Showing papers on "Water flow published in 2003"

Osmotic water transport through carbon nanotube membranes

Abstract: We use molecular dynamics simulations to study osmotically driven transport of water molecules through hexagonally packed carbon nanotube membranes. Our simulation setup comprises two such semipermeable membranes separating compartments of pure water and salt solution. The osmotic force drives water flow from the pure-water to the salt-solution compartment. Monitoring the flow at molecular resolution reveals several distinct features of nanoscale flows. In particular, thermal fluctuations become significant at the nanoscopic length scales, and as a result, the flow is stochastic in nature. Further, the flow appears frictionless and is limited primarily by the barriers at the entry and exit of the nanotube pore. The observed flow rates are high (5.8 water molecules per nanosecond and nanotube), comparable to those through the transmembrane protein aquaporin-1, and are practically independent of the length of the nanotube, in contrast to predictions of macroscopic hydrodynamics. All of these distinct characteristics of nanoscopic water flow can be modeled quantitatively by a 1D continuous-time random walk. At long times, the pure-water compartment is drained, and the net flow of water is interrupted by the formation of structured solvation layers of water sandwiched between two nanotube membranes. Structural and thermodynamic aspects of confined water monolayers are studied.

A coupled model of stomatal conductance, photosynthesis and transpiration

Abstract: A model that couples stomatal conductance, photosynthesis, leaf energy balance and transport of water through the soil–plant–atmosphere continuum is presented. Stomatal conductance in the model depends on light, temperature and intercellular CO2 concentration via photosynthesis and on leaf water potential, which in turn is a function of soil water potential, the rate of water flow through the soil and plant, and on xylem hydraulic resistance. Water transport from soil to roots is simulated through solution of Richards’ equation. The model captures the observed hysteresis in diurnal variations in stomatal conductance, assimilation rate and transpiration for plant canopies. Hysteresis arises because atmospheric demand for water from the leaves typically peaks in mid-afternoon and because of uneven distribution of soil matric potentials with distance from the roots. Potentials at the root surfaces are lower than in the bulk soil, and once soil water supply starts to limit transpiration, root potentials are substantially less negative in the morning than in the afternoon. This leads to higher stomatal conductances, CO2 assimilation and transpiration in the morning compared to later in the day. Stomatal conductance is sensitive to soil and plant hydraulic properties and to root length density only after approximately 10 d of soil drying, when supply of water by the soil to the roots becomes limiting. High atmospheric demand causes transpiration rates, LE, to decline at a slightly higher soil water content, θs, than at low atmospheric demand, but all curves of LE versus θs fall on the same line when soil water supply limits transpiration. Stomatal conductance cannot be modelled in isolation, but must be fully coupled with models of photosynthesis/respiration and the transport of water from soil, through roots, stems and leaves to the atmosphere.

Applied Stochastic Hydrogeology

Abstract: Stochastic hydrogeology, which emerged as a research area in the late 1970s, involves the study of subsurface, geological variability on flow and transport processes and the interpretation of observations using existing theories. Lacking, however, has been a rational framework for modeling the impact of the processes that take place in heterogeneous media and for incorporating it in predictions and decision-making. This book provides this important framework. It covers the fundamental and practical aspects of stochastic hydrogeology, coupling theoretical aspects with examples, case studies, and guidelines for applications.

Rivers and Floodplains: Forms, Processes, and Sedimentary Record

Abstract: 1. Introduction. 2. Overview of River Systems. 3. Fundamentals of Water Flow. 4. Fundamentals of Sediment Transport. 5. Bed forms and Sedimentary Structures. 6. Alluvial Channels and Bars. 7. Floodplains. 8. Along--valley Variations in Channels and Floodplains. 9. Channel--belt movements across floodplains. 10. Long--term, Large--scale Evolution of Fluvial Systems. 11. Fossils in Fluvial Deposits. Appendix 1. Methods of Measuring Bed Topography, Water flow, Sediment Transport, Erosion and Deposition in Rivers. Appendix 2. Methods of Describing and Interpreting Sedimentary Strata. References

Apparent slip flows in hydrophilic and hydrophobic microchannels

Abstract: The slip effects of water flow in hydrophilic and hydrophobic microchannels of 1 and 2 μm depth are examined experimentally. High-precision microchannels were treated chemically to enhance their hydrophilic and hydrophobic properties. The flow rates of pure water at various applied pressure differences for each surface condition were measured using a high-precision flow metering system and compared to a theoretical model that allows for a slip velocity at the solid surface. The slip length was found to vary approximately linearly with the shear rate with values of approximately 30 nm for the flow of water over hydrophobic surfaces at a shear rate of 105 s−1. The existence of slip over the hydrophilic surface remains uncertain, due to the sensitivity of the current analysis to nanometer uncertainties in the channel height.

An α-syntrophin-dependent pool of AQP4 in astroglial end-feet confers bidirectional water flow between blood and brain

Abstract: The water channel AQP4 is concentrated in perivascular and subpial membrane domains of brain astrocytes. These membranes form the interface between the neuropil and extracerebral liquid spaces. AQP4 is anchored at these membranes by its carboxyl terminus to α-syntrophin, an adapter protein associated with dystrophin. To test functions of the perivascular AQP4 pool, we studied mice homozygous for targeted disruption of the gene encoding α-syntrophin (α-Syn−/−). These animals show a marked loss of AQP4 from perivascular and subpial membranes but no decrease in other membrane domains, as judged by quantitative immunogold electron microscopy. In the basal state, perivascular and subpial astroglial end-feet were swollen in brains of α-Syn−/− mice compared to WT mice, suggesting reduced clearance of water generated by brain metabolism. When stressed by transient cerebral ischemia, brain edema was attenuated in α-Syn−/− mice, indicative of reduced water influx. Surprisingly, AQP4 was strongly reduced but α-syntrophin was retained in perivascular astroglial end-feet in WT mice examined 23 h after transient cerebral ischemia. Thus α-syntrophin-dependent anchoring of AQP4 is sensitive to ischemia, and loss of AQP4 from this site may retard the dissipation of postischemic brain edema. These studies identify a specific, syntrophin-dependent AQP4 pool that is expressed at distinct membrane domains and which mediates bidirectional transport of water across the brain–blood interface. The anchoring of AQP4 to α-syntrophin may be a target for treatment of brain edema, but therapeutic manipulations of AQP4 must consider the bidirectional water flux through this molecule.

Liquid–vapor oscillations of water in hydrophobic nanopores

Abstract: Water plays a key role in biological membrane transport. In ion channels and water-conducting pores (aquaporins), one-dimensional confinement in conjunction with strong surface effects changes the physical behavior of water. In molecular dynamics simulations of water in short (0.8 nm) hydrophobic pores the water density in the pore fluctuates on a nanosecond time scale. In long simulations (460 ns in total) at pore radii ranging from 0.35 to 1.0 nm we quantify the kinetics of oscillations between a liquid-filled and a vapor-filled pore. This behavior can be explained as capillary evaporation alternating with capillary condensation, driven by pressure fluctuations in the water outside the pore. The free-energy difference between the two states depends linearly on the radius. The free-energy landscape shows how a metastable liquid state gradually develops with increasing radius. For radii > approximately 0.55 nm it becomes the globally stable state and the vapor state vanishes. One-dimensional confinement affects the dynamic behavior of the water molecules and increases the self diffusion by a factor of 2-3 compared with bulk water. Permeabilities for the narrow pores are of the same order of magnitude as for biological water pores. Water flow is not continuous but occurs in bursts. Our results suggest that simulations aimed at collective phenomena such as hydrophobic effects may require simulation times >50 ns. For water in confined geometries, it is not possible to extrapolate from bulk or short time behavior to longer time scales.

Heat pump water heater

Abstract: A flash water heater using a heat pump includes a heat exchanger in which a refrigerant flow path exchanges heat with a water flow path. Tap water is led directly to the water flow path, and hot water supplied from the water flow path is used. The water heater includes at least one of the following elements: 1) a load setter for setting a heating amount in the heat exchanger, and a heating controller for regulating a heating amount in response to an amount set by the load setter; 2) a heater for heating water flowing through the water flow path in the heat exchanger and water flowing the path before and after the heat exchanger; 3) plural compressors; and 4) plural heat-pump cycles. The water heater is excellent in start-up of hot water temperature when the hot water supply starts, controllability, and efficiency.

The ecological significance of long-distance water transport: short-term regulation, long-term acclimation and the hydraulic costs of stature across plant life forms

Abstract: Plant hydraulic conductance, namely the rate of water flow inside plants per unit time and unit pressure difference, varies largely from plant to plant and under different environmental conditions. Herein the main factors affecting: (a) the scaling between whole-plant hydraulic conductance and leaf area; (b) the relationship between gas exchange at the leaf level and leaf-specific xylem hydraulic conductance; (c) the short-term physiological regulation of plant hydraulic conductance under conditions of ample soil water, and (d) the long-term structural acclimation of xylem hydraulic conductance to changes in environmental conditions are reviewed. It is shown that plant hydraulic conductance is a highly plastic character that varies as a result of multiple processes acting at several time scales. Across species ranging from coniferous and broad-leaved trees to shrubs, crop and herbaceous species, and desert subshrubs, hydraulic conductance scaled linearly with leaf area, as expected from first principles. Despite considerable convergence in the scaling of hydraulic properties, significant differences were apparent across life forms that underlie their different abilities to conduct gas exchange at the leaf level. A simple model of carbon allocation between leaves and support tissues explained the observed patterns and correctly predicted the inverse relationships with plant height. Therefore, stature appears as a fundamental factor affecting gas exchange across plant life forms. Both short-term physiological regulation and long-term structural acclimation can change the levels of hydraulic conductance significantly. Based on a meta-analysis of the existing literature, any change in environmental parameters that increases the availability of resources (either above- or below-ground) results in the long-term acclimation of a less efficient (per unit leaf area) hydraulic system.

An experimental tracer study of the role of macropores in infiltration in grassland soils

Abstract: Water flow in macropores is an important mechanism of infiltration in natural soils and, as such, is crucial for the prediction of runoff generation. The major flow processes controlling macropore flow are the initiation of macropore flow (water supply into macropores) and the water transfer from the macropores into the surrounding soil matrix (interaction). The water movement during infiltration and the resulting flow paths were studied with combined sprinkling and dye tracer experiments under different rainfall intensities and initial soil moisture conditions. The dye tracer was continuously applied with the sprinkling water on 1 m2 plots. After the sprinkling, horizontal and vertical soil sections were prepared for surveying dye patterns, which showed the cumulated flow pathways in the soils. These experiments were carried out on four hillslope sites covered with grassland, where earthworms mainly built the macropore system. The evaluation of the flow processes in the soil was based on classified dye patterns and measurements of water content and matric potential. The results illustrate how flow in earthworm channels influences general hydrological flow processes during extreme rainfall events. Macropore flow was initiated from the soil surface or from a saturated or partially saturated soil layer. Transfer of water from the macropores into the soil matrix was mainly influenced by the soil properties and soil water content. The permeability of the underlying bedrock in combination with this transfer of water controlled the drainage of the macropores. Finally, major effects of macropore flow processes on the hydrological response were extracted. Infiltration excess overland flow was reduced if water bypassed the less permeable layer through macropores, saturation excess overland flow was less affected by macropores, and subsurface flow was activated very rapidly because the infiltrated water bypassed the soil matrix. This study highlights the most important processes that have to be considered in order to understand better and to model infiltration in natural soils in the future. Copyright © 2003 John Wiley & Sons, Ltd.

Cool Indonesian throughflow as a consequence of restricted surface layer flow

Abstract: Approximately 10 million m3 x s(-1) of water flow from the Pacific Ocean into the Indian Ocean through the Indonesian seas. Within the Makassar Strait, the primary pathway of the flow, the Indonesian throughflow is far cooler than estimated earlier, as pointed out recently on the basis of ocean current and temperature measurements. Here we analyse ocean current and stratification data along with satellite-derived wind measurements, and find that during the boreal winter monsoon, the wind drives buoyant, low-salinity Java Sea surface water into the southern Makassar Strait, creating a northward pressure gradient in the surface layer of the strait. This surface layer 'freshwater plug' inhibits the warm surface water from the Pacific Ocean from flowing southward into the Indian Ocean, leading to a cooler Indian Ocean sea surface, which in turn may weaken the Asian monsoon. The summer wind reversal eliminates the obstructing pressure gradient, by transferring more-saline Banda Sea surface water into the southern Makassar Strait. The coupling of the southeast Asian freshwater budget to the Pacific and Indian Ocean surface temperatures by the proposed mechanism may represent an important negative feedback within the climate system.

Theory and Practical Application of Heat Pulse to Measure Sap Flow

Abstract: Heat pulse methods can be used for accurate measurements of sap flow in plant stems provided a reliable calibration procedure is used to relate the measured heat pulse velocity to the actual sap flow. This paper reviews the theory underpinning both the compensation and T-max heat pulse methods that use a linear heater and temperature probes inserted radially into the plant stem. These probes not only disrupt the sap stream, but they also alter the thermal homogeneity of the sapwood in the vicinity of the probes. The degree of disturbance depends on the size and geometry of the probes and the corresponding wound width of the nonconducting sapwood. A two-dimensional model of heat and water flow was used here to derive appropriate correction factors to account for the influence of both probe thermal properties and flow blockage. Wound width has a large influence on the heat pulse measurements while sensor material appears to have little or no influence. A table of correction factors is presented for both the compensation and T-max methods. These new correction factors are confirmed by comparing heat pulse measurements in the trunk of a willow (Salix alba L.) and a poplar (Populus deltoides W. Bartram ex Marsh), against actual rates of transpiration determined from measured weight loss of the trees growing in large lysimeters. On a daily basis, both heat pulse measurements were found to be within 5 to 10% of the actual transpiration. The compensation method accurately measured flows close to 2 cm/h. The T-max method had difficulty resolving any flows slower than about 10 cm/h.

Dynamic changes in hydraulic conductivity in petioles of two savanna tree species: factors and mechanisms contributing to the refilling of embolized vessels

Abstract: Diel variation in specific hydraulic conductivity (ks) was recorded in petioles of two savanna tree species, Schefflera macrocarpa and Caryocar brasiliense, from central Brazil. These two species have compound leaves with long petioles (10–30 cm). In both species, petiole ks decreased sharply with increasing transpiration rates and declining leaf water potentials (ψL) during the morning. Petiole ks increased during the afternoon while the plants were still transpiring and the water in the non-embolized vessels was still under tension. Dye experiments confirmed that in both species diel variation in ks was associated with embolism formation and repair. When transpiration was prevented in individual leaves, their petiole ks and water potential remained close to their maximum values during the day. When minimum daily ψL on selected branches was experimentally lowered by 0.2–0.6 MPa, the rate of ks recovery during the afternoon was slower in comparison with control branches. Several field manipulations were performed to identify potential mechanisms involved in the refilling of embolized petiole vessels. Removal of the cortex or longitudinal incisions in the cortex prevented afternoon recovery of ks and refilling of embolized vessels. When distilled water was added to petiole surfaces that had been abraded to partially remove the cuticle, ks increased sharply during the morning and early afternoon. Evidence of starch to sugar conversion in the starch sheath cells surrounding the vascular bundles of the petioles was observed during periods of rapid transpiration when the abundance of starch granules in the starch sheath cells surrounding the vascular bundles decreased. Consistent with this, petiole sugar content was highest in the early afternoon. The most parsimonious explanation of the field observations and the experimental results was that an increase in osmotically active solutes in cells outside the vascular bundles at around midday leads to water uptake by these cells. However, the concurrent increase in tissue volume is partially constrained by the cortex, resulting in a transient pressure imbalance that may drive radial water movement in the direction of the embolized vessels, thereby refilling them and restoring water flow. This study thus presents evidence that embolism formation and repair are two distinct phenomena controlled by different variables. The degree of embolism is a function of tension, and the rate of refilling a function of internal pressure imbalances.

Alveolar Type I Cells: Molecular Phenotype and Development

Abstract: Understanding of the functions and regulation of the phenotype of the alveolar type I epithelial cell has lagged behind studies of its neighbor the type II cell because of lack of cell-specific molecular markers. The recent identification of several proteins expressed by type I cells indicates that these cells may play important roles in regulation of cell proliferation, ion transport and water flow, metabolism of peptides, modulation of macrophage functions, and signaling events in the peripheral lung. Cell systems and reagents are available to characterize type I cell biology in detail, an important goal given that the cells provide the extensive surface that facilitates gas exchange in the intact animal.

Analysis of soil wetting and solute transport in subsurface trickle irrigation

Abstract: The increased use of trickle or drip irrigation is seen as one way of helping to improve the sustainability of irrigation systems around the world. However, soil water and solute transport properties and soil profile characteristics are often not adequately incorporated in the design and management of trickle systems. In this paper, we describe results of a simulation study designed to highlight the impacts of soil properties on water and solute transport from buried trickle emitters. The analysis addresses the influence of soil hydraulic properties, soil layering, trickle discharge rate, irrigation frequency, and timing of nutrient application on wetting patterns and solute distribution. We show that (1) trickle irrigation can improve plant water availability in medium and low permeability fine-textured soils, providing that design and management are adapted to account for their soil hydraulic properties, (2) in highly permeable coarse-textured soils, water and nutrients move quickly downwards from the emitter, making it difficult to wet the near surface zone if emitters are buried too deep, and (3) changing the fertigation strategy for highly permeable coarse-textured soils to apply nutrients at the beginning of an irrigation cycle can maintain larger amounts of nutrient near to and above the emitter, thereby making them less susceptible to leaching losses. The results demonstrate the need to account for differences in soil hydraulic properties and solute transport when designing irrigation and fertigation management strategies. Failure to do this will result in inefficient systems and lost opportunities for reducing the negative environmental impacts of irrigation.

Hydrologic and hydraulic control of macrophyte establishment and performance in streams

Abstract: Macrophytes play a key role in many unshaded lotic ecosystems, but little is known of the factors controlling their presence, abundance, and composition. Macrophyte abundance, diversity, and composition were studied in 15 New Zealand streams to test the hypotheses that the presence and development of macrophytes in lotic systems is primarily controlled by the hydrologic regime (frequency of high-velocity flood events) and that the interflood spatial distribution and performance of taxa in more stable systems is strongly influenced by local hydraulic conditions (depth/velocity/sediments). Both hypotheses were supported by our results. We found that the abundance and diversity of macrophytes decreased as flood disturbance frequency increased ( r 2 5 0.52, P 5 0.002 for abundance; r 2 5 0.53, P 5 0.022 for diversity) and that vegetation was absent in streams with more than ;13 highflow disturbances per year. An experiment in an ecohydraulics flume identified that the main mechanism causing these effects was not stem breakage at high water velocity but probably uprooting associated with bed sediment erosion. We found that plants with high propagule production constituted a greater proportion of the vegetation in more flood disturbed streams than in stable streams, suggesting that this species trait is important for the maintenance of macrophyte communities in flood prone streams. Distinct velocity, depth, and substrate particle size habitat preferences were displayed by four common species in the study streams. None of the macrophytes showed overlapping preferences for all three habitat variables, suggesting coexisting of the species in streams by physical niche separation. These results significantly expand our understanding of the role of flow regimes in determining lotic ecosystem structure and functioning. Macrophytes play a key role in unshaded streams by increasing physical heterogeneity, trapping fine sediments, and providing extensive habitat for periphyton, invertebrates, and fish (Biggs 1996a). However, macrophytes can also proliferate and severely impede water flow, degrade water quality through their effects on pH and dissolved oxygen, and degrade aesthetic/recreational values in streams (Haslam 1978; Nichols and Shaw 1986; Biggs 1996a). Optimal management of streams will require information to predict macrophyte abundance and diversity. At present, we cannot even answer basic questions such as why macrophytes colonize and grow successfully in some streams but not others, and once they do colonize what controls patchiness, overall biomass, and community structure. Obtaining such knowledge is very important because stream macrophytes can drive physical conditions, periphyton, benthic invertebrates, and (possibly) fish communities to quite different states compared with unvegetated channels (e.g., Burkholder 1996; Death 2000). Biggs (1996a) posited a hierarchical conceptual model of factors that may strongly influence macrophyte development

Fluid Motion Generated by Impact

Abstract: In this paper we describe laboratory experiments and numerical simulations of the impact between a rigid body and water. The rigid body consists of a weighted rectangular box that slides down a curved ramp to enter the water at an angle to the horizontal of approximately 15°. As the box enters the water, a vigorous spray projects fluid beyond the box, then, as the water is heaved up, it falls back on the upper surface of the box and initiates a solitary wave. The experiments cover a wide range of impact velocities and three water depths in the main body of the tank. The experiments have been simulated using the Lagrangian particle method smoothed particle hydrodynamics (SPH).

The Rule of Water: Statecraft, Ecology, and Collective Action in South India

Abstract: This volume uses long-term anthropological fieldwork, oral histories and detailed archival work to explore the changing ecology, political significance and cultural meaning of water in south India. Focusing on the ancient and complex 'tank' irrigation systems of a coastal plains region, the book develops an account of the interplay between social and political organization and the ecology of water flows. This begins with an account of the centrality of water resources to the organization of a pre-colonial warrior state in which power and the control of resources were decentralized, and goes on to explore the conflicts and contradictions that emerged within this social system of water use under colonial rule. In its ethnographic chapters, the book describes cultural practices and ritual systems that connect hydrology and power within and between inter-linked villages, and then examines contrasting levels of collective action in common property water use across a catchment, and underlying 'cultural ecologies'. The book's historical and social analysis of water as a medium of political and social relations challenges narrow economistic interpretations of common property resources. It argues for a more historically grounded understanding of landscapes, rights and rules or resource use. At the same time the book indicates the importance of water in the idioms and organizations of power, whether of kings, colonial bureaucrats or development institutions. Through this work the reader not only encounters the intricate technology, ecology and politics of water in south India, but also the colonial, ecological and development visions that have and continue to be the centre of important policy debates on the relationship between state and society.

Hydrological studies on blanket peat: the significance of the acrotelm‐catotelm model

Abstract: 1 Runoff production in blanket peat catchments of the northern Pennine hills, UK was measured through monitoring and experimentation at the plot, hillslope and catchment scale. Water flow from soil pipes was measured in one of the study catchments and overland flow, throughflow and water table were measured in runoff plots; rainfall simulation and tension-infiltrometry provided information on infiltration characteristics of the peat. 2 Saturation-excess overland flow was found to dominate the flashy flow regime; acrotelm stormflow, subsurface pipeflow and macropore flow were also found to be important components of the ecohydrological system. 3 Surface cover, topography and preferential flowpaths were found to be important factors in controlling infiltration and runoff production. 4 Streamflow generation processes that are consistent with the acrotelm-catotelm model are shown to occur in blanket peat with and without Sphagnum cover, but in one of the catchments studied an estimated 10% of the discharge bypassed this route and discharged via pipes. 5 The spatial and temporal variation in hillslope-scale runoff production was demonstrated in the study catchments. This variability in runoff production will be important for hydroecological understanding in peatlands but is often neglected because of over-simplification of processes provided by the traditional two-dimensional acrotelm-catotelm model.

Relationship between the Hydraulic Conductivity Function and the Particle-Size Distribution

Abstract: We present a model to compute the hydraulic conductivity, K, as a function of water content, θ, directly from the particle-size distribution (PSD) of a soil. The model is based on the assumption that soil pores can be represented by equivalent capillary tubes and that the water flow rate is a function of pore size. The pore-size distribution is derived from the PSD using the Arya-Paris model. Particle-size distribution and K(θ) data for 16 soils, representing several textural classes, were used to relate the pore flow rate and the pore radius according to q i = cr i x , where q i is the pore flow rate (cm 3 s -1 ) and r i is the pore radius (cm). Log c varied from about -2.43 to about 2.78, and x varied from 2.66 to = 4.71. However, these parameters did not exhibit a systematic trend with textural class. The model was used to independently compute the K(θ) function, from the PSD data for 16 additional soils. The model predicted K(θ) values from near saturation to very low water contents. The agreement between the predicted and experimental K(θ) for individual samples ranged from excellent to poor, with the root mean square residuals (RMSR) of the log-transformed K(θ) ranging from 0.616 to 1.603 for sand, from 0.592 to 1.719 for loam, and from 0.487 to 1.065 for clay. The average RMSR for all textures was 0.878.

Experimental study on flow characteristics of liquid in circular microtubes

Abstract: Glass, silicon, and stainless steel microtubes with diameters of 79.9–166.3 μm, 100.25–205.3 μm, and 128.76–179.8 μm, respectively, were employed to study the characteristics of frictional resistance for deionized water flow in microtubes. Glass and silicon microtubes can be treated as smooth ones, whereas stainless steel microtubes with 3%–4% relative roughness has to be treated as coarse ones. It can be concluded from experimental results that for fully-developed water flow in smooth glass and silicon microtubes, the product of Darcy friction factor f and Reynolds number Re remains approximately 64, which is consistent with the results in macrotubes. While the value of f ˙ Re for water flow in rough stainless steel microtubes is 15%–37% higher than 64, it is distinctly different from the conventional conclusion that relative roughness below 5% has no effect on the flow resistance for incompressible fluid flow in macrotubes.

Running Pure : The Importance of Forest Protected Areas to Drinking Water

Abstract: This report focuses on one specific interaction: the role of forests, and particularly protected forests, in maintaining quality of drinking water for large cities. There are many reasons for this focus: many city dwellers already face a crisis of water quality, and contaminated water spreads a vast and largely unnecessary burden in terms of short and long-term health impacts including infant mortality, with knock-on effects on ability to work, industrial productivity and on already over-stretched health services. The poorest members of society, unable to afford sterilized or bottled water, suffer the greatest impacts. Similar problems affect the rural poor as well of course, and sometimes these can be even more severe. However, in a rapidly urbanizing world the scale of the problem facing cities is particularly acute.

Soil macropore dynamics affected by tillage and irrigation for a silty loam alluvial soil in southern Portugal

Abstract: Soil tillage can have a significant effect on soil porosity and water infiltration. This study reports field measurements of near saturated hydraulic conductivity in an undisturbed soil under two tillage treatments, conventional tillage (CT) and minimum tillage (MT). The objective was to determine effective macro and mesoporosities, porosity dynamics during the irrigation season, and their contribution to water flow. Field observations were performed during the 1998 maize ( Zea mays L.) cropping season in an Eutric Fluvisol with a silty loam texture, located in the Sorraia River Watershed in the south of Portugal. Infiltration measurements were done with a tension infiltrometer. At each location an infiltration sequence was performed corresponding to water tensions ( φ ) of 0, 3, 6 and 15 cm. Five sets of infiltration measurements were taken in both treatments in the top soil layer between May and September. One set of measurements was done at the depth of 30 cm at the bottom of the plowed layer in the CT plot. After 5 years of continuous tillage treatments the results show that regardless of the tillage treatment, saturated conductivity values K ( φ 0 ) were several times larger than near saturation conductivity K ( φ 3 ). This indicates that subsurface networks of water conducting soil pores can exist in both CT and MT maize production systems. In CT, the moldboard plow created macro and mesoporosity in the top soil layer while breaking pore continuity at 30 cm depth. This porosity was partially disrupted by the first irrigation, resulting in a significant decrease of 45% in the macropore contribution to flow. Later in the season, the irrigation effect was overlaid by the root development effect creating new channels or continuity between existing pores. In MT macroporosity contribution to flow did not show significant differences in time, representing 85% of the total flow. In both the treatments, macropores were the main contributing pores to the total flow, in spite of the very low macroporosity volumes.

Growth rate, condition, and shell shape of Mytilus galloprovincialis: responses to wave exposure

Abstract: Growth rates, condition indices and shell shapes of Mytilus galloprovincialis, an inva- sive alien mussel that has colonised the west coast of South Africa, were measured at a series of sites with different wave exposure regimes in 2 regions 500 km apart. Wave action at the sites was deter- mined by maximum wave-force dynamometers. M. galloprovincialis grew faster and had higher con- dition values on exposed than on sheltered shores, probably due to higher food availability at sites with greater water flow. Growth rates and condition values, however, declined at sites experiencing extreme wave action. This resulted in a polynomial relationship between the growth coefficient K, and wave force. Mussels grew slower in the southern region, where food concentrations are lower. The shells of M. galloprovincialis tended to be lower and narrower at exposed sites, perhaps reduc- ing the effect of hydrodynamic forces. Mussel shells were thickest on sheltered and extremely exposed shores. The results are discussed in the context of the impact that M. galloprovincialis is likely to have on indigenous species. Because M. galloprovincialis is scarce and slow-growing at sheltered sites, its competitive effects there are likely to be minimal, whereas on exposed sites its density, growth and condition are highest and its effects will peak, diminishing again at extremely exposed sites.