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  • 1
    Language: English
    In: Journal of Hydrology, July 2016, Vol.538, pp.339-354
    Description: The objective of this study is to assess recharge rates and their timing under layered loessial deposits at the edge of arid zones. Particularly, this study is focused on the case of the coastal plain of Israel and Gaza. First, results of a large-scale field infiltration test were used to calibrate the van Genuchten parameters of hydraulic properties of the loessial sediments using HYDRUS (2D/3D). Second, optimized soil hydraulic parameters were used by HYDRUS-1D to simulate the water balance of the sandy-loess sediments during a 25-year period (1990–2015) for three environmental conditions: bare soil, and soil with both sparse and dense natural vegetation. The best inverse parameter optimization run fitted the infiltration test data with the RMSE of 0.27 d (with respect to a moisture front arrival) and of 96%. The calibrated model indicates that hydraulic conductivities of the two soil horizons, namely sandy loam and sandy clay loam, are 81 cm/d and 17.5 cm/d, respectively. These values are significantly lower than those previously reported, based on numerical simulations, for the same site. HYDRUS-1D simulation of natural recharge under bare soil resulted in recharge estimates (to the aquifer) in the range of 21–93 mm/yr, with an average recharge of 63 mm/yr. Annual precipitation in the same period varied between 100 and 300 mm/yr, with an average of 185 mm/yr. For semi-stabilized dunes, with 26% of the soil surface covered by local shrub ( ), the mean annual recharge was 28 mm. For the stabilized landscape, with as much as 50% vegetation coverage, it was only 2–3 mm/yr. In other words, loessial sediments can either be a source of significant recharge, or of no recharge at all, depending on the degree of vegetative cover. Additionally, the time lag between specific rainy seasons and corresponding recharge events at a depth of 22 m, increased from 2.5 to 5 years, and to about 20 years, respectively, with an increasing vegetative cover. For this reason, and also likely due to a great depth of loessial sediments, no correlation was found between annual recharge and annual precipitations of the same year or subsequent years. Similarly, no differences were found between summer and winter recharge fluxes. Instead, numerical simulations indicated continuous year-round recharge of the aquifer. We conclude that the layered subsurface acts as a short-term (annual) and long-term (multi-annual) buffer to smooth sudden precipitation/infiltration events. Vegetation conditions can help in predicting long-term recharge rates (as percentage of annual precipitation), which in turn need to be considered when assigning recharge characteristics in regional assessments and models.
    Keywords: Infiltration Test ; Groundwater Recharge ; Arid Vegetation ; Hydrus ; Sandy Loess ; Layered Profile ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 2
    In: Journal of Geophysical Research: Biogeosciences, September 2011, Vol.116(G3), pp.n/a-n/a
    Description: Soil water dynamics and drainage are key abiotic factors controlling losses of atmospherically deposited N in Southern California. In this paper soil N leaching and trace gaseous emissions simulated by the DAYCENT biogeochemical model using its original semi‐dynamic water flow module were compared to that coupled with a finite element transient water flow module (HYDRUS), for two mixed conifer forests with annual deposition rates of about 70 and 9 kg N ha, in the San Bernardino National Forest. Numerical solution of the Richards equation implemented in HYDRUS water module could improve response of surface soil water dynamics to precipitation pattern, compared to the original, and consequently it resulted in annual N gaseous emission loss about 1.5 ∼ 2 times higher. While the two flow modules predicted similar amounts of annual water drainage, the HYDRUS water module simulated more frequent, but smaller drainage fluxes, which favors soil mineralization and downward transport. In normal precipitation years, annual leaching losses predicted by the HYDRUS coupled DAYCENT model was about 5–18 kg N ha higher due to different temporal patterns of daily water drainage. In dry and wet years, leaching losses were similar. Our analysis suggests that it is necessary to fully capture dynamics of transient water flow (e.g., by numerically solving the transient Richards equation) in order to adequately estimate soil N gaseous emissions and N transport and thus leaching, although it requires more computational resources while the uncertainty in model improvement is still large due to lack of measurements. Daily N loss estimation requires transient soil water model Semidynamic water module could underestimate N emission and leaching
    Keywords: Drainage ; Nitrogen Deposition ; Semidynamic Soil Water Model ; Soil N Losses ; Soil Water Dynamics ; Transient Soil Water Model
    ISSN: 0148-0227
    ISSN: 21698953
    E-ISSN: 2156-2202
    E-ISSN: 21698961
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  • 3
    Language: English
    In: Water Research, 01 February 2017, Vol.109, pp.358-366
    Description: Saturated soil column experiments were conducted to investigate the transport, retention, and release behavior of a low concentration (1 mg L ) of functionalized C-labeled multi-walled carbon nanotubes (MWCNTs) in a natural soil under various solution chemistries. Breakthrough curves (BTCs) for MWCNTS exhibited greater amounts of retardation and retention with increasing solution ionic strength (IS) or in the presence of Ca in comparison to K , and retention profiles (RPs) for MWCNTs were hyper-exponential in shape. These BTCs and RPs were well described using the advection-dispersion equation with a term for time- and depth-dependent retention. Fitted values of the retention rate coefficient and the maximum retained concentration of MWCNTs were higher with increasing IS and in the presence of Ca in comparison to K . Significant amounts of MWCNT and soil colloid release was observed with a reduction of IS due to expansion of the electrical double layer, especially following cation exchange (when K displaced Ca ) that reduced the zeta potential of MWCNTs and the soil. Analysis of MWCNT concentrations in different soil size fractions revealed that 〉23.6% of the retained MWCNT mass was associated with water-dispersible colloids (WDCs), even though this fraction was only a minor portion of the total soil mass (2.38%). More MWCNTs were retained on the WDC fraction in the presence of Ca than K . These findings indicated that some of the released MWCNTs by IS reduction and cation exchange were associated with the released clay fraction, and suggests the potential for facilitated transport of MWCNT by WDCs.
    Keywords: Multi-Walled Carbon Nanotubes ; Soil ; Breakthrough Curves ; Retention Profiles ; Cation Exchange ; Soil Fractionation ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 4
    Language: English
    In: Journal of Hydrology, May 2017, Vol.548, pp.263-277
    Description: Mechanistic models have proven to be accurate tools for the numerical analysis of the hydraulic behavior of Low Impact Development (LIDs) techniques. However, their widespread adoption has been limited by their computational cost. In this view, surrogate modeling is focused on developing and using a computationally inexpensive of the model. While having been previously applied to various water-related and environmental modeling problems, no studies have used surrogate models for the analysis of LIDs. The aim of this research thus was to investigate the benefit of surrogate-based modeling in the numerical analysis of LIDs. The kriging technique was used to approximate the deterministic response of the widely used mechanistic model HYDRUS-2D, which was employed to simulate the variably-saturated hydraulic behavior of a contained stormwater filter. The Nash-Sutcliffe efficiency ( ) index was used to compare the simulated and measured outflows and as the variable of interest for the construction of the response surface. The validated kriging model was first used to carry out a Global Sensitivity Analysis of the unknown soil hydraulic parameters of the filter layer, revealing that only the shape parameter α and the saturated hydraulic conductivity significantly affected the model response. Next, the Particle Swarm Optimization algorithm was used to estimate their values. The value of 0.85 indicated a good accuracy of estimated parameters. Finally, the calibrated model was validated against an independent set of measured outflows with a value of 0.8, which again corroborated the reliability of the surrogate-based optimized parameters.
    Keywords: Urban Hydrology ; Surrogate-Based Modeling ; Sensitivity Analysis ; Infiltration ; Lids ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 5
    Language: English
    In: Atmospheric Environment, February 2013, Vol.66, pp.33-40
    Description: The increasing registration of the fumigant methyl iodide within the USA has led to more concerns about its toxicity to workers and bystanders. Emission mitigation strategies are needed to protect the public and environmental health while providing effective pest control. The effectiveness of various methods on emissions reduction and pest control was assessed using a process-based mathematical model in this study. Firstly, comparisons between the simulated and laboratory measured emission fluxes and cumulative emissions were made for methyl iodide (MeI) under four emission reduction treatments: 1) control, 2) using soil with high organic matter content (HOM), 3) being covered by virtually impermeable film (VIF), and 4) irrigating soil surface following fumigation (Irrigation). Then the model was extended to simulate a broader range of emission reduction strategies for MeI, including 5) being covered by high density polyethylene (HDPE), 6) increasing injection depth from 30 cm to 46 cm (Deep), 7) HDPE + Deep, 8) adding a reagent at soil surface (Reagent), 9) Reagent + Irrigation, and 10) Reagent + HDPE. Furthermore, the survivability of three types of soil-borne pests (citrus nematodes [ ], barnyard seeds [ ], fungi [ ]) was also estimated for each scenario. Overall, the trend of the measured emission fluxes as well as total emission were reasonably reproduced by the model for treatments 1 through 4. Based on the numerical simulation, the ranking of effectiveness in total emission reduction was VIF (82.4%) 〉 Reagent + HDPE (73.2%) 〉 Reagent + Irrigation (43.0%) 〉 Reagent (23.5%) 〉 Deep + HDPE (19.3%) 〉 HOM (17.6%) 〉 Deep (13.0%) 〉 Irrigation (11.9%) 〉 HDPE (5.8%). The order for pest control efficacy suggests, VIF had the highest pest control efficacy, followed by Deep + HDPE, Irrigation, Reagent + Irrigation, HDPE, Deep, Reagent + HDPE, Reagent, and HOM. Therefore, VIF is the optimal method disregarding the cost of the film since it maximizes efficacy while minimizing volatility losses. Otherwise, the integrated methods such as Deep + HDPE and Reagent + Irrigation, are recommended. ► The effects of various methods on fumigant emissions and pest control were assessed using a model. ► The models provide reasonably accurate emissions of methyl iodide. ► Being covered by VIF is the best method among nine treatments, followed by integrated methods.
    Keywords: Methyl Iodide ; Emission ; Modeling ; Pest Control ; Pesticide ; Engineering ; Environmental Sciences
    ISSN: 1352-2310
    E-ISSN: 1873-2844
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  • 6
    Language: English
    In: Journal of Hydrology, January 2015, Vol.520, pp.123-133
    Description: As an important part of a transition zone surrounding a lake, lakeshore plays a critical role in connecting hydrology and biochemistry between surface water and groundwater. The shape, slope, subsurface features, and seepage face of a lakeside slope have been reported to affect water and nutrient exchange and consequently the water quality of near-shore lake water. Soil tank experiments and Hydrus-2D model simulations were conducted to improve our understanding of the influence of slope revetment materials (SRMs) on water flow and solute transport in a lakeshore zone. The low hydraulic conductivity of SRMs affected flow patterns in the lakeshore zone and resulted in a local increase of the groundwater table near the slope face. Water and solute flux distributions on the slope face under bare-slope conditions followed an exponential function. Fluxes were concentrated within a narrow portion of the slope surface near the intersection point between the lake water level and the slope face. Surface pollutants (for example from fishponds and paddy fields surrounding a lake) were transported into the lake along shallow groundwater through both unsaturated and saturated zones. The SRMs on the slope face affected the ratio of water and solute fluxes in the unsaturated zone, increasing along with the decline of the hydraulic conductivity of SRMs. Furthermore, as the hydraulic conductivity of SRMs decreased, the retention time and the potential for oxygen reduction correspondingly increased, which affected the nitrogen transport and transformations in the lakeshore zone. Simulated and experimental results indicate that if concrete along the shoreline of Lake Taihu is replaced with a relatively high-conductivity lime or the slope is left bare, water fluxes will increase less than solute fluxes, which will rise significantly, in particular in the unsaturated zone and along the seepage face. On the other hand, the largest water and solute fluxes along the shoreline for the bare and lime-slope conditions will be located higher at the slope than for the concrete-slope conditions. Hydrus-2D provided a good description of complicated hydrodynamic and solute transport/transformation conditions in the lakeshore zone.
    Keywords: Lakeshore ; Groundwater ; Flow Regime ; Nitrate ; Slope Revetment Material ; Hydrus-2d ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 7
    Language: English
    In: Environmental Pollution, May 2018, Vol.236, pp.195-207
    Description: Packed column experiments were conducted to investigate the transport and blocking behavior of surfactant- and polymer-stabilized engineered silver nanoparticles (Ag-ENPs) in saturated natural aquifer media with varying content of material 〈 0.063 mm in diameter (silt and clay fraction), background solution chemistry, and flow velocity. Breakthrough curves for Ag-ENPs exhibited blocking behavior that frequently produced a delay in arrival time in comparison to a conservative tracer that was dependent on the physicochemical conditions, and then a rapid increase in the effluent concentration of Ag-ENPs. This breakthrough behavior was accurately described using one or two irreversible retention sites that accounted for Langmuirian blocking on one site. Simulated values for the total retention rate coefficient and the maximum solid phase concentration of Ag-ENPs increased with increasing solution ionic strength, cation valence, clay and silt content, decreasing flow velocity, and for polymer-instead of surfactant-stabilized Ag-ENPs. Increased Ag-ENP retention with ionic strength occurred because of compression of the double layer and lower magnitudes in the zeta potential, whereas lower velocities increased the residence time and decreased the hydrodynamics forces. Enhanced Ag-ENP interactions with cation valence and clay were attributed to the creation of cation bridging in the presence of Ca . The delay in breakthrough was always more pronounced for polymer-than surfactant-stabilized Ag-ENPs, because of differences in the properties of the stabilizing agents and the magnitude of their zeta-potential was lower. Our results clearly indicate that the long-term transport behavior of Ag-ENPs in natural, silicate dominated aquifer material will be strongly dependent on blocking behavior that changes with the physicochemical conditions and enhanced Ag-ENP transport may occur when retention sites are filled.
    Keywords: Engineered Silver Nanoparticles ; Contaminant Transport ; Groundwater ; Column Experiments ; Blocking ; Engineering ; Environmental Sciences ; Anatomy & Physiology
    ISSN: 0269-7491
    E-ISSN: 1873-6424
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  • 8
    Language: English
    In: Soil Science Society of America journal, 2012, Vol.76(6), pp.1999-2005
    Description: It has recently been proposed to couple the Beerkan method with the Beerkan Estimation of Soil Transfer parameters (BEST) algorithm to facilitate the estimation of soil hydraulic parameters from an infiltration experiment. Although this simplified field procedure is relatively rapid and inexpensive, it has been doubted if the Beerkan method can represent a valid and reliable alternative to other conventional methods. This study explored the impact of the tortuosity parameter (p) and two infiltration constants (β and γ) included in the BEST algorithm using a sensitivity analysis applied to three experimental soils. The analysis that was validated using the numerical model HYDRUS 2D/3D indicates that the tortuosity is relatively insignificant compared to parameters β and γ that have a large impact on the estimation procedure. ; p. 1999-2005.
    Keywords: Soil Hydraulic Properties ; Mathematical Models ; Algorithms
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 9
    Language: English
    In: Journal of hazardous materials, 2012, Vol.243, pp.223-231
    Description: Organic amendments often represent a source of trace metals (TMs) in soils, which may partly leach into the groundwater. The objectives of this study were (1) to validate Hydrus-2D for modeling the transport of Zn and Cu in an Alfisol amended with pig slurry (PS) by comparing numerical simulations and experimental field data, and (2) to model the next 50 years of TM movements under scenarios of suspended or continued PS amendments. First, between 2000 and 2008, we collected detailed Zn and Cu data from a soil profile in Santa Maria, Brazil. Two hypotheses about Zn and Cu reactivity with the solid phase were tested, considering physical, hydraulic, and chemical characteristics of six soil layers. Using a two-site sorption model with a sorption kinetic rate adjusted based on laboratory EDTA extractions, Hydrus simulations of the vertical TM transport were found to satisfactorily describe the soil Zn and Cu concentration profiles. Second, the long-term fate of Zn and Cu in the soil was assessed using the validated parameterized model. Numerical simulations showed that Zn and Cu did not present risks for groundwater pollution. However, future Cu accumulation in the surface soil layer would exceed the Brazilian threshold for agricultural soils. ; p. 223-231.
    Keywords: Zinc ; Sorption ; Soil Profiles ; Copper ; Agricultural Soils ; Field Experimentation ; Groundwater Contamination ; Alfisols ; Edta (Chelating Agent) ; Groundwater ; Models ; Risk ; Pig Manure ; Swine
    ISSN: 0304-3894
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 10
    Language: English
    In: Journal of Hazardous Materials, December 2012, Vol.243, pp.223-231
    Description: ► We performed a model validation of Zn and Cu settings in a pig-slurry amended soil. ► A two-site model with reduced kinetic constants present the best fit with field data. ► Future 50-years scenarios related to the pig slurry applications were simulated. ► Downward Zn and Cu solute fluxes will not present risk to groundwater pollution. ► Continuous pig slurry amendments will lead to a high Cu accumulation on soil surface. Organic amendments often represent a source of trace metals (TMs) in soils, which may partly leach into the groundwater. The objectives of this study were (1) to validate Hydrus-2D for modeling the transport of Zn and Cu in an Alfisol amended with pig slurry (PS) by comparing numerical simulations and experimental field data, and (2) to model the next 50 years of TM movements under scenarios of suspended or continued PS amendments. First, between 2000 and 2008, we collected detailed Zn and Cu data from a soil profile in Santa Maria, Brazil. Two hypotheses about Zn and Cu reactivity with the solid phase were tested, considering physical, hydraulic, and chemical characteristics of six soil layers. Using a two-site sorption model with a sorption kinetic rate adjusted based on laboratory EDTA extractions, Hydrus simulations of the vertical TM transport were found to satisfactorily describe the soil Zn and Cu concentration profiles. Second, the long-term fate of Zn and Cu in the soil was assessed using the validated parameterized model. Numerical simulations showed that Zn and Cu did not present risks for groundwater pollution. However, future Cu accumulation in the surface soil layer would exceed the Brazilian threshold for agricultural soils.
    Keywords: Two-Site Sorption Model ; Solute Movement ; Hydrus-2d ; Trace Metals ; Groundwater Pollution ; Engineering ; Law
    ISSN: 0304-3894
    E-ISSN: 1873-3336
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