bluuebunny/crossref_metadata_2025 huggingface dataset:
The brown‐green color transition in marine sediments: A marker of the Fe(III)‐Fe(II) redox boundary1
Authors: Lyle Mitchell
Published: April 2010

The color transition from brown to green in marine sediments marks the depth at which the nitrate in porewaters has been reduced and the Fe(III) reduced to Fe(II), as shown by published and newly acquired evidence from porewater profiles. The color change is rapidly reversible and is probably due to the oxidation or reduction of iron in smectite clays. A map of the depth of this boundary in the eastern tropical Pacific Ocean shows that thin, brown, Fe(III)‐bearing layers occur under waters of high primary productivity (high organic carbon flux to sediments) or on topographic features that have higher sedimentation rates than surrounding areas. The depth to the brown‐green transition provides a rapid way to estimate redox conditions in sediments and a measure of the rate of depositional flux and consumption of organic carbon in sediments on a regional basis.
Seasonal and short term fluctuations in zooplankton abundance in tropical Lake Malawi1
Authors: Twombly Saran
Published: April 2010

A growing body of data documents seasonal variations in the abundance of tropical zooplankton populations, in contrast to persistent impressions that these populations are stable in size and in age structure. Four of the six most common crustacean zooplankton species in southern Lake Malawi exhibited seasonal changes in population size over a period of 2.5 years. Seasonal trends were repeated between years, but both seasonal and annual patterns in zooplankton abundance were confounded by short term fluctuations in population size. These short term fluctuations represented demographic changes and could not be dismissed as sampling error. As a result, patterns of zooplankton abundance varied considerably between years, and no one year’s data accurately described the dynamics of zooplankton in this tropical lake.
The time‐course of uptake of inorganic and organic nitrogen compounds by phytoplankton from the Eastern Canadian Arctic: A comparison with temperate and tropical populations
Authors: Harrison W. G.
Published: April 2010

Uptake of inorganic (NO3‒, NH4+) and organic (urea) nitrogen compounds by arctic phytoplankton was linear for at least 30 h of incubation under natural temperature and light conditions. Extrapolation of linear fits of the data showed positive ordinal intercepts for NH4+, suggesting relatively more rapid uptake early in the incubation period. Short term uptake experiments confirmed this; rates computed from 20‐min incubations were on the average 3‐fold higher than 24‐h uptake rates. The transient nature of these enhanced uptake rates resulted in their contributing little (<10%) to the total mass flux observed over 24 h. Comparison of these experiments with similar measurements from temperate and tropical waters suggests that the often observed nonlinearity in nitrogen uptake in the field may be more a consequence of isotope dilution and recycling than substrate exhaustion.
Silicon‐32 as a tool for studying silicon behavior in estuaries
Authors: Nijampurkar V. N. , Martin J. M. , Maybeck M.
Published: April 2010

Cosmogenic 32Si has been used as a tracer to study the behavior of stable silicon in the Gironde estuary, southwest France, particularly to identify the source of excess stable silicon observed in low salinity areas.

The results indicate that the dissolved 32Si behaves conservatively in mixing in the estuary and that the excess stable silicon found in the low salinity zone is likely to be anthropogenic.
The effect of the Asiatic clam, Corbicula fluminea, on phytoplankton of the Potomac River, Maryland
Authors: Cohen Ronald R. H. , Dresler Paul V. , Phillips Elizabeth J. P. , Cory Robert L.
Published: April 2010

In the summers of the 1960s and 1970s, phytoplankton in the fresh, tidal Potomac River showed a downstream gradient of low to high abundance. Phytoplankton abundance in a 6–8‐km segment of the river, in summer 1980 and 1981, was 40–60% below that upstream and downstream, forming a “sag.”

In 1980, the highest densities of the Asiatic clam Corbicula fluminea were in the same reach as the phytoplankton sag. Filtration rates indicate that the volume of the sag reach could be pumped through the Corbicula population in 3–4 days. Corbicula removed 30% of the phytoplankton chlorophyll a from a river water sample in 2 h. Pheophytin a in surficial sediments correlated well with clam biomass as a consequence of phytoplankton excreted in pseudofeces.

The hypotheses that peak discharges, zooplankton, toxic substances, and nutrient limitation induced the sag were not supported.
Computer modeling of 15N uptake and remineralization experiments1,2
Authors: Garside C. , Glibert P. M.
Published: April 2010

A computer model simulating 15NH4+ or 15NO3‒ uptake experiments in which regeneration of the same nutrient occurs is described. The use of this model within a reiterative program which fits values of uptake and remineralization rates to experimental data is demonstrated and the results of such computations are compared to other commonly used methods of calculating ammonium fluxes. Some advantages of the computer model approach over more standard calculation approaches are presented, the greatest being a predictive capability that permits testing of several experimental designs before the actual experiments are done.
Relationship between nitrate reductase and nitrate uptake in phytoplankton in the Peru upwelling region1,2
Authors: Blasco Dolors , Maclsaac J. J. , Packard T. T. , Dugdale R. C.
Published: April 2010

Nitrate reductase (NR) activity and 15NO3‒ uptake in phytoplankton were compared under different environmental conditions on two cruises in the upwelling region off Peru. The NR activity and NO3‒ uptake rates responded differently to light and nutrients and the differences led to variations in the uptake; reductase ratio. Analysis of these variations suggests that the re‐equilibration time of the two processes in response to environmental perturbation is an important source of variability. The nitrate uptake system responds faster than the nitrate reductase system. Considering these differences in response time, the basic differences in the two processes, and the differences in their measurement, we conclude that the NR activity measures the current nitrate‐reducing potential, which reflects NO3‒ assimilation before the sampling time, while 15NO3‒ uptake measures NO3‒ assimilation in the 6‐h period following sampling. Thus, considering the sampling time as a point of reference, the former is a measure of the past and the latter is a measure of the future.
Isotope dilution models and the mystery of the vanishing 15N
Authors: Laws Edward
Published: April 2010

An examination of recently published 15NH4+ uptake data shows that the amount of 15N which disappeared from the NH4+ phase was consistently greater than that which appeared in the particulate phase. The discrepancy, which ranged from 1.5 to 5.6 times at nine stations, did not seem to be caused by analytical errors in NH4+ or isotope ratio measurements. Possible mechanisms for the loss include nitrification, adsorption of NH4+ to clay particles or to container walls, and release of 15N as dissolved organic nitrogen. A new method for calculating the average atom % excess of the NH4+ improves estimates of NH4+ assimilation in cases where experimental data indicate that uptake and regeneration are not in balance. Correction of a mathematical misconception regarding the Blackburn‐Caperon model allows more accurate estimates of NH4+ uptake and regeneration rates.
Extraction of 14C‐labeled photosynthate from aquatic plants with dimethyl sulfoxide (DMSO)1
Authors: Filbin Gerald J. , Hough R. Anton
Published: April 2010

DMSO was tested as a solvent to extract 14C‐labeled photosynthate from three species of aquatic plants in photosynthesis measurements and compared with the dry oxidation method for plant radioassay. Extraction of ca. 300 mg of fresh or rehydrated dry plant tissue samples in 10 ml of reagent‐grade DMSO for 8 h at 65°C resulted in a stable, nonviscous solution with excellent liquid scintillation counting characteristics. Extraction efficiency was in the range of 96–99% of fixed 14C, and precision was comparable to, or better than, that obtained with dry oxidation. The method is simple and inexpensive, and for fresh tissue the same sample extracts can be used for chlorophyll analyses.
Spatial autocorrelation of plankton community composition in a continental shelf ecosystem
Authors: Mackas David L.
Published: April 2010

The spatial autocorrelation of plankton compositional pattern is described for a productive continental shelf region for separations from 10 to 100 km. The resemblance metric (squared chord length) used to quantify community dissimilarity is a multivariate analog of the structure function used in meteorology and physical oceanography and is well suited to measuring shifts in relative dominance within a region showing very little spatial variability in species occurrence. Zooplankton biomass and zooplankton and phytoplankton community composition all show significant positive spatial autocorrelation (Mantel test). Dissimilarity correlograms for the various types of data show that the community pattern is stretched parallel to the bathymetric contours, with roughly a 3:1 ratio of alongshore: cross‐shelf correlation lengths. The zooplankton community pattern shows the most gradual loss of correlation (roughly 30‐km cross‐shelf and 100‐km alongshore). Both zooplankton biomass and phytoplankton community composition become uncorrelated at significantly smaller separations (5–25 km).
Chaoborus predation on typical and spined morphs of Daphnia pulex: Behavioral observations1
Authors: Havel John E. , Dodson Stanley I.
Published: April 2010

Behavioral observations of Chaoborus americanus predation on juvenile instars of typical and spined forms of Daphnia pulex were used to answer two questions: Does the spined morph (SM) have a higher escape efficiency than the typical morph (TM)? Is handling time of ingested SM longer than that of TM?

Results indicate that SM was clearly superior to TM in escaping the grasp of both third and fourth instar Chaoborus larvae and visible injuries to escapees were rare. The escape efficiency of larger Daphnia was higher than that of smaller Daphnia when tested with fourth instar Chaoborus. Differences in handling time for the two morphs could not be demonstrated. Handling times were short but highly variable, being partly dependent on Chaoborus length and orientation of the prey item. Within the range of 0.8–1.3 mm, Daphnia body length had no discernible influence on handling time.
Isotopic analyses (18O, 13C, 14C) of two meromictic lakes in the Canadian Arctic Archipelago1
Authors: Pagé P. , Ouellet M. , Hillaire‐Marcel C. , Dickman M.
Published: April 2010

Meromictic Lakes Garrow and Sophia in the Canadian Arctic Archipelago were sampled to establish the origin and age of their waters by isotopic studies. The δsmow18O values reflect the permanent stratification of the waters in both lakes. The mixolimnia contain waters with an isotopic signal between ‒13.16 and ‒21.98‰, coherent with the values for precipitation in these high latitudes. The short residence time of the water in this layer makes it possible to record episodic variations of the freshwater inputs to the lakes. In the chemoclines, the δ18O values increase to ‒10‰ concomitantly with a rise in chloride content to 42 g·liter‒1. This corresponds to a conservative mixing of surficial and deep waters. In the monimolimnia, hypersaline waters (up to 2.5 times the salinity of seawater) show negative δ18O values (ca. ‒8‰). These waters result from brine production during permafrost growth in the watershed, according to a Rayleigh process. The brines drained toward the deepest part of each lake, after postglacial uplift, and became isolated. 14C dating of total inorganic carbon in the Lake Garrow monimolimnion gave an age of 2,580 ± 260 years b.p. In Lake Sophia, the deep waters exhibit recent 14C activity (121.4% modern carbon) that suggests recent infiltration of seawater into the lake basin.
Activity of heterotrophic bacteria and its coupling to primary production during the spring phytoplankton bloom in the southern bight of the North Sea
Authors: Lancelot Christiane , Billen Gilles
Published: April 2010

Parallel measurements were made of particulate and dissolved products of primary production, utilization rate of amino acids, monosaccharides, and glycollate, thymidine incorporation into DNA, and exoproteolytic activity before and during the spring bloom at different stations in the southern bight of the North Sea and in the English Channel. High correlations were found between the three methods used for estimating the activities of heterotrophic bacteria. A reasonable quantitative agreement was found between the estimate of bacterial production based on thymidine incorporation into DNA and the estimate of total carbon utilization based on the sum of the utilization rates of amino acids, monosaccharides, and glycollate. A close coupling between microheterotrophic activity and primary production was demonstrated. Examination of the nitrogen balance during the spring bloom shows that microheterotrophic activity could play an important role in food‐web dynamics by partly satisfying the nitrogen needs of phytoplankton, which represents about twice the mineral nitrogen stock initially present in the water column.
The distribution and cycling of hydrogen gas in the waters of two anoxic marine environments1,2
Authors: Scranton Mary I. , Novelli Paul C. , Loud Peter A.
Published: April 2010

Using a highly sensitive analytical method and careful attention to the possibility of contamination, we have measured hydrogen gas in the waters of a coastal anoxic salt pond and of the Cariaco Trench. Hydrogen concentrations in the anoxic portion of the coastal pond ranged from 0.4 to 3.5 nM and showed strong diel variations (factor of 2–4 at a single depth over 24 h) just below the anoxic interface; no diel variations were seen near the bottom. Concentrations also varied systematically with depth (factor of 6) and from day to day at a single depth (factor of 2). Uptake experiments designed to evaluate the importance of light and sulfate reduction to hydrogen cycling indicated that hydrogen consumption is not light‐dependent either just below the anoxic interface (3.5 m) or near the bottom of the pond (4.5 m), and addition of 20 mM NaMoO4 (an inhibitor of sulfate reduction) decreased hydrogen consumption at 4.5 m but not at 3.5 m. Because hydrogen uptake was independent of light, we suggest that diel variations in hydrogen concentration may be due to production of hydrogen in dark reactions by photosynthetic sulfur bacteria rather than to variations in uptake. In the Cariaco Trench hydrogen concentrations were uniform at about 0.2 nM throughout the anoxic portions of the basin. However, there was an indication of a maximum (0.4 nM) just below the anoxic interface, perhaps due to a greater supply of labile organic compounds to the fermentative bacteria at these depths or to physiological differences in bacteria with depth.
Organic complexation of zinc in estuarine interstitial and surface water samples1
Authors: van den Berg Constant M. G. , Dharmvanij Sirichai
Published: April 2010

The organic complexing capacity for zinc in natural water samples was determined by equilibration of added 65Zn with MnO2. Stability constants for complexes with EDTA and NTA in seawater were determined in preliminary tests. Samples were collected from interstitial waters in surficial sediments from the upper Gulf of Thailand and the estuary of the River Mersey in England and from surface water from the estuaries of the Rivers Dee and Ribble in England. Complexing capacities for zinc of between 0.02 and 2 × 10−6 M (averaging 0.66 × 10−6 M) were detected in the interstitial water and between 0.006 and 0.04 × 10−6 M (averaging 0.024 × 10−6 M) in the surface water. Values for conditional stability constants, log K′znl, ranged from 7.4 to 9.3 and decreased with increasing salinity. At a salinity of 32‰ the observed values for log K′ were similar to that of EDTA. It was calculated that the organic fraction of zinc represents 93–98% of total zinc in most interstitial water samples, 13–26% in most surface water samples. The organic zinc fraction was smaller in cases where the complexing capacity had been saturated with zinc and other metal ions as a result of pollution.
Post‐collection molting rates of planktonic, marine copepods: Measurement, applications, problems1
Authors: Miller Charles B. , Huntley Mark E. , Brooks Elaine R.
Published: April 2010

Rates of molting of a specific copepodite stage can be determined by sorting the stage from a new collection, waiting, then counting the number that have molted to the next stage in the interval. In principle, stage duration can be determined as the inverse of the measured rate, and molting rates can be used directly in evaluation of mortality rates. In practice there are usually immediate molting bursts, higher initial rates than predicted from independently determined stage durations. For a coastal population of Calanus pacificus there was no difference between fed and unfed groups in the initial molting rates, suggesting that some animals had passed a threshold in the molting cycle before collection. Some instances of molting burst are by concentration of molting activity in the night.
Diffusive boundary layers and the oxygen uptake of sediments and detritus1
Authors: Jørgensen Bo Barker , Revsbech Niels Peter
Published: April 2010

The thickness of diffusive boundary layers and their role for the oxygen uptake of sediments and detritus were studied by the use of microelectrodes. Gradients of oxygen were always detectable within the boundary layer, which varied in thickness from 0.2 mm to > 1 mm. The thickness depended on the flow velocity of the water and on the roughness of the solid surface. Oxygen diffused through the boundary layer with a mean diffusion time of 1.2–9 min. The diffusive boundary layer constituted a transfer resistance for oxygen flux across the solid‐water interface which limited the oxygen flux at high uptake rates. Sediments or detritus exposed to aerated water could therefore be almost anoxic at the surface, provided that they had sufficiently high rates of oxygen uptake. This can explain the occurrence of microaerophilic or anaerobic bacteria on exposed sediments where fully oxic conditions would intuitively have been expected.
Morphological separation of Daphnia pulex and Daphnia obtusa in North America1
Authors: Schwartz Steven S. , Innes David J. , Hebert Paul D. N.
Published: April 2010

Although earlier taxonomic surveys failed to reveal its presence, Daphnia obtusa is common in the midwestern United States. The species has been confused with Daphnia pulex, but may be distinguished by conventional morphological features. Females of D. obtusa are characterized by large antennular mounds and weak carapace spinulation; males distinguished from D. pulex by their short postabdominal process and lack of a postabdominal bay. Principal component analysis indicates that these features clearly discriminate between the two species. The presence of hairs on the inner lip of the carapace of females is the most reliable means of recognizing the species from D. pulex.
Bacterivory by microheterotrophic flagellates in seawater samples
Authors: Andersen P. , Fenchel T.
Published: April 2010

Changes in the population sizes of bacteria and of heterotrophic microflagellates in seawater during the first 30–60 h after sampling indicate that these protozoa control bacterial numbers in situ. The observations allow crude estimates of in situ grazing rates and of the minimum bacterial concentration which sustains protozoan growth. In the water samples studied, an average flagellate will clear 1–2 × 10−5 ml h−1 (15°C). If this result is extrapolated to other areas, typical concentrations of microflagellates in the sea suggest that between 5 and 250% of the water column is cleared of bacteria per day. Bacterial numbers above about 106 ml−1 will sustain flagellate growth.
The growth of heterotrophic bacteria in the surface waters of warm core rings1
Authors: Ducklow Hugh W. , Hill Suzanne M.
Published: April 2010

The “seawater culture” approach is evaluated as a means of observing changes in cell numbers over time to estimate specific growth rates and production of heterotrophic bacterioplankton in oligotrophic open ocean waters. We use models of exponential growth limited by grazers, and of logistic growth limited by substrate availability, to estimate the specific growth rates of natural bacterial populations in warm core Gulf Stream rings. The two models yielded somewhat different rate estimates, but in general the results suggest that in situ specific growth rates for bacterial populations in oligotrophic ocean waters are as fast as rates in rich coastal waters and lakes (1–2 d−1). Estimates of hourly bacterial production averaged 10% of hourly primary production. Since bacteria grew at night, up to 40% of the daytime primary production was estimated to pass through the bacteria every 24 h. Estimates of removal rates by grazers are about the same as bacterial growth rates. However we estimate that only 3–7% of primary production was converted to protozoan biomass via ingestion of bacteria.

Our data suggest that simple dilution of natural samples with cell‐free water is a useful, valid method for estimation of bacterial specific growth rates.
A remote‐sensing reflectance model of a red‐tide dinoflagellate off west Florida1
Authors: Carder K. L. , Steward R. G.
Published: April 2010

A mathematical model that simulates the spectral curves of remote‐sensing reflectance of blooms of the red‐tide dinoflagellate Ptychodiscus brevis is developed. The model is compared to measurements obtained from a low‐flying helicopter for P. brevis populations with chlorophyll‐like pigment concentrations from 7 to 77 mg m−3 found in the case 2 waters along the west Florida shelf in October 1983.

The model simulates the effects of backscattering from water, phytoplankton, and detritus, and the effects of absorption due to water, phytoplankton, detritus, and yellow dissolved matter (“Gelb‐stoff”) for case 1 and case 2 waters. It can be easily modified to simulate the spectral reflectance of phytoplankton from other pigment color groups. Matching the model spectral curves to measured remote‐sensing reflectance curves provides accurate estimates of chlorophyll a plus pheophytin a and also estimates of Gelbstoff and detritus concentrations. Comparison of remote‐sensing reflectance data to model reflectance data allows calculation of the quantum efficiency of fluorescence for a given phytoplankton population, which provides a remote measurement of a factor that has been found to increase with the nutrient stress of the population.
Water flows produced by Daphnia and Diaptomus: Implications for prey selection by mechanosensory predators
Authors: Kirk Kevin L.
Published: April 2010

Calibrated hot‐wire anemometer probes with 100‐µm‐long sensitive elements were used to quantify the water flows produced by the swimming motions of Daphnia pulex and Diaptomus hesperus. A free‐swimming Daphnia produces aperiodic, rapidly accelerating flow pulses. As Diaptomus swims past stationary hot wires, feeding appendage movements produce slowly accelerating flows that contain a 50‐Hz oscillatory component. Data concerning the attenuation of flow speed and acceleration with distance from tethered Daphnia, together with attack distances of Chaoborus trivittatus larvae on Daphnia, were used to estimate the threshold signal amplitude necessary to release the attack behavior of the predator. Comparison of the threshold signal for attack allows active prey selection to be distinguished from passive prey selection.
Kinetics of microbial manganese oxidation and trace metal binding in sediments: Results from an in situ dialysis technique
Authors: Kepkay Paul E.
Published: April 2010

Sediments associated with freshwater ferromanganese concretions in Lake Charlotte, Nova Scotia, contained microscopic precipitates of manganese and iron. These precipitates were dispersed throughout the sediment and were as rich in nickel, cobalt, and copper as deep sea concretions. In addition, the development of the precipitates appeared to be associated with the microbial oxidation of manganese. Results from the deployment of poisoned and unpoisoned dialysis probes or “peepers” demonstrated that microbial manganese oxidation and nickel binding were closely associated, causing a fivefold enhancement of abiotic processes such as adsorption. The microbial enhancement of copper binding was far less pronounced, due to organic‐metal interactions in competition with manganese oxidation. Organic‐metal interactions and oxidation may both have been in effect during iron binding, but the relative importance of the two processes could not be determined from the kinetic data.
Polarographic analysis of sulfur species in marine porewaters1
Authors: Luther George W. , Giblin Anne E. , Varsolona Richard
Published: April 2010

We describe a scheme to determine the major sulfur species found in marine porewaters. With polarographic techniques, it is possible to measure thiosulfate, sulfite, bisulfide, and polysulfide ions at a mercury electrode. Polysulfide ions, Sx2−, can be considered to be composed of one sulfur in the 2− oxidation state, S(2−), and the remaining (x − 1) sulfurs in the zero‐valent oxidation state, S(0). The number of sulfur atoms in each is measurable. Tetrathionate and other polythionates can be measured as well but have not been detected in porewaters studied to date. Salt marsh and subtidal porewater profiles contain significant concentrations of thiosulfate, bisulfide, and polysulfide. The ratio of S(2−) to S(0) is higher in subtidal porewaters than in salt marsh porewaters and indicates the importance of zero‐valent sulfur to the biogeochemical processes prevalent in the salt marsh ecosystem. The S(0) concentrations in porewaters from salt marsh sediments are greater than those predicted from equilibrium calculations.
Absorption and photosynthetic action spectra for natural phytoplankton populations: Implications for production in the open ocean1
Authors: Lewis Marlon R. , Warnock Roderick E. , Platt Trevor
Published: April 2010

The hypothesis that variation in the initial slope of the photosynthesis‐irradiance curve clue to variations in wavelengths of light could be responsible for lower rat es of estimated photosynthesis in the open ocean is tested by direct measurement of photosynthetic action spectra (12‐λ bands, 25‐nm bandpass, eight intensities per band) for natural populations from the well mixed waters containing the spring plankton bloom in the Sargasso Sea. We conclude that this possibility is unlikely, at least at this time of year. The spectral shape of a was similar to that of laboratory diatom or dinoflagellate populations, with a peak at 450 nm, a valley between 500 and 600 nm, and a slight rise at 675 nm. No evidence was found for absorption or photosynthesis by phycobiliproteins and there was little variation with depth. The action spectra covaried with the absorption spectra (determined on glass‐fiber filters) except at 400 nm, where higher absorption and relatively little photosynthetic response was observed. Apparent quantum requirements estimated from absorption and action spectra were spectrally invariant (except 400‐nm band) and ranged from 60 to 200 moles quanta per mole carbon reduced. It is concluded that estimates of open ocean production from chlorophyll‐light models with parameters estimated from laboratory algal cultures are likely to be too high because of a large component of absorption that, while covarying spatially and spectrally with photosynthetic pigment, is itself photosynthetically inactive.
Coupled transformation of inorganic stable carbcn‐13 and nitrogen‐15 isotopes into higher trophic levels in a eutrophic shallow lake1
Authors: Otsuki Akira , Aizaki Morihiro , Iwakuma Toshio , Takamura Noriko , Hanazato Takayuki , Kawai Takayoshi , Yasuno Masayuki
Published: April 2010

Enclosure and bag experiments were done in a eutrophic shallow lake with simultaneous use of inorganic 13C and 15N isotopes. It was demonstrated that coupled transformation of inorganic carbon and nitrogen can occur into herbivorous zooplankton through phytoplankton. Direct evidence is provided that there is an apparent coupling between photosynthesis and inorganic nitrogen uptake by phytoplankton during daytime under natural conditions and that the coupling occurs at a constant ratio.
An analysis of the feeding behavior of Daphnia pulex1
Authors: Meise Carol J. , Munns Wayne R. , Hairston Nelson G.
Published: April 2010

The feeding abilities of Daphnia pulex were investigated by offering it suspensions of the small alga Chlamydomonas minutissima and its larger congener Chlamydomonas capensis. The suspensions differed in the relative abundance of the two algae and in th e presence or absence of intermediately sized latex spheres. The experiments were designed to distinguish between mechanistic and behavioral modes of feeding.

Daphnia showed marked flexibility in its feeding patterns, consistent with the behavioral hypothesis. It preferred to feed on C. minutissima. Significant feeding on C. capensis occurred only when C. capensis‐conditioned animals were presented suspensions relatively low in C. minutissima or in the presence of latex spheres. Analysis of gut contents revealed a reduction in the ingestion of latex spheres over time. Total carbon and life history analyses suggest that the preferred food, C. minutissima, is the superior food as well.
Differences between two species of Daphnia in the use of 10 species of algae in Lake Washington1
Authors: Infante Aida , Litt Ami H.
Published: April 2010

The ability of Daphnia pulicaria and Daphnia thorata to grow and reproduce when given the same concentrations of single species of algae was compared. The 10 algae selected included some of those most frequently found in the guts of Daphnia in Lake Washington. Clearing rates were determined and consumption of food expressed as number of cells ingested per day, cell volume, and carbon content. Cryptomonas erosa and Stephanodiscus hantzschii supported the highest egg production and increase in biomass. Colonial forms (Asterionella formosa, Fragilaria crotonensis, Tabellaria fenestrata, and Melosira italica) were less favorable as food. Growth and reproduction were lowest with Chlorella sp. and Melosira italica tenuissima. Daphnia pulicaria grew and reproduced faster than D. thorata with 7 of the 10 food species. The greater success of D. pulicaria than of D. thorata in the lake may be explained partly by its ability to use more effectively the energy available in a variety of foods.
Shipboard comparison of micro‐ and minielectrodes for measuring oxygen distribution in marine sediments
Authors: Helder Willem , Bakker Joop F.
Published: April 2010

We have compared the shipboard

performance of laboratory‐made microelectrodes (o.d., 5–10 µm; Pt‐electrode tip, 2–8 µm) with a commercially available minielectrode (o.d., 700 µm; Pt‐electrode tip, 35–40 µm) for measuring oxygen distributions in marine sediment. The performance of the two types of electrodes was similar. The general availability, the relative ease of modifications necessary for work on marine sediment, the rugged construction, and the high current output (∼ 5,000 pA) make the minielectrodes satisfactory for measuring O2 distributions in marine sediments.
Dimethylsulfide in the water column and the sediment porewaters of the Peru upwelling area1
Authors: Andreae Meinrat O.
Published: April 2010

The concentration of dimethylsulfide (DMS) and supporting parameters were determined on longshore and cross‐shelf traverses in the Peru upwelling area. Vertical DMS profiles were measured at several stations in the marine water column and in the sedimentary porewaters. The distribution of DMS in surface waters is related to the patchiness of the upwelling process and of the resulting phytoplankton biomass. Substantial concentrations of DMS were found in the sedimentary porewaters, with a sharp maximum a few centimeters below the sediment‐water interface. The source of this DMS is most likely the decomposition of algal material which settles to the bottom beneath the upwelling areas. The rates of DMS production in the water column and its flux into the atmosphere across the air‐sea interface are only a small fraction of the rate of sulfate assimilation by the plankton community. The concentrations of DMS in the surface waters of the Peru shelf are similar to those found in other coastal areas; the fluxes of reduced sulfur gases to the atmosphere from this upwelling region do not require special consideration in the global atmospheric sulfur budget.
Food limitation in naupliar and adult Diaptomus pallidus1
Authors: Williamson Craig E. , Butler Nancy M. , Forcina Lorraine
Published: April 2010

The relationships between survivorship and fecundity of Diaptomus pallidus and algal food concentrations (Cryptomonas reflexa) were examined with a flow‐through system that prevents the depletion and settling of algal cells. Egg production in adult females increased with increasing food concentration up to a maximum at 600 µg dry wt liter−1. Under starvation conditions, egg production stopped and survival decreased, whereas at 60 µg dry wt liter−1 production was halted and survival was high. Adults survived longer under conditions of starvation than did nauplii. Adult survival was high at all food concentrations; naupliar survival was highest at 60 µg dry wt liter−1, slightly lower at 600 µg dry wt liter−1, and much lower at 6,000 µg dry wt liter−1. Naupliar development was faster at 600 and 6,000 µg dry wt liter−1 than at 60 µg dry wt liter−1.
Dependence of the rate of release of phosphorus by zooplankton on the P: C ratio in the food supply, as calculated by a recycling model1
Authors: Olsen Yngvar , Jensen Arne , Reinertsen Helge , BØrsheim Knut Yngve , Heldal Mikal , Langeland Arnfinn
Published: April 2010

In two enclosure experiments, Daphnia pulex ingested cryptophytes, bacteria, and probably detritus particles. The specific clearance rate of the zooplankton increased when the concentration of food decreased. The P : C ratio of the food also increased. More than 92% of the particulate phosphorus was located in the living cells (algae and bacteria); the detritus was practically phosphorus‐free. The specific release rate of phosphorus estimated for the daphnids by use of the recycling model increased as the P : C ratio of the food increased and became zero at a critical low P : C ratio, Q, of 6–8 µg P mg−1 C. At this concentration, all the ingested phosphorus is needed for growth and reproduction, and no release of the element can be expected. This indicates that Daphnia may experience P limitation in nature, since the P : C ratio of P‐starved algae and detritus may be considerably <6–8 µg P mg−1 C.

The use of mass balance also appears to be suitable for modeling phosphorus and carbon fluxes through zooplankton in pelagic ecosystems.
Chlorophyll production, degradation, and sedimentation: Implications for paleolimnology1
Authors: Carpenter Stephen R. , Elser Monica M. , Elser James J.
Published: April 2010

Chlorophyll a production, degradation, and sedimentation were studied simultaneously during summer stratification in three lakes with contrasting plankton communities. Pigment budgets showed that chlorophyll production and pigment resuspension were both major sources of water column pigments. Photodegradation rates were rapid and indicated that detritus particles that remained in the epilimnion for periods longer than about 3 days lost nearly all detectable pigments. Therefore, only rapidly sinking detrital particles or those produced in deep layers at low light intensity could make appreciable contributions to sedimentary chlorophyll degradation products. Pheophorbide a, a grazing indicator, was the dominant chlorophyll a degradation product found in sediment traps. Pigment sedimentation increased significantly with mean size of cladocerans and omnivorous copepods. In contrast, sedimentation rates of chlorophyll degradation products did not increase with primary production. In these lakes, the deposition of chlorophyll degradation products in sediments depended primarily on the size and biomass of grazers.
Inorganic nitrogen uptake by epilithic periphyton in a N‐deficient lake1
Authors: Reuter John E. , Loeb Stanford L. , Goldman Charles R.
Published: April 2010

Seasonal patterns of dissolved inorganic nitrogen and inorganic carbon uptake by the sublittoral epilithic periphyton community in N‐deficient, oligotrophic Lake Tahoe were examined. The biomass dominants of this community, N2‐fixing blue‐green algae (e.g. Calothrix, Tolypothrix, and Nostoc) were persistent and retained their nitrogenase activity throughout the year. Seasonal rates of N2 fixation exhibited considerable variation, with a distinct summer maximum and winter minimum. Uptake of both NO3− and NH4+ followed Michaelis‐Menten kinetics. K, values were typically extremely high (>100 µg N liter−1) compared to the ambient concentrations of these forms of nitrogen (<10 µg N liter−1). N2 fixation was the most important source of inorganic N to the yearly N budget of this benthic community. Low ambient substrate concentrations coupled with a low physiological affinity for these substrates at ambient levels were responsible for the relative unimportance of NO3− and NH4+ uptake. Dark uptake of NO3−, NH4+, and N2 fixation were all significant and could not be neglected in determining rates of daily inorganic nitrogen utilization. This blue‐green algal community is not adapted for efficient use of NO3− or NH4+ and can survive in the N‐deficient environment because of its ability to use N2. In striking contrast, the phytoplankton in Lake Tahoe has no N2‐fixing organisms and depends on NO3− and NH4+ for its production.
Mechanisms influencing the circulation and distribution of water mass in a medium residence‐time lake
Authors: Carmack Eddy C. , Wiegand Ronald C. , Daley Ralph J. , Gray Colin B. J. , Jasper Steve , Pharo Christopher H.
Published: April 2010

The seasonality of physical structure in a deep, temperate lake (Kootenay Lake) is described in relation to its major river inputs (Kootenay and Duncan Rivers). The lake’s volume is 37 km3 and its annual outflow is 25 km3 yr−1, yielding a residence time of about 1.5 years. Water mass distributions are controlled by the interactions of three processes: riverine circulation, mixed‐layer dynamics, and internal wave behavior. The riverine circulation is determined by the inflow rate and by the relative density of incoming water and ambient lake water. Mixed‐layer structure varies in relation to the combined action of the wind and surface heat flux on both seasonal and synoptic time scales. Internal waves may periodically raise a given stratum of water, such as the riverine layer, to a depth where wind mixing is more intense. Knowledge of these processes, their relative importance, and their time‐space variability can aid in understanding the ecology of the lake.
Metabolic activities in flocculent surface sediments and underlying sandy littoral sediments1
Authors: Sweerts J. P. , Rudd John W. M. , Kelly C. A.
Published: April 2010

Parts of the sandy littoral sediment of a Precambrian shield lake (Lake 302S) were intermittently covered with a layer of flocculent organic‐rich material 1–20 mm thick. Sandy sediments with flocculent surface sediment had higher rates of respiration (31–105%) and photosynthesis (37– 224%) than those without. Densities of invertebrate macrofauna were 10 times higher in the flocculent surface sediment than in the underlying sandy sediment, accounting for 17 vs. 5% of the total respiration. Microprofiles of oxygen concentration showed that almost all of the dissolved oxygen in the overlying water was consumed as it diffused through 5–7 mm of the flocculent surface sediment, so that the underlying sandy sediment was almost completely anaerobic in the presence of flocculent surface material. The presence of flocculent surface sediment also decreased the depth of penetration of sulfate into the sandy sediment since the zone of sulfate reduction was located closer to the sediment‐water interface. In this experimentally acidified lake, neutralization of H2SO4 via sulfate reduction was more rapid (2.04 × 10−1 mmol H+ m−2 d−1) in the presence of surface flocculent sediment than in its absence (1.57 × 10−1 mmol H+ m−2 d−1).
Metabolic regulation of amino acid uptake in marine waters1
Authors: Kirchman David L. , Hodson Robert E.
Published: April 2010

To determine the relationships among the processes of uptake, intracellular pool formation, and incorporation of amino acids into protein, we measured the uptake of dipeptides and free amino acids by bacterial assemblages in estuarine and coastal waters of the southeast U.S. The dipeptide phenylalanyl‐phenylalanine (phe‐phe) lowerd Vmax of phenylalanine uptake when the turnover rate of phenylalanine was relatively high. When the turnover rate was relatively low, phe‐phe either had no effect or increased Vmax of phenylalanine uptake. An analytical model was developed and tested to measure the turnover time of the intracellular pool of phenylalanine. When phe‐phe was not added the turnover time of the intracellular pool was 0.89 min. Addition of 1.0 nM phe‐phe increased the turnover time of this pool to 3.8 min in waters where phe‐phe lowered Vmax of phenylalanine uptake. These results suggested that the size of the intracellular pool is regulated, which precludes high assimilation rates of both phenylalanine and phe‐phe. In waters with relatively low phenylalanine turnover rates, bacterial assemblages appear to have a greater capacity to assimilate phenylalanine and phe‐phe simultaneously. Marine bacterial assemblages do not substantially increase the apparent respiration of amino acids when concentrations increase. We conclude that sustained increases in uptake rates and mineralization by marine bacterial assemblages in response to an increase in the concentration of dissolved organic nitrogen is determined by the rate of protein synthesis.
The response of the salp, Pegea confoederata, to high levels of particulate material: Starvation in the midst of plenty1
Authors: Harbison G. R. , McAlister V. L. , Gilmer R. W.
Published: April 2010

When the pelagic tunicate Pegea confoederata is presented with concentrations of particulate material equivalent to levels found in neritic areas, its feeding mechanism is disrupted. A bolus is formed that blocks the esophagus, dramatically decreasing the amount of material that enters the stomach. This bolus never occurs at particle concentrations <0.5 ppm, and always forms at particle concentrations > 5.0 ppm. For oceanic waters, 0.5 ppm lies in the upper range of values, so that it appears that P. confoederata is adapted for feeding on average concentrations of particulate material in the open sea. These results are in contrast to those with most of the calanoid copepods that have been studied. Because P. confoederata feeds on oceanic average amounts of food, it can be more evenly distributed throughout the great oceanic central water masses, decreasing the likelihood of its discovery by predators.
Poststarvation feeding and swimming activity in Calanus pacificus and Metridia pacifica
Authors: Mackas David L. , Burns Karen E.
Published: April 2010

Gut fluorescence analysis of Calanus pacificus and Metridia pacifica is used to describe variation in food intake rate at time scales of one to several hours. The animals are starved before each experiment, then exposed continuously to phytoplankton cultures. Variability of gut fullness is large (order 10‐fold) between individual copepods captured at the same time and is about proportional to the within‐time‐period average. The gut fullness curve shows a strong initial peak 1– 2 h after food is supplied and drops to about 20% of the peak level after 7–9 h of exposure to high food levels. For Calanus gut fullness and swimming activity at the time of capture are strongly correlated. Active animals have on average 2–5 times as much pigment in their guts as inactive animals captured at the same time. However, inactive animals resume swimming and feeding activity in 1–3 h. The changes in gut fullness appear to involve episodic on‐off switching of feeding activity as well as regulation of maximum instantaneous feeding rate and of either or both satiation and hunger thresholds.
The specific absorption coefficients of chlorophyllide a and pheophorbide a in 90% acetone, and comments on the fluorometric determination of chlorophyll and pheopigments1
Authors: Lorenzen C. J. , Newton Downs J.
Published: April 2010

Chromatographically pure chlorophyllide a and pheophorbide a were obtained from cultured algae by thin layer chromatography. After 7–10 cell divisions in the presence of 14C, the cells (and all inclusions) used for the study were uniformally labeled. Measurement of the optical densities and radioactivities of chlorophyll a and these other pigments permits calculation of the specific absorption coefficients for the latter. The specific absorption coefficients measured were: pheophytin a−49.5; chlorophyllide a−128; and pheophorbide a−69.8.
Does adenine incorporation into nucleic acids measure total microbial production?1
Authors: Fuhrman Jed A. , Ducklow Hugh W. , Kirchman David L. , Hudak John , McManus George B. , Kramer Jonathan
Published: April 2010

Incorporation of radioactive adenine into DNA has recently been used as a measure of total microbial production in marine environments, sometimes with unexpected results. We have examined two of the assumptions on which the method is based, particularly regarding the distribution of adenine uptake and nucleic acid content in mixed natural microbial assemblages. Size fractionation, autoradiography, and metabolic inhibition data indicate that the requirement that bacteria, algae, and protozoa have a uniform uptake and metabolism of added dissolved adenine does not appear to hold. In systems where the biomass and productivity were greatly dominated by large phytoplankton, bacteria took up almost all of the adenine added at nanomolar concentrations. A separate experiment with marine ciliates also showed adenine uptake by eucaryotes to be negligible compared to that by bacteria. The method requires a measurement of microbial adenosine triphosphate (ATP) specific activity. In our experiments this quantity would be dominated by ATP in the eucaryotes that took up negligible adenine. In this situation, mostly eucaryotic biomass and not production would influence the “total microbial production” measurement. Second, the C: DNA ratio of 50 used in reports to date is too high for natural bacteria, which have a ratio closer to 5. We conclude that the method is likely to have produced large overestimates of production and that variations (e.g. with depth) may not reflect growth rates, but rather a complicated combination of activities and ratios of eucaryotic: procaryotic biomasses.