bluuebunny/crossref_metadata_2025 huggingface dataset:
Littoral‐pelagic phosphorus dynamics during nighttime convective circulation
Authors: James William F. , Barko John W.
Published: April 2010

Littoral phosphorus dynamics and P exchanges between littoral and pelagic zones, driven by nighttime convective circulation, were examined in Eau Galle Reservoir, Wisconsin, during summer 1989. Rates of P release from littoral sediments, measured in laboratory incubation systems, increased linearly with pH under both aerobic and anaerobic conditions. Estimated rates of P release from littoral sediments, based on field measurements of pH and oxygen, averaged 3.6 mg m‒2 d‒1 under aerobic conditions and were in close agreement with independently determined diffusional fluxes across the littoral‐sediment interface. Marked vertical gradients in P developed during summer in bottom waters of the littoral zone. The littoral zone cooled more rapidly at night than the pelagic zone on 72% of midsummer days (June–August), promoting nighttime convective circulation. On the basis of patterns of dye dispersion during these periods of circulation, cooler littoral bottom water moved into the pelagic zone as an interflow confined to the base of the epilimnion, while warmer pelagic water moved into the littoral zone as a surface flow. Hourly volumetric flow rates were linearly related to mean negative horizontal temperature gradients that developed at night. Net total P flux from the littoral to the pelagic zone ranged from 0.12 to 0.43 mg m‒2 h‒1 (avg. 0.22) for the summer. Nighttime convective circulation seems to be an important mechanism for movement of littoral P to the pelagic zone in this reservoir.
Nutrient cycling in a freshwater marsh: The decomposition of fish and waterfowl carrion
Authors: Parmenter Robert R. , Lamarra Vincent A.
Published: April 2010

We measured decomposition rates and nutrient loss sequences of rainbow trout (Oncorhynchus mykiss) and pintail duck (Anas acutas) carcasses in a Wyoming marsh over a 10‐month period (July–May). Data on carcass mass loss were fit to single‐ and double‐exponential decomposition models. Fish carrion decomposed more rapidly and completely than waterfowl carrion; after 10 months, fish carcasses had lost 85% of their initial dry mass (leaving only scales and bones), while duck carcasses had lost only 30% (leaving feathers and bones). Fish carrion lost 95% of the original carcass N and 60% of carcass P; waterfowl carrion lost 65% of carcass N, but only 30% of carcass P. The sequence of total elemental loss rates from carcasses was K > Na > N > S > P > Ca Mg and was similar for fish and waterfowl carrion. Percentage elemental compositions of carcasses changed temporally with K, Na, and N decreasing in concentration and Mg, Ca, P, and S increasing. Vertebrate carrion decomposition differed from plant litter decomposition, both qualitatively (different nutrient loss sequences) and quantitatively (faster mass loss rates). We suggest that vertebrate carrion can function as a nutrient source for some elements (N, K, Na, and S) and as a partial nutrient sink for others (P, Ca, and Mg). Although the quantitative importance of carrion‐derived elements to ecosystem nutrient budgets is site‐specific, studies have shown that in aquatic environments supporting large vertebrate populations, carrion decomposition can contribute significant amounts of important nutrients that ultimately influence the structure and functioning of the aquatic ecosystem.
Gas exchange with saline waters
Authors: Gat Joel R. , Shatkay Michal
Published: April 2010

The salt effect on the gas exchange rate is a combination of an effect on solubility, which is considerably lower in the saline solution, and on piston velocity. These effects reinforce each other to reduce gas influx rates by as much as one order of magnitude in the case of a brine as salty as the Dead Sea, whereas the effect on the rate of escape of gas is smaller. At high wind‐speeds, when bubble entrainment becomes the dominant mode of gas transport, several opposing salt effects come into play that depend not only on the salt concentration but also on the nature of the salt. Even though gas exchange is more sluggish in the saline solution, the higher persistence of bubbles and foams under saline conditions may result in a higher degree of aeration of a brine as a result of a storm surge, when compared to a similar event in a freshwater system.
Aquatic fulvic acids in microbially based ecosystems: Results from two desert lakes in Antarctica
Authors: McKnight Diane M. , Aiken George R. , Smith Richard L.
Published: April 2010

We characterized fulvic acids from two Antarctic lakes to determine the chemical characteristics of dissolved fulvic acid derived from organic material of microbial origin. These lakes receive very limited inputs of organic material from the surrounding barren desert, but they sustain algal and bacterial populations under permanent ice cover. One lake has an extensive anoxic zone and high salinities; the other is oxic and has low salinities. Despite these differences, fulvic acids from both lakes had similar elemental compositions, carbon distributions, and amino acid contents, indicating that the chemistry of microbially derived fulvic acids is not strongly influenced by chemical conditions in the water column. Compared to fulvic acids from other natural waters, these fulvic acids have low C : N atomic ratios (19–25) and low contents of aromatic carbons (5–7% of total carbon atoms); they are most similar to marine fulvic acids.
The oxidation of H2S in Framvaren Fjord
Authors: Millero Frank J.
Published: April 2010

The oxidation of H2S with O2 was measured in Framvaren Fjord at 25°C. The measurements were made on mixtures of surface waters and waters collected from below the anoxic interface (20 m). Measurements were also made on deep waters after a rapid equilibration with air. Oxidation rates varied according to the concentration of Fe(II) and Mn(II) in the solutions, in agreement with earlier studies. For waters collected at the particle maximum (22 m) t1/2 = 20 min for poisoned and unpoisoned samples. The intermediates SO32‒ and S2O32‒ were followed along with the disappearance of H2S during the course of oxidation. The formation of the intermediates was modeled with the overall rates of oxidation of (k1) and SO32‒ (k2) and the formation of S2O32‒ (k3). The values were all larger than found for seawater. These results indicate that Fe(II) and Mn(II) also affect the oxidation of SO32‒ and the formation of S2O32‒ in anoxic waters. The deep waters contained concentrations of H2S as high as 6,000 µM. Low levels of SO32‒ and S2O32‒ were found near the anoxic interface. Quite variable levels (1–35 µM) of what is thought to be S2O32‒ were found in the deep waters. No SO32‒ was detected below the interface.
Studies of vertical mixing in the Southern California Bight with cosmogenic radionuclides 32P and 7Be
Authors: Lee T. , Barg E. , Lal D.
Published: April 2010

We measured concentrations of the two cosmogenic nuclides 32P and 7Be and radiogenic 234Th in the Southern California Bight during June and October 1989 in water depths up to 80 m. The depth of the mixed layer was 18 and 28 m, respectively, and the thermocline was well developed. The depth profiles of 32P are similar to an earlier profile in September 1987 but the column inventories are ∼5 times lower. 32P activity is fairly uniform in the mixed layer and decreases monotonically with depth below it. On the other hand, 7Be concentrations are nearly uniform to depths of 60–80 m. The integrated inventories of both dissolved 32P and 7Be are appreciably lower, by factors of 5–10, than their expected secular equilibrium concentrations for their mean oceanic injection rates. We show that the low inventories of 32P and 7Be are not due primarily to their decreased injection rates but rather to vertical mixing. The vertical eddy diffusivity and the consequent sustained new production based on upward NO3‒ fluxes have been estimated as >7 cm s and ∼1 g C m‒2 d‒1 from the observed profiles of 7Be, 32P, and NO3‒.
An expatriate red tide bloom: Transport, distribution, and persistence
Authors: Tester Patricia A. , Stumpf Richard P. , Vukovich Fred M. , Fowler Patricia K. , Turner Jeflerson T.
Published: April 2010

In November 1987, the toxic dinoflagellate Gymnodinium breve bloomed in North Carolina nearshore waters. This occur rence was the first record of G. breve north of Florida, a range extension of >800 km. We propose the (Gulf of Mexico) Loop Current‐Florida Current‐Gulf Stream system as the transport mechanism for G. breve cells from a late summer bloom off the southwest coast of Florida (Charlotte Harbor‐Sarasota). The estimated transit time for cells around the peninsula and northward to the continental shelf off North Carolina is 22–54 d.

About 30 d after the Charlotte Harbor‐Sarasota bloom, satellite images of sea‐surface temperature substantiated the shoreward movement of a filament of Gulf Stream water onto the narrow continental shelf between Cape Hatteras and Cape Lookout. This filament, the likely source of G. breve cells, remained in nearshore waters and was identifiable in satellite images for >19 d. Once the bloom was inshore, both windspeed and direction were important in determining its distribution.
The control of soft‐shell clam (Mya arenaria) recruitment on intertidal sandflats by bedload sediment transport
Authors: Emerson Craig W. , Grant Jonathan
Published: April 2010

Bedload sediment transport, clam transport across the sediment surface, clam population density, and spat settlement were measured daily for 10 months to determine the magnitude and frequency of clam transport and its dependency on bedload transport and to evaluate the relative importance of this phenomenon to population growth of Mya arenaria. From July to April, the transport of juvenile clams was observed frequently on a sheltered and an exposed intertidal sandflat. The maximum rate of clam transport on the sheltered sandflat (790 ind. m‒1 d‒1) and on the exposed site (2,600 ind. m‒1 d‒1) coincided with peaks of bedload sediment transport (∼35 kg m‒1 d‒1). At both sites, bedload transport was positively correlated with clam transport (r = 0.33 and 0.51; sheltered and exposed sites, P < 0.001); on the sheltered site, clam transport was negatively correlated with clam density (r = ‒0.47, P < 0.001). Cross‐spectral analysis showed that bedload and clam transport time series were significantly coherent with zero lag at periods of <10 d. Clam transport on the high‐energy sand flat accounted for an order‐of‐magnitude increase in clam density in early September, a precipitous decline 2 months later, and the complete removal of recently settled spat. A net population increase on this sandflat was most likely a result of clam import during bedload events.
Adaptive and demographic responses of plankton populations to environmental change
Authors: Lynch Michael , Gabriel Wilfred , Wood A. Michelle
Published: April 2010

Because of their large population sizes, short generation times, and clonal mode of propagation, microorganisms should often be the first members of a community to respond evolutionarily to temporal changes in the environment. Because the planktonic microbial community directly or indirectly influences all other members of aquatic ecosystems, it is useful to have a general theory for the magnitude and limits of such response. Models are presented for the expected dynamics of evolutionary change for the mean and variance of a quantitative character under natural selection toward a fixed or a moving optimum. It is also shown how the rate of population growth is related to the phenotypic composition of the population and the selective aspects of the environment. These models, which lead to the identification of extinction thresholds for the rate of environmental change beyond which a population cannot maintain itself, provide a heuristic basis for understanding the response of ecosystems to environmental perturbations. The analyses also indicate that clones of microorganisms isolated into novel laboratory environments are likely to undergo substantial evolutionary change over periods of a few hundred days, which raises questions about the utility of such cultures for inferring ecological properties of natural populations.
Diagenesis of belowground biomass of Spartina alterniflora in salt‐marsh sediments
Authors: Benner Ronald , Fogel Marilyn L. , Sprague E. Kent
Published: April 2010

Belowground biomass of Spartina alterniflora lost 55% of its organic matter during 18 months of decomposition in salt‐marsh sediments. Significant losses of lignin were observed under highly reducing conditions confirming previous reports of lignin degradation in the absence of molecular oxygen. The submolecular components of lignin varied in susceptibility to degradation and were ranked in the following descending order of resistance to decomposition: V∼P>S∼C. The preferential degradation of the cinnamyl and syringyl components constrains the quantitative usefulness of these compounds for estimating the contributions of herbaceous and angiosperm tissues to pools of dissolved and particulate organic matter. The relative concentration of lignin increased about 1.6‐fold during decomposition owing to the more rapid loss of polysaccharides.

Two phases in nitrogen dynamics were evident during the decomposition study. During the first 4 months of decomposition there was a net loss of N from Spartina tissues at a rate of about 10 N g‒1 tissue d‒1. After this initial phase of net N loss, a phase of N immobilization was evident and was tightly coupled with rates of microbial degradation of the tissues. Net rates of N immobilization were ∼ 19 µg N g‒1 tissue d‒1; by the end of the 18‐month study more N had accumulated in the tissues than was initially present. Stable N isotope compositions of decaying Spartina were also very dynamic and reflected the sources of N that were immobilized during decomposition and the N transformations that occurred on the detrital particles.

The stable C isotope composition of the polysaccharide components of Spartina was ∼6‰ heavier than that of the lignin component. The isotopic compositions of these components retained the 6‰ difference throughout the 18‐month study. The stable C isotope composition of the bulk tissues, however, decreased gradually during decomposition as the isotopically heavier polysaccharides were preferentially lost. Residual material was relatively enriched in the isotopically lighter, lignin‐derived C.
CO2emission and soil Eh responses to different hydrological conditions in fresh, brackish, and saline marsh soils
Authors: Nyman J. A. , DeLaune R. D.
Published: April 2010

The effects of various water‐table depths during continuous and simulated tidal drainage on CO2 emissions and soil Eh were examined in intact fresh, brackish, and saline marsh soil cores. CO2 emissions did not differ between continuous and tidal drainage. CO2 emissions were greatest in fresh cores and least in brackish cores at all water‐table depths tested. Eh was higher in brackish cores and lower in fresh and saline cores at all water‐table depths tested. Eh increased with decreasing water‐table depth and increased more during continuous drainage than during tidal drainage. These results exclude the possibility that reported differences in field measurements of CO2 emission among fresh, brackish, and saline marsh soils relate to different hydrological conditions in the marsh types; they also indicate that fundamental differences in decomposition processes and soil Eh exist among these marsh types. Although not tested, differences were attributed to the different species of emergent vegetation occupying the different marsh types and which are the sources of soil organic matter.
Procaryotes on the tentacles of deep‐sea holothurians: A novel form of dietary supplementation
Authors: Roberts D. , Billett D. S. M. , McCartney G. , Hayes G. E.
Published: April 2010

Bathyal and abyssal epibenthic holothurians have a layer of bacteria lying over the tentacular epidermis and below the cuticle. Thus the tentacles of deep‐sea holothurians may provide ideal conditions for subcuticular bacteria. These bacteria appear to be regulated by phagocytosis, which, together with pinocytosis would facilitate transfer of bacterial metabolites to the holothurian. Their abundance suggests a previously unknown pathway for energy transformation and assimilation of particular significance in an environment where food is limiting.
Comparison of fluorescamine and o‐phthaldialdehyde methods for measuring amino acid exchange in marine organisms
Authors: Clements Lee Ann J. , Hilbish Thomas J.
Published: April 2010

Two methods routinely used to quantify total primary amine concentrations in seawater are the fluorescamine bulk assay and o‐phthaldialdehyde derivatization with chromatographic separation (OPA‐HPLC). Investigators using OPA‐HPLC have observed net amino acid uptake by marine invertebrates; those using fluorescamine observe excretion of primary amines. We systematically compared the two methods with amino acid and ammonium standards and also conducted two excretion experiments with two species of bivalve molluscs. Mytilus edulis exhibits both uptake and excretion of primary amines and the flux is correlated with the initial concentration of amino acids. The two methods give comparable results, particularly after correcting the fluorescamine data for differences in relative fluorescence among amino acids. Mercenaria mercenaria exhibits net uptake of amino acids when flux is measured by OPA‐HPLC and net excretion of fluorescamine‐positive substances. Small peptides may contribute to the discrepancy between assay methods.
In situ characterization of sediments: Measurements of oxygen and sulfide profiles with a novel combined needle electrode
Authors: Visscher Pieter T. , Beukema Jan , van Gemerden Hans
Published: April 2010

A combined polarographic oxygen and ion‐selective sulfide electrode built in a stainless steel needle was developed to determine in situ profiles of oxygen and sulfide in sediments. The combination of these two sensors (tip diameter: oxygen, 10 µm; sulfide, 100 µm) in one needle (1‐mm o.d., up to 750 mm long) enabled detection of coexistence of oxygen and sulfide in patchy sediments.
A 14C‐incubation technique for measuring microphytobenthic primary productivity in intact sediment cores
Authors: Jönsson Benno
Published: April 2010

A 14C‐incubation technique makes it possible to percolate isotope down into intact sediment cores. The technique contrasts with two commonly used techniques: the slurry technique and that in which the isotope is mixed with the overlying water of an intact sediment core but not percolated into the sediment. The three techniques were tested on two different sediment types. The slurry technique yielded 3–8 times higher productivity values compared with the percolation technique. Productivity measured with the unpercolated tube was lower than values obtained in the percolated tube by a factor varying between 1.6 and 32 for sandy sediment and between 1.2 and 1.6 for silty sediment. The choice of incubation technique is of utmost importance and no standard correction factor should be used to correct values obtained by the slurry method because the degree of overestimation apparently is highly dependent on the sediment type and amount of microalgae present.
Smearing of gravity core profiles in soft sediments
Authors: Chant L. A. , Cornett R. J.
Published: April 2010

Gravity coring of soft sediments can result in smearing of sediment between adjacent vertical sections in a core. We have quantified this artifact in a laboratory experiment with soft, highly porous gyttja using radiotracers to label the surface of the sediments. After coring, extrusion, and sectioning, the radiotracers were measured down to 5 cm in inner core sections and to 10 cm in outer core sections. We have estimated the impact of smearing on the interpretation of concentration‐depth profiles, and gradients calculated from smeared profiles can be less than those occurring in situ in the sediments. This effect seems most pronounced near the mud— water interface. We have simulated radionuclide profiles in sediments from Chernobyl fallout (e.g. 134Cs) and natural emissions (e.g. 210Pb) to examine this problem. Concentration gradients of these radionuclides and of other contaminants used to establish geochronologies can be altered significantly depending on sediment type. A tracer layered on the surface of the sediments can be used to quantitate smearing effects, and corrections can then be made to concentration‐depth profiles.
Population dynamics and body‐size selection in Daphnia
Authors: Tessier Alan J. , Young Andrew , Leibold Mathew
Published: April 2010

We examined the population dynamics and seasonal change in body size of a population of Daphnia galeata mendotae experiencing strong vertebrate predation. The intensity of food limitation was quantified seasonally by in situ food addition. We also collected live animals early and late in the summer for laboratory studies designed to estimate genetic variation and seasonal change in life‐history traits for the population.

The population was characterized by nearly equal short‐term birth and death rates that were strongly correlated with population density, suggesting density dependence. The population generally exhibited very high birth and death rates and no significant response to experimental food addition. The one exception was June 1988, when the population achieved high densities and exhibited strong food limitation. Throughout both summers, minimal and average body sizes of adults decreased.

Laboratory studies document substantial genetic variation for body size and other life‐history traits among animals collected early in summer. By late summer, however, there was little genetic variation for these same traits. Furthermore, clones collected early in summer were genetically larger in body size at birth and maturity than clones collected in late summer. We interpret these results as indicating natural selection for body size.
Prey capture by the four larval instars of Chaoborus crystallinus
Authors: Swift Michael C.
Published: April 2010

Prey capture ability of fourth‐instar Chaoborus larvae has been studied widely but relatively little comparable information is available for the first three larval instars. In this laboratory study I measured strike and contact efficiencies of all four instars of Chaoborus crystallinus. The effectiveness of prey escape behavior was also recorded. As larval size increased the size of successfully captured and ingested prey also increased. There was no loss of ability to ingest the smallest prey by the largest larvae. Prey width was a better index of successful capture and ingestion than was prey length. Fast swimming and infrequent swimming were effective precontact prey escape behaviors. The effectiveness of akinesis and spininess, two postcontact escape mechanisms, depended on larval size; they were effective when prey width approached larval gape diameter but relatively ineffective when prey width was much less than larval gape diameter. Gelatinous prey were readily attacked once but were almost always immediately rejected and seldom attacked again. Early instar Chaoborus larvae are abundant and effective predators whose role in structuring zooplankton communities is only beginning to be appreciated.
Feedback interactions between zinc and phytoplankton in seawater
Authors: Sunda William G. , Huntsman Susan A.
Published: April 2010

In Zn ion‐buffered media, oceanic species (Thalassiosira oceanica and Emiliania huxleyi) grew at near‐maximal rates at the lowest free Zn ion concentration ([Zn2+] = 10‒12.3 M), whereas coastal species (Thalassiosira pseudonana and Thalassiosira weissflogii) were limited at [Zn2+] < 10‒11 M. The ability of the oceanic species to outgrow coastal ones at low [Zn2+] was due almost entirely to a reduced growth requirement for cellular Zn rather than to an increased capability for uptake. All isolates exhibited similar sigmoidal relationships between cellular Zn: C ratios and [Zn2+] with minimal slopes at [Zn2+] of 10‒10.5 to ∼10‒9.5 M and increasing slopes above and below this range. The minimal slopes at intermediate [Zn2+] could be explained by negative feedback regulation of a high‐affinity Zn uptake system, while increased slopes at high [Zn2+] appeared to be related to uptake by a low‐affinity site. Measured relationships between cellular Zn: C ratios and [Zn2+] agreed well with those computed from a modified Redfield model based on depth profiles for Zn and PO4 concentrations and Zn chelation in the nutricline of the North Pacific. This agreement provides evidence that Zn concentrations in the nutricline are controlled by biological uptake and regeneration as occurs for major nutrients.
Effects of variable irradiance on phytoplankton productivity in shallow estuaries
Authors: Mallin Michael A. , Paerl Hans W.
Published: April 2010

Primary productivity in estuaries is profoundly affected by water‐column mixing which can be attributed to currents, tides, and wind. Mixing in shallow systems has the dual effect of increasing light attenuation in the water column through resuspension of particulate matter, while allowing entrained phytoplankton cells to experience a constantly varying light regime. We investigated the latter effect during a 7‐month period in the lower Neuse River, North Carolina, a well‐mixed, coastal plain estuary. A rotating light‐field simulator was devised to assess phytoplankton productivity while considering the problems of mixing and light attenuation. This technique was compared to a fixed‐light level (static) incubation method. We found that constantly varying irradiance stimulated phytoplankton productivity by both reducing photoinhibition and mitigating the growth‐limiting effects of turbidity‐induced light limitation found under static incubation conditions. Our results demonstrate that static incubations may, at times, significantly underestimate true phytoplankton productivity in shallow, well‐mixed aquatic systems.
MAGIC: A sensitive and precise method for measuring dissolved phosphorus in aquatic environments
Authors: Karl David M. , Tien Georgia
Published: April 2010

A simple and straightforward method has been developed for the precise determination of nanomolar concentrations of soluble reactive phosphorus (SRP) and total dissolved phosphorus (TDP) in marine and freshwater environments. The method relies on the quantitative removal of P from solution by in vitro formation of brucite [Mg(OH)2], initiated by the addition of NaOH. The precipitate is collected by centrifugation and either dissolved in HCl for SRP determinations or hydrolyzed (8 M HCl, 80°C, 1 h), dried, and ashed (450°C, 3 h) for TDP determinations. Both procedures are completed by reaction with the standard Murphy‐Riley molybdenum blue reagents. This magnesium‐induced coprecipitation (MAGIC) procedure can be used to effect a 100‐fold concentration, thereby providing a method which can reliably detect 1 nmol SRP liter‒1 of seawater. MAGIC can also be used to determine P in Mg2+‐amended freshwater samples. The method is highly reproducible; typical estimates of precision for triplicate SRP determinations in the 10–100 nM range are from 1 to 3%. Field trials of the MAGIC procedure in the North Pacific Ocean reveal mixed‐layer SRP concentrations from 30 to 100 nM, with substantial temporal variability. The method is versatile and has many other potential applications.
Effectiveness of various treatments in retarding microbial activity in sediment trap material and their effects on the collection of swimmers
Authors: Lee Cindy , Hedges John I. , Wakeham Stuart G. , Zhu Ningli
Published: April 2010

Laboratory and field experiments were conducted to determine the effectiveness of various poison, preservative, and antibiotic treatments currently in common use in sediment trap work. Our results agree with previous reports that most biological activity in sediment traps can be inhibited by appropriate concentrations of formaldehyde, chloroform, or mercuric chloride. Sodium azide appears to be less effective at inhibiting biological activity, while antibiotics and salt alone are probably too ineffective for long‐term deployments. On the basis of laboratory experiments, effective concentrations when sustained throughout the deployment are 50% saturated chloroform, 37 mM formaldehyde, or 180 µM HgCl2. Our results also indicate, however, that the weight of swimmers (zooplankton which swim into the trap and die there from contact with the poison) collected in sediment traps is higher when more effective treatments are used. The presence of large numbers of swimmers can greatly affect the flux and composition of particulate organic matter collected in sediment traps and may decrease the effectiveness of the various treatments in inhibiting microbial activity in the traps.
Ammonium enhancement of dark carbon fixation and nitrogen limitation in symbiotic zooxanthellae: Effects of feeding and starvation of the sea anemone Aiptasia pallida
Authors: Cook Clayton B. , Muller‐Parker Gisèle , D'Elia Christopher F.
Published: April 2010

The nutrient status of algae symbiotic with marine invertebrates is controversial. We assessed the nitrogen status of zooxanthellae symbiotic with the sea anemone Aiptasia pallida using NH4+ enhancement of dark C fixation; enhancement increases with N limitation in other microalgae. Freshly isolated symbionts obtained from laboratory populations of known feeding history and from field populations were assayed: NH4+ enhancement depended on the nutritional history of the host anemones. Zooxanthellae from well‐fed laboratory populations showed little enhancement of dark 14C fixation by NH4+, while mean dark enhancement ratios (NH4+ rates: seawater rates) exceeded 2.3 for zooxanthellae from anemones unfed for 1–6 weeks. Photosynthetic rates of the isolated algae declined with starvation. VD′ : VL, an index which includes both dark NH4+ enhancement and photosynthesis, increased markedly with time since feeding. Three of four field samples of A. pallida yielded zooxanthellae with dark enhancement ratios similar to those of fed laboratory populations; VD′ : VL values were somewhat higher. Symbionts from anemones collected on a fourth date had a mean enhancement ratio of 2.88, and VD′ : VL values similar to those from laboratory anemones that had not fed for 1–2 weeks, indicative of increased N limitation.
Carbonate production and sediment transport in a marl lake of southeastern Wisconsin
Authors: Brown Bruce E. , Fassbender Judy L. , Winkler Ronald
Published: April 2010

Calcium fluxes in a southeastern Wisconsin marl lake are dominated by groundwater seepage and sedimentation. Essentially all Ca enters via groundwater inseepage. Half of it is deposited as CaCO3 in the sediment; the other half leaves via outseepage and outflow. Aragonite, as determined by quantitative X‐ray diffractometry, is the major phase present in the sediment. Aragonite: calcite ratios in six cores from epilimnetic sediment average 61 : 22. Aragonite : calcite ratios in six cores from hypolimnetic sediment average 23 : 20. The aragonite is derived from mollusc shells and is produced in the epilimnetic sediment because seasonal anoxia prevents growth in the hypolimnion. Rates of sedimentation are derived from 210Pb methods. Ratios of mass accumulation rates (g m‒2 yr‒1) for aragonite : calcite average 302 : 91 in epilimnetic sediment and 74 : 68 in hypolimnetic sediment. The hypolimnetic aragonite deposition is due to horizontal transport, with the probable decreasing order of dominance being downslope transport, wave redistribution. and intermittent complete mixing.
Estimating the impact of fungal parasites on phytoplankton populations
Authors: Bruning Kees , Lingeman Rob , Ringelberg Joop
Published: April 2010

A population‐dynamic model is formulated to estimate the impact of chytrid and related fungal parasites on phytoplankton populations. The specific loss rate of uninfected host cells due to infection is used as a measure of the impact. Calculating this loss rate requires information about four parameters: prevalence of infection (i.e. the proportion of the host cells infected), development time of the sporangia of the parasite, specific growth rate of the uninfected host, and difference between loss rates of infected and uninfected host cells due to loss factors other than parasitism. When only cell counts of the host population are available instead of growth and loss rate values, the model can be used to calculate a minimum estimate of the impact of the parasite. The impact of the parasite at a given prevalence of infection can vary considerably as a consequence of environmental effects on the latter three parameters. Therefore, prevalence is not a good parameter to judge the severity of fungal epidemics. A phytoplankton population starts to decline when prevalence exceeds a certain threshold value. This critical prevalence of infection can be calculated with the model and is also highly dependent on external conditions.

The model is applied to epidemics of the chytrid Rhizophydium planktonicum Canter emend. in a population of the diatom Asterionella formosa Hass. in Lake Maarsseveen 1. The end of both the spring and summer 1984 bloom of the diatom was caused by epidemics of the chytrid. Model results suggested also that higher sinking rates, caused by an increasing proportion of dead cells in the colonies, resulted in an additional loss factor due to parasitism for this colonial diatom.
Anomalous mass transfer of phosphate on coral reef flats
Authors: Bilger R. W. , Atkinson M. J.
Published: April 2010

To estimate a maximal rate of phosphate (P) uptake into coral reef‐flat communities, we introduce analogies between fluid flow in pipes and water flow over coral reef flats. On the basis of results from engineering studies of mass transfer in pipes, the best estimate of the Stanton number (Stm, a dimensionless number giving the ratio of uptake rate to the rate of advection of the substance past the uptake surface) for P uptake into a sample reef flat is 5 × 10‒5. Field observations yield a value of at least 1.7 × 10‒3, a factor of 40 higher. This very large enhancement is due in part to wave surge but also could be due to the difference between the nature of the biotic surfaces and that of the engineering surfaces. The engineering data have been obtained for simple geometries with low ratios of wetted area to projected surface area. It is likely that much of the enhancement arises from the large ratio of wetted to projected area for the coral reef‐flat community and the fractal nature of this surface.
Temporal variations of 234Th activity in the water column of Dabob Bay: Particle scavenging
Authors: Wei Ching-Ling , Murray James W.
Published: April 2010

Monthly measurements of total, dissolved, and particulate 234Th, along with fluxes of total mass and particulate 234Th, were made throughout 1987 in Dabob Bay, Washington. Vertical distributions of total 234Th showed a large deficiency relative to 278U throughout the water column during all sampling periods.

Total 234Th activities in surface waters were generally higher in winter and lower in summer, in response to seasonal biological activity. In spite of this variation, the steady state assumption seems valid for modeling 234Th of the bay because the magnitude of variation is insignificant in the mass balance calculation. The range of residence times of total, dissolved, and particulate 234Th estimated from an irreversible scavenging model are 4–70, < 1–10, and 3–60 d, respectively. The residence time of 234Th is controlled by the suspended particles whose distribution is determined by biological production in the surface layer and resuspension of bottom sediments.

Vertical fluxes of 214Th measured by sediment traps also showed wide seasonal variation and generally increased monotonically from 200–1,000 dpm m‒2 d‒1 at 20 m to 2,000–4,000 at 100 m. The flux of 234Th predicted with the steady state scavenging model tends to be about twice the directly measured 234Th flux. This difference may be due either to low trap efficiency for 234Th‐containing particles or to boundary scavenging at the sides of the basin. The residence times of particulate 234Th and total suspended matter agree well, and both are influenced by biological processes.
The chromium cycle in a seasonally anoxic lake
Authors: Johnson C. Annette , Sigg Laura , Lindauer Ursula
Published: April 2010

The Cr cycle was investigated in seasonally anoxic Greifensee, Switzerland. Cr(III), Cr(VI), and total dissolved (<0.45 µm) Cr and total Cr concentration profiles were measured from January until November 1989 together with other redox sensitive species of N, Mn, Fe, and S. Cr(VI) was the predominant species even under anoxic conditions. Concentrations of Cr(VI) ranged from 1 to 4 nM. Reduction of Cr(VI) could be observed only in extremely reducing conditions in the presence of S(‐II) and Fe(II). It was concluded that a suitable reducing agent had to be present for the reduction of CR(VI) to Cr(III) to take place and that organic reductants most probably played a minor role. In addition, calculations indicated the occurrence of a slow removal process, with a half‐time of 100–230 d, that reduced Cr(VI) concentrations by either adsorption or reduction in both oxic and suboxic waters. Dissolved free Cr(III) species were not detected, which was explained by the strong tendency of this species to bind with surfaces and organic ligands and colloids. Even in oxic conditions, the sediments did not appear to be a source of Cr(VI).
Incorporating lotic meiofauna into our understanding of faunal transport processes
Authors: Palmer Margaret A.
Published: April 2010

This work represents the first detailed study using field data and flume experiments to evaluate the magnitude and pattern of meiobenthic drift in a stream, the evidence that both active and passive processes operate during entry and transport, and how meiofaunal transport in streams compares with what is currently known about the transport of lotic macrofauna and of the meiofauna and larval macrofauna of marine systems. Abundances of drifting meiofauna in Goose Creek, Virginia, were extremely high (up to 250,000 per 100 m3) and represented a significant amount of biomass when compared to literature biomass estimates for macrobenthic drift in other warm‐water streams. Drift of the dominant taxa in this study (rotifers, early instar chironomids, oligochaetes, copepods) was flow‐dependent. Flume experiments examining live and dead entry processes provided evidence that a critical threshold velocity existed (∼9–12 cm s‒1), above which the number of animals entering the water increased dramatically. This threshold was less than the critical threshold velocity of the streambed substrate (∼14–17 cm s‒1), suggesting that whenever the streambed is scoured, potentially large numbers of meiofauna may enter the water. Despite the evidence that animals may enter the water passively due to entrainment by flow, active control over drift entry also operated since all four of the dominant taxa exhibited significant increases in drift at night. These diel drift patterns were reflected in reduced streambed abundances at night for chironomids and oligochaetes but not for copepods and rotifers. Additionally, in flume experiments which examined the return of live vs. dead drifting fauna to the bottom, copepods were able to influence their return to the bottom once in transport, a finding consistent with field observations.
Body size and egg production in the marine copepod Acartia hudsonica during a winter‐spring diatom bloom in Narragansett Bay
Authors: Durbin Edward G. , Durbin Ann G. , Campbell Robert G.
Published: April 2010

Seasonal changes in size and egg production in the copepod Acartia hudsonica were investigated during the 1984 winter–spring bloom in Narragansett. Bay. Possible food limitation was investigated through comparisons of short‐term weight change and egg production rate in copepods incubated in ambient Narragansett Bay water and in bay water enriched with cultured algae. A preliminary experiment showed that egg production responded in <24 h to a change in food availability at 4°C—the coldest experimental temperature. Food was not limiting in February–April, but mild food limitation developed in May–June, affecting body weight more than egg production. These results contrast with strong food limitation of the summer dominant, Acartia tonsa. Empirical regressions describe relationships between A. hudsonica length and weight, and egg production in relation to temperature, weight, and field Chl a.

A separate study suggested that A. hudsonica adults were dominated by changing age groups during the winter–spring period. Present results indicate that the adult age distribution affects mean body weight, condition factor, and egg production rate, especially in April and May when the autumn‐hatched, overwintering copepods are being replaced by newly matured, winter–spring hatched adults.
Effects of temperature and food abundance on grazing and short‐term weight change in the marine copepod Acartia hudsonica
Authors: Durbin Edward G. , Durbin Ann G.
Published: April 2010

Ingestion and short‐term weight change in adult female Acartia hudsonica were investigated at 4.5°, 8°, 12°, and 16°C with the solitary diatom Thalassiosira constricta as food. Narragansett Bay copepods were preadapted to the desired temperature and saturating food level for 3 d to standardize feeding history before the experiments. Maximal ingestion rates at the four temperatures were 16,460, 14,120, 21,470, and 29,960 cells copepod‒1d‒1 or 43.9, 37.2, 67.9, and 92.9% body C(Q10 = 2.3) and 34.2, 30.7, 42.6, and 74.7% body N d‒1 (Q10 = 2.4). The critical concentration varied between 840 and 1,900 cells ml‒1 (0.17–0.23 µg C ml‒1) and was not significantly related to temperature. Maximal clearance rate was similar at all temperatures (20.8–23.9 ml copepod‒1d‒1), but on a weight‐specific basis increased from 3.3 to 6.0 ml (µg copepod C)‒1d‒1 between 4.5° and 16°C (Q10 = 1.8). Feeding rates at 4.5° and 8°C were similar; the seemingly low ingestion rates at 8°C were interpreted as evidence for a senescent population of adult copepods in the bay from late April to early May.

During preadaptation at high food, A. hudsonica body C and N either stayed constant (indicating saturating food in the field) or increased (indicating food limitation in situ). Body weight was sensitive to variation in food supply; during the 24‐h feeding experiments weight remained stable at the two highest food levels, but declined significantly at lower levels. Maximal observed weight loss was temperature‐dependent, increasing from ∼ 15% C and 12% N d‒1 at 4.5°C to 25% C and 17% N d‒1 at 16°C.
Seasonal changes in size frequency distribution and estimated age in the marine copepod Acartia hudsonica during a winter‐spring diatom bloom in Narragansett Bay
Authors: Durbin Ann G. , Durbin Edward G.
Published: April 2010

Seasonal changes in length frequency and estimated age distributions indicated that Acartia hudsonica adult females are dominated by successive age groups during the winter–spring bloom in Narragansett Bay. The biomass peak during March and April was composed of over‐wintering, late autumn‐spawned copepods. Winter‐spawned copepods entered the adult population during a brief period in late April to early May, and the influx of spring‐spawned copepods began during the second week of May. Concurrent studies of egg production and feeding suggested senescence of the adult population prior to the transition between the autumn‐spawned and the winter–spring‐spawned copepods. Thus population productivity may reflect not only environmental conditions, but also the age‐dependent physiological condition of the adults.

Modeling indicated that small interannual variations in temperature (±1°C) will significantly affect development rate and maturation of A. hudsonica during winter and spring. The 2°C temperature range corresponded to a 3‐week shift in the timing of peak maturation and could significantly alter the intensity of grazing and degree of coupling between primary producers and herbivores during the spring bloom.
A microencapsulation technique for introducing pure compounds in zooplankton diets
Authors: Cary S. C. , Lovette J. T. , Perl P. J. , Huntley M. E. , Vernet M.
Published: April 2010

Sodium alginate microcapsules have low permeability, high digestibility, and are specifically suited as artificial food particles for zooplankton. The microcapsules may be used to introduce pure compounds into zooplankton diets and to study the biochemical fate of those compounds. We encapsulated a highly labile molecule, Chl a, and traced it and its principal degradation products in zooplankton grazing experiments. Chlorophyll was not degraded or lost during the encapsulation procedure and remained stable for at least 6 d at 4°C in the dark. The microcapsules were ingestible and digestible by female Calanus pacificus, and fecal pellets were formed at normal rates, 40–60 min after ingestion. Two quantitative feeding experiments were conducted with pure chlorophyll. The mean loss of ingested pigment was 85.9% (±7.2%) and 76.1% (±6.1%). In the second experiment, we analyzed the medium to determine if any chlorophyll may have gone into solution; <2% of the total “lost” chlorophyll went into solution. We conclude that a significant amount of ingested Chl a is degraded into non‐fluorescent compounds during passage through copepod guts.
A random encounter model for the microbial planktonic community
Authors: Kiefer Dale A. , Berwald Juli
Published: April 2010

The numeric concentration of procaryotic and eucaryotic cells that form the planktonic microbial community decreases monotonically and rapidly with increasing size. This size distribution has been interpreted to be the result of allometric control of growth and respiration rates, but we propose an alternative “random encounter” hypothesis to explain such a distribution. According to this hypothesis, the size distribution of cells that range from 0.3 to 100 µm results from size‐selective predation by protozoans. A phagotrophic population will swim randomly through the water encountering both prey and predators. At steady state, such a population must ingest smaller prey at a sufficient rate to balance its rate of loss to larger predators. The size distribution of cells must, therefore, satisfy this condition. In particular, a mathematical statement of the hypothesis is based on the following relationships: volume of a cell varies as the cube of its diameter; clearance rate (L3T−1) by a predator varies as the square of its diameter; and, for a given population, its range of possible prey sizes varies with its prey diameter at the same time that the range of predator sizes able to capture the given population varies with its predator diameter.
Does energy control the sinking rates of marine diatoms?
Authors: Waite Anya M. , Thompson Peter A. , Harrison Paul J.
Published: April 2010

There is an energy requirement for the maintenance of low sinking rates (<0.1 m d−1) in the marine diatom Ditylum brightwellii. The lowest sinking rates occurred when cells were grown under irradiances saturating for growth. The highest sinking rates occurred when cells grown at growth‐limiting irradiances were placed in the dark, or in cells treated with a respiratory inhibitor. Small cells sank more rapidly than large cells under saturating light, but under severe energy limitation sinking rates were directly proportional to cell volume. When cells were grown under saturating irradiance and then placed in the dark, their sinking rate increased as their respiration rate decreased over time. We suggest that when light is unavailable, a diatom’s ability to use energy gained from respiration may be the principal determinant of its sinking rate. We provide the first estimate of the dependence of cell sinking rate on cell respiration and suggest that the sinking‐respiration relationship may be useful in predicting the sinking dynamics of diatoms during a bloom. We speculate that energetic sinking control may have evolved to allow diatoms to colonize the photic zone and that larger diatoms with lower sinking rates may have an ecological advantage over smaller diatoms with higher sinking rates early in a bloom.