bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Behaviour of Stainless Steel Wire for Urology
Authors: Walke Witold , Przondziono Joanna
Published: June 2010

The study presents results of pitting corrosion tests and analysis of chemical composition of X2CrNiMo 17-12-2 steel surface layer with diversified strain hardening and the method of surface preparation after 30-day exposure to artificial urine. Samples with electrochemically polished as well as with electrochemically polished and chemically passivated surface were selected for the tests. Electrochemical passivation was applied in order to obtain extremely smooth surface (Ra0.16 m). Pitting corrosion tests were performed by means of potentiodynamic method, where analysis of chemical composition of the layer formed on the steel surface was conducted using X-ray photoelectron spectroscopy (XPS). The tests were carried out in order to determine suitability of X2CrNiMo 17-12-2 steel with modified surface and diversified strain hardening for production of wire used in urology.
Alternative oblique head CT scanning technique reduces bone artifact and improves interpretability of brainstem anatomy
Authors: Kampondeni Sam Douglas , Birbeck Gretchen Lano , Oostveen Robert J. , Hammond Colleen , Potchen Michael James
Published: June 2010

Brainstem pathology due to infections, infarcts and tumors are common in developing countries, but neuroimaging technology in these resource-poor settings is often limited to single slice, and occasionally spiral, CT. Unlike multislice CT and MRI, single slice and spiral CT are compromised by bone artifacts in the posterior fossa due to the dense petrous bones, often making imaging of the brainstem non-diagnostic. With appropriate head positioning, the petrous ridges can be avoided with 40˚ sagittal oblique scans parallel to either petrous ridge. We describe an alternative sagittal oblique scanning technique that significantly reduces brainstem CT artifacts thereby improving clarity of anatomy. With Inst­itutional Ethical approval, 13 adult patients were enrolled (5 males; 39%). All patients had routine axial brain CT and sagittal oblique scans with no lesions found. Images were read by 2 readers who gave a score for amount of artefact and clarity of structures in the posterior fossa. The mean artifact score was higher for routine axial images compared to sagittal oblique (2.92 vs. 1.23; P<0.0001). The mean anatomical certainty scores for the brainstem were significantly better in the sagittal oblique views compared to routine axial (1.23 vs. 2.77; P<0.0001). No difference was found between the two techniques with respect to the fourth ventricle or the cerebellum (axial vs. sag oblique: 1.15 vs. 1.27; P=0.37). When using single slice CT, the sagittal oblique scanning technique is valuable in improving clarity of anatomy in the brainstem if axial images are non-diagnostic due to bone artifacts.
Liver Transplantation in Greek Children: 15 Years Experience
Authors: Xinias Ioannis , Mavroudi Antigoni , Vrani Olga , Imvrios George , Takoudas Dimitrios , Spiroglou Kleomenis
Published: June 2010

Liver transplantation (LT) is the only available live-saving procedure for children with irreversible liver failure. This paper reports our experience from the follow-up of 16 Greek children with end-stage liver failure who underwent a LT. Over a period of 15 years, 16 pediatric liver recipients received follow up after being subjected to OLT (orthotopic liver transplantation) due to end-stage liver failure. Nine children initially presented with extrahepatic biliary atresia, 2 with acute liver failure after toxic mushroom ingestion, 2 with intrahepatic cholestasis, 2 with metabolic diseases and one with hepatoblastoma. Ten children received a liver transplant in the Organ Transplantation Unit of Aristotle University of Thessaloniki and the rest in other transplant centers. Three transplants came from a living-related donor and 13 from a deceased donor. Six children underwent immunosuppressive treatment with cyclo­sporine, mycophenolate mofetil and corticosteroids, and 7 with tacrolimus, mycophenolate mofetil and corticosteroids. Three out of 16 children died within the first month after the transplantation due to post-transplant complications. Three children presented with acute rejection and one with chronic organ rejection which was successfully managed. Five children presented with cytomegalovirus infection, 5 with Epstein-Barr virus, 2 with HSV1,2, 2 with ParvoB19 virus, 2 with varicella-zoster virus and one with C. Albicans infection. One child presented with upper gastrointestinal hemorrhage and one with small biliary paucity. A satisfying outcome was achieved in most cases, with good graft function, except for the patient with small biliary paucity who required re-transplantation. The long-term clinical course of liver transplanted children is good under the condition that they are attended in specialized centers.
Spectrofluorometric characterization of dissolved organic matter for indication of precursor organic material and aromaticity
Authors: McKnight Diane M. , Boyer Elizabeth W. , Westerhoff Paul K. , Doran Peter T. , Kulbe Thomas , Andersen Dale T.
Published: June 2010

We studied the fluorescence properties of fulvic acids isolated from streams and rivers receiving predominantly terrestrial sources of organic material and from lakes with microbial sources of organic material. Microbially derived fulvic acids have fluorophores with a more sharply defined emission peak occurring at lower wavelengths than fluorophores in terrestrially derived fulvic acids. We show that the ratio of the emission intensity at a wavelength of 450 nm to that at 500 nm, obtained with an excitation of 370 nm, can serve as a simple index to distinguish sources of isolated aquatic fulvic acids. In our study, this index has a value of ~1.9 for microbially derived fulvic acids and a value of ~1.4 for terrestrially derived fulvic acids. Fulvic acids isolated from four large rivers in the United States have fluorescence index values of 1.4–1.5, consistent with predominantly terrestrial sources. For fulvic acid samples isolated from a river, lakes, and groundwaters in a forested watershed, the fluorescence index varied in a manner suggesting different sources for the seepage and streamfed lakes. Furthermore, we identified these distinctive fluorophores in filtered whole water samples from lakes in a desert oasis in Antarctica and in filtered whole water samples collected during snowmelt from a Rocky Mountain stream. The fluorescence index measurement in filtered whole water samples in field studies may augment the interpretation of dissolved organic carbon sources for understanding carbon cycling in aquatic ecosystems.
Microbial degradation of organic carbon and nitrogen on diatom aggregates
Authors: Grossart Hans-Peter , Ploug Helle
Published: June 2010

The major pathways of transformation of particulate organic matter by heterotrophic bacteria are respiration and production of new biomass. Until today only a limited number of studies have measured simultaneously respiration and production by aggregate‐associated bacteria. To study their role in the carbon cycle of aquatic systems we have formed model particles from diatoms (Skeletonema costatum, Thalasiosira weissflogii, Chaetoceros debilis) in roller tanks filled with natural seawater from Øresund, Denmark. Changes in bacterial community structure were analyzed by in situ hybridization and revealed members of the Cytophaga/Flavobacterium cluster and of the g subclass of Proteobacteria to be the main actors. The combination of radiotracer and microsensor techniques allowed determination of bacterial protein production and community respiration on the same aggregate and hence the apparent growth efficiency. Apparent growth efficiency (bacterial production/[bacterial production 1 community respiration]) was 0.50 ± 0.03 (se) on 1.5–2.5 d old aggregates and independent of bacterial growth rate. The initial carbon‐specific bacterial production and community respiration was 0.082 d-1 and 0.084 d-1, respectively. Thereafter, the carbon‐specific bacterial production decreased to 0.020 d-1, whereas specific community respiration decreased to 0.057 d-1. Hence, the apparent net growth efficiency decreased, partly as a result of grazing by protozoa, and it was much lower (0.23 ±; 0.04) at the end of incubation. Bacterial production was best correlated to particulate amino acids, whereas community respiration was best correlated to particulate organic carbon (POC). Protease activity was correlated to bacterial production and particulate combined amino acid content, whereas b‐glucosidase activity was better correlated to POC and community respiration than to particulate combined amino acid content. Turnover times of radiolabeled amino acids increased from 17.8 to 1,190 h during incubation and were tightly coupled to particulate combined amino acids and POC. Eighty‐seven percent of the decrease in particulate organic nitrogen (PON) over time could be explained by turnover of particulate combined amino acids by aggregate‐associated food web. Thus, transformation and remineralization of freshly produced particulate organic matter by aggregate‐attached food web is significant and the vertical flux of particulate organic matter in the ocean is highly reduced during sedimentation.
Diel integration of food quality by Daphnia: Luxury consumption by a freshwater planktonic herbivore
Authors: Sterner Robert W. , Schwalbach Michael S.
Published: June 2010

The chemical content of living algal food is an important determinant of zooplankton herbivore fitness. Previous studies have restricted diets to a single food type presented over multiple body mass turnover times; these have established that phosphorus content is one factor closely associated with growth of some zooplankton. In nature, however, algal P content and other potentially important dimensions to food quality vary in space and time. It would be unlikely for a grazing animal to experience a single constant food type over a major portion of its life. Many grazers likely experience diel variation in food quality associated with their vertical migration through nutritional gradients. It is not known how long‐term growth under fluctuating food relates to growth rates expected for single, constant food types. We tested whether grazers could integrate over daily variation in their food and thus realize body growth rates higher than would be expected from growth determined on single constant food types alone. We found that Daphnia magna grow near maximal rates when exposed to high‐quality food for half or less of the day. These results suggest that nutritional gradients associated with vertical migration bear close examination. They also strongly suggest that some form of diel P storage in zooplankton, a form of luxury consumption, occurs, and allows for integration over temporal variation in supply of this essential dietary ingredient.
Pelagic—benthic coupling in the abyssal eastern North Pacific: An 8‐year time‐series study of food supply and demand
Authors: Smith Kenneth Jr. L. , Kaufmann Ronald S. , Baldwin Roberta J. , Carlucci A. F.
Published: June 2010

An 8‐yr time‐series study of the trophic coupling between a pelagic food supply and its utilization by the sediment community was conducted at 4,100‐m depth in the eastern North Pacific between 1989 and 1998. Supply of sinking particulate organic carbon (POC) and particulate total nitrogen (PTN) was estimated from collections made with sediment traps moored at 3,500‐ and 4,050‐m depth (600 and 50 m above bottom). Sediment community oxygen consumption (SCOC), an estimate of aerobic utilization of organic matter, was measured in situ. POC and PTN fluxes at both depths declined significantly from October 1989 through 1996 then increased in 1998. Organic carbon : total nitrogen (C : N) of the sinking particulate matter fluctuated ~10 throughout the study, except for a major peak (84.8) at 50 m above bottom in summer 1995, indicating lateral advection of organic material of terrestrial origin. POC: SCOC declined progressively over the first 7 yr, from a high of 0.99 in 1989–1990 to 0.22 in 1995–1996. In 1998, there was an increase in POC: SCOC to 0.43, suggesting that the food deficit was reduced by an increase in sinking flux. A continuing deficit in food supply cannot be sustained without ultimately affecting the structural and functional characteristics of the sediment community. The importance of undersampling by sediment traps, lateral advection of marine and terrestrial organic matter from the continental slope and shelf, and dissolved organic matter is evaluated. These other sources of nutrients for benthic organisms may be important in explaining some of the observed discrepancy between supply and demand in the abyssal Pacific. Decadal‐scale climate variations that influence marine primary production and terrestrial discharges into the ocean may be extremely important in understanding biogeochemical processes in the deep sea.
DOC cycling in a temperate estuary: A mass balance approach using natural 14C and 13C isotopes
Authors: Raymond Peter A. , Bauer James E.
Published: June 2010

We measured dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and their corresponding △14C and γ13C values in order to study the sources and fates of DOC in the York River Estuary (Virginia, U.S.A.). The d△14C and γ13C values of DOC and DIC at the freshwater end‐member indicate that during periods of moderate to high flow, riverine DOC entering the York was composed of decadal‐aged terrestrially organic matter. In nearly all cases, DOC concentrations exceeded conservative mixing lines and were therefore indicative of a net DOC input flux from within the estuary that averaged 1.2 µM L−1 d−1.
Effect of fluid shear and irradiance on population growth and cellular toxin content of the dinoflagellate Alexandrium fundyense
Authors: Juhl Andrew R. , Trainer Vera L. , Latz Michael I.
Published: June 2010

The potential for in situ turbulence to inhibit dinoflagellate population growth has been demonstrated by experimentally exposing dinoflagellate cultures to quantified shear flow. However, despite interest in understanding environmental factors that affect the growth of toxic dinoflagellates, little is known of the effect of shear on the growth of toxin‐producing dinoflagellate species. Cultures of the dinoflagellate, Alexandrium fundyense, a producer of toxins responsible for paralytic shellfish poisoning, were exposed to quantified laminar shear generated in Couette flow for 1–24 h d−1 over 6–8 d. Shear stress in all experiments was 0.003 N m−2, similar to levels expected in near‐surface waters on a windy day. Net population growth decreased with shear exposures ≫1 h d−1 and became negative with exposures ≫12 h d−1. Cellular toxin content at the end of each experiment was measured by a receptor‐binding assay that used [3H]saxitoxin. Toxin cell−1 of cultures sheared for ≫1 h d−1 increased up to three times that of control cultures. Cellular toxin content increased significantly as growth rate of sheared cultures decreased. However, varying culture growth rate using irradiance had no significant effect on toxin cell−1. Because shear stress levels used in this study were plausible for near‐surface turbulent flows, oceanic turbulence may inhibit population growth and increase cellular toxin content of A. fundyense. However, in natural populations it would be difficult to distinguish the effect of turbulence on toxin content from other influences on toxin variability, particularly if volume‐or mass‐specific, rather than cell‐specific, measures of toxin are used.
Epilithic nitrogen fixation in the rocky littoral zones of Lake Malawi, Africa
Authors: Higgins Scott N. , Hecky Robert E. , Taylor William D.
Published: June 2010

Rates of epilithic N2 fixation in the rocky littoral zones of Lake Malawi, determined by in situ incubations and the acetylene reduction method, declined with depth, were highly correlated to light intensity and heterocyst biovolume, and are among the highest observed values for freshwater or marine systems. Daytime N2 fixation rates were similar between sites at similar depths, except at sediment and nutrient impacted sites, where rates were lower and more variable. Daytime N2 fixation rates were measurable in all transparent chambers and were negligible in opaque chambers, which indicates that phototrophic diazotrophs (organisms capable of utilizing atmospheric nitrogen) were responsible for all day‐time N2 fixation. Nocturnal N2 fixation was ~60% of daytime fixation. A model that integrated N2 fixation over depth and time predicted that epilithic N2 fixation may contribute up to 35% of N inputs to the epilimnion of Lake Malawi.
Large‐scale patterns in seagrass (Thalassia testudinum) demographics in south Florida
Authors: Peterson Bradley J. , Fourqurean James W.
Published: June 2010

An examination of the population age structure of 118 spatially separated subpopulations of Thalassia testudinum over the extent of the Florida Keys National Marine Sanctuary (FKNMS) during a 2‐yr period revealed significant spatial variation in short shoot (SS) demographic characteristics and population dynamics. Shoot age was determined for 12,031 SS. The number of leaf scars on individual shoots was converted to shoot age by use of observed seasonally and spatially variable leaf emergence rates. The yearly mean leaf emergence rate was 0.0295 ± 0.0128 leaves SS−1 d−1 (±1 SD), and the median age of counted shoots was ~5 yr. A significant relationship between asexual reproductive effort and gross recruitment of SS into the populations (r2 = 0.15, P < 0.001) and between mortality of SS and gross recruitment (r2 = 0.72, P < 0.001) existed. Thus, the greatest risk of mortality occurred in areas where gross recruitment was highest. The net population growth for T. testudinum within the boundaries of FKNMS was stable (mean = −0.006 ± 0.089 yr−1). However, areas within FKNMS fluctuated between positive and negative net growth rates (−0.20–0.50 yr−1). The power of such large‐scale observations is the ability to identify areas of management concern and to frame questions that address the controlling mechanisms that influence these regions of fluctuating population growth.
Genetic changes within freshwater bryozoan populations suggest temporal gene flow from statoblast banks
Authors: Freeland Joanna R. , Rimmer Vivien K. , Okamura Beth
Published: June 2010

Temporal changes in the genetic structure of populations of the freshwater bryozoan Cristatella mucedo were investigated by genotyping colonies at five microsatellite loci. Colonies were collected from five different locations over time periods ranging from 1 month to 5 yr. Our findings identified substantial within‐site genetic changes, both within and between years, that were not consistent with variation produced by sexual reproduction. There was a general trend toward a decrease in genetic diversity throughout the growing season, possibly due to clonal selection. In addition, 18 out of 21 within‐site comparisons showed a significant difference in the allele frequencies at one or more loci. Two of the populations revealed identical clones in >1 yr. At one site, an apparent population crash occurred in 1993; nevertheless, numerous clones were present in 1994 and 1995, including two multilocus genotypes that were present at the same site in 1992. Since the populations from before and after the bottleneck remained genetically similar, the most plausible source of these clones is reintroduction from a statoblast bank rather than through introductions from other genetically distinct populations. These findings, in conjunction with earlier studies, indicate that propagule banks influence the population dynamics of a wide range of freshwater invertebrates in a number of ways, including the enhancement of within‐population genetic diversity and a decreased likelihood of local extinctions.
Changes in marine bacterioplankton phylogenetic composition during incubations designed to measure biogeochemically significant parameters
Authors: Massana Ramon , PedrόsߚAliό, Carlos , Casamayor Emilio O. , Gasol Josep M.
Published: June 2010

Bottle incubations, during which the activity and growth of prokaryotes is monitored during several days, are frequently carried out to study functional aspects of marine prokaryotic assemblages. These experiments will relate directly to in situ activities if all populations grow harmonically during the incubation. We tested whether this was the case by analyzing the composition of bacterial assemblages at the beginning and at the end of the incubation by denaturing gradient gel electrophoresis. Five experiments were done in different Antarctic regions. Bacterial assemblages north and south of the Polar Front were very different. In all cases, the final assemblages were very different from the initial ones, and these changes were often accompanied by a significant decrease of diversity indices. Our experiments included treatments with different temperature and organic matter amendments. Whereas the increase in temperature tested had a minor effect on prokaryotic growth rate and specific composition, the addition of organic matter strongly stimulated growth rate and selected a particular bacterial assemblage in some experiments but not in others. A significant component of bacterial assemblages from waters south of the Polar Front appeared to be Polaribacter franzmannii, a gas vacuolated bacterium of the CytophagaߚFlavobacteriumߚBacteroides group that was originally isolated from Antarctic sea ice. This phylotype was enriched and dominated in almost all final assemblages. Our results indicate that longߚterm bottle incubations mostly measure the activity of a few opportunistic bacteria and not that of the original assemblage. This should be taken into account if data obtained in these experiments are used for balancing whole ecosystem carbon budgets and to derive biogeochemical conclusions.
Phagotrophy and toxicity variation in the mixotrophic Prymnesium patelliferum (Haptophyceae)
Authors: Legrand C.
Published: June 2010

Phagotrophy was investigated in the photosynthetic and ichthyotoxic Prymnesium patelliferum (Haptophyceae) using fluorescent microspheres, fluorescently labeled bacteria, and live bacteria cells. Ingestion rates were estimated both from prey uptake and disappearance experiments in phosphorus (P)‐limited and ‐replete algal cultures. Prymnesium patelliferum was feeding preferentially on bacteria (bact) compared to fluorescent microspheres (FM). Large fluorescent microspheres (1.6 and 3 ±m) were ingested at very low rates (<0.1 FM alga−1 h−1), and small microspheres (0.5 µm) were not ingested. Ingestion of bacteria (mean size 2 ±m) was highest in P‐limite P. patelliferum cultures (up to four bact alga−1 h−1) compared to P‐replete culture (0–1.2 bact alga−1 h−1). In addition, cellular P content of P‐limited cells fed with bacteria became similar to those of P‐replete cultures after 48 h, indicating a close relation between cellular P content and feeding behavior. Hemolytic activity of P. patelliferum was up to four times higher in P‐limited cultures compared to P‐replete cultures. During the transition from P‐limiting to P‐replete conditions, the addition of bacteria and/or the corresponding bacterial filtrate (<0.2 ±m) and/or PO43- to P limited cultures resulted in a decrease (50%) of the hemolytic activity after 24 h in relation to controls (no addition of bacteria, filtrate, or P). No PO43- was detectable as a result of enriching cultures with bacterial cells or bacterial filtrates. These results indicate that P. patelliferum can use different sources of P (inorganic and dissolved, organic and particulate) and adapt its mode of nutrition in a short time. Furthermore, the decrease of hemolytic activity in the highly toxic P‐limited cells also occurred rapidly following a recovery in cellular P status through mixotrophic feeding or uptake of inorganic phosphate, suggesting that toxicity in P. patelliferum cells can be minimized by nutrient manipulation.
Fluctuations of nitrogen isotope ratio of gobiid fish (Isaza) specimens and sediments in Lake Biwa, Japan, during the 20th century
Authors: Ogawa Nanako O. , Koitabashi Tadatoshi , Oda Hirotaka , Nakamura Toshio , Ohkouchi Naohiko , Wada Eitaro
Published: June 2010

Nitrogen isotope ratios (Δ15N) of sediment and formalinߚfixed fish specimens (Isaza fish, Chaenogobius isaza, Tanaka), which had been collected and preserved over 40 yr, were used to provide a new methodology to reconstruct recent eutrophication and historical changes in the nitrogen cycle in Lake Biwa. Δ15N records of Isaza fish collected in the north basin of Lake Biwa, a lake that had been rapidly eutrophicated in the last several decades, showed a rapid increase from the early 1960s to 1980s with an overall amplitude of >3‰. The same trend was simultaneously observed from that of sedimentary nitrogen. We evaluated several factors controlling Δ15N of Isaza fish and sediments during the 20th century and concluded that an increase of Δ15N was either associated with an increase in loading nitrate with high Δ15N values from the watershed or enhanced denitrification in the lake.
The contribution of picophytoplankton in marine and freshwater systems of different trophic status and depth
Authors: Bell Thomas , Kalff Jacob
Published: June 2010

Although there are a number of single system and regional studies on the importance of picophytoplankton (PP; 0.2–2 µm), there has been little effort to quantify their importance on a larger scale and to integrate marine and freshwater studies. We developed empirical models from data in the literature to assess the absolute and relative importance of PP in marine and freshwater. The PP biomass (chlorophyll a [Chl a]) increases with trophic status, here represented by the total Chl a, in both marine and freshwater systems. In addition, PP abundance in freshwater, and primary production in marine waters, increases with trophic status. Even so, the relative importance of the PP biomass and primary production declines systematically with increasing trophic status in both marine and freshwater systems. Both the absolute biomass of PP and the relative contribution of PP biomass to the total phytoplankton community biomass are larger in freshwater at any particular value of total Chl a. In eutrophic lakes, which are typically shallow and particularly susceptible to the greatest phytoplankton resuspension and sediment recruitment, the on average small relative contribution of PP biomass appears affected by a relatively high but variable contribution of resuspended microplankton.
Biogeochemical effects of iron availability on primary producers in a shallow marine carbonate environment
Authors: Chambers Randolph M. , Fourqurean James W. , Macko Stephen A. , Hoppenot Regis
Published: June 2010

We completed a synoptic survey of iron, phosphorus, and sulfur concentrations in shallow marine carbonate sediments from south Florida. Total extracted iron concentrations typically were <50 µmol g−1 dry weight (DW) and tended to decrease away from the Florida mainland, whereas total extracted phosphorus concentrations mostly were <10 µmol g−1 DW and tended to decrease from west to east across Florida Bay. Concentrations of reduced sulfur compounds, up to 40 µmol g−1 DW, tended to covary with sediment iron concentrations, suggesting that sulfide mineral formation was ironߚlimited. An index of iron availability derived from sediment data was negatively correlated with chlorophyll a concentrations in surface waters, demonstrating the close coupling of sedimentߚwater column processes. Eight months after applying a surface layer of iron oxide granules to experimental plots, sediment iron, phosphorus, and sulfur were elevated to a depth of 10 cm relative to control plots. Biomass of the seagrass Thalassia testudinum was not different between control and iron addition plots, but individual shoot growth rates were significantly higher in experimental plots after 8 months. Although the iron content of leaf tissues was significantly higher from iron addition plots, no difference in phosphorus content of T. testudinum leaves was observed. Iron addition altered plant exposure to free sulfide, documented by a significantly higher d34S of leaf tissue from experimental plots relative to controls. Iron as a buffer to toxic sulfides may promote individual shoot growth, but phosphorus availability to plants still appears to limit production in carbonate sediments.
CO2 and HCO3 ߚ uptake in marine diatoms acclimated to different CO2 concentrations
Authors: Burkhardt Steffen , Amoroso Gabi , Riebesell Ulf , Sültemeyer Dieter
Published: June 2010

Rates of cellular uptake of CO2 and HCO3− during steadyߚstate photosynthesis were measured in the marine diatoms Thalassiosira weissflogii and Phaeodactylum tricornutum, acclimated to CO2 partial pressures of 36, 180, 360, and 1,800 ppmv. In addition, in vivo activity of extracellular (eCA) and intracellular (iCA) carbonic anhydrase was determined in relation to CO2 availability. Both species responded to diminishing CO2 supply with an increase in eCA and iCA activity. In P. tricornutum, eCA activity was close to the detection limit at higher CO2 concentrations. Simultaneous uptake of CO2 and HCO3− was observed in both diatoms. At airߚequilibrated CO2 levels (360 ppmv), T. weissflogii took up CO2 and HCO3− at approximately the same rate, whereas CO2 uptake exceeded HCO3− uptake by a factor of two in P. tricornutum. In both diatoms, CO2 :HCO3− uptake ratios progressively decreased with decreasing CO2 concentration, whereas substrate affinities of CO2 and HCO3− uptake increased. Halfߚsaturation concentrations were always <=5 mM CO2 for CO2 uptake and <700 mM HCO3− for HCO3− uptake. Our results indicate the presence of highly efficient uptake systems for CO2 and HCO3− in both diatoms at concentrations typically encountered in ocean surface waters and the ability to adjust uptake rates to a wide range of inorganic carbon supply.
Influences of benthic boundary‐layer flow on feeding rates of ciliates and flagellates at the sediment‐water interface
Authors: Shimeta Jeff , Starczak Victoria R. , Ashiru Oladipo M. , Zimmer Cheryl Ann
Published: June 2010

Heterotrophic protists are integral to sedimentary food webs, but influences on their activities are poorly understood, especially the role of benthic boundary‐layer flow. Effects of flow on ingestion rates were measured for bacterivorous protists at the sediment surface in a flume. Results from four common, benthic suspension‐feeding ciliates were species specific. Mean clearance rates of the scuticociliates Cohnilembus sp. and Paranophrys magna and the hypotrich Euplotes minuta increased by factors of two to three as friction velocity (u*) increased from 0 to 1.0 cm s21. Above u* = 1.0 cm s−1, clearance rates of Cohnilembus sp. and P. magna were constant, whereas the clearance rate of E. minuta was reduced by 40% at u* = 1.5 cm s−1. E. minuta thus revealed an optimal flow regime for feeding. In contrast, the mean clearance rate of the scuticociliate, Cyclidium sp., was unrelated to u*. In experiments with sediment cores from a subtidal, silty sand site, the mean clearance rate of the bacterivorous ciliate community of the sediment‐water interface increased by a factor of five between u* = 0 and 0.9 cm s−1. The effects of flow were likely due to enhanced advection of prey to the ciliates. In contrast, the clearance rate of the nanoflagellate community in sediment cores was unrelated to u*. Tidal currents at the field site were estimated to increase the ciliate community's daily integrated feeding by a factor of 3.2 compared to still water. Epibenthic ciliates create a dynamic link between planktonic and benthic food webs, mediated strongly by benthic boundary‐layer flow.
Stratification produced by surface cooling in lakes with significant shallow regions
Authors: Wells Mathew Graeme , Sherman Bradford
Published: June 2010

A reservoir with distinct shallow and deep regions can produce stratification in response to uniform surface heat loss. The shallow region cools more rapidly, and a cold dense gravity current forms that results in stratification at the base of the deep region and an upwelling of cold water. The surface mixed layer deepens by convective entrainment, and a steady mixed‐layer depth can result when the cold upwelling balances the rate at which the mixed layer deepens. The steady depth of the mixed layer depends on the ratio of the area of the shallow region to the area of the deep region. Significant stratification only results when the reservoir has shallow regions that account for more than 50% of the surface area. The depth of the surface mixed layer also depends on the ratio of the depths of the shallow and deep regions, and no significant stratification can form if this ratio is greater than 0.5. For a wedge‐shaped geometry, these observations can be generalized by considering the ratio of the average depth to the maximum depth in a reservoir; the gravity current can produce stratification in more than 50% of the depth when this ratio is less than 0.5. Results from a laboratory study and field data from Chaffey Reservoir, Australia, are presented on the surface mixed‐layer depth, along with estimates of the time scales needed for atmospheric forcing to lead to the development of stratification.
A comparison of two N‐irradiance interaction models of phytoplankton growth
Authors: Flynn Kevin J. , Marshall Helen , Geider Richard J.
Published: June 2010

The N‐photoacclimation interaction models of Geider et al. (GM) and Flynn et al. (FM) are compared by tuning them to data from a light‐shift experiment for a diatom. Both the original model constructs have failings, GM in its Nassimilation component and FM in its photoacclimation component. However, both of these models can be modified readily to overcome these problems. In addition, hybrid models that use the N‐assimilation component of FM and the photoacclimative component of GM work well. For situations where a model is required to simulate the interaction between a single N source and light, the use of the revised GM structure should be considered first. The revised FM is better suited for more complex environmental scenarios—for example where detailed simulations of ammonium‐nitrate interactions are required. GM and FM are to be preferred over models that use a fixed Chl : C, because they may both be tuned directly to real chlorophyll a data in ecosystem simulators.
Tracking the fate of a high concentration groundwater nitrate plume through a fringing marsh: A combined groundwater tracer and in situ isotope enrichment study
Authors: Tobias Craig R. , Macko Stephen A. , Anderson Iris C. , Canuel Elizabeth A. , Harvey Judson W.
Published: June 2010

A groundwater plume enriched in 15NO3− was created upgradient of a mesohaline salt marsh. By measuring the changes in concentration and isotopic enrichment of NO3−, N2O, N2, NH4+, and particulate organic nitrogen (PON) during plume transport through the marsh, in situ rates of dissimilatory nitrate reduction to ammonium (DNRA) and denitrification (DNF) were estimated, as well as N storage in the reduced N pools. For groundwater discharge within the top 10 cm of marsh, NO3− removal was 90% complete within the 50 cm of marsh nearest the upland border. The peak NO3− loss rate from the plume ranged from 208 to 645 µM d−1. Rates of DNRA (180 µM d−1) and DNF (387–465 µM d−1) processed 30% and 70% of the NO3− load, respectively. Terminal N2 production was approximately equal to N2 production rates during DNF. Comparison of 15N lost from the 15NO3− pool and 15N gained in each of the reduced products accounted for only 22% of the reduced 15N, thus indicating N export from the system. Despite high rates of DNRA, the NH4+ produced was not a long‐term repository for the groundwater‐derived N but was instead rapidly immobilized into marsh PON and retained on longer timescales. The small inventory of 15N in the N2 and N2 pools relative to DNF rates, coincident with an undersaturation of dissolved argon, indicated that denitrified N was exported to the atmosphere on short timescales. The relative magnitudes of DNF and DNRA in conjunction with the immobilization of NH4+ and evasion of N gases dictated the extent of export versus retention of the groundwater NO3− load.
Individual variability in diel vertical migration of a marine copepod: Why some individuals remain at depth when others migrate
Authors: Hays G. C. , Kennedy H. , Frost B. W.
Published: June 2010

The diel vertical migration (DVM) of the copepod Metridia pacifica was examined in Dabob Bay (47°45.05′N, 122°49.71′W), a fjord in Washington state. Although the population showed deep daytime residence (75–175 m), a proportion of the population was found in the surface waters at night. For individuals that migrated to the surface, the mean size of the oil sac was much smaller than those that remained at depth (mean lengths of oil sac 0.25 mm for individuals collected between 0 and 25 m at night, compared with 0.43 mm for individuals from between 125 and 175 m). Similarly, the C:N ratio was lower for animals collected from near the surface, indicative of their lower lipid reserves. These results suggest that individual variability in DVM was influenced by body condition, with those animals with larger lipid stores not needing to risk coming to the surface to feed at night.
Nearshore circulation during upwelling inferred from the distribution of dissolved cadmium off the Oregon coast
Authors: Takesue Renee K. , van Geen Alexander
Published: June 2010

The effectiveness of dissolved cadmium (Cd) as a tracer of coastal upwelling is demonstrated by comparing its water column distribution to that of traditional upwelling indicators, in particular phosphate (P) and salinity, as well as equatorward wind forcing at the Oregon coast. Cd and P concentrations in samples collected on board ship on 17—27 August 1995 between 3 and 100 km from the coast offshore of Cape Blanco, Oregon, ranged between 0.2 and 0.9 nmol kg−1 and <0.1 and 2.5 µmol kg−1, respectively. Both tracers behaved conservatively during onshore transport at depth; linear Cd‐salinity and P‐salinity relations in offshore source waters were preserved in bottom waters over the shelf. Following upwelling to the surface, however, Cd and P distributions diverged, with Cd remaining essentially constant while P was taken up by phytoplankton, predominantly diatoms. The Cd content of nearshore water collected from the beach inshore of the cruise area was very similar to that of upwelling source waters sampled from the ship, suggesting efficient exchange of waters between the shelf bottom layer and the very nearshore region, including the surfzone. A simple box model, in which onshore Ekman transport occurs through a well‐mixed bottom layer extending from the edge of the continental shelf to the very nearshore region, illustrates a close link between upwelling‐favorable wind forcing and very nearshore Cd concentrations. The close agreement between Cd time series generated by the model and surfzone Cd sampled every 2—4 weeks during 1994—1996 suggests that the effectiveness of Cd as a tracer of wind‐driven coastal upwelling off the Oregon coast is due in large part to conveyor‐like circulation and the remarkably efficient mixing of newly upwelled water into the very nearshore region.
Landscape variation in phosphorus concentration and effects on detritus‐based tropical streams
Authors: Rosemond Amy D. , Pringle Catherine M. , Ramírez Alonso , Paul Michael J. , Meyer Judy L.
Published: June 2010

Landscape‐scale variation in streamwater phosphorus (P) concentration can affect aquatic food webs. Such variation occurs naturally in streams at La Selva Biological Station in Costa Rica due to spatially variable inputs of geothermally modified groundwater. We examined effects of this gradient on detrital food web components at 16 stream sites. The Michaelis‐Menten model provided a good fit of the relationship between soluble reactive phosphorus (SRP) and leaf decay rate, fungal biomass, and invertebrate biomass, indicating that these variables were controlled by P concentration and that half‐saturation constants were relatively low (7—13 µg L−21 SRP). In a subsequent short‐term (3 week) whole‐stream P enrichment study, we found no effect of P addition on leaf decay rate or on biomass or density of invertebrates. However, laboratory tests of P, N, and Ca concentrations on mass loss of leaves showed detectable stimulation by both N and P after 3 weeks. A fourth study assessed the relative contribution of invertebrate consumption versus P concentration in determining decay rates among streams. The majority of variation was due to P concentration (71%), compared to effects of invertebrates (3%) or invertebrate × P interactions (14%). Overall, we found that a landscape‐scale natural gradient in P concentration influenced decay rates of organic matter and biomass of consumers, providing evidence that benthic detrital food webs can be limited from the bottom up by nutrients. Microbial processes appeared to be most important in driving differences in organic matter decay among sites, but invertebrates also contributed to elevated decay rates at high‐P sites.
Effects of groundwater flux on open‐channel estimates of stream metabolism
Authors: McCutchan James Jr. H. , Saunders James III. F. , Lewis William Jr. M. , Hayden Matthew G.
Published: June 2010

The open‐channel oxygen method can produce precise estimates of photosynthesis (P) and respiration (R) over a wide range of stream conditions. It is widely recognized that flux of groundwater contributes to the oxygen mass balance for a stream. However, groundwater flux is rarely considered in open‐channel estimates of stream metabolism, and no guidelines have been established regarding the conditions under which it can be ignored. The purpose of this paper is to describe a method for predicting the effect of groundwater flux on estimates of metabolism and thereby establish the conditions under which flux of groundwater can lead to large errors in estimates of metabolism. Estimation of P is not significantly affected by flux of groundwater. Ecosystem R, however, can be greatly overestimated where the oxygen concentration of groundwater is substantially lower than the concentration in the channel. Although the effects of groundwater flux on estimates of metabolism often are trivial, rates of flux can be sufficiently high in many streams, at least during some part of the year, to affect estimates of R where the oxygen concentration differs substantially between groundwater and surface water. Thus, the potential contribution of groundwater flux to oxygen mass balance should always be evaluated when the
Cycling of phosphorus maintains the production of microphytobenthic communities in carbonate sediments of a coral reef
Authors: Suzumura Masahiro , Miyajima Toshihiro , Hata Hiroshi , Umezawa Yu , Kayanne Hajime , Koike Isao
Published: June 2010

The phosphorus (P) cycle that maintains the production of microphytobenthic communities in carbonate sediments was investigated in the fringing Shiraho coral reef system located off the east coast of Ishigaki Island, Japan. Production rates of the diatom‐dominated microphytobenthic communities and the P flux at the sediment‐water interface were determined by in situ benthic enclosure experiments. The daily net production (6.9–24 mmol C m−2 d−1) by microphytobenthic communities in carbonate sediments accounted for 14–27% of organic carbon excess production by the bulk reef communities. Despite the observed active photosynthesis, the exchange of P across the sediment‐water interface was negligible. This implies that P in seawater is a minor source for the production of microphytobenthic communities. In situ bottle incubation experiments also demonstrated that P in seawater is a minor source and that P adsorbed on sediment particles is the significant source for production. Laboratory experiments led to an estimated concentration of adsorbed P in the carbonate sediments of ~0.39 μmol P g−1 dry wt, which corresponds to 5.5% of total P. This source can be rapidly released into seawater as dissolved reactive P, the most available P form. Thus, high primary productivity rates of the microphytobenthic communities is largely maintained by this sedimentary pool of P. Furthermore, the communities play an important role in retaining P in the carbonate sediments through uptake at the sediment‐water interface before it can diffuse away.
Calanoid copepods feed and produce eggs in the presence of toxic cyanobacteria Nodularia spumigena
Authors: Koski Marja , Schmidt Katrin , Engström-Öst Jonna , Viitasalo Markku , Jónasdóttir Sigrún , Repka Sari , Sivonen Kaarina
Published: June 2010

Feeding and fecundity of two calanoid copepod species (Acartia bifilosa and Eurytemora affinis) were studied in a food assemblage dominated by toxic cyanobacteria, to reveal whether mesozooplankton are able to obtain sufficient good quality food in different phases of a cyanobacteria bloom. Bloom conditions were simulated in a mesocosm by adding a high concentration of cultured hepatotoxic Nodularia spumigena to 100 mm filtered natural sea water. This seston was fed to copepods at days 1, 7, and 14 from the start of the mesocosm experiment, when it consisted of actively growing cyanobacteria (days 1 and 7) and increasing amounts of heterotrophic organisms and probably detritus (day 14). From bulk changes in chlorophyll and estimated ratios between chlorophyll and accessory pigments, it appears that both copepod species ingested large quantities of cyanobacteria in the first experiment but switched to ciliates when those became more abundant. Egg production of A. bifilosa was observed in all experiments, irrespective of the high concentration of nodularin in the mesocosm. The results demonstrate that the dominant copepod species of the Baltic Sea are able to feed, survive, and produce eggs in a plankton community dominated by toxic cyanobacteria.
Variation in iron(III) solubility and iron concentration in the northwestern North Pacific Ocean
Authors: Nakabayashi Shigeto , Kuma Kenshi , Sasaoka Kohsei , Saitoh Seiichi , Mochizuki Mamiko , Shiga Naonobu , Kusakabe Masashi
Published: June 2010

Vertical distributions of Fe(III) hydroxide solubilities (≪0.025 µm) and dissolved Fe (≪0.2 µm) concentrations at 0–250 m depth were studied inside (HP) and outside (LP) a high‐production (phytoplankton spring bloom) patch area in the northwestern North Pacific Ocean during May 1999. In the surface mixed layer, the Fe(III) solubility values at HP were much higher (2–4 nM) than those (0.3–0.9 nM) at LP and strongly correlated with chlorophyll a and nutrient concentrations. The high Fe(III) solubility observed in the surface mixed layer was probably due to a higher concentration or stronger affinity of natural organic Fe(III) chelators. In the surface waters, the dissolved Fe concentrations were generally lower than the Fe(III) solubility values, resulting from the active biological removal of dissolved Fe and excess concentration of Fe‐binding organic ligands. The Fe(III) solubility minima (0.2–0.4 nM) were present in a narrow depth range (40–125 m) below the surface mixed layer at all stations. The subsequent Fe(III) solubility levels appeared to increase up to 0.6–0.8 nM with depth at 100–250 m, in association with the increase in nutrient concentrations. The strong linear correlations between Fe(III) solubility values and nutrient concentrations in middepth waters suggest that the formation of organic Fe(III) chelators may be related to microbial decomposition of sinking biogenic organic matter. In middepth waters, the dissolved Fe concentrations were generally higher than the Fe(III) solubility values, which suggests that the small colloidal iron phases may be present in the dissolved Fe (≪0.2 µm) fraction.