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Knowledge of water movement from the hillslope critical zone is important for water management. However, the runoff process resulting from extreme rainfall events remains unclear due to rare field‐based natural monitoring data. We investigated rainwater infiltration and runoff generation processes in two plots with deep and relatively shallow soil thicknesses (66 vs. 35 cm depth on average, respectively) on karst hillslopes. Rainwater, soil water and lateral discharge runoff in the soil‐epikarst system were monitored using hydrometric and 18O isotope methods in September 2020, which was the wettest month on record at the study s, including three normal rainfalls (29.6 mm in 8.5 h, 25 mm in 8.5 h, and 27.4 in 3.5 h) and three extreme rainstorms (335 mm in 11.5 h, 77.8 mm in 9 h, and 129.2 mm in 5 h). Soil moisture and water table responded rapidly (<30 min) during the extreme rainfall. However, the soil‐epikarst interface exhibited the strongest stability (coefficient variation [CV] < 8.18%) and collected more pre‐event water, reflected by the isotopic signature of the soil water. Accordingly, low permeability at the soil‐epikarst interface played an important role in buffering rainwater infiltration. Controlled by infiltration‐excess and saturation‐excess runoff mechanisms, the contribution of surface runoff to total discharge was less than 3% during normal rainfall events, which was significantly less than that during extreme rainfall events (13%–60%). This was supported by the evolution of δ18O values of surface runoff that were similar to rainwater and more 18O‐depleted than that of subsurface runoff. Higher rainfall intensity which exceeded soil permeability during extreme rainstorms further increased the possibility of exceeding infiltration‐saturation processes. For the deep soil plot (DSP), surface runoff (>44%) dominated the extreme rainfall process; while for the shallow‐soil plot (SSP), surface runoff (60%) dominated only during the maximum rainfall events. Moreover, the surface runoff contribution to total runoff in DSP was greater than that in SSP. Surface runoff from slopes with thicker soil layers is an important part of karst watershed flood processes in extreme rainfall events, which should be considered carefully for water resource management. Highlights: Hydrometric and isotope methods are used to assess extreme hydrological processes.The surface runoff of extreme rainfalls is much higher than that of normal rainfall.The infiltration‐excess mechanism dominates the surface runoff of extreme rainfall.Slopes with thicker soil layers are more vulnerable to flooding in the karst region. [ABSTRACT FROM AUTHOR]

Context: The karst region of southwestern China, one of the largest continuous karsts in the world, is known for its unique landscapes and rich biodiversity. This region has suffered severe environmental degradation (e.g., vegetation cover loss, soil erosion and biodiversity loss). In recent decades, Chinese governments at different levels have initiated several ecological programs (e.g., Green for Grain, Mountain Closure) to restore the degraded environment and to alleviate poverty. Objectives: This study summarizes landscape studies of karst landscapes patterns, their dynamics and interactions among landscape pattern, hydrological processes and ecosystem services (ES). Methods: We conducted a systematic literature review of science and land use policy to identify knowledge gaps and recommend future research and policy directions. Results: Karst landscapes have experienced rapid turnover in recent decades due largely to the overlap of intense human activity on the fragile karst ecosystems. Many studies have comprehensively examined hydrology, soil processes and ecosystem services (ES) and their relationships with landscape pattern. Most of these studies have found that karst ecosystems recover with improved ES. However, the importance of epikarst in hydrological and soil processes, intense anthropogenic disturbance and landscape heterogeneity in landscape models remains elusive. Conclusions: Future research should focus on in-depth examination and modelling of karst specific hydrological and soil processes, investigating relationships between climatic change, landscape change, ecological processes, and region-specific ES assessments. Results from such research should provide the necessary scientific support for a comprehensive, national karst rocky desertification treatment project (Stage II) and poverty alleviation initiatives. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the effects of soil physicochemical properties and environmental factors on the spatial patterns of surface soil water content (SWC) based on the state-space approach and linear regression analysis. For this purpose, based on a grid sampling scheme (10 m × 10 m) applied to a 90 m × 120 m plot located on a karst hillslope of Southwest China, the SWC at 0–16 cm depth was measured 3 times across 130 sampling points, and soil texture, bulk density (BD), saturated hydraulic conductivity (Ks), organic carbon (SOC), and rock fragment content as well as site elevation (SE) were also measured at these locations. Results showed that the distribution pattern of SWC could be more successfully predicted by the first-order state-space models (R2 = 67.5–99.9% and RMSE = 0.01–0.14) than the classic linear regression models (R2 = 10.8–79.3% and RMSE = 0.11–0.24). The input combination containing silt content (Silt),Ks, and SOC produced the best state-space model, explaining 99.9% of the variation in SWC. And Silt was identified as the first-order controlling factor that explained 98.7% of the variation. In contrast, the best linear regression model using all of the variables only explained 79.3% of variation. [ABSTRACT FROM PUBLISHER]

Temperature is an important near-surface microclimate parameter that plays a key role in hydrological, ecological, and biogeochemical functions. However, the spatio-temporal distribution of temperature on the invisible and inaccessible soil–weathered bedrock continuum, wherein hydrothermal processes are most active, remains poorly understood. Temperature dynamics were monitored at 5 min intervals in the air–soil–epikarst (∼3 m) system at different topographical positions of the karst peak-cluster depression in southwest China. The weathering intensity was characterized based on the physicochemical properties of samples collected through drilling. No significant difference was observed in air temperature across slope positions, which was related to the limited distance and elevation resulting in roughly consistent energy input. The control effect of air temperature on the soil–epikarst was weakened with the decrease in elevation (±0.36 to ±0.25 °C). It is attributed to the enhanced temperature regulation capacity of vegetation cover from the up slope (shrub dominant) to down slope (tree dominant) in a relatively uniform energy environment. Temperature stability is clearly distinguished in two adjacent hillslopes that were differentiated by weathering intensity. For every 1 °C change in the ambient temperature, the amplitude of soil-epikasrt temperature variation on the strongly and weakly weathered hillslopes were ±0.28 and ± 0.32 °C, respectively. The response of soil-epikarst temperature to ambient temperature was more sensitive in the wet season (±0.40 °C) than in the dry season (±0.20 °C), which was related to the cooling effect caused by abundant rainfall. The cooling effect was particularly prominent in the preferential flow development area composed of pipeline cracks, which appear in the hillslope with relatively weak weathering intensity. These demonstrate that soil–epikarst temperature responds more gently to the variability of rainfall and ambient temperature on a relatively strong weathered hillslope. Accordingly, this study highlights that the sensitivity of soil–epikarst temperature to climate change is regulated by vegetation and weathering intensity on karst hillslopes in southwest China. • Heterogeneity of epikarst temperature studied through direct in situ measurements. • The regulating effect on soil-epikarst temperature enhanced from up-to downslope. • Weathering intensity controls the spatial distribution of soil–epikarst temperature. • The cooling effect of rainfall is more prominent on weakly weathered hillslope. [ABSTRACT FROM AUTHOR]

• Multiple runoff components in a soil-epikarst system were directly monitored. • Critical zone structure exerted more evident influence on carbon loss than land uses. • Thicker soils with less undulating soil-epikarst contact facilitated carbon loss. • Artificial forage grasslands reduced carbon loss. In karst hillslopes, the soil-epikarst system is not only the main reservoir of soluble carbon, but also the hot spots of hydrological and biogeochemical processes. However, the soluble carbon loss mechanism through various runoff components occurring in the soil-epikarst system is not clear. We hypothesize that the karst critical zone structure determines the runoff and soluble carbon loss, and that these response processes can be regulated by land use. 12 experimental plots on a typical karst hillslope (each with 5 × 20 m projected area) of four land uses (naturally recovered shrubland, forage grassland, economic forest land, and cropland) were intensively instrumented for separately monitoring surface, subsurface, and epikarst seepage runoffs and their dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentration. Results show that economic forest land had the highest total runoff and soluble carbon loss, followed by cropland, naturally recovered shrubland, and forage grassland. Generally, karst critical zone structure was the most important factors for controlling DOC and DIC loss through surface, subsurface, and epikarst seepage runoffs. Critical zones with thicker soil and less undulating soil-epikarst contact were more susceptible to runoff and soluble carbon loss. Although not as important as critical zone structures, land use can effectively regulate runoff and prevent soluble carbon loss by affecting rainfall partitioning in karst hillslopes. Planting forage grassland is an effective method of reducing carbon loss, due to its remarkable ability of reducing runoff in the soil-epikarst systems. Our results provide useful insights for determining appropriate land uses and optimizing soil and water conservation strategies in karst hillslopes. [ABSTRACT FROM AUTHOR]

Knowledge of the temporal variability of soil water content (SWC) at the hillslope scale is essential for guiding rehabilitation strategies and for optimizing water resource management in the karst region of southwest China. This study aimed to use temporal stability analysis to upscale point-scale measurements to represent mean areal SWC on two typical karst hillslopes. Based on a grid sampling scheme (10 m × 10 m) applied to two 90 m × 120 m plots located on two hillslops, the SWC at a depth of 0-16 cm was measured 11-12 times across 259 sampling points, using time domain reflectometry (TDR) from April 2011 to October 2012. Soil texture, bulk density (BD), saturated hydraulic conductivity ( K ), organic carbon (SOC), rock fragment content (RFC), and site elevation (SE) were also measured at these locations. Results showed the hillslope with more shrub cover was wetter than the hillslope with mixed grass-shrub cover. This difference was related to the differences in soil texture, soil hydraulic permeability, and topography. Through a comparison of values obtained with the Spearman correlation coefficient ( r ), standard deviation of mean relative difference (SDRD), and mean absolute bias error (MABE), we inferred that there is a higher degree of temporal stability for SWC in wet conditions than in drier conditions on the two hillslopes. Based on the values of the index of temporal stability (ITS), which combine the mean relative difference (MRD) and SDRD, the two locations were determined to be representative of mean SWC on both hillslopes. Moreover, these locations captured changes in mean SWC (NSCE = 0.69, and 0.65, and RMSE = 1.96, and 1.96 %, respectively). This demonstrates the feasibility of using the temporal stability of SWC to acquire mean SWC on karst hillslopes of southwestern China. The indirect method, which estimates mean SWC by considering the offset between the mean and the measurement value at a time-stable location, predicted mean SWC (NSCE = 0.86, and 0.76, and RMSE = 1.29, and 1.63 %, respectively) more precisely than the direct method (mean SWC directly measured at a time-stable location), because it eliminates deviation by introducing a constant offset (MRD). We recommended the use of the indirect method to acquire mean SWC values, when an allowable bias of 5 % for both MRD and SDRD can not be achieved. In addition, we found that soil texture, RFC, and elevation affect the pattern of SWC on the shrub hillslope. These results are expected to be useful for monitoring soil water dynamics on karst hillslopes, especially for restoration purposes. [ABSTRACT FROM AUTHOR]

• DOM molecular compositions in multi-interface runoffs were quantified by FT-ICR MS. • Soil-epikarst structures controlled the DOM quantity and molecular compositions. • High microbially-derived carbon was detected in epikarst flow. • Flow rate and discharge effected DOM quantity and quality during runoff process. • Soil thicknesses affected runoff DOM dynamics by impacting hydrological processes. Understanding the chemical composition, origin, and molecular structure of dissolved organic matter (DOM) in multi-interface runoff is essential for comprehending the fate of laterally transported DOM in complex soil-epikarst systems of karst hillslopes. Limited information, however, is available for the optical properties and molecular compositions of the transported OM in multiple runoff components on the karst hillslope in relation to land-uses and soil thicknesses. In this study, we conducted a study to observe the changes in the quantity and quality of DOM in multiple interface flow (surface, subsurface, and epikarst) during natural rainfall events in 2022 in karst hillslopes that are covered by different land uses (cropland and shrubland) and soil thicknesses (with mean depths of 66.0 cm for deeper soil and 35.4 cm for shallower soil) in the karst region of southwest China. chemcial compositions of runoff DOM were determined by optical analysis and microbial compositions in runoff were inferred with high-throughput sequencing. The results showed that the soil-epikarst structure was controlling the runoff DOM quantity and quality during rainfall events. A decrease in the aromaticity, humification, unsaturation, and oxidation degree and an increase in carbohydrate, aminosugars, protein, and lipid compounds were found from surface to epikarst flow, indicating that plant-and soil-derived carbon decreased, while the microbially-derived carbon increased. The results were further comfirmed by the higher bacterial richness and diversity, along with fungal diversity in the epikarst flow compared to other runoff components. The bio-labile protein materials (C2) were the most important component of runoff DOM output in karst hillslopes. In surface and subsurface flow, rainfall amount, runoff rate, and discharge significantly affected the DOM concentration and quality during rainfalls, indicating that the dynamics of DOM in runoff from karst hillslopes were predominantly influenced by hydrological processes. Furthermore, the runoff DOM quality in cropland was dominated by lower unsaturation and oxidation degrees and higher protein component, compared to those in shrubland. The compositions of DOM in runoff from hillslope plots with thicker soils were primarily characterized by microbially-derived materials. Our findings were conducive to understanding the mechanism governing the migration of DOM quality and quantity in discharge during multi-interface hydrological processes on karst hillslopes. [ABSTRACT FROM AUTHOR]

• Surface and bedrock topography are closely coupled in shallow soil-covered plot. • Soil moisture in thick soil plot is notably affected by the surface topography. • Runoff in thinner soil plot is remarkably affected by the bedrock topography. • Soil thickness is a critical factor in distinguishing hydrological processes. Topography plays a crucial role in predicting rainfall-runoff processes under climate change, as it affects the spatial distribution of water flow pathways. However, understanding the potential impact of high micro-topography heterogeneity on runoff generation remains challenging. We conducted high-resolution monitoring of soil moisture, instantaneous water table, and subsurface runoff in two 3D plots with different soil thicknesses (66 cm vs. 35 cm) in the karst region of southwest China. The topographic features were characterized by the soil thickness, relative elevation, and topographic wetness index obtained from a 1 × 1 m grid. The topography of the shallow-soil plot (SSP) exhibited a higher level of complexity, with a greater variability (approximately 80.0 %) in soil thickness compared to that of the deep-soil plot (DSP; approximately 61.5 %). Additionally, the SSP was prone to forming a micro-topography characterized by a combination of exposed bedrock and soil cover. In DSP, the variation in soil moisture was strongly controlled by surface topography, with elevation contributing to 52 % and 81 % of the explanation for the soil moisture at 30 cm and soil–bedrock interface, respectively. In SSP, the contribution of topography to the variation in soil moisture did not exceed 31 %. The controlling effect of topography on runoff is highlighted in SSP, with the contribution rates of surface and bedrock relative elevation reaching 79% and 97%, respectively.The weaker water storage capacity of the SSP resulted in a higher volume of subsurface runoff (161 t vs. 116 t) and frequency of runoff events (2248 vs. 1994) compared to the DSP. Accordingly, this study emphasizes that the soil–bedrock spatial heterogeneity will control the relationship between soil moisture, subsurface runoff, and terrain, which will contribute to providing a basis for flood prediction and model simulation in regions with complex topography. [ABSTRACT FROM AUTHOR]

[Display omitted] • Runoff connectivity on a karst hillslope are identified by isotopic signals. • The proportion of young water and event water decreases from upslope to downslope. • Runoff from the upslope is connected to the downslope by the soil–bedrock interface. • Soil-epikarst structure controls the hydrological connectivity of karst hillslopes. Hydrologic connectivity along the hillslope critical zone is essential for the transmission of water, solutes, and nutrients to streams. However, the influences of critical zone structure on hydrological connectivity are not adequately understood, especially for hillslopes with complex topography. We investigated the hydrological connectivity along different topographical positions of two adjacent dolomite hillslope plots in southwest China: a deep soil plot (average value: 66 cm) and shallow soil plot (average value: 35 cm). We characterized the dynamics of multiple-interface runoff and soil water based on observations of stable isotopes (δ18O and δD) and hydrometric monitoring, and computed the lc -excess, young water fraction (y w), and hydrograph separation from June 2020 to July 2021. On both hillslopes, soil depth gradually increased from up-slope to down-slope, and the contribution of event water and y w to soil water gradually decreased (100 % to 69 %). In the vertical depth, a sudden decrease in the contribution of y w (98 % to 47 %) and event water (44 % to 11 %) in the down-slope of the soil-epikarst interface was observed. These results indicate that the infiltration of rainwater from up-slope to down-slope was altered by vertical flow to lateral flow, which was connected through the soil-epikarst interface and finally converged in the low-lying area. Contrary to expectations, the contribution of y w at the soil-epikarst interface was lower in the shallow soil plot (43 %) than in the deep soil plot (71 %). As a supplement, moisture at the soil-epikarst interface was significantly higher in the shallow soil plot. This indicates that the renewal cycle of groundwater was slower in shallow soil-covered hillslopes not only because almost all rainwater (∼98 %) entered the soil-epikarst to redistribute as well as the higher water storage area in the soil-epikarst interface. Accordingly, the soil-epikarst structure, which is differentiated by soil depth, controls hillslope hydrological connectivity and groundwater storage capacity in the karst region of southwest China. [ABSTRACT FROM AUTHOR]

• Subsurface runoff dominates the runoff components in karst hillslope. • Thinner soils decrease surface runoff and increase subsurface runoff. • Bedrock topography controlled subsurface runoff generation in the thinner soils. • Thinner soils had a higher contribution of new water than that in the thick soils. Hydrological processes in the critical zone are closely related to the soil–bedrock structures. However, the effect of soil thickness on the rainfall-runoff relationship on the hillslope with complex topography remains unclear. Surface runoff, lateral subsurface runoff from soil–epikarst interface, and epikarst runoff from the epikarst–bedrock interface were monitored on two adjacent plots with deep and shallow (66.0 vs. 35.4 cm) soil thicknesses from June 2019 to December 2020 in the karst region of southwest China. During the monitoring period, surface and subsurface runoff account for 20% and 37% of the total runoff in the deep-soil plot (DSP), and 3% and 43% in the shallow-soil plot (SSP). This demonstrates that runoff from the soil-epikarst system is predominant compared to the relatively small contribution of surface runoff. In the SSP, the surface topography wetness index (TWI) was highly coupled with bedrock TWI , and the bedrock TWI had a significant negative linear relationship (p < 0.01) with subsurface runoff. Moreover, isotope hydrogen-separation results showed that subsurface and epikarst runoff were dominated by pre-event water, but a higher contribution of event water was observed in the SSP than in the DSP. These findings supported the hypothesis that rainwater could infiltrate the epikarst more easily in shallow soil slopes. Rainfall and surface runoff exhibited a linear relationship in the dry season and a non-linear relationship in the rainy season, indicating the occurrence of threshold rainfall–runoff behavior. The rainfall amount threshold for surface runoff was higher in DSP (44.7 mm) than in SSP (39.5 mm), and the corresponding variation of rainfall intensity interpretation was greater (54% vs. 38%). For subsurface runoff, the rainfall amount threshold was higher in the DSP than in the SSP (91.0 vs 79.4 mm), and the corresponding variation of soil moisture interpretation was higher (56% vs. 20%). This demonstrated that runoff can be better predicted at deeper soil hillslopes by rainfall and antecedent soil moisture. Accordingly, this study emphasizes the importance of evaluating the spatial heterogeneity of soil thickness in hydrological process research. [ABSTRACT FROM AUTHOR]

• SR, SSR, and ESR coefficients were 2.2%, 3.8%, and 31.2%, respectively. • Epikarst zone exerted a critical role in partitioning, storage and release of water. • Soil depth was positively related to SR. • Rainfall depth thresholds for SR and SSR generation were 36 ± 2 mm and 43 ± 7 mm, respectively. Water balance characteristics and rainfall-runoff relationships of karst slope, are poorly understood worldwide, even though karst landscapes occupy 10–15% the planet's land surface. Dynamic hydrological responses were monitored for 43 rainfall events on a karst slope in southwest China over two years (2018–2019). The responses included surface, subsurface, and epikarst seepage runoff (abbreviated as SR, SSR, and ESR, respectively) and soil water content at different depths (10 cm, 30 cm, and the soil-epikarst interface) in twelve plots (5 m × 20 m , total 1200 m 2 ). Results showed that: (1) The hillslope-scale SR, SSR, and ESR coefficients were 2.2% (0.4%–5.2%), 3.8% (0.2%–12.4%), and 31.2% (0.6%–89.1), respectively. SR and SSR were relatively rare and of short duration, while ESR was a crucial component of the karst hillslope water balance and its duration was longer, demonstrating the critical role of epikarst zone in regulating flow functions such as water storage and release; (2) Soil depth exerted the greatest direct effect on SR, which increased as soil deepened. Factors controlling the rainfall-SSR response were difficult to identify. They require other geophysical exploration methods; (3) Threshold-like runoff responses to rainfall inputs were observed on karst slope, and the rainfall depth (P) runoff initiation thresholds for SR and SSR were 36 ± 2 mm and 43 ± 7 mm, respectively. The strength of the threshold-like input–output relationships was slightly greater when the P + ASI (antecedent soil water content index) was used as the hydrological input variable rather than without consideration of ASI. The differing shapes of nonlinear hydrological behaviours, such as the 'hockey stick', 'heaviside' function, or the sigmoid function were detected in karst slope. This suggests karst hydrological system complexity. Threshold values should be determined according to the shapes of nonlinear hydrological behaviours. These results extend the understanding of karst hydrological processes. [ABSTRACT FROM AUTHOR]

Vegetation restoration effectively prevents soil degradation. However, the changes in soil properties that occur in fragile ecosystems in response to vegetation restoration are unclear. The aim of this study was to investigate the effects of vegetation restoration on soil physicochemical properties and saturated hydraulic conductivity (Ks) at different elevations. Restoration strategies included natural shrubland (NR), managed plantation forest (PF), cropland (CR), and secondary forest (SF). Topsoil (0–15 cm) samples were collected from seven counties in the karst region of southwest China. The soil nutrients were significantly (p < 0.05) higher in both NR and PF than in CR but were lower in SF. Soil physical properties (bulk density, porosity, texture, and Ks) were significantly (p < 0.05) different between CR and SF but not significantly different between NR and PF. Hence, the short restoration period (~15 years) had a stronger influence on soil nutrients than on soil physical properties. The soil properties following different land-use types were affected by elevation. For SF and PF, soil Ca, total nitrogen, and sand content were significantly (p < 0.05) negatively correlated with elevation. For NR, only sand content was significantly (p < 0.05) negatively correlated with elevation. No soil parameters were significantly correlated with elevation in CR. Soil nutrients increased to a greater extent in the low-elevation area (150–500 m) than in the high-elevation (1000 to 1200 m) areas. This discrepancy could be explained by the relatively increased biomass after vegetation restoration. Clay content variation was the main factor controlling Ks variation. The change in clay content was greater in low-elevation areas than in higher-elevation areas, where higher weathering and erosion rates were caused by strong hydrothermal conditions. Accordingly, the present study showed that the variations in soil properties observed after vegetation restoration are influenced by both land-use types and elevation. • The influence of elevation & land use type on karst soil properties were assessed. • The short restoration period (~15 y) had a stronger influence on soil nutrients. • Soil nutrients increased greater in low-elevation than in high-elevation areas. • Clay content was the main factor controlling Ks variation under restoration. [ABSTRACT FROM AUTHOR]

• Rock surface flow accelerated the rill erosion of excavated slope. • Soil and water loss of SRS and KRS were higher than the bare slope. • Rills below rock outcrops didn't develop into a rill network after formation. • Effects of rock outcrops on the rill morphological characteristics and hydrodynamic mechanisms were investigated. Rock surface flow is the secondary distribution of precipitation and inflow on the rock surface, an essential runoff generation mode in karst areas. The effects of rock surface flow on soil erosion in karst regions cannot be ignored. However, its impact on rill erosion in karst slopes remains unclear. The objectives of this study were to investigate the impact of rock surface flow on rill erosion, rill morphological characteristics, rill flow hydraulic characteristics, and hydrodynamic mechanisms. A field runoff plot (3 m long, 1 m wide and 0.3 m deep) with three inflow rates (2, 3, and 4 L/min) was subjected to runoff simulation experiments under two typical rock surface morphologies in karst areas: smooth rock surface (SRS) and karren rock surface (KRS), with bare slope (BS) as the control group. The results revealed that rock surface flow aggravated the soil and water loss of the excavated slope. Compared to BS, the runoff yield for SRS and KRS increased by 81.49 % and 61.91 %, respectively. Meanwhile, the soil loss of SRS and KRS were 2.50 times and 5.56 times greater. The rills below the rock outcrops didn't develop into a rill network after formation, owing to the rock surface morphology. Rill depth was the best indicator of rill morphology for evaluating rill erosion on slopes below rock outcrops. The Reynolds number and Darcy–Weisbach resistance coefficient were the optimal hydraulic parameters to predict the rill erosion of the SRS and KRS, respectively. At the same time, the runoff power and flow shear stress were the best hydrodynamic parameters to describe the rill erosion mechanism of SRS and KRS. These results provide a scientific basis for further understanding the mechanism of soil erosion on karst slopes and for preventing soil erosion on karst slopes in mining areas. [ABSTRACT FROM AUTHOR]

Carbonate landscapes make up one-fifth of the terrestrial land area, a better understanding of the coupling relationship between the soil–epikarst form and hydrological function is imperative for hydrology and landscape evolution modeling. In this study, we monitored a total of 158 rainfall-runoff events on a karst slope between 2019/4 and 2022/5 in southwest China, while simultaneously examining the soil–epikarst architecture (924 pairs of soil thickness and epikarst weathering degree). The results indicated that soil thickness increased with the underlying epikarst weathering degree, and soil thickness was positively correlated with epikarst thickness (P < 0. 001). Additionally, a significant positive relationship (P < 0. 001) was observed between surface runoff (SR) and soil thickness, as well as a significant negative relationship (P = 0. 0018) between subsurface runoff (SSR) and soil thickness. These findings imply the dominance of SR and SSR (under normal rainfall conditions) in runoff plots with deep soil layers and thin soil layers, respectively. The soil thickness threshold at which the hillslope discharge shifted from being SSR-dominated to SR-dominated was approximately 50 c m. Nonetheless, a positive relationship was found between SR and SSR under extreme rainfall events, indicating the establishment of hydrological connectivity between the surface and subsurface. Moreover, the hillslope discharge when the rainfall depth is lower than 50 mm is primarily composed of either SR or SSR from different plots. In other words, the hillslope discharge is typically influenced by both SR and SSR when the rainfall depth exceeds 50 mm. We finally proposed a positive feedback loop among soil thickness, epikarst weathering degree, and the hydrological function of the soil–epikarst system (water storage and release). These findings enhance our understanding of the complex interactive relationships in hillslope hydrology by illuminating the physical links between critical zone structures and hydrological processes on the karst slope. [Display omitted] • Soil thickness increased with weathering degree of epikarst. • SR dominated deep soil sites under normal rainfall conditions. • SSR dominated thin soil sites under normal rainfall conditions. • SR had a positive relationship with SSR under extreme rainfall events. • Bedrock weathering degree, soil thickness, and SR form a positive feedback loop. [ABSTRACT FROM AUTHOR]

Satellite remote sensing of vegetation has indicated that vegetation greenness has increased globally. However, the feedback mechanisms of vegetation restoration on eco-hydrological functions remain unclear, especially in fragile ecosystems. In this study, twelve three-dimensional hillslope plots with different vegetation restoration strategies were selected and their surface and subsurface runoff (SR and SSR, respectively) were monitored in the karst region of southwest China. These strategies were classified as either natural restoration (NR) or artificial management methods (PF, planted forest; GL, grassland), using cropland (CL) as a reference. The results showed that vegetation restoration effectively reduced both SR and SSR. Runoff from the three restoration strategies (59–66 mm) was significantly lower than that from the CL (119 mm). All the strategies had lower runoff than that of CL, except for PF, which exhibited higher SR because of its sparse canopy. Vegetation restoration reduced SR by increasing vegetation cover, which can intercept rainwater and weak the contribution (2.9–12.9%) of rainfall intensity to runoff, thereby reducing runoff generated by "infiltration-excess" mechanisms. This decrease in SSR may be due to an increased water storage capacity in the soil-root zone, causing the soil-bedrock interface to require more rainwater to "fill" and then "spill" to form lateral SSR during the rainfall events. These findings demonstrate that both canopy interception and root-soil interactions contribute to the improvement in hydrological function after vegetation restoration. Among the environmental factors contributing to runoff variation, soil depth was identified as the most crucial (51% of the variance) and showed a positive and negative correlations with SR and SSR, respectively. Consequently, restoration strategies with higher rainwater retention capacity can be selected to reduce SR losses, especially in areas with deeper soil layers. Accordingly, this study reveals that vegetation restoration reduces runoff and highlights the influence of soil depth in karst areas of southwest China. • Runoff with restoration strategies was lower than that of cropland. • Vegetation restoration weakens rainfall intensity's contribution to runoff. • Vegetation restoration reduced runoff generated by infiltration-excess mechanisms. • Soil depth contributes to 51% of the explained variability in runoff. [ABSTRACT FROM AUTHOR]

[Display omitted] • Epikarst thickness in depression is markedly greater than that on hillslope. • Spherical model fits for the interpolation of spatial structure of epikarst thickness. • Soil thickness is identified as the primary control on epikarst thickness. • ANNs model is suitable for predicting epikarst thickness based on RFE for variable selection. Epikarst, as a distinct layer of karst critical zone, plays a crucial role in water storage-transfer functions and biogeochemical processes. The epikarst thickness, which shows high spatial variability, is an important parameter that controls the dynamic characteristics of the water cycle. Due to the time-cost constraints in conventional field surveys and coarse resolution of remote sensing interpretation, empirical statistical models based on epikarst forming factors are an alternative to quantify the epikarst thickness. In this study, we investigated the spatial variability of epikarst thickness in Huanjiang, Guangxi of southwest China, based on electrical resistivity tomography with 36 sampling lines (1,658 sampling points) in a dolomite catchment. The controlling factors of epikarst thickness were defined based on selecting terrain-vegetation-soil variables with GLM (generalized linear model), RFE (recursive feature elimination) and PLSR (partial least squares regression) methods. Then, the best method for predicting epikarst thickness was selected based on the model with the highest accuracy. Results showed that the mean epikarst thickness was 6.32 m; the epikarst was significantly thicker in the depression (7.2 m) than on the hill slope (5.8 m), whereas there were no significant differences among slope positions. Geostatistical analysis showed that the spherical model reflected the strong spatial autocorrelation of epikarst thickness. Based on the prediction performance of the models, the terrain-vegetation variables alone could not explain epikarst thickness satisfactorily (explanation rate, 32.9 %; testing accuracy, R2 <0.5). By contrast, the modeling accuracy significantly increased (64.7 %, 0.7) when soil properties were considered as predictors. Based on validation criteria (R2 and RMSE), RFE for selecting variables and ANNs for prediction (0.814, 2.137 m) were the optimal model set to predict the epikarst thickness. This study provides a reference method for predicting epikarst thickness at a hillslope scale and the information would be helpful for hydrological catchment modeling. [ABSTRACT FROM AUTHOR]