we identified various sediment sources and quantitatively reconstructed the dust deposition fluxes and soil erosion modulus during the late Quaternary. Additionally, we examined the patterns of sediment source evolution with environmental changes at LYH. Our findings reveal that dust constitutes an average of 32.3% of the lake sediments, with an average deposition rate of 40.2 g/cm2/ka. Notably, after the Last Glacial period, dust deposition became the dominant component of the lake sediment. During the Marine Isotope Stages (MIS) 5b, 5d, 4 and 2, enhanced dry climatic conditions, decreased vegetation cover and composition, leading to significant soil erosion. Based on the results of this research, future studies should aim to reconstruct the watershed's erosion and deposition processes throughout geological periods by integrating aspects of lake evolution, such as water levels and developmental stages.

Flow Resistance Coefficient Under Rigid Vegetation Coverage: An Experimental Study

ABSTRACTRigid vegetation is prevalent in the Loess Plateau region. Most simulation studies assume that vegetation grows perpendicularly to the slope surface (BS), overlooking the influence of growth perpendicular to the horizontal plane (BH) on the slope flow resistance coefficient. Therefore, this study explores the effects of rigid vegetation on the slope flow resistance coefficient by conducting indoor simulated scouring experiments under different vegetation coverage (0–15.89%), two growth directions (BS and BH), four slopes (5°, 10°, 15° and 20°), and five flow rates (5, 10, 20, 30 and 40 L·min−1). The results showed that the resistance coefficient increased non‐linearly with vegetation coverage; however, the growth rate slowed with increasing slope at high coverage, showing a decreasing trend. The resistance coefficient under BS conditions was generally higher than that under BH conditions. As the coverage increased (0–15.89%), the resistance coefficient under BS conditions became 1.51–1.99, 1.1–1.26 and 1.52–1.59 times that under BH conditions. The resistance coefficient ratio negatively correlated with the flow rate and water depth and positively with the slope. Furthermore, the relationship between the Reynolds number (Re) and resistance coefficient under BS and BH conditions significantly differed, with a negative correlation under BS conditions and a positive one under BH conditions. The Froude number (Fr) exhibited a strong negative correlation with the resistance coefficient, and the impact became more significant as vegetation coverage increased. Through dimensional analysis and nonlinear fitting, a high‐precision resistance coefficient prediction model (adjR2 = 0.98, NSE = 0.99, RRMSE = 0.04) was developed, which provided theoretical support for engineering designs and enhancing soil and water conservation strategies on the Loess Plateau.

Quantifying the Geomorphological Susceptibility of the Piping Erosion in Loess Using LiDAR-Derived DEM and Machine Learning Methods

Soil piping erosion is an underground soil erosion process that is significantly underestimated or overlooked. It can lead to intense soil erosion and trigger surface processes such as landslides, collapses, and channel erosion. Conducting susceptibility mapping is a vital way to identify the potential for soil piping erosion, which is of enormous significance for soil and water conservation as well as geological disaster prevention. This study utilized airborne radar drones to survey and map 1194 sinkholes in Sunjiacha basin, Huining County, on the Loess Plateau in Northwest China. We identified seventeen key hydrogeomorphological factors that influence sinkhole susceptibility and used six machine learning models—support vector machine (SVM), logistic regression (LR), Convolutional Neural Network (CNN), K-Nearest Neighbors (KNN), random forest (RF), and gradient boosting decision tree (GBDT)—for the susceptibility assessment and mapping of loess sinkholes. We then evaluated and validated the prediction results of various models using the area under curve (AUC) of the Receiver Operating Characteristic Curve (ROC). The results showed that all six of these machine learning algorithms had an AUC of more than 0.85. The GBDT model had the best predictive accuracy (AUC = 0.94) and model migration performance (AUC = 0.93), and it could find sinkholes with high and very high susceptibility levels in loess areas. This suggests that the GBDT model is well suited for the fine-scale susceptibility mapping of sinkholes in loess regions.

Effects of Perennial Alfalfa on the Structure and Function of Soil Micro-Food Webs in the Loess Plateau

The Loess Plateau is one of the most vulnerable areas in the world. Numerous studies have been conducted to investigate alfalfa fields with different planting years. Soil microorganisms and nematodes are vital in ecosystem functionality and nutrient cycling. Therefore, comprehending their response to alfalfa fields with varying years of planting is essential for predicting the direction and trajectory of degradation. Alfalfa fields with different planting years (2 years, 9 years, and 18 years) were used as the research object, and farmland was used as the control (CK). High-throughput sequencing and morphological methods determined the community composition of microorganisms and nematodes. Carbon metabolic footprints, correlation networks, and structural equations were used to study soil microorganisms and nematode interactions. Principal component analysis (PCA) results showed that alfalfa fields with different planting years significantly impacted soil microorganisms and nematode community structures. Planting alfalfa significantly increased the nematode channel ratio (NCR) and Wasilewska index (WI), but significantly reduced the soil nematode PPI/MI and dominance (λ). The correlation network results indicated that, for the 2-year and 18-year treatments, the total number of links and positive links are higher than other treatments. Conversely, the 9-year treatment had fewer positive links and more negative links compared to other treatments. Additionally, the keystone species within each network varied based on the treatment years. Structural equation results show that alfalfa planting years directly impact soil fungal community structure and plant-parasitic nematodes’ carbon metabolism omnivorous-predatory nematodes. Furthermore, the carbon metabolism of omnivorous-predatory nematodes directly influences soil organic carbon fixation. Moreover, as the duration of alfalfa planting increases, the metabolic footprint of plant-parasitic nematodes decreases while that of omnivorous-predatory nematodes rises. Among treatments varying in alfalfa planting durations, the 9-year treatment exhibited the most incredible energy conversion and utilization efficiency within the soil food web, demonstrating the most stable structure. This study reveals optimal alfalfa planting duration for soil ecosystem stability in the Loess Plateau. Future research should explore sustainable crop rotations and alfalfa–soil–climate interactions for improved agricultural management.

Climate Regulates the Effects of Abrupt Vegetation Shifts on Soil Moisture in the Loess Plateau, China

Climate Regulates the Effects of Abrupt Vegetation Shifts on Soil Moisture in the Loess Plateau, China

Two species of Polycelis (Platyhelminthes, Tricladida, Planariidae) newly recorded for the Qinling Mountains and the Loess Plateau in China, with a comparative discussion on their karyotypes

The paper details new geographic records of two species of the genus Polycelis Ehrenberg,1831 (Platyhelminthes, Tricladida, Planariidae) for the Qinling Mountains and the Loess Plateau in China and provides redescriptions of these species based on an integrative taxonomic study involving morphology, karyology, and histology. This new information considerably expands our knowledge on these species, for which until now only limited data was available. The species Polycelis asiatica Selinova, 1985 is characterized by the following features: 63–80 eyes; sperm ducts that exhibit an intrabulbar knee-shaped bend towards the ventral surface before opening separately and symmetrically into the antero-dorsal portion of a large seminal vesicle; the latter is ventrally displaced, thus creating a narrow ventral lip on the penis papilla; dorsal wall of the seminal vesicle is provided with several well-developed folds; more or less bulbous penis papilla protrudes from the dorsal wall of the male atrium and is provided with a slender and flexible tip; chromosome complement diploid with 30 metacentric chromosomes, 8 submetacentric chromosomes, and 2 subtelocentric chromosomes. The species Polycelis eudendrocoeloides (Zabusova, 1929) is characterized by: 49–80 eyes; highly reduced and blunt penis, provided with a kind of flagellum that projects into the seminal vesicle; a relatively thick coat of circular and longitudinal muscles around the entire male atrium; generally, a very large intrabulbar seminal vesicle, extending from near the ventral body surface to occupy the major part of both the penis bulb and the dorso-ventral space of the body; diploid chromosome complement consisting of 36 metacentric chromosomes.

The Spatiotemporal Dynamics of Vegetation Cover and Its Response to the Grain for Green Project in the Loess Plateau of China

The Spatiotemporal Dynamics of Vegetation Cover and Its Response to the Grain for Green Project in the Loess Plateau of China

Study on the Evolution of Spatial and Temporal Patterns of Carbon Emissions from Land Use in a River Basin

Land-use change significantly contributes to carbon emission. Analyzing this relationship fosters exploration of low-carbon, efficient land-use patterns at regional levels. Using ArcGIS 10.5 and the PLUS model, this study investigated land transfer trends across six counties and one district in the Malian River Basin between 2000 and 2020. It quantified carbon emissions from land use and performed spatial distribution analysis using land-use and socio-economic data. The study demonstrates the following: (1) Between 2010 and 2020, significant land-use changes occurred in the Malian River Basin with 72,919.49 km2 of land undergoing transformation. Notably, the farmland-to-forest and grassland conversion project in Qingyang City was a major factor contributing to the shift from arable land to forest and grassland. (2) Natural factors influencing land conversion in the Loess Plateau region primarily include precipitation and elevation. Conversely, social factors such as population density, road networks, and local government establishments in districts and counties are pivotal in driving land-use changes within the Malian River Basin. (3) Carbon emissions vary significantly among different land-use types, with building land, cropland, unutilized land, watershed, grassland, and forest land showing descending emissions. The rapid expansion of building land notably increases carbon emissions in the study region, while forest land, a significant carbon sink, absorbs approximately 88% of total carbon emissions. (4) Districts and counties in the study area exhibit varying levels of carbon emissions, with Ning County, Xifeng District, Huan County, Qingcheng County, Zhengning County, Heshui County, and Huachi County listed in descending order. Regions with higher carbon emissions typically host abundant energy resources and significant energy production and consumption activities. Variations in carbon emission levels are largely influenced by resource availability and development priorities. Variations in resource levels and developmental focus are pivotal in explaining differences in carbon emission levels. Thus, it is crucial to explore the dynamic interplay between land-use carbon emission efficiency and land evolution in the Malian River Basin. This research will support ecological management and sustainable economic development in the Yellow River Basin, while also contributing to the achievement of the “double carbon” goals.

Optimizing plastic film mulch to improve the yield and water use efficiency of dryland maize in the Loess Plateau, China.

Knowledge on the variation of yield and water use efficiency under different mulching methods is important for guiding rained maize production in the Loess Plateau area. In this study, eight different plastic film mulching methods was established to analyze the maize growth, soil water content and soil temperature changes of dryland maize, and increase yield and water use efficiency (WUE). The field experiment was conducted in 2019, and eight treatments were set up, including a traditional flat planting without mulching (CK), ridge-furrow with ridges mulching black plastic film and furrows mulching straw (HJ), ridge-furrow with ridges mulching black plastic film and furrows bare (HL), ridge-furrow with ridges mulching liquid plastic film and furrows mulching straw (YJ), ridge-furrow with ridges mulching liquid plastic film and furrows bare (YL), ridge-furrow with ridges mulching biodegradable plastic film and furrows mulching straw (SJ), ridge-furrow with ridges mulching biodegradable plastic film and furrows bare (SL) and ridge-furrow with ridges bare and furrows mulching straw (NJ). Furthermore, the AHP-TOPSIS was employed to evaluate the optimal mulching method for maize. The results showed that compared with CK and NJ treatment, the soil water content and soil storage were significantly changes with other treatments in the reproductive period of maize. Among the six mulching methods, maize yield in HJ, HL, YJ, YL, SJ, and SL treatments were 46.28%, 61.95%, 70.30%, 51.02%, 52.02% and 53.53% significantly greater than CK treatment. In addition, dryland maize WUE was 66.53% and 84.01% higher in the YJ and YL treatments with ridges mulching liquid plastic film than in the CK treatment, respectively. The optimal treatments of economic benefits were YL and HJ. Through AHP-TOPSIS comprehensive analysis, the optimal mulching methods were YL and HJ treatment. Current field trials indicate that YL treatment could serve as a promising option to improve dryland maize yield, WUE, and reducing environmental risks in the Loess Plateau of China.

Long-term alfalfa planting mediates the coupling of soil water and organic carbon storage in a semi-arid area of the Loess Plateau, China

The key to restoring arid and semi-arid ecosystems is maintaining soil water and organic carbon contents. Alfalfa (Medicago sativa L.) is a high-yield perennial forage crop and performs ecological functions as a drought-resistance leguminous herb. It has been widely planted for reconstruction of degraded soils in the Loess Plateau in northwestern China, but long-term planting may affect soil carbon–water coupling and lead to crop yield reduction. To maximize the benefits of reconstructed grassland, this study explored the couplings of soil water, organic carbon, and alfalfa productivity along a reconstruction chronosequence in a semi-arid area of the Loess Plateau. Space-for-time substitution approach was used to select different-aged stands of reconstructed grassland (1, 5, 7, 10, 15, 20, 30 years old). Alfalfa above-ground biomass (AGB), soil water storage (SWS), organic carbon storage (SOCS), and carbon–water coupling coordination degree (D) were measured in the 0–100 cm soil profile. Alfalfa AGB reached a peak in the 7th year, and the degradation began in the 10th year. Both SWS and SOCS varied nonlinearly with stand age. The greatest loss of SWS occurred in the 15th year (80–100 cm depth), whereas the largest increase of SOCS occurred in the 30th year (0–20 cm depth). There was a negative feedback relationship between AGB and SWS over the 30-year study period (Pearson r = −0.835, P = 0.098). AGB and SOCS initially showed a trade-off within the first 10 years (Pearson r = −0.7431, P = 0.2569), in contrast to their positive feedback in the 20–30th years (Pearson r = 0.9978, P = 0.0421). A decoupling between SWS and SOCS (D < 0.6) was observed after 12 years of alfalfa planting. For agricultural production, a greater supply of water and organic fertilizer is required from the 7th year of alfalfa planting, and reseeding may be needed around the 10th year to prolong the life of alfalfa community. Alfalfa should be planted for no more than 12 consecutive years in the study area for ecological protection.

Biochar application improves maize yield on the Loess Plateau of China by changing soil pore structure and enhancing root growth

Biochar application emerges as a valuable soil management strategy for enhancing crop yield; however, the mechanisms underlying the relationships between soil and plants remain unclear after biochar application. In this study, soil pore characteristics and maize yield were assessed in a five-year biochar-application experiment on the Loess Plateau of China, including four treatments: Control (no biochar), low-dose biochar application (LB, 3 t ha−1), moderate-dose biochar application (MB, 6 t ha−1), and high-dose biochar application (HB, 9 t ha−1). Root growth traits were evaluated by cultivating maize in intact soil cores collected from field conditions using X-ray computed tomography. Our findings indicate that, compared to the Control, the HB treatment enhanced macroporosity (> 0.1 mm in diameter), porosity of 0.1–0.5 mm pores, and saturated water content, while reducing macropore connectivity and penetration resistance. However, biochar application treatments did not alter the water retention characteristics from field capacity to permanent wilting point or the plant-available water content (PAWC). Furthermore, the mean angle of primary and seminal roots as well as the length and surface area of entire roots increased in the HB treatment, showing a positive correlation with the porosity of 0.1–0.5 mm pores. The mean diameter of primary and seminal roots, leaf fresh and dry weights, and maize yield also increased in the HB treatment compared to the Control. Partial least squares path modeling analysis indicated that biochar application rates positively impacted on root growth and plant productivity through an indirect influence of soil pore size distribution, with 0.1–0.5 mm pores being particularly crucial for facilitating deeper root penetration and root elongation. These findings demonstrate that biochar application primarily augmented 0.1–0.5 mm pores, rather than affecting smaller pores capable of retaining plant-available water or larger macropores, enhancing deeper rooting and root elongation, thus improving plant productivity and crop yield.

To Investigate the Impact of Land Use Change on the Potential Groundwater Recharge on Hillslope With Deep Loess Deposits

ABSTRACTAccurately estimating groundwater recharge in hilly areas with limited water and thick vadose zones is challenging. This study investigated the impact of land use changes on groundwater recharge at a hillslope scale of Yuanzegou Watershed in China's Loess Plateau. Three adjacent hillslopes were selected for three different land uses: arbor (jujube, Ziziphus jujuba Mill.), subshrub (native grass, Artemisia gmelinii), and crop (millet, Setaria italica). Soil cores (as deep as 10–16/18 m) were collected at each of the three landscape positions on a hillslope. Reported tritium profiles in the watershed were used to estimate the net chloride input into vadose zone on hillslope associated with inverse chloride mass balance (CMB) method/chloride accumulation method (CAM). Soil water content and chloride profiles in the study were measured to determine recharge rates at each landscape position beneath different vegetation types. For the first time, we evaluated the actual chloride input into vadose zone on hillslopes as 540.2 ± 23.8 mg m−2 yr.−1, excluding the impact of runoff. Then, estimated recharge rates ranged from 42.7 ± 3.5 to 62.4 ± 4.7 mm yr.−1, consistent with nearby studies. Results showed that groundwater recharge does not change with landscape position except for higher value on upslope beneath subshrub hillslope. In contrast, groundwater recharge did significantly reduce by 12.9% ± 5.4% and 26.5% ± 4.5% after conversion from cropland to subshrub/arbor on the hillslope, respectively. Our findings contribute to understanding the ecohydrological effects of land use changes on groundwater recharge on hillslope and help to select suitable afforested vegetation for greening efforts in water‐limited hilly areas, with a priority on groundwater safety.

Investigating the influence of land cover on land surface temperature

The increasingly serious urban heat island (UHI) effect is unfavorable to urban development. This study utilized land cover data and land surface temperature (LST) data of China in 2020 by using correlation analysis and spatial regression models to analyze the relationships between LST and two influencing factors (land cover and digital elevation model (DEM)). The results showed the following: (1) The correlation between LST and forest was highest in the Northeast China Plain (NCP), Huang-Huai-Hai Plain (HHP), Qinghai Tibet Plateau (QTP), and Loess Plateau (LP). DEM mean displayed its highest correlation in the Northern arid and semiarid region (NAR), Sichuan Basin and surrounding regions (SCR), Yunnan-Guizhou Plateau (YGP), and Middle-lower Yangtze Plain (MYP). Southern China (SC) had the highest correlation between LST and construction land. (2) There was spatial heterogeneity between land cover and LST. Unused land on LP had larger impact on LST. For every 1% increase in the proportion of unused land area, the LST increased by 0.250 °C. LST in some central and western regions of China (the NAR, the LP, the SCR, and the YGP) was mainly affected by local land cover; LST in eastern coastal regions (the HHP, MYP, NCP, SC) and QTP was not only affected by local land cover, but also by LST or land cover of neighboring regions. The warming effect of construction land on LST was more significant, with LST increasing by 0.079 °C to 0.338 °C for every 1% increase in the proportion of construction land area. Coordination of land use planning and synergistic remediation in different regions and rational planning of construction land are essential to mitigate the UHI effect. (3) Water bodies in the NCP, NAR, and MYP had the greatest cooling impact on LST, with LST decreasing by 0.277 °C, 0.246 °C, and 0.079 °C, respectively, for every 1% increase in the proportion of water bodies area. Forest on the QTP, LP, SC, and YGP had the greatest cooling impact on LST, and for every 1% increase in the proportion of forest area, LST decreased by 0.144 °C, 0.089 °C, 0.086 °C, and 0.038 °C, respectively. Actively planting trees and increasing the area of forests and water bodies are of positive significance in alleviating the UHI effect and improving the ecological environment.

Effects of human and tectonic activities on groundwater in the upper Yellow River terraces of the loess Plateau

Terraces of the Yellow River are among the most crucial geomorphological landforms pertaining to human survival on the Loess Plateau. After more than half a century of surface flood irrigation, rapid rises in groundwater levels have led to frequent geological disasters, causing a rapid short-term evolution of Yellow River terraces, and an increasingly serious contradiction between this rapid evolution and human survival. However, the process by which water transfers through the thick loess vadose zone and causes a rapid groundwater response within months or years remains controversial. Using the Heitai platform of Yellow River terrace IV as an example, we found, on the basis of regional geological surveys, that at least 112 tectonically-induced cracks have developed in this area. We contend that the superimposed effects of earthquake ground motions from historical and ancient earthquakes since the Late Pleistocene have driven the development of such densely distributed cracks in the loess layer. These cracks, together with a series of fault planes generated by NE-directed extrusive stress at the regional scale, constitute a potential network of preferential channels for water transport within the Heitai platform. Combined with the results of a large-scale in situ ponding test and electrical resistivity tomography, we found that this network of cracks helps to establish catchment areas within the loess layer, thereby increasing soil saturation at a more extensive spatial scale, which may then increase the overall movement velocity of the wetting front. We semi-quantified the efficiency of the crack network in enhancing the recharge of surface water to groundwater, and suggested that the impact of human and tectonic activities substantially shortens the response time of groundwater to surface water, with the reduced time far exceeding one order of magnitude. The results of a field investigation of structural traces and terrace groundwater after the Ms 6.2 Jishishan earthquake on 18 December 2023 further emphasize that a causal mechanism of human and tectonic activities leading to the rapid short-term evolution of groundwater distribution patterns may be universally applicable to all Yellow River terraces on the Loess Plateau. This study mitigates the long-standing controversy concerning the mode of surface water infiltration, including piston flow and preferential flow, and the infiltration medium by which rapid surface water recharge to groundwater occurs in loess areas over short time periods.

Anthropogenic activities mitigate the impacts of climate extremes on high flow regimes on the Loess Plateau

The hydrological cycle is anticipated to become increasing variable due to intensified global climate extremes and frequent floods. Understanding the evolution and driving mechanisms of floods in the context of climatic extremes is essential, particularly on the Loess Plateau (LP) where anthropogenic activities are significant. Here, we examined the spatiotemporal variability of climate extremes and their impacts on flood processes on the LP during 1956–2015. We employed a paired year approach to quantitatively assess the driving role of anthropogenic activities on flood changes in 11 major basins. Our findings indicated a general decline in extreme precipitation indices, while temperature has increased across most of the LP. Both annual runoff (Q) and high flow (Q5) magnitude significantly decreased in all basins. We identified that the major climatic indices driving Q5 included erosive precipitation amount, flood season precipitation, heavy precipitation amount, and maximum 7-day precipitation amount. Importantly, anthropogenic activities have mitigated the impact of climate extremes on Q5 regimes. Compared the post-2000 with reference period (1956–1979), under similar climatic conditions, we observed a reduction in the average Q5 magnitude by 30.19–78.14%, and a decrease in the average Q5 duration by 46.48–100.00% across the basins. The contributions of climate variability and anthropogenic activities to Q5 magnitude changes among 11 basins ranged from –37.58% to 22.02% and –56.84% to –15.08%, respectively, highlighting the crucial role of ecological restoration in reducing Q5 magnitude. These results underscore the importance of ecological restoration in flood regulation and offer valuable insights for basin management in the Yellow River Basin.

Influence of micromorphology and water content on the rheological properties and performance evaluation model of loess mudflow

Evaluation of the rheological characteristics of loess mudflow is of great significance to ecological environment protection (by loess, we mean a wind-blown Quaternary silt deposit), and geological disaster assessment in the Loess Plateau of China. Rheological characteristics of rheology for loess mudflow are highly variable due to heterogeneity in particle micromorphology and water content, and current rheological models struggle to reconcile the structural dynamics with the equilibrium behavior of soil at different concentrations and microstructures. A rheological study of loess mudflow for five regions on the Loess Plateau was carried out in this investigation, and the results showed that loess transformed from a solid-like stage to a liquid-like stage under steady loads and exhibited significant shear thinning characteristics and shear rate dependence, in which the shear rate less than 2 s−1 was the main region of loess strength attenuation and the maximum yield stress is about 1411 Pa. A smaller water content and more complex particle micromorphology led to a higher yield stress, but there was no significant correlation between flow index and particle shape and water content. Additional structural dynamics and particle fractal theory were then introduced, providing an improved model that could reconcile the structural dynamics and particle micromorphology of loess with its equilibrium behavior at different water contents and shear stresses. All the test data were distributed around a dimensionless master curve. Considering the difficulty of obtaining rheological parameters, an evaluation criterion containing three levels (clay-rich, silt-rich, and sand-rich) for the evaluation of the rheological properties of loess mudflow was proposed, which can reconcile the test results and models under different working conditions. Such an evaluation criterion can also be applied to soils of other textures, providing a straightforward manner to determine the relevant rheological parameters. The research results provide a theoretical basis for ecological environmental protection and geological disaster assessment in the Loess Plateau region based on rheological characteristics.

Adaptation strategies of soil microorganisms in resource changes and stoichiometric imbalances induced by secondary succession on the loess plateau

Sequestering farmland for secondary succession is an effective method of restoring ecosystem services to degraded farmland, but long-term secondary succession often alters ecosystem environments, resources, and substrate stoichiometry. Currently, it is not known how resource changes and stoichiometric imbalances due to secondary succession affect soil microbial community structure and function, hindering our understanding of the natural resilience for degraded ecosystems. Here, we assessed nutrient limitation elements, community structure, metabolic functions, co-occurrence network complexity, and community stability of soil microorganisms during secondary succession of abandoned farmlands on the Loess Plateau. Results showed that secondary succession significantly altered plant characteristics and soil properties, as well as causing stoichiometry imbalances in nutrient resources. Along the secondary succession chronosequence, microbial nutrient metabolism shifted from phosphorus (P) limitation to carbon (C) and nitrogen (N) co-limitation. Microbial diversity, eutrophic flora, plant growth-promoting bacteria, and metabolism functional groups increased significantly during the 20 years after the abandonment of the farmlands, but decreased significantly with long-term succession. However, oligotrophic flora and P-solubilizing bacteria became dominant after 30 years of secondary succession on abandoned farmlands. The topological features of microbial co-occurring networks, including nodes, degree, closeness, betweenness, and eigenvector complexity, natural connectivity, and community stability first increased and then decreased with secondary succession. Correlation and random forest analyses indicated that secondary succession-induced stoichiometry imbalances in C:N and N:P, as well as changes in soil organic C and lignin phenols, were the key factors influencing microbial community structure and function. Overall, these results enhance our understanding of the adaptation strategies of soil microbial communities in ecologically managed regions to changes in ecosystem resources and stoichiometric imbalances.

Effects of freeze–thaw on the detachment capacity of soils with different textures on the Loess Plateau, China

Soil detachment capacity (Dc) is a crucial indicator for quantifying erosion intensity. However, the combined actions of freeze–thaw and water flow complicate the erosion process, leaving the variation mechanism of Dc under this condition systematically unexplored. This study examined five loess soils from a seasonal freeze–thaw area. The mechanism driving changes in Dc was quantified through freeze–thaw simulation combined with flow scouring tests, and a Dc prediction model was established. The results revealed that the shear strength (τm), cohesion (Coh), and internal friction angle (φ) in silt loam were higher than in sandy loam. After freeze–thaw cycles (FTC), τm, Coh, and φ of the five loess soils decreased by 1.02–1.37, 1.07–9.15, and 0.92–1.05 times, respectively. As FTC increased, τm and Coh gradually stabilized, while φ showed minimal fluctuation, indicating that FTC had a cumulative effect on the deterioration of soil mechanical properties. During FTC, Dc in Wuzhong sandy loam was the largest, being 1.14–3.24 times greater than in other soils, suggesting a significant main effect of soil type on Dc variation, with a contribution rate of 19.27 %. Dc eventually stabilized with increasing, indicating a critical FTC of around 10 for its impact on Dc. Compared to unfrozen soils, Dc increased by 33.69 %–102.40 % under the combined effects of freeze–thaw and water flow, clarifying that FTC aggravated soil instability. Effective stream power was the optimum hydraulic parameter, contributing the most to Dc (45.94 %). FTC (6.41 %) and initial soil moisture content (8.59 %) were less influential, as FTC initially degraded soil properties, and then the combined action with water flow intensified soil damage, causing the role of freeze–thaw factors to be obscured by other variables. A Dc prediction model using a general flow intensity index estimated well Dc, with both R2 and NSE at 0.94. Model performance comparison emphasized the need for validation when extending the application range beyond development conditions. These findings provide new insights into the detachment mechanisms of different textured soils under compound freeze–thaw and hydrodynamic influence in freeze–thaw region.