Soil Hydrological Properties Research Articles

Soil-hydrological properties response to grazing exclusion in a steppe grassland of the Loess Plateau

Soil–water characteristics are necessary for water quality monitoring, solute migration and plant growth. Soil–water characteristic curve (SWCC) is a relationship between suction and water content or degree of saturation. However, little information is available concerning the impacts of grazing exclusion management on soil–water characteristics. Here, the soil–water characteristics of grasslands, which were excluded grazing for 5 (GE5) and 15 years (GE15), were studied. The saturated hydraulic conductivity (K s), SWCC, particle composition, field capacity and some other indexes were determined. Results showed that the clay content and K s of grassland soil were higher for GE15 than GE5. For both treatments, in low suction condition (≤100 kPa), the water holding capacity of 0–10 cm soil was the best. Water holding capacity of topsoil decreased gradually with the increasing of suction, and it reached the strongest when the suction reached 600 kPa. In all soil water suction, the water holding capacity of subsoil was the weakest. The van Genuchten expression was applicable for most of the samples, except 20–30 cm of GE5 and 10–20 cm of GE15. Dual porosity equation was applicable for all the samples. The soil–water capability and soil structure of which was fenced for 15 years is superior to that of 5 years. This study suggests that the enclosure management improved the soil structure and soil–water capability.

Role of Vegetation on Slope Stability under Transient Unsaturated Conditions

We examine the role of vegetation on the stability of shallow soils under unsaturated transient regime. Two main positive effects of the vegetation on slope stability are discussed: i) a geo-mechanical effect, i.e., the reinforcement of soil by plant roots; ii) a soil-hydrological effect, i.e., the soil suction regime affected by root water uptake. The root distribution is assessed by an eco-hydrological model, which predicts the root density as function of local climatic conditions in growing season and soil hydrological properties. The predicted root distribution is employed for assessing the vertical variability of both the apparent soil cohesion provided by roots and the root water uptake. A one-dimensional model of vertical soil water dynamics is employed for simulating soil suction regime, assumed representative of well-drained soils on steep forested plane slopes. The geo-mechanical and the soil-hydrological effects on slope stability are examined with an infinite slope stability model, generalized for unsaturated conditions. We show that in the case of a loamy-sand soil under a Mediterranean climatic regime, the geo-mechanical effect tends to be more relevant than the soil-hydrological effect during the rainy season, within depths up to twice the average root depth.

Modeling Soil Water Movement under Low Head Ponding and Gravity Infiltration Using Data Determined with Different Methods

The aim of this work is to analyze differences in experimental and calculated model study of the processes of movement of soil water under low head ponding and gravity infiltration. In the forecast of the water regime two kinds of hydrological information were used – experimental and pedotransfer functions (PTFs). The experimental information: the hydraulic conductivities (HC) in saturated conditions were determined in the field conditions, unsaturated conductivity function was calculated (van Genuchten-Mualem model) using HC and water retention curves (WRC), WRC were investigated in laboratory condition with the help of capillarimeters, sand-kaolin boxes and by the centrifuge method. PTFs included: regional PTF, based on the data of the original database for the soil hydrological properties of the study area relying on the soil density and soil organic content, PTF based on particle size distribution, based on field capacity and wilting point as a predictors, and PTFs based on physico-mechanical properties, specifically Atterberg limits. The spatial distribution of moisture indicates that after infiltration under low head ponding, the soil water content variation is rather high (at depths of 50 and 60cm the quartiles were about 2-3 and 6-12%), but in the case of gravity infiltration the quartiles were about 2 and 5%. This points to the presence of preferential flows. The best forecast of the real-mode soil water regime gave experimental hydrological information: no systematic errors in the high min-max range of modeling errors. Among PTFs the modeling results were placed in the following order: regional PTFs work better (>) than PTFs based on the field capacity and wilting point >PTFs based on Atterberg limits> PTF based on particle size distribution. The statistical analysis of the modeling errors by Williams-Klute nonparametric statistical criteria is evidence that models describe best gravity filtration.

Impact of Different Tillage Methods on Silty Loam Luvisol Water Content in Sugar Beet (<i>Beta vulgaris</i> L.) Crop

The regulation of water regime in the soil is the most important task in semi-humid climate with not even precipitation distribution conditions. Reduced or minimum tillage may change soil hydrological properties. The objectives of this study were to investigate the possibilities to manage soil water regime during the whole soil tillage system for sugar beet, which are especially sensitive for water deficit or abundance. Five field experiments were carried out at the Experimental Station of the Lithuanian University of Agriculture (Aleksandras Stulginskis University since 2011) (54°52'N, 23°49'E) during 1995-2010. The soil of the experiments was silty loam Luvisol. In this study we highlighted the reduction of primary soil tillage from deep annual soil ploughing to shallow ploughing, deep and shallow cultivation and no till, comparison of soil ploughing and subsoiling, presowing ploughed or unploughed soil tillage with different cultivators—S-tine, complex, rotary and others, soil compressing with Cambridge and spur rollers before and after sugar beet sowing investigations. According to the results of experiments, reduction of primary soil tillage conserved soil water. The highest storage of soil water in spring was observed in non-reversibly tilled or not tilled soil. Subsoiling led higher water infiltration rate, and top layer of subsoiled soil consisted less moisture content than ploughed. Sugar beet seedbed moisture mostly depended on soil tillage intensity and depth. Presowing rotary tilling was the top tillage method in the case of water preservation in ploughed or unploughed soil. Soil compressing with rollers mostly had negative or low influence on light loam Luvisol moisture content. Rolling with Cambridge roller effected on more rapid water transport from deeper to top sugar beet seedbed layers and higher evaporation rate.

Soil Databases in Support of Pan-European Soil Water Model Development and Applications

Parallel to the advancement of soil hydrological models an evolution of soil datasets available for continental scale applications has taken place in Europe in the last two decades.A milestone in this development was the release of the digital European Soil Database, which includes a full coverage of soil information on a 1:1M scale, a Soil Profile Analytical Database and a Pedotransfer Rules Database. The ESDB allows adaptation of soil hydrological models, such as HYPRES, for spatial representation of soil water properties and for various further modeling applications.The establishment of the European Soil Data Center (ESDAC), hosted in the Joint Research Centre marked the beginning of a new era of soil information provision in Europe. Main aim of the ESDAC is to serve primary and derived, well documented soil information through a harmonized system. The ESDAC - one of the European environmental data centers – is the infrastructural framework to satisfy increased data demand. General (e.g. the ESDB) and thematic (eg. soil organic carbon map; soil salinity map) soil datasets are stored in the ESDAC, which is constantly updated with new data.To answer the increasing need for up-to-date coherent soil data in Europe, the European Commission carried out a topsoil survey in 2009 within the LUCAS (Land use and Land Cover Area Frame Survey). During this survey more than 20,000 soil samples were taken in 25 EU Member States. In 2012 two additional new Member States (Bulgaria and Romania) were sampled applying the same sampling methodology and soil analysis. The LUCAS Soil database, among others, includes measured information on soil attributes which are most needed for soil hydrological models(e.g. particle size distribution, organic carbon and CaCO3 content). Although limited to topsoil, the LUCAS Soil dataset, in combination with other information, has a potential to provide basic soil information for regional scale modeling.Leading institutes in soil hydrological research in Europe have decided to establish a common European Soil Hydropedological Data Inventory (EU-HYDI) in 2012. The EU-HYDI dataset contains information on both basic and hydrological soil properties of over 16,000 soil samples from 18 countries, covering all major biophysical regions of Europe, from Portugal to Russia. The EU-HYDI, being the most comprehensive dataset of its kind is foreseen to yield a series of new research results, including accurate and reliable inputs for soil water models in the coming years. This expected new information, combined with evolving spatial datasets can contribute to a number of applications that build on pan-European soil water models and maps.

The link between peat hydrology and decomposition: Beyond von Post

Summary Hydrology is central to the formation, growth and utilisation of peat soils. However, peat presents a difficult medium in which to measure hydrologic properties, due to its soft structure and high water content. The von Post scale is a widely used measure of the extent of decomposition of peat, which can be applied in the field or the laboratory without specialised equipment. von Post decomposition has been shown to correlate with hydraulic conductivity. However, it is a categorical and subjective measure of decomposition. Technological advances now enable peat chemistry to be described quantitatively and objectively. 13C nuclear magnetic resonance (NMR) is now routinely used to describe peat chemistry, and the capability of this technique has been extended by the development of the molecular mixing model (MMM). The MMM predicts the molecular composition of organic material from the spectral information provided by 13C NMR. We found significant relationships between the hydrologic properties hydraulic conductivity and water yield and peat chemistry as described by 13C NMR and the MMM. These relationships have potential application in all fields where the hydrologic properties of peat soils are of interest (i.e. peat mining, peatland restoration, catchment management) and also in modelling of peatland development and responses to climate change.

Long‐Term Tillage and Crop Rotations for 47–49 Years Influences Hydrological Properties of Two Soils in Ohio

Research is lacking concerning soil water retention (SWR) and infiltration rates (qs) as affected by long‐term tillage and crop rotation. Thus, soil hydrological properties were measured at two long‐term experimental sites near Wooster (49 yr) and Hoytville (47 yr) in central Ohio. The Wooster soil is silt loam in texture and well‐drained, whereas, the Hoytville soil is clay loam in texture and poorly‐drained. Tillage treatments were, no‐tillage (NT), minimum‐tillage (MT), and plow‐tillage (PT), and crop rotations were continuous corn (Zea mays L.), and corn‐soybean (Glycine max L.) in a 2‐yr rotation. Soil hydrological properties were compared with those of adjacent and undisturbed woodlots (WL). The SWR characteristics indicated higher volumetric water content at almost all matric potentials (Ψm) under WL soils than for the three tillage systems at both sites. Among tillage treatments, soils under NT had higher SWR than those under MT and PT for all four (0–10, 10–20, 20–30, and 30–40 cm) depths. In general, long‐term NT contained a higher proportion of macropores (>1000 μm) and micropores (<10 μm), and hence had higher SWR than MT and PT for all depths. The qs was 1.9 and 4.2 times higher in well‐drained soils under NT as compared to those under MT and PT, respectively, and 2.1 and 4.2 times higher in poorly‐drained soils. Two physical based infiltration models, Green‐Ampt and Parlange, fitted the measured infiltration data well with the coefficients of determination (r2) ranging from 0.91 to 0.98, and root mean square error values from 0.06 to 0.66 mm h−1. Results support the conclusion that long‐term (47–49 yr) use of NT practices in both well‐drained and poorly‐drained soils improves SWR, pore‐size distribution, and qs compared to PT and MT practices.

The estimation of soil organic carbon distribution and storage in a small catchment area of the Loess Plateau

The distribution and storage of soil organic carbon serve as basic data for the study of soil productivity, soil hydrological properties, and the balance among carbon-based greenhouse gases. In this study, the organic carbon storage and density distribution characteristics of the soil in the Zhifanggou catchment on the Loess Plateau were studied based on field investigations, laboratory measurement, and geostatistics analysis. A total of 1,282 soil samples were collected from 215 sites in addition to 10 profiles from the catchment. The landuse within the catchment was divided into 4 types: farmland, grassland, shrubland, and woodland. The following results were obtained. 1. In the Zhifanggou catchment, the average organic carbon content of the soil at a depth of 0-100 cm is between 2.81 and 3.50 g. kg(-1). The soil organic carbon content (SOCC) for different landuse types follows the trend shrubland > woodland > grassland > farmland, whereas the soil bulk density follows. The relationship between soil organic carbon content and bulk density follows a power law function. 2. The soil organic carbon density (SOCD) at a depth of 0-100 cm is 1.24-8.34 kg m(-2). The coefficient of variation is 0.40, indicating a moderate variation in the average carbon density of 2.63 kg m(-2). The soil organic carbon density for different landuse types follows the trend shrubland > woodland > grassland > farmland. In the entire catchment, the proportion of average soil organic carbon density at a depth of 0-20 cm is 50.24%, which decreases with soil depth. The spatial distribution of the soil organic carbon density is closely related to the landuse types and topography. 3. The total soil organic carbon storage (SOCS) at a depth of 0-100 cm in the Zhifanggou catchment is 21.84x 10(6) kg. The relationship between soil depth and total organic carbon storage is linear. (c) 2012 Elsevier B.V. All rights reserved.

Soil physical and hydrological properties under three biofuel crops in Ohio

While biofuel crops are widely studied and compared for their energy and carbon footprints, less is known about their effects on other soil properties, particularly hydrologic characteristics. Soils under three biofuel crops, corn (Zea mays), switchgrass (Panicum virgatum), and willow (Salix spp.), were analyzed seven years after establishment to assess the effects on soil bulk density (ρb), penetration resistance (PR), water-holding capacity, and infiltration characteristics. The PR was the highest under corn, along with the lowest associated water content, while PR was 50–60% lower under switchgrass. In accordance with PR data, surface (0–10 cm) bulk density also tended to be lower under switchgrass. Both water infiltration rates and cumulative infiltration amounts varied widely among and within the three crops. Because the Philip model did not fit the data, results were analyzed using the Kostiakov model instead. Switchgrass plots had an average cumulative infiltration of 69 cm over 3 hours with a constant infiltration rate of 0.28 cm min−1, compared with 37 cm and 0.11 cm min−1 for corn, and 26 cm and 0.06 cm min−1 for willow, respectively. Results suggest that significant changes in soil physical and hydrologic properties may require more time to develop. Soils under switchgrass may have lower surface bulk density, higher field water capacity, and a more rapid water infiltration rate than those under corn or willow.

Soil hydrology and soil properties on a partially reforested hillside in the Central Alps

  The landscape on southern exposed hillsides in the inneralpine Vinschgau Valley (Northern Italy) is shaped by many thousand years of cultivation. Phases of intensive land use and deforestation were followed by phases of natural regeneration and later by governmental programs of reforestation. The result in the present landscape is the juxtaposition of reforested woodland (RF-areas) and xeric grassland with steppe species (XG-areas) on the same hillside. The scenic and ecological contrast presents ideal conditions for comparative studies in ecology, forest and soil science. On the side of soil science especially the depth and intensity of soil development on the whole hillside have been underrated, whereas the existence of podzolised soils in the reforested area has mostly been overrated so far. One aim of this study was to investigate differences in the development of soils. A further aim was the comparative investigation of the recent hydrological and physical properties as well as the present dynamics of the hillside soils. With regard to that some results of the field and laboratory studies are presented which are contradictory to results of other studies concerning this region.  

Mapping estimated deep drainage in the lower Namoi Valley using a chloride mass balance model and EM34 data

The Murray Darling Basin accounts for half of all water used for irrigation in Australia. However, improvements in water use efficiency (WUE) are required, owing to increasing demands on water (e.g., environmental flows). This requires data on the spatial distribution of soil-hydrological properties, such as deep drainage (DD). Measuring DD using lysimeters, although accurate, is site-specific. Alternatively, estimates are commonly made using chloride mass balance (CMB) models. Gaining this information across a large area is still problematic due to the prohibitive cost of drilling, sampling, and laboratory analysis. Ancillary data, obtained from electromagnetic (EM) instruments, have been used to add value to a limited number of DD estimates. We evaluated the use of a hierarchical spatial regression technique to map the estimated DD using a steady state CMB model coupled to EM34 measurements. We first compared a standard least squares and a stepwise multiple linear regression model. The former includes the use of EM34 signal data in the horizontal (EM34-10H, EM34-20H, and EM34-40H) and vertical (EM34-10V, EM34-20V, and EM34-40V) dipoles, as well as two trend surface variables (scaled easting and northing). The latter model only includes a statistically significant ancillary variable (EM34-10H) and a trend surface parameter (scaled northing), and we use this to estimate DD across the lower Namoi Valley. EM34 data available on a 1 km grid proved useful for mapping DD on a reconnaissance level, with the results closely related to the physiography. In particular, large DD estimates are associated with the prior stream channels. Conversely, smaller DD estimates characterize the agriculturally significant clay plain which is used extensively for irrigated cotton production. The map of estimated DD will allow improved siting of dams and irrigation fields, as well as indicate where more efficient cropping or irrigation systems can be implemented to increase WUE.

Hydrologic control on redox and nitrogen dynamics in a peatland soil

Soils are a dominant source of nitrous oxide (N2O), a potent greenhouse gas. However, the complexity of the drivers of N2O production and emissions has hindered our ability to predict the magnitude and spatial dynamics of N2O fluxes. Soil moisture can be considered a key driver because it influences oxygen (O2) supply, which feeds back on N2O sources (nitrification versus denitrification) and sinks (reduction to dinitrogen). Soil water content is directly linked to O2 and redox potential, which regulate microbial metabolism and chemical transformations in the environment. Despite its importance, only a few laboratory studies have addressed the effects of hydrological transient dynamics on nitrogen (N) cycling in the vadose zone. To further investigate these aspects, we performed a long term experiment in a 1.5m depth soil column supplemented by chamber experiments. With this experiment, we aimed to investigate how soil moisture dynamics influence redox sensitive N cycling in a peatland soil. As expected, increased soil moisture lowered O2 concentrations and redox potential in the soil. The decline was more severe for prolonged saturated conditions than for short events and at deep than at the soil surface. Gaseous and dissolved N2O, dissolved nitrate (NO3−) and ammonium (NH4+) changed considerably along the soil column profile following trends in soil O2 and redox potential. Hot spots of N2O concentrations corresponded to high variability in soil O2 in the upper and lower parts of the column. Results from chamber experiments confirmed high NO3− reduction potential in soils, particularly from the bottom of the column. Under our experimental conditions, we identified a close coupling of soil O2 and N2O dynamics, both of which lagged behind soil moisture changes. These results highlight the relationship among soil hydrologic properties, redox potential and N cycling, and suggest that models working at a daily scale need to consider soil O2 dynamics in addition to soil moisture dynamics to accurately predict patterns in N2O fluxes.

Monitoring soil-water and displacement conditions leading to landslide occurrence in partially saturated clays

Shallow landslides frequently occur during transient rainfall infiltration and under partially saturated conditions. However, a detailed analysis of what triggers them, particularly in clayey soils, is often hindered by the lack of field measurements. It is uncommon, in fact, to capture their occurrence in an instrumented natural slope. This paper presents results from an integrated field experiment monitoring the soil-water and displacement conditions that lead to the occurrence of a shallow landslide in partially saturated clays. The integration of a variety of experimental techniques allowed for the examination of interplay between soil hydrological and mechanical properties. This research also evaluates a slope stability model based on the suction stress concept. Since the model was applied after the occurrence of the landslide, the results are interpreted as a hind-casting technique for model evaluation. Nevertheless, the detailed field measurements acquired during the monitoring activity and the occurrence of a landslide during the experiment provided significant information on model parameters and data interpretation. The station provides remote satellite monitoring of data on weather variables, soil water content and soil suction. A time domain reflectometry cable was installed vertically to detect potential soil failure. The experimental area had a high probability of landslide occurrence. Indeed, slope failure occurred during the observation period, showing the effectiveness of the station in detecting the occurrence, time and depth of landslides. The landslide was triggered in consequence of changes in suction stress. The failure plane occurred at a depth of 1.4m, corresponding to the interface between a superficial layer of higher permeability of 1 to 1.45m thickness, slipping over a compacted substrate having lower permeability. The analysis allowed for testing of the validity of the model and the description of the triggering mechanisms of the observed shallow landslide in unsaturated conditions, indicating that oscillations in soil matric suction were the dominant variables determining soil failure.

VARIABILITY OF HYDRAULIC CONDUCTIVITY DUE TO MULTIPLE FACTORS

Soil properties are greatly influenced by intrinsic factors of soil formation as well as extrinsic factors associated with land use and management and vary both in time and space. Intrinsic variability is caused by the pedogenesis and usually takes place at large time scales. The variability caused by extrinsic factors could take effect relatively quickly and could not be treated as regionalized. Saturated hydraulic conductivity is one of the most important soil properties for soil-water-plant interactions, water and contaminant movement and retention through the soil profile. It is a critically important parameter for estimation of various other soil hydrological parameters necessary for modeling flow through the naturally unsaturated vadose zone. Among different soil hydrological properties, saturated hydraulic conductivity is reported to have the greatest statistical variability, which is associated with soil types, land uses, positions on landscape, depths, instruments and methods of measurement and experimental errors. The variability of saturated hydraulic conductivity has a profound influence on the overall hydrology of the soil system. Therefore, focus of this review is centered on the variability of saturated/unsaturated hydraulic conductivity due to a large number of factors. This study reviews recent experimental and field studies addressing the measurements and variability of hydraulic conductivity. A synthesis of a large amount of data available in literature is presented and the possible sources of the variability and its implications are discussed. The variability of a soil hydraulic conductivity can be expressed by range, interquartile range, variance and standard deviation, coefficient of variation, skewness and kurtosis. The spatial and temporal variability of hydraulic conductivity and the influences of sample support, measurement devices/methods, soils, land uses and agricultural management on hydraulic conductivity are evaluated. Methods of measurements strongly impact variability, for example, saturated hydraulic conductivity measured using a single ring may produce significantly different mean and standard errors than those measured using a double ring. The sample support can also influence the variability, for example, increasing or decreasing the size of the infiltrometer rings can change the mean and variability of the saturated hydraulic conductivity. Similarly, hydraulic conductivity measured in the field could show a much larger variability than those measured in the laboratory. The spatial and temporal variations of hydraulic conductivity and interactions among soil characteristics, land uses, agricultural management, climatic and environmental conditions and measurement methods are rather complex, which should take into account multiple factors discussed in this review. Decisions and choices made by investigators during sampling, sampling designs, availability of resources, number of investigators involved in sampling and analysis, skill level of investigators, type and quality of tools and equipments used to collect samples and analyses, scale of the domain, availability of time, accessibility of sites, criteria of success and assumptions made for the sampling and analysis have profound influence on the variability of hydraulic conductivity.

Stability of infinite slopes under transient partially saturated seepage conditions

Prediction of the location and timing of rainfall‐induced shallow landslides is desired by organizations responsible for hazard management and warnings. However, hydrologic and mechanical processes in the vadose zone complicate such predictions. Infiltrating rainfall must typically pass through an unsaturated layer before reaching the irregular and usually discontinuous shallow water table. This process is dynamic and a function of precipitation intensity and duration, the initial moisture conditions and hydrologic properties of the hillside materials, and the geometry, stratigraphy, and vegetation of the hillslope. As a result, pore water pressures, volumetric water content, effective stress, and thus the propensity for landsliding vary over seasonal and shorter time scales. We apply a general framework for assessing the stability of infinite slopes under transient variably saturated conditions. The framework includes profiles of pressure head and volumetric water content combined with a general effective stress for slope stability analysis. The general effective stress, or suction stress, provides a means for rigorous quantification of stress changes due to rainfall and infiltration and thus the analysis of slope stability over the range of volumetric water contents and pressure heads relevant to shallow landslide initiation. We present results using an analytical solution for transient infiltration for a range of soil texture and hydrological properties typical of landslide‐prone hillslopes and show the effect of these properties on the timing and depth of slope failure. We follow by analyzing field‐monitoring data acquired prior to shallow landslide failure of a hillside near Seattle, Washington, and show that the timing of the slide was predictable using measured pressure head and volumetric water content and show how the approach can be used in a forward manner using a numerical model for transient infiltration.

Hydrologic properties of biochars produced at different temperatures

Abstract Adding charcoal to soil (biochar soil amendment) can sequester carbon and improve soil performance, although the extent and exact mechanisms of soil improvement are not clear. Additionally, biochar properties can vary significantly with production conditions. Here we characterize the impact of pyrolysis temperature on two important soil hydrologic properties: field capacity and hydrophobicity. We show that pure biochar exhibits a wide range in both properties depending on feedstock and pyrolysis conditions. We find that both properties can be controlled by choice of pyrolysis temperature; 400 °C–600 °C produced biochars with the most desirable hydrological properties (peak field capacity and minimum hydrophobicity). Further, we show that hydrophobicity is strongly correlated ( R 2 = 0.87; p

周氷河地形プロセス研究最前線

Periglacial process studies, which began in the mid-20th century, have greatly advanced in recent years following several breakthroughs. This paper reviews the latest breakthroughs supported by new technologies, themes, and international projects. New technologies have enabled small, high-resolution data loggers to monitor rock and soil movements, and thermal and hydrological properties in polar and alpine areas; enabled geophysical instruments to visualize two- and three- dimensional subsurface structures below periglacial features; and, enabled numerical simulations to predict future landform evolution. In particular, dramatic progress has been achieved in understanding bedrock shattering and falls, soil movements induced by freeze-thaw oscillations, controls on rock glacier creep, critical conditions for ice-wedge cracking, and biogeophysical impacts on non-sorted circles. Two key words, global warming and Mars, are appearing often in periglacial research. High mountains and polar lowlands face the fate of potential natural hazards associated with rock slides, debris flows and thermokarst subsidence, possibly originating from permafrost thawing. High-resolution orbital images and on-site explorations on Mars provide detailed information on small-scale, potential periglacial features, which are the morphologically equivalent of terrestrial counterparts. International collaboration is expected to further promote modeling various periglacial features on a global scale, improve the resolutions of periglacial climate indicators, and increase understanding of past and present Martian environments.

Surface runoff and erosion after prescribed burning and the effect of different fire regimes in forests and shrublands: a review

This paper examines the state of knowledge about the effects of prescribed burning on surface runoff and erosion at point to catchment scales in forests and shrublands. Fires can increase surface runoff and erosion by removing vegetation, changing soil hydrologic properties and providing a readily erodible layer of sediment and ash. Catchment-scale studies in prescribed-burnt areas usually report minimal impacts from the burn. However, measurements at smaller spatial scales suggest that large changes to hydrologic properties and processes do occur, and a debris-flow example from Australia demonstrates that large catchment-scale impacts are possible. It appears that existing catchment-scale studies in prescribed burns do not capture these large events as the sample size (i.e. number of studies) is too small relative to the infrequency of such events. Furthermore, numerous knowledge gaps across all spatial scales limit understanding of the processes contributing to post-prescribed burn runoff and erosion. Understanding the influence of fire regime characteristics on post-fire runoff and erosion is particularly important in the context of prescribed burning, as fire regimes can be manipulated to reduce erosion and water-quality impacts. Therefore, two directions for future research are recommended: (1) process-based studies to understand the factors controlling surface runoff and erosion, particularly in relation to aspects of the fire regime; and (2) landscape-scale surveys to quantify large erosion events.

A hillslope scale comparison of tree species influence on soil moisture dynamics and runoff processes during intense rainfall

Summary This study investigates how different tree species influence soil hydrological properties that are relevant for the rainfall–runoff response of a given soil type. We hypothesize that for the same soil type, tree species that differ in rooting system, water consumption and associated soil fauna and soil flora lead to different soil moisture dynamics and lateral flow processes during rainfall and hence to different runoff responses. To test this hypothesis, we compare soil moisture patterns and interflow at different soil depths in a Norway spruce (Picea abies (L.) Karst) forest and in a European beech (Fagus sylvatica L.) forest during sprinkling experiments on two 6 × 10 m hillslope segments with the same soil type. Spruce with a shallow rooting system and sinkers that remain very shallow on poorly aerated soils and beech with a heart shaped, often deeper rooting system are two of the most important tree species in Central Europe. At each hillslope, volumetric soil water contents were measured in 6 min intervals with 48 TDR waveguides during and after sprinkling with intensities of 100 mm/h and 60 mm/h (for 1 h). The waveguides were installed in 12 soil pits, whereby a single soil pit consisted of four 20 cm buriable waveguides installed in 10 cm, 30 cm, 50 cm and 70 cm soil depth. Surface and shallow interflow at 10 cm soil depth and interflow at soil depths of 30 cm and 60 cm was automatically recorded. Despite the high rainfall intensities, no surface flow was observed in any of the experiments and only small amounts of shallow interflow were measured. Soil moisture patterns of lateral cross sections during and after the sprinkling reveal how tree species can alter runoff dynamics: under spruce, coinciding with rooting patterns, a water table develops in approximately 30 cm soil depth while the soil water content in 50 and 70 cm depth remains low. At the beech site, where coarse roots are found in deeper soil horizons, more water is directed towards deeper, already wetter soil horizons, from where the water table raises into the topsoil with high lateral conductivity. Because the higher water content on top of the stagnic layer allows segments of macropores like old root channels to connect earlier under beech, the beech hillslope exhibits a faster runoff response than the spruce hillslope. A lower water table and a higher macro-porosity makes saturation excess overland flow unlikely under beech. With the shallow water table and a lower available soil volume for preferential flow, a site planted with spruce is prone to saturation excess overland flow under natural rainfall conditions with inflow from the top. The results suggest that different tree species can lead to different rainfall–runoff responses at the same soil type. Though the study site showed minimal variation in soil properties, we cannot exclude that some of the differences in runoff processes we observed are caused by factors other than tree species, because only one large hillslope segment in each forest stand was sprinkled.

Seasonal variation of soil physical properties under different water managements in irrigated rice

While soil porosity and soil hydrological properties are key characteristics that define different soil types, they are influenced by many factors: land use, tillage management, and agricultural practices such as irrigation. As expected, water management impacts the physical properties of soil in irrigated rice significantly; however, the importance of seasonal variation on those soil properties requires further consideration, especially given the period of continuous submersion. In this paper, the different soil physical properties have been studied with two goals in mind: (1) to compare the bulk densities, cumulative pore size distribution curves, and near-saturated hydraulic conductivity values associated with seasonal variation induced by submerging water or rainfall on irrigated rice cultivated under two different water managements and in one rain-fed crop, and (2) to describe and parameterize the relationship that links near-saturated hydraulic conductivity to soil porosity in a generic semi-empirical model independent of treatment differences and seasonal variability. The experiment was conducted in the Piedmont Region (NW Italy) in sandy loam soil on three contiguous fields cultivated as follows: (i) continuous rice in submersion, (ii) continuous rice seeded in dry soil submerged one month after the first field, and (iii) maize in rotation with rice (rain-fed treatment). The physical properties of the soil were measured five times over the year at depths of 0–12 cm and 12–25 cm. Results showed a progressive compaction of the soil and a consequent reduction of the near-saturated hydraulic conductivity due to submersion. Macro- and meso-porosity decreased while micro-porosity increased. At the end of submersion, new large porosity was created and the situation reverted to that noted at the start of the year. The non-submerged field showed a different behaviour; in the absence of submersion, bulk density reduced as a result of rainfall but the effect on the different classes of pores was reversed. Finally, a new semi-empirical model is presented that describes near-saturated hydraulic conductivity as a function of soil porosity.