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Water Volume (water + volume)
Selected AbstractsNon-equilibrium water flow characterized by means of upward infiltration experimentsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2001Summary Upward infiltration experiments under tension were used to demonstrate the presence of non-equilibrium flow in soils, the phenomenon that has important implications for the accelerated movement of fertilizers, pesticides, non-aqueous liquids, and other pollutants. Data obtained from these experiments were analysed using the single-porosity Richards equation, as well as a variably saturated, dual-porosity model and a dual-permeability model for characterizing non-equilibrium water flow. The laboratory experiments were carried out on 0.10-m-long soil cores having an internal diameter of 0.10 m. Constant pressure heads of ,0.10 and ,0.01 m were used as the lower boundary condition. Each infiltration was followed by a single-rate evaporation experiment to re-establish initial conditions, and to obtain the drying soil hydraulic properties. Pressure heads inside the cores were measured using five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The data were analysed to estimate parameters using a technique that combined a numerical solution of the governing flow equation (as implemented in a modified version of the Hydrus-1D software) with a Marquardt,Levenberg optimization. The objective function for the parameter estimation was defined in terms of pressure head readings, the cumulative infiltration rate, and the final total water volume in the core during upward infiltration. The final total water volume was used, as well as the pressure head readings during the evaporation part. Analysis of flow responses obtained during the infiltration experiment demonstrated significant non-equilibrium flow. This behaviour could be well characterized using a model of physical non-equilibrium that divides the medium into inter- and intra-aggregate pores with first-order transfer of water between the two systems. The analysis also demonstrated the importance of hysteresis. [source] Context-dependent effects of freshwater mussels on stream benthic communitiesFRESHWATER BIOLOGY, Issue 6 2006DANIEL E. SPOONER Summary 1. We asked whether unionid mussels influence the distribution and abundance of co-occurring benthic algae and invertebrates. In a yearlong field enclosure experiment in a south-central U.S. river, we examined the effects of living mussels versus sham mussels (shells filled with sand) on periphyton and invertebrates in both the surrounding sediment and on mussel shells. We also examined differences between two common unionid species, Actinonaias ligamentina (Lamarck 1819) and Amblema plicata (Say 1817). 2. Organic matter concentrations and invertebrate densities in the sediment surrounding mussels were significantly higher in treatments with live mussels than treatments with sham mussels or sediment alone. Organic matter was significantly higher in the sediment surrounding Actinonaias than that surrounding Amblema. Actinonaias was more active than Amblema and may have increased benthic organic matter through bioturbation. 3. Living mussels increased the abundance of periphyton on shells and the abundance and richness of invertebrates on shells, whereas effects of sham mussels were similar to sediment alone. Differences in the amount of periphyton growing on the shells of the two mussel species reflected differences in mussel activity and shell morphology. 4. Differences between living and sham mussel treatments indicate that biological activities of mussels provide ecosystem services to the benthic community beyond the physical habitat provided by shells alone. In treatments containing live mussels we found significant correlations between organic matter and chlorophyll a concentrations in the sediment, organic matter concentrations and invertebrate abundance in the sediment and the amount of chlorophyll a on the sediment and invertebrate abundance. There were no significant correlations among these response variables in control treatments. Thus, in addition to providing biogenic structure as habitat, mussels likely facilitate benthic invertebrates by altering the availability of resources (algae and organic matter) through nutrient excretion and biodeposition. 5. Effects of mussels on sediment and shell periphyton concentrations, organic matter concentrations and invertebrate abundance, varied seasonally, and were strongest in late summer during periods of low water volume, low flow, and high water temperature. 6. Our study demonstrates that freshwater mussels can strongly influence the co-occurring benthic community, but that effects of mussels are context-dependent and may vary among species. [source] Patient preparation before surgery for cholangiocarcinomaHPB, Issue 3 2008E. Oussoultzoglou Abstract Aim. Multiorgan dysfunction is often encountered in jaundiced patients and may compromise the postoperative outcome after liver resection for cholangiocarcinoma (CCA). The aim of the present study was to elucidate evidence-based medicine regarding the benefit of the available preoperative treatments currently used for the preparation of patients before surgery for hilar CCA. Material and methods. An electronic search using the Medline database was performed to identify relevant articles relating to renal dysfunction, bacterial translocation, hemostasis impairment, malnutrition, liver failure, and postoperative outcome in jaundiced patients undergoing liver resection for CCA. Results. There is grade B evidence to expand the extracellular water volume and to administer oral synbiotic supplements. Intravenous vitamin K administration is an effective treatment. Perioperative nutritional support should be administered preferably by the enteral route in severely malnourished patients with compromised liver function undergoing extended liver resection (grade A evidence). There is only grade C evidence to recommend a portal vein embolization in patients with CCA when the future remnant liver volume is <40%. Conclusions. A simplified scheme that might be useful in the management of patients presenting with obstructive jaundice was presented. Despite surgical technique improvements, preparation of patients for surgery will continue to be one of the major determinants for the postoperative prognosis of jaundiced patients. [source] Kinetics of solute acquisition from the dissolution of suspended sediment in subglacial channelsHYDROLOGICAL PROCESSES, Issue 18 2001Giles H. Brown Abstract Twenty five laboratory dissolution experiments have been conducted to quantify rates of solute acquisition, measured as Ca2+ concentration against time, from glacigenic sediments suspended in cold, dilute waters. Suspended sediment character was constrained by field-calibrated ranges of both concentration in meltwater (g cm,3) and specific surface area by sediment mass (cm2 g,1). This constraint yielded, for the first time in a glacier hydrochemical study, dissolution rate data as a function of the specific sediment surface area by water volume (cm2 cm,3). The resulting experimental data are used to calibrate a kinetic dissolution model, where the rate of solute acquisition is considered in terms of three parameters: an initial concentration C0, reflecting rapid ion-exchange reactions; an ultimate steady-state concentration Cs; and a rate parameter k. Results indicate an excellent fit between the laboratory-measured Ca2+ concentrations and model output, with goodness-of-fit, expressed as ,2, reducing in all cases to less than 1·7 × 10,14 following iterative curve fitting for each experiment. Plotting the resulting best-fit equation parameters against specific surface area by water volume reveals a strong positive relationship for both C0 and Cs, respectively yielding straight-line slopes of 4·2 × 10,8 (R2 = 0·88) and 1·2 × 10,7 (R2 = 0·77). However, k was found to be insensitive to changes in specific surface area by water volume (R2 = 0·00), largely reflecting the dominance of variability in C0 and Cs in this model. Copyright © 2001 John Wiley & Sons, Ltd. [source] The Branchiopoda (Crustacea: Anomopoda, Ctenopoda and Cyclestherida) of the rain forests of Cameroon, West Africa: low abundances, few endemics and a boreal,tropical disjunctionJOURNAL OF BIOGEOGRAPHY, Issue 9 2005George Y. Chiambeng Abstract Aim, We provide the first in-depth study of the Branchiopoda of the rain forests of Cameroon and also of the African continent. Location, Surface water environments, Cameroon. Methods, Qualitative plankton samples were collected in all types of surface water environments present, ranging from big lakes to water collected in rock crevices or fallen fruit cavities. A tow or hand-held plankton net of mesh size 100 ,m was used, and water volumes filtered were at least several m3 in large water bodies, or half to whole water volume in small water bodies. Results, We recorded 61 species (53 first records for the country), based on 700+ samples collected between September 1998 and March 2002. Anomopoda (92%) was the dominant order, followed by Ctenopoda (6.5%) and Cyclestherida (1.5%). Chydoridae (67%) was the most speciose family followed by Macrothricidae (6.5%) and Daphniidae (5%). Alona (11%) was the dominant genus followed by Chydorus (10%) and Pleuroxus (8%). Several species of Chydorinae, especially of the genus Pleuroxus, are shared with continental Eurasia,North America, but are absent from the Mediterranean and desert,steppe,savanna zones of Africa (boreal,tropical disjunction). Daphnia was absent, as in most tropical lowlands. No single species was really abundant, and a majority were rare to very rare, and of restricted occurrence within the rain forest patches. Comparing Africa, South America and Southeast Asia, we found a current total of 196 species for the combined rain forest areas, out of a world total of 500+ species. Systematic trends in richness at three taxonomic levels were the same for all continents: Anomopoda,Ctenopoda,Cyclestherida at ordinal level, Chydoridae,Daphniidae,Macrothricidae,Sididae at family level and Alona,Chydorus,Macrothrix,Diaphanosoma at genus level. Southeast Asia was richest (111 species, 14 endemics) with South America a close second (110 species, 27 endemics). Africa was the most species-poor (95 species, of which only 5 are endemics). Main conclusions, We hypothesize that the post-Miocene cooling and aridization of the world climate hit the freshwater biota of Africa particularly hard, with more extinction here than elsewhere, and little recolonization. Most extinction occurred in the savanna-desert belt, and eight disjunct boreal species (four Pleuroxus, Picripleuroxus laevis, Kurzia latissima, Alonella exigua, and Monospilus dispar) survive morphologically unchanged since pre-Pleistocene times in the Cameroon rain forest. Slow evolution thus appears typical of these cyclic parthenogenetic branchiopods in which sexual recombination occurs only at intervals. Illustrative of the same slow evolution is the fact that the two endemic cladocerans of Cameroon (Nicsmirnovius camerounensis and Bryospilus africanus) belong to tropicopolitan genera of Gondwanan age. [source] An evaluation of horizontal echo sounding as a method for behavioural studies of 0+ fish in field experimentsJOURNAL OF FISH BIOLOGY, Issue 6 2001P. Romare A 120 kHz echo sounder, with two split-beam transducers, was used horizontally to monitor the behaviour of 0 + roach Rutilus rutilis, from June to August, in field enclosures. 0+ roach outside the vegetated area of the enclosures were registered both as schools and as single swimming fish. Combining echo counting and tracking with direct observation of echograms, an estimate of relative abundance of 0 + roach in the open water volume was obtained also. With this set up, intermediate sized field experiments studying 0 + fish, may be performed during the whole summer season. [source] Effects of chlorpyrifos in freshwater model ecosystems: the influence of experimental conditions on ecotoxicological thresholdsPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 10 2005René PA van Wijngaarden Abstract Three experiments were conducted to determine the impact of the insecticide chlorpyrifos (single applications of 0.01 to 10 µg AI litre,1) in plankton-dominated nutrient-rich microcosms. The microcosms (water volume approximately 14 litres) were established in the laboratory under temperature, light regimes and nutrient levels that simulated cool ,temperate' and warm ,Mediterranean' environmental conditions. The fate of chlorpyrifos in the water column was monitored and the effects on zooplankton, phytoplankton and community metabolism were followed for 4 or 5 weeks. The mean half-life (t1/2) of chlorpyrifos in the water of the test systems was 45 h under ,temperate' conditions and about 30 h under ,Mediterranean' environmental conditions. Microcrustaceans (cladocerans and copepod nauplii) were amongst the most sensitive organisms. All three experiments yielded community NOEC (no observed effect concentrations) of 0.1 µg AI litre,1, similar to those derived from more complex outdoor studies. Above this threshold level, responses and effect chains, and time spans for recovery, differed between the experiments. For example, algal blooms as an indirect effect from the impact of exposure on grazing organisms were only observed under the ,Mediterranean' experimental conditions. The relatively simple indoor test system seems to be sufficient to provide estimates of safe threshold levels for the acute insecticidal effects of low-persistence compounds such as chlorpyrifos. The robustness of the community NOEC indicates that this threshold level is likely to be representative for many freshwater systems. Copyright © 2005 Society of Chemical Industry [source] Modelling advection and diffusion of water isotopologues in leavesPLANT CELL & ENVIRONMENT, Issue 8 2007MATTHIAS CUNTZ ABSTRACT We described advection and diffusion of water isotopologues in leaves in the non-steady state, applied specifically to amphistomatous leaves. This explains the isotopic enrichment of leaf water from the xylem to the mesophyll, and we showed how it relates to earlier models of leaf water enrichment in non-steady state. The effective length or tortuosity factor of isotopologue movement in leaves is unknown and, therefore, is a fitted parameter in the model. We compared the advection,diffusion model to previously published data sets for Lupinus angustifolius and Eucalyptus globulus. Night-time stomatal conductance was not measured in either data set and is therefore another fitted parameter. The model compared very well with the observations of bulk mesophyll water during the whole diel cycle. It compared well with the enrichment at the evaporative sites during the day but showed some deviations at night for E. globulus. It became clear from our analysis that night-time stomatal conductance should be measured in the future and that the temperature dependence of the tracer diffusivities should be accounted for. However, varying mesophyll water volume did not seem critical for obtaining a good prediction of leaf water enrichment, at least in our data sets. In addition, observations of single diurnal cycles do not seem to constrain the effective length that relates to the tortuosity of the water path in the mesophyll. Finally, we showed when simpler models of leaf water enrichment were suitable for applications of leaf water isotopes once weighted with the appropriate gas exchange flux. We showed that taking an unsuitable leaf water enrichment model could lead to large biases when cumulated over only 1 day. [source] Fluid Volumes Determination by Impedance Spectroscopy and Hematocrit Monitoring: Application to Pediatric HemodialysisARTIFICIAL ORGANS, Issue 2 2001Marianne Fenech Abstract: A method for extracting fluid volumes from multifrequency bioimpedance, which takes into account the body geometry and the presence of nonconducting elements, was tested on 12 young dialyzed patients against correlations for total body water volumes (TBW) from Watson et al. and Humes et al. Our calculations of TBW from impedance were found to overestimate Humes' values by 0.25 L (0.8%) postdialysis and by 2.08 L (6.5%) predialysis. Extracellular water (ECW) was found to contribute an average of 93% of ultrafiltered volume. Intracellular water volume (ICW) determination from impedance was found to be too imprecise to predict its variation during dialysis; therefore, ICW variations were calculated as the difference between ultrafiltration and ECW changes. The continuous recording of hematocrit by an optical device monitored changes in plasma and interstitial volumes. In most cases, ultrafiltration was compensated mainly by a contribution from interstitial fluid, and the drop in plasma volume was generally moderate. [source] Impact of stone content on water movement in water-repellent sandEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2009E. Urbanek Summary Soils are commonly stony, especially in steep upland or heavily degraded sites. The hydrological effect of large stone contents has been previously investigated in wettable but not in water-repellent soils. For the latter, the focus has instead been on the impact of other soil characteristics (e.g. cracks and macropores) likely to promote water percolation. This paper investigates stone effects on water flow in water-repellent sand under laboratory conditions. Seventy-five experiments were performed on a water-repellent sand mixed with a range of quantities of different-sized wettable and water-repellent stones. The time taken for water to pass through each sand,stone mix, the percolated water volumes and numbers of dry and wet stones following each 60-minute experiment were recorded. At large stone contents (> 55% or > 65% by weight, depending on stone wettability), percolation occurred relatively quickly and in comparatively large quantities. At intermediate stone contents (45,65%) percolation response was variable and at stone contents < 45% for wettable and < 55% for water-repellent soils no water percolation occurred. We argue that with large stone contents flow pathways develop along sand,stone interfaces and a continuous preferential flow path can form provided there are sufficient stone-to-stone connections. The distribution and alignment of the stones, especially at intermediate stone contents, are important for promoting water movement. Water repellency determinations based only on the fine sediment component in stony soils could therefore be misleading as regards determining their hydrological response: the influence of the clastic component must also be considered. [source] Hydrogeochemical balance of forest umbrisol profiles (,Sierra de Gata', central western Spain)HYDROLOGICAL PROCESSES, Issue 14 2007I. Menéndez Abstract Three techniques for obtaining soil water solutions (gravitational and matrical waters extracted using both in situ tension lysimeters and in vitro pressure chambers) and their later chemical analysis were performed in order to know the evolution of the soil-solution composition when water moves down through the soil, from the Ah soil horizon to the BwC- or C-horizons of forest soils located in western Spain. Additionally, ion concentrations and water volumes of input waters to soil (canopy washout) and exported waters (drainage solutions from C-horizons) were determined to establish the net balance of solutes in order to determine the rates of leaching or retention of ions. A generalized process of sorption or retention of most components (even Cl,) was observed, from the soil surface to the C-horizon, in both gravitational and matrical waters, with H4SiO4, Mn2+, Na+, and SO42, being the net exported components from the soil through the groundwater. These results enhance the role of the recycling effect in these forest soils. The net percentages of elements retained in these forest soils, considering the inputs and the outputs balance, were 68% K+, 85% Ca2+, 58% Mg2+, 7% Al3+, 5% Fe3+, 34% Zn2+, 57% Cl,, and 20% NO3,, and about 75% of dissolved organic carbon was mineralized. Copyright © 2007 John Wiley & Sons, Ltd. [source] The ability of rufous hummingbirds Selasphorus rufus to dilute and concentrate urineJOURNAL OF AVIAN BIOLOGY, Issue 1 2004Chris N. Lotz Most terrestrial animals face the challenge of having to conserve water in a desiccating environment. Not surprisingly, the ability to produce concentrated urine has been relatively well studied in birds. Nectar-feeding birds are unusual among terrestrial animals in that they often ingest and excrete prodigious water volumes to obtain adequate energy. Thus, they confront the unusual challenge of having to conserve electrolytes. The diluting abilities of birds and the renal mechanisms that may correlate with them have been relatively neglected. To elucidate diluting and concentrating abilities in nectar-feeding birds, we fed rufous hummingbirds Selasphorus rufus an electrolyte-free nectar and a nectar containing a range of NaCl concentrations. Hummingbirds had a spectacular (and possibly unique) diluting ability: when fed on electrolyte-free food they produced excreta containing less than 0.5 mM l,1 each of sodium and potassium. Hummingbirds also had a poor concentrating ability, retaining sodium and chloride when their food (0.632 M l,1 sucrose) contained more than 35 mM l,1 of NaCl. The kidneys of hummingbirds do not appear to be suited for concentrating urine, and possibly contain structural features that give them a unique diluting ability compared with those of birds that do not feed on nectar. [source] Fluid Volumes Determination by Impedance Spectroscopy and Hematocrit Monitoring: Application to Pediatric HemodialysisARTIFICIAL ORGANS, Issue 2 2001Marianne Fenech Abstract: A method for extracting fluid volumes from multifrequency bioimpedance, which takes into account the body geometry and the presence of nonconducting elements, was tested on 12 young dialyzed patients against correlations for total body water volumes (TBW) from Watson et al. and Humes et al. Our calculations of TBW from impedance were found to overestimate Humes' values by 0.25 L (0.8%) postdialysis and by 2.08 L (6.5%) predialysis. Extracellular water (ECW) was found to contribute an average of 93% of ultrafiltered volume. Intracellular water volume (ICW) determination from impedance was found to be too imprecise to predict its variation during dialysis; therefore, ICW variations were calculated as the difference between ultrafiltration and ECW changes. The continuous recording of hematocrit by an optical device monitored changes in plasma and interstitial volumes. In most cases, ultrafiltration was compensated mainly by a contribution from interstitial fluid, and the drop in plasma volume was generally moderate. [source] Comparison of the Surface and Underground Natural Gas Occurrences in the Tazhong Uplift of the Tarim BasinACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010TIAN Jun Abstract: The oil, gas and water volumes revealed by the productivity of exploratory wells do not reflect the actual underground situations. Under the geologic conditions, a certain amount of dissolved natural gas is stored in oil or water. Based on the production test data of exploratory wells in the Tazhong uplift of the Tarim basin, this paper discusses in detail the differences in occurrence and distribution featrues between the surface and underground natural gases; presents a restoration of the surface gas occurrence to actual underground geologic conditions according to the dissolubility of natural gas under different temperature, pressure and medium conditions; and classifies the natural gas into three states, i.e. the oversaturated, saturated and undersaturated, according to its relative content underground. Through a comparative analysis of the differences in surface and underground occurrences of natural gas, it discusses the hydrocarbon reservoir formation mechanism and distribution rules, thereby providing guidances as new methods and technologies for the prediction of potential natural gas reservoir distribution in the study area. [source] | ||||||||||||||||