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1.
Water infiltration rate and hydraulic conductivity in vegetated soil are two vital hydrological parameters for agriculturists to determine availability of soil moisture for assessing crop growths and yields, and also for engineers to carry out stability calculations of vegetated slopes. However, any effects of roots on these two parameters are not well‐understood. This study aims to quantify the effects of a grass species, Cynodon dactylon, and a tree species, Schefflera heptaphylla, on infiltration rate and hydraulic conductivity in relation to their root characteristics and suction responses. The two selected species are commonly used for ecological restoration and rehabilitation in many parts of the world and South China, respectively. A series of in‐situ double‐ring infiltration tests was conducted during a wet summer, while the responses of soil suction were monitored by tensiometers. When compared to bare soil, the vegetated soil has lower infiltration rate and hydraulic conductivity. This results in at least 50% higher suction retained in the vegetated soil. It is revealed that the effects of root‐water uptake by the selected species on suction were insignificant because of the small evapotranspiration (<0.2 mm) when the tests were conducted under the wet climate. There appears to have no significant difference (less than 10%) of infiltration rates, hydraulic conductivity and suction retained between the grass‐covered and the tree‐covered soil. However, the grass and tree species having deeper root depth and greater Root Area Index (RAI) retained higher suction. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

2.
In semiarid ecosystems, the transfer of water, sediments, and nutrients from bare to vegetated areas is known to be crucial to ecosystem functioning. Rainfall simulation experiments were performed on bare‐soil and vegetated surfaces, on both wet and dry soils, in semiarid shrub‐steppe landscapes of SE Spain to investigate the spatial and temporal factors and interactions that control the fine‐scale variation in water infiltration, runoff and soil loss, and hence the water and sediment flows in these areas. Three types of shrub‐steppe landscapes varying in plant community and physiography, and four types of plant patches (oak shrub, subshrub, tussock grass, and short grass mixed with chamaephytes) were studied. Higher infiltration and lower runoff and soil loss were measured on vegetation patches than on bare soils, for both dry and wet conditions. The oak‐shrub patches produced no runoff, while the subshrub patches showed the highest runoff and soil loss. Despite these differences among patch types, the influence of vegetation patch type on the variables analysed was not significant. The response of bare soil surfaces clearly varied between landscape types, yet the differences were only relevant under dry soil conditions. Stone cover, particularly the cover of embedded stones, and crust cover, were the key explanatory variables for the hydrological behaviour of bare soils. The study documents quantitatively how bare soils and vegetation patches function as runoff sources and runoff sinks, respectively, for a wide range of soil moisture conditions, and illustrates that landscape‐type effects on bare‐soil runoff sources may also exert an important control on the site hydrology, while the role of the vegetation patch type is less important. The effects of the control factors are modulated by antecedent soil moisture, with dry soils showing the most contrasting soil water infiltration between landscapes and surface types. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

3.
Biochar has the potential to be a soil amendment in green roofs owing to its water retention, nutrient supply, and carbon sequestration application. The combined effects of biochar and vegetated soil on hydraulic performance (e.g., saturated hydraulic conductivity, retention and detention, and runoff delay) are the crucial factor for the application of the novel biochar in green roofs. Recent studies investigated soil water potential (i.e., suction) either on vegetated soil or on biochar-amended soil but rarely focused on their integrated application. With the purpose of investigating the hydraulic performance of green roofs in the application of biochar, the combined effect of biochar and vegetated soil on hydrological processes was explored. Artificial rainfall experiments were conducted on the four types of experimental soil columns, including natural soil, biochar-amended soil, vegetated natural soil, and vegetated biochar-amended soil. The surface ponding, bottom drainage and the volumetric water content were measured during the rainfall test. Simulation method by using HYDRUS-1D was adopted for estimating hydraulic parameters and developing modelling analysis. The results indicated that the saturated hydraulic conductivity of vegetated soil columns were higher than bare soil columns. The addition of biochar decreased the saturated hydraulic conductivity, and the magnitude of decrease was much significant in the case of vegetated soil. The influence of vegetation on permeability is more prominent than biochar. The vegetated biochar-amended soil has the highest retention and detention capacity, and shows a preferable runoff delay effect under heavy rain among the four soil columns. The results from the present study help to understand the hydrological processes in the green roof in the application of biochar, and imply that biochar can be an alternative soil amendment to improve the hydraulic performance.  相似文献   

4.
Vegetation evapotranspiration (ET) induced soil water suction reduces hydraulic conductivity and increases shear strength of slopes. Several field studies have been conducted to investigate suction distribution in vegetated slopes. However, these studies were conducted on natural slopes, which are prone to heterogeneity in vegetation and soil conditions. Moreover, studies quantifying the effect of different vegetation species, root characteristics (root depth and root area index) and transpiration reduction function (Trf) on suction in slopes under natural variation are rare. This study investigated the suction distribution and root characteristics in recompacted slopes vegetated with two different species, i.e. Cynodon dactylon (Bermuda grass) and Schefflera heptaphylla (ivy tree). Bare slope served as a control. Suction distributions during different seasons and rainfall events were monitored. It is found that during the dry season, slope vegetated with young Schefflera heptaphylla seedlings have substantially higher suction within the root zone compared with bare slope and slope vegetated with Cynodon dactylon. This is because Schefflera heptaphylla has a higher root biomass, Trf and ET than Cynodon dactylon. It was also found that suctions within root zones of vegetated slopes and bare slope were completely destroyed under rainfall events corresponding to 2 years and 20 years return period. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

5.
Dry saline soils are common in the arid and hyper‐arid basins located in the Chilean Altiplano, where evaporation from shallow groundwater is typically the major component of the water balance. Thus, a good understanding of evaporation processes is necessary for improving water resource planning and management in these regions. In this study, we conducted laboratory experiments with a natural saline soil column to estimate evaporation rates and assess the liquid and water vapor fluxes under different water table levels. Water content, electrical conductivity and temperature at different depths were utilized to assess the liquid and water vapor fluxes in the soil column. We observed movement of water that dissolves salts from the soil and transports them to areas in the column where they accumulate. Isothermal liquid flux was predominant, while thermal and isothermal liquid and thermal water vapor fluxes were negligible, except for deep water table levels where isothermal and thermal water vapor fluxes had similar magnitude but opposite directions. Differences observed in total fluxes for all water table levels were due to different upward and downward fluxes, which depend on changes in water content and temperature within the soil profile. Both the vapor flux magnitude and direction were found to be very sensitive to the choice of empirical parameters used in flux quantification, such as tortuosity and the enhancement factor for local temperature gradients in the air phase within the column. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

6.
In cold climates, the process of freezing–thawing significantly affects the ground surface heat balance and water balance. To better understand the mechanism of evaporation from seasonally frozen soils, we performed field experiments at different water table depths on vegetated and bare ground in a semiarid region in China. Soil moisture and temperature, air temperature, precipitation, and water table depths were measured over a 5‐month period (November 1, 2016, to March 14, 2017). The evaporation, which was calculated by a mass balance method, was high in the periods of thawing and low in the periods of freezing. Increased water table depth in the freezing period led to high soil moisture in the upper soil layer, whereas lower initial groundwater levels during freezing–thawing decreased the cumulative evaporation. The extent of evaporation from the bare ground was the same in summer as in winter. These results indicate that a noteworthy amount of evaporation from the bare ground is present during freezing–thawing. Finally, the roots of Salix psammophila could increase the soil temperature. This study presents an insight into the joint effects of soil moisture, temperature, ground vegetation, and water table depths on the evaporation from seasonally frozen soils. Furthermore, it also has important implications for water management in seasonally frozen areas.  相似文献   

7.
This study examines the effect of water repellency on controlling temporal variability of runoff generation mechanisms and soil detachment on metamorphic derived soils under dry‐Mediterranean climate. The research is carried out in an unburnt Mediterranean hillslope in souther Spain characterized by a patchy vegetation pattern and shallow soils. The Water Drop Penetration Time test (WDPT) is applied to measure water repellency at the end of summer (Sep‐2008), mid autumn (Nov‐2008) and mid winter (Feb‐2009). Rainfall simulations were used to obtain runoff generation and soil detachment in the same periods of time. The main shrub specie is Cistus monspeliensis which leaves a load of litter during the summer due to the lack of water. This great amount of organic material is accumulated under the shrubs triggering an extreme water repellence (WDPT > 6,000 s) that limits infiltration processes. This process is enforced due to the low soil water content at the end of dry season. Certain water repellency (WDPT > 1,500 s) is also observed on bare soil as consequence of their sandier texture and the accumulation of annual plants which die at the end of the wet season. Soil moisture increases during the autumn and water repellency disappears in both shrub and bare soil at the middle of the wet season (WDPT < 5 s). The main consequence is that the temporal trend of water repellency controls the mechanism and frequency of runoff generation and, hence, soil detachment. At the end of the summer, Hortonian mechanisms predominates when water repellency is extreme, even in soils under Cistus monspeliensis where runoff generation can reach higher peaks of overland flow and sediment concentration. Conversely, only the saturation of soil could generate runoff during the wet season being this quite less frequent in bare soil and absent in shrub. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
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9.
The need to understand and simulate hydrological phenomena and their interactions, and the impact of anthropogenic and climate changes on natural environments have promoted the study of evaporation from bare soils in arid climates. In closed Altiplano basins, such as those encountered in arid and hyper arid basins in northern Chile, evaporation from shallow groundwater is the main source of aquifer depletion, and thus, its study is crucial for water resources management. The objective of this work is to understand the mechanisms of evaporation in saline soils with shallow water tables, in order to better quantify evaporation fluxes and improve our understanding of the water balance in these regions. To achieve this objective, a model that couples fluid flow with heat transfer was developed and calibrated using column experiments with saline soils from the Huasco salt flat basin, Chile. The model enables determination of both liquid and water vapour fluxes, as well as the location of the evaporation front. Experimental results showed that salt transport inside the soil profile modified the water retention curve, highlighting the importance of including salt transport when modelling the evaporation processes in these soils. Indeed, model simulations only agreed with the experimental data when the effect of salt transport on water retention curves was taken into account. Model results also showed that the evaporation front is closer to the soil surface as the water table depth reduces. Therefore, the model allows determining the groundwater level depth that results in disconnection of liquid fluxes in the vadose zone. A sensitivity analysis allowed understanding the effect of water‐flux enhancements mechanisms on soil evaporation. The results presented in this study are important as they allow quantifying the evaporation that occurs in bare soils from Altiplano basins, which is typically the main water discharge in these closed basins. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

10.
This study integrated spatially distributed field observations and soil thermal models to constrain the impact of frozen ground on snowmelt partitioning and streamflow generation in an alpine catchment within the Niwot Ridge Long-Term Ecological Research site, Colorado, USA. The study area was comprised of two contrasting hillslopes with notable differences in topography, snow depth and plant community composition. Time-lapse electrical resistivity surveys and soil thermal models enabled extension of discrete soil moisture and temperature measurements to incorporate landscape variability at scales and depths not possible with point measurements alone. Specifically, heterogenous snowpack thickness (~0–4 m) and soil volumetric water content between hillslopes (~0.1–0.45) strongly influenced the depths of seasonal frost, and the antecedent soil moisture available to form pore ice prior to freezing. Variable frost depths and antecedent soil moisture conditions were expected to create a patchwork of differing snowmelt infiltration rates and flowpaths. However, spikes in soil temperature and volumetric water content, as well as decreases in subsurface electrical resistivity revealed snowmelt infiltration across both hillslopes that coincided with initial decreases in snow water equivalent and early increases in streamflow. Soil temperature, soil moisture and electrical resistivity data from both wet and dry hillslopes showed that initial increases in streamflow occurred prior to deep soil water flux. Temporal lags between snowmelt infiltration and deeper percolation suggested that the lateral movement of water through the unsaturated zone was an important driver of early streamflow generation. These findings provide the type of process-based information needed to bridge gaps in scale and populate physically based cryohydrologic models to investigate subsurface hydrology and biogeochemical transport in soils that freeze seasonally.  相似文献   

11.
Estimates of soil hydraulic properties using pedotransfer functions (PTF) are useful in many studies such as hydrochemical modelling and soil mapping. The objective of this study was to calibrate and test parametric PTFs that predict soil water retention and unsaturated hydraulic conductivity parameters. The PTFs are based on neural networks and the Bootstrap method using different sets of predictors and predict the van Genuchten/Mualem parameters. A Danish soil data set (152 horizons) dominated by sandy and sandy loamy soils was used in the development of PTFs to predict the Mualem hydraulic conductivity parameters. A larger data set (1618 horizons) with a broader textural range was used in the development of PTFs to predict the van Genuchten parameters. The PTFs using either three or seven textural classes combined with soil organic mater and bulk density gave the most reliable predictions of the hydraulic properties of the studied soils. We found that introducing measured water content as a predictor generally gave lower errors for water retention predictions and higher errors for conductivity predictions. The best of the developed PTFs for predicting hydraulic conductivity was tested against PTFs from the literature using a subdata set of the data used in the calibration. The test showed that the developed PTFs gave better predictions (lower errors) than the PTFs from the literature. This is not surprising since the developed PTFs are based mainly on hydraulic conductivity data near saturation and sandier soils than the PTFs from the literature. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

12.
Rainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface. For a given cover level, rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation. Compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface. For the same cover level, rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer. The effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage. Micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by Poesen (1986): i.e. runoff generated as rock flow or as Horton overland flow can (partly) infiltrate into the unsealed soil surface under the rock fragments, provided that they are not completely embedded in the top layer. Hence, rock fragment position, beside other rock fragment properties, should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers. A simple model, based on the proportions of bare soil surface, soil surface occupied by embedded rock fragments, and soil surface covered with rock fragments resting on the soil surface, describes the runoff coefficient data relatively well.  相似文献   

13.
Within the scope of the upcoming launch of a new water related satellite mission (SMOS) a global evaluation study was performed on two available global soil moisture products. ERS scatterometer surface wetness data was compared to AMSR-E soil moisture data. This study pointed out a strong similarity between both products in sparse to moderate vegetated regions with an average correlation coefficient of 0.83. Low correlations were found in densely vegetated areas and deserts. The low values in the vegetated regions can be explained by the limited soil moisture retrieval capabilities over dense vegetation covers. Soil emission is attenuated by the canopy and tends to saturate the microwave signal with increasing vegetation density, resulting in a decreased sensor sensitivity to soil moisture variations. It is expected that the new low frequency satellite mission (SMOS) will obtain soil moisture products with a higher quality in these regions. The low correlations in the desert regions are likely due to volume scattering or to the dielectric dynamics within the soil. The volume scattering in dry soils causes a higher backscatter under very dry conditions than under conditions when the sub-surface soil layers are somewhat wet. In addition, at low moisture levels the dielectric constant has a reduced sensitivity in response to changes in the soil moisture content. At a global scale the spatial correspondence of both products is high and both products clearly distinguish similar regions with high seasonal and inter annual variations. Based on the global analyses we concluded that the quality of both products was comparable and in the sparse to moderate vegetated regions both products may be beneficial for large scale validation of SMOS soil moisture. Some limitations of the studied products are different, pointing to significant potential for combining both products into one superior soil moisture data set.  相似文献   

14.
Abstract

Time-domain reflectometry (TDR) is an electromagnetic technique for measurements of water and solute transport in soils. The relationship between the TDR-measured dielectric constant (Ka ) and bulk soil electrical conductivity ([sgrave]a) to water content (θW) and solute concentration is difficult to describe physically due to the complex dielectric response of wet soil. This has led to the development of mostly empirical calibration models. In the present study, artificial neural networks (ANNs) are utilized for calculations of θw and soil solution electrical conductivity ([sgrave]w) from TDR-measured Ka and [sgrave]a in sand. The ANN model performance is compared to other existing models. The results show that the ANN performs consistently better than all other models, suggesting the suitability of ANNs for accurate TDR calibrations.  相似文献   

15.
Soil piping is a widespread land degradation process that may lead to gully formation. However, the processes involved in sediment detachment from soil pipe walls have not been well studied, although their recognition is a crucial step to protect soils from piping erosion. This study aims to recognize the factors affecting cohesion and to identify the mechanisms which are likely to be responsible for the disintegration of soil. The study has been conducted in mid-altitude mountains under a temperate climate (the Bieszczady Mountains, the Carpathians, SE Poland). The research was based on the detailed field and laboratory analyses of morphology, and the physical and chemical properties of soil profiles with and without soil pipes. Moreover, experiments with flooding the undisturbed soil samples using different solutions (deionized water, ammonium oxalate, dithionate citrate, 35% hydrochloric acid and 30% hydrogen peroxide) were conducted in order to check the role of air slaking, the removal of soil organic carbon (SOC), and Fe and Al oxides on sediment detachment. The obtained results have confirmed that soil pipes develop in quite cohesive soils (silt loams), which allow the formation and maintenance of pipes with a diameter up to 30 cm. Soil cohesion, and thus susceptibility to piping, are impacted by the content of major oxides, soil particle size distribution, biological activity and porosity. The tested soils affected by piping erosion have a lower content of Al2O3 and Fe2O3, and free Fe (Fe(DCB)), lower clay content, higher biological activity (more roots and animal burrows), higher porosity, and more and larger pores than the profile without soil pipes. The experiments have indicated that especially SOC along with Fe and Al oxides are an important cohesion source in the study area. This suggests that the removal of SOC, and Fe and Al oxides may weaken and disintegrate aggregates in soil pipes. Further study of soil leaching and tensile strength will broaden understanding of which chemical processes control where pipes will develop in other cohesive piping-prone soils. © 2020 John Wiley & Sons, Ltd.  相似文献   

16.
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17.
Water is a limiting factor for life in the McMurdo Dry Valleys (MDV), Antarctica. The active layer (seasonally thawed soil overlying permafrost) accommodates dynamic hydrological and biological processes for 10–16 weeks per year. Wetted margins (visually wetted areas with high moisture content) adjacent to lakes and streams are potential locations of great importance in the MDV because of the regular presence of liquid water, compared with the rest of the landscape where liquid water is rare. At 11 plots (four adjacent to lakes, seven adjacent to streams), soil particle size distribution, soil electrical conductivity, soil water content and isotopic signature, width of the wetted margin, and active layer thaw depth were characterised to determine how these gradients influence physicochemical properties that determine microbial habitat and biogeochemical cycling. Sediments were generally coarse‐grained in wetted margins adjacent to both lakes and streams. Wetted margins ranged from 1·04 to 11·01 m in average length and were found to be longer at lakeside sites than streamside. Average thaw depths ranged from 0·12 to 0·85 m, and were found to be deepest under lake margins. Lake margins also had much higher soil electrical conductivity, steeper topographic gradients, but more gradual soil moisture gradients than stream margins. Patterns of soil water δ18O and δD distribution indicate capillary action and evaporation from wetted margins; margin pore waters generally demonstrated isotopic enrichment with distance from the shore, indicating evaporation of soil water. Lake margin pore waters were significantly more negative in DXS (DXS = δD‐8δ18O) than streamside pore waters, indicating a longer history of evaporation there. Differences between lake and stream margins can be explained by the more consistent availability of water to lake margins than stream margins. Differences in margin characteristics between lakes and streams have important consequences for the microbial habitat of these margins and their functional role in biogeochemical cycling at these terrestrial–aquatic interfaces. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

18.
Infiltration is the primary mechanism in green stormwater infrastructure (GSI) systems to reduce the runoff volume from urbanized areas. Soil hydraulic conductivity is most important in influencing GSI infiltration rates. Saturated hydraulic conductivity (Ksat) is a critical parameter for GSI design and post-construction performance. However, Ksat measurement in the field is problematic due to temporal and spatial variability and measurement errors. This review paper focuses on a comparison of methods for in-situ Ksat measurement and the causes of temporal and spatial variations of Ksat within GSI systems. Automated infiltration testing methods, such as the Modified Philip–Dunne (MPD) and SATURO infiltrometers, show promise for efficient Ksat measurements. Soil Ksat values can change over time and substantially vary throughout a GSI, which can be attributed to multiple factors, including but not limited to temperature changes, soil composition and properties, soil compaction level, plant root morphology and distribution, biological and macrofauna activities in the soil, inflow sediment characteristics, quality of infiltrating water, and measurement errors. There is evidence that infiltration rates in vegetated urban GSI systems are sustained given an appropriate GSI design, reasonable concentration of suspended sediments in the inflow runoff, and routine maintenance procedures. These observations indicate that clogging can be counteracted by processes that tend to increase the soil hydraulic conductivity (e.g., plant root and biological activities). This self-sustainability underlines that infiltration-based GSI systems are a reliable long-term stormwater management solution. Recommendations on how to incorporate the temporal changes of Ksat in GSI design and on obtaining a spatially-representative Ksat for the GSI design are presented.  相似文献   

19.
Recent studies have highlighted the importance of understanding ecohydrological drought feedbacks to secure water resources under a changing climate and increasing anthropogenic impacts. In this study, we monitored and modelled feedbacks in the soil–plant-atmosphere continuum to the European drought summer 2018 and the following 2 years. The physically based, isotope-aided model EcH2O-iso was applied to generic vegetation plots (forest and grassland) in the lowland, groundwater-dominated research catchment Demnitzer Millcreek (NE Germany; 66 km2). We included, inter alia, soil water isotope data in the model calibration and quantified changing “blue” (groundwater recharge) and “green” (evapotranspiration) water fluxes and ages under each land use as the drought progressed. Novel plant xylem isotope data were excluded from calibration but were compared with simulated root uptake signatures in model validation. Results indicated inter-site differences in the dynamics of soil water storage and fluxes with contrasting water age both during the drought and the subsequent 2 years. Forest vegetation consistently showed a greater moisture stress, more rapid recovery and higher variability in root water uptake depths from a generally younger soil water storage. In contrast, the grassland site, which had more water-retentive soils, showed higher and older soil water storage and groundwater recharge fluxes. The damped storage and flux dynamics under grassland led to a slower return to younger water ages at depth. Such evidence-based and quantitative differences in ecohydrological feedbacks to drought stress in contrasting soil-vegetation units provide important insights into Critical Zone water cycling. This can help inform future progress in the monitoring, modelling and development of climate mitigation strategies in drought-sensitive lowlands.  相似文献   

20.
We introduce the freely available web-based Water in an Agricultural Landscape—NUčice Database (WALNUD) dataset that includes both hydrological and meteorological records at the Nučice experimental catchment (0.53 km2), which is representative of an intensively farmed landscape in the Czech Republic. The Nučice experimental catchment was established in 2011 for the observation of rainfall–runoff processes, soil erosion processes, and water balance of a cultivated landscape. The average altitude is 401 m a.s.l., the mean land slope is 3.9%, and the climate is humid continental (mean annual temperature 7.9°C, annual precipitation 630 mm). The catchment is drained by an artificially straightened stream and consists of three fields covering over 95% of the area which are managed by two different farmers. The typical crops are winter wheat, rapeseed, and alfalfa. The installed equipment includes a standard meteorological station, several rain gauges distributed across the basin, and a flume with an H-type facing that is used to monitor stream discharge, water turbidity, and basic water quality indicators. Additionally, the groundwater level and soil water content at various depths near the stream are recorded. Recently, large-scale soil moisture monitoring efforts have been introduced with the installation of two cosmic-ray neutron sensors for soil moisture monitoring. The datasets consist of observed variables (e.g. measured precipitation, air temperature, stream discharge, and soil moisture) and are available online for public use. The cross-seasonal, open access datasets at this small-scale agricultural catchment will benefit not only hydrologists but also local farmers.  相似文献   

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