Typical Hillslope Research Articles

Surface and subsurface runoff generation processes and their influencing factors on a hillslope in northern China

Runoff processes are essential to the hydrological cycle in mountainous areas. However, many aspects of surface and subsurface runoff generation mechanisms and their influencing factors remain to be fully understood. In this study, rainfall simulation experiments were conducted in micro runoff plots in different slope positions on a typical hillslope to explore runoff processes and their influencing factors in the Taihang Mountain region in northern China. The surface and subsurface runoff and soil water content (SWC) variation processes were analyzed. Moreover, the impact of the soil properties, such as soil saturated hydraulic conductivity (Ks), bulk density (BD), capillary porosity (CP), non-capillary porosity (NCP), and soil organic matter (SOM), on these processes were investigated. The results revealed that the response of the SWC to rainfall was significantly different in different soil layers and slope positions. The response time was slower and the period was longer on the lower slope. However, the middle and upper slopes had a faster response time and shorter period. The surface runoff was the dominant type in the lower slope (67.26 % of the total runoff), while the subsurface runoff was the dominant type in the middle (78.83 %) and upper (83.67 %) slopes. The subsurface runoff was mainly generated in the 40 cm layer on the lower slope, 20 and 30 cm layers on the middle slope, and 30 and 40 cm layers on the upper slope. These layers exhibited good correspondence with the Ks' vertical distribution, but were inconsistent with the other soil properties. These results indicate that the Ks was the most critical factor influencing the runoff generation process. The ratio of the upper layer's horizontal Ks to the lower layer's vertical Ks controlled the subsurface runoff generation process in the hillslope. These findings provide useful information for understanding the hydrological processes in mountainous areas.

Energy efficiency in transient surface runoff and sediment fluxes on hillslopes – a concept to quantify the effectiveness of extreme events

Abstract. Surface runoff over time shapes the morphology of the landscape. The resulting forms and patterns have been shown to follow distinct rules, which hold throughout almost all terrestrial catchments. Given the complexity and variety of the Earth's runoff processes, those findings have inspired researchers for over a century, and they resulted in many principles and sometimes proclaimed laws to explain the physics that govern the evolution of landforms and river networks. Most of those point to the first and second law of thermodynamics, which describe conservation and dissipation of free energy through fluxes depleting their driving gradients. Here we start with both laws but expand the related principles to explain the co-evolution of surface runoff and hillslope morphology by using measurable hydraulic and hydrological variables. We argue that a release of the frequent assumption of steady states is key, as the maximum work that surface runoff can perform on the sediments relates not only to the surface structure but also to “refueling” of the system with potential energy by rainfall events. To account for both factors, we introduce the concept of relative dissipation, relating frictional energy dissipation to the energy influx, which essentially characterizes energy efficiency of the hillslope when treated as an open, dissipative power engine. Generally, we find that such a hillslope engine is energetically rather inefficient, although the well-known Carnot limit does not apply here, as surface runoff is not driven by temperature differences. Given the transient and intermittent behavior of rainfall runoff, we explore the transient free energy balance with respect to energy efficiency, comparing typical hillslope forms that represent a sequence of morphological stages and dominant erosion processes. In a first part, we simulate three rainfall runoff scenarios by numerically solving the shallow water equations, and we analyze those in terms of relative dissipation. The results suggest that older hillslope forms, where advective soil wash erosion dominates, are less efficient than younger forms which relate to diffusive erosion regimes. In the second part of this study, we use the concept of relative dissipation to analyze two observed rainfall runoff extremes in the small rural Weiherbach catchment. Both flood events are extreme, with estimated return periods of 10 000 years, and produced considerable erosion. Using a previously calibrated, distributed physics-based model, we analyze the free energy balance of surface runoff simulated for the 169 model hillslopes and determine the work that was performed on the eroded sediments. This reveals that relative dissipation is largest on hillslope forms which relate to diffusive soil creep erosion and lowest for hillslope profiles relating to advective soil wash erosion. We also find that power in surface runoff and power in the complementary infiltration flux are during both events almost identical. Moreover, there is a clear hierarchy of work, which surface runoff expended on the sediments and relative dissipation between characteristic hillslope clusters. For hillslope forms that are more energy efficient in producing surface runoff, on average, a larger share of the free energy of surface runoff performs work on the sediments (detachment and transport) and vice versa. We thus conclude that the energy efficiency of overland flow during events does indeed constrain erosional work and the degree of freedom for morphological changes. We conjecture that hillslope forms and overland dynamics co-evolve, triggered by an overshoot in power during intermittent rainfall runoff events, towards a decreasing energy efficiency in overland flow. This implies a faster depletion of energy gradients during events and a stepwise downregulation of the available power to trigger further morphological development.

Influence of successive landslides on topographic changes revealed by multitemporal high-resolution UAS-based DEM

Landslides are recognized as dominant geomorphic events of morphological evolution in most mountainous and hilly landscapes. However, the lack of multitemporal high-resolution topographic data has resulted in a lack of quantitative estimates of topographic changes influenced by successive landslides. Taking a typical hillslope with successive loess landslides in the Heifangtai loess tableland, China, as an example, we conducted four unmanned aerial system (UAS) surveys and created corresponding high-resolution digital elevation models (HRDEMs) and orthophotos. We found that multitemporal UAS surveys have become a powerful new approach for addressing local topographic changes and evolution over a relatively long time series. Moreover, landslides can leave persistent geomorphic imprints on hillslope topography. The frequency distributions of topographic indexes are significantly influenced by successive landslides. The mean slope gradient, roughness and local relief decreased with successive landslide occurrences, whereas the mean topographic wetness index (TWI) increased. However, the mean slope aspect was almost unchanged by successive landslides. Furthermore, analysis of the coefficient of variation demonstrates that the frequency distribution of the slope gradient becomes more dispersed with landslide occurrences, while the slope aspect and TWI become more concentrated. The slope gradient changes with elevation. More broadly, this study provides new insights into the prediction of the local topographic feature changes and morphology evolution trends caused by successive landslides.

Decay and erosion-related transport of sulfur compounds in soils of rubber based agroforestry

Elemental sulfur is intensively used to control weeds and rubber leaf diseases. However, the mechanisms contributing to elemental sulfur dissipation and decay (hereafter decay) in rubber agroforestry remains unclear. This study relates hydrological processes such as runoff and soil loss to the changes in soil total sulfur (Stot) and sulfate (S–SO4) in typical hillslope rubber agroforestry intercropped with cocoa in Xishuangbanna. The elemental sulfur decay kinetics were studied at two slopes (top and bottom) and three agrosystems (weed, no-weed and mixed). The results show that soil moisture and hydraulic conductivity was uniformly distributed in the experimental rubber agroforestry settings. Higher soil loss and runoff occurred in the bottom slope than the top slope, and in no-weed agrosystem than the herbaceous agrosystems (weed and mixed). The soil loss was mainly driven by runoff. Moreover, Stot and S–SO4 in runoff water were higher in weed agrosystem than no-weed agrosystems. Soil Stot best fit a two-compartments kinetics model, with lower kinetic rates in elemental sulfur applied treatments than in the no-added elemental sulfur treatments, particularly for the weed agrosystem. The soil Stot dissipation time 50% (DT50) was 10–14 times higher in top slope than bottom slope; but 4 and 20 times higher in mixed and no-weed agrosystems, respectively, compared to the weed agrosystem. The soil Stot and S–SO4 contents negatively correlated with soil microbial respiration (CO2 efflux), indicating an adverse influence of elemental sulfur on soil microbial activity. In short, elemental sulfur decay and its S–SO4 transformation depended on soil moisture, runoff, soil erosion and soil CO2, which are in turn affected by slope and agrosystem. This study not only clarifies the mechanisms of elemental sulfur dissipation and decay for its use as an environmental friendly agrochemical; but it also provides information to understand the contribution of runoff and soil loss on these mechanisms in rubber agroforestry.

Predicting Annual Mean Profile Soil Moisture from Soil Particle‐Size Distributions on a Small‐Scale Hillslope on the Chinese Loess Plateau

Soil water content (SWC) varies notably over time and space due to soil heterogeneity, climatic conditions, vegetation, and topography. To restore vegetation rationally in arid and semiarid regions, it is important to have an accurate and rapid estimation of annual mean soil water content (AMSWC). Research on predicting of profile AMSWC from routinely available soil parameters, however, is still underrepresented in the literature. Our objective was to explore the ability of pedotransfer functions to accurately predict profile AMSWC from routinely available soil particle‐size distributions (PSDs) for a small‐scale hillslope on the Chinese Loess Plateau. The SWCs in soil profiles from 0‐ to 400‐cm depths were measured regularly at 30 monitoring sites on a typical hillslope during the growing seasons in 2014 and 2015. A total of 750 soil samples were taken from the same soil layers (0–400 cm) of these sites and their PSDs were determined using a laser diffraction technique. The results indicated that AMSWC increased exponentially (P < 0.001) with the clay (R2 = 0.632), silt (R2 = 0.480), and fractal dimensions (R2 = 0.616), however, they decreased exponentially (P < 0.001) with the sand content (R2 = 0.572). Using clay content as a predictor variable, the model established separately for each 100 cm depth soil sample resulted in a higher R2 (0.915), lower mean error (ME, 0.120%), and lower root mean squared error (RMSE, 0.999%), than the model of the whole 0‐ to 400‐cm soil depth (R2 = 0.830, ME = 0.199%, RMSE = 1.262%). These results showed that profile AMSWC at hillslope was able to be well‐estimated from routinely available soil clay content data. The model established separately for each 100‐cm depth soil sample performed well at predicting AMSWC on a small‐scale hillslope on the Chinese Loess Plateau. Our study proposed a precise and rapid method for estimating profile AMSWC at hillslope, serving for the optimization of soil water management and vegetation construction in dry regions.

Length‐Scale‐Dependent Relationships between VS30 and Topographic Slopes in Southern California

AbstractIn engineering seismology, the time‐averaged shear‐wave velocity (VS) of the upper 30 m of the crust (VS30) is the primary parameter used in ground‐motion models to predict seismic site effects. VS30 is typically derived from in situ recordings of VS, although proxy‐based approaches (using geologic and/or geomorphometric classifications) are provisionally adopted when measurement‐based VS30 are sparse or not readily available. Despite the acceptance of proxy approaches, there are limited studies that examine the empirical relationships between VS30 and topographic attributes measured from various length scales and different resolutions of the digital elevation model. In this study, we examine the relationships between compiled VS30 measurements from 218 sites in southern California and topographic metrics of slope and relief measured over various length scales. We find that the correlations between topographic metrics and VS30 are weak but statistically significant. The correlations are improved when topographic slopes and relief are measured over length scales longer than typical hillslopes and VS30 sites are separated by different geologic groups. This is likely because VS30, especially on the rock sites, is better reflected in topographic metrics that capture large‐scale topographic relief, as well as landscape positions such as hilltops and valley bottoms.

Distributed landscape response to localized uplift and the fragility of steady states

A primary goal of geomorphology is to infer from topographic form the processes that drive landscape evolution. Often implicit is the assumption that orogen-scale (>1010 m2 planform area) transient landscape changes on Earth are driven by equally large-scale transient tectonics, climate, or sea level. Here we argue that meso-scale (105–1010 m2) uplift perturbations may affect landscapes on scales that far exceed their size and duration. We study the consequences of transient variations in uniform surface uplift that are localized in space, such as may occur in volcanic landscapes or during landslide emplacement. These localized uplift perturbations define a class of landforms that are larger than typical hillslope lengths but smaller than orogens, and grow at rates that are rapid compared to fluvial bedrock erosion. We use 1D and 2D landscape evolution models to show that uplift perturbations drive transient lateral migration and vertical amplification of nearby ridges, sometimes generating a spatially distributed imbalance between uplift and erosion that causes plateau-like topography. Relaxation to steady-state conditions, in which erosion balances uplift everywhere, depends on the degree to which wave-like adjustment within channels or of ridges dominates subsequent landscape erosion. We find that the spatial structure and timescales of landscape response are predictable given uplift perturbation parameters. In 2D models, localized uplift generates a radial pattern of channel network and drainage divide reorganization that remains long after the perturbation is eroded. The spatial pattern of ridges and channels in a landscape thus may record both the scale and pace of perturbations to the uplift field.

Identifying representative sites to simultaneously predict hillslope surface and subsurface mean soil water contents

Many approaches have been proposed to identify the representative sampling sites for estimating the spatial mean soil water contents. However, comparisons on these approaches have seldom been conducted to simultaneously predict the surface and subsurface mean soil water contents. In this study, five approaches were evaluated in identifying representative sites to estimate the surface and subsurface mean soil water contents on a typical hillslope in Taihu Lake Basin, China. They were temporal stability analysis (TSA), k-means clustering with environmental factors as inputs (EFs), combinations of TSA and EFs (EFs + TSA), k-means clustering with surface soil water contents as inputs (Theta), and combinations of TSA and Theta (Theta+TSA). The correlation coefficient (r) and root mean squared error (RMSE) between estimated and measured mean soil water contents were used to evaluate the accuracies during the calibration period (the first 25 dates) and validation period (the last 18 dates). Results showed the optimal number of representative sites on this hillslope was six. When >6 representative sites were selected, the TSA had the lowest accuracies for estimating both surface and subsurface mean soil water contents during validation period (mean RMSE ≥ 0.011 m3 m−3). The Theta and Theta + TSA had better accuracies in estimating surface mean soil water contents during both calibration and validation periods (mean RMSE < 0.007 m3 m−3). However, to estimate surface and subsurface mean soil water contents simultaneously, the EFs and EFs + TSA were more promising (mean RMSE < 0.011 m3 m−3 during validation period), especially the EFs which only required one-time collection of environmental factors. These findings will be beneficial for choosing proper approach to calibrate and validate the remote sensed soil water contents.

Adapting the Caesium-137 technique to document soil redistribution rates associated with traditional cultivation practices in Haiti

Large-scale deforestation, intensive land use and unfavourable rainfall conditions are responsible for significant continuous degradation of the Haitian uplands. To develop soil conservation strategies, simple and cost-effective methods are needed to assess rates of soil loss from farmland in Haiti. The fallout radionuclide caesium-137 (137Cs) provides one such means of documenting medium-term soil redistribution rates. In this contribution, the authors report the first use in Haiti of 137Cs measurements to document soil redistribution rates and the associated pattern of erosion/sedimentation rates along typical hillslopes within a traditional upland Haitian farming area. The local 137Cs reference inventory, measured at an adjacent undisturbed flat area, was 670 Bq m−2 (SD = 100 Bq m−2, CV = 15%, n = 7). Within the study area, where cultivation commenced in 1992 after deforestation, three representative downslope transects were sampled. These were characterized by 137Cs inventories ranging from 190 to 2200 Bq m−2. Although, the study area was cultivated by the local farmers, the 137Cs depth distributions obtained from the area differed markedly from those expected from a cultivated area. They showed little evidence of tillage mixing within the upper part of the soil or, more particularly, of the near-uniform activities normally associated with the plough layer or cultivation horizon. They were very similar to that found at the reference site and were characterized by high 137Cs activities at the surface and much lower activities at greater depths. This situation is thought to reflect the traditional manual tillage practices which cause limited disturbance and mixing of the upper part of the soil. It precluded the use of the conversion models normally used to estimate soil redistribution rates from 137Cs measurements on cultivated soils and the Diffusion and Migration conversion model frequently used for uncultivated soils was modified for application to the cultivated soils of the study area, in order to take account of the unusual local conditions. The model was also modified to take account of the fact that cultivation in the study area commenced in 1992, rather than predating the period of weapons test fallout which extended from the mid 1950s to the 1970s. Erosion rates on the upper parts of the hillside involved in the study were found to be relatively high and ca. −23 t ha−1 y−1 with low spatial variability. In the lower, flatter areas at the bottom of the slope, deposition occurred. Deposition rates were characterized by high spatial variability, ranging from 6.0 to 71 t ha−1 y−1. Soil redistribution rates of this magnitude are a cause for concern and there is an urgent need to implement soil conservation measures to ensure the longer-term sustainability of the local agricultural practices.

Uncertainty analysis in near-surface soil moisture estimation on two typical land-use hillslopes

Purpose Spatial prediction of near-surface soil moisture content (NSSMC) is necessary for both hydrologic modeling and land use planning. However, uncertainties associated with the prediction are always neglected and lack of quantitative analysis. The objective of this study was to investigate the influences of different sources of uncertainty on NSSMC estimation at two typical hillslopes (i.e., tea garden and forest).

The influence of terracettes on the surface hydrology of steep-sloping and subalpine environments: some preliminary findings

Abstract. Alpine and mountain slopes represent important pathways that link high-altitude grazing areas to meadows and rangelands at lower elevations. Given the often acute gradients associated with such environments, they potentially represent highly efficient runoff conveyance routes that facilitate the downslope movement of runoff and associated material during erosion events. Many such slopes host series of small steps, or "terracettes". The juxtaposition of terracettes against the natural downslope flow path of non-complex slopes leads us to hypothesise that they may influence typical hillslope processes by intercepting or capturing surface runoff. Here we report preliminary results and some tentative conclusions from ongoing work to explore this possibility. Google Earth was used to initially identify a ca. 400 m2 well-developed terracette system situated on a west-facing slope with gradients ranging from 25 to 40° (46 to 84 %). A digital elevation model (DEM) of the terracettes was constructed using spatial data taken from a relevant section of topographic map. The DEM was then queried using a flow-accumulation algorithm and the results displayed in a geographic information system. The output data provided "proof of concept" that terracettes can capture surface runoff. The generation of empirical data from a series of rainfall/runoff simulations performed on the same section of terracettes supports this finding. Results from both work components indicate that sections of a terracette system may intercept runoff and could act as preferential flow pathways. By contrast, some sections appeared to act as depositional sites. We cautiously predict that these areas could act as retention zones for the temporary storage of runoff-associated substances. Greater understanding of the exact influence of terracettes on surface hydrology in steep-sloping and subalpine environments could benefit the future management of grazing and rangelands in such areas.

Soil aggregate stability to predict organic carbon outputs from soils

Soil structure (e.g. aggregation) has been recognized as a key element in the stabilization of soil organic matter. While aggregate bre akdown is assumed to expose the enclosed soil organic carbon (SOC) to preferential erosion and to accelerated decomposition, the link between the stability of soil aggregates and SOC exports from soils, has either been overlooked or unaccounted for, especially when developing carbon cycle models. This study compared SOC losses in particulate (POC), dissolved (DOC) and gaseous (GOC) forms to an indicator of the soil aggregate stability, the mean weight diameter of aggregates (MWD). SOC outputs were considered at 24 locations of a typical hillslope of the South African Highveld showing clayey to sandy soils. Both POC and DOC were evaluated in-situ under natural rains using 1×1m2 runoff plots while soil CO2 emissions were assessed in the laboratory from undisturbed 0–0.05m soil samples. MWD was finally compared to selected soil and terrain attributes for predictive purpose and as a means to further the understanding of SOC outputs from soils. MWD ranged between 1.4mm for unstable aggregates and 3.4mm for stable aggregates. The increase in aggregate stability resulted in a significant increase in POC and DOC concentrations in the eroded sediments (r=0.76) and in GOC losses from soils (r=0.91 when expressed as g C-CO2 per gram of soil; r=0.95 when as g C-CO2 per gram of soil carbon). In contrast, high aggregate stability induced low total DOC and POC losses (r=−0.81 and −0.77, respectively). The lower POC and DOC losses in the most stable soil aggregates were explained by increased soil infiltration by water and reduced transport by runoff, while the greater CO2 emissions correlated with high SOC concentration. Furthermore, there was a tendency for clayey soils which were fully covered by grass to present stable aggregates and thus to yield greater CO2 emissions but lower POC and DOC outputs than degraded sandy soils of low aggregate stability. Such a quantitative assessment of the role of soil aggregation on SOC outputs might enhance knowledge on organic matter persistence in soils, a prerequisite for developing more accurate global carbon cycle models. Finally further research is required to investigate the downslope to downstream fate of the eroded SOC and to develop land management strategies that aim at lessening carbon losses from soils while enhancing adaptation to climate change.

黄土丘陵沟壑区不同植被恢复格局下土壤微生物群落结构的研究

PDF HTML阅读 XML下载 导出引用 引用提醒 黄土丘陵沟壑区不同植被恢复格局下土壤微生物群落结构 DOI: 10.5846/stxb201306081455 作者: 作者单位: 河南省科学院地理研究所,河南省科学院地理研究所,中国科学院生态环境研究中心城市与区域生态国家重点实验室 作者简介: 通讯作者: 中图分类号: s154.36 基金项目: 中国科学院战略性先导科技专项资助（XDA01050104） Soil microbial community structure under different vegetation restoration patterns in the loess hilly area Author: Affiliation: Institute of Geographical Sciences, Henan Academy of Sciences,,Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:针对典型黄土丘陵沟壑区陕西延安羊圈沟小流域坡面上单一刺槐林、单一撂荒草地以及林草搭配的草地-林地-草地及林地-草地-林地4种不同植被格局，利用磷脂脂肪酸（phospholipid fatty acid，PLFA）谱图分析法对土壤微生物群落结构进行监测研究，旨在揭示坡面上不同的植被恢复格局对土壤微生物群落结构的影响。研究发现4种不同植被格局下，2种林草搭配的植被格局磷脂脂肪酸的结构比较相似，与单一植被格局相比，表层土壤中表征真菌的特征脂肪酸所占的比例有所提高。主成分分析显示4种植被格局0-10 cm土壤微生物群落结构存在差异，差异主要存在于2种林草搭配的植被格局与2种单一的植被格局之间，其中草地-林地-草地的植被格局与刺槐林和撂荒草地之间土壤微生物群落结构的差异均达到了显著水平。不同微生物菌群的量在4种植被格局土壤间显著性差异主要存在于表层土壤中的细菌菌群和革兰氏阳性菌，革兰氏阴性菌和真菌在4种植被格局土壤之间无显著差异。总之，4种不同植被恢复格局的土壤微生物群落结构存在差异且差异主要存在于表层土壤，坡面上人工林的种植及林草搭配的恢复模式较直接撂荒更有利于提高微生物菌群的生物量。 Abstract:Soil erosion is still severe in the Loess Plateau, and vegetation restoration practices are effective measures to fight it by reducing nutrient loss and improving soil quality. Soil microorganisms are important for soil ecosystem, which play crucial roles in biogeochemical cycling and ecosystem functioning. Soil biological and biochemical properties, such as microbial biomass, microbial community composition, and microbial functional diversity are frequently used for detecting accurate changes in soil properties. The major purpose of this study therefore, is to discover the effects of different vegetation restoration patterns on soil microbial community structures in the Loess Plateau. The study area was located in Yangjuangou catchment, a typical loess hilly area near Yan'an city of northern Shaanxi province, China. Four typical hillslopes, including F (artificial forest), G (grass), G-F-G (grass on the upper and lower slopes and artificial forest on the middle slope), and F-G-F (artificial forest on the upper and lower slopes and grass on the middle slope), were chosen. Several soil sampling sites, each covered by an area of 200m2, were conducted on the summit, shoulder, backslope, footslope and toeslope along each hillslope, respectively. Three experimental plots in each site were conducted with an area of 25 m2. Soil samples in the first two vertical layers (0-10 cm and 10-20 cm) were collected in August of 2007, for analyzing soil microbial community structure and soil physicochemical properties. Soil microbial community structure was analyzed by using phospholipid fatty acid (PLFA) analytical method and soil physicochemical properties were done by general soil and agricultural chemistry analytical methods. Results showed that significant difference of phospholipid fatty acid composition existed between different soil layers and soils with different vegetation restoration patterns, mainly in surface soil layer collected from G-F-G and F-G-F differing with that from F and G. The proportion of phospholipid fatty acid indicated fungi was higher in the surface soils under G-F-G and F-G-F, compared to F and G. Principal components analysis (PCA) showed that in the 0-10 cm soil layer, the phospholipid fatty acid structure of G-F-G was different with that of F and G, while the phospholipid fatty acid structure of F-G-F was different with F significantly. The biomass of soil bacteria, fungi, Gram-negative bacteria and Gram-positive bacteria under F-G-F pattern were all captured the highest values. There was significant difference of soil bacteria biomass and Gram-positive bacteria biomass in the surface soil layers among the four mentioned vegetation restoration patterns. The biomass of soil bacteria and fungi, however, had non-significant difference among 10-20 cm soil layers with different vegetation restoration patterns. Redundancy analysis (RDA) showed that soil organic carbon and total nitrogen had more important relationship with soil microbial community. However, the effects of some physicochemical properties such like pH and bulk density on soil microbial community needed more study. In conclusion, microbial community structure was dissimilar in soils and significant difference mainly appeared in surface soil layers under four vegetation restoration patterns. The roles of artificial forestation and forest-grass collocation on the slope in improving soil microbial biomass were believed much better than abandoned farmland. 参考文献 相似文献 引证文献

Evaluating surface and subsurface water storage variations at small time and space scales from relative gravity measurements in semiarid Niger

[1] The acquisition of reliable data sets representative of hydrological regimes and their variations is a critical concern for water resource assessment. For the subsurface, traditional approaches based on probe measurements, core analysis, and well data can be laborious, expensive, and highly intrusive, while only yielding sparse data sets. For this study, an innovative field survey, merging relative microgravimetry, magnetic resonance soundings, and hydrological measurements, was conducted to evaluate both surface and subsurface water storage variations in a semiarid Sahelian area. The instrumental setup was implemented in the lower part of a typical hillslope feeding to a temporary pond. Weekly measurements were carried out using relative spring gravimeters during 3 months of the rainy season in 2009 over a 350 × 500 m2 network of 12 microgravity stations. Gravity variations of small to medium amplitude (≤220 nm s−2) were measured with accuracies better than 50 nm s−2, revealing significant variations of the water storage at small time (from 1 week up to 3 months) and space (from a couple of meters up to a few hundred meters) scales. Consistent spatial organization of the water storage variations were detected, suggesting high infiltration at the outlet of a small gully. The comparison with hydrological measurements and magnetic resonance soundings involved that most of the microgravity variations came from the heterogeneity in the vadose zone. The results highlight the potential of time lapse microgravity surveys for detecting intraseasonal water storage variations and providing rich space-time data sets for process investigation or hydrological model calibration/evaluation.

不同护坡草本植物的根系特征及对土壤渗透性的影响

Plant root system plays important role in soil erosion protection and affects hillslope hydrological process through infiltration.To quantitatively investigate root features of typical herb plants for hillslope protection in the Three Gorges Reservoir Region and their influence on soil infiltration,soil initial infiltration,average infiltration,stable infiltration and accumulative infiltration were measured on 4 typical hillslope protection herb plants,Vetiveria zizanioides(Lin.) Nash,Paspalum notatum Flugge,Cynodon dactylon(L) Pers.and Medicago sativa L.,ith bare land as a control.Soil samplers were used to take soil samples from the test area for laboratory experiments.Double-rings method was applied to make on-site measurement of soil infiltration.Root analysis system,WinRHIZOPro.2004c was used to characterize the root systems.The results indicated that:(1) Vetiveria zizanioides(Lin.) Nash and Medicago sativa L.had considerable higher root length density and root surface area density,as compared with paspalum notatum Flugge,Cynodon dactylon(L) Pers.(2) The soil infiltration rates were significantly amongst the different herb plants and at different soil layers under the same herb plants.The soil infiltration rates of soil under herb plants were significantly higher that of bare soil and declined with the increase in soil depth.The soil infiltration rates from high to low were in the order of Vetiveria zizanioides(Lin.) Nash,Medicago sativa L.,Paspalum notatum Flugge,Cynodon dactylon(L) Pers.(3) The initial,average and steady infiltration rates were 2.42,1.65 and 1.38 mm/min for Cynodon dactylon(L) Pers.,3.87,2.42 and 2.11 mm/min for Medicago sativa L.,4.84,3.37 and 3.00 mm/min for Vetiveria zizanioides(Lin.) Nash and 2.93,1.79 and 1.39 mm/min for Paspalum notatum Flugge and 1.31,0.86 and 0.71 mm/min for bare land respectively.(4) The soil initial,steady and average infiltration rates as well as cumulative infiltration were increased with increases in root length density and root surface area density,which were evidently correlated with root diameter from 0.50 to 5.00 mm.(5)Root length density and root surface density had significant impacts on Kostiakov′s model parameters,K and a.The K value,representing initial infiltration rate increased with increase in root length density and root surfer area density and the a value,representing the decrease rate of infiltration decreased with them.The K value from high to low were in the order of Vetiveria zizanioides(Lin.) Nash,Medicago sativa L.,Paspalum notatum Flugge,Cynodon dactylon(L) Pers.,Bare land.The K value and a value were 1.382 and 0.473 for Bare land,4.275 and 0.307 for Vetiveria zizanioides(Lin.) Nash,3.814 and 0.312 for Medicago sativa L,3.325 and 0.452 for Paspalum notatum Flugge and 2.742 and 0.404 for Cynodon dactylon(L) Pers.respectively.The results will be useful for hillslope vegetation protection and soil erosion control.

Runoff and sediment modeling in a peri-urban artificial landscape: Case study of Olympic Forest Park in Beijing

In recent years, many ecological parks have been constructed in the peri-urban areas of Chinese cities to relieve the ecological pressure of high-speed urbanization. Compared with the natural landscape, the artificial ecological park is totally a man-regulated system, which is fragile and very sensitive to the runoff and sediment disturbance from severe storms. Thus, a case study was performed in the artificially constructed Beijing Olympic Forest Park to study its hydrological response to severe storms and to identify the critical areas for implementing Best Management Practices (BMPs). The monitored rainfall–runoff data revealed that infiltration excess runoff was the predominant runoff generation mechanism in the study area. A Dynamic Watershed Simulation Model (DWSM) was used to simulate the runoff and sediment transport processes from monitored and design storms. Owing to the complexity of topography and lack of a single outlet, the DWSM was calibrated and validated in a typical hillslope with a nested structure to acquire scale appropriate parameters. Then, the DWSM was applied to other overland segments and scaled consistently to perform scenario analysis under design storm conditions. Results showed that, the shift of rainfall intensity in design storms could produce amplified hydrologic responses, but had little impact on the overland rankings based on runoff depth or specific sediment yield. However, the different spatial patterns between runoff and sediment revealed the spatially varied soil erosion processes (transport-limited or supply-limited) and the necessity of site-specific BMPs. Generally, the areas with high runoff and sediment potentials were mostly related to the segments with small drainage areas and short, steep slopes, while the constructed drainage system could function as interception BMPs to reduce runoff and sediment discharges. The analysis of the relationship between overland rankings and overland features could provide guidance to identify critical areas and to implement site-specific BMPs in peri-urban artificial landscapes.

Controls of infiltration–runoff processes in Mediterranean karst rangelands in SE Spain

Semiarid karst landscapes represent an important ecosystem surrounding the Mediterranean Basin for which little is known on runoff generation. Knowledge of the sources and patterns of variation in infiltration–runoff processes and their controls is important for understanding and modelling the hydrological functions of such ecosystems. The objectives of this paper are to determine the infiltration rates and their controls in a representative mountain karst area (Sierra de Gádor, SE Spain) at micro-plots and to investigate the integrated response of rainfall on a typical hillslope. Rainfall simulations in micro-plots and natural rainfall-runoff monitoring on a hillslope were carried out complementarily. We investigated the role of soil surface components (vegetation, rock outcrop, fracture, and soil crust), topographic position, antecedent soil moisture, and rainfall characteristics in regulating infiltration–runoff processes. Results of rainfall simulation revealed the importance of vegetation cover and the presence of rock fractures in promoting the infiltration in the limestone karst landscape, while bare patches and rock outcrops acted as sources for runoff. All plots with > 50% vegetation cover had no runoff with up to 55 mm h− 1 of simulated rain. In contrast, nearly all bare plots had runoff under the same simulated rain, with runoff coefficients ranging from 3.1 to 20.6% on dry soil surface conditions, and from 2.0 to 65.4% on wet soil surfaces. Runoff coefficients amounted to 59.0–79.5% for rock outcrops without cracks, but were drastically reduced by the presence of cracks. The surfaces with rock fragments resting on the soil (generally located in the middle of the slopes) prevented more effectively the runoff generation than those surfaces where rock fragments were embedded in the top soil. Antecedent soil moisture had significant impact on runoff generation, with wet soil having doubled runoff coefficient, shortened time to runoff, and increased runoff rate compared to the same but dry soil. Linear regressions indicated that the main controls for constant infiltration rate were the cover percentages of vegetation and litter, plus rainfall intensity; while the major controls for runoff coefficient were the bare soil and vegetation coverage, plus rainfall intensity. High infiltration rates measured at the micro-plots agreed with low intra-event runoff coefficients (mostly below 1%) observed under natural rainfalls at the hillslope. Runoff depth and coefficient at the hillslope was significantly correlated with rainfall depth, maximum hourly rainfall intensity and antecedent precipitation over 20 days (AP20). During the 1.5-year monitoring period from Sep-2003 to Mar-2005, the overall infiltration was 41% of the total rainfall amount and the maximum infiltration rate was almost 94% of the largest single rainfall event. The results from this study contribute to improved understanding of the magnitude and controls of the surface runoff in semiarid karst mountain areas.

Runoff formation in a small catchment at hillslope and catchment scales

AbstractThe study is focused on runoff formation processes at two scales: the scale of a small mountainous catchment at its outlet and the scale of an experimental plot located in a typical hillslope subregion. The heterogeneous soil profile of the catchments is formed by Cambisols developed on granite bedrocks. The surface runoff appears rarely, the subsurface flow forms a dominant part of the hydrograph. From the period 1998–2008, a set of 44 rainfall–runoff episodes was selected to analyse the rainfall–runoff relationship using multiple regression analysis. From a set of physical parameters, the initial soil water content came out as the statistically significant parameter that controls the runoff forming process at the catchment scale. The rainfall–runoff relationship at the experimental plot scale is more scattered. The dynamic thresholds of rainfall totals apparently control the ratio and the magnitude of stormflow at both scales. Up to the threshold value, the runoff strongly depends on the initial saturation conditions. Above the threshold value, the initial soil moisture conditions are less important. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Characterization and classification of soils along a typical Hillslope in Afikpo area of Ebonyi state, Nigeria

Three pedons representing soils on the summit to shoulder (Pedon 1), backslope to footslope (Pedon 2) and toeslope (Pedon 3) positions along a typical hillslope in Afikpo area of Ebonyi State of Nigeria were studied regarding their morphological, physico-chemical and mineralogical properties. The soils were also classified according to the criteria of the USDA Soil Taxonomy and the FAO World Reference Base for Soil Resources. Soils of Pedons 1 & 2 occur on very strongly sloping, severely eroded uplands and are derived from ferruginous, feldspathic sandstone with shale intercalations. The soils in the toeslope position, occur on extensive, nearly level plains which are seasonally waterlogged with colluvio-alluvial sediments constituting the parent material. Irrespective of slope position, all the soils are very strongly acidic with a narrow pH range of 4.6 – 5. 1 and an average exch. Al3+ content of 3.77cmol kg-1 in all the horizons studied. Levels of organic C, total N, avail. P, exch. Ca, Mg, and K, range from being very low in Pedon 1, low to moderate in Pedon 2 but moderate to high in Pedon 3 indicating a gradual improvement in soil fertility from the summit to the toeslope of the hillslope . Kaolinite, mica, quartz, microcline, plagioclase, goethite and gibbsite were detected in the silt fraction of all the soils while kaolinite and poorly ordered illite as well as Fe-rich chlorite dominated the clay mineralogy. According to the criteria of the USDA Soil Taxonomy, the upland soils are Typic Udorthents while the valley bottom soils are Mollic Fluvaquents. In the FAO-WRB system, they qualify as Hper-Dystric Regosols and Mollic Gleysols respectively. Recommendations regarding soil management options have been included.Key words: acid soils, characterization, classification, Entisols, hillslope

Fractal Analyses of Steady Infiltration and Terrain on an Undulating Agricultural Field

Analysis of spatially distributed quasi‐steady infiltration measurements is important because of the effects of infiltration capacity on spatial patterns of soil water, nutrients, and plant development and production. We explored fractal models of quasi‐steady infiltration rates, emphasizing apparent changes in scaling exponents with domain size. Quasi‐steady infiltration rates were measured using single‐ring (0.30‐m‐diameter) constant‐head infiltrometers at 150 locations over 10 landscape positions (30 by 30 m, or approximately 0.1 ha) across a field (approximately 100 ha). At each landscape position, 15 rings were distributed randomly in nested patterns. The field in northeastern Colorado comprises undulating agricultural terrain cropped with dryland winter wheat (Triticum aestivum L.) under conventional tillage. Data were analyzed for multifractal and monofractal behavior. A monofractal model fit the infiltration data best, while terrain attributes other than elevation deviated from monofractals to different degrees. The Hurst exponent (H) was estimated by fitting power‐law variograms at different scales across the field. Values of H changed with the maximum lag distance, peaking near H = 0.9 at approximately 200 m, which represents a typical hillslope length. Spatial persistence in steady infiltration was not observed at long distances (&gt;300 m). Using dense and sparsely sampled terrain attributes as proxy data indicated that the observed spatial scaling of infiltration was not solely due to the clustering of infiltration measurements. These results shed new light on research needed to address spatial variability of soil hydraulic properties, with implications for hillslope process interactions between land areas when modeling distributed infiltration, runoff and run‐on, and plant water use.