bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Lake acidification: Its effect on lead in the sediment of two Adirondack lakes1,1
Authors: Davis Andrew O. , Galloway James N. , Nordstrom D. Kirk
Published: March 2010

Sediment cores from two remote lakes, Sagamore and Woods (Adirondack State Park, New York), were analyzed for lead. A marked increase was found in the top 10 cm of the sediment of both lakes. The effect of lake acidification on the release of lead from the sediments was determined in laboratory studies. Significant lead desorption (>5% of the total) only occurred at a pH <3.0 in sediment from Woods Lake and <2.0 in sediment from Lake Sagamore. Since the pH of the two lakes is always >4.4, lead is not being released from the sediments.
Forces on intertidal organisms due to breaking ocean waves: Design and application of a telemetry system1
Authors: Denny Mark W.
Published: March 2010

A new telemetry system measures the direction and magnitude of the forces imposed on intertidal organisms by individual breaking waves. Cast epoxy replicas of organisms are mounted on three transducers embedded in an exposed rock surface. Force data are encoded as a frequency‐modulated audio signal and transmitted as an FM radio signal a sufficient distance so that the receiving and recording apparatus is safely away from the wave‐swept shore. The system measures forces in the range of 0.1–10 N, but can be scaled to fit a variety of applications. The apparatus is simple to build and inexpensive.
The use of electronically counted microspheres in absolute diatom analysis
Authors: Battarbee R. W. , Kneen M. J.
Published: March 2010

A method of estimating diatom concentrations in sediment samples by the addition of known quantities of microspheres is described. Polystyrene or glass microspheres can be used and their concentration in suspensions can be rapidly calculated with an electronic particle counter. Test results are compared with results from other techniques. Calibrated stock suspensions can be obtained from commercial sources.
A simple device for sampling shallow waters1
Authors: Fletcher W. K. , Poison D.
Published: March 2010

A simple polypropylene sampling head is described that enables virtually any type of bottle to be used for sampling shallow waters. By opening and closing the bottle at the sampling depth some potential contamination problems are avoided.
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.
Blue‐green algal scums: An explanation for their occurrence during freshwater blooms1
Authors: Paerl Hans W. , Ustach Joseph F.
Published: March 2010

Nuisance blue‐green algal (cyanobacterial) scums are a sign of advanced eutrophication in aquatic systems. Previous workers have concluded that scums arc a sign of cyanobacterial senescence, or uncontrollable buoyancy. Our studies, however, indicate that scum formation may represent a mechanism by which the cyanobactcria can dominate surface waters. The mechanism is based on a preference for CO2 over HCO3− and CO32− as a photosynthetic carbon source, particularly in poorly buffered (low total inorganic carbon) waters. On calm days, when surface waters are thermally stratified, supplies of free CO2 are depleted, resulting in an increase in ambient pH. In response to CO2 depletion, cyanobacteria form surface scums, enabling them to use CO2 at the air‐water interface. This also promotes optimal photosynthetic growth and N2 fixation while simultaneously shading underlying noncyanobacterial phytoplankton.
In situ response of phytoplankton fluorescence to rapid variations in light1
Authors: Abbott Mark R. , Richerson Peter J. , Powell Thomas M.
Published: March 2010

Phytoplankton chlorophyll a fluorescence responded to rapid fluctuations in light intensity in Lake Tahoe at three depths: 10, 35, and 60 m. Fluorescence yield was negatively correlated with surface irradiance at all depths, but there was a strong depth dependence in the intensity of this response. Phytoplankton at 35 m reacted more strongly to fluctuations than those at 10 or 60 in and therefore could show a noticeable response to more rapid variations. This may have been due to near‐optimal light levels at 35 m, light inhibition at 10 m, and light limitation at 60 m.
Phytoplankton photosynthesis and carbon‐specific growth: Light‐saturated rates in a nutrient‐rich environment1
Authors: Malone Thomas C.
Published: March 2010

Light‐saturated photosynthesis from short term (2 h) and daily (24 h) measurements were correlated in phytoplankton of two size fractions, net plankton dominated by diatoms and nanoplankton dominated by chlorophytes. Diurnal variations in short term photosynthesis were characterized by a midday maximum and tended to be of a greater amplitude in net plankton than in nanoplankton populations. Nanoplankton photosynthesis varied on a seasonal scale while net plankton photosynthesis varied on a daily scale—a phenomenon which appeared to be reflected in the relationship between short term photosynthesis and growth. The latter, calculated from daily photosynthesis, increased exponentially with temperature and was more closely coupled to short term photosynthesis in nanoplankton than in net plankton populations. These differences seem to be related to the way in which the two size fractions are distributed in time and space as a consequence of interactions between physical process and time‐dependent growth.
The trophic response of ciliated protozoans in freshwater lakes1
Authors: Beaver John R. , Crisman Thomas L.
Published: March 2010

The abundance, biomass, composition, and size distribution of planktonic ciliated protozoans were analyzed monthly during 1979 along a trophic gradient represented by 20 Florida lakes. Both the abundance and biomass of ciliates were positively related to trophic state. Eutrophic assemblages were codominated by members of the Scuticociliatida, Oligotrichida, and Haptorida; oligotrophic lakes were dominated principally by the Oligotrichida. In addition to a compositional shift, large‐bodied ciliates (40–50 m) were progressively replaced by small‐bodied ciliates (20–30 µm) as trophic state increascd. The response is attributed to changes in food availability. Small‐bodied (<30 µm) bactivorous taxa are reduced in oligotrophic lakes where bacterial concentrations are limiting and are replaced by those larger‐bodied taxa (>30 µm) able to ingest nannoplanktonic algae in addition to bacteria.
Behavioral response of Daphnia to rate of temperature change: Possible enhancement of vertical migration1
Authors: Gerritsen Jeroen
Published: March 2010

Daphnia magna, Daphnia pulex, Daphnia parvula, and Daphnia laevis respond to small temperature changes by changing the duration and frequency of upward swimming, in proportion to the rate of change of temperature. When temperature rises, animals swim up more frequently in direct proportion to the rate of change of temperature. In falling temperatures, the animals tend to sink. This response is opposite to previously reported reactions of zooplankton to heating or cooling. It may be adaptive in light‐initiated vertical migration by reinforcing upward swimming in ascending animals and by reinforcing sinking in descending animals.
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.
Organic matter and the surface charge of suspended particles in estuarine waters1
Authors: Hunter K. A. , Liss P. S.
Published: March 2010

The surface electrical charge on suspended particles in four estuaries of the U.K. has been measured as a function of salinity by the technique of particle microelectrophoresis. Two characteristic types of behavior were found. In rivers low in dissolved cations, especially Ca2+ (Conwy, Beaulieu), the electrophoretic mobility uE was negative in sign at all salinities, increasing slightly in magnitude from the seawater end member to lower salinities of 5–10‰, with a more pronounced increase toward the river water end member. In rivers draining calcareous terrain and having relatively high concentrations of Ca2+ (Alde, Orwell) uE showed a similar dependence on salinity above 5–10‰ but no marked increase in magnitude at lower salinities. Ionic composition of the water appears to be the major factor controlling changes in uE with salinity. Positively charged particles were entirely absent. The charge distribution of all samples was highly uniform, in spite of the mixed nature of the suspended matter, indicating a dominant control of surface properties by adsorbed organic matter, metallic oxides, or both. This implies that differential flocculation of different suspended minerals is largely suppressed in the estuarine zone. Measurements of dissolved organic carbon (DOC) and surface‐active substances (by suppression of polarographic maximum) in the same estuaries indicate a sufficient supply of organic matter for the adsorption process. No evidence for nonconservative removal of DOC or surface‐active substances was found. Sewage inputs into some of the estuaries are clearly seen by the measurements of surface‐active substances. Significant quantities of surface‐active materials are injected into the Alde estuary through tidal flushing of a salt marsh area.
Diel and depth variations in dissolved free amino acids and ammonium in the Baltic Sea determined by shipboard HPLC analysis1
Authors: Mopper Kenneth , Lindroth Peter
Published: March 2010

A precolumn fluorimetric labeling method was tested for shipboard HPLC analysis of dissolved free amino acids (DFAA) in natural waters. No sample preparation is required and all naturally occurring amino acids plus ammonium are sufficiently separated within 30 min. Striking diel trends were observed to a depth of at least 60 m, with maximal DFAA concentrations (200–400 nM) in the late evening and minimal concentrations (30–40 nM) in the early day. Concurrent with the evening concentration maxima were elevated relative abundances of basic amino acids (especially ornithine and lysine) and ammonium. During the day very low levels of amino acids were found in the upper water. The magnitude of the night‐to‐day drop in total DFAA suggests a net heterotrophic uptake rate of up to 6 µg AA·liter−1 h−1. A pronounced amino acid maximum at the O2−HS− interface in the water column was presumably derived from microbial populations inhabiting this region. Pronounced, coincidental minima in amino acid and ammonium concentrations just above this interface may be related either to scavaging by precipitating metal oxyhydroxides or to enhanced heterotrophic utilization.
High frequency endogenous periodicities of chlorophyll synthesis in estuarine phytoplankton1
Authors: Auclair J. C. , Demers S. , Fréchette M. , Legendre L. , Trump C. L.
Published: March 2010

A 6‐h endogenous periodicity in chlorophyll synthesis, phased to tidally induced changes in the stability of the water column, was evidenced in a large volume sample of a natural estuarine phytoplankton population. Chlorophyll concentrations nearly doubled over a period of 2–3 h. This field evidence is in conceptual agreement with a physiological model of light‐shade adaptation based on changes in the rates of chlorophyll synthesis.
Germanic acid inhibition of carbon fixation in natural phytoplankton assemblages
Authors: Davies Anthony G. , Sleep Jillian A. , Harbour D. S.
Published: March 2010

Germanic acid (5 mg Ge · liter−1) is shown to inhibit not only 67% of the carbon fixation in diatoms but also 21% of that in the sub‐10‐µm microflagellates of natural phytoplankton assemblages. Use of the reagent for quantifying primary production in the diatom component of mixed populations should take account of this.
The application of ac polarography to the determination of surface‐active substances in seawater1
Authors: Cosović Božena , Vojvodić Vjeročka
Published: March 2010

An electrochemical method based on the measurement of the capacity current at the hanging mercury drop electrode by alternating‐current polarography was developed and applied to the analysis of surface‐active substances in seawater and in sea‐surface microlayer samples. Surfactant activities of natural samples collected in the Adriatic Sea in 1978–1980 are compared with different model surfactants (Triton‐X‐100, albumin, fatty acid, humic acid, polysaccharide) and with parallel measurements by the polarographic maximum method. The shape of the capacity current‐potential curves of natural samples indicates that the adsorption effect at the electrode is produced predominantly by high molecular weight compounds. The surfactant activity corresponds to about 0.01–0.5 mg·liter−1 for bulk seawater and 0.1–2 mg·liter−1 for sea‐surface microlayer samples, relative to Triton‐X‐100. Seasonal variations in surfactant activity values at offshore stations were related to biological activity.
A device for the production of small bubbles in seawater1
Authors: Johnson Bruce D. , Gershey Robert M. , Cooke Robert C. , Sutcliffe William H.
Published: March 2010

The failure to consider the effect of small bubbles in many studies of particle scavenging by rising bubbles and of aerosol formation from bursting bubbles has been due primarily to the lack of a method for producing them. An apparatus constructed so that bubbles emerging from a frit are sheared by water flow restricted to a narrow channel produces bubble populations typically having mean radii <100 µm.
Preparation of 15N‐labeled phytoplankton samples for optical emission spectrometry1
Authors: Kristiansen S. , Paasche E.
Published: March 2010

A method is described whereby the 15N content of phytoplankton on a filter can be determined in an optical emission spectrometer after Kjeldahl digestion, microdiffusion, and Dumas oxidation. Total N content can be measured in the same sample, and the procedure offers some additional advantages. Values of 15N content obtained in this way were the same, within the limits of analytical error, as those obtained by direct Dumas oxidation of 15N‐labeled plankton samples.
Interference in the determination of calcium in seawater
Authors: Olson Eric J. , Chen Chen-Tung A.
Published: March 2010

The interference of magnesium and strontium with the EGTA complexometric titration of calcium was insignificant at the level of accuracy used for the molar ratios found in seawater. Interference effects were found, however, for samples containing higher magnesium or strontium to calcium ratios. An average value of 0.02103 (SD ± 0.00001) was obtained for Ca:Cl‰ for nine bottles of IAPSO Standard Seawater (P79, 19.376 Cl‰).
A vertical free fall plankton net with no mouth obstructions
Authors: Heron A. C.
Published: March 2010

A newly developed vertical free fall net uses a weighted ring to propel it downward through the water at a standard speed. It is closed after a preselected time by a strangling rope secured aboard ship. This design eliminates the three‐point bridle and the long wire in front of a vertically hauled net which cause avoidance reactions in active zooplankton. The depth and volume filtered are unaffected by drift. The net does not require an oceanographic winch for its operation, only a warping drum for retrieval after closure, and therefore can also be used on unspecialized vessels. These properties recommend it is a standard survey sampler.
Stable carbon isotope ratio of submerged freshwater macrophytes1,1
Authors: LaZerte Bruce D. , Szalados James E.
Published: March 2010

The stable carbon isotope ratio of submerged freshwater macrophytes is substantially higher than that of terrestrial C3 plants. This difference is consistent with the high diffusion resistance to inorganic carbon flux in the aquatic medium but also appears to be a function of the more negative carbon ratio of the dissolved inorganic carbon available to freshwater plants.
Effects of naturally senescing aquatic macrophytes on nutrient chemistry and chlorophyll a of surrounding waters1
Authors: Landers Dixon H.
Published: March 2010

Field experiments were performed to demonstrate the effects of senescing stands of Myriophyllum spicatum (Eurasian water milfoil) on water chemistry and chlorophyll a in a large soft‐water Indiana reservoir. Replicate enclosures were used to isolate water columns over monospecific stands of M. spicatum until annual dieback began. Systems were sampled routinely for 119 days before, during, and after fall dieback. Decomposing macrophytes supplied significant inputs of nitrogen and phosphorus to surrounding waters. Nitrogen inputs were sharply pulsed and never accounted for >2.2% of annual allochthonous inputs. Phosphorus inputs from senescing plants equaled up to 18% of the annual (1978) total phosphorus loading for the reservoir. Annual dieback occurred in late summer and early autumn when conditions were suitable for phytoplankton response. Phytoplankton biomass (Chl a) showed significant increases in response to senescing macrophytes.
Nitrogen fixation in the temperate estuarine intertidal sediments of the River Lune
Authors: Jones Keith
Published: March 2010

In situ measurements of acetylene reduction in undisturbed temperate intertidal estuarine sediments show that activity occurs from late spring to early autumn and amounts to an annual rate of 1.4 kg of N fixed per hectare. The low rates are caused by the combination of low temperatures, high salinities, and a shortage of carbon substrates for heterotrophic nitrogen‐fixing bacteria. The main contributing organisms are the sulfate‐reducers and salinity‐tolerant strains of Klebsiella pneumoniae. Other nitrogen‐fixing bacteria (photosynthetic bacteria, salinity‐tolerant strains of Azotobacter chroococcum, and cyanobacteria) are present only in low numbers or are unable to fix nitrogen at the salinities found in the sediments.
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.
Spectral absorption by marine particles of coastal waters of Baja California1
Authors: Kiefer Dale A. , SooHoo Janice Beeler
Published: March 2010

During March 1979 spectral absorptance for the suspended particles of the coastal waters of Baja California was determined by measuring the diffuse transmittance of filters containing the particles with a simply designed spectrophotometer. The absorptance for the upper water of 20 stations varied by over an order of magnitude, but the spectra were generally similar in shape and indicated that phytoplankton pigments were the dominant absorbers. A region of major spectral change was found between 400 and 435 nm, where a shift in maximal absorptance toward shorter wavelengths was correlated with increased concentrations of pheopigments relative to chlorophyll. A multivariate analysis of the data yielded two spectra for the specific absorptance in units of m2·mg pigment−1 of those particles containing chlorophyll and those containing pheopigments. The specific absorptance for chlorophyll‐containing particles is compared with previous measurements in the field and laboratory; the specific absorptance for pheopigment‐containing particles has not been measured before.
Bio‐optical classification and model of natural waters. 21
Authors: Baker Karen S. , Smith Raymond C.
Published: March 2010

A bio‐optical technique is presented which allows both the classification and optical modeling of natural waters. The spectral diffuse attenuation coefficient for irradiance (300–700 nm) has been related to two biological quantities: the total concentration of chlorophyll‐like pigments and the dissolved organic material (DOM). The model is a component model which augments our previous work in that it includes new data in the analysis, utilizes an improved analytic fit, extends into the UV region of the spectrum, and adds a DOM component. Our model, which permits quantitative calculation of spectral irradiance at any point in the water column in a variety of nonterrigenous water types, facilitates predictive modeling.
Diffusion coefficients in nearshore marine sediments1
Authors: Ullman William J. , Aller Robert C.
Published: March 2010

The formation resistivity factor, F, necessary to calculate bulk sediment diffusion coefficients of interstitial solutes from free solution diffusion coefficients, can be estimated from ϕ, the sediment porosity. Empirical relationships between F and ϕ indicate that F ≈ ϕ−2 for unlithified marine sands or muds when ϕ ≲ 0.7 and F ≈ ϕ−2.5 to ϕ−3 for high porosity muds when ϕ ≳ 0.7.
A “dipstick” sampler for rapid, continuous chemical profiles in sediments1
Authors: Reeburgh William S. , Erickson Roy E.
Published: March 2010

Polyacrylamide gels dosed with lead acetate and supported in a Lucite “dipstick” provide a means of obtaining rapid, continous depth distributions of sulfide in anoxic marine sediments.
UV‐sensitive complex phosphorus: Association with dissolved humic material and iron in a bog lake1
Authors: Francko David A. , Heath Robert T.
Published: March 2010

The concentration of UV‐sensitive complex phosphorus compounds in water from an acid bog lake was linearly related to the concentration of dissolved high molecular weight humic material (DHM) both seasonally and diurnally. The first‐order rate of photoreduction (F3+ to Fe2+) of DHM ·· iron equaled the rate of release of orthophosphate (SRP) from these compounds. The rate of photoreduction of DHM ·· iron was the same as the rate of photoreduction of ferric citrate under similar conditions. Reduced DHM ·· iron was auto‐oxidizable (Fe2+ to Fe3+); ferrous citrate was not. These data support the view that orthophosphate sorbed to ferric iron ·· DHM complexes may be released by a mechanism involving UV‐induced photoreduction of ferric iron to the ferrous state.
Size fractionation of phytoplankton as an estimate of food available to herbivores1
Authors: Runge Jeffrey A. , Ohman Mark D.
Published: March 2010

Eight species of phytoplankton with sizes and shapes common in temperate oceans were partitioned into categories with six or seven sizes of screens and filters. Analysis of chlorophyll a, particle numbers, and volume in successive size fractions showed clear cell or colony breakage for only one species. The size fractionation technique thus seems to be an informative way to partition phytoplankton into size classes available to suspension‐feeding zooplankton. The technique does not always separate elongate species on the basis of their longest axial dimension, as some species seem more likely than others to orient in the direction of the flow.
A transportable microprocessor‐controlled precise Winkler titration suitable for field station and shipboard use1
Authors: Williams P. J. leB. , Jenkinson N. W.
Published: March 2010

An automatic Winkler titration based on a photometric end‐point detector is described. The titration is controlled by a system based on a RCA 1800 series microprocessor. It takes about 3–4 min and in normal use has a coefficient of variation in the range 0.03–0.1%. The system is transportable and has been used at sea.
Meromixis in an equatorial African soda lake1
Authors: MacIntyre Sally , Melack John M.
Published: March 2010

Lake Sonachi, a small volcanic crater lake in central Kenya, was chemically stratified on all of 17 sampling dates spanning 8 years. Values of chemical stability, the amount of work required to mix a stratified lake to a uniform concentration, were low (700–200,300 ergs·cm−2). Factors that contribute to the maintenance of meromixis are basin morphometry, the diurnal periodicity of the winds and of thermal stratification, biological decomposition, and seasonal and yearly changes in rainfall. Lake Sonachi is sheltered from wind by crater walls 30–115 m above its surface. Wind speeds have a diurnal pattern and typically were maximal when the lake was thermally stratified. Higher values of hydrogen sulfide, soluble reactive phosphate, and ammonia in the deeper waters, as well as a lower pH value, suggest that biological processes contributed to the meromixis. Rainfall during 1971–1976 totaled less than average, and chemical stability declined to 700 ergs·cm−2. When the lake was again sampled after 2 years of above average and 1 year of average rainfall, the level had risen 3 m and the stability had increased to 200,300 ergs·cm−2. Freshening of the surface waters by rain contributed to the increased stability, and the conductivity and the volume of water below the chemocline had increased substantially. We suggest that chemical stratification is enhanced by ground‐waters that dissolve evaporites in the lake sediments and seep into the lake.
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.
Diagenetic models of interstitial nitrate profiles in deep sea suboxic sediments1
Authors: Goloway Frances , Bender Michael
Published: March 2010

Quantitative models are developed to describe three different profiles of nitrate observed in the porewater of pelagic sediments: nitrification only is observed; a surficial zone of nitrification is underlain by a zone of denitrification; the zone of nitrification is underlain by a zone of no reaction and then a zone of denitrification. Oxygen consumption and nitrate re duction are assumed to be first‐order processes. by fitting the models to observed [NO3−] profiles, we have estimated benthic nitrate and oxygen fluxes, denitrification rates, first‐order rates constants for O2, organic matter, and NO3− consumption, and the stoichiometric ratio d[NO3−]:d[O2].
Isotope dilution models of uptake and remineralization of ammonium by marine plankton1
Authors: Gilbert Patricia M. , Lipschultz Fredric , McCarthy James J. , Altabet Mark A.
Published: March 2010

The utility of 15N isotope dilution models for the calculation of uptake and remineralization of NH4+ by marine phytoplankton was examined in light of model limitations when applied to field data either when ambient NH4+ levels border on our limit of detection or when there is no statistically significant difference between ambient NH4+ at the beginning and end of an incubation. Through specific examples of field and laboratory data we show that the limitations are a function both of analytical error inherent in the methodology and of changes in rates of uptake and remineralization over the course of a given experiment. We propose modifications to the existing models of NH4+ uptake and remineralization which overcome some of these limitations. The results show that uptake rates have been traditionally underestimated by a factor of ≈2 in routine 15N uptake methodology and that regeneration of NH4+ over relatively brief periods can supply the daily nitrogen requirements of the phytoplankton when there are no losses from the system.
1,2
Authors: McCarthy James J. , Wynne D. , Berman T.
Published: March 2010

The uptake rates of NH4+, NO3−, and urea‐N were determined for Lake Kinneret microplankton over a 2‐year period. NO3− was usually the most abundant (0.2–19.3 µg‐atoms N·liter−1), NH4+ occasionally reached similar concentrations (<0.05–16.4 µg‐atoms N·liter−1), and urea‐N was always present in low concentrations (<0.5–1.5 µg‐atoms N·liter− 1). NO3− dominated the total nitrogenous nutrient pool during spring (>90% ∑N as NO3−) when Peridinium cinctum was dominant, but at all times phytoplankton showed preferential NH4+ uptake. The Peridinium bloom periods were characterized by the highest specific uptake and transport rates for NH4+. Turnover times throughout the study ranged from 21‐>7,000 h for NO3−, I‐630 h for NH4+, and 5‐>560 h for urea‐N. Patterns of preferential utilization for NO3−, NH4+, and urea‐N were similar to those reported for Chesapeake Bay plankton. Midday uptake rates for NO3−, NH4+, and urea‐N were all higher under natural light than in darkness.
Zooplankton production in the eastern tropical Atlantic Ocean: Net growth efficiency and P:B in terms of carbon, nitrogen, and phosphorus
Authors: Le Borgne Robert
Published: March 2010

Daily production rates in terms of carbon, nitrogen, and phosphorus are calculated for 0–100‐m mixed zooplankton from its measured excretion rates and net growth efficiency (K2). The latter was calculated from : phosphorus (N : P) and carbon:nitrogen (C:N) ratios of microzooplankton (50–200 µm) and mesozooplankton (200–5,000 µm), their excretion and assimilation efficiencies, and particulate food material over periods of several days at each of 21 stations representing several offshore ecosystems. Average K2 values for mesozooplankton were 0.372, 0.489, and 0.373 in terms of C, N, and P and 0.568 and 0.480 in terms of N and P for microzooplankton. P:B of microzooplankton (range: 34–230%) is 3.8 times that of mesozooplankton (15–62%). Calculations were also made for particular animals such as Salpa and Glaucus (nudibranch). The lack of a significant correlation between mesozooplankton P:B or K2 and the usual environmental factors is explained by the complexity of mixed populations. However, significant correlations with the N:P ratio of particulate food, or the assimilation number (that also refer to mixed populations), show that P:B and K2 values are not so erratic.
Feeding by the chaetognath, Sagitta elegans, at low temperatures in Vineyard Sound, Massachusetts1
Authors: Feigenbaum David
Published: March 2010

Feeding rates were determined for S. elegans feeding in Vineyard Sound, Massachusetts, at a temperature of 0°C by applying a digestion time (10.2 h), obtained from laboratory observations, to an analysis of gut contents. The specific daily ration of large individuals was about 1–2% of body dry wt·d−1, that of small chaetognaths (3.5 mm) was about 46%. Feeding rates for all but the smallest animals are similar to those predicted from respiration data; the smallest individuals consumed more than their estimated no‐growth requirements.
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.
Free ionie nickel accumulation and localization in the freshwater zooplankter, Daphnia magna1
Authors: Hall T. M.
Published: March 2010

The processes which lead to the accumulation of free ionic nickel (radioactive) from solution by Daphnia magna were studied and incorporated into a model which describes accumulation at different concentrations. Adsorption proved to be a relatively small component of nickel accumulation. The accumulation rate eventually approached zero, which represented an equilibrium between uptake and loss of nickel. However, elimination experiments did reveal a pool of relatively static nickel. The appearance and distribution of nickel within five body parts (body fluid, carapace, gut, filtering appendages, and eggs) of D. magna supported the accumulation data and added to the understanding of the pathways of nickel through the organism.
Determination of shell deposition rates of Arctica islandica from the New York Bight using natural 228Ra and 228Th and bomb‐produced 14C1
Authors: Turekian K. K. , Cochran J. K. , Nozaki Y. , Thompson I. , Jones D. S.
Published: March 2010

Shell deposition rates of specimens of Arctica islandica (Mollusca: Bivalvia) from the New York Bight were determined using natural 228Ra and 228Th and bomb 14C. The specimens from deep (>55 m) offshore waters show annual growth banding. A shell obtained from the inner bight at <30‐m depth seems to be younger than indicated by band counting.
Displacement of northern Wisconsin crayfish by Orconectes rusticus (Girard)1
Authors: Capelli Gregory M.
Published: March 2010

Orconectes rusticus, an introduced species in northern Wisconsin, is confirmed as displacing other species of crayfish. Displacement rates are extremely rapid in some cases but are highly variable among lakes. Displacement mechanisms and ecological implications are not well known; however, significant reductions in macrophyte populations are an apparent result.
Reversal of cadmium toxicity in a diatom: An interaction between cadmium activity and iron1
Authors: Foster Patricia L. , Morel Francois M. M.
Published: March 2010

In batch cultures of Thalassiosira weissflogii subjected to high Cd2+ activities, normal growth rates are resumed when the cadmium ion activity is lowered by either dilution of the medium or addition of a chelating agent (EDTA). Toxicity reversal is possible after up to several days of high (Cd2+) exposure, depending on the initial Cd2+ activity. A sufficiently high ferric ion activity is critical for toxicity reversal; Fe must be added when the Cd2+ activity is decreased by addition of EDTA. The order of Fe and EDTA addition is unimportant for the reversal process. An antagonism between Cd and Fe is clearly indicated, implying that the mechanism of Cd toxicity involves in some way an impairment of iron nutrition.
Vertical and horizontal distributions of dinoflagellate cysts in sediments1
Authors: Anderson Donald M. , Aubrey David G. , Tyler Mary A. , Coats D. Wayne
Published: March 2010

Studies of the distribution of dinoflagellate resting cysts have typically focused on the flocculent layer at the sediment— water interface. Simple coring methods now reveal a wide variety of vertical distributions of cysts in different estuarine and nearshore environments, often with significant subsurface concentrations of viable cysts. Both subsurface and surface maxima are found in both coarse and fine sediments. The results have implications with respect to maps of cyst distribution, to correlations between the observed patterns and hydrographic or sedimentary parameters, and to assessments of the role of this life cycle stage in “seeding” dinoflagellate blooms.
Decomposition of organic detritus: A selective role for microflagellate Protozoa1
Authors: Sherr Barry F. , Sherr Evelyn B. , Berman Thomas
Published: March 2010

The decomposition of Peridinium cells was accelerated in the presence of bacterivorous microflagellates. The microflagellates enhanced the bacterial breakdown of the polysaccharide cell wall (theca) but did not increase the rate of degradation of the cell protoplasm. Hydrolytic bacteria which preferentially attacked the theca were stimulated by protozoan grazing and by the addition of inorganic phosphorus. An important role of microprotozoa in aquatic ecosystems may therefore be to selectively facilitate the breakdown of detritus with a high structural carbohydrate/low mineral content.
A technique for estimating phytoplankton division rates by using a DNA‐binding fluorescent dye1
Authors: Falkowski Paul G. , Owens Thomas G.
Published: March 2010

Phytoplankton division rates were estimated by following time‐course changes in DNA using a DNA‐specific fluorescent dye. The method is simple, inexpensive, and rapid. A technique using a light bottle minus dark bottle method is described for estimating division rates of phytoplankton samples in natural waters.
The calculation of in situ growth rates of phytoplankton populations from fractions of cells undergoing mitosis: A clarification1
Authors: McDuff R. E. , Chisholm S. W.
Published: March 2010

A review of existing approaches used to calculate phytoplankton population growth rates from fractions of cells undergoing mitosis (mitotic index) has revealed inconsistencies in their content and underlying assumptions. The appropriate expressions are derived for populations in exponential growth and those which exhibit phased cell division. Growth rate estimates calculated from the maximum mitotic index in phased populations are shown to be accurate when the duration of the mitotic stage is greater than the interval during which the increase in cell number occurs. This characteristic is manifested in a plateau‐shaped curve of mitotic index vs. time. The alternative approach of averaging sequential observations is also considered, and the conditions for which one can obtain exact results are defined. The magnitude of uncertainties is examined as a function of the frequency of sampling.
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.
Carbon dioxide hydration and dehydration kinetics in seawater1
Authors: Johnson Kenneth S.
Published: March 2010

Rate constants for the hydration and dehydration reactions of carbon dioxide with water and with hydroxyl ion were measured in seawater by a pH‐stat method at salinities (× 103) from 3.4 to 37.06 at 25°C and from 5° to 35°C at a salinity of 33.77. Transition state theory was used to extrapolate the rate constants to infinite dilution, with the following results at 25°C: kco2 = 0.037 ± 0.002·s−1, koh‐Kw = (7.1 ± 0.7) × 10−11 mol·dm−3·s−1, kd = (7.6 ± 1.1) × 104 dm3·mol−1·s−1, and khco3− = (1.8 ± 0.3) x 10−4·s−1. The corresponding values in seawater of 33.77 salinity and 25°C calculated from equations fit to the experimental data are 0.036, 13.5×10−11, 3.5 × 104, and 1.40 × 10−4.
Acid precipitation: Its role in the alkalization of a lake in Michigan1
Authors: Kilham Peter
Published: March 2010

The watershed of Weber Lake in northern lower Michigan has experienced a nearly 20‐fold increase in proton loading from acid precipitation in the past 25 years. But, owing to alkalinity production by biologically mediated processes (nitrate uptake by plants and sulfate reduction by bacteria) and increased rates of carbonate weathering, acid precipitation has doubled the alkalinity, raised the equilibrium pH, and made this soft‐water seepage lake more eutrophic.

An acid‐base budget for Weber Lake and its watershed was constructed from the difference between bulk precipitation input and lake water output. Strict application of the first law of thermodynamics and the principle of electroneutrality permits the calculation of the acid‐base budget from the input‐output budget. The acid‐base budget indicates that alkalinity production resulting from nitrate uptake and sulfate reduction is sufficient to completely neutralize the hydrogen ions entering the system from acid precipitation (including biologically mediated hydrogen ion production). The acid‐base budget shows that the alkalinity of Weber Lake has doubled primarily as a result of increased rates of weathering in the watershed. Weathering rates have increased as an indirect result of acid precipitation.