bluuebunny/crossref_metadata_2025 huggingface dataset:
Big Soda Lake (Nevada). 3. Pelagic methanogenesis and anaerobic methane oxidation1
Authors: Iversen Niels , Oremland Ronald S. , Klug Michael J.
Published: April 2010

In situ rates of methanogenesis and methane oxidation were measured in meromictic Big Soda Lake. Methane production was measured by the accumulation of methane in the headspaces of anaerobically sealed water samples; radiotracer was used to follow methane oxidation. Nearly all the methane oxidation occurred in the anoxic zones of the lake. Rates of anaerobic oxidation exceeded production at all depths studied in both the mixolimnion (2–6 vs. 0.1–1 nmol liter−1 d−1) and monimolimnion (49–85 vs. 1.6–12 nmol liter−1 d−1) of the lake. Thus, a net consumption of methane equivalent to 1.36 mmol m−2 d−1 occurred in the anoxic water column. Anaerobic methane oxidation had a first‐order rate constant of 8.1±0.5 × 10−4 d−1, and activity was eliminated by filter sterilization. However, in situ methane oxidation was of insufficient magnitude to cause a noticeable decrease of ambient dissolved methane levels over an incubation period of 97 h.
Big Soda Lake (Nevada). 4. Vertical fluxes of particulate matter: Seasonality and variations across the chemocline
Authors: Cloern James E. , Cole Brian E. , Wienke Sally M.
Published: April 2010

Vertical fluxes of particulate organic matter were measured with sediment traps above and below the chemocline of Big Soda Lake to define the seasonality of sinking losses from the mixolimnion and determine the effectiveness of the chemocline (pycnocline) as a barrier to the sinking of biogenic particles. Seasonality of sedimentation rates reflected seasonal changes in the community of autotrophs. During summer‐autumn, when production is dominated by autotrophic bacteria, vertical fluxes were small: 100 mg C m−2 d−1 and ≅0.5 mg Chl a m−2 d−1. Following the winter diatom bloom, vertical fluxes increased markedly: ≅570 mg C m−2 d−1 and 23 mg Chl a m−2 d−1. The bulk of the seston (> 80%) and particulate carbon (≅ 65%) sinking to the chemocline passed through it, showing that this very sharp density discontinuity does not effectively retard the sinking of particulate matter. However sinking losses of particulate carbon were generally small (≅10%) relative to previous measures of primary productivity, indicating that the mixolimnion is a zone of efficient carbon cycling. Exceptions occurred following the winter bloom when sinking losses were a larger fraction (≅40%) of productivity.
Field experiment on the influences of suspended clay and P on the plankton of a small lake1
Authors: Cuker Benjamin E.
Published: April 2010

Independent and interactive effects of phosphorus and clay loading on pelagic community organization and productivity were tested in a small piedmont lake in North Carolina. Twelve limnocorrals (2‐m diam, 3 m deep) were used for field manipulations. Treatments (in triplicate) were unaltered controls, P loading of 3.3 mg m−2 d−1, kaolinite clay loading of 100 g m−2 d−1, and combined clay and P loading. Fertilization with P significantly increased rates of turbidity reduction in comparison to controls (Secchi depth increasing at 7.2 vs. 5.8 cm d−1) and also significantly lowered sustained turbidity in treatments under clay loading. Clay loading reduced net community productivity (NCP), Chl a concentrations, and algal cell numbers. Suspended clay also caused a shift in algal community composition; Trachelomonas superba and other flagellates replaced the otherwise dominant blue‐green Spirulina major. Fertilization with P increased NCP and algal densities and favored development of the N2‐fixing blue‐green algae Anabaena spiroides and Anabaena circinalis. Combined P and clay loading produced intermediate values of turbidity, NCP, and Chl a. Simultaneous clay loading eliminated the influence of P fertilization on algal community structure, yielding an assemblage dominated by flagellates. Clay turbidity also caused a shallowing in the daytime distribution of zooplankton.
High phytoplankton growth and production rates in the North Pacific subtropical gyre1,2
Authors: Laws E. A. , DiTullio G. R. , Redalje D. G.
Published: April 2010

Rates of phytoplankton growth and production were measured with 14C techniques at stations near the Hawaiian Islands and at about 28°N, 155°W in the North Pacific subtropical gyre during August and September 1985. Ratios of light‐saturated assimilation averaged 9.5 ± 1.4 g C (g Chl a)−1 h−1 during the photoperiod. Doubling times in the upper 30 m of the water column averaged 14±3 h. Relative growth rates were estimated to be 85–90% of nutrient‐saturated values. Over the upper 200 m of the water column photosynthetic rates uncorrected and corrected for grazing and phytoplankton respiration losses were 315 ± 26 and 450±37 mg C m−2 d−1, respectively. The former figure is comparable to the highest daily photosynthetic rates inferred from 14C studies at this station during 1968–1980 and is about twice the mean of those historical productivity numbers. These results contradict the paradigm of subtropical gyres as vast biological deserts characterized by constantly low biomass and low turnover rates limited by the supply of nutrients. However, further studies will be needed to determine whether these high growth and production rates are typical or atypical of the central regions of the oceans.
Vertical temperature gradients in muddy intertidal sediments in the Forth estuary, Scotland1
Authors: Harrison S. J. , Phizacklea A. P.
Published: April 2010

When exposed at low water, muddy sediments tend to develop less steep vertical subsurface temperature gradients than do sandy beach sediments. Changes in these gradients are rapid during tidal inundation. Measurements of subsurface temperature and atmospheric variables were made from an instrument tower at Skinflats on the extensive intertidal mudflats of the Forth estuary in Scotland. There was a marked seasonal change in the direction and magnitude of gradients. Gradients developed at low water were related to antecedent net radiant energy influx at the mud surface and latent heat flux into the atmospheric boundary layer. The relationship between the change in gradient during an incoming tide and the time of high water showed a well‐defined association.
Acid hydrolysis of dissolved combined amino acids in seawater: A precautionary note1
Authors: Robertson K. J. , Williams P. M. , Bada J. L.
Published: April 2010

Hydrolyses of dissolved combined amino acids in seawater with 6 N HCl result in oxidative degradation of α‐amino acids when seawater nitrate concentrations exceed 6 ± 2 µmol liter−1. The addition of excess ascorbic acid before hydrolysis prevents these oxidative reactions.
Prediction of hydrothermal vent locations from distributions of brachyuran crabs1,2
Authors: Van Dover Cindy Lee , Franks Peter J. S. , Ballard Robert D.
Published: April 2010

We apply a model of symmetrical, exponential decreases in brachyuran crab density with distance from vent centers to a video census of crab density along the neovolcanic zone of the East Pacific Rise to predict the number of vents and their locations. Our model, calibrated by data from two known vents, accurately locates one other known vent and predicts the locations of three additional vents presumably skirted by the towed camera sled. Analysis of crab distributions may thus be a valuable tool for mapping the locations of hydrothermal vents with remotely operated camera gear.
Growth rate and quantum yield time response for a diatom to changing irradiances (energy and color)1
Authors: Morel Andre , Lazzara Luigi , Gostan Jacques
Published: April 2010

The growth rate of a diatom (Chaetoceros protuberans) was followed during transfers from moderate to higher or lower irradiances (PAR) with differing spectral compositions (“white,” “blue,” and “green” light). Chlorophyll‐specific and carbon‐specific absorption coefficients of the algae were monitored, allowing changes in the quantum yield for growth (Φµ) to be assessed. All the parameters appear to be practically unaffected by chromatic conditions, provided that the photosynthetically usable radiation (PUR) is made equal. Diatoms respond to the energy level whatever the color. Nevertheless, due to opposite influences of the modifications in the “package” effect and in the C : Chl a ratio (Θ), the light‐harvesting capabilities of the living carbon pool vary only weakly. Therefore the growth rate change (from 0.3 to 1.2 d−1) is essentially governed by the change in Φµ (from 0.01 to 0.052 mol C retained mol−1 quanta absorbed). The kinetics of the Chl‐a‐per‐cell modification and of the Φµ response is rather fast (within approximately one generation). Quantum yield for growth is halved after a transfer to high irradiance; thereafter it remains low and steady. Conversely the enhanced value observed just after transfer to low irradiance is not maintained beyond 2 or 3 d; after that, Φµ is restored practically to its initial value.
A comparison of internal phosphorus loads in lakes with anoxic hypolimnia: Laboratory incubation versus in situ hypolimnetic phosphorus accumulation1
Authors: Nürnberg Gertrud K.
Published: April 2010

Phosphorus release rates from anoxic sediments were determined from laboratory incubations of minimally disturbed sediment cores from seven lakes. These release rates were multiplied by an “anoxic factor,” based on the area and duration of hypolimnetic anoxia, to estimate internal phosphorus load. Despite individual variation, the experimentally derived internal loads were not significantly different from internal loads determined from hypolimnetic phosphorus increases at the end of summer stratification, except at internal loads <50 mg m−2 yr−1. Therefore, laboratory release rates can help predict internal loads after lake conditions have changed, e.g. after in‐lake restoration measures.
Nitrogen mineralization and denitrification in Lake Michigan sediments1
Authors: Gardner Wayne S. , Nalepa Thomas F. , Malczyk John M.
Published: April 2010

Organic nitrogen mineralization mechanisms, fluxes, and fates in Lake Michigan sediments were examined by measuring accumulation rates of inorganic nitrogen in laboratory microcosms. Neither ammonium nor nitrate increased substantially in flow‐cell or slurry microcosms of offshore, silty sediments. In experiments with gastight chambers containing “intact” offshore, silty sediment cores (sampled at 45‐ and 100‐m water depths), the total fluxes of nitrogen (NH4+, NO3−, and N2) across the sediment‐water interface ranged from 14 to 51 µg‐atomns N m−2 h−1. Nitrogen gas accounted for 93–98% of the total inorganic nitrogen flux from the sediment to the water. Inputs of inorganic nitrogen via mineralization processes (mediated by microbial decomposition and invertebrate excretion) appeared to be the major factors controlling the rates of both nitrification and denitrification in these sediments. The overlying water did not serve as a significant net source of nitrate driving the denitrification reaction. These results thus indicate that denitrification is a dominant sink for mineralized nitrogen in these silty Lake Michigan sediments and that this process is closely coupled with the initial mineralization of organic nitrogen in the sediments.
The geochemical character of upland waters of northeast New South Wales
Authors: Banens R. J.
Published: April 2010

The water chemistry of 18 small reservoirs in the New England Tablelands of northeast New South Wales was strongly influenced by catchment geology. Cluster analysis distinguished three types of waters. One group, strongly dominated by Mg2+ and HCO3− and also having high Ca2+, pH, and total conductivity, was characteristic of catchments underlain by alkali olivine basalt. A second group dominated by Na+ and HCO3−, and having a relatively low conductivity and pH, was characteristic of waters draining granitic rocks of adamellite composition. A third less well‐defined group, similar to group two waters but having high conductivity, drained catchments underlain by acid igneous rocks with a slightly more basic geochemistry and also mixed igneous and sedimentary catchments. Ratios of major cations in waters were highly determined by ratios in igncous catchment rocks (Mg2 +, R2 = 0.983; Na+, R2 = 0.917; Ca2+, R2 = 0.801; K+, R2 = 0.390). The importance of marine salt varied from <7% of ions for waters draining basalts to as high as 65% for dilute water draining a granitic catchment. The leaching of accumulated cyclic salt from the soil was inferred to be the principal source of these ions for all but the waters draining the younger basalts. The presence of relict sea salts in the soils of the acid igneous and sedimentary rock is believed to be due to elevated accession during arid periods of the Cretaceous and early Tertiary. Present‐day cyclic salt accession, connate salts, and anthropogenic sources were unimportant ion sources. The waters deviated substantially from the world average freshwater and also from the world water chemistry model of Gibbs.
Energy sources for recruitment of the subantarctic copepod Neocalanus tonsus1
Authors: Ohman M. D.
Published: April 2010

Neocalanus tonsus Brady was collected in subantarctic waters off southeastern New Zealand to test experimentally the importance of storage lipids and particulate matter as energy sources for recruitment. Reproductive copepods occur in mesopelagic depths (1,000‐500 m) in austral winter and in epipelagic depths (150‐0 m) in spring. Winter copepods released up to 19 eggs female −1 d−1 in filtered seawater; spring copepods required a particulate food source to release eggs. Winter females ingested diatoms at half the rate of spring females. Winter CVs did not ingest diatoms, in contrast to spring and summer CVs. Winter females had 24 times the wax ester content, half the phospholipid, and half the nitrogen content of spring females. In contrast, the two groups did not differ in dry mass or carbon content. Application of a proposed method for estimating reproductive potential, combined with experimental results, suggests that stored lipids are the energy source for recruitment of mesopelagic winter animals but not epipelagic spring animals. Subantarctic N. tonsus is distinguished from subarctic Pacific Neocalanus plumchrus and Neocalanus cristatus by residence of adult females in surface waters, active suspension feeding, and the dependence of egg production on particulate food in spring. Divergent life history traits may be observed for copepod species occupying parallel subpolar habitats in the southern and northern hemispheres.
Techniques of fluorescence depolarization for measuring seawater viscosities1
Authors: Carlson David J. , Morrill Lynn E. , Brophy Jennifer E.
Published: April 2010

Conventional techniques are unsuited for measuring the viscosity of seawater when organisms, particles, or surface‐active organic materials are present. We have adapted a fluorescence depolarization technique to measure intrinsic solution viscosity and find that all of the factors listed can influence seawater viscosity. The technique, which determines viscosity by measuring the rotational freedom of fluorochromes added to seawater, is accurate in the presence of seawater particles and organics and requires only small volumes, making it useful for samples taken from locations or under conditions in which influences of viscosity on molecular‐scale processes may be important.
Zooplankton‐mediated transitions between N‐ and P‐limited algal growth1
Authors: Elser James J. , Elser Monica M. , MacKay Neil A. , Carpenter Stephen R.
Published: April 2010

Limitation of algal growth by nitrogen and phosphorus was assessed in three north‐temperate lakes with physiological bioassays and nutrient enrichment experiments. In addition, mesocosm experiments were performed in the three lakes to examine the effects of nutrient enrichment and zooplankton biomass and size on algal nutrient status. In situ indicators of N and P availability were inversely related in magnitude and transitions between N and P limitation were abrupt. Physiological bioassay results did not indicate simultaneous limitation by N and P. However, limited responses to single‐nutrient enrichment and pronounced responses to simultaneous N and P addition in enrichment experiments suggested that potential limitation by the secondary nutrient was usually in close proximity to limitation by the primary nutrient. Transitions between N and P limitation closely accompanied major shifts in the zooplankton community. The importance of the zooplankton community in regulating the relative degree of N or P limitation was confirmed by the mesocosm experiments, which demonstrated that transitions between algal N or P limitation could be induced by manipulations of zooplankton biomass or size. This result supports a hierarchical view of the function of planktonic systems, in which biotic interactions structure the response of the algal community to a given nutrient load.
Comparative transparency, depth of mixing, and stability of stratification in lakes of Cameroon, West Africa1
Authors: Kling George W.
Published: April 2010

Morphometry, oxygen concentration, temperature, and transparency were studied in 39 natural lakes in Cameroon, West Africa. Thermal profiles from 31 of the lakes and data from published studies were used to calculate stability of thermal stratification and evaluate morphological correlates of mixing depth. Twenty‐six lakes showed some degree of stratification and 17 had distinct thermoclines and well‐developed, anoxic hypolimnia. Total stability of the water column ranged from 0 to 5,784 J m‐2. The high values were similar to or greater than those of other tropical and temperate lakes. Lake depth seems to exert a stronger influence on stability than does lake area, but depth or stability measures alone provide little information about heat distribution or mixing regime. A strong positive relationship between water transparency and thermocline depth in both tropical and temperate lakes suggests that reductions in buoyant resistance to vertical mixing, caused by deeper penetration of solar radiation, are important in establishing mixing depths in various lakes. Comparisons of persistent thermocline depth in tropical vs. temperate lakes, regardless of size, indicate that mixing depths in tropical lakes are often greater than those in their temperate counterparts. This difference is caused in part by the narrow ranges of temperature and smaller absolute density gradients in these tropical lakes, against which the mixed layer is deepened.
Factors controlling nutrient concentrations in Amazon floodplain lakes1
Authors: Forsberg Bruce R. , Devol Allan H. , Richey Jeffrey E. , Martinelli Luiz A. , dos Santos Humberto
Published: April 2010

Nutrient chemistry in lakes of the central floodplain of the Amazon River is influenced by the relative mix of waters of river and local origin. At high water the lakes contained primarily river water, lake and river total nitrogen (TN) levels were similar, concentrations of total suspended solids (TSS), soluble reactive phosphorus (SRP), dissolved inorganic nitrogen (DIN), and total phosphorus (TP) in the lakes were significantly lower than those in the river, and chlorophyll a (Chl a), transparency, and TN : TP levels were higher. The apparent decline in TP in the lakes was correlated with river TSS, suggesting a sedimentation loss. The higher TN : TP in the lakes reflected the differential loss of TP. At low water the percentage of local water in most lakes increased. The relative magnitude of this increase and its effect on nutrient chemistry depended on the ratio of drainage basin area to lake area (BA: LA). Lakes with BA: LA ≲20 contained a mixture of river and local water by the end of the low water period with a variable nutrient composition; lakes with BA: LA 20 contained primarily local water with a nutrient composition similar to that of forest runoff. Concentrations of TP in the lakes were near the levels expected from conservative mixing, suggesting a partial recovery of TP lost during high water. Levels of TN and TN : TP were higher than those expected from conservative mixing, suggesting an additional source of N.
Tritium hydrologic studies in four closed‐basin lakes in the Great Basin, U.S.A.1
Authors: Herczeg Andrew L. , Imboden Dieter M.
Published: April 2010

Four closed‐basin lakes in the Great Basin (Lake Abert, Oregon; Mono Lake, California; Pyramid Lake and Walker Lake, Nevada) were analyzed for tritium (3H) in water samples collected in 1969, 1976, 1980, and 1981. In each case the tritium concentration increased to a maximum in the mid‐to late 1960s in response to fallout produced by nuclear weapons testing and then slowly decreased soon after the 1966 moratorium. The highest level attained was a function of the water residence time of the lake (i.e. shorter residence time corresponding to higher maximum tritium concentration), and the rate of decrease was slowest for lakes with longer water residence times. The residence time of tritium is less than the water residence time and depends strongly on the evaporative exchange of tritium with the atmosphere.

A tritium hydrologic model was constructed in an attempt to constrain hydrologic properties such as evaporation rate, relative humidity, and the degree of homogeneity of the water column with respect to tritium. If evaporation rates determined from hydrologic balance are within 20% of the true rates, then the tritium input must be between 50 and 90% enriched over that calculated from data on tritium fallout in Portland rain. This enrichment is considerably reduced if the surface waters are on the average depleted by about 10% in tritium relative to the whole lake. Calculated mean relative humidities lie between 0.45 (Mono Lake) and 0.25 (Walker Lake). Calculated exchange velocities in the gas phase are between 17 and 27 m h−1, which corresponds to a mean wind speed of about 4 m s−1.
Alkalinity and major ion budgets for a Massachusetts reservoir and watershed1
Authors: Eshleman Keith N. , Hemond Harold F.
Published: April 2010

A detailed field study of the major ion and alkalinity budgets of Bickford Reservoir and its forested watershed in Massachusetts was conducted to quantify the hydrochemical response of the ecosystem to acid deposition. Three years of alkalinity data from this oligotrophic reservoir exhibit repeating seasonal variability but no clear trend. The annual acid‐base status of the system is predominantly determined by the following terrestrial biogeochemical processes: wet and dry acidic deposition, production of base cations by mineral weathering or cation exchange, biological retention of HNO3, and production of natural humic substances. Although HNO3 deposition was completely neutralized by biological retention, measured bulk SO42− deposition could account for only about 50% of streamwater SO42− output; dry sulfur deposition estimated from throughfall enrichment accounts for an additional 40%. Monthly budgets show a strong seasonal SO42− sink in summer, but estimation of the magnitude of net biotic SO42− removal is confounded by evidence that the weathering of sulfur‐containing minerals is significant. Watershed budgets suggest that increased sulfur deposition may cause a decrease in surface water alkalinity—possibly on an equivalent for equivalent basis—unless SO42− reduction and base cation supply increase accordingly.
Laboratory studies on core sampling with application to subtidal meiobenthos collection
Authors: Rutledge P. A. , Fleeger J. W.
Published: April 2010

Three aspects of subtidal meiobenthic sampling were examined through laboratory simulation experiments with Sephadex gel beads as an epibenthic meiofaunal mimic. Results indicate that corer diameter (i.d. from 2.6 to 10.5 cm) does not affect sampling efficiency if slow corer penetration takes place. Disturbance in cores mimicking conditions during retrieval by a diver resulted in a bias when these cores were subsampled after collection. Such effects may also be present in larger (e.g. box) corers when a distinct flocculent layer is present. A dramatic effect on vertical profile was found when cores were preserved by fast‐freezing. Cores should be of a size that can be analyzed in their entirety, subsampled as a homogenate, or subsampled with a device in place as the corer enters the sediment.
Latitudinal variation in size structure of the west coast purple sea urchin: A correlation with headlands1
Authors: Ebert Thomas A. , Russell Michael P.
Published: April 2010

Size structure of the purple sea urchin Strongylocentrotus purpuratus was sampled from central California to central Oregon (36°– 45°N). Size frequency and inferred recruitment events are correlated with major topographic features. Capes and headlands—predictable sites of upwelling and locations of cold water plumes— show size frequencies indicative of low recruitment rates. Sites without predictable upwelling or regions that are between headlands have size frequencies that indicate substantial annual recruitment.
Field measurements of air‐sea CO2 exchange1
Authors: Frankignoulle M.
Published: April 2010

The direction and magnitude of air‐sea exchanges depend on the difference of gas partial pressure (ΔP) between phases and on a gas exchange coefficient (K). In this work, field air‐sea CO2 exchange and ΔPco2 have been measured simultaneously to study the in situ relations between parameters. Experiments have been carried out at three sites: the Bay of Calvi (Corsica), the Ligurian Sea, and the North Sea. Flux measurements were made with a direct chamber method to detect invasion or evasion of gas.

Due to its bed of seagrass (P(Posidonia), the Bay of Calvi is the site of regular, daily, and yearly variations of surface CO2 content. Daily variations are often too small to overcome the variation of K and to find a correlation between hourly measured fluxes and daily changes of ΔP. The yearly variation of Pco2 in surface water (from 300 ppm in winter to 900 ppm in summer) has however permitted derivation of a linear relationship between mean fluxes and ΔP that fits well with fluxes measured at the two other sites under similar meteorological conditions and thus with nearly the same K. Calculated coefficients range between 10−5 and 4 × 10−5 m s−1 and so agree well with those determined with radiotracers or in wind tunnels.

Measurements in the North Sea under different meteorological conditions show the influence of wind speed and sea state on exchanges measured by the in situ methodology used and allow the results to be compared with those obtained by others in wind tunnels.
Thermal simulation of a lake with winter ice cover1
Authors: Patterson J. C. , Hamblin P. F.
Published: April 2010

A one‐dimensional thermodynamic model of a two‐component ice and snow cover is added to an existing one‐dimensional lake mixing model. Emphasis is placed on the thermodynamic coupling between the ice and mixing models—absent in previous models. The two‐dimensional effects of partial ice cover are incorporated into this one‐dimensional framework by using a minimum ice thickness. The model is applied to Lake Laberge, Yukon Territory, and to Babine Lake, British Columbia, for periods covering the formation and demise of full ice cover. The results of the model are compared to snow and ice measurements in the first case and to water column data during the spring period in the second. The comparisons are good, implying that the ice and snow model is performing satisfactorily and emphasizing the importance of the coupling between the ice and the underlying water. The successful simulation of the observed mixed layer under the ice, driven by convective stirring caused by short‐wave heating below the temperature of maximum density, is an example of the ability of the model to provide physical insight into processes occurring in lakes.
Records of riverbome turbidity currents and indications of slope failures in the Rhone delta of Lake Geneva
Authors: Lambert André , Giovanoli Federico
Published: April 2010

The sublacustrine topography of the Rhone delta in Lake Geneva is characterized by a channel that can be traced about 9 km beyond the mouth of the river. Two instrumented moorings were deployed from June to August 1985 in the channel axis at depths of 150 and 201 m to detect underflows of dense, sediment‐laden river water. Each array consisted of three current meters and a thermistor chain. Data were recorded every 15 min (currents) or 30 min (temperatures). During 78 d of effective measurement, 31 well‐defined downslope events were recorded, five with speeds >50 cm s−1. Major events correlate with discharge peaks of the Rhone, and current activity is characterized by single pulses lasting a few hours. Some flow events were accompanied by temperature increases of up to 3°C, suggesting two different current origins: the first is intrusion of sediment‐laden, warm river water into the cold bottom water of the lake as a dense turbidity underflow, and the second is turbidity‐current flow triggered by sliding or slumping of delta deposits. Damage caused to instruments and breakage of mooring links suggests sliding of large amounts of deltaic sediments or avalanchelike turbidity currents.
Growth and phosphorus status of limnetic phytoplankton and bacteria
Authors: Vadstein Olav , Jensen Arne , Olsen Yngvar , Reinertsen Helge
Published: April 2010

The phosphorus status [total phosphorus (P), surplus P, and alkaline phosphatase activity (APA)] of phytoplankton and bacteria were followed in a eutrophic Norwegian lake. On average 36% (range 20–60) of the particulate P and 57% (range 10–100) of the surplus P were bound by bacteria. The P : C ratio of phytoplankton and bacteria varied between 2.5 and 55 (median 5.1) and 34 and 360 (median 89) µg P (mg C)−1, indicating that bacteria have a substantially higher P requirement than do phytoplankton.

The inverse relation found between surplus P : C and APA : C ratios during a Microcystis aeruginosa bloom and the positive relation between P : C ratio and growth rate of the cryptophyte‐dominated community in summer indicate that the phytoplankton were P limited during most of the ice‐free period. This is supported by the fact that the data from the cryptophyte‐dominated community could be described by the Droop model for nutrient‐limited growth. For the bacteria a positive relation was found between growth rate and cellular P (i.e. the P : C and the surplus P : C ratios), as predicted by the Droop model. Although the bacteria obviously were P subsaturated, it cannot be concluded that they were P limited since C may have been supplied at an even lower rate. Because of their high P requirements the bacteria acted as consumers of inorganic P and their net consumption of P was four times higher than that of the phytoplankton.
The effect of pH on iron and manganese uptake by a green alga
Authors: Schenck R. C. , Tessier A. , Campbell P. G. C.
Published: April 2010

Experiments were conducted with 54Mn and 59Fe in buffered synthetic solutions to determine the short‐term uptake of manganese and iron by the green alga Chlamydomonas variabilis as a function of pH and metal concentration. Over the pH range 7 to 5, the adsorption of Fe(II) and Mn(II) onto the cell surface was independent of pH, but the fluxes of metals into the cells decreased 2–2.5 times for each unit decrease in pH. Thus increasing acidity decreased metal uptake and, by inference, the effects of the metal on the cell.

We also compared the uptake of Fe(II) and Fe(III) at the same external concentration (0.1 µM), under conditions where all the metal was dissolved (pH 5). The uptake rates were nearly identical, even though the ratio [Fe2+]:[Fe3+] was ∼106. The measured fluxes of Fe(III) into an algal cell were l04 times greater than the calculated diffusive flux of Fe3+ to the cell surface. The results indicate that the uptake of Fe(III) involves transport to the cell surface of hydroxy‐Fe(III) species that are in rapid protolytic equilibrium with each other and with the free hydrated ferric iron.
Reproductive costs and hydrodynamic benefits of chemically induced defenses in Keratella testudo
Authors: Stemberger Richard S.
Published: April 2010

Food concentration differentially affected reproductive rates and hydrodynamic characteristics of spined and unspined phenotypes of the polymorphic rotifer Keratella testudo. The intrinsic rate of population growth (0.15 d−1) of the predator‐induced phenotype was less than half that of the unspined morph (0.39 d 1) at high food concentrations. The spined phenotype had considerably lower survivorship and fecundity than the unspined one after the first 3–4 d of life. At low food concentrations population growth rates were not statistically different; their age‐specific survivorship and fecundity schedules were nearly identical.

Sinking rates and swimming speeds of both morphs were significantly and negatively correlated (r = −0.96). Attached eggs increased sinking rates regardless of food level. Changes in sinking rate occurred within 6 h of transferring animals acclimated to high food to conditions of starvation. Food concentration greatly influenced the center of gravity of the morphs and, consequently, affected orientation during sinking. They sank posterior‐end downward in high food conditions and in a more horizontal plane in low food treatments. The latter position should give maximal resistance to sinking, consistent with the slower sinking rates in low food conditions.

The specific gravity of both phenotypes increased in high food concentrations—the spined morph being consistently higher than the unspined one at both food levels. Lorica densities of both phenotypes were >1.3 g cm−3 suggesting that this structure may contribute significantly to body mass and may be energetically costly to produce or maintain. The coefficient of form resistance (the ratio of the sinking rate of the rotifer to the sinking rate of a sphere having an equivalent volume and specific gravity) was ∼27% higher in the spined phenotype than in the unspined one in low food treatments. Greater form resistance may provide an energetic benefit which offsets the costs associated with the spined phenotype.
A high‐precision respirometer for measuring small rates of change in the oxygen concentration of natural waters
Authors: Griffith Peter C.
Published: April 2010

A computer‐controlled system is described that can detect very low respiration rates of planktonic organisms in unconcentrated samples of ocean water. The polarographic sensor used consumed < 10−4 µmol O2 h−1 and thus required little stirring. Estimates of community respiration of −2.23±0.06 and −0.19±0.04 µM O2 h−1 were made during short‐term incubations of the waters of the middle and outer continental shelf of Georgia.
Vortex feeding from pits in the sand: A unique method of suspension feeding used by a stream invertebrate
Authors: Soluk Daniel A. , Craig Douglas A.
Published: April 2010

Larvae of the mayfly Ametropus neavei have a unique method of suspension feeding that uses hydrodynamic properties of vortices and pits in the sediment to facilitate capture of fine particles from flowing water. Modified setae on the forelegs function both as “aerosol” filters and in initiating formation of a vortex that spirals within a specially constructed pit. The vortex concentrates seston and transports it to filtering devices below the surface of the sediments. We suggest that vortex feeding allows Ametropus larvae to occupy noncohesive sands of rivers—areas that offer no solid substrate for attachment and are devoid of other suspension feeders.
A framework for discussing seasonal succession and coexistence of phytoplankton species
Authors: Evans Geoffrey T.
Published: April 2010

Any explanation of seasonal succession of phytoplankton communities should discuss why replaced species reappear, in roughly the same concentrations, in following years. A model of an annual cycle, representing two or more groups of phytoplankton but only one type each of nutrient and herbivore, can exhibit seasonal succession of two groups, and coexistence of three. It shows some of the features common to many instances of succession. Although the model’s physical environment repeats exactly from year to year, its plankton populations commonly oscillate with a period of 2 yr or longer. Models with a single, undifferentiated phytoplankton component may overestimate the predictability of plankton populations.
Organic matter sources to the water column and surficial sediments of a marine bay
Authors: Hedges John I. , Clark Wayne A. , Come Gregory L.
Published: April 2010

Sediment trap and net plankton samples were collected monthly for a year at three depths in a marine bay (Dabob Bay, Washington). These materials and subsamples from a sediment box core were analyzed for lignin oxidation products as well as elemental and stable carbon isotope compositions. The sediment core was compositionally uniform over its entire 50‐cm length. The elemental and lignin compositions of the sediment trap and core samples indicate nitrogen‐rich (atomic C : N ≅ 7.5) plankton‐derived organic matter mixed with vascular plant debris.

At most, vascular plant debris accounts for 10% (nonwinter months) to 35% (winter months) of the total organic carbon in the upper water column (30 m) sediment trap samples and consists predominantly of gymnosperm wood along with some nonwoody gymnosperm tissues and angiosperm woods. Bulk land‐derived organic matter in Dabob Bay contains a maximum of 50% vascular plant debris and comprises an average of one‐third of the total organic carbon in the sediment trap samples and two‐thirds of the total organic carbon in the underlying sediments. Lignin in the sediment trap and core samples shows evidence (from elevated vanillic acid:vanillin ratios) of white‐rot fungal degradation before (but not after) introduction to the water column at the study site. Vascular plant debris introduced to the bay has already lost almost half of its initial bulk polysaccharide. Glucose yields are particularly low whereas rhamnose and fucose are obtained in excess of expected yields and must have additional sources.

Lignin and neutral sugars together account for <20% of the total organic carbon in the sediment trap and core samples. Overall, the sediments of Dabob Bay compositionally resemble the gymnosperm wood‐rich particulate material introduced to the overlying water column during winter and poorly record the input of plankton and other types of vascular plant debris during nonwinter months.
Interactions of inorganic carbon and light availability as controlling factors in aquatic macrophyte distribution and productivity
Authors: Hough R. Anton , Fornwall Mark D.
Published: April 2010

The roles of inorganic carbon and light availability in the quantitative distribution and photosynthetic productivity of submersed aquatic macrophytes were investigated in two lakes in a stream‐connected hard‐water lake chain where light availability and pH increase and total inorganic carbon decreases as water flows from a turbid productive lake through progressively clearer less productive lakes. Bicarbonate‐using species dominated the macrophyte communities of both lakes, but species requiring free CO2 were present, primarily in the more turbid lake. In photosynthesis experiments, CO2‐requirer Najas flexilis was significantly competitive when light limitation reduced the efficiency of HCO3−‐user Potamogeton pectinatus. The results suggest that inorganic carbon availability can be important in macrophyte growth even within relatively small ranges of total alkalinity and that light availability is a potentially important interacting factor.
Importance of diversity in the functioning and structure of riverine communities
Authors: Patrick Ruth
Published: April 2010

The natural diversity of biological communities provides many alternative pathways by which nutrients and energy may move through ecosystems. Many different species are capable of performing similar functional roles in nature. When disturbed or polluted, natural systems often become restored first through the activities of species that had not previously been common. Human activities often result in reduction or loss of diversity within ecosystems, particularly through the loss of rare species. Maintenance of diversity is vital because it provides protection against both natural and human‐caused catastrophies.
Precancerous Lesions of Oral Cavity
Authors: Pawar Uday , Souza Chris de
Published: April 2010

The term premalignant (precancerous) lesion has been replaced by the term potentially malignant lesion. Such lesions have as their cause, tobacco use, exposure to the human papilloma virus and the chewing of the betel nut. These substances contain carcinogens. The mucosa of the oral cavity is normally quite robust. Exposure to these substances can cause it to undergo change. These changes are usually initiated as a leukoplakic patch. While some leucoplakic patches recover and resolve, some progress into invasive squamous cell carcinoma. Oral submucus fibrosis is another such potentially malignant condition caused by the abuse of betel nut.
Evaluation of Applicability of Standard Growth Curves to Indian Women by Fetal Biometry
Authors: Acharya Ashini , Acharya Prashant
Published: April 2010

Objective

To verify the applicability of standard fetal growth curves proposed for western populations to an Indian population.

Method

Thirty patients were included and ultrasound scans were performed on Indian pregnant women to measure fetal growth parameters of biparietal diameter, head circumference, abdominal circumference and femur length for every weekly interval from 14 to 40 weeks. Twenty-five hundred women had ultrasonic measurements of fetal BPD, HC, AC and FL between 12 to 42 weeks of pregnancy were also included in study for confirming the growth parameters and plotting of Growth curves. The data were compared with the commonly recommended standards of Hadlock, Campbell, Jeanty and Chitty.

Results

First and second trimester biometry findings are comparable to western charts but none of the standard charts agreed with the data in the present study particularly in third trimester.

Conclusion

Since most parameters of the standard growth curves developed in the west are not applicable for assessing the intrauterine growth of Indian babies we have developed growth curves for the Indian population to prevent over-diagnosis of intrauterine growth retardation and correct prediction of fetal age in Indian population.
Is Pneumoperitoneum Really Required before Primary Trocar Insertion in Laparoscopy?
Authors: Kapur Krishan
Published: April 2010

Objectives

Traditionally a Veress needle is used to create a pneumoperitoneum before entering the primary trocar/cannula for laparoscopy. Insufflation of gas into the peritoneal cavity with the Veress needle is not without its problems. To do away with these problems the technique of direct trocar access was started.

Materials and methods

Between 01 Jan 2003 and 31 Dec 2008— 2958 laparoscopic procedures were carried out in a Government hospital. 345 patients out of these had undergone previous laparotomies. In all cases direct trocar insertion without pneumoperitoneum was done.

Result

In this series there were no complications except in one case there was mesenteric injury with bleeding which required a laparotomy. There were no failed laparoscopies.

Conclusion

We have found that direct trocar insertion before creating pneumoperitoneum is a safe and effective method for laparoscopic access and offers advantages over the conventional access modality of using a Veress needle for pneumoperitoneum.
Challenges for Utilization of Antenatal and Delivery Care Services in Urban Setting of Bangladesh
Authors: Tasnim Saria , Rahman Aminur , Chowdhury Sameena , Shahabuddin AKM
Published: April 2010

In most developing countries like Bangladesh the health care facilities are not optimally available and usually are underutilized. The study explored the perception of urban poor women regarding pregnancy, childbirth and obstetric care services of the health centers and factors for utilization and/or nonutilization of such services.

Focus group discussions were conducted among mothers with a child aged one year or below, their husband and elder female members of the family between May and June 2001 in selected geographical clusters of Dhaka city.

It was revealed that women regard pregnancy and child birth as a natural process that needs no medical care unless some dire emergency arises. Taking tetanus toxoid during pregnancy was equated with availing antenatal care. Traditional birth attendant (Dai) was more preferable as birth attendant as they are available at home, like a kin to them, and affordable. Reason for not availing the services were high cost, nonavailability of drugs, hassles to get free bed, ignorance about the complications, negative cultural norm, rude behavior of health care providers, fear of cesarian section and an unfamiliar environment in the hospitals. Utilization of maternity care services can be improved through a combined effort of increasing awareness to avail skilled care and made the services more accessible and with better quality.
Antenatal Care Counseling Pamphlet and Emergency Obstetric Care
Authors: Begum Ferdousi , Bhuiyan AB
Published: April 2010

A prospective longitudinal study with experimental design was undertaken among the MCH providers and antenatal mothers in 2 zones of Dhaka city, between July 1997 to June 1998. One of the objective of the study was to find out the effect of using antenatal care counselling pamphlet by the MCH service providers on quality of their antenatal care delivery and change in awareness of pregnant mother's on emergency obstetric care (EOC). A colored pamphlet on antenatal care counselling was developed and finalized after focal group discussion, pretesting and general discussion among professionals. Different category of MCH care providers were trained on why and how to use such pamphlet. Service providers (n-307) who used ANC pamphlet discussed various obstetric emergencies more frequently (p < .05 to p < .001) with the pregnant mothers in comparison to those who did not use such card. Similarly, knowledge among the service providers on place and person of referral for different obstetric complications also increased significantly (p < .04 to p < .001) after orientation on use of ANC pamphlet. Pregnant mothers who received at least 2 ANC session were interviewed during antenatal care, before (n-172) and after (n-300) the use of ANC pamphlet. Scoring on recognizing the pictures as obstetric emergency and being able to mention places and person of contact if such emergency arise (self referral) increased significantly (p <. 001). Use of ANC pamphlet increased quality of ANC counselling and the knowledge of pregnant mothers on obstetric complications and self referral.
Operant Self‐Administration Models for Testing the Neuropharmacological Basis of Ethanol Consumption in Rats
Authors: June Harry L. , Gilpin Nicholas W.
Published: April 2010

Operant self‐administration procedures are used to assess the neural basis of ethanol‐seeking behavior under a wide range of experimental conditions. In general, rats do not spontaneously self‐administer ethanol in pharmacologically meaningful amounts. This unit provides a step‐by‐step guide for training rats to self‐administer quantities of ethanol that produce moderate to high blood‐alcohol content. Different protocols are used for rats that are genetically heterogeneous versus rats that are selectively bred for high alcohol preference. Also, these protocols have different sets of advantages and disadvantages in terms of the ability to control for caloric intake and taste of solutions in operant testing. Basic self‐administration protocols can also be altered to focus on different aspects of the motivational properties of ethanol (for example, those related to dependence). This unit provides multiple protocols that lead to alcohol intake in rats, which can be pharmacologically probed relative to a variety of control conditions.Curr. Protoc. Neurosci. 51:9.12.1‐9.12.26. © 2010 by John Wiley & Sons, Inc.