Decrease In Hydraulic Conductivity Research Articles

Measuring and estimating the hydrological properties of a soil crust

Formation of soil crusts results in reduced infiltration, increased runoff, and reduced rainfall and irrigation efficiency. Improved knowledge of the hydrological properties of soil crusts is required to improve simulation of infiltration and soil water movement in crop-soil-water models. Development of soil crust algorithms in soil water models is limited by a lack of in situ and laboratory approaches for measuring the physical properties of soil crusts. In this study we evaluate a number of novel and modified approaches for determining changes in the hydraulic properties of soil crusts formed in an intensively cropped sandy loam. Physical crust formation over a 71 day period resulted in an increase in surface soil density from 1.17 to 1.51 g cm−3, a reduction in infiltration from 474 to 33.2 mm h−1, and a decrease in unsaturated hydraulic conductivity at −0.05 kPa from 136.9 to 10.14 mm h−1. Whilst the ability to determine the van Genuchten properties of soil crusts was progressed, uncertainty with matching crust thickness to sampling depth, and difficulty measuring the total porosity of soil crusts resulted in error and uncertainty in the estimation of the θs parameter and to a lesser extent the α and ɳ parameters. Further work is required to improve the development of simple, in situ means of measuring or estimating the physical properties of soil crusts.

Using Beerkan experiments to estimate hydraulic conductivity of a crusted loamy soil in a Mediterranean vineyard

Abstract In bare soils of semi-arid areas, surface crusting is a rather common phenomenon due to the impact of raindrops. Water infiltration measurements under ponding conditions are becoming largely applied techniques for an approximate characterization of crusted soils. In this study, the impact of crusting on soil hydraulic conductivity was assessed in a Mediterranean vineyard (western Sicily, Italy) under conventional tillage. The BEST (Beerkan Estimation of Soil Transfer parameters) algorithm was applied to the infiltration data to obtain the hydraulic conductivity of crusted and uncrusted soils. Soil hydraulic conductivity was found to vary during the year and also spatially (i.e., rows vs. inter-rows) due to crusting, tillage and vegetation cover. A 55 mm rainfall event resulted in a decrease of the saturated soil hydraulic conductivity, Ks , by a factor of 1.6 in the inter-row areas, due to the formation of a crusted layer at the surface. The same rainfall event did not determine a Ks reduction in the row areas (i.e., Ks decreased by a non-significant factor of 1.05) because the vegetation cover intercepted the raindrops and therefore prevented alteration of the soil surface. The developed ring insertion methodology on crusted soil, implying pre-moistening through the periphery of the sampled surface, together with the very small insertion depth of the ring (0.01 m), prevented visible fractures. Consequently, Beerkan tests carried out along and between the vine-rows and data analysis by the BEST algorithm allowed to assess crusting-dependent reductions in hydraulic conductivity with extemporaneous measurements alone. The reliability of the tested technique was also confirmed by the results of the numerical simulation of the infiltration process in a crusted soil. Testing the Beerkan infiltration run in other crusted soils and establishing comparisons with other experimental methodologies appear advisable to increase confidence on the reliability of the method that seems suitable for simple characterization of crusted soils.

The semi-analytical productivity equations for vertically fractured coalbed methane wells considering pressure propagation process, variable mass flow, and fracture conductivity decrease

As an unconventional gas resource, coalbed methane (CBM) reservoir has unique flow mechanism and production scheme compared with conventional and other unconventional gas reservoirs. At present, many investigators have done a lot of researches on CBM productivity prediction. However, few studies consider variable mass flow within hydraulic fracture and hydraulic fracture conductivity decrease in the model. Thus in order to accurately forecast gas productivity, the pressure propagation process, gas-water two phase flow in coal formation, stress sensitivity and coal matrix shrinkage in cleat system, variable mass flow within hydraulic fracture, and fracture conductivity decrease should be considered simultaneously when establishing gas production model of CBM wells.In this work, firstly the pressure propagation model is established for vertically fractured CBM wells and vertical CBM wells without fracturing. Secondly, the pressure drop model in the hydraulic fracture is developed considering variable mass flow and conductivity decrease in the hydraulic fracture. Thirdly, based on the pressure propagation model, the dynamic permeability model considering stress sensitivity effect and matrix shrinkage effect, the pressure drop model in the hydraulic fracture considering variable mass flow and conductivity decrease in the hydraulic fracture, a multi-factor coupled CBM well productivity equation is established and solved using numerical methods. Fourthly, the proposed models are validated by numerical simulation and compared with numerical simulation when variable mass flow and conductivity decrease in the hydraulic fracture are considered. Finally, the main factors influencing the productivity of CBM wells are analyzed. Excellent agreements between gas (water) production rate by the proposed models and simulations are obtained when variable mass flow and conductivity decrease in the hydraulic fracture are not considered, indicating that the degradation form of the proposed gas productivity model for CBM wells is rational and accurate to predict the gas production of CBM wells. More importantly, when variable mass flow and conductivity decrease in the hydraulic fracture are considered, the proposed model matches the actual data better than the commercial simulator, exhibiting the superiority of the proposed model in some cases. Preliminary study results show that: the cumulative gas production of CBM wells (CGPC) decreases sharply when permeability is less than 0.5 mD. CGPC increases with increasing the hydraulic fracture length but reaches a plateau after a given value. The stress sensitivity of the cleat system decreases early production, while, the matrix shrinkage improves the productivity of CBM wells at late production stage. The permeability decreasing index of the hydraulic fracture directly leads to the rapid decrease in gas production rate of CBM wells.Because the pressure propagation process, the dynamic permeability, the variable mass flow within the hydraulic fracture, and fracture conductivity decrease are accounted for in the productivity equation of CBM wells, it can predict the actual productivity of CBM wells more accurately and provide a theoretical basis for the development of CBM reservoirs.

복합재해 영향을 고려한 산불 후 산사태 잠재적 피해 위험도 분석

Compound disaster is the type that increases the impact affected by two or more hazard events, and attention to compound disaster and multi-hazards risk is growing due to potential damages which are difficult to predict. The objective of this study is to analyze the possible impacts of post-fire landslide scenario quantitatively by using TRIGRS (Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Analysis), a physics-based landslide model. In the case of wildfire, soil organic material and density are altered, and saturated hydraulic conductivity decrease because of soil exposed to high temperature. We have included the change of soil saturated hydraulic conductivity into the TRIGRS model through literature review. For a case study, we selected the area of 8km2 in Pyeongchang County. The landslide modeling process was calibrated before simulate the post-wildfire impact based on landslide inventory data to reduce uncertainty. As a result, the mean of the total factor of safety values in the case of landslide was 2.641 when rainfall duration is 1 hour with rainfall intensity of 100mm per day, while the mean value for the case of post-wildfire landslide was lower to 2.579, showing potential landslide occurrence areas appear more quickly in the compound disaster scenario. This study can be used to prevent potential losses caused by the compound disaster such as post-wildfire debris flow or landslides.

Effects of Biochar and Synthetic Polymer on the Hydro-Physical Properties of Sandy Soils

Synthetic polymers, such as polyacrylamide (PAM), and biochar are generally used as soil amendments to improve soil properties. This paper explores a laboratory column experiment conducted to investigate the effects of biochar (pyrolysis at 400–450 °C) and polymers, with different application rates, on the hydro-physical properties of sandy soil. The experiment evaluated four rates each of biochar (0.0% (C), 2% (B1), 4% (B2), 6% (B3) and 8% (B4)) and polymers (0.0% (C), 0.2% (P1), 0.4% (P2), 0.6% (P3), and 0.8%(P4)), as well as a mixture of them. The infiltration rate decreased significantly when a mixture of biochar and polymers was adopted. B1 showed a decrease of 32.73% while a mixture of 8% (B4) and (0.8%) P4 exhibited a decrease of 57.31%. The polymers increased the infiltration rate at low concentrations (P1 and P2) and reduced it at high concentrations (P3 and P4). The cumulative evaporation decreased significantly for most treatments. B1 recorded the highest decrease in cumulative evaporation with a percentage decrease of 31.9%. The highest decrease in hydraulic conductivity (Ks) was for B1. However, the mixture of B4 and P4 resulted in the highest increase in soil moisture content at field capacity compared to the control and other treatments. P4 and the mixture of B2 and P2 showed significant (p < 0.05) increases in the percentage of stable aggregate (SA) in fraction size (0.25–0.125 mm). Although the mixture of B4 and P4 had the highest increase in soil moisture content, this study recommends using the B1 treatment on sandy soil in arid environments due to its strong hydro-physical properties and affordability.

Aquaporin regulation in roots controls plant hydraulic conductance, stomatal conductance, and leaf water potential in Pinus radiata under water stress.

Stomatal regulation is crucial for forest species performance and survival on drought-prone sites. We investigated the regulation of root and shoot hydraulics in three Pinus radiata clones exposed to drought stress and its coordination with stomatal conductance (gs ) and leaf water potential (Ψleaf ). All clones experienced a substantial decrease in root-specific root hydraulic conductance (Kroot-r ) in response to the water stress, but leaf-specific shoot hydraulic conductance (Kshoot-l ) did not change in any of the clones. The reduction in Kroot-r caused a decrease in leaf-specific whole-plant hydraulic conductance (Kplant-l ). Among clones, the larger the decrease in Kplant-l , the more stomata closed in response to drought. Rewatering resulted in a quick recovery of Kroot-r and gs . Our results demonstrated that the reduction in Kplant-l , attributed to a down regulation of aquaporin activity in roots, was linked to the isohydric stomatal behaviour, resulting in a nearly constant Ψleaf as water stress started. We concluded that higher Kplant-l is associated with water stress resistance by sustaining a less negative Ψleaf and delaying stomatal closure.

C4 photosynthesis and climate through the lens of optimality

CO2, temperature, water availability, and light intensity were all potential selective pressures that determined the competitive advantage and expansion of the C4 photosynthetic carbon-concentrating mechanism over the last ∼30 My. To tease apart how selective pressures varied along the ecological trajectory of C4 expansion and dominance, we coupled hydraulics to photosynthesis models while optimizing photosynthesis over stomatal resistance and leaf/fine-root allocation. We further examined the importance of nitrogen reallocation from the dark to the light reactions. We show here that the primary selective pressures favoring C4 dominance changed through the course of C4 evolution. The higher stomatal resistance and leaf-to-root ratios enabled by C4 led to an advantage without any initial difference in hydraulic properties. We further predict a reorganization of the hydraulic system leading to higher turgor-loss points and possibly lower hydraulic conductance. Selection on nitrogen reallocation varied with CO2 concentration. Through paleoclimate model simulations, we find that water limitation was the primary driver for a C4 advantage, with atmospheric CO2 as high as 600 ppm, thus confirming molecular-based estimates for C4 evolution in the Oligocene. Under these high-CO2 conditions, nitrogen reallocation was necessary. Low CO2 and high light, but not nitrogen reallocation, were the primary drivers for the mid- to late-Miocene global expansion of C4 We also predicted the timing and spatial distribution for origins of C4 ecological dominance. The predicted origins are broadly consistent with prior estimates, but expand upon them to include a center of origin in northwest Africa and a Miocene-long origin in Australia.

Hydro-mechanical behavior of a lateritic fiber-soil composite as a waste containment liner

In waste disposal landfill projects, the hydraulic conductivity of the barriers is a major consideration. The use of fibers mixed with backfill may improve the overall performance of the barriers. Fiber-soil composites show a more resistant and ductile behavior than the soil alone. The presence of fibers may reduce cracking problems related to shrinkage or traction in liners or covers. In this study, laboratory tests were performed to evaluate the use of fiber-soil composites as a containing barrier. Hydraulic conductivity and diametral-compression tests were carried out on PET fiber reinforced and unreinforced compacted soil specimens. The tests were conducted under confinement conditions similar to those found in the field. Diametral-compression tests were used to induce cracks in the specimens. Hydraulic conductivity was measured at different stages during the diametral loading. In the tests performed under low confinement pressure (10 kPa), the crack openings led to a significant increase in hydraulic conductivity. The results showed that the addition of fibers increases the tensile strength of the soil-fiber mass and delays the opening of cracks. Moreover, in the tests under high confinement pressure (100 kPa), a decrease in hydraulic conductivity occurred at all stages of the diametral load application.

Soil Microbial Populations Shift as Processes Protecting Organic Matter Change During Podzolization

In the upper part of the solum of mineral soils, soil organic and mineral constituents co-evolve through pedogenesis, that in turn impacts the transformation and stabilization of soil organic matter (SOM). Here, we assess the reciprocal interactions between soil minerals, SOM and the broad composition of microbial populations in a 530-year chronosequence of podzolic soils. Five pedons, derived from beach sand, are studied. From young to old soils, net acidification parallels mineral dissolution and the formation of eluvial and illuvial horizons. Organo-mineral associations (OMA) accumulate in the illuvial B horizon of the older soils (330-530 yrs). Apart from contributing to SOM stabilization and protection, organo-mineral compounds progressively fill up interparticle voids. The subsequent loss of porosity leads to horizon induration, decrease of hydraulic conductivity, which promote redoximorphic processes. While recalcitrant SOM is preserved in the topsoil of the old soils, the largest quantity of protected SOM occurs in the indurated, temporalily waterlogged B horizons, through both the OMA accumulation and inhibition of microbial decomposition. SOM protection is thus both time- and horizon-specific. The microbiota also evolve along the chronosequence. Fungi dominate in all horizons of the younger soils and in the topsoil of the older soils, while bacteria prevail in the cemented B horizons of older soils. This shift in microbial community composition is due to the interdependent co-evolution of SOM and minerals during pedogenesis. Our results call for considering the microenvironment and parameters inherent to decomposer microorganisms to understand SOM protection processes in soils.

Effects of lime treatment on the hydraulic conductivity and microstructure of loess

Lime treatment of loess in foundation engineering modifies the soil structure, leading to changes in mechanical and hydraulic properties of soil, which in turn will affect the flow of water and transport of contaminants in the loess. In light of this, it is essential to identify the dominant effects of different lime treatments on hydraulic conductivity, and to ascertain the optimum lime treatment. For this purpose, we investigated the effects of dry density and lime content on changes in hydraulic conductivity and microstructure of loess in Yan’an City, China. The results indicate that hydraulic conductivity has a log negative correlation with dry density, and lime addition can result in a decrease of hydraulic conductivity of loess at the same dry density. Under a given degree of compaction, however, lime addition can lead to a decrease in dry density due to an increase in flocculation and aggregations. The significant decrease of dry density leads to an increase in hydraulic conductivity when lime content (in mass percentage) is lower than 3%. Nevertheless, when lime content is higher than 3%, the reactions between loess particles and lime will be intensified with an increase in lime content, and become the primary factors affecting pore characteristics. These reactions can further decrease the hydraulic conductivity of lime-treated loess, and the lowest hydraulic conductivity was obtained for lime-treated loess with 9% lime content. The excess lime (above 9% lime content) dramatically increased pore size, leading to a significant increase in hydraulic conductivity. Therefore, 9% is the optimum lime content for loess treatment, and the degree of compaction in engineering should be higher than 95%. In addition, statistical analysis of microstructure of lime-treated loess shows that the distribution trends of macro- and meso-pores coincided with that of saturated hydraulic conductivity, which indicates that lime content affects saturated hydraulic conductivity of lime-treated loess by changing the soil structure, especially the properties of pores larger than 8 µm.

Effect of Oil Pollution on Water Characteristics of Loessial Soil

Northern Shaanxi is the birthplace of the oil industry. In the process of large-scale oil and gas transportation and extraction, oil leakage and inevitability will inevitably result, causing some pollution to soil and groundwater. The purpose of this study is to investigate the impact of oil pollution on soil moisture characteristics. In this study, the loessial soil in northern Shaanxi was used as the research object to determine the wettability, capillary water rise and saturated hydraulic conductivity of soils under five different pollution gradients (0%, 0.5%, 1%, 2% and 4%). The results showed that when the soil was polluted by oil, the wettability of the soil will change, resulting in a certain degree of water repellence. In the same rising period, the uncontaminated soil capillary water rose significantly higher than the oil-contaminated soil, and the higher the degree of pollution, the smaller the capillary water rise. Oil pollution made soil saturated hydraulic conductivity decrease with the increase of pollution concentration, although saturated hydraulic conductivity decreases, but for loessial, it was within an order of magnitude.

SOLOS FLORESTAIS EM FRAGMENTO DE FLORESTA URBANA NA MATA DE DOIS IRMÃOS, RECIFE, PERNAMBUCO, BRASIL

O remanescente florestal que compõe o Parque Estadual Dois Irmãos (PEDI) é considerado como um dos maiores fragmentos florestais urbanos do Brasil. Há relatos no Parque da ocorrência de frequentes quedas de árvores sadias em condições naturais na reserva, o que pode comprometer seu equilíbrio natural e sua função como fragmento florestal urbano. É provável que este fenômeno possa estar associado com características químicas e físicas dos solos que compõem o PEDI. A presente pesquisa teve como objetivo avaliar química e fisicamente os solos do PEDI, identificando, mapeando e analisando o solo nas áreas de ocorrência de queda das árvores no locus da pesquisa. Foram mapeados 12 pontos de coleta de amostras em área representativa do PEDI. Amostras deformadas foram coletadas nas profundidades 0-0,10 m; 0,10-0,30 m; e 0,30-0,60 m e amostras não deformadas foram coletadas nas profundidades 0-0,05 m e 0,10-0,15 m. Nas amostras deformadas determinaram-se todos os atributos químicos e parte dos atributos físicos. Em amostras não deformadas determinaram-se apenas atributos físicos. Os solos do PEDI apresentaram baixa fertilidade natural. Mostraram reação ácida e com elevadas concentrações de Al3+ até 0,60 m de profundidade, que podem formar barreiras químicas que prejudicam o crescimento das raízes das plantas e podem estar causando a frequente queda de árvores no Parque. Os solos foram, em sua maioria, classificados como de textura argilosa a muito argilosa, muito permeáveis ao movimento vertical e lateral de água. Apresentaram uma elevada variabilidade na condutividade hidráulica e redução abrupta de umidade volumétrica com aplicação de pequenas tensões em camadas superficiais, além de maior retenção de água pelo Latossolo em subsuperfície. Com a finalidade de ampliar as informações e criar um banco de dados para estudos futuros, sugere–se o monitoramento das espécies mais vulneráveis à queda, além de analisar outros elementos químicos e físicos do solo do PEDI, como a abertura de perfis para compreender a dinâmica das raízes pivotantes.

Impacts of forest conversion and agriculture practices on water pathways in Southern Brazil

AbstractLand‐use/cover change (LUCC), and more specifically deforestation and multidecadal agriculture, is one of the various controlling factors of water fluxes at the hillslope or catchment scale. We investigated the impact of LUCC on water pathways and stream stormflow generation processes in a subtropical region in southern Brazil. We monitored, sampled and analysed stream water, pore water, subsurface water, and rainwater for dissolved silicon concentration (DSi) and 18O/16O (δ18O) signature to identify contributing sources to the streamflow under forest and under agriculture. Both forested and agricultural catchments were highly responsive to rainfall events in terms of discharge and shallow groundwater level. DSi versus δ18O scatter plots indicated that for both land‐use types, two run‐off components contributed to the stream discharge. The presence of a dense macropore network, combined with the presence of a compact and impeding B‐horizon, led to rapid subsurface flow in the forested catchment. In the agricultural catchment, the rapid response to rainfall was mostly due to surface run‐off. A 2‐component isotopic hydrograph separation indicated a larger contribution of rainfall water to run‐off during rainfall event in the agricultural catchments. We attributed this higher contribution to a decrease in topsoil hydraulic conductivity associated with agricultural practices. The chemical signature of the old water component in the forested catchment was very similar to that of the shallow groundwater and the pore soil water: It is therefore likely that the shallow groundwater was the main source of old water. This is not the case in the agricultural catchments where the old water component had a much higher DSi concentration than the shallow groundwater and the soil pore water. As the agricultural catchments were larger, this may to some extent simply be a scale effect. However, the higher water yields under agriculture and the high DSi concentration observed in the old water under agriculture suggest a significant contribution of deep groundwater to catchment run‐off under agriculture, suggesting that LUCC may have significant effects on weathering rates and patterns.

Comparing Transient and Steady-State Analysis of Single-Ring Infiltrometer Data for an Abandoned Field Affected by Fire in Eastern Spain

This study aimed at determining the field-saturated soil hydraulic conductivity, Kfs, of an unmanaged field affected by fire by means of single-ring infiltrometer runs and the use of transient and steady-state data analysis procedures. Sampling and measurements were carried out in 2012 and 2017 in a fire-affected field (burnt site) and in a neighboring non-affected site (control site). The predictive potential of different data analysis procedures (i.e., transient and steady-state) to yield proper Kfs estimates was investigated. In particular, the transient WU1 method and the BB, WU2 and OPD methods were compared. The cumulative linearization (CL) method was used to apply the WU1 method. Values of Kfs ranging from 0.87 to 4.21 mm·h−1 were obtained, depending on the considered data analysis method. The WU1 method did not yield significantly different Kfs estimates between the sampled sites throughout the five-year period, due to the generally poor performance of the CL method, which spoiled the soil hydraulic characterization. In particular, good fits were only obtained in 23% of the cases. The BB, WU2 and the OPD methods, with a characterization based exclusively on a stabilized infiltration process, yielded an appreciably lower variability of the Kfs data as compared with the WU1 method. It was concluded that steady-state methods were more appropriate for detecting slight changes of Kfs in post-fire soil hydraulic characterizations. Our results showed a certain degree of soil degradation at the burnt site with an immediate reduction of the soil organic matter and a progressive increase of the soil bulk density during the five years following the fire. This general impoverishment resulted in a slight but significant decrease in the field-saturated soil hydraulic conductivity.

Evaluating the hydraulic and transport properties of peat soil using pore network modeling and X-ray micro computed tomography

Micro-scale properties of peat pore space and their influence on hydraulic and transport properties of peat soils have been given little attention so far. Characterizing the variation of these properties in a peat profile can increase our knowledge on the processes controlling contaminant transport through peatlands. As opposed to the common macro-scale (or bulk) representation of groundwater flow and transport processes, a pore network model (PNM) simulates flow and transport processes within individual pores. Here, a pore network modeling code capable of simulating advective and diffusive transport processes through a 3D unstructured pore network was developed; its predictive performance was evaluated by comparing its results to empirical values and to the results of computational fluid dynamics (CFD) simulations. This is the first time that peat pore networks have been extracted from X-ray micro-computed tomography (µCT) images of peat deposits and peat pore characteristics evaluated in a 3D approach. Water flow and solute transport were modeled in the unstructured pore networks mapped directly from µCT images. The modeling results were processed to determine the bulk properties of peat deposits. Results portray the commonly observed decrease in hydraulic conductivity with depth, which was attributed to the reduction of pore radius and increase in pore tortuosity. The increase in pore tortuosity with depth was associated with more decomposed peat soil and decreasing pore coordination number with depth, which extended the flow path of fluid particles. Results also revealed that hydraulic conductivity is isotropic locally, but becomes anisotropic after upscaling to core-scale; this suggests the anisotropy of peat hydraulic conductivity observed in core-scale and field-scale is due to the strong heterogeneity in the vertical dimension that is imposed by the layered structure of peat soils. Transport simulations revealed that for a given solute, the effective diffusion coefficient decreases with depth due to the corresponding increase of diffusional tortuosity. Longitudinal dispersivity of peat also was computed by analyzing advective-dominant transport simulations that showed peat dispersivity is similar to the empirical values reported in the same peat soil; it is not sensitive to soil depth and does not vary much along the soil profile.

Hydraulic performance of anionic polymer-treated bentonite-granular soil mixtures

Abstract In this study, hydraulic conductivity and viscosity determination tests were performed on two different bentonite-granular soil mixtures having various amounts of bentonite in order to obtain the optimum mixture to be used as a liner for waste containment facilities. To enhance the hydraulic capability of these mixtures, an anionic polymer was added to the bentonite. In bentonite-granular soil mixtures, two different aggregate compositions were used: A typical aggregate composition used in the production of C20 type concrete with a void ratio of 0.33 and an aggregate composition with a void ratio of 0.21 that was the minimum void ratio determined by testing various granular soil compositions. In these two mixtures, the bentonite content varied from 8 to 15% whereas the polymer content was within the range of 0.5–10% by mass. Test results indicated that intrinsic permeability decreased drastically due to an increase in the bentonite content. 15% bentonite addition caused a decrease of almost 5.5 orders of magnitude when compared with the granular soils without any bentonite content. 2% anionic polymer addition resulted in a decrease of approximately 2.5 orders of magnitude in hydraulic conductivity. However, further increase in polymer content had almost no effect on lowering hydraulic conductivity. 2% polymer addition in bentonite-granular soil mixtures provided hydraulic conductivity values as low as 10−11 m/s. The decrease in hydraulic conductivity was attributed to the increase in the viscosity of the fluid. Due to polymer addition, an inverse relationship existed between hydraulic conductivity and intrinsic permeability. As a result, polymer-treated bentonite-granular soil mixtures can effectively be used as barrier layers in waste containment facilities.

A Study On Influence Of Real Municipal Solid Waste Leachate On Properties Of Soils In Warangal, India

Warangal city generates three hundred tons of garbage daily which is dropped into the Rampur dump yard by Warangal Municipal Corporation (WMC). Dumping of wastes will lead to the formation of leachate which in turn will cause environmental issues like soil and ground water contamination. Chemical analysis of leachate indicates that calcium, chloride, sodium and magnesium are the major ions, along with organic content. This leads to contamination of soil as well as ground water bodies. In this study, authors have attempted to know the behavior of soil under the influence of leachate. Contaminated specimens were prepared and tested for Atterberg limits, shear strength, swell potential and hydraulic conductivity of CH and SC which are present in the dumping yard. Index properties, hydraulic conductivity and swell potential decreased with increase in leachate concentration. Unconfined compressive strength also showed an increase. The decrease in hydraulic conductivity indicated the clogging of pores. In a nutshell, the present work deals with the impact of leachate on the index and engineering properties of CH and red soil.

Inverse estimation of soil hydraulic properties and water repellency following artificially induced drought stress

Abstract Global climate change is projected to continue and result in prolonged and more intense droughts, which can increase soil water repellency (SWR). To be able to estimate the consequences of SWR on vadose zone hydrology, it is important to determine soil hydraulic properties (SHP). Sequential modeling using HYDRUS (2D/3D) was performed on an experimental field site with artificially imposed drought scenarios (moderately M and severely S stressed) and a control plot. First, inverse modeling was performed for SHP estimation based on water and ethanol infiltration experimental data, followed by model validation on one selected irrigation event. Finally, hillslope modeling was performed to assess water balance for 2014. Results suggest that prolonged dry periods can increase soil water repellency. Inverse modeling was successfully performed for infiltrating liquids, water and ethanol, with R2 and model efficiency (E) values both > 0.9. SHP derived from the ethanol measurements showed large differences in van Genuchten-Mualem (VGM) parameters for the M and S plots compared to water infiltration experiments. SWR resulted in large saturated hydraulic conductivity (Ks ) decrease on the M and S scenarios. After validation of SHP on water content measurements during a selected irrigation event, one year simulations (2014) showed that water repellency increases surface runoff in non-structured soils at hillslopes.

Wet front penetration with unsteady state wicking in mortar studied by Magnetic Resonance Imaging (MRI)

The movement of water or water carrying aggressive ions is one of the leading causes of deterioration of concrete structures worldwide. Moisture profiles during unsteady state wicking were determined by one dimensional magnetic resonance imaging of 10 cm mortar specimens. Bulk free induction decay and T 2 lifetime mapping results show a bi-exponential behavior of the MR signal lifetime, T 2 , in all samples, indicating at least two different water populations. From T 2 mapping, the short T 2 lifetime, assigned to interlayer water (water between C–S–H layers), and its associated amplitude are constant along the sample. The long T 2 lifetime and its associated amplitude, related to water in the pore space (micro and macropores), change with local moisture content. To the best of our knowledge, this is the first time that interlayer water has been spatially resolved in MRI of cement-based materials. Gravimetric sorptivity measurements show two regimes of water absorption in the four samples studied. In the first regime, a capillary transport mechanism is dominant in filling the macropores. In the second regime, the interaction between water and solid matrix is postulated to cause swelling that results in a reduction of the water absorption rate. After swelling, diffusion controls pore filling. Water front penetration behavior observed with magnetic resonance imaging, and bulk free induction decay measurements showed changes in behavior that can be linked to sorptivity changes from an initial to a secondary regime. Inverse modelling was conducted to extract the transport properties, using the Hydrus program with the one-dimensional moisture content profiles. Modelling results showed a decrease in saturated hydraulic conductivity with water exposure time.

Elevated ozone concentration decreases whole-plant hydraulic conductance and disturbs water use regulation in soybean plants.

Elevated tropospheric ozone (O3 ) concentration has been shown to affect many aspects of plant performance including detrimental effects on leaf photosynthesis and plant growth. However, it is not known whether such changes are accompanied by concomitant responses in plant hydraulic architecture and water relations, which would have great implications for plant growth and survival in face of unfavorable water conditions. A soybean (Glycine max (L.) Merr.) cultivar commonly used in Northeast China was exposed to non-filtered air (NF, averaged 24.0nl l-1 ) and elevated O3 concentrations (eO3 , 40 nl l-1 supplied with NF air) in six open-top chambers for 50 days. The eO3 treatment resulted in a significant decrease in whole-plant hydraulic conductance that is mainly attributable to the reduced hydraulic conductance of the root system and the leaflets, while stem and leaf petiole hydraulic conductance showed no significant response to eO3 . Stomatal conductance of plants grown under eO3 was lower during mid-morning but significantly higher at midday, which resulted in substantially more negative daily minimum water potentials. Moreover, excised leaves from the eO3 treated plants showed significantly higher rates of water loss, suggesting a lower ability to withhold water when water supply is impeded. Our results indicate that, besides the direct detrimental effects of eO3 on photosynthetic carbon assimilation, its influences on hydraulic architecture and water relations may also negatively affect O3 -sensitive crops by deteriorating the detrimental effects of unfavorable water conditions.