bluuebunny/crossref_metadata_2025 huggingface dataset:
How important are oceanic algal nanoflagellates in bacterivory?1
Authors: Estep Kenneth W. , Davis Paul G. , Keller Maureen D. , Sieburth John McN.
Published: April 2010

Open ocean chloroplast‐containing chrysomonads have been observed to prey on bacteria. Predominant among these forms are new species of Ochromonas and Chrysamoeba. These algae coexist with nearly identical apochlorotic forms, are abundant in oceanic nanoplankton (averaging 100 cells ml−1), will not grow axenically, can be maintained for extended periods with endogenous bacteria enriched by rice grain culture in the light, and contain bacteria within their food vacuoles. The results demonstrate that protists with and without chloroplasts can occupy overlapping trophic roles and should therefore be studied together. They also challenge recent estimates of nanoflagellate predation on bacteria, as these estimates have assumed that only apochlorotic forms are predatory. If other groups of pelagic nanoflagellates with chloroplasts also prey on bacteria, the transfer of material from bacteria to protists in the open ocean could approach twice previous estimates.
thermodynamic properties for natural waters covering only the limnological range1
Authors: Chen Chen‐Tung A. , Millero Frank J.
Published: April 2010

Dissolved salts affect the thermodynamic properties of lake waters. Equations are given to calculate the following properties over the range of 0–0.6 salinity, 0°–30°C, and 0–180 bars: density, thermal expansibility, temperature of maximum density, maximum density and minimum specific volume, isothermal compressibility, specific heat at constant pressure, specific heat at constant volume, sound speed, adiabatic compressibility, freezing point, adiabatic temperature gradient, and static stability.
Compositions and fluxes of particulate organic material in the Amazon River1
Authors: Hedges John I. , Clark Wayne A. , Quay Paul D. , Richey Jeffrey E. , Devol Allan H. , Santos M.
Published: April 2010

Lignin, elemental, and stable carbon isotope compositions are reported for local plants and for coarse (>63 µm) and fine (<63 µm) suspended particulate materials collected along a 1,950‐km reach of the lower Amazon River during four contrasting stages of the 1982–1983 hydrograph. Fluxes of chemically recognizable lignin in the two size classes generally parallel each other along the mainstem with the fine fraction usually predominating. Particulate organic matter transported in the coarse size fraction of the mainstem and its major tributaries is composed of recently formed and well preserved tree leaf debris along with some wood. Organic matter in the fine size fraction is comparatively old, degraded, and rich in immobilized nitrogen and derives primarily from soils. C‐4 grasses, which are abundant in the mainstem floodplain (várzea), are not major components of either the coarse or fine particulate material in the river.

Particulate organic matter in both size fractions is introduced largely from upstream sources within the Rio Solimões and Rio Madeira drainage basins. Most of this organic matter is unreactive and is transported conservatively with mineral particles along the Amazon mainstem. However, some downstream compositional trends are seen in both size fractions which reflect the addition or exchange of highly degraded, 13C‐depleted, and lignin‐poor organic materials from lower basin sources.
Simultaneous photoreduction and microbial oxidation of iron in a stream in the New Jersey Pinelands1
Authors: Madsen Eugene L. , Morgan Mark D. , Good Ralph E.
Published: April 2010

Photoreduction of ferric to ferrous iron was determined in water held in bottles placed in a New Jersey Pinelands stream, although concentrations of ferrous iron in the stream itself remained below detection (15 ng ml−1). The low ambient levels of ferrous iron apparently resulted from the action of iron‐oxidizing microorganisms in water and soil, as shown by a temperature optimum for, and by the inhibitory effect of sterilization upon, the disappearance of ferrous iron. Measurements of 14CO2 incorporation into soil organic matter indicated that the iron‐oxidizing microorganisms were not chemolithoautotrophs, but might have been iron‐depositing bacteria or chemolithoheterotrophs.
Secchi disk science: Visual optics of natural waters1
Authors: Preisendorfer Rudolph W.
Published: April 2010

The Secchi disk is a circular white disk that is lowered into a natural body of water by a human observer until it disappears from view. The depth of disappearance is a visual measure of the clarity of the water. This review examines the physical and physiological basis of the Secchi disk procedure. The theory of the white disk is detailed to show the underlying assumptions and the consequent strengths and limitations of the procedure. The theory shows how to use a calibrated Secchi disk to predict illuminance levels as a function of depth. In particular it is shown how to predict the euphotic depth of a medium. Ten laws of the Secchi disk are stated verbally and in mathematical form. The laws show how variations in properties of the disk and the surrounding light field affect the depth of disappearance of the disk. Theory and examples lead to the following three main conclusions of this paper: (i) the Secchi disk reading zsd (in meters) yields a quantitative estimate of a single apparent optical property (a + K) (in meter−1) of a natural hydrosol, where a is the (photopic) beam attenuation coefficient and K the (photopic) diffuse attenuation coefficient of the medium; (ii) the primary function of a Secchi disk is to provide a simple visual index of water clarity via zsd or α + K; (iii) to extend the use of the Secchi disk by auxiliary objective electronic measurements of a or of K, or both, is to risk obviating or abusing this primary function.
Nutrient limitation of the bottom‐ice microalgal biomass (southeastern Hudson Bay, Canadian Arctic)1
Authors: Maestrini Serge Y. , Rochet Martin , Legendre Louis , Demers Serge
Published: April 2010

In April 1983, differential‐enrichment bioassays were conducted on natural sea‐ice microalgae from Hudson Bay, Canadian Arctic. Incubations were done both in the laboratory (at about 4°– 5°C), and in situ at the ice‐water interface (−1.5°C). Actual growth of the cultures was nutrient limited. On the basis of our observations and using recalculated data from the literature, we tentatively set the mean generation time of Arctic‐ice microalgae between 8 and 17 days. Nitrogen was demonstrated to govern the algal yield when illumination and grazing allowed the algae to grow. The low (NO3− + NO2− + NH4+):PO43− mean ratio (5.9) in the water at the ice interface leads to the same conclusion. In situ dissolved inorganic nitrogen and phosphorus progressively decreased during the course of sampling, but were never exhausted. We hypothesize that the Ks of epontic as well as of other benthic microalgae is higher than that of phytoplankton, so that they cannot deplete the natural nutrient reservoir. We conclude that the bottom‐ice dynamics is controlled not only from above, by the seasonal (climatic) changes in light intensity as generally assumed, but also from below, by the shorter term (hydrodynamic) events of vertical mixing that replenish the ice‐water interface with nutrients.
Characterization of uranium(VI) in seawater1
Authors: Djogić Renata , Sipos Laszlo , Branica Marko
Published: April 2010

The physicochemical characterization of uranium(VI) in seawater is described on the basis of species distribution calculations and experiments using polarography and spectrophotometry in artificial seawater at elevated uranium concentrations. Various dissolved uranium(VI) species are identified under different conditions of pH and carbonate concentration. Below pH 4, the hydrated uranyl ion is present in the “free” state (forming “labile” complexes). Above pH 4, a stepwise coordination of uranyl by the carbonate ion occurs. The monocarbonate complex is formed in the pH range 4–5, the bicarbonate uranyl complex between 5 and 6. Above pH 8, uranium is present predominately as the tricarbonate and to a smaller extent as a trihydroxide complex. There is satisfactory agreement between our experiments and the theoretically computed distribution of uranium(VI) in seawater based on published stability constants.

The experiments done at higher concentrations are justified by theoretical distributions showing that there is no great difference in species distribution between the uranium at concentrations of 10−4 and 10−8 mol dm−3.
The role of sulfate reduction in long term accumulation of organic and inorganic sulfur in lake sediments1
Authors: Rudd John W. M. , Kelly C. A. , Furutani Akira
Published: April 2010

Sulfate reduction and the accumulation of reduced sulfur in epilimnetic sediments were studied in lakes in southern Norway, the Adirondack Mountains, and at the Experimental Lakes Area (ELA) of northwestern Ontario. In all of the lakes, in addition to the previously known formation of acid volatile sulfur, sulfate reduction also produced substantial quantities of pyrite and organic sulfur compounds. In 9‐month in situ experiments at ELA using 35S, there was a large loss (55%) with time of the S initially reduced and deposited in the sediments and a preferential loss of inorganic S compounds which led to a predominance of organic 35S accumulation in the sediments. An intensive study of long term accumulation of sulfur in the epilimnetic sediments of four Adirondack lakes also showed that the most important long term end product of sulfate reduction was organic S and that sulfate reduction was the major source of S to the sediments.

Because of the high concentrations of iron in all of the sediments we sampled and because of the long term storage of sulfur in sediments, mostly as organic S, iron did not limit iron sulfide accumulation in these sediments. Iron limitation is unlikely to occur except in unusual circumstances.

This study indicates that formation of organic S in epilimnetic sediments is primarily responsible for H consumption via sulfate reduction in acidified lakes.
A time resolution methodology for assessing the quality of lake sediment cores that are dated by 137Cs
Authors: Miller Kevin M. , Heit Merrill
Published: April 2010

A methodology is proposed for grading the utility of lake sediment cores used to reconstruct pollution histories. The observed distribution of 137Cs with depth in the core is compared to that expected from independent, historic measurements of fallout deposition. The width of the 137Cs peak in the core profile that corresponds to the fallout maximum of 1963, or the combined maxima of 1959 and 1963, is used to infer the inherent time resolution of the core, i.e. the ability to distinguish events in the deposition history of the watershed. The method is applied to a number of core profiles from various lakes in the U.S. and appears to provide self‐consistent results.
Littlefield Lake, Michigan: Carbonate budget of Holocene sedimentation in a temperate‐region lacustrine system1
Authors: Dustin Nina M. , Wilkinson Bruce H. , Owen Robert M.
Published: April 2010

Littlefield Lake is in a late stage of marl lake evolution characterized by reduced rates of carbonate precipitation. Long and short term carbonate budgets show that the volume of calcite in the lake basin is 3–7 times that expected from annual calcium depletion in the epilimnetic water. This Holocene decrease in carbonate production is also recorded as a gradual increase in the amount of organic and carbonate material in cores from the deep lake basin. Late‐stage reduction in carbonate production is evidently a natural consequence of lakeward progradation of littoral marl benches, encroachment of terrestrial vegetation, and reduced colonization by carbonate‐producing lake macrophytes.
Bacterial growth on macrophyte leachate and fate of bacterial production1
Authors: Findlay Stuart , Carlough Les , Crocker M. Tad , Gill H. Kay , Meyer Judy L. , Smith Phillip J.
Published: April 2010

The role bacteria play in transferring organic carbon to other trophic levels in aquatic ecosystems depends on the efficiency with which they convert dissolved organic carbon into bacterial biomass and on the ability of consumers to graze bacteria. We have measured the conversion efficiency for bacteria growing on macrophyte‐derived dissolved organic carbon and estimated the amount of bacterial production removed by grazing. Bacteria converted this DOC into new tissue with an efficiency of 53%, substantially higher than the apparent conversion efficiency of macrophyte‐derived particulate organic carbon or other types of DOC. Two estimates of grazing indicate that the decline in bacterial numbers after the bloom was probably due to grazing by flagellates. These results show the significance of the bacterial link between DOC and other trophic levels.
Dynamics of bottom currents in a small lake1
Authors: Lemmin U. , Imboden D. M.
Published: April 2010

The dynamics of bottom currents in Baldeggersee, Switzerland, were investigated with a specially designed recording current meter sensitive to current velocities of 0.3–2.5 cm s−1. Supporting information was obtained from thermistor‐chain temperature recordings and from records of atmospheric boundary‐layer parameters measured in the center of the lake. During 1980–1981 bottom currents recorded for 1‐week periods on the central bottom plateau of the lake (65‐m water depth) were highly variable. The mean speed was slightly > 1 cm s−1 with no seasonal trend. Speeds >2.5 cm s−1 occurred after periods of high wind; quiescent periods were rare and seldom lasted more than 1 h. Spectral analysis shows that the primary mechanism generating bottom currents during stratification is internal gravity waves in the thermocline. During winter mixing when chemical stratification is observed below 30 m, the wind stress distribution is directly reflected in the bottom current pattern. In both periods wind‐induced disturbances were felt in the bottom layer with little time delay, indicating the event‐dominated structure of bottom current dynamics. Bursts of particle transport in the bottom layer are observed during periods of high wind, suggesting episodic particle resuspension. Such events may be important for the control of mass exchange at the sediment‐water interface.
Free amino acids in lakes: Concentrations and assimilation rates in relation to phytoplankton and bacterial production1
Authors: Jørgensen Niels O. G.
Published: April 2010

Diel changes of concentrations and assimilation rates of dissolved free amino acids (DFAA) were followed every third day during periods of 3–5 weeks in eutrophic Frederiksborg Slotssø and Lake Hylke and oligotrophic Lake Almind. Concentrations of DFAA varied from 78 to 3,672 nM, but most concentrations were between 200 and 1,600 nM. Diel variations of DFAA ranged from < 10%, but were occasionally 500%. In Fr. Slotssø, concentrations were maximal in the morning and minimal at noon. The high morning concentrations coincided with the diel minimum bacterial production. In Lake Hylke mean concentrations were measured at noon, but in Lake Almind no diel trends were obvious. Statistical analyses demonstrate that long‐term changes of the DFAA pools in the lakes were negatively correlated with both primary production (except Lake Almind) and bacterial production.

In Fr. Slotssø and Lake Hylke, assimilation of DFAA (based on assimilation of five abundant DFAA) did not demonstrate diel trends, but within the study periods, the mean diel assimilation rates correlated negatively with primary production. In Lake Almind, no tendencies in the DFAA assimilation rates were observed. Carbon flux of DFAA assimilation in the lakes on the average made up from 6.9 to 11.3% of the primary production, and from 28.5 to 93.1% of the bacterial production, determined with the [3H]thymidine incorporation procedure. Data from the two eutrophic lakes suggest that degradation of phytoplankton can be a major source of DFAA in lakes.
Vertical transport of heavy metals by settling particles in Lake Zurich
Authors: Sigg Laura , Sturm Michael , Kistler David
Published: April 2010

Transport into sediments of the trace elements Cu, Zn, Pb, Cd, Cr, and Sr by settling particles was investigated in Lake Zurich; the concentrations of these elements in settling particles collected in sediment traps and in the water column were determined at different times of year. Correlations of trace element concentrations with the various main components of the settling particles (biological material, calcium carbonate, manganese and iron oxides, silicate minerals) and examination of seasonal variations both of these concentrations in particles and of particle fluxes to the sediments show that biological material is an important carrier phase (especially for Cu and Zn). Iron and manganese oxides also contribute to trace element transport; calcium carbonate is inefficient as a carrier material.
The relative abundance of pheophorbide a and pheophytin a in temperate marine waters1
Authors: Vernet Maria , Lorenzen Carl J.
Published: April 2010

This article is in Free Access Publication and may be downloaded using the “Download Full Text PDF” link at right.
Computer‐automated flow respirometry: Metabolism measurements on a Caribbean reef flat and in a microcosm1
Authors: Griffith Peter C. , Cubit John D. , Adey Walter H. , Norris James N.
Published: April 2010

This article is in Free Access Publication and may be downloaded using the “Download Full Text PDF” link at right.
Photosynthesis and light adaptation in epiphyte‐macrophyte associations measured by oxygen microelectrodes1
Authors: Sand‐Jensen Kaj , Revsbech Niels Peter
Published: April 2010

This article is in Free Access Publication and may be downloaded using the “Download Full Text PDF” link at right.
Hydrogen distributions in marine sediments1,2
Authors: Novelli Paul C. , Scranton Mary I. , Michener Robert H.
Published: April 2010

Hydrogen concentrations have been measured in sulfate‐reducing sediments of a British Columbian fjord and in Skan Bay, Alaska, as well as in the hemipelagic sediments of the eastern north tropical Pacific off the Mexican coast. In the sediments of both the Mexican shelf and Canadian fjord, hydrogen levels were lowest near the surface, increased with depth and reached a maximum pore‐water concentration of about 25–35 nM before sulfate was totally depleted. Deeper in the sediments, H2 levels decreased again. In Skan Bay sediments, concentrations of pore‐water hydrogen increased almost linearly with depth to a maximum level of 60 nM. Measured rates of hydrogen production in Skan Bay sediments varied little with depth (about 200 nM d−1), and in Skan Bay the hydrogen pool had a turnover time of, at most, several hours. Model‐predicted net rates of hydrogen production in Skan Bay are not significantly different than zero. These results are consistent with the hypothesis of interspecies hydrogen transfer between hydrogen‐producing and ‐consuming bacterial populations, which predicts low ambient hydrogen concentrations and tight coupling between production and consumption.
The hypothesis of antarctic larval starvation examined for the asteroid Odontaster validus1
Authors: Olson Richard Randolph , Bosch Isidro , Pearse John S.
Published: April 2010

A persistent hypothesis to explain the prevalence of nonfeeding larvae in benthic invertebrates at high latitudes has been the assumed lack of available food. This hypothesis is based in turn on the assumption that the only significant source of larval food is phytoplankton. Calculation of the carbon requirement (from respiration data) of larvae of the antarctic asteroid Odontaster validus suggests that they could not survive on natural levels of phytoplankton. To test whether starvation occurs, we cultured O. validus larvae in situ. After 5 weeks, survivorship was (N = three cultures of 30 larvae each). These data suggest that Chlorophyll a concentration is not a good indicator of food availability, and other sources of nutrition may be sufficiently abundant that starvation is not a major factor affecting the ecology of antarctic echinoderm larvae.
Methyl halide (CH3X) production from the giant kelp, Macrocystis, and estimates of global CH3X production by kelp1
Authors: Manley Steven L. , Dastoor Minoo N.
Published: April 2010

Production of methyl chloride (CH3Cl), methyl bromide (CH3Br), and methyl iodide (CH3I) was measured from short‐term incubations (light and dark) of Macrocystis pyrifera (kelp) blade tissue and from long‐term culture of Macrocystis blades. Seawater from within a natural Macrocystis bed had elevated CH3X concentrations compared to seawater from outside the kelp bed. Highest concentrations were associated with regions of high biomass density: surface canopy and sporophyll/juvenile frond zone. Rates of methyl halide production (normalized to kelp biomass) were determined from the short‐term incubation, blade culture, and natural population, the latter based on a simple hydrodynamic model. Estimates of global CH3X production based on these production rates and published estimates of global kelp standing stock suggest that kelps (and other marine macroalgae) are not a significant source of global CH3X.
Some evidence for boundary mixing near coral reefs
Authors: Wolanski Eric
Published: April 2010

Temperature profiles and acoustic images suggest that boundary mixing at reef surfaces may account for all the vertical mixing in coral reef lagoons.
Depth localization of denitrification in a deep‐sea sediment from the Madeira Abyssal Plain1
Authors: Sorensen J. , Jorgensen K. S. , Colley S. , Hydes D. J. , Thomson J. , Wilson T. R. S.
Published: April 2010

Sediments of the Madeira Abyssal Plain are dominated by alternate sequences of pelagic sediment and “turbidites” composed of relatively organic‐rich material transported from the continental margin. After the deposition of a turbidite and resumption of pelagic sedimentation, the zones of O2 and NO3− respiration progress slowly into the turbidite from above. The oxidation front is characterized by depletion of O2 and NO3 at almost identical depths. Data are presented to show that NO3− respiration (denitrification) within such a turbidite is localized in a very small depth interval at the oxidation front.
Prey size selection by carnivorous stoneflies1
Authors: Allan J. David , Flecker Alexander S. , McClintock Nancy L.
Published: April 2010

To investigate prey size preference by carnivorous stoneflies, we conducted choice experiments and directly observed predatory behavior in laboratory streams. Small, medium, and large size classes of Hesperoperla pacifica (Perlidae), small Kogotus modestus, and medium and large Megarcys signata (both of the Perlodidae) were offered an array of sizes of the mayfly Baetis as prey. Small predators displayed strong positive selection for the smallest size class of prey, and preference declined steadily with increasing prey size. Large predators displayed hump‐shaped preference curves, exhibiting strongest preference for intermediate size classes of prey. Thus size selectivity was demonstrated and varied with the size class of predator.

Direct observations of encounters between predators and their prey revealed that percent attacks/ encounters by small predators was strongly biased toward small prey and by large predators was weakly biased toward large prey. Capture success always was greater and handling times shorter with small prey compared to large prey.
Hydrogen production and nitrogen fixation by Oscillatoria thiebautii during in situ incubations1,2
Authors: Scranton Mary I. , Novelli Paul C. , Michaels Anthony , Horrigan Sarah G. , Carpenter Edward J.
Published: April 2010

We have examined net hydrogen production, acetylene reduction, and 15N2 fixation by the marine nitrogen fixer, Oscillatoria thiebautii, using both “standard” conditions and ultraclean and in situ techniques. Rates of hydrogen production and acetylene reduction appeared to be independent of incubation technique. This finding contrasts with previous reports that marine nitrogen fixers might be very sensitive to handling or trace metal contamination. Hydrogen production was highest at the surface and decreased sharply with depth, and no production (or acetylene reduction) was observed during dark incubations. Hydrogen production rates were two to three orders of magnitude lower than nitrogen fixation rates. In addition, the ratio of acetylene reduction to nitrogen fixation determined on one date, 4.1(±1.6): 1, is consistent with the hypothesis that hydrogen is not released from O. thiebautii in significant amounts.
Nonsphericity of suspended marine particles and its influence on light scattering1
Authors: Jonasz Miroslaw
Published: April 2010

Nonsphericity of marine particles causes underestimation of their projected areas calculated from equivalent spherical volumes determined with volume‐sensitive particle counters (e.g. Coulter Counter). A nonsphericity parameter has been defined as the ratio of the projected area averaged over all orientations of a particle to the projected area of a sphere with volume equal to that of the particle. The mean nonsphericity parameter of marine particles, determined with a scanning electron microscope, increases from about 1 for particles with a spherical equivalent diameter of 0.1 µm to about 2 for 10‐µm particles. Most particles appear to be moderately nonspherical. Significant discrepancy between measured and calculated light scattering reported for suspended marine particles could be explained by underestimation with a Coulter Counter of the projected area of the particles.
Nitrogen uptake and phytoplankton growth in coastal upwelling regions1
Authors: Kokkinakis Steven A. , Wheeler Patricia A.
Published: April 2010

Uptake of nitrogenous nutrients by microplankton off the Washington and Oregon coasts was measured during the 1985 upwelling period. Nitrogen uptake rates in low‐NO3− waters (<5 µM) were 0.020–0.258 µmol N liter−1 h−1 and were primarily supported by regenerated nitrogen (71% of total uptake). Nitrogen uptake rates in high‐NO3 waters(≥20 µM) were 0.281–1.480 µmol N liter−1 h−1 and new (NO3−) nitrogen supported 83% of total uptake. Phytoplankton N was estimated by assuming a constant Chl a : PN for phytoplankton and was used to calculate phytoplankton‐specific uptake rates.

Despite differences in nutrient concentrations, PN and Chl a at three upwelling sites (Oregon, Benguela, and Peru), NO3 uptake normalized to Chl a, and estimates of NO3−‐supported phytoplankton growth rates are remarkably similar. Nitrate uptake supports growth rates on the order of 1–2 d−1. Estimates of phytoplankton growth from rates of NH4+ + NO3− uptake range from 1.36 to 4.79 d−1 and are negatively correlated with concentrations of NO3− and phytoplankton N. The apparent increase in phytoplankton growth rates for waters with lower nitrogen availability may result from heterotrophic bacterial utilization of NH4+ nitrogen.
Sulfur, carbon, and nitrogen isotopes used to trace organic matter flow in the salt‐marsh estuaries of Sapelo Island, Georgia1
Authors: Peterson Bruce J. , Howarth Robert W.
Published: April 2010

The stable isotopes of sulfur, nitrogen, and carbon were used to trace organic matter flow in salt marshes and estuarine waters at Sapelo Island, Georgia. Organic matter inputs from terrestrial sources as detrital input either from forests adjacent to the marshes or from rivers were not detectable by their isotopic signatures in estuarine consumers. The results suggest that there are two major sources of organic matter for the fauna of the marshes and estuarine waters of Sapelo Island: Spartina and algae. The long‐standing debate about the relative importance of Spartina detritus and algae in supporting marsh and estuarine secondary production appears from this analysis to be a draw; both sources are important and their relative importance is determined by feeding mode, size, location, and trophic position of the marsh and estuarine consumers.
Causes of seasonality in the chemistry of a lake on the Orinoco River floodplain, Venezuela1
Authors: Hamilton Stephen K. , Lewis William M.
Published: April 2010

Lake Tinco, which lies on the Orinoco floodplain, passes through four seasonal phases (filling, through‐flow, drainage, and isolation), during which the lake volume changes 20‐fold. During filling and through‐flow, when the lake is inundated by river water, floating grasses (Paspalum repens) and phytoplankton grow rapidly, causing depletion of inorganic N and P between inflow and outflow, although phytoplankton biomass does not accumulate because of flushing. Inundation of the surrounding forest has no quantifiable effects on concentrations of major ions or macronutrients. Following through‐flow, phytoplankton biomass accumulates, and high abundances of blue‐green algae increase N in the lake by fixation (15 kg ha‐1). Quantities of some elements released by decomposition of floating grasses over a 4‐week period are very high in relation to lake‐water inventories (K, 126%; Cl, 66%; organic C, 170%; N, 74%; and P, 89%). Mass balance for Lake Tinco shows, on an annual basis, net retention of N (27%)— partly because most nitrogen fixation is limited to the isolation phase—and P (39%), and net yield of inorganic C (24%). There is neither detectable net retention nor yield of organic C, major cations, sulfate, or chloride. The major chemical transformation of river water during passage through the lake is conversion of inorganic N and P to organic forms.
Sources and fate of dissolved free amino acids in epilimnetic Lake Michigan water1
Authors: Gardner Wayne S. , Chandler Joann F. , Laird Gwenyth A. , Carrick Hunter J.
Published: April 2010

A seasonal series of light‐ and dark‐ bottle experiments was conducted on epilimnetic Lake Michigan water during 1986 to examine the dynamics of dissolved free amino acids (DFAA) in the pelagic microbial food web. When microbial uptake sites were saturated with DFAA, net primary amine removal rates were lower in light than in dark bottles, presumably due to release of DFAA by phytoplankton. Release rates ranged from 0.8 to 3.5 ng‐atoms N liter−1 h−1 in bottled lake water held several days at in situ temperatures. Ammonium accumulation rates in the dark ranged from <0.4 to 4 nmol liter−1 h−1. Ammonium regeneration was enhanced (up to 3–8 nmol liter−1 h−1) by the addition of DFAA (0.94 µM) to unfiltered lake water. On average, the increases in ammonium‐N accumulation equaled losses of amino acid nitrogen from the same water samples [ratio = 1.01 (SE = 0.08, n = 29)]. This result suggests that Lake Michigan microheterotrophs may deaminate DFAA and not maintain the nitrogen in food‐web biomass.
Cyanophyte blooms: The role of cell buoyancy1
Authors: Humphries Stella E. , Lyne Vincent D.
Published: April 2010

A one‐dimensional model of growth diffusion and scaling arguments show that bloom formation in epilimnetic cyanophytes is attributable to the passive mechanism of positive buoyancy of the cells, which enhances the average exposure of the population to light. The effects of interacting turbulent diffusion, photic depth, mixed‐layer depth, and diurnal mixed‐layer excursions on population growth rate and biomass production differ radically for positively and negatively buoyant cells. Over the typical range of sinking and rising velocities for lake phytoplankton and the characteristic velocities of turbulent mixing, the proportion of the maximum achievable growth rate attained is always greater for a positively buoyant species until significant self‐shading occurs. The magnitude of the difference is determined by the ratio of photic depth (zp) to mixed‐layer depth (z,); the advantages of positive buoyancy decrease as zp approaches zm. Results furthermore suggest that a positively buoyant population is able to track diurnal mixed‐layer excursions and thus to experience a more favorable average daily zp : zm ratio than is possible for a negatively buoyant population.
Microphotometric analysis of individual particle absorption spectra1
Authors: Iturriaga R. , Mitchell B. G. , Kiefer D. A.
Published: April 2010

We describe a microphotometric procedure to measure directly the absorption efficiency factor (Qa)a) of individual phytoplankton cells and detrital particles. The technique has spectral resolution comparable to traditional spectrophotometric techniques and allows direct measurement of absorption by the major photosynthetic pigments. This procedure was used to study the photoadaptive response in Qa(λ) for the diatom Navicula saprophila grown at high and low irradiance. Observed spectral flattening of Qa(λ) for the low light culture is interpreted in the context of the theory of absorption by discrete particles, which predicts nonlinearity between Qa and intracellular pigment concentration. Measurement of Qa(λ) for individual field particles revealed great intrasample variability in spectral shape and magnitude.
Infrared gas analysis of both gaseous and dissolved CO2 in small‐volume marine samples1
Authors: Roberts D. G. , Smith D. M.
Published: April 2010

A simple, inexpensive infrared gas analysis system for use with small‐volume marine samples has been developed. The method involves injecting between 10 and 250 µl of a seawater sample onto an acidified gas‐stripping column. The CO2 released is transported via a nitrogen carrier gas to an infrared gas analyzer. The C.V. from seven replicate injections of a 1.0 mM Na2CO3 solution ranged from <0.3% to 1.8% depending on sample size.

Evacuated blood collection tubes were used to collect and store aqueous and gaseous samples in the laboratory and field. Aqueous samples were preserved with chloroform to eliminate the possibility of changes following collection. The results indicate that samples collected in this manner can be stored for 4 weeks before analysis and that the method is efficient and cost‐effective.
Ammonium and phosphate uptake rates, N: P supply ratios, and evidence for N and P limitation in some oligotrophic lakes1
Authors: Suttle C. A. , Harrison P. J.
Published: April 2010

Natural assemblages of freshwater phytoplankton were grown in daily‐dilution culture (0.50 d−1) at six N : P supply ratios (5 : 1, 10 : 1, 15 : 1, 25 : 1, 35 : 1, and 45 : 1; by atoms), to create a range of N‐ and P‐limited conditions. After a minimum of 30 d in culture, subsamples were removed for determination of saturated phosphate (PO43) and ammonium (NH4+) uptake rates. A relationship [y = 0.0148e exp(0.1496x)] was found between the ratio of PO43− to NH4+ uptake rates (y) and N : P supply ratio (x), indicating that this index was sensitive to the N : P supply ratio under which phytoplankton are grown. Community composition in the 5 : 1, 15 : 1, and 45 : 1 treatments was influenced by supply ratio. Cultures grown at the highest ratio were dominated by a chroococcoid cyanobacterium (probably Synechococcus sp.), while those grown at the two lower ratios were dominated by the diatoms Nitzschia and Synedra and the chlorophyte Scenedesmus. Saturated NH4+ and PO43 uptake rates were determined for Synechococcus and Synedra, grown under different N : P supply ratios. The good competitor for P (Synechococcus) demonstrated a low capacity for NH4+ uptake under N‐limited conditions, while the good competitor for N (Synedra) showed poor ability to sequester PO43 under P‐limited conditions. Additional experiments were conducted on two oligotrophic lakes in an effort to determine if N and P co‐occurred as limiting resources. Nutrient bioassay studies on water from one of these lakes indicated that N was in short supply among members of the phytoplankton community. Estimates of in situ N: P supply ratios in the lakes ranged from 18 : 1 to >45 : 1, as well. Results of these experiments were consistent with limitation by N and P at times.
The dissociation of hydrogen sulfide in seawater1
Authors: Millero Frank J. , Plese Tinka , Fernandez Marino
Published: April 2010

The pK1* for the dissociation of H2S

has been measured in artificial seawater as a function of salinity (S = 5–40) and temperature (5°– 25°C). Results have been fitted to an equation of the form

urn:x-wiley:00243590:media:lno19883320269:lno19883320269-math-0001

where pK1 is the value at infinite dilution given by

urn:x-wiley:00243590:media:lno19883320269:lno19883320269-math-0002

(σ = 0.033 in pK*, mol kg−1 seawater). The results at S = 35 show a 0.08 shift in pK* from the results in the literature, as was also found in 0.7 m NaCl solutions. The results are in good agreement with the apparent pK1′ results when adjusted to the same pH scale. Using values for the apparent activity coefficient of the proton, we combined our results with those results to derive the consensus values of

urn:x-wiley:00243590:media:lno19883320269:lno19883320269-math-0003
In situ settling behavior of marine snow1
Authors: Alldredge Alice L. , Gotschalk Chris
Published: April 2010

The settling velocities of undisturbed macroscopic aggregates known as marine snow were measured with SCUBA in surface waters off southern California and analyzed as a function of aggregate size, mass, and density. The mean settling velocity was 74±39 m d−1 for aggregates ranging from 2.4 to 75 mm in maximum length. Sinking rates in the field varied exponentially with aggregate size and dry weight and were consistently up to four times slower than rates measured in the laboratory.

The excess densities of the 80 aggregates examined were calculated from volume and dry weight and ranged over four orders of magnitude with a median of 1.4 × 10−4 g cm−3. Aggregates of marine snow sank more slowly than predicted for either solid or porous spheres of equivalent volume and density, although their velocities were within the range expected for equivalent sinking prolate ellipsoids. No relationships between settling velocity and either excess density or particle shape were found. Drag coefficients of marine snow were also higher than predicted by theory for spheres of equivalent volume and density. These deviations from theoretical expectations may be partially explained by errors in the estimation of the excess densities of aggregates. Variability in the densities of the heterogeneous primary particles comprising marine snow (fecal pellets, clay‐mineral particles, phytoplankton, molts, etc.) and the potential for buoyancy regulation by individual phytoplankton cells inhabiting aggregates make determination of excess density especially problematic.
Myxococcal predation on cyanobacterial populations: Nutrient effects1
Authors: Fraleigh Peter C. , Burnham Jeffrey C.
Published: April 2010

Myxococcus fulvus BGO2, a cyanobacteriolytic bacterium, reduced densities of the cyanobacteria Nostoc muscorum and Phormidium luridum in six inorganic media and in filtered water from Lake Erie when inoculated to give initial myxococcal densities of 5 × 106 cells ml−1. When initial myxococcal densities were lower, the reduction in Nostoc density was delayed in a nutrient‐rich medium and did not occur in a nutrient‐poor medium. These laboratory results suggest that the absence of myxobacteria in cyanobacterial blooms and the absence of cyanobacterial population control by related lytic bacteria, found in natural blooms, may be due, in part, to insufficient inorganic nutrient fertility to support growth of lytic bacterial populations to densities necessary to cause significant cell lysis in host populations.
The microflagellate‐picoplankton food linkage in the water column of Lake Biwa
Authors: Nagata Toshi
Published: April 2010

Seasonal variations of abundance and biomass of heterotrophic microflagellates (HMF), bacteria, and unicellular chroococcoid cyanobacteria (UCB) at a pelagic site (water depth, ∼72 m) in the north basin of Lake Biwa were measured during May to November 1984. The cell densities of HMF, bacteria, and UCB were 102–103, 106, and 102–105 cells ml−1, and the biomass estimates were <1–7, 10–70, and <1–20 µg C liter−1. Active phagocytosis of UCB by HMF was indicated from microscopic observation of HMF food vacuoles; when UCB density was high, up to 52% of HMF cells contained one or more UCB cells. Incubation of size‐fractionated epilimnetic waters indicated that bacterial net production rates (5–25 µg C liter−1 d−1) were usually almost equal to rates of consumption of bacteria by HMF populations. Estimates of gross growth efficiencies of HMF fed on natural picoplankton were 11–53% in terms of carbon. HMF may be a significant link transferring picoplankton energy to macrozooplankters which cannot collect picoplankton. Lack of information on the fate of HMF makes it difficult, however, to directly address the “sink vs. link” argument about the microbial loop in Lake Biwa.
Measuring water clarity with a black disk
Authors: Davies‐Colley Robert J.
Published: April 2010

Black targets have a major theoretical advantage over reflective targets such as the Secchi disk for assessing the visual clarity of water because their sighting ranges depend only on two optical properties of the water: the beam attenuation coefficient and the diffuse attenuation coefficient. The theory of visibility of black objects applies to observations made with a black disk in 11 rivers and eight lakes ranging 60‐fold in water clarity. The horizontal sighting range of the black disk is similar to visual ranges of practical importance in water, for aquatic animals as well as man, and yields an immediate estimate of the beam attenuation coefficient. The black disk is expected to be of particular value for assessing the clarity of river waters that are too shallow for deployment of the Secchi disk.
Particulate thiols in coastal waters: The effect of light and nutrients on their planktonic production
Authors: Matrai Patricia A. , Vetter Russell D.
Published: April 2010

Reduced sulfur compounds of low molecular weight, mainly particulate glutathione, were present in concentrations up to 600 pM in Saanich Inlet and off southern California. The vertical distributions of particulate glutathione (PGSH) in Saanich Inlet showed a subsurface maximum and decreased with depth in close correspondence with chlorophyll profiles. As with other measures of phytoplankton standing stock, PGSH decreased offshore in the Southern California Bight. In response to exposure to lower than ambient light levels, PGSH decreased in samples after 24‐h, on‐deck incubations except when the ambient nitrate concentration was high. Nitrate enrichment experiments, however, did not lead to enhanced PGSH production in offshore samples that were initially low in nitrate. Diel changes in PGSH were calculated to represent 0.5–4.5% of the corresponding calculated change in total particulate sulfur.
Phytoplankton succession in microcosm experiments under simultaneous grazing pressure and resource limitation
Authors: Sommer Ulrich
Published: April 2010

The influence of grazing pressure on the occurrence and outcome of nutrient competition among planktonic algae was studied in two‐chamber microcosms where there was a flow in both directions between a light reactor without zooplankton and a dark reactor with zooplankton (Daphnia longispina and Daphnia magna). The phytoplankton inoculum was a mixed, natural assemblage. Zooplankton could influence the dynamics of phytoplankton both by selective grazing and by differential excretion of limiting nutrients. Grazing pressure did not prevent the occurrence of nutrient limitation in algae and, hence, of nutrient competition between them. Zooplankton did, however, influence the outcome of competition by lowering Si: P ratios. A comparison with my previous experiments shows that diatoms need higher Si: P supply ratios for dominance over green algae in the presence of grazers than in grazing‐free competition with steady or weekly pulsed nutrient supply.
Aquatic heterotrophic bacteria: Modeling in the presence of spatial autocorrelation
Authors: Legendre Pierre , Troussellier Marc
Published: April 2010

Microbial ecologists often obtain data from sampling a piece of geographic space. These are likely to be spatially autocorrelated. Autocorrelation removes degrees of freedom from the usual tests of inferential statistics and can generate spurious correlations among variables, with the consequence that suspected causal relations may not hold. This paper describes methods that can be used to explore the spatial structure of ecological data and to include spatial location as a variable in the study of relationships and models. The relationship between environmental heterotrophic bacteria and phytoplankton, well established in aquatic environments, is re‐examined in the Thau brackish lagoon (Mediterranean coast of France). It did not hold for the bacteria growing on bioMérieux nutrient agar (BNA), which are presumably of continental origin; their spatial gradient can only partly be explained by the particulate organic carbon variable (POC) and not at all by phytoplankton biomass (CHL A), despite the existence of a spurious correlation between BNA and CHL A. The spatial gradient of abundance of heterotrophs growing on marine agar (MA), expected to be mostly of marine origin, can be entirely explained by POC and CHL A. Different segments of the bacterial community, both reacting positively to variations of the particulate organic carbon, may follow partly, or not, variations of phytoplankton biomass. The mode of analysis developed here extends to many other spatially distributed processes in ecology and other fields.
Fluxes and reactivities of organic matter in a coastal marine bay
Authors: Hedges John I. , Clark Wayne A. , Come Gregory L.
Published: April 2010

Vertical fluxes of bulk particulate material, organic carbon, nitrogen, lignin‐derived phenols, and neutral sugars through the water column and into surface sediments of Dabob Bay, Washington, were determined monthly for 1 yr by sediment trap deployments at 30, 60, and 90 m at a site 110 m deep. Vertical fluxes of sinking bulk particulate material in this marine bay were elevated during winter and increased in consistent proportion to sediment trap deployment depth throughout the year. Although annual average particle fluxes at 30 and 60 m bracketed the mean accumulation rate of the underlying sediment, the flux at 90 m was higher by a factor of 2 due to resuspension, horizontal advection, or both.

The monthly fluxes of lignin‐derived phenols paralleled those of total particulate material, indicating a common riverine origin. The annual average fluxes of vanillyl and cinnamyl phenols through the water column closely matched the corresponding accumulation rates in the underlying sediment, whereas about a third of the total syringyl phenol input was degraded at the water‐ sediment interface. Although p‐hydroxyacetophenone exhibited a stability typical of lignin‐derived phenols, the distinctly higher reactivities (> 60% degradation) of p‐hydroxybenzaldehyde and p‐hydroxybenzoic acid indicate a predominantly nonlignin source.

On average, 60 and 70%, respectively, of the total particulate organic carbon and nitrogen and 65–75% of all neutral sugars settling through the midwater column were degraded at the water‐ sediment interface. The elemental and carbohydrate composition of the degraded material was similar to that of local net plankton except for higher percentages of glucose and total neutral sugars. Land‐derived organic material accounted for about one‐third of the total organic carbon passing through the midwater column and two‐thirds of the organic carbon accumulating in the underlying sediments. The amounts of plankton‐derived organic matter sinking through the midwater column and being preserved in the sediments below corresponded to 14 and 3% of the annual mean primary productivity. Plankton‐derived organic matter exhibited about 5 times the reactivity of local land‐derived organic matter at the water‐sediment interface of Dabob Bay and supported essentially all of the benthic respiration.