bluuebunny/crossref_metadata_2025 huggingface dataset:
Rowing Force Simulation and Control System
Authors: Grigas Vytautas , Legha Alexandra , Sulginas Anatolijus , Toločka Rymantas Tadas
Published: June 2010

The rowing force simulation and control system is to be developed to generate the loading on the oar during the rowing stroke most adequate to the one acting during waterborne rowing. The paper presents the methodology of defining the law of change of loading on the oar by changing the cross-sectional area of flow channel of hydraulic loading unit at indoor rowing training facility. An example of the rowing force variation during one cycle obtained by using such a system is provided.
Monitoring of Velocity of Manufacturing Machines Subassemblies by Means of a DAQ System
Authors: Blacharski Wojciech
Published: June 2010

The paper deals with design of data acquisition (DAQ) systems and application of quadrature encoders in order to measure velocity of subassemblies of manufacturing machines for diagnostic purposes. Cooperation of general-purpose counter/timer boards with the quadrature encoders during measurements was discussed. Operating principles of three different measuring modes were compared. Some conclusions should be taken into account when a DAQ application has to be developed, for instance, in LabVIEW and when the needed hardware has to be selected.
Study of Influence of Increased Bus Voltage on Motor Insulation System
Authors: Nesvadba Martin , Duroň Jiří , Singule Vladislav
Published: June 2010

The target of this paper is to evaluate influence of increased bus voltage of power converter on motor insulation system. This is required for the evaluation of motors for 800 V DC bus based servo-amplifiers. Increase of DC bus voltage is a logical consequence of higher power needs for servo-drive systems.
Simulation and Experiments of High Speed Machining Vibration Monitoring with Variable Spindle Velocity
Authors: Kaliński Krzysztof J. , Galewski Marek A.
Published: June 2010

The paper is devoted to vibration monitoring of rotating tools in modern milling machines. Dynamic analysis of slender ball-end milling process was performed and dynamics of the controlled structure was described. Instantaneous change in the spindle speed is applied in order to reduce vibration level. The method of vibration monitoring by means of spindle speed optimal-linear control was developed and implemented with success. Vibration monitoring during high speed milling was performed on the basis of results of computer simulation. These results were verified during experimental investigation on the Alcera Gambin 120CR milling machine.
Theoretical Analysis of Vibrations of a Mass Connected with a Support through a Chain of Elastic Elements
Authors: Marcinkevičius Andrejus Henrikas
Published: June 2010

Vibrations of a mass are analyzed when the mass is connected with the support in succession of two elastic elements characterized by stiffness and damping coefficients. It is demonstrated that upon harmonic excitation of the mass and considering different values of stiffness and damping coefficients the system can respond differently in comparison to the case when the mass is connected to the support by means of single elastic element. Reduction of stiffness and damping coefficients of a pair of elements to a single one (as it is proposed in calculations of considered systems) can lead to incorrect results. This is confirmed by presented calculations and dependences.
Selection of Parameters of External Electric Circuit for Control of Dynamic Flexibility of a Mechatronic System
Authors: Buchacz Andrzej , Płaczek Marek
Published: June 2010

This paper deals with the analysis of mechatronic systems including piezoelectric materials used as sensors or actuators for stabilization and damping of mechanical vibration. This work presents the analysis of the flexural vibrating one-dimensional mechatronic system – a cantilever beam and the piezoelectric transducer bonded on the beam surface by means of a glue layer. The external RC circuit is connected to the transducer clamps. Dynamic equations of motion of the considered mechatronic system were written down using
the discrete-continuous mathematical model, taking into consideration the influence of the connection layer and the external electric circuit. Dynamic flexibility of the mechatronic system was assigned on the basis of the approximate Galerkin method.
Dynamic Analysis of Vibrating Device
Authors: Trąbka Arkadiusz , Majewski Ludwik , Kłosiński Jacek
Published: June 2010

Dynamics of two models (simplified and complex) of a small, typical vibrating table is considered in the paper. The table consists of vibrating plate and electrical vibrator, mounted in the central position of the plate, which excites the vibrations of the table. The coefficient of transversal stiffness of the spring has been determined on the basis of numerical simulation. The spring is an essential element of the system. The results of performed numerical simulations are presented in the graphical form.
Modeling of Vertical Planar Two-Link Manipulator
Authors: Gosiewski Zdzisław , Michałowski Grzegorz
Published: June 2010

Modeling of kinematics of hydraulically-driven manipulator is presented in the paper. The analyzed electrically-controlled vertical planar two-link manipulator has two rotary degrees of freedom and includes two hydraulic cylinders that form additional links thereby resulting in excavator type mechanism. Equations of motion are derived. Provided simulation results of the manipulator endpoint position, velocity, and acceleration are obtained by Matlab/Simulink.
Optimization of Transport Movement Parameters of the Transfer Manipulator for the Quenching Bath According to the Technological Process Requirements
Authors: Slivinskas Kastytis , Gichan Vladimir , Striška Vytautas , Poška Algimantas Juozas
Published: June 2010

The paper analyzes problems related to optimal selection and possible control of parameters of transport movements of the manipulator serving galvanizing and quenching baths. Evaluation of the acceleration and braking processes as well as minimization of the deflection during oscillations of the suspended loading are considered. Mathematical models of the transfer manipulator together with the loading unit were developed, which enable dynamic evaluation of transporting movements. Calculations of the dynamics of the model and simulations of the transfer process were performed. The obtained research results allow to improve the quality of the processing and reduce the emission of pollutions.
Modification of W and Re Powders by Plasma Technique
Authors: Majewski Tomasz
Published: June 2010

Selected measurement results of plasma spheroidization of tungsten and rhenium powders are presented in the paper. The powders can be applied for production of sinters intended for armor-piercing penetrating cores (kinetic energy penetrators) or high-current electric contacts. Spheroidization of these powders was carried out on the stand for plasma spraying in a chamber filled with neutral gas. Changes of shape and size of powder particles after spheroidization are demonstrated. Measurement results of internal stresses in powder particles are presented.
Assessments of Shrinkage Degree in Bioceramic Sinters HA+ZrO2
Authors: Dudek Agata , Kolan Cezary
Published: June 2010

In the aspect of growing popularity of hydroxyapatites and HA-based composites (with addition of ZrO2 phase) used in medicine, it seems to be crucial to determine accurate percentage content of ZrO2 phase addition in the mixture ensuring invariable or predictable changes in dimensions of implants or coatings after the process of sintering. In consideration of the aforementioned statement, combined mathematical and statistical analysis enabling prediction of such changes was carried out.
Estimation of the Influence of Burnishing Parameters on X5CrNi18-10 Steel
Authors: Labuda Wojciech , Starosta Robert
Published: June 2010

Angular momentum pumps are very often applied in ships. Because the pumps are operating in hard conditions they are produced from cavitation wear-proof and electrochemical corrosion-resistant materials. The most common damage of pump shaft is neck wear in place where seals are mounted.
Burnishing as modern finish plastic tooling method makes it possible to achieve high technological quality of elements. Due to many burnishing advantages, the method was proposed for treatment of angular momentum pumps shafts instead of finish machining (finish turning, grinding, lapping). The goal was to estimate optimal burnishing parameters that enable obtaining higher strength and the lowest roughness factor of angular momentum pumps shafts. Shaft necks were made of stainless steel type X5CrNi1810. Roller burnishing tool SRMD type produced by Yamato was used in the research work. Its axis was parallel to working shaft axis. During working, technological parameters such as force, velocity and feed were changed.
Multicomponent Layers for Aluminium Alloys Surface Consolidation
Authors: Serbiński Waldemar
Published: June 2010

The main reason of the surface modification of the components such as pistons and cylinder blocks made of cast aluminium alloys is to obtain high hardness, wear and corrosion resistance of the working surface for larger lifetime of the motor-car and aircraft engines. In that aspect, the new conception of development – by hybrid method – of surface layers containing manganese, nitrogen, sulphur (Mn-N-S) and manganese, nitrogen, oxygen (Mn-N-O) on aluminium alloys was considered in this paper. These layers are diffusively connected with aluminium base, possess high hardness and good tribological properties. The aim of this paper is to present the influence of the proposed consolidation method on microstructure, phase composition, microhardness, wear and corrosion characteristics of the surface layers produced on AlSi13Mg1CuNi alloy.
Influence of Material Model on Tensile Loaded Joint
Authors: Szymczyk E. , Slawinski Grzegorz
Published: June 2010

The paper deals with the numerical analysis of a tensile loaded riveted joint. Finite element simulations of the upsetting process were carried out with the use of Marc code to determine the residual stress field. The contact with friction is defined between the mating parts of the joint. The computations were performed for four cases of material and load conditions and a comparison was performed on the basis of results obtained for standard elasto plastic and Gurson material models. Moreover, the influence of material model and residual stress on the tensile loaded joint was analyzed.
The Mechanism of Defects Formation in Silicon Substrates
Authors: Bogorosh A. , Voronov S. , Višniakov N. , Ščekaturovienė D. , Bubulis Algimantas
Published: June 2010

Components of navigating devices can be affected by acoustic emission and vibration. Therefore prototype samples and electronic components must be tested in such conditions. Heterostructures, which destructed under the action of external physical factors and kinetics of formations of porous defects in silicon substrates, were analyzed.
Regulation of bacterial biomass and community structure by metazoan and protozoan predation
Authors: Langenheder Silke , Jürgens Klaus
Published: June 2010

We performed food web manipulation experiments in three eutrophic Daphnia‐dominated ponds, to compare the predation impact on planktonic bacteria exerted by metazoan and protozoan bacterial consumers. We analyzed the bacterial morphological composition by image analysis and the taxonomic composition by fluorescent in situ hybridization with group‐specific oligonucleotide probes. The removal of Daphnia always resulted in a microbial succession in which first free‐living bacteria and then heterotrophic nanoflagellates (HNFs) increased. Distinct stages of bacterial grazing either exclusively by Daphnia or by HNFs allowed a quantitative and qualitative comparison of their predation impact on the bacterial assemblage. Both bacterial consumers showed a strong size‐selective impact that shifted the free‐living bacterial community structure toward small cells. Suppression of bacterial biomass below the carrying capacity was similar with Daphnia or HNFs in one experiment and was significantly stronger with Daphnia as bacterial consumer in two experiments. This was due to the fact that bacteria that were resistant to protozoan predation partially compensated grazing mortality. Bacteria attached to aggregates and detrital particles were more important as grazing‐resistant forms than bacterial filaments and constituted up to 50% of total bacterial biomass at the end of the experiments. Changes in predation pressure were also associated with shifts in bacterial community composition. Bacteria belonging to the beta subclass of the class Proteobacteria and to the Cytophaga/Flavobacterium group dominated originally. The latter were most strongly reduced by HNF grazing, whereas other groups, in two experiments the alpha sublass (ALF) of Proteobacteria and in one experiment bacteria hybridizing with the probe for Archaea, even increased during HNF grazing. The composition also differed between bacteria associated with aggregates and freely suspended bacteria, the most obvious being the dominance of ALF growing on detrital aggregates. The experiments demonstrated that predation is a major structuring force for planktonic bacterial communities and that changes in predation regime probably have a much stronger impact on the structure of the bacterial community than on bacterial abundance and biomass.
Composition and cycling of marine organic phosphorus
Authors: Kolowith Lauren Clark , Ingall Ellery D. , Benner Ronald
Published: June 2010

Using tangential‐flow ultrafiltration and solid‐state 31P nuclear magnetic resonance (NMR) spectroscopy, the dominant compound classes of marine high‐molecular weight (1‐100‐nm size fraction) dissolved organic phosphorus (DOP) have been characterized in 16 samples from the Pacific Ocean, the Atlantic Ocean, and the North Sea. NMR spectra of ultrafiltered dissolved organic matter (UDOM) from all sites and depths reveal that P esters (75%) and phosphonates (25%) are the major components of ultrafiltered DOP (UDOP). P esters and phosphonates are present in unchanging proportions throughout the ocean. The homogeneity of UDOP from different oceanic regions suggests that processes leading to this chemical composition are ubiquitous. Ultrafiltered particulate organic matter (UPOM; 0.1‐60‐mm size fraction) samples from the Pacific Ocean and the North Sea were also analyzed using 31P NMR. In these samples, P esters are the only P compound class measured. Differences in the observed chemical compound classes of UDOM versus UPOM may result from (1) less‐reactive phosphonates accumulating relative to P esters as particulate organic matter (POM) decomposes to DOM or (2) phosphonates originating from another source. C: N: P ratios of UDOM are significantly higher than Redfield ratios for POM. In general, C: P and N: P ratios of UDOM double between surface waters and the deep ocean. Increasing C: P and N: P ratios suggest that P is preferentially remineralized from UDOM relative to C and N throughout the water column.
Organic complexation of copper in surface waters of Galveston Bay
Authors: Tang Degui , Warnken Kent W. , Santschi Peter H.
Published: June 2010

The importance of colloidal ligands in the organic complexation of Cu was elucidated in the estuarine waters of Galveston Bay by use of a number of instrumental techniques. Ultrafiltration was conducted to isolate the ultra‐permeate fraction from the filter‐passing fraction and competitive ligand equilibration/adsorptive cathodic stripping voltammetry measurements were conducted by use of varying amounts of catechol as the competitive ligand. Greater than 99.9% of Cu was bound by strong organic ligands with log[K′ (M−1)] values of 12.3 ± 0.15 and 11.1 ± 0.29 in the filter‐passing and ultrapermeate fractions, respectively. The concentrations of Cu complexing ligands were lower in the ultrapermeate than in the filter‐passing fraction, and the calculated K9 values for the colloidal ligands (log K′ = 12.9) were 60 times greater than those for the ultrapermeate fraction, suggesting that good separation of the colloidal fraction during ultrafiltration was achieved. Total Cu concentrations in the filter‐passing fraction ranged from 2.27 to 12.9 nM and were fairly constant at salinity <20 but decreased at salinity ≫20. The calculated free Cu concentrations (0.05–0.49 pM) showed an overall increasing trend with salinity, possibly resulting from decreasing concentrations of Cu complexing ligands toward the seawater endmember. The concentration of Cu complexing ligands (21–54 nM) in the estuarine regions of Galveston Bay was approximately equal to the concentration of total reduced sulfur species (20–60 nM) in the filter‐passing fraction, suggesting that reduced sulfur species could account for most of the Cu‐complexing ligands in these waters.
Phytoplankton distribution and survival in the thermocline
Authors: Sharples Jonathan , Moore Mark C. , Rippeth Tom P. , Holligan Patrick M. , Hydes David J. , Fisher Neil R. , Simpson John H.
Published: June 2010

Observations of the vertical structure of density, concentrations of chlorophyll a and nitrate, and turbulent dissipation rates were made over a period of 25 h in a well‐stratified shelf region in the Western English Channel, between neap and spring tides. Maximum turbulent dissipation at the base of the thermocline occurred almost 5 h after maximum tidal currents. This turbulence aids phytoplankton growth by supplying bottom‐layer nutrients into the subsurface chlorophyll maximum but reduces phytoplankton concentrations in the thermocline by mixing cells from the base of the subsurface maximum into the bottom mixed layer. The turbulent dissipation observations were used to estimate an average nitrate flux into the thermocline of 2.0 (0.8‐3.2, 95% confidence interval) mmol m−2 d−1, which is estimated to have been capable of supporting new phytoplankton growth at a rate of 160 (64–256) mg C m−2 d−1. Turbulent entrainment of carbon from the base of the subsurface biomass maximum into the bottom mixed layer was observed to be 290 (120–480) mg C m−2 d−1. This apparent excess export from the chlorophyll maximum is suggested to be a feature of the spring‐neap cycle, with export dominating as the tidal turbulence increases toward spring tides and erodes the base of the thermocline. The observed rate of carbon export into the bottom mixed layer could account for as much as 25% of the gross annual primary production in stratifying shelf seas. Such turbulent losses, combined with grazing losses and low light levels, suggest that phytoplankton need to be highly adapted to environmental conditions within the thermocline in order to survive.
Fluxes of methylmercury to the water column of a drainage lake: The relative importance of internal and external sources
Authors: Sellers Patricia , Kelly Carol A. , Rudd John W. M.
Published: June 2010

We studied fluxes of methylmercury (MeHg) through a Precambrian Shield lake using a mass balance approach. The primary goal of the study was to determine the importance of various sources of MeHg to the water column of the lake. The relative importance of all sources was: in‐lake production >>> inflow from a brown‐water lake with riparian wetlands >>> wet deposition > inflow from an upstream oligotrophic lake > direct inflow from uplands surrounding the lake. MeHg accumulated in the hypolimnion of Lake 240 when oxygen was present. Water‐column sinks for MeHg included photodegradation of MeHg, which was about 3.5 times greater than the loss of MeHg through outflow. At present, there are few studies available on mass balance fluxes of MeHg in lakes, and this is the first study that includes losses of MeHg by photodegradation. The inclusion of photodegradation in this study results in a clear demonstration that in‐lake production of MeHg is very important. In drainage lakes, the relative importance of in‐lake production versus inflow of MeHg from wetlands will vary according to the extent of wetlands in the drainage basin, as well as the volume of precipitation, which produces runoff and transports MeHg from wetlands to downstream lakes.
Dominance of bacterial metabolism in oligotrophic relative to eutrophic waters
Authors: Biddanda Bopaiah , Ogdahl Megan , Cotner James
Published: June 2010

Heterotrophic bacteria are a key component driving biogeochemical processes in aquatic ecosystems. In 1998, we examined the role of heterotrophic bacteria by quantifying plankton biomass and bacterial and planktonic respiration across a trophic gradient in several small Minnesota lakes as well as Lake Superior. The contribution of bacteria (<1‐ µm fraction) to total planktonic respiration ranged from ~10 to 90%, with the highest contribution occurring in the most oligotrophic waters. The bacterial size fraction constituted a substantial reservoir of planktonic carbon, nitrogen, and phosphorus (14‐58%, 10‐49%, and 14‐48%, respectively), being higher in oligotrophic than in eutrophic waters. However, we saw no clear evidence for the selective enrichment of either nitrogen or phosphorus in the bacteria size fraction relative to total plankton. Carbon : nitrogen and carbon : phosphorus ratios in both the total particulate matter and <1‐ µm fractions were similar and above Redfield values in oligotrophic waters, but approached them in eutrophic waters. Carbon‐based bacterial growth efficiencies (BGE) were variable (4‐40%) but were lowest in oligotrophic systems and increased in eutrophic systems. BGE varied negatively with carbon : nitrogen : phosphorus ratios, suggesting increased maintenance costs in low‐nutrient waters. In oligotrophic waters most of the organic matter is dissolved, supporting a predominantly microbial food web, whereas in eutrophic waters there is an increased abundance of particulate organic matter supporting a food web consisting of larger autotrophs and phagotrophic heterotrophs.
Strong bottom‐up and top‐down control of early life stages of macroalgae
Authors: Lotze Heike K. , Worm Boris , Sommer Ulrich
Published: June 2010

In contrast to most pelagic primary producers, benthic macrophytes pass through morphologically distinct life stages, which can be subject to different ecological controls. Using factorial field experiments, we investigated how grazing pressure (three levels) and nutrient supply (four levels) interact in controlling the passage of marine macroalgae through an apparent recruitment “bottleneck” at the germling stage. In comparative experiments, we asked whether relative bottom‐up and top‐down effects on early life stages (≪4 week germlings) vary (1) between the eutrophic Baltic Sea and the oligotrophic NW Atlantic, (2) across seasons in the NW Atlantic, and (3) among annual and perennial macroalgae. In both systems nutrient enrichment favored and grazers suppressed recruitment of green and brown annual algae; however, enrichment effects were much more pronounced in the Baltic, whereas grazer effects dominated in the NW Atlantic. Grazers induced a shift from grazer‐susceptible green to more resistant brown algae in the Baltic without reducing total germling density. In the NW Atlantic, grazers strongly reduced overall recruitment rate throughout all seasons. Effects on perennials were similar in both systems with moderate losses to grazing and no effects of nutrient enrichment. Recruit densities and species composition shifted with season in the NW Atlantic. We conclude that the relative effects of grazers and nutrient enrichment depended on the nutrient status of the system, algal life history strategy, and season. Strong bottom‐up and top‐down controls shape benthic community composition before macroalgae reach visible size.
Direct use of inorganic colloidal iron by marine mixotrophic phytoplankton
Authors: Nodwell Lisa M. , Price Neil M.
Published: June 2010

Three species of photosynthetic flagellates capable of phagotrophy (mixotrophic species) were tested for their abilities to use inorganic iron colloids for growth. Ochromonas sp., Chrysochromulina ericina (a coastal strain), and C. ericina (an oceanic strain) were grown in iron‐free seawater supplemented with 1 µM Fe‐ferrihydrite (amorphous hydrous ferric oxide), magnetite (Fe3O4)/maghemite ( gamma‐Fe2O3), hematite ( a‐Fe2O3), or goethite ( a‐FeOOH). Desferrioxamine B, an iron‐binding siderophore, was used to reduce the concentration of dissolved iron in the colloid‐amended media, and none of the flagellates were able to use its iron complex as an iron source under the conditions of the experiments. Both strains of Chrysochromulina grew at 35%–70% of their maximum rates with goethite, hematite, and magnetite/maghemite but were unable to use ferrihydrite. Ochromonas grew well with ferrihydrite but could not use any of the other forms. Thalassiosira oceanica (clone 1003) and Thalassiosira pseudonana (clone 3H), diatoms that could only take up dissolved forms of iron, were unable to use any of the colloids tested. The mechanism of iron acquisition by the flagellates appeared to involve ingestion of the iron colloids, because bacteria resident in the cultures were too iron poor to be a significant source of iron and were unable to use the iron contained in the colloids themselves. Variations in the sizes of the colloids were hypothesized to account for differences in their availability, independent of colloid chemical stability. The results provide the first strong evidence for direct use (i.e., without prior dissolution) of colloidal iron by mixotrophic phytoplankton and document a new pathway of iron acquisition that may be important for their survival in low‐iron waters of the sea.
Minireview: Ciliary filter feeding and bio‐fluid mechanics—present understanding and unsolved problems
Authors: Riisgård Hans Ulrik , Larsen Poul S.
Published: June 2010

The energy cost for various ciliary filter feeders shows that useful pump work constitutes 0.3–1.1% of the total metabolic expenditure. The ‘water processing potential’ (liters of water pumped per milliliter O2 consumed by the animal) is a useful tool for characterizing filter feeding and adaptation to the environment. The six types of ciliary‐capture mechanisms (collar sieving, cirral trapping, ciliary sieving, ciliary downstream collecting, ciliary upstream collecting, mucus‐net sieving) are reviewed as well as the aerosol/hydrosol filtration theory. A brief overview of fluid mechanical principles and tools for studying ciliary functions is given.
The use of photolytic rhodamines WT and sulpho G as conservative tracers of dispersion in surface waters
Authors: Upstill-Goddard Robert C. , Suijlen Jo M. , Malin Gillian , Nightingale Philip D.
Published: June 2010

We describe the use of sulpho rhodamine G (SG) and rhodamine WT (WT) as oceanographic tracers in tidally active waters of the southeastern North Sea. Ten kilograms of SG and 5 kg of WT dissolved in 1,000 liters of sea water were released to produce an initial tracer patch ~10 X ~0.5 km. Tracer dispersal was monitored for 11 d by high‐performance liquid chromatography analysis of samples collected close to the patch center. The patch center was initially identified during surveys for sulfur hexafluoride released simultaneously, and its position was subsequently confirmed by use of a two‐dimensional tracer dispersion model. Temporal changes in the SG/WT ratio were undetectable, so photolytic tracer losses were not directly quantified. A simple photolysis model was used to correct to conservative behavior for WT. Results are compared with the dispersal of spores of Bacillus globigii var. niger released simultaneously. Photolytic tracer pairs are ideally suited to tracer experiments in unconstrained water
Predation by omnivorous copepods on early developmental stages of Calanus finmarchicus and Pseudocalanus spp.
Authors: Sell Anne F. , van Keuren Donna , Madin Laurence P.
Published: June 2010

Predation is thought to be an important source of mortality in the early life stages of fish and copepods on Georges Bank. Omnivorous copepods may be predators on copepod eggs and nauplii, but data on feeding rates or selectivity are scarce. As part of the GLOBEC Georges Bank program, we generated functional response curves for the omnivorous copepods Metridia lucens, Centropages typicus, and Temora longicornis feeding on the eggs and nauplii of Calanus finmarchicus or Pseudocalanus spp. in shipboard predation trials. Neither C. typicus nor M. lucens reached saturation feeding on Calanus eggs until prey concentration was >400 L−1. Individual M. lucens and C. typicus ingested up to 34 ± 9 (mean ± SD, n = 3) and 24 ± 14 eggs d−1, respectively (68C). T. longicornis was more abundant in late spring, when they ingested Calanus eggs at rates similar to those of C. typicus. At ambient prey concentrations, ingestion rates of Calanus nauplii were higher than rates of Calanus eggs for the predator M. lucens but were similar for C. typicus. Advanced naupliar stages were less susceptible to predation than young stages. Pseudocalanus nauplii moved faster and were ingested at lower rates than similarly sized Calanus nauplii. Predation rates increased with increasing temperature for the warm‐water species C. typicus but decreased for the cold‐water species M. lucens. These results may contribute to models predicting the development of copepod populations and their availability to larval fish.
Spatio‐temporal geochemistry of mercury in waters of the Tapajós and Amazon rivers, Brazil
Authors: Roulet M. , Lucotte M. , Canuel R. , Farella N. , De Freitos Goch Y. G. , Pacheco Peleja J. R. , Guimarães J.-R. D. , Mergler D. , Amorim M.
Published: June 2010

Spatial and temporal variations of mercury (Hg) concentrations were monitored in the surface waters from the lower portion of the Tapajós River, the Arapiuns River, its principal tributary, and the Amazon River at its confluence with the Tapajós. In the rivers, Hg concentrations in the water column are governed by the concentration of suspended particles. Hg in the filtered water showed very little seasonal variation with low concentrations in the lower Tapajós (<1.8 ng L−1), Arapiuns (<0.8 ng L−1), and Amazon (<2.8 ng L−1). Concentrations of fine particulate Hg (0.6–29.7 ng L−1) represent 40%–90% of the total volumetric concentration of Hg. In relation to their oxyhydroxide contents, suspended particles are not richer in Hg than nearby soils where oxyhydroxides control the accumulation of Hg. The study shows that the dominant stock of Hg in the aquatic ecosystems of this region is derived from erosion of natural soils in the catchment rather than from anthropogenic pollution. The input of natural Hg coming from soils into the aquatic ecosystems may have increased over historical levels in the region. This increase of total Hg in aquatic ecosystems could potentially account for high levels of methylmercury recently reported in fish and humans in the lower Tapajós River area, but the link between the different processes that promote high levels of methylmercury exposure for the human community remains to be proved.
Iron availability, cellular iron quotas, and nitrogen fixation in Trichodesmium
Authors: Berman-Frank Ilana , Cullen Jay T. , Shaked Yeala , Sherrell Robert M. , Falkowski Paul G.
Published: June 2010

Iron availability is suggested to be a primary factor limiting nitrogen fixation in the oceans. This hypothesis is principally based on costߚbenefit analyses of iron quotas in the dominant nitrogenߚfixing cyanobacteria, Trichodesmium spp., in the contemporary oceans. Although previous studies with Trichodesmium have indicated that iron availability enhanced nitrogen fixation and photosynthesis, no clear relationship has been reported between cellular iron quotas and nitrogen fixation. We reߚexamined the proposed link between iron availability and nitrogen fixation in laboratory isolates and natural populations collected from coastal waters north of Australia. In laboratory cultures grown under ironߚlimiting conditions, we measured a decline in cellular iron quotas, photochemical quantum yields, the relative abundance of photosystem I to photosystem II reaction centers, and rates of nitrogen fixation. Nitrogen fixation displayed a critical threshold of the dissolved sum of total inorganic Fe species ([Fe′]) of ca. log[Fe′] = –9.7. Field populations of Trichodesmium, collected during bloom conditions, showed high iron quotas consistent with high nitrogen fixation rates. Using seasonal maps of aeolian iron fluxes and modelߚderived maps of surface water total dissolved Fe, we calculated the potential of nitrogen fixation by Trichodesmium in the global ocean. Our results suggest that in 75% of the global ocean, iron availability limits nitrogen fixation by this organism. Given present trends in the hydrological cycle, we suggest that iron fluxes will be even more limiting in the coming century.
Marine snow, organic solute plumes, and optimal chemosensory behavior of bacteria
Authors: Kiørboe Thomas , Jackson George A.
Published: June 2010

Leaking organic solutes form an elongated plume in the wake of a sinking aggregate. These solutes may both be assimilated by suspended bacteria and guide bacteria with chemokinetic swimming behavior toward the aggregate. We used modifications of previously published models of the flow and concentration fields around sinking aggregates and of chemokinetic behavior of bacteria to identify the behavior that optimizes aggregate colonization and plume utilization. The optimal solution is governed by physical constraints and is a trade off between a high sensitivity to chemical signals and a long signal integration time. For a runߚandߚtumble swimming behavior, the predicted tumbling frequency is between 1 and 10 s21, similar to that reported for marine bacteria. The predicted optimal sensitivity to chemical signals is similar to or greater than that known for Escherichia coli. The optimal behavior was used to examine the potential contribution of aggregateߚgenerated solute plumes for water column bacterial production. Despite occupying only a small volume fraction, the plumes may provide important growth habitats for free bacteria and account for a significant proportion of water column bacterial production at typical concentrations of marine snow aggregates.
Light scattering by nonspherical particles: Application to coccoliths detached from Emiliania huxleyi
Authors: Gordon Howard R. , Du Tao
Published: June 2010

Computation of the light scattering properties of marine particles has typically been effected using Mie theory (i.e., modeling the particles as homogeneous or layered spheres). Because scattering by irregularly shaped particles is significantly different from that of spheres, particularly in backscattering directions, it is of interest to examine the efficacy of using more complex formulations of light scattering that are not limited to spherically symmetric particles. We applied the discrete dipole approximation (DDA) to the computation of the scattering properties of detached calcium carbonate coccoliths from the coccolithophorid Emiliania huxleyi. Three distinct models of E. huxleyi coccoliths were studied: thin disks with a diameter of approximately 2.75 µm, washers with a 1.38‐ µm hole in the disk, and two parallel disks joined by a hollow tube (a "fishing reel"). The model coccoliths all had the same volume (mass ~ 0.19 pg carbon) and disk diameter and a refractive index of 1.20 relative to water. DDA computations for randomly oriented model coccoliths showed that the total scattering cross section and its spectral variation are similar for each of the three particle shapes and agree well with measurements made in natural E. huxleyi blooms both on a per‐coccolith and per‐calcite concentration basis. The backscattering cross section and its spectral variation was found to be strongly dependent on particle morphology. This dependence was shown to be due to multiple reflections within the particle. Scattering and backscattering coefficients for volume‐equivalent spheres were within a factor of two of those for the disklike models.
Resource competition between sympatric sibling rotifer species
Authors: Ciros-Pérez Jorge , Carmona María José , Serra Manuel
Published: June 2010

Mechanisms underlying competitive interactions are important in understanding the structure of planktonic communities, particularly the coexistence of similar species. Here we present experimental results of exploitative competition among three sympatric sibling species of the Brachionus plicatilis complex for two differently‐sized species of food microalgae. These three rotifer species are to be found in seasonal succession in brackish ponds on the Spanish Mediterranean coast; they can, however, co‐occur for long periods. The functional and numerical responses of the three Brachionus species to both food microalgae, although similar, differed. Neither rotifer population growth nor grazing rates showed a clear positive correlation between rotifer and alga sizes. Tilman's models were applied to these results in order to predict the outcome of competition in two rotifer, two resources systems. For testing predictions and addressing the possibility of rotifer coexistence, we performed pairwise competition experiments in semicontinuous cultures, which introduces periodic disturbance as an additional factor. Results confirmed the pattern expected from Tilman's models regarding the competitive superiority of each rotifer species, when food composition was biased toward one of the two resources. This shows the relevance of the food threshold concept to predict the superior competitor. However, coexistence of rotifers was found in conditions in which Tilman's models had predicted an unstable equilibrium, with the winning species depending on the initial conditions. We hypothesize that variance in food availability mediated coexistence. Our results suggest that both food partitioning and disturbance are important in explaining the coexistence of these sibling species in nature.
Response of marine bacterial community composition to iron additions in three iron‐limited regimes
Authors: Cary S. Craig
Published: June 2010

In high‐nutrient low‐chlorophyll (HNLC) regimes, iron additions consistently result in primary productivity increases, and the phytoplankton community shifts from small species toward large diatoms. Heterotrophic bacterial production and abundance also increase in HNLC Fe addition experiments, but whether changes in bacterioplankton community composition also occur when Fe is added is unknown. We used trace metal clean shipboard incubation experiments, and molecular biological methods to examine this question in three Fe‐limited environments: the subarctic Pacific, the subantarctic Southern Ocean, and the California coastal upwelling region. After Fe additions and subsequent phytoplankton community shifts, changes in bacterial community composition were examined using denaturing gradient gel electrophoresis and terminal restriction fragment length polymorphism of polymerase chain reaction—amplified bacterial 16S rRNA genes. Responsive bacterial phylotypes in either +Fe or control treatments were classified using phylogenetic analyses of DNA sequences. In general, iron‐mediated changes in bacterial communities in all three environments were surprisingly minor compared to the changes in phytoplankton community composition. Responsive phylotypes were mostly γ‐proteobacteria in the subarctic and California HNLC areas, but no changes were noted in the subantarctic experiments. Although bacterial growth and biomass are closely linked to phytoplankton‐derived carbon supplies, our results suggest that on the time scale of our experiments (4–5 d), species composition of algal and bacterial communities can be decoupled in Fe‐limited waters.
Supplementation of cyanobacterial food with polyunsaturated fatty acids does not improve growth of Daphnia
Authors: Von Elert Eric , Wolffrom Tania
Published: June 2010

The hypothesis that the low food quality of nontoxic, ingestible cyanobacteria for Daphnia is due to the absence of long‐chained polyunsaturated fatty acids (PUFAs) was tested. Synechococcus elongatus, which is well assimilated by Daphnia and is deficient in PUFAs, was chosen as a model food organism. A newly devised method was used to load single fatty acids and mixtures of fatty acids on beads of bovine serum albumin, which then were added as supplements to cyanobacterial suspensions. Growth rates of juvenile Daphnia galeata on Synechococcus elongatus were low and were not enhanced by the addition of C18‐PUFAs and C20‐PUFAs singly or together on beads. Supplementation of lipids from the green alga Scenedesmus obliquus significantly enhanced growth of D. galeata, indicating that the low quality of cyanobacterial carbon is due to a deficiency in a lipid other than PUFAs. The low food quality of Synechococcus elongatus was partly mitigated when the animals first fed on Scenedesmus obliquus, suggesting that the storage of algal lipids provides a mechanism to cushion the effect of short episodes of cyanobacterial dietary deficiencies on the growth of D. galeata.
Climatic influences on algal populations of boreal forest lakes in the Experimental Lakes Area
Authors: Findlay D. L. , Kasian S. E. M. , Stainton M. P. , Beaty K. , Lyng M.
Published: June 2010

We examined long‐term phytoplankton data records for four oligotrophic boreal lakes situated in the Experimental Lakes Area (ELA), western Ontario, for responses to climatic change. ELA experienced a cyclical wet‐dry‐wet pattern from 1968 to 1998, with the early 1970s and 1990s having above‐average precipitation and the 1980s being a period of drought with a 2°C increase in air temperature. During this drought, the length of ice‐free season, duration of stratification, depth of the euphotic zone, and light extinction increased while precipitation and nutrient inputs to the lakes decreased. Phytoplankton assemblages of four study lakes were temporally coherent. During the drought, phytoplankton biomass and the number of phytoplankton species increased despite decreased nutrient inputs. There was a noticeable shift in species composition to greater abundances of dinoflagellates and large chrysophytes—mixotrophic species capable of cycling through the deeper, lower light, high‐nutrient waters, presumably to consume bacteria as an alternative to autotrophic production. These species have slow turnover times; therefore, suspended nutrients were held in the water column for a longer period of time. Phytoplankton photosynthesis was less responsive.
Antagonistic effect of selenium on mercury assimilation by fish populations near Sudbury metal smelters?
Authors: Chen Yu-Wei , Belzile Nelson , Gunn John M.
Published: June 2010

In this study, the concentrations of Se and Hg were determined in perch (Perca flavescens) and walleye (Stizosedion vitreum) muscle from nine lakes that varied in distance (4–204 km) from the metal smelters of Sudbury, Canada. Significant inverse relationships between Se and Hg in perch (r2 = 0.79, P < 0.05) and walleye tissue (r2 = 0.97, P < 0.01) were detected, which suggests a strong antagonistic effect of Se on Hg assimilation by these fish species. Concentration of Hg decreased exponentially with an increase of Se in fish muscle. Total dissolved Se concentrations of lake water declined with distance from smelters and were correlated to Se in perch (r2 = 0.75, P < 0.05) and walleye (r2 = 0.95, P < 0.01). Hg concentrations in the fish from lakes near the smelter were well below average values in fish in boreal shield lakes of this region.
Production and neutral aldose composition of dissolved carbohydrates excreted by natural marine phytoplankton populations
Authors: Hama Takeo , Yanagi Katsumi
Published: June 2010

Natural populations of diatoms were incubated for 4–12 h with H13CO3−1. The production of particulate and dissolved fractions of organic carbon and neutral aldoses (NAld) was followed by gas chromatography/mass spectrometry. The extracellular production rate of dissolved organic carbon (DOC) ranged from 4.1% to 6.4% of total (particulate and dissolved) production rate. Glucose was a major component of the excreted dissolved neutral aldoses (DNAld), and galactose, rhamnose, fucose, xylose, and mannose were found as secondary components of the excreted DNAld. The comparison of NAld composition with cellular products suggests that glucose in the excreted DNAld is composed mainly of storage glucan. On the other hand, the high ratios of dissolved production to total (dissolved and particulate) production of galactose, rhamnose, fucose, xylose, and mannose probably reflect the active excretion of heteropolysaccharides by diatoms. By assuming steady‐state concentrations, turnover rates of DOC and DNAld can be estimated from the phytoplankton production of 13C‐labeled material. The estimated turnover rates of DNAld through phytoplankton photosynthesis is 4.2–5.1 times higher than that of total DOC, which indicates the bioreactive nature of DNAld. This high turnover rate of DNAld mainly resulted from the high turnover rate of glucose, and it is likely that dissolved glucan is important as a carbon and energy carrier in the marine food web. The fact that the turnover rates of DNAld, which is considered to constitute heteropolysaccharides, are lower than that of glucose, would suggest that heteropolysaccharides are more resistant to biological degradation than glucan.
Measurement of local bed shear stress in streams using a Preston‐static tube
Authors: Ackerman Josef Daniel , Hoover Trent M.
Published: June 2010

Local bed shear stress (Τw) is a fluid dynamic parameter of importance in determining the physical and biological characteristics of stream‐bed environments. Unfortunately, it is often difficult to measure Τw under field conditions. Herein we describe the use of a Preston‐static tube, which is essentially a surface‐mounted Pitot‐static tube, to measure Τw in mountain streams. Our results indicate that it is possible to measure local shear stress quickly, consistently, and inexpensively in the field. This technique also provides high spatial resolution, which should allow for detailed in situ studies of local shear stress at scales relevant to lotic organisms. Such information will be invaluable in studies of benthic organisms and hydraulically relevant phenomena in the near‐bottom zone of lotic systems.