bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectrum of surgical trauma and associated head injuries at a university hospital in eastern Nepal
Authors: Bajracharya A , Agrawal A , Yam B R , Agrawal C S , Lewis Owen
Published: May 2010

Background: Trauma is one of the common surgical emergencies presenting at B. P. Koirala Institute of Health Sciences (BPKIHS), Nepal, a tertiary referral center catering to the needs of the population of Eastern Nepal and nearby districts of India. Objective: The objective of this study is to analyze the magnitude, epidemiological, clinical profile and outcome of trauma at B P Koirala Institute of Health Sciences. Materials and Methods: This descriptive case series study includes all patients with history of trauma coming to BPKIHS emergency and referred to the surgery department. We noted the detailed clinical history and examination, demographics, mechanism of injury, nature of injury, time of reporting in emergency, treatment offered (operative or non operative management) and analyzed details of operative procedure (i.e. laparotomy, thoracotomy, craniotomy etc.), average length of hospital stay, morbidity and outcome (according to Glasgow outcome scale). Collected data were analyzed using EpiInfo 2000 statistical software. Results: There were 1848 patients eligible to be included in the study. The mean age of the patients was 28.9 ± 19.3 years. Majority of the patients (38%) belonged to the age group of 21 - 40 years and the male to female ratio was 2.7:1. Most of the trauma victims were students (30%) followed by laborers (27%) and farmers (22%) respectively. The commonest causes of injury were fall from height (39%), road traffic accident (38%) and physical assault (18%); 78% of the patients were managed conservatively and 22% underwent operative management. Postoperative complications were seen in 18%. Wound infection 7.5%, neurological deficit including cerebrospinal fluid (CSF) otrorrhea was seen in 2.2% patients. Good recovery was seen in 84%, moderate disability in 5.2% patients and severe disability in 1.4% patients. The mortally was 6.3% and most of the deaths were related to traumatic brain injuries. Conclusions: In Nepal, trauma-related injury contributes significantly to morbidity and mortality and is the third leading cause of death. There are very few studies on trauma from this country and hence this study will help in understanding the etiology and outcome particularly in the Eastern region of Nepal.
Pituitary tuberculoma
Authors: Shukla S , Trivedi A , Singh K , Sharma V
Published: May 2010

Tuberculosis of pituitary gland is rare. We report a case of tuberculosis of pituitary gland in a 68-year-old male presented with holocranial headache of four months duration with left temporal hemianopia, with visual acuity of 6/6, without any localizing sign. Magnetic resonance imaging showed a sellar ring enhancing mass with suprasellar extension. Patient was taken up for surgery and put on antitubercular treatment and hormone replacement therapy.
Giant solitary neurofi broma presenting as a neck mass in an infant
Authors: Dwivedi Sankalp , Baisakhiya Nitish , Bhake Arvind , Bhatt Manisha , Agrawal Amit
Published: May 2010

Solitary neurofi broma is a rare tumor of the head and neck region. It is more common in viscera, where it is associated with features of NF1. It occurs most often between the third and fourth decade. These lesions are extremely rare in infants. We report a case of giant, solitary neurofi broma presenting as a progressive mass in parotid region in an infant. This case is unique in its age of presentation (11 months), site, size (about 8 x 15 cm) without any symptoms or neurological defi cit.
Hirayama disease
Authors: Tayade Atul T , Kale Sushilkumar K , Pandey Arvind , Kalantri Shriprakash
Published: May 2010

A 17-year-old male, who gave up his favorite sport cricket and started playing football, presented with one-year history of slowly progressive atrophic weakness of forearms and hands. Neurological examination showed weak and wasted arms, forearms and hand but no evidence of pyramidal tract, spinothalmic tract and posterior column lesions. Plain cervical spine radiographs showed no abnormal fi ndings. Cervical magnetic resonance imaging (MRI) showed asymmetric cord atrophy; images obtained with neck fl exed showed the anterior shifting of the posterior wall of the lower cervical dural sac resulting in cord compression. These fi ndings suggest Hirayama disease, a kind of cervical myelopathy related to the fl exion movements of the neck.
Microconsumer grazing and sources of limiting nutrients for phytoplankton growth: Application and complications of a nutrient‐depletion/dilution‐gradient technique
Authors: Elser James J. , Frees David L.
Published: May 2010

A series of eight nutrient‐deletion/dilution‐gradient experiments was performed in Castle Lake during summer 1993 to quantify and characterize microconsumer grazing and contributions of nutrient supply sources (external, cell quota, recycling) supporting phytoplankton production. Responses of net chlorophyll production rate to dilution under nutrient‐saturated conditions were frequently nonlinear, indicating saturation of micrograzer feeding at low biomass levels within the dilution gradient (dilutions of < 10–30% whole lake water). Despite feeding saturation, micrograzers exerted substantial grazing pressure on phytoplankton: microconsumer grazing coefficients (0.05–0.22 d–1, mean: 0.14 d−1) exceeded previous measures of crustacean grazing in this system. Nonlinear feeding kinetics required that piecewise multiple regression be used to estimate contributions of external, cell quota, and recycling to N and P supply. In deep‐water layers, phytoplankton were growing at nutrient‐saturated rates, indicating that phytoplankton growth was more likely light limited. In the epilimnion, recycled and internal sources were important for both N and P in different experiments, but the importance of various supply sources did not systematically differ for N and P. In epilimnetic experiments, there was strong experiment‐to‐experiment variation in contributions of recycling sources of N and P, suggesting that resupply of N and P via grazers was decoupled. Comparison of phytoplankton responses to nutrient deletion in undiluted vs. highly diluted treatments indicated that inferences regarding frequency and magnitude of nutrient limitation, as well as identity of the primary limiting nutrient, depended on dilution.
Dynamics of dissolved organic car‐bon lability in a eutrophic lake
Authors: Søndergaard Morten , Hansen Benni , Markager Stiig
Published: May 2010

The concentration of labile dissolved organic C([DOCL]) and the plankton community structure were measured weekly during a diatom spring bloom and the subsequent clear‐water phase in a eutrophic, temperate lake. The DOCL concentration was assessed by a bacterial regrowth method based on direct measurements of the increase in bacterial biomass and its respiratory demand. [DOC] ranged from 560 to 1,130 µg C liter−1 and accounted for only 5–9% of total DOC. DOCL oscillated around 800 µg C liter−1, and the amplitude over 7‐d periods was within ± 16% of the in situ bacterial carbon demand. One period (3 weeks) with consistently increasing [DOCL] took place concomitant with the increase in macrozooplankton and bacterial biomass. Thus, DOCL was positively related to decreases in chlorophyll and zooplankton grazing. The increase in DOCL was followed by 3 weeks with decreasing concentrations, when the relationship between DOCL and bacterial production was negative. This pattern gives support to the hypothesis that grazing is a quantitatively important process in the flow of carbon to bacteria. The variations of DOCL were analyzed with a model describing interactions among substrate, bacteria, and grazing. Short‐term (days) oscillations probably result from pulses of substrate production that are followed within a few days by bacterial uptake, and long‐term (weeks) variations are explained by a variable bacterial substrate affinity (Km).
Nitrate reductase activity quantitatively predicts the rate of nitrate incorporation under steady state light limitation: A revised assay and characterization of the enzyme in three species of marine phytoplankton
Authors: Berges John A. , Harrison P. J.
Published: May 2010

The enzyme nitrate reductase (NR) has been proposed as an index of nitrate incorporation rates in marine phytoplankton, but it has proven difficult to interpret NR measurements in field settings because many previous NR assays have been poorly optimized and NR activity in phytoplankton has been poorly characterized under steady state conditions. An NR assay was developed for the diatom Thalassiosira pseudonana using an extraction in phosphate buffer with Triton X‐100, EDTA, dithiothreitol, polyvinyl pyrrolidone, and bovine serum albumin. NR activity in homogenates was stable for up to 1 h, but filtered samples could be stored for 96 h in liquid nitrogen without significant loss of activity. Addition of FAD to crude extracts of T. pseudonana had no effect, whereas the effect on desalted extracts or crude extracts from other species, varied from decreases in NR activity to over 250% increases. Half‐saturation constants (Km) varied between species; high levels of NADH or nitrate were found to be inhibitory in some cases. These results indicate a wide diversity of forms of NR in marine phytoplankton. Under continuous, light‐limited growth, NR activity was quantitatively related to calculated rates of nitrate incorporation (µN) in T. pseudonana, Skeletonema costatum, and three other diatom species examined. The relationship differed for 10 other species; NR activity was equal to µN in some cases, but higher or lower in others. In dinoflagellates, in particular, NR activity was highly correlated with µN, but accounted for <20% of µN in Amphidinium carterae.
Significance of colloids in the biogeochemical cycling of organic carbon and trace metals in the Venice Lagoon (Italy)
Authors: Martin Jean‐Marie , Dai Min‐Han , Cauwet Gustave
Published: May 2010

Colloidal organic C and trace metals from the waters of a highly productive coastal environment (the Venice Lagoon, Italy) have been separated by a cross‐flow ultrafiltration device. On average, 18% of organic C, 34% of Cd, 46% of Cu, 87% of Fe, 18% of Ni, 58% of Pb, and 54% of Mn which previously would have been considered in the dissolved phase are actually associated with colloidal material. Thus, past studies overestimate the dissolved trace‐metal concentration in the nearshore environment. Compared to total concentration, the proportion of the colloidal fraction represents on average 15% of organic C, 18% of Cd, 28% of Cu, 11% of Fe, 11% of Ni, 29% of Pb, and 12% of Mn. This fraction acts differently from the truly dissolved and macroparticulate phases. The behavior of organic C and trace elements during mixing between freshwater and seawater is more complicated than expected when a colloidal fraction is involved. The flocculation of colloids, encountered normally during estuarine mixing, is not very significant on the time scale of mixing in the lagoon. Conversely, the interaction between colloidal and truly dissolved phases seems important. The partitioning of trace metals between different fractions of organic C appears variable, Fe and Mn are preferentially tied to macroparticulate organic matter, and Cu and Cd are preferentially tied to colloidal organic matter in seawater. Truly dissolved organic C appears to be important for Ni. Pb is mainly associated with macroparticulate organic matter at most stations except in the highly productive region where Pb prefers colloidal organic C.
A physical estimate of new production in the equatorial Pacific along 150°W
Authors: Carr Mary‐Elena , Lewis Marlon R. , Kelley Dan , Jones Burton
Published: May 2010

New production was estimated for the equatorial Pacific by quantifying the supply of nitrate into the euphotic zone. The turbulent flux of nitrate, estimated by assuming gradient transport and by direct measurements of dissipation and nitrate concentration along a cross‐equatorial transect, was maximum (1–3 mmol m−3 d−1) at 0° and 1°S. Poleward of the equatorial region, there was little vertical diffusion of nitrate (< 10−3 mmol m−2 d−1). An estimate was made of the two‐dimensional advective balance of nitrate between upwelling and the meridional divergence in the equatorial region. The net supply of nitrate into the euphotic zone (vertical supply minus meridional loss) was 4.3 mmol m−2 d−1 between 1°N and 1°S; between 5°N and 5°S, it was 1.9 mmol m−2 d−1. The total supply of nitrate was larger than the concurrently measured incorporation of nitrate into particles but was comparable to the integrated local rate of nitrate disappearance. The discrepancy between new production estimated from physical supply or from nitrate disappearance and that estimated from nitrate incorporation into particles suggests that uptake by small cells (< 1 µm), dissolved organic N, or both play an important role in the equatorial region.
Genetic comparisons reveal the same unknown bacterial lineages in Atlantic and Pacific bacterioplankton communities
Authors: Mullins Thomas D. , Britschgi Theresa B. , Krest Robin L. , Giovannoni Stephen J.
Published: May 2010

The phylogenetic diversity of oligotrophic bacterioplankton communities was compared with 16S ribosomal RNA genes cloned from natural populations. The data reported here extend a previous analysis of a bacterioplankton 16S rRNA clone library with 15 additional nucleic acid clone sequences, to provide information on 60 16S rDNA clones from hydrostation S in the Sargasso Sea. The data were compared to partial sequences of 37 Bacterial 16S rDNA clones reported from a surface picoplankton population collected at the Aloha station in the North Pacific gyre, and partial sequences of 29 Bacterial 1 6S rRNA clones obtained from sites near Bermuda and the western California Current. The results support reports of diverse groups of previously unknown a‐proteobacteria, γ‐proteobacteria, and cyanobacteria in oceanic surface samples. Three novel lineages (SAR 121, 125, 145) of proteobacteria were found. Several genes cloned from the Sargasso Sea were nearly identical to genes cloned from the Pacific samples, suggesting that these previously unrecognized bacteria groups (SAR11, SAR122, SAR86) are distributed widely in the surface waters of subtropical oceans. Two gene clones closely matched nucleotide sequences from the cultivated bacterial species Photobacterium phosphoreum and A lteromonas haloplanktis.
Importance of surface‐subsurface exchange in stream ecosystems: The hyporheic zone
Authors: Findlay Stuart
Published: May 2010

In many streams, significant amounts of water are exchanged between saturated sediments surrounding the open channel (the hyporheic zone) and the channel itself. Such exchanges with the hyporheic zone have the potential to cause large changes in streamwater chemistry because the rates of biogeochemical processes and the actual types of processes (e.g. anaerobic vs. aerobic metabolism) may be fundamentally different. I propose an organizational scheme for grouping stream systems into clusters of minimal, moderate, and maximal contribution of hyporheic metabolism to the overall ecosystem. Lack of information on quantitative hydrology for different stream systems prohibits actual testing of this framework. An alternative scheme is presented that organizes several well‐studied streams as a function of subsurface residence time and differences in oxygen content. This second scheme is intended to stimulate discussion of conceptual frameworks for cross‐system comparisons of the importance of hyporheic sediments in stream ecosystems.
Response of larval fish assemblages to a riverine plume in coastal waters of the central Great Barrier Reef lagoon
Authors: Thorrold Simon R. , McKinnon A. David
Published: May 2010

Ichthyoplankton assemblages were compared among stations in the vicinity of a riverine plume in coastal waters of the central Great Barrier Reef lagoon, Australia, during January 1991. Although the plume dramatically influenced both community structure and abundance of larval fish, effects were temporally dynamic and taxon‐specific. Mullids were the only family to show significantly higher densities at the plume front than either inside or outside the plume. Samples from the plume front and coastal waters outside the plume showed similar taxonomic affinities. These affinities appeared to be driven by the offshore movement of the plume translocating coastal larvae offshore, which also led to accumulation of these larvae at the plume front. Given the large area that the plume covered and the high zooplankton biomass and secondary production in these waters, we suggest that the plume may have affected larval fish survival and recruitment more than the associated plume front.
Enhanced bacterial growth in response to photochemical transformation of dissolved organic matter
Authors: Lindell Måns J. , Granéli Wilhelm , Tranvik Lars J.
Published: May 2010

We tested the hypothesis that light, especially UV‐B radiation, increases the availability of dissolved organic matter (DOM) to pelagic bacteria in lake water. Filtered (0.2 µm) and autoclaved humic lake water (water color 70 mg Pt liter−1, 12 mg dissolved organic C liter−1) was exposed to simulated sunlight (UV‐B, 1.14 W m−2; UV‐A, 3.87 W m−2; and PAR, 20 W m−2) for various periods of time (0–100 h). Irradiated water was then inoculated with a natural bacterial assemblage (0.6‐µm filtered water) and bacterial yield was measured in the stationary phase of the resulting batch cultures. Both bacterial numbers and cell volumes increased (numbers by 65% and volumes as much as 360%) with increasing UV radiation, resulting in an almost sixfold increase in bacterial biomass. Our experiment shows that light exposure can enhance availability of natural lake DOM to bacteria, possibly through cleavage of macromolecules into smaller units, and may influence both carbon cycling and food webs in lake water.
The role of sex in the sedimentation of a marine diatom bloom
Authors: Crawford Richard M.
Published: May 2010

A longitudinal transect in the Atlantic sector of the Southern Ocean extending from the ice‐covered Weddell Sea across the Antarctic Circumpolar Current and into the Polar Frontal Zone was studied repeatedly during the austral spring. The centric diatom Corethron criophilum was found at most stations in variable numbers, but in the Polar Frontal Zone I encountered a large bloom undergoing a mass sexual phase. This event apparently triggered downward transport of empty diatom cell walls in numbers that suggest the phenomenon is significant for the vertical silica flux and the formation of monospecific layers of this important diatom species in Southern Ocean sediments. Comparison of the cell‐wall dimensions of such a monospecific layer with those in the plankton in the sexual phase reveals a characteristic signature that may indicate the provenance of these layers.
Bosmina remains in Lake Washington sediments: Qualitative heterogeneity of bay environments and quantitative correspondence to production1
Authors: Kerfoot W. Charles
Published: May 2010

Bay environments differ in productivity and species composition from open waters. Transects of surface sediments in Lake Washington (Seattle) reveal significant morphological gradients in the small pelagic cladoceran Bosmina longirostris. In all bays examined, these bosminids range from shorter featured clones nearshore to longer featured clones offshore. However, because bays constitute such a limited areal extent of the lake (4.9%), only 2.3% of remains in midlake sediments came from bay populations. A core taken from midlake waters indicates nearly uniform long‐featured morphology of offshore Bosmina over the past 80–125 yr. The localized deposition of remains in bays underscores that biodiversity surveys of large lakes need to include bays in addition to open‐water samples.

Clarifying how abundant cladoceran remains are produced, transported to, and preserved in sediments is crucial for interpreting historical sequences. A simple vertical model, derived from molting and death schedules, accurately predicts relative seasonal fluxes for remains at a midlake site (r = 0.9−0.95). However, the absolute flux is low, <7% of the expected rate, suggesting substantial loss through decomposition and fragmentation. Use of abundant cladoceran microfossils to reconstruct species‐specific or general secondary production requires careful calibration studies, although the potential dividends are great.
Effects of nutrient loading on mass‐transfer rates to a coral‐reef community
Authors: Bilger R. W. , Atkinson M. J.
Published: May 2010

The apparent first‐order rate constants for NH4+ (N) and PO43− (P) uptake into a coral‐reef community (SN and SP) were measured 61 times in a 9‐m experimental flume over 43 d. Water velocities (Ub) varied from 4 to 39 cm s−1 to determine the apparent mass‐transfer exponent—the slope between log SN or log SP and log Ub. SN varied from 26 to 147 × 10−6 m s−1, while SP varied from 4.8 to 60. Apparent mass‐transfer exponents varied from 0.3 to 0.7. Both SN and SP and their apparent mass‐transfer exponents were inversely correlated with nutrient loading. We consider these effects to be caused by decreases in the rate constants for the real surface reactivity, SrN and SrP, following abnormally high loading of nutrients. As a result of nutrient loading, concentrations of nutrients at the surface of the benthos rise and reduce the rate of diffusion through the boundary layer. A method is presented for calculating mass‐transfer coefficients and Stanton numbers for mass transfer from such data. Results for these physically determined quantities are consistent with earlier measurements and theoretical predictions. To avoid such nutrient‐satiation effects, it appears to be important to avoid exceeding the nutrient‐loading levels of the natural habitat.
Fecal pellet flux in Dabob Bay during a diatom bloom: Contribution of microzooplankton
Authors: Buck Kurt R. , Newton Jan
Published: May 2010

During a spring bloom primarily composed of the centric diatom Thalassiosira pacifica in Dabob Bay, Washington, an unarmored dinoflagellate, Gyrodinium sp., phagocytized chains of Thalassiosira. The diatoms were egested in peritrophic membrane‐bound fecal pellets that were collected in sediment traps. The dinoflagellate pellets accounted for an average of 29% (SD = 16%) of the volume of fecal pellet flux at 50 m. The diatoms in the pellets were intact but void of plasma content, thus reducing the flux of both POC and pigments per volume of fecal pellets, as was apparent in the sediment trap measurements. Grazing by these dinoflagellates on the large diatoms and the export of relatively carbon‐ and pigment‐deplete pellets have much different implications for organic material cycling than if the diatoms were consumed by mesozooplankton or if they sank.
Settlement and transport of benthic invertebrates in an intermittent upwelling region
Authors: Wing Stephen R. , Largier John L. , Botsford Louis W. , Quinn James F.
Published: May 2010

We monitored settlement of sea urchins (Strongylocentrotus spp.) and crabs (primarily Cancer spp.) and concurrent physical variables at Bodega Marine Laboratory (BML) and Salt Point (northern California) from April through August 1992. Upwelling favorable winds led to lower temperatures, higher salinities, and lower subsurface pressures at BML, while periods of relaxation from upwelling typically caused a lagged reversal of each of these trends. This response to relaxation was due to a combination of alongshore and onshore flow of near‐surface water at this site. Crab settlement was significantly correlated with the rate of temperature increase, corresponding to relaxation events. In contrast, sea urchins settled primarily during an unusual relaxation event which possibly involved remote forcing. Sea urchin and crab settlement were negatively correlated. Possible reasons include residence in different water masses, different biomechanical characteristics, and predation by crab larvae on sea urchin larvae. The time‐course of settlement at Salt Point was similar to that at BML for both species groups.
Diagnostic modeling of trace metal partitioning in south San Francisco Bay
Authors: Wood T. W. , Baptista A. M. , Kuwabara J. S. , Flegal A. R.
Published: May 2010

The two‐dimensional numerical model ELAmet was used to investigate the effect of adsorption kinetics on the apparent distribution coefficients of Cu, Cd, and Zn in south San Francisco Bay, California. The numerical experiments were designed to determine whether adsorption kinetics can control the basin‐scale variability of the observed partitioning and to define the conditions under which adsorption kinetics could account for strong interannual variability in partitioning.

The numerical results indicate that aqueous speciation will control basin‐scale spatial variations in the apparent distribution coefficient, Kda, if the system is close to equilibrium. However, basin‐scale spatial variations in Kda are determined by the location of the sources of metal and the suspended solids concentration of the receiving water if the system is far from equilibrium. The overall spatial variability in Kda also increases as the system moves away from equilibrium.
The physical response of temperate lakes to artificial destratification
Authors: Schladow S. G. , Fisher I. H.
Published: May 2010

Prolonged periods of thermal stratification in a lake suppress convective motions capable of vertical transport of dissolved oxygen and other dissolved and suspended matter. When this leads to anoxia in the hypolimnion, it can give rise to profound water quality implications. Artificial destratification is one means whereby low oxygen levels in the hypolimnion may be averted. The operating principles of bubble plume destratification and its effect on the physical transport and mixing that occurs in a lake are described. Monitoring of temperature and dissolved oxygen was conducted at Lake Nepean, Australia, prior to the destratification, and then continued for two summers while the destratification system was operating. The results showed that artificial destratification had an immediate effect on lake motions across a range of scales. The actual process of destratification occurred by the erosion of the base of the thermocline. Deep‐water temperatures were elevated well above historical values, the heat storage in the lake increased, and the time of turnover was brought forward 2.5 months. An integral plume model coupled with a one‐dimensional lake model is shown to predict the effect of the bubble plume entrainment and the subsequent redistribution of the entrained water throughout the lake.
Observations and numerical simulation of a shallow ice‐covered midlatitude lake
Authors: Rogers Christopher K. , Lawrence Gregory A. , Hamblin Paul F.
Published: May 2010

We have developed a numerical model to simulate the heat budget of a shallow ice‐covered midlatitude lake. New features include: snowmelt due to rain, sediment heat transfer, formation of snow‐ice, and variability in snow density, snow conductivity, and albedo. To test this model we conducted a field study of a shallow, midlatitude lake where there was no thermal stratification in winter beyond that associated with the ice and sediment interfaces. The absence of stratification allowed us to focus our attention on the heat fluxes across these interfaces rather than the details of the thermal structure within the lake. Discrepancies between field observations and model predictions are accounted for by parameter uncertainties and expected observation error. Sediment heat transfer may be important in early winter in preventing a net loss of heat from the lake water. Significant heat gains in the latter part of winter, however, are attributed to the penetration of solar radiation through the ice.
What role does UV‐B radiation play in freshwater ecosystems?
Authors: Williamson Craig E.
Published: May 2010

Increases in incident UV‐B radiation (280–320 nm) have been observed at temperate as well as polar latitudes in recent decades. Although UV‐B radiation makes up only a small portion of the total energy of solar radiation and attenuates rapidly in the water column, the high sensitivity of living organisms to UV‐B radiation makes the observed increases potentially important in aquatic ecosystems. To date, research has focused largely on the primary producers in marine ecosystems in Antarctica where ozone depletion and subsequent increases in UV‐B radiation have been most pronounced. This review addresses the potential role of UV‐B radiation in freshwaters by taking into account some of the information available in marine systems and applying some of the recent advances in our understanding of the ecology of freshwaters. The potential for complex rather than simple responses of freshwater ecosystems to UV‐B radiation is emphasized.
In situ methods for measuring the inherent optical properties of ocean waters
Authors: Bricaud Annick , Roesler Collin , Zaneveld J. Ronald V.
Published: May 2010

In situ attenuation (488 and 660 nm), absorption (488, 676, and 750 nm), backscattering (at 488 nm), and stimulated fluorescence were determined as functions of depth in oceanic and coastal waters off Oregon, using both commercial instruments and recently developed prototypes. The inability to perfectly constrain scattered light in these instruments necessitates correction to retrieve accurate optical coefficients. Because scattering is usually one order of magnitude higher than absorption, the correction is most critical for absorption coefficients. A correction procedure based on values obtained with the absorption meter in the infrared region (750 nm) was used to correct the measured spectral absorption coefficients. Realistic values of the backscattering coefficient were obtained from a prototype instrument, although accurate calibration could not be performed for this study.

These measurements resulted in the first‐ever data set ofin situ profiles of attenuation, absorption, scattering, backscattering, and the backscattering ratio. The blue and red attenuation coefficients were tightly correlated, with a relationship varying from site to site. The red‐to‐blue absorption ratio varied both from site to site and vertically, indicating changes in the relative concentrations of chlorophyllous (phytoplankton) and nonchlorophyllous (biogenous or mineral) particles. The backscattering ratio also appeared to be very sensitive to vertical changes in particle composition. The in situ scattering coefficients were compared to those estimated with a Mie scattering model, using measured particle size distributions and particulate absorption coefficients as input parameters. By allowing the real part of the refractive index of particles to vary over the range of realistic values, convergence between measured and modeled values was obtained.
The use of in situ and airborne fluorescence measurements to determine UV absorption coefficients and DOC concentrations in surface waters
Authors: Vodacek Anthony , Hogel Frank E. , Swift Robert N. , Yungel James K. , Peltzer Edward T. , Blough Neil V.
Published: May 2010

We compared the fluorescence (λex = 355 nm, λem = 450 nm) of chromophore‐containing dissolved organic matter (CDOM) determined in the laboratory to that determined with a shipboard fluorometer and an airborne laser fluorosensor off the U.S. mid‐Atlantic coast. Fluorescence was highly correlated with CDOM absorption at the excitation wavelength despite the presence of multiple sources of CDOM and a changing contribution of CDOM to the total dissolved organic C (DOC) pool, both in surface waters and down the water column. The mean quantum yield (0.8±0.1%) fell within the narrow range of yields previously determined for U.S. east coast and south Florida waters. These results show that CDOM absorption can be reliably determined from in situ or airborne fluorescence over wide areas of the ocean and that it may be possible to estimate DOC concentration from fluorescence or absorption measurements.
Relationships between light availability, chlorophyll a, and tripton in a large, shallow subtropical lake
Authors: Phlips E. J. , Aldridge F. J. , Schelske C. L. , Crisman T. L.
Published: May 2010

The relationships between planktonic chlorophyll a and mean light availability in the mixed layer were examined for Lake Okeechobee, a shallow eutrophic lake in south‐central Florida. There were significant spatial differences in the nature of this relationship. In the northern and central regions of the lake, concentrations of nonalgal suspended solids, tripton, were high due to muddy sediments and polymictic conditions. Light attenuation was predominantly correlated to the concentration of tripton and chlorophyll a concentrations were positively correlated to mean light availability in the mixed layer, Im. The western and southern regions of the lake had lower concentrations of tripton and light attenuation was correlated to chlorophyll a concentrations in summer and fall. Variables which estimate mean light availability in the mixed layer, such as Im, may provide insight into the role of light availability in the control of phytoplankton standing crop.
Accumulation of marines now at density discontinuities in the water column
Authors: MacIntyre Sally , Alldredge Alice L. , Gotschalk Chris C.
Published: May 2010

The vertical distribution of marine snow—aggregated particles >0.5 mm in diameter—was strongly correlated with density discontinuities in the upper 100 m of the water column at 33 stations off central California. Eighty‐seven percent of peaks in aggregate abundance were associated with density discontinuities in which N2 (the Brunt‐Väisälä frequency) exceeded 1.25 × 10−4 s−2 (N = 6 cph). For 56% of the peaks, N2 exceeded 2.5 × 10−4 s−2 (N = 9 cph). Absolute abundances of aggregates increased from a mean of 38.7± 18.3 aggregates liter−1 above peaks to 59.3 ± 26.0 aggregates liter−1 within peaks. Accumulations of aggregates could result from sinking into denser water if sinking rates were reduced by at least 20% due to slow equilibrium of either interstitial water or mucus within the flocs with the surrounding, higher density water. However, our observed increases in σt were insufficient to cause such slowing for flocs whose porosity was 99% or less; such flocs comprised a significant proportion of aggregates in the observed peaks. However, larger flocs of moderate to high porosity were likely to decelerate as they encountered denser water and could even become neutrally or negatively buoyant for changes in σt such as we observed. Equilibration times of the interstitial water of these generally larger flocs ranged from hundreds of seconds up to 3 h. Results of a random walk simulation of particle motion indicated that turbulence was likely to cause localized accumulations of aggregates and to increase particle aggregation. Because we found subcritical values of the Richardson number (an indicator of turbulent mixing) at the top of regions of peak abundance but not at the base, for 68% of the peaks observed, we infer that turbulence may contribute to the accumulation of the smaller flocs. Occurrence of strong shear and deviations of temperature and salinity profiles from typical patterns suggest that at least 23% of these aggregate peaks were associated with horizontal intrusions.
Amino acid degradation by sulfate‐reducing bacteria: Evaluation of four methods
Authors: Hansen Lars Stenvang , Blackburn Thlomas Henry
Published: May 2010

Four methods were evaluated for estimating the proportion of dissolved free amino acids (DFAAs) metabolized by sulfate‐reducing bacteria (SRB). Our main aim was to assess the problems associated with each method, each of which used molybdate (Mo) as an inhibitor of SRB activity. Mo had some side effects that clouded interpretation of the results. Mo treatment did not increase the accumulation rate of protein amino acids, but the nonprotein amino acids [δ‐amino‐valeric‐acid (δ‐AVA), γ‐amino‐butyric‐acid (GABA), β‐amino‐glutaric‐acid (BAGA), and unidentified amines] accumulated, resulting in a total amino pool increase of 6.1 nmol cm−3 d−1. There was no decrease in NH4+ production rate. SRB appeared to degrade 14C‐labeled aspartic acid, serine, glutamic acid, and alanine and were also involved in the degradation of δ‐AVA, BAGA, GABA, and taurine. Mo appeared to release DFAAs which were either bound to sediment particles or were from killed SRB. These additional DFAAs complicated comparisons between incubations with and without Mo. We suggest that in the case of Mo‐amended incubations, surplus DFAAs were metabolized by fermenting bacteria, resulting in no accumulation of protein DFAA and an increased NH4+ production rate. The uninhibited rate of NH4+ production (111 nmol cm−3 d−1) indicated that SRB were responsible for 5% of this rate.
Bioavailable amino acids in sediments: A biomimetic, kinetics based approach
Authors: Mayer Lawrence M. , Linda L. Schick , Sawyer Thomas , Plante Craig J. , Jumars Peter A. , Sel Robert L.
Published: May 2010

We developed a biomimetic approach, based on direct incubation with proteolytic enzymes, to measure bioavailable amino acids in sediments. The kinetics of release of monomers and oligopeptides, which are amenable to absorption by cells, is measured as either individual or total amino acids. Microbial proteases incubated with fresh sediments yield amino acids at a similar rate as gut juices from a deposit‐feeding holothuroid. Amino acid release from fresh sediment was dominated by a slow hydrolysis step from a refractory substrate, which can be described with a first‐order rate law. Typical rate constants for release were in the range 0.15–0.52 h−1, consistent with gut residence times of deposit feeders. The bioavailable pool of peptides had a composition resembling that of average biological tissue, but comparisons with tissue composition suggested dietary deficiency of some essential amino acids. The early stages of release exhibited significant contributions from osmolytes (e.g. glutamic acid and taurine), while a larger, more slowly released pool was anomalously low in methionine, suggesting a contribution from microbial coat proteins. Freezing the sediment led to greater yields of amino acids, which reduced the simulation of a deposit feeder’s gut but indicated a larger pool of potentially bioavailable substrate protected by some kind of matrix. This larger pool of peptide substrate was usually dominated by higher molecular weight polypeptides as measured by the Coomassie Blue method.
Phytoplankton functional attributes along trophic gradient and season
Authors: Seip K. L. , Reynolds C. S.
Published: May 2010

Each of the following phytoplankton functional attributes could be described by significant (P < 0.05) response surfaces defined by trophic status (T) from oligotrophy to hypertrophy and season (S) from early vernal period to late summer: phytoplankton cell volume, growth rate, the ratio between minimum quotas of total N and total P, affinity for P, half‐saturation constant for growth with respect to P, and temperature optimum and light optimum for growth. Sinking rate could not be so described. The response surfaces were calculated by multiple regressions, including first‐ and second‐order terms of T and S and the interaction term T · S. Although the data base was rather limited (number of phytoplankton species ranged from 10 to 31), the resulting surfaces often reflected a corresponding attribute of the water along T and S (e.g. phytoplankton temperature optimum for growth reflected water temperature). The results support the frequent use of physical factors as explanatory variables for the distribution and abundance of phytoplankton.
Polyphosphate in lake sediments: 31P NMR spectroscopy as a tool for its identification
Authors: Hupfer Michael , Gtichter Red , Ruegger RedHeinz R.
Published: May 2010

Variations in the nonreactive P content of lake sediments as a consequence of changing redox conditions suggest that microorganisms may contribute to uptake and release of P. In this study, 31–50% of the nonreactive P was identified as polyphosphate (poly‐P) in NaOH extracts of sediments from eutrophic Lake Baldegg and oligo‐mesotrophic Lake Lucerne by means of 31P NMR spectroscopy. Poly‐P was present in surface sediments but not in deeper sediment layers. In samples where poly‐P was detected, analysis under a scanning transmission electron microscope equipped with energy‐dispersive X‐ray spectroscopy indicated the presence of sediment bacteria containing P‐rich granules. Although poly‐P is stable in pure NaOH solution, it partially hydrolyzes during and after sediment extraction with NaOH. Cracking of poly‐P molecules to shorter fragments is, however, much slower if the sediment is pre‐extracted with EDTA and NaOH is replaced by a mixture of NaOH/EDTA to extract nonreactive P from sediments.
A comparison of nutrient‐limited productivity in Sargassum natans from neritic vs. oceanic waters of the western North Atlantic Ocean
Authors: Lapointe Brian E.
Published: May 2010

Physiological studies and seawater nutrient analysis showed that the productivity of the macroalga Sargassum natans was significantly enhanced by higher N and P availability in neritic compared to oceanic waters of the western North Atlantic Ocean (17–40°N). The initial slope of the P vs. I curve (α), photosynthetic capacity (Pmax), dark respiration, and the light saturation irradiance (I) were all significantly greater in neritic compared to oceanic populations. The higher productivity of neritic S. natans correlated with higher levels of tissue N and P; C: N, C: P, and N: P ratios averaged 27.9, 347, and 10.2 in neritic populations compared to 49.4, 877, and 18.1 in oceanic populations. Lower alkaline phosphatase activity in neritic vs. oceanic populations corroborated the higher P limitation in oceanic waters. Experimental pulses with dissolved inorganic N, DIN (NO3−), and soluble reactive phosphate, SRP (PO43−), significantly enhanced net Pmax and dark respiration of oceanic but not neritic S. natans, demonstrating that increased N and P availability enhances productivity of nutrient‐depleted S. natans. Higher DIN and SRP concentrations within Sargassum windrows along shelf fronts in neritic regions explained the higher productivity and suggest that chronic nutrient limitation in oceanic regions is related to highly patchy nutrient supply.
Bacterial secondary production in oxic and anoxic freshwaters
Authors: Cole Jonathan J. , Pace Michael L.
Published: May 2010

Across a series of nine lakes that ranged from ultraoligotrophic to eutrophic, bacterial production was greatest in anoxic hypolimnetic water despite lower hypolimnetic temperatures. Mean (by lake) aerobic bacterial production ranged from 2.6 to 17 mg C m−3d−1 while mean anaerobic bacterial production ranged from 1.1 to 47 C mg C m−3d−1. Overall mean anaerobic bacterial production was 1.6 times greater than mean aerobic bacterial production. The relatively high rates of bacterial production in anoxic waters are due to larger bacterial populations growing slightly more slowly than their aerobic counterparts. Our data suggest that bacterial production in cold, anoxic water is as large or larger than that in warm, oxic surface waters and bacterial production in anoxic water is much greater than aerobic bacterial production at comparable temperatures.

We measured hypolimnetic accumulation of dissolved inorganic C to estimate the minimum possible growth efficiency for hypolimnetic bacteria. Growth efficiency, bacterial production/(bacterial production+bacterial respiration), ranged from 6 to 40% and averaged from 16 to 30% in anoxic water, depending on how it was calculated. The growth efficiency of anaerobic bacteria is about equal to that reported for aerobic bacteria.
Biodegradation of Azotobacter vinelandii exopolymer by Lake Superior microbes
Authors: Weaver Daniel T. , Hicks Randall E.
Published: May 2010

Exopolymer and cells from Azotobacter vinelandii, a soil bacterium, and cells of Scenedesmus bijugatus, a eucaryotic alga, were radiolabeled to experimentally measure their mineralization by hypolimnetic microbes from Lake Superior during July and August 1992. Rates of mineralization were calculated from measurements of microbially respired 14CO2 released in respiration bottles during 14–22‐d incubations. Hypolimnetic microbes mineralized the exopolymer from A. vinelandii (0.32–0.36% d−1) about twice as fast as they mineralized S. bijugatus cells (0.16–0.20% d−1). A. vinelandii cells were mineralized 5 times faster than S. bijugatus cells were mineralized. Bacterial growth efficiencies for these substrates were estimated at the end of the experiments by dividing the cumulative amounts of bacterial biomass produced by the mass of substrate that was utilized in the different respiration bottles. Although the Azotobacter cells were rapidly mineralized, they were a poor substrate for producing new bacterioplankton biomass. Hypolimnetic bacterioplankton were more efficient at converting S. bijugatus into new biomass (growth efficiency = 18–30%) than at converting either the A. vinelandii cells or exopolymer (2% and 8–10% growth efficiencies, respectively). Decaying bacterioplankton blooms may be rapidly mineralized in the upper hypolimnion of Lake Superior, based on the results from the model bacterium (A. vinelandii). Conversely, exopolymers or phytoplankton from the epilimnion may support heterotrophic bacterial production throughout the water column and limit bacterioplankton growth during periods when small amounts of these substrates are produced.
Direct counts of viruses in natural waters and laboratory cultures by epifluorescence microscopy
Authors: Hennes Kilian P. , Suttle Curtis A.
Published: May 2010

Epifluorescent microscopy was used to determine the abundance of viruses in samples from marine and freshwater environments and in laboratory cultures that were filtered onto 0.02‐µm pore‐size filters and stained with a cyanine‐based dye (Yo‐Pro‐1). Estimates of viral abundance based on Yo‐Pro‐stained samples were 1.2–7.1 times greater than estimates obtained with transmission electron microscopy (TEM). Moreover, the precision of the Yo‐Pro‐based method was much greater than that for TEM (C.V. 7% vs. 20%, respectively). DNase treatment of samples did not result in lower numbers of particles that could be stained by Yo‐Pro, suggesting that the fluorescence was not the result of nucleic acids associated with the surface of particles. These results indicate that the concentration of viruses in natural waters may be higher than previously recognized and imply that the TEM‐based method significantly underestimates virus abundance. Virus abundances ranged from 107−> 108 ml−1 in surface waters along a transect in the western Gulf of Mexico to 109 ml−1 in water overlying a submerged cyanobacterial mat. High counting efficiency, ease of preparation, modest equipment requirements, and the possibility of preparing specimens for long‐term storage, make the Yo‐Pro‐based method ideal for routine environmental analysis.