bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-term Effects of LASIK on Corneal Innervation and Tear Neuropeptides and the Associations With Dry Eye
Authors: Chao Cecilia , Golebiowski Blanka , Zhao Xiangtian , Chen Shihao , Zhou Shi , Stapleton Fiona
Published: August 2016

PURPOSE:

To investigate the associations between dry eye, corneal nerves, and tear neuroptides in dry eye after LASIK.

METHODS:

A single visit cross-sectional study was performed. Twenty participants who had LASIK more than 12 months prior and 20 healthy participants were recruited. Ocular comfort, tear functions, ocular surface sensitivity, basal tear collection, and corneal nerve morphology assessments were conducted. Tear substance P and calcitonin gene-related peptide (CGRP) concentrations were determined using ELISAs. Differences in variables between groups were examined using an independent
t
test or Mann–Whitney
U
test, as appropriate. Associations between variables in the post-LASIK group were examined using a Spearman's correlation test. A
P
value of less than .05 was considered significant.

RESULTS:

Central corneal nerve morphology parameters were all altered in the post-LASIK group (
P
< .05). Higher ocular discomfort (
P
= .01), tear CGRP concentration (
P
= .001), and conjunctival sensitivity (
P
< .009) were found in the post-LASIK group. There was a positive association between dry eye symptoms and superior corneal sensitivity (
P
= .51,
P
= .02) and tear substance P concentration (
P
= .52,
P
< .03).

CONCLUSIONS:

This study provides evidence of the association between tear neuropeptides, conjunctival sensitivity, and symptoms in symptomatic patients after LASIK. The differences in nerve morphology, neuropeptide, and ocular surface sensitivity between symptomatic and asymptomatic patients after LASIK are required to better understand the mechanism of dry eye after LASIK.

[
J Refract Surg
. 2016;32(8):518–524.]
Decision Making Approach using Weighted Coefficient of Correlation along with Generalized Parametric Fuzzy Entropy Measure
Authors: Gupta Priti , Tiwari Pratiksha
Published: August 2016

Decision making involves various attributes along with several decision takers. Recently it has become more complex. This gives raise to uncertainty and associated with the information provided. So it may be appropriate to suggest that uncertainty demonstrates itself in numerous forms and of different types. Uncertainties may arise due to human behaviour, fluctuations of information, unknown facts. Fuzzy set theory is tool to deal with uncertainty in a better way. Both Fuzzy set theory and information theory are involved in dealing with various real-world problems such as segmentation of images, medical diagnosis, managerial decision making etc. Several methods and concepts dealing with imprecision and uncertainty have been proposed by many researchers. In the present communication, the authors have proposed a parametric generalization of entropy introduced by De Luca and Termini along with its basic properties. Further, a new measure of weighted coefficient of correlation is developed and applied to solve decision making problems involving uncertainty.
A Fuzzy Expert System for Star Classification Based on Photometry
Authors: Pakniyat Aida , Hosseini Rahil , Mazinai Mahdi
Published: August 2016

The application of fuzzy systems is emerging in science where experts' knowledge plays a vital role. This paper utilizes the capability of fuzzy set theory for managing uncertainty associated to star classification problem. The fuzzy classifies uses a dataset of stars obtained from Harvard classification. This paper, for the first time, presents fuzzy starts classification based on photometry. For performance evaluation, an ROC analysis was performed. The results reveal a classifier with an accuracy of 83.5% and with the 72% area under the ROC curve. The mean square error (MSE) was ?3.77*10?^(-5) which reveals superiority of the proposed fuzzy expert system compared to the other classification methods.
Linking Natural Modeling to Techno-centric Modeling for the Active Involvement of Process Participants in Business Process Design
Authors: Oppl Stefan , Alexopoulou Nancy
Published: August 2016

Actively involving participants in business process modeling enables integration between elicitation and modeling steps of the BPM lifecycle. Such integration may lead to a more efficient design procedure and ultimately to a more accurate representation of the business process. However, active involvement of process participants creates several challenges, as the latter are not expected to have modeling skills. The purpose of this paper is to present a business process design approach, called CoMPArE /WP, which tightly integrates the elicitation and modeling stages of process design, through the active involvement of process participants. To achieve effective involvement of process participants, CoMPArE/WP adopts the principles of natural modeling. However, being a business process design approach aiming at supporting the whole BPM lifecycle, CoMPArE /WP deals also with the transition of natural modeling to formal process representations that can be enacted using a BPMS.
Automating the Migration of Enterprise Architecture Models
Authors: Silva Nuno , Ferreira Francisco , Sousa Pedro , Mira da Silva Miguel
Published: August 2016

The evolution of Enterprise Architectures (EA) is the result of applying EA development projects within organizations with the goal of accomplishing specific business requirements. Recent approaches seek to automate and improve EA practice within organizations by employing EA management tools. Thus, evolving the organization's EA meta-model is a consequence of fulfilling such initiatives. Currently, the migration of EA models conforming to a specific EA meta-model evolution is a manual task in which EA data corresponding to the actual models is gathered and the models re-designed. This results in an error-prone and time-consuming task. To address this issue, the authors propose a set of migration rules to automate the migration process. The proposed migration rules were implemented within an EA tool and then demonstrated and validated using a fictitious organization migration scenario.
Individual Learning Strategies and Choice in Student-Generated Multimedia
Authors: McGahan William T. , Ernst Hardy , Dyson Laurel Evelyn
Published: August 2016

There has been an increasing focus on student-generated multimedia assessment as a way of introducing the benefits of both visual literacy and peer-mediated learning into university courses. One such assessment was offered to first-year health science students but, contrary to expectations, led to poorer performance in their end-of-semester examinations. Following an analysis, the assignment was redesigned to offer students a choice of either a group-based animation task or an individual written task. Results showed improved performance on the assignment when students were offered a choice of assignments over when they were offered only the multimedia assignment. Student feedback indicated that students adopt deliberate individual learning strategies when offered choices in assessment. The study suggests that assumptions regarding the superiority of student-generated multimedia over more traditional assessments are not always correct, but that students' agency and individual preferences need to be recognized.
Emerging Cloud Computing Services
Authors: Yao Yulin
Published: August 2016

Cloud Computing has offered many services to organizations and individuals. The emerging types of services such as analytics, mobile services and emerging software as a service have been offered but there is a lack of analysis on the current status. Core technologies for emerging Cloud services have been identified and presented. This brief opinion paper provides an overview of the current emerging Cloud services and explains the benefits for several disciplines. Four areas have been identified that may bring in more positive impacts for the future direction.
Interpreting Experiences of Students Using Educational Online Technologies to Interact with Students in Blended Tertiary Environments
Authors: Tuapawa Kimberley
Published: August 2016

This paper is part of a phenomenological study that examined teachers' and students' experiences using educational online technologies (EOTs) in blended tertiary environments (BTEs). Its aim was to understand how EOT engagement was experienced, to inform insights on EOT interactions, challenges, functionality and benefits. Phenomenological interviews were conducted with 10 teachers and 10 students from New Zealand and Australia, and their EOT experiences explored, under a range of different interactions. This paper reports on students' EOT interactions with other students, in reference to four types of EOTs: Online conference tools (Adobe Connect), learning management systems (LMS) (Blackboard, Moodle), online social networks (Facebook), and online collaboration tools (Google Docs). This research helps tertiary education institutes (TEIs) understand how, why and where EOT support for stakeholders is necessary. The outcomes assist TEIs to design approaches to tackle EOT challenges, deliver meaningful EOT support, and inform institutional strategies to strengthen the future of BTEs.
Immunotherapy Expands and Maintains the Function of High-Affinity Tumor-Infiltrating CD8 T Cells In Situ
Authors: Moran Amy E. , Polesso Fanny , Weinberg Andrew D.
Published: August 2016

Cancer cells harbor high-affinity tumor-associated Ags capable of eliciting potent antitumor T cell responses, yet detecting these polyclonal T cells is challenging. Therefore, surrogate markers of T cell activation such as CD69, CD44, and programmed death-1 (PD-1) have been used. We report in this study that in mice, expression of activation markers including PD-1 is insufficient in the tumor microenvironment to identify tumor Ag-specific T cells. Using the Nur77GFP T cell affinity reporter mouse, we highlight that PD-1 expression can be induced independent of TCR ligation within the tumor. Given this, we characterized the utility of the Nur77GFP model system in elucidating mechanisms of action of immunotherapies independent of PD-1 expression. Coexpression of Nur77GFP and OX40 identifies a polyclonal population of high-affinity tumor-associated Ag-specific CD8+ T cells, which produce more IFN-γ in situ than OX40 negative and doubles in quantity with anti-OX40 and anti-CTLA4 mAb therapy but not with anti–PD-1 or programmed death ligand-1. Moreover, expansion of these high-affinity CD8 T cells prolongs survival of tumor-bearing animals. Upon chronic stimulation in tumors and after adoptive cell therapy, CD8 TCR signaling and Nur77GFP induction is impaired, and tumors progress. However, this can be reversed and overall survival significantly enhanced after adoptive cell therapy with agonist OX40 immunotherapy. Therefore, we propose that OX40 agonist immunotherapy can maintain functional TCR signaling of chronically stimulated tumor-resident CD8 T cells, thereby increasing the frequency of cytotoxic, high-affinity, tumor-associated Ag-specific cells.
Schistosoma mansoni in Gabon: Emerging or Ignored?
Authors: Červená Barbora , Brant Sara Vanessa , Fairet Emilie , Shirley Matthew H. , Petrželková Klára Judita , Modrý David
Published: August 2016

Schistosomiasis affects millions of people across Africa. We detected eggs of Schistosoma mansoni in western lowland gorilla and central chimpanzee fecal samples in Loango National Park, Gabon. We analyzed nuclear and mitochondrial DNA, namely internal transcribed spacer and cytochrome c oxidase subunit 1 fragments, and the resulting maximum likelihood phylogenetic analyses and haplotype network of the ITS and COI, respectively, showed that the samples from gorillas and chimpanzees clustered clearly within the S. mansoni clade. This is the first confirmed record of S. mansoni from Gabon, which urges surveillance in the area and prompts questions regarding the extent of zoonotic transmission and the clinical impact.
Learnings From the Pilot Implementation of Mobile Medical Milestones Application
Authors: Page Cristen P. , Reid Alfred , Coe Catherine L. , Carlough Martha , Rosenbaum Daryl , Beste Janalynn , Fagan Blake , Steinbacher Erika , Jones Geoffrey , Newton Warren P.
Published: August 2016

Background 

Implementation of the educational milestones benefits from mobile technology that facilitates ready assessments in the clinical environment. We developed a point-of-care resident evaluation tool, the Mobile Medical Milestones Application (M3App), and piloted it in 8 North Carolina family medicine residency programs.

Objective 

We sought to examine variations we found in the use of the tool across programs and explored the experiences of program directors, faculty, and residents to better understand the perceived benefits and challenges of implementing the new tool.

Methods 

Residents and faculty completed presurveys and postsurveys about the tool and the evaluation process in their program. Program directors were interviewed individually. Interviews and open-ended survey responses were analyzed and coded using the constant comparative method, and responses were tabulated under themes.

Results 

Common perceptions included increased data collection, enhanced efficiency, and increased perceived quality of the information gathered with the M3App. Residents appreciated the timely, high-quality feedback they received. Faculty reported becoming more comfortable with the tool over time, and a more favorable evaluation of the tool was associated with higher utilization. Program directors reported improvements in faculty knowledge of the milestones and resident satisfaction with feedback.

Conclusions 

Faculty and residents credited the M3App with improving the quality and efficiency of resident feedback. Residents appreciated the frequency, proximity, and specificity of feedback, and faculty reported the app improved their familiarity with the milestones. Implementation challenges included lack of a physician champion and competing demands on faculty time.
SOME CHARACTERISTICS OF “FISHBITE” DAMAGE ON DEEP‐SEA MOORING LINES1
Authors: Turner Harry J. , Prindle Bryce
Published: August 2016

Moored deep‐sea installations are frequently set adrift when their synthetic fiber mooring lines are bitten by some organism, presumably a fish. Some information on the causative organism has been obtained by mooring buoys in 2,000 m of water near Bermuda with lines sheathed or coated with plastic materials that took dental impressions. The evidence provided by this material suggests that the causative organism is active from 150 to over 1,500 m in depth, with the greatest concentration from 600 to 1,000 m. The jaw ranges from 30 to slightly over 100 mm in width and the teeth are located either in the upper or lower jaw but not both. The teeth are sharp with a fine. band of rounded serrations along the cutting edge.
OBSERVATIONS ON THE ANALYSIS OF IRON IN SEAWATER WITH PARTICULAR REFERENCE TO ESTUARINE WATERS1
Authors: BURTON J. D. , HEAD P. C.
Published: August 2016

Certain aspects of the analysis of particulate and soluble iron in estuarine waters have been investigated. Determinations of total particulate iron by the method of Lewis and Goldberg showed an average coefficient of variation of about 8%. It is suggested that this degree of variability is attributable to sampling errors and inhomogeneity of iron in the particulate matter. The use of thioglycollic acid to render iron reactive has been examined for the measurement of total soluble iron. The method gave reproducible blank values and an average coefficient of variation of about 9% under normal laboratory conditions. The accuracy of the procedure may be affected by incomplete recovery of iron in some organic compounds and by positive interference from copper, which, however, exceeds 10% only when the weight ratio of copper to iron is greater than 7. On the basis of experiments with 59Fe as a tracer, it is recommended that filtered samples be acidified to about pH 2 if they must be stored before analysis.
Nutrient limitation of phytoplankton in freshwater and marine environments: A review of recent evidence on the effects of enrichment1
Authors: Hecky R. E. , Kilham P.
Published: August 2016

Phytoplankton can become limited by the availability of nutrients when light and temperature are adequate and loss rates are not excessive. The current paradigms for nutrient limitations in freshwater, estuarine, and marine environments are quite different. A review of the experimental and observational data used to infer P or N limitation of phytoplankton growth indicates that P limitation in freshwater environments can be demonstrated rigorously at several hierarchical levels of system complexity, from algal cultures to whole lakes. A similarly rigorous demonstration of N limitation has not been achieved for marine waters. Therefore, we conclude that the extent and severity of N limitation in the marine environment remain an open question. Culture studies have established that internal cellular concentrations of nutrients determine phytoplankton growth rates, and these studies have shown that it is often difficult to relate growth rates to external concentrations, especially in natural situations. This should lead to a greater reliance on the composition of particulate matter and biomass‐based physiological rates to infer nutrient limitation. Such measurements have demonstrated their utility in a wide variety of freshwater and marine environments, and, most importantly, they can be applied to systems that are difficult to manipulate experimentally or budget accurately. Dissolved nutrient concentrations are most useful in determining nutrient loading rates of aquatic ecosystems. The relative proportions of nutrients supplied to phytoplankton can be a strong selective force shaping phytoplankton communities and affecting the biomass yield per unit of limiting nutrient.
The ecological role of chemical stimuli for the zooplankton: Predator‐avoidance behavior in Daphnia
Authors: Dodson Stanley
Published: August 2016

Eight different clones (seven species) of Daphnia had behavioral responses to fish and invertebrate predators. The behavioral response was measured in the laboratory as a change in the average population depth, relative to controls, when exposed to a predator. Behavior for each clone was tested with three common predators: Chaoborus, Lepomis, and Notonecta. Each Daphnia clone responded to at least one predator. Some clones responded to all three predators. The responses are both predator and. prey‐specific. The stimulus produced by the predator is a water‐soluble chemical that persists for up to 7 h in the laboratory. The number of predator species to which a clone responds shows a positive correlation with average body size of the Daphnia. Number of responses per clone is independent of lake size, although there was a tendency (not statistically significant) for the number of responses to decrease with lake size. Behavioral responses may be components of diel vertical migration and horizontal distribution patterns seen in nature.
Stable isotope evidence for alternative bacterial carbon sources in the Gulf of Mexico
Authors: Kelleyl Cheryl A. , CofJin Richard B. , Cifuentes Luis A.
Published: August 2016

In temperate coastal waters, it is generally assumed that carbon cycling is primarily supported by phytoplankton production, having δ13C values ranging from −22 to −18‰. In a transect leading out from the Mississippi River, riverine and seawater δ13C endmembers of particulate organic matter have previously been measured at −25.5 and −20.0‰, respectively. In addition, δ13C values of dissolved organic carbon in the northern Gulf of Mexico range from −24.7 to −19.6‰, with the more 13C‐depleted values from fresher waters. Assumptions about coastal transport of dissolved organic matter predict that the bacterial δ13C values should fall along the conservative salinity mixing line between terrestrial and marine carbon sources. However, in the field survey presented here, δ13C values of bacteria in coastal regions of the Gulf of Mexico adjacent to the Mississippi River are considerably 13C‐depleted, with values as low as −33‰. These isotope values suggest that carbon from sources other than phytoplankton production or terrestrial organic matter are supporting the production of the bacterial assemblage. Possibilities include the incorporation of carbon derived from light hydrocarbons from seep areas and the chemoautotrophic processes of methane oxidation and nitrification. These 13C‐depleted stable isotope data are evidence that bacterially assimilated carbon in the northern Gulf of Mexico may be seasonally uncoupled to surface phytoplankton production.
Absorbance, absorption coefficient, and apparent quantum yield: A comment on common ambiguity in the use of these optical concepts
Authors: Hu Chuanmin , Muller-Karger Frank E. , Zepp Richard G.
Published: August 2016

Several important optical terms, such as “absorbance” and “absorption coefficient,” are frequently used ambiguously in the current peer‐reviewed literature. Because these terms are important when deriving other quantities, such as the apparent quantum yield of photoproduction, ambiguity in the application of these concepts leads to results that are difficult or impossible to interpret correctly. Such ambiguity also hinders comparison of results between studies and ultimately harms proper parameterization of numerical models of oceanic processes, as well as the refinement of remote sensing algorithms. We review these concepts and the implications of such ambiguities. A few simple recommendations that follow conventions developed by optical oceanographers are provided to authors dealing with these concepts. In particular, the symbol a is recommended for the absorption coefficient (in Napierian form, m−1), which is also preferred over absorbance (dimensionless) when data are presented; the symbol a is not recommended for absorbance; A should be used with caution because, although it has been used widely for absorbance in photochemistry and photobiology, it has also been used for absorptance in physics and optical oceanography; the term “absorptivity” is not recommended because of conflicting definitions in the current literature; the pathlength should always be given whenever absorbance data are presented; and normalization of photoproduction rates to absorbance or absorption coefficient should be performed only on optically thin samples, unless the inner filter effects are accounted for and corrected.
Inorganic carbon and biological oceanography above a shallow oxygen minimum in the entrance to the Gulf of California in the Mexican Pacific
Authors: Maske Helmut , Medrano Ramón Cajal , Castro Armando Trasviña , Mercado Alejandrina Jiménez , Almeda Jauregui Cesar O. , Castro Gilberto Gaxiola , Ochoa José
Published: August 2016

The eastern Pacific intermediate oxygen minimum layer (OML) is particularly well‐developed and shoals close to the Mexican coast. We obtained hydrographic profiles including oxygen concentration [O], measured dissolved inorganic carbon (DIC), continuous surface pCO2 in water and air and took biological data south of the Gulf of California in March 2005. The core of the OML, with close to zero [O] was centered around 475 m with a thickness of the core varying between 80 m and 700 m and the upper limit of the core ranging from 500 m to 80 m. At the surface [O] was close to air‐saturation and showed no relation with the depth of the OML contrary to DIC and pCO2 concentrations. Below 50‐m depth the changes in DIC and Apparent Oxygen Utilization (AOU) yielding a molar ratio of δDIC = 0.79 x δAOU. When the OML shoaled, surface temperature, chlorophyll concentration [CHL], and depth‐integrated zooplankton increased, resulting in positive correlations among plankton biomass, pCO2, and DIC in surface waters. When [CHL] is recalculated as particulate organic carbon (POC), a linear relationship with the sum of DIC and POC is observed as expected for concomitant transport of DIC and inorganic nutrients supporting POC formation. Neglecting ventilation of carbon into the atmosphere and the production of dissolved organic carbon, the results suggested that ~16% of the carbon transported up from the OML was present in surface waters in the form of POC and the rest in inorganic form.
Production, dissolution, accumulation, and potential export of biogenic silica in a Sargasso Sea mode‐water eddy
Authors: Krause Jeffrey W. , Nelson David M. , Lomas Michael W.
Published: August 2016

Rates of biogenic silica (bSiO2) production, dissolution, accumulation, and potential bSiO2 export were determined in a Sargasso Sea mode‐water eddy (MWE) during two occupations in April 2007. Standing stocks and production rates of bSiO2 within the MWE were 15–20 mmol Si m−2 and 0.8–1.1 mmol Si m−2 d−1, respectively; these values were about six times those reported in April at the nearby Bermuda Atlantic Time‐series Study (BATS) site. The MWE also showed positive net bSiO2 production in the upper 140 m (> 0.5 mmol Si m−2 d−1 produced during both occupations), and thus a capacity for bSiO2 accumulation and export. Consistent with previous observations in eddies, the diatom community was dramatically different from that typically observed at the BATS site; diatom abundances were an order of magnitude higher, and larger forms (e.g., Chaetoceros sp.) were prominent. When accounting for both the loss of bSiO2 (between occupations) and the observed positive net bSiO2 production within the MWE, the estimated bSiO2 export rate (1.27 mmol Si m−2 d−1) was twenty times higher than the mean export flux measured at the BATS site with no bloom in progress. If similar processes occur in eddies of other types, then these mesoscale features may be quantitatively important in the regional silica balance, with a strong coupling between increased bSiO2 export and altered diatom community structure.
Direct and indirect coupling of primary production and diel nitrate dynamics in a subtropical spring‐fed river
Authors: Heffernan James B. , Cohen Matthew J.
Published: August 2016

We used high‐frequency in situ measurements of nitrate (NO3−) and dissolved oxygen (DO) from the springfed Ichetucknee River, Florida, to derive multiple independent estimates of assimilatory nitrogen (N) demand, and to evaluate the short‐term dependence of heterotrophic assimilation and dissimilation (e.g., denitrification) on gross primary productivity (GPP). Autotrophic N assimilation estimates derived from diel DO variability and GPP stoichiometry agreed closely with estimates based on integration of diel variation in NO3− concentration, although the correspondence of these metrics depended on the method used to estimate NO3− baselines. In addition, day‐to‐day changes in nocturnal NO3− concentration maxima were strongly negatively correlated with day‐to‐day changes in GPP. Diel temperature variation in the Ichetucknee River indicated that this pattern could not be explained by hydrologic dispersion, while relationships between N assimilation and O2 production at hourly intervals indicated minimal physiological lags. The estimated magnitude of heterotrophic assimilation was small, indicating that the relationship between changes in GPP and changes in nocturnal NO3− maxima reflects sensitivity of denitrification to variation in exudation of labile organic matter by primary producers. We estimate that ~ 35% of denitrification may be fueled by the previous day’s photosynthesis; this result is consistent with the broader hypothesis that the magnitude of autochthonous production in aquatic systems influences the fate of N via both direct and indirect mechanisms.
Exchange between suspended and sinking particles in the northwest Mediterranean as inferred from the organic composition of in situ pump and sediment trap samples
Authors: Abramson Lynn , Lee Cindy , Liu Zhanfei , Wakeham Stuart G. , Szlosek Jennifer
Published: August 2016

The extent to which sinking particles disaggregate and exchange with surrounding material affects the efficiency of particulate organic carbon export to the deep sea. In 2003 and 2005, we compared the pigment and amino acid compositions of sediment trap and in situ pump samples collected in the northwest Mediterranean Sea to assess exchange between sinking and suspended particles. While sediment traps collected only sinking particles, in situ pumps collected both larger (> 70‐µm) particles, believed to represent the sinking fraction, as well as smaller (1–70‐µm) particles, believed to represent the suspended fraction. The organic compound compositions of sinking and suspended particles were very different and remained consistently so with depth, suggesting that exchange between them was limited. This difference was particularly pronounced during the high flux periods in spring. Sinking particles appeared to be composed of many fecal pellets and a few phytoplankton aggregates, and were enriched in diatom indicators. Suspended particles appeared to be more enriched in fresh phytoplankton and contained indicators of calcium carbonate‐bearing organisms. During the low‐flux summer period, the contribution of fecal pellet indicators to sinking particles was lower, whereas the contribution of microbial degradation products in both particle types was higher, possibly indicating greater exchange during periods of low flux when fecal pellets were not as abundant. Results from this study suggest that fecal pellets, although already degraded upon formation, are more robust than phytoplankton aggregates and, therefore, more likely to resist disaggregation and further decomposition during transit through the water column.
The isotopic and hydrologic response of small, closed‐basin lakes to climate forcing from predictive models: Simulations of stochastic and mean state precipitation variations
Authors: Steinman Byron A. , Rosenmeier Michael F. , Abbott Mark B.
Published: August 2016

A hydrologic and isotope mass‐balance model is applied to two small, closed‐basin lakes, Castor and Scanlon, in north‐central Washington to describe the influence of hydroclimatic forcing on lake hydrologic and isotopic evolution. Simulations of lake responses to the combined effects of stochastic variability (i.e., random interannual fluctuations) and long‐term (i.e., multidecade to century), mean‐state changes in precipitation were conducted using 300 yr of randomly generated precipitation data as model inputs. Simulation results demonstrate that average (long‐term) closed‐basin, lake‐water, oxygen‐isotope values are dependent largely upon lake‐water outseepage (i.e., subsurface outflow) rates, with lower (higher) outseepage resulting in decreased (increased) isotopic sensitivity to long term precipitation changes, and that the lake basin surface‐area‐to‐volume (SA :V) ratio changes with depth influence the direction of the isotopic response. Simulation results also suggest that, as average lake volume decreases as a consequence of decreasing mean‐state precipitation amounts, interannual lake‐water isotopic variability in response to stochastic forcing will increase. Conversely, as the average lake volume increases in response to increasing mean‐state precipitation amounts, interannual lake‐water isotopic variations associated with stochastic forcing will decrease. Additional model experiments demonstrate that increased (decreased) variance in precipitation leads to increased (decreased) water volume within lakes over the long term, which (if stochastic variance changes are large enough) could result in decreased (increased) lake‐water oxygen‐isotopic sensitivity to stochastic precipitation.
Kelp rafts in the Humboldt Current: Interplay of abiotic and biotic factors limit their floating persistence and dispersal potential
Authors: Rothä usler Eva , Gómez Ivàn , Hinojosa Ivàn A. , Karsten Ulf , Miranda Leonardo , Tala Fadia , Thiel Martin
Published: August 2016

During summer 2009, we conducted a field experiment and a field survey at 30°S in the coastal Humboldt Current to determine how floating time affects the physiological performance of kelp rafts. For the field experiment kelp rafts were tethered in coastal waters and the field survey was specifically designed to collect free‐floating Macrocystis pyrifera across a latitudinal temperature gradient that reflects natural floating time. Experimental kelps were kept under photosynthetic active radiation (PAR) and PAR + ultraviolet (UV; PAR + UV) using filter foils, and tethered at the sea surface in their natural habitat. Ultraviolet radiation (UVR) did not affect kelp physiology, but caused a decrease in kelp biomass. The field survey confirmed that sea‐surface temperature increased with distance from upstream source populations of M. pyrifera. Rafts sampled at increasing distance from sources showed high epibiont cover and reduced blade lengths. Physiological performance declined with increasing size of algal epibionts, which are indicators of floating time. Rafts that were farthest from the southern source populations had lost their sporophylls, suggesting that dispersal potential decreases with increasing floating time. The combined effects of abiotic (UVR and temperature) and biotic factors accelerate degradation of M. pyrifera and, thus, can impede successful dispersal in the Humboldt Current at 30°S. This suggests that floating macroalgae can be important dispersal vectors in areas with moderate environmental stress (i.e., in temperate oceans).
Chelator‐induced inhibition of copper metalloenzymes in denitrifying bacteria
Authors: Moffett James W. , Tuit Caroline B. , Ward B. B.
Published: August 2016

Copper (Cu) is required by the enzyme nitrous oxide reductase (N2OR), which catalyzes the last step of the complete denitrification pathway in denitrifying bacteria. Some denitrifiers also require copper for nitrite reductase (NiRK), whereas others use the iron nitrite reductase (NiRS). We report the inhibition of the activity of these enzymes in three strains of denitrifiers (two containing NiRK, the other NiRS), by forming nonbioavailable complexes with 1,4,8,11‐tetraazacyclotetradecane1,4,8,11‐tetraacetic acid hydrochoride hydrate (TETA), a strong Cu(II) chelator, and tetrathiomolybdate (TTMo), a strong Cu(I) chelator. Both ligands complex Cu with stability constants comparable to naturally occurring ligands and much more strongly than other widely used chelators, such as ethylenediaminetetraacetic acid. Addition of TETA to growth media lowered free Cu2+ concentrations below 10−16 mol L−1 and induced Cu limitation in all organisms. While Cu is strongly complexed in seawater, 10−16 mol L−1 free Cu2+ is lower than most reported values, suggesting that the organisms have evolved high‐affinity Cu transport systems. TTMo had different effects, and inhibited NiRK more effectively than N2OR. It is likely that TTMo inhibits NiRK through direct, noncompetitive inhibition, as reported for other reduced sulfur compounds, rather than by inducing Cu limitation. The activity of NiRK may be sensitive to trace levels of reduced sulfur, which could account for its scarcity in marine systems. While Cu limitation of denitrification is probably uncommon in aquatic systems, the presence of reduced sulfur compounds may induce Cu limitation or enzyme inhibition leading to the accumulation of nitrite and nitrous oxide.
Hypoxia and nitrogen processing in the Baltic Sea water column
Authors: Hietanen Susanna , Jäntti Helena , Buizert Christo , Jürgens Klaus , Labrenz Matthias , Voss Maren , Kuparinen Jorma
Published: August 2016

Steep redoxclines form between oxic surface water and the stagnant, sulfidic hypolimnion in the eutrophied, brackish water Baltic Sea. Nitrification, denitrification, and anammox were measured at and below the redoxcline to quantify the role of water‐column nitrogen processes in the overall magnitude of nitrogen removal in the Baltic Sea. Rates of nitrification were very high (up to 85 nmol N L−1 d−1) at the oxic‐anoxic interface, but, surprisingly, nitrification was separated from the processes reducing nitrate to N2 (up to 810 nmol N L−1 d−1) by tens of meters in depth. N2 production was dominated by chemolithotrophic denitrification, with anammox playing only a negligible role, and limited to the water layers in which nitrite or nitrate coexisted with sulfide. The alternating oxygen concentrations in the basin induce irregular bursts of nitrogen removal. Nitrification takes place after mixing of ammonium‐rich deep water with oxic water, and denitrification uses the formed nitrite and nitrate once anoxic conditions re‐establish. Although removal rates can be high, conditions allowing such rates are likely short‐lived. While the sedimentary denitrification rates at the shallower, oxic areas are lower, they are more constant in time, highlighting the need to avoid hypoxia, which would prevent sedimentary denitrification.
Assessing nonpoint‐source nitrogen loading and nitrogen fixation in lakes using δ15N and nutrient stoichiometry
Authors: Jankowski KathiJo , Schindler Daniel E. , Holtgrieve Gordon W.
Published: August 2016

Runoff from human‐dominated watersheds has greatly altered nitrogen (N) and phosphorus (P) cycling in lakes. Nutrients from human sources are distinct from those from undisturbed ecosystems in several ways including lower N : P ratios, which can drive ecosystems to N‐limited conditions, and enriched stable N isotope ratios. In this study, we used these distinct characteristics to estimate shifts in N sources to 27 lakes across a human density gradient in western Washington. We compared an N stable isotope two‐source mixing model with a mixing model that coupled N stable isotopes to N : P stoichiometry and included N fixation. We found that a two‐source mixing model (human and watershed sources) did not explain observed variation in δ15N of particulate organic matter (POM) and primary consumers (R2 = 0.60) as well as a model that included a third N source (N fixation; R2 = 0.72). When fixed N was facultatively added to the ecosystem below a critical N : P ratio, the more complex mixing model captured the observed patterns in POM and primary‐consumer δ15N among lakes extremely well. In lakes with P concentrations > 20 µg L−1 (N : P mass ratio < 15.3), N fixation became an increasingly important component of the N cycle, accounting for > 50% of lake N budgets. This model provides a novel way to estimate the contribution of nonpoint N sources and N fixation to lakes in watersheds subject to human nutrient inputs.
To kill or not to kill: The balance between lytic and lysogenic viral infection is driven by trophic status
Authors: Payet Jérôme P. , Suttle Curtis A.
Published: August 2016

Experiments were conducted to investigate spatiotemporal patterns in lytic and lysogenic viral infection using water samples collected on the Canadian Arctic Shelf, southern Beaufort Sea. Viral production (VP) and viral‐induced mortality of bacteria (VMB) were determined using a viral reduction approach during a full seasonal cycle, while the percentage of lysogenic bacteria (PLB) in spring and summer was determined in virus‐reduced samples by induction with mitomycin C. Overall, VP (range: 0.3 × 108‐77 × 108 viruses L−1 d−1), VMB (range: 0.2 × 107‐43 × 107 bacteria L−1 d−1), and PLB (range: 4–38%) displayed marked spatiotemporal variations concomitant with changes in chlorophyll a, bacterial abundance, and production. Highest VP and VMB occurred in summer when the water was warmest, stratified, and most productive, and when viruses removed up to 29% of bacterial standing stock d−1 and released up to 4.3 µg of organic carbon L−1 d−1. In contrast, the highest PLB occurred in spring when the water was colder, well mixed, and oligotrophic. Correlative and regression analyses indicated viral lytic and lysogenic variables were significantly coupled with chlorophyll a and the abundance, production, and growth rate of bacteria, implying that viral lytic and lysogenic lifestyles were dependent on system productivity. Furthermore, lytic VP and the proportion of lysogenized bacteria were inversely related, suggesting a dynamic interplay between viral infection pathways. Lytic infection was more pronounced when system productivity was high, while lysogeny prevailed when system productivity was low. These data demonstrate the important role of viruses in bacterial mortality and carbon cycling in the Arctic Ocean, and show how their effect is influenced by trophic status.
An inducible antipredatory defense in haploid cells of the marine microalga Emiliania huxleyi (Prymnesiophyceae)
Authors: Kolb Amelia , Strom Suzanne
Published: August 2016

Microzooplankton are important consumers of phytoplankton primary production, but phytoplankton defenses against these predators are not well understood despite their expected importance. We tested for inducible defenses in the coccolithophore Emiliania huxleyi, an abundant and cosmopolitan bloom‐forming species with a heteromorphic haploid‐diploid life cycle, against the ciliate predator Strombidinopsis acuminatum. We hypothesized that the two life‐cycle phases (calcifying diploid and motile noncalcifying haploid) of E. huxleyi are differently defended against predation. Using short‐term (30 min) ingestion rate assays, we compared predation on E. huxleyi that had been previously exposed to predators for 24 h to predation on naïve (unexposed) E. huxleyi. Prey were considered to have a defense response when ingestion rates on naïve cells were higher than ingestion rates on predator‐exposed cells. Haploid E. huxleyi had a strong defense response, with a 25–43% reduction in ingestion rate due to predator exposure, whereas diploid E. huxleyi had no defense response. Haploid E. huxleyi grown with reduced nutrient availability showed no defense response when initially offered to ciliates (although there was evidence of a delayed defense response). Additionally, the presence of defended haploid E. huxleyi did not reduce ciliate ingestion on another prey species (Heterocapsa triquetra). This defense system points to complex predator‐prey interactions as key factors controlling the structure and function of marine planktonic communities.
Cross‐ecosystem differences in lipid composition and growth limitation of a benthic generalist consumer
Authors: Lau Danny C. P. , Goedkoop Willem , Vrede Tobias
Published: August 2016

In a field study, we analyzed the fatty acid (FA) composition of the benthic generalist Asellus aquaticus collected from boreal lakes, ponds, and streams across gradients in ambient nutrient levels. In laboratory feeding experiments, we tested the diet‐quality and seasonal effects on somatic growth and FAs of spring‐ and autumn‐collected Asellus that were fed four different diets containing increasing concentrations of polyunsaturated FAs (PUFA): conditioned leaf litter, algal flakes, mixed litter and algal flakes (Mixed), or Mixed plus fish‐food flakes. Ambient nutrients were strong determinants of FA variation of field Asellus, explaining > 44% in total. The ratios of eicosapentaenoic acid (EPA) to total FAs, EPA : ω3, and ω3 : ω6 of Asellus increased up to four times with increasing trophic state and decreasing humic matter content, likely because dietary ω3 FAs were more prevalent in benthic habitats of eutrophic than of oligotrophic systems. In the feeding trials, growth of Asellus collected in both seasons was markedly lower on leaf litter than on higher PUFA diets. However, autumn‐collected Asellus fed a Mixed or Mixed+fish‐food diet grew 3–10 times faster, but retained < 50% EPA and PUFA than spring counterparts. Asellus optimized PUFA accumulation in spring but somatic growth in autumn. Our field survey suggests ambient nutrient concentrations modify dietary PUFA supply from basal resources, while laboratory studies show that growth response and PUFA accumulation of Asellus differ between seasons, likely due to its season‐specific physiological status and diet quality. An increase in nutrients will release benthic consumers from growth limitation and favor more efficient trophic transfer.
Chlorophyll‐normalized isoprene production in laboratory cultures of marine microalgae and implications for global models
Authors: Exton D. A. , Suggett D. J. , McGenity T. J. , Steinke M.
Published: August 2016

We used laboratory cultures of marine microalgae to investigate the effects of growth conditions and their taxonomic position on the production of isoprene, a gas that has major effects on atmospheric chemistry and provides stress tolerance to many primary producers. Isoprene was quantified from 21 microalgal strains sampled during exponential growth, using purge‐and‐trap pre‐concentration and gas chromatography with flame‐ionization detection. Isoprene production rates varied by two orders of magnitude between strains (0.03–1.34 µmol [g chlorophyll a]−1 h−1), and were positively correlated with temperature (r2 = 0.52, p < 0.001, n = 59). Three distinct sea surface temperature (SST)‐dependent relationships were found between isoprene and chlorophyll a (µmol [g chlorophyll a]−1 h−1), an improvement in resolution over the single relationship used in previous models: for three polar strains grown at −1°C (slope = 0.03, R2 = 0.76, p < 0.05, n = 9), nine strains grown at 16°C (slope = 0.24, R2 = 0.43, p < 0.05, n = 27 with Dunaliella tertiolecta excluded), and eight strains grown at 26°C (slope = 0.39, R2 = 0.15, p < 0.05, n = 24). We then used a simple model that applied the SST‐dependent nature of isoprene production to three representative bioregions for the growth temperatures used in this study. This approach yielded an estimate of global marine isoprene production that was 51% higher than previous attempts using an SST‐independent single relationship. Taking into account the effect of temperature therefore potentially allows more precise modeling of marine isoprene production, and suggests that increasing the SST‐based resolution of data beyond the three groups used here could further improve future modeling simulations.
Biological production rates off the Southern California coast estimated from triple O2 isotopes and O2 : Ar gas ratios
Authors: Munro David R. , Quay Paul D. , Juranek Laurie W. , Goericke Ralf
Published: August 2016

The isotopic composition of dissolved O2 (17Δ) and the biological O2 saturation from O2 : Ar ratios were measured in the surface ocean during six cruises off the coast of southern California from November 2005 to August 2008 to determine rates of gross oxygen production (GOP), net oxygen production (NOP), and the NOP : GOP ratio (a measure of potential export efficiency). In the mixed layer, 17Δ of dissolved O2 (17Δdiss) ranged from 24 to 108 per meg and biological O2 saturation ranged from 101% to 113% for all regions and cruises. Mixed‐layer 17Δ‐GOP ranged from 49 ± 23 mmol O2 m−2 d−1 to 533 ± 185 mmol O2 m−2 d−1 with an annual mean for the California Cooperative Oceanic Fisheries Investigations (CalCOFI) grid of 151 ± 59 mmol O2 m−2 d−1. Mixed‐layer O2 : Ar‐NOP ranged from 8 ± 6 mmol O2 m−2 d−1 to 135 ± 31 mmol O2 m−2 d−1 with an annual mean of 25 ± 8 mmol O2 m−2 d−1, implying that the CalCOFI grid is autotrophic year‐round. 17Δ‐GOP estimates were consistently greater than on‐deck incubation‐based 14C‐primary production (14C‐PP) by a factor of 5.6 ± 0.4 and greater than satellite PP estimates by a factor of 3.5 ± 0.3 (mmol O2 : mmol C). The 17Δ‐GOP to 14C‐PP factor was twice the expected factor of 2.7 determined from comparisons of incubation‐based 18O‐GOP and 14C‐PP. The annual mean NOP : GOP ratio was 0.16 ± 0.06, suggesting a potential export efficiency that is surprisingly similar to the open ocean using comparable methods.