bluuebunny/crossref_metadata_2025_split huggingface dataset:
The phytoplankton and protozooplankton of the euphotic zone of Lake Tanganyika: Species composition, biomass, chlorophyll content, and spatio‐temporal distribution1
Authors: Hecky R. E. , Kling H. J. 
Published: March 2010

The seasonal cycle of phytoplankton and protozooplankton biomass observed at two widely separated pelagic stations in the euphotic zone of Lake Tanganyika from February through November 1975 could be divided into three phases, based on algal abundance and species succession and coinciding with three phases of annual thermal stratification. Phytoplankton biomass was minimal (as low as 60 mg·m‒3) during the phase of stable stratification and maximal, as high as 930 mg·m‒3, at the end of the period of deep mixing. Diatoms, especially Nitzschia spp., were abundant only during the period of mixing, while filamentous blue‐greens, principally Anabaena sp., were prominent during a period of rapid surface warming which produced shallow mixed layers following the period of deepest mixing. The biomass of Strombidium cf. viride nearly equaled or exceeded the phytoplankton biomass during much of the stably stratified period; this protozoan probably has a symbiotic relationship with zoochlorellae, which were always present in it.Lake Tanganyika showed a greater relative annual range between maximum and minimum phytoplankton and chlorophyll a concentrations than other tropical lakes and the temperate Great Lakes. Chlorophyll a ranged from 0.1 to 4.5 mg·m‒3 in the euphotic zone and from 0.2 to 20.4 in surface waters; phytoplankton biomass ranged from 25 to 1,570 mg·m‒3 in the euphotic zone. Annual mean concentrations were among the lowest known, 140 mg·m‒3 for phytoplankton biomass and 1.2 mg·m‒3 for chlorophyll a. Explanations for both the low annual means and the high annual variabilities may lie in he lake’s steep morphometry, which affects nutrient regeneration, and in high loss which cause high algal growth rates but low algal biomass much of the year.
Role of nutrient limitation and competition in controlling the populations of Asterionella formosa and Microcystis aeruginosa in semicontinuous culture1
Authors: Holm Nancy Peterson , Armstrong David E. 
Published: March 2010

The nutrient uptake and growth kinetics of the freshwater diatom Asterionella formosa and the blue‐green alga Microcystis aeruginosa under P or Si limitation were determined in batch cultures at 20°C. Asterionella had a higher maximum growth rate and a lower half‐saturation constant for growth than Microcystis under P limitation. The maximum uptake velocity for P was higher for Asterionella than for Microcystis while the half‐saturation constants for P uptake were similar for the two species.The Monod model of growth predicted a switch from Si limitation to P limitation for Asterionella at Si:P of about 93 (±15). In experiments with the two species grown together at various Si:P ratios, Asterionella dominated steady state semicontinuous cultures when both species were P‐limited, Si:P > 100. Microcystis became dominant when Asterionella was Si‐limited, Si:P < 100. The competition experiments showed the importance of the concentration of nutrients, as well as the ratio of the nutrients and rate of supply, in controlling the cell densities of the algal species.
The effect of environmental factors on phytoplankton growth: Light and the interactions of light with nitrate limitation1
Authors: Rhee G-‐ull , Gotham Ivan J. 
Published: March 2010

The effects of simultaneous limitations of light and nutrient on growth were investigated with turbidostat and chemostat cultures of Scenedesmus sp. and Fragilaria crotonensis. The combined effects were greater than the sum of individual effects and were not multiplicative.Under nitrate‐limited conditions the cell quota of the limiting nutrient for a constant growth rate and the subsistance quota (qo) increased as irradiance decreased. Within a certain limit of growth rates, light and qN can compensate for each other in maintaining growth rate.Under nutrient‐sufficient conditions, cell quotas of C, N, and P, and cellular chlorophyll a concentration increased as light decreased below saturation. The cell quotas are the maximum level (qm) that can be achieved at a given irradiance. Cell quotas of nonlimiting nutrients in nutrient‐limited cultures are the same as these qm values. The increasing levels of qm and qo with decreasing irradiance indicate that nutrient requirements increase as irradiance decreases.
Summer internal phosphorus supplies in Shagawa Lake, Minnesota
Authors: Larsen David P. , Schults Donald W. , Malueg Kenneth W. 
Published: March 2010

Phosphorus budget calculations for Shagawa Lake show that significant increases in lake P during July and August 1971–1975 originated from within the lake basin. Mass increases of 2,000–2,900 kg (35–50 µg·liter‒1) were measured, corresponding to internal supply rates of 240–680 kg·wk‒1 over a 3–9‐week interval. After anaerobi: conditions developed in late June, release from the profundal zone sediments contributed significant amounts of P to lake water.Sediment chemical properties were determined to estimate the size of the P reservoir in the profundal zone (at water depths > 6.5 m). The P content of the surficial profundal zone sediments was 0.2–0.5% (dry wt) and a significant fraction was potentially mobile (NaOH extractable). We calculate that the upper 10 cm of these sediments contain 50,000 kg of potentially mobile P, of which a small fraction is released each summer. Although external sources of phosphorus have been reduced by about 80%, the feedback of P from the sediments is supporting the productivity of Shagawa Lake and may continue to do so for many years.
Nitrous oxide in fresh waters of the Great Lakes Basin1
Authors: Lemon Edgar , Lemon Donna 
Published: March 2010

Evidence presented favors the hypothesis that little N2O is transported by rivers into or out of the Great Lakes; rather it is generated or consumed in situ. However transport of nutrients into and out of the lakes probably influences production and consumption within the lakes, i.e. NO3− and organic matter in runoff from land and effluent from cities.Exchange values of N2O between the atmosphere and the lakes calculated from two models are related to the degree of N2O saturation of surface water. The range of fluxes is about 10 times larger than estimates made for the open ocean, i.e. ± 4 pg·cm−2·s−1.Groundwater under a large dairy farm was rich in N2O, but once the N2O seeped into a headwaters tributary it was lost to the atmosphere.
Competition and nutrient kinetics along a temperature gradient: An experimental test of a mechanistic approach to niche theory1
Authors: Tilman David , Mattson Mark , Langer Sara 
Published: March 2010

A resource‐based model of competition correctly predicted the equilibrium outcome and approximated the population and nutrient dynamics of many nutrient‐limited competition experiments with two algal species at temperatures from 8° to 24°C. Silicate growth kinetics of temperature‐acclimated Asterionella formosa and Synedra ulna predicted that Asterionella should competitively displace Synedra below 20°C and Synedra should displace Asterionella above 20°C, as was observed. Although the growth kinetics showed no significant difference in silicate requirements at 20°C, Synedra displaced Asterionella for all starting conditions at 20°C. These experiments support a major prediction of an equilibrium theory of competition for a single resource: independent of initial population densities, the species with the lowest resource requirement should displace all competitors. Thus resource requirements, as defined by a mechanistic model, may be appropriate for defining niche boundaries.In single species experiments, fit to the Monod model with a nutrient threshold, the nutrient‐saturated growth rate of Synedra increased from 0.16·d−1 at 8°C to 0.75 at 13°C and above; its half‐saturation constant for growth was ca. 5.0 µM SiO2, independent of temperature from 8° to 24°C. The nutrient‐saturated growth rate of Asterionella increased from 0.35·d−1 at 4°C to 0.8 at 13°C, and decreased to 0.66 at 24°C; its half‐saturation constant for growth had a temperature‐independent value of 2.1 µM SiO2 from 4° to 13°C, but increased to 10 µM SiO2 at 24°C. Half‐saturation constants for silicate‐limited growth may be temperature‐independent for temperatures within or below the optimal temperature range, but increase sharply for temperatures above it.
Primary production and the anchovy population in the Southern California Bight: Comparison of time series1
Authors: Smith Paul E. , Eppley Richard W. 
Published: March 2010

Two new time series for the Southern California Bight are presented: anchovy biomass, 1951–1979, and primary production, estimated for the years 1920–1979 from 15 cruises conducted between 1974 and 1979. Annual and longer term averages show little relationship to each other except that values for both were low in the climatically warm water years 1957– 1958. The primary production time series is similar to two existing time series: CalCOFI zooplankton in the bight and microplankton in Santa Monica Bay, 1951–1966. Thus estimated primary production does reflect the carrying capacity of these waters for lower trophic level consumers.Seasonal averages of anchovy larvae are highest in the winter and spring quarters when primary production is increasing. Interannual variation was pronounced in both seasonal average primary production and seasonal average abundance of anchovy larvae. About 50% of the variation in number of anchovy larvae was explained by variation in primary production in the same quarter and zooplankton standing stock three quarters earlier. In 1966, the year of maximum anchovy abundance, the energy expended in anchovy egg production was equivalent to about 1.8% of primary production. The anchovy ration was about 18% of primary production. The ratio of zooplankton biomass to primary production was highest in years when anchovy biomass was greatest.
Inorganic nitrogen assimilation in a subalpine lake1
Authors: Axler Richard P. , Gersberg Richard M. , Goldman Charles R. 
Published: March 2010

Isotope tracer techniques were used to determine the seasonal patterns of inorganic nitrogen and carbon assimilation in the epilimnion of meso‐oligotrophic Castle Lake, California. Kinetics experiments with 15N‐labeled ammonium and nitrate indicated that the nitrogen assimilation rate was generally limited by low ambient concentrations of inorganic nitrogen (DIN). The half‐saturation constants for DIN assimilation were low (0.7–9.3 µg · liter−1) and comparable to ambient levels during the nutrient‐depleted, ice‐free growing season. Ammonium assimilation was always higher than nitrate assimilation, even when nitrate concentration greatly exceeded ammonium during early summer, This observation was also supported by the results of 13NO3− uptake experiments.The midsummer proliferation of nonheterocystous blue‐green algae was accompanied by increased carbon and nitrogen assimilation, and higher rates of particulate C and N turnover. Carbon to nitrogen and carbon to maximum nitrogen assimilation ratios were generally high (34.5 ± 13.3 and 15.6 ± 4.5 g C:g N), did not show obvious seasonal differences, and were not correlated significantly with seston compositional ratios.These results integrated with other Castle Lake studies suggest that phytoplankton growth is maintained by efficient use of internally regenerated ammonium, in agreement with many such studies in nitrogen‐deficient marine waters.
Modeling exchangeable NH4+ adsorption in marine sediments: Process and controls of adsorption1,2
Authors: Boatman Charles D. , Murray James W. 
Published: March 2010

The process and controls of ammonium adsorption in marine sediments have been studied using data from adsorption experiments with sediments from Saanich Inlet, British Columbia, and with standard reference clays. The average NH4+ adsorption constant determined experimentally for a Saanich Inlet core of 5.3 ± 1.8 liters·mol−1 was not significantly different from the constant measured in situ of 6.1 liters·mol−1.Equations similar to a Langmuir‐type isotherm are derived which express ammonium adsorption in terms of equilibrium exchange expressions (selectivity coefficients) and activities of the major cations. An ammonium adsorption constant calculated from the model for a montmorillonite clay of 12.6 ± 1.7 liters·mol−1 agrees very well with the experimentally measured values of 11.7 ± 0.3 for a montmorillonite reference clay and 11.8 ± 1.2 for a montmorillonite‐rich pelagic sediment. The proposed model is also general enough to describe the adsorption of any minor component in seawater which undergoes ion exchange.Comparison of ammonium adsorption constants before and after the extraction of organic matter indicates that in organic‐rich sediments a “clay‐humic complex” may be controlling ammonium adsorption. However, in organic‐poor sediments, the clay mineralogy will tend to dictate ammonium adsorption behavior.
Sediment focusing in Mirror Lake, New Hampshire1
Authors: Davis Margaret Bryan , Ford Mary S. (Jesse) 
Published: March 2010

Analyses of multiple sediment cores from Mirror Lake, New Hampshire, dated by 14C and pollen, show that between 14,000 and 11,000 b.p. silts and sands were deposited over 85% of the basin. After 11,000 b.p. organic‐rich sediments were focused into the deeper parts of the basin, and no sediment accumulated in water <5 m deep.Late‐glacial particulate inorganic inputs were 33 times greater than modern losses from forested watersheds at Hubbard Brook. After trees became established, inorganic inputs fell sharply to modern levels. Late‐glacial organic inputs were a half the average during the last 11,000 years. At four of the sites studied, accumulation rates reached a maximum between 7000 and 4000 b.p. The precise date varies from site to site, suggesting that it would be misleading to link peak accumulation in a single core to events in the watershed. After 4000 b.p. organic sediment accumulation rates declined at all four sites. Parallel declines in accumulation rates of both pollen and inorganic sediments suggest that this decline is due to the process of sediment focusing rather than to a change in decomposition rates or in organic inputs related to autochthonous or allochthonous primary production.
Photosynthetic response of two submersed macrophytes to dissolved inorganic carbon concentration and pH1
Authors: Titus John E. , Stone Walter H. 
Published: March 2010

The photosynthetic responses of Myriophyllum spicatum and Vallisneria americana to total dissolved inorganic carbon (DIC) concentration (pH 8.0; 25°C; saturating light) indicate that both species are sensitive to changes in DIC concentrations at natural lake levels, and that M. spicatum has a somewhat lower half‐saturation constant than V. americana for that relationship. This difference is probably not ecologically significant.Carbon uptake rates of V. americana decline by 61% from pH 7 to 8, but change little from pH 8 to 9, whereas those of M. spicatum decline by 35% from pH 7 to 8 and by a further 58% from pH 8 to 9. These decreases do not parallel the corresponding decline in free CO2 availability over this pH range.Carbon compensation points expressed as total DIC, free CO2, or the atmospheric CO2 concentration in equilibrium with the corresponding free CO2 level are strongly pH‐dependent and do not differ substantially between M. spicatum and V. americana.
Population dynamics of Dunaliella parva in the Dead Sea1
Authors: Oren Aharon , Shilo Moshe 
Published: March 2010

A bloom of the unicellular green alga Dunaliella parva in the Dead Sea is described, and physicochemical factors triggering its rise and decline are analyzed. The bloom developed in summer 1980, reached population densities of up to 8,800 cells·ml−1, and gradually declined until finally collapsing during the first months of 1981. Algal development was limited to a thin layer of less saline water floating on top of the heavy brines. Laboratory experiments showed that both dilution of Dead Sea water and increase in phosphate concentration are required for algal development in the Dead Sea.The Dunaliella community followed the deepening of the pycnocline to depths of 15–25 m in September–October 1980, with resultant light limitation to part of the population and cell death by starvation in the absence of light. The inflow of new floodwaters generated a new pycnocline which may have prevented the cells below from reaching the euphotic surface layer, resulting in the death of most of the remaining population.
Oxygen consumption and ammonia and phosphate excretion in pond zooplankton
Authors: Blažka Pavel , Brandi Zdeněk , Procházková Lidmila 
Published: March 2010

Respiration and ammonia and phosphate excretion were studied in the temperature‐acclimated zooplankton of a small eutrophic fishpond. The zooplankton included species of Cyclopoida, Cladocera, and Rotatoria. Their body size varied from ng to µg of protein nitrogen. Oxygen consumption was linearly related to body size at 11°C or higher, but proportional to the 0.86 power of size at 4°C. Similar size relationships applied for N and P excretion. Relationship of oxygen uptake to temperature was virtually identical in well fed Cyclops vicinus and Daphnia hyalina.The oxygen equivalent of ammonia excretion for protein catabolism was never higher than the measured oxygen consumption; there was no suggestion of an apparent gluconeogenesis or lipogenesis in well fed Cyclops. Relative excretion rates of ammonia and phosphate were related to feeding level. The lowest rates of ammonia excretion were at low natural levels of feeding while they increased both in fasting and well fed animals. Relative phosphate excretion rates increased with increasing food concentration, but individual experiments were not comparable. Herbivorous pond plankton had lower N‐excretion rates than carnivorous, which is comparable with planktophagous fish rates published previously.
Zooplankton of a bathyal benthic boundary layer: In situ rates of oxygen consumption and ammonium excretion1
Authors: Smith K. L. 
Published: March 2010

Oxygen consumption and ammonium excretion rates of bathyal macro‐ and megazooplankton from a benthic boundary layer were measured in situ. Collections of plankton were made using a four‐chambered slurp gun respirometer manipulated by the submersible Alvin in the Santa Catalina Basin off southern California at levels 1, 5, 10, and 50 in above bottom in a 1,300‐m water column. Abundance, biomass, oxygen consumption, and ammonium excretion of the mixed macrozooplankton decreased with increased elevation above the bottom.Two specimens of the scyphomedusa Poralia rufescens, a dominant megazooplankton species, were individually collected at 1‐ and 5‐m elevations. Oxygen consumption rates of P. rufescens are similar to those of shallow‐water gelatinous zooplankton. However, excretion rates for P. rufescens are significantly lower.Integrated mixed macrozooplankton oxygen consumption for the 50‐m benthic boundary layer is 1,575.5 µl·m−2 d−1, with the contribution from P. rufescens being only 91.6 This combined zooplankton respiration is only 3% of that measured for the sediment community in the Santa Catalina Basin.
A model of oxygen reduction, denitrification, and organic matter mineralization in marine sediments1
Authors: Jahnke Richard A. , Emerson Steven R. , Murray James W. 
Published: March 2010

Porewater nutrient profiles are sensitive indicators of organic matter degradation in sediments. To interpret these data, we have derived a kinetic model of oxygen reduction, nitrification, and denitrification which quantitatively relates the rates of oxygen reduction and denitrification to the depth separating these processes and the carbon oxidation rate.We have compared model profiles with porewater profiles of the sum of NO2−, NO3−, and NH4+ (∑N) from both Atlantic and Pacific Ocean stations. Calculated rates of oxygen reduction and denitrification vary proportionally at these stations. Extrapolation along this relationship predicts a maximum in NO3− even where the nitrification zone is so thin that only a decrease from bottom water samples is measured with a 1–2‐cm sampling interval. The model also predicts that the maximum amount of organic matter that can be oxidized by denitrification is only 30% of that oxidized by oxygen respiration in the Pacific and only 13% in the Atlantic Ocean.
Estimating food limitation in cladoceran populations1
Authors: Tessier Alan J. , Goulden Clyde E. 
Published: March 2010

Cladocerans store energy for reproduction and survival in the form of triglyceride droplets. The amount of storage in adults is lowest just after egg production and increases during the intermolt period. The bright orange‐yellow of the lipid droplets allows rapid visual indexing of an individual’s body reserves. This lipid index is an extremely sensitive indicator of the feeding success of individual cladocerans. Procedures are presented for using the lipid index to estimate food limitation in natural populations of cladocerans.The relationship between lipid levels, body size, and reproduction was investigated for three species of Daphnia in three lakes of different trophic status. In adults, lipid storage is positively correlated to clutch size. All species provided their neonates with a lipid reserve (maternal investment) but the amount was different for each species. Juvenile lipid reserves were generally lower than adult reserves, but differences in allocation strategy (between juvenile and adult) and neonate maternal reserves precluded a direct relationship between lipid content and body size.
The influence of aqueous iron chemistry on the uptake of iron by the coastal diatom Thalassiosira weissflogii1
Authors: Anderson Michael A. , Morel Francois M. M. 
Published: March 2010

Iron uptake by the coastal diatom, Thalassiosira weissflogii, was measured by a technique that exploits the Fe(III) reducing property of ascorbate to dissolve filterable colloidal iron. For the well defined chemical conditions imposed by a large excess of the aminocarboxylate complexing agents, EDTA, CDTA, DTPA, and NTA, in the absence of light, the iron uptake rate was a function of the activity of Fe3+. In the light, the uptake rate in the presence of EDTA and CDTA was enhanced by factors of 2 and 6 due to photodegradation of the Fe(III) complex yielding Fe(II). An even greater enhancement resulted from the addition of ascorbate, a Fe(III) reductant, to the medium.In the absence of chelators, iron uptake rates appeared to depend on the total iron concentration for both Fe(II) and Fe(III) additions to the medium. A saturated uptake rate (1.5 × 10−16 mol·cell−1·h−1) was observed in the presence of unchelated Fe(II) or colloidal Fe(III), as well as in the presence of chelators. Uptake rates measured in the presence of metabolic inhibitors are consistent with the hypothesis that a membrane‐bound metal binding complex (termed phytotransferrin) transfers iron across the membrane by a process not directly coupled to photosynthetic or respiratory activity. On the basis of all the experiments done, it is suggested that the iron uptake rate is determined by the extent of Fe binding to phytotransferrin, which is in turn controlled by pseudo‐equilibrium with free (reactive) iron in the medium, even when the medium is not at equilibrium due to (photo)reduction of Fe(III) or dissolution of ferric hydroxide.