bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of the thermal structure of a lake using a submarine
Authors: Thorpe S. A.
Published: May 2010

This note describes how a submarine, the F.A. Forel, carrying a vertical array of high‐resolution temperature sensors, was used along with conventional measurements from a lowered conductivity‐temperature‐depth probe (CTD) to make novel measurements of the temperature field in Lake Geneva during summertime conditions of stable stratification and during winter convection. The submarine speed was about 0.5 m s−1. In addition to the temperatures, the pressure, orientation, and tilt were recorded at frequencies of at least 10 Hz. Observations were made on a vertical scale of 0.1 to 2.5 m and on a horizontal scale from 0.5 m to 1 km. Examples of the data are presented. During the summer, evidence was found of internal waves and of extensive layers of low vertical temperature gradient, with vertical and horizontal scales of 0.5 m and 0.5 km, respectively; within this gradient, the temperature changed monotonically in the horizontal. During periods favoring convection, in the winter, when air temperatures were about 7°C below the surface‐water temperature, convectively unstable regions, typically of 5‐m horizontal scale, were observed in the mixed layer. These appeared to be convective plumes. These winter measurements also included observations of a layer of cold water that was adjacent to the sloping boundary of the lake. This was identified as being a plume of dense cold water with thickness on the order of 10 m, which was driven by surface cooling, and consequent more rapid temperature decrease, in the shallow nearshore water. On meeting the thermocline at a depth of about 100 m, this plume spread horizontally and formed an intrusion some 30 m thick.
Ferredoxin and flavodoxin as biochemical indicators of iron limitation during open‐ocean iron enrichment
Authors: Erdner Deana L. , Anderson Donald M.
Published: May 2010

Substitution of the noniron protein flavodoxin for the iron‐sulfur protein ferredoxin is an iron‐stress response employed by a variety of unicellular organisms, including many phytoplankton. The relative abundance of these two proteins has been shown to vary with the severity of growth limitation by iron in marine diatoms. During the IronEx II mesoscale iron‐enrichment experiment, large volume (100–600 liters) phytoplankton samples were collected for analysis of community ferredoxin and flavodoxin abundance using a high‐pressure liquid chromatography (HPLC) technique. In addition, three pennate diatom species isolated from the fertilization‐induced phytoplankton bloom were used for follow‐up laboratory experiments, which examined their iron physiology.

Prior to iron enrichment, biomass levels were insufficient to obtain any ferredoxin or flavodoxin signals. Measurements were successful after iron enrichment, with unexpected results. The strength of the HPLC signal tracked the biomass levels of the IronEx II phytoplankton bloom. Chromatographic peaks were evident on the fifth day following enrichment and persisted throughout the experiment before they declined and eventually disappeared following the last iron infusion. The main chromatographic peak was identified as flavodoxin; there was no evidence of ferredoxin in any of the samples. Pennate diatom clones isolated from the fertilization‐induced bloom and grown in the laboratory retain the ability to make ferredoxin when iron‐replete and induce flavodoxin when iron‐stressed. When iron‐limited, they are able to completely repress flavodoxin expression in about 1 d in response to iron resupply. Thus, the unexpected absence of ferredoxin and the persistence of flavodoxin during IronEx II, despite the observed increases in biomass and photosynthetic efficiency, suggest that the iron additions were insufficient to completely relieve physiological iron limitation.
Effects of nutrients (phosphorous, nitrogen, and carbon) and zooplankton on bacterioplankton and phytoplankton—a seasonal study
Authors: Vrede Katarina , Vrede Tobias , Isaksson Anneli , Karlsson Anna
Published: May 2010

The effects of inorganic nutrients (P and N), organic C, and metazoan zooplankton on bacterioplankton production and abundance and on phytoplankton biomass were studied in five experiments (from May to September) in Lake Erken. In addition, the seasonal dynamics of bacterioplankton and phytoplankton were followed in the lake from April to November.

Bacterioplankton production was P limited from May to August. N alone never stimulated bacterioplankton production, but bacterioplankton growth was close to colimited by P and N in July and August. Organic C stimulated bacterial production in June and September. Zooplankton enhanced bacterioplankton production in June, when bacterioplankton production was limited by P and C and the phytoplankton biomass in the lake was low. N alone stimulated phytoplankton growth in all experiments. In addition, P alone stimulated phytoplankton growth in May and July, and the combination of P and N stimulated phytoplankton growth in July and August. Zooplankton additions resulted in a decrease in phytoplankton biomass in May and September, mainly owing to grazing on Cryptophyceae.

The experimental results indicate that bacterioplankton and phytoplankton growth were uncoupled during most of the open‐water period because P primarily limited bacterioplankton growth and N limited phytoplankton growth. The response of the bacterioplankton community was most likely a direct effect of nutrient additions. Primary production and bacterioplankton production were correlated during the season, but partial correlations analysis indicates that this relationship can be attributed to the fact that both primary production and bacterioplankton production showed strong positive correlations with temperature. We suggest that uncoupling of bacterioplankton production and phytoplankton production may be a common phenomenon in lakes.
Shifts in bacterial community composition associated with different microzooplankton size fractions in a eutrophic reservoir
Authors: Šimek Karel , Kojecká Petra , Nedoma Jiří , Hartman Petr , Vrba Jaroslav , Dolan John R.
Published: May 2010

Using oligonucleotide probes for Eubacteria and four eubacterial subgroups, we monitored changes in bacterial community composition (BCC) with different degrees of grazing pressure, as follows: unfiltered water (UNF, all bacterivores present); <20 μm (bacteria, heterotrophic nanoflagellates [HNF], and small ciliates); <5 μm (bacteria and HNF only); and <1 μm or <0.8 μm (bacteria only), incubated in dialysis bags. Experiments were conducted in the Rimov Reservoir (South Bohemia) during the clear‐water phase (experiment I), a period of low protistan grazing pressure on reservoir bacterioplankton, and during the late summer phytoplankton peak (experiment II), a period of high protistan grazing pressure. In both experiments, there was a significant shift in BCC in the <5 μm treatments, which came in the form of increased proportions of alpha subclass of the class Proteobacteria (ALF) and Cytophaga/Flavobacterium group (C/F), corresponding with increased bacterivory of the ungrazed HNF populations. Changes in BCC in other experimental treatments were related to preincubation protistan grazing pressure. In experiment I, bacterioplankton were subjected to negligible protistan bacterivory in the reservoir and did not show a change in BCC in the predator‐free treatment (<1 μm), while BCC changed in treatments that yielded increases in protistan bacterivory compared with that in the ambient reservoir water. In experiment II, a significant shift in BCC was induced when bacterioplankton that were subjected to heavy predation pressure in the reservoir were transferred into the predator‐free treatment. Treatments that induced small changes in protistan grazing pressure (<20 μm and UNF in experiment II) did not show significant BCC shifts. Proportions of filamentous bacteria (>4 μm) increased in treatments that yielded large increases in bacterivory. Filament formation also showed season‐specific features; in experiment I, all filaments belonged into ALF, whereas in experiment II, most of them hybridized with the C/F probe. We conclude that the sudden shifts that violate the established balance between bacterial production and the protist‐induced bacterial mortality led to the significant shifts in cell morphology and BCC.
Contrasting effects of solar radiation on dissolved organic matter and its bioavailability to marine bacterioplankton
Authors: Obernosterer Ingrid , Reitner Bettina , Herndl Gerhard J.
Published: May 2010

The effect of ultraviolet radiation on the bioavailability of dissolved organic matter (DOM) to marine bacterioplankton was investigated in the Mediterranean Sea (Strait of Gibraltar, South and North Aegean Sea) and in the Caribbean Sea off Curacao. Surface‐water samples (collected between 1 and 85 m in depth) exposed to solar radiation did not show a distinct pattern in subsequent bacterial growth. However, samples collected from a pronounced chlorophyll maximum (two stations in the Strait of Gibraltar and four stations in the Aegean Sea) displayed in a 50% lower bacterial activity in the radiation‐exposed treatments compared with the dark controls. In contrast, mesopelagic water samples (200–350 m in depth) exposed to surface solar radiation exhibited a two‐ to fourfold increase in bacterial activity compared with the corresponding dark controls. Addition of the model protein bovine serum albumin (BSA) to mesopelagic‐water samples and subsequent exposure to solar radiation resulted in a 50% lower rate of bacterial activity compared with the dark treatments, thus indicating the occurrence of photochemically induced changes to this labile compound. This decrease in bacterial activity in BSA‐amended, irradiated water was also detectable in surface waters sampled off Curaçao, whereas BSA amendment to surface water from the Mediterranean Sea did not result in a distinct pattern of bacterial activity.

Our data indicate that exposure of DOM to solar radiation causes a reduced bioavailability of the exposed DOM to bacterioplankton, if the bacterial activity : dissolved organic carbon (DOC) concentration ratio is high (indicative of labile DOM). If the bacterial activity:DOC ratio is low (indicative of more refractory DOM), the bioavailability of the DOM is increased upon exposure to solar radiation.
The impact of larval and juvenile fish on zooplankton and algal dynamics
Authors: Romare Pia , Bergman Eva , Hansson Lars-Anders
Published: May 2010

The impact of young‐of‐the‐year (YOY) fish predation on zooplankton dynamics and cascading effects down to phytoplankton were studied in lake enclosures using different densities of larval and juvenile European perch (Perca fluviatilis). Two experiments, one in June and one in August, were performed in Lake Dagstorpssjon, a slightly eutrophic lake in Scania, southern Sweden. In our experiments, we found that in August, there was a negative relation between YOY perch density and cladoceran biomass and between YOY perch density and cladoceran size. Moreover, in August, both rotifer and algal abundance increased with increasing YOY density, and species composition of algae was affected. At high YOY densities, there was also a negative effect on water transparency. In June, when growth of larval perch was slow and daphnid abundance low, larval perch was not the major structuring force on either zooplankton or algal communities. In early summer, the likelihood of YOY perch having an impact on cladoceran biomass is dependent on the timing of many factors. One factor is the timing between larval occurrence and the increase in large cladoceran biomass that will enhance larval growth. In late summer, however, a high enough predation pressure of juvenile fish will prevent recovery of large herbivores after the midsummer decline in zooplankton abundance and will drive the algal community toward a late summer species composition of small algal cells and blue‐green algae.
Phosphorus sorption characteristics of intertidal marsh sediments along an estuarine salinity gradient
Authors: Sundareshwar P. V. , Morris James T.
Published: May 2010

The phosphate sorption capacity of intertidal vegetated marsh sediments was measured along a salinity gradient in the Cooper River estuary, South Carolina. The phosphate sorption capacity of the surface sediments (0–10 cm) of a freshwater marsh was higher than the sorption capacity of sediments from brackish and saline marshes, and surface sediments had greater sorption capacity than subsurface (10–20 cm) sediments. These trends were opposite that of available phosphorus, which increased downstream and with depth. Freshwater marsh sediments trap phosphorus in a less‐bioavailable form as evidenced by the low zero equilibrium phosphorus concentration (ZEPC) of the ambient sediment and low exchangeable phosphorus found there. Soil ZEPC values were similar to the in situ mean pore‐water phosphate concentrations, which shows that sorption has a major effect on the spatial distribution of pore‐water phosphorus along the estuarine salinity gradient. The magnitude of phosphorus sorption by the fresh‐water marsh sediments greatly reduced the pore‐water phosphate concentration, while the phosphorus sorption properties of brackish and salt marsh sediments maintained in situ equilibrium pore‐water phosphorus concentrations at surplus levels (with respect to its availability to plants). These differences in P sorption properties of the sediments can be explained on the basis of their physical and chemical characteristics. For instance, approaching the sea, the surface area of sediments declined, with freshwater marsh sediments (0–10 cm) supporting 8.5× higher surface area than the salt marsh sediments. However, the sorption capacity of freshwater sediments was 33× greater than that of salt marsh sediments, which indicates that other properties such as sediment mineral composition are important. The concentrations of important elements such as Al and Fe in sediments also declined downstream. The results suggest that the differences in phosphorus exchange properties among these marshes are a function of sediment type and sedimentary concentrations of Fe and Al. These in turn are related to the changes in ionic strength and associated parameters (e.g., pH) and physical sorting mechanisms.
Rates and routes of trace element uptake in zebra mussels
Authors: Roditi Hudson A. , Fisher Nicholas S.
Published: May 2010

The zebra mussel, Dreissena polymorpha, a nonindigenous invasive species, is now widespread throughout the eastern half of North America. Because zebra mussels are ubiquitous and because they effectively filter particulate matter out of suspension, the cycling and residence times of particle‐reactive metals will likely be affected in waters with zebra mussels. This study describes experiments designed to assess the possibility of using this species as a bioindicator of metals in ambient freshwater environments. Laboratory exposures of zebra mussels to 110mAg, 109Cd, 51Cr, 14C, 203Hg, and 75Se were employed to measure their assimilation efficiencies (percentage of ingested element that crosses gut lining) from eight food types (four algal species and bacteria, seston, and mineral assemblages), absorption efficiencies from water (percentage of element pumped by the mussel that is absorbed by the animal), and rates of depuration of these elements from mussels following long‐term exposures to food and water. Assimilation efficiencies of elements from foods ranged from 4 to 29% for silver (Ag), 19 to 72% for cadmium (Cd), 42 to 85% for carbon (C), 2 to 19% for chromium (Cr), 4 to 40% for mercury (Hg), and 8 to 46% for selenium (Se). Absorption efficiencies from the dissolved phase were 1.87% for Ag, 1.02% for Cd, 0.47% for Cr(III), 0.27% for Cr(VI), 1.17% for Hg, and 0.03% for Se. Efflux rate constants (d 21 ) following long‐term exposure to food and water were 0.067 and 0.084 for Ag, 0.013 and 0.011 for Cd, 0.019 and 0.011 for Cr, 0.050 for Hg (food only), and 0.026 and 0.035 for Se. These loss rates corresponded to biological half‐lives ranging from 8 d for Ag to 76 d for Se. Loss rates of trace elements from zebra mussel feces followed the following sequence: Cr < Ag < Se < Hg ≤ Cd, with average retention half‐times being 59, 43, 11, 6.7, and 5.1 d, respectively, which indicates that geochemical cycling rates from zebra mussel biodeposits are element specific. Egestion patterns of the radioisotopes indicated two digestive phases, extracellular and intracellular digestion. The extent of intracellular digestion ranged from 7 to 40%, depending on the food source, and correlated with assimilation efficiency for Ag, Cd, and Hg. The bioaccumulation parameters measured for D. polymorpha can be used in kinetic models to quantify the relative importance of food and water as sources of metals and to predict on a site‐specific basis the tissue concentrations of metals in these mussels, as shown for Cd. Because D. polymorpha accumulates metals from dissolved and particulate sources in proportion to ambient concentrations, this species can be an effective bioindicator of freshwater metal contamination.
A novel DGT‐sediment trap device for the in situ measurement of element remobilization from settling particles in water columns and its application to trace metal release from Mn and Fe oxides
Authors: Hamilton‐Taylor J. , Smith E. J. , Davison W. , Zhang H.
Published: May 2010

A device has been developed for the direct in situ measurement of metal remobilization into solution from settling particles in water columns, based on the technique of diffusion gradients in thin films (DGT). The device comprises a hollow cylinder with a DGT assembly at its base and acts as a traditional sediment trap, except that any remobilization from settling particles is reflected in the mass of metal taken up from solution by the DGT assembly. A control‐DGT device (an upside‐down trap) was used to measure the metal taken up by the assembly in the absence of remobilization from particles. Deployments of the control device under laboratory conditions and below the well‐mixed surface layer of a lake showed that the cylindrical trap design, with a height:diameter ratio of 5:1, resulted in negligible turbulence near the base of the trap so that uptake by the control was governed by molecular diffusion. The DGT‐trap and ‐control devices were deployed together within and immediately below the main oxycline of a seasonally anoxic lake in 1996 and 1997. The reproducibility of the metal uptakes measured by the devices in the field was typically better than ±10% for the controls and ±20% for the traps. The uptakes of Mn, Co, Al, Ba, and Ni, but not Fe and Cu, were significantly and consistently higher in the trap devices than in the controls. Reductive dissolution of Mn oxide appeared to be the source of the four remobilized trace metals, whereas Fe oxides made no significant contribution. The remobilization of Mn, Co, Al, Ba, and Ni was also reflected in elevated dissolved concentrations in the vicinity of the oxycline. Comparisons of the metal:Mn ratios obtained from the DGT‐trap data with those calculated from the water‐column concentrations indicated that the elevated concentrations of dissolved Co were derived solely from Mn oxide dissolution, whereas Ba, Al, and Ni also appear to be affected by other processes.
Changes of the plankton spring outburst related to the North Atlantic Oscillation
Authors: Weyhenmeyer Gesa A. , Blenckner Thorsten , Pettersson Kurt
Published: May 2010

Changes in the timing, composition, and intensity of freshwater phytoplankton blooms are known to have an impact on water quality and aquatic ecosystem functions. Factors provoking these changes are, therefore, of major importance. In Lake Erken in southeastern Sweden considerable changes in the timing and large variations in the composition of phytoplankton spring peaks have been observed during the past 45 yr. Here we show that long‐term changes and variations in Lake Erken are strongly related to a single global parameter—the North Atlantic Oscillation (NAO). Even regional parameters that are known to have most influence onthe spring development of phytoplankton such as ice break‐up and nutrient concentrations could not provide a more conclusive explanation of the observed changes in spring phytoplankton, making the NAO a very powerful and simple tool in determining the timing and composition of phytoplankton spring peaks in a temperate lake.
Evaluating the spatial resolution of an acoustic Doppler velocimeter and the consequences for measuring near‐bed flows
Authors: Finelli Christopher M. , Hart David D. , Fonseca Dina M.
Published: May 2010

The acoustic Doppler velocimeter (ADV) has recently been suggested as a promising instrument for characterizing near‐bed flows, particularly in the first 10 mm above the bed where many benthic organisms live. Flow characteristics in such settings often exhibit steep vertical gradients, however, so the reliable use of the ADV requires knowledge of the size and location of the instrument's acoustic sampling volume. We describe simple procedures for quantifying the vertical size of the ADV's sampling volume and assessing its height above the bed. Our results indicate that the vertical size of the sample volume for the ADV we tested was much larger than expected based on the values predicted by software configuration. Moreover, this system incorrectly reported several distances needed to accurately position the sample volume near the bed (e.g., the transmitter‐to‐bed distance, the sample volume‐to‐bed distance, and the transmitter‐to‐sample volume distance). We also demonstrate that incorrect assumptions about the size and location of the sampling volume can lead to inaccurate near‐bed flow measurements by comparing the time‐averaged flow speed profiles generated by our ADV with those obtained using a hot‐film velocimeter (HFV). At heights > 10 mm above the bed, both instruments yielded similar flow speed estimates. Closer to the bed, however, the flow speeds reported by ADV were as much as 60–80% less than those from HFV. These large errors in estimating near‐bed flow speeds are a direct consequence of incorrect assumptions about the centerpoint and size of the ADV's sample volume. Specifically, when the vertical size of the sampling volume is larger than its nominal size, users may mistakenly position the ADV so that the bed is included within the sampling volume, which in turn results in the underestimation of flow speeds. By validating the size and location of the sampling volume, as well as carefully monitoring signal quality parameters, users can ensure proper placement of the ADV relative to the bed and avoid erroneous measurements.
Use of a high‐resolution pore‐water gel profiler to measure groundwater fluxes at an underwater saline seepage site in Lake Kinneret, Israel
Authors: Mortimer R. J. G. , Krom M. D. , Boyle D. R. , Nishri A.
Published: May 2010

We have used new gel pore‐water profilers and conventional seepage meters to determine the advective flux of water from an underwater saline seep into Lake Kinneret. The gel probes sampled pore waters from medium to coarse sands that could not be sampled by conventional coring methods. The anions Cl, Br, and SO4 were constant at levels just above those for the lake for 3–5 cm into the sediment due to wave action or other turbulent mixing processes. There was then a sharp increase in concentration to values of approximately 8,000 mg Cl liter−1, 370 mg SO4 liter−1, and 120 mg Br liter−1 at a depth of ∼8.5 cm. Using an advection‐diffusion model, the linear interstitial advection velocity (LIV) of the groundwater into the lake was calculated to vary between 140 and 275 cm yr−1. The LIV values from conventional seepage flux meters at the same site were 30 and 164 cm yr−1. Differences between the LIV measurements of these two methods may be due to a number of possible factors, including ground‐water flux heterogeneity.
Linking diagenetic alteration of amino acids and bulk organic matter reactivity
Authors: Dauwe Birgit , Middelburg Jack J. , Herman Peter M. J. , Heip Carlo H. R.
Published: May 2010

Examination of amino acids in particulate samples from a variety of marine environments (fresh phytoplankton to deep‐sea sediments) revealed systematic compositional changes upon progressive degradation. These consistent trends have been used to derive a quantitative degradation index (DI) that is directly related to the reactivity of the organic material, as indicated by its lability to enzymatic decay and its first‐order degradation rate constant. This direct link between molecular composition and degradation rate allows us to quantify the quality of organic matter based solely on its chemical composition.
Mercury methylation in periphyton of the Florida Everglades
Authors: Cleckner Lisa B. , Gilmour Cynthia C. , Hurley James P. , Krabbenhoft David P.
Published: May 2010

Trophic accumulation of mercury (Hg) in aquatic ecosystems is of global concern due to health effects associated with eating fish with elevated Hg levels. The methylated form of Hg bioaccumulates so it is important to understand how inorganic Hg is transformed to methylmercury in the environment. Here, a new site for Hg methylation, the periphyton communities that are prevalent in the Florida Everglades, is described. It is hypothesized that periphyton communities that support an active microbial sulfur cycle support Hg methylation. This new methylation site has implications for trophic transfer of methylmercury since periphyton can be the base of the food web in aquatic ecosystems.
Plankton availability and retention efficiencies of cold‐seep symbiotic mussels
Authors: Pile Adele J. , Young Craig M.
Published: May 2010

Mussels from deep‐sea methane/sulfide seeps in the Gulf of Mexico supplement their symbiotically acquired nitrogen by feeding selectively on nitrogen‐rich bacterioplankton. The previously unknown natural diet of the mussels consists of bacteria, Synechococcus‐type cyanobacteria, and protozoans. Overall retention increased with increasing mussel size, though the largest mussels did not retain bacteria. Mussels can obtain as much as 0.12 mmol N g−1 h−1 by filter feeding on natural water‐column communities. Previous calculations indicate that nitrogen acquired through the symbionts is inadequate for maximal growth, but our conservative estimates suggest that nitrogen obtained by filter feeding is similar to that acquired by symbionts and may be an important component in the nutritional requirements of seep mussels. Additionally, we conducted a series of in situ measurements of flow and food availability over an extensive mussel bed located at the Brine Pool. Our measurements indicate that biogenic flow due to mussel pumping generates near‐bottom turbulence that prevents the development of a food‐depleted layer over the mussel bed.
Benthic bacterial secondary production measured via simultaneous 3H‐thymidine and 14C‐leucine incorporation, and its implication for the carbon cycle of a shallow macrophyte‐dominated backwater system
Authors: Kirschner A. K. T. , Velimirov B.
Published: May 2010

The role of the benthic bacterial community in the carbon cycle of a temperate, macrophyte‐dominated oxbow was investigated in a 2‐yr study from 1994 to 1996. Simultaneous incorporation of 3H‐thymidine into DNA and 14C‐leucine into proteins was monitored as a tool for the measurement of bacterial secondary production in the aerobic zone of the sediment along with bacterial numbers, morphotype composition, cell volumes, biomass, frequency of dividing cells (FDC), and abiotic variables. Bacterial numbers ranged from 2.5 × 109 to 8.5 × 109 cells ml−1 , corresponding to bacterial biomass values of 64 and 288 μg C ml−1, respectively. Both bacterial production methods yielded similar and reliable results over the whole investigation period, varying between 42 and 2,350 mg C L−1 h−1 for the thymidine method and between 67 and 2,490 μg C L−1 h−1 for the leucine method, and also corresponded well with the FDC values. Only during late spring and early summer was the thymidine uptake uncoupled from leucine incorporation. Temperature was found to be of significant importance for the variation of all bacterial parameters. In addition carbon inputs from the water column were apparently crucial stimulators of benthic bacterial growth. The spring phytoplankton bloom together with higher temperatures led to a strong positive response of the bacterial community in the sediment. However, the planktonic algal production was not sufficient to cover the benthic bacterial C‐demand and, as derived from mass‐balance calculations, decaying macrophytes of the previous season seemed to provide the main energy source until the middle of spring. From the middle of August to the beginning of October, the period of maximal biomass of submerged macrophytes, all bacterial parameters exhibited their annual maximum. The benthic bacterial community was dependent on leachates and decay products of the submerged vegetation during this time. Temperature limitation was most probably the reason for the low biomass and production values observed during autumn and winter.
Pelagic microbial activity in an arctic polynya: Testing for temperature and substrate interactions using a kinetic approach
Authors: Yager Patricia L. , Deming Jody W.
Published: May 2010

To test the hypothesized inhibition of high‐latitude marine bacteria living at lower temperatures when organic matter is scarce, the effects of temperature and organic substrate concentration on pelagic microbial heterotrophy were investigated in the perennially cold surface waters of a summertime arctic polynya. Utilization (incorporation plus respiration) of radiolabeled amino acids was measured as a function of increasing added substrate concentration at in situ (subzero) temperature and under short‐term warming. Results analyzed using analysis of variance (ANOVA) showed that increased substrate concentration had a significant effect on utilization rates at all stations, suggesting that communities were always living well below saturating levels of substrate. About half of the communities sampled revealed a significant temperature response using ANOVA; interactions between temperature and substrate concentration were detected only rarely. Kinetic parameters, used to link microbial activity and substrate utilization with temperature sensitivity, exhibited mixed responses to short‐term warming. Maximum specific utilization rates showed the greater temperature sensitivity, with Q10 values ranging from 0.25 to 13. Specific affinities responded to temperature significantly at only about half of the stations in the polynya. Psychrophilic behaviors (e.g., highest specific affinities and oligotrophic capacities at lower incubation temperatures) were observed at stations most likely to be influenced by direct Arctic Ocean outflow. Complete agreement with the hypothesis of enhanced substrate requirement by bacteria living at subzero temperature was not found. An improved understanding of the diversity of cold‐tolerant and cold‐loving microorganisms is needed before generalizing or predicting the role of temperature in the cycling of organic matter at high latitudes.
Century changes in Connecticut, U.S.A., lakes as inferred from siliceous algal remains and their relationships to land‐use change
Authors: Siver Peter A. , Lott Anne Marie , Cash Ethan , Moss Jamal , Marsicano Laurence J.
Published: May 2010

Scaled chrysophytes and planktonic diatoms are used to infer changes in lake water pH, specific conductivity, trophic score, and total nitrogen in 23 Connecticut waterbodies over the last 100 yr, and the changes are correlated with quantified changes in land use in the surrounding watersheds. In general, there was good agreement between the changes inferred from both organismal groups in this suite of lakes. Significant correlations were observed between chemical conditions inferred from organisms in surface sediments and present‐day land uses, especially the percentages of the watersheds that are forest or residential land cover types. Approximately 20% of the water‐bodies have significantly increased in pH since 1890, and none of the lakes have significantly declined in pH despite the fact that this region receives significant amounts of acidic deposition. These findings support previous work, indicating that the pH of Connecticut lakes has not declined over the recent past. One fourth of the lakes have significantly increased in specific conductivity, especially those situated in watersheds that have become highly residential in nature. Inferred specific conductivity has more than doubled in six of the lakes during the last century. Six of the lakes have become significantly more eutrophic, while only one lake has become more oligotrophic since 1890. The majority of the lakes situated in watersheds that have remained over ∼80% forested have not significantly changed, whereas those that have become over ∼25% residential have experienced the greatest amount of change. The potential influences of watershed‐based alkalinity generation, winter road salt use, and implications of these findings in lake management are discussed.
The fate of nitrogen in the Orbulina universa foraminifera‐symbiont system determined by nitrogen isotope analyses of shell‐bound organic matter
Authors: Uhle Maria E. , Macko Stephen A. , Spero Howard J. , Lea David W. , Ruddiman William F. , Engel Michael H.
Published: May 2010

To trace the flow of nitrogen through the foraminifera‐symbiont system, juvenile specimens of the symbiont‐bearing planktonic foraminifera, Orbulina universa were collected by SCUBA divers off the coast of Santa Catalina Island, California, and grown in filtered seawater solutions spiked with 15N‐labeled nitrate. Our work isolated each pathway of this symbiotic system to determine the amount of nitrogen translocated to the foraminifera from its endosymbionts and its captured diet. Our model results show that when the nitrate uptake by the symbionts is at a maximum, between 50 and 57% of the foraminiferal nitrogen was translocated from the symbionts and the remainder was derived from the captured diet. In nitrate‐deficient environments, when the symbiont nitrate uptake was at a minimum, ∼90–100% of the nitrogen was transferred to the foraminifer by the symbionts from the recycled nitrogen (NH4+) pool. In nitrate‐deficient conditions, the primary role of the captured diet may be to provide the system with phosphorous. Highly efficient nutrient use is particularly important to the foraminifera‐symbiont system, especially when nutrient concentrations are low. The results indicate a limited correlation between the isotopic composition of the NO3− in the culture solutions and the Δ15n values of the foraminifera. However, the δ15n values of the foraminifera much more strongly reflect the δ15n values of the NH4+ recycled through the system. It appears that recycled nitrogen (NH4+) is a more important source of nitrogen to the symbionts and the foraminifera than nitrate; therefore, the δ15n values of the foraminifera may not reflect the isotopic composition of the surface‐water nutrients. Understanding the nitrogen flow within modern foraminifera‐symbiont associations is also important to ancient marine systems, because symbiont‐bearing foraminifera are ubiquitous in the fossil record. This study shows that analysis of individual, symbiont‐bearing foraminifera species is a necessary first step toward the development of more reliable use of nitrogen isotopes for paleoceanographic reconstructions.
The effect of eelgrass decomposition on sediment carbon and nitrogen cycling: A controlled laboratory experiment
Authors: Pedersen Anna‐Grethe U. , Berntsen Jørgen , Lomstein Bente Aa.
Published: May 2010

The initial benthic degradation of senescent Zostera marina leaves was studied in controlled flowthrough microcosm chambers for 33 d. Sediment chambers without added eelgrass leaves served as control chambers. The in‐flowing artificial seawater and ouflowing seawater were analyzed for dissolved organic carbon and nitrogen (DOC and DON), total acid‐hydrolyzable amino acids (THAA), dissolved free amino acids (DFAA), urea, NH4+, NO3−, CO2, and O2 during the 33 d of incubation. Sediment profiles of particulate organic carbon and nitrogen, sediment acid‐hydrolyzable amino acids, DON, DFAA, urea, NH4+ and the turnover rate of urea were measured at four different times during the 33 d of incubation. There was an immediate increase in carbon oxidation and the effluxes of DOC, DON, and NH4+ after the addition of eelgrass leaves to the sediment surface. During the course of incubation, 24.3% of the DON efflux was identified as acid‐hydrolyzable amino acids, dissolved free amino acids, and urea in the chambers with eelgrass addition, whereas these compounds accounted for 33.8% of the DON efflux in the control chambers. There were indications of a stimulated bacterial growth on the eelgrass leaves during the first 7 d after leaf addition that was measured as an increase in acid‐hydrolyzable amino acids. Further, there was a gradual increase in acid‐hydrolyzable amino acids in the sediment throughout the incubation that could only be explained as bacterial growth (and/or protein synthesis). Most of the nitrogen for microbial growth was mobilized from the indigenous particulate organic nitrogen pool, whereas it could be inferred that the energy source for bacterial growth was mainly supplied from the added eelgrass leaves. Most of the nitrogen mineralized within the sediment was incorporated into the microbial biomass with a resultant low efflux of inorganic nitrogen from the sediment to the water column.
An experimental study on effects of submersed macrophytes on nitrification and denitrification in ammonium‐rich aquatic systems
Authors: Eriksson Peder G. , Weisner Stefan E. B.
Published: May 2010

We have examined the role of microbial communities on the surface of submersed macrophytes and in the underlying sediment for nitrification and denitrification in light and dark in NH4+‐enriched microcosm systems using isotope pairing and dilution techniques. Potamogeton pectinatus L. and intact sediment cores were collected in a shallow reservoir receiving treated municipal wastewater and containing dense submersed vegetation. Chambers containing P. pectinatus shoots, sediment, or both P. pectinatus shoots and sediment were exposed to 6 h of darkness, 6 h of light, and 6 h of darkness. 14NH4+ and 15NO3− were added at ambient concentrations of 15 and 5 mg N liter−1, respectively. NH4+ was primarily nitrified in the epiphytic microbial communities, and NO3− was denitrified in the underlying sediment. In chambers containing macrophytes, there was a net production of O2 and NO3− in light and a net consumption in dark, and nitrification was higher in light than in dark. In chambers with only sediment, there was always a net consumption of NO3−, and nitrification was similar in light and dark. The results show that submersed macrophytes can be important for the N metabolism in NH4+‐ rich freshwaters (e.g., wastewater treatment systems) by stimulating nitrification through providing surfaces for attached nitrifying bacteria and possibly also through diurnal changes in the water chemistry.
Major flux of terrigenous dissolved organic matter through the Arctic Ocean
Authors: Opsahl Stephen , Benner Ronald , Amon Rainer M. W.
Published: May 2010

High‐latitude rivers supply the Arctic Ocean with a disproportionately large share of global riverine discharge and terrigenous dissolved organic matter (DOM). We used the abundance of lignin, a macromolecule unique to vascular plants, and stable carbon isotope ratios (δ13C) to trace the high molecular weight fraction of terrigenous DOM in major water masses of the Arctic Ocean. Lignin oxidation products in ultrafiltered DOM (UDOM; >1,000 Da) from Arctic rivers were depleted in syringyl relative to vanillyl phenols (S/V = 0.3–0.5) compared to UDOM in temperate and tropical rivers (S/V = 0.5–1.2), indicating that gymnosperm vegetation is a major source of terrigenous UDOM to the Arctic Ocean. High concentrations of lignin oxidation products (83–320 ng L−1) and a depletion of 13C (δ13C = −23.0 to −21.9) in UDOM throughout the surface Arctic Ocean indicate that terrigenous UDOM accounts for a much greater fraction of the UDOM in the surface Arctic (5–33%) than in the Pacific and Atlantic oceans (0.7–2.4%). In contrast, UDOM in deep water from the Arctic Ocean as well as waters from throughout the Greenland Gyre had relatively low concentrations of lignin oxidation products (24–45 ng L−1 ) and was enriched in 13C (δ13C = −21.0 to −20.8). Terrigenous UDOM has a relatively short residence (∼1–6 yr) in surface polar waters prior to export to the north Atlantic Ocean. Assuming that the bulk of Arctic‐derived DOM is compositionally similar to the UDOM fraction, we estimate that 12–41% of terrigenous DOM (2.9–10.3 Tg C yr−1 ) discharged by rivers to the Arctic Ocean is exported to the North Atlantic via surface waters of the East Greenland Current. It appears very little terrigenous DOM from the Arctic is incorporated into North Atlantic Deep Water and distributed globally via deep thermohaline circulation.
Modelling the reversible uptake of chemical species in the gas phase by ice particles formed in a convective cloud
Authors: Marécal V. , Pirre M. , Rivière E. D. , Pouvesle N. , Crowley J. N. , Freitas S. R. , Longo K. M.
Published: May 2010

Abstract. The present paper is a preliminary study preparing the introduction of reversible trace gas uptake by ice particles into a 3-D cloud resolving model. For this a 3-D simulation of a tropical deep convection cloud was run with the BRAMS cloud resolving model using a two-moment bulk microphysical parameterization. Trajectories within the convective clouds were computed from these simulation outputs along which the variations of the pristine ice, snow and aggregate mixing ratios and concentrations were extracted. The reversible uptake of 11 trace gases by ice was examined assuming applicability of Langmuir isotherms using recently evaluated (IUPAC) laboratory data. The results show that ice uptake is only significant for HNO3, HCl, CH3COOH and HCOOH. For H2O2, using new results for the partition coefficient results in significant partitioning to the ice phase for this trace gas also. It was also shown that the uptake is largely dependent on the temperature for some species. The adsorption saturation at the ice surface for large gas mixing ratios is generally not a limiting factor except for HNO3 and HCl for gas mixing ratio greater than 1 ppbv. For HNO3, results were also obtained using a trapping theory, resulting in a similar order of magnitude of uptake, although the two approaches are based on different assumptions. The results were compared to those obtained using a BRAMS cloud simulation based on a single-moment microphysical scheme instead of the two moment scheme. We found similar results with a slightly more important uptake when using the single-moment scheme which is related to slightly higher ice mixing ratios in this simulation. The way to introduce these results in the 3-D cloud model is discussed.
Bromide and other ions in the snow, firn air, and atmospheric boundary layer at Summit during GSHOX
Authors: Dibb J. E. , Ziemba L. D. , Luxford J. , Beckman P.
Published: May 2010

Abstract. Measurements of gas phase soluble bromide in the boundary layer and in firn air, and Br− in aerosol and snow, were made at Summit, Greenland (72.5° N, 38.4° W, 3200 m a.s.l.) as part of a larger investigation into the influence of Br chemistry on HOx cycling. The soluble bromide measurements confirm that photochemical activation of Br− in the snow causes release of active Br to the overlying air despite trace concentrations of Br− in the snow (means 15 and 8 nmol Br− kg−1 of snow in 2007 and 2008, respectively). Mixing ratios of soluble bromide above the snow were also found to be very small (mean <1 ppt both years, with maxima of 3 and 4 ppt in 2007 and 2008, respectively), but these levels clearly oxidize and deposit long-lived gaseous elemental mercury and may perturb HOx partitioning. Concentrations of Br− in surface snow tended to increase/decrease in parallel with the specific activities of the aerosol-associated radionuclides 7Be and 210Pb. Earlier work has shown that ventilation of the boundary layer causes simultaneous increases in 7Be and 210Pb at Summit, suggesting there is a pool of Br in the free troposphere above Summit in summer time. Speciation and the source of this free tropospheric Br are not well constrained, but we suggest it may be linked to extensive regions of active Br chemistry in the Arctic basin which are known to cause ozone and mercury depletion events shortly after polar sunrise. If this hypothesis is correct, it implies persistence of the free troposphere Br− for several months after peak Br activation in March/April. Alternatively, there may be a~ubiquitous pool of Br− in the free troposphere, sustained by currently unknown sources and processes.
Presence of enterococci in cow milk and their antibiotic resistance
Authors: Fabianová Jana , Ducková Viera , Čanigová Margita , Kročko Miroslav
Published: May 2010

Enterococci represent an important part of contaminate microflora in raw milk and dairy products. They constitute significant part of nosocomial pathogens with a remarkable capacity of expressing resistance to several antimicrobial  agents. We aimed to assess occurrence and antibiotic resistance of enterococci in the raw milk samples and pasteurized milk samples. In this study total bacterial count, psychrotrophic count and count of enterococci were determine in raw milk cistern samples, storage tank milk samples and milk samples after pasteurization. A collection of 46 enterococcal isolates were identified and screened for their antibiotic resistance. Isolates of E. faecalis were dominant in raw milk samples (56.5 %). Sensitive to teicoplanine (30 mcg/disk) were 97.9 % of enterococcal isolates and 15.2 % isolates were resistant to vankomycin (30 mcg/disk).
Physicochemical quality of selected strawberry jams with fructose
Authors: Gałkowska Dorota , Fortuna Teresa , Zagórska Weronika Prochwicz
Published: May 2010

Four different commercially available strawberry jams with fructose were characterized in relation to acidity and reducing sugar, ash, micro- and macroelement contents. The results showed that the jams differed in active and total acidity, ash, as well as reducing sugar content. Differences between the jams were more pronounced for microelements than for macroelements.
Migration of phthalates from plastic tank to vegetable oil as a part of feeding mixtures used for chicken broilers fattening
Authors: Jarošová Alžbeta , Stancová Vlasta , Harazim Jiří­ , Suchý Pavel
Published: May 2010

The concentrations of phthalic acid esters (PAEs) as di-n-butyl phthalate (DBP) and di-2-ethylhexyl phthalate (DEHP) were measured in samples of rapeseed oil, which was used as a feed. First samples were collected during the production process and second after the storage in plastic tank (21 days). The results of measurements are that there is 2.93-10.10 mg PAEs.kg-1 in the oil before storage and 22.73-61.55 mg PAEs.kg-1 after storage.
For the monitoring of distribution and accumulation of PAEs in animal tissues and organs (muscles, adipose tissue, skin and liver) broiler chicks ROSS 308 were used. The chicks were divided into 4 groups (50 chicks each). All the chicks were fed by commercial diets (complete feed, KKS) for broiler chicks (starter – BR1; grower – BR2 and finisher – BR3). The experimental diets were supplemented with vegetable oil (RO) with low (group N) or high (group V) phthalate content, or animal fat with high phthalate content (group Z). Neither the control diets (K) nor the grower (BR1) diets contained vegetable oil or animal fat. DBP and DEHP were found in all tissues of all chicks. The highest concentration of DBP of 1.28 1.00 mg.kg-1 of fresh sample (an average value from 8 chicks) was determined in the adipose tissue of V chicks. The highest concentration of DEHP of 3.27 2.87 mg.kg-1 of fresh sample (average of 8 chicks) was also determined in the V group.