High Discharge Conditions Research Articles

Influence of Stream Profile and Abiotic Factors on the Performance and Residual Dosages of Two Commercial Formulations of Bacillus thuringiensis subsp. israelensis During a 2-Year Experiment

Recently, results of a 3-year study showed the importance of abiotic factors such as water temperature, stream discharge and the hyporheic zone on the behaviour, performance and loss of the residual dosages (amount of the injected dosage left at each station) of two commercial liquid formulations of Bacillus thuringiensis subsp. israelensis ( Bti ), Teknar HP-D and Vectobac 1200L. Experiments were performed in the same stream and under environmental conditions that allowed comparisons of results between formulations. To improve our understanding of the influence of abiotic factors on the behaviour and the performance of these formulations, a 2-year experiment using the same products was conducted in another river characterized by a much different profile, higher discharges and colder temperatures. A field procedure based on a system of gutters located on the bank of the river already used in the previous 3-year experiment was utilized. Black fly larval mortalities were recorded along the river at different distances (stations) to evaluate the behaviour and the performance of the products while water samples taken at the stations were tested in the laboratory against mosquito neonate larvae to evaluate the residual dosages of Bti at each station. Results showed that higher residual dosages of the Vectobac 1200L were recovered compared to Teknar HP-D along the river. Although higher dosages were recovered, higher mortality was observed only for the Vectobac 1200 L in high discharge conditions. As seen before, the hyporheic zone (interstitial water between the streambed and groundwater) produced a major loss of the dosages in the first meters of the river. But because of the river profile, the hyporheic zone had a lesser effect on the loss of the dosages further in the river resulting in very long carries for both Teknar HP-D and Vectobac 1200L.

Diversity, distribution and seasonality of the Simuliidae fauna in a glacial stream system in the Swiss Alps

Spatial and seasonal patterns in the densities and species richness of Simuliidae (blackflies) were examined in the glacier-fed Roseg River, Switzerland. We also investigated how selected environmental factors were related to the observed community structure. Overall, 7 blackfly species were found in streams of this glacial flood plain. Total densities and species richness differed significantly among sampling dates, and densities showed a significant downstream increase. Non-metric multidimensional scaling supported these findings and suggested that seasonal changes were affected strongly by extent of glacial influence. Furthermore, our results were indicative that spatio-temporal habitat heterogeneity ameliorated the negative effects of high discharge conditions in summer. This resulted in enhanced overall ecosystem stability in this glacier-fed stream ecosystem, and enabled biotic assemblages to sustain populations under the harsh environmental conditions experienced at this time of the year. Low temperatures and channel instability limited Simuliidae colonization close to the glacier terminus. Suspended particles represented the most important food source for simuliids in the Roseg River.

00/00222 Electrochemical evaluation of additives for lead-acid batteries under high-discharge conditions

00/00222 Electrochemical evaluation of additives for lead-acid batteries under high-discharge conditions

Suspended sediment dynamics in a large drainage basin: the River Rhine

The behaviour of suspended sediment in rivers is often a function of energy conditions, i.e. sediment is stored at low flow and transported under high discharge conditions. The timing of maximum sediment transport can, however, also be related to mixing and routing of water and sediment from different sources. In this study suspended sediment transport was studied in the River Rhine between Kaub and the German–Dutch border. As concentrations decrease over a runoff season and as the relationship between water discharge and suspended sediment concentrations during most floods is characterized by clockwise hysteresis, it is concluded that sediment depletion occurs during a hydrological year and during individual floods. However, analyses of the sediment contribution from the River Mosel indicate that clockwise hysteresis may result from sediment depletion as well as from early sediment supply from a tributary. Thus, although the suspended sediment behaviour in the downstream part of the River Rhine is partly a transport phenomenon related to energy conditions, mixing and routing of water from different sources also plays an important role. Suspended sediment transport during floods was modelled using a ‘supply-based’ model. Addition of a sediment supply term to the sediment rating curve leads to a model that produces better estimates of instantaneous suspended sediment concentrations during high discharge events. A major constriction of the model is that it cannot be used to predict suspended sediment concentrations as long as the amount of sediment in storage and the timing of sediment supply are unknown. Copyright © 1999 John Wiley & Sons, Ltd.

Electrochemical evaluation of additives for lead–acid batteries under high-discharge conditions

Abstract Organic expanders play an important role in the lead–acid battery. This study presents the design of an electrochemical method which evaluates the influence of some commercial expanders on the performance of the negative plate. Examination is made of different commercial expander formulations which are prepared in the laboratory under carefully controlled conditions. In order to compare their influence on the behaviour of the negative plate, potential step and cyclic voltammetric techniques using high-potential polarization are performed. The results allow the selection of those expander additives which exert the best electrochemical effect on high-rate discharge reactions at negative plates.

Historical background to floodplain morphology: examples from the East European Plain

Abstract Floodplain morphology is described in relation to channel pattern changes in the past. The oldest segments of the present-day floodplains were formed in the Late Valdai (Weichselian). Their morphology is inherited from large palaeomeanders (macromeanders) formed under extremely high discharge conditions. A map of the spatial distribution of Late Valdai macromeander relics on the East European Plain is given. Various floodplain segments have a spectrum of ages that may reflect only selected portions of the river history. The most widespread morphological units correspond to the periods when the river was undergoing its widest lateral migration. Periods of stable channel position may result in a gap in the floodplain age spectrum. The channel pattern and rates of river migration are controlled both by hydrological conditions and by valley floor morphology inherited from the preceding river regime. Heterogeneity of floodplains is illustrated from three key sites: the Khoper River (Southern Russia), the Protva River (Central Russia) and the Vychegda River (Northern Russia).

Wastewater dispersion measurements in the Fraser River estuary, Canada, for the Annacis Island Wastewater treatment plant outfall

Detailed measurements of effluent dilution and dispersion were completed in 1995 in the Fraser River estuary, Canada, as part of a larger study to design an environmental effects monitoring program. Wastewater is discharged at rates of 4-9 m3/s through an 18-port, 3-barrel diffuser in about 10 m of water in a tidal estuary 24 km upstream of the mouth. Rhodamine WT dye was used as a tracer and coordinated in situ measurements were carried out using a towed fluorometer system and a profiling system, each operated from separate vessels. Dispersion measurements were obtained for high and low river discharge conditions and for the complete tidal cycle. The surveying methods proved to be effective for both weak and strong current conditions. It was found that vertical mixing was rapid in the unstratified portion of the estuary and usually complete within 200-500 m of the diffuser. Lateral mixing was relatively slow and cross-channel mixing was not observed even at distances exceeding 12 km. Maximum intertidal zone exposure to effluent occurred on ebb tides but at low concentrations (dilution > 300:1) and confined to the north bank of the river. Minimum dilutions, of the order of 5:1 to 10:1, were found over the outfall at slack tide as the current reversed.

Speciation of Selenium in a Nile Delta Lagoon and SE Mediterranean Sea Mixing Zone

Dissolved selenium species have been measured in Mex Bay located west of Alexandria, which receives intermittently oxic/suboxic water from the Mariut Lagoon. Total dissolved selenium concentrations in the lagoon reached 12·02nMkg−1during the summer, with Se(IV) as the predominant species constituting about 38%. Total dissolved Se behaved conservatively upon mixing with the bay water. Selenite (range 0·13–3·9nMkg−1and 0·09–1·9nMkg−1) and selenate (range 0·89–2·6nMkg−1and 0·63–1·6nMkg−1) during high and low discharge conditions correlate linearly with salinity. During high flow, selenite predominates below salinity 26. Se(IV) (38–47%) and organic Se (37–40%) dominated under suboxic conditions in the Mariut Lagoon, while Se(VI) (67–72%) was predominant in the oxygenated Mex Bay waters followed in abundance by organic Se (20–22%) and Se(IV) (8–11%). Selenium behaviour in the bay seemed more related to phosphorus than silicon; all are simply diluted when brackish lagoon water mixes with neritic Mediterranean waters. The absence of selenium reactivity is caused by the short residence time (28 days) of the bay water.About 1500kgyear−1of total dissolved selenium reaches the bay from the Mariut Lagoon with the peak during July–October. This constitutes 58% of the total dissolved Se flux to the SE Mediterranean derived from landbased sources. Selenium residence time in Mex Bay is 12·6 days, while its assimilative capacity for Se is 5515kgyear−1μgl−1. About a 40% reduction in the present day discharge from Mariut Lagoon will decrease selenium levels in the bay water to safe limits.

Factors regulating the distribution of boron in water in the River Dee catchment in north east Scotland

Boron concentrations have been measured on four occasions, two under high discharge conditions and two under low discharge conditions, in 59 subcatchments of the River Dee catchment in north east Scotland. Correlations between B concentration and % land use cover, other river water constituents and distance from the coast have been examined. The results, especially the strong link with Na and Cl concentrations and their distributions, suggest that a primary source of B in relatively unpolluted river water in north east Scotland is input in precipitation, ultimately derived from oceanic spray. However, precipitation inputs alone do not account for the observed B:Cl ratio in river water, and other atmospheric inputs must also be important. It is suggested that inputs in precipitation and dry deposition approximately balance outputs in river water, except where agricultural land use disrupts the biogeochemical cycling of B.

Wastewater dispersion measurements in the Fraser River estuary, Canada, for the Annacis Island wastewater treatment plant outfall

Detailed measurements of effluent dilution and dispersion were completed in 1995 in the Fraser River estuary, Canada, as part of a larger study to design an environmental effects monitoring program. Wastewater is discharged at rates of 4-9 m 3 /s through an 18-port, 3-barrel diffuser in about 10 m of water in a tidal estuary 24 km upstream of the mouth. Rhodamine WT dye was used as a tracer and coordinated in situ measurements were carried out using a towed fluorometer system and a profiling system, each operated from separate vessels. Dispersion measurements were obtained for high and low river discharge conditions and for the complete tidal cycle. The surveying methods proved to be effective for both weak and strong current conditions. It was found that vertical mixing was rapid in the unstratified portion of the estuary and usually complete within 200-500 m of the diffuser. Lateral mixing was relatively slow and cross-channel mixing was not observed even at distances exceeding 12 km. Maximum intertidal zone exposure to effluent occurred on ebb tides but at low concentrations (dilution > 300:1) and confined to the north bank of the river. Minimum dilutions, of the order of 5:1 to 10:1, were found over the outfall at slack tide as the current reversed.

An assessment of the flux of 90Sr contamination through the Ob' River and estuary to the Kara sea

The Ob' River system, consisting of the Ob' River drainage and its tributaries, connects the Mayak and Tomsk nuclear facilities to the Kara Sea. The Ob' River system and estuary have been modeled to explore the pathways of transport and the flux of 90Sr. We have also examined the processes controlling the hydrological regime of the Ob' and its tributaries. The simulations demonstrate that 90Sr levels within the observed ranges can be reproduced along the course of the Ob' River using these coupled models. These simulations indicate that 90Sr has a residence time of about 200 days in the estuary under high river discharge (1985) conditions, assuming that all of the material is soluble. The coupled models used 1985 river flow data and measured 90Sr levels along lower portions of the river and throughout the Ob estuary in the simulation of transport and fate. Estimated 90Sr levels are lower than those observed, because only the Mayak source is included; the portion of the flux due to fallout has not yet been incorporated.

Anti-cyclonic circulation driven by the estuarine circulation in a gulf type ROFI

Baroclinic residual circulation processes are examined in gulf type Regions Of Freshwater Influence (ROFIs), which have large rivers discharging into a rounded head wider than the Rossby internal deformation radius. Theoretical and observational investigations concentrate on Ise Bay, Japan, with supporting data from Osaka Bay and Tokyo Bay. Simplified analytical solutions are derived to describe the primary features of the circulation. Three dimensional residual current data collected using moored current meters and shipboard acoustic doppler current profilers (ADCPs), satellite imagery and density structure data observed using STDs, are presented for comparison to the theoretical predictions. There are three key points to understanding the resulting circulation in gulf type ROFIs. First, there are likely to be three distinct water masses: the river plume, a brackish upper layer, and a higher salinity lower layer. Second, baroclinic processes in gulf type ROFIs are influenced by the Earth's rotation at first order. Residual currents are quasi-geostrophic and potential vorticity is approximately conserved. Third, the combined effects of a classical longitudinal estuarine circulation and the Earth's rotation are both necessary to produce the resulting circulation. Anti-cyclonic vorticity is generated in the upper layer by the horizontal divergence associated with upward entrainment, which is part of the estuarine circulation. The interaction between anti-cyclonic vorticity and horizontal divergence results in two regions of qualitatively different circulation, with gyre-like circulation near the bay head and uniformly seaward anti-cyclonicly sheared flow further towards the mouth. The stagnation point separating the two regions is closer to (further away from) the bay head for stronger (weaker) horizontal divergence, respectively. The vorticity and spin-up time of this circulation are-(ƒ−ω 1)/2 and h/2w 0 , respectively, where ƒ is the Coriolis parameter, ω 1 is the vorticity of the lower layer, h is the depth of the upper layer and w 0 is the upward entrainment velocity across the pycnocline. Under high discharge conditions the axis of the river plume proceeds in a right bounded direction, describing an inertial circle clearly seen in satellite images. Under low discharge conditions the river plume is deflected in a left bounded direction by the anti-cyclonic circulation of the upper layer.

Modeling Species and Energy Transport in Moderate Pressure Diamond Deposition H2 Plasmas

A one-dimensional diffusion model for H 2 plasma obtained under moderate pressure discharge conditions is presented. The transport equations resulting from this model are solved and enable the estimation of the axial profiles of the plasma species densities and of plasma temperatures on the axis of a diamond deposition microwave plasma reactor. The comparison between the calculated results and experimental measurements shows that the temperatures are well predicted by the model, while some discrepancy was observed for H-atom mole fraction. The analysis of the energy dissipation channels shows that, at low pressure, most of the power lost by the electron is dissipated in activating electron-impact H 2 dissociation reaction. The model is also used to investigate the effect of the microwave power density on the plasma composition and temperatures. It shows that the increase of the power density leads to a strong and non-linear increase of gas temperature and H-atom mole fraction. This result is also in a good agreement with measurements and is consistent with the high quality of the diamond films obtained at high power density discharge conditions.

Modeling of Cylindrical Alkaline Cells: V . High Discharge Rates

A one‐dimensional mathematical model of a AA size alkaline cell is presented to describe nonisothermal, high constant current discharge conditions. The model accounts for the variation of the overpotential, current density, porosity, volume, average velocity, hydroxyl ion concentration, and zincate ion concentration throughout a complete cell, including the anode, cathode, and separator regions. This model is the first to examine the importance of the zincate ion concentration. Three variations of the model are presented: (i) the zincate ion is restricted to the anode region, (ii) the zincate ion is unconfined in the cell, but can precipitate as in the anode, and (iii) the zincate ion is unconfined in the cell but can precipitate in both the anode and separator. Experimental data are best represented by model (iii). Pore plugging, particularly in the separator, has been found to be an important factor limiting cell performance. Additionally, the sensitivity of several parameters on the cell performance is evaluated.

Comparison of Nutrient and Trace Element Distributions in the Delta and Shelf Outflow Regions of the Mississippi and Atchafalaya Rivers

Nutrient and trace element distributions were determined in the outflow region of the Mississippi and Atchafalaya rivers during high river discharge. This outflow region can be divided into two physiographic areas: the broad, shallow Louisiana Shelf off the Atchafalaya River and the narrow shelf off the Mississippi Delta. The physiographic differences between these two areas lead to observable differences in the chemical distributions. During high discharge conditions, nutrient depletion occurs at lower salinities on the Louisiana Shelf, relative to the delta outflow plume, and significant uptake of nickel and cadmium is apparent in these shelf waters, too. Important factors that appear to connect the physiographic to the chemical include the fate of the fluvial suspended load, rates of mixing, and the extent of productivity supported by recycled nutrients. The results suggest that the Mississippi-Atchafalaya outflow region may provide a natural laboratory for examining the possible effects of sea-level change on the biogeochemistry of estuarine and coastal environments.

Trace metal transport in a tropical estuary

The distributions of soluble and particulate trace metals in the Bang Pakong Estuary, Thailand were studied during high (wet) and low (dry) discharge conditions. Particulate trace metals and particulate organic C concentrations are controlled by physical processes. Dissolved Cu and Ni are, in general, conservatively mixed through the estuary. The behavior of Fe and Pb result in net removal during estuarine transport. Fe removal appears to be due to decreased solubility as pH increases in estuarine waters. Mn is removed at low salinities, when riverine concentrations are high, and remobilized at higher salinities. Dissolved Cd, Co and Zn concentration distributions have mid-estuary maxima which coincide with nutrient maxima. The metal-nutrient relationship is interpreted as the result of metal regeneration during organic matter decomposition.

Simulation of the tubular positive electrode of the lead-acid battery

The discharge performance of a tubular electrode of the lead-acid battery based on a pseudo steadystate approach was simulated. It was found that the discharge reaction started from the central interior region instead of from the outer surface as in the usual plate-type electrodes. This is due to the fact that the central region has a smaller reaction surface than the outer region of the tubular electrode. This consequently causes a higher current density near the center. A comparison of the theoretical prediction and experimental result shows that the model is fairly accurate except for very high rate discharge conditions.

Discharge Kinetics of the Nickel Electrode

The kinetics of nickel electrode discharge are found to be controlled by solid‐state proton diffusion under normal high rate discharge conditions. As the nickel electrode is discharged, the conductivity of the active material decreases until eventually mixed kinetics are observed where the electrode impedance has significant contributions from both proton diffusion and charge transfer resistance. Further discharge results in the formation of a semiconductor layer at the metal‐active material interface that is depleted in charge carriers and has a relatively high electronic resistance. The depletion layer is responsible for the secondary discharge plateau of the nickel electrode at 0.0 to −0.5 V vs. . Changes in electrode capacitance during depletion layer formation appear to provide a sensitive measure of the uniformity of electrode discharge. The effects of cobalt additives on the kinetics have been experimentally measured, and while cobalt does not change the discharge mechanism, it does increase the ionic and electronic conductivity of the active material allowing a greater depth of discharge before depletion layer formation.

Performance and Discharge Characteristics of Ca / LiCl , LiNO3 / LiNO3, AgNO3 / Ni Thermal Battery Cells

Thermal battery cells utilizing molten as an oxidizing electrolyte with calcium anodes have been characterized for high rate discharge conditions. The presence of small amounts of greatly improves the cathode reaction. Half‐cell studies of anode characteristics show little variation of anode potential with temperature. Gassing at the anode‐electrolyte interface increases with temperature and current density. Overall anode consumption rates increase with increasing temperature, while anode coulombic efficiencies drop at high rates of discharge (300 mA/cm−2). Cathode half‐cell data reveal that high rate reduction of dissolved in yields masses of dendritic growth at low temperatures (260°–275°C) while at higher temperatures (> 400°C) correspondingly fewer dendritic structures are observed. Cell experiments show anticipated current‐voltage‐temperature relationships, effectively mirroring half‐cell experiments. Cell voltages sustain over 2V at 75 mA/cm−2 for periods which vary according to temperature of discharge.

Suspended-sediment response to semidiurnal and fortnightly tidal variations in a mesotidal estuary: Columbia River, U.S.A.

A turbidity maximum is the dominant feature of the suspended-sediment concentration field in the Columbia River Estuary, U.S.A. In this estuary, the turbidity maximum is an unsteady feature which changes on semidiurnal, fortnightly and seasonal time scales. In response to the semidiurnal tides, the turbidity maximum is advected landward and seaward and may have an excursion of approximately 20 km. In response to the fortnightly tidal variations, the turbidity maximum degenerates, or decreases in concentration, during neap tides and regenerates, or increases in concentration, during spring tides. Finally, in response to seasonal freshwater discharge variations, suspended-sediment concentrations in the turbidity maximum increase and its general location is pushed seaward during high discharge conditions and, conversely, concentrations decrease and its general location is farther landward during low discharge conditions. The magnitude of suspended-sediment concentration variations for these three time scales is similar. Therefore, any consideration of estuarine dynamics and the suspended-sediment concentration field in the Columbia River Estuary should include the semidiurnal and fortnightly time scales as well as the seasonal ones. Because the Columbia is a mesotidal estuary and fortnightly tidal variations are not extremely large, it is expected that these time scales (and associated processes) may be important in many other estuarine systems.