bluuebunny/crossref_metadata_2025 huggingface dataset:
Microsensor for in situ flow measurements in benthic boundary layers at submillimeter resolution with extremely slow flow
Authors: Brand Andreas , Müller Beat , Wüest Alfred , Dinkel Christian , Revsbech Niels Peter , Nielsen Lars Peter , Pedersen Ole , Damgaard Lars Riis , Larsen Lars Hauer , Wehrli Bernhard
Published: April 2011

The currents in the lowest few millimeters of the bottom boundary layer of lakes are highly important for the dissipation of kinetic energy and for chemical processes such as oxygen transfer into the sediment. So far, no high‐resolution flow velocity profiles close to the sediment‐water interface have been reported for such systems because a suitable flow meter was lacking. This article introduces a novel sensor for the measurement of extremely low‐flow velocities. The sensor is based on a gas transducer surrounded by a gas reservoir. It measures the change in the partial pressure of a tracer gas outside the reservoir tip due to advective transport. The sensor is suitable for measurements of velocities smaller than 1 mm s−1, with a spatial resolution of 100 to 250 µm. The flow measurements prove to be insensitive to temperature changes between 5 and 15 °C. The sensor is robust against relative pressure changes, and angular differences in the sensitivity can be calibrated. We present high‐resolution in situ measurements at the bottom of a pre‐alpine lake with shear velocities as low as 0.13 ± 0.02 cm s−1. The velocity profile nicely resolves the transition zone between the viscous and the logarithmic boundary layer.
Automated taxonomic classification of phytoplankton sampled with imaging‐in‐flow cytometry
Authors: Sosik Heidi M. , Olson Robert J.
Published: April 2011

High‐resolution photomicrographs of phytoplankton cells and chains can now be acquired with imaging‐in‐flow systems at rates that make manual identification impractical for many applications. To address the challenge for automated taxonomic identification of images generated by our custom‐built submersible Imaging FlowCytobot, we developed an approach that relies on extraction of image features, which are then presented to a machine learning algorithm for classification. Our approach uses a combination of image feature types including size, shape, symmetry, and texture characteristics, plus orientation invariant moments, diffraction pattern sampling, and co‐occurrence matrix statistics. Some of these features required preprocessing with image analysis techniques including edge detection after phase congruency calculations, morphological operations, boundary representation and simplification, and rotation. For the machine learning strategy, we developed an approach that combines a feature selection algorithm and use of a support vector machine specified with a rigorous parameter selection and training approach. After training, a 22‐category classifier provides 88% overall accuracy for an independent test set, with individual category accuracies ranging from 68% to 99%. We demonstrate application of this classifier to a nearly uninterrupted 2‐month time series of images acquired in Woods Hole Harbor, including use of statistical error correction to derive quantitative concentration estimates, which are shown to be unbiased with respect to manual estimates for random subsamples. Our approach, which provides taxonomically resolved estimates of phytoplankton abundance with fine temporal resolution (hours for many species), permits access to scales of variability from tidal to seasonal and longer.
Vacuum‐pressure prewetting—A simple and rapid method to water saturate wood for experimental purposes
Authors: Spänhoff Bernd
Published: April 2011

A simple and rapid method to prepare water‐saturated wood by vacuum‐pressure prewetting is presented. Submerged wood pieces can be prepared easily for any experimental purposes without long periods of prewetting and without additional tools for holding the wood under water. The particular wood piece must be submerged in a water filled suction flask that is connected to a diaphragm vacuum pump. Due to the evacuation of the air from the flask the wood rapidly soaks up water until it is saturated. In the experiments, branches displayed a logarithmic water saturation curve soaking up the highest amount of water during the first 10 s of air evacuation. Most branches were water saturated during this time. The method works best for wood pieces with a low or medium density supporting a rapid soaking of water, whereas very dense wood needs much more time to become water saturated. The main problem of the method is the loss of bark material from natural branches and the splitting of larger woods due to the rapid swelling caused by the water uptake. However, this method could be used for any experimental purposes needing standardized submerged wood, like investigations of epixylic biofilm development, colonization of wood by aquatic invertebrates, decomposition of submerged wood, or invertebrate food choice experiments.
The inclusion of sub‐detection limit LA‐ICPMS data, in the analysis of otolith microchemistry, by use of a palindrome sequence analysis (PaSA)
Authors: Ben‐Tzvi O. , Abelson A. , Gaines S. D. , Sheehy M. S. , Paradis G.L. , Kiflawi M.
Published: April 2011

Fish otoliths are a reliable source of historical data regarding individual fish. Optical and chemical data obtained from otoliths are used to reveal the fish's age, natal areas, dispersal trajectories, and more. However, whereas optical methods are well established and widely practiced, methods for obtaining and interpreting chemical data continue to evolve. Despite rapid advances in the past decade, analytical approaches to otolith microchemisty continue to develop as new opportunities and limitations emerge. Otolith chemistry often reflects environmental conditions such as the chemical composition, temperature, and salinity of the ambient water. However, it is not always clear how these interact to produce the chemical signature observed in the otolith. Such gaps and inconsistencies in our knowledge may result partly from valuable information being discarded when measured concentrations fall below customarily defined detection limits (DL). Below we review some of the inaccuracies that may arise when analyzing chemical data obtained from laser‐ablation inductively coupled mass spectrometry (LA‐ICPMS). We argue that measurements traditionally defined as sub‐DL can contain valuable information that would otherwise be discarded. We base our argument on the analysis of sub‐DL signals obtained from both sides of otoliths core. Specifically, we show that these signals often form sequences that are symmetrical about the core (palindrome), and that the probability of obtaining even the simplest palindromic sequence by chance falls well below the customary 5% significance level. We conclude by discussing how this microchemical data can be analyzed in a manner that is insensitive to errors in concentration readings.
Quantifying gas ebullition with echosounder: the role of methane transport by bubbles in a medium‐sized lake
Authors: Ostrovsky I. , McGinnis D. F. , Lapidus L. , Eckert W.
Published: April 2011

In lakes and reservoirs with variable water level, gas ebullition can play a substantial role in methane transport in the water column and to the atmosphere. However, measuring methane ebullition from sediment is difficult as releases are highly heterogeneous and intermittent on macro‐ and micro‐scales. In contrast to conventional gas traps and optical methods, hydroacoustic technology allows rapid scanning over large volumes of the water column synoptically to quantify gas bubble abundance. A 120‐kHz dual beam downward‐looking echosounder was used to measure the size distributions of bubbles that do not resonate at the sonar frequency. Data obtained with this sonar permit accurate calculation and evaluation of ebullition flux from the bottom. A robust relationship was established between gas volumes and backscattering cross‐section of individual bubbles in experimental conditions, and rise velocities of bubbles were precisely measured. The volume backscattering coefficient was shown to be a good gauge of the total volume of bubbles per cubic meter of water, allowing the use of a single‐beam sonar for measuring volumetric bubble concentrations. Data obtained from hydroacoustic surveys on Lake Kinneret, where gaseous methane is emitted from randomly dispersed sediment sources, indicated that ~90% of bubbles escaping from soft sediments ranged from 1.3 mm to 4.5 mm and ~50% ranged from 2.0 mm to 3.2 mm in equivalent radius. In summer‐fall 2001, the gaseous methane fluxes from hypolimnetic sediments was ~10 mmol m−2 d−1, accounting for one‐third of the observed methane accumulation in the hypolimnion. This relatively high ebullition rate could be attributed to the gradual decreasing of the mean water level in preceding years.
Effects of acidification in multiple stable isotope analyses
Authors: Jaschinski Sybill , Hansen Thomas , Sommer Ulrich
Published: April 2011

The effect of in situ acidification on the stable isotope ratios of carbon and nitrogen was tested in several invertebrates living in an eelgrass system. Dried and ground samples of individuals were weighted in silver cups and treated in situ with 10% HCl. Control samples were measured without acidification. This treatment to remove inorganic carbon significantly decreased the δ13C values. The δ15N values were not affected by this method of acidification. In contrast to the acid‐washing method the tested procedure seems suitable to remove inorganic carbon in small invertebrate species.
The influence of schlieren on in situ optical measurements used for particle characterization
Authors: Mikkelsen Ole A. , Milligan Timothy G. , Hill Paul S. , Chant Robert J. , Jago Colin F. , Jones Sarah E. , Krivtsov Vladimir , Mitchelson‐Jacob Gay
Published: April 2011

In pycnoclines, the density differences can cause light scattering —schlieren —even though only few particulate scatterers may be present. This may pose problems for the interpretation of results obtained with instruments relying on light scattering and transmission, for example the LISST (Laser In Situ Scattering and Transmissometry) particle sizer, and various cameras. Here, the influence of schlieren on in situ forward light scattering, beam attenuation and image analysis is evaluated using a LISST‐100 and a digital floc camera. Automated image analysis routines detect schlieren as particles, causing an apparent increase in particle size and volume. Re‐analysis omitting schlieren‐affected parts of the images reveals no increase. LISST beam attenuation and Volume Scattering Function (VSF) measurements indicate that schlieren can cause increases in beam attenuation due to a marked increase in the VSF at angles smaller than ~1.5°‐2°, and falsely indicate accumulation of suspended particles in the pycnocline. Light scattering caused by density differences can also cause multiple scattering, which produces an apparent decrease in particle size derived from the LISST. Schlieren is visible in images when the buoyancy frequency exceeds ~0.12 s−1. Buoyancy frequencies above 0.025 s−1 may cause increases in beam attenuation due to scattering from the density gradients and complete extinction of beam transmission can occur at buoyancy frequencies above ~0.20 s−1. All instruments measuring light scattering can potentially be affected by density differences, and results obtained in waters where buoyancy frequencies exceeds 0.025 s−1 should be interpreted carefully.
Mapping phytoplankton in situ using a laser‐scattering sensor
Authors: Rienecker Erich , Ryan John , Blum Marguerite , Dietz Caroline , Coletti Luke , Marin Roman , Bissett W. Paul
Published: April 2011

A primary limitation of phytoplankton ecology research is the difficulty of describing patchiness and distributions of different phytoplankton groups. Chlorophyll fluorescence and optical backscatter are useful measurements that provide information about phytoplankton, but these measurements do not allow distinction of phytoplankton taxa. Traditional phytoplankton identification methods (such as microscopy, HPLC analysis, and flow cytometry) are labor intensive and therefore can provide only very limited coverage and resolution. Through lab experiments we show that the Laser In Situ Scattering and Transmissometer (LISST‐100) instrument can accurately quantify phytoplankton cell dimensions for some cell shapes. Pseudo‐spherical dinoflagellates are described with a single peak in the particle size distribution (PSD) at the cross‐sectional dimension of the cells. Pennate diatoms are described with peaks in the PSD at the major and minor axis dimensions of the cells. Diatom cells with minor axis dimensions that vary along the major axis are described with one peak across the range of minor axis dimensions and a second peak at the major axis dimension. Through field experiments, we show that mapping the PSD in situ at high resolution permits description of patchiness and evolution of phytoplankton populations. We present two examples: (1) growing dominance of Ceratium species during a red tide bloom, and (2) concentration of Pseudo‐nitzschia australis, a harmful algal bloom (HAB) species, at a water mass front. We conclude that synoptic mapping of the PSD can significantly advance phytoplankton ecology research in the coastal ocean.
Field assessment of a new membrane‐free microelectrode dissolved oxygen sensor for water column profiling
Authors: Sosna Maciej , Denuault Guy , Pascal Robin W. , Prien Ralf D. , Mowlem Matt
Published: April 2011

This article reports on the field trials of a membrane‐free amperometric microelectrode dissolved oxygen sensor, which were performed during oceanographic cruise D279 of RRS Discovery. The sensor was used to obtain full depth oxygen profiles while mounted on a wire‐operated CTD (conductivity, temperature, depth) instrument. A stable performance was achieved by carefully designed electrochemical cleaning conditions of the sensing platinum microdisk cathode. The flow issues inherent to moving probes were resolved by a novel stop‐flow cell fitted with a pumping system for sample exchange and flow control. The details of the sensor operation, calibration, and construction, including the flow control system, are described. The sensor response is validated by calibration and by an analytical approach that yields oxygen data directly from the current readings. The accuracy of the microelectrode response is critically assessed using Winkler titrations on bottle samples taken during the relevant sensor deployments. The results lead to the conclusion that due to high accuracy, fast response time, and lack of membrane‐related problems the device is particularly suitable for moving probes and high spatial resolution water column oxygen profiling.
Use of open‐top chambers to study the effect of climate change in aquatic ecosystems
Authors: Netten Jordie J.C. , van Nes Egbert H. , Scheffer Marten , Roijackers Rudi M.M.
Published: April 2011

The aim of this research was to explore the possibility to use inexpensive open‐top chambers (OTCs) as passive artificial warming devices in experimental aquatic studies. Our results show that OTCs give a significant temperature increase compared with the control. The measured increase (up to an average of 2.3°C) corresponds with predicted climatic warming. Due to their open top, the light quantity and quality is only minimally reduced. We found that OTCs are especially suited for studying the effect of climate change in small waters as the vertical temperature gradients remain unchanged. They can also easily be transported to remote environments. We discuss other advantages and disadvantages of these devices for aquatic studies and compare them with other warming devices.
New cell extraction procedure applied to deep subsurface sediments
Authors: Kallmeyer Jens , Smith David C. , Spivack Arthur J. , D'Hondt Steven
Published: April 2011

A new method is presented for the separation of cells from a marine sediment matrix. Different methods and reagents were tested for detaching microbial cells from sediment particles; the highest yields were achieved in a solution of EDTA, Tween 80, sodium‐pyrophosphate, and methanol plus gentle ultrasonic treatment, followed by density centrifugation through a cushion of Nycodenz. If present, carbonates were dissolved before extraction. Comparison with untreated sediments and pure cultures verified that this technique minimizes cell lysis. The new procedure was tested on seafloor sediment from several locations and water depths (<1 to >4000 m) and subseafloor sediment from the Arctic Ocean (IODP Expedition 302). Cell extraction efficiency was relatively high (65% to 100%) and consistent for each sediment type, with significantly (P < 0.01) lower variability of counts of separated cells compared with conventional counts on slurried sediments. Concentrating cells before enumeration allows for a much lower minimum detection limit and lower uncertainty than the conventional approach of simply slurrying sediment. Resolving relatively small differences in the distribution of microorganisms will allow for comparisons to other parameters (porewater chemistry, lithology, etc). Additionally, this method has potential for the use of molecular techniques that were previously difficult owing to coelution of interfering compounds from the sediment matrix.
Carbonate removal from coastal sediments for the determination of organic carbon and its isotopic signatures, δ13C and Δ14C: comparison of fumigation and direct acidification by hydrochloric acid
Authors: Komada Tomoko , Anderson Mark R. , Dorfmeier Corin L.
Published: April 2011

Acidification of a solid sample to separate inorganic carbon (IC) from organic carbon (OC) is a widely encountered procedure in limnology and oceanography. Traditionally, OC was isolated to determine the weight‐% of OC (%OC), but it is becoming increasingly common to determine the isotopic signatures of the OC (δ13COC and Δ14COC). This raises a need for a closer scrutiny of the currently used acidification methods. First, because IC and OC typically have distinct carbon‐isotopic signatures, δ13COC and Δ14COC values can be compromised if IC is not completely removed. Second, it is possible to isotopically fractionate a sample if a small portion of OC is lost during acidification, because OC itself is both chemically and isotopically heterogeneous. This study evaluated two acidification methods by HCl—in the vaporous (HClvap) and aqueous (HClaq) phases—to determine %OC, δ13COC, and Δ14COC in coastal sediments. Each method was assessed according to the criteria that it (1) has low blank levels, (2) is able to remove dolomite, (3) yields accurate %OC, and (4) yields accurate δ13COC and Δ14COC values. HClvap fulfilled all criteria, given that the samples were not overexposed to acid. Overexposure led to underestimation of δ13COC and Δ14COC values. HClaq gave similar results but was less reliable in that it consistently underestimated %OC and yielded inaccurate δ13COC value for one test sample. It is recommended that an optimal acid exposure is carefully determined for each sample type to obtain most accurate δ13COC and Δ14COC values.
New method for presenting nutritionally defined food sources to marine organisms
Authors: Andrews Gareth O. , Simpson Stephen J. , Pile Adele J.
Published: April 2011

To study nutritional ecology in aquatic and marine ecosystems, it is important to be able to perform feeding trials enabling feeding and nutrient selection behavior of organisms to be observed in situ. Current studies in marine nutritional ecology are limited to laboratory and shallow water studies using food sources of undefined nutrient concentration. Here we describe a technique for delivering standardized nutrient sources in situ to both pelagic and benthic organisms as a feeding choice array, in a way that allows the amounts eaten of different foods and nutrients to be quantified and correlated with precise descriptions of the feeding behavior of individual organisms. A pilot study proved that this feeding choice array can be successfully deployed in marine environments. It will also be possible to use this technique to explore patterns of nutrient limitation and to investigate the nutritional regulatory response of marine and aquatic organisms.
High‐frequency measurements of productivity of planktonic algae using rugged nondispersive infrared carbon dioxide probes
Authors: Hari Pertti , Pumpanen Jukka , Huotari Jussi , Kolari Pasi , Grace John , Vesala Timo , Ojala Anne
Published: April 2011

We have constructed a system based on commercially available inexpensive NDIR CO2 sensors to continuously monitor CO2 concentrations in water bodies. Here we demonstrate its use in a boreal humic lake. With the system, we collect high frequency data with a 10‐min time resolution for determination of CO2 consumption and production. We use and modify the computational methods commonly used in forest ecology to enable characterization of aquatic primary production. To demonstrate the advantages of the method, we present the results against the observations from the long‐term monitoring program applying traditional bottle methods. With the probes, we can detect a clear, photosynthesis‐driven daily pattern in the CO2 concentration and determine the CO2 consumption or production resulting in more than a 10‐fold improvement in the time resolution when compared with traditional incubation methods. The measuring frequency is high enough to determine the dependence of photosynthesis on irradiance. The high‐frequency data highlights the inherent problems of discrete bottle incubations and bring into question their reliability. Our free water approach yielded productivity and mineralization rates that were clearly higher than obtained with incubations.
Comparison of methods to determine algal δ13C in freshwater
Authors: Marty Jérôme , Planas Dolors
Published: April 2011

To accurately assess the flux of mass and energy to higher trophic levels in a food web using stable isotopes, the isotopic signature of basal sources is required. When studying aquatic food webs, it is difficult to obtain a signature for algae because of challenges associated with isolating small organisms from a bulk sample. In this study, we compared freshwater algal δ13C values obtained using five approaches from the literature. Results indicated that the signatures derived from a primary consumer such as Daphnia sp., from particulate organic carbon with a correction for algal biomass, and from isolated algal samples were comparable. By contrast, algal δ13C values based on the signature of carbon dioxide and algal carbon fractionation were significantly lower than those of the other approaches. The inconsistent values produced by this method were likely due to problems in determining fractionation values based on current models and were potentially related to bicarbonate uptake by algae.
In situ bacterial mitigation of the toxic cyanobacterium Microcystis aeruginosa: implications for biological bloom control
Authors: Kim Baik‐Ho , Sang Miao , Hwang Soon‐Jin , Han Myung‐Soo
Published: April 2011

The algicidal bacterium Xanthobacter autotrophicus HYS0201‐SM02 (SM02) was isolated from the surface water of a eutrophic lake (Lake Daechung, Korea). In vivo and in situ experiments showed that SM02 had algicidal activity against both a cultured strain and natural colonial morphs of the toxic cyanobacterium, Microcystis aeruginosa. Both the SM02 bacteria and its culture filtrate showed anti‐algal activity against M. aeruginosa, indicating that an algicidal substance was released from SM02. The threshold concentration of SM02 for maximal algicidal activity against a natural bloom of M. aeruginosa was 107 CFU/mL. In situ co‐culture of SM02 and M. aeruginosa showed that SM02 did not benefit from the massive decay of M. aeruginosa. In fact, repeated inoculations with a low concentration of SM02 were required for optimal algicidal activity, suggesting that water quality worsened during co‐culture (i.e., nutrients and microcystin‐LR concentration increased). These results suggest a role for the algicidal bacterium X. autotrophicus SM02 in biorestoration but probably not in treating outdoor Microcystis blooms. When developing a biological agent to control M. aeruginosa blooms in the field, it will be important to screen for specific agents with low threshold concentrations and high algicidal activity.
Characterizing dissolved organic matter fluorescence with parallel factor analysis: a tutorial
Authors: Stedmon Colin A. , Bro Rasmus
Published: April 2011

A sub‐fraction of dissolved organic matter fluoresces when excited with ultraviolet light. This property is used to quantify and characterize changes in dissolved organic matter (DOM) in aquatic environments. Detailed mapping of the fluorescence properties of DOM produces excitation emission matrices (EEM), which are well suited to multi‐way data analysis techniques (chemometrics). Techniques such as parallel factor analysis (PARAFAC) are increasingly being applied to characterize DOM fluorescence properties. Here, an introduction to the technique and description of the advantages and pitfalls of its application to DOM fluorescence is presented. Additionally a MATLAB based tutorial and toolbox specific to PARAFAC analysis of DOM fluorescence is presented.
Testing of the CHEMTAX program in contrasting Neotropical lakes, lagoons, and swamps
Authors: Guisande Cástor , Barreiro Aldo , Acuña Alberto , Marciales Lili J. , Hernández Esnedy , Torres Angélica M. , Aranguren Nelson , López Willian , Duque Santiago R. , Gallo Lina J. , Aguirre Néstor , Mogollón Marta , Palacio Jaime , Rueda‐Delgado Guillermo
Published: April 2011

The problem using the CHEMTAX program in freshwater environments is that the few matrices of pigment ratios available have not been tested in a wide range of environments. Sixteen Amazonian, Andean, and Caribbean lakes, lagoons, and swamps were sampled over a year. The aim was to determine if it was possible to obtain a reliable matrix of input pigment ratios that may be used in freshwater habitats with different environmental conditions. There were no clear differences among regions for most of the ratios of marker pigments to Chlorophyll a (Chl a) in most of the phytoplankton groups. Only the zeaxanthin/Chl a ratio showed clear variations among areas. The estimates for the mean relative contribution of each phytoplankton group calculated for the pigment ratios obtained in each separate habitat and season were very similar to the estimates calculated using the average pigment ratio obtained for all habitats and seasons. Our study suggests that the matrix of the average pigment ratio obtained in this study can be used to estimate phytoplankton class abundances with the CHEMTAX program in freshwater habitats with different limnological conditions.
Lighting up phytoplankton cells with quantum dots
Authors: Orcutt Karen M. , Gundersen Kjell , Wells Mark L. , Poulton Nicole J. , Sieracki Michael E. , Smith G. Jason
Published: April 2011

Quantum dots (Qdots) are semiconducting nanocrystals composed of periodic elements with different intrinsic band‐gap energies that yield unique fluorescent signatures. Unlike conventional organic fluorophores, Qdots are photo‐chemically stable and have a wide absorption spectrum, but a narrow, tunable emission spectrum. Multiple colors can be imaged from a single excitation wavelength allowing for labeling of many different target sites (e.g., membrane proteins) simultaneously.

We conjugated Qdots to primary antibodies specific for the soluble enzyme nitrate reductase (NR) and a light‐harvesting structural protein localized in the chloroplast, the fucoxanthin chlorophyll a/c protein (FCP), in the marine diatom Skeletonema costatum. By fluorescence microscopy, we successfully detected NR and FCP in single cells of S. costatum with a clarity and definition that was not obtainable with conventional organic fluorophores. Biotinylated cells labeled with Qdot‐strepavidin conjugate and Qdot‐FCP immuno‐labeled cells were detected by flow cytometry. Qdot bioconjugates provide an alternative photostable probe for surface or intracellular protein immuno‐localization in the study of marine bacteria and phytoplankton metabolism and physiology.
An improved flow‐injection analysis method for the determination of dissolved aluminum in seawater
Authors: Brown Matthew T. , Bruland Kenneth W.
Published: April 2011

An improved, highly sensitive, flow‐injection analysis method for the determination of dissolved aluminum in seawater, based on the work of Resing and Measures (1994), is presented. The most significant modification to this earlier work is the use of in‐line preconcentration of seawater onto a commercially available resin, eliminating the resin‐synthesis step. Other modifications include the addition of a column‐conditioning step prior to sample loading that increases the quantitative retention and sensitivity, in‐line buffering of samples prior to column loading to achieve optimal sample pH, an increased acid‐eluent concentration to efficiently remove Al from the resin column, and an increased reaction buffer concentration. The method has a detection limit of 0.1 nM Al when preconcentrating 10 mL sample and a precision of 2.5% based on replicate analyses of a 5 nM Al sample when preconcentrating 2.5 mL sample. The method was applied to surface and deepwater samples collected in the North Pacific (2004 Sampling and Analysis for Fe [SAFe] cruise) and from surface water samples collected across the Columbia River plume. Results suggest that the SAFe samples could potentially serve as seawater reference materials for dissolved Al following further investigation by other researchers using different methods. The use of low‐density polyethylene bottles with low‐density polyethylene caps as standard protocol for storage of acidified seawater samples for Al analysis is also discussed.
Optimal evaluation of the surface ocean CO2 system in the northern North Atlantic using data from voluntary observing ships
Authors: Nondal Gisle , Bellerby Richard G. J. , Olsen Are , Johannessen Truls , Olafsson Jón
Published: April 2011

This work evaluates whether an accurate calculation of the entire CO2 system in the northern North Atlantic can be carried out using a combination of in situ fugacity of CO2 (fCO2) and ancillary data often measured on Voluntary Observing Ships (VOS), i.e., sea surface temperature (SST) and sea surface salinity (SSS), as well as nitrate (NO3−). Two approaches are tested: (I) determination of At from SSS and then calculating Ct from measured fCO2 and estimated At; and (II) determination of Ct from SSS, SST, and NO3− and then calculating At from measured fCO2 and estimated Ct. The optimal approach was found to be determination of At from SSS and then calculating Ct from measured fCO2 and estimated At. This allowed At to be determined with a mean bias of −1.8 µmol kg−1 and root mean square (rms) deviation 6.2 µmol kg−1 and then Ct to be calculated with a mean bias of −1.0 µmol kg−1 and standard error of calculation of 7.4 µmol kg−1, as validated using independent data sets.
Development of an in situ underwater particle image velocimetry (UWPIV) system
Authors: Liao Qian , Bootsma Harvey A. , Xiao Jianen , Klump J. Val , Hume Andrew , Long Matthew H. , Berg Peter
Published: April 2011

A low‐cost self‐contained underwater particle image velocimetry (UWPIV) system has been developed to measure small‐scale turbulent flow structures in situ. The UWPIV employs a compact continuous‐wave laser and an optical scanner to deliver a light sheet that illuminates naturally occurring particles. Particle images are taken by a CCD camera along with an ultra‐compact PC. The nontethered and compact design can be fit in two small underwater housings with all components powered by batteries: an ideal design for a variety of in situ deployments. The system has been field‐tested in the coastal zone of Lake Michigan. Turbulent flow structures of the wave‐current bottom boundary layer are measured right above the nearshore lakebed, which is densely covered by quagga mussels (Dreissena bugensis). Vertical profiles of mean velocity, Reynolds stresses, dissipation rate of the turbulent kinetic energy, turbulent viscosity, plankton particle concentration, and the turbulent flux of particles are presented and discussed.
A simple technique for continuous measurement of time‐variable gas transfer in surface waters
Authors: Tobias Craig R. , Böhlke John Karl , Harvey Judson W. , Busenberg Eurybiades
Published: April 2011

Mass balance models of dissolved gases in streams, lakes, and rivers serve as the basis for estimating whole‐ecosystem rates for various biogeochemical processes. Rates of gas exchange between water and the atmosphere are important and error‐prone components of these models. Here we present a simple and efficient modification of the SF6 gas tracer approach that can be used concurrently while collecting other dissolved gas samples for dissolved gas mass balance studies in streams. It consists of continuously metering SF6‐saturated water directly into the stream at a low rate of flow. This approach has advantages over pulse injection of aqueous solutions or bubbling large amounts of SF6 into the stream. By adding the SF6 as a saturated solution, we minimize the possibility that other dissolved gas measurements are affected by sparging and/or bubble injecta. Because the SF6 is added continuously we have a record of changing gas transfer velocity (GTV) that is contemporaneous with the sampling of other nonconservative ambient dissolved gases. Over a single diel period, a 30% variation in GTV was observed in a second‐order stream (Sugar Creek, Indiana, USA). The changing GTV could be attributed in part to changes in temperature and windspeed that occurred on hourly to diel timescales.
Zooplankton biomass estimation from digitized images: a comparison between subtropical and Antarctic organisms
Authors: Lehette Pascal , Hernández‐León Santiago
Published: April 2011

The measurement of mesozooplankton biomass in the ocean requires the use of analytical procedures that destroy the samples. Alternatively, the development of methods to estimate biomass from optical systems and appropriate conversion factors could be a compromise between the accuracy of analytical methods and the need to preserve the samples for further taxonomic studies. The conversion of the body area recorded by an optical counter or a camera, by converting the digitized area of an organism into individual biomass, was suggested as a suitable method to estimate total biomass. In this study, crustacean mesozooplankton from subtropical waters were analyzed, and individual dry weight and body area were compared. The obtained relationships agreed with other measurements of biomass obtained from a previous study in Antarctic waters. Gelatinous mesozooplankton from subtropical and Antarctic waters were also sampled and processed for body area and biomass. As expected, differences between crustacean and gelatinous plankton were highly significant. Transparent gelatinous organisms have a lower dry weight per unit area. Therefore, to estimate biomass from digitized images, pattern recognition discerning, at least, between crustaceans and gelatinous forms is required.
Determination of ultra‐low oxygen concentrations in oxygen minimum zones by the STOX sensor
Authors: Revsbech Niels Peter , Larsen Lars Hauer , Gundersen Jens , Dalsgaard Tage , Ulloa Osvaldo , Thamdrup Bo
Published: April 2011

The methods used until now have not been able to reliably resolve O2 concentrations in oceanic oxygen minimum zones below 1–2 µmol L−1. We present a new amperometric sensor for the determination of ultra‐low O2 concentrations under in situ conditions. The electrochemical STOX O2 sensor contains a primary sensing cathode and a secondary cathode that, when polarized, prevents entry of O2 into the sensor. This arrangement enables frequent in situ zero calibration and confers the sensor with a detection limit of 1‐10 nmol L−1 O2, even during application on a Conductivity‐Temperature‐Depth (CTD) profiler at great water depths. The sensor was used during the Galathea 3 Expedition to demonstrate that the core of the oxygen minimum zone (OMZ) off Peru contained < 2 nM O2. Application in a reactor on board demonstrated that changes in O2 concentrations in OMZ water containing < 200 nmol L−1 O2 could be monitored over periods of hours to days. The linear decrease in O2 concentration in the reactor indicated very low (< 20 nmol L−1) half saturation constants for the O2 respiring microbial community.
Measuring production—dissolution rates of marine biogenic silica by 30Si‐isotope dilution using a high‐resolution sector field inductively coupled plasma mass spectrometer
Authors: Fripiat François , Corvaisier Rudolph , Navez Jacques , Elskens Marc , Schoemann Véronique , Leblanc Karine , André Luc , Cardinal Damien
Published: April 2011

Regional and seasonal variability of the Si dissolution:production ratios in the surface ocean have not been well assessed. Here, we propose a new method for determining these rates, using the 30Si‐isotopic dilution technique with a high‐resolution sector field inductively coupled plasma mass spectrometer (HR‐SF‐ICP‐MS). Relative analytical precision of the isotopic measurement is better than 1%, similar to that obtained by thermal ionization‐quadrupole mass spectrometry (TIMS). Accuracy and reproducibility of the isotopic measurements have been checked on artificial and natural solutions by intercomparison between two HR‐SF‐ICP‐MS instruments and one TIMS. Measurements of real Si production and dissolution rates are illustrated for two contrasted situations with an average relative precision of 10%, including one from waters with low Si content (2 µmol L−1), which required an additional purification step by cation exchange chromatography. Si production rate from this later incubation was not significantly different from the one measured by radioactive 32Si. The new method is faster and simpler than TIMS or isotope ratio mass spectrometry (IRMS). Its sensitivity is more than one order of magnitude better than TIMS, and it can cover the whole range of Si concentrations encountered in the ocean.
In vivo DMSP‐biosynthesis measurements using stable‐isotope incorporation and proton‐transfer‐reaction mass spectrometry (PTR‐MS)
Authors: Stefels Jacqueline , Dacey John W.H. , Elzenga J. Theo M.
Published: April 2011

Assessing turnover rates of dimethylsulfoniopropionate (DMSP), precursor of the climate‐active gas dimethylsulfide (DMS), under different environmental conditions is fundamental to accurately modeling the marine sulfur cycle. Current gas chromatographic methods only provide net results of all processes acting on the different sulfur pools and are unable to measure fluxes, leaving room for speculation on the controlling factors and magnitudes of turnover processes. Here we present a new method in which stable isotope additions (D2O or NaH13CO3) are used to follow the in vivo production of DMSP. Incorporation of deuterium or 13C into DMSP was monitored using a proton‐reaction‐transfer mass spectrometer (PTR‐MS). A growth model was developed to calculate specific DMSP synthesis rates from the progress in mass ratio of labeled versus nonlabeled DMSP over time. Instead of measuring the amount of incorporated isotope, our method uses ratios of molecule masses. This approach has the advantage that the effect of the isotope addition on the change in mass ratio is amplified by the number of positions the label can occupy within the molecule. Application of the method was demonstrated in cultures of the ubiquitous DMSP producer Emiliania huxleyi and further developed for use in short‐time incubation studies with water from the Sargasso Sea during July 2004. Very low specific synthesis rates between 0.05 and 0.2 d−1 could be measured. The method is the first to measure in vivo DMSP production rates. It is relatively easy to apply, highly sensitive, and may also be applicable to other biogenic compounds.
A large‐volume microfiltration system for isolating suspended particulate organic matter: fabrication and assessment versus GFF filters in central North Pacific
Authors: Roland Leslie A. , McCarthy Matthew D. , Peterson Tawnya D. , Walker Brett D.
Published: April 2011

We describe the construction and testing of a home‐built ultrafiltration (UF) system, based on commercially available hollow fiber polysulfone membranes, for isolation of suspended particulate organic matter (POMsusp) from large volumes (2000–10,000 L) of ocean water. The overall apparatus consists of two sequential UF steps: a main filtration system (100 L reservoir) driven by a stainless steel centrifugal pump, and a subsequent reduction/ diafiltration system (2 L reservoir) driven by a peristaltic pump. The system can be readily assembled using off‐the‐shelf parts at a fraction of the cost of commercial UF systems. Our system functioned comparably to previously described commercial units. We conducted a series of tests using both surface (21 m) and mesopelagic (674 m) N. Pacific central seawater from ocean pipeline sources at the Natural Energy Laboratory Authority of Hawaii (NELHA), while simultaneously collecting GFF‐POM samples. We evaluated flow rates, fouling behavior, carbon and nitrogen recoveries and compositions, and also bacteria and virus retention of ultrafiltered‐POM (UPOM) using both 0.1 µm and 500 kilodalton pore size membranes. We also compared composition of UPOM versus GFF‐POM, finding clear differences, which also varied between surface and mesopelagic waters. Finally, to evaluate the appeal of large‐volume filtrations at NELHA to study central N. Pacific Gyre POMsusp, we compared our data with offshore station ALOHA.
Biosensor for laboratory and lander‐based analysis of benthic nitrate plus nitrite distribution in marine environments
Authors: Revsbech Niels Peter , Glud Ronnie Nøhr
Published: April 2011

We present a psychotropic bacteria—based biosensor that can be used in low—temperature seawater for the analysis of nitrate + nitrite (NOx−). The sensor can be used to resolve concentrations below 1 µmol L−1 at low temperature (<2.5°C) and high salinity (35‰), and in situ use in the deep sea was demonstrated by measuring NOx− profiles in sediment at 1500 m depth, where the temperature was 2.5°C. Analysis of marine sediment at 70 m depth showed very heterogeneous NOx− profiles, most of which exhibited pronounced maxima due to nitrification in the oxic surface layer. At this shallow water site, the in situ profiles were similar to profiles measured in the laboratory, but generally laboratory profiles appeared more uniform, presumably as a result of reduced fauna activity and disturbance of the microstructure of the sediment surface during core recovery.
Laser Optical Plankton Counter and Zooscan intercomparison in tropical and subtropical marine ecosystems
Authors: Schultes Sabine , Lopes Rubens M.
Published: April 2011

Two recently developed instruments, the Laser Optical Plankton Counter (LOPC) and the Zooscan, have been applied to study zooplankton biomass size spectra in tropical and subtropical marine ecosystems off Brazil. Both technologies rely on optical measurements of particles and may potentially be used in zooplankton monitoring programs. Vertical profiles of the LOPC installed in a 200 µm ring net have been obtained from diverse environmental settings ranging from turbid and nearshore waters to oligotrophic open ocean conditions. Net samples were analyzed on the Zooscan and counted under a microscope. Particle biovolume in the study area estimated with the LOPC correlated with plankton displacement volume from the net samples, but there was no significant relationship between total areal zooplankton biomass determined with LOPC and the Zooscan. Apparently, normalized biomass size spectra (NBSS) of LOPC and Zooscan overlapped for particles in the size range of 500 to 1500 µm in equivalent spherical diameter (ESD), especially at open ocean stations. However, the distribution of particles into five size classes was statistically different between both instruments at 24 of 28 stations. The disparities arise from unequal flow estimates, from different sampling efficiencies of LOPC tunnel and net for large and small particles, and possibly from the interference of non‐zooplankton material in the LOPC signal. Ecosystem properties and technical differences therefore limit the direct comparability of the NBSS slopes obtained with both instruments during this study, and their results should be regarded as complementary.
Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)
Authors: Holmborn Towe , Dahlgren Kristin , Holeton Claire , Hogfors Hedvig , Gorokhova Elena
Published: April 2011

Biochemical proxies are becoming increasingly common for growth assessment in zooplankton. Their suitability is often unknown, however, and proper calibration is lacking. We investigated correlations between physiological variables (ingestion, egg production, and respiration rates) and biochemical indices related to protein synthesis (RNA content, RNA:DNA ratio, RNA:protein ratio, and protein specific aminoacyl‐tRNA synthetases [spAARS] activity) in copepods Acartia bifilosa exposed to different algal concentrations (0–1200 µg C L−1). All variables assayed increased with increasing food concentration either linearly (spAARS) or nonlinearly (all other variables). Egg production and ingestion rates were significantly and positively correlated with RNA content and RNA:protein ratio, whereas correlations with spAARS and RNA:DNA ratio were weaker or nonsignificant. However, when RNA:DNA ratio and spAARS activity were used as predictors of ingestion, together they had higher explanatory value than did either variable separately. As there were substantial differences in saturating food concentrations among the assayed variables, applicability of biomarkers as proxies of physiological rates will be more reliable if restricted to the nonsaturated phase of the functional response of either variable, unless both variables saturate simultaneously. These findings contribute to methodology of zooplankton growth assessment and to our understanding of biochemical processes underlying growth and metabolism in copepods.
Developing information literacy skills in nursing and rehabilitation therapy students
Authors: Durando Paola , Oakley Patricia
Published: April 2011

The environment in which nurses and rehabilitation therapists practice is rapidly evolving, resulting in changes in the skill sets and competencies required of new graduates. Evidence-based practice models, for example, require that entry-level nurses, physical therapists, and occupational therapists have the ability to identify, locate, and critically appraise research findings. This paper will describe curriculum-integrated, for-credit information literacy programs developed by the authors in collaboration with faculty members from the Schools of Nursing and Rehabilitation Therapy at Queen's University in Kingston, Ontario. The short-term goal of these programs is to teach undergraduate and graduate students advanced search strategy skills and critical appraisal techniques that will enable them to explore the implications of their literature findings. The long-term goal is to graduate practitioners who not only will have the skills to practice evidence-based health care but also will participate in scholarly activities and thus contribute to the evidence base in their disciplines.