bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass transfer to and from small particles in the sea1,2
Authors: Csanady G. T.
Published: April 2010

Slowly sinking particles exchange mass with their liquid environment if dissolution processes within the particles maintain a surface concentration excess or deficiency χ0 of a soluble substance above background. If the exchange is controlled by diffusion in the liquid phase, the total mass loss is proportional to χ0, diffusivity D, and particle diameter d. If advection associated with the sinking of the particle dominates over diffusion, the exchange rate varies as χ0D⅔d2 and is weakly affected by particle density and fluid viscosity. This is the case for spherical particles of a diameter 70 µm.

The resulting dissolution rate per unit depth of sinking is constant for large particles, but increases sharply once the particles are small and slow enough for mass exchange to be controlled by diffusion. With oxygen supply supposed the rate‐controlling process of particle decomposition, a realistic depth of decomposition of order 1 km is calculated for 200‐µm‐diameter spherical particles. The generation of an oxygen minimum at such depths then requires the production near the sea surface of sufficiently large organic particles in sufficient numbers.
The relevance of scavenging kinetics to modeling of sediment‐water interactions in natural waters1,1
Authors: Nyjfeler Urs P. , Santschi Peter H. , Li Yuan‐Hui
Published: April 2010

The uptake of radioactive trace metals by suspended particles in natural aquatic systems is often slow and the time constants for scavenging are of the same order of magnitude as the residence times of particles in the water column. Therefore, models simulating removal of radioactive trace metals from water to sediments in shallow aquatic systems with short particle residence times need to include sorption (i.e. scavenging) kinetics. We present a numerical kinetic transport model designed to simulate tracer movements from a well mixed water column where particles are generated by both primary production and sediment resuspension processes. Tracers are allowed to penetrate into underlying sediments by diffusion and particle and porewater mixing. All model parameters can be experimentally determined either in the ecosystem itself or in separate laboratory experiments. Model simulations of three kinds of experiments are presented: tracer diffusion in benthic flux chambers, and tracer removal in marine mesocosms and in lacustrine limnocorrals. Limited sensitivity analyses and simulations of actual experiments indicate that under conditions of particle cycling in the sediments and the water, tracer removal can be affected and—in the case of high particle fluxes, as in summer—even be limited by the slow kinetics of tracer uptake by suspended particles. The model is also useful in identifying and quantifying critical pathways in the complicated web of interrelated processes of an aquatic ecosystem.
Reconciling measured and predicted fluxes of oxygen across the deep sea sediment‐water interface1
Authors: Reimers Clare E. , Smith K. L.
Published: April 2010

Rates of sediment community oxygen consumption determined in situ are compared to fluxes predicted from oxygen microelectrode gradients measured in cores from ∼3,750‐m water depth in the eastern North Pacific. Oxygen concentrations decrease exponentially over > 1.5 cm and suggest that organic matter in the sediments is degraded most rapidly immediately below the sediment‐water interface.

Molecular diffusion of oxygen across the interface is modeled as an “internal regime” and can account for nearly all the directly measured in situ flux, 0.20±0.02 µmol cm−2 d−1. This differs from published accounts of nearshore marine environments, where activity of bottom‐dwelling macrofauna or bubble ebullition enhances benthic fluxes of dissolved nutrients or gases 2–4 times. Millimeter depth‐scale profiles of porosity, organic C, carbonate C, and bacterial abundance are reported to provide additional constraints on interface processes, including the relative effects of organic matter degradation and bioturbation. The highest organic C, bacterial, and porosity values are in the uppermost sediments (0–0.2 cm). Within the stratum 0–1 cm, porewater flux ratios of oxygen to nitrate support a model of exchange by diffusion leading to organic matter oxidation and nitrification according to Redfield stoichiometry. Below the oxygen reduction zone, changes in the porewater concentrations of NO3−, Mn2+, Fe2+, NH4+, and alkalinity indicate that anaerobic respiration reactions using NO3−, MnO2, Fe2O3, and SO42− as electron acceptors complete the early oxidation of organic matter at this site.
Benthic respiration measured by total carbonate production
Authors: Anderson Leif G. , Hall Per O. J. , Iverfeldt Ake , Rutgers van der Loejf Michiel M. , Sundby Bjørn , Westerlund Stig F. G.
Published: April 2010

The suitability of total carbonate production instead of oxygen consumption as a measure of benthic respiration has been investigated. In situ fluxes of total carbonate, oxygen, calcium, total alkalinity, nutrients, and sulfide across the sediment‐water interface were measured in diver‐operated benthic flux chambers. Two chambers were run in parallel to test the influence of oxygen and pH levels on total carbonate production. In one, oxygen and pH were kept constant near ambient levels; in the other, benthic respiration was allowed to deplete oxygen and lower the pH. We found that the flux of total carbonate, corrected for CaCO3 precipitation/dissolution, is a suitable measure of benthic mineralization in sediments where methane production can be neglected. The production rate of total carbonate was not seriously affected as long as the oxygen concentration remained > 100 µM.
Benthic community—water column coupling during the 1982‐1983 El Niño. Are community changes at high latitudes attributable to cause or coincidence?1
Authors: Paine R. T.
Published: April 2010

The 1982–1983 El Niño generated a strong signal which diminished poleward. Although water mass properties were clearly influenced at 48°N, no effects were identified on a rocky intertidal community which could unambiguously be attributed to El Niño. The analyses included long term studies of the upper limits to the distribution of a red alga (7 years) and two species of mussels (14 years). No effect was identified on the recruitment, mortality, or growth of a brown alga, Postelsia. Major sea urchin recruitments have occurred on the Washington outer coast four times in the last 22 years, only two of which have been El Niño events, although all were in years of warmer than average water. Major (extreme) episodes of mussel bed disruption occurred immediately after the latest El Niño, but also during a cold water winter (1975–1976). The data suggest that it is difficult to distinguish the influence of even a potentially strong perturbation against a biologically variable background when a long term data base exists.
Visual predation in My sis relicta Lovén1
Authors: Ramcharan Charles W. , Sprules W. Gary
Published: April 2010

Feeding coefficients of Mysis on both Daphnia magna and Diacyclops bicuspidatus thomasi were higher in light than in darkness. Vision is inferred because this light/dark difference is inconsistent with a mechano‐receptive predation model that considers experimental biases caused by light/dark behavioral changes in both predator and prey. Feeding coefficients of Mysis on Daphnia pulex were the same in light and dark; we suggest that the transparent body of this species reduces its visibility. From low light level experiments we are able to extrapolate that mysids cruising the metalimnia of clear northern temperate lakes at night may be able to see by moonlight.
Time‐series feeding rates of the euphausiid Thysanoessa raschii in a temporally patchy food environment1
Authors: McClatchie Sam
Published: April 2010

A flow‐through system was used to measure grazing rates of Thysanoessa raschii under conditions simulating encounters with gradients of phytoplankton concentration. Ingestion rates of krill fed Chaetoceros gracilis, measured over 10‐min intervals, closely tracked changes in phytoplankton concentration. The relationship between ingestion rates and pigment concentration was linear from 0.5–9 µg pigment liter−1, and zero ingestion was predicted at 0.25 µg pigment liter−1 (intercept significantly different from zero, P < 0.05). Clearance rates were almost constant (15.4±3 ml krill−1 h−1) at all concentrations. This indicated that the changes in ingestion rate resulted from changes in food concentration, rather than as an active response of the krill to the food gradient. The results do not support the hypothesis that krill elevate their feeding rates in response to encounters with high concentrations of phytoplankton in patches or layers. The strategy of krill may be to remain within food concentrations encountered in the field, rather than to feed faster.
Acute toxic effects of the cyanobacterium Microcystis aeruginosa on Daphnia magna1
Authors: Nizan Shulamit , Dimentman Chanan , Shilo Moshe
Published: April 2010

Various axenic strains of Microcystis aeruginosa were found to have different short term toxic effects on Daphnia magna. One of these toxic manifestations, the “blocking” effect, markedly reduced the food uptake by the daphnids. In addition, several of the Microcystis strains are lethal for juvenile and adult daphnids. No correlations were found between the blocking of ingestion, lethality to daphnids, and the “mouse‐killing” factors of Microcystis. Thus, several toxic principles are responsible for the different short term toxic manifestations.
Redox state of iron in the offshore waters of Peru1
Authors: Hong Huasheng , Kester Dana R.
Published: April 2010

The total concentration and redox state of iron were examined along a transect across the continental shelf off the Peruvian coast during January 1984. Total and dissolved iron (0.4‐µm filter) were measured by the Co‐APDC coprecipitation method. Fe(II) was measured by a preconcentration step with 8‐hydroxyquinoline bonded to silica as the stationary phase, followed by elution and the ferrozine method.

Up to 40 nmol kg−1 of Fe(II) was detected in the bottom water at 5–10 km offshore and decreased markedly upward in the water column and with distance offshore. A good correlation between the distribution of Fe(II) and nitrite in the bottom water indicated a common source from the shelf sediments. Elevated Fe(II) concentrations near the sea surface and a diel change were probably due to photochemical reactions involving iron.

Total iron levels were >300–500 nmol kg−1 in the surface and the bottom water at 5–6 km offshore. About 80–90% of the iron was in the particulate form, indicating a substantial input of iron from continental dust and from the sediments on the shelf. The total iron level decreased considerably within 35 km of the coastline and the iron seemed to be trapped on the shelf.
Light utilization efficiency and quantum yield of phytoplankton in a thermally stratified sea1
Authors: Kishino Motoaki , Okami Noboru , Takahashi Masayuki , Ichimura Shun‐ei
Published: April 2010

Light utilization efficiency and quantum yield of phytoplankton in a thermally stratified temperate sea were evaluated. Underwater spectral irradiance was measured with a specially designed underwater irradiance meter and the specific absorption coefficient of phytoplankton was determined by a modified opal glass method. The light utilization efficiency of phytoplankton at each depth was derived from photosynthetically fixed energy divided by the energy penetrating into that depth, and quantum yield was estimated from photosynthetic rate divided by quanta absorbed by phytoplankton. Vertical profiles of in situ photosynthetic rates per unit volume of water showed two peaks, the first at the depth of about 30% light level (ca. 45,000 cal m−2 h−1) and the second at the depth of about 1.5% light level (ca. 2,500 cal m−2 h−1) with about the same rates. The light utilization efficiency was about 0.5% at the first peak and 5% at the second. The quantum yield was about 0.02 mol C Einst−1 at the surface peak and 0.1 at the subsurface peak. The latter value was nearly the same as the maximum yield reported from culture experiments.
Production of planktonic bacteria in Lake Michigan
Authors: Scavia Donald , Laird Gwenyth A. , Fahnenstiel Gary L.
Published: April 2010

Bacterial production rates were estimated for the surface waters of a station 100‐m deep in southeastern Lake Michigan during 1984. Production was calculated from incorporation of [3H‐methyl]thymidine and from empirical conversion factors determined from dilution experiments performed throughout the study. The conversion factors (with typical C.V. <40%) varied between 4.7 and 18.3 × l09 cells produced per nanomole of thymidine incorporated into ice‐cold trichloroacetic acid extracts. Our estimates yielded bacteria exponential growth rates between 0.05 and 0.24 h‐1 (C.V. typically <50%) based on the empirical conversion factors. The growth estimates are much lower (0.004–0.020 h‐1) when based on measured 47% thymidine incorporation into DNA and a theoretical conversion factor. The higher growth estimates appear more consistentwith estimated grazing losses. Carbon flux estimates are less certain, due to the possible range of bacterial carbon content and growth efficiencies, but most of the higher growth estimates imply a bacterial carbon demand higher than concurrent 14C‐based primary production measurements. This may mean that a source other than recent primary production is needed to meet this demand.
Sources of nitrogen for primary production in warm‐core rings 79‐E and 81‐D1
Authors: McCarthy James J. , Nevins John L.
Published: April 2010

Profound changes in concentrations of phytoplankton biomass and rates of primary production in warm‐core Gulf Stream rings can occur, apparently in response to nutrient enrichment, within a few months after a ring separates from the Gulf Stream.

In Ring 81‐D at 3 months of age the dependence on NO3− was 2½–3 times as high as in the northern Sargasso Sea and in Ring 79‐E shortly after formation. The NO3− gradient at the base of the mixed layer in the new Ring 79‐E was 0.09 µmol kg−1 m−1, whereas that for the older Ring 81‐D was 0.30. The increase in proximity of NO3− to the mixed layer may be a general phenomenon associated with the aging process of warm‐core rings. The increase in this gradient enhances the potential for episodic bursts of production in warm‐core rings in response to turbulent mixing at the base of the mixed layer.

Following an interaction with the Gulf Stream and a gale force storm, the mixed layer of Ring 81‐D cooled and its NO3− content increased. In response to increased availability of NO3−, both the rate of phytoplankton utilization of NO3− and the rate of primary production increased. Integrated rates for NO3− uptake in the mixed layer increased sevenfold (from 28 to 195 µmol m−2 h−1).
Decomposition of 14C‐labeled organic substances in marine sediments1
Authors: Henrichs Susan M. , Doyle Allen P.
Published: April 2010

The depth variation of total organic carbon (TOC), organic matter composition, and porewater composition in marine sediments suggests that different components of the organic matter undergo decomposition at widely different rates. The decomposition of 14C‐labeled organic substances was followed in sediment microcosms in the laboratory. The substances used were chosen to simulate a portion of material settling to the sediment‐water interface (a marine diatom) or hypothesized components of refractory sediment organic matter (melanoidins and a bacterial polymer). The microcosms were found to be good models of the sediment‐water interface in terms of how well they mimicked sediment decomposition rates and processes. The decomposition of the labeled material and the natural sediment TOC were monitored over 1 month: the water overlying the sediment remained oxic, and net consumption of nitrate was small. There was no detectable sulfate reduction. The algae and the bacterial polymer were decomposed on average 9 × faster than the melanoidins and 90 × faster than the natural sediment TOC. The soluble fraction of the algae was decomposed more rapidly than the particulate material.
Effects of daphnid size and density on interference between Daphnia and Keratella cochlearis1
Authors: Burns Carolyn W. , Gilbert John J.
Published: April 2010

The cladocerans Daphnia pulex, Daphnia ambigua, Daphnia rosea, Daphnia magna, and Daphnia galeata mendotae were tested in the laboratory for their competency to kill Keratella cochlearis (f. tecta) in the course of their normal filter‐feeding behavior. At daphnid sizes > 1.2 mm of body length, all five species killed the rotifers at rates that increased with body length as y = 0.485x − 0.588 where y is Keratella killed Daphnia−1 h−1 and x is daphnid body length in mm. No species‐specific differences in ability to kill rotifers were detected. Keratella was found in the gut contents of some Daphnia, indicating carnivory and a new pathway in trophic interactions in freshwater ecosystems. Keratella density did not affect Keratella mortality rate within the range tested (1251,000 liter−1). Daphnia cleared live Keratella from the medium at rates about three times those at which it cleared Cryptomonas from the medium. Relations between Keratella mortality, Daphnia density, and Daphnia size were used to derive a family of curves from which the potential impact of Daphnia‐induced mortality on field populations of Keratella can be calculated. When the daphnids are large (>2 mm) and present at densities ≳ 1–5 individuals liter−1, they could have a major impact on the population dynamics of the rotifers.
Direct observations of the mechanisms of interference between Daphnia and Keratella cochlearis1
Authors: Burns Carolyn W. , Gilbert John J.
Published: April 2010

Direct observation was used to describe and quantify four types of interaction between Daphnia (D. pulex, D. rosea, D. galeata mendotae, D. ambigua, and D. magna) and the rotifer, Keratella cochlearis f. tecta. The types of encounter differed primarily in duration, in the appendage movements elicited in Daphnia, and in the damage to Keratella. Egg‐carrying rotifers were just as susceptible to damage by Daphnia as nonovigerous rotifers. The frequency of interactions lethal to Keratella increased with increasing body size of Daphnia and decreased at algal concentrations above the incipient limiting concentration. By combining direct observations of the proportions of Keratella killed with measurements of Keratella‐based clearance rates by Daphnia, the actual pumping rate of Daphnia could be estimated.
Probable loss of chlorophyll‐derived pigments during passage through the gut of zooplankton, and some of the consequences
Authors: Conover R. J. , Durvasula Ravi , Roy Suzanne , Wang Rong
Published: April 2010

By use of biogenic silica as an inert marker, it is shown that chlorophyll a and its derivatives can be destroyed or absorbed during passage through the gut of a herbivorous copepod. This observation is contradictory to the hypothesis that chlorophyll a is converted to pheophorbide a with 100% molar efficiency. The currently used equations for measuring chlorophyll and pheopigment by fluorescence cannot be used to give concentration of pheopigment.
A flow‐measuring system for use in small lakes1
Authors: MacIntyre Sally
Published: April 2010

Currents, internal waves, and turbulence can be studied with a flowmeter consisting of a heated thermistor in a Wheatstone bridge circuit. Flow is proportional to the imbalance of the Wheatstone bridge caused by cooling of the heated thermistor bead as water flows past. Because the flow‐sensing element is spherical, speed can be measured but not direction of flow. The flowmeter can measure speeds as low as 0.1 cm s−1 and can resolve frequencies up to 5 Hz. Frequency responses were determined by comparison with a laser‐Doppler velocimeter and by spectral analysis of field data. At low speeds (<0.3 cm s−1), thermally driven convection contributes to the signal, but flow speeds can be estimated reliably by using a calibration equation that has as one of its parameters the voltage output at zero velocity.
Phytoplankton growth and phosphate uptake (for P limitation) by natural phytoplankton populations from the Loosdrecht lakes (The Netherlands)1
Authors: Riegman Roel , Mur Luuc R.
Published: April 2010

Phosphate uptake capacity of natural phytoplankton populations was used as a physiological indicator of P limitation in the Loosdrecht lakes. During a substantial period of the growth season of 1983, P‐limited growth was observed in Lake Breukeleveen and Lake Loosdrecht, but P limitation was less severe in the latter. In Lake Breukeleveen the maximum initial phosphate uptake rate (Vm) varied between 0.3 and 5.7 µg P(µg Chl)−1 h−1 during P‐limited growth, whereas in Lake Loosdrecht, Vm varied between 0.3 and 2.1 µg P(µg Chl)−1 h−1. Both at the end of June and the beginning of July, growth was not P limited in either lake. Phytoplankton in Lake Loosdrecht was not limited by phosphorus in September. The frequent occurrence of P limitation led to the prediction that reduction of the P loadings of Lake Loosdrecht will result in a reduction of the phytoplankton biomass.
Calcite precipitation in Lake Constance: Chemical equilibrium, sedimentation, and nucleation by algae1
Authors: Stabel H.‐H.
Published: April 2010

Seasonal shifts in calcium carbonate solution equilibria in the limnetic zone of Lake Constance were documented between 1981 and 1983. Except during mixing times, lake water was supersaturated with respect to calcite; epilimnetic supersaturation maxima were closely related to changes in pH. Sedimentation of calcium from the lower boundary of the euphotic zone to the lake bottom was also assessed. The daily sedimentation flux for calcium during the season varied over three orders of magnitude. Differences in the calcium content of sediments trapped at various depths were insignificant. Sedimentation rates of titanium were used as tracers for the fluxes of calcium bound on allochthonous clastic material. Lacustrine calcite precipitation (39–49% of the total sedimentation rate) was obtained by subtracting fluxes of allochthonous Ca from the rates of total Ca sedimentation.

Calcium supersaturation maxima were not in phase seasonally with maximum fluxes of autochthonous Ca. Instead, calcite precipitation was associated with the occurrence of Stephanodiscus hantzschii, Fragilaria crotonensis, Asterionella formosa, Chlorella sp., Pandorina morum, and Mougeotia thylespora, indicating that calcite formation was triggered by heterogeneous nucleation induced by certain algal species.
Genetic heterogeneity in euphausiid populations: Euphausia krohnii and Nematoscelis megalops in North Atlantic Slope Water1
Authors: Bucklin Ann , Wiebe Peter H.
Published: April 2010

Genetic heterogeneity of samples of Euphausia krohnii and Nematoscelis megalops collected from a 6,000‐km2 area in western North Atlantic Slope Water was investigated by electrophoretic assay of allozymic variability at eight enzyme loci. Both species exhibited significant among‐sample heterogeneity of allozyme frequencies. Genetic distances between samples were large for intraspecific comparisons (D̄ = 0.116 for E. krohnii and D̄ = 0.203 for N. megalops). This heterogeneity indicates that both species are genetically structured.
On phytoplankton growth rates and particulate C: N: P ratios at low light1
Authors: Goldman Joel C.
Published: April 2010

In a series of continuous culture experiments involving N‐limited growth of the chrysophyte Pavlova lutheri (Mono) I found that large deviations in cellular C: N: P ratios from the Redfield ratio of 106 : 16 : 1 occurred only as a function of low relative growth rate and not of low light intensity. By contrast, light‐limited phytoplankton in continuous culture can attain the Redfield chemical proportions at all combinations of light intensity and dilution rate. Because the absolute magnitude of the maximum growth rate is variable with respect to light intensity and other abiotic factors, the chemical composition of particulate matter can be used as a diagnostic tool to estimate the degree of nutrient deficiency of both laboratory‐grown and natural phytoplankton populations at all light intensities. There is an abundance of data from recent oceanic studies to substantiate the possibility that the chemical composition of oceanic phytoplankton typically is in the Redfield proportions. These results support the hypothesis that oceanic phytoplankters are growing at relative growth rates close to unity.
A technique to assess the harmful effects of sampling and containment for determination of primary production1,2
Authors: Jergensen Bo Barker , Des Marais David J.
Published: April 2010

We address here the hypothesis that massive mortality, photosynthetic debility, or both may be associated with sampling and enclosing open ocean phytoplankton. We propose that the hypothesis can be tested by measuring in vivo Chl a fluorescence of enclosed phytoplankton assemblages. Experiments on the effects of acute copper toxicity and mechanical disruption were performed to validate our approach. Reports in the literature and results from the experiments show that the difference between in vivo fluorescence before and after treatment with the photosynthetic inhibitor DCMU is a reliable, albeit qualitative, indicator of photosynthetic ability. Fluorescence measurements are thus suitable to assess damage to phytoplankton during measurement of photosynthesis. An example from the tropical ocean demonstrates that the low measured rate of primary production is probably not an artifact of sampling and containment.
Growth, mortality, and secondary production of the copepod Acartia tranteri in Westemport Bay, Australia1
Authors: Kimmerer W. J. , McKinnon A. D.
Published: April 2010

We measured the growth rate of Acartia tranteri and related variables in Westernport Bay, Australia, on 19 occasions in 1982–1984. Acartia tranteri is numerically dominant in the bay zooplankton, with a mean abundance of all life stages of 12,000 m−3. Growth rates, measured by an incubation method, varied between 0.025 and 0.26 d−1 with a time‐weighted mean of 0.11 d and chlorophyll concentrations together explained 50% of the variance in growth rate, which was usually food limited.

Annual secondary production of A. tranteri was 130 mg C m−3, < 1% of phytoplankton primary production. Zooplankton production is a minor constituent of the energy budget of the bay, compared to benthic production.

Mortality rates, estimated from stage abundances and development times, were very low except in early naupliar stages. Median adult longevity was 26 d when water temperature was <17°C, and only 4 d when temperature was >20°C. The low mortality and high longevity are consistent with the observed low abundances of planktonic predators and with the low consumption rates of Acartia by planktivorous fish in the bay.
Resource depletion by active suspension feeders on tidal fiats: Influence of local density and tidal elevation1
Authors: Peterson Charles H. , Black R.
Published: April 2010

Sampling at two elevations from a tidal flat on the Shark Bay (Western Australia) shoreline at Monkey Mia revealed abundant suspension‐feeding bivalves of numerous (>17) species. Their total density increased by 3 × up the tidal elevation gradient from the subtidal margin of the flat to intertidal sites ≃97 cm higher. Factorial field experiments were used to test the effect of site (tidal elevation), local bivalve density, and their interaction on growth and survivorship of three species of suspension‐feeding bivalves. Survivorship was high and did not vary significantly with site or local density. Individual growth was generally lower at higher density for both Anomalocardia squamosus and Circe lenticularis, but growth of Callista impar never responded significantly to local density. Site effects on individual growth were far stronger than density effects and operated on all three species: growth at the intertidal site was substantially lower than at the subtidal site. The intensity of the site effect on individual growth about doubled from the first (February–June) to the second (June–December) experimental interval, probably because average daily exposure to air also doubled. Despite the success of tidal exposure in explaining seasonal variation in growth differences between sites, at a given season clams at the intertidal site grew substantially less than predicted from duration of aerial exposure and density. We hypothesize that density effects estimated locally within 1‐m2 areas fail to assess the full magnitude of food depletion that occurs over broader scales and that suspension feeders low on the flat deplete suspended foods in incoming tidal flows before they ever reach clams at higher elevations.
Oceanic stratified euphotic zone as elucidated by 234Th: 238U disequilibria1
Authors: Coale Kenneth H. , Bruland Kenneth W.
Published: April 2010

Profiles of dissolved and particulate 234Th were determined at the VERTEX 2 and 3 stations off Manzanillo, Mexico, and at the VERTEX 4 station about 900 km north of Hawaii. By modeling the disequilibria between 234Th and 238U in the dissolved and particulate form, estimates of scavenging rates for Th from the dissolved to particulate phases, particle residence times, and the flux of Th via particle removal can be obtained. 234Th:238U activity ratio profiles indicate that the euphotic zone can be separated into two layers: An upper oligotrophic layer characterized by low new production values, low net scavenging, and long dissolved 234Th residence times; and a subsurface eutrophic layer with higher new production values, more intense scavenging, and shorter dissolved 234Th residence times.

New production, rather than total primary production may determine net scavenging rates of reactive elements from oceanic surface waters. These results contribute to the emerging descriptions of the layered structure of oligotrophic euphotic zones and support the notion that this may be a general and ubiquitous feature of global stratified oligotrophic regimes. These layered systems can be structured not only in biological and nutrient parameters, but also in terms of the rates of chemical scavenging and elemental transport.
The effects of darkness and anaerobiosis on dinoflagellate cyst germination1,2
Authors: Anderson Donald M. , Taylor Craig D. , Armbrust E. Virginia
Published: April 2010

This article is in Free Access Publication and may be downloaded using the “Download Full Text PDF” link at right.
Dissolved organic phosphorus production in surface seawaters1
Authors: Orrett K. , Karl D. M.
Published: April 2010

This article is in Free Access Publication and may be downloaded using the “Download Full Text PDF” link at right.
Effects of prescreening on productivity of size‐fractionated phytoplankton1
Authors: Furnas Miles J.
Published: April 2010

This article is in Free Access Publication and may be downloaded using the “Download Full Text PDF” link at right.
Microbial oxidation of manganese in a North Carolina estuary1
Authors: Sunda William G. , Huntsman Susan A.
Published: April 2010

Experiments were conducted with 54Mn(II) to determine the kinetics of particulate manganese formation in seawater from the lower Newport River estuary, North Carolina. Dissolved Mn was rapidly converted into particles at constant rates that ranged from 0.36 to 6.2% h−1 (0.62–3.5 nmol liter−1 h−1), yielding turnover times of the dissolved manganese pool of 0.7–11 d. Dissolved Mn turnover rates increased with temperature (Q10 = 2) up to a maximum at 25°–35°C and also increased with the ratio of particulate to dissolved Mn. These two factors explained most of the variation in the observed turnover rates.

Sample deoxygenation reduced the formation of particulate 54Mn by 94% and virtually all the particulate 54Mn formed in natural oxygen‐containing samples could be dissolved by 10 µM ascorbic acid, a strong reducing agent. These results indicated that the formation of particulate 54Mn resulted primarily from the oxidation of Mn(II) to manganese oxides (MnOx). The oxidation rates, however, were much too rapid to be accounted for by abiotic mechanisms, and the rate was reduced by 97% following heat sterilization of the seawater. In addition, the rates conformed to the Michaelis‐Menten enzyme kinetics model with Vmax equal to 1.2 × 10−8 mol liter−1 h−1 and Ks equal to 1.9 × 10−7 M. These findings provide strong evidence that oxidation of Mn in the estuarine samples is microbially catalyzed. This catalysis appears to be instrumental in the rapid redox cycling of Mn and in the scavenging of dissolved Mn onto particles in aquatic systems.
Biomass and production of small and large free‐living and attached bacteria in Lake Constance1
Authors: Simon Meinhard
Published: April 2010

Cell numbers, biomass, and secondary production of small (0.2–1 µm) and large (1.0–3.0 µm) free‐living and attached bacteria were studied in Lake Constance. Biomass as well as production rates exhibited large fluctuations vertically and seasonally. When averaged over a year, small free‐living bacteria were most important for recycling of organic matter since they comprised 77% of total cell numbers and 66% of bacterial secondary production. Large free‐living bacteria contained roughly half of the total bacterial biomass because of their relatively larger cell size. Although attached bacteria usually were of minor importance, they occasionally comprised about half of total bacterial production. During the phytoplankton spring bloom when bacterial production reached its maximum, 60–80% of all free‐living bacteria were active as shown by autoradiography. During that period a high portion of detrital particles was colonized by metabolically active cells.

The data suggest that biomass, cell size, and production of free‐living bacteria are controlled by substrate input and grazing of either heterotrophic microflagellates or crustacean zooplankton. In contrast, biomass and production of attached bacteria appear to be predominantly controlled by substrate input of readily decomposable particulate organic matter.
Quantitative in vivo absorption spectra of phytoplankton: Detrital absorption and comparison with fluorescence excitation spectra1
Authors: Maske Helmut , Haardt Hauke
Published: April 2010

Spectral absorption of phytoplankton from cultures and natural samples was measured on filters with various optical setups including collimated and diffuse irradiation and measurements of wetted filters within an integrating sphere. In suspensions within an integrating sphere, specific absorption coefficients for laboratory cultures varied by a factor of only two.

Measurements on filters yielded values dependent on filter load. Specific absorption coefficients derived from measurements of sample filters were considerably higher than values obtained from suspensions in an integrating sphere due to increased diffuseness of irradiance and to pathlength amplification by filter‐particle and particle‐particle interactions. Measured absorption of phytoplankton in the blue can be increased greatly by absorption of detritus, evident from absorption spectra of depigmented samples on filter. After subtracting detrital absorption, absorption spectra of phytoplankton are qualitatively similar to the corresponding quantum‐corrected fluorescence excitation spectra. The detritus‐corrected ratio of absorption at 440 vs. 675 nm shows average values between 1 and 1.5.

Comparison with published values shows that specific in vivo absorption coefficients of phytoplankton are mostly overestimated as a result of the methodology applied. In the blue region of the spectrum, overestimation of phytoplankton absorption in field samples is possible if detrital absorption is neglected.
Effects of colonial morphology on zooplankton utilization of algal resources during blue‐green algal (Microcystis aeruginosa) blooms1
Authors: Fulton Rolland S. , Paerl Hans W.
Published: April 2010

Experiments were conducted to test the following proposed mechanisms whereby blooms of colonial blue‐green algae (Microcystis aeruginosa) may more negatively affect large‐bodied cladocerans than other zooplankton taxa: that colonial morphology most strongly interferes with the feeding of larger cladocerans, and that larger cladocerans more readily ingest toxic or nonnutritious colonial blue‐greens. Experiments were conducted with both colonial and unicellular M. aeruginosa, in order to distinguish the effects of coloniality from chemical inhibitory factors associated with blue‐green algae. Experiments with colonial M. aeruginosa provided some support for both mechanisms, particularly with the cladoceran Diaphanosoma brachyurum. However, some small‐bodied species associated with blue‐green algal blooms did not conform to the proposed mechanisms, showing relatively strong reductions in clearance rates in the presence of colonial M. aeruginosa (Bosmina longirostris, Ceriodaphnia quadrangula) or relatively high consumption of colonial M. aeruginosa (Brachionus calyciflorus, B. longirostris). Our results indicate that, contrary to earlier proposals, neither body size, taxonomic position, nor association with blue‐green algal blooms are good predictors of the response to colonial M. aeruginosa.
Ethological observations on foraging behavior of the ctenophore Leucothea sp. in the open sea1
Authors: Hamner W. M. , Strand S. W. , Matsumoto G. I. , Hamner P. P.
Published: April 2010

Of all the Leucothea seen during daylight dives in the Catalina Channel, 45% were between the depths of 18 and 22 m, usually feeding at the thermocline on a layer of copepods, primarily Clausocalanus. Undisturbed individuals were observed and video recorded for periods up to 40 min. The ctenophores actively selected specific depths for foraging and spent about 60% of their time foraging horizontally in the water column, 20% of their time swimming rapidly either directly upward or downward, and 20% of their time immobile and neutrally buoyant. The extent and importance of long‐distance horizontal foraging activity of zooplankton and the relationship of individual behavior of zooplankton to patch dynamics has been underestimated.
Effect of interreplicate variance on zooplankton sampling design and data analysis1
Authors: Downing John A. , Pérusse Martin , Frenette Yves
Published: April 2010

The variance of replicate marine and freshwater zooplankton samples is related (r2 > 0.99) to the mean population density and the volume of the sample taken. A general variance relationship calculated from 1,189 sets of replicate samples taken throughout the world is presented. This function can predict the variance of both marine and freshwater samples taken with several types of sampling gear. Only 12% of individual taxa examined showed variance relationships that departed significantly from this general function. The variance function shows how the requisite number of samples decreases with increased population density, sampler volume, and lowered precision requirements. The X0.2power transformation is recommended on empirical grounds, although caution is advised in the use of all data transformations.
Individual feeding variability of protozoan and crustacean zooplankton analyzed with flow cytometry1
Authors: Gerritsen Jeroen , Sanders Robert W. , Bradley Susan W. , Porter Karen G.
Published: April 2010

Feeding of protozoan and crustacean zooplankton was analyzed by flow cytometry (FCM), resulting in direct counts of particles ingested by each individual. Ciliates (Cyclidium sp.) were allowed to feed on Microcystis aeruginosa and analyzed directly on a flow cytometer for cyanobacterial autofluorescence coincident with each ciliate. Numbers of Microcystis cells ingested (e.g. 0, 1, 2, 3, or 4 ciliate−1) were estimated from the total fluorescence intensity of each ciliate. Crustaceans (Daphnia magna and Bosmina tubicen) were fed fluorescent beads or Microcystis, sonicated to release their gut contents, and the resulting suspension from each individual was quantitatively analyzed by FCM. These methods allow estimation of several aspects of feeding behavior, including particle selectivity, mechanisms of particle capture, gut volume of small organisms, feeding and clearance rates, and individual variation of the preceding parameters. Flow cytometry is more rapid than direct counts by microscope and more accurate than many indirect methods.
Flatworm predator (Mesostoma cf. lingua) releases a toxin to catch planktonic prey (Daphnia magna)1
Authors: Dumont Henri J. , Carets Inez
Published: April 2010

In aquaria, Daphnia magna decreased in numbers as the population density of the substrate‐bound predaceous flatworm Mesostoma cf. lingua increased. Above a threshold worm density, Daphnia disappeared completely. It was shown experimentally that this was due to the presence in the environment of a neurotoxin diffusing from webs of mucus produced by the worm. The toxin decomposed rapidly, and its inactivation rate was strongly temperature‐dependent. It is concluded that Mesostoma is an ambush predator with a strategy that comes closest to that of a web‐building spider, but with the complication that both the worm and the web are poisonous.
Spatial and temporal variation in hypolimnetic oxygen deficits of a multidepression lake
Authors: Lind Owen T.
Published: April 2010

Marked differences in areal hypolimnetic oxygen deficits were found among three depressions of a single lake. These differences were similar to those measured 11 yr before and indicate that regional patterns of nutrient input, production, and eutrophication exist. The patterns are related to lakeshore land use and development. The rate of eutrophication has accelerated across the lake over the 11‐yr span. This increase in eutrophication rate would not have been detected had not the hypolimnetic oxygen deficit data also taken into account the differences in hypolimnetic temperatures between the two studies. In fact, without considering temperature, opposite conclusions would have been reached; i.e. that the rate of eutrophication was lessening.
Chloride budgets in transient lakes: Lakes Baringo, Naivasha, and Turkana1
Authors: Barton C. E. , Solomon D. K. , Bowman J. R. , Cerling T. E. , Sayer M. D.
Published: April 2010

Lakes Baringo, Naivasha, and Turkana, East Africa, are being filled with sediment at a rapid rate. A finite‐difference numerical model that includes diffusion and advection terms can describe the chemical evolution of chloride in lake water or pore water in these or other shoaling lakes. For the cases of Baringo and Turkana this model suggests chloride accumulation times on the order of 100–200 and 3,000–5,000 yr. Stable isotopic studies of waters from the East African Rift show that these three lakes are highly evaporated and that Lake Naivasha is the source of water of the Ol Oserian geothermal field.
Geochemical and mineralogical indications of pH in lakes and soils in central New Hampshire in the early Holocene1
Authors: Ryan Douglas F. , Kahler David M.
Published: April 2010

In central New Hampshire, sediments of some early Holocene lakes were alkaline and contained carbonate minerals despite granitic bedrock and currently acid soils and surface water in their watersheds. Nearby calcareous bedrock contributed to the till of these watersheds while other lakes, more remote from calcareous bedrock, had early Holocene sediments of neutral pH and devoid of carbonate minerals. Calcite rock fragments in alkaline sediments were eroded from alkaline soils in the watershed. Chemical weathering later acidified these soils and surface waters before modem acid precipitation.
Big Soda Lake (Nevada). 1. Pelagic bacterial heterotrophy and biomass1
Authors: Zehr Jon P. , Harvey Ronald W. , Oremland Ronald S. , Cloern James E. , George Leah H. , Lane Judith L.
Published: April 2010

Bacterial activities and abundance were measured seasonally in the water column of meromictic Big Soda Lake which is divided into three chemically distinct zones: aerobic mixolimnion, anaerobic mixolimnion, and anaerobic monimolimnion. Bacterial abundance ranged between 5 and 52 x 106 cells ml−1, with highest biomass at the interfaces between these zones: 2–4 mg C liter−1 in the photosynthetic bacterial layer (oxycline) and 0.8–2.0 mg C liter−1 in the chemocline. Bacterial cell size and morphology also varied with depth: small coccoid cells were dominant in the aerobic mixolimnion, whereas the monimolimnion had a more diverse population that included cocci, rods, and large filaments. Heterotrophic activity was measured by [methyl‐3H]thymidine incorporation and [14C]glutamate uptake. Highest uptake rates were at or just below the photosynthetic bacterial layer and were attributable to small (<1 µm) heterotrophs rather than the larger photosynthetic bacteria. These high rates of heterotrophic uptake were apparently linked with fermentation; rates of other mineralization processes (e.g. sulfate reduction, methanogenesis, denitrification) in the anoxic mixolimnion were insignificant. Heterotrophic activity in the highly reduced monimolimnion was generally much lower than elsewhere in the water column. Therefore, although the monimolimnion contained most of the bacterial abundance and biomass (∼60%), most of the cells there were inactive.
Big Soda Lake (Nevada). 2. Pelagic sulfate reduction
Authors: Smith Richard L. , Oremland Ronald S.
Published: April 2010

The epilimnion of hypersaline, alkaline, meromictic Big Soda Lake contains an average 58 mmol sulfate liter−1 and 0.4 µmol dissolved iron liter−1. The monimolimnion, which is permanently anoxic, has a sulfide concentration ranging seasonally from 4 to 7 mmol liter−1. Depth profiles of sulfate reduction in the monimolimnion, assayed with a 35S tracer technique and in situ incubations, demonstrated that sulfate reduction occurs within the water column of this extreme environment. The average rate of reduction in the monimolimnion was 3 µmol sulfate liter−1 d−1 in May compared to 0.9 in October. These values are comparable to rates of sulfate reduction reported for anoxic waters of more moderate environments. Sulfate reduction also occurred in the anoxic zone of the mixolimnion, though at significantly lower rates (0.025–0.090 µmol liter−1 d−1 at 25 m). Additions of FeS (1.0 mmol liter−1) doubled the endogenous rate of sulfate reduction in the monimolimnion, while MnS and kaolinite had no effect. These results suggest that sulfate reduction in Big Soda Lake is iron limited and controlled by seasonal variables other than temperature. Estimates of the organic carbon mineralized by sulfate reduction exceed measured fluxes of particulate organic carbon sinking from the mixolimnion. Thus, additional sources of electron donors (other than those derived from the sinking of pelagic autotrophs) may also fuel monimolimnetic sulfate reduction in the lake.