bluuebunny/crossref_metadata_2025 huggingface dataset:
A transplant experiment to identify the factors controlling bacterial abundance, activity, production, and community composition in a eutrophic canyon‐shaped reservoir
Authors: Gasol Josep M. , Comerma Marta , García, Juan Carlos , Armengol Joan , Casamayor Emilio O. , Kojecká Petra , Šimek Karel
Published: June 2010

We performed a transplant experiment in eutrophic Sau reservoir to assess the factors that control bacterial abundance, activity, growth rate, and community composition. Samples from the lacustrine and the riverine ends of the reservoir were incubated in dialysis bags placed in situ and transplanted to the other side of the reservoir and also incubated after 1 µm filtration to measure predator effects. The bags were sampled at 12‐h intervals to estimate bacterial abundance, whole community activity, activity structure (by flow cytometry), and phylogenetic composition (by in situ hybridization with group‐specific phylogenetic probes). Bacterial production was always regulated by nutrient supply, but abundance and activity were differently regulated at both sites. The riverine bacteria were limited by predator activity, whereas the lacustrine were regulated by a combination of predation and nutrient supply. Therefore, even in the same environment, different modes of control can act simultaneously. Bacterial activity structure was also regulated in the same way. Abundance of high DNA bacteria and cells hybridizing with the universal EUB338 probe were well correlated. In the lacustrine sample, bacterial community structure did not change significantly, whereas in the riverine sample, Α‐ and Δ‐Proteobacteria reduced their growth when transplanted, whereas Β‐Proteobacteria were stimulated by the presence of predators. Members of the Cytophaga/Flavobacterium phylum grew only when incubated in situ in the absence of predators. This different behavior in the different bacterial groups resulted in strong changes in bacterial assemblage composition, evident already after 24 h. The experiment demonstrates that, together with the effect of predators, nutrient supply affects bacterial community properties and that a complex regulation involving both types of control can occur in a single heterogeneous planktonic system.
Light‐dependent carbon isotope fractionation in the coccolithophorid Emiliania huxleyi
Authors: Rost Björn , Zondervan Ingrid , Riebesell Ulf
Published: June 2010

The carbon isotopic composition of marine phytoplankton varies significantly with growth conditions. Aqueous CO2 concentration [CO2] and algal growth rate (µ) have been suggested to be important factors determining isotope fractionation (εp). Here we examine εp of the coccolithophorid Emiliania huxleyi in relation to CO2 concentration and light conditions in dilute batch cultures. Cells were incubated at different irradiance cycles, photon flux densities (PFDs), and [CO2]. Isotope fractionation varied between 6.7 and 12.3‰ under 16 : 8 h light : dark cycle (L :D) and between 14.7 and 17.8‰ at continuous light. εp was largely independent of ambient [CO2], varying generally by less than 2‰ over a range of [CO2] from 5 to 34 mmol L−1. Instantaneous carbon‐specific growth rates (µC) and PFDs, ranging from 15 to 150 mmol m−2 s−1, positively correlated with εp. This result is inconsistent with theoretical considerations and experimental results obtained under constant light conditions, suggesting an inverse relationship between εp and µ. In the present study the effect of PFDs on εp was stronger than that of mand thus resulted in a positive relationship between µ and εp. In addition, the L:D cycle of 16 : 8 h resulted in significantly lower εp values compared to continuous light. Since the observed offset of about 8‰ could not be related to daylength dependent changes in µC, this implies a direct influence of the irradiance cycle on εp. These findings are best explained by invoking active carbon uptake in E. huxleyi. If representative for the natural environment, these results complicate the interpretation of carbon isotope data in geochemical and paleoceanographic applications.
Changes in bacterial β‐glucosidase diversity during a coastal phytoplankton bloom
Authors: Arrieta Jesùs M. , Herndl Gerhard J.
Published: June 2010

Bacterial enzymatic hydrolysis of high molecular weight organic matter is the rate‐limiting step in the bacterially mediated carbon cycling in the global ocean. Despite the importance of this process, only bulk measurements of these hydrolytic activities are available, and the dynamics and diversity of the ectohydrolases involved in the cleavage of high molecular weight organic matter are poorly understood. In this study we monitored the dynamics of bacterial β‐glucosidase diversity during the wax and wane of a coastal phytoplankton bloom using a newly developed capillary electrophoretic assay. Up to eight different β‐glucosidases were detected in a single sample and 11 over the whole study period, revealing a previously unnoticed β‐glucosidase diversity. A close link was found between the temporal succession ofβ‐glucosidase diversity and bacterioplankton species richness as determined by terminal‐restriction fragment length polymorphism analysis. This indicates that the regulation of the β‐glucosidase activity and diversity was driven by shifts in the bacterial community structure rather than by simple induction of enzyme expression within a stable bacterioplankton community.
Annual primary production: Patterns and mechanisms of change in a nutrient‐rich tidal ecosystem
Authors: Jassby Alan D. , Cloern James E. , Cole Brian E.
Published: June 2010

Although nutrient supply often underlies long‐term changes in aquatic primary production, other regulatory processes can be important. The Sacramento‐San Joaquin River Delta, a complex of tidal waterways forming the landward portion of the San Francisco Estuary, has ample nutrient supplies, enabling us to examine alternate regulatory mechanisms over a 21‐yr period. Delta‐wide primary productivity was reconstructed from historical water quality data for 1975–1995. Annual primary production averaged 70 g C m−2, but it varied by over a factor of five among years. At least four processes contributed to this variability: (1) invasion of the clam Potamocorbula amurensis led to a persistent decrease in phytoplankton biomass (chlorophyll a) after 1986; (2) a long‐term decline in total suspended solids—probably at least partly because of upstream dam construction—increased water transparency and phytoplankton growth rate; (3) river inflow, reflecting climate variability, affected biomass through fluctuations in flushing and growth rates through fluctuations in total suspended solids; and (4) an additional pathway manifesting as a long‐term decline in winter phytoplankton biomass has been identified, but its genesis is uncertain. Overall, the Delta lost 43% in annual primary production during the period. Given the evidence for food limitation of primary consumers, these findings provide a partial explanation for widespread Delta species declines over the past few decades. Turbid nutrient‐rich systems such as the Delta may be inherently more variable than other tidal systems because certain compensatory processes are absent. Comparisons among systems, however, can be tenuous because conclusions about the magnitude and mechanisms of variability are dependent on length of data record.
Stable carbon and nitrogen isotope composition of aquatic and terrestrial plants of the San Francisco Bay estuarine system
Authors: Cloern James E. , Canuel Elizabeth A. , Harris David
Published: June 2010

We report measurements of seasonal variability in the C‐N stable isotope ratios of plants collected across the habitat mosaic of San Francisco Bay, its marshes, and its tributary river system. Analyses of 868 plant samples were binned into 10 groups (e.g., terrestrial riparian, freshwater phytoplankton, salt marsh) to determine whether C‐N isotopes can be used as biomarkers for tracing the origins of organic matter in this river‐marsh‐estuary complex. Variability of δ13C and δ15N was high (~5–10‰) within each plant group, and we identified three modes of variability: (1) between species and their microhabitats, (2) over annual cycles of plant growth and senescence, and (3) between living and decomposing biomass. These modes of within‐group variability obscure any source specific isotopic signatures, confounding the application of C‐N isotopes for identifying the origins of organic matter. A second confounding factor was large dissimilarity between the δ13C‐δ15N of primary producers and the organic matter pools in the seston and sediments. Both confounding factors impede the application of C‐N isotopes to reveal the food supply to primary consumers in ecosystems supporting diverse autotrophs and where the isotopic composition of organic matter has been transformed and become distinct from that of its parent plant sources. Our results support the advice of others: variability of C‐N stable isotopes within all organic‐matter pools is high and must be considered in applications of these isotopes to trace trophic linkages from primary producers to primary consumers. Isotope‐based approaches are perhaps most powerful when used to complement other tools, such as molecular biomarkers, bioassays, direct measures of production, and compilations of organic‐matter budgets.
Cell viability in natural phytoplankton communities quantified by a membrane permeability probe
Authors: Agustí Susana , Sánchez M. Carmen
Published: June 2010

A nonstaining method, based on the digestion of dead cells, the membranes of which are permeable when exposed to an enzymatic cocktail (DNAse I and Trypsin), was used to identify living cells in cultured and natural phytoplankton populations. The cell digestion method was applied to cultures of nine phytoplankton species, encompassing a broad taxonomic range. The percentage of living cells obtained with the enzymatic digestion test was found to be consistent with that obtained with the vital stain fluorescein diacetate, which could be applied to only six of the species used. Use of the cell digestion method showed the phytoplankton community viability in Blanes Bay (NW Mediterranean littoral) to be very low at the beginning of the summer (34% and 31% of diatoms and cyanobacteria cells were alive, respectively), when oligotrophic conditions prevailed. The phytoplankton viability increased slightly by midsummer, with the entire cyanobacteria population, which dominated the community, composed of living cells, and most (81%) of the diatom cells were living in the fall. The patterns in cell viability revealed by the cell digestion method were consistent with the seasonal variability in phytoplankton lysis rates and the shifting contribution of different groups to the phytoplankton community.
The role of dust in supplying nitrogen and phosphorus to the Southeast Mediterranean
Authors: Herut Barak , Collier Robert , Krom Michael D.
Published: June 2010

This study assesses the role of the atmospheric dry fallout as a source of new nitrogen and phosphorus to the surface Levantine seawater. Leaching experiments of inorganic nitrogen (LINO3−, LINH4+) and phosphorus (LIPO4), using SE Mediterranean surface seawater, were performed on 41 aerosol (hereafter dust) samples collected on Whatman 41 filters between April 1996 and January 1999 at Tel Shikmona, Israel and on four desert‐event dust powder samples. A geometric mean of 2.8 and 3.2 mmol NO3− and NH4+ per gram of dust was leached by seawater from normal (background) dry deposition captured by the filters. Significantly lower amounts of IN with lower NH4+:NO3− ratios were leached from both the 1 2 filters and the dust powder sampled during dust events (mean of 0.18 and 0.02 mmol NO3− and NH4+ per gram of dust). Similarly, relatively lower values of LIPO4 were measured in desert type events, attributed to systematic decrease in IP solubility with increased rock/soil component. The calculated LINO3− and LINH4+ fluxes were 34 and 20 mmol m−2 yr−1 from normal dry deposition, 2.5 higher than the wet IN deposition, and twice the riverine input (23 mmol m−2 yr−1, Guerzoni et al.). This high ratio is due to the semiarid climate in this basin. The estimated flux of total dry IP was 1 mmol P m−2 yr−1, approximately 3 times higher than the input of wet IP and somewhat lower than the estimated riverine input (1.4 mmol m−2 yr−1, Guerzoni et al. 1999). The similarity of atmospheric and burial fluxes of P in the Levantine basin reinforces the hypothesis that the atmosphere is the dominant source of P to the sediments in the deeper parts of the basin. It was estimated that the leachable fluxes of IP and IN (dry 1 wet) can support between ~15 or ~70% (1–4 g C m−2 yr−1) of the new production in the SE Mediterranean, effective mainly during dust events and stratification. This input may contribute significantly to the relatively high N: P ratios in Levantine deep water (~27).
Size‐dependent visual predation risk and the timing of vertical migration: An optimization model
Authors: De Robertis Alex
Published: June 2010

Diel vertical migration (DVM) by zooplankton to deep, poorly illuminated habitats during the day is thought to reduce the probability of attack by visual predators at the cost of decreased net energy gain. Herein, I develop a trade‐off model used to predict the timing of vertical migration of zooplankton. The model is based on “Gilliam's rule”—the notion that animals will select habitats that minimize the ratio of mortality risk/energy gain—and incorporates light‐and size‐dependent vulnerability to visual predators. The model predicts that smaller, less vulnerable prey should ascend into food‐rich surface waters earlier and descend later than larger, more conspicuous organisms over a wide range of conditions. The model has been parameterized for a population of Euphausia pacifica in Saanich Inlet, British Columbia, and predicts that 7‐mm (larval) animals will ascend/descend ~35 min earlier/later than more conspicuous 24‐mm adults. These predictions are consistent with acoustic observations of the timing of DVM in this population. The proposed mechanism for size‐dependent timing of DVM is based on the potential for increased energy gain in surface waters and diel changes in vulnerability to size‐selective predators. These conditions prevail in both freshwater and marine pelagic environments, and size‐dependent DVM is likely to be widespread in zooplankton.
Feeding and energy budgets of Antarctic krill Euphausia superba at the onset of winter—II. Juveniles and adults
Authors: Atkinson A. , Meyer B. , Stuϋbing D. , Hagen W. , Schmidt K. , Bathmann U. V.
Published: June 2010

The overwintering success of Euphausia superba is a key factor that dictates population size, but there is uncertainty over how they cope with the scarcity of pelagic food. Both nonfeeding strategies (reduced metabolism, lipid use, or shrinkage in size) and switching to other foods (carnivory, ice algae, or detritus) have been suggested. We examined these alternatives in the southwest Lazarev Sea in autumn (April 1999), when sea ice was forming and phytoplankton was at winter concentrations. Both juveniles and adults had a very high lipid content (36% and 44% of dry mass, respectively) of which >40% was phospholipid. However, their low O:N ratios suggested that these reserves were not being used. Results from gut contents analysis and large volume incubations agreed that juveniles fed mainly on phytoplankton and adults fed on small (<3 mm) copepods. This dietary difference was supported possibly by elevated concentrations of 20 : 1 and 22 : 1 fatty acids in the adults. The feeding methods also confirmed that feeding rates were low compared with those in summer. Even when acclimated to high food concentrations, clearance and ingestion rates were <30% of summer rates. Respiration and ammonium excretion rates of freshly caught krill were 60%–80% of those in summer and declined significantly during 18 d of starvation. These findings suggest both switch feeding and energy conservation strategies, with a trend of reduced and more carnivorous feeding with ontogeny. This points to a “compromise” strategy for postlarvae, but there are alternative explanations. First, the krill may have reduced their feeding in an autumn transition to a nonfeeding mode, and, second, some of the population may have maintained a high feeding effort whereas the remainder was not feeding.
The role of fish and fisheries in Baltic Sea nutrient dynamics
Authors: Hjerne Olle , Hansson Sture
Published: June 2010

Many studies show that fish and fisheries management can be important to freshwater nutrient dynamics, but similar reports from marine environments are scarce. In the Baltic Sea, we estimate the removal of nutrients by the fishery to be 1.4% and 7% of the total nitrogen and phosphorus load to the Baltic Sea. Moreover, compared with the anthropogenic load of nutrients that reaches the open sea, the fishery removes 2.4% and 18% of the nitrogen and phosphorus. In addition, we show that the summer increase of fish biomass can explain up to one third of the summer decrease in “total phosphorus” in the upper 40 m of the water column. This suggests that fish may compete with primary producers (particularly cyanobacteria) for phosphorus. The fish and the fishery can thus influence nutrient dynamics in marine systems substantially, and this should be considered in ecosystem oriented fisheries management.
Carbon, nitrogen, and phosphorus budgets for a shallow subtropical coastal embayment (Moreton Bay, Australia)
Authors: Eyre Bradley D. , McKee Lester J.
Published: June 2010

Average annual carbon, nitrogen, and phosphorus budgets were constructed for Moreton Bay. Primary production was the dominant source of carbon (by two orders of magnitude), N fixation was the dominant source of nitrogen, and point sources were the dominant source of phosphorus to the bay. About 41% of the nitrogen and 70% of the phosphorus entering Moreton Bay was exported to the ocean, and about 56% of the nitrogen was lost to denitrification. The high percentage loss of phosphorus to the ocean was directly related to the short residence time of the bay (46 d), which was consistent with other shallow coastal ecosystems. In contrast, the percentage loss of nitrogen to the ocean was low compared to other coastal systems due to the high percentage loss through denitrification associated with autotrophic sediments in the bay that enhance denitrification. Because most denitrification studies have been carried out using only dark incubations, the importance of denitrification to the nitrogen budgets of coastal systems in general may be underestimated. Carbon loss from Moreton Bay was dominated (by two orders of magnitude) by atmospheric exchange of CO2 associated with benthic and pelagic respiration. The distinct difference between Moreton Bay (subtropical) and temperate systems was the dominance of biological (microbial: N fixation and denitrification) over physical inputs and losses of nitrogen. High N fixation in turn fuels a positive annual mean net ecosystem metabolism (NEM) of 21 g C m-2 yr-1 and suggests that primary production in the bay is phosphorus limited at the whole ecosystem scale.
Acetate cycling in the water column of the Cariaco Basin: Seasonal and vertical variability and implication for carbon cycling
Authors: Ho Tung‐Yuan , Scranton Mary I. , Taylor Gordon T. , Varela Ramon , Thunell Robert C. , Muller‐Karger Frank
Published: June 2010

Acetate oxidation frequently has been used as proxy of organic carbon decomposition in marine anoxic sediments. However, the importance of acetate uptake in carbon cycling in marine anoxic water columns is less well studied. Acetate concentrations and uptake rate constants, together with total bacterial numbers, primary and chemoautotrophic production rates, and particulate organic carbon (POC) fluxes, were measured in the water column of the Cariaco Basin during upwelling and nonupwelling seasons between November 1995 and May 1999 as part of the international CARIACO (Carbon Retention In A Colored Ocean) program. Acetate uptake was found to vary strongly with depth and season. Zones of elevated acetate uptake were found in the surface waters and near the suboxic/anoxic interface. High acetate uptake in the surface oxic layer suggests that acetate cycling may be an important component of organic carbon oxidation in oxic environments as well as under anoxic conditions. Depthintegrated acetate uptake rates were correlated with the rates of organic carbon supply in the two zones (r2 = 0.37, P = 0.017). Comparisons of acetate oxidation rates with rates of primary production, chemoautotrophic production, and POC flux show that, on average, acetate oxidation can account for respiration of between 16 and 46% of the organic carbon fixed in the water column.
Distribution, size, and bacterial colonization of pico‐ and nano‐detrital organic particles (DOP) in two lakes of different trophic status
Authors: Carrias Jean-François , Serre Jean-Philippe , Sime-Ngando Télesphore , Amblard Christian
Published: June 2010

Abundance, size spectra, and bacterial colonization of three types of freshwater pico‐ and nano‐detrital organic particles (DOP), namely transparent exopolymeric particles (TEP), Coomassie‐stained proteinaceous particles (CSP), and 4',6‐diamidino‐2‐phenylindole (DAPI) yellow particles (DYP), were examined by epifluorescence microscope equipped with a color camera and a video recorder. The study was conducted during spring in the oligomesotrophic Lake Pavin and the eutrophic Lake Aydat, France. Pico‐ and nano‐DOP were abundant (105–108 particles L−1) and exhibited significant variations in morphometric characteristics and numerical density within and among lakes, which is consistent with comparable studies known mostly from marine systems. Surface area and abundance of pico‐ and nano‐DYP and nano‐TEP were significantly higher in Lake Aydat than in Lake Pavin. Both these variables significantly increased with chlorophyll a concentration and the abundance of total heterotrophic bacteria. Bacterial colonization of DOP was highly related to the nature of the particle. Attached bacterial counts were on the order of 107–108 bacteria L−1, representing 1–17% of the total bacterial counts. Overall, we conclude that nonliving particulate organic matter are ubiquitous and abundantly occurring components in lakes where, at least, they serve as support for the attachment and as substrate for the metabolism of bacteria, the latter role being likely dependent on the composition of the particles and the trophic status of the milieu.
Light availability indirectly limits herbivore growth and abundance in a high rocky intertidal community during the winter
Authors: Harley Christopher D. G.
Published: June 2010

Light availability and consumer pressure are fundamental factors that structure aquatic communities, but their integrated effects are rarely studied in marine benthic systems. Using a factorial experiment, I investigated the effects of light availability and grazing by limpets (Lottia digitalis) to determine the relative influence of each on the growth and abundance of producers and consumers in a rocky intertidal community during the winter. Light reduction via shading reduced the abundance of filamentous algae and reduced the abundance of the herbivorous periwinkle Littorina sitkana. The effects of limpet grazing reduced the abundance of filamentous algae, Porphyra spp., and diatom mats. Higher limpet densities were also associated with significantly lower densities of adult, but not juvenile, Littorina spp. Light and limpet density interacted to determine Lottia growth, which was high in unshaded, single‐limpet enclosures but was negligible in plots with two limpets, shades, or both. Variation in bottom‐up (resource‐driven) and top‐down (consumer‐driven) forces are important determinants of abundance at both trophic levels, but the effects are complex, taxon‐specific, and, for littorine snails, size‐specific. Because the study species accomplish most of their growth and reproduction during the winter, the interplay of light and herbivory during this season will likely influence long‐term community dynamics.
Biological and physical dynamics of domoic acid production off the Washington coast
Authors: Trainer Vera L. , Hickey Barbara M. , Horner Rita A.
Published: June 2010

The relationship among Pseudo‐nitzschia distributions, particulate toxin levels in seawater, and the energetic and highly variable water masses of an upwelling‐dominated region are explored using data collected during summer cruises off the Washington coast in 1997 and 1998. In the early summer of both years, an area of maximum domoic acid (DA) accumulation was located approximately 50 km off the coast within a counterclockwise, cold feature known as the Juan de Fuca eddy. The stations in the eddy with the highest domoic acid concentrations coincided with high numbers of Pseudo‐nitzschia pseudodelicatissima (Hasle) Hasle (2.7 µg DA equivalents L-1, up to 0.6 X 106 cells L-1 in 1997 and 0.2 µg DA equivalents L-1, up to 0.2 X 106 cells L-1 in 1998), a species known to produce toxin in this region. Other known toxin‐producing species were sometimes present, but at ≪5% of the total Pseudo‐nitzschia population when ≫0.1 µg DA equivalents L-1 were measured. In 1998, large‐scale surveys indicated that high levels of particulate DA in seawater persisted at least until 1 October, covering a maximum area of 100 km2 off the Washington coast in midsummer. The appearance of high levels of DA (up to 2.7 µg DA equivalents L-1), coincident with high numbers of P. pseudodelicatissima (up to 15.4 X 106 cells L-1) at Kalaloch beach on the central coast in late September, was followed by the accumulation of record levels of toxin in razor clams. This toxic episode was preceded by a downwelling‐favorable wind event, with associated onshore transport in near‐surface layers. We suggest that the Juan de Fuca eddy may be one source of DA to the Washington coast. The duration of upwelling and the exact timing of fall storms likely play an influential role in the intensity of the bloom and the movement of toxic cells from the eddy to the coast.
Maximum rates of N2 fixation and primary production are out of phase in a developing cyanobacterial bloom in the Baltic Sea
Authors: Gallon J. R. , Evans A. M. , Jones D. A. , Albertano P. , Congestri R. , Bergman B. , Gundersen K. , Orcutt K. M. , von Bröckel K. , Fritsche P. , Meyerhöfer M. , Nachtigall K. , Ohlendieck U. , Hekkert S. te Lintel , Sivonen K. , Repka S. , Stal L. J. , Staal M.
Published: June 2010

Although N2‐fixing cyanobacteria contribute significantly to oceanic sequestration of atmospheric CO2, little is known about how N2 fixation and carbon fixation (primary production) interact in natural populations of marine cyanobacteria. In a developing cyanobacterial bloom in the Baltic Sea, rates of N2 fixation (acetylene reduction) showed both diurnal and longer‐term fluctuations. The latter reflected fluctuations in the nitrogen status of the cyanobacterial population and could be correlated with variations in the ratio of acetylene reduced to 15N2 assimilated. The value of this ratio may provide useful information about the release of newly fixed nitrogen by a cyanobacterial population. However, although the diurnal fluctuations in N2 fixation broadly paralleled diurnal fluctuations in carbon fixation, the longer‐term fluctuations in these two processes were out of phase.
Elemental C, N, and P cell content of individual bacteria collected at the Bermuda Atlantic Time‐series Study (BATS) site
Authors: Gundersen Kjell , Heldal Mikal , Norland Svein , Purdie Duncan A. , Knap Anthony H.
Published: June 2010

Accurate assessments of the true elemental cellular content of carbon (C), nitrogen (N), and phosphorus (P) in bacteria have been a major difficulty in microbial research for some time. This study is the first to present single‐cell elemental C, N, and P measurements on natural populations of bacteria from the Sargasso Sea using a transmission electron microscope (TEM) equipped with an X‐ray detector unit. Elemental cell content showed a best fit as a power function of the cell size, and smaller bacteria had significantly more elemental C, N, and P per cell volume than the larger ones (scaling factor a < 1). Contrary to coastal, brackish, and freshwater systems, the bacteria collected in this study appeared to have a molar elemental P :N close to the Redfield ratio of 0.063 (N:P = 16). The geometric mean of C per cell volume analyzed in this study (148 fg C µm−3) was higher than any other estimates reported from coastal and brackish water systems. Total amount of bacterial C calculated from abundance estimates requires an average conversion factor, and the choice of a representative bacterial cell volume is therefore critical. We were able to demonstrate that the outcome of biomass assessments is highly dependant on the choice of cell‐specific conversion factors. By applying cell volumes previously reported from the BATS site, the average 0–250 m depth integration of bacterial C between 1991 and 1996 ranged between 1.7 and 2.5 times less than other recent biomass estimates for these waters.
Nitrogen fixation and nitrogen isotope abundances in zooplankton of the oligotrophic North Atlantic
Authors: Montoya Joseph P. , Carpenter Edward J. , Capone Douglas G.
Published: June 2010

Deep‐water nitrate is a major reservoir of oceanic combined nitrogen and has long been considered to be the major source of new nitrogen supporting primary production in the oligotrophic ocean. 15N:14N ratios in plankton provide an integrative record of the nitrogen cycle processes at work in the ocean, and near‐surface organic matter in oligotrophic waters like the Sargasso Sea is characterized by an unusually low 15N content relative to average deep‐water nitrate. Herein we show that the low dΔ15N of suspended particles and zooplankton from the tropical North Atlantic cannot arise through isotopic fractionation associated with nutrient uptake and food web processes but are instead consistent with a significant input of new nitrogen to the upper water column by N2 fixation. These results provide direct, integrative evidence that N2 fixation makes a major contribution to the nitrogen budget of the oligotrophic North Atlantic Ocean.
Seasonal variation in the attachment strength of blue mussels: Causes and consequences
Authors: Carrington Emily
Published: June 2010

The midintertidal zone of temperate rocky coasts is often dominated by mussels that form dense beds and exclude other primary space holders. The rate at which storms remove mussels from their substrate consequently has a controlling influence on intertidal community structure. The rate of disturbance by waves can be predicted mechanistically by comparing the attachment strength of an organism to the force it encounters. One simplifying assumption often implemented with this approach is that organismal strength is temporally constant. This study demonstrates that such an assumption is not valid for Mytilus edulis in Rhode Island, where byssal attachment strength (tenacity) increases twofold in winter compared to summer. Time series analysis of monthly samples (1998–2000) indicates tenacity generally tracks seasonal fluctuations in wave height, which suggests that mussels sense and respond to changes in their flow environment. However, the ability of mussels to respond to wave climate is not precise; during September and October (hurricane season), mussels remain weakly attached and are prone to major mortalities. Mussel reproductive condition also displays seasonal cycles, peaking 3–4 months after attachment strength. This suggests a possible energetic constraint on the ability of mussels to respond to their flow environment, as mussels trade byssal thread production for gonad development. This study demonstrates that accurate predictions of disturbance events must consider not only a storm’s magnitude, but its timing relative to the cycle in attachment strength. Given the recent shift to increased hurricane activity in the North Atlantic, it is likely that mussels will begin to suffer more frequent and more severe disturbances compared to those that occurred during 1971–1994.
Temperature‐dependent ultraviolet responses in zooplankton: Implications of climate change
Authors: Williamson Craig E. , Grad Gabriella , De Lange Hendrika J. , Gilroy Shawna , Karapelou Danielle M.
Published: June 2010

Climate warming and stratospheric ozone depletion increase temperature and ultraviolet (UV) in mid‐ to highlatitude ecosystems; however, little is known about the interactive effects of temperature and UV on organisms. We exposed Daphnia catawba, Leptodiaptomus minutus, and Asplanchna girodi to UV‐B at four different temperatures: 10, 15, 20, and 25°C. Elevated temperatures increased UV tolerance in D. catawba and L. minutus, species that depend heavily on photoenzymatic repair (PER), but decreased UV tolerance in A. girodi, a species that has less PER. Also, body size in Daphnia decreased with increasing UV dose. These results demonstrate that climate change can alter responses to UV through temperature‐mediated effects in aquatic ecosystems, and these effects can be species‐specific and dependent on PER ability.
Direct evidence of a biologically active coastal silicate pump: Ecological implications
Authors: Ragueneau Olivier , Chauvaud Laurent , Leynaert Aude , Thouzeau Gérard , Paulet Yves-Marie , Bonnet Sophie , Lorrain Anne , Grall Jacques , Corvaisier Rudolph , Le Hir Maryvonne , Jean Frédéric , Clavier Jacques
Published: June 2010

Ecological shifts from diatoms to other phytoplankton species have been related to decreasing Si : N and Si : P nutrient ratios. The Bay of Brest is such a perturbated ecosystem where Si has become limiting but where diatoms continue to dominate the phytoplankton throughout the productive period. Several hypothesis have been invoked to account for this dilemma. The most recent combines suspension feeder activity and Si recycling. Suspension feeder activity, stimulated by the proliferation of the invasive species Crepidula fornicata, would be the driving force of a biologically active silicate pump which would (1) retain Si within the Bay during spring and (2) provide the Si necessary for diatoms during summer. During the year 2000, this hypothesis was successfully tested. Direct evidence of silicic acid limitation has been provided, and during summer, benthic fluxes measured at a site with a high density of C. fornicata are one order of magnitude higher than those measured at the site with no C. fornicata. Seasonal budgets of Si inputs and diatom demand demonstrated that diatom production during summer depends strongly on Si recycling at the sediment‐water interface. Thus, if C. fornicata decreases benthic biodiversity and perturbates the development of the native Great Scallop (Pecten maximus), it also helps the Bay cope with elevated N inputs. The proposed removal of C. fornicata might be economically desirable from a fisheries economic viewpoint, but it clearly would be associated, in the present context of excessive N inputs, to a potential risk of harmful algal blooms during summer.
The role of solar radiation in structuring the shallow benthic communities of boreal forest lakes
Authors: Donahue William F. , Turner Michael A. , Findlay David L. , Leavitt Peter R.
Published: June 2010

We have attempted to quantify the roles of physical, chemical, and biological interactions structuring the attached algal and invertebrate communities in eight boreal lakes at the Experimental Lakes Area, northwestern Ontario, varying in dissolved organic carbon (DOC) concentrations (3–9 mg L−1). Attached benthic communities on rocky, south‐facing shores were sampled at 0.1, 0.3, 0.7, and 1.5 m depths. Multivariate redundancy analysis explained 58% of the variance in algal communities and 75% of the variance in invertebrate communities. Algal composition was determined most by photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) fluxes, whereas the composition of associated invertebrates was driven by a combination of exposure to solar radiation and food quality and quantity. Communities on rock surfaces exposed to high solar fluxes in these lakes had very high concentrations of a photoprotective scytonemin‐like pigment (SLP‐A), and were dominated by filamentous green algae. Conversely, deeper, more shielded communities were dominated by diatoms and had low concentrations of SLP‐A. This suggests that previous paleolimnological evidence of SLP‐A increases might reflect changes in littoral attached algal communities rather than planktonic ones. Decreases in DOC concentrations as a result of climate warming will result in increased penetration of solar radiation in boreal lakes. As a result, in the event of decreased precipitation, we predict that the dominance of UVR‐resistant epilithic algae in littoral zones will occur in deeper waters than before, with coincident reductions in densities of many invertebrate taxa in algal biofilms increasingly exposed to high solar fluxes.
Carbon acquisition of bloom‐forming marine phytoplankton
Authors: Rost Björn , Riebesell Ulf , Burkhardt Steffen , Sültemeyer Dieter
Published: June 2010

Carbon acquisition in relation to CO2 supply was investigated in three marine bloom‐forming microalgae, the diatom Skeletonema costatum, the flagellate Phaeocystis globosa, and the coccolithophorid Emiliania huxleyi. In vivo activities of extracellular (eCA) and intracellular (iCA) carbonic anhydrase activity, photosynthetic O2 evolution, CO2 and HCO3− uptake rates were measured by membrane inlet mass spectrometry in cells acclimated to pCO2 levels of 36, 180, 360, and 1,800 ppmv. Large differences were obtained between species both with regard to the efficiency and regulation of carbon acquisition. While eCA activity increased with decreasing CO2 concentration in S. costatum and P. globosa, consistently low values were obtained for E. huxleyi. No clear trends with pCO2 were observed in iCA activity for any of the species tested. Half saturation concentrations (K1/2) for photosynthetic O2 evolution, which were highest for E. huxleyi and lowest for S. costatum, generally decreased with decreasing CO2 concentration. In contrast, K1/2 values for P. globosa remained unaffected by pCO2 of the incubation. CO2 and HCO3− were taken up simultaneously by all species. The relative contribution of HCO3− to total carbon uptake generally increased with decreasing CO2, yet strongly differed between species. Whereas K1/2 for CO2 and HCO3− uptake was lowest at the lowest pCO2 for S. costatum and E. huxleyi, it did not change as a function of pCO2 in P. globosa. The observed taxon‐specific differences in CO2 sensitivity, if representative for the natural environment, suggest that changes in CO2 availability may influence phytoplankton species succession and distribution. By modifying the relative contribution of different functional groups, e.g., diatomaceous versus calcareous phytoplankton, to the overall primary production this could potentially affect marine biogeochemical cycling and air—sea gas exchange.
Using natural distributions of short‐lived radium isotopes to quantify groundwater discharge and recharge
Authors: Krest James M. , Harvey Judson W.
Published: June 2010

Radium activity in pore water of wetland sediments often differs from the amount expected from local production, decay, and exchange with solid phases. This disequilibrium results from vertical transport of radium with groundwater that flows between the underlying aquifer and surface water. In situations where groundwater recharge or discharge is significant, the rate of vertical water flow through wetland sediment can be determined from the radium disequilibrium by a combined model of transport, production, decay, and exchange with solid phases. We have developed and tested this technique at three sites in the freshwater portion of the Everglades by quantifying vertical advective velocities in areas with persistent groundwater recharge or discharge and estimating a coefficient of dispersion at a site that is subject to reversals between recharge and discharge. Groundwater velocities (v) were determined to be between 0 and −0.5 cm d−1 for a recharge site and 1.5 ± 0.4 cm d−1 for a discharge site near Levee 39 in the Everglades. Strong gradients in 223Ra and 224Ra usually occurred at the base of the peat layer, which avoided the problems of other tracers (e.g., chloride) for which greatest sensitivity occurs near the peat surface—a zone readily disturbed by processes unrelated to groundwater flow. This technique should be easily applicable to any wetland system with different production rates of these isotopes in distinct sedimentary layers or surface water. The approach is most straightforward in systems where constant pore‐water ionic strength can be assumed, simplifying the modeling of radium exchange.
Assimilation of micro‐ and mesozooplankton by zebra mussels: A demonstration of thefood web link between zooplankton and benthic suspension feeders
Authors: Wong Wai Hing , Levinton Jeffrey S. , Twining Benjamin S. , Fisher Nicholas
Published: June 2010

We tested the hypothesis that rotifer species in the micro‐ and mesozooplankton are a potential food source for zebra mussels. We labeled phytoplankton with 14C, fed them to two species of rotifers (140–210 µm length) that were previously found abundantly in the Hudson River and had declined following a zebra mussel invasion, and estimated the assimilation of carbon. Assimilation efficiencies were found to be ~37.47–54.0%. Combined with our feeding experiments, the data on rotifer densities before and after the invasion allowed us to calculate the energy budgets for zebra mussels. Before zebra mussels dominated the Hudson River in 1992, the absorption of energy from rotifers was about two to three times higher than that necessary to maintain its routine metabolic rate and contributed about 0.349–0.662 J h−1 to mussel growth and reproduction, conferring a positive scope for growth. Since the zebra mussels became abundant in the Hudson River, assimilation of rotifers is still sufficient to explain ~16.4–23.1% of the mussels' routine metabolic rate. Therefore, rotifers play a conceivably large role in the energy budget of zebra mussels, whether at high rotifer concentrations (before the invasion) or at low rotifer concentrations (after the invasion). This is the first quantitative evidence for a trophic link between benthic bivalve mollusks and larger micro‐ and mesozooplankton that might extend to marine systems where bivalves can derive nutrition from microzooplankton, including planktonic invertebrate larvae. Combined with other recent results, this study documents a benthos‐zooplankton trophic loop, demonstrating potentially strong top‐down control by dense bivalves on aquatic systems.
The effect of bottom substrate on inherent optical properties: Evidence of biogeochemical processes
Authors: Boss Emmanuel , Zaneveld J. Ronald V.
Published: June 2010

Measurements of inherent optical properties (IOP) were conducted over bottoms with different substrates by use of a sampling package mounted on and operated by a SCUBA diver. It was found that in areas of low ambient currents the distribution of IOP varies with bottom type in (1) its value relative to a nearby bottom of different type, (2) its vertical gradient, and (3) its variability. This implies that radiative transfer modeling in shallow environments may need to include, besides the bottom characteristics, the bottom effect on in‐water IOP. In tidally flushed shallow banks, vertical and horizontal gradients over scales of O(1, 10 m), respectively, are as large as temporal gradients over scales of minutes and cannot be separated in our measurements. However, bottom‐substrate‐related processes over the banks result in gradients over large horizontal spatial scales and tidal timescales. The distribution of IOP is consistent with several biogeochemical processes that may be active at a given bottom substrate and suggest that optical measurements may provide a useful tool to infer and quantify bulk rates of biogeochemical processes.
Size-dependent aerosol deposition velocities during BEARPEX'07
Authors: Vong R. J. , Vong I. J. , Vickers D. , Covert D. S.
Published: June 2010

Abstract. Aerosol concentrations and 3-D winds were measured from 9 to 25 September 2007, above a pine forest in California. The measurements were combined using the eddy covariance (EC) technique to determine aerosol eddy fluxes as a function of particle diameter within the accumulation mode size range (0.25 μm≤Dp≤1 μm here). Measured heat and water vapor fluxes were utilized to correct the aerosol eddy fluxes for aerosol hygroscopic growth. The hygroscopic growth correction was necessary despite the low RH and relatively hygrophobic nature of the particles. Uncertainties associated with particle counting also were evaluated from the data. Aerosol deposition velocities (Vd = EC turbulent flux/mean particle concentration) during daytime were shown to vary from −0.2 to −1.0 cm s−1; the magnitude of particle Vd increases with friction velocity and particle diameter.
LMI‐based stability analysis of linear hybrid systems with application to switched control of a refrigeration process
Authors: Cai Chaohong , Mijanovic Stevo
Published: June 2010

We consider continuous‐time switched linear systems associated with linear state reset during mode switches, which are called linear hybrid systems and can be commonly found in switched control systems via bumpless transfer during controller switches. We use a multiple Lyapunov functions approach to develop constructive tools for stability analysis of linear hybrid systems. In particular, we derive a linear‐matrix‐inequalities based procedure to compute upper bounds of dwell time for uniform global exponential stability in linear hybrid systems, and we apply it to a refrigeration process that is regulated by several switched proportional‐integral controllers via bumpless transfer.

Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society
ChemInform Abstract: Bonding and Electronic Properties of Cs3Te22.
Authors: BOUCHER F. , ROUSSEAU R.
Published: June 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Mechanism of Electrochemical Oscillations in the System Fe/H2SO4(aq), K2Cr2O7(aq)/Pt.
Authors: BOURCEANU G. , MELNIG V. , VATAMANU J. , VASILIU R.
Published: June 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Effective 1,4‐Asymmetric C—C/C—O Stereoinduction in Indium‐Promoted Coupling Reactions of Aldehydes to Protected and Unprotected [1‐(Bromomethyl)vinyl] Alkanols. The Status of Intramolecular Chelation within Functionalized Allylindium Reagents.
Authors: PAQUETTE L. A. , BENNETT G. D. , ISAAC M. B. , CHHATRIWALLA A.
Published: June 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Chloride‐Assisted Nitrolysis of Cyclic Tertiary Amines.
Authors: CLIFF M. D.
Published: June 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.