Unidirectional Water Flow Research Articles

Hydrodynamic stimuli and the fish lateral line.

Sensory systems need to distinguish biologically relevant stimuli from background noise. Here we investigate how the lateral-line mechanosensory system of the fish senses minute water motions1 in the vicinity while exposed to running water. We find that one class of receptor in the lateral line, the canal neuromasts, can respond to hydrodynamic stimuli even in the presence of unidirectional water flow, whereas superficial neuromasts, which predominate in still-water fish, cannot.

Responses of Anterior Lateral Line Afferent Neurones to Water Flow

The mechanoreceptive lateral line system detects hydrodynamic stimuli and plays an important role in a number of types of fish behaviour, including orientation to water currents. The lateral line is composed of hair cell receptor organs called neuromasts that occur as superficial neuromasts on the surface of the skin or canal neuromasts located in subepidermal canals. Both are innervated by primary afferents of the lateral line nerves. Although there have been extensive studies of the response properties of lateral line afferents to vibrating sources, their response to water flow has not been reported. In this study, we recorded extracellularly from anterior lateral line afferents in the New Zealand long-fin eel Anguilla dieffenbachii while stimulating the eel with unidirectional water flows at 0.5-4 cm s(-)(1). Of the afferents, 80 % were flow-sensitive to varying degrees, the response magnitude increasing with flow rate. Flow-sensitive fibres gave non-adapting tonic responses, indicating that these fibres detect absolute flow velocity. Further studies are needed to confirm whether flow-sensitive and flow-insensitive fibres correlate with superficial and canal neuromasts, respectively.

Preliminary communication:Novel method for uniform orientation of liquid crystal molecules by a polyimide surface exposed to a water flow

A novel technique for surface-induced orientation of liquid crystal (LC) molecules is proposed, using a polyimide surface exposed to a unidirectional water flow. The LC molecules director was unidirectionally oriented along the water flow direction on the polyimide surface. The orientational state of the LC director was strongly dependent upon whether the water flow exposure was carried out before or after thermal curing for imidization, and also upon the temperature of water flow.

The existence of molecular water pumps in the nervous system: a review of the evidence

Recently, the presence of both influx and efflux molecular water pumps (MWPs) in vertebrate cells has been reported. These appear to use a common mechanism; the intercompartmental cotransport of water uphill against a gradient as a hydrophylic osmolyte is transported down its own gradient, in a regulated fashion, by a membrane spanning cotransporter protein. In each case, the dwell time of the transported osmolyte is short in that it is metabolically converted and its products either eliminated or recycled, thereby maintaining the required high intercompartmental gradient. An influx water pump osmolyte has been identified as a sodium-glucose complex, and an efflux water pump osmolyte as N-acetylhistidine. These osmolytes may also be archetypal representatives of many other osmolytes with similar functions in a variety of cells. When recycled, the osmolyte metabolites appear to be dewatered during high affinity binding that is associated with their active transport back across the membrane prior to intracellular resynthesis of the osmolyte. Since these cyclical systems result in the pumping of water, they also appear to create a previously unrecognized motive force which results in the establishment of unidirectional transcellular water flows between apical and basolateral cell membranes. As neurons represent highly specialized forms of animal cells, and cells which are also extremely sensitive to changes in osmotic pressure, the presence of these water pumps in the CNS could be significant. There would be connotations with regard to how neurons regulate water balance and transaxonal flow as well as to how these factors affect the integrated function of the nervous system. In this article, evidence of the presence of MWPs in the nervous system, and how they might relate to aspects of both normal and abnormal brain function is reviewed.

Effects of unidirectional and oscillatory water flow on nitrogen fixation (acetylene reduction) in coral reef algal turfs, Kaneohe Bay, Hawaii

Rates of acetylene reduction (nitrogenase activity) by algal turf communities from Kaneohe Bay, Oahu, Hawaii, were measured as a function of increasing water flow speeds under unidirectional and oscillatory flow regimes in an enclosed incubation chamber. Water flow speeds, shear stress, and turbulence intensities were measured with thermistor probes in the chamber and over the turfs in the field. The thickness of the boundary layer varied significantly and linearly with bulk water flow speeds in the field. Although the boundary layer in the chamber also decreased with increasing flow speeds, turbulence intensity and flow speeds in the chamber were mostly lower than those typically measured in the field. Rates of acetylene reduction were positively related to water flow speed. Oscillatory water flow, which increased turbulence intensity five times, resulted in a significant increase in acetylene reduction compared to unidirectional flow. Even at the lowest mean flow speeds measured in the field (<0.1 m s −1), mean rates of acetylene reduction (27 nmol ethylene cm −2 h −1±11 SD) were high under oscillatory flow. Equivalent high rates under unidirectional flow were not achieved until flow speed was more than doubled. The slope of log–log linear regressions of acetylene reduction versus flow speed was 0.5 for both oscillatory and unidirectional regimes. This result suggests that acetylene reduction rates in the chamber were controlled by mass transfer of a rate-controlling solute, such as acetylene or oxygen (inhibitory to nitrogenase), through a laminar diffusion boundary layer. Because coral reefs exist in areas of very low nitrogen availability, nitrogen fixation is fundamentally important for coral reef primary production and biogeochemistry. Yet, current understanding of nitrogen fixation on coral reefs has been derived primarily from measurements made under unnatural conditions of no or low water flow. This study lends support to the importance of water flow as a major control of the metabolism of organisms occupying coral reefs.

HOW BENTHIC MACROALGAE COPE WITH FLOWING FRESHWATER: RESOURCE ACQUISITION AND RETENTION

ABSTRACTThe unidirectional water flow to which stream macro‐algae are exposed imposes mechanical strseses that vary with the life‐form of the algae. The stress, and thus the possibility of breaking or detaching with loss of previously accumulated resources, is least in the boundary‐layer forms (crusts, turfs) and greatest in the semierect forms (mucilaginous and nonmucilaginous filaments, and tissuelike thalli). Present evidence on the resource costs of providing semierect forms with the observed safety factor in minimizing the chance of breakage under normal flow conditions does not permit useful comparisons to be made with resource acquisition benefits of exposure to rapid water flow. These benefits relate to minimizing boundary‐layer thickness, with a consequent increase in the potential flux of nutrient solutes to the algal surface. Such enhanced fluxes are significant in habitats in which (as is often the case) algal growth is nutrient‐limited. By contrast, crusts and turfs have lower potential nutrient fluxes due to the thick boundary layers around the substratum to which they are attached. A possible advantage for resource acquisition of the thick boundary layers associated with crusts and turfs relates to the use of extracellular catalysis by the alga of the conversion of the supplied form of nutrient (e.g. HCO3‐, organic P, Fe3+) into the form taken up (CO2, inorganic P, Fe2+, respectively). A thick boundary layer restricts the loss of the transformed nutrient species to the bulk, rapidly flowing medium thus favoring uptake of CO2, inorganic P, or Fe2+. The influence of the stream on photosynthesis and growth via light supply involves shading by riparian vegetation and shading of low‐growing algae (crusts and turfs) by semierect algae as well as by semierect submerged bryophytes and tracheophytes. The shading of boundary‐layer forms by semierect plants further constrains the photo synthetic rate achieved in situ by crusts and turfs. The negative effect of shading on productivity is mitigated by the generally low (less than 25% of full sunlight) photon flux density needed for photosyn‐thetic (and net productivity) saturation of stream macro‐algae, especially when nutirents are limiting. There is relatively little acclimation to changed total photon flux density and its spectral distribution within the natural range. Problems of upstream migration could be partially resolved by herbivorous motile animals as vectors. Despite potential problems for grazers on semierect algae due to rapid water movement, it is not clear that such algae are less grazed than crusts or turfs. Further work in certain areas could yield important results using currently available techniques. Examples are 1) the role of water flow per se (independent of boundary layer effects) on growth, 2) the allocation of resources to structural elements as a function of water flow, 3) the effect of flow on bidirectional transmembrane fluxes (influx and efflux measured with tracers) of nutrients (corrected for boundary‐layer effects), and 4) the role of animal vectors in upstream dispersal. Positive results in 1–3, that is, an effect of increased flow on growth, resource allocation, and transplasmalemma fluxes, could indicate a role for mechanosensitive (= stretch‐sensitive) ion channels and other membrane transport systems.

Kinematics of Aquatic Prey Capture in the Snapping Turtle Chelydra Serpentina

ABSTRACT The kinematics of feeding on two prey types is studied quantitatively in the common snapping turtle, Chelydra serpentina, to provide a description of prey capture mechanisms and to determine whether kinematic patterns can be altered in response to prey that vary in escape capability. High-speed video recordings of prey capture (200 fields s-1) provide data for field-by-field analysis of 12 kinematic variables characterizing head and neck movement. Feedings on fish were accomplished in 78 ms, with peak head extension velocities of 152.5 cm s-1. Worm feedings lasted 98 ms with maximum head extension velocities of 54cms-1. Both univariate and multivariate statistical analyses demonstrate significant differences in kinematic patterns between fish and earthworm feedings: Chelydra serpentina possesses the ability to modulate its kinematic pattern depending on the prey. The pattern of bone movement during the fast opening phase of the gape cycle is similar to that found in ray-finned fishes, lungfishes and aquatic salamanders. However, movements of the cranium and lower jaw during the closing phase are markedly different. Our data show Chelydra to be predominantly a ram-feeder, with any intraoral negative pressures generated during the strike having a negligible effect on the prey, which remains largely stationary relative to a fixed background. Hyoid and esophageal expansion during the closing phase may function to allow a unidirectional flow of water and prey into the mouth until the gape closes and to delay reverse flow until the prey has been trapped inside the mouth. The independent evolutionary acquisition of aquatic feeding in fishes and turtles reveals some kinematic similarities that may be the result of hydrodynamic constraints on aquatic prey capture systems, as well as kinematic differences that result from the fundamentally different morphological design of the prey capture apparatus.

Measurement of filtration rates by infaunal bivalves in a recirculating flume

A flume system and protocol for measuring the filtration rate of infaunal bivalves is described. Assemblages of multi-sized clams, at natural densities and in normal filter-feeding positions, removed phytoplankton suspended in a unidirectional flow of water. The free-stream velocity and friction velocity of the flow, and bottom roughness height were similar to those in natural estuarine waters. Continuous variations in phytoplankton (Chroomonas salinay) cell density were used to measure the filtration rate of the suspension-feeding clam Potamocorbula amurensis for periods of 2 to 28 h. Filtration rates of P. amurensis varied from 100 to 580 liters (gd)-1 over a free-stream velocity range of 9 to 25 cm s-1. Phytoplankton loss rates were usually constant throughout the experiments. Our results suggest that suspension-feeding by infaunal bivalves is sensitive to flow velocity.

Physiological and Anatomical Factors Affecting Intestinal Drug Absorption and Absorption Enhancement by Modifying Their Factors.

As physiological and anatomical factors affecting intestinal drug absorption, unidirectional water flow, solvent drag, absorptive site blood flow and electrophysiological parameters such as membrane resistance and capacitance were examined. Effects of some absorption enhancers on the two absorption pathways, the transcellular and paracellular pathways, were also examined from the alteration of the above factors. One of the effective enhancers, sodium caprate (C10), increased the following absorption parameters for the paracellular pathways : (i) the equivalent pore radius which was obtained by the water absorption ; (ii) the permeabilities of water-soluble nonelectrolytes and ionic drugs ; (iii) junctional resistance and basolateral membrane capacitance which were obtained by impedance analysis. The C10 effects on the trancellular pathway were found in the membrane perturbation which was obtained by fluorescence polarization. For the action mechanism of C10 in the paracellular pathways, the C10 effect on the physiological regulation of membrane, stimulation of C10 to contraction of perijunctional actomyosin ring, is now under investigation.

Bed configuration in steady unidirectional water flows; Part 2, Synthesis of flume data

Data from 39 flume studies that report equilibrium bed configuration as well as water temperature, flow depth, flow velocity, and sediment size are used to develop the best approximation to the relationships among bed phases (ripples, dunes, lower-regime plane bed, upper-regime plane bed, and antidunes) produced by flows of water over loose sediments. We use a three-axis graph with dimensionless measures of mean flow depth, mean flow velocity, and sediment size along the axes. The relationships are presented as a series of depth-velocity sections and velocity-size sections through the dimensionless diagram. Boundaries between stability fields of the bed phases were drawn as smooth surfaces that minimize misplacement of data points. A large subset of the data, for which reliable values of bed shear stress are reported, was used to represent the stability relationships of the bed phases in a graph of dimensionless boundary shear stress against dimensionless sediment size. The graph shows substantial overlapping of the fields for dunes, upper plane bed, and antidunes owing to the decrease in bed shear stress in the transition from dunes to plane bed with increasing flow velocity. The topology of bed-phase boundaries was guided by the relationships shown in the dimensionless depth-velocity-size diagram.

Bed configurations in steady unidirectional water flows; Part 3, Effects of temperature and gravity

ABSTRACT A change in bed configuration caused by a change in water temperature without any change in flow and sediment variables in a unidirectional flow is analyzed in the context of the dimensionless depth-velocity-size diagram discussed in Part 2. Bed states that differ only in water temperature are termed temperature-related states. These are attainable from any given state solely by a change in water temperature. Such a set of bed states forms a curve in the dimensionless depth-velocity-size diagram. This curve, a straight line in a log-log-log plot, is termed a temperature-change line. To predict the change in bed state consequent upon a change in water temperature alone, one finds the temperature-related state lying along the temperature-change line passing through the ori inal bed state in the dimensionless depth-velocity-size diagram. Three examples from the literature are analyzed in this way to show how such changes in bed configuration can be put into the context of existing stability relationships among the various bed phases, without however addressing the general dynamical problem of why those relationships are as they are. The effect of the acceleration of gravity on the bed configuration is also examined from the standpoint of the dimensionless depth-velocity-size diagram. The results show that in a hypothetical open-channel water flow on Mars a given transition between two adjacent bed phases with increasing flow velocity (e.g., ripples to dunes) would take place at a lower velocity on Mars than on earth, by a factor of 0.74.

Bed Configurations in Steady Unidirectional Water Flows. Part 1. Scale Model Study Using Fine Sands

ABSTRACT Reynolds-Froude scale modeling using hot-water flows to model cold-water flows was applied to the study of unidirectional-flow bed configurations in a large, thermally insulated laboratory flume. Three different water temperatures, ranging from 14 to 75°C, provided three different scale ratios, from 1.1 to 2.3. Effective sand sizes, scaled to 10°C water, were about 0.12 mm, 0.18 mm, and 0.28 mm. Relative to 10°C water, use of hot water multiplied the effective flow depth and all flume dimensions by factors of up to 2.3, the flow velocity by factors of up to 1.5, and the water discharge by factors of up to 8. The effective dimensions of the flume, scaled to 10°C water temperature, ranged up to over 26 m long and 2 m wide, with a flow depth of up to 0.5 m. In the coarser sand sizes (0.17-0.26 mm), three bed phases were observed: ripples, dunes, and upper-regime plane bed. Dunes tended to be two-dimensional (crests straight and continuous) at low flow velocities and three-dimensional (crests sinuous and discontinuous) at relatively high flow velocities, except that at flow velocities transitional between ripples and dunes the bed showed a complex intermingling of irregular larger dunelike bed forms and smaller irregular ripples. In the dune range, ripples were prominently superimposed at relatively low flow velocities but nearly absent at relatively high flow velocities.

Cohesive Material Erosion by Unidirectional Current

The initiation of motion of consolidated cohesive sediments under a unidirectional flow of clear water was studied. Experiments were performed in a flume‐tunnel capable of providing a bed shear stress up to 26 Pa and a velocity of 3.5 m/s, 3 mm above the bed. Samples were prepared in a specially designed press using a carefully controlled consolidation procedure. Critical shear stress and velocity were found to increase with compressive strength, vane shear strength, plasticity index, clay content, and consolidation pressure.

Sedimentation in fluvial and lacustrine environments

Sedimentation in rivers is dominated by a complex set of physical processes, associated with the unidirectional flow of water. Variations in these processes give rise to different fluvial channel types, whose character can commonly be recognised in the ancient record. Chemical and biological processes are comparatively unimportant in fluvial sedimentation.

Differential Transport of Sand Grains: Ripples and Dunes, A Suspension Criterion: ABSTRACT

Differential transport of sand grains by unidirectional water flow over a cohesionless bed material having superimposed ripples or dunes results in hydraulic sorting. Hydraulic sorting occurs on many scales in natural fluvial systems, e.g., flood plain vs. channel deposits, bed vs. load in transit, various parts of cross-bed sets or individual laminae, etc. The mechanisms of hydraulic sorting include differential entrainment at the source, differential deposition and differential transport rates which are sensitive to prevailing bed configurations. By comparing transport rates of individual grain sizes calculated from size analysis of bed material and load under ripple and dune conditions, it is shown that the sampled load may be differentiated into two subpopulations of rains moved by different transport mechanisms, namely, those particles confined to transport within bed forms, and intermittent suspension load. Due to practical limitations in the flume, this study is limited to the two coarsest subpopulations observed in typical samples of river sediment. Theory and results of flume experiments suggest the following approximate hydraulic criterion for separating the two mechanisms of sediment transport: the point where the relative difference in transport rates between size fractions increases abruptly. This criterion is confirmed by flume experiments for flow conditions spanning the stability fields for ripples and dunes. End_of_Article - Last_Page 1682------------

Source of net water and electrolyte loss following intestinal ischaemia.

Ischaemia of the dog intestine lasting 1 h causes desquamation of the epithelium at the villus tips and congestion in the villus capillaries. The crypt cells are relatively undamaged. These changes are associated with a loss of active transport of organic solutes, determined in vitro, a reduction in mucosal sucrase activity and an abolition of glucose absorption in vivo. A profuse net loss of water and electrolytes into the lumen in vivo develops. The net sodium loss is due primarily to an inhibition of the lumen-blood flux of this ion, the blood-lumen flux being relatively unchanged. In uraemic dogs, the loss of urea into the lumen is the same in control and ischaemic loops, testifying to the lack of change in the unidirectional water flow from blood to lumen. Perfusion of the dog intestine with 1% Triton X-100 leads to morphological changes that have certain similarities with those provoked by ischaemia. Damage was restricted to the villus tips, protection from further alterations apparently being provided by a mucus layer that forms on the mucosal surface; the crypt region remained unchanged. After 10 min exposure, organic solute transport in vitro and glucose absorption in vivo were both reduced by not abolished; sodium and water absorption in vivo were suppressed, but no net secretion occurred. To account for these observations, we have suggested that the normal crypt cell is a secretory element with respect to sodium and water. During maturation, its absorptive properties develop such that the mature enterocyte, possessing both absorptive and secretory mechanisms, is capable of net absorption of sodium. After destruction of the villus tips, net secretion continues in the crypts; if there are insufficient villus cells remaining to ensure reabsorption, a net secretory capacity is observed.

Modification of Linear Sand Ridges by Bed-Form Migration--Bering Sea and United States Atlantic Shelf: ABSTRACT

Linear sand ridges are a dominant topographic feature of the United States mid-Atlantic shelf and the northeastern Bering Sea, as well as other coastal plain shelves of the world. Similarities in geometry, lithology, and stratigraphy of ridges in these two areas of markedly different oceanographic environments reflect a similarity in the processes that modify and shape these ridges. The best development of ridge topography occurs on the Atlantic shelf off Maryland where all stages of formation and modification can be identified. Progressive changes in ridge shape and relief and in bed-forms occur from onshore to offshore. Side slopes of ridges demonstrate characteristic trends related to water depth, and textural properties are 90° out of phase with topography. Historical documentation, seismic reflection and vibracore data, and sonographs of migrating sand waves all indicate southward migration of ridges, the dominant direction of storm-directed bottom flow. Ridges in the Bering Sea are exposed to a strong unidirectional and continuous flow of water northward into the Bering Strait. Repeated surveys of these features show that families of large north-facing sandwaves undergo migration infrequently. These periods of transport occur only when the strong oceanic flow is reinforced by northward storm-driven currents. End_of_Article - Last_Page 706------------

Ground‐Water Pollution by Transfer of Oil Hydrocarbons

ABSTRACTAn important aspect of the pollution of a phreatic aquifer by hydrocarbons is the oil‐water contact and transfer of soluble substances from the oil into the ground water.A systematic study of this transfer of matter in a saturated porous medium (initial condition of contact when the impregnation body is submitted to fluctuations of the piezometric level) is performed with an experimental device made up of a porous matrix containing the oil phase, steady and crossed by a unidirectional flow of water. The transfer is very efficient; for all compounds which have been studied, the maximum possible concentration is reached after a distance of the order of 10 cm with specific flow rates greater than those generally encountered in a gravel‐sand aquifer. The selective impoverishment of the oil product with time, due to differences in the solubility of various hydrocarbons, modifies the dissolved phase composition. Downstream of an in‐situ impregnation body, this phenomenon only appears after a constant concentration has been reached for a long time. A source model is thus obtained, where the pollutant massic flow rate is proportional to the flow rate of the water which crosses the impregnation body. Such an initial condition has a fundamental effect on the determination of the contaminated aquifer domain, with the help of the dispersion scheme, with hydrocarbon concentrations evolving according to a general diffusion‐convection law.

Dispersion‐affected transport of reacting solutes in saturated porous media: Galerkin Method applied to equilibrium‐controlled exchange in unidirectional steady water flow

Equations describing dispersion and ion exchange affected one‐dimensional transport of solutes in saturated porous media are solved numerically by means of the Galerkin method. It is assumed that water flow is steady and that local chemical equilibrium exists throughout the systems considered. No constancy restrictions are placed on the total concentration of the dissolved ions participating in exchange. The cases treated involve (1) homogeneous or layered systems, (2) exchange reactions with constant or concentration dependent selectivity coefficients, (3) binary or multicomponent exchange, and (4) systems in which one of the exchanging ions is also involved in a precipitation‐dissolution reaction. The results of computations show that the approach presented may be useful in analyzing a variety of solute transport processes of hydrologic interest. They also demonstrate at least for some of the ion transport cases the importance of taking into account the effects of dispersion and ion exchange.