bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of gross growth efficiency and ammonium regeneration in bacteria by substrate C: N ratio1
Authors: Goldman Joel C. , Caron David A. , Dennett Mark R.
Published: April 2010

Natural assemblages of marine bacteria were cultured on combinations of C and N sources (amino acids, glucose, and NH4+) to span a range of substrate C : N ratios from 1.5 : 1 to 10 : 1. Catabolic metabolism of the N component of amino acid substrates led to NH4+ regeneration during exponential growth. The efficiency of this regeneration (RN) and also of the carbon gross growth efficiency (GGE) generally was independent of the sources of C and N, but increased as the C : N ratio of the substrate (C : NS) decreased relative to the C : N ratio of the bacterial biomass (C : NB). The elemental chemical composition (C : N : P ratio) of the bacterial biomass was relatively invariant at about 45 : 9 : 1 and the gross growth efficiency varied from a threshold value of about 40–50% at C : NS > 6 : 1 up to 94% when C : NS was 1.5 : 1. Hence, Rn varied from 0% when C: NSwas 10 : 1 up to 86% when C : NS was 1.5 : 1. Inorganic sources of both N and P were taken up only in stoichiometric quantities during this phase of growth. Regeneration of NH4+ during the stationary phase as well as of PO43− occurred, most likely due to endogenous metabolism or cell death, but the magnitude of this regeneration seemed to increase greatly only when C : NS was > 6 : 1. Considering that amino acids frequently do not provide all of the N required and that carbohydrates often are the major C source for growth of marine bacteria, we speculate that C: NS of available substrates in marine waters is > 10 : 1. Hence, actively growing bacteria may be inefficient remineralizers of N.
Simulating chemosensory responses of marine microorganisms1
Authors: Jackson George A.
Published: April 2010

I have studied the nature of chemosensory interactions in situations relevant to aquatic ecosystems by incorporating a model of chemokinesis by laboratory bacteria into a Monte Carlo simulation of bacterial movement around leaky microalgae. I assumed that the concentration field of the substrate around an alga is determined by molecular diffusion. Results of simulations and various theoretical arguments imply that there is a smallest organism size with a radius >2 µm which bacteria can find using chemosensory responses. Bacteria most easily find algae that are large and have a high specific leakage rate. Because its feeding also involves chemosensing of food items, a copepod’s observed inability to feed on small algae may also be the result of its inability to sense this potential food. The lack of sensory mechanisms to detect small organisms at a distance implies that the sensing of small organisms must, by default, involve physical contact. This inference agrees with filtration mechanisms noted for microzooplankton feeding.
Positively charged suspended particles: Studies in an iron‐rich river and its estuary1
Authors: Newton Philip P. , Liss Peter S.
Published: April 2010

Natural particles in suspension in fresh, marine, and estuarine surface waters generally display a narrow range of negative electrophoretic mobilities. The measured mobilities are thought to be controlled by organic and oxide surface coatings, and there is considerable evidence for control by the organic coatings. Here we present results which indicate that oxide‐hydroxide coatings can control the mobility under conditions found in a river fed by acid‐mine drainage, but that organic coatings, when present, assume overall mobility control. Electrophoretic measurements show positively charged river particles acquiring less positive and then negative charges in estuarine waters. In the river and at low salinities mobility is affected by the pH of the water. At higher salinities the oxide‐hydroxide character is less evident, and particles assume the negative mobilities normally found in natural waters and attributed to organic surface coatings.
Origin and composition of surface slicks in lakes of differing trophic status1
Authors: Södergren Anders
Published: April 2010

The chemical and biological composition of freshwater microlayers was followed in surface slicks of eutrophic, oligotrophic, and dystrophic lakes and compared with conditions in the subsurface water. The slicks were sampled with a revolving cylinder coated with hydrophilic Teflon which collected a layer that ranged in thickness from 23 to 48 µm when collected at surface pressures of 3–8 mN m−1. The levels of organic and inorganic residues in the slicks were generally higher than those in the subsurface water. POC was enriched to a significantly greater extent in the dystrophic lake than in the three other lakes, but no relationship between trophic status and DOC enrichment was noted. Dissolved lipids were enriched by factors of 2.6–5.2 but represented only a minor fraction of the DOC content (~ 5%) of the microlayer. The DOC: DON ratio, color, UV absorbance, and fatty acid composition of the slicks suggested that most of the microlayer components were derived allochthonously. Combining the results of chemical and biological observations suggests that olizotrophic lakes may be partly covered by a thin layer of water with eutrophic properties.
Accuracy and precision of secondary production estimates1
Authors: Morin Antoine , Mousseau Timothy A. , Roff Derek A.
Published: April 2010

We used computer simulations to examine the accuracy of the increment‐summation, instantaneous‐growth, Allen curve, and size‐frequency estimates for various growth and mortality functions, patterns of prolonged recruitment, and sampling efforts; describe the sampling distribution of the estimates for aggregated populations of stream benthos; and test the reliability of parametric and nonparametric (bootstrap) confidence intervals for production estimates. Sampling schedule is critical for synchronous populations, and all methods underestimate true production when sampling intervals do not cover periods of intense production. The size‐frequency method tends to underestimate production of perfectly synchronous populations severely and is recommended only when cohorts are absolutely indistinguishable. Biases of cohort methods generally range from −30% to + 10% of true production. Sampling error of production estimates can range from −60% to +300% of true production for highly aggregated populations sampled with low effort and from −10% to + 10% at low aggregation level and high sampling effort. Published parametric and nonparametric confidence intervals are reliable only in the best circumstances (i.e. when aggregation is weak and sampling effort is high). Reliable confidence intervals can be obtained for the Allen curve estimate of production if the raw data can be transformed to stabilize the variance of density estimates and to linearize the relationship between density and mean individual mass.
Concurrent grazing effects of two stream insects on periphyton1
Authors: Hill Walter R. , Knight Allen W.
Published: April 2010

The grazing effects of caddisfly larvae (Neophylax) and mayfly nymphs (Ameletus) were measured in Barnwell Creek, a second‐order stream in northern California. The densities of these grazers were manipulated in situ with flow‐through Plexiglas channels that contained natural cobble substrate. After 13 d, log‐transformed measures of periphyton standing crop (ash‐free dry matter, chlorophyll a, and algal biovolume) were inversely proportional to Neophylax biomass. The negative effect of caddisfly larvae on algal biomass resulted primarily from depletion of Epithemia sp. 1, an undescribed diatom species that accounted for most of the algal biovolume in the periphyton. Neophylax guts contained disproportionately large numbers of Epithemia sp. 1. Ameletus had no significant effect on overall Chl a or algal biovolume but substantially decreased the biovolume densities of Nitzschia spp., Synedra spp., Amphipleura pellucida, and Melosira varians. Ameletus guts contained disproportionately large numbers of a small Nitzschia species. Neophylax growth in the channels was density‐dependent, implicating intraspecific competition for food. Periphyton from the unmanipulated streambed resembled periphyton in experimental channels stocked with natural densities of grazers, allowing extrapolation of experimental results to the unmodified stream.
Seasonal variation of the surface chlorophyll distribution along the British Columbia coast as shown by CZCS satellite imagery
Authors: Pan D. , Gower J. F. R. , Borstad G. A.
Published: April 2010

A series of 40 satellite images from the Coastal Zone Color Scanner (CZCS) on the Nimbus‐7 satellite is used to examine variation of the surface phytoplankton distribution along the coast of British Columbia from March to October 1979. Coverage is limited by cloud and restricted scheduling of satellite observations, but the images show the major patterns of the spring bloom, the subsequent high phytoplankton levels on and near the continental shelf, and large‐scale phytoplankton patterns farther offshore. Occasional cloud‐free images show eddies, fronts, and filaments in great detail. Over intervals of a few days, the boundary of the more highly pigmented coastal water is displaced offshore at a rate that appears correlated with the local Bakun upwelling index. Values of chlorophyll concentration derived from the satellite data are in agreement with ship data collected near the coast to within ±40% over the range 0.5–3 mg m−3 but seem to underestimate the much higher values (up to 20 mg m−3) recorded in ship observations on the continental shelf.
The marine cladoceran Penilia avirostris and the “microbial loop” of pelagic food webs1
Authors: Turner Jefferson T. , Tester Patricia A. , Ferguson Randolph L.
Published: April 2010

We used quantitative microscopy to examine feeding of Penilia avirostris on natural (<1 µm) and cultured (0.5–2.0 µm) bacterioplankton, autotrophic phytoplankton, heterotrophic microflagellates (2–5 µm), and bacteria‐sized (0.2–1.0 µm) fluorescent beads. Natural and cultured bacterioplankton were not appreciably ingested, except for extremely high concentrations (>9.0 × 106 cells ml−1) of clumped cells from bacterial cultures. Bacterivorous microflagellates were ingested. Most species of available natural phytoplankton (chain‐forming or large diatoms) and Pseudoisochrysis paradoxa (5–6 µm) were not ingested, but the 4–6‐µm diatom Thalassiosira pseudonana and the 10–12‐µm Thalassiosira weissflogii were. Food choice and feeding rate appeared related to food concentration as well as cell size. Our results contrast with previous reports of bacterivory by P. avirostris and other cladocerans, possibly due to preferential bacterivory on large or aggregated bacteria, elevated bacterial abundance levels in cultures, or failure to recognize heterotrophic microflagellates as an unseen intermediate trophic step in studies with nonmicroscopic techniques. Although P. avirostris does not feed on free‐living bacterioplankton, it may be an important component of the “microbial loop” between bacterioplankton and higher consumers because of its predation on bacterivorous microflagellates.
Underice grazing by planktonic, calanoid copepods in relation to a bloom of ice microalgae in southeastern Hudson Bay
Authors: Runge Jeffrey A. , Ingram R. Grant
Published: April 2010

A spring bloom of ice microalgae was observed at a station on southeastern Hudson Bay. Levels of pheopigments in guts of females of Calanus glacialis and Pseudocalanus spp., the dominant calanoid copepods in this region, increased by an order of magnitude after onset of the bloom. Feeding had a diel cycle and was associated with a nighttime migration of females to the ice‐water interface. Fragments of pennate, ice diatoms were observed microscopically in most guts of Calanus and Metridia, but only rarely in Pseudocalanus, which may have been feeding on flagellates associated with the ice‐water interface. The results suggest that ice microalgae in Hudson Bay are a regular and significant source of nutrition for planktonic copepods before the phytoplankton bloom. The structure of the layer at the ice‐water interface may influence feeding behavior on ice microalgae by arctic copepods.
Manganese oxidation in pH and O2 microenvironments produced by phytoplankton1,2
Authors: Richardson Laurie L. , Aguilar Carmen , Nealson Kenneth H.
Published: April 2010

Pure cultures of Chlorella sp. catalyzed the oxidation of soluble Mn(II) to particulate, extracellular, manganic oxides. Manganese oxidation was dependent on photosynthetic activity: no oxidation was observed in the dark when cells were grown heterotrophically on glucose, or in the light when photosystem II was inhibited by the addition of DCMU. Manganates were not formed when media were buffered below pH 8.0, suggesting that an important driving force for manganese oxidation was the high pH resulting from photosynthesis. Field studies with minielectrodes in Oneida Lake, New York, demonstrated steep gradients of O2 and pH and the presence of particulate manganic oxides associated with pelagic aggregates of the cyanobacterium Microcystis sp. The manganese oxidation reaction apparently occurs only when photosynthesizing algae are present as dense populations that can generate microenvironments of high (>9.0) pH, either as aggregates in the pelagic zone or concentrated cell cultures in the laboratory. A large‐scale transition from soluble to particulate manganese was measured in the surface waters of Oneida Lake throughout summer 1986. Removal of Mn(II) was correlated with the presence of aggregate‐forming cyanobacteria that oxidize Mn(II) by the mechanism described above.
Patterns of sulfate reduction and the sulfur cycle in a South Carolina salt marsh1,2
Authors: King Gary M.
Published: April 2010

Rates of sulfate reduction and the magnitude of various sediment parameters related to the sulfur cycle were measured at about quarterly intervals for a 3‐yr period at sites in a South Carolina salt marsh containing tall‐ or short‐form Spartina alterniflora. Sulfate reduction rates were greater at all times in the short‐form sites and decreased markedly with depth. Seasonal changes were highly correlated with ambient temperature except in May and August when interactions with plants may have affected rates directly. In the short‐form site, the annual integrated sulfate reduction rate accounted for about 47.5–67.0% of the estimated belowground plant production. Dissolved sulfides and pH varied seasonally in the short‐ but not tall‐form sites; seasonal minima in the short‐form site occurred during May and were probably due to oxidation of the sediment with the onset of plant production. Mechanisms resulting in oxidation were not evident however. Chromium‐reducible sulfur, which is primarily pyrite, was substantially greater in the tall‐ than short‐form site but apparently stable temporally at both sites. The differences in pool sizes of pyrite were probably due to differences in iron dynamics and the extent of sulfide oxidation. Microprofiles of dissolved oxygen were consistent with greater oxidation at the short‐form site since the penetration of oxygen was deeper. Differences in sediment texture and tidal inundation may have contributed to greater oxygen inputs at the short‐form site.
Discrimination between algae and artificial particles by freshwater and marine copepods1
Authors: DeMott William R.
Published: April 2010

Chemically mediated food selection was studied with combinations of living algae and algal‐flavored and untreated polystyrene spheres. The freshwater calanoid Eudiaptomus exhibited a strong preference for flavored spheres over untreated spheres when algae were scarce, but ingested few spheres of either type when algae were abundant. Experiments using a “zooplankton sandwich technique” revealed a distinct ranking of preference: 6‐µm Chlamydomonas >6‐µm Chlamydomonas‐flavored spheres >6‐µm untreated spheres. Consistent with foraging theory, Eudiaptomus very strongly selected algae over flavored spheres when algae were abundant but was less selective when algae were scarce.

Sandwich experiments revealed differences in selectivity among individuals and between species of marine and freshwater zooplankton. In experiments with 12‐µm algae and untreated 12‐µm spheres, Eudiaptomus was highly selective, ingesting about 1,000 × more algae than spheres, whereas the cladocerans Daphnia and Sida fed nonselectively. The marine copepod Temora longicornis was less selective than Pseudocalanus sp., and both marine copepods were less selective than Eudiaptomus. These complex foraging patterns emphasize the need for carefully designed experiments with mixtures of natural particles of differing nutritional quality.
Effect of microhabitat features, seston quality, and periphyton on abundance of overwintering black fly larvae in southern Québec1,2
Authors: Morin Antoine , Peters Robert H.
Published: April 2010

Maximum biomass of overwintering larvae of simuliids before emergence was measured in 34 riffles from 16 lake outlets in southern Québec in April 1985. Biomass was correlated with measurements of current velocity, water depth, periphyton abundance, distance from the lake, and indices of seston quantity and quality. The quantity of seston tended to increase with distance from the lake mainly because of an increase in inorganic material. Seston quality, as measured by chlorophyll concentration, protein concentration, and chlorophyll and protein content per unit of mass of seston, tended to decrease with increasing distance from the lake. Chlorophyll concentration in the water and in the seston and protein content of the seston were the best correlates of black fly biomass in these sites. Multiple regression models were used to describe the microdistribution of the three species of simuliids present (Prosimulium mixtum/fuscum, Stegopterna mutata, and Simulium vitatum). Biomass of all three species varied with distance from the lake, current velocity, water depth, and chlorophyll concentration. In addition, both Prosimulium and Stegopterna biomasses were negatively correlated with standing stocks of periphyton. A large‐scale model predicting mean biomass in riffles was also constructed with distance from the lake, mean current velocity and depth, and a topographic estimate of lake trophy. This model was successfully validated on an independent data set collected in 1984 from 32 riffles in seven lake outlets.
Spatial patchiness in the lacustrine sedimentary environment1
Authors: Downing John A. , Rath Laurel C.
Published: April 2010

Spatial patchiness of sediment characteristics in central, bathymetrically uniform sites in eight lakes was examined by comparison of within‐ and among‐core variation in water, organic matter, pigment, and phosphorus concentrations. Sampling sites were chosen to avoid known sources of sediment heterogeneity. Regression analysis of within‐core and among‐core variance on mean sediment characteristics was used to examine sampling exigencies. Comparisons of microscale and analytical variation with variation in sediment characteristics among core samples, within sites, showed significant (P < 0.05) sediment heterogeneity in >62% of the comparisons. All sediment characteristics and all sampling sites showed some significant heterogeneity. The variance in sediment characteristics among core samples, within sites, was from 2 to 320 times greater than analytical or microscale variation. Spatial heterogeneity might result from aggregated benthic animals, slow currents, or small‐scale variations in bottom profile.
Coupling between ammonium uptake and incorporation in a marine diatom: Experiments with the short‐lived radioisotope 13N
Authors: Zehr Jonathan P. , Falkowski Paul G. , Fowler Joanna , Capone Douglas G.
Published: April 2010

The coupling between ammonium transport and incorporation in the neritic marine diatom Thalassiosira pseudonana (3H) was investigated with the short‐lived radioisotope 13N (t½ = 9.96 min). In ammonium‐limited continuous cultures, growing at rates from 0.2 to 3.2 d−1, no trend in uptake rates per cell was apparent, but the rate of incorporation of radiolabeled ammonium into trichloroacetic acid (TCA)‐insoluble material, following a saturating pulse of ammonium, was linearly correlated with growth rate (r2 = 0.93). Calculated growth rates overestimated the measured rates. The ratio of calculated growth requirements (μQ) to growth requirements based on incorporation of 13N into TCA‐insoluble material (µq) was nonlinearly related to growth rate. The discrepancy between µQ and µq was explained by isotope dilution in the internal free amino acid pool. The ratio of uptake to incorporation, corrected for isotope dilution in the amino acid pool, showed that uptake and growth were uncoupled at low growth rates but were coupled at µmax. The ratio of short‐term uptake to incorporation was found to be a direct measure of enhanced uptake and decreased with increasing growth rate. This ratio may be a useful parameter for determining growth rates and nitrogen deficiency in natural phytoplankton communities.
Uptake of urea C and urea N by the coastal marine diatom Thalassiosira pseudonana
Authors: Price Neil M. , Harrison Paul J.
Published: April 2010

Urea uptake rates of Thalassiosira pseudonana (clone 3H) were determined using [14C]urea, [15N]urea, and by measuring disappearance of dissolved urea from the medium after adding 10 µg‐atoms urea‐N liter−1. In nitrate‐sufficient cultures, the average [14C]urea uptake rate was 60% of the urea disappearance rate. Nitrate uptake continued in the presence of urea at a reduced rate, and only 15% of the urea N taken up was retained by the phytoplankton. The increase in PON during incubation was roughly equal to the total NO3 and urea N taken up. Average urea uptake rates measured by all methods in 24‐h nitrate‐starved cultures were in excellent agreement with the rate of increase in PON during a 1‐h incubation. Uptake rate of [14C]urea and disappearance rate of urea were constant and equal. In neither nitrate‐sufficient nor nitrate‐starved cultures were [15N]urea uptake rates constant, with maximal rates measured 5–15 min after the addition of urea. Ammonium was released by T. pseudonana following uptake of urea and was then taken up. A model of urea uptake and assimilation by T. pseudonana that involves efflux of urea N as NH3 and its rapid reabsorption is proposed. These results can explain previous observations and have implications for utilization and cycling of urea N by phytoplankton in nature.
Phosphorus flux from lake sediments: Effect of epipelic algal oxygen production
Authors: Carlton Richard G. , Wetzel Robert G.
Published: April 2010

Previous studies utilizing oxygen‐sensitive microelectrodes have demonstrated that as a result of epipelic algal photosynthesis and microbial metabolism, and regardless of the oxygen concentration of the overlying water, sediments within the euphotic zone of lakes undergo marked diel fluctuations in the extent of oxygen penetration. This investigation utilized oxygen‐sensitive microelectrodes,32PO43− radiotracer, and a novel flow‐through system to examine the effect of epipelic algal photosynthesis on sediment oxygen dynamics and the concomitant pattern of phosphorus release from lake sediments. Epipelic algae mediated release of phosphorus from sediments to overlying water via daily formation and breakdown of the oxidized microzone. During illumination, surficial sediments rapidly became oxygenated, and release of phosphorus diffusing from deeper sediment layers was inhibited. During darkness the microzone became anoxic, and phosphorus was released to overlying water at an accelerated rate, producing marked diel fluctuation in efflux rate. Observed patterns of release are consistent with recent evidence for a mechanism consisting of rapid uptake or release of dissolved phosphate by sediment microorganisms in response to respective oxic or anoxic conditions.
Secondary production and trophic relationships in a spring invertebrate community
Authors: Iversen Torben Moth
Published: April 2010

The invertebrate fauna of a shaded area of the Danish spring Rold Kilde was sampled for a year. There was a large input of allochthonous beech litter, and the water trickled between waterlogged beech leaves. Discharge was constant and temperature amplitudes were small. Primary consumer biomass and production were 3.24 g AFDM m−2 and 8.65 g AFDM m−2 yr−1 and were dominated by shredders (70 and 69%) and gathering collectors (29 and 30%). The seasonal variation in shredder biomass and production was considerably larger within each shredder species than within the total shredder population, implying a relatively uniform processing of energy during the year. The shredder community processed about half of the total leaf input. The primary consumer P : B̄ was as low as 2.67 yr−1 due to many species with long life cycles. Average P : B̄ for eight univoltine species and five semivoltine species was as low as 3.6 and 2.3 yr−1, mainly due to low rates of elimination. Invertebrate biomass and production in low‐order streams are compared, and it is concluded that streams with a shading canopy have a significantly lower mean biomass, production, and P : B̄ ratio than streams of similar order with reduced or no canopy.
Convective circulation in littoral water due to surface cooling
Authors: Horsch G. M. , Stefan H. G.
Published: April 2010

Cooling of littoral waters of a lake under calm conditions creates a horizontal temperature gradient because surface heat loss is distributed over progressively larger depth by plunging sheets (thermals). Resulting convective circulation establishes an exchange flow between littoral and open waters. Numerical simulations illustrate the development of the flow from the formation of thermals to the establishment of a horizontal circulation. Circulation flow rate was found to be proportional to ℛ1/n, 2 < n < 3 (ℛ is the Rayleigh number) for values in the range 104–108. A laboratory visualization experiment at ℛ ∼ 109 confirmed the main features of the simulation. To consider applications to vegetated littoral slopes, we interpreted the results with a formula accounting for the added resistance offered to the flow by the aquatic plants. An example showed that convective circulation can be a significant factor in renewing littoral waters.
A simple model for predicting the date of fall turnover in thermally stratified lakes
Authors: Nürnberg Gertrud K.
Published: April 2010

The date of fall turnover c.an be predicted from average midsummer hypolimnetic temperature in acidic and non‐acidic lakes in central Ontario. The prediction of fall turnover date is improved by inclusion of two further independent variables, mean depth (z̄) and adjusted latitude (for altitude), in a global data set (ranges of z̄, 1.1–86 m; adjusted latitude, 38°–65°). The models explain 67–80% of the variance of fall turnover date and are potentially useful in the design of monitoring programs and for predicting impacts of anthropogenic activities that influence lake thermal budgets, e.g. diversion for cooling waters or damming of cold inflows.
Indirect prey effects: Some morphological and life history responses of Daphnia pulex exposed to Notonecta undulata1
Authors: Dodson Stanley I. , Havel John E.
Published: April 2010

Although protected by enclosures from direct contact, three clones of Daphnia pulex respond similarly to the presence of the predator Notonecta undulata by producing small eggs and offspring having a 3.7% reduction in growth per instar, compared to Daphnia grown in the absence of Notonecta. Primiparous adults were 15% shorter in the presence of Notonecta. Predator enclosure experiments showed that the decrease in prey body size was not due to direct size‐selective predation. Results of experiments in which water was pumped from predator cultures to D. pulex clone SBL cultures suggested that the signal is carried by water, possibly a water‐soluble chemical, produced by actively feeding Notonecta. This “prey response” to Notonecta includes a smaller adult and neonatal body size, a lower lipid index, a shorter developmental time from neonate to adult, and no change in the clutch size or the percent survival, compared to predator‐absent controls. Food level had a complex effect on prey response: at low food levels the prey response disappeared. These morphological and developmental prey responses suggest that previous field experiments of predation and competition may have been improperly designed, that the lipid index depends on the presence of a predator as well as food concentration, and that secondary productivity based on the Edmondson egg ratio technique may be underestimated in the presence of predators.
Response of Anabaena and Synechococcus to manipulation of nitrogen: phosphorus ratios in a lake fertilization experiment
Authors: Stockner John G. , Shortreed Ken S.
Published: April 2010

Additions of inorganic nitrogen and phosphorus to selected areas of oligotrophic Kennedy Lake began in 1978 and resulted in development of late‐summer blooms of the nitrogen‐fixing cyanobacteria Anabaena circinalis in 1981 and 1982. In subsequent years the blooms were successfully eliminated by increasing the molar N : P ratio of added nutrients to 35 : 1. The nutrient additions also resulted in dramatic increases in both autotrophic (predominantly Synechococcus sp.) and heterotrophic (bacteria) picoplankton numbers, with respective maxima of 4.0 × 105 ml‒1 and >4.0 × 106 ml‒1. Chlorophyll concentrations were generally <2 µg liter‒1 during untreated conditions and increased to as much as 50 µg liter‒1 during blooms. In the years following the Anabaena blooms, hypolimnetic nitrate concentrations were significantly higher in the treated basin of the lake than they were in an adjacent untreated basin or than they were before the blooms. Development of nitrogen‐fixing cyanobacteria blooms is dependent on both a low N: P supply ratio and a sufficient phosphorus supply.
The effect of the Mt. Mazama ashfall on the planktonic diatom community of Lake Washington1
Authors: Abella Sally E. B.
Published: April 2010

Preserved diatom assemblages are found in deep water sediments in Lake Washington above and below an ash layer originating from an eruption of Mt. Mazama 6800 b.p. Total abundance of frustules did not change after the ash event, but a significant shift in community structure occurred. Melosira italica var. subarctica increased after the ashfall, and Fragilaria crotonensis decreased. The changes most likely indicate an increase in the Si: P ratio and decreased light penetration in the euphotic zone during winter and spring.
Alona weinecki Studer on the subantarctic islands, not Alona rectangula Sars (Chydoridae, Cladocera)1
Authors: Frey David G.
Published: April 2010

Since Harding in 1967 named the Alona on Signy Island (South Orkneys) Alona rectangula, this binomen has persisted there and has been extended to other island groups in the Scotia Arc. Elsewhere among the subantarctic islands the binomen Alona weinecki has been used, based on a description in 1878 and a redescription in 1914. A detailed redescription of A. rectangula from Norway and Denmark permitted comparison with available populations of A. weinecki from Signy and South Georgia and of the synonymous taxa Alona bukobensis var. subantarctica and Alona subantarctica. The two taxa, although related, are completely different. Alona rectangula sens. str. does not occur on the subantarctic islands at all.

Whether the A. weinecki populations on these islands are the same species is presently unknown. Specimens on Kerguelen Island are reported to be larger than those on the Scotia Arc islands, and among the latter populations there are differences in structure of at least the labrum. The islands in the Scotia Arc, except the Falklands, were completely ice covered during the last glacial age, with documented advances and retreats of the glaciers during the Holocene until 2000 b.p. Conditions on at least some other subantarctic islands were probably comparable. If the Cladocera were eliminated by glacier advances, the islands must have been recolonized during the Holocene from a refugic population, possibly in the Falklands. Strong westerly winds and migration of sea birds might have spread the taxon. If the populations are different, however, then the taxa must have survived on their respective islands during the glacial ages. Large populations containing ephippial females and the three instars of males are needed to resolve this uncertainty.

Lectotypes of A. rectangula Sars, A. bukobensis var. subantarctica Ekman, and A. subantarctica Ekman have been selected and are on deposit in the Zoological Museums in Oslo and Stockholm.
Epidemiology and Medical Mycology of Fungal Rhinosinusitis
Authors: Chatterjee Shiv Sekhar , Chakrabarti Arunaloke
Published: April 2010

Fungal rhinosinusitis (FRS) refers to a spectrum of disease ranging from benign colonization of the nose and sinuses by pathogenic fungi to acute invasive and fatal inflammation extending to the orbit and brain. FRS is classified into two categories: invasive and noninvasive. Invasive FRS may again be subcategorized into acute invasive (fulminant) FRS, granulomatous invasive FRS, and chronic invasive FRS; while noninvasive FRS is subcategorized into localized fungal colonization, sinus fungal ball and eosinophil related FRS (including allergic fungal rhinosinusitis, eosinophilic fungal rhinosinusitis). This classification is not without controversies, and intermediate and semi-invasive forms may also exist in particular patients. Acute invasive FRS is an increasingly common disease worldwide among the immunocompromised patients and caused most frequently byRhizopus oryzae, andAspergillusspp. Granulomatous invasive FRS has mostly been reported from Sudan, India, and Pakistan and is characterized by noncaseating granuloma formation, vascular proliferation, vasculitis, perivascular fibrosis, sparse hyphae in tissue, and isolation ofA. flavusfrom sinus contents. Chronic invasive FRS is an emerging entity occurring commonly in diabetics and patients on corticosteroid therapy, and is characterized by dense accumulation of hyphae, occasional presence of vascular invasion, sparse inflammatory reaction, involvement of local structures, and isolation ofA. fumigatus. While localized fungal colonization describes the most benign of all fungal sinusitis in the superficial nasal crusts, sinus fungal ball is a dense mycetoma like aggregate of fungal hyphae in diseased sinuses. Common in southern Europe, especially France, majority of them are sterile on culture while 30-50% may yieldAspergillusspp. The definitions and pathogenesis of the group of syndromes in eosinophil related FRS (AFRS, EFRS) are contentious and a matter of intense research among otolaryngologists, pathologists, immunologists and microbiologists. While dematiaceous fungi are the foremost initiators of these syndromes in the west,Aspergillus flavusis the predominant pathogen in India and the Middle-East.
Invasive Fungal Sinusitis: An Overview
Authors: Sant Kailashnath
Published: April 2010

Currently two main categories of fungal sinusitis are described; invasive and noninvasive. The invasive type can be; 1. Acute, fulminant, 2. Chronic, indolent, and 3. Granulomatous type. The noninvasive types are more common of which Allergic fungal sinusitis is commonly present in almost all extensive polyposis cases in India. The other noninvasive type is mycetoma or fungal ball, which carries the best prognosis if treated surgically well. The acute invasive fugal infection of sinuses by mucormycosis is an aggressive opportunistic infection caused by phycomycetes, first described in 1885 by Paltauf. The genera most commonly causing mucormycosis are Mucor or Rhizopus. Sinus and nasal infection by mucor causes orbitocerebral spread. Other organs involved are the lungs, GI tract and skin. Rhinorbito-cerebral mucormycosis has a mortality rate as high as 50%, since they occur in immunocompromised state like uncontrolled diabetes, metabolic acidosis, chronic renal failure, AIDS, leukemia, etc.
Intracranial Extension of Fungal Sinusitis
Authors: Rathore Anamika , Shah Nishit J
Published: April 2010

Intracranial extension is the most dreaded complication of fungal sinusitis with high mortality rates. Fungal sinusitis is notorious for insidious and rapid intracranial spread. Therefore the most appropriate approach lies in timely diagnosis and early intervention.

With various diagnostic modalities available; like CT scan, MRI, fungal stains, cultures and nasal endoscopy, the diagnosis has become much simpler, nevertheless, a high degree of clinical suspicion is a must.

The treatment outcomes have now improved a lot, with the advancement in medical and surgical technology. The new antifungal agents and other drugs have immensely contributed to better results by minimizing the toxic side effects of the traditional drugs and showing better efficacy. The surgical approach, with the advent of endoscopes has led to successful outcomes.

Despite this, in about 50% of the cases, since the host is immunocompromised, the prognosis is guarded and mortality rates of approximately 85 to 100% are noted.

So, it is very important to treat intracranial extension of fungal sinusitis as a medical and surgical emergency.
Postoperative Radiotherapy in Head and Neck Cancer
Authors: Murthy Vedang , Kundu Sayan , Shahid Tanweer , Budrukkar Ashwini , Gupta Tejpal , Laskar Sarbani Ghosh , Agarwal Jaiprakash
Published: April 2010

Though early stage head and neck cancers can be cured either by surgery or radiation, patients with locally advanced disease continues to pose a therapeutic challenge. Locoregional failure is the major cause of death in head and neck cancers. As the outcome of locally advanced head and neck cancer is less than promising, a combined modality approach is generally undertaken in this group of patients. The combination of surgery, radiation and more recently, chemotherapy and targeted therapy can improve outcomes in locally advanced head and neck cancer patients. This overview discusses the rationale and role of postoperative radiotherapy (PORT) in advanced head and neck cancers, the radiotherapy technique in brief and methods of enhancing the efficacy of postoperative RT by altering the fractionation schedules and adding chemotherapy and targeted therapy.
Complications in Head and Neck Surgery
Authors: Pai Prathamesh S
Published: April 2010

Surgical outcomes are more or less predictable with a reasonable degree of accuracy. Head and neck surgery has potential for many complications due to presence of a large number of major vessels and nerves. In head and neck surgery, complications can arise due to airway compromise, vascular injury, infections and rarely physiologic causes. Carefully performed surgery is the cornerstone of success. Step by step approach with attention to details and a thorough check after completion of the procedure will ensure optimal results without complications.
Transoral Laser Microsurgery for Malignancies of the Upper Aerodigestive Tract
Authors: Durel Jason , Gaudet Jacques , Kunduk Melda , McWhorter Andrew J
Published: April 2010

Transoral laser microsurgery (TLM) is an important option in the treatment plan for tumors of the oral cavity, oropharynx, larynx, and hypopharynx. For properly selected patients, TLM provides equivalent oncologic outcomes when compared to traditional therapies, while improving the functional aspects of postoperative speech, voice and swallowing.
Sequential Screening with Cytology and Colposcopy in Detection of Cervical Neoplasia
Authors: Desai BR , Malur PR , Anita Dalal , Geeta Durdi , Bhavana Sherigar , Pallav Gupta
Published: April 2010

Background

Pap smear is the most commonly used screening test for cervical cancer, however it has disadvantage of having low sensitivity. Colposcopy has higher sensitivity as compared to Pap smear but low specificity. Sequential screening with both Pap smear and colposcopy can overcome these problems.

Aim

The study was aimed to find out the diagnostic efficacy of both Pap smear and colposcopy. It was also intended to find out the advantages of sequential use of Pap smear and colposcopy in screening for cervical cancer.

Design

It was a cross-sectional study conducted in colposcopy clinic of KLE's Dr. Prabhakar Kore Hospital and MRC, Belgaum from November 2006 to September 2008.

Material and methods

A total of 190 patients with complaints of postcoital bleeding, intermenstrual bleeding, postmenopausal bleeding, persistent vaginal discharge or those found to have an unhealthy cervix on per speculum examination were included in the study. In all the 190 cases Pap smear, colposcopic evaluation and colposcopic directed biopsy were performed.

Statistical analysis

Sensitivity, specificity, positive predictive value, negative predictive value of both Pap smear and colposcopy were calculated with histopathology as a gold standard, keeping LSIL as a disease threshold for test positivity.

Results

Pap smear was positive in 14.21% (27/190) cases, colposcopy was positive in 37.89% (72/190) cases. Biopsy confirmed LSIL and higher lesions in 31.57% cases. The sensitivity, specificity, positive predictive value and negative predictive value of Pap smear were 41.66%, 96.92%, 86.21% and 78.26% respectively and 80%, 81.54%, 66.66% and 89.83% respectively for colposcopy. Combined colposcopy and Pap smear could accurately diagnose 53/60 biopsy confirmed cases of LSIL and higher lesions with an accuracy of 88.33%.

Conclusion

Sequential use of Pap smear and colposcopy in screening for cervical cancer increases the accuracy of the test.
Letrozole versus Clomiphene Citrate in Patients with Anovulatory Infertility
Authors: Paul PG , Gada Dhiraj , Parihar Mandakini , Bhowmik Shravanti
Published: April 2010

Objective

To compare the effectiveness of letrozole and clomiphene citrate (CC) in patients with anovulatory infertility.

Design

Open, prospective, randomized, parallel group, multicentric, comparative trial.

Setting

Outpatient clinics of infertility centers in India.

Patient(s)

Fifty-five patients with anovulatory infertility were recruited. Twenty-seven patients (59 cycles) were given letrozole and twenty-eight patients (68 cycles) were given CC. Both drugs were given orally on days 3-7 of menstrual cycle.

Intervention(s)

Letrozole, CC, ovulation induction, vaginal micronized progesterone, IUI.

Main outcome measure(s)

Occurrence of ovulation, endometrial thickness and pregnancy rates.

Result(s)

Ovulation occurred in 77.9 % (46/59) of letrozole cycles and in 80.9 % (55/68) of CC cycles. The mean endometrial thickness on the day of human chorionic gonadotropin administration was 9 mm in letrozole group and 8.76 mm in the CC group. Pregnancy rate per cycle was 11.9 % (7/59) in the letrozole group and 8.8 % (6/68) in the CC group.

Conclusion(s)

Letrozole and CC have comparable effectiveness in anovulatory infertility patients. Letrozole may be an acceptable alternative to CC as an ovulation-inducing drug.
Cervical Ectopic Pregnancy: Case Reports and Management Modalities
Authors: Gupta Vineeta , Acharya Rajiv , Rani Aruna
Published: April 2010

Cervical pregnancy is a rare variety of ectopic pregnancy. The diagnosis of cervical pregnancy can be missed by an unsuspecting mind inspite of the routine use of first trimester ultrasonography. We present two cases of cervical pregnancy managed at our hospital alongwith a brief review of literature highlighting the various treatment modalities.
Dramatic Regression of Dermatoses after Delivery
Authors: Inamdar SA , Hinduja Ritu , Bhute SB , Shrivastava Deepti , Patil VS
Published: April 2010

Atopic eruptions of pregnancy may be sometimes very distressing to mother because of intense itching and aggressive appearing and difficult to manage due to nonresponding to symptomatic treatment but usually regress very well after delivery without any adverse maternal and fetal out come. We are presenting a case which appeared very virulent antenatally but resolved dramatically after delivery.
Predicting Preclinical Disease by Using The Mixed‐Effects Regression Model
Authors: Sheng Shan L. , Brant Larry J.
Published: March 2010

Most methods of disease prediction are generally restricted to logistic or Cox proportional hazards model regression using only baseline values of the risk factor, and where the individuals age and sex account for most of the predictive capacity of the method. This chapter presents a method of risk prediction appropriate for repeated measures or time‐dependent risk factors from longitudinal studies. The method is based on posterior probabilities calculated from mixed‐effects regression models to model intra‐ and inter‐individual differences in the serial risk factor measurements, to predict a disease‐related outcome or other future event according to age changes within gender groups. While aging is inevitable and the occurrence of disease increases with age, disease and aging are not synonymous. Disease is a selective event that occurs in only some members of the population; others maintain a greater degree of physiological function as they age and remain relatively disease free. Thus, longitudinal data that considers each individual as their own control and the use of an appropriate method of prediction can play an important role in promoting a healthy human life throughout the aging process.
Probabilistic and Statistical Models for Conception
Authors: Scarpa Bruno
Published: March 2010

Statistical models of fertility studies play a crucial role in understanding the biology of conception. Heterogeneity in women and men's requires specific statistical methods to be used in order to allow for the variability in behavioral and physical characteristics, as well as for the variability in frequency and timing of sexual intercourse and for the progressive selection of patients during the fertility studies that provide data. A review of the most used models is offered, starting from classical population models, based only on aggregated data we then discuss time to pregnancy models and the models that predict the day‐specific probability of conception.
Change Point Methods in Genetics
Authors: Chen Jie
Published: March 2010

In this review article, recent applications of change point methods in genetics will be discussed. The latest advances in bio‐technology have provided new tools for scientists to carry out health and life science research. The array, or microarray, technology has made it possible to simultaneously quantify expression patterns of thousands or hundreds of thousands of genes in various cell lines, tissues, and conditions. The resulting datasets from various experiments using microarray technology are of high‐throughput and cast challenges to data analysts.

Specifically, to study the genetic reasons of tumor growth, cancer formation, and genetic diseases, geneticists can now use microarray technology to conduct DNA copy number experiments to obtain gene positions, log base 2 ratio intensities, and DNA copy numbers along the genome. It turns out that identifying loci of DNA copy number variations along the chromosome or genome can be viewed as a change point problem of detecting the changes presented in the sequence of log ratio intensities. The author will discuss the background of DNA copy number experiments, especially the experiments using the array comparative genomic hybridization (aCGH) technique, the resulting aCGH data, and the appropriate change point methods that can be used to analyze the aCGH data. Several applications of the change point methods to the analysis of fibroblast cell line data, the breast tumor data, and the breast cancer data will be given.
Interrater Agreement
Authors: Choudhary Pankaj K.
Published: March 2010

As the technology advances, new methods of measuring a continuous clinical variable become available that may be cheaper or less invasive than the old ones. But before a new method is adopted for general use, it is validated by evaluating its agreement with an established standard. This article presents a comparative discussion of the various approaches for measuring agreement between two measurement methods. Their application is illustrated using a blood pressure data from the literature.