bluuebunny/crossref_metadata_2025 huggingface dataset:
TNF Production in Macrophages Is Genetically Determined and Regulates Inflammatory Disease in Rats
Authors: Gillett Alan , Marta Monica , Jin Tao , Tuncel Jonatan , Leclerc Patrick , Nohra Rita , Lange Stefan , Holmdahl Rikard , Olsson Tomas , Harris Robert A. , Jagodic Maja
Published: May 2010

Dysregulation of TNF is an important pathophysiological phenotype for many diseases. Recently, certain genetically regulated loci have been identified to regulate several inflammatory diseases. We hypothesized that a region on rat chromosome 4 known to regulate experimental autoimmune encephalomyelitis, experimental arthritis and experimental autoimmune neuritis harbors a gene regulating central inflammatory molecules, such as TNF. We therefore mapped TNF production using linkage analysis in the 12th generation of an advanced intercross line between DA and PVG.AV1 rats, which differ in susceptibility to several inflammatory conditions. A single TNF-regulating quantitative trait locus with a logarithm of odds score of 6.2 was identified and its biological effect was confirmed in a congenic rat strain. The profound TNF regulation mapped in congenic strains to the macrophage population. Several TLR signaling cascades led to the same reduced proinflammatory phenotype in congenic macrophages, indicating control of a convergence point for innate inflammatory activity. The decreased TNF potential and reduced proinflammatory macrophage phenotype in congenic rats was also associated with reduced clinical severity in experimental autoimmune encephalomyelitis, pristane-induced arthritis and sepsis experimental models. Determination of genes and mechanisms involved in this genetically determined TNF regulation will be valuable in understanding disease pathogenesis and aid treatment development.
The Politics of Media Policy
Authors: Rayburn Sarah
Published: May 2010

No abstract available.
The kinetics of nitrogen utilization in the oceanic mixed layer: Nitrate and ammonium interactions at nanomolar concentrations
Authors: Harrison W. G. , Harris L. R. , Irwin B. D.
Published: May 2010

The concentration‐dependent uptake of nitrate (NO3) and its inhibit ion by ammonium (NH4) were surveyed in surface waters of the North Atlantic Ocean. Low‐level NO3 determinations combined with conventional tracer methods provided the first comprehensive data set on NO3 utilization kinetics at nanomolar concentrations. Uptake followed saturation kinetics described by the Michaelis‐Menten equation. The half‐saturation parameter for uptake (KN) ranged 2–3 orders of magnitude, covarying with ambient NO3 concentrations. KN concentrations in oceanic waters averaged ~20–30 nM. NH4 half‐saturation parameters could only be approximated (i.e. KA + A), but observations suggested that KA and KN were of similar magnitude in oceanic waters. Maximum uptake rates of nitrate, pm(N), and ammonium, pm(A), covaried, but pm(A) almost always exceeded p,(N); in oceanic waters, the disparity was an order of magnitude or greater. Most of the variability in pm(N) and pm(A) could be explained by variations in phytoplankton biomass and temperature. The slope of the uptake vs. concentration relationship, a, was also investigated but was highly variable and could not be related to any of the oceanographic properties observed; αA was generally greater than αN. Kinetics analysis showed that NH4 is preferentially utilized over NO3 over the full spectrum of nitrogen concentrations, nanomolar to micromolar.

The inhibition of NO3 uptake by NH4 was also parameterized using the Michaelis‐Menten expression. The inhibition half‐saturation parameter (Ki) covaried with KN, but Ki concentrations in oceanic waters (~40– 50 nM) always exceeded Kn. Maximum inhibition (Im) was rarely complete (i.e. Imn < 1), even at 2,000 nM ammonium. Overall, results suggest that nitrogen utilization parameters currently used in ecosystem models of the open ocean should be re‐examined.
Mercury phase speciation in the surface waters of three Texas estuaries: Importance of colloidal forms
Authors: Stordal M. C. , Gill G. A. , Wen L.‐S. , Santschi P. H.
Published: May 2010

Surface‐water samples were collected from Galveston Bay, Corpus Christi Bay, Sabine Lake, and Laguna Madre and analyzed for Hg in the <0.45‐µm, 0.45‐µm‐1‐kDa, and <1‐kDa fractions. Colloidal material was isolated with an Amicon cross‐flow ultrafiltration system which was rigorously tested. Filter‐passing Hg concentrations (< 0.45 µm) ranged from 0.12 to 13.6 pM, with the highest values in Corpus Christi Bay. Within Galveston and Corpus Christi Bays, filter‐passing Hg exhibited nonconservative estuarine mixing behavior. The colloidal Hg fraction ranged from 12 to 93% of the filter‐passing pool and averaged 57 ± 20%, indicating that a major portion of the operationally defined “dissolved” Hg is associated with submicron particles and macromolecules > 1 kDa. Colloidal Hg covaries with colloidal organic C concentrations in Galveston Bay waters, suggesting that most of the filter‐passing Hg pool is associated with large organic macromolecules. The log of the particle‐water partition coefficient (Kd) ranged from 4.6 to 5.2, and covaried with suspended particulate matter concentrations, likely due to the presence of colloidal Hg.
The sulfur cycle in the chemocline of a meromictic salt lake
Authors: Overmann Jörg , Beatty J. Thomas , Krause H. Roy , Hall Ken J.
Published: May 2010

An extremely dense layer of the purple sulfur bacterium Amoebobacter purpureus in the chemocline of meromictic Mahoney Lake (British Columbia) was investigated over a 2‐yr period. Within this layer, sulfide, elemental sulfur, and polysulfides were the main species of reduced sulfur. The oxidative part of the sulfur cycle was dominated by anoxygenic photosynthesis of A. purpureus. During summer, when sulfide concentrations in the layer were limiting, intracellular sulfur became the main electron donor for photosynthesis. δ34S determinations revealed that the intracellular sulfur reacts chemically with dissolved sulfide to form polysulfides. Polysulfide concentrations decreased over summer, accompanied by an increase in numbers of sulfur‐reducing bacteria. Sulfate reduction was the major pathway of sulfide formation. The annual carbon requirement of sulfate‐reducing bacteria in the chemocline (22.5 g C m‐2 yr‐ 1) was met by the photosynthetic C fixation of A. purpureus (33.5 g C m‐2 yr‐1). Carbon demand exceeded the concomitant C fixation temporarily in summer, however. The activities of biomass‐degrading enzymes and the formation of volatile fatty acids were sufficient to provide the carbon substrates. Our data indicate that in Mahoney Lake, anoxygenic photosynthesis and sulfate reduction are only indirectly coupled via degradation and autolysis of photosynthetically formed biomass.
Calculation of cell‐specific growth rates: A clarification
Authors: McCormick Michael J. , Fahnenstiel Gary L. , Lohrenz Steven E. , Redalje Donald G.
Published: May 2010

Cell‐specific growth and cell‐specific production estimates of phytoplankton have been calculated in the past by a simple exponential model (constant uptake‐division) that describes the time rate of change of carbon, C*, and assumes both continuous division and continuous carbon uptake. We propose three new models (variable uptake‐division, variable uptake‐constant division, and diurnal) for making more accurate estimates of the algal growth rate, µ. The variable uptake‐division model is the most complex and requires species‐specific information on the division pattern. The diurnal model can provide accurate µ estimates while requiring only two measurements of C* and no other parameters, but it requires 48‐h incubation times. The variable uptake‐constant division model can also provide accurate µ estimates and can be applied to data with <24‐h incubation times. The variable uptake‐division and variable uptake‐constant division models require additional work compared to the constant uptake‐division model, but the effort is warranted because they also provide a direct approach for quantifying the dependence of µ on the photoperiod and thus enable greater confidence in applying µ to ecological studies, in which the light climate may differ from that of the experiment.
The relative role of denitrification and immobilization in the fate of inorganic nitrogen in mangrove sediments (Terminos Lagoon, Mexico)
Authors: Rivera‐Monroy Victor H. , Twilley Robert R.
Published: May 2010

Rates of direct and coupled nitrification‐denitrification were measured with 15N isotope techniques in intact sediment cores from fringe, basin, and riverine mangroves in Terrminos Lagoon, Mexico. We used intact sediment cores to evaluate differences in denitrification rates. The lack of 15N2 production in all cores amended with 200 (or 100) µmol core‐1 15NH4+ and the high recovery of 15N in the sediment in five of eight such experiments indicate that coupled nitrification‐denitrification was riot important to nitrogen transformation during the 8–10‐d incubations. However, when we added 450 µmol core−1 15NH4+ and 15NO3− to cores from the riverine mangrove, N2 production rates ranged from 28.9 to 221.1 µmol N m−2 h−1 for each nutrient. We compare coupled nitrification‐denitrification rates among different types of mangrove forests under natural conditions in the neotropics. Our results with nitrogen isotopes suggest that the uptake of inorganic N from tidal waters within mangrove ecosystems does not necessarily represent a nitrogen sink via denitrification, but rather a retention of nitrogen in mangrove sediments.
Parent lithology, surface–groundwater exchange, and nitrate retention in headwater streams
Authors: Valett H. Maurice , Morrice John A. , Dahm Clifford N. , Campana Michael E.
Published: May 2010

We address the ecological ramifications of variation in hydrologic interaction between streams and alluvial aquifers in catchments with alluvium derived from parent materials of contrasting geologic composition. We present a conceptual model in which solute retention in streams results from hydrologic retention (increased water residence time resulting from surface‐groundwater exchange), biological nutrient cycling, and chemical processes. Solute injection experiments were done in study catchments comprised of sandstone‐siltstone (site 1), volcanic tuff (site 2), and granite‐gneiss (site 3). Distribution of an injected conservative tracer (Br) illustrated that rate and extent of surface‐water penetration into the alluvial aquifer increased across study catchments as was predicted from increasing alluvial hydraulic conductivity. Concurrently, groundwater inputs at baseflow represented between 13 and 57% of aboveground discharge at upstream transects, indicating bidirectional hydrologic exchange along the study reaches. N: P ratios in surface water ranged from 4 to 16, suggesting strong biotic demand for inorganic N. Coinjection of NaBr and NaNO3 revealed longest nitrate uptake length (Sw) at site 1, intermediate Sw at site 2, and shortest uptake length at site 3. Modeling of transient hydrologic solute storage revealed that Sw correlated with hydraulic storage, suggesting an important role for subsurface processes in total nitrate retention.
Seasonal variation in the flux of microplankton and radiolarian assemblage compositions in the northeastern tropical Atlantic at 2,195 m
Authors: Boltovskoy Demetrio , Uliana Eleonora , Wefer Gerald
Published: May 2010

Fluxes of silicoflagellates, the dinoflagellate Actiniscus sp., polycystine and phaeodarian radiolarians, tintinnids, ciliate(?) cysts, and pelagic molluscs were estimated for 13 sediment trap samples from the northeastern tropical Atlantic (20°55.3′N, 19°44.5′W) at 2,195 m between 22 March 1988 and 8 March 1989 (site CB1). Each sample integrated the flux over 27 d, and polycystines were identified to species in all samples. Polycystines had the highest fluxes. For phytoplankters, our estimates are lower than most reported data, and for polycystines and tintinnids the values are among the highest ever recorded. Temporal variations in the fluxes of the heterotrophic organisms counted generally were in good agreement with total mass flux, suggesting fairly tight couplings with primary production at the surface. Fluxes of tintinnids were more variable through time and better associated with variations in total mass flux than those of the slower reproducing radiolarians. We identified 145 polycystine taxa. Species compositions changed little throughout the year and did not vary with changes in total mass flux. Comparison of our data with a similar survey of sediment trap samples retrieved between 1 March 1989 and 16 March 1990 from 853 m at the nearby GBN3 site showed significant differences in the fluxes of the groups and in the percentages of many polycystine species. All groups (except silicoflagellates) had higher output rates at CBI, and proportions of several polycystines associated with colder or more productive environments also were higher at CB1. Conversely, GBN3 yielded higher proportions of various radiolarians characteristic of warmer, more oligotrophic waters. Because temperatures below ∼70 m are higher at CB1 than at GBN3, different productivity levels, rather than different surface temperatures, may be important in structuring the specific differences recorded.
Nitrate uptake by phytoplankton and periphyton: Whole‐lake enrichments and mesocosm‐15N experiments in an oligotrophic lake
Authors: Axler Richard P. , Reuter John E.
Published: May 2010

Periphyton nitrate uptake and denitrification, not phytoplankton assimilation, accounted for ∼90% and 73% of the depletion of ∼35 µg NO3‐N liter−1 added as whole‐epilimnion enrichments of ammonium nitrate to Castle Lake, California, in midsummer 1980 and 1981. The importance of benthic processes is suggested by similar rates of depletion for nitrate and ammonium in the whole‐lake experiments; these rates are inconsistent with previous microcosm studies of phytoplankton that showed strong preferential uptake of ammonium and low uptake rates of nitrate. The importance of the benthic pathways was confirmed by an NH415NO3 mesocosm experiment, which simulated the whole‐epilimnion experiments. Less than 9% of the 15N transformed was associated with water‐column pools; the remainder was incorporated into epipelic periphyton and sediments (56%) or attributed to 15N2‐15N2O loss via denitrification. Historical analysis of nitrate depletion in the epilimnion during spring suggests that periphyton may outcompete phytoplankton for water‐column nutrients.
Unbalanced particle flux budgets in Crater Lake, Oregon: Implications for edge effects and sedimentfocusing in lakes
Authors: Dymond Jack , Collier Robert , McManus James , Larson Gary L.
Published: May 2010

Flux estimates show that upward mixing of the deep‐water nitrate pool accounts for more than 85% of the total new nitrogen input to the euphotic zone of Crater Lake. Because measured primary productivity (360 mg C m−2 d−1) is 10–30 times higher than a level supported solely by the input of new nitrogen into the euphotic zone, nitrogen must be recycled in the euphotic zone many times before it is transferred by particles to the deep lake. Nitrogen recycling in the deep lake is also very efficient. Sediment trap measurements of particulate nitrogen fluxes reveal a major imbalance in our estimates of the lake’s internal nitrogen budget. We propose the imbalance reflects an “edge effect,” whereby enhanced biological production occurs near the lake margin and the shallower portions of the lake. Our measurements also reveal that Al, an element carried by refractory phases, is accumulating in basin sediments at a rate 15–30 times higher than the flux we measure with sediment traps. This difference is maintained by the near‐bottom transport of lithogenic particles from the lake margins to the deep basins of the lake. These comparisons of nutrient and refractory element fluxes reflect two important lake processes— enhanced productivity at the lake margin that may be due to greater availability of macro‐ and micronutrients at the lake edges and focusing of particulate material into the deep lake basins.
Stream hydrological and ecological responses to climate change assessed with an artificial neural network
Authors: Poff N. LeRoy , Tokar Sezin , Johnson Peggy
Published: May 2010

An artificial neural network (ANN) was used to evaluate the hydrological responses of two streams in the northeastern U.S. having different hydroclimatologies (rainfall and snow+rain) to hypothetical changes in precipitation and thermal regimes associated with climate change. For each stream, historic precipitation and temperature data were used as input to an ANN, which generated a synthetic daily hydrograph with high goodness‐of‐fit (r2 > 0.80). Four scenarios of climate change were used to evaluate stream responses to climate change: +25% precipitation, ‒25% precipitation, 2× the coefficient of variation in precipitation regime, and +3°C average temperature. Responses were expressed in hydrological terms of ecological relevance, including flow variability, baseflow conditions, and frequency and predictability of floods. Increased average precipitation induced elevated runoff and more frequent high flow events, while decreased precipitation had the opposite effect. Elevated temperature reduced average runoff. Doubled precipitation variability had a large effect on many variables, including average runoff, variability of flow, flooding frequency, and baseflow stability. In general, the rainfall‐dominated stream exhibited greater relative response to climate change scenarios than did the snowmelt stream.
Changes in atmospheric circulation patterns affect midcontinent wetlands sensitive to climate
Authors: LaBaugh J. W. , Winter T. C. , Swanson G. A. , Rosenberry D. O. , Nelson R. D. , Euliss N. H.
Published: May 2010

Twenty‐seven years of data from midcontinent wetlands indicate that the response of these wetlands to extremes in precipitation—drought and deluge—persists beyond the extreme events. Chemical changes transcend such simple relations as increased salinity during dry periods because drought provides mechanisms for removal of salt by deflation and seepage to groundwater. Inundation of vegetation zones including rooted or floating mats of cattail (Typha glauca) can stimulate sulfate reduction and shift the anion balance from sulfate to bicarbonate dominance. Disruptions in the circulation of moisture‐laden air masses over the midcontinent, as in the drought of 1988 and the deluge of 1993, have a major effect on these wetlands, which are representatives of the primary waterfowl breeding habitat of the continent.
Annual cycle of autotrophic and heterotrophic production in a small, monomictic Piedmont lake (Lake Oglethorpe): Analog for the effects of climatic warming on dimictic lakes
Authors: Porter Karen G. , Saunders Patricia A. , Haberyan Kurt A. , Macubbin Alexander E. , Jacobsen Timothy R. , Hodson Robert E.
Published: May 2010

Lake Oglethorpe, Georgia, is a small, monomictic impoundment in the southeastern U.S. Piedmont region. Seasonal differences in ecological processes correspond to the two major stratification patterns and result in seasonal differences in pelagic community structure. The winter mixed period (November–March) provides light and temperatures suitable for active nutrient regeneration and uptake, population growth of edible phytoplankton and crustacean zooplankton, and low bacterial abundance and production. Monthly estimates of daily primary productivity are in the mesoeutrophic range (40–1,420 mg C m‒2 d‒1); however, mean annual primary productivity is in the eutrophic range (500 mg C m‒2 yr‒1) because of greater activity in winter and an extended “growing season.” The stratified period (April–October) is characterized by rapid development of hypolimnetic anoxia, high bacterial production, cyanobacteria and large algae, heterotrophic flagellates, ciliates, rotifers, small cyclopoid copepods, and Chaoborus. Heterotrophic activity, HPLC chlorophyll a, and grazer activity were highest at the epilimnetic‐metalimnetic boundary. Bacterial abundances (1.5–32 × 106 cells ml‒1) increased in the hypolimnion during the stratified period. Long‐term (1978–1994) warming within the water column (0.061–0.10°C yr‒1) follows midwinter (January) air temperature trends. Using Lake Oglethorpe as an analog, we predict as consequences of climatic warming in northern dimictic lakes: increases in nutrient cycling rates, winter primary and secondary productivity, summer heterotrophic production, and microbial components of the food web.
Climatic forcing on zooplankton richness in lakes of the northeastern United States
Authors: Stemberger Richard S. , Herlihy Alan T. , Kugler Danny L. , Paulsen Steven G.
Published: May 2010

The June 1991 eruption of Mt. Pinatubo had a marked cooling on global climate that was evident in the regional air temperatures of the northeastern U.S. This climatic perturbation coincided with the 1991–1994 pilot surveys initiated by the Environmental Monitoring and Assessment Program—Surface Waters (EMAP‐SW). Regional air and summer profile water temperatures for 1992 were significantly lower (∼1–2°C) than in the same July–August sampling period in 1991, 1993, or 1994. Richness of major zooplankton groups such as rotifers and small cladocerans also varied markedly with the 1992 cooling. The median of 323 randomly selected survey lakes had 2–10 additional species of zooplankton per lake in 1992 than in the warmer years of 1991, 1993, or 1994. This response represented an increase of 7–34% in local richness across lakes. Regional richness was also 17–32% higher in the cooler year. ANOVA showed that total zooplankton richness had a highly significant year effect, suggesting a response to annual climatic differences. The difference in total richness in 1992 was attributed primarily to richness of rotifers and small cladocerans. On the other hand, the richness of large cladocerans and copepods did not show significant year effects, suggesting that their responses may occur at time scales that are longer than the temporal scale of this 4‐yr survey. These results indicate that local zooplankton richness can be effectively extrapolated to regional scales for the monitoring of lakes to climate change.
Global warming impacts on lake trout in arctic lakes
Authors: McDonald Michael E. , Hershey Anne E. , Miller Michael C.
Published: May 2010

Arctic freshwater ecosystems may be sensitive indicators of climatic warming trends because they have relatively few species and simple food webs. Many of these systems are dominated by lake trout, which act as keystone predators. For arctic Alaska Toolik Lake, we have a 16‐yr record of physical, chemical, and biological data. Our temperature data show a 3°C increase in mean July epilimnetic temperatures. An individual‐based bioenergetics model for young‐of‐year (YOY) lake trout in the lake was used to examine the effects of climate warming on growth of YOY lake trout. Our simulation models predicted that with a July temperature increase, YOY lake trout would need to consume >8‐fold more food (>10‐fold with seasonally increased temperatures) to achieve the same end‐of‐year size as historically surviving YOY lake trout. We have observed no increase in food availability in the lake, and recent analysis shows that primary productivity has actually decreased. If recent changes in the lake foreshadow a long‐term trend, our model results suggest that YOY lake trout will not survive their first winter. Such changes, coupled with other current anthropogenic impacts in the arctic, may disrupt lake trout control of the trophic structure in arctic lakes.
Simulated long term temperature and dissolved oxygen characteristics of lakes in the north‐central United States and associated fish habitat limits
Authors: Stefan H. G. , Hondzo M. , Fang X. , Eaton J. G. , McCormick J. H.
Published: May 2010

Water temperatures and dissolved oxygen (DO) concentrations in lakes are related to climate. Temperature and DO in 27 lake classes (3 depth classes × 3 surface area classes × 3 trophic states) were simulated by numerical models with daily weather data input. The weather data used are from the 25‐yr period 1955– 1979. The lakes and the weather are representative of the north‐central U.S. Daily profiles of water temperature and DO concentrations were computed and several temperature and DO characteristics extracted from this information base. Temperature and minimum oxygen requirements for good growth of cold, cool, and warm water fish were then applied to determine the length of the good‐growth periods and the relative lake volumes available for good growth. All characteristics are presented in graphical form using lake surface area, maximum lake depth, and Secchi depth as independent variables. The surface area and maximum depth were combined in a lake geometry ratio which is a relative measure of the susceptibility of a lake to stratification; Secchi depth was retained as a measure of lake transparency and trophic state. To determine an effect of latitude, we investigated a southern and northern region separately. The effect of climate change due to a projected doubling of atmospheric CO2 was investigated by applying the output from the GISS 2 × CO2 global circulation model to the lake models.
Relation between presence‐absence of a visible nucleoid and metabolic activity in bacterioplankton cells
Authors: Choi Joon W. , Sherr Evelyn B. , Sherr Barry F.
Published: May 2010

We investigated the report of Zweifel and Hagström that only a portion of marine bacteria contain nucleoids—the DNA‐containing regions of procaryotic cells—and that such bacteria correspond to the active or viable fraction of bacterioplankton. In Oregon coastal waters, 21–64% of bacteria had visible nucleoids; numbers of nucleoid‐visible (NV) bacteria were greater than numbers of metabolically active bacteria, based on cells with active electron transport systems (ETS) and intact cell membranes. During log growth of a marine isolate, proportions of NV and ETS‐active cells approached 100%. In stationary growth phase, the fraction of ETS‐active cells decreased rapidly, while that of NV cells remained high for 7 d. When starved cells of the isolate were resupplied with nutrient (50 mg liter‒1 peptone), total cell number did not increase during the initial 6 h, but the proportion of NV cells increased from 27 to 100%, and that of ETS‐active cells from 6 to 75%. In an analogous experiment with a bacterioplankton assemblage, a similar trend was observed: the number of NV cells doubled during the initial 6 h prior to an increase in total cell counts. These results show that some bacteria without visible nucleoids are capable of becoming NV cells, and thus have DNA in a nucleoid region not detectable with the method used here.
Suspension feeding: Basic mechanisms controlling recognition and ingestion of larvae
Authors: Tamburri Mario N. , Zimmer‐Faust Richard K.
Published: May 2010

Oysters (Crassostrea virginica) are valuable subjects for investigations of basic mechanisms regulating suspension feeding on invertebrate larvae. In separate laboratory experiments, we introduced inert particles or larvae to the oyster mantle cavity. Small inert particles (<40‐µm diam) equal to phytoplankton cells in size were eaten, whereas large inert particles (> 100‐µm diam) equal to larvae in size were rejected. Neither particle specific gravity nor phytoplankton in the seawater medium affected ingestion of inert particles or larvae. Oysters consumed a wide range of invertebrate larval forms, including conspecific veligers. Nearly all larvae (>75%) delivered to the oyster mantle cavity, except those of Bugula neritina, were eaten and digested. Feeding stimulants in the larvae were a mixture of polar and nonpolar compounds that were insoluble in seawater. Although contrasting mechanisms regulated feeding on different‐sized particles, ingestion of larvae was strictly controlled by particle surface chemistry (=flavor).
Acoustic remote sensing of benthic activity: A statistical approach
Authors: Jumars Peter A. , Jackson Darrell R. , Gross Thomas F. , Sherwood Christopher
Published: May 2010

Acoustic backscatter at 40 kHz was recorded from a circular area of silt 75 m in radius every 0.1 d at a water depth of 91 m off the coast of northern California for 49 d in winter 1988–1989. Data were resolved into pixels that extended 7.5 m radially and 5° azimuthally. We analyzed the relatively small change in backscatter intensity and phase from a given pixel. In a time‐series analysis, this change in backscatter was decomposed into three components putatively due to large, rare, transient nekton and epibenthos; more abundant benthopelagic organisms that caused volume reverberation; and more sedentary benthos. Benthic change in backscatter was presumed due to movement of animals and other biogenic modifications of sound speed in the sediment‐water medium. Patterns of benthic activity and volume backscatter near the seabed changed abruptly twice, with the middle interval showing highest levels. During this middle interval, winter storms disturbed surficial sediments, offshore transport occurred near the seabed, and the benthic component was dominated by activity perfectly in phase with and linearly proportional to median, local, downwelling irradiance. We suspect that this circadian pattern was due to the burrowing urchin Brisaster latifrons that is known from previous studies at this site to emerge on the sediment surface at night when food resources are available there and to reburrow during the lighted part of the day. Extensive correlative physical data collected at the site as part of interdisciplinary studies (CODE and STRESS) allowed us to exclude other physical forcings as likely explanations for diurnal change in backscatter. In a spatial analysis, the transient component was removed explicitly pixel by pixel, and volume reverberation was removed implicitly to leave a benthic remainder that could be analyzed for spatial variation. Benthic activity showed distinct patchiness with coherence scales of roughly 5–10 m and negative spatial autocorrelation in activity levels near the largest spatial lag available (∼140 m). Patches did not move appreciably during the study.
Phytoplankton photosynethetic characteristics from fluorescence induction assays of individual cells
Authors: Olson Robert J. , Chekalyuk Alexander M. , Sosik Heidi M.
Published: May 2010

Saturating‐flash fluorescence techniques, which can provide information about the physiological state of phytoplankton, at present measure bulk water samples and so provide “averaged” values for all the fluorescent particles present. In analyzing natural samples, however, more detailed information about the distribution of photosynthetic characteristics among different cell types and(or) individual cells is desirable. Therefore we developed two methods for applying a “pump‐during‐probe” technique on a cell‐by‐cell basis. We used either an epifluorescence microscope or a flow cytometer to make time‐resolved measurements of the increase in chlorophyll fluorescence induced by a rectangular excitation pulse of 100‐µs duration. We used a biophysical model of fluorescence induction to obtain information about the quantum yield of photochemistry in photosystem 2 (PS2) and the functional absorption cross‐section for PS2. For several species (including the smallest phytoplankton, Prochlorococcus, which are 0.7 µm in diameter), the maximum quantum yield of photochemistry in PS2 obtained by averaging data from many individual cells agreed well with estimates derived from bulk measurements of DCMU enhancement of Chl fluorescence.
Transport mechanisms of larval and pelagic juvenile bluefish (Pomatomus saltatrix) from South Atlantic Bight spawning grounds to Middle Atlantic Bight nursery habitats
Authors: Hare Jonathan A. , Cowen Robert K.
Published: May 2010

In this study we examined the mechanisms by which Pomatomus saltatrix (Pisces: Pomatomidae) larvae and pelagic juveniles are transported from South Atlantic Bight spawning grounds to Middle Atlantic Bight estuarine nursery habitats. Data on larval and pelagic juvenile distributions, estuarine juvenile recruitment, hydrography, wind speed and direction and satellite‐derived, sea surface temperature were used to examine potential larval transport mechanisms. On the basis of these analyses, a scenario for northward transport of P. saltatrix was developed. Gulf Stream‐associated flow moves P. saltatrix larvae northeastward from their South Atlantic Bight spawning grounds. Larval transport from the Gulf Stream to the Middle Atlantic Bight shelf edge occurs in warm‐core ring streamers, but some more developed individuals may swim across. Finally, P. saltatrix pelagic juveniles actively swim across the Middle Atlantic Bight shelf, a behavior initiated when the surface shelf‐slope temperature front dissipates in late spring. This scenario predicts that the number of South Atlantic Bight‐spawned P. saltatrix juveniles entering estuaries (i.e. recruitment) is determined in part by warm‐core ring streamer activity. The timing of recruitment, however, is determined almost entirely by the timing of the dissipation of the surface shelf‐slope temperature front.
Opposing predation pressures and induced vertical migration responses in Daphnia
Authors: Nesbitt Leslie M. , Riessen Howard P. , Ramcharan Charles W.
Published: May 2010

Induced vertical migration by Daphnia pulex in response to two invertebrate predators was examined in lake enclosures to determine the adaptive benefit of this behavior. Daphnia reduced spatial overlap with Chaoborus larvae, which occupied the lower strata in the enclosures, by moving upward in the water column. In the presence of both Chaoborus and the backswimmer Notonecta, which resides near the surface, this upward migration response was modified in the daytime (but not at night) to simultaneously avoid areas occupied by each predator. D. pulex thus seems capable of sophisticated antipredator behavior that increases individual fitness by reducing predation risk.
Jellyfish Lake, Palau: Regeneration of C, N, Si, and P in anoxic marine lake sediments
Authors: Lyons W. Berry , Lent Robert M. , Burnett William C. , Chin Philip , Landing William M. , Orem William H. , McArthur John M.
Published: May 2010

Sediment cores from Jellyfish Lake were processed under an inert atmosphere and the pore waters extracted and analyzed for the following parameters: pH, titration alkalinity (TA), Cl−, H4SiO4, PO43−, NH4+, Ca2+, Mg2+, SO42−, and H2S. Additionally, in one set of pore‐water samples (core 10), the δ13C of the ∑CO2 was also determined. The TA, H4SiO4, PO43−, NH4+, and H2S increased with depth in the pore waters above anoxic bottom‐water values. H2S values increased to 3.8 M. In one case, both H4SiO4 and PO43− concentrations increased to a maximum value and then decreased with depth, suggesting removal into solid phases. The H4SiO4 concentrations are equal to or greater than pore‐water value observed in sediments underlying upwelling areas. PO43− concentrations are, in general, lower than pore‐water values from terrigenous nearshore areas but higher than nearshore carbonate pore‐water values from Florida Bay or Bermuda. The Ca2+, Cl−, and Mg2+ : Cl− ratios show slight decreases in the top 15–20 cm, suggesting that authigenic carbonate may be forming. This suggestion is supported by the fact that the pore waters are saturated with respect to CaCO3 due to the very high TAs. The δ13C measurements of the pore‐water ∑CO2 are from a shorter core. These measurements reach their most negative concentration at 72 cm and then become slightly heavier. This change is accompanied by a decrease in TA, suggesting the onset of methanogenesis at this location in this core.
Regeneration, recycling, and trophic transfer of trace metals by microbial food‐web organisms in the pelagic surface waters of Lake Erie
Authors: Twiss Michael R. , Campbell Peter G. C. , Auclair Jean-Christian
Published: May 2010

Rapid regeneration of 109Cd and 65Zn from their picoplankton prey into the dissolved phase by microzooplankton was observed in water sampled from the pelagic surface waters of Lake Erie (summer 1994 and 1995). Trace metals were added to grazing (lake water <210 µm) and control (lake water <0.2 µm) treatments in the form of radiolabeled Synechococcus. Picoplankton (0.2–3 µm) were grazed heavily by consumers in the nanoplankton (3–20 µm) and microplankton (20–210 µm) size classes (collectively referred to as microzooplankton) as confirmed by dilution assays used to independently measure grazing activity. Most consumed trace metals were regenerated into the dissolved phase (<0.2 µm), but some trophic transfer of 109Cd and 65Zn from radiolabeled prey into the nanoplankton and microplankton did occur: 65Zn was transferred 2.5 times more efficiently into the microplankton and 2.9 times more efficiently into the nanoplankton than was 109Cd. Recycling o:f regenerated 109Cd back into plankton biomass was greater than that for 65Zn. Grazing by microzooplankton influenced the molecular size distribution of regenerated trace metal in the dissolved phase (77±6% 109Cd <5,000 MW; 8 ± 24% 65Zn <5,000 MW). These results show that microzooplankton grazing tends to prolong the residence times of metals such as Cd and Zn in the pelagic surface waters of large lakes.
Growth and development in the subtropical copepod Acrocalanus gibber
Authors: McKinnon A. D.
Published: May 2010

Growth rates of the subtropical copepod Acrocalanus gibber were measured in field incubations. Prosome length of adult females was correlated with rearing temperature, but variation in condition of copepods masked any correlation of temperature with carbon and nitrogen content. The resulting N‐specific growth rates (GN) were log‐linear and ranged from 0.49 to 0.72 d−1 at temperatures of 24.4–29.2°C. Highest growth rates occurred in the middle of the temperature range, but no relationship between Gn and temperature could be established, although molting rate and generation time were correlated with temperature. Growth rate was negatively related to chlorophyll a concentration and was independent of particulate C and N. Nitrogen‐specific egg production, measured either from wild‐caught females or from females produced in the incubations, never exceeded 0.28 d−1 (representing only 46% of GN) and was frequently near zero. In this respect, juvenile growth was less food‐limited than was adult growth (measured as egg production). The measured duration of A. gibber developmental stages, particularly copepodite stages 1 and 5, varied in laboratory experiments, apparently as a result of variation in food composition. Molting rate, copepod weight, and the resulting growth rates appear to be influenced by food quality.
Regulation of bacteria by resources and predation tested in whole‐lake experiments
Authors: Pace Michael L. , Cole Jonathan J.
Published: May 2010

Food webs in three lakes were manipulated by altering fish communities to promote or suppress the abundance of large Daphnia. These lakes and an unmanipulated reference lake were monitored for 2 yr. The three experimental lakes were then fertilized for 2 yr with nitrogen and phosphorus. Bacterial responses to these manipulations were examined by means of weekly measurements of abundance and production. Bacterial production, measured both by thymidine and leucine incorporation, increased substantially in the fertilized lakes, whereas abundance increased a small amount. Time‐series models based on P loading explained substantial variation in both measures of bacterial production, suggesting strong regulation by P. Phytoplankton also increased with fertilization, but covariation of primary production and chlorophyll with bacterial production was relatively weak. Protozoans did not consume the increased bacterial production observed in the fertilized lakes. Bacterial abundance was instead regulated by consumption by Daphnia in at least two of the three fertilized lakes. Interannual variation in bacterial production during the 2 yr of fertilization was related to variation in pH, suggesting that environmental conditions also drive variability in bacterial activity. Overall, the experiments indicate that bacterial aburdance and production are regulated by nutrients and, at high nutrient loading, by metazoan rather than by protozoan predators. With fertilization, bacterial production increased more rapidly than did abundance because bacterial predators limited abundance. The primary response of bacteria to eutrophication was higher specific growth rates.
A vertical life table approach to zooplankton mortality estimation
Authors: Aksnes Dag L. , Ohman Mark D.
Published: May 2010

Zooplankton mortality is commonly estimited from time series of abundances (horizontal life table approach) with the assumption that transport processes are of minor influence. This assumption is commonly violated in the marine environment. We provide equations appropriate for analysis of stage distributions in zooplankton samples at a single time (vertical life table approach) that, in certain circumstances, facilitate mortality estimation without requiring time series of abundances. A primary assumption is that daily recruitment to a particular stage should not be characterized by a strong upward or downward trend. To improve the accuracy of parameter estimates, however, knowledge about such trends may be taken into account. The accuracy and precision of mortality estimation were assessed with an individual‐based simulation model. Results obtained from application of the vertical approach to the copepod Pseudocalanus newmani are comparable to those obtained independently by a horizontal method. We conclude that the vertical approach may provide mortality estimates under conditions in which horizontal techniques are inappropriate. In contrast to estimates obtained with horizontal techniques, vertical estimates represent snapshots of the population.
Field investigation of winter thermo‐ and hydrodynamics in a small Karelian lake
Authors: Bengtsson Lars , Malm Joakim , Terzhevik Arkady , Petrov Michail , Boyarinov Pjotr , Glinsky Alexander , Palshin Nikolqj
Published: May 2010

During late winter (18 March–7 April 1994), temperature and current measurements were made in Lake Vendyurskoe, Russia, including three surveys at six cross sections of the lake. Also, the temperature profile evolution was registered with two thermistor chains at two stations (bottom depths of 7.6 and 11.5 m) until the time of ice breakup. Temperature gradients were measured just below the ice cover and in the upper 10‐cm layer of the bottom sediments.

The isotherms were found to be almost horizontal and evenly spaced vertically, so no conditions for large‐scale, density‐induced currents existed. The heat flux from sediments to water ranged from 0.6 to 2.0 W m−2. These values were inversely related to the depth. The heat flux from water to ice ranged from 0.7 to 1.2 W m−2. When water heating from solar radiation penetration became apparent, this flux increased by a factor of two. When solar radiation increased, convection occurred in the upper layers of the water column. When solar radiation heating became significant at the beginning of spring, the average net heat flux at the ice‐water interface during daytime was 7.7 W m−2. Weak currents (few mm s−1) with a seiche‐like character were observed, which most likely resulted from ice‐cover oscillations.
Factors regulating phytoplankton and zooplankton biomass in temperate rivers
Authors: Bum Ben K. , Pick Frances R.
Published: May 2010

By measuring Chl a, zooplankton biomass, nutrient concentrations, and water residence time in 31 rivers in eastern Canada, we tested the following hypotheses: Chl a is positively related to nutrient concentrations and water residence time, and zooplankton biomass is positively related to Chl a and water residence time. Chl a ranged from 1.8 to 27.6 µg liter−1, total phosphorus (TP) from 7.3 to 212.3 µg liter−1, and water residence time from 3.3 to 19.4 d. There was a positive relationship between Chl a and TP (R2 = 0.76) and no relationship between Chl a and residence time. In contrast, zooplankton biomass was positively related to water residence time (R2 = 0.33). There was only a weak positive relationship between Chl a and zooplankton biomass. Mean river zooplankton biomass was low (11.3 µg liter−1 dry mass) compared to lakes of similar Chl a concentration.
Microscale distribution of bacterioplankton in relation to phytoplankton: Results from 1‐nl samples
Authors: MÜller‐Niklas Gerald , Agis Martin , Herndl Gerhard J.
Published: May 2010

The microspatial distribution of marine bacterioplankton was investigated by comparing the bacterial abundance in 100‐nl subsamples of natural seawater. For sampling, staining with DAPI, and filtering, we designed capillary microtips that allowed pipetting of 100 nl with a sampling error <10%. Highly significant correlations were obtained between the 100‐nl method and the conventional direct‐counting method. Frequency distributions of bacterial cells were determined in experiments with natural seawater during bloom conditions as well as with seawater enriched with diatom cells from cultures of Chaetoceros muelleri. Bacteria in 100‐nl subsamples were normally distributed in each single experiment and in the Formalin‐fixed control. Mean bacterial abundance in subsamples containing at least one phytoplankton cell was never significantly different from samples lacking algal cells. Based on our results we conclude that bacteria are homogeneously distributed in subsample volumes of 100 nl, and therefore we could not verify the current concept that bacteria may cluster around phytoplankton cells.
Particulate organic carbon export from a subtropical mountainous river (Lanyang Hsi) in Taiwan
Authors: Kao Shuh‐Ji , Liu Kon‐Kee
Published: May 2010

Small mountainous rivers have received increasing attention in recent years because of their high yield of sediments and particulate organic matter. A one‐year (1993–1994) study of the fluxes of the total suspended matter (TSM) and particulate organic carbon (POC) in different parts of Lanyang Hsi, a typical small mountainous river in subtropical northeastern Taiwan indicated that the mean TSM and POC yields of the whole drainage area were high (3,600 and 23 g m‒2 yr‒1, respectively) but that the yields of less disturbed (control) tributaries were only 1/30 of the mean yields of the whole area. Radiocarbon analysis by accelerator mass spectrometry gave very old apparent ages (>10,000 yr) to the POC in the main channel, indicating that >70% of the POC produced in the drainage basin was probably derived from kerogen in the bedrock. TSM yields for 1970–1991, calculated from historical records of runoffs and TSM concentrations, showed large fluctuations from year to year; however, the average yield after 1976 (8,335 g m‒2 yr‒1) was higher than that before 1976 (3,127 g m‒2 yr‒1) by a factor of 2.7, suggesting a significant increase in sediment production related to massive road construction in 1975–1980. The average POC yield for 1977–1994 was calculated to be 53 g m‒2 yr‒1. The very high yields of TSM and POC in recent years are attributable to human disturbances.