bluuebunny/crossref_metadata_2025 huggingface dataset:
Denitrification in nitrate‐rich streams: Diurnal and seasonal variation related to benthic oxygen metabolism
Authors: Christensen Peter Bondo , Nielsen Lars Peter , Sørensen Jan , Revsbech Niels Peter
Published: April 2010

Seasonal variation of chlorophyll content, photosynthesis, O2 respiration, and denitrification was measured under light and dark conditions in the sediment of a nutrient‐rich Danish lowland stream. Exponential growth of benthic microalgae was observed in early spring (April–May) and photosynthetic capacity persisted until fall. The benthic algae were a major C source for heterotrophic activity as indicated by a close correlation between O2 respiration and Chl content in the sediment. Denitrification activity was related to Chl content, NO3− availability, and O2 conditions. Diffusion from the overlying water was always the major NO3− source for denitrification. Under lighted conditions, photosynthetic O2 production increased the oxic zone and reduced denitrification activity by up to 85% in spring. A simple diffusion‐reaction model allowed denitrification rates to be estimated from O2 respiration rates and concentrations of O2 and NO3− in the stream water. Throughout the season, estimated denitrification rates correlated well with those actually measured. The model demonstrated that denitrification activity was controlled primarily by the thickness of the oxic surface layer which served as a diffusion barrier for NO3− to the denitrification zone.
Availability of well‐defined iron colloids to the marine diatom Thalassiosira weissflogii
Authors: Rich Hans Walter , Morel François M. M.
Published: April 2010

Three different types of iron oxo‐hydroxo colloids with well‐defined sizes and chemistries have been synthesized by hydrolysis of Fe(III) in acidic and alkaline medium as well as by oxidative hydrolysis of Fe(II), resulting in solutions of β‐FeOOH (30 nm), a hexanuclear complex (HN; 2 nm), and a polynuclear oxidation product (OP; 3 nm). These colloids were tested for their availability to the coastal diatom Thalassiosira weissflogii. Iron‐limited cells were grown in synthetic seawater containing 0–0.5 µM of total iron in colloidal form as the only iron source. We found no evidence of direct uptake of colloids by the algae. The β‐FeOOH colloids, which dissolve exceedingly slowly in the light or in the dark, did not support diatom growth. In contrast, maximal growth rates and cell yields were observed in the presence of either 50 nM OP or HN. Photoreduction accounted for the availability of HN. In the case of OP, thermal (dark) dissolution of the colloid appears sufficient to satisfy the iron requirement of the diatom.
A study of model bivalve siphonal currents
Authors: Monismith Stephen G. , Koseff Jeffrey R. , Thompson Janet K. , O'Riordan Catherine A. , Nepf Heidi M.
Published: April 2010

We carried out experiments studying the hydrodynamics of bivalve siphonal currents in a laboratory flume. Rather than use living animals, we devised a simple, model siphon pair connected to a pump. Fluorescence‐based flow visualization was used to characterize siphon‐jet flows for several geometric configurations and flow speeds. These measurements show that the boundary‐layer velocity profile, siphon height, siphon pair orientation, and size of siphon structure all affect the vertical distribution of the excurrent flow downstream of the siphon pair and the fraction of excurrent that is refiltered. The observed flows may effect both the clearance rate of an entire population of siphonate bivalves as well as the efficiency of feeding of any individual. Our results imply that field conditions are properly represented in laboratory flume studies of phytoplankton biomass losses to benthic bivalves when the shear velocity and bottom roughness are matched to values found in the field. Numerical models of feeding by a bivalve population should include an effective sink distribution which is created by the combined incurrent‐excurrent flow field. Near‐bed flows need to be accounted for to properly represent these benthic‐pelagic exchanges. We also present velocity measurements made with a laser‐Doppler anemometer (LDA) for a single configuration (siphons flush with bed, inlet downstream) that show that the siphonal currents have a significant local effect on the properties of a turbulent boundary layer.
Seasonal patterns of grazing and nutrient limitation of phytoplankton in a eutrophic lake
Authors: Vanni Michael J. , Temte Jo
Published: April 2010

Observations and experiments on zooplankton grazing and nutrient (N and P) limitation of phytoplankton of Lake Mendota, Wisconsin, revealed that the relative strength of the two factors varied markedly during the seasonal succession of phytoplankton. Furthermore, seasonal changes in grazing and nutrient limitation were caused not only by seasonal changes in zooplankton community structure and nutrient availability but also by changes in phytoplankton community structure, which led to changes in edibility to zooplankton. The spring phytoplankton bloom of diatoms and small flagellates was highly vulnerable to grazing by both cyclopoid copepods and Daphnia, although Daphnia had a much stronger effect. Increased Daphnia grazing in late spring resulted in low phytoplankton biomass (the clear‐water period) and a phytoplankton community dominated by colonial green algae — taxa vulnerable to grazing by Daphnia but not other zooplankton. Nutrients (N and P) did not limit phytoplankton growth during the spring bloom or the clear‐water period. After the clear‐water period, the summer phytoplankton community was dominated by blue‐greens and Ceratium. Grazing effects by both Daphnia and copepods were low in summer, while nutrient limitation (both N and P) became severe. Reduced grazing impacts in summer may have resulted from prior intense grazing impacts, which led to dominance of grazing‐resistant taxa. These results suggest that seasonal variation in the strength of grazing and nutrient controls in eutrophic lakes results from changes in zooplankton biomass and community structure, nutrient availability, and phytoplankton community structure interacting to determine phytoplankton seasonal succession.
The role of nutrition in regulating the population dynamics of opportunistic, surface deposit feeders in a mesohaline community
Authors: Marsh Adam G. , Tenore Kenneth R.
Published: April 2010

The role of food resources in regulating seasonal population dynamics was determined in a benthic community typical of mesohaline regions in Chesapeake Bay. Four macroinvertebrates dominated the community: the bivalve Macoma balthica, the polychaetes Streblospio benedicti and Nereis succinea, and the amphipod Leptocheirus plumulosus. Several factors seem to regulate population dynamics at different times of the year. In March, growth and reproduction rates accelerated as temperature and phytodetrital sedimentation increased. In April, invertebrate growth rates plateaued while estimated community N requirements were equivalent to estimated N availability. In May, invertebrate growth and reproduction rates rapidly declined while estimated community energy requirements were greater than sedimenting energy supplies. In June, larval recruitment was heavy for S. benedicti and L. plumulosus; however, these juveniles showed no apparent growth during June and their densities rapidly declined. The sudden appearance and disappearance of these juveniles was solely responsible for the boom‐and‐bust dynamics of S. benedicti and L. plumulosus. Essential W3‐polyunsaturated fatty acids and essential amino acids were present at high levels in spring but were present in only trace amounts during summer. Growth of juvenile S. benedicti and L. plumulosus recruits was most likely limited by food supply in June and July, especially by the availability of essential nutrients. Estimates of predation rates could not account for these population declines.
Chromium speciation in seawater: The probable role of hydrogen peroxide
Authors: Pettine M. , Millero Frank J.
Published: April 2010

The rates of oxidation of Cr(III) to Cr(VI) with H2O2 were measured in NaClO4 solutions as a function of pH, temperature, ionic strength, and H2O2 concentration. The rate of oxidation of Cr(III) was found to be first order with respect to 1/[H+] or [OH−] (pH 7–9) and [H2O2] (112–2,621 µM). The rate equation is given by

urn:x-wiley:00243590:media:lno19903530730:lno19903530730-math-0001

where the value of k2 = k1/[H2O2][OH−] = k1 [H+]/ [H2O2] Kw* (k1 is the pseudo‐first‐order rate constant and Kw* is the stoichiometric dissociation constant for the ionization of water). The values of k2 were independent of ionic strength and fit the equation

urn:x-wiley:00243590:media:lno19903530730:lno19903530730-math-0002

with SD = 0.06 in log k2. The energy of activation for the reaction is 9.9±0.8 kcal mol−1. The rate constant was used to estimate the half‐time of Cr(III) in surface seawater. At a concentration of 0.1 µM H2O2, the lifetime of Cr(III) is controlled by H2O2.
Epiphytic alkaline phosphatase on natural and artificial plants in an oligotrophic lake: Re‐evaluation of the role of macrophytes as a phosphorus source for epiphytes
Authors: Burkholder JoAnn M. , Wetzel Robert G.
Published: April 2010

Alkaline phosphatase activity (APA) and Chl a concentrations of epiphytes were measured from two species of aquatic macrophytes (Potamogeton illinoensis and Scirpus subterminalis) and structurally similar artificial plants in a P‐limited lake. The artificial substrata were incubated serially in situ to simulate the age of the natural plant leaves. Throughout the macrophyte growing season, APA per unit of algal Chl on both new and aging leaves was consistently greater for intact epiphytes on artificial plants. This enhancement increased 2‐fold to 20‐fold (mean 4.5‐fold and 7.4‐fold for epiphytes from natural and artificial plants) when epiphytes were removed from the plants and suspended before enzymatic assay, exposing more algal cells to the amended PO43− substrate. Comparisons of APA for epiphytes on natural and artificial plants indicated that in this oligotrophic lake, submersed macrophytes were a source of P for epiphytes throughout the growing season and significantly influenced the P metabolism of the microflora. Epiphyte Chl was significantly greater from artificial than from natural plants in 6 of 11 comparisons, however, perhaps indicating a trade‐off between improved P availability and some nonbeneficial factor associated with the macrophyte.
Anomalous temperature and oxygen gradients under the ice of a high‐plains lake in Wyoming
Authors: Rahel Frank J.
Published: April 2010

Temperatures up to 7.0°C and unusual oxygen profiles were observed under the ice of Gelatt Lake, Wyoming. A layer of warm water near the lake bottom appeared to result from solar heating of bottom sediments. Local increases in the oxygen profile were present in association with a bed of rooted macrophytes (Chara spp.) and a layer of phytoplankton just above bottom. This unusual stratification appeared to be maintained by density differences imposed by a gradient of dissolved solids from surface to bottom. Persistence of a layer of elevated oxygen concentrations, maintained by the stable density stratification, may explain the successful overwintering of fish in this lake.
Biomineralization of barite in the shell of the freshwater Asiatic clam Corbicula fluminea (Molluscs: Bivalvia)
Authors: Fritz Lowell W. , Ragone Lisa M. , Lutz Richard A. , Swapp Susan
Published: April 2010

Rosette‐shaped clusters of barite crystals were found on the depositional surface and in the inner, complex crossed‐lamellar shell layer of Corbicula fluminea collected from the Maurice River, New Jersey. Morphological analyses revealed that barite crystallized directly from the extrapallial fluid onto the inner shell layer in summer and was covered by inner shell‐layer aragonite in fall. Ba, S, and Sr were detected in energy‐dispersive X‐ray analyses of rosettes, while X‐ray diffraction of the heavy fraction of finely ground shells revealed the presence of a barite mineral composed of ∼75 mol% BaSO4 and 25 mol% SrSO4. It is suggested that barite formation resulted from the purging of soluble Ba from the tissue into the extrapallial fluid where it crystallized onto the shell in a biologically inert form.
A method for distinguishing subitaneous and diapausing eggs in preserved samples of the Calanoid copepod genus Diaptomus
Authors: Lohner Linda M. , Hairston Nelson G. , Schaflner William R.
Published: April 2010

The current method to distinguish freshwater diaptomid copepod subitaneous eggs from diapausing eggs involves hatching live eggs and cannot be used on preserved eggs. Comparisons of preserved Diaptomus minutus, Diaptomus sanguineus, and Diaptomus spatulocrenatus egg types revealed a space between the chorion and the vitelline membrane in subitaneous eggs that is absent in diapausing eggs. Ratios of subitaneous to diapausing eggs in preserved samples calculated with the presence or absence of the space were regressed on ratios obtained from hatching of live samples (r = 0.97, P < 0.001). With this method, determination of D. minutus egg types in preserved samples from a lake supported the trend in diapausing egg production indicated by cohort data.
Indirect effects of the mosquitofish Gambusia affinis on the mosquito Culex tarsalis
Authors: Blaustein Leon , Karban Richard
Published: April 2010

Culex tarsalis Coquillet larvae developed faster and had a higher survival rate from first instar to pupae in rice field enclosures that contained mosquitofish (Gambusia affinis Baird and Girard) than in enclosures that did not contain any fish. The mosquito immatures were in predator‐exclusion cages within the enclosures which protected them from predation by mosquitofish but subjected them to indirect changes caused by mosquitofish. Mosquitofish reduced Cladocera populations to low levels in these enclosures. The results suggest that, in the absence of fish, cladocerans may compete with mosquito larvae in at least some rice fields and may affect mosquito population dynamics.
Effect of wind on the distribution of phytoplankton cells in lakes
Authors: Webster I. T.
Published: April 2010

A model is developed that demonstrates how the tendency of phytoplankton cells to float or sink, coupled with wind‐induced circulation, leads to horizontal heterogeneity in phytoplankton concentrations in lakes. For the unstratified case after steady state conditions have been attained, modeled concentrations are approximately uniform in the vertical, but they increase (or decrease) at an exponential rate toward the downwind end of the lake if the plankton cells float (or sink). The rate of increase or decrease of concentration along the downwind axis of the lake is shown to depend simply on wind speed, rising or sinking velocity, and lake water depth. The degree of phytoplankton heterogeneity in a lake depends on the ratio of the spatial scale over which concentration varies to the length of the lake. Under certain conditions, the model can be extended to stratified lakes as well. Thus, the model can explain some observations of heterogeneity in plankton concentration within both unstratified and stratified lakes.
lron transport in marine phytoplankton: Kinetics of cellular and medium coordination reactions
Authors: Hudson Robert J. M. , Morel FraÇois M. M.
Published: April 2010

Iron is taken up via specific sites on the cell surface in two coastal phytoplankters—the coccolithophorid Pleurochrysis carterae and the diatom Thalassiosira weissflogii. Direct uptake from the cell surface of ∼ 10−17 mol Fe cell−1 was observed in pulse‐chase experiments with cells grown under Fe limitation. This quantity corresponds to the theoretical number of transport sites needed by each cell given the slow coordination kinetics and the low seawater concentrations of Fe. The observed turnover time of Fe in the sites—6–20 min—the observed half‐saturation constants for uptake—0.7 and 3.1 nM for P. carterae and T. weissflogii—and maximal Fe complexation rates are consistent with a standard model for carrier‐mediated transport. Analysis of the reaction kinetics indicates that the sites are not at equilibrium with dissolved Fe species. Iron uptake rates are thus controlled by the complex formation kinetics of the transport site with monomeric ferric hydroxide species.

Fe‐limited P. carterae and T. weissflogii can take up Fe at rates up to 14–20% of the maximum rate at which dissolved inorganic Fe can diffuse to the cell. Since oceanic phytoplankters must also be subject to the same strongly size‐dependent limit on uptake rates imposed by diffusion, large species are more likely to experience growth rate limitation under low‐Fe conditions in the ocean.
The role of dormancy and emergence patterns in the dynamics of a freshwater zooplankton community
Authors: De Stasio Burt T.
Published: April 2010

Emergence rates of two cladoceran species (Ceriodaphnia reticulata and Eubosmina longispina) and two calanoid copepod species (Epischura nordenskioldi and Diaptomus sanguineus) from sediments were monitored weekly in Bullhead Pond (Rhode Island) over a 3.5‐yr period with permanently deployed plastic, inverted‐funnel traps. Emergence rates of C. reticulata decreased over the study period, dropping to zero in the third year, and determined timing of first appearance as well as fluctuations in population size. Emergence of E. longispina was sporadic and correlated poorly with population abundance variations, but continued throughout the study. Significantly fewer ephippia of C. reticulata were recovered from under traps compared to adjacent sediments, suggesting that reserves of ephippia had been depleted during the study. Reserves of E. longispina ephippia were not significantly depleted under traps during the study. Patterns of emergence for E. nordenskioldi and D. sanguineus were very similar to each other in timing and importance in determining planktonic standing stocks. For each, nauplii emerged synchronously and initiated the population each year. Both species hatched during every year of the study, suggesting that eggs can remain viable in the sediments for at least 3 yr.
Granite weathering and the sensitivity of alpine lakes to acid deposition
Authors: Staufer Robert E.
Published: April 2010

Lake chemical data from the National Surface Water Survey (NSWS) were corrected for the effects of regional atmospheric deposition and then used to evaluate the role of weathering in supplying base cations, silica, sulfate, and alkalinity to surface waters in alpine vs. subalpine, and in glaciated vs. unglaciated granitic terrane of the western and southeastern United States. Thermodynamic models, idealized reaction stoichiometry, and multivariate regression involving solutes and geographic variables indicate that irreversible weathering can largely account for lake chemistry. By contrast, relatively minor roles are played by reversible ion exchange in soils and sediments, terrestrial bioaccumulation, and transformations in lakes. The regional patterns in lake acidity components (NO3, SO4, DOC, CO2), and statistical relationships between acidity and base cations demonstrate that rock weathering is limited by acid inputs in many alpine catchments prior to fall overturn. The empirical success of the Henriksen alkalinity model depends on a high Ca : Na weathering ratio. The latter increases with increasing physical disturbance of the catchment (juvenility), hence under natural circumstances attains a maximum as a result of on‐going or recent glaciation. The Henriksen model fails in geochemically “old” terrane, where cation losses accompanying silicate weathering attain steady state proportions.
Amino acid and ammonium utilization by heterotrophic marine bacteria grown in enriched seawater
Authors: Tupas Luis , Koike Isao
Published: April 2010

The nitrogen metabolism of natural bacterial assemblages was studied in seawater cultures enriched with the dissolved materials released by the mussel Mytilus edulis. The mussel released dissolved organic C, NH4+, and dissolved organic N (DON), mostly in the form of combined amino acids (∼70–100%) that constituted 30% of the total N released. 15NH4+ techniques showed that the contribution of NH4+ to total microbial N demand during growth ranged from 50 to 88% even when large amounts of DON were utilized (∼70–260% of total bacterial N produced). An average of 80% of the DON used was converted to NH4+, showing simultaneous assimilation and regeneration of NH4+ by the natural microbial population and contradicting the idea that NH4+ assimilation occurs only when organic N is limiting.
Winter presence of prochlorophytes in surface waters of the northwestern Mediterranean Sea
Authors: Vaulot Daniel , Partensky FrÉdÉric , Neveux Jacques , Mantoura R. Fauzi C. , Llewellyn Carole A.
Published: April 2010

Cells with characteristics similar to the recently discovered oceanic prochlorophytes have been detected with ship‐board flow cytometry during winter in the surface waters of the northwestern Mediterranean Sea as well as in the low‐salinity dilution zone of the Rhône River. Maximum abundances reached 50,000 cells ml−1 at the surface and were only slightly lower than those observed previously at the bottom of the euphotic zone in the Atlantic and Pacific Oceans. The concentration, light scatter, and pigment fluorescence of these cells correlated tightly with those of Synechococcus spp. cyanobacteria. These results point out that the ecological niches of oceanic prochlorophytes are probably more diverse than initially thought.
High‐sensitivity flow cytometer for studying picoplankton
Authors: Frankel Sheila L. , Binder Brian J. , Chisholm Sallie W. , Shapiro Howard M.
Published: April 2010

We developed a relatively small, inexpensive, laser‐based flow cytometer suitable for studying marine picoplankton. The instrument uses an air‐cooled He‐Cd laser with low power consumption and a commercially available, square quartz flow cell. Sensitivity and resolution are sufficient to detect marine prochlorophytes in forward light scatter and autofluorescence and marine bacteria in forward light scatter and stained DNA fluorescence.
Azimuthal inhomogeneity in the forward light scattered from microalgal colonies, and its use as a morphological indicator in flow cytometry
Authors: Buonaccorsi Giovanni , Cunningham Alexander
Published: April 2010

The forward scattering of laser illumination by colonial freshwater algae was studied by microscopy and flow cytometry. The scattering patterns generated by Pandorina morum (which forms globular clusters) and Oscillatoria redekei (which forms extended filaments) differ significantly in their azimuthal distribution of light intensity. They provide a means of distinguishing between the two species that is relatively insensitive to intraspecific variations in colony size. The discrimination technique was implemented in a flow cytometer with four photodiodes positioned in the forward‐scattering region: the two species can be distinguished at throughput rates of up to 1,000 colonies s−1. We conclude that azimuthally resolved scattering measurements can be used to derive shape‐dependent cytometric parameters suitable for incorporation in automated, multivariate analysis of phytoplankton samples.
Iron redox effects on photosensitive phosphorus release from dissolved humic materials
Authors: Cotner James B. , Heath Robert T.
Published: April 2010

Factors controlling the release of P from dissolved humic material (DHM)‐iron complexes were studied in an acid bog lake. Gel‐permeation chromatography of lake water labeled with 32PO43− was used to separate high‐ and low‐molecular‐weight fractions of P compounds. Fe3+ additions and irradiation with ultraviolet (UV) light increased the release of a labeled compound coeluting with orthophosphate from void volume fractions. Oxidation rates of Fe2+ in whole‐lake water were much slower than photoreduction rates, which suggests that, in UV light, Fe accumulated as Fe2+. Fe2+ concentrations decreased concomitant with a June increase in Chl a in the lake water. Biotic uptake of Fe2+ may deplete the ambient pool of both Fe2+ and Fe3+ in summer and make photosensitive processes less important at this time.
Oxygen isotopic composition of bottom seawater and tunicate cellulose used as indicators of water masses in the northern Bering and Chukchi Seas
Authors: Grebmeier Jacqueline M. , Cooper Lee W. , DeNiro Michael J.
Published: April 2010

Oxygen isotopic composition of bottom seawater and tunicate cellulose were used as short‐term and long‐term indicators, respectively, of water‐mass characteristics in the northern Bering and Chukchi Seas. Oxygen isotopic composition of northeastern Bering Sea waters is influenced by Yukon River inflows of 18O‐depleted continental water mixing with relatively 18O‐enriched waters contributed by the Anadyr Current. Tunicate cellulose sampled under Alaska coastal water is more depleted in 18O than that collected under Bering shelf and Anadyr waters, which reflects the oxygen isotopic composition of these waters. Tunicate cellulose collected under the mixed Bering shelf water displays intermediate δ18O values. Oxygen isotopic analyses of bottom seawater were used to determine the spatial location and influence of continental and coastal‐derived precipitation and of sea‐ice formation on water‐mass structure on the continental shelf of the northern Bering and Chukchi Seas. Results indicate that the oxygen isotopic composition of tunicate cellulose, averaged over multiple seasons, may serve as a long‐term biochemical indicator of water‐mass patterns in ice‐covered polar regions where continuous sampling is impractical.
Predicting diel vertical migration of zooplankton
Authors: Dodson Stanley
Published: April 2010

Amplitude of diel vertical migration is predicted by water clarity measured by Secchi depth. The model assumes that vertical migration serves to minimize mortality from visually feeding fish and to maximize grazing rate within this predation context. Three of the 24 observations of diel vertical migration are outliers which are either ultraoligotrophic, or have minimal populations of plankton‐eating fish, or both. The other 21 observations in lakes with average photosynthetic rates ≳300 mg C m−2 d−1 and more than ∼2 g m−2 of plankton‐eating fish showed diel vertical migration proportional to Secchi depth, with a correlation coefficient of about 0.880. The residual of the migration‐water clarity relationship is significantly and inversely correlated with percent illumination of the moon. Water clarity and moon intensity together account for 84% of the variation in migration amplitude for the 21 observations.
Short‐range atmospheric transport: A significant source of phosphorus to an oligotrophic lake
Authors: Cole Jonathan J. , Caraco Nina F. , Likens Gene E.
Published: April 2010

During summer stratification, particles transported by wind from surrounding forest were a major source of P into Mirror Lake, a small, oligotrophic lake in New Hampshire. These particles consisted largely of terrestrial insects, insect parts, and plant fragments of various sizes. This atmospheric fallout of P was greatest near the shoreline and decreased exponentially with increasing distance from shore. Integrated for the entire 15‐ha lake, it represented an input of ∼11–13 µmol P m−2 d−1 of lake surface in midsummer. The input of P from atmospheric fallout was highly significant to the summer P economy of the lake and was 50‐fold to 70‐fold greater than the input of P in either streamflow or rainfall in the same period.
Carbon limitation of ammonium uptake by heterotrophic bacteria in the subarctic Pacific
Authors: Kirchman David L. , Keil Richard G. , Wheeler Patricia A.
Published: April 2010

The purpose of this study was to test the hypothesis that NH4+ uptake by heterotrophic bacteria in the subarctic Pacific is C limited. Addition of glucose (0.5–1.0 µM) stimulted NH4+ uptake in unfractionated water but had no effect on bacterial abundance. Glucose stimulation of NH4+ uptake was even greater in the bacterial size fraction (<0.8 µm). Regeneration of 15NH4+ from added [15N] amino acids was measurable in the bacterial size fraction, but glucose additions prevented net NH4+ excretion because of increased uptake of NH4+. In the subarctic Pacific, NH4+ concentrations range from undetectable (≤0.05 µM) to 0.4 µM, whereas the maximal estimate of monosaccharide concentrations was 0.025 M. These results indicate that the supply of C compounds like glucose can limit NH4+ uptake by heterotrophic bacteria.
Ammonium recycling limits nitrate use in the oceanic subarctic Pacific.
Authors: Wheeler Patricia A. , Kokkinakis Steven A.
Published: April 2010

Seasonal and diel changes in nutrient concentrations and nitrogen assimilation rates were used to assess the effects of NH4+ on NO3− assimilation. Surface‐water NO3− concentrations ranged from 6 to 17 µM while NH4+ concentrations ranged from 0 to 0.4 µM. Total N assimilation ranged from 84 to 732 nM d−1 but showed no seasonal trend. NH4+ and urea concentrations were <1% of total dissolved inorganic N, but use of this “regenerated” N still accounted for 44–89% of total N assimilation. Rates of NO3− assimilation were negatively correlated with ambient NH4+ concentrations, and concentrations of NH4+ between 0.1 and 0.3 µM caused complete inhibition of NO3− assimilation. NO3− was more important as a source of N in spring than in summer. We attribute this pattern to a summer increase in turnover rates for NH4+. Turnover times for the dissolved NH4+ pool were half as long in August as in May. Grazing and recycling in the euphotic zone apparently both play significant roles in preventing depletion of NO3− in the oceanic subarctic Pacific.
Phosphate uptake along a coastal plain estuary
Authors: Lebo Martin E.
Published: April 2010

Biotic PO43− uptake rates were measured along the Delaware estuary to examine seasonal and spatial patterns of variation. Uptake was highest (40–90 nmol liter−1 h−1) in summer and lowest (<10 nmol liter−1 h−1) in winter. The highest rates of PO43− uptake were measured in the tidal river and the lower bay (salinity > 15‰) where primary productivity is high. Between the river and the lower bay, the concentration of suspended sediment is high, and PO43− uptake was reduced (<5 nmol liter−1 h−1) at all times of the year. Partitioning of uptake by size revealed that both bacteria and phytoplankton are important in the uptake of PO43− throughout the estuary. The proportion of uptake by bacteria, however, changed spatially. In the tidal river where anthropogenic inputs are high, bacteria dominated PO43− uptake and accounted for up to 70% of the total. Within the salinity gradient of the estuary, the proportion of bacterial uptake was much lower, with bacteria accounting for only 15–25% of PO43− uptake. The competition between bacteria and phytoplankton for PO43− was affected by anthropogenic inputs into the tidal river.
Stable carbon isotopes and the C : N ratio In the estuaries of the Pamlico and Neuse Rivers. North Carolina
Authors: Matson Ernest A. , Brinson Mark M.
Published: April 2010

The C: N and stable C isotope ratios (δ13C) of sedimentary and seston organic C (OC) were used to identify OC sources and sites of deposition in two large estuaries in North Carolina. In the upper 10 km of the oligohaline zones, C : N ratios of sediment are characteristic of particulate terrestrial plant material (>15). The δ13C values increase linearly with distance from freshwater tributaries to the mouths of the estuaries (∼20‰ salinity), >40 km from the ocean. Observed gradients in isotopic and C : N ratios imply that conservative mixing of freshwater and marine OC occurs. Phytoplankton in the estuaries produce at least 10 times more particulate OC than is delivered in runoff, however, and its biomass is recycled at rates much faster than those of water exchange. The observed gradients are therefore largely attributed to recycling of a resident pool of estuarine C, atmospheric CO2, and an increasing marine bicarbonate fraction from the salt wedge downriver. Essentially lentic conditions in these estuaries ensure the dominance of in situ biological processes.
Mass flux estimation and mass transport mechanism in estuaries
Authors: Park J. K. , James A.
Published: April 2010

Hydrodynamic surveys were conducted in a partially stratified estuary. Longitudinal salt fluxes through a cross‐section were measured and the optimal number of lateral and vertical points for observation and estimation of fluxes of pollutants found. The hydrodynamic data were decomposed to investigate the mechanism of instantaneous and tidally averaged mass fluxes.

The decomposition method developed showed that instantaneous salt flux arose principally from the combination of velocity fluctuation with the tidal mean salinity. The error analysis showed that the estimate of mass flux was sensitive to the error inherent in the velocity data and the error range was within ±10% of the total flux. Seven depth and four width points gave acceptable estimates of the water flux, salt flux, and longitudinal dispersion.
Ontogcnetic vertical migration in Sebastolobus altivelis as a mechanism for transport of particulate organic matter at continental slope depths
Authors: Wakefield W. W. , Smith K. L.
Published: April 2010

Ontogenetic vertical migration by a demersal fish inhabiting the continental slope off central California was studied as a mechanism for coupling transport of particulate matter between surface waters and the bathyal sea floor. We conducted a 1‐yr survey of Sebastolobus altivelis, a dominant demersal fish, over much of its depth range (400–1,600 m), with a camera sled and bottom trawl. This scorpaenid spawns gelatinous masses of eggs which float to the surface. After hatching, S. altivelis has a protracted pelagic phase and settles as a benthic juvenile at a length of ∼55 mm. We determined the production of particulate organic matter (POM) in masses of eggs as a measure of the passive upward flux of POM, and the recruitment of POM by settling juveniles as a measure of active transport back to the sea floor. Upward and downward fluxes of particulate organic carbon (POC) associated with planktonic development and ontogenetic migration of S. altivelis were 4.1–5.8 and 3.0–5.5 mg C m−2 yr−1. These upward and downward fluxes are lower by factors of ∼10 and ∼104 than the reported passive upward and downward fluxes measured with particulate interceptor traps in the eastern North Pacific. These data suggest that at bathyal depths, it is unlikely that vertical ontogenetic migrations contribute >1% to the POC flux reaching the deep‐sea floor. The upward flux of POC as buoyant eggs could represent, however, a significant portion of the total upward flux.
The sulfur cycle of freshwater sediments: Role of thiosulfate
Authors: Jørgensen Bo Barker
Published: April 2010

The formation and pathways of thiosulfate (S2O32−) in anoxic sediment were studied in the Odder River and Brabrand Lake, Denmark. Time‐course experiments were done in slurries with four 35S tracers: SO42−, H2S, and S2O32− with either the inner (oxidized) or the outer (reduced) S atom labeled. The two sediments gave similar results. Of all the S2O32− consumed in Brabrand Lake sediment, 6% was oxidized, 50% was reduced, and 44% was disproportionated. S2O32− disproportionation is an inorganic fermentation in certain SO42−‐reducing bacteria by which the inner and outer S atoms are simultaneously transformed into SO42− and sulfide, respectively. Altogether, 28% of the S2O32−‐S was converted into SO42− and 72% was converted into sulfide. S2O32− inhibited SO42− reduction by 75%. The immediate products of anoxic sulfide oxidation were 34% SO42− and 66% S2O32−. Half of the oxidized sulfide was ultimately converted into SO42− and half was recycled back to sulfide via S2O32−. Two‐thirds of the S in the sulfide‐thiosulfate “minicycle” remained at an oxidation state of −2. S2O32− is thus a key intermediate in the S cycle, both as a main product of anoxic sulfide oxidation and as a shunt between oxidative and reductive pathways.
The diffusive boundary layer of sediments: Oxygen microgradients over a microbial mat
Authors: Jørgensen Bo Barker , Des Marais David J.
Published: April 2010

Oxygen microelectrodes were used to analyze the distribution of the diffusive boundary layer (DBL) at the sediment‐water interface in relation to surface topography and flow velocity. The sediment, collected from saline ponds, was covered by a microbial mat that had high oxygen consumption rate and well‐defined surface structure. Diffusion through the DBL constituted an important rate limitation to the oxygen uptake of the sediment. The mean effective DBL thickness decreased from 0.59 to 0.16 mm as the flow velocity of the overlying water was increased from 0.3 to 7.7 cm s−1(measured 1 cm above the mat). The oxygen uptake rate concurrently increased from 3.9 to 9.4 nmol cm−2 min−1. The effects of surface roughness and topography on the thickness and distribution of the DBL were studied by three‐dimensional mapping of the sediment‐water interface and the upper DBL boundary at 0.1‐mm spatial resolution. The DBL boundary followed mat structures that had characteristic dimensions >½ DBL thickness but the DBL had a dampened relief relative to the mat. The effective surface area of the sediment‐water interface and of the upper DBL boundary were 31 and 14% larger, respectively, than a flat plane. Surface topography thereby increased the oxygen flux across the sediment‐water interface by 49% relative to a one‐dimensional diffusion flux calculated from the vertical oxygen microgradients.
Bivariate and trivariate analysis in flow cytometry: Phytoplankton size and fluorescence
Authors: Li W. K. W.
Published: April 2010

A curve‐fitting method was used to characterize bivariate and trivariate flow cytometric data (cell volume, chlorophyll a fluorescence, phycoerythrin fluorescence) from a mixture of cultured algae and from natural populations of phytoplankton. The frequency distribution of cells in two or three dimensions was approximated by a sum of n bivariate or trivariate log‐normal distributions, where n was the number of subpopulations in the assemblage. Each subpopulation was parameterized by the number of cells, the mean and standard deviation for each of the two or three variables, and a correlation coefficient for each pair of variables.
Labyrinth of doom: A device to minimize the “swimmer” component in sediment trap collections
Authors: Coale Kenneth H.
Published: April 2010

A simple device used to discriminate between “swimmers” and “nonswimmers” in sediment trap collections has been developed. It consists of a series of funnels which concentrate passively sinking material into a central collection tube, whereas swimmers are distributed randomly between the inner and outer collection tubes. The degree to which swimmer/nonswimmer fractionation is achieved depends on the number and spacing of funnels and the ratio of inner to outer collection tube areas. Although inner collection tube samples contain a few swimmers, there are considerably fewer than are collected in cod ends without this device. Furthermore, outer tube contents are devoid of passively sinking material providing a “pure swimmer” fraction which can be compared to inner collection tube contents. This device has been successfully deployed on many occasions in traps of the Soutar (conical) and Knauer (cylindrical) type as part of the VERTEX program in the NE Pacific.
A multilevel in situ pore‐water sampler for use in intertidal sediments and laboratory microcosms
Authors: Watson Peter G. , Frickers Trish E.
Published: April 2010

A sampler for in situ separation of pore fluids from intertidal sediments and in laboratory microcosms offers marked improvements in resolution, number of sampling depths, compactness, and simplicity over previously reported devices. The sampler is operated by applying a vacuum to chambers linked, through porous segments, to successive depths in the sediment profile. Analyses of replicate samples taken at hourly intervals [total alkalinity, pH, dissolved Fe(II), and Mn(II)] show that concentration changes induced by the sampler with time are small compared to those due to natural sediment variability. Sampling accuracy is assessed from comparative analyses of pore waters obtained with samplers and by centrifuging core sections. Applications include field sampling of intertidal pore waters, deployment inside benthic chambers, laboratory studies of temporal changes in porewater compositions, and shipboard sampling of cores collected subtidally.
Flow around phoronids: Consequnces of a neighbor to suspension feeders
Authors: Johnson Amy S.
Published: April 2010

Dye visualization was used to assess the effects of closely spaced conspecifics to the flow microhabitat of the benthic suspension feeder Phoronopsis viridis Hilton (Phoronida), which lives in dense populations over a wide range of natural densities. Spacing between upstream‐downstream neighbors affected water movement near the animals and the source of water processed by their filter‐feeding tentacles. Visualization of flow around and between pairs consisting of living and model P. viridis revealed that water encountered tentacle crowns (lophophores) via upward transport from near the sandy substratum rather than from above the lophophore, close spacing of individuals (<1 lophophore diam) inhibited this upward flow for the upstream neighbor, and turbulence generated by an upstream neighbor increased the useful area of feeding surface of the lophophore in the downstream individual. Upward movement of water is important because benthic food particles are an important component of the diet of P. viridis. Thus the presence of neighbors within populations of P. viridis could enhance the incorporation of benthic food particles into their diets. The consequences to feeding of having a neighbor should shift from positive at low densities (>1 lophophore apart) to negative at high densities (≤1 lophophore apart).
The physical strength of marine snow and its implications for particle disaggregation in the ocean
Authors: Alldredge Alice L. , Granata Timothy C. , Gotschalk Chris C. , Dickey Tommy D.
Published: April 2010

Abiotic fragmentation of large, rapidly sinking aggregates into smaller, suspended particles by fluid shear has been suggested as an important process governing the particle size spectrum in the ocean and as one explanation for the exponential decrease of particulate flux with depth below the euphotic zone. We investigated this process by quantifying the small‐scale energy dissipation rates required to disaggregate marine snow settling through a gradient of turbulent kinetic energy in a laboratory tank.

Aggregates of detrital debris, gelatinous houses of larvacean tunicates, and aggregates of living bacteria did not break apart even at energy dissipation rates ≫1 cm2 s−3. The rate of energy dissipation required to disaggregate fragile diatom flocs up to 25 mm long ranged from 10−3 to > 1 cm2 s−3 and increased exponentially with decreasing maximum aggregate diameter. Aged diatom aggregates were significantly stronger than otherwise identical but unaged particles. These results indicate that only the highest shears associated with storm events or flows in tidal channels would be able to fragment even the most fragile organic aggregates in the upper ocean. Biological processes of disaggregation, such as animal grazing, appear far more likely to mediate the size spectrum of aggregated particulate matter in the ocean than abiotic fragmentation due to fluid motion.
Prey‐size selection by freshwater flagellated protozoa
Authors: Chrzanowski Thomas H. , Šimek Karel
Published: April 2010

Planktonic bacteria may represent a substantial nutrient resource available to support the next higher trophic level in the microbial loop (heterotrophic flagellates). In this work we examined the utilization of different size classes of bacteria by flagellated protozoan predators of various sizes. The emphasis was to determine if prey‐size selection was a function of predator size. Pseudomonas sp. was grown in chemostats under conditions to yield “large” (mean size, 1.19 µm3) or “small” individuals (mean size, 0.36 µm3). Cells were fluorescently labeled (DTAF), mixed in various proportions, and fed to four protozoans ranging in size from 21 to 119 µm3. Bacteria in food vacuoles were enumerated and measured. Size distributions of both offered and taken prey were compared, and a selectivity index was calculated. Protozoans of all four sizes preferred large bacteria (between 0.8 and 1.2 µm3).
Large‐scale variability and interactions among phytoplankton, bacterioplankton, and phosphorus
Authors: Currie David J.
Published: April 2010

The literature suggests two models describing the relationship between phyto‐ and bacterioplankton abundance in freshwater: that total P abundance determines algal abundance, which in turn determines bacterial abundance, or that algae and bacteria compete for P. In four data sets investigating the variability of algae, bacteria, and P among lakes, bacterial abundance was more closely related to P concentration than to chlorophyll. Bacterial abundance was strongly related to the residuals of the Chl‐P relationship, explaining 18–65% of the residual variance. The partial correlation is positive, however, indicating that algal‐bacterial competition for P does not determine algal or bacterial abundance. The data are most consistent with an alternative model postulating that P directly influences both algal and bacterial abundance, that algae and bacteria directly influence each other’s abundance, and that a third factor (temperature or perhaps bacterivore abundance) also influences both algal and bacterial abundance in the same manner.
Effects of fish chemical cues on vertical migration behavior of Chaoborus
Authors: Tjossem Sara F.
Published: April 2010

I quantified the diel vertical distributions of Chaoborus (phantom midge) larvae in water that had been conditioned by fish or not exposed to fish, using flow‐through laboratory columns and reciprocal transfers of larvae between a pond with fish and another without fish. The larvae that received fish‐conditioned water underwent a significantly greater intensity of migration than did those that received fish‐free water. Results support the hypothesis that Chaoborus larvae alter their vertical migration behavior in response to the presence of planktivorous fish, in particular, to associated chemical cues. Their behavioral flexibility in migrating permits response to a patchy environment that is variable both seasonally and between habitats.
Modeling spectral diffuse attenuation, absorption, and scattering coefficients in a turbid estuary
Authors: Gallegos Charles L. , Correll David L. , Pierce J. W.
Published: April 2010

Spectral diffuse attenuation coefficients were measured in the Rhode River and Chesapeake Bay, Maryland, on 28 occasions in 1988 and 1989. The model of Kirk was used to extract scattering and absorption coefficients from the measurements in waters considerably more turbid than those in which the model was previously applied. Estimated scattering coefficients were linearly related to mineral suspended solids. Estimates of total absorption coefficients were decomposed as the sum of contributions by water, dissolved organic matter, phytoplankton chlorophyll, and particulate detritus, each having a characteristic spectral shape. The 1988 data were used to develop a model of scattering and absorption coefficients based on the specific curves regressed against water‐quality parameters. Diffuse attenuation coefficients in the 1989 data ranging from 1 to 10 m−1 and photic depths ranging from <1 to 4.5 m were predicted with a C.V. of about 25%.

The problem of estimating concentrations of water‐quality constituents from optical measurements was indeterminate due to the similarity in shape of the specific curves of dissolved substances and depigmented particulates. Chlorophyll concentration could be estimated because it was strongly related to water‐corrected absorption in the 670‐nm waveband, but several outliers occurred due to biological variability in specific absorption of pigments.