Soil Hydrological Properties Research Articles

Quantification of biochar effects on soil hydrological properties using meta-analysis of literature data

The use of biochar as a soil amendment had been increasingly advocated for its effects on carbon sequestration and greenhouse gas emission mitigation as well as on improvement of soil fertility. However, lack of a general assessment of biochar effects on soil physical properties made it difficult for the recommendations for its practical use for soil quality improvement in global agriculture. In this study, we performed a meta-analysis of literature data published by October 2015 and quantified biochar effects on selected soil physical properties. The literature data covered a range of feedstocks, pyrolysis temperature, soil and experimental conditions. Results showed that biochar amendment significantly improved all the soil physical properties tested. On average, soil bulk density was significantly reduced by 7.6% whereas soil porosity significantly increased by 8.4%, aggregate stability by 8.2%, available water holding capacity (AWC) by 15.1% and saturated hydraulic conductivity by 25.2%. Furthermore, the changes in soil bulk density were negatively correlated to porosity and AWC. In addition, these effects were greater in coarse textured soils than in fine textured soils. While the size of biochar effect on soil physical properties varied with the amount of biochar added, changes in bulk density only was correlated to application rates of crop residue and wood biochar. Overall, biochar amendments could likely improve soil hydrological properties though varying with biochar and soil conditions. Use of biochar thus could offer a viable option to improve moisture storage and water use efficiency for soils poor in organic carbon in arid/semiarid zones. More studies on dynamics of soil hydrological behaviors following biochar amendment should be deserved in field conditions for a sound understanding of biochar's potential in world agriculture.

Effects of Ant (Formica subsericea) Nests on Physical and Hydrological Properties of a Fine-Textured Soil

Ants are known to preferentially line subsurface nest components with coarser or finer material and may expand or backfill areas as colony size expands and contracts. These modifications may contribute to significant redistribution of soil material, leading to changes in soil physical and hydrological properties. A total of 102 small-volume (∼1 cm³) soil samples were taken from the surface mound, near individual subsurface nest components, and in soils within 1 m of two Formica subsericea colonies to determine how ants affect soil bulk density, organic C content, and particle-size distributions. Overall, the surface mound had higher soil organic C and silt contents than the rest of the nest, soil near galleries in the upper horizons had higher bulk density, and soil near chambers in the lower horizons had higher C values. Ant-modified soil properties extended beyond the extent of the surface mound and could be seen up to 1 m away. Cracks exacerbated by the vertic properties of the surrounding soil provided higher surface area for C mineralization and spaces for ants to travel through, which could explain the lower bulk density outside the nest if ants modify interpedal pore spaces during dry periods. Modeling results from the soils in this study showed that soils with ant-modified properties were associated with more rapid increases and decreases in moisture content than the control soil (i.e., unmodified by ants). Physical and chemical alterations of ant-modified soil diminish with increasing depth, as nest structures decrease in density.

Microclimate buffering and fertility island formation during Juniperus communis ontogenesis modulate competition–facilitation balance

AbstractAimsFacilitation has been reported in a wide range of plant communities, with evidence of positive interactions between beneficiary and nurse plants shifting during their ontogenetic development. This study explored the hypothesis that shrubs of Juniperus communis subsp. nana (thereafter Juniperus) play a crucial role in the successional sequence of plant communities acting as nurse for different species, but only after reaching a certain size. In addition, we examined whether plant–plant interaction changes during ontogenesis of these shrubs in the presence of contrasting disturbance regimes in terms of substrate stability.LocationSibillini National Park, central Italy. The vegetation is semi‐natural dry grasslands (92/43/EEC Habitats Directive: Habitat 6210 ‐ Festuco‐Brometalia).MethodsField measurements were carried out to assess the effects of Juniperus on (1) the distribution of co‐existing vascular species, (2) the above‐ and below‐ground microclimate, and (3) changes in soil fertility and hydrology.ResultsThe capacity of Juniperus shrubs to facilitate heterospecific plants considerably increases during its ontogenetic development, i.e. small shrubs mainly compete for resources with local vegetation, whereas large shrubs act as nurse plants for herbaceous and especially for woody species. The facilitation effect was slight, albeit significantly higher in the disturbed area than in the more stable one. Juniperus was able to promote the formation of an island of fertility under its canopy by accumulating a considerable amount of organic matter, N, P, Ca2+, Mg2+ and K+ in a few decades. Juniperus shrubs improve soil hydrological properties and mitigate the daily range of soil temperature, reducing the exposure of co‐existing plants to high temperatures and water loss through soil evaporation, particularly during the growing periods in spring and summer.ConclusionsThis study demonstrates that biogenic amelioration of soil quality, coupled with the mitigation of below‐canopy microclimatic conditions, control the establishment and growth of co‐existing plants during Juniperus shrub development.

IMatTOUGH: An open-source Matlab-based graphical user interface for pre- and post-processing of TOUGH2 and iTOUGH2 models

TOUGH2 and iTOUGH2 are powerful models that simulate the heat and fluid flows in porous and fracture media, and perform parameter estimation, sensitivity analysis and uncertainty propagation analysis. However, setting up the input files is not only tedious, but error prone, and processing output files is time consuming. In this study, we present an open source Matlab-based tool (iMatTOUGH) that supports the generation of all necessary inputs for both TOUGH2 and iTOUGH2 and visualize their outputs. The tool links the inputs of TOUGH2 and iTOUGH2, making sure the two input files are consistent. It supports the generation of rectangular computational mesh, i.e., it automatically generates the elements and connections as well as their properties as required by TOUGH2. The tool also allows the specification of initial and time-dependent boundary conditions for better subsurface heat and water flow simulations. The effectiveness of the tool is illustrated by an example that uses TOUGH2 and iTOUGH2 to estimate soil hydrological and thermal properties from soil temperature data and simulate the heat and water flows at the Rifle site in Colorado.

Simulated high-latitude soil thermal dynamics during the past 4 decades

Abstract. Soil temperature (Ts) change is a key indicator of the dynamics of permafrost. On seasonal and interannual timescales, the variability of Ts determines the active-layer depth, which regulates hydrological soil properties and biogeochemical processes. On the multi-decadal scale, increasing Ts not only drives permafrost thaw/retreat but can also trigger and accelerate the decomposition of soil organic carbon. The magnitude of permafrost carbon feedbacks is thus closely linked to the rate of change of soil thermal regimes. In this study, we used nine process-based ecosystem models with permafrost processes, all forced by different observation-based climate forcing during the period 1960–2000, to characterize the warming rate of Ts in permafrost regions. There is a large spread of Ts trends at 20 cm depth across the models, with trend values ranging from 0.010 ± 0.003 to 0.031 ± 0.005 °C yr−1. Most models show smaller increase in Ts with increasing depth. Air temperature (Tsub>a) and longwave downward radiation (LWDR) are the main drivers of Ts trends, but their relative contributions differ amongst the models. Different trends of LWDR used in the forcing of models can explain 61 % of their differences in Ts trends, while trends of Ta only explain 5 % of the differences in Ts trends. Uncertain climate forcing contributes a larger uncertainty in Ts trends (0.021 ± 0.008 °C yr−1, mean ± standard deviation) than the uncertainty of model structure (0.012 ± 0.001 °C yr−1), diagnosed from the range of response between different models, normalized to the same forcing. In addition, the loss rate of near-surface permafrost area, defined as total area where the maximum seasonal active-layer thickness (ALT) is less than 3 m loss rate, is found to be significantly correlated with the magnitude of the trends of Ts at 1 m depth across the models (R = −0.85, P = 0.003), but not with the initial total near-surface permafrost area (R = −0.30, P = 0.438). The sensitivity of the total boreal near-surface permafrost area to Ts at 1 m is estimated to be of −2.80 ± 0.67 million km2 °C−1. Finally, by using two long-term LWDR data sets and relationships between trends of LWDR and Ts across models, we infer an observation-constrained total boreal near-surface permafrost area decrease comprising between 39 ± 14 × 103 and 75 ± 14 × 103 km2 yr−1 from 1960 to 2000. This corresponds to 9–18 % degradation of the current permafrost area.

On the hydrological properties of mountain soils, from measurement to the geotechnical implications

Aiming at contributing with a hydrological perspective to the geotechnical investigation in mountain environments, particularly focusing on landslides triggered by perched water tables, we present some findings of a longlasting experimental and theoretical investigation of mountain—soils hydrology. After recalling a theoretical framework suitable to describe the hydrology of shallow, sloping and heterogeneous soils, we discuss some relevant difficulties concerning the measurement of the hydrological properties of heterogeneous and non mature soils, and we finally focus on the role played by the soil heterogeneity in the perched water tables onset.

Research on Urban Heat-Island Effect

Urban heat island (UHI) effect is a kind of heat accumulation phenomenon within urban area due to urban construction and human activities. It is recognized as the most evident characteristic of urban climate. The increase of land surface temperature caused by UHI effect will definitely influence material flow and energy flow in urban ecological systems, as well as alter their structure and functions, exerting a series of ecological and environmental effects on urban climates, urban hydrologic situations, soil properties, atmospheric environment, biological habits, material cycles, energy metabolism and residents’ health. Through the improvement of energy efficiency, urban landscape optimization, green roof construction, high reflectivity material utilization and green land cultivation, UHI effects could be significantly mitigated. Based on remote sensing technology and numerical simulation methods, research on the ecological and environmental effects of UHI has been multi-scaled conducted, providing theoretical reference for the improvement of urban ecological environment and realization of urban sustainable development.

Impact of long term soil management practices on the fertility andweed flora of an almond orchard

Soil management techniques can definitely influence soil quality, and particularly soil organic matter content, biological complexity, structure, and water holding capacity. Tillage may also have a negative effect by increasing erosion and organic matter oxidation processes, which have unavoidable repercussions on fertility. The objective of the current research was to test the effects of five different management techniques applied for 35 years on a rain-fed almond grove (Prunus amygdalus Batsch) in a hot-dry environment on some physicochemical, hydrological, and biological parameters. The following soil management techniques were compared: no-till (NT), with weed control by preemergence herbicides; NT, with chemical weed control by foliar herbicides; NT, with weed control by mowing; tillage, with sowing and field bean green manuring; and conventional tillage. The current survey supplied interesting results, considering the typical soil and climate conditions of the tested area (southern Italy), characterized by high summer temperatures, low rainfall, clay loam soil, and an arable layer of 0.40 m. The most influenced values are those concerning the organic matter due to the supply of biomass resulting from weed mowing or field bean green manuring. The NT system with a single mowing in the spring seems to induce a higher water holding capacity (-15,000 hPa) as compared with the traditionally plowed soil. The biomass incorporation through field bean green manure resulted in a higher available water content (11.82%). All practices favoring an increase in organic matter induced a subsequent increase of microbial biomass content. The number of existing families and species of weed flora was largely influenced by different soil management techniques, as shown by the greater adaptation of grasses to the management practices involving weed control by foliar herbicide or mowing, and of several species associated with the technique involving the application of preemergence herbicides. In general, the almond orchard management involving minimum soil disturbance and the supply of biomass resulting from specially sown cover crops or weed development have shown substantial benefits to the physicochemical, hydrologic, and biologic soil properties.

Mathematical Modeling the Hydrological Properties of Soil for Practical Use in the Land Ecological Management

An original and convenient (from a practical point of view) method to estimate the supply of productive moisture in the soil is offered. The method is based on a physically adequate mathematical model of the soil hydrological properties considering the hysteresis of the water-retention capacity. The computation of the irrigation rates, which is based on such estimates, minimizes the water wastage if the excess of the gravitational water is formed and this water percolates out of the moisturized soil profile under watering conditions. The practical applying of the method is able to optimize the crop irrigation techniques, eliminates any inefficient losses of irrigation water and nutrients (and other agricultural chemicals), promotes the rational usage of the water resources as well as provides developing effective solutions of urgent problems of the land ecological management.

Advanced Soil Hydrological Studies in Different Scales for Sustainable Agriculture

Abstract A comprehensive study of interactive processes between soil, water, plant, animal and atmosphere to protect the natural resources requires knowledge of parameters and processes in different scales. Soil hydrological studies in North-East Germany were carried out in different scales, starting with laboratory, lysimeter measurements and in the field. The measurements of soil hydrological properties were executed with the Extended Evaporation Method (EEM) and the HYPROP device. A method for quantifying deep seepage and solute leaching under field conditions was developed, tested and applied at more than 40 soil hydrological field plots in NE Germany. The hypothesis was confirmed that arable land constitutes the main source of deep drainage and groundwater recharge in Northeast Germany. Deep seepage was strongly reduced under forest. For decision support on landscape renovation and land rededication by afforestation in NE Germany the seepage reduction under forest is to be taken into consideration, especially with respect to the conservation or restoration of wetlands in regions with negative climatic water balance. The EEM and the soil hydrological field method so called “virtual lysimeter” have the potential for the improvement of soil hydrological studies in Asia as a whole.

Water and solute dynamics during rainfall events in headwater catchments in the Central Swiss Alps under the influence of green alder shrubs and wetland soils

AbstractIn the Swiss Alps, shrubs (e.g. Alnus viridis (Chaix) DC) are encroaching into formerly open habitats. The shrub encroachment might affect soil hydrological properties, which in turn influence runoff generation. Moreover, alder species (Alnus spp.) are known to affect chemical soil properties (e.g. increase of nitrate concentrations in the soil solution) and can therefore alter the water quality of stream water. In our study, we investigated four small alpine headwater catchments to assess the influence of shrub encroachment and wetland soils on stream water geochemistry during storm runoff. Stream water was sampled in the growing season of 2010 at hourly intervals during one single rainfall event. Stable isotope values (δ18O) of stream water (ranging from −13.8 to −8.5‰) and rainfall (bulk mean δ18O value of about −5.6‰) during the single event were used to estimate the fraction of event water in stream discharge. Continuously measured electrical conductivity in the growing seasons of 2010 and 2011 was used to infer information on runoff generation during 15 rainfall events. Riparian wetland soils were flushed by a high fraction of event water of up to 72% during peak discharge, which increased the dissolved organic carbon export during the single rainfall event. Besides the atmospheric input through nitrate in rainwater, the expected expansion of green alder shrubs in the region, associated with increasing number and intensity of summer rainfall events in the future, might increase the episodic export of nutrients such as dissolved organic carbon and NO3− from these catchments. Copyright © 2015 John Wiley & Sons, Ltd.

Impact of tree planting configuration and grazing restriction on canopy interception and soil hydrological properties: implications for flood mitigation in silvopastoral systems

Compaction of upper soil layers by intensive sheep grazing has been connected with increased local flood risk in silvopastoral systems. A 12�week field study was conducted at the Henfaes Research Station near Bangor, Wales to compare canopy interception, soil water infiltration, and bulk density between a control pasture and two silvopastoral tree planting configurations: trees clumped in fenced-off ungrazed plots and trees planted evenly and grazed. The study's aim was to characterize the potential of these tree planting configurations to reduce local flood risk. Automated throughfall gauges were installed in each silvopastoral treatment along with a similarly designed control gauge located in the grazed control pasture. Soil water infiltration and bulk density were measured 20 times in a stratified random design for each treatment and control. Results showed that the mean soil infiltration capacity in clumped configuration was 504% greater than the control pasture and 454% greater than the even spaced configuration. Average canopy interception was higher in the clumped configuration (34%) than in the even spaced configuration (28%). Soil bulk density was lower in the clumped configuration (0.87�Mg/m3) than in the control pasture (0.93�Mg/m3) and even spaced configuration (1�Mg/m3). Results suggest that silvopastoral systems are more likely to benefit from clumped and ungrazed tree configurations than from evenly-spaced and grazed tree configurations due to enhanced infiltration, lower soil compaction, and increased canopy interception. Our findings support the growing evidence base that fenced-off tree areas in silvopastoral settings can increase infiltration and thus reduce local flood risk. This article is protected by copyright. All rights reserved.

Irrigation water requirements for seed corn and coffee under potential climate change scenarios

The impact of potential future climate change scenarios on the irrigation water requirements (IRRs) of two major agricultural crops (coffee and seed corn) in Hawai'i was studied using the Irrigation Management System (IManSys) model. In addition to IRRs calculations, IManSys calculates runoff, deep percolation, canopy interception, and effective rainfall based on plant growth parameters, site specific soil hydrological properties, irrigation system efficiency, and long-term daily weather data. Irrigation water requirements of two crops were simulated using historical climate data and different levels of atmospheric CO2 (330, 550, 710 and 970 ppm), temperature (+1.1 and +6.4 °C) and precipitation (±5, ±10 and ±20%) chosen based on the Intergovernmental Panel on Climate Change (IPCC) AR4 projections under reference, B1, A1B1 and A1F1 emission scenarios. IRRs decreased as CO2 emission increased. The average percentage decrease in IRRs for seed corn is higher than that of coffee. However, runoff, rain canopy interception, and deep percolation below the root zone increased as precipitation increased. Canopy interception and drainage increased with increased CO2 emission. Evapotranspiration responded positively to air temperature rise, and as a result, IRRs increased as well. Further studies using crop models will predict crop yield responses to these different irrigation scenarios.

Hydro-depositary and hydro-transmitting properties of soddy-podzolic soils in the course of simulating the water transfer by physically-grounded models

The results of field experiments conducted on the medium loamy agro soddy-podzolic soil showed that due to the hydraulic head of water at the soil surface the moisture movement occurs predominantly through migration ways that deteriorate the hydro-depositary properties of soils. The moisture movement was studied by a special method performed in two soil monoliths identical in size (42 cm in diameter and 60 cm high). The monolith walls were covered by a film, foamed and buried with the view of avoiding the lateral water loss. Both monoliths were simultaneously saturated with water: one of them was under a constant head of water in 5 cm, the other monolith was watered by fine-dispersed sprinkler without the formation of the water layer at the soil surface. The study was aimed at modeling the water movement under conditions of small headed infiltration and without the head of water as well as comparing the calculated and experimental data with the view of assessing the most adequate experimental provision of the model - the major hydrophysical characteristics obtained by empiric methods in the experiment or those calculated on the basis of hydrological constants and soil properties (pedo-transmitting functions). It seemed reasonable to establish that the experimental provision of the model can be shown in the following order: the use of regional pedo-transmitting functions provides better results as compared to the major hydrophysical characteristics, the latter being obtained by the method of tensiometers and capillarometers is better than the pedo-transmitting characteristics used the particle-size distribution as a predictor in Agrotool program (ROSETTA database) as well as those obtained by Voronin’s “secants”.

Corn stover harvest increases herbicide movement to subsurface drains-Root Zone Water Quality Model simulations.

Crop residue removal for bioenergy production can alter soil hydrologic properties and the movement of agrochemicals to subsurface drains. The Root Zone Water Quality Model (RZWQM), previously calibrated using measured flow and atrazine concentrations in drainage from a 0.4 ha chisel-tilled plot, was used to investigate effects of 50 and 100% corn (Zea mays L.) stover harvest and the accompanying reductions in soil crust hydraulic conductivity and total macroporosity on transport of atrazine, metolachlor and metolachlor oxanilic acid (OXA). The model accurately simulated field-measured metolachlor transport in drainage. A 3 year simulation indicated that 50% residue removal reduced subsurface drainage by 31% and increased atrazine and metolachlor transport in drainage 4-5-fold when surface crust conductivity and macroporosity were reduced by 25%. Based on its measured sorption coefficient, approximately twofold reductions in OXA losses were simulated with residue removal. The RZWQM indicated that, if corn stover harvest reduces crust conductivity and soil macroporosity, losses of atrazine and metolachlor in subsurface drainage will increase owing to reduced sorption related to more water moving through fewer macropores. Losses of the metolachlor degradation product OXA will decrease as a result of the more rapid movement of the parent compound into the soil. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Effects of different backfill soils on artificial soil quality for cut slope revegetation: Soil structure, soil erosion, moisture retention and soil C stock

Large-scale railway/highway construction in hilly areas in China has created a number of bare rock cut slopes. Artificial soil is often sprayed onto those slopes to promote revegetation. The artificial soil used is a mixture of backfill soil, humus, straws, soluble chemical fertilizer, composite material and plant seeds. The backfill soil is the most important component of the artificial soil. Knowledge of the changes in the artificial soil quality induced by backfill soil is important for the management of the revegetation of rock cut slopes. This study was conducted to assess the effects of different backfill soils on soil quality parameters and slope restoration parameters, including the particle size distribution, water-stable aggregates, soil organic carbon (SOC), organic carbon fractions, soil water characteristics (SWC), plant coverage, Margalef index and Shannon-Wiener diversity index. In experiment one, the treatments included slopes backfilled with rock fragment (RF), slopes backfilled with agricultural soil (AS) and a natural slope (NS). In experiment two, the treatments were experiment plots with different proportions of agricultural soil to rock fragments. Soils were sampled from the surface layer (0-5 cm) of the slopes. The results indicated that the backfill soil significantly affected the soil structure. RF increased the percentage of large particles (>0.25 mm) and decreased that of microparticles (<0.25 mm). The fractal dimension and the water-stable aggregate content of RF were smaller than those of AS. Moreover, RF exhibited the highest soil destruction rate of soil aggregates among the three treatments. Our findings also indicate that RF conserved a smaller percentage of SOC in less degraded forms (coarse and fine particulate organic matter (POM) fractions) than AS management. At almost all of the soil suctions studied, AS retained more volumetric water content (theta(v)) than RF or NS. The AS soil contained 17.3% more plant available water (PAW) than the RF soil. The plant coverage, Margalef index and Shannon-Winner were investigated to evaluate the restoration of the rock cut slopes compared with natural slopes. The three parameters of the RF were all smaller than those of the AS and NS. Overall, RF exhibited poorer soil structure and hydrological properties, increasing the risk of surface runoff and soil erosion because it had not undergone sufficient soil-forming processes and lacked SOC. Therefore, the use of rock fragments as backfill soil was not helpful for maintaining artificial soil with sufficiently high quality for the slope revegetation. (C) 2015 Elsevier B.V. All rights reserved.

Hydrological factors affecting rainfall-induced shallow landslides: From the field monitoring to a simplified slope stability analysis

Rainfall-induced shallow landslides can seriously affect cultivations and infrastructures and cause human losses. A continuous monitoring of unsaturated soil hydrological properties is needed to understand the effects of pore water pressure and water content on shallow landslides triggering and slope safety factor. In this work, the impact of water content, pore water pressure and hydrological hysteresis on safety factor reconstruction is analyzed by applying two different models (Lu and Godt's and SLIP models) to a monitored slope located in Oltrepò Pavese (Northern Italy). A shallow landslide event in the studied slope during the monitoring allowed for identifying the triggering mechanism and modeling the safety factor changes. The conditions of instability mechanism develop in periods with frequent rainfalls: the uprising of a perched water table in the soil profile gets nil or positive pore water pressure, which, linked with the nil effective soil cohesion of some soil horizons, allows for the shallow landslide triggering. The safety factor trends correctly predicted unstable conditions (safety factor≤1.0) in correspondence of the shallow landslide triggering time on the basis of both water content and pore water pressure. A better prediction gets when the safety factor is modeled considering the hysteresis effects. Modeling the safety factor on the basis of water content can make a good assessment of shallow failures triggering conditions only for failures in unsaturated soils and for completely saturated soils. Instead, considering pore water pressure, it is possible estimating safety factor changes linked with the development of positive pore water pressures, which can be linked in some cases to shallow landslide development.

Sensitivity of LEACHN Model Predictions to Changes in Nitrogen Transformation Rate Constants and Bulk Density

LEACHN is a deterministic model that could be used as a decision support tool to simulate NO 3 -N (nitrate-N) movement through the soil profile in order to make management decisions (i.e., when and how much effluent to apply on land) at effluent-irrigated land disposal sites. However, using this model as a “black box” is not satisfactory, and an in-depth understanding of how the model works is essential before the model is used by the operators and managers of land treatment systems. This article provides a brief description of LEACHN, the N (nitrogen) cycle and soil hydrological properties in LEACHN, and an assessment of LEACHN. This article also provides the key findings of a previous study as background knowledge for the current study. The main focus of this article is to investigate the sensitivity of LEACHN predictions to changes in N transformation rate constants, i.e., K min (mineralization), K nit (nitrification), and K den (denitrification), at field scale, and also to explore the effect of changes in soil bulk density on leachate NO 3 -N concentrations and amount of N leached. This study shows that LEACHN was sensitive to K min values, and this parameter had a significant impact on soil humus-N and the amount of NO 3 -N leached. The total amount of NO 3 -N leached was slightly affected by K nit values. However, the K den value had no significant impact on the total amount of NO 3 -N leached. This analysis also highlighted the need for accurate measurements of bulk density as inputs to the LEACHN model. The optimized LEACHN model (using the best N transformation rate constants values) was tested successfully for two field data sets.

Resolving precipitation induced water content profiles by inversion of dispersive GPR data: A numerical study

Summary Surface-based ground-penetrating radar (GPR) measurements have significant potential for monitoring dynamic hydrologic processes at multiple scales in time and space. At early times during infiltration into a soil, the zone above the wetting front may act as a low-velocity waveguide that traps GPR waves, thereby causing dispersion and making interpretation of the data using standard methods difficult. In this work, we show that the dispersion is dependent upon the distribution of water within the waveguide, which is controlled by soil hydrologic properties. Simulations of infiltration were performed by varying the n-parameter of the Mualem–van Genuchten equation using HYDRUS-1D; the associated GPR data were simulated to evaluate the influence of dispersion. We observed a notable decrease in wave dispersion as the sharpness of the wetting front profile decreased. Given the sensitivity of the dispersion effect to the wetting front profile, we also evaluated whether the water content distribution can be determined through inversion of the dispersive GPR data. We found that a global grid search combined with the simplex algorithm was able to estimate the average water content when the wetted zone is divided into 2 layers. This approach was incapable, however, of representing the gradational nature of the water content distribution behind the wetting front. In contrast, the shuffled complex evolution algorithm was able to constrain a piece-wise linear function to closely match the shallow gradational water content profile. In both the layered and piece-wise linear case, the sensitivity of the dispersive data dropped sharply below the wetting front, which in this case was around 20 cm, i.e., twice the average wavelength, for a 900 MHz GPR survey. This study demonstrates that dispersive GPR data has significant potential for capturing the early-time dynamics of infiltration that cannot be obtained with standard GPR analysis approaches.

Anchor Chaining’s Influence on Soil Hydrology and Seeding Success in Burned Piñon-Juniper Woodlands

Broadcast seeding is one of the most commonly applied rehabilitation treatments for the restoration of burned piñon and juniper woodlands, but the success rate of this treatment is notoriously low. In piñon-juniper woodlands, postfire soil−water repellency can impair seeding success by reducing soil−water content and increasing soil erosion. Implementing anchor chaining immediately after seeding can improve establishment of seeded species by enhancing seed-to-soil contact and may improve restoration success by decreasing soil−water repellency through soil tillage. The objectives of this research were to 1) determine if anchor chaining in postfire pinyon-juniper woodlands diminishes soil−water repellency, and 2) determine meaningful relationships between soil−water repellency, unsaturated hydraulic conductivity [K(h)], and the establishment of seeded and invasive species. Research was conducted on two study sites, each located on a burned piñon-juniper woodland that had severe water repellency and that was aerially seeded. At each location, plots were randomly located in similar ecological sites of chained and unchained areas. At one location, anchor chaining considerably improved soil hydrologic properties, reducing the severity and thickness of the water-repellent layer, and increasing soil K(h) 2- to 4-fold in the first 2 yr following treatment. At this same location, anchor chaining increased perennial grass cover 16-fold and inhibited annual grass and annual forb cover by 5- and 7-fold, respectively. Results from the second site only showed improvements in soil K(h); other hydrologic and vegetative treatment responses were not significantly improved. Overall, this research suggests that anchor chaining has the potential to improve restoration outcomes, though additional research is warranted for understanding the direct impact of anchor chaining on soil−water repellency without the interaction of a seeding treatment.