Showing papers on "Water flow published in 1991"

The Dynamic Two-Fluid Model OLGA: Theory and Application

Abstract: Dynamic two-fluid models have found a wide range of application in the simulation of two-phase-flow systems, particularly for the analysis of steam/water flow in the core of a nuclear reactor Until quite recently, however, very few attempts have been made to use such models in the simulation of two-phase oil and gas flow in pipelines This paper presents a dynamic two-fluid model, OLGA, in detail, stressing the basic equations and the two-fluid models applied Predictions of steady-state pressure drop, liquid hold-up, and flow-regime transitions are compared with data from the SINTEF Two-Phase Flow Laboratory and from the literature Comparisons with evaluated field data are also presented

Simple field method for determining unsaturated hydraulic conductivity

Abstract: A new method is proposed for determining in situ unsaturated hydraulic conductivities from unsaturated infiltration measurements made at several tensions on the same infiltration surface. Wooding's equation for steady-state unconfined infiltration rates is used in calculating hydraulic conductivities. Hydraulic conductivities calculated with the new method are consistent with unit gradient laboratory measurements of saturated and unsaturated hydraulic conductivity. This simple field method is potentially valuable because it is faster than unit gradient laboratory methods, and it is less disruptive of pore continuity than other field infiltration techniques. R OF SOIL WATER INFILTRATION and SUbSUrface water movement are important to researchers developing soil management practices to minimize potential groundwater contamination from land applied chemicals. A simple and rapid field technique of determining field unsaturated hydraulic conductivity would be useful in achieving this objective. Field and laboratory techniques for measurement of unsaturated hydraulic properties of soil were described by Green et al. (1986) and by Klute and Dirksen (1986), respectively. Solution of unsaturated flow problems generally requires experimental determination of the relationship between hydraulic conductivity and water potential or water content. Field methods used to obtain these relationships include the instantaneous profile method, steady-flux methods (with sprinkler irrigation or artificial crusts), sorptivity measurements, and use of tension infiltrometers (Clothier and White, 1981; Ankeny et al., 1988, 1989; Elrick et al., 1988a; White and Perroux, 1987, 1989; Smettem and Clothier, 1989). Because instantaneous profile and steady-flux techniques require laborious installation of tensiometers or neutron probe access tubes, sample numbers and the extensiveness of a site characterization can be limited. Sorptivity is an unsaturated soil parameter sometimes measured in the field (Green et al., 1986). Although sorptivity measurements are fast and simple, these measurements usually require that initial water content be known. White and Perroux (1989) have proposed a laboratory method for calculating unsaturated hydraulic conductivity from sorptivity measurements. Their method, however, requires air drying the sample between measurements at different tensions, which increases experimental time and may cause wetting/drying effects on soil structure. The Guelph infiltrometer (Soilmoisture Equipment Corp., Santa Barbara, CA) compares infiltration rates for difM.D. Ankeny, Daniel B. Stephens & Assoc., 4415 Hawkins NE, Albuquerque, NM 87109; M. Ahmed, Bangladesh Univ. of Engineering and Technology, Dhaka-1000, Bangladesh; T.C. Kaspar, National Soil Tilth Lab., Ames, IA 50011; and R. Horton, Dep. of Agronomy, Iowa State Univ., Ames, IA 50011. Joint contribution from USDA-ARS and Iowa State Univ. Journal Paper no. J-13716 of the Iowa Agric. and Home Economics Exp. Stn. Projects no. 2659 and 2715. Received 6 Nov. 1989. *Corresponding author. Published in Soil Sci. Soc. Am. J. 55:467-470 (1991). ferent radii surface disks and does not require driving a ring. Different soil surface areas, however, are being compared, which may introduce spatial variability associated with the different soil surfaces. A field method to measure in situ hydraulic conductivity at low water tensions is needed for studies of macroporosity and water flow in agricultural soils. The desired criteria for such a method are: 1. Only steady-state infiltration rate measurements are needed. Knowledge of the initial water potential or content should not be required. 2. Soil pore structure should not be disturbed by driving a ring into soil to obtain one-dimensional flow. This way, larger pores are not truncated or collapsed and infiltration through larger pores is less likely to be underestimated. 3. Measurements should be taken on the same soil surface. Measurements taken by using different radii (e.g., Elrick et al. 1988a) are more dependent on the assumption of soil homogeneity. 4. Calculation of hydraulic conductivities should be straightforward. We present a simple scheme for determination of in situ hydraulic conductivity that meets these criteria.

Stomatal control of xylem embolism

Abstract: . The potential role of stomatal closure in the control of xylem embolism is investigated by means of a simple model of hydraulic flow in plants. Maintenance of a maximally efficient conducting system requires the stomata to close in an appropriate fashion as evaporative demand increases in order to prevent shoot water potentials falling below the threshold value at which cavitations occur. The model showed that the optimal stomatal behaviour required depends on soil water availability. Further analysis of the model demonstrated that there could be certain circumstances where loss of a proportion of the conducting tissue by embolisms can, perhaps surprisingly, be beneficial in terms of maximizing stomatal aperture and hence short-term productivity. The results are discussed in relation to the signals controlling stomatal aperture, and it is shown that (1) optimal control cannot be obtained using information on leaf water potential alone, and (2) information relating to soil water potential is a necessary requirement for optimal control.

Retention of Greenland runoff by refreezing: Implications for projected future sea level change

Abstract: Melting produced at the surface of subfreezing permeable firn does not freely percolate but instead refreezes near its point of origin, raising the firn temperature and decreasing the pore space. If sufficient meltwater is introduced, the firn will warm to 0°C, and subsequent water will fill the remaining pore space without freezing. Only after the residual water content of the firn is exceeded will water flow through the firn and possibly escape as runoff. This process prevents summer melt on high Arctic glaciers and ice caps from escaping in its entirety, and it must be accounted for in modeling glacier runoff on the basis of surface energy balance. A model is presented here which describes in a simple way the transient process of infiltration, refreezing, and runoff in a future warming climate. The model is applied to Greenland, for which predictions of runoff-induced sea level rise that do not consider the refreezing process could be as much as 5.0 cm too high over 150 years.

Quantitative sampling of soft bottom sediments problems and solutions

Abstract: Since the pioneering attempts to obtain quantitative soft-bottom sediment samples at the beginning of this century, many different devices for sampling soft bottoms have been presented. Most techniques, however, yield semi-quantitative samples only. For studies dealing with certain aspects of microlayering, freezing in situ seems to be a good method. In more general studies, quantitative samples appear to be best obtained using instruments based on the coring principle. Improper handling or faulty design of the conng device, however, results in unrepresentative samples. Major factors in b ~ a s are (1) loss of surficial sediments. ( 2 ) redistribution, resuspension and loss of enclosed sediment, ( 3 ) core shortening, and ( 4 ) repenetratlon. Frictional drag and consequent smearing against the coring tube is also a potential source of error General design features improving the reliability of sampling are a supporting stand and, when dealing with open corers, an unimpeded water flow through the sample compartment. Box corers appear best suited for sampling certain macrofauna and sediments of coherent and silty/sandy character. Adequately designed and properly operated tube corers are the most versatile instruments at present. A general concern, however, is that coring tubes enter and penetrate the sediment carefully and slowly. Under favourable conditions, an open-barrel gravity corer can be used for sampling the unshortened upper layer, in combination with a larger box corer and subsequent piston-coring technique for sampling the underlying layers. When sampling under less favourable conditions, or when extreme care is required, the corer must be based on a structure with a supporting stand, which permits the device to settle on the bottom before the coring tubes enter the sediment. Mounting an underwater video camera as a standard on such devices is recommended since l t enables visual inspection and recording of each sampling. Other tested means and promising improvements in instrument design to improve sampling reliability are also discussed.

Habitat structure and community dynamics in marine benthic systems

Abstract: Animals and plants of the marine benthos depend on their substrata for attachment, on surfaces or within sediments, and for access to a source of prey and nutrients. In the case of sessile species, the two-dimensional surface is a primary resource for which individuals and colonies of many species potentially compete. However, substratum is not as simple a resource as one might expect. Even solid rock surfaces are usually dissected by small to large crevices, have different orientations with respect to each other and to water flow, and are often made of varied rock types. Soft substrata can be extremely diverse, consisting of both organic and inorganic materials differing in grain sizes and in chemical composition. These materials are further modified through the activities of the residents themselves, adding organic material, aggregating particles and sometimes changing the nature of the substratum so much that other species can be totally excluded. On hard substrata, biogenic effects can also be extremely important. These include the provision of secondary substratum through growth processes and calcium carbonate deposition, and the addition of physical relief that affects water flow and thus the transport of resources and propagules within the community.

Water Relations and Hydraulic Architecture of a Tropical Tree (Schefflera morototoni) Data, Models, and a Comparison with Two Temperate Species (Acer saccharum and Thuja occidentalis)

Abstract: The water relations and hydraulic architecture of a tropical tree (Schefflera morototoni) and of two temperate species (Acer saccharum and Thuja occidentalis) are reported. Among the water relations parameters measured were leaf and stem water storage capacity, leaf water potential, transpiration, and vulnerability of stems to cavitation and loss of hydraulic conductivity by embolisms. Among the hydraulic architecture parameters measured were hydraulic conductivity per unit pressure gradient, specific conductivity, leaf-specific conductivity, and Huber value. In terms of vulnerability of stems to cavitation, stem and leaf capacitances, and leaf-specific conductivity, all three species followed the same sequence: Schefflera > Acer > Thuja. It is argued here that the high stem capacitance and high leaf-specific conductivity of Schefflera are necessary to compensate for its high vulnerability to cavitation. Extractable water storage per unit leaf area in Schefflera stems is >100 times that of Acer and may permit the species to survive unusually long, dry seasons in Panama. Although Schefflera frequently grows >20 meters, the biggest resistance to water flow in the shoots resides in the leaves.

Channel morphology and bedload pulses in braided rivers: a laboratory study

Abstract: Bedload pulses in gravel-bed rivers have been widely reported in recent years and attempts have been made to relate them to channel morphology. Bedload transport and channel morphology were measured in a small-scale generic model of braided gravel-bed streams. Two experiments are described in which braided channels developed in a 14 m × 3 m sand tray. Total bedload output from the tray was weighed every 15 minutes. Stream bed geometry was surveyed every four hours. Pulses were observed in the bedload output time series, and were qualitatively related to the channel morphology immediately upstream of the measuring section. The Bagnold (1980) bedload equation generally overpredicts measured bedload transport rates when applied to channels that were in equilibrium or aggrading. Underprediction occurred when applied to degrading channels. Aggradation was associated with channel multiplication and bar deposition. Channel pattern simplification occurred when degradation took place, and bars emerged from the water flow. Development of phases of aggradation and degradation is dependent upon the three-dimensional geometry of the stream beds. Spatial and temporal feedback loops can be identified, enabling links between channel morphology and bedload transport rate to be directly identified.

Effects of water movement on prey capture and distribution of reef corals

Abstract: The water flow regimes on a coral reef change with depth, distance from shore, and orientation to incoming waves. Low flow conditions may limit the ability of corals to capture prey, because the rate of encounter with particles suspended in the water column depends on the transport of water past the corals’ feeding structures. High flow speeds, however, cause deformation or collapse of feeding structures, and prey capture success is likely to decrease under such conditions. The specific relationship between flow speed and particle capture by passive suspension feeders like anthozoans may be determined by tentacle size and shape, tentacle and polyp stiffness and colony morphology. The importance of particle capture, as well as the types (zooplankton, detritus) and the size range of particles captured by corals, are almost unknown. The only published information for any species to date is Porter’s (1974) report on coelenteron contents of Montastrea cavernosa. The relationship between water flow and particle (hydrated Artemia cysts) capture has been studied for two octocoral (Alcyonium) species by Patterson (1984) and McFadden (1986) and for one scleractinian coral (Meandrina meandrites, Johnson & Sebens, unpubl.) in laboratory flume studies. The present study is an attempt to relate prey capture to water flow under field conditions for two species (Meandrina meandrites, Madracis decactis) in Salt River Canyon, St Croix, U.S.V.I., using the underwater habitat ‘Aquarius’ in July 1988. Concurrent measurements of water flow and wave height were made at several positions on the reef between 7 and 45 m using recording electromagnetic current meters (Interocean S4) mounted on rigid posts 0.5 m off the substrate. During the same two-week period, particle release (hydrated Artemia cysts) experiments were carried out over colonies of Meandrina and Madracis in the field. Particles were released upstream of the corals for 3 min, after which corals were caused to retract their tentacles, and flow above the coral was measured using macrovideo photography of moving cysts in a slit beam of light parallel to the flow. The corals were then collected and preserved under water for coelenteron content analysis, including both captured cysts and natural prey (Zooplankton). Particle concentrations were determined from samples collected by pumping water from directly over the coral during the experiment, using intake heads that allowed omnidirectional lateral sampling.

Stochastic analysis of simulated vadose zone solute transport in a vertical cross section of heterogeneous soil during nonsteady water flow

Abstract: The problem of transport of a conservative nonreactive solute in a vertical cross section of a hypothetical partially saturated, scale-heterogeneous soil under transient water flow was analyzed here. It was assumed that locally the water flow and the solute transport can be described by the Richards' equation and by the one-component convection dispersion equation, respectively. The simulated water content and the solute concentration distributions in the vertical cross section of the soil at different elapsed times were quantified in terms of space averages and two-point autocorrelation functions. The time evolution of the solute plume was quantified in terms of its first two normalized spatial moments, from which the time dependence of the longitudinal and the transverse components of the solute velocity vector, and the spatial covariance tensor, were estimated. The results of this study, which are relevant to solute transport at the local or the plume scale, demonstrated the considerable variability in the solute concentration in space and time, due to the complex heterogeneity of the soil hydraulic properties in both the vertical and the horizontal directions. Consequently, the movement of the solute plume was characterized by a compression-expansion phenomenon, attributed to the decrease in the effective solute velocity through the zones of relatively fine-textured soil material. It was concluded that existing stochastic vadose zone transport models may be applicable to shallow depths but may fail to describe the actual spread of a solute plume when the transport takes place at relatively large depths, mainly because of the neglect of the significant vertical heterogeneity in the soil hydraulic properties.

Measurement of methylmercury and mercury in run-off, lake and rain waters

Abstract: During one year, samples from eight drainage lakes, seven run-off stations and three deposition sites from various geographical areas in Sweden were collected and analyzed for methyl Hg (MeHg) and total Hg (Hg-tot). The MeHg concentrations ranged from 0.04 to 0.64 ng L−1, 0.04 to 0.8 ng L−1, and <0.05 to 0.6 ng L−1 in run-off, lake water and rain water, respectively. The corresponding Hg-tot concentrations were found in the range 2 to 12 ng L−1, 1.35 to 15 ng L−1, and 7 to 90 ng L−1, respectively. A Hg-tot level of about 60 ng Hg L−1 was found in throughfall water. The MeHg and Hg-tot concentrations are positively correlated in both run-off and lake water, but not in rain and throughfall water. A strong positive correlation between the MeHg, as well as the Hg-tot concentration, and the water color is observed in both run-off and lake waters, which suggests that the transport of MeHg and other Hg fractions from soil via run-off water to the lake is closely related to the transport of organic substances; and is a consequence of the biogeochemical processes and the water flow pathway. The ratio between the mean values of MeHg and Hg-tot seems to be an important parameter, with an indicated negative coupling to the mean value of pH for run-off water, but a strong positive correlation to Hg-content in fish, the ratio between the area of the catchment and the lake, as well as to the retention time of lake.

Simulating nitrogen dynamics in soils using a deterministic model

Abstract: . LEACHN is a deterministic model for simulating nitrogen dynamics in soil. Transport processes are based upon numerical solutions to the Richards equation for water flow and the convection-dispersion equation for solute transport. Transformations of urea, ammonium, nitrate and three organic pools are included, and the influence of water content and temperature can be reflected. Lack of measured input data sometimes limits the more general use of models such as these. Approaches to estimating data values using soil survey information and a limited number of measured data are discussed. Simple model sensitivity studies and a limited number of field measurements can guide the choice of input data values and lead to simulations that reflect the main features of the field soil nitrogen regime. Such an approach provides initial values for a modelling exercise, and improves intuition regarding the relative importance of processes and interactions in the field nitrogen cycle.

The Las Cruces Trench Site: Characterization, Experimental Results, and One‐Dimensional Flow Predictions

Abstract: A comprehensive field trench study was conducted in a semiarid area of southern New Mexico to provide data to test deterministic and stochastic models of vadose zone flow and transport. A 4 m by 9 m area was irrigated with water containing a tracer using a carefully controlled drip irrigation system. The area was heavily instrumented with tensiometers and neutron probe access tubes to monitor water movement and with suction tubes to monitor solute transport. Approximately 600 disturbed and 600 core samples of soil were taken to support deterministic and stochastic characterization of the soil water hydraulic parameters. The core sample-based saturated hydraulic conductivities ranged from 1.4 to 6731 cm/d with a mean of 533 cm/d and a standard deviation of 647 cm/d, indicating significant spatial variability. However, visual observation of the wetting front on the trench wall shows no indication of preferential flow or water flow through visible root channels and cracks. The tensiometer readings and the neutron probe measurements also suggest that the wetting front moves in a fairly homogeneous fashion despite the significant spatial variability of the saturated hydraulic conductivity. In addition to the description of the experiment and the presentation of the experimental results, predictions of simple one-dimensional uniform and layered soil deterministic models for infiltration are presented and compared to field observations. These models are presented here to provide a base case against which more sophisticated deterministic and stochastic models can be compared in the future. The results indicate that the simple models give adequate predictions of the overall movement of the wetting front through the soil during infiltration. However, the models give poor predictions of point values for water content due to the spatial variability of the soil. Comparisons between the one-dimensional infiltration model predictions and field observations show that the use of the layered soil model rather than the uniform soil model does not consistently improve the accuracy of the predictions for this particular field application. This result illustrates that increasing the spatial resolution of the deterministic characterization of the site in the vertical direction does not always improve the model predictions. Uncertainties due to horizontal spatial variability and due to other difficulties associated with experimental characterization appear to be more significant.

History of Lysimeter Design and Use for Evapotranspiration Measurements

Abstract: Lysimeters are devices for measuring percolation of water through soils and sampling soil water for chemical analyses. Lysimeters have been used for over 300 years to determine water use by vegetation. Precision lysimetry for measuring evapotranspiration (ET) has developed mainly within the past 50 years. Weighing lysimeter designs are quite varied to suite individual research requirements. Surface areas from 1.0 m 2 to over 29 m 2 have been used. ET accuracy depends directly on the lysimeter area, mass, and the type of scale, but many lysimeters have accuracies better than 0.05 mm. Few weighing lysimeters exceed 2.5-m profile depth. Mechanical, floating, hydraulic, and electronic scales have been used in weighing lysimeters with varying types of data recording methods. Lysimeter wall construction can affect heat transfer to the lysimeter and water flow along the walls. ET accuracy of weighing lysimeters can be affected by many additional factors (personnel traffic, cultural operations, crop height, etc.).

In vitro validation of Doppler indices using blood and water.

Abstract: Using an in vitro flow model, volume flow and pressure were measured to compare calculated resistance with simultaneously measured continuous-wave Doppler indices during imposed changes in downstream resistance to pulsatile flow. With stepwise reductions in flow, the peak (S) and trough (D) points of the maximum shifted-frequency envelope fell in parallel in a linear fashion until D reached zero. Pressure remained constant, and the pressure waveform remained unchanged. As calculated resistance increased, resistance index (RI) and pulsatility index (PI) both increased in a linear fashion until the point at which D became zero. However, S/D ratio was not linear, and the slope increased as resistance increased. The results obtained from microspheres suspended in water and with heparinized sheep's blood were similar. The results indicate that, with reductions in flow at constant pressure in vitro, S/D ratio does not relate to calculated resistance in the same linear manner as PI and RI.

A Large-Scale Flow and Tracer Experiment in Granite: 2. Results and Interpretation

Abstract: Water and tracer flow has been monitored in a specially excavated drift in the Stripa mine. Several new experimental techniques and equipment were developed and used. The whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected. Eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift. The flow rate and tracer monitoring was kept up for more than 2 years. The tracer breakthrough curves and flow rate distributions were used to study the flow paths, velocities, hydraulic conductivities, dispersivities and channeling effects in the rock. In a companion paper the experimental design and performed experiments are described. The present paper describes the interpretation of flow and tracer movement in the rock outside the drift. The tracer movement was measured by the more than 160 individual tracer curves. The tracer experiments have permitted the flow porosity and dispersion to be studied. The possible effects of channeling and the diffusion of tracers into stagnant waters in the rock matrix and in stagnant waters in the fractures have also been addressed.

Numerical Modeling of Aggradation and Degradation in Alluvial Channels

Abstract: The Saint-Venant equations describing unsteady flow in open channels and the continuity equation for the conservation of sediment mass are numerically solved to determine the aggradation and degradation of channel bottom due to an imbalance between water flow and sediment discharge. For this purpose, the MacCormack explicit finite-difference scheme is introduced. This scheme is second-order accurate, handles shocks and discontinuities in the solution without any special treatment, and allows simultaneous solution of the water and sediment equations, thereby obviating the need for iterations. The sediment transport relationship in any form may be included in the computations. Computational procedures are outlined for incorporating the typical boundaries for hydraulic engineering applications. The mathematical model presented here is applied to predict (1) Bed-level changes due to sediment overloading; (2) development of longitudinal profile due to base-level lowering; (3) and bed-level changes associated with the migration of knickpoints. The computed results are compared with the available experimental data obtained on laboratory flumes. The agreement between the computed and experimental results is satisfactory.

Water Transport across Maize Roots : Simultaneous Measurement of Flows at the Cell and Root Level by Double Pressure Probe Technique

Abstract: A double pressure probe technique was used to measure simultaneously water flows and hydraulic parameters of individual cells and of excised roots of young seedlings of maize (Zea mays L.) in osmotic experiments. By following initial flows of water at the cell and root level and by estimating the profiles of driving forces (water potentials) across the root, the hydraulic conductivity of individual cell layers was evaluated. Since the hydraulic conductivity of the cell-to-cell path was determined separately, the hydraulic conductivity of the cell wall material could be evaluated as well (Lpcw = 0.3 to 6.10−9 per meter per second per megapascal). Although, for radial water flow across the cortex and rhizodermis, the apoplasmic path was predominant, the contribution of the hydraulic conductance of the cell-to-cell path to the overall conductance increased significantly from the first layer of the cortex toward the inner layers from 2% to 23%. This change was mainly due to an increase of the hydraulic conductivity of the cell membranes which was Lp = 1.9.10−7 per meter per second per megapascal in the first layer and Lp = 14 to 9.10−7 per meter per second per megapascal in the inner layers of the cortex. The hydraulic conductivity of entire roots depended on whether hydrostatic or osmotic forces were used to induce water flows. Hydrostatic Lpr was 1.2 to 2.3.10−7 per meter per second per megapascal and osmotic Lpr = 1.6 to 2.8.10−8 per meter per second per megapascal. The apparent reflection coefficients of root cells (σs) of nonpermeating solutes (KCI, PEG 6000) decreased from values close to unity in the rhizodermis to about 0.7 to 0.8 in the cortex. In all cases, however, σs was significantly larger than the reflection coefficient of entire roots (σsr). For KCI and PEG 6000, σsr was 0.53 and 0.64, respectively. The results are discussed in terms of a composite membrane model of the root.

Environmental effects on co2 efflux from water track and tussock tundra in arctic alaska, u.s.a.

Abstract: CO2 efflux and variation in soil environmental characteristics were examined in two tundra vegetation communities, water track (a small drainage of intermittent water flow) and tussock tundra, in the northern foothills of the Philip Smith Mountains in arctic Alaska Correlation analyses were performed on the observations made at six times during the growing season in order to evaluate the relationships between system CO2 loss and soil moisture, soil temperature, depth of thaw, and depth to the water table The two sites differed significantly in terms of soil moisture, soil temperature, depth of thaw, and water table depth on several of the sampling dates During four of the six measurement periods, the rate of CO2 efflux differed significantly between sites Early in the season, respiration was greater in tussock tundra than at the water track, but later in the season, rates at the water track exceeded those at the tussock site Highest rates were measured at the water track near mid-season Efflux of CO2 at both sites was positively correlated with soil temperature Soil surface (0-5 cm depth) environmental conditions were better predictors of CO2 efflux than were conditions measured at greater depth (5-10 cm) Soil moisture appeared to increase respiration between 100 and 700% of soil dry weight and decrease soil respiration at higher water contents The effects of soil moisture were stronger in tussock tundra than in the water track community These data suggest that both soil temperature and soil moisture limit C02 efflux in water track and tussock tundra communities and that the relative importance of these factors changes throughout the growing season

A Large-Scale Flow and Tracer Experiment in Granite: 1. Experimental Design and Flow Distribution

Abstract: This paper describes the Stripa three-dimensional experiment where water and tracer flow has been monitored in a specially excavated drift in the Stripa mine. Several new experimental techniques and equipment were developed and used. The experiment was performed in a specially excavated drift, 100 m long, at the 360 m level in granite. The whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected. Eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift. The flow rate and tracer monitoring was kept up for more than 2 years. The tracer breakthrough curves and flow rate distributions were used to study the flow paths, velocities, hydraulic conductivities, dispersivities and channeling effects in the rock. This paper describes the experimental techniques, the fracture mapping, the tracer and flow rate measurements and the results of the flow rate measurements. The detailed observations made possible by the plastic sheeting technique have given some qualitative as well as quantitative information on flow rate distribution in fractured rock which previously has not been available. These observations may be of importance for assessing the transport of dissolved species such as radionuclides through fractured rock.

Diacylglycerols induce both ion pumping in patch-clamped guard-cell protoplasts and opening of intact stomata.

Abstract: Stomatal guard cells in leaves regulate the apertures of microscopic pores through which photosynthetic gas exchange and water vapor loss occur. Environmental signals, including light, high humidity, and low CO2 concentrations, open stomata by increasing the volume of guard cells. Activation of a plasma membrane H+ pump initiates K+ and Cl- influx, accompanied by malate synthesis, resulting in osmotic water flow into the guard cells, a bowing apart of the guard-cell pair, and consequent stomatal opening. Physiological and electrophysiological techniques were employed to investigate the possibility that a second-messenger lipid, 1,2-diacylglycerol, is involved in the transduction of opening stimuli. The synthetic diacylglycerols 1,2-dihexanoylglycerol and 1,2-dioctanoylglycerol enhanced light-induced stomatal opening in Commelina communis and induced stomatal opening under darkness, whereas an isomer with no known second-messenger role, 1,3-dioctanoylglycerol, did not affect stomatal responses. 1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine (H-7), an inhibitor of protein kinase C, the enzyme typically activated by 1,2-diacylglycerol in animal cells, inhibited light-stimulated stomatal opening and enhanced dark-induced stomatal closure. N-[(2-Methylamino)ethyl]-5-isoquinolinesulfonamide (H-8), which inhibits cyclic nucleotide-dependent protein kinases preferentially over lipid-dependent protein kinases such as protein kinase C, had little effect on stomatal apertures. Whole-cell patch clamping of guard-cell protoplasts of Vicia faba revealed that 1,2-dihexanoylglycerol and 1-oleoyl-2-acetylglycerol activated an ATP-dependent, voltage-independent current, suggesting activation of an electrogenic ion pump such as the H+ pump. Diacylglycerol or functionally similar lipids may act through protein phosphorylation to provide the intracellular signals that mediate H+-ATPase activation and stomatal opening in response to light or other opening stimuli.

Variable feeding behavior in three species of Macoma (Bivalvia: Tellinacea) as a response to water flow and sediment transport

Abstract: Many species of tellinacean bivalves mainly deposit-feed but are also known to vary their feeding behavior in response to predation and to the availability of suspended organic matter relative to that of sedimentary organic matter. This study showed that three species of the Pacific genusMacoma (Macoma nasuta Conrad, 1937,Macoma secta Conrad, 1837, andMacoma inquinata Deshayes, 1855, from the San Juan Islands, Washington, USA) varied their deposit-feeding behavior in response to water flow near the sediment-water interface and to sediment transport. In the summers of 1987, 1988 and 1989, water velocity was varied in a large racetrack flume, in order to change both water velocity and bottom sediment transport. In quiet water, the inhalant siphon was protruded far from the siphon hole. As water velocity increased, with little or no sediment transport, the deposit-feeding radius decreased. Qualitative observations suggested that this was related to the drag on the siphon. InM. secta, the distance of siphon protrusion was not related to body size. Under conditions of higher near-bottom water velocity, combined with bottom sediment transport, some individuals ceased to deposit-feed, while others sustained feeding by ingesting sediment within the siphon hole, at least 1 cm beneath the sediment-water interface. These results suggest that hydrodynamic conditions are a major determinant of feeding behavior, and previous explanations of variable feeding behavior as a response to predation may have to be adjusted to accommodate this expanded set of responses.

Mercury in the surface water of Swedish forest lakes —concentrations, speciation and controlling factors

Abstract: Concentrations of total Hg and five operationally defined Hg species were determined in the surface water of 25 Swedish forest lakes of different type. Regional and seasonal variations were studied during the ice-free season of 1986. The concentration of total Hg was usually in the range of 2 to 10 μg m-3. Hg concentrations were highly correlated to the concentration of humic matter measured as water color. Hg concentrations were about twice as high in acidic lakes (pH 5) than in circumneutral lakes, which is attributed basically to the acidity of humic compounds acting as Hg carriers in boreal waters. Significant seasonal variations were caused by hydrological processes. During periods of high water flow, Hg concentrations increased dramatically, especially in humic lakes. Between spring and autumn, chemically reactive Hg compounds were gradually replaced by more inert species. Hg/C ratios were higher than in surface runoff from forest watersheds, indicating a significant impact of direct deposition of Hg on lake surfaces during summer. Regional differences were small despite differences in Hg contamination.

Mechanisms of stomatal movement in response to air humidity, irradiance and xylem water potential.

Abstract: Turgor, and osmotic and water potentials of subsidiary cells, epidermal cells and mesophyll cells were measured with a pressure probe and a nanoliter osmometer in intact transpiring leaves of Tradescantia virginiana L. Xylem water potential was manipulated by changing air humidity, light, and water supply. In a transpiring leaf the water potential of mesophyll cells was lower, but turgor was higher, than in cells surrounding the stomatal cavity owing to the presence of a cuticle layer which covers the internal surface of subsidiary and guard cells. Cuticular transpiration from the outer leaf surface was negligibly small. When stomata closed in dry air, transpiration decreased despite an increasing vapor-pressure difference between leaf and air, and the water potential of subsidiary cells dropped to the level of the water potential in mesophyll cells. We suggest that the observed decrease of transpiration at increasing vapor-pressure difference can be attributed to a shortage of water supply to the guard cells from subsidiary cells, causing turgor to decrease in the former more than in the latter. The leafs internal cuticle appears to play a special role in channelling the internal water flow during a water shortage.