Showing papers on "Water flow published in 1994"

Seaweed ecology and physiology

Abstract: Part I. Morphology, Life Histories and Morphogenesis: 1. Introduction: the plants and their environments 2. Seaweed morphology and anatomy 3. Seaweed cells 4. Seaweed genetics and molecular biology 5. Seaweed life histories 6. Settlement and germination 7. Thallus morphogenesis 8. Synopsis Part II. Seaweed Communities: 1. Seaweed communities T. A. Norton et al. 2. Intertidal zonation patterns 3. Submerged zonation patterns 4. Some other seaweed habitats and communities P. H. Nienhuis et al. 5. Community analysis 6. Synopsis Part III. Biotic Interactions: 1. Competition 2. Grazing 3. Symbiosis 4. Synopsis Part IV. Light and Photosynthesis: 1. An overview of photosynthesis 2. Irradiance 3. Light harvesting 4. Carbon fixation: the 'dark reactions' of photosynthesis 5. Seaweed polysaccharides 6. Carbon translocation 7. Photosynthetic rates and primary productivity 8. Synopsis Part V. Nutrients: 1 Nutrient requirements 2. Nutrient availability in seawater 3. Pathways and barriers to ion entry 4. Nutrient uptake kinetics 5. Uptake, assimilation and metabolic role of essential nutrients 6. Long distance transport translocation 7. Growth kinetics 8. Effects of nutrient supply 9. Synopsis Part VI. Temperature and Salinity: 1. Natural ranges of temperature and salinity 2. Temperature effects 3. Biochemical and physiological effects of salinity 4. Dessication 5. Salinity-temperature interactions and estuarine distribution 6. Synopsis Part VII. Water Motion: 1. Water flow over surfaces 2. Wave action 3. Synopsis Part VIII. Pollution: 1. Introduction 2. Thermal pollution 3. Heavy metals 4. Oil 5. Synthetic organic chemicals 6. Complex wastes and eutrophication 7. Synopsis Part IX. Seaweed Mariculture: 1. Introduction 2. Porphyra mariculture 3. Lamineria mariculture 4. Undaria mariculture 5. Eucheuma and Kappaphycus mariculture 6. Other seaweeds 7. Domestication of seaweeds - application of ecology and physiology 8. Seaweed biotechnology 9. Synopsis Appendix: Taxonomic classification of algae mentioned in the text P. C. Silva and R. L. Moe Index.

Molecular characterization of an aquaporin cDNA from brain: candidate osmoreceptor and regulator of water balance

Abstract: The aquaporins transport water through membranes of numerous tissues, but the molecular mechanisms for sensing changes in extracellular osmolality and regulating water balance in brain are unknown. We have isolated a brain aquaporin by homology cloning. Like aquaporin 1 (AQP1, also known as CHIP, channel-forming integral membrane protein of 28 kDa), the deduced polypeptide has six putative transmembrane domains but lacks cysteines at the known mercury-sensitive sites. Two initiation sites were identified encoding polypeptides of 301 and 323 amino acids; expression of each in Xenopus oocytes conferred a 20-fold increase in osmotic water permeability not blocked by 1 mM HgCl2, even after substitution of cysteine at the predicted mercury-sensitive site. Northern analysis and RNase protection demonstrated the mRNA to be abundant in mature rat brain but only weakly detectable in eye, kidney, intestine, and lung. In situ hybridization of brain localized the mRNA to ependymal cells lining the aqueduct, glial cells forming the edge of the cerebral cortex and brainstem, vasopressin-secretory neurons in supraoptic and paraventricular nuclei of hypothalamus, and Purkinje cells of cerebellum. Its distinctive expression pattern implicates this fourth mammalian member of the aquaporin water channel family (designated gene symbol, AQP4) as the osmoreceptor which regulates body water balance and mediates water flow within the central nervous system.

Numerical methods for shallow-water flow

Abstract: Preface. 1. Shallow-water flows. 2. Equations. 3. Some properties. 4. Behaviour of solutions. 5. Boundary conditions. 6. Discretization in space. 7. Effect of space discretization on wave propagation. 8. Time integration methods. 9. Effects of time discretization on wave propagation. 10. Numerical treatment of boundary conditions. 11. Three-dimensional shallow-water flow. List of notations. References. Index.

Constraints on hydrothermal heat flux through the oceanic lithosphere from global heat flow

Abstract: A significant discrepancy exists between the heat flow measured at the seafloor and the higher values predicted by thermal models of the cooling lithosphere. This discrepancy is generally interpreted as indicating that the upper oceanic crust is cooled significantly by hydrothermal circulation. The magnitude of this heat flow discrepancy is the primary datum used to estimate the volume of hydrothermal flow, and the variation in the discrepancy with lithospheric age is the primary constraint on how the hydrothermal flux is divided between near-ridge and off-ridge environments. The resulting estimates are important for investigation of both the thermal structure of the lithosphere and the chemistry of the oceans. We reevaluate the magnitude and age variation of the discrepancy using a global heat flow data set substantially larger than in earlier studies, and the GDHI (Global Depth and Heat Flow) model that better predicts the heat flow. We estimate that of the predicted global oceanic heat flux of 32 x 10(exp 12) W, 34% (11 x 10(exp 12) W) occurs by hydrothermal flow. Approximately 30% of the hydrothermal heat flux occurs in crust younger than 1 Ma, so the majority of this flux is off-ridge. These hydrothermal heat flux estimates are upper bounds, because heat flow measurements require sediment at the site and so are made preferentially at topographic lows, where heat flow may be depressed. Because the water temperature for the near-ridge flow exceeds that for the off-ridge flow, the near-ridge water flow will be even a smaller fraction of the total water flow. As a result, in estimating fluxes from geochemical data, use of the high water temperatures appropriate for the ridge axis may significantly overestimate the heat flux for an assumed water flux or underestimate the water flux for an assumed heat flux. Our data also permit improved estimates of the 'sealing' age, defined as the age where the observed heat flow approximately equals that predicted, suggesting that hydrothermal heat transfer has largely ceased. Although earlier studies suggested major differences in sealing ages for different ocean basins, we find that the sealing ages for the Atlantic, Pacific, and Indian oceans are similar and consistent with the sealing age for the entire data set, 65 +/- 10 Ma. The previous inference of a young (approximately 20 Ma) sealing age for the Pacific appears to have biased downward several previous estimates of the global hydrothermal flux. The heat flow data also provide indirect evidence for the mechanism by which the hydrothermal heat flux becomes small, which has often been ascribed to isolation of the igneous crust from seawater due to the hydraulic conductivity of the intervening sediment. We find, however, that even the least sedimented sites show the systematic increase of the ratio of observed to predicted heat flow with age, although the more sedimented sites have a younger sealing age. Moreover, the heat flow discrepancy persists at heavily sedimented sites until approximately 50 Ma. It thus appears that approximately 100-200 m of sediment is neither necessary nor sufficient to stop hydrothermal heat transfer. We therefore conclude that the age of the crust is the primary control on the fraction of heat transported by hydrothermal flow and that sediment thickness has a lesser effect. This inference is consistent with models in which hydrothermal flow decreases with age due to reduced crustal porosity and hence permeability.

A cellular model of braided rivers

Abstract: A BROAD sheet of water flowing over non-cohesive sediment typically breaks up into a network of interconnected channels called a braided stream (Fig. 1). The dynamics of such networks are complex; channels migrate laterally, split, rejoin and develop bars, with the flow shifting unpredictably from one part of the network to another. Many processes are known to operate in a braided river1–3, but it is unclear which of these are essential to explain the observed dynamics. We describe here a simple, deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers. The patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge. Although the morphology of the resulting network depends in detail on the sediment-transport rule used in the model, our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free-surface flow.

Finite‐Volume Two‐Dimensional Unsteady‐Flow Model for River Basins

Abstract: The paper presents a two‐dimensional unsteady‐flow model, RBFVM‐2D, based on the finite‐volume method with a combination of unstructured triangular and quadrilateral grids in a river‐basin system. The attractive feature of this model is that it calculate of the mass and momentum flux across each side of elements as a Riemann problem, which is solved using the Osher scheme. This feature enables this model to deal with the wetting and drying processes for flood‐plain and wetland studies, dam breaking phenomena involving discontinuous flows, subcritical and supercritical flows, and other cases. The computations of tributary inflows and regulated flows through gates, weirs, and culverts or bridges are also included. Sample applications of this model to two dam‐break problems showed fairly satisfactory results. Also, this model was applied to a portion of the Kissimmee River Basin in Florida for flow simulations and the results agreed well with the field and laboratory data in a physical‐model study of this ri...

Simultaneous modeling of transient three-dimensional root growth and soil water flow

Abstract: A model is presented for the simultaneous, dynamic simulation of soil water movement and plant root growth. Root apices are translocated in individual growth events as a function of current local soil conditions. A three-dimensional finite-element grid over the considered soil domain serves to define the spatial distribution of soil physical properties and as framework for the transient water flow model. Examples illustrate how field-observed morphology of root systems can be approximated by including even a coarsely discretized description of the soil environment. Intended as a tool for testing of hypotheses on soil-plant interaction, simulations can be performed for different levels of model complexity, depending on how much information is available. At the simplest level, root growth is simulated without soil water uptake, whereas the most comprehensive level includes growth of the shoot and dynamic assimilate allocation to root and shoot.

New Acoustic Meter for Measuring 3D Laboratory Flows

Abstract: A small, robust, and relatively inexpensive current meter was developed to measure uniform and oscillatory water flows in both open-weather and enclosed-physical-model facilities. The 10-MHz acoustic-doppler volocimeter (ADV) measures three-dimensional current velocity over the speed range of 0 to 2.5 m/s at a sampling rate of up to 25 Hz. Measurements are made in a small sampling volume located 5 cm from a slim transmit-receive assembly. Comparison tests of the ADV in several engineering model facilities together with other velocity-measurement instruments and in a precision tow-channel facility were highly successful. The ADV is rugged and portable, and it can remain installed in facilities for extended periods without recalibration.

Adaptive faucet controller measuring proximity and motion

Abstract: An electronically controlled automatic faucet has a pulsed infrared beam intersecting the water stream discharged by the faucet. Infrared signals reflected from the water stream are thus detected in addition to any signals reflected from a user's hand(s). A reasonable approximation of the signal received from the water stream alone is subtracted from the sum of all detected signals whenever water is flowing in order to provide a compensated proximity signal. This compensation method, which may be implemented in hardware or software, prevents a shift in the sensor's sensitivity during periods when water is flowing, and eliminates the possibility that water flow might "lock-on" once initiated. Compensating for water flow improves sensor performance by allowing the infrared detection field to encompass a larger volume of space where a user's hands might be found. In addition, the same, or similar, hardware can be used to detect a user's hand motion. The disclosed motion detection method can be used alone, or it can be used as an adjunct to the water stream compensation method, in which case it prevents extended intervals of water flow that could otherwise occur when foreign objects are left in view of the sensor.

Influence of Macrophytes on Nitrate Removal in Wetlands

Abstract: Efficient nitrate removal from wetlands depends on denitrification. Macrophytes support denitrification by supplying organic carbon. Organic carbon available to denitrifying bacteria is released from plant litter and from living macrophytes. Macrophytes offer attachment surfaces for epiphytes, also producing organic matter, and for denitrifying bacteria. Emergent macrophytes are generally more productive than submerged macrophytes, but submerged macrophytes have more epiphytes and offer a larger attachment area in the water column for denitrifying bacteria. Emergent and submerged vegetation differ in their seasonal patterns of release of organic carbon. We conclude that a mixture of emergent and submerged macrophytes may be beneficial for nitrogen removal in wetlands with a surface-flow of nitrate-rich water. The influence of vegetation on wetland hydraulics must also be considered. A wetland design with deeper parts favoring submerged macrophytes alternating, along the water flow, with shallower parts covered by emergent macrophytes, may promote denitrification processes and distribution of water flow.

Water transport across roots

Abstract: Usually, roots are looked at as rather perfect osmometers with the endodermis being the ‘root membrane’ which is equivalent to the plasma membrane of cells. However, this ‘single-equivalent-membrane model’ of the root does not explain the findings of a variable hydraulic resistance of roots as well as of differences between hydraulic and osmotic water flow and of low reflection coefficients of roots. Recent work with the root pressure probe is reviewed and discussed which indicates that the simple osmometer model of the root has to be extended by incorporating its composite structure, i.e. the fact that there are different parallel pathways for water in the root, namely, the cell-to-cell and apoplasmic path. The new ‘composite transport model of the root’ readily explains the experimental findings mentioned above. Pressure probe work with roots in which the endodermis was punctured to create an additional parallel path as well as anatomical studies support the model.

Hydraulic architecture of Acer saccharum and A. rubrum: comparison of branches to whole trees and the contribution of leaves to hydraulic resistance

Abstract: Hydraulic resistance to water flow was measured in the xylem and leaves of above-ground portions of Acer saccharum and Acer rubrum for trees with trunk diameters (D) ranging from 0.02 to 0.2 m. Resistance (area basis) to water flow in leaves and petioles was 24 and 13×10 3 MPa m 2 s kg -1 for A. saccharum and A. rubrum, respectively. Leaf area of whole trees was proportional to D 1.82 . Absolute xylem resistance (MPa s kg -1 ) was proportional to D -1.64 . So xylem resistance (area basis) was proportional to D 0.2 , which was not significantly different from a zero dependence (D 0 ) for D≤0.2 m

Discharge Coefficient of Rectangular Side Weirs

Abstract: The characteristics of flow over side weirs are taken into account to determine the discharge coefficient for subcritical flow conditions under the assumption of constant‐specific energy. The main‐channel discharge, length of the weir crest, and sill height of the weir are treated as the controlled variables. The discharge coefficient Cd is found to depend on the upstream Froude number F1 and, contrary to earlier findings, also on the ratio of sill height to upstream flow depth s/y1. Multiple regression analysis is conducted to establish the relationship of Cd with both F1 and s/y1 taken together. The relationship is of linear form and provides an easy means of estimating Cd.

Axial and radial water flow in the trunks of oak trees: a quantitative and qualitative analysis.

Abstract: Axial water flow in the trunks of mature oak trees (Quercus petraea (Matt.) Liebl. and Q. robur L.) was studied by four independent techniques: water absorption from a cut trunk, sap flowmeters, heat pulse velocity (HPV) and thermoimaging. Estimation of the total water flow with sap flowmeters, HPV and water absorption yielded comparable results. We concluded from dye colorations, thermograms and axial profiles of sap flow and heat pulse velocity that, in intact trunks, most of the flow occurred in the current-year ring, where early-wood vessels in the outermost ring were still functional. Nevertheless, there was significant flow in the older rings of the xylem. Total water flow through the trunk was only slightly reduced when air embolisms were artificially induced in early-wood vessels, probably because there was little change in hydraulic conductance in the root-leaf sap pathway. Embolization of the current-year vessels reactivated transport in the older rings.

Settlement of oyster (Crassostrea virginica) larvae: Effects of water flow and a water-soluble chemical cue

Abstract: Although previous evidence indicates that larvae of benthic marine invertebrates can respond to waterborne cues in still water, the importance of waterborne cues in mediating natural settlement out of flowing water has been questioned. Here, we summarize the results of flume experiments demonstrating enhanced settlement of oyster larvae in small target wells (circles of 7-cm diam) with the release of a waterborne settlement cue compared to identical substrates without the cue. In concurrent still-water experiments, more oyster larvae settled in solutions of waterborne cue than in seawater controls. Velocity and electrochemical measurements of a conservative tracer verified that at low flow velocities (2 and 6 cm s-l) with U, values ~0.25 cm s-l, the waterborne cue was present above the targeted substrate to a height of 14 mm. Rapid vertical swimming or sinking in response to the waterborne cue can concentrate larvae in near-bottom waters and enhance larval settlement. Our investigation provides the first experiimental evidence to demonstrate that dissolved chemical cues can mediate settlement by larvae under hydrodynamic conditions approaching those of natural benthic habitats.

Examining the contributions of glacial till water to storm runoff using two‐ and three‐component hydrograph separations

Abstract: Two- and three-component hydrograph separations based on 18O and dissolved silica are used to investigate the contributions of glacial till water to the storm runoff of a headwater stream on the Canadian Shield. Two-component isotopic hydrograph separations based on 18O indicate that the volume and flux of event water could be accounted for by direct precipitation onto saturated areas. Three-component hydrograph separations distinguish between event water, preevent soil water, and preevent till water. These results show that groundwater flow through coarse-textured glacial tills can make a significant contribution to stream discharge during runoff events (29 and 62% in this study) despite the lower hydraulic conductivities of the tills compared to the overlying soils. The three-component hydrograph separations also demonstrate that the relative contributions of preevent soil water and preevent till water changed during one runoff event such that the average water chemistry of the preevent component varied during the event. Two-component hydrograph separations using dissolved silica indicate that seasonal changes in the till water contributions also occur and are related to groundwater levels. Measurements of vertical hydraulic gradients during runoff events indicate that the increase in flow from the tills to the soils is minimal and cannot account for the large and rapid increase in till water flow into the stream. Till water that has discharged to the soils prior to the event is probably being flushed from the soils into the stream during events.

Salmonid fishes and the estuarine environment

Abstract: Salmonid fishes are typically anadromous, that is, they achieve the bulk of their growth in the sea, and migrate into rivers to reproduce. As juveniles, they may arrive in the estuary almost immediately after emergence from a gravel bed in the river, or after a few days, weeks, months, or years in fresh water, according to species and developmental opportunity. Thereafter, the length of estuarine residence depends on the estuary’s size, shape, and productivity; on water flow patterns and velocities; on salinity and temperature; and on the species and size of the salmon. It is supposed that estuaries offer salmonids three primary advantages: productive foraging, relative refuge from predators, and a physically intermediate environment for transition from fresh water to marine physiological control systems. The present paper finds the evidence for the foraging advantage strong, for the predator refuge equivocal, and for the physiological transition function applicable particularly to Pacific species migrant at the fry stage.

Broad‐Crested Weir

Abstract: The flow features over the broad-crested weir with vertical upstream wall and sharp-crested corner are analyzed experimentally. Only the long-crested weir is considered, for which the discharge coefficient remains practically constant. For a relative overflow depth between 10% and 40%, the surface profile, the bottom pressure profile, the boundary separation profile, and the velocity profiles close to the upper corner are self-similar, provided effects of scale may be dropped. For extremely long-crested weirs, undular flow occurs. The first wave profile is shown to be identical with the solitary wave profile. The main properties of the undular hydraulic jump are explored. The broad-crested weir is characterized by insensitivity to tailwater submergence. The modular limit is found practically constant at 75% of the tailwater level, independent of the relative head on the weir. The discharge-head relation for submerged flow is analyzed under a novel approach. Finally, recommendations are specified under which a broad-crested weir may be used as a discharge measurement structure.

Digital brewer control

Abstract: A control system for a beverage brewing apparatus which includes a programmable control module and a separate input device. The control system is used with a beverage brewing apparatus of the type having an infusion assembly for retaining and filtering a brewing substance, a heated water source and a water distribution system for transporting water from the heated water source to the infusion assembly. The programmable control module controls numerous adjustable functions associated with the brewer and stores at least one function limit for each of the functions which it controls. The separate input device is selectively attachable to the control module for manipulating the function limits of the programmable function retained and controlled by the control module. Function controls are associated with the input device for selecting a function to manipulate and for incrementing and decrementing the limit or limits of the selected function. The control module and input device allow selection of control limits which affect a valve for controlling water flow from the heated water source to the infusion assembly. These control limits establish a dispensing cycle which periodically dispenses water from the heated water source through the water distribution system to the infusion assembly to prevent overflowing the infusion assembly.

Origin and diagenesis of Quaternary travertine shrub fabrics, Rapolano Terme, central Italy

Abstract: Millimetre to centimetre sized arborescent shrub-like calcite precipitates are common constituents of hot water travertine shallow pool deposits of Quaternary age at Rapolano Terme, Tuscany, Italy. In the presently forming travertines, the shrubs consist of apparently random associations of (i) micrite aggregates and (ii) subhedral to euhedral rhombic spar crystal aggregates. In thin section, the micrite aggregates appear dark and the spar-rhomb aggregates light, giving the shrubs a mottled appearance. Travertines are basically produced by CaCO3 precipitation due to degassing and evaporation of the spring waters, although biological influence may also stimulate precipitation. The formation of masses of erect shrubs, rather than dense crystal crusts that form on slopes, is probably due to limited water flow in the pool environments. Microbes, including bacteria and diatoms, are important influences on shrub microfabric and external shape. The micrite aggregates are associated with bacteriform bodies, seen as tiny rods and spheres. The micrite precipitates around these bodies and in adjacent biofilm. Spar-rhomb precipitation appears to be external to the biofilm, and may be related to the presence of diatoms which are locally closely associated with the spar-rhombs, although an essentially inorganic origin, particularly for the more euhedral rhombs, cannot be ruled out. In the older Quaternary travertines, the original microfabric of the shrubs has been diagenetically altered. The original mottled appearance of the shrubs has become uniformly dark and micritic, and the evidence for the dual micritic and spar-rhomb origin of the shrubs is obscured or destroyed. Spar-micritization of the shrubs is probably due to abiotic, and locally biotic, dissolution. Previous studies did not recognize the diagenetic micritization and attributed shrub formation entirely to bacterial activity.

Quantitative Effects of Atyid Shrimp (Decapoda: Atyidae) on the Depositional Environment in a Tropical Stream: Use of Electricity for Experimental Exclusion

Abstract: Effects of biotic (shrimp) and abiotic (discharge) factors on the depositional environment were quantified in a montane stream in Puerto Rico. Electricity was used experimentally to exclude large (...

Bed‐Form Development

Abstract: Based upon the results of a series of 47 bed‐development experiments, the evolution of bed features subsequent to their initial generation from flat bed conditions is examined. For each such experiment, bed profiles were measured at frequent time intervals as sand‐wave configurations developed under the action of open‐channel water flow. The two sediments used for these experiments were of geometric mean size 0.20 mm and 0.82 mm, respectively. In line with the bed‐form unification model of bed development postulated by Saudkivi and Witte in 1990, the principle of bed‐form propagation speed decreasing with increasing bed‐form height and the mechanisms of bed‐form coalescence and bed‐form throughpassing are all found to be central to bed evolution processes. A quantitative relation between bed‐form speed and bed‐form height is presented. Bed‐development predictions based upon bed‐form unification models can be seen to clearly parallel the present experimental results. Stability analyses based upon potential...

Gravel Saltation: 2. Modeling

Abstract: A Lagrangian model for the motion of a sediment particle in a water flow is proposed. The particle motion equation is averaged over flow turbulence, specialized to the case of coarse sediment particles saltating in water, and coupled with a stochastic model for particle collision with the bed. Model predictions of statistics of gravel saltation generally agree well with experimental observations. As an application of the saltation model, bed load transport rates are estimated from modeled mean saltation streamwise velocity and a dynamic friction coefficient. The results obtained compare favorably with typical bed load equations, but they overestimate experimental measurements of gravel transport, which would suggest that a Bagnoldean formulation for bed load transport of coarse material by saltating particles may not be valid.

Water extractable organic matter in arable soils : effects of drought and long-term fertilization

Abstract: The concentration of water extractable organic carbon (WEOC) was determined over 2 yr at three different depths from three agricultural fields, which have been used for fertilization productivity studies for over two decades. The overall mean value for all samples was 9.40 μg WEOC g−1. The use of mineral fertilizer alone had no significant effect while organic fertilizer resulted in an overall increase of 15 ng WEOC g−1 (soil dry weight basis) or 220 g WEOC ha−1 per 1 kg N ha−1 yr−1 . This increase was usually non-linear for any given field or depth. Water flow appeared to play a role in that the deepest samples (60–90 cm) from the field with the highest leaching rate had consistently low WEOC values. The samples taken in a year (1991) with exceptionally low precipitation before sampling had significantly (P < 0.001) more (+33%) WEOC than in the other year. The magnitude of this effect was equivalent to that of the application of organic fertilizer at the rate of ca175 kg N ha−1 yr−1. Therefore, in situ soil moisture content can have a relatively high effect on this organic carbon pool. Surprisingly the increase in WEOC due to drought was also present in the samples from the greatest depth. Again the field with the highest leaching rate was affected differently than the other two fields. No relationship was found between short term organic carbon mineralization and fertilization history. However, a significant but loose (R2< 50%) linear relationship was found between the mineralization rate and WEOC concentration.

Evaluating GCM Land Surface Hydrology Parameterizations by Computing River Discharges Using a Runoff Routing Model: Application to the Mississippi Basin

Abstract: To relate general circulation model (GCM) hydrologic output to readily available river hydrographic data, a runoff routing scheme that routes gridded runoffs through regional- or continental-scale river drainage basins is developed. By following the basin overland flow paths, the routing model generates river discharge hydrographs that can be compared to observed river discharges, thus allowing an analysis of the GCM representation of monthly, seasonal, and annual water balances over large regions. The runoff routing model consists of two linear reservoirs, a surface reservoir and a groundwater reservoir, which store and transport water. The water transport mechanisms operating within these two reservoirs are differentiated by their time scales; the groundwater reservoir transports water much more slowly than the surface reservior. The groundwater reservior feeds the corresponding surface store, and the surface stores are connected via the river network. The routing model is implemented over the Global Energy and Water Cycle Experiment (GEWEX) Continental-Scale International Project Mississippi River basin on a rectangular grid of 2 deg X 2.5 deg. Two land surface hydrology parameterizations provide the gridded runoff data required to run the runoff routing scheme: the variable infiltration capacity model, and the soil moisture component of the simple biosphere model. These parameterizations are driven with 4 deg X 5 deg gridded climatological potential evapotranspiration and 1979 First Global Atmospheric Research Program (GARP) Global Experiment precipitation. These investigations have quantified the importance of physically realistic soil moisture holding capacities, evaporation parameters, and runoff mechanisms in land surface hydrology formulations.

Effect of Flow Velocity on Sediment Oxygen Demand: Theory

Abstract: A model of sediment oxygen demand (SOD) is presented that relates the SOD to flow velocity over the sediment. Previous analyses emphasize, almost exclusively, the relationship between SOD and sediment composition, i.e., their chemistry and biology. Herein a quantitative relationship is established between SOD and the velocity and dissolved oxygen concentration in the bulk water. Oxygen consumption in the sediment is expressed as the sum of biological consumption with Michaelis‐Menten kinetics, and the chemical consumption assumed to be a first order reaction of oxygen. At very low flow velocities, transport through the diffusive water boundary layer is the limiting factor of SOD, and SOD is expressed as a linear increasing function of velocity. On the other hand, when flow velocities are increased, SOD becomes independent of velocity, since the reactions in the sediment become rate‐limiting. The model also suggests that SOD is an increasing function of dissolved oxygen concentration in the water overlying...

High-speed thermal cycling system and method of use

Abstract: A thermal cycling system and method of use are described. The thermal cycling system is based on the-circulation of temperature-controlled water directly to the underside of thin-walled polycarbonate microtiter plates. The water flow is selected from a manifold fed by pumps from heated reservoirs. The plate wells are loaded with typically 15-20 μl of reagent mix for the PCR process. Heat transfer through the thin polycarbonate is sufficiently rapid that the contents reach thermal equilibrium with the water in less than 15 seconds. Complete PCR amplification runs of 40 three-step cycles have been performed in as little as 14.5 minutes, with the results showing substantially enhanced specificity compared to conventional technology requiring run times in excess of 100 minutes. The plate clamping station is designed to be amenable to robotic loading and unloading of the system. It includes a heated lid, thus eliminating the need for mineral oil overlay of the reactants. The present system includes three or more plate holder stations, fed from common reservoirs but operating with independent switching cycles. The system can be modularly expanded.