bluuebunny/crossref_metadata_2025 huggingface dataset:
Bacterial control of silicon regeneration from diatom detritus: Significance of bacterial ectohydrolases and species identity
Authors: Bidle Kay D. , Azam Farooq
Published: June 2010

Bacteria (and possibly archaea) accelerate silica dissolution in the sea by colonizing and enzymatically degrading the organic matrix of diatom frustules. We tested whether colonizer species composition and ectohydrolase profiles critically control silicon regeneration by allowing diatom (Thalassiosira weissflogii and Chaetoceros simplex) detritus to be colonized by natural bacterial assemblages and 12 phylogenetically characterized marine isolates. We characterized the colonizers' ectohydrolase profiles and rates of silicon regeneration. The colonizers' cell‐specific protease activity was consistently the dominant ectohydrolase, and it strongly correlated with silica dissolution rates. Cell‐specific glucosidase, lipase, and chitinase activities showed no correlation with silicon regeneration. Denaturing gradient gel electrophoresis (DGGE) of PCR‐amplified 16S rRNA genes was used to monitor colonization of detritus by natural microbial assemblages and to identify colonizing phylotypes. Representatives from gammaproteobacteria and sphingobacteria‐flavobacteria classes dominated colonizer populations by comprising 65% and 25% of detected phylotypes, respectively. Archaea were not detected among colonizer populations. All bacterial isolates accelerated silica dissolution, but individual rates varied by >300%. Significant variability was observed within the Alteromonadaceae, which indicates different abilities to process diatom organic matter. Isolates that displayed enhanced colonization and protease activities were the most effective at regenerating silicon. The most effective isolate belonged to the sphingobacteria‐flavobacteria, a group specialized in colonizing marine particles. Other effective isolates grouped with Pseudoalteromonas, Alteromonas, and Vibrio genera. One isolate caused intense aggregation of diatom detritus, significantly reducing silicon regeneration. Our results indicate that bacterial species identity strongly controlled silicon regeneration by influencing the colonization potential and ectohydrolytic profiles of bacteria as well as aggregate formation. Mechanistic models of oceanic silica cycling should incorporate species composition and ectohydrolase profiles of bacteria involved in silicon regeneration.
Evaluation of community respiratory mechanisms with oxygen isotopes: A case study in Lake Kinneret
Authors: Luz Boaz , Barkan Eugeni , Sagi Yftach , Yacobi Yosef Z.
Published: June 2010

Gross and net O2 production between May 1996 and February 1999 was determined in bottle incubation experiments with H218O spike and from the change in O2 concentration. Carbon fixation rates were obtained from 14C incubations. In general, production rates determined using the H218O‐spike were about twice the primary production determined by the 14C method, where the latter was close to net oxygen evolution. These relationships are similar to results for the open ocean. During the spring bloom, when the dinoflagellate Peridinium was abundant, the ratio of gross O2 production to carbon fixation was about 7.5, and net O2 production was greater than carbon fixation. The difference between O2 gross production and carbon fixation results, at least in part, from uptake by Mehler reaction and from recycling of the 14C tracer by dark respiration and the alternative oxidase (AOX). We used the difference in isotopic discrimination against 18O, occurring during O2 consumption by various biological pathways, to place constraints on the relative engagement of these pathways. We estimated the overall discrimination against 18O in the lake from O2 isotopic mass balance as 20.5—29‰. The only mechanism that can explain the strong overall fractionation in the lake is AOX, which strongly discriminates against 18O (~31‰). Our results show, for the first time, that uptake by AOX is widespread and quantitatively important to oxygen consumption in aquatic systems.
Assessment of the relationships between dominant cell size in natural phytoplankton communities and the spectral shape of the absorption coefficient
Authors: Ciotti Áurea M. , Lewis Marlon R. , Cullen John J.
Published: June 2010

Size‐fractionated chlorophyll concentration and phytoplankton absorption spectra were compared for a wide variety of natural communities. We found that, in general, when phytoplankton abundance increases, larger sizeclasses are added incrementally to a background of smaller cells. Natural phytoplankton communities from surface waters were explicitly characterized according to their dominant cell size and taxonomic group, and the relationships between this classification and the spectral shape of the phytoplankton absorption coefficient for the whole assemblage was described. By specifying the cell size of the dominant organism (pico‐, ultra‐, nano‐, or microplankton), more than 80% of the variability in spectral shape of the phytoplankton absorption coefficient from 400 to 700 nm could be explained. This is a result of the strong covariation of the size of dominant organisms and several factors controlling the spectral shape of the phytoplankton absorption coefficient, such as pigment packaging and concentration of accessory pigments. Consequently, the shapes of phytoplankton absorption spectra can be reproduced using a spectral mixing model, where two spectra, representing the normalized phytoplankton absorption coefficients for the smallest and the largest cells found in our data set, are combined additively, using a single parameter to specify the complementary contribution of each. The differences between reproduced and measured spectra contain taxonomic and physiological information. This parameterization provides a simple tool for extracting ecological information from optical measurements. It can also be used in sensitivity analyses to describe the influence of the dominant cell size of phytoplankton on optical properties of surface waters.
Primary production, respiration, and calcification of a coral reef mesocosm under increased CO2 partial pressure
Authors: Leclercq Nicolas , Gattuso Jean-Pierre , Jaubert Jean
Published: June 2010

The effect of increased CO2 partial pressure (pCO2) on the community metabolism (primary production, respiration, and calcification) of a coral community was investigated over periods ranging from 9 to 30 d. The community was set up in an open‐top mesocosm within which pCO2 was manipulated (411, 647, and 918 µatm). The effect of increased pCO2 on the rate of calcification of the sand area of the mesocosm was also investigated. The net community primary production (NCP) did not change significantly with respect to pCO2 and was 5.1 ± 0.9 mmol O2 m−2 h−1. Dark respiration R increased slightly during the experiment at high pCO2, but this did not affect significantly the NCP:R ratio (1.0 ± 0.2). The rate of calcification exhibited the trend previously reported; it decreased as a function of increasing pCO2 and decreasing aragonite saturation state. This re‐emphasizes the predictions that reef calcification is likely to decrease during the next century. The dissolution process of calcareous sand does not seem to be affected by open seawater carbonate chemistry; rather, it seems to be controlled by the biogeochemistry of sediment pore water.
Interpreting stable isotopes from macroinvertebrate foodwebs in saline wetlands
Authors: Hart E. Andrew , Lovvorn James R.
Published: June 2010

We compared stable‐isotope (δ13C and δ15N) and gut‐content analyses of macroinvertebrate foodwebs in saline wetlands of the Laramie Basin, Wyoming, USA. Standard assumptions of stable‐isotope fractionation between trophic levels (<1‰ for δ13C, mean of 3.4‰ for δ15N) suggested that zygopteran (damselfly) larvae consumed mainly amphipods. However, the guts of zygopterans contained no amphipods but rather a mix of chironomid larvae and zooplankton. In all wetlands the gut contents of zygopterans indicated that they were secondary consumers (trophic level 3), but enrichment of δ15N between zygopterans and their prey (Δδ15N) varied from 1 to 3.4‰ between wetlands. In other studies, such variation in Δδ15N has been interpreted to mean that food‐chain length differed between aquatic systems. We review alternative interpretations of variable 15N enrichment, namely, varying C:N ratios in food, differential enrichment between consumer species, and habitat‐specific variation of δ15N at the base of foodwebs. We also suggest that variation in the timing and rates of nitrogen cycling can affect measured Δδ15N both within and between foodwebs. For aquatic macroinvertebrates, we urge that stable isotopes be supplemented with independent observations to avoid incorrect conclusions about trophic pathways, trophic levels, and food‐chain lengths in different ecosystems.
Mortality estimates from age distributions: Critique of a method used to study seagrass dynamics
Authors: Ebert Thomas A. , Williams Susan L. , Ewanchuk Patrick J.
Published: June 2010

Age structure of seagrass samples has been used to estimate survival and recruitment and then used to estimate population growth rate. Survival rate can be estimated from age structure only if the population is neither growing nor declining (r = 0), so the age distribution is both stable and has stationary structure. If survival is estimated from age structure, it must be assumed that r = 0 or additional information about the population must be known. If a decaying exponential model is used for number (N) in each age class, ln N versus age has a slope of −(M + r), and so an incorrect survival rate, exp (−M), would be estimated if r ≠ 0. Simulations show that when r > 0, the slope of the regression of ln N versus age is too steep and hence mortality rate would be overestimated, and the reverse when r < 0. Ignoring the assumption of r = 0 is a fundamental flaw in many seagrass studies and calls into question the mortality and population growth rates that have been published.
Stage‐specific mortality of Calanus spp. under different predation regimes
Authors: Eiane Ketil , Aksnes Dag L. , Ohman Mark D. , Wood Simon , Martinussen Monica B.
Published: June 2010

We have applied the population surface method to estimate the mortality rates of eggs, nauplii, and copepodids of Calanus spp. in two Norwegian fjords with contrasting predator guilds. Efforts were concentrated in Lurefjorden on the western coast (sampled weekly from late February to mid‐June), an unusual fjord dominated by invertebrate (tactile) planktivores. In addition, monthly sampling in Sørfjorden was carried out for comparisons. The latter fjord resembles most Western Norwegian fjords in that it contains populations of vertebrate (visual) planktivores but lower abundance of the invertebrate planktivores. In Lurefjorden, mortality of Calanus spp. was high early in life (~0.35 d−1), but significantly lower (~0.00 d−1) in the early copepodid stages. In Sørfjorden, mortality was rather uniform throughout ontogeny (~0.08 d−1). The noted differences are consistent with different patterns of selective predation between the two fjords. Visual predation in SÄrfjorden gave rise to persistent high mortality over the life cycle. Tactile predation in Lurefjorden gave rise to a concave mortality curve for the later developmental stages. Our results indicate that mortality patterns suffered by natural zooplankton populations may differ greatly over short geographical distances, and we suggest that the predator community and mortality patterns must be considered when addressing the spatial and temporal dynamics of zooplankton populations.
Recruitment of intertidal invertebrates in the southeast Pacific: Interannual variability and the 1997–1998 El Niño
Authors: Navarrete Sergio A. , Broitman Bernardo , Wieters Evie A. , Finke Gerhard R. , Venegas Roberto M. , Sotomayor Alvaro
Published: June 2010

We evaluated interannual variability and the effect of the 1997–1998 El Niño event on recruitment of intertidal mussels and barnacles along the coast of central Chile in the southeast Pacific. Monthly monitoring of recruitment at 11 sites spread over 900 km (29–348S) during the 1997–1998 El Niño and over the same months in 1998–1999 and 1999–2000 allowed us to assess geographic patterns in interannual recruitment variation. The geographically most consistent interannual trend was observed for the mussel Perumytilus purpuratus, which showed overall lower recruitment rates during the 1997–1998 El Niño year. However, the magnitude of the effect at any given site was small. Interannual variation in recruitment rates of the other two intertidal mussel species, as well as two chthamaloid barnacles, were not consistent across the region, and overall, few sites exhibited significant differences among years. Differences between two and three orders of magnitude in mean annual recruitment of mussels and barnacles were observed among sites, yet the relative ranking of sites was fairly similar among years for most species. Contrary to the large positive effect that the 1997–1998 El Niño had on barnacle recruitment along the coast of central and northern California, our results show that recruitment of dominant intertidal barnacles along central Chile were not significantly altered by this strong oceanographic event. Lack of consistent trends among sites emphasizes the need to study several sites when looking at large‐scale oceanographic anomalies and shows that El Niño effects on interannual recruitment variation are not predictable.
The role of small‐scale sediment topography for oxygen flux across the diffusive boundary layer
Authors: Røy Hans , Hüttel Markus , Jørgensen Bo Barker
Published: June 2010

At the scale of centimeters or millimeters, marine sediment surfaces are sculptured into complex three‐dimensional landscapes. A detailed study of fluxes through the diffusive boundary layer (DBL) therefore requires concurrent information on the surface structure. Using natural sediment in a laboratory flume, we investigated the impact of small‐scale sediment topography on diffusive oxygen flux through the DBL. Topographic maps of the sediment surface with 0.1 mm horizontal resolution were acquired with a custom‐made optical technique, and immediately afterward the oxygen diffusion field across the sediment‐water interface was measured with microsensors in known orientation within the described topography. A method was developed to calculate the three‐dimensional diffusive flux through the DBL, based on the combination of vertical O2 microprofiles and the high‐resolution topographic data. Even though the sediment surface investigated was elaborately sculptured by fauna, the combined influence of increased surface area and horizontal concentration gradients within the DBL induced less than 10% difference between one‐dimensional and three‐dimensional diffusive flux calculations. The relatively low impact of surface topography is explained by the geometry of the diffusion field, as well as effects of the rapid diffusion of O2 at small scales.
Surface seiches in lakes of complex geometry
Authors: Rueda Francisco J. , Schladow S. Geoffrey
Published: June 2010

In lakes of small to medium size, the characteristic frequencies of free oscillations of the water surface (seiches) depend only on the basin geometry. In irregularly shaped basins, such as dendritic reservoirs and multibasin lakes, these characteristic frequencies are not easily determined with simple formulas. Clear Lake, a multibasin lake in Northern California, is presented here as a case in point. The signature of the seiches in Clear Lake were only revealed after solving the eigenvalue problem governing the structure and frequency of seiches derived from the linear and frictionless depth‐averaged shallow water equations in a nonrotating frame.
Sources of inorganic carbon for phytoplankton in the eastern Subtropical and Equatorial Pacific Ocean
Authors: Tortell Philippe D. , Morel François M. M.
Published: June 2010

We present the results of a field study examining inorganic carbon utilization by phytoplankton assemblages in the eastern Subtropical and Equatorial Pacific Ocean. Data from isotope disequilibrium experiments demonstrate that HCO3- was the principal form of inorganic carbon taken up by all of the in situ phytoplankton populations we sampled. In a cyanobacteria‐dominated assemblage, HCO3- uptake occurred chiefly through a direct transmembrane transport mechanism. Diatom‐dominated assemblages expressed extracellular carbonic anhydrase and transported CO2 derived from the catalyzed dehydration of HCO3-. Direct HCO3- transport by the diatoms may have also occurred. In a 3‐d incubation experiment, we observed the CO2‐dependent regulation of inorganic C uptake in diatom‐dominated phytoplankton assemblages. Phytoplankton assemblages grown at 150 ppm CO2 possessed external carbonic anhydrase activity and took up HCO3- following its dehydration to CO2. In contrast, the assemblages cultured with 750 ppm CO2 appeared to lack external carbonic anhydrase activity and rely solely on CO2 as an exogenous source of carbon for photosynthesis. The CO2 effect on inorganic C utilization occurred in the absence of a detectable difference in phytoplankton growth rates between the 150 and 750 ppm CO2 treatments. Our field data provide compelling evidence that HCO3- utilization is prevalent in natural marine phytoplankton communities and is regulated by ambient CO2 concentrations. We discuss the ecological and biogeochemical implications of these results.
Rapid deep‐water renewal in Lake Issyk‐Kul (Kyrgyzstan) indicated by transient tracers
Authors: Hofer Markus , Peeters Frank , Aeschbach-Hertig Werner , Brennwald Matthias , Holocher Johannes , Livingstone David M. , Romanovski Vladimir , Kipfer Rolf
Published: June 2010

Simultaneous profiles of the transient tracers sulfur hexafluoride (SF6), 3H‐3He, and the chlorofluorocarbons CFC‐11 and CFC‐12 were measured in Lake Issyk‐Kul, a large, deep lake in Kyrgyzstan. Apparent water ages derived from these measurements suggest rapid mixing, with a deepwater renewal rate >10% yr−1 at 650 m depth. SF6 and 3H‐3He ages agree reasonably well, whereas CFC ages are significantly greater. The discrepancy is explained by the nonlinear relationship between tracer age and tracer concentration and by the flattening of the atmospheric growth curves for CFCs. Novel to physical limnology is the application of SF6 dating, which proves to be an excellent tool for the study of mixing in lakes, complementing 3H‐3He and CFC dating techniques.
The interaction of phytoplankton and bacteria in a high mountain lake: Importance of the spectral composition of solar radiation
Authors: Carrillo Presentación , Medina-Sánchez Juan Manuel , Villar-Argaiz Manuel
Published: June 2010

The role of spectral composition of solar radiation has seldom been considered as a critical factor controlling the algae‐bacteria relationship. A coupled algae‐bacteria relationship mediated by C released from algae was observed during a 2‐yr period (1996–1997) in an oligotrophic high mountain lake, except at upper depths. The intensity of photosynthetically active radiation was negatively related to primary production, and the highest percentages of excretion of organic carbon (%EOC) from algae were found at upper depths of the water column. The effect of different spectral regions of solar radiation on the algae‐bacteria relationship was assessed by in situ experiments, in which the exposure, tracer uptake by target organisms, and interactions among abiotic and biotic factors were simultaneous. Primary production was ultraviolet radiation (UVR) inhibited by 33–83% depending on depth and date, with ultraviolet‐A radiation (UVA) exerting the main effect. EOC and %EOC yielded highest values under UVR exposure. Sunlight affected bacterial production (BP) only at upper depths. UVB inhibited BP by 39–82%, whereas UVA + photosynthetic active radiation (PAR) and PAR enhanced BP three‐ to fourfold. Full sunlight increased BP 2.5‐fold in midsummer but inhibited it (37%) in the late open‐water period. The percentage of photosynthetic exudates assimilated by bacteria, and photosynthetic carbon use efficiency by bacteria, showed a similar pattern to that of BP. The experimental results support our hypothesis that increased organic C release from UV‐stressed algae stimulates bacterial growth if the bacteria are relatively well adapted to sunlight, determining a coupled algae‐bacteria relationship. Thus, sunlight may play a key role as the underlying abiotic factor that regulates algae‐bacteria interaction in shallow and clear‐water ecosystems.
Interactive effect of temperature and food concentration on growth rate: A test case using the small freshwater ciliate Urotricha farcta
Authors: Weisse Thomas , Stadler Peter , LindstrÖm Eva S. , Kimmance Susan A. , Montagnes David J. S.
Published: June 2010

The combined effect of temperature and food concentration on the growth rate, cell volume, and production of the freshwater ciliate Urotricha farcta was investigated in laboratory batch cultures. Experimental temperatures ranged from 9 to 25°C and food levels ranged from 0.1 to 4.4 µg C ml-1. The ciliates were fed the small cryptophyte Cryptomonas sp. The combined effect of temperature and food on growth and cell volume resulted in negative production rates at high temperatures and low to moderate food supply. Three main changes were observed in the shape of the numerical response (growth vs. food concentration) of U. farcta with temperature: change in the threshold level, where population net growth rates are zero; change in the initial slope of the numerical response curve; and change in maximum growth rate ( mmax). The threshold food concentration and mmax were shifted up at the highest temperatures. The threshold level was also higher at the lowest experimental temperature. The initial slope of the numerical response curve was several‐fold lower at both high and low temperatures. The analysis suggests that temperature altered the numerical response so that the species shifted from being adapted to low food concentrations at moderate temperatures to requiring, and potentially thriving at, high food concentrations at the temperature extremes. These findings support and extend conclusions previously obtained for metazooplankton and indicate that changes as small as 38C could alter the role of protozoa in planktonic food webs.
Environmental and algal forcing of Daphnia production dynamics
Authors: Scheuerell Mark D. , Schindler Daniel E. , Litt Arni H. , Edmondson W. T.
Published: June 2010

Recent studies of lakes suggest that the relative availability of light and phosphorus in the mixed layer helps determine the quality of phytoplankton consumed by herbivorous zooplankton. In turn, increases in algal quality positively affect zooplankton growth and reproductive rates. However, these studies have concentrated on explaining variation among lakes over relatively short time periods and have not evaluated the temporal dynamics in the physical‐chemical forcing on zooplankton production. We investigated whether there were seasonal changes in the relationship between Daphnia fecundity and the physical‐chemical environment, algal community characteristics, and Daphnia length using dynamic linear models (DLM) to analyze a high‐resolution, 16‐yr time series from Lake Washington. We used two metrics to describe algal quality: the percentage of blue‐green algae and the light to total phosphorus (TP) ratio as an indirect metric for algal C: P. Chlorophyll a (Chl a) concentration and algal biovolume served as measures of algal quantity. As expected, both the light :TP ratio and the percentage of blue‐green algae had negative effects on Daphnia fecundity, and Chl a concentration and biovolume had positive effects on fecundity. However, we found a comparatively stronger effect of Daphnia length on fecundity, although it was negative and therefore opposite to expectation. In all cases, we observed strong seasonal differences in environmental effects, but no temporal change in the fundamental relationships between our indices of algal quantity and quality, allometry, and Daphnia reproduction. Our results support a hypothesis of physical‐chemical coupling to algal quality and zooplankton production but highlight the importance of temporal variation in this forcing.
Production in aquatic macrophyte communities: A theoretical and empirical study of the influence of spatial light distribution
Authors: Binzer Thomas , Sand‐Jensen Kaj
Published: June 2010

Many terrestrial plant canopies regulate spatial patterns in leaf density and leaf inclination to distribute light evenly between the photosynthetic tissue and to optimize light utilization efficiency. Sessile aquatic macrophytes, however, cannot maintain the same well‐defined three‐dimensional structure because of the strong drag and shear forces of moving water. This difference in canopy structure has been suggested to account for the three‐ to fivefold higher gross production rates in terrestrial than aquatic communities. To evaluate the effect of community structure in aquatic habitats, we combined a simple mechanistic model and empirical measurements on artificially structured macroalgal communities (Ulva lactuca) with varying thallus absorptance and community density. Predicted and measured values corresponded closely and revealed that gross production in high‐light environments was markedly enhanced by a vertical orientation of thalli when absorptance and community density were both high. This result implies that aquatic macrophytes of high thallus absorptance and community density exposed to high light are limited in attaining high gross production rates because of their inability to distribute photons evenly between the photosynthetic tissues. As scattering and attenuation in the water column increase, the effect of thallus structure on production declines and thin transparent macrophytes are more efficient at utilizing light than thick opaque macrophytes. The results confirm that inefficient distribution of light can account for the low community production rates in aquatic habitats and the depth distribution of form‐functional groups of macroalgae with different canopy structure.
Bidirectional reflectance measurements of sediments in the vicinity of Lee Stocking Island, Bahamas
Authors: Zhang Hao , Voss1 Kenneth J. , Reid R. Pamela , Louchard Eric M.
Published: June 2010

In situ measurements of bidirectional reflectance factors (REFFs) are presented for submerged carbonate sediments at six sites in the vicinity of Lee Stocking Island. Sediment grain sizes ranged from 400 µm to ≫1000 µm. Several features were common to all data sets. Although overall sediment reflectance varied spectrally, normalized REFF was independent of wavelength within the natural sample variability. This allowed us to derive a model REFF which, when multiplied by REFF(Θi = 0°, Θr = 45°, Ø) at a specific wavelength, represented the data well. In addition, normally illuminated samples were almost Lambertian, but samples with larger grain sizes had an REFF that decreased with increasing view angles. As the illumination angle increased, samples became increasingly non‐Lambertian. The dominant feature of the REFF in these non‐Lambertian surfaces is in the backscattering direction. In this direction the REFF was significantly larger than the nadir value. The largest backscattering REFFs correspond to large grain sizes and increases with increasing illumination angles. The empirical model, which represents the data within one standard deviation of sample variation, is presented for these sediments. This model is well behaved at angles out to 90° and thus can be used in radiative transfer models. This model provides a realistic bottom reflectance that can be used to improve light field predictions in shallow water.
Impact of West African Monsoon convective transport and lightning NOx production upon the upper tropospheric composition: a multi-model study
Authors: Barret B. , Williams J. E. , Bouarar I. , Yang X. , Josse B. , Law K. , Pham M. , Le Flochmoën E. , Liousse C. , Peuch V. H. , Carver G. D. , Pyle J. A. , Sauvage B. , van Velthoven P. , Schlager H. , Mari C. , Cammas J.-P.
Published: June 2010

Abstract. Within the African Monsoon Multidisciplinary Analysis (AMMA), we investigate the impact of nitrogen oxides produced by lightning (LiNOx) and convective transport during the West African Monsoon (WAM) upon the composition of the upper troposphere (UT) in the tropics. For this purpose, we have performed simulations with 4 state-of-the-art chemistry transport models involved within AMMA, namely MOCAGE, TM4, LMDz-INCA and p-TOMCAT. The model intercomparison is complemented with an evaluation of the simulations based on both spaceborne and airborne observations. The baseline simulations show important differences between the UT CO and O3 distributions simulated by each of the 4 models when compared to measurements from the MOZAIC program and fom the Aura/MLS spaceborne sensor. We show that such model discrepancies can be explained by differences in the convective transport parameterizations and, more particularly, the altitude reached by convective updrafts (ranging between ~200–125 hPa). Concerning UT O3, the models exhibit a good agreement with the main observed features. Nevertheless the majority of models simulate low O3 concentrations compared to both MOZAIC and Aura/MLS observations south of the equator, and rather high concentrations in the Northern Hemisphere. Sensitivity studies are performed to quantify the effect of deep convective transport and the influence of LiNOx production on the UT composition. These clearly indicate that the CO maxima and the elevated O3 concentrations south of the equator are due to convective uplift of air masses impacted by Southern African biomass burning, in agreement with previous studies. Moreover, during the WAM, LiNOx from Africa are responsible for the highest UT O3 enhancements (10–20 ppbv) over the tropical Atlantic between 10° S–20° N. Differences between models are primarily due to the performance of the parameterizations used to simulate lightning activity which are evaluated using spaceborne observations of flash frequency. Combined with comparisons of in-situ NO measurements we show that the models producing the highest amounts of LiNOx over Africa during the WAM (INCA and p-TOMCAT) capture observed NO profiles with the best accuracy, although they both overestimate lightning activity over the Sahel.
Estimated total emissions of trace gases from the Canberra Wildfires of 2003: a new method using satellite measurements of aerosol optical depth & the MOZART chemical transport model
Authors: Paton-Walsh C. , Emmons L. K. , Wilson S. R.
Published: June 2010

Abstract. In this paper we describe a new method for estimating trace gas emissions from large vegetation fires using satellite measurements of aerosol optical depth (AOD) at 550 nm, combined with an atmospheric chemical transport model. The method uses a threshold value to screen out normal levels of AOD that may be caused by raised dust, sea salt aerosols or diffuse smoke transported from distant fires. Using this method we infer an estimated total emission of 15±5 Tg of carbon monoxide, 0.05±0.02 Tg of hydrogen cyanide, 0.11±0.03 Tg of ammonia, 0.25±0.07 Tg of formaldehyde, 0.03±0.01 of acetylene, 0.10±0.03 Tg of ethylene, 0.03±0.01 Tg of ethane, 0.21±0.06 Tg of formic acid and 0.28±0.09 Tg of methanol released to the atmosphere from the Canberra fires of 2003. An assessment of the uncertainties in the new method is made and we show that our estimate agrees (within expected uncertainties) with estimates made using current conventional methods of multiplying together factors for the area burned, fuel load, the combustion efficiency and the emission factor for carbon monoxide. A simpler estimate derived directly from the satellite AOD measurements is also shown to be in agreement with conventional estimates, suggesting that the method may, under certain meteorological conditions, be applied without the complication of using a chemical transport model. The new method is suitable for estimating emissions from distinct large fire episodes and although it has some significant uncertainties, these are largely independent of the uncertainties inherent in conventional techniques. Thus we conclude that the new method is a useful additional tool for characterising emissions from vegetation fires.
Improvement and evaluation of simulated global biogenic soil NO emissions in an AC-GCM
Authors: Steinkamp J. , Lawrence M. G.
Published: June 2010

Abstract. Soil biogenic NO emissions (SNOx) play important direct and indirect roles in chemical processes of the troposphere. The most widely applied algorithm to calculate SNOx in global models was published 15 years ago by Yienger and Levy (1995), was based on very few measurements. Since then numerous new measurements have been published, which we used to build up a atabase of field measurements conducted world wide covering the period from 1978 to 2009, including 108 publications with 560 measurements. Recently, several satellite based top-down approaches, which recalculated the different sources of NOx (fossil fuel, biomass burning, soil and lightning), have shown an underestimation of SNOx by the algorithm of Yienger and Levy (1995). Nevertheless, to our knowledge no general improvements of this algorithm have yet been published. Here we present major improvements to the algorithm, which should help to optimize the representation of SNOx in atmospheric-chemistry global climate models, without modifying the underlying principal or mathematical equations. The changes include: 1) Using a new up to date land cover map, with twice the number of land cover classes, and using annually varying fertilizer application rates; 2) Adopting the fraction of SNOx induced by fertilizer application based on our database; 3) Switching from soil water column to volumetric soil moisture, to distinguish between the wet and dry state; 4) Tuning the emission factors to reproduce the measured emissions in our database and calculate the emissions based on their mean value. These steps lead us to increased global yearly SNOx, and our total SNOx source ends up being close to one of the top-down approaches. In some geographical regions the new results agree better with the top-down approach, but there are also distinct differences in other regions. This suggests that a ombination of both top-down and bottom-up approaches could be combined in a future attempt to provide an even better calculation of SNOx.
Sensitivity of precipitation forecasts to convective parameterization in the October 2007 Flash Flood in the Valencia Region (Eastern Spain)
Authors: Gómez I. , Pastor F. , Estrela M.
Published: June 2010

Abstract. The Valencia region, on the Mediterranean coast of the Iberian Peninsula, is an area prone to torrential rains, especially the north of Alicante province and the south of Valencia province. In October 2007, a torrential rain event with accumulated rainfall values exceeding 400 mm in less than 24 h affected the aforementioned areas, producing flash floods that caused extensive economic losses and human casualties. Several simulations of this rain event have been performed with the Regional Atmospheric Modeling System (RAMS) to test the influence of the different convective parameterization scheme implemented in the model on the precipitation forecast.
Thermophysical property anomalies of Baltic seawater
Authors: Feistel R. , Marion G. M. , Pawlowicz R. , Wright D. G.
Published: June 2010

Abstract. While the thermodynamic properties of Standard Seawater are very well known, the quantitative effect of sea salt composition anomalies on various properties is difficult to estimate since comprehensive lab experiments with the various natural waters are scarce. Coastal and estuarine waters exhibit significant anomalies which also influence to an unknown amount the routine salinity calculation from conductivity measurements. Recent numerical models of multi-component aqueous electrolytes permit the simulation of physical chemical properties of seawater with variable solute composition. In this paper, the FREZCHEM model is used to derive a Gibbs function for Baltic seawater, and the LSEA_DELS model to provide estimates for the conductivity anomaly relative to Standard Seawater. From additional information such as direct density measurements or empirical salinity anomaly parameterisation, the quantitative deviations of properties between Baltic and Standard Seawater are calculated as functions of salinity and temperature. While several quantities show anomalies that are comparable with their measurement uncertainties and do not demand special improvement, others exhibit more significant deviations from Standard Seawater properties. In particular density and sound speed turn out to be significantly sensitive to the presence of anomalous solute. Suitable general correction methods are suggested to be applied to Baltic Sea samples with known Practical Salinity and, optionally, directly determined density.
A numerical study of glacier advance over deforming till
Authors: Leysinger Vieli G. J.-M. C. , Gudmundsson G. H.
Published: June 2010

Abstract. The advance of a glacier over a deforming sediment layer is analysed numerically. We treat this problem as a contact problem involving two slowly-deforming viscous bodies. The surface evolution of both bodies, and that of the contact interface between them, is followed in time. Using various different till rheologies we show how the mode of advance depends on the relative effective viscosities of ice and till. Three modes of advances are observed: 1) overriding, where the glacier advances through ice deformation only and without deforming the sediment; 2) plug-flow, where the sediment is strongly deformed, the ice moves forward as a block and a bulge is built in front of the glacier; and 3) mixed-flow, where the glacier overrides deforming sediment. An inverse depth-age relationship is obtained for a glacier advance by both overriding and mixed-flow. An additional model experiment, using a till with near plastic rheology, shows that the contrast in effective viscosity between ice and till is the single most important model parameter defining the mode of advance and the resulting thickness distribution of the till. Furthermore, the model calculations imply that measurements of sediment thickness and sediment deformation taken close to the glacier front significantly overestimate the average sediment thickness and displacement due to sediment deformation. Given sufficiently large contrast in effective viscosity between ice and till, a sediment bulge is formed in front of the glacier. During glacier advance, the bulge quickly reaches a steady state form strongly resembling single-crested push moraines. Inspection of particle paths within the sediment bulge, shows the material particle of the till to travel at different speed to that of the bulge itself, and the push moraine to advance as a form-conserving non-linear wave.
Teilsicherheitsfaktoren für die Berechnung von Großkraftwerken
Authors: Glowienka Simon , Hansen Heribert
Published: June 2010

Die Baustrukturen von Großkraftwerken werden in Deutschland u. a. auf Basis der VGB‐Richtlinie R 602 U berechnet und bemessen. In dieser Richtlinie sind unter Berücksichtigung der Besonderheiten des Großkraftwerksbaus Einwirkungen und Teilsicherheitsfaktoren definiert. Während die Lasten auf diese Randbedingungen abgestimmt wurden, hat man die Teilsicherheitsfaktoren auf der Lastseite aus der DIN 1055‐100 entnommen und lediglich die Kombinationsbeiwerte angepasst. Diese Sicherheitsbeiwerte tragen jedoch den speziellen Randbedingungen eines Kraftwerks oder Schwerindustriebaus nur bedingt Rechnung. Im Rahmen des Beitrags werden die Teilsicherheitsbeiwerte auf der Einwirkungsseite – insbesondere für das Konstruktionseigengewicht – für die Bemessung von Stahlbetonteilen vor diesem Hintergrund kritisch diskutiert und ein optimierter, wissenschaftlich abgesicherter Vorschlag unterbreitet.

Partial Safety Factors for the Design of Power Plants

In Germany power plants are designed in accordance to VGB regulation R 602 U. In this code load actions and partial safety factors are applied taking the special characteristics of power plants into consideration. The actions are defined regarding these circumstances, however the safety coefficients are assumed according to DIN 1055‐100 and only the combination coefficients are adjusted. However it has to be recognized that the partial safety factors in DIN 1055‐100 are calibrated for building constructions and thus do not consider the specialities of power plants in an adequate manner. In this paper the partial safety factors for the design of power plants and other heavy industry buildings are discussed for structural concrete elements and a scientific based optimized approach for the safety factor for dead load is presented.
Grundlagen des Lebensdauermanagements im Kraftwerksbau
Authors: Pfister Tobias , Lehnen Dieter , Bockhold Jörg , Meyer Joachim
Published: June 2010

Der Begriff des “Lebensdauermanagements” rückt im Kraftwerksbau auch bei der Planung von Neubauten verstärkt in das Blickfeld der Betreiber. Darüber hinaus werden für Bestandsbauwerke unter dem Einfluss von Laufzeitverlängerungen Maßnahmen erforderlich, die die Restlebensdauer zuverlässig bewerten und sicherstellen können. Der vorliegende Beitrag zeichnet die rechtlichen Rahmenbedingungen nach, aus denen sich das Erfordernis eines aktiven Lebensdauermanagements ergibt und stellt die Vorgehensweise und grundlegenden Elemente einer derartigen begleitenden Überwachungsstrategie dar.

Fundamentals of Lifetime Management in Power Plants

The concept of “lifetime management” moves more and more into the focus of power plant owners, also in the context of new constructions. Additionally, for existing buildings there is a demand for methods, which are able to estimate the remaining lifetime in a reliable way. The present contribution collocates the legal general conditions, which lead to a requirement of an active lifetime management, and presents the procedure and basic elements of such an accompanying inspection strategy.
Querkraftbemessung von bügel‐ oder wendelbewehrten Bauteilen mit Kreisquerschnitt
Authors: Bender Michél , Mark Peter , Stangenberg Friedhelm
Published: June 2010

Für bügel‐ oder wendelbewehrte Stahlbetonbauteile mit Kreisquerschnitt – mit oder ohne zusätzlich drückenden Normalkräften – werden aus dem speziellen inneren Schubfluss die Spannungen in Bügeln und im geneigten Druckfeld abgeleitet und in Widerstandsgleichungen zur Querkraftbemessung umgesetzt. Die Gleichungen besitzen die bekannte Form aus DIN 1045‐1 bzw. EC2 und sind erweitert durch einen so genannten Wirksamkeitsfaktor, welcher die Widerstände gegenüber Rechteckquerschnitten auf rund 75% herabsetzt. Alternativ zur bekannten Gleichungsart wird eine additive Widerstandsform aus Betontraganteilen, Fachwerkwirkung und Sprengwerk für die maßgebende Zugstrebentragfähigkeit vorgeschlagen. Eine umfangreiche Versuchsserie verifiziert die Ansätze und zeigt Einzeleffekte von Bügelspannungen, Bewehrungsgrad und Bügelaktivierung sowie Wendel‐ und Normalkrafteinflüsse.

Shear Design of Members with Circular Sections Reinforced by Stirrups or Spirals

For RC members with circular sections the stresses within stirrups or spiral reinforcements as well as within the inclined compression field are derived from the specific inner shear flow and elaborated to gain equations for the shear resistances. The equations use the established scheme of DIN 1045‐1 or EC 2 extended by an efficiency factor reducing resistances compared to rectangular sections to about 75%. Alternatively, an additive approach for the resistance of the tensile strut is proposed. It sums up from concrete contributions, strut‐and‐tie actions as well as arch contributions introduced by axial forces. Both approaches are verified to experimental data taken from extensive test series. The characteristics of stirrup stresses and stirrup activation as well as effects from the shear reinforcement ratio, the use of inclined spirals and axial forces are presented.
Querkraftbemessung nach DIN 1045‐1
Authors: Heuer Andreas
Published: June 2010

Im vorliegenden Beitrag werden Arbeitshilfen für die Querkraftbemessung nach DIN 1045‐1 entwickelt. Unter Anwendung der vorgestellten Bemessungstabellen erfolgt die Bestimmung der Querkraftbewehrung auf sehr einfache Weise. Der Aufwand bei der Bemessung wird auf ein Minimum reduziert, positive Nebeneffekte bestehen in der Übersichtlichkeit und Wirtschaftlichkeit der Bemessungsergebnisse – auch bei Querkraft unter dem Einfluss von Längsspannungen.

Aus dem vorgestellten Nomogramm für Vollplatten lässt sich in Abhängigkeit vom Rechenwert der bezogenen Querkraft – τEd = VEd/z, der Betonfestigkeit und der statischen Höhe direkt bestimmten, welche Längsbewehrung erforderlich ist, um Querkraftbewehrung zu vermeiden.

Die wichtigsten Bemessungshilfen – Diagramme für Bauteile ohne Querkraftbewehrung sowie eine Bemessungstabelle für die Querkraftbemessung ohne Längskraft – sind im Anhang als Arbeitsblatt zusammengefasst.

Shear Force Design according to DIN 1045‐1. A simple procedure

In the present paper are deduced worksheets for lateral force design according to DIN 1045‐1. By using the tabulars the amount of shear reinforcement can be determined in a very simple way. There are positive side effects in the clarity and economy of the calculation results – even with shear force under the influence of longitudinal stresses.

Beside the tabulars a nomogram for the design of solid slabs is presented. It is possible to determine in a direct way the amount of main reinforcement, wich is required in order to eliminate the assembling of reinforcement stirrups in dependence on the related shear force – τEd = VEd/z, the concrete strength and the effective depth.

The basic measuring tools for the design without a longitudinal force are summarized in the annex as a worksheet.
ChemInform Abstract: Crystal Structure, Ferromagnetic Ordering and Magnetic Anisotropy for Two Cyano‐Bridged Bimetallic Compounds of Formula Mn2(H2O)5Mo (CN)7×nH2O.
Authors: LARIONOVA J. , SANCHIZ J. , GOHLEN S. , OUAHAB L. , KAHN O.
Published: June 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Dimeric and Polymeric Pnictidostannate(IV) Anions — Preparation and Crystal Structures of Na2K3[SnP3], Na2Cs3[SnP3] and Na2K3[SnBi3].
Authors: ASBRAND M. , EISENMANN B. , ENGELHARDT H. , ROESSLER U.
Published: June 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: (NH4)2Na3 (V3W3O19)×12H2O.
Authors: XU Y. , XU J.‐Q. , YANG G.‐Y. , WANG T.‐G. , XING Y. , LIN Y.‐H. , JIA H.‐Q.
Published: June 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Bright UV‐Blue Luminescent Colloidal ZnSe Nanocrystals.
Authors: HINES M. A. , GUYOT‐SIONNEST P.
Published: June 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.