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Water Velocity (water + velocity)
Kinds of Water Velocity Selected AbstractsSpatial and ontogenetic variability in the microhabitat use of stream-dwelling spined loach (Cobitis taenia) and stone loach (Barbatula barbatula)JOURNAL OF APPLIED ICHTHYOLOGY, Issue 6 2004G. H. Copp Summary Ontogenetic and spatial variability in microhabitat use of spined loach Cobitis taenia (Linnaeus), considered as one species for the purposes of this study, and stone loach Barbatula barbatula (Linnaeus) were examined in the River Great Ouse basin, England, using multivariate and habitat suitability methods, including a technique for handling spatial variation in collections of preference curves. Distinct ordinations of spined age classes and stone loach developmental stages, respectively, in canonical correspondence analysis of species × variables × samples relationships suggest that the two species occupy completely different microhabitats; however, young-of-the-year spined loach occurred more often than expected with all developmental stages of stone loach except young larvae. Water velocity and filamentous algae were the most influential microhabitat variables, the latter decreasing in importance with increasing age of both fish species. Preferred water velocities generally decreased with age in spined loach and increased in stone loach, with substratum size generally increasing with fish age in both species. Spatial variation in microhabitat preferences was great in both species but less so in the spined loach, suggesting that limited plasticity in habitat use could account, at least in part, for the latter species' limited distribution and abundance in the catchment. Preference curves for a species, if generated and verified for all life intervals and all seasons, could be used as a management tool for a given stream or sector of river basin. But preference curves should be generated for each location to ensure that river management decisions with regard habitat and species conservation consider local-level species requirements. Thus, a multi-(eco)species and multi-scale approach is required in habitat suitability assessments. [source] How well are velocity effects on ,13C signatures transmitted up the food web from algae to fish?FRESHWATER BIOLOGY, Issue 6 2010JOSEPH B. RASMUSSEN Summary 1. Benthic algae fractionate carbon isotopes less at low water velocities because of reduced boundary layer exchange, and this effect on ,13C is passed on to consumers via trophic transfer. This study examines the relationships between ,13C signatures of consumers (invertebrates and salmonid fishes) and water velocity in the Sainte Marguerite River, QC, Canada, and compares them to patterns for periphyton, both along the river main-stem and in a small tributary. 2. Relationships of ,13C signatures of herbivore/grazers and collector/gatherers with water velocity were strong and similar to those of periphyton, but relationships for filter-feeders were weak, probably reflecting the effect of spatial averaging of their food supply as a result of downstream transport. 3. Velocity effects on salmonid signatures were much weaker than those of lower trophic levels, being barely significant except in the small tributary where the fish were resident and isolated from the main river. In the river main-stem, even when reach standardised (reach mean subtracted from each data point), fish signatures were only weakly related to water velocity. 4. The fidelity with which velocity effects are transmitted to consumers from benthic algae is highly variable, and depends on a combination of consumer and resource movements, in addition to the trophic position of the consumer. [source] Day,night changes in the spatial distribution and habitat preferences of freshwater shrimps, Gammarus pulex, in a stony streamFRESHWATER BIOLOGY, Issue 4 2005J. M. ELLIOTT Summary 1. As many invertebrates are nocturnal, their spatial distribution and habitat preferences may change from day to night. Both aspects are examined for Gammarus pulex by testing the hypotheses: (i) a power function was a suitable model for the spatial distribution of the shrimps in both day and night; (ii) diurnal and nocturnal spatial distributions were significantly different; (iii) diurnal and nocturnal habitat preferences were significantly different. Five different life-stages were treated separately. To ensure that the conclusions were consistent, large samples were taken near midday and midnight in April, June and November over 4 years at two sites about 3 km apart in a stony stream: downstream (n = 30) and upstream (n = 50). 2. The first and second hypotheses were supported at both sites. A power function, relating spatial variance (s2) to mean (m), was an excellent fit in all analyses (P < 0.001, r2 > 0.91), i.e. the spatial variance was density-dependent. All five life-stages were aggregated in the day. At night, the degree of aggregation increased for juveniles at higher densities but decreased for juveniles at lower densities, increased for immature females and males, but decreased slightly for mature females and especially mature males, the latter being close to a random distribution. There were no significant differences between sites, in spite of the lower numbers at the downstream site. 3. The third hypothesis was tested at only the upstream site and supported by comparisons between shrimp densities and 13 physical variables (distance from bank, water depth, water velocity, ten particle size-classes), and three non-physical variables (dry weights of bryophytes, leaf material, organic detritus). During the day, densities were strongly related to particle sizes with the following preferences: 0.5,8 mm for juveniles, 8,256 mm for the other life-stages with a weaker relationship for males. There were no significant positive relationships with the other variables, apart from bryophytes for immature shrimps and adults. At night, densities were unrelated to particle size; juveniles and immature shrimps preferred low water velocities near the banks, often where leaf material and organic detritus accumulated, females often preferred medium water velocities slightly away from the banks, and males showed no habitat preferences. 4. Day samples do not provide a complete picture of habitat preferences and probably identify refuge habitats. Day,night changes in spatial distribution and habitat preferences are an essential part of the behavioural dynamics of the shrimps and should be investigated in other species. [source] Determination of Transverse Dispersion Coefficients from Reactive Plume LengthsGROUND WATER, Issue 2 2006Olaf A. Cirpka With most existing methods, transverse dispersion coefficients are difficult to determine. We present a new, simple, and robust approach based on steady-state transport of a reacting agent, introduced over a certain height into the porous medium of interest. The agent reacts with compounds in the ambient water. In our application, we use an alkaline solution injected into acidic ambient water. Threshold values of pH are visualized by adding standard pH indicators. Since aqueous-phase acid-base reactions can be considered practically instantaneous and the only process leading to mixing of the reactants is transverse dispersion, the length of the plume is controlled by the ratio of transverse dispersion to advection. We use existing closed-form expressions for multidimensional steady-state transport of conservative compounds in order to evaluate the concentration distributions of the reacting compounds. Based on these results, we derive an easy-to-use expression for the length of the reactive plume; it is proportional to the injection height squared, times the velocity, and inversely proportional to the transverse dispersion coefficient. Solving this expression for the transverse dispersion coefficient, we can estimate its value from the length of the alkaline plume. We apply the method to two experimental setups of different dimension. The computed transverse dispersion coefficients are rather small. We conclude that at slow but realistic ground water velocities, the contribution of effective molecular diffusion to transverse dispersion cannot be neglected. This results in plume lengths that increase with increasing velocity. [source] Ground Water Flow Analysis of a Mid-Atlantic Outer Coastal Plain Watershed, Virginia, U.S.A.GROUND WATER, Issue 2 2002Michael A. Robinson Models for ground water flow (MODFLOW) and particle tracking (MODPATH) were used to determine ground water flow patterns, principal ground water discharge and recharge zones, and estimates of ground water travel times in an unconfined ground water system of an outer coastal plain watershed on the Delmarva Peninsula, Virginia. By coupling recharge and discharge zones within the watershed, flowpath analysis can provide a method to locate and implement specific management strategies within a watershed to reduce ground water nitrogen loading to surface water. A monitoring well network was installed in Eyreville Creek watershed, a first-order creek, to determine hydraulic conductivities and spatial and temporal variations in hydraulic heads for use in model calibration. Ground water flow patterns indicated the convergence of flow along the four surface water features of the watershed; primary discharge areas were in the noontide portions of the watershed. Ground water recharge zones corresponded to the surface water features with minimal development of a regional ground water system. Predicted ground water velocities varied between < 0.01 to 0.24 m/day, with elevated values associated with discharge areas and areas of convergence along surface water features. Some ground water residence times exceeded 100 years, although average residence times ranged between 16 and 21 years; approximately 95% of the ground water resource would reflect land use activities within the last 50 years. [source] Age of Irrigation Water in Ground Water from the Eastern Snake River Plain Aquifer, South-Central IdahoGROUND WATER, Issue 2 2000L.N. Plummer Stable isotope data (2H and 18O) were used in conjunction with chlorofluorocarbon (CFC) and tritium/helium-3 (3H/3He) data to determine the fraction and age of irrigation water in ground water mixtures from farmed parts of the Eastern Snake River Plain (ESRP) Aquifer in south-central Idaho. Two groups of waters were recognized: (1) regional background water, unaffected by irrigation and fertilizer application, and (2) mixtures of irrigation water from the Snake River with regional background water. New data are presented comparing CFC and 3H/3He dating of water recharged through deep fractured basalt, and dating of young fractions in ground water mixtures. The 3H/3He ages of irrigation water in most mixtures ranged from about zero to eight years. The CFC ages of irrigation water in mixtures ranged from values near those based on 3H/3He dating to values biased older than the 3H/3He ages by as much as eight to 10 years. Unsaturated zone air had CFC-12 and CFC-113 concentrations that were 60% to 95%, and 50% to 90%, respectively, of modern air concentrations and were consistently contaminated with CFC-11. Irrigation water diverted from the Snake River was contaminated with CFC-11 but near solubility equilibrium with CFC-12 and CFC-113. The dating indicates ground water velocities of 5 to 8 m/d for water along the top of the ESRP Aquifer near the southwestern boundary of the Idaho National Engineering and Environmental Laboratory (INEEL). Many of the regional background waters contain excess terrigenic helium with a 3He/4He isotope ratio of 7 × 10,6 to 11 × 10,6 (R/Ra= 5 to 8) and could not be dated. Ratios of CFC data indicate that some rangeland water may contain as much as 5% to 30% young water (ages of less than or equal to two to 11.5 years) mixed with old regional background water. The relatively low residence times of ground water in irrigated parts of the ESRP Aquifer and the dilution with low-NO3 irrigation water from the Snake River lower the potential for NO3 contamination in agricultural areas. [source] Vulnerability of age-0 pallid sturgeon Scaphirhynchus albus to fish predationJOURNAL OF APPLIED ICHTHYOLOGY, Issue 1 2010By W. E. French Summary Stocking is a commonly employed conservation strategy for endangered species such as the pallid sturgeon, Scaphirhynchus albus. However, decisions about when, where and at what size pallid sturgeon should be stocked are hindered because vulnerability of pallid sturgeon to fish predation is not known. The objective of this study was to evaluate the vulnerability of age-0 pallid sturgeon to predation by two Missouri River predators under different flow regimes, and in combination with alternative prey. To document vulnerability, age-0 pallid sturgeon (<100 mm) were offered to channel catfish Ictalurus punctatus and smallmouth bass Micropterus dolomieu in laboratory experiments. Selection of pallid sturgeon by both predators was measured by offering pallid sturgeon and an alternative prey, fathead minnows Pimephales promelas, in varying prey densities. Smallmouth bass consumed more age-0 pallid sturgeon (0.95 h,1) than did channel catfish (0.13 h,1), and predation rates did not differ between water velocities supporting sustained (0 m s,1) or prolonged swimming speeds (0.15 m s,1). Neither predator positively selected pallid sturgeon when alternative prey was available. Both predator species consumed more fathead minnows than pallid sturgeon across all prey density combinations. Results indicate that the vulnerability of age-0 pallid sturgeon to predation by channel catfish and smallmouth bass is low, especially in the presence of an alternative fish prey. [source] Spatial and ontogenetic variability in the microhabitat use of stream-dwelling spined loach (Cobitis taenia) and stone loach (Barbatula barbatula)JOURNAL OF APPLIED ICHTHYOLOGY, Issue 6 2004G. H. Copp Summary Ontogenetic and spatial variability in microhabitat use of spined loach Cobitis taenia (Linnaeus), considered as one species for the purposes of this study, and stone loach Barbatula barbatula (Linnaeus) were examined in the River Great Ouse basin, England, using multivariate and habitat suitability methods, including a technique for handling spatial variation in collections of preference curves. Distinct ordinations of spined age classes and stone loach developmental stages, respectively, in canonical correspondence analysis of species × variables × samples relationships suggest that the two species occupy completely different microhabitats; however, young-of-the-year spined loach occurred more often than expected with all developmental stages of stone loach except young larvae. Water velocity and filamentous algae were the most influential microhabitat variables, the latter decreasing in importance with increasing age of both fish species. Preferred water velocities generally decreased with age in spined loach and increased in stone loach, with substratum size generally increasing with fish age in both species. Spatial variation in microhabitat preferences was great in both species but less so in the spined loach, suggesting that limited plasticity in habitat use could account, at least in part, for the latter species' limited distribution and abundance in the catchment. Preference curves for a species, if generated and verified for all life intervals and all seasons, could be used as a management tool for a given stream or sector of river basin. But preference curves should be generated for each location to ensure that river management decisions with regard habitat and species conservation consider local-level species requirements. Thus, a multi-(eco)species and multi-scale approach is required in habitat suitability assessments. [source] Sorption of copper by a highly mineralized peat in batch and packed-bed systemsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2010Marta Izquierdo Abstract BACKGROUND: The performance of peat for copper sorption was investigated in batch and fixed-bed experiments. The effect of pH was evaluated in batch experiments and the experimental data were fitted to an equilibrium model including pH dependence. Hydrodynamic axial dispersion was estimated by tracing experiments using LiCl as a tracer. Six fixed-bed experiments were carried out at copper concentrations between 1 and 60 mg dm,3 and the adsorption isotherm in dynamic mode was obtained. A mass transport model including convection,dispersion and sorption processes was applied for breakthrough curve modelling. RESULTS: Maximum uptake capacities in batch mode were 22.0, 36.4, and 43.7 mg g,1 for pH values of 4.0, 5.0, and 6.0, respectively. Uptake capacities in continuous flow systems varied from 36.5 to 43.4 mg g,1 for copper concentrations between 1 and 60 mg dm,3. Dynamic and batch isotherms showed different shapes but a similar maximum uptake capacity. Sorbent regeneration was successfully performed with HCl. A potential relationship between dispersion coefficient and velocity was obtained with dispersion coefficients between 5.00 × 10,8 and 2.95 × 10,6 m2 s,1 for water velocities ranging between 0.56 × 10,4 and 5.03 × 10,4 m s,1. The mass transport model predicted both the breakpoints and the shape of the breakthrough curves. CONCLUSIONS: High retention capacities indicate that peat can be used as an effective sorbent for the treatment of wastewater containing copper ions. Copyright © 2009 Society of Chemical Industry [source] Habitat preferences of European grayling in a medium size stream, the Ain river, FranceJOURNAL OF FISH BIOLOGY, Issue 6 2000J. P. Mallet The three grayling Thymallus thymallus age-classes had strong preferences for their local habitat in the Ain river. All age-classes preferred high water velocities between 70 and 110 cm s -1, confirming that grayling is a typical rheophilic species. An important intraspecific segregation regarding depth occurred, as large individuals preferred deeper water than small ones (optimal ranges=50,60, 80,120 and 100,140 cm for 0+, 1+ and adults respectively). The three age-classes had similar preferences for small substratum articles, with optimal values between 0·5 and 16·0 mm. Preference curves were generally comparable between the two sites, despite important differences in habitat availability. It is emphasized that grayling needs various habitat conditions to achieve its entire life cycle. The increasing scarcity of this species underlines the urgency of protecting lotic habitat integrity and diversity. [source] The effects of water velocity on the Ceratomyxa shasta infectious cycleJOURNAL OF FISH DISEASES, Issue 2 2009S J Bjork Abstract Ceratomyxa shasta is a myxozoan parasite identified as a contributor to salmon mortality in the Klamath River, USA. The parasite has a complex life cycle involving a freshwater polychaete, Manayunkia speciosa and a salmonid. As part of ongoing research on how environmental parameters influence parasite establishment and replication, we designed a laboratory experiment to examine the effect of water flow (velocity) on completion of the C. shasta infectious cycle. The experiment tested the effect of two water velocities, 0.05 and 0.01 m s,1, on survival and infection of M. speciosa as well as transmission to susceptible rainbow trout and comparatively resistant Klamath River Chinook salmon. The faster water velocity facilitated the greatest polychaete densities, but the lowest polychaete infection prevalence. Rainbow trout became infected in all treatments, but at the slower velocity had a shorter mean day to death, indicating a higher infectious dose. Infection was not detected in Chinook salmon even at a dose estimated to be as high as 80 000 actinospores per fish. The higher water velocity resulted in lower C. shasta infection prevalence in M. speciosa and decreased infection severity in fish. Another outcome of our experiment is the description of a system for maintaining and infecting M. speciosa in the laboratory. [source] Measurement of the spatial distribution of fluvial bedload transport velocity in both sand and gravelEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2004Colin D. Rennie Abstract Maps are presented of the spatial distribution of two-dimensional bedload transport velocity vectors. Bedload velocity data were collected using the bottom tracking feature of an acoustic Doppler current pro,ler (aDcp) in both a gravel-bed reach and a sand-bed reach of Fraser River, British Columbia. Block-averaged bedload velocity vectors, and bedload velocity vectors interpolated onto a uniform grid, revealed coherent patterns in the bedload velocity distribution. Concurrent Helley-Smith bedload sampling in the sand-bed reach corroborated the trends observed in the bedload velocity map. Contemporaneous 2D vector maps of near-bed water velocity (velocity in bins centered between 25 cm and 50 cm from the bottom) and depth-averaged water velocity were also generated from the aDcp data. Using a vector correlation coef,cient, which is independent of the choice of coordinate system, the bedload velocity distribution was signi,cantly correlated to the near-bed and depth-averaged water velocity distributions. The bedload velocity distribution also compared favorably with variations in depth and estimates of the spatial distribution of shear stress. Published in 2004 by John Wiley & Sons, Ltd. [source] Laboratory simulation of clast abrasionEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2002J. Lewin Abstract Experimental abrasion of river-bed materials has been widely undertaken, producing ,downstream' fining rates that generally are believed to be much less than those observed in the field. A conclusion commonly adopted has been that sorting processes are more effective than abrasion processes. A comparative evaluation of results from an abrasion tank and a tumbling barrel are presented, which show that abrasion patterns and rates differ according to the equipment used, clast size and shape, the clast charge (barrel) and water velocity and bed material (tank). Abrasion is a composite process, and the effects achieved appear to be dominated by percussion in the tank and grinding in the barrel. Breakage, crushing and sandblasting are not modelled effectively, nor are effects achieved on clasts when they form part of the bed. Comparisons are made with other equipment used, the very limited amount of direct field abrasion monitoring, and with the probable suite of processes that may occur under field conditions. Also reviewed are the problems that arise when laboratory weight-loss abrasion coefficients are used or converted into ones of size diminution, as usually derived from field observations of down-channel trends. It is concluded that field abrasion rates generally have been underestimated, as the processes involved are at best only selectively represented by the experimental equipment so far used, and because the results obtained experimentally are capable of misinterpretation when related to field trends. Copyright © 2002 John Wiley & Sons, Ltd. [source] Denil fishway utilization patterns and passage of several warmwater species relative to seasonal, thermal and hydraulic dynamicsECOLOGY OF FRESHWATER FISH, Issue 4 2001C. M. Bunt Abstract , Two different Denil fishways on the Grand River, Ontario, were used as check-points to evaluate the upstream movement of fishes past a low-head weir and to examine the proportions and inferred swimming performance of non-salmonid warmwater fishes that used each fishway type. Traps installed at fishway exits were used to collect fish during 24-hour sampling periods, over 40,51 days each year, from 1995 to 1997. Passage rates, size selectivity, water temperature, water velocity and turbidity for the periods of maximum passage for each year were examined. General species composition from trap samples shifted from catostomids to cyprinids to ictalurids to percids and centrarchids, with some overlap, as water temperatures increased from 8 °C to 25 °C in the spring and early summer. Water depths, and therefore water velocities in each fishway, were independent of river discharge due to variable accumulations of debris on upstream trash-racks. Relationships between the water velocity and the swimming and position-holding abilities of several species emerged. Turbidity was directly related to river discharge and precipitation events, and many species demonstrated maximum fishway use during periods of increased turbidity. This study 1) provided evidence of strongly directional upstream movements among several species that were previously considered non-migratory and 2) describes physical and hydraulic conditions during fishway use for 29 non-salmonid fish species., [source] Physicochemical factors controlling the release of dissolved organic carbon from columns of forest subsoilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2002J.-M. Münch Summary Retention of dissolved organic carbon in soil depends on the chemical and physical environment. We studied the release of organic carbon from three carbonate-free forest subsoil materials (Bs1, Bs2, Bg) in unsaturated column experiments as influenced by (i) variations of the flow regime and (ii) varied chemical properties of the irrigation solution. We investigated the effect of flow initiation, constant irrigation, interruptions to flow, and variation in the effective pore water velocity on the release of organic C. The influence of ionic strength and cation valence in the irrigation solution was studied by stepped pulses of NaCl and CaCl2. The release of C from all materials was characterized by an initial large output and a decline to constant concentrations under long-term irrigation. Interrupting the flow increased its release when flow was resumed. The release from the Bs1 material was not related to the duration of the interruption. The Bs2 material, in contrast, released organic carbon in a way that was successfully described by a kinetic first-order model. Increased pore water velocity decreased the concentrations of C in the effluent from it. The pH of the irrigation solution had negligible effects on the mobilization of C. Increased ionic strength reduced the release, whereas rinsing with distilled water increased the concentrations of C in the effluent. The response of dissolved C to pulses of weak solutions, however, was sensitive to the type of cation in the previous step with strong solutions. The results suggest that the release of organic matter in the soils depends on its colloidal properties. [source] How well are velocity effects on ,13C signatures transmitted up the food web from algae to fish?FRESHWATER BIOLOGY, Issue 6 2010JOSEPH B. RASMUSSEN Summary 1. Benthic algae fractionate carbon isotopes less at low water velocities because of reduced boundary layer exchange, and this effect on ,13C is passed on to consumers via trophic transfer. This study examines the relationships between ,13C signatures of consumers (invertebrates and salmonid fishes) and water velocity in the Sainte Marguerite River, QC, Canada, and compares them to patterns for periphyton, both along the river main-stem and in a small tributary. 2. Relationships of ,13C signatures of herbivore/grazers and collector/gatherers with water velocity were strong and similar to those of periphyton, but relationships for filter-feeders were weak, probably reflecting the effect of spatial averaging of their food supply as a result of downstream transport. 3. Velocity effects on salmonid signatures were much weaker than those of lower trophic levels, being barely significant except in the small tributary where the fish were resident and isolated from the main river. In the river main-stem, even when reach standardised (reach mean subtracted from each data point), fish signatures were only weakly related to water velocity. 4. The fidelity with which velocity effects are transmitted to consumers from benthic algae is highly variable, and depends on a combination of consumer and resource movements, in addition to the trophic position of the consumer. [source] Tracing energy flow in stream food webs using stable isotopes of hydrogenFRESHWATER BIOLOGY, Issue 5 2010JACQUES C. FINLAY Summary 1. Use of the natural ratios of carbon and nitrogen stable isotopes as tracers of trophic interactions has some clear advantages over alternative methods for food web analyses, yet is limited to situations where organic materials of interest have adequate isotopic separation between potential sources. This constrains the use of natural abundance stable isotope approaches to a subset of ecosystems with biogeochemical conditions favourable to source separation. 2. Recent studies suggest that stable hydrogen isotopes (,D) could provide a robust tracer to distinguish contributions of aquatic and terrestrial production in food webs, but variation in ,D of consumers and their organic food sources are poorly known. To explore the utility of the stable hydrogen isotope approach, we examined variation in ,D in stream food webs in a forested catchment where variation in ,13C has been described previously. 3. Although algal ,D varied by taxa and, to a small degree, between sites, we found consistent and clear separation (by an average of 67,) from terrestrial carbon sources. Environmental conditions known to affect algal ,13C, such as water velocity and stream productivity did not greatly influence algal ,D, and there was no evidence of seasonal variation. In contrast, algal ,13C was strongly affected by environmental factors both within and across sites, was seasonally variable at all sites, and partially overlapped with terrestrial ,13C in all streams with catchment areas larger than 10 km2. 4. While knowledge of isotopic exchange with water and trophic fractionation of ,D for aquatic consumers is limited, consistent source separation in streams suggests that ,D may provide a complementary food web tracer to ,13C in aquatic food webs. Lack of significant seasonal or spatial variation in ,D is a distinct advantage over ,13C for applications in many aquatic ecosystems. [source] Day,night changes in the spatial distribution and habitat preferences of freshwater shrimps, Gammarus pulex, in a stony streamFRESHWATER BIOLOGY, Issue 4 2005J. M. ELLIOTT Summary 1. As many invertebrates are nocturnal, their spatial distribution and habitat preferences may change from day to night. Both aspects are examined for Gammarus pulex by testing the hypotheses: (i) a power function was a suitable model for the spatial distribution of the shrimps in both day and night; (ii) diurnal and nocturnal spatial distributions were significantly different; (iii) diurnal and nocturnal habitat preferences were significantly different. Five different life-stages were treated separately. To ensure that the conclusions were consistent, large samples were taken near midday and midnight in April, June and November over 4 years at two sites about 3 km apart in a stony stream: downstream (n = 30) and upstream (n = 50). 2. The first and second hypotheses were supported at both sites. A power function, relating spatial variance (s2) to mean (m), was an excellent fit in all analyses (P < 0.001, r2 > 0.91), i.e. the spatial variance was density-dependent. All five life-stages were aggregated in the day. At night, the degree of aggregation increased for juveniles at higher densities but decreased for juveniles at lower densities, increased for immature females and males, but decreased slightly for mature females and especially mature males, the latter being close to a random distribution. There were no significant differences between sites, in spite of the lower numbers at the downstream site. 3. The third hypothesis was tested at only the upstream site and supported by comparisons between shrimp densities and 13 physical variables (distance from bank, water depth, water velocity, ten particle size-classes), and three non-physical variables (dry weights of bryophytes, leaf material, organic detritus). During the day, densities were strongly related to particle sizes with the following preferences: 0.5,8 mm for juveniles, 8,256 mm for the other life-stages with a weaker relationship for males. There were no significant positive relationships with the other variables, apart from bryophytes for immature shrimps and adults. At night, densities were unrelated to particle size; juveniles and immature shrimps preferred low water velocities near the banks, often where leaf material and organic detritus accumulated, females often preferred medium water velocities slightly away from the banks, and males showed no habitat preferences. 4. Day samples do not provide a complete picture of habitat preferences and probably identify refuge habitats. Day,night changes in spatial distribution and habitat preferences are an essential part of the behavioural dynamics of the shrimps and should be investigated in other species. [source] A comparative study of the dispersal of 10 species of stream invertebratesFRESHWATER BIOLOGY, Issue 9 2003J. M. Elliott Summary 1. Apart from downstream dispersal through invertebrate drift, few quantitative data are available to model the dispersal of stream invertebrates, i.e. the outward spreading of animals from their point of origin or release. The present study provides comparative data for 10 species, using two independent methods: unmarked animals in six stream channels built over a stony stream and marked animals in the natural stream. Experiments were performed in April and June 1973 and 1974, with initial numbers of each species varying from 20 to 80 in the stream channels and 20 to 60 for marked animals. 2. Results were the same for marked invertebrates and those in the channels. Dispersal was not density-dependent; the number of dispersing animals was a constant proportion of the initial number for each species. The relationship between upstream or downstream dispersal distance and the number of animals travelling that distance was well described by an inverse power function for all species (exponential and log models were poorer fits). Results varied between species but were similar within species for the 4 months, and therefore were unaffected by variations in mean water velocity (range 0.04,0.35 m s,1) or water temperature (range 6.7,8.9 °C in April, 12.1,14.8 °C in June). 3. Species were arranged in order, according to their dispersal abilities. Three carnivores (Perlodes, Rhyacophila, Isoperla) dispersed most rapidly (70,91% in 24 h, maximum distances 9.5,13.5 m per day), followed by two species (Protonemura, Rhithrogena) in which about half their initial numbers dispersed (50,51% in 24 h, 7.5,8 m per day), and four species (Ecdyonurus, Hydropsyche, Gammarus, Baetis) in which less than half dispersed (33,40% in 24 h, 5.5,7 m per day). Dispersal was predominantly upstream for all nine species. Few larvae (20%) of Potamophylax dispersed, with similar maximum upstream and downstream distances of 3.5 m per day. The mean time spent drifting downstream was known for seven species from previous studies, and correlated positively with their dispersal distances. Therefore, the species formed a continuum from rapid to very slow dispersers. These interspecific differences should be considered when evaluating the role of dispersal in the maintenance of genetic diversity in stream invertebrates, and in their ability to colonise or re-colonise habitats. [source] Predicting the Tails of Breakthrough Curves in Regional-Scale Alluvial SystemsGROUND WATER, Issue 4 2007Yong Zhang The late tail of the breakthrough curve (BTC) of a conservative tracer in a regional-scale alluvial system is explored using Monte Carlo simulations. The ensemble numerical BTC, for an instantaneous point source injected into the mobile domain, has a heavy late tail transforming from power law to exponential due to a maximum thickness of clayey material. Haggerty et al.'s (2000) multiple-rate mass transfer (MRMT) method is used to predict the numerical late-time BTCs for solutes in the mobile phase. We use a simple analysis of the thicknesses of fine-grained units noted in boring logs to construct the memory function that describes the slow decline of concentrations at very late time. The good fit between the predictions and the numerical results indicates that the late-time BTC can be approximated by a summation of a small number of exponential functions, and its shape depends primarily on the thicknesses and the associated volume fractions of immobile water in "blocks" of fine-grained material. The prediction of the late-time BTC using the MRMT method relies on an estimate of the average advective residence time, tad. The predictions are not sensitive to estimation errors in tad, which can be approximated by , where is the arithmetic mean ground water velocity and L is the transport distance. This is the first example of deriving an analytical MRMT model from measured hydrofacies properties to predict the late-time BTC. The parsimonious model directly and quantitatively relates the observable subsurface heterogeneity to nonlocal transport parameters. [source] Simulations to Verify Horizontal Flow Measurements from a Borehole FlowmeterGROUND WATER, Issue 3 2006Scott C James This paper reports on experiments and simulations of subsurface flow from a slotted acrylic tube deployed in a sand-tank flow chamber for two different purposes. In the first instance, the slotted tube is used to represent a single fracture intersected by an uncased well. In the second instance, the slotted tube is used to represent a multislot well screen within a porous medium. In both cases, the scanning colloidal borescope flowmeter (SCBFM) measures ground water velocity within the well by imaging colloids traveling through a well to measure their speed and direction. Measurements are compared against model simulations. For the case of a slotted tube representing a single fracture, SCBFM and model results agree with respect to the flow direction and to within a factor of 1.5 for the speed near the well's center. Model and experimental agreement lend confidence that for an uncased well drilled in a fractured-rock medium, a calibrated SCBFM could be used to identify and quantify flowing features. Next, the SCBFM was deployed in a four-column multislotted casing with slots aligned with the flow direction. Another numerical model was developed to estimate the flow field within this well screen to evaluate the potential usefulness of employing the SCBFM in a screened well to estimate flow speed and direction in the surrounding porous medium. Results indicate that if the slots are not aligned with the flow, the SCBFM may only provide order-of-magnitude speed measurements and direction measurements with an uncertainty of approximately ±25°. [source] Degradation of TCE with Iron: The Role of Competing Chromate and Nitrate ReductionGROUND WATER, Issue 3 2000Oliver Schlicker This study evaluates the potential of using granular iron metal for the abiotic removal of the organic ground water pollutant trichloroethene (TCE) in the presence of the common inorganic co-contaminants chromate and nitrate, respectively. Our long-term column experiments indicate a competitive process between TCE dechlorination and reductive transformation of chromate and nitrate, which is reflected in a significantly delayed onset of TCE dechlorination. Delay times and therefore the ranges of the nonreactive flowpaths increased with increasing experimental duration, resulting in a migration of the contaminants through the iron metal treatment zone. The present investigation also indicates that the calculated migration rates of TCE and the added cocontaminants chromate and nitrate are linearly related to the initial content of the cocontaminants. With an average pore water velocity of 0.6 m/d and a surface area concentration of 0.55 m2/mL in the column, the calculated migration rates varled between 0.10 cm/d and 5.86 cm/d. The particular similarity between the values of TCE migration and the migration of the strong oxidants chromate and nitrate and the long-term steady state of the TCE dechlorination in the absence of the chromate and nitrate indicates that these competitive transformations are the driving force for the gradual passivation of the granular iron due to the buildup of an electrically insulating Fe(III)-oxyhydroxide. Based on these passivation processes, general formulae were developed that allow a simplified approximation of breakthrough times for the contaminants TCE, chromate, and nitrate. [source] Mineral Precipitation Upgradient from a Zero-Valent Iron Permeable Reactive BarrierGROUND WATER MONITORING & REMEDIATION, Issue 3 2008R.L. Johnson Core samples taken from a zero-valent iron permeable reactive barrier (ZVI PRB) at Cornhusker Army Ammunition Plant, Nebraska, were analyzed for physical and chemical characteristics. Precipitates containing iron and sulfide were present at much higher concentrations in native aquifer materials just upgradient of the PRB than in the PRB itself. Sulfur mass balance on core solids coupled with trends in ground water sulfate concentrations indicates that the average ground water flow after 20 months of PRB operation was approximately twenty fold less than the regional ground water velocity. Transport and reaction modeling of the aquifer PRB interface suggests that, at the calculated velocity, both iron and hydrogen could diffuse upgradient against ground water flow and thereby contribute to precipitation in the native aquifer materials. The initial hydraulic conductivity (K) of the native materials is less than that of the PRB and, given the observed precipitation in the upgradient native materials, it is likely that K reduction occurred upgradient to rather than within the PRB. Although not directly implicated, guar gum used during installation of the PRB is believed to have played a role in the precipitation and flow reduction processes by enhancing microbial activity. [source] Analytical power series solutions to the two-dimensional advection,dispersion equation with distance-dependent dispersivitiesHYDROLOGICAL PROCESSES, Issue 24 2008Jui-Sheng Chen Abstract As is frequently cited, dispersivity increases with solute travel distance in the subsurface. This behaviour has been attributed to the inherent spatial variation of the pore water velocity in geological porous media. Analytically solving the advection,dispersion equation with distance-dependent dispersivity is extremely difficult because the governing equation coefficients are dependent upon the distance variable. This study presents an analytical technique to solve a two-dimensional (2D) advection,dispersion equation with linear distance-dependent longitudinal and transverse dispersivities for describing solute transport in a uniform flow field. The analytical approach is developed by applying the extended power series method coupled with the Laplace and finite Fourier cosine transforms. The developed solution is then compared to the corresponding numerical solution to assess its accuracy and robustness. The results demonstrate that the breakthrough curves at different spatial locations obtained from the power series solution show good agreement with those obtained from the numerical solution. However, owing to the limited numerical operation for large values of the power series functions, the developed analytical solution can only be numerically evaluated when the values of longitudinal dispersivity/distance ratio eL exceed 0·075. Moreover, breakthrough curves obtained from the distance-dependent solution are compared with those from the constant dispersivity solution to investigate the relationship between the transport parameters. Our numerical experiments demonstrate that a previously derived relationship is invalid for large eL values. The analytical power series solution derived in this study is efficient and can be a useful tool for future studies in the field of 2D and distance-dependent dispersive transport. Copyright © 2008 John Wiley & Sons, Ltd. [source] Solute movement through intact columns of cryoturbated Upper ChalkHYDROLOGICAL PROCESSES, Issue 13 2008M. Mahmood-ul-Hassan Abstract Cryoturbated Upper Chalk is a dichotomous porous medium wherein the intra-fragment porosity provides water storage and the inter-fragment porosity provides potential pathways for relatively rapid flow near saturation. Chloride tracer movement through 43 cm long and 45 cm diameter undisturbed chalk columns was studied at water application rates of 0·3, 1·0, and 1·5 cm h,1. Microscale heterogeneity in effluent was recorded using a grid collection system consisting of 98 funnel-shaped cells each 3·5 cm in diameter. The total porosity of the columns was 0·47 ± 0·02 m3 m,3, approximately 13% of pores were , 15 µm diameter, and the saturated hydraulic conductivity was 12·66 ± 1·31 m day,1. Although the column remained unsaturated during the leaching even at all application rates, proportionate flow through macropores increased as the application rate decreased. The number of dry cells (with 0 ml of effluent) increased as application rate decreased. Half of the leachate was collected from 15, 19 and 22 cells at 0·3, 1·0, 1·5 cm h,1 application rates respectively. Similar breakthrough curves (BTCs) were obtained at all three application rates when plotted as a function of cumulative drainage, but they were distinctly different when plotted as a function of time. The BTCs indicate that the columns have similar drainage requirement irrespective of application rates, as the rise to the maxima (C/Co) is almost similar. However, the time required to achieve that leaching requirement varies with application rates, and residence time was less in the case of a higher application rate. A two-region convection,dispersion model was used to describe the BTCs and fitted well (r2 = 0·97,0·99). There was a linear relationship between dispersion coefficient and pore water velocity (correlation coefficient r = 0·95). The results demonstrate the microscale heterogeneity of hydrodynamic properties in the Upper Chalk. Copyright © 2007 John Wiley & Sons, Ltd. [source] Coupled simulation of wave propagation and water flow in soil induced by high-speed trainsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2008P. Kettil Abstract The purpose of this paper is to simulate the coupled dynamic deformation and water flow that occur in saturated soils when subjected to traffic loads, which is a problem with several practical applications. The wave propagation causes vibrations leading to discomfort for passengers and people in the surroundings and increase wear on both the vehicle and road structure. The water flow may cause internal erosion and material transport in the soil. Further, the increased pore water pressure could reduce the bearing capacity of embankments. The saturated soil is modelled as a water-saturated porous medium. The traffic is modelled as a number of moving wheel contact loads. Dynamic effects are accounted for, which lead to a coupled problem with solid displacements, water velocity and pressure as primary unknowns. A finite element program has been developed to perform simulations. The simulations clearly demonstrate the induced wave propagation and water flow in the soil. The simulation technique is applicable to railway as well as road traffic. Copyright © 2007 John Wiley & Sons, Ltd. [source] Shoreline tracking and implicit source terms for a well balanced inundation modelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2010Giovanni FranchelloArticle first published online: 31 JUL 200 Abstract The HyFlux2 model has been developed to simulate severe inundation scenario due to dam break, flash flood and tsunami-wave run-up. The model solves the conservative form of the two-dimensional shallow water equations using the finite volume method. The interface flux is computed by a Flux Vector Splitting method for shallow water equations based on a Godunov-type approach. A second-order scheme is applied to the water surface level and velocity, providing results with high accuracy and assuring the balance between fluxes and sources also for complex bathymetry and topography. Physical models are included to deal with bottom steps and shorelines. The second-order scheme together with the shoreline-tracking method and the implicit source term treatment makes the model well balanced in respect to mass and momentum conservation laws, providing reliable and robust results. The developed model is validated in this paper with a 2D numerical test case and with the Okushiri tsunami run up problem. It is shown that the HyFlux2 model is able to model inundation problems, with a satisfactory prediction of the major flow characteristics such as water depth, water velocity, flood extent, and flood-wave arrival time. The results provided by the model are of great importance for the risk assessment and management. Copyright © 2009 John Wiley & Sons, Ltd. [source] Leaf Breakdown in a Tropical StreamINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 2 2006José Francisco Gonçalves Jr. Abstract The objectives of this study were to investigate leaf breakdown in two reaches of different magnitudes, one of a 3rd (closed riparian vegetation) order and the other of a 4th (open riparian vegetation) order, in a tropical stream and to assess the colonization of invertebrates and microorganisms during the processing of detritus. We observed that the detritus in a reach of 4th order decomposed 2.4 times faster than the detritus in a reach of 3rd order, in which, we observed that nitrate concentration and water velocity were greater. This study showed that the chemical composition of detritus does not appear to be important in evaluating leaf breakdown. However, it was shown to be important to biological colonization. The invertebrate community appeared not to have been structured by the decomposition process, but instead by the degradative ecological succession process. With regards to biological colonization, we observed that the density of bacteria in the initial stages was more important while fungi appeared more in the intermediate and final stages. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Changes of taxonomic and trophic structure of fish assemblages along an environmental gradient in the Upper Beni watershed (Bolivia)JOURNAL OF FISH BIOLOGY, Issue 1 2006M. Pouilly The distribution and the diet of 28 fish species were evaluated, during the dry season, in 12 streams of the Upper Beni watershed (Amazon basin, Bolivia). The 12 streams were of similar size (stream width and water depth) but situated on a gradient of altitude in the Andean and sub-Andean areas. The environmental conditions in the stream changed in relation to the altitude. As altitude decreased, slope and water velocity also decreased, while temperature, conductivity, pH and the proportion of pools increased. Although the diets of the species were mainly based on two aquatic autochthonous food resources, invertebrates and sediment, species were classified into five trophic guilds: detritivores, algivores, piscivores, invertivores-omnivores and aquatic specialist invertivores. In all streams invertivores dominated or co-dominated with detritivores. The trophic structure of the assemblages, however, changed in relation to the environmental gradient. The fish species richness increased and the trophic composition became more diverse at lower altitudes, when slope decreased and temperature increased. At the same time, the relative number of invertivore species decreased, whereas the relative number of detritivore, algivore and piscivore species increased. Decreasing altitude appeared to play a role similar to increasing stream size along the longitudinal gradient. This could be explained by geomorphological and temperature variations that may generate environmental conditions favourable to an increase of productivity. [source] Microhabitat use and preferences of the endangered Cottus gobio in the River Voer, BelgiumJOURNAL OF FISH BIOLOGY, Issue 4 2005C. Van Liefferinge Microhabitat use and preferences of juvenile and adult bullhead Cottus gobio, from the River Voer, Flanders, were studied and compared across different seasons. Water depth, water velocity near the substratum, surface water velocity and substratum type used by C. gobio differed between seasons. These differences, however, were not attributable to differences in microhabitat availability. Adults appeared to prefer higher water velocities and coarser substrata than the average ones available in the basin. Although water depth appeared to have little influence on seasonal variation of microhabitat use in adult C. gobio, juveniles preferred deeper water and coarser substrata in winter, whereas in summer they appeared to use shallower water. There was a difference in microhabitat use between juvenile and adult bullhead only in summer. [source] | ||||||||||||||||