bluuebunny/crossref_metadata_2025 huggingface dataset:
Design Process Innovation of Mechanical Objects with the Use of Design for Six Sigma Methodology
Authors: Koziołek Sebastian , Derlukiewicz Damian , Ptak M.
Published: June 2010

According to the strategy of Total Quality Management (TQM) [7] effective quality assurance of mechanical objects is maintained by means of permanent monitoring processes carried out in the cycle of product formation. The quality assessment of processes and the optimization of their crucial elements are the necessary condition for the improvement of efficiency and achievement of high level of customer satisfaction [15]. So far most of the techniques used for the process improvement are adopted to Lean Six Sigma methodology [1, 2, 11, 12, 17]. Achieving the quality on the level of 6 sigma is a primary goal of applying this methodology. Opinions exist that Lean Six Sigma should be implemented in the large number of areas of the life, and its effects (essential improvement in financial results through the reduction of poor quality costs) are hard to overrate. High effectiveness of every single process that is possible to achieve by applying the Lean Six Sigma strategy, became a source of inspiration for the study of Design For Six Sigma (DFSS) [4, 8, 12, 13], with purpose to improve object quality by implementing the innovation in product development.
Sensing of Carbon Dioxide and Hydrocarbons Using Photonic Bandgap Fiber
Authors: Pawłat Joanna , Li Xue Feng , Sugiyama Tadashi , Matsuo Takahiro , Zimin Yurij , Ueda Toshitsugu
Published: June 2010

The sensing setup for detection and measurement of carbon dioxide and methane was designed. Absorption spectra of many compounds indicate several weak peaks around 1400-1600 nm wavelength. Thus, tunable lasers with 20 micron core photonic bandgap fiber matching above wavelengths were chosen for the optical measurement system. Measurements were performed at low pressure to eliminate pressure broadening effect and to sharpen the absorption peaks. The angled cut was performed to improve signal to noise ratio.
The Biology of Myelodysplastic Syndromes: Unity Despite Heterogeneity
Authors: Raza Azra , Cruz Raymond , Latif Tahir , Mukherjee Siddhartha , Galili Naomi
Published: June 2010

Myelodysplastic syndromes (MDS) traditionally have been grouped together as a disease entity based on clinical phenomena seen in association. Despite the similarities, there is great heterogeneity among the syndromes. Recent insights have shown, however, that there exists a biologically cohesive theme that unifies and thereby validates the conceptual interconnectedness. The first suggestion that such a relationship existed where biology could directly explain the observed cytopenias was the finding of excessive premature apoptosis of hematopoietic cells in MDS marrows. This apoptosis was mediated by paracrine as well as autocrine factors implicating both the seed and the soil in the pathology of the disease. Pro-inflammatory cytokines in the marrow microenvironment were mainly the paracrine mediators of apoptosis, but how the clonal cells committed suicide because of autocrine stimulation had remained a mystery for more than a decade. It has been shown now that deregulation of ribosome biogenesis can initiate a stress response in the cell through the p53 signaling pathway. Congenital anemias had been associated with mutations in ribosomal protein genes. The surprise came with the investigation of 5q- syndrome patients where haplo-insufficiency of the ribosomal protein gene RPS14 was found to be the cause of this MDS subtype. Similar ribosomal deregulation was shown to be present in all varieties of MDS patients, serving as another unifying characteristic. In addition to these findings, there are other DNA-related abnormalities such as uniparental disomy, mutations in the TET2 gene, and epigenetic phenomena that are associated with and occur across all types of MDS. This paper summarizes the themes unifying this heterogeneous group of diseases.
Light‐induced redox cycling of iron in circumneutral lakes
Authors: Emmenegger Lukas , Schönenberger René , Sigg Laura , Sulzberger Barbara
Published: June 2010

The light‐induced redox cycling of FeII/FeIII was studied both in laboratory experiments and in the field in two circumneutral Swiss lakes: Greifensee, a eutrophic, natural water body, and Melchsee, an oligotrophic, artificial mountain lake. To determine FeII at the nanomolar level, an automated flow‐injection analysis system was used. Irradiation by simulated sunlight leads to pH dependent (pH 6.9–9.1) steady‐state FeII concentrations which are similar in samples from both lakes. However, the kinetics of FeIII reduction and of apparent Fe II oxidation are considerably faster in Melchsee. On the basis of experimental results and on modeling that uses literature values of known chemical transformation processes, we suggest that superoxide may be a key parameter for light‐induced iron redox cycling in these lakes. Field measurements of [FeII] in Greifensee and Melchsee show a pronounced day/night cycle, with FeII concentrations of ~0.1–0.2 nM at night and up to 0.9 nM near the surface during the day (pH 8.0–8.5). Depth profiles of [FeII] have two maxima: one at the surface and the second one at a depth of 5–10 m. Empirical rates and measured physical parameters were included in a model to simulate [FeII] as a function of time and depth. The model results indicate that FeII at the surface of both lakes is produced by light‐induced processes, whereas the deeper FeII maxima at depths with maximal chlorophyll a concentrations are probably due to a combination of biologically and photochemically induced processes.
Enhancement of coupled nitrification‐denitrification by benthic photosynthesis in shallow estuarine sediments
Authors: An Soonmo , Joye Samantha B.
Published: June 2010

Net sediment‐water interface fluxes of oxygen, dinitrogen, and dissolved inorganic carbon and nitrogen were determined in shallow, subtidal estuarine sediments (Galveston Bay, Texas) using in situ benthic chamber incubations. Diel variability in the sediment oxygen demand and in the flux of dinitrogen were attributable to the occurrence of benthic photosynthesis. Daytime denitrification rates exceeded nighttime rates. During daytime chamber incubations, small changes in dissolved oxygen concentration were observed. At night, oxygen concentrations decreased, as consumption reactions dominated the oxygen flux. Oxygen production by benthic microalgae enhanced rates of, and coupling between, nitrification and denitrification when ammonium was not limiting, resulting in significant loss of nitrogen from sediments as dinitrogen gas. A transient three box model was used to assess the effect of benthic primary production on sediment nitrogen cycling. Model results demonstrate increased rates of nitrification and denitrification in the presence of benthic photosynthesis and agree well with observed patterns of dissolved dinitrogen‐ and oxygen‐flux data obtained during benthic chamber incubations. When no photosynthesis was permitted during the model runs, rates of nitrification and denitrification decreased significantly. Together, our results suggest that denitrification estimates for shallow estuaries could be underestimated if the influence of benthic primary production on denitrification is not considered.
Light absorption and size scaling of light‐limited metabolism in marine diatoms
Authors: Finkel Zoe Vanessa
Published: June 2010

Previous studies have found that the size‐scaling exponent of metabolic rates in unicellular algae often deviates from the exponent of −1/4 usually found for heterotrophs. This study confirms a significant linear relationship between log cell volume (mm3) and log intrinsic growth rate (h−1), carbon‐normalized photosynthetic capacity and performance (h−1), and carbon−normalized respiratory rate (h−1) for eight marine centric diatoms under nutrient−saturated, light‐limited conditions. The intrinsic growth rate and carbon‐normalized respiratory rate have size‐scaling exponents not significantly different from −1/4, whereas the carbon‐specific photosynthetic rates deviate from −1/4. The size dependence of the optical absorption cross section (m2 mg chlorophyll a−1) due to the package effect provides a mechanistic model that explains the anomalous size scaling of the anabolic rates of unicellular phytoplankton.
Quantifying bioirrigation in aquatic sediments: An inverse modeling approach
Authors: Meile Christof , Koretsky Carla M. , Cappellen Philippe Van
Published: June 2010

An inverse model was developed to quantify the depth distributions of bioirrigation intensities in sediments based on measured solute concentration and reaction rate profiles. The model computes statistically optimal bioirrigation coefficient profiles; that is, profiles that best represent measured data with the least number of adjustable parameters. A parameter reduction routine weighs the goodness‐of‐fit of calculated concentration profiles against the number of adjustable parameters by performing statistical F‐tests, whereas Monte Carlo simulations reduce the effects of spatial correlation and help avoid local minima encountered by the downhill simplex optimization algorithm. A quality function allows identification of depth intervals where bioirrigation coefficients are not well constrained. The inverse model was applied to four different depositional environments (Sapelo Island, Georgia; Buzzards Bay, Massachusetts; Washington Shelf; Svalbard, Norway) using total CO2 production, sulfate reduction, and 222Rn/226Ra disequilibrium data. Calculated bioirrigation coefficients generally decreased rapidly as a function of depth, but distinct subsurface maxima were observed for sites in Buzzards Bay and along the Washington Shelf. Irrigation fluxes of O2 computed with the model‐derived bioirrigation coefficients were in good agreement with those obtained by difference between total benthic O2 fluxes measured with benthic chambers and diffusive fluxes calculated from O2 microprofiles.
An invasion history for Cercopagis pengoi based on mitochondrial gene sequences
Authors: Cristescu Melania E. A. , Hebert Paul D. N. , Witt Jonathan D. S. , MacIsaac Hugh J. , Grigorovich Igor A.
Published: June 2010

The predatory cladoceran Cercopagis pengoi has extended its range over the past decade from the Ponto‐Caspian basin into the Baltic Sea and the Laurentian Great Lakes. This study employs mitochondrial DNA (mtDNA) sequence analysis to elucidate the invasion corridors exploited during this range expansion. The Caspian and Black Sea populations of C. pengoi exhibit marked genetic divergence, enabling their discrimination as potential sources of the Baltic and Great Lakes populations. The limited mtDNA haplotype diversity detected in the Baltic populations suggests they were founded by a small number of colonists from the Black Sea. The colonization of North America was apparently a result of the transfer of animals from the Baltic Sea in ballast water.
Littoral zone structures as Daphnia refugia against fish predators
Authors: Burks Romi L. , Jeppesen Erik , Lodge David M.
Published: June 2010

The assumption that macrophytes can provide zooplankton a daytime refuge against fish predation is central to the diel horizontal migration hypothesis. However, previous observations and experiments have shown that largeߚbodied zooplankton avoid macrophytes. To directly test these contrasting roles of macrophytes, we measured the reaction of Daphnia pulex to macrophytes (Elodea canadensis or plastic) in the presence and absence of chemical cues from two commonly occurring European fishes, roach (Rutilus rutilus) and perch (Perca fluvialitis). In the same series of laboratory experiments, we then tested the ability of different densities of E. canadensis and plastic macrophytes to reduce predation by roach or perch. In the absence of fish, only 27% of daphnids occurred in the macrophytes. However, 70–80% of daphnids occurred in the macrophytes when either roach or perch occurred. In addition, significantly more daphnids occurred in plastic versus real macrophytes, indicating that some chemically mediated avoidance of real macrophytes by Daphnia occurred. In the presence of fish chemical cues from either roach or perch, the differences between real and plastic macrophytes quickly disappeared as daphnids moved into macrophytes. However, this behavior decreased mortality only from roach predation, because perch spent significantly more time than roach foraging among macrophytes. Thus, although daphnids sought macrophyte refuge in the presence of both fishes, the effectiveness of the refuge depended on macrophyte density and predator identity. These results support the idea that macrophytes can increase survival of Daphnia populations in shallow lakes, depending on the fish species present.
Growth rates of large and small Southern Ocean diatoms in relation to availability o iron in natural seawater
Authors: Timmermans Klaas R. , Gerringa Loes J. A. , de Baar Hein J. W. , van der Wagt Bas , Veldhuis Marcel J. W. , de Jong Jeroen T. M. , Croot Peter L. , Boye Marie
Published: June 2010

Blooms of large diatoms dominate the CO2 drawdown and silicon cycle of the Southern Ocean in both the past and present. The growth of these Antarctic diatoms is limited by availability of iron (and light). Here we report the first assessment of growth rates in relation to iron availability of two truly oceanic Antarctic diatom species, the large, chain‐forming diatom Chaetoceros dichaeta and the small, unicellular diatom C. brevis. In Filtered natural, untreated Southern Ocean water, a maximum specific growth rate of 0.62 ± 0.09 d−1 and a Km for growth of 1.12 x 109 M dissolved iron was calculated for C. dichaeta. This response could only be seen during a long‐day light period. C. brevis maintained growth rates of 0.39 ± 0.09 d−1 with and without iron addition, even under short‐day light conditions, and could only be forced into iron limitation by adding the siderophore desferri‐ferrioxamine B (DFB), an iron immobilizing agent. Using this approach, the low Km value for growth of 0.59 × 10−12 M dissolved Fe was calculated for this species. The size‐class dependent growth response to iron (and light) confirms the key role of these parameters in structuring Southern Ocean ecosystems and thus the CO2 dynamics and the silicon cycle.
Production of colloidal organic carbon and trace metals by phytoplankton decomposition
Authors: Wang Wen-Xiong , Guo Laodong
Published: June 2010

Colloids are important intermediates and can considerably influence the biogeochemical cycling of organic carbon and trace metals in aquatic systems. Previous studies have determined the release of carbon and trace elements from decomposing phytoplankton debris, but the degradation of biogenic particles to colloids and their significance in metal and carbon cycling remain unknown. In this study, we measured the release of carbon and trace elements (Cd, Cr, Se, and Zn) from the debris of two phytoplankton (diatom Thalassiosira pseudonana, and dinoflagellate Prorocentrum minimum) into a colloidal phase (operationally defined as 5 kDa–0.2 mm). In general, Cd, Se, and Zn were released at a faster rate and Cr was released at a slower rate than the release of C from the decomposing debris into the dissolved phase (<0.2 mm). Release of trace metals appeared to closely follow C release. The release rate coefficients of Cd, Cr, Se, Zn, and C in the two phytoplankton debris with microbial addition were 1.67–1.68 d−1 for Cd, 0.147–0.239 d−1 for Cr, 0.712–0.845 d−1 for Se, 0.765–1.14 d−1 for Zn, and 0.443–0.512 d−1 for C. The percentages of trace elements (Cr, Se, Zn) and C associated with the colloidal phase were relatively high within the first 5 d ofdecomposition. After 5 d, the fraction of colloidal trace elements in the <0.2–µm dissolved phase was 5–10% for Cd, 13–52% for Cr, 13–28% for Se, 14–30% for Zn, and 16–41% for C in the diatom decomposing experiment; and 4–9% for Cd, 15–62% for Cr, 15–31% for Se, 3–27% for Zn, and 22–38% for C in the dinoflagellate decomposing experiment, respectively. The partitioning of metals in the colloidal phase was not greatly affected by the microbial activity. Although the overall percentage of organic carbon release was related to that of metals from decomposing debris, no significant correlation between the percentages of colloidal metals and colloidal organic carbon was observed, implying that organic C and metals have different partitioning behavior during their release from decomposing phytoplankton debris. Our study demonstrated that the decomposition of biogenic particles may contribute considerably to the production of colloids in marine environments.
Linkages among the bioreactivity, chemical composition, and diagenetic state of marine dissolved organic matter
Authors: Amon Rainer M. W. , Fitznar Hans-Peter , Benner Ronald
Published: June 2010

Bacterial growth and the chemical composition of dissolved organic matter (DOM) were followed during a 10ߚd decomposition experiment with fresh, algalߚ;derived DOM from an Arctic ice floe. During the experiment ~30% of the dissolved organic carbon (DOC) was used by bacteria, indicating the highly reactive nature of this fresh DOM. Over half of the DOC consumption was accounted for as losses of combined neutral sugars and amino acids. The initial composition of the DOM was characterized by high neutral sugar (14% DOC) and amino acid (7.4% DOC) yields and the dominance of glucose (~75 mol%) and glutamic acid (~25 mol%). During microbial degߚradation the neutral sugar and amino acid yields decreased, and the molecular composition of the DOM became more uniform. The relatively constant abundance of D amino acids and the dramatic changes in the neutral sugar and amino acid compositions indicated that bacteria were important in shaping the chemical composition of marine DOM by selectively removing bioreactive components and by leaving behind biorefractory components. Based on principal component analysis and other parameters, neutral sugars and amino acids were found to be excellent indicators of the diagenetic state and bioavailability of marine DOM.
Mixing and turbulent fluxes in the metalimnion of a stratified lake
Authors: Saggio Angelo , Imberger Jörg
Published: June 2010

Turbulent mixing within the metalimnion of a stratified lake was investigated using a portable flux profiler (PFP) capable of resolving all three components of the velocities, the conductivity, and the temperature microstructure. Presented is a detailed description of the techniques used in the data processing, particularly in the separation of the turbulence from the internal wave signal. The sampling, carried out in Lake Kinneret (Israel) during the summer for 3 consecutive years, showed that most of the time the vertical flux through the metalimnion was negligible, but, at times, the eddy diffusivity did reach values as high as 10−2 m2 s−1. A comparison between direct measurement of the vertical fluxes obtained from the PFP data with that from indirect estimates of the fluxes shows good agreement for the 6 ≪= Frg ≪100 range. Scaling of the turbulence based on Frg and Ri reveal two classes of turbulent regimes: (1) due to traumata characteristic of internal wave‐wave interaction and, another, (2) more energetic and due to shear‐driven turbulence. The PFP penetrated the water relatively slowly (0.1 m s−1) allowing the measurement of temperature fluctuations down to 1 mm and, at the same time, also providing information of the velocity fluctuations. This is different from previous oceanographic measurements, which are always gathered with instrument traversing the water column at velocities closer to 1 m s−1, preventing regime (1) from being detected.
Bivalve diets in a midwestern U.S. stream: A stable isotope enrichment study
Authors: Raikow David F. , Hamilton Stephen K.
Published: June 2010

This study examined a community of stream bivalves (unionids and fingernail clams) in a second‐order woodland stream in southern Michigan using both the natural abundance of 15N and a 6‐week whole‐stream 15N enrichment experiment, as part of the Lotic Intersite Nitrogen eXperiment (LINX). Objectives included addressing what made up the diet of these bivalves and whether suspended algae consumed by bivalves were derived from pelagic phytoplankton imported from an upstream lake or attached algae sloughed from instream surfaces. Within the examination of bivalve diets, we considered whether suspension‐ and/or deposit‐feeding modes were employed and whether bivalves selectively assimilated the algal and microbial portions of bulk material they ingested. All 12 unionid species reached a level of 15N enrichment greater than the bulk suspended organic matter. Sphaerium striatinum (Sphaeriidae) were enriched to levels greater than all presumed food sources. Suspended algae were derived both from sloughed epilithon and pelagic phytoplankton originating from lentic waters upstream. A mixing model suggested that unionids were consuming 80% deposited and 20% suspended material. Alternatively, these bivalves were preferentially assimilating the highly enriched living component of suspended and/or benthic organic matter rather than assimilating the bulk material. These results advance our understanding of freshwater bivalve‐feeding ecology, which is necessary if conservation efforts of these increasingly threatened organisms are to succeed.
Wholeߚstream metabolism in two montane streams: Contribution of the hyporheic zone
Authors: Fellows Christine S. , Valett Maurice H. , Dahm Clifford N.
Published: June 2010

We used whole‐stream and benthic chamber methods to measure rates of metabolism and determine the contribution of the hyporheic zone to ecosystem respiration (R) in two streams with differing surface‐subsurface exchange characteristics, Rio Calaveras and Gallina Creek, New Mexico. We used the difference between whole‐stream and benthic R to calculate the rate of hyporheic zone R and coupled this estimate to an independent measure of hyporheic sediment R to estimate the cross‐sectional area of the hyporheic zone (AH) for two reaches from each stream. Conservative tracer injections and solute transport modeling were used to characterize surface‐subsurface hydrologic exchange by determining values of the cross‐sectional area of the transient storage zone (As). The hyporheic zone contributed a substantial proportion of whole‐stream R in all four study reaches, ranging from 40 to 93%. Whole­stream R, hyporheic R, and percent contribution of hyporheic R all increased as transient storage increased, with whole‐stream and hyporheic R exhibiting significant relationships with As. All three measures of respiration and values of AH were much greater for both reaches of the stream with greater surface‐subsurface exchange. AH is valuable for cross‐site comparisons because it accounts for differences in rates of both benthic and hyporheic sediment R and can be used to predict the importance of the hyporheic zone to other stream ecosystem processes.
Unusual bacterioplankton community structure in ultra‐oligotrophic Crater Lake
Authors: Urbach Ena , Vergin Kevin L. , Young Lei , Morse Ariel , Larson Gary L. , Giovannoni Stephen J.
Published: June 2010

The bacterioplankton assemblage in Crater Lake, Oregon (U.S.A.), is different from communities found in other oxygenated lakes, as demonstrated by four small subunit ribosomal ribonucleic acid (SSU rRNA) gene clone libraries and oligonucleotide probe hybridization to RNA from lake water. Populations in the euphotic zone of this deep (589 m), oligotrophic caldera lake are dominated by two phylogenetic clusters of currently uncultivated bacteria: CL120–10, a newly identified cluster in the verrucomicrobiales, and ACK4 actinomycetes, known as a minor constituent of bacterioplankton in other lakes. Deep‐water populations at 300 and 500 m are dominated by a different pair of uncultivated taxa: CL500–11, a novel cluster in the green nonsulfur bacteria, and group I marine crenarchaeota. b‐Proteobacteria, dominant in most other freshwater environments, are relatively rare in Crater Lake (<=16% of nonchloroplast bacterial rRNA at all depths). Other taxa identified in Crater Lake libraries include a newly identified candidate bacterial division, ABY1, and a newly identified subcluster, CL0–1, within candidate division OP10. Probe analyses confirmed vertical stratification of several microbial groups, similar to patterns observed in open‐ocean systems. Additional similarities between Crater Lake and ocean microbial populations include aphotic zone dominance of group I marine crenarchaeota and green nonsulfur bacteria. Comparison of Crater Lake to other lakes studied by rRNA methods suggests that selective factors structuring Crater Lake bacterioplankton populations may include low concentrations of available trace metals and dissolved organic matter, chemistry of infiltrating hydrothermal waters, and irradiation by high levels of ultraviolet light.
Sources and sinks of dissolved free amino acids and protein in a large and deep mesotrophic lake
Authors: Rosenstock Bernd , Simon Meinhard
Published: June 2010

We studied the microbial cycling of dissolved free amino acids (DFAAs) and protein in mesotrophic Lake Constance, Germany, by examining their release by phytoplankton and various heterotrophic organisms and incorporation by heterotrophic bacterioplankton. Release processes of both substrate classes, measured by an isotope dilution approach, comprised, as an annual mean, 15% of primary production and as much as 64% during the clear‐water phase. DFAAs accounted for ~70% of total release during the spring bloom, in the early phase predominantly as photosynthetic extracellular products of rapidly growing algae and toward the end as a result of copepod grazing. Thereafter, during the clear‐water phase, when daphnids were most abundant, release was dominated by protein. At this time, and again in late summer, lysis of grazing‐damaged and senescent algae, including as well the hydrolytic activity of attached bacteria was one of the most important sources of protein. Rotifers, protozoans, and release processes in the fraction <1 ³m were minor sources of DFAA + protein. Concentrations of dissolved combined amino acids (DCAAs) and protein ranged between 750−1,900 and 1−280 nM, respectively, and peaked duringphytoplankton blooms in spring and summer. As an annual mean, concentrations of labile protein constituted 8% of DCAAs, and the ratio of DFAAs to DCAAs was 0.16. About 50% of the DCAAs occurred in the molecular weight fraction between DFAA and 3 kDa and 30% in that >30 kDa. Concentrations of DCAAs >3 kDa were closely correlated to chlorophyll a, suggesting their phytoplankton origin and thus a ready availability. Protein was the preferred bacterial substrate. As an annual mean, its incorporation supported 45% of bacterial biomass produc­tion, compared with 13% by DFAAs. During winter and spring, when DFAA concentrations were highest, DFAA incorporation constituted up to 40% of bacterial production. Annually, the sum of DFAA + protein supported 58% and 80% of the bacterial C and N demand, respectively, indicating that they were the most important bacterial C and N sources.
Langmuir circulations disturb the low‐oxygen refuge of phantom midge larvae
Authors: Malinen Tommi , Horppila Jukka , Liljendahl-Nurminen Anne
Published: June 2010

The previously unknown effects of wind‐induced Langmuir circulations on the distribution of phantom midge larvae (Chaoborus flavicans) were studied by echosounding. The study was carried out in the eutrophic Lake Hiidenvesi, where chaoborids use a metalimnetic oxygen minimum as a daytime refuge against fish predation. At a wind velocity of 8—9 m s−1, the upwelling water circulations snatched clouds of chaoborids from the metalimnion (12‐15 m depth) to the more oxygenated epilimnion. The average density of C. flavicans in the clouds was 790 ind. m−2, whereas, elsewhere in the epilimnion, it was 380 ind. m−2. Planktivorous fish (smelt Osmerus eperlanus) were actively aggregated in the upwellings. When the wind velocity decreased to 3 m s−1, chaoborids disappeared from the epilimnion. The results suggest that Langmuir circulations may affect the abundance of chaoborids by disturbing their low‐oxygen refuges.
A preliminary assessment of the geochemical dynamics of Issyk‐Kul Lake, Kirghizstan
Authors: Lyons W. B. , Welch K. A. , Bonzongo J.-C. , Graham E. Y. , Shabunin G. , Gaudette H. E. , Poreda R. J.
Published: June 2010

Issyk‐Kul Lake is one of the largest brackish water lakes in the world. Being a closed‐basin lake, it is susceptible to volume changes caused by natural climatic variability, as well as human‐induced water diversion from the basin. Long‐term lake level records indicate that lake levels are declining and that salinity is increasing because of evapoconcentration. We present the first trace element data for this important lacustrine system and, using both ours and previously published data, investigate the geochemical dynamics within the watershed.
Organic particles in a shallow sediment trap: Substantial loss to the dissolved phase
Authors: Kähler Paul , Bauerfeind Eduard
Published: June 2010

We used multivariate statistics to divide the solubilized organic matter in a shallow time‐series trap into fractions derived from swimmers and from the passive flux. Most of the dissolved organic matter in the traps originated from swimmers, but the contribution from passively trapped material was also substantial. Accounting for this fraction attributable to the passively trapped material yields a vertical organic carbon flux 2.7 times larger than the conventional estimate, which is based on recovered particles only. For organic nitrogen, this correction is even greater (six times). Solubilization is a fast process that is significant within a few days.
Biogeochemical and physical factors influencing seawater ƒCO2 and air‐sea CO2 exchange on the Bermuda coral reef
Authors: Bates Nicholas R. , Samuels Leone , Merlivat Liliane
Published: June 2010

It is uncertain whether coral reef ecosystems are oceanic sources or sinks of carbon dioxide (CO2). Understanding the complex interactions between biogeochemical and physical processes within reef ecosystems is important for determining the contribution of coral reefs to the global carbon cycle and the air‐sea flux of CO2 . The influence of biogeochemical and physical processes on CO2 cycling was examined for 1 month at Hog Reef Flat, part of the rim reef of Bermuda. The fugacity of seawater CO2 (CO2) was measured hourly by use of a Carbon Interface Ocean Atmosphere buoy, providing the longest time series of seawater CO2 data on a coral reef ecosystem. Seawater CO2 ranged from ~340 to 470 µatm, with a diurnal variability ranging from ~20–60 µatm. Air‐sea CO2 was directed from ocean to atmosphere with a mean flux of 3.3 ± 4.6 mmoles CO2 m−2 d−1. The reef data are compared with a seawater CO2 time series collected at the U.S. Joint Global Ocean Flux Study Bermuda Atlantic Time‐series Study (BATS) site (31°50'N, 64°10'W) in the Sargasso Sea surrounding Bermuda. Sargasso Sea waters are the original source for Bermuda platform water, providing a context for understanding the biogeochemical modification of reef water at Hog Reef Flat. Seawater fCO2 at Hog Reef Flat was elevated relative to the Sargasso Sea by ~0 to ~120 µatm, primarily as a result of calcium carbonate production. However, the ability of the reef to act either as a source or sink of CO2 to/from the atmosphere largely depended on the air‐sea CO2 disequilibrium of offshore Sargasso Sea waters impinging on the reef site. This study also revealed that an assessment of the fate of CO2 on coral reefs is dependent on understanding the reef's physical regime and forcing. The dynamics of wind, tide, platform circulation, and fluxes of offshore or onshore waters are necessary context for all coral reef sites.
Carbon dioxide and methane evasion from a temperate peatland stream
Authors: Hope Diane , Palmer Sheila M. , Billett Michael F. , Dawson Julian J. C.
Published: June 2010

Peatland streams potentially represent important conduits for the exchange of gaseous carbon between the terrestrial ecosystem and the atmosphere. We investigated how gaseous evasion of carbon from the stream surface compared with downstream carbon transport at three locations on a Scottish headwater stream. Carbon dioxide was consistently above atmospheric saturation in the stream, with mean concentrations of 159.1, 81.8, and 29.5 µmol L−1 at the lower, middle, and upper sites, respectively (i.e., 7.6, 3.9, and 1.2 times in excess of atmospheric equilibrium concentrations). Methane concentrations in stream water were much lower but showed a similar pattern. Rates of gaseous evasion from the stream surface to the atmosphere, determined experimentally using direct measurement of dissolved gas concentrations in conjunction with coinjection of conservative solute and volatile gas tracers, also declined downstream. Combined stream losses of all forms of carbon from the entire catchment (i.e., degassing from the stream surface and exports downstream) totaled 54,140 kg C yr−1. Evasion of carbon dioxide from the stream surface accounted for 34% of this total, compared to 57% lost as dissolved organic carbon via export downstream. When expressed per unit area of watershed, the gaseous C evasion from the stream represents a loss of 14.1 g C m−2 yr−1, which equals 28–70% of the estimated net carbon accumulation rate for such peatlands. This study shows that gaseous carbon loss from the surface of temperate headwater streams can be both spatially variable and significant in terms of rates of net annual land surface‐atmosphere exchange at the catchment scale.
Use of size spectra and empirical models to evaluate trophic relationships in streams
Authors: Morin Antoine , Bourassa Nathalie , Cattaneo Antonella
Published: June 2010

We measured the biomass size distributions of algae, protozoa, and invertebrates in several streams of Eastern Ontario and Western Quebec and related assemblage biomass to nutrient (nitrogen and phosphorus) concentrations in the water. Size spectra and measurement of periphytic chlorophyll were then combined with existing empirical models to estimate primary production, invertebrate production, and grazer removal, to examine herbivory in these natural assemblages. In general, biomass of organisms increased with nutrients but the response of invertebrates was stronger than that of algae and protozoans. Secondary production (range 1.7%–4.2%) and algal removal by grazers (range 62%–175%) were high relative to primary production. This suggests that grazers exert top‐down control on algae in these streams and that increases in nutrient inputs to oligo‐ and mesotrophic streams may benefit consumers more than primary producers.
Carbon dioxide partial pressure and 13C content of north temperate and boreal lakes at spring ice melt
Authors: Striegl Robert G. , Kortelainen Pirkko , Chanton Jeffrey P. , Wickland Kimberly P. , Bugna Glynnis C. , Rantakari Miitta
Published: June 2010

Carbon dioxide (CO2) accumulates under lake ice in winter and degasses to the atmosphere after ice melt. This large springtime CO2 pulse is not typically considered in surface‐atmosphere flux estimates, because most field studies have not sampled through ice during late winter. Measured CO2 partial pressure (pCO2) of lake surface water ranged from 8.6 to 4,290 Pa (85–4,230 µatm) in 234 north temperate and boreal lakes prior to ice melt during 1998 and 1999. Only four lakes had surface pCO2 less than or equal to atmospheric pCO2, whereas 75% had pCO2 >5 times atmospheric. The δ13CDIC (DIC = ΣCO2) of 142 of the lakes ranged from –26.28‰ to +0.95‰. Lakes with the greatest pCO2 also had the lightest δ13CDIC, which indicates respiration as their primary CO2 source. Finnish lakes that received large amounts of dissolved organic carbon from surrounding peatlands had the greatest pCO2. Lakes set in noncarbonate till and bedrock in Minnesota and Wisconsin had the smallest pCO2 and the heaviest d13CDIC, which indicates atmospheric and/or mineral sources of C for those lakes. Potential emissions for the period after ice melt were 2.36 ± 1.44 mol CO2 m−2 for lakes with average pCO2 values and were as large as 13.7 ± 8.4 mol CO2 m−2 for lakes with high pCO2 values.
The influence of filter‐feeding benthic macroinvertebrates on the transport and deposition of particulate organic matter and diatoms in two streams
Authors: Monaghan Michael T. , Thomas Steven A. , Minshall G. Wayne , Newbold J. Denis , Cushing Colbert E.
Published: June 2010

The transport and deposition of particulate organic matter (POM) in streams has received much attention in recent years. As with many ecosystem processes, determining the relative importance of physical and biological mechanisms for POM removal (e.g., sedimentation and filter‐feeding) remains an important task. We examined the influence of benthic filter‐feeding Hydropsyche and Simuliidae on downstream transport distance (SP) and deposition rate (vdep) of POM in two streams. We conducted five field experiments using radiolabeled (14C) natural detritus and living diatoms (Asterionella) to measure longitudinal loss (kP m−1 = 1/SP) before and after complete removal of filter‐feeding benthic macroinvertebrates. kP decreased following filter‐feeder removal in each experiment, although meta‐analysis indicated no consistent nonzero effect. However, the changes in kP were within the range to be expected from previously published rates of capture by the filter‐feeders, indicating limited statistical power. We also examined uptake of radiolabeled POM by filter‐feeders in three of the experiments. Simuliidae radioactivity increased significantly during two of the three releases of POM, although uptake accounted for up to 11% of wholestream POM deposition. Our results suggest that transported POM and diatoms are deposited from the water column rapidly and that mechanisms other than filter‐feeding by invertebrates are responsible for most of the transfer of POM from the water column to the sediments of streams.
Impact of bottom trawling on water turbidity and muddy sediment of an unfished continental shelf
Authors: Palanques A. , Guillén J. , Puig P.
Published: June 2010

Two experiments were carried out to study the effects of trawling in the muddy prodeltaic deposit of the Llobregat River in the northwestern Mediterranean. Trawling was conducted in two experimental lines, and bottom morphology, sediment texture, and water turbidity were analyzed before trawling and at different time intervals afterward. The tracks of the trawl gears were still observed in sonographs of the bottom 1 yr after the first experiment. The vertical grain size distribution of bottom deposits indicated that the thickness of the sediment removed by the net between the gears was about 2–3 cm on average, though the erosion produced by the gears was deeper. Resuspended aggregates with a high silt content settled during the first hour after trawling, generating a temporary increase in the silt content of the surface sediment. One day after trawling, the surface sediment was mixed and already had a similar grain size distribution to that before trawling. After the beginning of trawling, water turbidity increased first near the bottom for a few hours and later also at shallower levels of the water column within a period of 2–5 d after trawling. At the end of the experiment, about 10% of the sediment affected by trawling was diffused in the water column and the remaining 90% had settled on the bottom. Average turbidity in the water column increased by a factor of up to three for 4–5 d after trawling. This experiment shows that intense and continued trawling on continental shelves has a noticeable effect on water turbidity, which must be considered in addition to natural processes.
Phytoplankton phosphorus deficiency and alkaline phosphatase activity in the McMurdo Dry Valley lakes, Antarctica
Authors: Dore John E. , Priscu John C.
Published: June 2010

We assessed the nutrient (N, P) deficiency of phytoplankton from the perennially iceߚcovered lakes in Taylor Valley, Antarctica, with 14Cߚbased bioassays. Phytoplankton in the nearߚsurface waters from three of the four lakes displayed elevated photosynthetic carbon assimilation in the presence of added P relative to controls. Carbon assimilation in samples from deep chlorophyll layers was also enhanced by P addition in two of the lakes. No effect of N addition without simultaneous P addition was noted in any lake. Lake Bonney nearߚsurface phytoplankton consistently showed a strong response to P and N + P additions, suggesting P deficiency. The nearߚsurface phytoplankton of Lake Hoare responded to N + P but not N or P addition alone, suggesting a more general nutrient deficiency. Further investigation of phytoplankton phosphorus deficiency was carried out in the east lobe of Lake Bonney and in Lake Hoare. Water column dissolved and sestonic elemental ratios and planktonic alkaline phosphatase activity measurements corroborated the results of the bioassays. Despite the proximity of the lakes and their similarity in ice cover and watershed, a high degree of phytoplankton phosphorus deficiency was evident in Lake Bonney but not in Lake Hoare. We hypothesize that the difference in the degree of phytoplankton P deficiency between these lakes may not be due to differences in external P fluxes, but rather to differences in the internal cycling of phosphorus stemming from large differences in water column chemistry.
Bacterial influence on amino acid enantiomerization in a coastal marine sediment
Authors: Pedersen Anna-Grethe U. , Thomsen Trine R. , Lomstein Bente Aa. , Jørgensen Niels O. G.
Published: June 2010

The contribution of Dߚisomers of aspartate (Asp), glutamate (Glu), alanine (Ala), and serine (Ser) to the total concentrations of dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA), and total hydrolyzable amino acids (THAA) was studied in a <2,300ߚyrߚold coastal sediment. Concentrations of the different amino acid pools were typically 5 (DFAA), 100 (DCAA), and 20,000 nmol cmߚ3 (THAA), but variable amounts occurred, especially in the surface layer. Dߚamino acids were identified in all three amino acid fractions. The highest concentration of Dߚisomers occurred in the THAA fraction at a depth of 10 cm, where the maximum bacterial density has been observed (Jørgensen et al. 1990; Mar. Ecol. Prog. Ser. 59: 39–54). This coincidence suggests that the Dߚamino acids originated in peptidoglycan of bacterial cell walls. The proportion of DߚAsp, DߚGlu, DߚAla, and DߚSer increased through the pools of DFAA and DCAA to THAA, suggesting a selective removal of Lߚamino acids to Dߚamino acids. The percentage of the four Dߚamino acids in the THAA pool increased with sediment depth to at least 4.3 m (∼2,150 yr). This most likely indicated that peptidoglycan THAA were retained for a longer period of time in a particulate form compared to other proteinaceous material. The contribution of THAA from peptidoglycan to the THAA pool was estimated to range from >9% at the surface to at least 18% at 4.3 m deep, depending on the assumptions used in the calculation. The distribution of amino acid isomers in Aarhus Bay sediment demonstrated that bacterial peptidoglycan contributed to the pool of organic nitrogen (the four analyzed Dߚamino acids made up about 3% of particulate organic nitrogen [PON]). Although the peptidoglycan concentration increased with sediment depth, our observations do not indicate a longߚterm accumulation of peptidoglycanߚderived amino acids.
Dissolved organic carbon production by microbial populations in the Atlantic Ocean
Authors: Teira Eva , José Pazó María , Serret Pablo , Fernández Emilio
Published: June 2010

Dissolved organic carbon (DOC) production by microbial populations was measured at 19 stations in the Atlantic Ocean to quantify the fraction of photoassimilated carbon that flows through the dissolved organic pool at basin scale and to assess the relationship between the percentage of DOC production, phytoplankton size structure, and rates of net community production. Experiments were conducted during four cruises carried out between May 1998 and October 1999, covering three upwelling regions: Benguela (SW Africa), Mauritania (NW Africa) and NW Spain, and the oligotrophic North Atlantic subtropical gyre between 30°N and 36°N. Photic zone integrated particulate organic carbon (POC) production rates ranged from 10 to 1,178 mg C m−2 h−1, thus covering a wide productivity spectrum. The percentage of DOC production with respect to total integrated primary production ranged from 4 to 42%, being larger in oligotrophic, picoplanktonߚdominated waters, where a balanced metabolism of the microbial community was observed, than in productive, net autotrophic waters, where largeߚsized cells formed the bulk of the phytoplankton biomass. A highly significant relationship was calculated between DOC and POC production rates in upwelling conditions. By contrast, the relationship between these variables in oligotrophic environments was weak, which suggests that different processes could be controlling the release of dissolved organic matter in productive and unproductive waters.
Dissolved inorganic carbon in a highly polluted estuary (the Scheldt)
Authors: Hellings L. , Dehairs F. , Van Damme S. , Baeyens W.
Published: June 2010

During 34 months (1996–1999), we studied the dissolved inorganic carbon (DIC) system of the highly polluted Scheldt River and upper estuary. DIC ranged between 3,300 and 7,100 µM, with highest values in winter and lowest in summer. For the brackish and freshwater section of the river Δ13CDIC values ranged from −7.5 to −17.5‰, the most negative signals were during winter and the least negative during summer. In all seasons, surface waters were significantly supersaturated in CO2 with respect to the atmosphere (pCO2 ranged from 2,200 to a maximum of 15,500 µatm) indicating that the system is always heterotrophic. Biological processes (respiration and carbon fixation) and CO2 evasion to the atmosphere affected the isotopic composition and magnitude of the inorganic carbon pool. In spring and summer 1997 and 1998, large phytoplankton biomasses (>100 mg chlorophyll a [Chl a] L−1) coincided with lower pCO2 and CO2 waterߚair efflux and less negative Δ13CDIC values, indicating considerable CO2 drawdown by phytoplankton. Mass balance calculations indicated that organic carbon to DIC conversion exceeded CO2 consumption year round, (net organic carbon conversion ranged from 410 to 520 g C m−2 yr−1) emphasizing the effect of bacterial respiration. An intermediate river section receiving water from the main tributary (Rupel), which carries wastewater from the densely populated Brussels region, consistently showed decreased DIC, increased pCO2, and depletion in Δ13CDIC relative to the main river system.
Vertical distribution and mortality of overwintering Calanus
Authors: Bag×ien Espen , Kaartvedt Stein , Aksnes Dag L. , Eiane Ketil
Published: June 2010

Overwintering Calanus spp. were studied in four Norwegian fjords with different predator regimes and ranging in depth from 380 to 1300 m. Three fjords held both the planktivorous mesopelagic fish Maurolicus muelleri and Benthosema glaciale and invertebrate predators, whereas one lacked mesopelagic fish but had especially high abundance of several invertebrate predators. Co‐occurrence of C. finmarchicus, C. helgolandicus, and C. glacialis rendered distinction between effects of environmental conditions and inherent species properties in choice of depth difficult. The highest daily per capita mortality rate for Calanus was estimated at 0.024–0.027 d‐1 (95% CI) in a fjord with high fish abundance and with the clearest water. Predation by M. muelleri and B. glaciale alone could explain the estimated winter mortality. The fjord devoid of mesopelagic fish but particularly rich in invertebrate predators gave the lowest estimated mortality rate; 0.008–0.009 d‐1 (95% CI). Our results indicate that mesopelagic fish pose a stronger predatory threat than invertebrates to overwintering Calanus. This concurs with Calanus selection of oceanic winter habitats below depths where planktivorous fish can forage efficiently by sight.