bluuebunny/crossref_metadata_2025 huggingface dataset:
Efecto de la deformación por tracción sobre la orientación cristalográfica del recubrimiento y la resistencia a la corrosión en CNS de chapas de acero con recubrimientos base cinc
Authors: Sacco E. A. , Culcasi J. D. , Eisner C. L. , Di Darli A. R.
Published: May 2010

Se deformaron, por tracción uniaxial, chapas de acero recubiertas, por inmersión, con cinc o con aleación 55 % Al - 1,6 % Si - 43,4 % Zn (55Al-Zn), con el fin de analizar el modo de deformación y falla de los recubrimientos y su comportamiento en cámara de niebla salina (CNS). A medida que se incrementaba el grado de deformación, el recubrimiento de cinc mostró un cambio de la orientación basal hacia una prismática. Además, pudo apreciarse el desarrollo de numerosas maclas, algunas fisuras intergranulares y escasas fisuras transgranulares. Por otra parte, en las muestras recubiertas con aleación 55Al-Zn, la orientación de la fase α cambió desde {311} hacia {100} y {331}, mientras que la fase β conservó una orientación {10.1}. Para este material, el único modo de falla detectado fue la fisuración del constituyente interdendrítico. En CNS la resistencia a la corrosión de las chapas de acero/55Al-Zn fue, significativamente, mayor que en las de acero galvanizado.
Desarrollo de un nuevo método a escala de laboratorio para determinar la resistencia mecánica del coque
Authors: Díez M. A. , Álvarez R. , Radoslavov R. , Barriocanal C. , Canga C. S. , Xiberta J.
Published: May 2010

En este trabajo se describe la puesta a punto de un método a escala de laboratorio, que permite evaluar la cohesión y abrasión de coques obtenidos a escala piloto. Se definen dos índices de resistencia mecánica en frío, CS10 y CS1, como la cantidad de coque de tamaño mayor de 10 mm y menor de 1 mm, respectivamente, que se obtiene después de someter una muestra de 200 g de coque, con tamaño de partícula 19-22,4 mm, a 1.200 vueltas en un tambor que gira a 20 rpm. Los nuevos índices están relacionados con los derivados del ensayo normalizado IRSID, 120 e 110, utilizados por la industria siderúrgica para el control de la calidad de coque de horno alto. Los coques estudiados se obtuvieron en un horno de pared móvil de 250 kg de capacidad, a partir, tanto de carbones individuales como de mezclas industriales de carbones. De los resultados, se deduce que el método desarrollado utilizando el tambor descrito en el método NSC de resistencia mecánica después de reacción con dióxido de carbono, puede usarse en la valoración de coques obtenidos en hornos de menor escala, en los que la cantidad de coque producida es insuficiente para llevar a cabo ensayos normalizados que requieren una mayor cantidad de muestra.
Desgaste de las características mecánicas en las conducciones de acero Cr-Mo de baja aleación tras un uso prolongado en el transporte del vapor en una central térmica
Authors: Mihai D. , Bujoreanu L. G.
Published: May 2010

Se han determinado algunos efectos de la exposición prolongada a temperaturas y presiones altas, características del transporte del vapor en una central térmica, en las conducciones de acero 12HMF GOST (13CrMo44 DIN) Cr-Mo de baja aleación, a nivel macro y microestructural a través de ensayos mecánicos y microscopia óptica. Tras 128.625 h de servicio, se ha notado una notable degradación mecánica en los valores de la resistencia a la rotura, de la dureza y de la resilencia, que han disminuido entre un 14-16 %, un 45-48 % y un 47-59 %, respectivamente. La degradación mecánica se correlacionó, por una parte, con la coalescencia de los granos de ferrita y de las islas de perlita y, por otra, con el decrecimiento en la anisotropía de la morfología de los granos.
In Search of Social Television
Authors: Harboe Gunnar
Published: May 2010

This chapter provides an introduction to and overview of social television, in an attempt to find the real meaning of the term. It explores the history and current state of social television, looks at a number of examples of Social TV systems and their features, compares different definitions of the term, and outlines dimensions of design that have been used to organize the topic. The author argues that historically the notion of social television is intimately bound up with television itself, and that the two remain difficult to separate even today. The convergence of content and communication to create social media is turning Social TV into a reality and in the process turning television into what it was originally intended to be.
Audience Participation in Television and Internet
Authors: Quico Celia
Published: May 2010

This chapter seeks to evaluate the attitudes and practices of media participation amongst young Portuguese aged between 12-18 years, with a particular focus on content creation and sharing through media and information and communication technologies (ICT). Audience participation in television and internet will be addressed, having as basis the results and findings of three empirical studies integrated in the PhD research project of the author, namely: an ethnographical study about the usage of media and ICT usage by 10 families conducted at their own domestic contexts, a quantitative survey about the usage of media and ICT by young people aged 12-18 with a total of 962 respondents and, finally, an evaluation study of a participatory media format which was tested and evaluated by 77 teenagers from three different schools. The main objective is to better understand the attitudes and behaviors of young people in Portugal towards the practices of creation and sharing digital content through media and ICT, providing empirical data about the range and frequency of experiences of content creation by this specific population, as well as their interest and adherence to participatory media formats.
Examining the Roles of Mobility in Social TV
Authors: Chorianopoulos Konstantinos
Published: May 2010

Mobile TVs have been available for many years, without ever becoming very popular. Moreover, the first wave of research has been mostly concerned with technology and standards, which are necessary to ensure interoperability and market acceptance. Although, there has been a significant body of computer supported co-operative work (CSCW) and mobile human-computer interaction (HCI) research findings, there is limited investigation in the context of leisure activities, such as TV. In this chapter, the author proposes three concepts that drive the main paths for research and practice in mobile and social TV: (1) Mobile TV as a content format, (2) Mobile TV as user behavior and (3) Mobile TV as interaction terminal. Further research should elaborate on these three concepts and highlight the cultural impact of mobile TV.
“One Ring to Bind Them All”—Part II: Identification of Promising G‐Quadruplex Ligands by Screening of Cyclophane‐Type Macrocycles
Authors: Granzhan Anton , Monchaud David , Saettel Nicolas , Guédin Aurore , Mergny Jean-Louis , Teulade-Fichou Marie-Paule
Published: May 2010

A collection of 26 polyammonium cyclophane‐type macrocycles with a large structural diversity has been screened for G‐quadruplex recognition. A two‐step selection procedure based on the FRET‐melting assay was carried out enabling identification of macrocycles of high affinity (ΔT1/2 up to 30°C) and high selectivity for the human telomeric G‐quadruplex. The four selected hits possess sophisticated architectures, more particularly the presence of a pendant side‐arm as well as the existence of a particular topological arrangement appear to be strong determinants of quadruplex binding. These compounds are thus likely to create multiple contacts with the target that may be at the origin of their high selectivity, thereby suggesting that this class of macrocycles offers unique advantages for targeting G‐quadruplex‐DNA.
Differences in Forestry Students’ Perceptions across Study Years in a Brazilian Undergraduate Program
Authors: Arevalo Barbara Jarschel Javier , Pitkänen Sari , Tahvanainen Liisa , Enkenberg Jorma
Published: May 2010

Forestry higher curricula reform is being debated globally. This study examines the views of students on aspects related to forestry education and the profession, focusing on how these views differ across the study years of a higher education forestry program. The objective of the study was to investigate the differences across study years with regard to the students’ forestry‐related concerns, the value they give to competencies and experiences, and their preferences with respect to future work and studies. The case study of a 5‐year Brazilian undergraduate program was selected, analyzing the responses to a questionnaire of 268 students. Results indicate students in the later years of their study program have a much broader variety of forestry‐related concerns, have a greater interest in choosing a different university for doing a Master's degree, and more often consider working as consultants upon graduation. Additionally, students in the later years give a higher importance to competencies related to traditional forestry areas (silviculture, management, policy), computer‐related subjects (Forest Information Systems, statistics, computer skills), and generic communication competencies (oral and writing skills). On the contrary, students in the first years give a higher value to environmental and climate change–related issues and to international forestry, as well as to achieving their best. Our findings show there are numerous differences in students’ perceptions across the study years of a program. The consideration of these differences in the reform of forestry and life science curricula, aiming at increasing the attractiveness and effectiveness of the programs, is suggested.
Rapid oxygen cycling in Trichodesmium thiebautii
Authors: Kana Todd M.
Published: May 2010

Oxygen uptake and evolution were measured in Trichodesmium thiebautii trichomes with 18O membrane inlet mass spectrometry. Samples were collected in the vicinity of the Bahamas Islands and eastern Caribbean Sea. Trichodesmium exhibited high rates of oxygen uptake in the dark and in the light compared with previously studied cyanobacteria. Oxygen uptake in the dark averaged 23% of the maximum gross oxygen evolution rate and was suppressed minimally at low irradiances or after the addition of cyanide. Oxygen uptake in light increased between 50 and 200 µEinst m−2 s− 1 and was inhibited by 3‐(3,4‐)‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), indicating Mehler reaction activity. I estimate that 48% of the total photosynthetic linear electron flow went to oxygen reduction at moderate but nonsaturating irradiances. Light compensation points ranged from 50 to 300 µEinst m−2 s−1 with values highest for midday samples. Rapid oxygen cycling may contribute to the protection of nitrogenase by reducing the oxygen tension within the cell or colony during oxygenic photosynthesis and by providing a mechanism (pseudocyclic photophosphorylation) for generating excess ATP for nitrogen fixation.
Behavioral mechanisms controlling vertical migration in Daphnia
Authors: Young Stephen , Watt Penelope
Published: May 2010

We used infrared video monitoring to study cladoceran vertical migration in laboratory tanks exposed to natural and simulated daylight cycles. There are changes in the behavior patterns at different times of the year, with both Daphnia magna and Daphnia longispina showing increased vertical migration and greater average depth later in the year. This change in behavior pattern is due to temperature, not daylength, changes. Our animals show a complex endogenous migration pattern, with a strong downward excursion in the middle of the night, another before dawn, and then a morning rise, of which only the last depends on a visual stimulus. We propose that the morning rise acts as a correcting movement bringing animals to a depth just safe from visual predators. The midnight sinking is unlikely to be due to a random spreading‐out process. Fish taste cues enhanced the dawn excursion, but not the midnight one. Responses to fish cues were most pronounced for D. magna at low temperatures.
Ecosystem analysis based on biomass size distributions: A case study of a plankton community in a large lake
Authors: Gaedke Ursula
Published: May 2010

The plankton biomass size distribution and its seasonal changes were used to estimate seasonal fluctuations of the metabolic activity of the community and of the efficiency to transfer biomass to larger sized organisms in a large and deep prealpine lake (Bodensee: Lake Constance). The efficiency of transfer of biomass from small (e.g. autotrophic) to larger (e.g. herbivorous) organisms increased considerably during the first half of the year and reached maximum values when daphnid densities were high. This trend was attributed to the different generation times of the organisms involved in the food web. The trophic transfer efficiency may depend on the predator‐prey weight ratios, and the efficiency of growth and exploitation of the constituent organisms. The contribution of these factors to the overall change of the transfer efficiency was estimated from additional information on the food‐web structure. The results derived from the size spectra agreed reasonably well with previous studies of single populations, suggesting that biomass size distributions may substantially contribute to ecosystem analysis. The seasonal trend in slopes of the size spectrum was related to predictions derived from conceptual models. Empirical results from Lake Constance could be reconciled with those models accounting for seasonal changes of exploitation efficiency. Inference from the size spectra supported the hypothesis that natural assemblages of pelagic bacteria are unlikely to attain the potential productivity implied by allometric relationships.
Response of metallothionein concentrations in a freshwater bivalve (Anodonta grandis) along an environmental cadmium gradient
Authors: Couillard Yves , Campbell Peter G. C. , Tessier André
Published: May 2010

Surficial (oxic) sediments, overlying water, and specimens of the freshwater bivalve Anodonta grandis were collected by divers at 11 littoral lacustrine sites located along a geochemical gradient of pH, [Cd], [Cu], and [Zn] in an area influenced by mining and smelting activities. The molluscs were dissected (gills; hepatopancreas; remaining tissues) and analyzed for Cd, Cu, Zn, and metallothioneins (MT). Tissue concentrations of MT in A. grandis varied between 100 and 440 nmol metal binding sites (g dry wt)−1. Metallothionein levels in the gills, the remaining tissues, and the whole organism were significantly correlated (P < 0.01) with tissue Cd concentrations. In contrast, correlations between [MT] and tissue levels of Cu or Zn were weak or nonexistent. The intersite variations in MT concentrations were best related, not to total dissolved metal concentrations at the time of sampling, nor to extractable metal concentrations in the sediments, but to the free Cd2+ concentration at the sediment‐water interface, as estimated from sediment‐water sorptive equilibria. These observations suggest that Cd2+ activity is the key environmental factor to which metallothionein levels in A. grandis are responding in the studied lakes. The mollusc condition indices (C.I. = 1,000 × total dry wt of flesh of the animals/total intervalval volume) deteriorated as Cd concentrations in the tissues increased.
Carbonate dissolution and temporal abundances of Foraminifera in Long Island Sound sediments
Authors: Green Mark A. , Aller Robert C. , Aller Josephine Y.
Published: May 2010

The dynamics of benthic Foraminifera assemblages can be used to examine carbonate dissolution processes in nearshore sediments and as a general assay of physical‐chemical factors affecting survival of juvenile benthos. Abundances of total Foraminifera (live and dead) fluctuate regularly throughout the year in Long Island Sound (LIS) mud deposits, with highest numbers in spring‐summer and lowest in winter. Essentially all forams disappear each year. Pore‐water undersaturation with respect to carbonate minerals coincides with periods of rapid disappearance of forams and suggests that these fluctuations reflect a balance between the rate of production‐recruitment and the rates of death and dissolution of the calcareous tests of the animals. Reworking by macrofauna in LIS central basin sediments inhibits accumulation or depletion of pore‐water solutes and is responsible for minimizing pore‐water carbonate saturation states. Quantitative estimates of seasonal patterns of foram dissolution with a simple mass balance model give a minimum average annual flux of Ca2+ in LIS sediments of ∼6 mmol Ca2+ m−2 d−1 (due solely to Foraminifera dissolution). Abandoned tests have a maximum mean residence time of ∼86±13 d. Dissolution‐precipitation of forams may significantly affect benthic ∑CO2 fluxes and likely accounts for a large proportion (>30%) during some seasons or at some locales. Other organisms with carbonate tests of similar size, particularly juvenile bivalves, may also be affected by periods of undersaturated pore waters. Conditions promoting dissolution of tests may represent an important source of mortality for calcareous meiofauna.
Nutrient flux through soils and aquifers to the coastal zone of Guam (Mariana Islands)
Authors: Matson Ernest A.
Published: May 2010

Nitrification enriches terrestrial soil waters with nitrate, and other solutes also leach rapidly (within hours to days after saturating rain) through Guam’s northern karst plateau into a largely unconfined carbonate aquifer system. Nutrient chemistry and discharge of these enriched aquifer waters into the inter‐ and subtidal zone was measured to evaluate the importance of this flux to the coastal nutrient regime of the island. Aquifer waters mix with seawater in the coastal transition zone, produce about a 10% seawater mixture, and leak year‐round through cracks and fissures and from seeps in beaches around the entire perimeter (57 km) at rates of 2.2–110 m3 (m of shoreline)−1 d−1 (avg, 5.1 m3 m−1 d−1). The theoretical maximum rate can average. 14 m3 m−1 d−1, which is equal to net annual aquifer recharge. At the shoreline, the discharged aquifer waters average 3.14‰ salinity, 96±21 µM NO3−, 28±6.8 µM Si, 0.85±0.26 µM P, and 0.18±0.19 µM Fe (n = 238). Deep seawater under the aquifer averages 33.8‰ salinity, 8.5±2.1 µM NO3−, 7.2±1.8 µM. Si, and 0.05±0.04 µM Fe (n = 47). The aquifer system can potentially discharge 1,340, 390, 12, and 2.5 µmol m−1 d−1 of NO3−, Si, P, and Fe out to a distance of 1 km from shore, which enriches surface seawater by about 20 times the ambient concentration per day. In general, natural flux of nutrients in aquifer waters from tropical carbonate islands will increase as a function of island diameter, aquifer recharge, head, the thickness of the soil layers in which remineralization occurs, and as the acquisition of solutes from subterranean volcanics above sea level increases.
Interaction of iron and major nutrients controls phytoplankton growth and species composition in the tropical North Pacific Ocean
Authors: DiTullio Giacomo R. , Hutchins David A. , Bruland Kenneth W.
Published: May 2010

A 6‐d nutrient enrichment experiment was performed in the tropical North Pacific Ocean at 9°N, 147°W with ultraclean techniques. Changes in phytoplankton biomass, C and N assimilation rates, growth rates, and species composition were monitored with HPLC pigment analyses and flow cytometry techniques, as well as 14C fixation into particulate C, pigments, and protein. Prochlorophyte specific growth rates (from divinyl Chl a labeling) increased from an initial value of 0.15 d−1 to 0.96 d− following macronutrient addition (N, P, and Si). Diatoms, however, were unable to grow without added Fe. Diatom populations were severely colimited by Fe and macronutrients but achieved a specific growth rate of 2.5 d−1 following Fe and macronutrient additions. Results implied that grazing rates (g) on prochlorophytes were stimulated in approximate balance with prochlorophyte growth (µ) after 6 d (g : µ = 0.85), but that grazing processes were not as efficient (g : µ = 0.40) at controlling the diatom standing stock. Our results suggest that grazing processes may be the most important factor regulating procaryotic biomass, but Fe limitation is the proximate control of diatom biomass and hence may limit the utilization of macronutrients in the equatorial Pacific Ocean.
Colonization, interaction, and organization of cladoceran epibiont communities1
Authors: Threlkeld Stephen T. , Willey Ruth L.
Published: May 2010

The distribution of three genera of epibionts on two Daphnia species was examined in two subalpine beaver ponds. Epibiont prevalence and burden were proportional to body length in both species of Daphnia, but varied between the two Daphnia species and among female Daphnia with parthenogenic eggs in different stages of development. The most common epibiont appeared to have a doubling rate of 1 d−1, but this rapid growth rate was insufficient to increase epibiont burdens on Daphnia in a pond where salamanders fed selectively on Daphnia serving as epibiont substrates. There were two indications of significant interactions between epibiont taxa: inverse relationships between prevalence of each epibiont species and the burden of the most common epibiont, and nonrandom distributions of epibiont species combinations among the substrate organisms. There was no effect of two epibiont genera (Carchesium, Chlorangiella) on Daphnia egg production, but the negative effect of the third, most locally abundant, epibiont genus (Colacium) was proportional to its abundance.
How do parasites cost their hosts? Preliminary answers from trematodes and Daphnia obtusa
Authors: Schwartz Steven S. , Cameron Guy N.
Published: May 2010

Cladocerans (Daphnia obtusa) in seasonal ponds in southeast Texas are infected with a trematode parasite (n. sp.). Infestation rate varies considerably among ponds and years, and among ponds within years. The parasite is rare in individuals <1.00 mm long but is common in individuals 1.25–1.75 mm long. The parasite has no effect on whether females become gravid. Although there is a significant correlation between length and egg production for unparasitized females, this is not the case for parasitized individuals. An infection of 1–2 parasites does not aflect fecundity; however, greater infections are correlated with reduced egg production. Another cost to Daphnia of harboring the parasite is reduced survivorship, particularly among larger individuals. As these individuals have the capacity to produce more eggs than smaller individuals, it is likely that the parasite also causes a reduction in lifetime reproduction in addition to that in any one reproductive episode.
Organization of crustacean epizoan communities in a chain of subalpine ponds
Authors: Willey Ruth L. , Threlkeld Stephen T.
Published: May 2010

Crustacean zooplankton in high altitude ponds in Colorado support two suites of epizoans. Epizoans on Daphnia consisted of Colacium calvum, Characium gracilipes, and peritrich ciliates. Epizoans on Ceriodaphnia, Scapholeberis, and Eucyclops involved Colacium vesiculosum and the peritrich ciliates. Frequent, regular molting of most of the substrate organisms keeps attachment surfaces unoccupied. Epizoan attachment is site‐specific rather than a function of epizoan‐epizoan interaction. The presence of phototrophic epizoans may contribute to increased susceptibility of their substrate organisms to fish predation.
Effects of hydrostatic pressure on metabolic rates of six species of deep‐sea gelatinous zooplankton
Authors: Childress J. J. , Thuesen E. V.
Published: May 2010

This study addresses the effect of hydrostatic pressure on the metabolic rates of six species of deep‐living (∼500–1,500‐m typical depths) gelatinous zooplankton (three chaetognaths, two hydromedusans, and one polychaete). Metabolic rates were measured at 5°C and the hydrostatic pressure equivalent to that at either 0‐(0.101 MPa) or 1,000‐m depth (10.1 MPa). O2 consumption rate vs. wet weight relationships at the two pressures were compared by ANCOVA for each species separately. Five of the species studied (the chaetognaths and medusans) showed no significant difference in slope or elevation in these relationships, indicating there was no significant effect of hydrostatic pressure on the metabolic rates of these species under the experimental conditions. The metabolic rate relationships of the sixth species, Poeobius meseres, were significantly different in slope, but the lines intersected within the weight range studied so the metabolic rates were not different overall. These data support the validity of measuring the metabolic rates of such species at surface pressures and indicate that metabolic rates of deeper living gelatinous species are relatively insensitive to hydrostatic pressure.
Effects of algal turf canopy height and microscale substratum topography on profiles of flow speed in a coral forereef environment
Authors: Carpenter Robert C. , Williams Susan L.
Published: May 2010

Water motion can be an important variable affecting the recruitment, metabolism, growth rates, feeding efficiency, and distribution of aquatic organisms. Recent studies suggest that flow speed may be an important factor regulating primary productivity of reef algal turf communities. We measured profiles of flow speed over algal turfs with different canopy heights and over algal turfs growing on substrata that varied in microtopography. Profiles over sea urchin‐grazed algal turfs with low canopy heights and algal turfs growing on topographical high points indicate that the boundary layer is dominated by turbulent eddies. In contrast, flow over algal turfs with higher canopy heights and those growing within depressions in the substratum is influenced more by viscous forces that may lead to diffusion‐limited metabolism of these algal communities. These data demonstrate that flow speeds over coral reef algal turfs exhibit spatial variation over small spatial scales and temporal variation that is dependent on ambient flow speeds. Our results predict microscale variation in algal turf metabolism and suggest that photosynthetic rates of this component are likely to be below maximum capacity for a significant portion of the time.
Phytoplankton nutrient limitation and food quality for Daphnia
Authors: Sterner Robert W. , Hagemeier Douglas D. , Smith William L. , Smith Robert F.
Published: May 2010

The influence of nutrient limitation on the quality of Scenedesmus acutus as food for Daphnia obtusa is examined. The nature and degree of nutrient limitation greatly influences the rate at which Daphnia converts Scenedesmus biomass into herbivore biomass. From high to low quality, Scenedesmus food is ranked moderately N limited, severely N limited, and severely P limited. Even a very high concentration (3 mg DW liter−1) of low quality food yields slow Daphnia growth, and it appears that no amount of low quality food would support rapid Daphnia growth. Food‐limited animals display lowered intercepts of length‐weight regressions (prereproductive females), reduced rates of biomass gain (both males and females), increased ages at first reproduction, lowered clutch sizes, increased mortality, and lowered reproductive rate. The N and P contents and the N : P ratio of Scenedesmus all vary considerably under N and P limitation, while the N content (and possibly P content) of Daphnia is less variable and the N : P ratio of Daphnia is essentially constant. Clearance and feeding rates are lower on severely P‐limited cells than on severely N‐limited cells. These results indicate that the mineral nutrition of their algal food may influence the demographics of zooplankton herbivores to a degree not before realized.
The trophic significance of epilithic algal production in a fertilized tundra river ecosystem
Authors: Peterson Bruce , Fry Brian , Deegan Linda , Hershey Anne
Published: May 2010

Fertilization of a pristine tundra river with phosphorus and nitrogen changed the nitrogen and carbon stable isotope ratios in epilithic algae. Determination of δ15N and δ'3C values in consumers allowed this algal organic matter to be traced in the food web for several kilometers downstream of the fertilizer addition sites. Changes in the isotopic composition of consumers documented the tight coupling between algal production in response to fertilization and measured increases in the growth of insects and fish.
Modeling the significance of zooplankton grazing for export production
Authors: Aksnes Dug L. , Wassmann Paul
Published: May 2010

We present a theoretical model and different scenarios for the impact of herbivorous zooplankton grazing on planktonic production and vertical flux of particulate organic matter. Sedimentation of phytoplankton and fecal matter from the mixed layer (i.e. export production Pe) is given by Pe = [(1 − α) G/(ws + G)]P1, where α is a “pelagic assimilation efficiency” of the mixed layer, ws is phytoplankton sinking rate, G is grazing pressure of the herbivore stock, and P, is the integrated phytoplankton production in the mixed zone. The parameter α is influenced by herbivorous assimilation and decomposition of fecal matter in the upper water column. In the above expression the influence of grazing acts like a Michaelis‐Menten limitation term [G/(ws + G)], where sinking rate is the half‐saturation parameter and pelagic assimilation efficiency represents the maximal influence from grazing. The model seems predictive as it gives reasonable explanations to Pe : Pt relationships for both freshwater and marine systems, and therefore improves our understanding of several empirical models presented in the literature linking export production to primary production.
Nitrogen metabolism of the filter‐feeding bivalve Corbicula japonica and its significance in primary production of a brackish lake in Japan
Authors: Yamamuro Masumi , Koike Isao
Published: May 2010

Uptake of particulate nitrogen and nutrient excretion by the filter‐feeding bivalve Corbicula japonica in Lake Shinji was measured simultaneously by two methods: a continuous flow laboratory incubation with an intact sediment and an in situ measurement with a benthic chamber. The excretion rate of ammonium by C. japonica estimated from the in situ measurement exceeded the uptake rate of particulate organic nitrogen (PON), suggesting the involvement of bioturbation or other nonmetabolic process in the upward flux of ammonium. On the other hand, the results from the continuous incubation method agreed well with the growth rate of C. japonica under natural conditions. In the natural habitat of Lake Shinji, C. japonica excreted 4.5 mg‐atoms N m−2 d−1 as ammonium and 4.6 mg‐atoms N m−2 d−1 as feces and pseudofeces while taking up PON at a rate of 10.4 mg‐atoms N m−2 d−1. These results suggest that C. japonica plays an important role in stimulating primary production by maintaining rapid recycling of nitrogenous materials.
Meromixis in hypersaline Mono Lake, California. 1. Stratification and vertical mixing during the onset, persistence, and breakdown of meromixis
Authors: Jellison Robert , Melack John M.
Published: May 2010

Changes in vertical mixing in hypersaline Mono Lake, California, are described for the onset, persistence, and breakdown of meromixis, 1982 through 1990. In 1982 and 1983 exceptionally large runoff led to a 2.6‐m rise in surface elevation and the onset of meromixis. Chemical stratification accounted for a density difference between 2 and 28 m of 1.2–1.5 × 10−2 g cm−3 in 1984; the midsummer density difference between 2 and 28 m due to temperature was ~0.5 × 10−2 g cm−3. Salinities ranged from 77 to 98 g liter−1; sodium, chloride, sulfate, and carbonate are the major ions. The flux‐gradient heat method corrected for solar heating was used to calculate vertical mixing during the period from April to October. The eddy diffusivity at the thermocline ranged from molecular to 26 × 10−6 m2 s−1 and averaged 3.4 × 10−6 m2 s−1. Eddy diffusivity was found to regress on N2, the Brunt‐Väisälä frequency squared, to the −0.58 power, suggesting turbulence is generated by local shear rather than large‐scale processes.
Meromixis in hypersaline Mono Lake, California. 2. Nitrogen fluxes
Authors: Jellison Robert , Miller Laurence G. , Melack John M. , Dana Gayle L.
Published: May 2010

Vertical fluxes of nitrogen were examined in hypersaline Mono Lake over a 9‐yr period which encompassed the onset, persistence, and breakdown of meromixis. Under monomictic conditions, ammonia, which accumulates in the hypolimnion, is mixed into the euphotic region during autumn overturn. Following the onset of meromixis in 1983 and elimination of the winter period of holomixis, ammonia was depleted in the mixolimnion and accumulated beneath the chemocline. The mean rate of particulate nitrogen deposition, as measured by sediment traps over a 2‐yr period during meromixis, was 2.0 mmol m−2 d−1. Until meromixis weakened in 1988, ammonia concentrations in the euphotic zone remained below 5 µM and increased to ~500 µM beneath the chemocline. Meromixis ended in November 1988 and a large pulse of ammonia was injected into surface waters, resulting in surface ammonia concentrations of ~45 µM. Because the pH of Mono Lake is high (9.8) the : ratio is ~5, and elevated surface concentrations of ammonia during the 2 yr following breakdown of meromixis resulted in high losses of nitrogen via ammonia volatilization (mean, ~10 mmol m− 2 d−1). High release rates of ammonia from the sediments were estimated from both the ammonia gradients in pore‐water profiles (3–10 mmol m−2 d−1) and the balance of mixolimnetic nitrogen fluxes (4–10 mmol m−2 d−1). The monimolimnetic balance suggested fluxes of ammonia out of the sediments below the chemocline were reduced during meromixis.
Meromixis in hypersaline Mono Lake, California. 3. Biogeochemical response to stratification and overturn
Authors: Miller Laurence G. , Jellison Robert , Oremland Ronald S. , Culbertson Charles W.
Published: May 2010

Mono Lake is a terminal, saline lake that became ectogenically meromictic in 1982–1983 and remained stratified until November 1988. During this period, the monimolimnion remained anoxic and nearly isothermal, while the upper mixolimnion was well oxygenated and exhibited a seasonal thermal regime. Dissolved sulfide and methane increased in the monimolimnion as a result of diffusive flux from the sediments. Winter mixing down to the chemocline distributed sulfide and methane throughout the mixolimnion. Lakewide inventories of dissolved sulfide and methane reflected the balance between increased concentrations and decreased monimolimnion volume over time. At overturn, the entire water column was isothermal and anoxic. Dissolved sulfide (380 × 106 mol) was oxidized in 1 week by molecular oxygen. Methane (12 × 106 mol) was removed more slowly by microbial oxidation and ventilation across the air‐water interface.
Deep ventilation of Lake Baikal waters due to spring thermal bars
Authors: Shimaraev M.N , Granin N.G , Zhdanov A.A
Published: May 2010

Increase of density due to mixing (cabbeling instability) in a spring thermal bar in Lake Baikal results in the sinking of cold surface water (T = 3.2−3.4°C, w = 0.3 cm s−1) below the profile of Tmd. This density increase generates forced convection and subsequent movement of cold water along the underwater slope to maximum depths. Cooling of deep and near‐bottom waters caused by forced convection is compensated during other seasons of the year by eddy heat flux directed toward the bottom. On a long‐term basis, vertical temperature profiles in deep waters remain constant.
The investigation of kinetic growth of Chlorella vulgaris cells by the method of integral and dynamic light scattering
Authors: Witkowski Konrad , Woliński Leszlek , Turzyński Zbigniew , Gedziorowska Danuta , Zielifiski Andrzej
Published: May 2010

Laboratory measurements of light scattering on axenic cultures of the unicellular alga Chlorella vulgaris confirm multilevel light scattering by the cell (i.e. both by the outer cell membrane and the internal structure of the cell, as well as by its molecular structure). The technique of dynamic light scattering and analysis by the regulation method suggest that the light scattering phenomena is affected by particles of sizes corresponding either to the overall dimensions of the cell or to the dimensions of its internal structure. A correlation was found between the suggested sizes and the stage of physiological evolution of the culture. Three well‐known stages (adaptation, logarithmic and stationary growth) can be recognized easily in changes observed in the size distribution of the scattering centers as measured by the dynamic light scattering technique and in the shape changes of elements of the scattering matrix. The occurrence of cells containing large internal structure elements, such as autospores, affect elements of the scattering matrix, suggesting that cell structure should be taken into account as a scattering system producing rotatory polarization of the scattered light.
Differential effects of ultraviolet radiation on green and brown morphs of the Caribbean coral Porites astreoides
Authors: Gleason Daniel F.
Published: May 2010

In waters ≤2 m deep, green colonies of reef‐building Porites astreoides Lamarck are significantly more abundant than their brown counterparts. To determine whether this distributional pattern reflects differences in the ability of green and brown colonies to tolerate high intensities of ultraviolet‐A (320–400 nm) and ‐B (280−320 nm) radiation, I enhanced UV intensities by transplanting colonies of each color from 6 to 1 m deep. After 104 d, brown P. astreoides exposed to UV radiation at 1 m exhibited algal mitotic indices and linear skeletal extensions that were significantly lower than brown conspecifics shielded from UV light. In contrast, green P. astreoides were unaffected by UV radiation incident at 1 m. These morph‐specific differences in UV tolerance corresponded with variation in the quantities of UV light‐absorbing mycosporinelike amino acids (MAAs) present in the corals. Both morphs had mycosporine‐glycine (λmax = 310 nm), palythine (λmax = 320 nm), asterina‐330 (λmax = 330 nm), and shinorine (λmax = 334 nm), but green P. astreoides had significantly greater concentrations of asterina‐330 than brown colonies both before and after transplantation. Increasing the concentration of a single MAA with a broad absorbance range may represent an effective means of countering high UV intensities, and UV light may be an important abiotic factor structuring the shallow‐water distribution of P. astreoides.
Comparison of the response of Daphnia galeata and Daphnia obtusa to fish‐produced chemical substance
Authors: Macháček Jiří
Published: May 2010

Individuals of two clones of two Daphnia species were reared from neonata to primipara stage in a medium preconditioned with fish (Rutilus rutilus or Perca fluviatilis). Daphnia galeata, the species usually exposed in its natural habitats to fish predators, exhibited reduced juvenile length increments, earlier maturation, and relatively larger clutches of smaller eggs. Such reactions were not found in Daphnia obtusa, a species typical of fish‐free localities. Reaction to the fish factor did not include structural changes of the filtration apparatus.
Effect of dissolved organic carbon on 59Fe scavenging
Authors: Curtis P. Jeferson
Published: May 2010

The scavenging rates of tracer 59Fe via sedimentation and loss rates of dissolved organic C (DOC) from limnocorrals containing different proportions of DOC‐rich stream water and DOC‐poor lake water were measured. 59Fe scavenging rates were inversely correlated with concentration of DOC, decreasing by a factor of four as DOC increased from 550 to 1,550 µmol liter−1. In contrast to Fe, the loss rates for DOC increased with increasing DOC concentration; thus the mechanisms for loss of Fe and DOC appeared to be different. The effect of DOC on Fe scavenging was consistent with competition between organic ligands and particles for aqueous Fe and with DOC‐enhanced colloid stability. Fe scavenging was poorly related to particle concentration and settling velocity.
Angular distribution of fluorescence from phytoplankton
Authors: Gordon H. R. , Voss K. J. , Kilpatrick K. A.
Published: May 2010

The angular distribution of fluorescence for several natural oceanic phytoplankton cultures was measured in the laboratory. Of the six cultures examined, only Dunaliela tertiolecta exhibited measurable anisotropy. The anisotropy in this case was ~20%.
Bacterial biomass and cell size distributions in lakes: More and larger cells in anoxic waters
Authors: Cole Jonathan J. , Pace Michael L. , Caraco Nina F. , Steinhart Gail S.
Published: May 2010

We measured bacterial abundance, cell size distribution, and related microbiological and geochemical parameters in 20 stratified lakes from three regions in the U.S. Both largest cell size and greatest bacterial abundance occurred in anoxic waters. Bacterial size distributions from the hypolimnia of lakes that were oxic were identical to those in surface waters. Bacteria from anoxic hypolimnia were 2–10 times larger than those from oxic water and cell size was independent of temperature under either oxic or anoxic conditions. For all lakes and strata, bacterial abundance was strongly related to the concentration of total phosphorus (TP). Cell size was not related to TP or to bacterial abundance, suggesting that abundance and size may be regulated by different processes. Bacterial biomass (calculated from the product of mean cell size and bacterial abundance) was typically 4 times greater in anoxic than in oxic waters of lakes.
Exopolymer microenvironments of microbial flora: Multiple and interactive effects on trophic relationships
Authors: Decho Alan W. , Lopez Glenn R.
Published: May 2010

Microbial cells in natural environments are often encased in different types of exopolymer secretions (EPS), ranging from tight capsules surrounding individual cells to the looser slime matrices of biofilms. The different physical and chemical properties of exopolymers could have secondary effects on trophic interactions between microbial cells and consumer animals. Laboratory studies showed that capsule EPS is significantly less digestible to consumers than slime EPS, even when extracted from the same bacterial strain. Bacterial cells with EPS capsules are less efficiently digested than noncapsuled cells, suggesting that capsules protect against digestion. Follow‐up experiments determined that polysaccharide‐rich fractions of slime EPS are absorbed with very high efficiencies while protein portions, which are more abundant in capsular polymers, are absorbed relatively poorly. Another series of experiments showed that dissolved organic matter (DOM), when adsorbed directly to the mineralogical portions of sediment particles, is available to deposit feeders. However, the further presence of an exopolymer coating on sediments more than doubled the bioavailability of adsorbed DOM to the consumer. Observations using cold‐stage scanning electron microscopy indicated that exopolymer microenvironments are a common feature of natural marine sediments. Microbial exopolymers range from easily digestible carbon sources to relatively refractory ones that effectively protect some microbial cells from consumer digestion. Exopolymer microenvironments may also make recently adsorbed DOM highly accessible to particle‐ingesting animals.
Use of active fluorescence to estimate phytoplankton photosynthesis in situ
Authors: Kolber Zbigniew , Falkowski Paul G.
Published: May 2010

We describe the theory and practice of estimating photosynthetic rates from light‐stimulated changes in the quantum yield of chlorophyll fluorescence. By means of a pump‐and‐probe fluorescence technique, where weak probe flashes are used to measure the change in the quantum yield of fluorescence induced by the strong pump flash, it is possible to derive the absolute absorption cross sections for photosystem 2, the quantum yield for photochemistry, and the maximum rate of photosynthetic electron transport at light saturation. In conjunction with a semiempirical biophysical model of photosynthesis, these parameters can be used to calculate the instantaneous rate of gross photosynthesis in situ under ambient irradiance. A profiling pump‐and‐probe fluorometer was constructed and interfaced with a CTD, and vertical profiles of variable fluorescence were obtained on four cruises in the northwest Atlantic Ocean. The derived photosynthetic rates were compared with concurrent estimates of production based on radiocarbon uptake. The correlation coefficient between the two estimates of primary production, normalized to Chl a, was 0.86; linear regression analysis yielded a slope of 1.06. There is a 3‐4‐fold range in the maximum change in the quantum yields of photochemistry and absorption cross‐sections in natural phytoplankton communities. Uncertainties in the pump‐and‐probe‐derived estimates of photosynthesis are primarily due to temporal mismatches between instantaneous and time‐integrated measures of production and in biological variability in the ratio of the number of PS2 reaction centers to total Chl a.
Lake Kinneret: A seasonal mode1 for carbon flux through the planktonic biota
Authors: Stone Lewi , Berman Tom , Bonner Richard , Barry Stephen , Weeks Scott W.
Published: May 2010

Carbon standing stock distribution in the euphotic zone of Lake Kinneret and the immediate fate of primary‐produced carbon are very different during late winter–early spring (with the occurrence of the annual dinoflagellate bloom) than they are in late summer (when nanophytoplankton are the dominant primary producers). We used a linear programming model to construct balanced carbon flow charts for these two seasons based on measured primary productivity; on carbon standing stocks of algae, bacteria, flagellates, ciliates, cladocerans, rotifers, and fish; and on data on turnover times, respiration, and grazing rates obtained in 1989. The charts were compiled to fit as closely as possible all observed and inferred estimates of carbon fluxes while simultaneously ensuring that mass balance and key biological constraints were maintained for each of the 10 compartments representing the principal biota of the Kinneret food web. We used the model to examine the extent to which individual intercompartmental flux rates were free to vary while the mass‐balance and biological constraints were enforced. The model was also capable of generating different yet feasible flow‐chart scenarios; it thus proved useful in suggesting alternative hypotheses concerning the role of the microbial food web in the euphotic waters of’ Lake Kinneret.
A study of concentration boundary‐layer formation over a bed of model bivalves
Authors: O'Riordan C. A. , Monismith S. G. , koseff J. R.
Published: May 2010

We conducted experiments in a laboratory flume to study the interaction of bivalve siphonal currents with the turbulent boundary layer, using a bed of model Tapes japonica (625 animals m−2). Refiltration of excurrent fluid, which represents a decrease in aggregate feeding efficiency, was measured for 225 siphon pairs oriented perpendicular to the cross‐flow (free stream flow) direction. Refiltration was as high as 18% and related to position in the bed, pumping rate, and siphon height of the animals, as well as the cross‐flow speed. Scaling analysis of refiltration data suggests that the velocity ratio, VR = uj/u*, where uj is the jet velocity and u* is the boundary shear velocity of the cross flow, is a good predictor of refiltration forVR > 20.

Laser‐induced fluorescence was used to visualize the flow. Analysis of the height of maximum phytoplankton depletion and spreading width of the plume obtained from quantitative concentration profiles show that changes in the vertical momentum of the excurrent jet become more important in determining the phytoplankton removal efficiency as VR decreases. The hydrodynamics of this complex interaction suggest that changes in pumping rate and siphon height will improve phytoplankton removal efficiency only for animals feeding in a strong cross flow.