Showing papers on "Water flow published in 1988"

Developing joint probability distributions of soil water retention characteristics

Abstract: A method is presented for developing probability density functions for parameters of soil moisture relationships of capillary head [h(θ)] and hydraulic conductivity [K(θ)]. These soil moisture parameters are required for the assessment of water flow and solute transport in unsaturated media. The method employs a statistical multiple regression equation proposed in the literature for estimating [h(θ)] or [K(θ)] relationships using the soil saturated water content and the percentages of sand and clay. In the absence of known statistical distributions for either [h(θ)] or [K(θ)] relationships, the method facilitates modeling by providing variability estimates that can be used to examine the uncertainty associated with water flow or solute transport in unsaturated media.

Do Woody Plants Operate Near the Point of Catastrophic Xylem Dysfunction Caused by Dynamic Water Stress? : Answers from a Model

Abstract: We discuss the relationship between the dynamically changing tension gradients required to move water rapidly through the xylem conduits of plants and the proportion of conduits lost through embolism as a result of water tension. We consider the implications of this relationship to the water relations of trees. We have compiled quantitative data on the water relations, hydraulic architecture and vulnerability of embolism of four widely different species: Rhizophora mangle, Cassipourea elliptica, Acer saccharum, and Thuja occidentalis. Using these data, we modeled the dynamics of water flow and xylem blockage for these species. The model is specifically focused on the conditions required to generate ;runaway embolism,' whereby the blockage of xylem conduits through embolism leads to reduced hydraulic conductance causing increased tension in the remaining vessels and generating more tension in a vicious circle. The model predicted that all species operate near the point of catastrophic xylem failure due to dynamic water stress. The model supports Zimmermann's plant segmentation hypothesis. Zimmermann suggested that plants are designed hydraulically to sacrifice highly vulnerable minor branches and thus improve the water balance of remaining parts. The model results are discussed in terms of the morphology, hydraulic architecture, eco-physiology, and evolution of woody plants.

Wood-water relations

Abstract: Wood is formed in an essentially water-saturated environment in the living tree, and the cell wall remains in this state until the water flow from the roots is interrupted, such as by felling the tree. The wood then begins to lose most of its moisture by drying, resulting in changes in most of its physical properties. These changes, and their relationship to the environment to which the wood is subsequently ex posed, are the subject of this book. The text consists of six chapters. The first chapter discusses cer tain empirical relationships between wood and water, methods of measuring wood moisture content, factors which affect its equilib rium moisture content, and the effect of moisture content on wood strength. The second chapter treats the thermodynamics of moisture sorption by wood, inc1uding enthalpy, entropy, and free energy changes. The third chapter discusses some of the theories which have been proposed to explain the sorption isotherms for hygroscopic ma terials such as wood. Chapter 4 considers hygroexpansion or the shrinking and swelling of wood associated with moisture change. Chapter 5 is concerned with how moisture moves through the cell wall of wood in response to both moisture and temperature gradients. The sixth and final chapter discusses the theoretical and practical aspects of the electrical resistance and dielectric properties of wood, in c1uding the principles involved in their application in electrical moisture meters."

Constant rate rainfall infiltration: A versatile nonlinear model: 1. Analytic solution

Abstract: Analytic solutions are presented for a nonlinear diffusion-convection model describing constant rate rainfall infiltration in uniform soils and other porous materials. The model is based on the Darcy-Buckingham approach to unsaturated water flow and assumes simple functional forms for the soil water diffusivity D(θ) and hydraulic conductivity K(θ) which depend on a single free parameter C and readily measured soil hydraulic properties. These D(θ) and K(θ) yield physically reasonable analytic moisture characteristics. The relation between this model and other models which give analytic solutions is explored. As C→ ∞, the model reduces to the weakly nonlinear Burgers' equation, which has been applied in certain field situations. At the other end of the range as C→1, the model approaches a Green-Ampt-like model. A wide range of realistic soil hydraulic properties is encompassed by varying the C parameter. The general features of the analytic solutions are illustrated for selected C values. Gradual and steep wetting profiles develop during rainfall, aspects seen in the laboratory and field. In addition, the time-dependent surface water content and surface water pressure potential are presented explicitly. A simple traveling wave approximation is given which agrees closely with the exact solution at comparatively early infiltration times.

A contour-based topographic model for hydrological and ecological applications.

Abstract: A digital model for discretizing three-dimensional terrain into small irregularly shaped polygons or elements based on contour lines and their orthogonals is described. From this subdivision the model estimates a number of topographic attributes for each element including the total upslope contributing area, element area, slope, and aspect. This form of discretization of a catchment produces natural units for problems involving water flow as either a surface or subsurface flow phenomenon. The model therefore has wide potential application for representing the three-dimensionality of natural terrain and water flow processes in the fields of hydrology, sedimentology, and geomorphology. Three example applications are presented and discussed. They are the prediction of zones of surface saturation, the prediction of the distribution of potential daily solar radiation, and the prediction of zones of erosion and deposition in a catchment.

Automated remote water meter readout system

Abstract: An automated multi-purpose utility water meter readout system. The disclosed system obtains water usage information from an existing water meter without any modifications or attachments to the meter. The device needs only to be located in proximity to the water meter and obtains water flow information by sensing the magnetic flux lines generated by the internal rotating coupling magnets of the water meter. The varying magnetic flux is converted to a periodic electrical signal whose frequency is proportional to the flow rate. The instantaneous flow is continually totalized and stored in a solid-state counter, from which the totalized flow information is periodically transmitted to a remote receiver by a standard, well-proven radio frequency telemetry link. The remote receiver stores data from multiple meters (up to 10,000) and periodically sends the data to the data processing office by means of telephone lines, CATV cable, or RF link. As an option, the system offers a feature that can provide direct benefits to the water user, i.e. an interface unit located in the user's residence receives water use data from the meter and displays this data to aid in water conservation and provide warnings of water leaks. The disclosed system is optionally powered by a novel solid-state thermoelectric generator which converts ambient thermal energy to electrical energy and provides an operational life that far exceeds the economic life of the device.

Review of soil solution samplers

Abstract: Soil interstitial waters are an extremely important facet of many environmental studies. The biogeochemical cycles of important nutrients, metal migration across the landscape, and pollutant movement to groundwater are highly affected by the water flow characteristics in soils and sediments. The purpose of this review is to evaluate the various soil solution sampling techniques. There is no single device that will perfectly sample soil solution in all conditions encountered in the field; hence a critical literature review on the different soil solution samplers is given. The differences among the various soil solution samplers and their relative advantages and limitations are discussed. The problems involved in using these samplers are assessed and plausible solutions are presented.

A dynamic model for water flow in a single tree: evidence that models must account for hydraulic architecture.

Abstract: A model is presented for the dynamics of water flow in a single eastern white cedar tree (7’huja occidentalis L) The model takes into account the spatial and temporal dependence of the evaporative flux from leaves in the crown It also accounts for the quantitative hydraulic architecture of the tree, ie, the model characterizes the tree as a branched catena of > 4000 stem segments in which account is taken of the segment length, diameter, hydraulic resistance, and the total area of leaves attached to the segment Input values needed to run the model are measurements of evaporative flux, hydraulic conductance of stems versus stem diameter, and leaf and stem water storage capacitances Output parameters are the spatial and temporal characterization of stem and leaf water potentials, stem and leaf water deficits, sap flow rate, and relative sap velocity The input and output values of the branched catena model are compared and contrasted to that of an unbranched catena model It is shown that the branched catena model fits independently measured field parameters better than an unbranched catena model Close correspondence is found between model predictions and field measurements of shoot water potential, pressure gradients in stems, hysteresis in sap velocity between the lower and upper parts of the tree, and diurnal changes in stem and leaf water deficits This model is discussed in terms of both the hydraulic architecture of trees and the potential application of the model to questions of tree morphology, ecology, physiology and evolution

Measurements in turbulent swirling flow through an abrupt axisymmetric expansion

Abstract: Mesure a l'aide d'un anemometre laser Doppler des vitesses moyenne et quadratique moyenne dans un ecoulement d'eau

Flow and tracer transport in fractured media: A variable aperture channel model and its properties

Abstract: Field evidences indicate that the bulk of water flow in fractured crystalline rock often occurs in preferred flow paths, or channels. A theoretical approach was proposed by Tsang and Tsang (1987) to interpret flow and transport through a two- or three-dimensional fractured medium in terms of a system of statistically equivalent one-dimensional channels. The apertures along the flow channels are characterized by an aperture density distribution and a spatial correlation length. In this paper, we present detailed studies on the properties of these channels: channel volume, channel residence time, and channel volumetric flow rate. We also calculated the dispersion in tracer transport through groups of statistically equivalent channels. The one-dimensional channel model is then applied to breakthrough data from transport in a two-dimensional single fracture (Moreno et al., this issue) in both a forward and an inverse calculation. We show from the inverse calculation that the aperture density distribution parameters of the one-dimensional flow channels may be estimated from the dispersion and mean residence time of the tracer data. The tracer breakthrough curve should be obtained from line measurements with tracer sampled over several spatial correlation lengths of the variable apertures. This is in contrast to conventional point tracer measurements which is expected to fluctuate with statistical realization and may not yield pertinent information on the flow system. Based on the insight gained in such calculations, design, and analysis of field measurements are discussed. Both tracer breakthrough measurements and flow rate measurements are needed to obtain the aperture parameters of the flow systems. The permeability measurements alone are controlled by the small constrictions along the flow paths and therefore do not yield a good measure of the mean aperture in channel.

Seasonal occurrence of xylem embolism in sugar maple (acer saccharum)

Abstract: Xylem embolism, the reduction of water flow by air-filled vessels, was measured in a stand of 5- to 8-year-old sugar maple (Acer saccharum Marsh.) saplings growing in a nursery bed in northwestern Vermont. Embolism was quantified as percentage loss in hydraulic conductivity of trunk and branch segments relative to maximum values obtained by removing air from vessels by repeated high pressure (173 kPa) perfusions. Ten segments per tree were cut from 6 trees for each of 11 measurement periods spaced at roughly monthly intervals from May 1986 to June 1987. During the 1986 growing season, embolism increased significantly from 11 to 3 1% in the larger branches and trunk (segment diameter ?0.5 cm), but remained at about 10% in twigs (segment diameter <0.5 cm). This was unexpected because the greatest water stess and thus potential for embolism occurs in twigs. During the winter, embolism increased throughout the trees and the trend with diameter was reversed; by February, small twigs were 84% embolized vs. 69% for larger branches and trunk. Dye perfusions showed that winter embolism in trunks was localized on the south side; this may have resulted from water loss by sublimation or evaporation in the absence of water uptake. Beginning in late March, embolism decreased throughout the trees to approximately 20% in June. This decrease was associated with positive xylem pressure of at least 16 kPa which may have originated in the roots, because weather conditions at the time were unfavorable for the generation of stem pressures characteristic of Acer species in early spring. IN THE MEDICAL SCIENCES, embolism is the blockage of a blood vessel caused by a foreign particle or embolus. By analogy, the term can be applied to blockage of water flow in vessels and tracheids ofplants; in this case the embolus is an air bubble. These bubbles can arise from air forced out of solution during freezing of xylem water, or by an unknown mechanism associated with the characteristically negative pressure of the transpiration stream. There is evidence suggesting that air is sucked into vessels from neighboring air spaces via pores in the vessel wall (Zimmermann, 1983; Crombie, Hipkins, and Milburn, 1985; Sperry, Holbrook, and Tyree, 1987). Once an air bubble is inside a vessel, negative pressure causes it to expand and block water flow. There has undoubtedly been selective pressure to minimize xylem embolism, because if unchecked it would block water supply to foliage. Certainly the xylem is well designed in this regard; instead of containing a single open pipe which would conduct water with the least resistance but would become embolized by a single bubble, xylem consists of individual tra

Nonaqueous phase liquid transport and cleanup: 2. Experimental studies

Abstract: An analysis of the movement of nonaqueous liquids such as organic solvents and gasoline in part 1 (Hunt et al., this issue) showed that separate phase liquids are not completely displaced by groundwater flow under typical pumping conditions and that removal of the compounds by dissolution is mass transfer limited. Steam displacement was proposed as a more efficient cleanup strategy for separate phase organic liquids present in porous media. This paper presents the results of a series of laboratory sand column experiments designed to confirm the theoretical analyses presented in part 1 (Hunt et al., this issue). Experiments with trichloroethylene, a benzene-toluene mixture, and a commercial gasoline, showed that water flow at rates as high as 15 m d−1 could not displace the separate phase liquids when present in a sand matrix in quantities corresponding to a column average saturation of 2.5%. Steam injection, on the other hand, displaced the contaminants as a separate phase just ahead of the steam front, producing a concentrated, small-volume waste stream. Analysis of the laboratory data consisting of pressure gradients, temperature profiles, and water flow velocities shows that the laboratory results are consistent with the theoretical predictions. Moreover, computations of energy requirements show that steam displacement of separate phase contaminants is economically attractive.

Physiological Effects of Collecting and Transporting Emigrating Juvenile Chinook Salmon past Dams on the Columbia River

Abstract: Emigrating juvenile salmonids are collected at McNary Dam on the Columbia River and transported past the three downstream dams to avoid mortalities caused by passage through power-generating turbines. During the 1982–1984 seaward migrations of juvenile fall and spring chinook salmon Oncorhynchus tshawytscha, we used an array of physiological measurements (plasma cortisol and glucose, white blood cell counts) and challenge tests (saltwater challenge, secondary stress, and swimming endurance) to identify the stressful elements in these activities. Sequential increases in plasma cortisol titers offish sampled at the physically separable points in the collection system led us to conclude that the elements of the system stressed fish cumulatively. Furthermore, there were decreases in numbers of white blood cells, in osmoregulatory ability, and in swimming endurance during the first 24 h after fish were collected. Increasing the water flow rate in the system after the 1982 season seemed to reduce total...

Endosomes from kidney collecting tubule cells contain the vasopressin-sensitive water channel

Abstract: The mechanism by which vasopressin rapidly and dramatically increases the water permeability of target epithelial cell membranes is thought to involve a cycle of exo- and endocytosis during which vesicles carrying 'water channels' are successively inserted into, and removed from the apical plasma membrane of epithelial cells. Clusters of intramembranous particles, visible by freeze-fracture electron microscopy and presumed to represent water channels, appear on apical membranes in parallel with increased transepithelial water flow. In the collecting duct, these clusters are located in clathrin-coated pits which are subsequently internalized. There has been no direct evidence, however, that subcellular membranes in vasopressin-sensitive epithelia contain functional water channels. In this report, we have used fluorophores that are sensitive to volume and do not pass through membranes to label and to measure directly the osmotic water permeability of endocytosed vesicles isolated from renal papilla. We present direct evidence that vasopressin induces the appearance of a population of endocytic vesicles whose limiting membranes contain water channels.

Predicting Internal Roughness in Water Mains

Abstract: : A method is presented for predicting the Hazen-Williams C-factor for unlined metal water mains as a function of pipe age. The method has two steps: (a) finding the growth/rate of internal roughness, alpha, for the water main using either historical C-factor data or water quality data; and (b) using predictive equations for an estimate of a future C-factor. The predictive equations presented in this report were derived using linear regression of some 319 data points from seven utilities as well as values from the 1920 text entitled Hydraulic Tables, by G.S. Williams and A. Hazen. The regression equations for C-factor as a function of pipe age have a 95-percent confidence interval of + or - 15 and a coefficient of determination r squared of 0.87.

Factors influencing entry of pesticides into soil water

Abstract: Leaching of pesticides and hence the risk of contamination of ground-water depends on the physicochemical properties of the pesticide, the properties of the soil and the weather. Lipophilicity is the most important physicochemical property influencing the movement of un-ionised pesticides through soil. Water solubility is usually only an important factor in leaching for a few moderately polar solids with high melting points. Organic matter content is the most important property of the soil for un-ionised pesticides whilst the mobility of weak acids depends on soil pH. Permanent anions and weak acids can be very weakly adsorbed and hence might easily reach groundwater. Applications in autumn are more likely to reach groundwater than those in spring because soil temperatures are low and rainfall exceeds evaporation in winter, enabling mobile pesticides to penetrate to subsoils where degradation rates can be very slow. Concentrations of pesticide in water entering subsoils cannot be reliably simulated to an accuracy of better than an order of magnitude because the complex patterns of water flow and the slow diffusion processes of the pesticide are insufficiently understood. The consequences of applying a mobile pesticide to soil where drainage is impeded or where the water table is near the surface need to be anticipated before it is registered for treatment of the soil.

Two‐dimensional steady state unsaturated water flow in heterogeneous soils with autocorrelated soil hydraulic properties

Abstract: The stochastic nature of soil water pressure head and vertical and horizontal flux density under two-dimensional unsaturated steady state flow conditions was examined by using a Monte Carlo technique. Random autocorrelated scale factors were generated by a first-order nearest neighbor model and were used to describe a stationary random field of hydraulic conductivity functions. Scale factor values were assumed to vary only in the horizontal direction, perpendicular to the mean flow. The water flow equation was numerically solved for steady state infiltration and transpiration in a two-dimensional domain, of which the lower boundary was described by a groundwater level. Differences in results between a saturated and unsaturated soil water system were most likely caused by the direction in which the hydraulic properties are randomly autocorrelated and differences in the applied boundary conditions. In contrast to earlier findings with respect to the saturated system, the variability in fluxes for the unsaturated system decreased with an increase in the autocorrelation length, and the variation in soil water pressure head for one- and two-dimensional systems tended to be equal with increasing autocorrelation lengths. When considering a two-layer system it was found that the variability in the lateral flow component at the layer boundary was severely increased as compared to the single-layer simulations.

Clean in place system

Abstract: A system for cleaning cone/shake makers in place. Cone/shake makers have at least one freezer for making ice cream cones or milk shakes. Each freezer has a product inlet, a product pump for pumping product from the inlet into the freezer, and at least one draw valve for dispensing the product in the freezer. The cleaning system has a mixing tank for mixing water with a cleansing chemical, the mixing tank having a capacity of less than one-fourth the volume of the water and cleansing chemical mixture to be used while cleaning a cone/shake maker. The system controllably provides the cleansing chemical to the mixing tank at a rate corresponding to the rate at which water flow into the mixing tank, thereby making a cleansing chemical solution of predefined concentration on the fly as the mixture is being used to clean the cone/shake maker. The system monitors the conductivity of the water/cleansing solution and generates an error message if the conductivity falls outside a specified range for at least a threshold period of time, thereby providing the user with a warning that the system is having a chemical dispensing problem. The cleaning system includes a draw valve actuator for each of cone/shake maker's draw valves and a controller for opening and closing these draw valves in accordance with a specified schedule.

Hydrologic Factors Triggering a Shallow Hillslope Failure

Abstract: In February, 1983, an intense rainstorm triggered a shallow, rapid slump/debris-flow on a monitored hillslope of coastal central California. Discontinuous records of rainfall and maximum ground-water levels within the slide mass were collected before and after the event. These water levels show the development of a shallow perched water table in soil overlying an older, low permeability landslide deposit. Although this perched water table had an overall downslope hydraulic gradient, the slope failure occurred in an area of localized gradient decrease or mounding. The cause of this localized mounding was not apparent from field observations. We used a mathematical model of variably saturated water flow to investigate the pre-failure hillslope hydrology and to demonstrate a possible cause of the localized ground-water buildup. Simulations indicate that only a slight decrease in soil hydraulic conductivity, relative to the overall soil variability, would have been needed to create the observed buildup.

Effects of Soil Physical Structure on Solute Transport in a Weathered Tropical Soil

Abstract: Effects of soil structure on solute transport were studied in a clayey, well-aggregated Oxic Dystropept under grass and secondary forest at La Selva, Costa Rica Both fine pores ( 30 µm) are abundant, as indicated by a water content of 037 m³ m⁻³ at −1500 kPa matric potential, the shape of the moisture release curve, and an initial infiltration rate (at field capacity) averaging 3900 mm hr⁻¹ Field application of Rhodamine B dye without ponding (simulating heavy rainfall) showed preferential flow along decayed-root channels, animal burrows, cracks, and other macropores Dye application to intact cores under conditions of ponded steady-state flow gave a good correlation between flow rate and total stained area (p <001 under forest; p < 005 under grass) Solute (CaCl₂) breakthrough occurred very rapidly, often after < 01 pore volumes had percolated; however, relative concentration of the effluent did not exceed 095 even after five pore volumes had percolated These results indicate that most water flows between aggregates or through macropores (as preferential or channelized flow), even when the fine pores are not fully saturated, and in effect bypasses the fine pore space When solution inflow was interrupted after ∼18 pore volumes, then resumed after 10 min pause, relative concentration of the effluent dropped by 10 to 40%, then rose again This indicates that solute diffused slowly into the aggregates Taken together the results suggest that this soil strongly resists leaching Preferential water flow may serve to prevent nutrient loss from the matrix of all highly aggregated soils and of all noncultivated soils in which animal activity and turnover of woody roots create abundant macropores Research supported by NSF Grants BSR 83-17198 and BSR 86-05047 to the Organization for Tropical Studies, Duke Univ, Durham, NC 27706

Liquid‐liquid flows in an inclined pipe

Abstract: Experimental measurements are reported of oil-water flows in a 20 cm ID pipe at mean velocities between 2.7 and 35 cm/s, at deviation angles θ from vertical between 0 and 65°, and at water flow rate fractions between 30 and 100%. The distribution of the water volume fraction αw across a pipe section is obtained using local high-frequency probes. The mean water volume fraction in the section and the slip velocity Vs between oil and water are also determined. High Vs values (up to 50 cm/s) are measured at large deviation angles; they are associated with oil droplet swarms or continuous oil phase zones. Both αw profiles and Vs values depend only on the mean water volume fraction and not on the total flow rate Qt in the range investigated. At low oil volume fractions αo, all droplets are concentrated close to the upper side of the pipe. At larger αo values, a slower linear variation of αw with the distance y from the axis is measured. A model is suggested relating the slope ∂αw/∂y in a vertical plane to the existence of internal density waves in the stratified mixture.

Trophic Structure of Macrobenthic Communities in the Calcasieu Estuary, Louisiana

Abstract: Trophic groups were used to investigate broad patterns and predict species interactions of macrobenthic assemblages in Calcasieu Estuary, Louisiana. Macrobenthic assemblages of the estuary were numerically dominated by deposit-feeding species. Surface-deposit feeders were the most abundant macrobenthos of the upper estuary, subsurface-deposit feeders dominated the lower estuary, and a trophically well-mixed assemblage inhabited the middle estuary. There were periodic shifts in species dominance within each region, but the shifts were without temporal pattern and seldom led to changes in trophic structure of the region. The macrobenthic assemblages of the upper estuary were dominated by several early-colonizing species which switched feeding modes with changes in water flow, suggesting that disturbances in the upper estuary had a direct effect on macrobenthic communities. Disturbances also may have eliminated macrobenthic species before they could establish a well-mixed community. The presence of trophically mixed communities in the middle estuary probably was indicative of fewer disturbances there. The dominance by subsurface-deposit feeders in the lower estuary probably indicates that sedimentary food in Calcasieu Lake was seldom utilized at the sediment-water interface. Rather, most food became buried and was available only to subsurface-deposit feeders.

Vegetation of inland waters

Abstract: Water as an environment for plant life.- Methods of exploration and analysis of the environment of aquatic vegetation.- Photosynthesis of aquatic plants under natural conditions.- Structural aspects of aquatic plant communities.- The phytosociological approach to the description and classification of aquatic macrophytic vegetation.- Algal communities of continental waters.- Vegetation processes in swamps and flooded plains.- The vegetation of fens in relation to their hydrology and nutrient dynamics: a case study.- Water flow and the vegetation of running waters.- Analysis of flora and vegetation in rivers: concepts and applications.- Aquatic plants in extreme environments.

Automated fluorometric determination of formaldehyde in air

Abstract: A completely automated system is described which initially strips formaldehyde vapor (HCHO) from air into water at pH 2.0 by means of a glass coil through which air and water flow concurrently. The aqueous HCHO is then oxidized by nicotinamide adenine dinucleotide (NAD/sup +/) to produce the reduced form of the coenzyme (NADH), which is measured fluorometrically. This reaction occurs in the presence of the enzyme formaldehyde dehydrogenase. The detection limit is 120 parts per trillion by volume. The calibration curve is linear to approximately 100 parts per billion by volume (ppbv). The coefficient of variation is 2.0% at 20 ppbv HCHO. The rise time of the signal from 10% to 90% is 80 s.

Planting stress in newly planted jack pine and white spruce. 1. Factors influencing water uptake.

Abstract: Bareroot jack pine (Pinus banksiana Lamb.) seedlings (2 + 0) and bareroot white spruce (Picea glauca (Moench) Voss) transplants (1 1/2 + 1 1/2) were taken from cold storage and planted on a clearcut forest site in northeastern Ontario on several dates between May 6 and June 5 during which period soil temperature at 15 cm depth increased from 0 to 18 degrees C. Additional cold-stored trees were transferred to a greenhouse where they were grown in pots for 0, 7 or 28 days and then placed with their roots in aerated water maintained at one of a range of constant temperatures between 0 and 22 degrees C. In both species, daytime xylem pressure potentials (Psi(x)) and needle conductances (g(wv)) decreased with decreasing soil or water temperature. At all root temperatures, g(wv) was lower, and Psi(x) higher, in jack pine than in white spruce. After 28 days in the greenhouse, g(wv) of jack pine seedlings, and Psi(x) of white spruce, was higher than in plants just removed from cold storage. In both species, water-flow resistance through the soil-plant-atmosphere continuum (RSPAC) increased as root temperature decreased. At all root temperatures, RSPAC was higher in plants just removed from cold storage than in plants grown in the greenhouse for 28 days, during which time many new unsuberized roots were formed. At root temperatures above 10 degrees C, RSPAC of both species was higher in trees newly planted in mineral soil than in trees with roots in aerated water; presumably because the roots of planted trees had limited hydraulic contact with the soil. On the day following removal from cold storage, relative plant water flow resistance increased, in both species, more rapidly with declining root temperature than could be accounted for by the change with temperature in the viscosity of water, thus indicating an effect of temperature on root permeability. The same effect was evident in jack pine seedlings, but not white spruce transplants, that had been grown for 28 days in the greenhouse after removal from cold storage.