bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Simple Illuminance Model Performances under Clear-Sky Conditions for Athens (Greece)
Authors: López Gabriel , Frič Ondrej , Kambezidis Harry D.
Published: April 2010

Solar illuminance has become an important task in recent years as a new way of energy saving within the building sector. Incorporation and employ of new more efficient windows and light pipes in buildings require accurate information of external solar illuminance levels for a proper design. Unfortunately, illuminance data is not measured as often as solar radiation and therefore luminous efficacy models must be used. A large amount of these models are based on the empirical relationship existing between the components of luminous efficacy and the corresponding components of solar radiation, i.e. direct, diffuse and global. However, these relationships seem to be non-linear and site specific. In this article, the performance of five illuminance models to estimate clear-sky solar global and diffuse illuminances is analyzed. Experimental values of irradiance and illuminance have been obtained from a solar radiation station sited at the Institute of Environmental Research and Sustainable Development of the National Observatory of Athens (Athens, Greece). Results have shown that illuminance models based on solar geometry variables alone seem to exhibit a noted locality. Inclusion of radiometric variables is thus needed to improve illuminance estimation. This characteristic is noted for both diffuse and global components.
The Fabrication of Nanophotocatalytic Film with Aqueous Titania Nanofluid by Electrophoretic Deposition
Authors: Teng Tun Ping , Teng Tun Chien , Chen Chien Chih
Published: April 2010

This study employs a direct-synthesis method to produce titania (TiO2)/water nanofluid, which is a working fluid involved in the electrophoretic deposition (EPD) of nanophotocatalytic films. In general, using organic solvents and water as the bulk liquids in EPD produces environmental pollution and defective films due to the electrolysis of water. To mitigate water electrolysis, the fabrication method proposed in this study adds an anionic dispersant to the TiO2/water nanofluid. The anionic dispersant changes the surface charge of TiO2 nanoparticles to facilitate their deposition on the anode. For low voltage EPD processes, this method effectively improves defective nanophotocatalytic films. These defects are caused by bubbles from the water electrolysis, as the volume of oxygen produced at the anode amounts to half of the hydrogen produced at the cathode. The objective of this study is to propose empirical equations describing the relationship between film thickness and electric parameters.
Magnetic Field Effects on Electron Eigenstates in a Concentric Triple Quantum Ring
Authors: Salehani Hojjatollah K. , Esmaeilzadeh Mahdi , Shakouri Khosrow
Published: April 2010

In this paper, the electronic eigenstates and energy spectra of a two-dimensional system formed by three concentric, coupled, semiconductor quantum rings with a perpendicular magnetic field in the presence and the absence of a single ionized hydrogenic donor impurity are studied. It is found that the magnetic field localizes the electron wave function in the inner rings. The effects of hydrogenic donor on the electronic structure of concentric triple quantum rings are investigated in the both on- and off-center configurations. It is shown that as the donor moves away from the center of the system, the ground state energy decreases monotonically, the degeneracy is lifted and the gap between the energy levels increases. Also, the binding energy of donor impurity increases with increasing magnetic field.
Porous Hollow Gold Nanoparticles for Cancer SERS Imaging
Authors: Huang Chien Wen , Hao Yao Wu , Nyagilo James , Dave Digant P. , Xu Li Feng , Sun Xian Kai
Published: April 2010

Surface enhanced Raman spectroscopy (SERS) is a promising molecular imaging modality capable of simultaneously detecting multiple molecular biomarkers. With the biocompatibility and functionalizability of Au, Au-nanoparticle based Raman tags possess the potential for in vivo SERS cancer biomarker detection. Here, we report the large scale synthesis of a new type of Au nanoparticles, Porous Hollow Au Nanoparticles (PHAuNPs), and demonstrate their potential application as SERS imaging tags. PHAuNPs feature a sub-20 nm porous shell and a 50 nm void core. Such unique morphology enables them to strongly absorb and scatter near infrared lights due to the surface plasmon resonant effect of Au. This makes them particularly suitable for in vivo applications, where NIR wavelengths are considered as a ‘clear window’ for deeper penetration of light. The construction and characterization of PHAuNP-based Raman nanotag, including attachment of Raman dye, pegylation and their stability, are described. Cytotoxicity of Raman nanotags are tested using the radioactive [3H]thymidine incorporation method. The results show that pegylated Raman nanotags are stable and non-toxic and can potentially be used for in vivo applications.
Formation and Characterization of Nanolayered Pd-Based Metal/p-4H SiC Systems with Ohmic Behaviour
Authors: Kolaklieva Lilyana , Kakanakov Roumen , Polychroniadis Efstathios K. , Pavlidou Eleni , Tsiaousis Ioannis , Albert Bensely , Andreadou Ariadne
Published: April 2010

Three types of nanolayered Pd-based metal/p-4H SiC systems, Au/Pd, Au/Pd/Al and Au/Pd/Ti/Pd have been investigated and compared to Pd monolayered metallization regarding the electrical and thermal properties. The lowest contact resistivity of 2.8x10-5 .cm2 has been achieved with the Au/Pd/Ti/Pd contact. This contact exhibits excellent thermal stability during long-term heating at temperature of 700oC and at operating temperatures up to 450oC. The surface morphology investigation has shown that despite the observed decrease, the palladium agglomeration has been not avoided completely in the same contact. The dominated surface roughness was measured to be 75 nm. However, the formation of dendrites in certain places leads to increase the surface roughness to 125 nm. The structural analysis revealed that palladium silicides are formed at the interface metal/p-4H SiC which affects on decrease of the barrier height in more than two times and conversion of the contact from Schottky into ohmic.
Interacting Double InAs/GaAs Quantum Dots of Cylindrical Symmetry
Authors: Bochorishvili Beka , Polatoglou Hariton M.
Published: April 2010

The electron and hole energy states and oscillator strengths for interband transitions of two interacting Quantum dots (QDs) are theoretically studied. We explore how the properties of the system depend on the distance between them. Calculations are done for InAs QDs which are embedded in GaAs. The QDs have cylindrical form and are situated one on top of the other in such way that their symmetry axes coincide. The calculations are done in the envelope function approximation using position dependent effective masses. Finite Element Method (FEM) is utilized to find energy spectra, wavefunctions and oscillator strengths. We find that the hole states show less tunneling compared to the electron states, transitions in general show some anisotropy which decreases as the distance between the dots decrease and that the total oscillator strength for each particular transition is constant.
Siderophore production and nitrogenfixation are mutually exclusive strategies in Anabaena 712
Authors: Hutchins Dave A. , Rueter John G. , Fish William
Published: April 2010

The relationship between siderophore production and N fixation was investigated in cultures of the freshwater cyanobacterium Anabaena 7120 grown in chemically defined medium. Cultures were grown with and without 300 µM NO3− and 1 µM Fe in all four possible combinations. Chl a and protein concentrations were used to monitor growth response. Siderophore production and N fixation rates were measured throughout the experiments. Acid‐leachable cellular Fe was measured with the chromogen FerroZine. Siderophores were produced only by cultures with added NO3− but no added Fe. N‐fixing cultures of Anabaena 7120 did not make siderophores even at a saturating light irradiance. These results do not agree with previous theories that siderophore‐mediated Fe uptake facilitates N fixation, enabling cyanobacteria to become dominant. The economics of N and Fe acquisition systems are examined in terms of elemental investments, energy requirements, and the kinetics of siderophore‐Fe uptake. Our data are used to support a model that suggests that dilution of excreted siderophores or turbulent dispersion of the siderophore away from the cell surface would severely reduce the efficiency of siderophore‐mediated Fe uptake in aquatic systems. This model supports the idea that siderophores are most useful as an Fe recycling mechanism in quiescent waters with high cyanobacterial biomass.
Geographic variation of oceanic 14C dark uptake
Authors: Prakash A. , Sheldon R. W. , Sutcliffe W. H.
Published: April 2010

In a series of midocean stations extending from high northern to high southern latitudes in both the Pacific and Atlantic Oceans we found that 14C dark uptake followed a definite geographic pattern. In temperate and equatorial regions the dark uptake was normally ≾ 10% of that in the light, but in the subtropical gyres and at high southern latitudes the average dark uptake varied from 10 to >50% of the light uptake. There was a significant and complex relationship between dark uptake, production, and standing stock that seemed to depend on the structure of the plankton community, but a relatively simple pattern could also be discerned. At production levels of > l µg C liter−1 h−1 or at standing stock levels of >40 µg C liter−1, the average dark uptake was low. At lower levels the average dark uptake was high.
Zooplankton effects on phytoplankton in lakes of contrasting trophic status
Authors: Elser James J. , Goldman Charles R.
Published: April 2010

Studies were carried out in three lakes of strongly contrasting trophic state to evaluate how the effects of zooplankton on phytoplankton vary as a function of lake productivity. Chlorophyll and total P concentrations differed by 2–3 orders of magnitude among ultra‐oligotrophic Lake Tahoe, meso‐oligotrophic Castle Lake, and strongly eutrophic Clear Lake. Three experimental designs involving short‐term (4 d) manipulations of nutrients, ambient zooplankton, and the common crustacean grazer Daphnia were performed in each lake. Algal responses were assessed at both the “aggregate,” community (Chl, primary productivity, nutrient status) and species levels.

Experiments in Lake Tahoe revealed a high degree of nutrient sensitivity but negligible grazing impacts by the very low densities of ambient zooplankton. Daphnia grazing had substantial impacts on Tahoe phytoplankton, however, indicating high susceptibility to grazing in this assemblage of relatively small‐sized algal species. Castle Lake experiments revealed strong direct and indirect impacts of both ambient zooplankton and Daphnia on the nutrient‐limited algal assemblage. The cyanobacteria‐dominated algal community of Clear Lake was resistant to grazing impacts, responding relatively weakly only to the highest densities of Daphnia. Good correspondence between estimates of algal biomass made from chlorophyll measurements and microscopic examination were obtained, and, in Castle Lake, concordance between estimated community productivity turnover times made from species‐specific growth determinations and community productivity measurements was observed. The contrasting responses to experimental zooplankton manipulations in the three lakes provide support for the view that the coupling between zooplankton and phytoplankton is strongest in lakes of intermediate productivity and imply that food‐web alterations at the top of the food web are most likely to propagate to the level of the phytoplankton (and therefore lake water quality) in lakes of moderate trophic status.
Secchi disk and photometer estimates of light regimes in Alaskan lakes: Effects of yellow color and turbidity
Authors: Koenings J. P. , Edmundson J. A.
Published: April 2010

Variations in underwater light regimes among 58 Alaskan lakes were indexed by Secchi disk (SD) transparency and by vertical attenuation coefficients (Kd) and euphotic zone depths (EZD) derived from using a submarine photometer (SP) sensitive to photosynthetically active radiation (PAR). Lake‐specific ratios between turbidity (light scattering) and color (light absorption) explained 52% of the variation (P < 0.0001) in Kd × SD values, which ranged as a continuum between 0.52 and 3.83. A clear‐water median value of 1.86 (range, 1.13–3.26) is elevated by color to a median of 2.70 (range, 1.81–3.83), whereas turbidity reduces the median value of 0.93 (range, 0.52–2.56). EZD: SD, PAR at the SD depth, and PAR reflection (backscatter) also changed with the turbidity‐to‐color ratio. The nearly 10‐fold ranges between Kd × SD (0.59–4.09) and EZD: SD (0.89–8.67) values taken from 35 studies on lakes, estuaries, and oceans could be explained by color and turbidity differences. Background attenuation from small amounts of color (<10 Pt units) and turbidity (<5 NTU) uncoupled SD and SP measurements from changes in Chl a, limiting their use as an index of trophic state. Changes in Kd × SD can serve, however, as a useful index of system loading by turbid particulate material or organic color.
The role of seasonal turnover in lake alkalinity dynamics
Authors: Kling George W. , Giblin Anne E. , Fry Brian , Peterson Bruce J.
Published: April 2010

Elemental cycles and alkalinity (Alk) production and consumption were studied in sediments from two ponds (Mares and Gull) in coastal New England. Intact cores were incubated in the laboratory and manipulated to simulate water‐column anoxia during stratification and oxygenation during turnover. Reactions with S dominated Alk budgets in Mares Pond, whereas in Gull Pond reactions with N contributed most to Alk change. In Mares Pond, control cores held anoxically produced Alk at an average rate of 2.66 ±0.59 (SE, N = 3) meq m−2 d−1, mostly due to SO42−reduction. This rate was similar to calculations from hypolimnetic monitoring in the pond during summer stratification. In cores from Mares Pond where the water column was aerated to simulate turnover, the reoxidation of S (1.3 meq SO42− m−2 d−1) contributed most to consumption of Alk (3..5 meq m 2 d−1); half of all Alk lost during the 40‐d experiment was consumed in the first 4 d of turnover. In aerated cores from Gull Pond, Alk consumption (4.2 meq m−2 d−1) was driven mostly by nitrification (2.8 meq m−2 d−1). High rates of Alk consumption observed in oxidized cores illustrate the potential for rapid Alk loss during seasonal turnover.

Pore‐water profiles of SO42− and Alk suggest that sulfide oxidation was strongest in the top 1 cm of sediment and reached to a depth of 3–4 cm. Oxidation occurred rapidly in response to turnover, and although H2S may have been oxidized initially, the oxidation of solid‐phase species dominated after 1 or 2 d. An isotopic mass balance of S in two turnover cores showed that from 30 to 70% of the oxidized S originated as inorganic rather than organic S.
The effects of pH and aluminum on the growth of the acidophilic diatom Asterionella ralfsii var. americana
Authors: Gensemer Robert W.
Published: April 2010

The effects of pH and Al on the acidophilic diatom Asterionella ralfsii var. americana Körn. were examined in axenic batch cultures. Experiments were performed under conditions of both high (pH 5) and low (pH 6) Al solubility over a range of concentrations from 0 to 30 µmol liter−1 total Al. Growth rates were analyzed with respect to analytically determined Al concentrations and to predicted changes in dissolved metal ion speciation in response to Al additions.

Growth rates of A. ralfsii were significantly reduced above 15 µmol liter−1 total Al at both pH 5 and 6. Al additions increased estimated free ion activities of Al3+, Fe3+, and Cu2+ through indirect chelator interactions at pH 5 and 6; therefore, all three were significantly correlated with growth rate reductions. Independent manipulations of total Fe and Cu, however, suggested that Al was not indirectly increasing either Fe3+ or Cu2+ free ion activities to toxic levels. Relationships of growth rates to both inorganic monomeric Al (Alr) and to estimates of pAl were strongly pH‐dependent with toxicity being greater per unit of dissolved Al concentration at pH 6 than at pH 5. These results are consistent qualitatively with predictions that H ions can ameliorate dissolved metal toxicity by competitively excluding Al3+ ions from binding to cell‐surface ligands. The impact of Al on natural phytoplankton populations therefore is likely to depend on a combination of pH‐dependent Al solubility, the protonation of cell‐surface ligands, and chelator‐mediated metal speciation.
Dissolved oxygen concentrations in hypersaline waters
Authors: Sherwood J.E. , Stagnitti F. , Kokkinn M. J. , Williams W. D.
Published: April 2010

Henry’s law constants (ko) and equilibrium concentrations (Co*) of dissolved oxygen (DO) at 1 atm were measured in NaCl solutions of concentration (S) up to ∼260‰ and at temperatures (T) between 273 and 308K. An equation of the form

urn:x-wiley:00243590:media:lno19913620235:lno19913620235-math-0001

was found to predict DO values to within the experimental uncertainty. An equation of the same form satisfactorily described the variation of ln ko over the same temperature and concentration ranges. In order to develop these equations it was also necessary to develop ones to describe the variation of density and vapor pressure of NaCl solutions with T and S. The equations can be used to generate tables of oxygen solubility values that can be used for hypersaline waters dominated by NaCl. Theoretically, DO values based on NaCl can be corrected for the presence of other ionic salts in natural waters. At present this correction is limited by the availability of DO data for these subdominant electrolytes.
Cross‐shelf transport causes recruitment to intertidal populations in central California
Authors: Farrell Terence M. , Bracher David , Roughgarden Jonathan
Published: April 2010

The control of recruitment to intertidal barnacle populations along the central California coast was examined from April to mid‐October 1988. Four recruitment pulses occurred during periods of relaxation in alongshore winds and cessation of coastal upwelling. In each case recruitment ended when strong equatorward winds reappeared and upwelling resumed. Data on SST, salinity, adjusted sea level, and satellite (AVHRR) images revealed alternating periods of onshore and offshore transport of the surface water layer. The onset ofthe largest recruitment pulse was associated with the advection of warm, clear, low‐salinity water into the nearshore region. This oceanic water mass also contained a different zooplankton assemblage than the water mass it replaced.
Identification of bacteriochlorophylls in lakes via reverse‐phase HPLC
Authors: Hurley James P. , Watras Carl J.
Published: April 2010

Reverse‐phase HPLC has been used successfully to quantify phytoplankton pigments in lakes and oceans. Here we extend the technique to photosynthetic bacterioplankton and demonstrate the identification of five bacteriochlorophylls (BChl a, b, c, d, e) extracted from pure cultures with 90% acetone. The technique was then applied to natural plankton samples from two oligotrophic‐mesotrophic lakes in northern Wisconsin. In both lakes, previously undetected layers of phototrophic bacteria were identified based on their pigment compositions. In one of the lakes, the bacterial layer previously had been misidentified as a deep zone of abundant pheopigment. These observations re‐emphasize concerns that traditional protocols (i.e. measuring the absorbance of mixed acetone extracts at 665 nm before and after acidification) have serious limitations in natural systems and can lead to misinterpretations of planktonic distributions and processes. The potential importance of phototrophic bacteria in dimictic temperate lakes is demonstrated. Without significantly modifying standard reverse‐phase HPLC protocols, unamibiguous determinations of eucaryotic and procaryotic chlorophylls and degradation products can be made simultaneously.
Water temperature dynamics and heat transfer beneath the ice cover of a lake
Authors: Ellis Christopher R. , Stefan Heinz G. , Gu Ruochuan
Published: April 2010

Water temperature profiles were measured every 2 min in a small and shallow urban Minnesota lake from 8 February 1989 until ice‐out on 11 April. The temperature record showed two distinct segments. Before 24 March, the temperature profile remained relatively constant, but later (when air temperatures were mostly above freezing) temperatures were dynamic and rose.

During the quiescent period, the upper 3 m of the water column cooled slowly while the lower water remained virtually isothermal. The calculated thermal diffusion coefficient approached molecular thermal diffusivity near the ice cover and was roughly 3 times molecular diffusivity through much of the region of the thermocline (the upper 2 m). The average computed heat flux through the ice (50–55 cm thick) and snow (10– 30 cm deep) cover during this period was 2.8 W m−2.

With the onset of above‐freezing air temperatures, temperatures began to change rapidly. Observed intrusions of warm water were most likely the results of advected inflows of warm water from the periphery of the lake.
The post‐ 1979 thermohaline structure of the Dead Sea and the role of double‐diffusive mixing
Authors: Anati D. A. , Stiller M.
Published: April 2010

After centuries of meromixis (year‐ round stratification with a permanent halocline), the Dead Sea has passed through two distinct stages in the last decade: first a 4‐yr meromictic stage and then a holomictic stage. In the first stage, classic one‐dimensional processes dominated. In the second stage, three different regimes operated in a seasonal cycle: salt precipitation in spring and early summer, double‐diffusive mixing in late summer and autumn, and vertical mixing in winter. During the second (holomictic) stage the Dead Sea as a whole also underwent secular changes: a gradual change in the salt composition of its brines, an increase of salt concentration, and a gradual heating.
Separating the respiration rates of embryos and brooding females of Daphnia magna: Implications for the cost of brooding and the allometry of metabolic rate
Authors: Glazier Douglas S.
Published: April 2010

Rates of oxygen consumption were measured in eggs, embryos, and neonates, as well as in adults of Daphnia magna with or without their broods. There was no detectable energetic cost of carrying a brood, and there was no apparent effect of brooding on the respiration of eggs and 1–2‐d‐old embryos. The respiration rates of eggs and early embryos were only about a third of those of neonates and adults and thus accounted for very little respiration in brooding females.
Feeding currents and energy dissipation by Euchaeta rimana, a subtropical pelagic copepod
Authors: Yen Jeannette , Sanderson Brian , Strickler J. Rudi , Okubo Akira
Published: April 2010

Based on the pathlines of the flow field of the pelagic copepod Euchaeta rimana, we calculated some characteristics of the velocity gradient field: vorticity, shear, and squared rates of strain. We found that this copepod created a sheared laminar flow field, which is most intense near the moving paired second antennae and transports a volume of water similar to that measured in feeding experiments. The far‐field flow is a combination of first‐order and higher order scanning currents that serve to overcome nega
he effect of whole‐lake fish community manipulations on Daphnia migratory behavior
Authors: Dini Michael L. , Carpenter Stephen R.
Published: April 2010

A four‐summer study of vertical migration by Daphnia was conducted in two neighboring lakes during a two‐stage fish community manipulation. This manipulation produced discrete periods of low and high planktivory by fish. The migration pattern was variable and weak during the low predation stage, but became consistent and intense within weeks of the change to high levels of predation, confirming the pre‐eminence of predation avoidance among several extant hypotheses.
Bioerosion of coral reefs‐A chemical approach
Authors: Lazar Boaz , Loya Yossi
Published: April 2010

We measured total alkalinity changes as a direct clue to the rate and mechanism (chemical or mechanical) of boring of the bivalve Lithophaga lessepsiana in colonies of the coral Stylophora pistillata, the most abundant coral‐borer association in the reefs of the northern Gulf of Elat (Aqaba), Red Sea. Our experiments included comparison between total alkalinity measurements of seawater surrounding colonies of S. pistillata free of L. lessepsiana and colonies infected with it. It is suggested that L. lessepsiana is able to redissolve chemically up to 40% of the CaCO3 deposited by S. pistillata.
Paralytic shellfish poisoning toxins mediate feeding behavior of sea otters
Authors: Kvitek Rikk G. , DeGunge Anthony R. , Beitler Mark K.
Published: April 2010

Captive sea otters (Enhydra lutris)fed live Saxidomus giganteus (butter clams) ad libitum either reduced their prey capture and consumption rates or discarded the highly toxic siphons and kidneys when switched from clams containing very low levels of saxitoxin [37±9 µg STX (100 g)−1] to highly toxic clams [226±96 µg STX (100 g)−1]. Feeding rates returned to pretreatment levels when the otters were again switched to low‐toxicity clams, but siphon discard frequency remained high. Paralytic shellfish poisoning symptoms were observed only in an otter calculated to have consumed the most STX (154 µg kg−1 d−1), a dosage within the range of oral LD50s reported for other nonprimate mammals. None of the other otters displayed symptoms, and all subjects were eventually released in good health. These findings suggest that otters are not immune to paralytic shellfish poisoning toxins (PSPT) and that they have the ability to detect and avoid consumption of lethal amounts of toxic prey. This behavioral response is highly adaptive given the importance of butter clams in sea otter diets, and the chronic toxicity of butter clams in areas where toxic dinoflagellate blooms occur. A comparison of the distributions of otters and toxicity levels of butter clams in southeast Alaska suggests that the sequestering of PSPT may protect some clam populations from otter predation and limit the distribution of otters to the exposed outer coast where toxic clams are rare.
Volume scattering function, average cosines, and the underwater light field
Authors: Kirk John T. O.
Published: April 2010

The extent to which the relationship between the apparent optical properties of water bodies Kd,, R(0) (vertical attenuation coefficient, reflectance) and inherent optical properties of the water (a, b, bb,—absorption, scattering, backscattering coefficients) varies with the shape of the volume scattering function has been investigated via Monte Carlo modeling of the underwater light field for 12 different optical water types. The previously derived equation for the vertical attenuation coefficient of downward irradiance

urn:x-wiley:00243590:media:lno19913630455:lno19913630455-math-0001

has been shown to be of general applicability, but the coefficient G(µo) is a function not only of the cosine of the refracted incident photons (µo) but also of a shape factor of the volume scattering function in accordance with

urn:x-wiley:00243590:media:lno19913630455:lno19913630455-math-0002

where µ̄, is the average cosine of scattering derived from the volume scattering function in question, and ct, c2, c3, and c4 are numerical constants estimated from the modeling data.

The well‐known relationship

urn:x-wiley:00243590:media:lno19913630455:lno19913630455-math-0003

between the subsurface irradiance reflectance under zenith sun and the ratio of backscattering coefficient to absorption coefficient is shown to apply satisfactorily to all the water types for bb/a values up to ∼0.25, but is less satisfactory at higher values of this ratio. As the incident beam departs from the vertical, so the reflectance increases to an extent that depends on the shape of the volume scattering function.
Organic volatile sulfur in lakes of the Canadian Shield and its loss to the atmosphere
Authors: Richards S. R. , Kelly C. A. , Rudd John W. M.
Published: April 2010

Identities, concentrations, and fluxes of volatile sulfur compounds (VSCs) were determined in 11 lakes in northwestern Ontario. Carbonyl sulfide (COS: up to 1.1 nM) and dimethyl sulfide (DMS: up to 11 nM) were present in surface waters during most of the ice‐free season. Depth profiles showed accumulations below the mixed layer of methane thiol (MSH), DMS, and dimethyl disulfide (DMDS). There was no effect of low pH or increased [SO42−] (from 2.4 to 12.3 mg liter−1) on the concentrations and identities of surface‐water VSCs. Accumulation of DMS below the mixed layer was 9 × higher in an acidified system, however, when compared to an unacidified reference lake. Estimates of flux from two stratified lakes indicated that volatilization was not an important sulfur loss mechanism compared to others such as sedimentary SO42 reduction.

Concentrations of MSH, DMS, and DMDS in shallow Lakes 114 and 303 were often 5–30 × higher than in any other lake studied, and the flux from Lake 114 was ∼0.96–1.6 × the estimated oceanic DMS flux per unit of area. On a regional basis, in areas where SO42− in precipitation is low, export of VSCs to the atmosphere from shallow lakes and bog pools may be significant compared to sulfur inputs through precipitation.
Invertebrate predation in Lake Michigan: Regulation of Bosmina longirostris by Leptodora kindtii
Authors: Branstrator Donn K. , Lehman John T.
Published: April 2010

The density of Bosmina longirostris (O. F. Mueller) declined 100‐fold between 25 June and 20 August 1985 in Lake Michigan; a similar pattern of changing abundances was observed in 1986 but not in 1987 or 1988. Bosmina collected from periods before and during the decline in 1985 and 1986 were examined for size at maturity and clutch size. Population size‐frequency distributions suggest that some animals began to mature at smaller sizes during the decline in 1985. In some cases, the average clutch size for Bosmina of similar body lengths was significantly reduced during the decline in 1985 and 1986. These data suggest that food limitation was a factor in the species decline in both years. Gut content analyses indicate that of seven potential predators, Leptodora kindtii (Focke) was probably most responsible for Bosmina mortality. There is ample evidence that Leptodora does not consume strictly fluid from its prey: juvenile Leptodora ate mainly smaller prey that included Bosmina and the rotifer Conochilus; adults ate a broader size range of prey that included mainly Bosmina, Daphnia, and copepods. In 1987 and 1988, Bythotrephes cederstroemii Schoedler was abundant in Lake Michigan and was contemporaneous with collapse of the Leptodora population and concurrent increase of the Bosmina population in August and September. Predation by the large copepods Epischura lacustris S. A. Forbes and Limnocalanus macrurus Sars did not appear to have any significant effect on the population dynamics of Bosmina.
Jellyfish Lake, Palau: Early diagenesis of organic matter in sediments of an anoxic marine lake
Authors: Orem W. H. , Burnett W. C. , Landing W. M. , Lyons W. B. , Showers W.
Published: April 2010

Jellyfish Lake, a meromictic, marine lake in the Palau Islands, western Pacific Ocean, is accumulating organic matter‐rich sediments (46% wt/wt) below anoxic, highly sulfidic bottom water. Elemental and stable isotope (δ13C) data indicate that the sedimentary organic matter is primarily derived from vascular plant remains (65–90%) and would form a type 2 kerogen. A bacterial layer at the oxic‐anoxic interface in the water column may play an important role in the rapid recycling of algal‐derived organic matter from the highly productive surface waters.

The major postdepositional change in the sedimentary organic matter is carbohydrate biodegradation, as shown by 13C NMR. Lignin and aliphatic substances are preserved in the sediments. Dissolved organic matter in pore waters is primarily composed of carbohydrates, reflecting the degradation of sedimentary carbohydrates. Rate constants for organic carbon degradation and sulfate reduction in sediments of the lake are about 10 × lower than in other anoxic sediments. This may reflect the vascular plant source and partly degraded nature of the organic matter reaching the sediments of the lake.

Elemental results from sediment cores and stable isotope (δ18O, δ13C) studies of shells from the sediments indicate probable climatic or ecological fluctuations affecting the depositional environment of the lake between 80 and 110 yr ago. The high sedimentation rate and stable environment of Jellyfish Lake make it a possible environment for studies of climatic fluctuations during the Holocene.
Surfaces of hydrothermal vent invertebrates: Sites of elevated microbial CH4 oxidation activity
Authors: de Angelis Marie A. , Reysenbach Anna‐Louise , Baross John A.
Published: April 2010

The high levels of CH4 emanating from deep‐sea hydrothermal vents suggest that methane oxidation may be an important process in vent fields, especially in association with vent fauna. We measured the uptake of 14C‐labeled methane by tissues and surfaces of common vent animals at a vent site in the northeastern Pacific. Low and variable levels of CH4 uptake were observed with limpet gills. However, the external surfaces of vent invertebrates, including gastropod shells and tube‐worm tubes, were found to be extremely active sites of methanotrophic activity. Turnover times for CH4 based on 14CH4 oxidation rates averaged 1–2 d per individual limpet or vestimentiferan tube worm. These high rates provide the first evidence that methane oxidation can be a significant microbial process at a deep‐sea hydrothermal vent site and adds external invertebrate surfaces as sites of elevated microbial activity in this environment. The methanotrophic bacteria on invertebrate surfaces can be readily grazed and may serve as a source of food for vent animals.
Diel vertical migration and nocturnal uptake of nutrients by Chattonella antiqua under stable stratification
Authors: Watanabe Masataka , Kohata Kunio , Kimura Toshihiko
Published: April 2010

The ecological advantage of diel vertical migration for the nutrition and population growth of the flagellate Chattonella antiqua (Raphidophyceae) was examined in a large, axenic culture tank. Vertically stratified salinity, temperature, PO43, and NO3−, analogous to oceanographic conditions observed in the field with a red tide of this species in the Seto Inland Sea, were simulated in the tank. C. antiqua was capable of migrating through very sharp salinity and temperature gradients (max ΔS = 2.8‰, ΔT = 2°C) between surface and deep waters. At night the population migrated to deep, nutrient‐rich water and took up PO43− and NO3−. During the day it migrated to the nutrient‐depleted surface water and utilized accumulated nutrients for photosynthesis. Uptake of PO43− and NO3− was synchronized, even if only one was limiting in the water column. Under stable stratification of nutrients, diel vertical migration and nocturnal uptake of nutrients in the deep, nutrient‐rich water were essential for C. antiqua to grow at rates comparable with those of coastal diatoms, which have no migratory ability.
Biological and optical properties of mesoscale coccolithophore blooms in the Gulf of Maine
Authors: Balch William M. , Holligan Patrick M. , Ackleson Steven G. , Voss Kenneth J.
Published: April 2010

Two coccolithophore blooms in the Gulf of Maine were studied in 1988 and 1989. Each bloom was about 50,000 km2 in area and confined to the top 20 m of the water column. Maximal cell concentrations were 2,000 cells ml−1 and coccolith densities of 3 × 105 ml−1 were observed. The coccolith : cell ratio was highest in the bloom center (region of most intense reflectance) and lowest at the bloom periphery, an indication of varying organic vs. inorganic C production. Chlorophyll concentrations were generally low within the bloom and no relation could be observed between major nutrients and coccolithophore abundance. Backscattered light was profoundly affected by coccolith density and was slightly wavelength‐dependent. We calculated total backscattering as well as backscattering (bb) caused exclusively by coccoliths and derived the algorithm relating coccolith density to backscattering. Although cells were efficient light absorbers, coccoliths showed negligible light absorption. Diffuse attenuation was lowest in the green and blue‐green part of the visible spectrum. At the center of the bloom, coccoliths contributed >75% of the backscattering signal and > 50% of the beam attenuation signal. The most accurate way to estimate coccolith concentrations via remote sensing is to measure water‐leaving radiance in the green wavebands.
Photosynthesis–light relations of stream periphyton communities
Authors: Boston H. L. , Hill W. R.
Published: April 2010

The photosynthesis—irradiance (P−I) relationship was examined in 10 intact periphyton communities from sites in eight streams that differed in ambient light, nutrient concentrations, and grazing pressure. Algal biomass ranged from 2.3 to 86 µg Chl a cm−2 and taxonomic composition differed. Photoassimilation of 14C was measured in the laboratory at six light levels for each community. Photosynthesis by communities from shaded sites was photoinhibited at the highest light level. The light intensity at the onset of saturation (Ik) was positively correlated (P ≤ 0.05) with ambient light, but ranged only from ∼ 100 to 400 µmol m−2 s−1 among communities. Light‐saturated, Chl‐specific photosynthetic rates (PSChlM) ranged from 0.26 to 1.4 µg C(µg Chl a)−1 h−1. The initial slope (α) of the P−I response ranged from 0.80 to 6.4 µg C (mg Chl a)−1 (µmol quanta)−1 m−2 s−1. Unlike phytoplankton, α and PSM, (per unit Chl a) of the periphyton communities were not well related to the ambient light environment and tended to be lower for communities from high‐light habitats. Further, the P−I responses of the communities were better related to periphyton biomass than to the light environment. Self‐shading and other aspects of development in a matrix seem to be important determinants of periphyton P−I relationships.
Regeneration of dissolved substances in a seasonally anoxic lake: The relative importance of processes occurring in the water column and in the sediments
Authors: Carignan R. , Lean D. R. S.
Published: April 2010

We studied the release of inorganic C, CH4, NH4+, PO43−, reactive silica (RSi), Fe, Mn, and Ca from the sediments of a small, mesotrophic, shield lake (Williams Bay, Jacks Lake, Ontario). The diffusion of CH4, ΣCO2, NH4+, and RSi from the sediments, as estimated from pore‐water data, increases linearly with depth and sedimentation rate. Release associated with sedimentation rate accounts for 47–84% of the fluxes of these substances to the water column. Regeneration from both the water column and the sediments plays an important role. During summer anoxia, 70% of the hypolimnetic accumulation of NH4+ is accounted for by diffusion from the sediments. This proportion is 31% for ΣCO2, 62% for CH4, 54% for total P (TP), 36% for RSi, 15% for Fe, 12% for Mn, and 5% for Ca. Significant release of Fe, Mn, and PO43− is limited to the deepest part of the basin. Regeneration of PO43− is not well coupled to organic‐matter degradation, and undefined anoxic P‐immobilization reactions seem to be taking place in the sediments of the littoral and upper hypolimnion. Diagenetic modeling of the sediment pore‐water and solid‐phase data shows that the layer of sediment involved in nutrient release extends 50–100 cm below the interface. The global recycling of carbon and nitrogen in aquatic systems is attributed to the decomposition of three classes of organic compounds (G0, G1, and G2) that display well‐separated first‐order decay constants (k ≃ 40, 0.2, and 0.01 yr−1). Most of G0 appears to be decomposed during its descent in the water column. The longer lived sedimentary fractions (G1 and G2) show marked focusing in the basin, and most of the regeneration is attributable to decomposition of the less reactive fraction G2. The existence of long‐lived sedimentary organic‐matter fractions is consistent with the observed resilience of sediment catabolism to seasonal or long‐term changes in organic matter influx.
Long time series from the English Lake District: Irradiance‐dependent phytoplankton dynamics during the spring maximum
Authors: Neale Patrick J. , Talling Jack F. , Heaney S. Ivan , Reynolds Colin S. , Lund John W. G.
Published: April 2010

We analyzed rates of phytoplankton increase and decline during the spring maximum via long‐term (25 yr) records of biomass (Chl a) and abundance of the dominant diatom, Asterionella formosa, sampled from the surface waters of Windermere (English Lake District). Average rates of net increase in early spring (i.e. up until the end of March) are best correlated with the logarithm of surface irradiance (r2 = 0.71–0.87). Average spring growth rates in late February and March (weeks 6–13 of the year) defined by this analysis significantly exceed rates predicted from calculations of integrated production with existing physiological data for A. formosa but are similar to the predicted growth rates at the mean irradiance in the mixed layer. In late spring (April– May), stratification becomes well established and the rate of population increase lessens. This decrease occurs before dissolved silicate is depleted to growth‐limiting concentrations during increasing average irradiance in the surface layer. Near exhaustion of dissolved silicate and rapid loss of A. formosa from the surface layer follow. P limitation, enhanced sedimentation, and photoinhibition are factors that may slow net diatom accumulation before the onset of silicate limitation.
Absorption and scattering estimates from irradiance measurements: Monte Carlo simulations
Authors: Gordon Howard R.
Published: April 2010

A method of estimating the absorption (a), scattering (b), and backscattering (bb) coefficients of a homogeneous ocean based on near‐surface measurements of the beam attenuation coefficient (c), the irradiance reflectance (R), and the attenuation coefficient of downwelling irradiance (Kd) is proposed, and it is tested with Monte Carlo simulations of radiative transfer in the ocean‐atmosphere system. The technique utilizes the variation of R with solar zenith angle to estimate the value R would have if the sun were at zenith and the atmosphere were removed. This value of R is then combined with Kd to derive bb and the ratio of scattering to beam attenuation, from which a and b are obtained. In addition, the volume scattering function β(α) for scattering angles 60° a 150° is also estimated. Such estimates of bb and β(α), which are based on the diffuse light field existing over volumes of the order of 10–1,000 m3, are important in assessing the applicability of measurements made with classical scattering instruments (sampling volume ∼ 1 cm3) to predicting radiative transfer in the upper layers of the ocean. Direct application of the method is limited to situations in which the mixed layer is sufficiently deep and in which inelastic processes, e.g. Raman scattering and fluorescence, make negligible contributions to Kd and R near the sea surface.
Numerical modeling of effects of small‐scale sedimentary variations on groundwater discharge into lakes
Authors: Guyonnet Dominique A.
Published: April 2010

The effect of small‐scale sedimentary structural variations (on the order of a few tens of centimeters) on groundwater‐lake interaction is investigated with CROSSFLO, a finite‐element model that simulates two‐dimensional steady state flow in cross section via stream functions. Simulations show that relatively thin continuous or discontinuous layers can strongly influence migration paths, recharge‐discharge profiles, flowline inclinations at the sediment‐ water interface, and travel times. In the case of groundwater‐mediated contamination of lakes from sources located on land, results show that the presence of thin layers can change the point of contaminant entry into a lake by several hundreds of meters. Further, time required for the contaminants to reach the lake may be altered by decades or centuries. These results stress the importance of detailed description of subsurface geology for realistic predictions of contaminant migration from groundwater into lakes and for sound lake management.
Growth kinetics of the omnivorous oligotrich ciliate Strombidium sp
Authors: Ohman Mark D. , Snyder Richard A.
Published: April 2010

The marine ciliate Strombidium sp. can be raised through multiple generations on a monoxenic diet of the bacterium Vibrio natriegens, but Strombidium specific growth rates and yields are 3–4 times higher when a heterotrophic microflagellate is included as prey. In contrast to earlier studies we found that Strombidium grew inefficiently when feeding as a bacterivore, with gross growth efficiencies (K1) of 11–20% (determined on a nitrogen‐, carbon‐, and protein‐specific basis). On the same bacterial diet K1 of the scuticociliate Uronema sp. was 49–70%. Bacterivorous Uronema attained a 9‐fold higher specific growth rate and 30‐fold higher cell yield than Strombidium. Thus, the species composition of a ciliate assemblage can markedly influence the fate of microbial loop production.

Cell volume of live Strombidium sp. varied >3‐fold during a growth cycle. Cell organic composition also varied: the C:N (mass) ratio decreased from 7.7 in stationary phase cells to 4.5 in exponentially growing cells, reflecting the ingestion of N‐rich prey. In addition to these natural variations in cell volume, preservatives can shrink cells to half of their live volume, resulting in spurious values of ciliate growth efficiency if computed on a volume‐specific basis.
Recent changes in productivity and climate of Lake Ontario detected by isotopic analysis of sediments
Authors: Schelske Claire L. , Hodeli David A.
Published: April 2010

Cores from Lake Ontario provide a record of lake responses to increased phosphorus loading that began after early forest clearance in the mid‐1800s. We measured 13C/12C ratios of organic and inorganic C (calcite) in the sediments to infer recent trends in primary production. The δ13C of organic C increased in response to historic increases in P enrichment until the mid‐1970s and then decreased in response to reduced P loading. The δ13C of calcite increased after 1940 but did not decrease in response to reduced P loading. We conclude that the results differ because δ13C of organic C is determined by primary production early in the seasonal cycle when flux of organic C to the sediments is greatest, whereas δ13C of calcite depends on the isotopic composition of dissolved inorganic C during late summer when calcite is precipitated.

Calcite accumulation and its δ13C ratio oscillated after 1940 with peaks estimated at 1948, 1966, 1977, and 1983. These peaks correspond to minima in δ18O values, indicating calcite precipitation at higher temperature, and to years of early thermal stratification. We hypothesize that calcite accumulation and its stable isotopic ratios are controlled by interannual variability in onset of thermal stratification of the lake. Our results thus suggest a direct link from climate (i.e. thermal stratification) to interannual variation in lake productivity and to carbonate precipitation and its δ13C signature.