Internal Redistribution Of Water Research Articles

Two-phase transport in a cemented waste package considering spatio-temporal evolution of chemical conditions

The long-term evolution of cemented waste packages is governed by (bio)chemical reactions between waste, cement, and barrier materials, and by transport processes inside the waste package and through openings in the waste package hull. Inside a waste package, gases can be generated by pH-dependent anoxic corrosion of metals and the degradation of organic matter. The (bio)chemical reactions consume water and will not proceed under dry conditions. The degradation of cementitious materials lowers the alkaline pH of the pore water. The modeling of such a complex feedback system shows that the internal structure of a waste package and the exchange of mass with the environment (boundary conditions) are major factors that determine the importance of process couplings. The (bio)chemical reactions are controlled by internal re-distribution of water predominantly via vapor transport. Calculated gas generation rates were found to be affected by dry-out processes inside the drum.

The mechanism and effects of subgrade fluidisation under ballasted railway tracks

The rapid growth in railway infrastructure and the construction of high-speed heavy-haul rail network, especially on ground that is basically unsuitable, poses challenges for geotechnical engineers because a large part of the money invested in the development of railway lines is often spent on track maintenance. In fact around the world, the mud pumping of subgrade fines is one of the common reasons why track performance deteriorates and track stability is hindered. This article presents a series of laboratory tests to examine following aspects of mud pumping: (1) the mechanisms of subgrade fluidisation under undrained condition, (2) the effects of mud pumping on the engineering characteristics of ballast, and (3) the use of vertical drains to stabilize subgrade under cyclic loads. The undrained cyclic triaxial testing on vulnerable soft subgrade was performed by varying the cyclic stress ratio (CSR) from 0.2 to 1.0 and the loading frequency f from 1.0 to 5.0 Hz. It is seen from the test results that for a specimen compacted at an initial dry density of 1790 kg/m3, the top portion of the specimen fluidises at CSR = 0.5, irrespective of the applied loading frequency. Under cyclic railway loading, the internal redistribution of water at the top of the subgrade layer softens the soil and also reduces its stiffness. In response to these problems, this paper explains how the inclusion of vertical drains in soft subgrade will help to prevent mud pumping by alleviating the build-up of excess pore pressures under moving train loads.

Sap Flow Measurements in a Socotra Dragon’s Blood Tree (Dracaena cinnabari) in its Area of Origin

For the first time, in situ field measurements of sap flow were conducted in adult Dracaena cinnabari plant native to the arid tropical climate of Socotra Island. The heat field deformation (HFD) method was applied using both single and multi-point sensors to study azimuthal and radial sap flow variability in stem, roots and first-order branches over two weeks during a winter monsoon. The main aim of this work was to monitor sap flow in adult D. cinnabari in-situ to better understand its physiological adaptation to extreme arid environments. The second aim was to compare our results with earlier sap flow measurements in adult D. draco uing the same HFD method. The last question we wanted to answer was comparison of sap flow measurements in both, young and adult Dracaena species. We found that sap flow magnitude is low and of a similar range in all observed D. species. High sap flow variability was recorded in different parts of adult D. cinnabari plant which changed throughout the day responding to interplay between intrinsic and extrinsic water potential gradients induced by sunlight. Maximum sap flow levels had variable pattern around stem in response to sun exposure, similarly as it was observed in adult D. draco plant. Sensors installed tangentially in stem xylem showed that water transport in adult D. cinnabari may move in lateral direction. This work also presents several methodological aspects detected from earlier observations of dicots which proved to be more pronounced in adult D. species. These methodologies relate to interpreting negative sap flow rates in conjunction with established axial flow reversal during hydraulic redistribution usually occurring under low evaporative demands and dry soil. Conversely, flow reversal during the day under high evaporative demands and wet soil may designate lateral water movement induced by internal water redistribution.

Water fluxes between inter-patches and vegetated mounds in flat semiarid landscapes

It has been assumed that bare soil (BS) inter-patches in semi arid spotted vegetation behave as sources of water to near vegetated soil (VS) patches. However, little evidence has been gained from direct measurements of overland and infiltration water fluxes between bare soil inter-patches and shrub mounds at a scale compatible with available high resolution imagery and hydrological modeling techniques. The objective of this study is to address the thin scale internal redistribution of water between BS inter-patches and vegetated mounds at relatively flat spotted semiarid landscapes. The relation between plant cover, topography and runoff was inspected with non-parametric association coefficients based on high resolution remotely sensed imagery, ground truth topographic elevation and spatial-explicit field data on potential runoff. Measurements of advective flows at the same spatial scale were carried out at micro-plots of BS and shrub mounds. Water fluxes between BS inter-patch and a shrub mound were simulated under varying typical Patagonian rainfall scenarios with an hydrological model. Results obtained revealed that the soil properties, infiltration and overland flow metrics at the mounds and inter-patches exhibit spatially and dynamic variable hydraulic properties. High micro-topographic roughness and depression storage thickened overland flow depth at VS patches. At BS inter-patches prevailing low slopes and depression storage were found to be important variables attenuating the surface runoff. At both rainfall scenarios simulated, the soil under the shrub mound accumulated more moisture (from direct rain) and reached saturation long before this occurred in BS nearby inter-patch area. Overland flow at the inter-patch was attenuated as it reached the border of the patch, diverging from the latter as it followed the (small) topographic gradient. The overland flow generated inside the vegetated mound was effectively retained at the typical Summer rainfall scenario; while several threads of runoff were routed outside the mound at the typical Winter rainfall scenario. The results here shown fail to detect: (a) enough runoff momentum that could route runon onto the vegetated mounds and (b) a contrast in infiltration rates between BS and the vegetated mound enough to lead to a free-surface gradient in ponded water that could inundate the mound.

Surfactant-induced flow compromises determination of air-water interfacial areas by surfactant miscible-displacement

Surfactant miscible-displacement (SMD) column experiments are used to measure air-water interfacial area (AI) in unsaturated porous media, a property that influences solute transport and phase-partitioning. The conventional SMD experiment results in surface tension gradients that can cause water redistribution and/or net drainage of water from the system (“surfactant-induced flow”), violating theoretical foundations of the method. Nevertheless, the SMD technique is still used, and some suggest that experimental observations of surfactant-induced flow represent an artifact of improper control of boundary conditions. In this work, we used numerical modeling, for which boundary conditions can be perfectly controlled, to evaluate this suggestion. We also examined the magnitude of surfactant-induced flow and its impact on AI measurement during multiple SMD flow scenarios. Simulations of the conventional SMD experiment showed substantial surfactant-induced flow and consequent drainage of water from the column (e.g., from 75% to 55% SW) and increases in actual AI of up to 43%. Neither horizontal column orientation nor alternative boundary conditions resolved surfactant-induced flow issues. Even for simulated flow scenarios that avoided surfactant-induced drainage of the column, substantial surfactant-induced internal water redistribution occurred and was sufficient to alter surfactant transport, resulting in up to 23% overestimation of AI. Depending on the specific simulated flow scenario and data analysis assumptions used, estimated AI varied by nearly 40% and deviated up to 36% from the system's initial AI. We recommend methods for AI determination that avoid generation of surface-tension gradients and urge caution when relying on absolute AI values measured via SMD.

Variations in internal water distribution and leaf anatomical structure in maize under persistently reduced soil water content and growth recovery after re-watering

Episodes of regional drought are increasing and are frequently associated with increased duration and intensity. However, relatively little is known about effects of long-lasting drought on leaf microscopic structure and physiological metabolism of plants. In this study, we investigated internal water re-distribution and leaf anatomical structure of maize (Zea mays L.) grown under persistently reduced soil water content. Meanwhile, the threshold of soil water content at which maize cannot recover growth vitality after re-watering was determined. Our results showed that during persistent reductions in the field water capacity from 75 to 25 %, plant growth declined, while the water content in maize decreased following the order from the lower to upper leaves and their leaf sheathes to the stem and roots. At 20 % of field water capacity, the volume of bulliform cells declined, accompanied by an inward shrinkage of cell walls. Under field water capacity below 20 %, the number of chloroplasts in bundle-sheath cells decreased, chloroplasts in mesophyll cells deformed from oval to round, concomitant of a near to zero net photosynthetic rate. It was demonstrated that the growth vitality of maize plants could be recovered by re-watering even if field water capacity reduced to 15 %, but not to 10 %.

Ageing effects on swelling behaviour of compacted GMZ01 bentonite

Ageing effects on the swelling properties of compacted GMZ01 bentonite are investigated in this paper. Samples were compacted to prescribed dry densities and water contents and kept for ageing under constant volume and K0 confined conditions for target days of 0, 1, 7, 15, 30 and 90. Then, swelling deformation and swelling pressure tests were performed on the aged samples. Results indicate that both the swelling deformation and swelling pressure decrease with ageing time, with a more significant decrease at the first few days of ageing. Ageing effects are more pronounced for samples with large dry density and high water content. At the same initial dry density and water content, samples aged under constant volume conditions show much smaller decrease of swelling pressure compared to that of samples aged under K0 confined conditions. The decrease of swelling potential of samples with ageing days is mainly attributed to the bonding effects and the internal redistribution of water within the bentonite, which was confirmed by the changes of microstructure of samples with ageing.

Comparative hydrology across AmeriFlux sites: The variable roles of climate, vegetation, and groundwater

Watersheds can be characterized as complex space‐time filters that transform incoming fluxes of energy, water, and nutrients into variable output signals. The behavior of these filters is driven by climate, geomorphology, and ecology and, accordingly, varies from site to site. We investigated this variation by exploring the behavior of evapotranspiration signals from 14 different AmeriFlux sites. Evapotranspiration is driven by water and energetic forcing and is mediated by ecology and internal redistribution of water and energy. As such, it integrates biological and physical controls, making it an ideal signature to target when investigating watershed filtering. We adopted a paradigmatic approach (referred to as the null model) that couples the Penman‐Monteith equation to a soil moisture model and explored the deviations between the predictions of the null model and the observed AmeriFlux data across the sites in order to identify the controls on these deviations and their commonalities and differences across the sites. The null model reproduced evapotranspiration fluxes reasonably well for arid, shallow‐rooted systems but overestimated the effects of water limitation and could not reproduce seasonal variation in evapotranspiration at other sites. Accounting for plant access to groundwater (or deep soil moisture) reserves and for the effects of soil temperature on limiting evapotranspiration resolved these discrepancies and greatly improved prediction of evapotranspiration at multiple time scales. The results indicate that site‐specific hydrology and climatic factors pose important controls on biosphere‐hydrosphere interactions and suggest that plant–water table interactions and early season phenological controls need to be incorporated into even simple models to reproduce the seasonality in evapotranspiration.

Isolation of Six Novel Aquaporin Genes from Triticum aestivum L. and Functional Analysis of TaAQP6 in Water Redistribution

Water transport through the cell membranes is regulated largely by a family of proteins known as aquaporins (AQPs). In this study, six novel aquaporin genes, TaAQP1∼TaAQP6, were isolated from the common wheat Triticum aestivum L. var. Changle 5. These six TaAQPs share common features with other plant AQPs. Three of them (TaAQP2, 3, and 4) phylogenetically belong to plant PIP2 group, and the other three resemble proteins from PIP1(TaAQP1), TIP1(TaAQP6), and TIP2(TaAQP5) groups, respectively. The subcellular localization assay, determined by onion epidermal cell transient expression system, indicated that TaAQP6 is a membrane-associated protein. Transformation of TaAQP6 into Xenopus oocytes demonstrated that it facilitated water uptake, suggesting that this TaAQP is an active membrane-associated protein. The expression of TaAQP6 was upregulated in shoots of wheat seedlings, but downregulated in roots under polyethylene glycol (PEG) stress. In split-root experiment, the amount of TaAQP6 transcripts decreased in dry roots (cultured in PEG solution), but increased in wet roots (cultured in water), and remained unchanged in shoots. It is interesting to note that the osmolality changes of different parts in PEG-treated and split-root seedlings were related to the expression of TaAQP6. Taken together, we proposed that TaAQP6 participates in internal water redistribution of wheat seedlings during osmotic stress by regulating outflow of water from water-rich organs to the parts with poor water status under water deficit condition.

Importance of internal hydraulic redistribution for prolonging the lifespan of roots in dry soil

Redistribution of water within plants could mitigate drought stress of roots in zones of low soil moisture. Plant internal redistribution of water from regions of high soil moisture to roots in dry soil occurs during periods of low evaporative demand. Using minirhizotrons, we observed similar lifespans of roots in wet and dry soil for the grapevine 'Merlot' (Vitis vinifera) on the rootstock 101-14 Millardet de Gramanet (Vitis riparia x Vitis rupestris) in a Napa County, California vineyard. We hypothesized that hydraulic redistribution would prevent an appreciable reduction in root water potential and would contribute to prolonged root survivorship in dry soil zones. In a greenhouse study that tested this hypothesis, grapevine root systems were divided using split pots and were grown for 6 months. With thermocouple psychrometers, we measured water potentials of roots of the same plant in both wet and dry soil under three treatments: control (C), 24 h light + supplemental water (LW) and 24 h light only (L). Similar to the field results, roots in the dry side of split pots had similar survivorship as roots in the wet side of the split pots (P = 0.136) in the C treatment. In contrast, reduced root survivorship was directly associated with plants in which hydraulic redistribution was experimentally reduced by 24 h light. Dry-side roots of plants in the LW treatment lived half as long as the roots in the wet soil despite being provided with supplemental water (P < 0.0004). Additionally, pre-dawn water potentials of roots in dry soil under 24 h of illumination (L and LW) exhibited values nearly twice as negative as those of C plants (P = 0.034). Estimates of root membrane integrity using electrolyte leakage were consistent with patterns of root survivorship. Plants in which nocturnal hydraulic redistribution was reduced exhibited more than twice the amount of electrolyte leakage in dry roots compared to those in wet soil of the same plant. Our study demonstrates that besides a number of ecological advantages to protecting tissues against desiccation, internal hydraulic redistribution of water is a mechanism consistent with extended root survivorship in dry soils.

Modeling of Electrochemical-Mechanical Deformations of Ionic Polymer Metal Composite

The bending deformation of the ionic polymer metal composite (IPMC) upon low electric field is dominated by internal water redistribution. The one-dimensional finite element formulation is conducted for the basic field equations governing electrochemical response of the IPMC. The three-dimensional finite element analysis for the mechanical response of the IPMC beam is also conducted. Some numerical studies are carried out to show the validity of the present formulation.

Finite Element Analysis of Two-Dimensional Electrochemical-Mechanical Behaviors of Ionic Conducting Polymer Actuators

The two-dimensional finite element formulation for the basic field equations governing electrochemical responses of ionic conducting polymer-metal composite (IPMC) actuators is proposed in the present study. Biaxial bending deformation of a platinum plated Nafion actuator having 4 electrodes is dominated by internal water redistribution, which is associated with electroosmosis of hydrated ions and self-diffusion of free water molecules. Two processes can be considered separately in the way that fast electroosmosis is followed by much slower self-diffusion. Some numerical studies for IPMC actuators with several types of electric field are carried out in order to show the validity of the proposed formulation.

Finite Element Modeling of Electrochemical-Mechanical Behaviors of Ionic Conducting Polymer-Metal Composites

Bending deformation of an ionic conducting polymer-metal composite (a platinum plated Nafion) upon applied low electric field across its thickness is dominated by internal water redistribution. Internal water redistribution is associated with two phenomena, electroosmosis of hydrated ions and self-diffusion of free water molecules. Two processes can be considered separately in the way that fast electroosmosis is followed by much slower self-diffusion. Consequently, there is strain distribution due to different water content throughout the thickness. In the present study, finite element formulation is conducted for the basic field equations governing electrochemical-mechanical response of a platinum plated Nafion actuator upon applied electric field. Some numerical studies are carried out in order to show the validity of the present formulation.

Leaf rosette closure in the alpine rock species Saxifraga paniculata Mill.: significance for survival of drought and heat under high irradiation

ABSTRACTThe significance of leaf rosette closure for survival of drought and heat under high irradiation on alpine rock sites was investigated in the cushion forming rosette plant, Saxifraga paniculata Mill. With decreasing water content the leaves fold over the rosette centre reducing reversibly the evaporative leaf surface area by 80%. Internal water redistribution driven by an osmotic gradient from older to younger leaves occurs. The oldest leaves dry out to promote the survival of the individual. Leaf temperatures above 45 °C (which match heat tolerance limits 45–57 °C; LT50) co‐occurred with low substrate water potentials (less than – 0·5 MPa) on 11·3% of summer days. Shading by leaves can be crucial to surviving high temperatures as it keeps the rosette centre up to 10 °C colder. Mutual shading prevented sustained drought‐induced photoinhibition in upper leaf surfaces at relative water contents below 60%. In exposed lower leaf surfaces restoration of photosystem II took several days. Leaf temperatures above 40 °C (21·3% of summer days) induced photoinhibition in situ. Periods with sufficient water supply can be fully utilized as rehydration is fast (&lt; 12 h) and exposes the upper leaf surfaces that showed only minor photoinhibition. By reversible leaf rosette closure environmental extremes that otherwise could exceed tolerance are efficiently avoided.

The use of magnetic resonance imaging techniques in assessing the uptake of surface treatments and water movement through stone faces

This paper addresses some practical questions regarding the influence of hydrophobic treatments on the movement of water in sandstone. The broad line gradient echo magnetic resonance imaging technique has been used for monitoring the depth of penetration of alkyl alkoxysilane treatment into untreated sandstone and subsequently to visualise the movement and spatial distribution profile of water in the untreated and silane treated sandstone matrix. The experimental results show that the effect of hyrdrophobic treatment depends on whether the stone is in short-term or prolonged contact with water. For short term exposure, the presence of a silane treatment prevents the movement of water into and out of the sandstone matrix. However, after continuous long-term contact with water the hydrophobic treatment is unable to prevent the ingress and internal redistribution of water. The ability of water to infiltrate treated regions of sandstone has significant practical implication for stone structures where deterioration may be due to outward movement of water from the interior to the surface of the stone matrix.

Use of air permeability to estimate infiltrability of frozen soil

Infiltration rates in frozen soil may be extremely low due to pore blockage by ice, leading to accelerated runoff and erosion. It is difficult to test models of ice blockage effects during infiltration of water because both infiltrating water and resident ice undergo phase changes. We used air permeability, which can be measured without phase changes, to test the applicability of currently used soil hydraulic models to the simulation of ice blockage effects. We confirmed that Darcy's equation described air flow for both dry and moist soil conditions. It was then shown that a combination of the van Genuchten soil-water retention equation (M.Th. van Genuchten, Soil Sci. Soc. Am. J., 44 (1980) 892) and Mualem's (Y. Mualem, Water Resour. Res., 12 (1976) 513) hydraulic conductivity model, modified to account for the presence of trapped air, described the air permeability of unfrozen soils over a range of soil-water contents. However, when this model was extended to frozen soils, the measured reduction in air permeability in frozen soil was much greater than the model predicted. It appears that hydraulic models can be used to describe the conductivity of the air-filled porosity but that processes other than expansion of water when frozen, possibly internal redistribution of water, affect the conductivity of the air-filled porosity. Until freezing processes are better understood, calculations of infiltration based on soil water content alone are subject to large errors.

Water storage and osmotic pressure influences on the water relations of a dicotyledonous desert succulent

Abstract Water storage and nocturnal increases in osmotic pressure affect the water relations of the desert succulent Ferocactus acanthodes, which was studied using an electrical circuit analog based on the anatomy and morphology of a representative individual. Transpiration rates and osmotic pressures over a 24‐h period were used as input variables. The model predicted water potential, turgor pressure and water flow for various tissues. Plant capacitances, storage resistances and nocturnal increases in osmotic pressure were varied to determine their role in the water relations of this dicotyledonous succulent. Water coming from storage tissues contributed about one‐third of the water transpired at night: the majority of this water came from the nonphotosynthetic, water storage parenchyma of the stem. Time lags of 4 h were predicted between maximum transpiration and maximum water uptake from the soil. Varying the capacitance of the plant caused proportional changes in osmotically driven water movement but changes in storage resistance had only minor effects. Turgor pressure in the chlorenchyma depended on osmotic pressure, but was fairly insensitive to doubling or halving of the capacitance or storage resistance of the plant. Water uptake from the soil was only slightly affected by osmotic pressure changes in the chlorenchyma. For this stem succulent, the movement of water from the chlorenchyma to the xylem and the internal redistribution of water among stem tissues were dominated by nocturnal changes in chlorenchyma osmotic pressure, not by transpiration.

Responses of a CAM Plant to Drought and Rainfall: Capacitance and Osmotic Pressure Influences on Water Movement

Daily and seasonal patterns in water flow and water potential were investigated for the Crassulacean acid metabolism succulent Agave deserti during an extended summer drought and for a period following rainfall. Field measurements of transpiration and of osmotic pressure changes over selected 24 h periods were used as input variables for a computer model of water flow that was based on an electrical circuit analog of the whole plant. Parameters such as root resistance and tissue capacitance were also varied to reflect the effects of changing plant or soil water status. The model predicted internal water flow and water potential during the drought cycle and was used to assess the role of tissue osmotic properties in water uptake from the soil and in internal water redistribution. For plants under wet soil conditions, 55% of the night-time transpiration was derived from water storage, this storage being recharged during the day. As drought progressed, transpiration and the nocturnal increase in osmotic pressure declined, although the osmotic pressure itself increased. The difference in osmotic pressure between the water storage tissue and the chlorenchyma caused a net flow of water into the chlorenchyma after 3 weeks of drought, thereby increasing chlorenchyma turgor pressure. Simulations also indicated that a large increase in root resistance must occur to prevent substantial water loss from the plant to the dry soil. After rainfall, recharge of plant water storage was complete within one week, although full recovery in the amplitude of daily osmotic pressure variations took longer.

Pressure cycles and the water economy of insects

Water exchange between insects and their environment via the vapour phase includes influx and efflux components. The pressure cycle theory postulates that insects (and some other arthropods) can regulate the relative rates of influx and efflux of water vapour by modulating hydrostatic pressures at a vapour-liquid interface by compressing or expanding a sealed, gas-filled cavity. Some such cavities, like the tracheal system, could be compressed by elevated pressure in all or part of the haemocoele. Others, perhaps including the muscular rectum of flea prepupae, could be compressed by intrinsic muscles. MaddrellInsect Physiol. 8, 199 (1971)) suggested a pressure cycle mechanism of this kind to account for rectal uptake of water vapour inThermobiabut did not find it compatible with quantitative information then available. Newer evidence conforms better with the proposed mechanism. Cyclical pressure changes are of widespread occurrence in insects and have sometimes been shown to depend on water status. Evidence is reviewed for the role of the tracheal system as an avenue for net exchange of water between the insect and its environment. Because water and respiratory gases share common pathways, most published findings fail to distinguish between the conventional view that the tracheal system has evolved as a site for distribution and exchange of respiratory gases and that any water exchange occurring in it is generally incidental and nonadaptive, and the theory proposed here. The pressure cycle theory offers a supplementary explanation not incompatible with evidence so far available. The relative importance of water economy and respiratory exchange in the functioning of compressible cavities such as the tracheal system remains to be explored. Some further implications of the pressure cycle theory are discussed. Consideration is given to the possible involvement of vapour-phase transport in the internal redistribution of water within the body. It is suggested that some insect wings may constitute internal vapour-liquid exchange sites, where water can move from the body fluids to the intratracheal gas. Ambient and body temperature must influence rates of vapour-liquid mass transfer. If elevated body temperature promotes evaporative discharge of the metabolic water burden that has been shown to accumulate during flight in some large insects, their minimum threshold thoracic temperature for sustained flight may relate to the maintenance of water balance. The role of water economy in the early evolution of insect wings is considered. Pressure cycles might help to maintain water balance in surface-breathing insects living in fresh and saline waters, but the turbulence of the surface of the open sea might prevent truly marine forms from using this mechanism.

Water transport in relation to expansion and contraction of leaves and fruits of Calamondin orangef

SummaryDiurnal fluctuations in fruit diameter and leaf thickness of Calamondin orange trees were measured and related to transpiration from leaves and to internal redistribution of water from fruit...