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Sample records for comparing denitrification estimates

  1. Denitrification associated with stream periphyton: Chamber estimates from undisrupted communities

    USGS Publications Warehouse

    Duff, J.H.; Triska, F.J.; Oremland, R.S.

    1984-01-01

    Undisrupted periphyton communities from a N-rich (NO3- = 63 ??mol L-1) and pristine (NO3- = 2.9 ??mol L-1) stream were assayed for denitrifying activity (acetylene-blockage technique) in 40-L chambers incubated at in situ temperature and nutrient concentrations. Nitrous oxide formation associated with periphyton from the N-rich stream was immediate and linear (52.1 ??mol N2O m-2 h-1) in the dark, anaerobic chamber (50 kPa C2H2). In the corresponding light, aerobic chamber (50 kPa C2H2), N2O production was inhibited by 82% (9.3 ??mol N2O m-2 h-1). Nitrous oxide formation was not associated with periphyton from the pristine stream incubated in situ, either with or without NO3- amendment. Denitrification estimates made with undisrupted periphyton communities at in situ temperature and nutrient concentrations (40-L chambers) were less variable than estimates made with periphyton 'scrapings' in small flasks (room temperature). The calculated diel periphyton-associated denitrification rate based on a 14-h light-10-h dark day was 651 ??mol N2O m-2 d-1. The data suggest denitrification within periphyton mats may contribute toward removal of NO3- from N-rich fluvial environments.

  2. Use of stable nitrogen isotope fractionation to estimate denitrification in small constructed wetlands treating agricultural runoff.

    PubMed

    Søvik, Anne Kristine; Mørkved, Pål Tore

    2008-03-15

    Constructed wetlands (CWs) in the agricultural landscape reduce non-point source pollution through removal of nutrients and particles. The objective of this study was to evaluate if measurements of natural abundance of (15)NO(3)(-) can be used to determine the fate of NO(3)(-) in different types of small CWs treating agricultural runoff. Nitrogen removal was studied in wetland trenches filled with different filter materials (T1--sand and gravel; T3--mixture of peat, shell sand and light-weight aggregates; T8--barley straw) and a trench formed as a shallow pond (T4). The removal was highest during summer and lowest during autumn and winter. Trench T8 had the highest N removal during summer. Measurements of the natural abundance of (15)N in NO(3)(-) showed that denitrification was not significant during autumn/winter, while it was present in all trenches during summer, but only important for nitrogen removal in trench T8. The (15)N enrichment factors of NO(3)(-) in this study ranged from -2.5 to -5.9 per thousand (T3 and T8, summer), thus smaller than enrichment factors found in laboratory tests of isotope discrimination in denitrification, but similar to factors found for denitrification in groundwater and a large CW. The low enrichment factors compared to laboratory studies was attributed to assimilation in plants/microbes as well as diffusion effect. Based on a modified version of the method presented by Lund et al. [Lund LJ, Horne AJ, Williams AE, Estimating denitrification in a large constructed wetland using stable nitrogen isotope ratios. Ecol Engineer 2000; 14: 67-76], denitrification and assimilation were estimated to account for 53 to 99 and 1 to 47%, respectively, of the total N removal during summer. This method is, however, based on a number of assumptions, and there is thus a need for a better knowledge of the effect of plant uptake, microbial assimilation as well as nitrification on N isotopic fractionation before this method can be used to evaluate

  3. Estimation of the denitrification in Baltic Sea deep water from gas tension measurements

    NASA Astrophysics Data System (ADS)

    Loeffler, Annekatrin; Schmidt, Martin; Schneider, Bernd

    2010-05-01

    Denitrification is considered to be the most important process removing nitrogen in oceanic waters. 50-70% of marine denitrification occurs in organic rich sediments and oxygen depleted water bodies of continental shelf regions or marginal seas like the Baltic Sea, where a high percentage of riverine discharge of nitrogen is denitrified before entering the open ocean. Measurements of the gas tension (= sum of the partial pressures of all dissolved gases in the water) provide a new experimental way for the quantification of denitrification by directly measuring the reaction product of this process. Continuous pumping of water from a defined depth trough the gas tension device with a pump-CTD allows getting integrated results. Changes in N2 concentrations were calculated from gas tension by subtracting the partial pressures of the most important other dissolved gases (O2, Ar, CO2, H2S, water vapor). The pO2, pCO2 and H2S-concentrations were measured; other parameters (pAr, pH2O, solubility coefficients) were obtained from temperature and salinity. The method allows the estimation of N2-concentrations with a maximum error of 0.5%, corresponding to a standard error of 1.5 μmol L-1. Results of gas tension measurements and calculation of N2 concentrations in the Gotland Basin deep water, central Baltic Sea, from 2008 and 2009 are presented. In the deep water below the permanent halocline the estimated N2 partial pressure is continuously rising towards the oxygen depleted water layers. The calculated N2 excess compared to equilibrium concentration reached values up to 20 μmol N2 L-1 in the stagnant anoxic water layer, indicating a mean N release of 10 μmol N L-1 y-1 after 4 years of stagnation. The increase of total dissolved inorganic nitrogen (due to the N2 excess and formation of ammonium in the deep water) in relation to nitrogen background values was compared with the increase of total inorganic carbon due to mineralization processes. The resulting C:N ratios were

  4. A probabilistic estimate of global marine N-fixation and denitrification

    NASA Astrophysics Data System (ADS)

    Eugster, Olivier; Gruber, Nicolas

    2012-12-01

    We determine the global rates of marine N-fixation and denitrification and their associated uncertainties by combining marine geochemical and physical data with a new two-dimensional box model that separates the Atlantic from the IndoPacific basins. The uncertainties are estimated using a probabilistic approach on the basis of a suite of 2500 circulation configurations of this box model. N-fixation and denitrification are diagnosed in an inverse manner for each of these configurations using N*, P*, and the stable nitrogen isotope composition of nitrate as data constraints. Our approach yields a median water column denitrification rate of 52 TgN yr-1 (39 to 66 TgN yr-1, 5th to 95th percentile) and a median benthic denitrification rate of 93 TgN yr-1 (68 to 122 TgN yr-1). The resulting benthic-to-water column denitrification ratio of 1.8 confirms that the isotopic signature of water column denitrification has a limited influence on the global mean stable isotopic value of nitrate due to the dilution of the waters with a denitrification signal with the remainder of the ocean's nitrate pool. On the basis of two different approaches, we diagnose a global N-fixation rate of between 94 TgN yr-1 and 175 TgN yr-1, with a best estimate of 131 TgN yr-1 and 134 TgN yr-1, respectively. Most of the N-fixation occurs in the IndoPacific suggesting a relative close spatial coupling between sources and sinks in the ocean. Our N-fixation and denitrification estimates plus updated estimates of atmospheric deposition and riverine input yield a pre-industrial marine N cycle that is balanced to within 3 TgN yr-1 (-38 to 40 TgN yr-1). Our budget implies a median residence time for fixed N of 4,200 yr (3,500 to 5,000 yr).

  5. Directly measured denitrification reveals oyster aquaculture and restored oyster reefs remove nitrogen at comparable high rates

    EPA Science Inventory

    Coastal systems are increasingly impacted by over-enrichment of nutrients, which has cascading effects for ecosystem functioning. Oyster restoration and aquaculture are both hypothesized to mitigate excessive nitrogen (N) loads via benthic denitrification (DNF). However, this has...

  6. Landscape-scale estimation of denitrification rates and nitrous oxide to dinitrogen ratio at Georgia and Pennsylvania LTAR sites

    NASA Astrophysics Data System (ADS)

    Dell, C. J.; Groffman, P. M.; Strickland, T.; Kleinman, P. J. A.; Bosch, D. D.; Bryant, R.

    2015-12-01

    Denitrification results in a significant loss of plant-available nitrogen from agricultural systems and contributes to climate change, due to the emissions of both the potent greenhouse gas nitrous oxide (N2O) and environmentally benign dinitrogen (N2). However total quantities of the gases emitted and the ratio of N2:N2O are often not clearly understood, because N2 emissions cannot be directly measured in the field because of the high background level of N2 in the atmosphere. While variability in soil conditions across landscapes, especially water content and aeration, is believed to greatly impact both total denitrification rates and N2:N2O, the measurement limitations have prevented a clear understanding of landscape-scale emissions of denitrification products. The Cary Institute has developed an approach where soil core are maintained in a sealed system with an N2-free airstream, allowing emitted N2 and N2O emissions to be measured without interference from atmospheric N2. Emissions of the gases are measured under a range of oxygen concentrations and soil water contents. Laboratory responses can then be correlated with measured field conditions at the sampling points and resulting emission estimates extrapolated to the field-scale. Measurements are currently being conducted on peanut/cotton rotations, dairy forage rotations (silage corn/alfalfa), and bioenergy crops (switchgrass and miscanthus) at Long Term Agricultural Research (LTAR) sites at Tifton, GA and University Park, PA.

  7. Comparative analysis of microbial community between different cathode systems of microbial fuel cells for denitrification.

    PubMed

    Li, Chao; Xu, Ming; Lu, Yi; Fang, Fang; Cao, Jiashun

    2016-03-01

    Two types of cathodic biofilm in microbial fuel cells (MFC) were established for comparison on their performance and microbial communities. Complete autotrophic simultaneous nitrification and denitrification (SND) without organics addition was achieved in nitrifying-MFC (N-MFC) with a total nitrogen (TN) removal rate of 0.35 mg/(L·h), which was even higher than that in denitrifying-MFC (D-MFC) at same TN level. Integrated denaturing gradient gel electrophoresis analysis based on both 16S rRNA and nirK genes showed that Alpha-, Gammaproteobacteria were the main denitrifier communities. Some potential autotrophic denitrifying bacteria which can use electrons and reducing power from cathodes, such as Shewanella oneidensis, Shewanella loihica, Pseudomonas aeruginosa, Starkeya novella and Rhodopseudomonas palustris were identified and selectively enriched on cathode biofilms. Further, relative abundance of denitrifying bacteria characterized by nirK/16S ratios was much higher in biofilm than suspended sludge according to real-time polymerase chain reaction. The highest enrichment efficiency for denitrifiers was obtained in N-MFC cathode biofilms, which confirmed autotrophic denitrifying bacteria enrichment is the key factor for a D-MFC system. PMID:26278100

  8. Comparison of Whole-stream and Hyporheic-zone Estimates of Denitrification Determined Simultaneously During an Isotope Tracer Injection in a Nitrate-Rich Stream

    NASA Astrophysics Data System (ADS)

    Harvey, J. W.; Bohlke, J. K.; Voytek, M. A.

    2005-05-01

    15N labeled nitrate is increasingly being used as a reactive tracer in stream tracer tests to estimate whole-stream denitrification averaged at a spatial scale large enough to allow comparisons across disparate stream ecosystems. No matter how valuable, these whole-stream estimates are not very informative about controlling processes and will have limited transfer value unless processes controlling denitrification are investigated simultaneously at finer scales. Insights about the processes that influence the whole-stream rates could be especially informative if simultaneous rate measurements are made representing variable hydrologic and biogeochemical conditions near reactive surfaces in the stream and in the streambed. Our approach was to investigate factors that control denitrification by simultaneously measuring denitrification in-situ in a variety of streambed environments by sampling evolution of the (15NO3-) tracer during transport through shallow hyporheic flow paths. Here we report results from two tracer studies conducted in Sugar Creek, western Indiana, in a basin dominated by corn and soybean agriculture. The two tracer experiments were conducted in September 2001 and September 2003, when streamflows (40 and 20 L s-1) and stream NO3- concentrations (70 and 175 μmoles L-1) in the two reaches were near their annual minimum values. The experiments involved co-injection of conservative (Br), reactive (15NO3-), and dissolved gas (SF6) tracers into streamflow allowing quantification of advection, dispersion, gas evasion, hydrologic retention in "storage" zones, and also allowing in-situ estimation of denitrification within selected hyporheic flow paths. The experiments resulted in estimates of both whole-stream and hyporheic-zone rates of denitrification and related nitrogen reactions. The streambed of Sugar Creek is covered in most areas with a relatively thin layer (ranging from <1 to 3 cm) of fine granular and organic sediment and periphyton, overlying a

  9. Landscape scale estimation of denitrification rate and nitrous oxide to dinitrogen ratio at Georgia and Pennsylvania sites

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Denitrification results in a significant loss of plant-available nitrogen from agricultural systems and contributes to climate change, due to the emissions of both the potent greenhouse gas nitrous oxide and environmentally benign dinitrogen. However total quantities of the gases emitted and the ra...

  10. Nitrogen isotope fractionation as a tool for determining denitrification in constructed wetlands.

    PubMed

    Søvik, A K; Mørkved, P T

    2007-01-01

    Constructed wetlands (CWs) treat municipal wastewater through the retention of nutrients and particles. The retention of nitrogen (N) was studied in the laboratory using columns and meso-scale trenches filled with shellsand and light-weight aggregates (LWA). The objective was to examine whether measuring the natural abundance of delta15N in NO3(-) could be used to estimate the relative contribution of denitrification to the total NO3(-) removal in these treatment systems. In both the columns and the trenches it was seen that denitrification was more efficient in shellsand and LWA collected from on-site treatment systems compared to new LWA. This was due to the high pH value (about 10) of new LWA. The enrichment factors (epsilon) from the column study were in general lower than values found in laboratory tests of isotope discrimination in denitrification, but similar to epsilon values found for denitrification in groundwater systems. No enrichment factors could be found for the trench study due to simultaneous denitrification and nitrification and inhomogeneous N transformation patterns. When NH4+ was partially nitrified in the upper parts of the trench, this diluted the 15N enrichment of NO3(-) due to denitrification. Thus, in systems with high NH4+ concentrations and partial aerobic conditions, the method of natural abundance is not suitable for estimating the relative contribution of denitrification to the total NO3(-) removal. PMID:17802852

  11. Comparing net survival estimators of cancer patients.

    PubMed

    Seppä, Karri; Hakulinen, Timo; Läärä, Esa; Pitkäniemi, Janne

    2016-05-20

    The net survival of a patient diagnosed with a given disease is a quantity often interpreted as the hypothetical survival probability in the absence of causes of death other than the disease. In a relative survival framework, net survival summarises the excess mortality that patients experience compared with their relevant reference population. Based on follow-up data from the Finnish Cancer Registry, we derived simulation scenarios that describe survival of patients in eight cancer sites reflecting different excess mortality patterns in order to compare the performance of the classical Ederer II estimator and the new estimator proposed by Pohar Perme et al. At 5 years, the age-standardised Ederer II estimator performed equally well as the Pohar Perme estimator with the exception of melanoma in which the Pohar Perme estimator had a smaller mean squared error (MSE). At 10 and 15 years, the age-standardised Ederer II performed most often better than the Pohar Perme estimator. The unstandardised Ederer II estimator had the largest MSE at 5 years. However, its MSE was often superior to those of the other estimators at 10 and 15 years, especially in sparse data. Both the Pohar Perme and the age-standardised Ederer II estimator are valid for 5-year net survival of cancer patients. For longer-term net survival, our simulation results support the use of the age-standardised Ederer II estimator. Copyright © 2015 John Wiley & Sons, Ltd. PMID:26707551

  12. Comparative investigation on integrated vertical-flow biofilters applying sulfur-based and pyrite-based autotrophic denitrification for domestic wastewater treatment.

    PubMed

    Kong, Zhe; Li, Lu; Feng, Chuanping; Dong, Shanshan; Chen, Nan

    2016-07-01

    Two parallel biofilters applying sulfur/pyrite-based autotrophic denitrification were investigated for removing COD, TP and TN by a coordinated process. Results demonstrated good performance by removing 86.32% vs 87.14% COD and 92.56% vs 89.65% NH4(+)-N. Biofilter with sulfur (BS) was superior on nitrate (89.74% vs 80.72%) and TN removal (83.18% vs 70.42%) while biofilter with pyrite (BP) was better on TP removal (82.58% vs 77.40%) and maintaining sulfate (27.56mgL(-1) vs 41.55mgL(-1)) and pH (7.13 vs 6.31). Water-permeable adsorbents lowered clogging risk and buffered loading. Clone library revealed reasons of diversities, pH variation and sulfate accumulation of both biofilters. Sulfur was efficient on denitrification but whose byproducts were troublesome, pyrite produced less byproduct but which was sensitive to organics. This research was the first attempt to systematically compare two promising alternatives and their merits/demerits for rural wastewater on-site treatment. PMID:27015019

  13. Comparing population size estimators for plethodontid salamanders

    USGS Publications Warehouse

    Bailey, L.L.; Simons, T.R.; Pollock, K.H.

    2004-01-01

    Despite concern over amphibian declines, few studies estimate absolute abundances because of logistic and economic constraints and previously poor estimator performance. Two estimation approaches recommended for amphibian studies are mark-recapture and depletion (or removal) sampling. We compared abundance estimation via various mark-recapture and depletion methods, using data from a three-year study of terrestrial salamanders in Great Smoky Mountains National Park. Our results indicate that short-term closed-population, robust design, and depletion methods estimate surface population of salamanders (i.e., those near the surface and available for capture during a given sampling occasion). In longer duration studies, temporary emigration violates assumptions of both open- and closed-population mark-recapture estimation models. However, if the temporary emigration is completely random, these models should yield unbiased estimates of the total population (superpopulation) of salamanders in the sampled area. We recommend using Pollock's robust design in mark-recapture studies because of its flexibility to incorporate variation in capture probabilities and to estimate temporary emigration probabilities.

  14. Comparing feed-forward versus neural gas as estimators: application to coke wastewater treatment.

    PubMed

    Machón-González, Iván; López-García, Hilario; Rodríguez-Iglesias, Jesús; Marañón-Maison, Elena; Castrillón-Peláez, Leonor; Fernández-Nava, Yolanda

    2013-01-01

    Numerous papers related to the estimation of wastewater parameters have used artificial neural networks. Although successful results have been reported, different problems have arisen such as overtraining, local minima and model instability. In this paper, two types of neural networks, feed-forward and neural gas, are trained to obtain a model that estimates the values of nitrates in the effluent stream of a three-step activated sludge system (two oxic and one anoxic). Placing the denitrification (anoxic) step at the head of the process can force denitrifying bacteria to use internal organic carbon. However, methanol has to be added to achieve high denitrification efficiencies in some industrial wastewaters. The aim of this paper is to compare the two networks in addition to suggesting a methodology to validate the models. The influence of the neighbourhood radius is important in the neural gas approach and must be selected correctly. Neural gas performs well due to its cooperation--competition procedure, with no problems of stability or overfitting arising in the experimental results. The neural gas model is also interesting for use as a direct plant model because of its robustness and deterministic behaviour. PMID:24191445

  15. Parameter estimation uncertainty: Comparing apples and apples?

    NASA Astrophysics Data System (ADS)

    Hart, D.; Yoon, H.; McKenna, S. A.

    2012-12-01

    Given a highly parameterized ground water model in which the conceptual model of the heterogeneity is stochastic, an ensemble of inverse calibrations from multiple starting points (MSP) provides an ensemble of calibrated parameters and follow-on transport predictions. However, the multiple calibrations are computationally expensive. Parameter estimation uncertainty can also be modeled by decomposing the parameterization into a solution space and a null space. From a single calibration (single starting point) a single set of parameters defining the solution space can be extracted. The solution space is held constant while Monte Carlo sampling of the parameter set covering the null space creates an ensemble of the null space parameter set. A recently developed null-space Monte Carlo (NSMC) method combines the calibration solution space parameters with the ensemble of null space parameters, creating sets of calibration-constrained parameters for input to the follow-on transport predictions. Here, we examine the consistency between probabilistic ensembles of parameter estimates and predictions using the MSP calibration and the NSMC approaches. A highly parameterized model of the Culebra dolomite previously developed for the WIPP project in New Mexico is used as the test case. A total of 100 estimated fields are retained from the MSP approach and the ensemble of results defining the model fit to the data, the reproduction of the variogram model and prediction of an advective travel time are compared to the same results obtained using NSMC. We demonstrate that the NSMC fields based on a single calibration model can be significantly constrained by the calibrated solution space and the resulting distribution of advective travel times is biased toward the travel time from the single calibrated field. To overcome this, newly proposed strategies to employ a multiple calibration-constrained NSMC approach (M-NSMC) are evaluated. Comparison of the M-NSMC and MSP methods suggests

  16. Wetland Characteristics and Denitrification

    EPA Science Inventory

    This presentation serves as an initial summary of our wetland field work's watershed characteristics hydrologic characteristics, water quality measurements, and denitrification assays. We present our measurement results in the context of wetland type (Estuarine, Freshwater Mars...

  17. Estimating rates of denitrification enzyme activity in wetland soils and direct simultaneous quantification of nitrogen and nitrous oxide by membrane inlet mass spectrometry

    EPA Science Inventory

    Denitrification enzyme activity (DEA) was measured in short-term (4 h) anaerobic assays using Membrane Inlet Mass Spectrometry (MIMS) and electron capture gas chromatography (GC-ECD). Using MIMS, modifications of the instrument and sample handling allowed for the simultaneous me...

  18. Comparative yield estimation via shock hydrodynamic methods

    SciTech Connect

    Attia, A.V.; Moran, B.; Glenn, L.A.

    1991-06-01

    Shock TOA (CORRTEX) from recent underground nuclear explosions in saturated tuff were used to estimate yield via the simulated explosion-scaling method. The sensitivity of the derived yield to uncertainties in the measured shock Hugoniot, release adiabats, and gas porosity is the main focus of this paper. In this method for determining yield, we assume a point-source explosion in an infinite homogeneous material. The rock is formulated using laboratory experiments on core samples, taken prior to the explosion. Results show that increasing gas porosity from 0% to 2% causes a 15% increase in yield per ms/kt{sup 1/3}. 6 refs., 4 figs.

  19. Denitrification in the water column of the central Baltic Sea

    NASA Astrophysics Data System (ADS)

    Dalsgaard, Tage; De Brabandere, Loreto; Hall, Per O. J.

    2013-04-01

    Removal of fixed nitrogen in the water column of the eastern Gotland Basin, central Baltic Sea, was studied during two cruises in September 2008 and August 2010. The water column was stratified with anoxic sulfidic bottom water meeting oxic nitrate containing water at the oxic-anoxic interface. Anammox was never detected whereas denitrification was found in all incubations from anoxic depths and occurred immediately below the oxic-anoxic interface. Sulfide (H2S + HS- + S2-) was in most cases the only electron donor for denitrification but, in contrast to previous findings, denitrification was in some situations driven by organic matter alone. Nitrous oxide (N2O) became an increasingly important product of denitrification with increasing sulfide concentration and was >80% of the total N gas formation at 10 μM sulfide. The potential rates of denitrification measured in incubations at elevated NO3- or sulfide concentrations were converted to in situ rates using the measured water column concentrations of NO3- and sulfide and the actual measured relations between NO3- and sulfide concentrations and denitrification rates. In situ denitrification ranged from 0.24 to 15.9 nM N2 h-1. Assuming that these rates were valid throughout the anoxic NO3- containing zone, depth integrated in situ denitrification rates of 0.06-2.11 mmol N m-2 d-1 were estimated. The thickness of this zone was generally 3-6 m, which is probably what can be maintained through regular turbulent mixing induced by internal waves at the oxic-anoxic interface. However, layers of up to 55 m thickness with low O2 water (<10 μM) were observed which was probably the result of larger scale mixing. In such a layer nitrification may produce NO3- and once the O2 has been depleted denitrification will follow resulting in enormous rates per unit area. Even with an active denitrification layer of 3-6 m thickness the pelagic denitrification per unit area clearly exceeded sediment denitrification rates elsewhere in

  20. Relative importance of plant uptake and plant associated denitrification for removal of nitrogen from mine drainage in sub-arctic wetlands.

    PubMed

    Hallin, Sara; Hellman, Maria; Choudhury, Maidul I; Ecke, Frauke

    2015-11-15

    Reactive nitrogen (N) species released from undetonated ammonium-nitrate based explosives used in mining or other blasting operations are an emerging environmental problem. Wetlands are frequently used to treat N-contaminated water in temperate climate, but knowledge on plant-microbial interactions and treatment potential in sub-arctic wetlands is limited. Here, we compare the relative importance of plant uptake and denitrification among five plant species commonly occurring in sub-arctic wetlands for removal of N in nitrate-rich mine drainage in northern Sweden. Nitrogen uptake and plant associated potential denitrification activity and genetic potential for denitrification based on quantitative PCR of the denitrification genes nirS, nirK, nosZI and nosZII were determined in plants growing both in situ and cultivated in a growth chamber. The growth chamber and in situ studies generated similar results, suggesting high relevance and applicability of results from growth chamber experiments. We identified denitrification as the dominating pathway for N-removal and abundances of denitrification genes were strong indicators of plant associated denitrification activity. The magnitude and direction of the effect differed among the plant species, with the aquatic moss Drepanocladus fluitans showing exceptionally high ratios between denitrification and uptake rates, compared to the other species. However, to acquire realistic estimates of N-removal potential of specific wetlands and their associated plant species, the total plant biomass needs to be considered. The species-specific plant N-uptake and abundance of denitrification genes on the root or plant surfaces were affected by the presence of other plant species, which show that both multi- and inter-trophic interactions are occurring. Future studies on N-removal potential of wetland plant species should consider how to best exploit these interactions in sub-arctic wetlands. PMID:26360231

  1. CROSS-STREAM COMPARISON OF SUBSTRATE-SPECIFIC DENITRIFICATION POTENTIAL

    SciTech Connect

    Findlay, Stuart; Mulholland, Patrick J; Hamilton, Stephen; Tank, Jennifer; Bernot, Melody; Burgin, Amy; Crenshaw, Chelsea; Grimm, Nancy; McDowell, William; Potter, Jody; Sobota, Daniel

    2011-01-01

    Headwater streams have a demonstrated ability to denitrify a portion of their nitrate (NO(3) (-)) load but there has not been an extensive consideration of where in a stream this process is occurring and how various habitats contribute to total denitrification capability. As part of the Lotic Intersite Nitrogen Experiment II (LINX II) we measured denitrification potential in 65 streams spanning eight regions of the US and draining three land-use types. In each stream, potential denitrification rates were measured in common substrate types found across many streams as well as locations unique to particular streams. Overall, habitats from streams draining urban and agricultural land-uses showed higher potential rates of denitrification than reference streams draining native vegetation. This difference among streams was probably driven by higher ambient nitrate concentrations found in urban or agricultural streams. Within streams, sandy habitats and accumulations of fine benthic organic matter contributed more than half of the total denitrification capacity (mg N removed m(-2) h(-1)). A particular rate of potential denitrification per unit area could be achieved either by high activity per unit organic matter or lower activities associated with larger standing stocks of organic matter. We found that both small patches with high rates (hot spots) or more widespread but less active areas (cool matrix) contributed significantly to whole stream denitrification capacity. Denitrification estimated from scaled-up denitrification enzyme assay (DEA) potentials were not always dramatically higher than in situ rates of denitrification measured as (15)N gas generation following 24-h (15)N-NO(3) tracer additions. In general, headwater streams draining varying land-use types have significant potential to remove nitrate via denitrification and some appear to be functioning near their maximal capacity.

  2. Limited occurrence of denitrification in four shallow aquifers in agricultural areas of the United States

    USGS Publications Warehouse

    Green, C.T.; Puckett, L.J.; Böhlke, J.K.; Bekins, B.A.; Phillips, S.P.; Kauffman, L.J.; Denver, J.M.; Johnson, H.M.

    2008-01-01

    The ability of natural attenuation to mitigate agricultural nitrate contamination in recharging aquifers was investigated in four important agricultural settings in the United States. The study used laboratory analyses, field measurements, and flow and transport modeling for monitoring well transects (0.5 to 2.5 km in length) in the San Joaquin watershed, California, the Elkhorn watershed, Nebraska, the Yakima watershed, Washington, and the Chester watershed, Maryland. Ground water analyses included major ion chemistry, dissolved gases, nitrogen and oxygen stable isotopes, and estimates of recharge date. Sediment analyses included potential electron donors and stable nitrogen and carbon isotopes. Within each site and among aquifer-based medians, dissolved oxygen decreases with ground water age, and excess N2 from denitrification increases with age. Stable isotopes and excess N2 imply minimal denitrifying activity at the Maryland and Washington sites, partial denitrification at the California site, and total denitrification across portions of the Nebraska site. At all sites, recharging electron donor concentrations are not sufficient to account for the losses of dissolved oxygen and nitrate, implying that relict, solid phase electron donors drive redox reactions. Zero-order rates of denitrification range from 0 to 0.14 ??mol N L-1d-1, comparable to observations of other studies using the same methods. Many values reported in the literature are, however, orders of magnitude higher, which is attributed to a combination of method limitations and bias for selection of sites with rapid denitrification. In the shallow aquifers below these agricultural fields, denitrification is limited in extent and will require residence times of decades or longer to mitigate modern nitrate contamination. Copyright ?? 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

  3. Ambient and potential denitrification rates in marsh soils of Northeast Creek and Bass Harbor Marsh watersheds, Mount Desert Island, Maine

    USGS Publications Warehouse

    Huntington, Thomas G.; Culbertson, Charles W.; Duff, John H.

    2012-01-01

    Nutrient enrichment from atmospheric deposition, agricultural activities, wildlife, and domestic sources is a concern at Acadia National Park on Mount Desert Island, Maine, because of the potential problems of degradation of water quality and eutrophication in estuaries. Degradation of water quality has been observed at Bass Harbor Marsh estuary in the park but only minimally in Northeast Creek estuary. Previous studies at Acadia National Park have estimated nutrient inputs to estuaries from atmospheric deposition and surface-water runoff, and have identified shallow groundwater as an additional potential source of nutrients. Previous studies at Acadia National Park have assumed that a certain fraction of the nitrogen input was removed through microbial denitrification, but rates of denitrification (natural or maximum potential) in marsh soils have not been determined. The U.S. Geological Survey, in cooperation with Acadia National Park, measured in-place denitrification rates in marsh soils in Northeast Creek and in Bass Harbor Marsh watersheds during summer 2008 and summer 2009. Denitrification was measured under ambient conditions as well as after additions of inorganic nitrogen and glucose. In-place denitrification rates under ambient conditions were similar to those reported for other coastal wetlands, although they were generally lower than those reported for salt marshes having high ambient concentrations of nitrate (NO3). Denitrification rates generally increased by at least an order of magnitude following NO3 additions, with or without glucose (as the carbohydrate) additions, compared with the ambient treatments that received no nutrient additions. The treatment that added both glucose and NO3 resulted in a variety of denitrification responses when compared with the addition of NO3 alone. In most cases, the addition of glucose to a given rate of NO3 addition resulted in higher rates of denitrification. These variable responses indicate that the amount of

  4. Effects of wetland plants on denitrification rates: a meta-analysis.

    PubMed

    Alldred, Mary; Baines, Stephen B

    2016-04-01

    Human activity is accelerating changes in biotic communities worldwide. Predicting impacts of these changes on ecosystem services such as denitrification, a process that mitigates the consequences of nitrogen pollution, remains one of the most important challenges facing ecologists. Wetlands especially are valued as important sites of denitrification, and wetland plants are expected to have differing effects on denitrification. We present the results of a meta-analysis, conducted on 419 published estimates of denitrification in wetlands dominated by different plant species. Plants increased denitrification rates by 55% on average. This effect varied significantly among communities as defined by the dominant plant species, but surprisingly did not differ substantially among methods for measuring denitrification or among types of wetlands. We conclude that mechanistically linking functional plant traits to denitrification will be key to predicting the role of wetlands in nitrogen mitigation in a changing world. PMID:27411242

  5. Denitrification in San Francisco Bay intertidal sediments

    USGS Publications Warehouse

    Oremland, Ronald S.; Umberger, Cindy; Culbertson, Charles W.; Smith, Richard L.

    1984-01-01

    The acetylene block technique was employed to study denitrification in intertidal estuarine sediments. Addition of nitrate to sediment slurries stimulated denitrification. During the dry season, sediment-slurry denitrification rates displayed Michaelis-Menten kinetics, and ambient NO3− + NO2− concentrations (≤26 μM) were below the apparent Km (50 μM) for nitrate. During the rainy season, when ambient NO3− + NO2− concentrations were higher (37 to 89 μM), an accurate estimate of the Km could not be obtained. Endogenous denitrification activity was confined to the upper 3 cm of the sediment column. However, the addition of nitrate to deeper sediments demonstrated immediate N2O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N2O in the presence of C2H2 was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cell suspensions of a marine pseudomonad confirmed that this N2O loss was caused by incomplete blockage of N2O reductase by C2H2 at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 μmol of N2 m−2 h−1 (for undisturbed sediments) to 17 to 280 μmol of N2 m−2 h−1 (for shaken sediment slurries).

  6. Linking Denitrification to Channel Geomorphology in Agricultural Streams

    NASA Astrophysics Data System (ADS)

    Opdyke, M. R.; David, M. B.; Rhoads, B. L.

    2005-05-01

    Agricultural streams in east-central Illinois have elevated nitrate concentrations (10 to 20 mg N L-1) contributing to greater denitrification rates in sediments. However, reduced retention times and extensive stream channelization limit the effectiveness of denitrification as a removal mechanism for water column nitrate. In this study, we compared geomorphic controls of denitrification in six channel reaches varying in geomorphology, organic matter, and nitrate concentration. Denitrification rates were measured monthly between June 2003 and February 2005 using the acetylene inhibition procedure (chloramphenicol was added to control for denitrifier growth). We found in meandering and channelized reaches of greater nitrate concentrations and fine substrate, denitrification rates averaged 19 mg N m-2 h-1. In areas of lesser nitrate concentrations and coarse substrates, denitrification rates were comparably lower at 3.0 mg N m-2 h-1 in meandering reaches and 0.80 mg N m-2 h-1 in channelized reaches. Our study concluded that denitrification rates were strongly linked to geomorphic variability, organic matter, substrate composition, and nitrate concentration. A strong geomorphic connection appeared with substrate composition showing that greater nitrogen removal in channel conditions of fine substrate are more effective.

  7. Hydrogen Station Cost Estimates: Comparing Hydrogen Station Cost Calculator Results with other Recent Estimates

    SciTech Connect

    Melaina, M.; Penev, M.

    2013-09-01

    This report compares hydrogen station cost estimates conveyed by expert stakeholders through the Hydrogen Station Cost Calculation (HSCC) to a select number of other cost estimates. These other cost estimates include projections based upon cost models and costs associated with recently funded stations.

  8. Regional oxygen reduction and denitrification rates in groundwater from multi-model residence time distributions, San Joaquin Valley, USA

    USGS Publications Warehouse

    Green, Christopher T.; Jurgens, Bryant; Zhang, Yong; Starn, Jeffrey; Singleton, Michael J.; Esser, Bradley K.

    2016-01-01

    Rates of oxygen and nitrate reduction are key factors in determining the chemical evolution of groundwater. Little is known about how these rates vary and covary in regional groundwater settings, as few studies have focused on regional datasets with multiple tracers and methods of analysis that account for effects of mixed residence times on apparent reaction rates. This study provides insight into the characteristics of residence times and rates of O2 reduction and denitrification (NO3− reduction) by comparing reaction rates using multi-model analytical residence time distributions (RTDs) applied to a data set of atmospheric tracers of groundwater age and geochemical data from 141 well samples in the Central Eastern San Joaquin Valley, CA. The RTD approach accounts for mixtures of residence times in a single sample to provide estimates of in-situ rates. Tracers included SF6, CFCs, 3H, He from 3H (tritiogenic He),14C, and terrigenic He. Parameter estimation and multi-model averaging were used to establish RTDs with lower error variances than those produced by individual RTD models. The set of multi-model RTDs was used in combination with NO3− and dissolved gas data to estimate zero order and first order rates of O2 reduction and denitrification. Results indicated that O2 reduction and denitrification rates followed approximately log-normal distributions. Rates of O2 and NO3− reduction were correlated and, on an electron milliequivalent basis, denitrification rates tended to exceed O2 reduction rates. Estimated historical NO3− trends were similar to historical measurements. Results show that the multi-model approach can improve estimation of age distributions, and that relatively easily measured O2 rates can provide information about trends in denitrification rates, which are more difficult to estimate.

  9. Evaluation of the denitrification rate of terraced paddy fields

    NASA Astrophysics Data System (ADS)

    Onishi, Takeo; Nakamura, Kimihito; Horino, Haruhiko; Adachi, Toru; Mitsuno, Toru

    2012-05-01

    SummaryRice is one of the most important staple foods in the world. Lowland paddy fields are well known for functioning as denitrification areas, but few studies have been conducted of paddy fields situated on hill slopes (terraced paddy fields). These terraced paddy fields have a characteristic artificial stepped shape, and this unique shape and periodic ponding from rice production may configure unique hydrological properties that might be different from lowland paddy fields. The shape and hydrological properties may also affect transport of nutrients such as nitrogen. This study is particularly focused on the denitrification rate in terraced paddy fields. To understand the hydrological properties of terraced paddy fields, a detailed water budget including the subsurface flow components was calculated. Combining the water budget components and chemical measurements of surface and subsurface water, a nitrogen budget was calculated. The results showed that about 10% of the total nitrogen input, mainly from fertilizers, was lost, suggesting the occurrence of denitrification in the area. The average denitrification rate of the study site was estimated at about 0.53-0.67 g N m-2 year-1. Spatial variations in the measured groundwater nitrate concentration suggest that denitrification is important in both the plough layer and the sloping area. The denitrification rate in the sloping area was estimated at 0.67-0.78 g N m-2 year-1, which is slightly higher than the estimates of denitrification rate in paddy lots, i.e., 0.56-0.61 g N m-2 year-1. The result indicates the importance of sloping areas for denitrification in terraced paddy fields.

  10. Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer

    USGS Publications Warehouse

    Green, C.T.; Böhlke, J.K.; Bekins, B.A.; Phillips, S.P.

    2010-01-01

    Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field-scale (apparent) estimated reaction rates and isotopic fractionations and local-scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and field observations were used to study the effects of physical heterogeneity on reaction parameter estimates. Field measurements included major ions, age tracers, stable isotopes, and dissolved gases. Parameters were estimated for the O2 reduction rate, denitrification rate, O 2 threshold for denitrification, and stable N isotope fractionation during denitrification. For multiple geostatistical realizations of the aquifer, inverse modeling was used to establish reactive transport simulations that were consistent with field observations and served as a basis for numerical experiments to compare sample-based estimates of "apparent" parameters with "true" (intrinsic) values. For this aquifer, non-Gaussian dispersion reduced the magnitudes of apparent reaction rates and isotope fractionations to a greater extent than Gaussian mixing alone. Apparent and true rate constants and fractionation parameters can differ by an order of magnitude or more, especially for samples subject to slow transport, long travel times, or rapid reactions. The effect of mixing on apparent N isotope fractionation potentially explains differences between previous laboratory and field estimates. Similarly, predicted effects on apparent O2 threshold values for denitrification are consistent with previous reports of higher values in aquifers than in the laboratory. These results show that hydrogeological complexity substantially influences the interpretation and prediction of reactive transport. ?? 2010 by the American Geophysical Union.

  11. Modeling denitrification in a tile-drained, corn and soybean agroecosystem of Illinois, USA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Denitrification is known as an important pathway for nitrate loss in agroecosystems. It is important to estimate denitrification fluxes to close field and watershed N mass balances, determine greenhouse gas emissions (N2O), and help constrain estimates of other major N fluxes (e.g., nitrate leaching...

  12. Denitrification, anammox, and N₂ production in marine sediments.

    PubMed

    Devol, Allan H

    2015-01-01

    Fixed nitrogen limits primary productivity in many parts of the global ocean, and it consequently plays a role in controlling the carbon dioxide content of the atmosphere. The concentration of fixed nitrogen is determined by the balance between two processes: the fixation of nitrogen gas into organic forms by diazotrophs, and the reconversion of fixed nitrogen to nitrogen gas by denitrifying organisms. However, current sedimentary denitrification rates are poorly constrained, especially in permeable sediments, which cover the majority of the continental margin. Also, anammox has recently been shown to be an additional pathway for the loss of fixed nitrogen in sediments. This article briefly reviews sedimentary fixed nitrogen loss by sedimentary denitrification and anammox, including in sediments in contact with oxygen-deficient zones. A simple extrapolation of existing rate measurements to the global sedimentary denitrification rate yields a value smaller than many existing measurement-based estimates but still larger than the rate of water column denitrification. PMID:25560607

  13. Denitrification, Anammox, and N2 Production in Marine Sediments

    NASA Astrophysics Data System (ADS)

    Devol, Allan H.

    2015-01-01

    Fixed nitrogen limits primary productivity in many parts of the global ocean, and it consequently plays a role in controlling the carbon dioxide content of the atmosphere. The concentration of fixed nitrogen is determined by the balance between two processes: the fixation of nitrogen gas into organic forms by diazotrophs, and the reconversion of fixed nitrogen to nitrogen gas by denitrifying organisms. However, current sedimentary denitrification rates are poorly constrained, especially in permeable sediments, which cover the majority of the continental margin. Also, anammox has recently been shown to be an additional pathway for the loss of fixed nitrogen in sediments. This article briefly reviews sedimentary fixed nitrogen loss by sedimentary denitrification and anammox, including in sediments in contact with oxygen-deficient zones. A simple extrapolation of existing rate measurements to the global sedimentary denitrification rate yields a value smaller than many existing measurement-based estimates but still larger than the rate of water column denitrification.

  14. Comparing interval estimates for small sample ordinal CFA models.

    PubMed

    Natesan, Prathiba

    2015-01-01

    Robust maximum likelihood (RML) and asymptotically generalized least squares (AGLS) methods have been recommended for fitting ordinal structural equation models. Studies show that some of these methods underestimate standard errors. However, these studies have not investigated the coverage and bias of interval estimates. An estimate with a reasonable standard error could still be severely biased. This can only be known by systematically investigating the interval estimates. The present study compares Bayesian, RML, and AGLS interval estimates of factor correlations in ordinal confirmatory factor analysis models (CFA) for small sample data. Six sample sizes, 3 factor correlations, and 2 factor score distributions (multivariate normal and multivariate mildly skewed) were studied. Two Bayesian prior specifications, informative and relatively less informative were studied. Undercoverage of confidence intervals and underestimation of standard errors was common in non-Bayesian methods. Underestimated standard errors may lead to inflated Type-I error rates. Non-Bayesian intervals were more positive biased than negatively biased, that is, most intervals that did not contain the true value were greater than the true value. Some non-Bayesian methods had non-converging and inadmissible solutions for small samples and non-normal data. Bayesian empirical standard error estimates for informative and relatively less informative priors were closer to the average standard errors of the estimates. The coverage of Bayesian credibility intervals was closer to what was expected with overcoverage in a few cases. Although some Bayesian credibility intervals were wider, they reflected the nature of statistical uncertainty that comes with the data (e.g., small sample). Bayesian point estimates were also more accurate than non-Bayesian estimates. The results illustrate the importance of analyzing coverage and bias of interval estimates, and how ignoring interval estimates can be misleading

  15. Comparing interval estimates for small sample ordinal CFA models

    PubMed Central

    Natesan, Prathiba

    2015-01-01

    Robust maximum likelihood (RML) and asymptotically generalized least squares (AGLS) methods have been recommended for fitting ordinal structural equation models. Studies show that some of these methods underestimate standard errors. However, these studies have not investigated the coverage and bias of interval estimates. An estimate with a reasonable standard error could still be severely biased. This can only be known by systematically investigating the interval estimates. The present study compares Bayesian, RML, and AGLS interval estimates of factor correlations in ordinal confirmatory factor analysis models (CFA) for small sample data. Six sample sizes, 3 factor correlations, and 2 factor score distributions (multivariate normal and multivariate mildly skewed) were studied. Two Bayesian prior specifications, informative and relatively less informative were studied. Undercoverage of confidence intervals and underestimation of standard errors was common in non-Bayesian methods. Underestimated standard errors may lead to inflated Type-I error rates. Non-Bayesian intervals were more positive biased than negatively biased, that is, most intervals that did not contain the true value were greater than the true value. Some non-Bayesian methods had non-converging and inadmissible solutions for small samples and non-normal data. Bayesian empirical standard error estimates for informative and relatively less informative priors were closer to the average standard errors of the estimates. The coverage of Bayesian credibility intervals was closer to what was expected with overcoverage in a few cases. Although some Bayesian credibility intervals were wider, they reflected the nature of statistical uncertainty that comes with the data (e.g., small sample). Bayesian point estimates were also more accurate than non-Bayesian estimates. The results illustrate the importance of analyzing coverage and bias of interval estimates, and how ignoring interval estimates can be misleading

  16. Modeling nitrogen removal for a denitrification biofilter.

    PubMed

    Samie, Guillaume; Bernier, Jean; Rocher, Vincent; Lessard, Paul

    2011-08-01

    Nitrous oxide (N2O) is a major greenhouse gas, heavily contributing to global warming. N2O is emitted from various sources such as wastewater treatment plants, during the nitrification and denitrification steps. ASM models, which are commonly used in wastewater treatment, usually consider denitrification as a one-step process (NO3- directly reduced to N2) and are as such unable to provide values for intermediate products of the reaction like N2O. In this study, a slightly modified ASM1 model was implemented in the GPS-X software to simulate the concentration of such intermediate products (NO2-, NO and N2O) and to estimate the amounts of gaseous N2O emitted by the denitrification stage (12 biofilters) of the Seine-Centre WWTP (SIAAP, Paris). Simulations running on a 1-year period have shown good agreements with measured effluent data for nitrate and nitrite. The calculated mean value for emitted N2O is 4.95 kgN-N2O/day, which stands in the typical range of estimated experimental values of 4-31 kgN-N2O/day. Nitrous oxide emissions are usually not measured on WWTPs and so, as obtained results show, there is a certain potential for using models that quantify those emissions using traditionally measured influent data. PMID:21340676

  17. Effective denitrification at the groundwater surface-water interface: exposure rather than residence time

    NASA Astrophysics Data System (ADS)

    Peiffer, Stefan; Frei, Sven

    2014-05-01

    Effective processing of material in aquatic systems, e. g. removal of nitrate upon denitrification, requires sufficient reaction time. This statement sounds trivial albeit its implication for biogeochemistry seems to be not fully recognized. The time teff required for effective processing of nitrate is controlled by the underlying biogeochemical rate law. In the simplest case of a 1st order reaction, teff is often calculated as the time when 63% of the initial concentration is consumed setting teff as 1/kreaction. It may, however, be more appropriate to derive teff,90%or teff,99% from the respective rate law. Hence a minimum time t > teff is required that exposes a specific biogeochemical process to conditions favourable for this process, which is anoxia in case of denitrification. This exposure time τexp is not necessarily identical to the residence time τ of water in the particular system or flow path. Rather, the exposure time can be much shorter and may even fluctuate with time. As a consequence, Damköhler numbers (Da = τexp/teff) for denitrification < 1 may be the consequence even though the age of water may be comparatively high. We therefore argue that the key for understanding denitrification efficiency at the groundwater surface-water interface (or in groundwater systems in general) is the quantification of the exposure time. This contribution therefore aims i) to estimate exposure times required for effective denitrification based on an analysis of rate constants for denitrification, ii) to relate these time scales to typical residence time distributions found at the groundwater surface-water interface and iii) to discuss implications for denitrification efficiencies. References: Oldham, C; Farrow, DE; Peiffer, S (2013): A generalized Damköhler number for classifying material processing in hydrological systems, Hydrology and Earth System Sciences, 17, 1133-1148 Frei, S; Knorr, KH; Peiffer, S; Fleckenstein, J (2012): Surface micro-topography causes

  18. It Pays to Compare: An Experimental Study on Computational Estimation

    ERIC Educational Resources Information Center

    Star, Jon R.; Rittle-Johnson, Bethany

    2009-01-01

    Comparing and contrasting examples is a core cognitive process that supports learning in children and adults across a variety of topics. In this experimental study, we evaluated the benefits of supporting comparison in a classroom context for children learning about computational estimation. Fifth- and sixth-grade students (N = 157) learned about…

  19. Denitrification enzyme activity in swine wastewater lagoons

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Recent publications of high levels of di-nitrogen emissions and high levels of potential surficial oxygen transfer indicated that large amounts of nitrogen may be removed via denitrification in anaerobic lagoons. If this denitrification is occurring via classical denitrification, the denitrification...

  20. Denitrification and inference of nitrogen sources in the karstic Floridan Aquifer

    USGS Publications Warehouse

    Heffernan, J.B.; Albertin, A.R.; Fork, M.L.; Katz, B.G.; Cohen, M.J.

    2011-01-01

    Aquifer denitrification is among the most poorly constrained fluxes in global and regional nitrogen budgets. The few direct measurements of denitrification in groundwaters provide limited information about its spatial and temporal variability, particularly at the scale of whole aquifers. Uncertainty in estimates of denitrification may also lead to underestimates of its effect on isotopic signatures of inorganic N, and thereby confound the inference of N source from these data. In this study, our objectives are to quantify the magnitude and variability of denitrification in the Upper Floridan Aquifer (UFA) and evaluate its effect on N isotopic signatures at the regional scale. Using dual noble gas tracers (Ne, Ar) to generate physical predictions of N2 gas concentrations for 112 observations from 61 UFA springs, we show that excess (i.e. denitrification-derived) N2 is highly variable in space and inversely correlated with dissolved oxygen (O2). Negative relationship between O2 and ??15NNO 3 across a larger dataset of 113 springs, well-constrained isotopic fractionation coefficients, and strong 15N: 18O covariation further support inferences of denitrification in this uniquely organic-matter-poor system. Despite relatively low average rates, denitrification accounted for 32% of estimated aquifer N inputs across all sampled UFA springs. Back-calculations of source ??15NNO 3 based on denitrification progression suggest that isotopically-enriched nitrate (NO3-) in many springs of the UFA reflects groundwater denitrification rather than urban- or animal-derived inputs. ?? Author(s) 2011.

  1. Comparative study of above ground biomass estimates for conterminous US

    NASA Astrophysics Data System (ADS)

    Neeti, N.; Kennedy, R. E.

    2013-12-01

    Accurate estimates of forest biomass are important for carbon accounting at both regional and national scale. There are four above ground biomass (AGB) maps available for conterminous US, one from the National Aeronautics and Space Administration (NASA), two from the United States Forest Service (USFS) (Blackard and Wilson) and one from the Woods Hole Research Center (WHRC). Although all four maps are meant to represent similar quantities, spatial patterns of AGB vary considerably from map to map. To use any of these AGB maps for carbon accounting, it is important to understand sources of uncertainty in individual maps and agreement and disagreement among them. Therefore, we compared the four AGB maps at ecoregion and state level to gain understanding of map consistency, leveraging discrepancies among maps to gain insight into the method and data sources. We also developed statewide summaries to compare with FIA forest AGB estimates, which are typically reported at the state level. We examined both absolute differences among these aggregated maps, and relative differences among regions within each map. The result shows that NASA biomass estimates are highest and Blackard estimates are lowest compared to other maps at both ecoregion and state level. The AGB for WHRC and Wilson are very similar at both ecoregion and state level specifically in the lower biomass regions compared to higher biomass regions. This could be associated with the differences in the spatial resolution of the data sources uses to generate these maps. At state level, WHRC map is found to be most similar and NASA biomass estimates least similar to FIA plot data. We discuss these differences in light of the different methods and data sources used to generate the maps.

  2. Denitrification and N2O emission in an N-saturated subtropical forest catchment, southwest China

    NASA Astrophysics Data System (ADS)

    Zhu, Jing; Mulder, Jan; Dörsch, Peter

    2010-05-01

    Increasing anthropogenic emissions of nitrogen have resulted in locally high deposition rates of reactive nitrogen in China (30-73 kg N ha-1 a-1; Zhang. et al., 2008), primarily as NOx (from fossil fuel combustion) and NH3 (from fertilizer production and animal husbandry). Due to the subtropical, monsoonal climate with high soil temperature and moisture in summer, forests in south China may be expected to show high nitrification and denitrification rates, both of which can cause high N2O emissions. To estimate the N2O source strength and to investigate N-turnover processes relevant for N removal in subtropical forest, we investigated spatiotemporal patterns of N2O emission along a hydrological flowpath from July to November of 2009 in the TSP catchment (Tieshanping), situated close to Chongqing, one of the biggest cities in southwest China. Results from the first study year revealed high N cycling rates and N2O emissions during the wet season, (June to September). Surprisingly, soils on the hill slopes showed higher denitrification potentials and N2O emission rates than the wetter groundwater discharge zone at the bottom of the hill slopes. This was probably due to higher soil bulk density and less organic carbon content in the groundwater discharge zone. Highest denitrification potential were found in the O and A layer (< 5cm) of the hillslopes, suggesting that the organic carbon is the limiting factor for N-removal by denitrification in this ecosystem. High N-removal on the hill slopes was confirmed by decreasing NO3- concentrations along the flowpath during hydrologically stable conditions. However, high NO3- concentrations found in stream water during rain events suggest that the retention time of N in the catchment is too short to allow complete removal by denitrification. N2O emission fluxes dropped by two orders of magnitude in the beginning of the dry season, reflecting lower N input and removal rates during winter. Our results show that denitrification and

  3. Hydrologic connectivity increases denitrification in the hyporheic zone and restored floodplains of an agricultural stream

    NASA Astrophysics Data System (ADS)

    Roley, Sarah S.; Tank, Jennifer L.; Williams, Maureen A.

    2012-09-01

    Stream ecotones, specifically the lateral floodplain and subsurface hyporheic zone, can be important sites for nitrogen (N) removal via denitrification, but their role in streams with constructed floodplains has not been examined. We studied denitrification in the hyporheic zone and floodplains of an agriculturally influenced headwater stream in Indiana, USA, that had floodplains added as part of a "two-stage ditch" restoration project. To examine the potential for N removal in the hyporheic zone, we seasonally measured denitrification rates and nitrate concentrations by depth into the stream sediments. We found that nitrate concentration and denitrification rates declined with depth into the hyporheic zone, but denitrification was still measureable to a depth of at least 20 cm. We also measured denitrification rates on the restored floodplains over the course of a flood (pre, during, and post-inundation), and also compared denitrification rates between vegetated and non-vegetated areas of the floodplain. We found that floodplain denitrification rates increased over the course of a floodplain inundation event, and that the presence of surface water increased denitrification rates when vegetation was present. Stream ecotones in midwestern, agriculturally influenced streams have substantial potential for N removal via denitrification, particularly when they are hydrologically connected with high-nitrate surface water.

  4. Denitrification mechanisms in the polar stratospheres

    NASA Technical Reports Server (NTRS)

    Toon, Owen B.; Turco, R. P.; Hamill, P.

    1990-01-01

    Microphysical simulations suggest that the time required for nitric acid particles to sediment from the stratosphere is comparable to the time required for falling ice particles to incorporate nitric acid vapor from the vapor phase. Since nitric acid particles form earlier in the winter than ice particles, these simulations favor denitrification being a separate process from dehydration, with denitrification being due to nitric acid particles and dehydration due to ice particles. In the simulations, the column abundance of nitric acid is only depleted if temperatures low enough for nitric acid particles to exist extend to the altitude above which the column is measured. Such low temperatures are infrequent in the Arctic lower stratosphere, which may be the main reason that the Arctic stratospheric column shows little loss of nitric acid during winter, while the colder Antarctic stratospheric column shows a substantial loss of nitric acid.

  5. Spatial Distribution of Hydrologic Ecosystem Service Estimates: Comparing Two Models

    NASA Astrophysics Data System (ADS)

    Dennedy-Frank, P. J.; Ghile, Y.; Gorelick, S.; Logsdon, R. A.; Chaubey, I.; Ziv, G.

    2014-12-01

    We compare estimates of the spatial distribution of water quantity provided (annual water yield) from two ecohydrologic models: the widely-used Soil and Water Assessment Tool (SWAT) and the much simpler water models from the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) toolbox. These two models differ significantly in terms of complexity, timescale of operation, effort, and data required for calibration, and so are often used in different management contexts. We compare two study sites in the US: the Wildcat Creek Watershed (2083 km2) in Indiana, a largely agricultural watershed in a cold aseasonal climate, and the Upper Upatoi Creek Watershed (876 km2) in Georgia, a mostly forested watershed in a temperate aseasonal climate. We evaluate (1) quantitative estimates of water yield to explore how well each model represents this process, and (2) ranked estimates of water yield to indicate how useful the models are for management purposes where other social and financial factors may play significant roles. The SWAT and InVEST models provide very similar estimates of the water yield of individual subbasins in the Wildcat Creek Watershed (Pearson r = 0.92, slope = 0.89), and a similar ranking of the relative water yield of those subbasins (Spearman r = 0.86). However, the two models provide relatively different estimates of the water yield of individual subbasins in the Upper Upatoi Watershed (Pearson r = 0.25, slope = 0.14), and very different ranking of the relative water yield of those subbasins (Spearman r = -0.10). The Upper Upatoi watershed has a significant baseflow contribution due to its sandy, well-drained soils. InVEST's simple seasonality terms, which assume no change in storage over the time of the model run, may not accurately estimate water yield processes when baseflow provides such a strong contribution. Our results suggest that InVEST users take care in situations where storage changes are significant.

  6. Denitrification, leaching, and river nitrogen export in the Community Earth System Model

    NASA Astrophysics Data System (ADS)

    Nevison, Cynthia; Hess, Peter; Riddick, Stuart; Ward, Dan

    2016-03-01

    River nitrogen export is simulated within the Community Earth System Model (CESM) by coupling nitrogen leaching and runoff fluxes from the Community Land Model (CLM) to the River Transport Model (RTM). The coupled CLM-RTM prognostically simulates the downstream impact of human N cycle perturbation on coastal areas. It also provides a framework for estimating denitrification fluxes of N2 and associated trace gases like N2O in soils and river sediments. An important limitation of the current model is that it only simulates dissolved inorganic nitrogen (DIN) river export, due to the lack of dissolved organic nitrogen (DON) and particulate nitrogen (PN) leaching fluxes in CLM. In addition, the partitioning of soil N loss in CLM between the primary loss pathways of denitrification and N leaching/runoff appears heavily skewed toward denitrification compared to other literature estimates, especially in nonagricultural regions, and also varies considerably among the four model configurations presented here. River N export is generally well predicted in the model configurations that include midlatitude crops, but tends to be underpredicted in rivers that are less perturbed by human agriculture. This is especially true in the tropics, where CLM likely underestimates leaching and runoff of all forms of nitrogen. River export of DIN is overpredicted in some relatively unperturbed Arctic rivers, which may result from excessive N inputs to those regions in CLM. Better representation of N loss in CLM can improve confidence in model results with respect to the core model objective of simulating nitrogen limitation of the carbon cycle.

  7. Simultaneous measurement at multiple depths of in situ rates of denitrification in the bed of a groundwater-fed river

    NASA Astrophysics Data System (ADS)

    Lansdown, Katrina; Trimmer, Mark; Heppell, Kate

    2010-05-01

    Typically characterised by steep chemical gradients and variable redox conditions, the hyporheic zone is considered a 'hotpot' or site of enhanced biogeochemical activity in the aquatic environment. As such the importance of the hyporheic zone for the attenuation of nutrients such as nitrate in a fluvial network has long been recognised. Controls on nitrogen transformations, however, especially at depths greater than 10cm below the sediment-water interface, remain comparatively less understood. Most work aimed at quantifying denitrification in the hyporheic zone has involved laboratory incubation of recovered sediments which is likely to affect the estimate of the true in situ rate. Results of such studies are usually cited as 'potential' rates of denitrification and have undoubtedly improved the understanding of nitrogen cycling in the aquatic environment. There is, however, a need for in situ measurement to improve our knowledge of nitrogen cycling in the river bed. Here, rates of denitrification in the hyporheic zone have been measured at multiple depths, simultaneously using 'push-pull' methodology (e.g. Snodgrass and Kitanidis 1998). The 'push-pull' technique involves injection of a solution containing reactant(s) (e.g. nitrate) and a conservative tracer (e.g. chloride) into the sediment and extraction of pore water samples over time. Recovered samples are screened for the removal of reactant(s) and/or the accumulation of products(s). Temporal changes in the conservative tracer are used to correct the concentration of the reactant(s) and product(s) for dispersion and advection. The disadvantage of the 'traditional' 'push-pull' methodology is that rates of nitrate removal are measured rather than rates of denitrification. In this research, comparison of measured and 'corrected' nitrate concentrations allowed the rate of nitrate removal (or production) to be quantified. In order to determine in situ rates of denitrification we used 15N-enriched nitrate as the

  8. Reaction chain modeling of denitrification reactions during a push-pull test

    NASA Astrophysics Data System (ADS)

    Boisson, A.; de Anna, P.; Bour, O.; Le Borgne, T.; Labasque, T.; Aquilina, L.

    2013-05-01

    Field quantitative estimation of reaction kinetics is required to enhance our understanding of biogeochemical reactions in aquifers. We extended the analytical solution developed by Haggerty et al. (1998) to model an entire 1st order reaction chain and estimate the kinetic parameters for each reaction step of the denitrification process. We then assessed the ability of this reaction chain to model biogeochemical reactions by comparing it with experimental results from a push-pull test in a fractured crystalline aquifer (Ploemeur, French Brittany). Nitrates were used as the reactive tracer, since denitrification involves the sequential reduction of nitrates to nitrogen gas through a chain reaction (NO3- → NO2- → NO → N2O → N2) under anaerobic conditions. The kinetics of nitrate consumption and by-product formation (NO2-, N2O) during autotrophic denitrification were quantified by using a reactive tracer (NO3-) and a non-reactive tracer (Br-). The formation of reaction by-products (NO2-, N2O, N2) has not been previously considered using a reaction chain approach. Comparison of Br- and NO3- breakthrough curves showed that 10% of the injected NO3- molar mass was transformed during the 12 h experiment (2% into NO2-, 1% into N2O and the rest into N2 and NO). Similar results, but with slower kinetics, were obtained from laboratory experiments in reactors. The good agreement between the model and the field data shows that the complete denitrification process can be efficiently modeled as a sequence of first order reactions. The 1st order kinetics coefficients obtained through modeling were as follows: k1 = 0.023 h- 1, k2 = 0.59 h- 1, k3 = 16 h- 1, and k4 = 5.5 h- 1. A next step will be to assess the variability of field reactivity using the methodology developed for modeling push-pull tracer tests.

  9. Reaction chain modeling of denitrification reactions during a push-pull test.

    PubMed

    Boisson, A; de Anna, P; Bour, O; Le Borgne, T; Labasque, T; Aquilina, L

    2013-05-01

    Field quantitative estimation of reaction kinetics is required to enhance our understanding of biogeochemical reactions in aquifers. We extended the analytical solution developed by Haggerty et al. (1998) to model an entire 1st order reaction chain and estimate the kinetic parameters for each reaction step of the denitrification process. We then assessed the ability of this reaction chain to model biogeochemical reactions by comparing it with experimental results from a push-pull test in a fractured crystalline aquifer (Ploemeur, French Brittany). Nitrates were used as the reactive tracer, since denitrification involves the sequential reduction of nitrates to nitrogen gas through a chain reaction (NO3(-)→NO2(-)→NO→N2O→N2) under anaerobic conditions. The kinetics of nitrate consumption and by-product formation (NO2(-), N2O) during autotrophic denitrification were quantified by using a reactive tracer (NO3(-)) and a non-reactive tracer (Br(-)). The formation of reaction by-products (NO2(-), N2O, N2) has not been previously considered using a reaction chain approach. Comparison of Br(-) and NO3(-) breakthrough curves showed that 10% of the injected NO3(-) molar mass was transformed during the 12 h experiment (2% into NO2(-), 1% into N2O and the rest into N2 and NO). Similar results, but with slower kinetics, were obtained from laboratory experiments in reactors. The good agreement between the model and the field data shows that the complete denitrification process can be efficiently modeled as a sequence of first order reactions. The 1st order kinetics coefficients obtained through modeling were as follows: k1=0.023 h(-1), k2=0.59 h(-1), k3=16 h(-1), and k4=5.5 h(-1). A next step will be to assess the variability of field reactivity using the methodology developed for modeling push-pull tracer tests. PMID:23500936

  10. Molecular Approaches to Studying Denitrification

    NASA Astrophysics Data System (ADS)

    Voytek, M. A.

    2001-05-01

    Denitrification is carried out by a diverse array of microbes, mainly as an alternative mode of respiration that allows the organisms to respire using oxidized N compounds instead of oxygen. A common approach in biogeochemistry to the study of the regulation of denitrification is to assess activity by mass balance of substrates and products or direct rate measurements and has intrinsically assumed resource regulation of denitrification. Reported rates can vary significantly even among ecosystems characterized by similar environmental conditions, thus indicating that direct control by abiotic factors often is not sufficient to predict denitrification rates accurately in natural environments. Alternatively, a microbiological approach would proceed with the identification of the organisms responsible and an evaluation of the effect of environmental factors on the biochemical pathways involved. Traditional studies have relied on culturing techniques, such as most probable number enrichments, and have failed to assess the role of the predominately uncultivable members of the microbial community. A combination of biogeochemical measurements and the assessment of the microbial community is necessary and becoming increasingly possible with the development and application of molecular techniques. In order to understand how the composition and physiological behavior of the microbial community affects denitrification rates, we use a suite of molecular techniques developed for phylogenetic and metabolic characterization of denitrifying communities. Molecular tools available for quantifying denitrifying bacteria and assessing their diversity and activity are summarized. Their application is illustrated with examples from marine and freshwater environments. Emerging techniques and their application to ground water studies will be discussed.

  11. Denitrification in human dental plaque

    PubMed Central

    2010-01-01

    Background Microbial denitrification is not considered important in human-associated microbial communities. Accordingly, metabolic investigations of the microbial biofilm communities of human dental plaque have focused on aerobic respiration and acid fermentation of carbohydrates, even though it is known that the oral habitat is constantly exposed to nitrate (NO3-) concentrations in the millimolar range and that dental plaque houses bacteria that can reduce this NO3- to nitrite (NO2-). Results We show that dental plaque mediates denitrification of NO3- to nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2) using microsensor measurements, 15N isotopic labelling and molecular detection of denitrification genes. In vivo N2O accumulation rates in the mouth depended on the presence of dental plaque and on salivary NO3- concentrations. NO and N2O production by denitrification occurred under aerobic conditions and was regulated by plaque pH. Conclusions Increases of NO concentrations were in the range of effective concentrations for NO signalling to human host cells and, thus, may locally affect blood flow, signalling between nerves and inflammatory processes in the gum. This is specifically significant for the understanding of periodontal diseases, where NO has been shown to play a key role, but where gingival cells are believed to be the only source of NO. More generally, this study establishes denitrification by human-associated microbial communities as a significant metabolic pathway which, due to concurrent NO formation, provides a basis for symbiotic interactions. PMID:20307293

  12. Inhibition of existing denitrification enzyme activity by chloramphenicol

    USGS Publications Warehouse

    Brooks, M.H.; Smith, R.L.; Macalady, D.L.

    1992-01-01

    Chloramphenicol completely inhibited the activity of existing denitrification enzymes in acetylene-block incubations with (i) sediments from a nitrate-contaminated aquifer and (ii) a continuous culture of denitrifying groundwater bacteria. Control flasks with no antibiotic produced significant amounts of nitrous oxide in the same time period. Amendment with chloramphenicol after nitrous oxide production had begun resulted in a significant decrease in the rate of nitrous oxide production. Chloramphenicol also decreased (>50%) the activity of existing denitrification enzymes in pure cultures of Pseudomonas denitrificans that were harvested during log- phase growth and maintained for 2 weeks in a starvation medium lacking electron donor. Short-term time courses of nitrate consumption and nitrous oxide production in the presence of acetylene with P. denitrificans undergoing carbon starvation were performed under optimal conditions designed to mimic denitrification enzyme activity assays used with soils. Time courses were linear for both chloramphenicol and control flasks, and rate estimates for the two treatments were significantly different at the 95% confidence level. Complete or partial inhibition of existing enzyme activity is not consistent with the current understanding of the mode of action of chloramphenicol or current practice, in which the compound is frequently employed to inhibit de novo protein synthesis during the course of microbial activity assays. The results of this study demonstrate that chloramphenicol amendment can inhibit the activity of existing denitrification enzymes and suggest that caution is needed in the design and interpretation of denitrification activity assays in which chloramphenicol is used to prevent new protein synthesis.

  13. Herbicide and antibiotic removal by woodchip denitrification filters: Sorption processes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Batch sorption and desorption experiments to evaluate the retention of the agrichemicals onto wood chips from an in situ wood chip denitrification wall were conducted for atrazine, enrofloxacin, monensin and sulfamethazine. Estimated Freundlich distribution coefficients (Kf) showed that the order of...

  14. Herbicide and antibiotic removal by woodchip denitrification filters: Sorption processes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Batch sorption and desorption experiments to evaluate the retention of the agrichemicals onto wood chips from an in situ wood chip denitrification wall were conducted for atrazine, enrofloxacin, monensin, and sulfamethazine. Estimated Freundlich distribution coefficients (Kf) showed that the order o...

  15. Effect of organic loading on nitrification and denitrification in a marine sediment microcosm

    USGS Publications Warehouse

    Caffrey, J.M.; Sloth, N.P.; Kaspar, H.F.; Blackburn, T.H.

    1993-01-01

    The effects of organic additions on nitrification and denitrification were examined in sediment microcosms. The organic material, heat killed yeast, had a C/N ratio of 7.5 and was added to sieved, homogenized sediments. Four treatments were compared: no addition (control, 30 g dry weight (dw) m-2 mixed throughout the 10 cm sediment column (30 M), 100 g dw m-2 mixed throughout sediments (100M), and 100 g dw m-2 mixed into top 1 cm (100S). After the microcosms had been established for 7-11 days, depth of O2 penetration, sediment-water fluxes and nitrification rates were measured. Nitrification rates were measured using three different techniques: N-serve and acetylene inhibition in intact cores, and nitrification potentials in slurries. Increased organic additions decreased O2 penetration from 2.7 to 0.2 mm while increasing both O2 consumption, from 30 to 70 mmol O2 m-2 d-1, and NO3- flux into sediments. Nitrification rates in intact cores were similar for the two methods. Highest rates occurred in the 30 M treatment, while the lowest rate was measured in the 100S treatment. Total denitrification rates (estimated from nitrification and nitrate fluxes) increased with increased organic addition, because of the high concentrations of NO3- (40 ??M) in the overlying water. The ratio of nitrification: denitrification was used as an indication of the importance of nitrification as the NO3- supply for denitrification. This ratio decreased from 1.55 to 0.05 with increased organic addition.

  16. Significance of dredging on sediment denitrification in Meiliang Bay, China: A year long simulation study

    USGS Publications Warehouse

    Zhong, Jicheng; Fan, Chengxin; Zhang, Lu; Edward, Hall; Ding, Shiming; Li, Bao; Liu, Guofeng

    2010-01-01

    An experiment for studying the effects of sediment dredging on denitrification in sediments was carried out through a one-year incubation of undredged (control) and dredged cores in laboratory. Dredging the upper 30 cm of sediment can significantly affect physico-chemical characteristics of sediments. Less degradation of organic matter in the dredged sediments was found during the experiment. Denitrification rates in the sediments were estimated by the acetylene blockage technique, and ranged from 21.6 to 102.7 nmol N2/(g dry weight (dw) x hr) for the undredged sediment and from 6.9 to 26.9 nmol N2/(g dw x hr) for dredged sediments. The denitrification rates in the undredged sediments were markedly higher (p < 0.05) than those in the dredged sediments throughout the incubation, with the exception of February 2006. The importance of various environmental factors on denitrification was assessed, which indicated that denitrification was regulated by temperature. Nitrate was probably the key factor limiting denitrification in both undredged and dredged sediments. Organic carbon played some role in determining the denitrification rates in the dredged sediments, but not in the undredged sediments. Sediment dredging influenced the mineralization of organic matter and denitrification in the sediment; and therefore changed the pattern of inherent cycling of nitrogen.

  17. Denitrification in the Upper Mississippi River: Rates, controls, and contribution to nitrate flux

    USGS Publications Warehouse

    Richardson, W.B.; Strauss, E.A.; Bartsch, L.A.; Monroe, E.M.; Cavanaugh, J.C.; Vingum, L.; Soballe, D.M.

    2004-01-01

    We evaluated patterns of denitrification and factors effecting denitrification in the upper Mississippi River. Measurements were taken over 2 years, during which river discharge ranged from record flooding to base flow conditions. Over the period of study, average denitrification enzyme activity was highest in backwater lakes and lowest in the main channel. Throughout the study reach, highest denitrification enzyme activity occurred during fall and lowest occurred in winter. Rates during spring floods (2001) were only slightly higher than during the preceding winter. Mean unamended denitrification rates ranged from 0.02 (fall 2001 in backwaters) to 0.40 ??g N??cm -2??h-1 (spring 2001 in backwaters). Laboratory experiments showed that denitrification rates increased significantly with addition of NO3- regardless of sediment C content, while rates increased little with addition of labile C (glucose). Denitrification in this reach of the upper Mississippi River appears to be NO3- limited throughout the growing season and the delivery of NO 3- is strongly controlled by river discharge and hydrologie connectivity across the floodplain. We estimate that denitrification removes 6939 t N??year-1 or 6.9% of the total annual NO 3- input to the reach. Hydrologic connectivity and resultant NO3- delivery to high-C sediments is a critical determinant of reach-scale processing of N in this floodplain system.

  18. Comparison of denitrification between Paracoccus sp. and Diaphorobacter sp.

    PubMed

    Chakravarthy, Srinandan S; Pande, Samay; Kapoor, Ashish; Nerurkar, Anuradha S

    2011-09-01

    Denitrification was compared between Paracoccus sp. and Diaphorobacter sp. in this study, both of which were isolated from activated sludge of a denitrifying reactor. Denitrification of both isolates showed contrasting patterns, where Diaphorobacter sp. showed accumulation of nitrite in the medium while Paracoccus sp. showed no accumulation. The nitrate reduction rate was 1.5 times more than the nitrite reduction in Diaphorobacter sp., as analyzed by the resting state denitrification kinetics. Increasing the nitrate concentration in the medium increased the nitrite accumulation in Diaphorobacter sp., but not in Paracoccus sp., indicating a branched electron transfer during denitrification. Diaphorobacter sp. was unable to denitrify efficiently at high nitrate concentrations from 1 M, but Paracoccus sp. could denitrify even up to 2 M nitrate. Paracoccus sp. was found to be an efficient denitrifier with insignificant amounts of nitrite accumulation, and it could also denitrify high amounts of nitrate up to 2 M. Efficient denitrification without accumulation of intermediates like nitrite is desirable in the removal of high nitrates from wastewaters. Paracoccus sp. is shown to suffice this demand and could be a potential organism to remove high nitrates effectively. PMID:21509603

  19. Denitrification by Pseudomonas Aeruginosa Under Simulated Engineered Martain Conditions

    NASA Astrophysics Data System (ADS)

    Hart, S. D.; Currier, P. A.; Thomas, D. J.

    The growth of Pseudomonas aeruginosa in denitrifying medium was observed for 14 days in the presence of a martian soil analog (JSC Mars-1) and elevated CO2 levels. A four-way test was conducted comparing growth of experimental samples to growth in the presence of inert silica (“Earth soil”) and normal terrestrial atmosphere. The combination of 50 mL of fluorescence-denitrification medium and 10 grams of soil additive simulated an aquatic environment, which was contained in sealed culture bottles. Nitrite assays of the media (to test for consumption during denitrification), gas sampling from the bottles to observe nitrogen production, and colony counts to quantify growth rate were all performed at 0, 7 and 14 days after inoculation. Supplemental tests performed included nitrate assays (to confirm the occurrence of denitrification) and culture fluorescence (as a non-invasive growth test). Growth and denitrification took place under all conditions, and no significant differ- ences were observed between samples. These data indicate that the presence of simulated martian regolith and elevated CO2 have little or no effect on the growth of or denitrification by P. aeruginosa at the concentrations used.

  20. Analysis of denitrification process in the groundwater of floodplains using a modelling approach

    NASA Astrophysics Data System (ADS)

    Bernard-Jannin, Léonard; Brito, David; Sun, Xiaoling; Teissier, Samuel; Neves, Ramiro; Sauvage, Sabine; Sánchez-Pérez, José-Miguel

    2016-04-01

    Nitrate contamination of freshwater systems is a global concern. In alluvial floodplains, highly vulnerable to nitrate pollution due to widespread agricultural activities, riparian areas have been proven to be efficient in nitrate removal through denitrification. However, denitrification presents complex spatio-temporal patterns and is controlled by many factors. Hence, modelling can provide useful knowledge about this biogeochemical process, by helping to identify key factors involved in denitrification process and its spatio-temporal variability. In this study, a modelling approach combining i) a distributed hydrodynamic model, coupling surface and subsurface flow (MOHID Land), with ii) a simplified denitrification calculation module including dissolved organic carbon (DOC borned by the river) and particulate organic carbon (POC present in soil) have been applied to a monitored meander area of the Garonne river (6.6 km²). The dataset include hydrological data and nitrates concentrations collected in a network of 25 piezometers during 12 monthly campaigns allowing the set up and the validation of the model application. The average denitrification rate was estimated to 28 kg N/ha/yr representing 38% of the lateral nitrate input from the agricultural area. Denitrification was the highest in the low elevation riparian area in relation with inundated soils releasing topsoil organic carbon fueling denitrification. In addition high denitrification rates were simulated in downstream part of the meander in relation with the high nitrates flux coming from the agricultural area. Geomorphological settings and groundwater flows in the area play a major role in controlling denitrification in floodplain area. Flood events lead to high denitrification periods by increasing topsoil layer POC availability with higher water level in the aquifer. However, the role of DOC borne by the river seems restricted. The model can be applied to estimate nitrate removal capacity of riparian

  1. Regional oxygen reduction and denitrification rates, San Joaquin Valley, USA

    NASA Astrophysics Data System (ADS)

    Green, C. T.; Jurgens, B. C.; Zhang, Y.; Starn, J. J.; Visser, A.; Singleton, M. J.; Esser, B. K.

    2015-12-01

    Rates of oxygen and nitrate reduction are key factors in determining the chemical evolution of groundwater. Little is known about how these rates vary in regional groundwater settings, as few studies have focused on regional datasets with multiple tracers and methods of analysis that account for effects of mixed residence times on apparent reaction rates. This study provides insight into residence times and rates of O2 reduction and denitrification using a novel approach of multi-model residence time distributions (RTDs) applied to a data set of atmospheric tracers of groundwater age and geochemical data from 141 well samples in the Central Eastern San Joaquin Valley, CA. The residence time distribution approach accounts for mixtures of residence times in a single sample to provide estimates of in-situ rates. Tracers included SF6, CFCs, 3H, He from 3H, 14C, and terrigenic He. Parameter estimation and multi-model averaging were used to establish RTDs with lower error variance than produced by individual RTD models. The set of multi-model RTDs was used in combination with NO3- and dissolved gas data to estimate zero order and first order rates of O2 reduction and denitrification. Results indicated that these rates followed approximately log-normal distributions. Rates of O2 reduction and denitrification were correlated and, on an electron milliequivalent basis, denitrification rates tended to exceed O2 reduction rates. Results indicate that the multi-model approach can improve estimation of age distributions, and that, because of the correlations, relatively easily measured O2 rates can provide information about trends in denitrification rates, which are more difficult to measure.

  2. The enzymes associated with denitrification

    NASA Technical Reports Server (NTRS)

    Hochstein, L. I.; Tomlinson, G. A.

    1988-01-01

    The enzymes involved in the reduction of nitrogenous oxides are thought to be intermediates in denitrification processes. This review examines the roles of nitrate reductase, nitrite reductases, nitric oxide reductase, mechanisms of N-N bond formation, and nitrous oxide reductases.

  3. DEMONSTRATION BULLETIN: BIOLOGICAL DENITRIFICATION PROCESS

    EPA Science Inventory

    NRMRL-CIN-1362 SAIC. Demonstration Bulletin: Biological Denitrification Process, Ecomat, Inc.. 2001. EPA/540/MR-01/501. 03/15/2001 EcoMat, Inc. of Hayward, CA has developed a two-stage ex situ anoxic biofilter biodenitrification process. The process is a fixed film bioremedia...

  4. Denitrification accelerates granular sludge formation in sequencing batch reactors.

    PubMed

    Suja, E; Nancharaiah, Y V; Krishna Mohan, T V; Venugopalan, V P

    2015-11-01

    In this study, the role of denitrification on aerobic granular sludge formation in sequencing batch reactors (SBRs) was investigated. Formation of aerobic granular sludge was faster in SBRs fed with varying concentrations of nitrate or nitrite as compared to control, which received no nitrate or nitrite in the feed. The majority of the fed nitrate or nitrite was denitrified in the anoxic static fill phase, prior to aerobic reaction phase. Sludge characterization showed accumulation of calcium and chemical signature of calcium carbonate in the nitrate-fed SBRs. Feeding of sodium nitroprusside, a known nitric oxide (NO) donor, enhanced aggregation, production of extracellular polymeric substances and formation of aerobic granular sludge. The results support the hypothesis that denitrification facilitates cell aggregation and accelerates aerobic sludge granulation through NO signaling and CaCO3 formation. Nitrate or other intermediates of heterotrophic denitrification, therefore, have a positive effect on aerobic granulation in SBRs. PMID:26218539

  5. Impact of chloride on denitrification potential in roadside wetlands.

    PubMed

    Lancaster, Nakita A; Bushey, Joseph T; Tobias, Craig R; Song, Bongkeun; Vadas, Timothy M

    2016-05-01

    Developed landscapes are exposed to changes in hydrology and water chemistry that limit their ability to mitigate detrimental impacts to coastal water bodies, particularly those that result from stormwater runoff. The elevated level of impervious cover increases not only runoff but also contaminant loading of nutrients, metals, and road salt used for deicing to water bodies. Here we investigate the impact that road salt has on denitrification in roadside environments. Sediments were collected from a series of forested and roadside wetlands and acclimated with a range of Cl(-) concentrations from 0 to 5000 mg L(-1) for 96 h. Denitrification rates were measured by the isotope pairing technique using (15)N-NO3(-), while denitrifying community structures were compared using terminal restriction fragment length polymorphism (T-RFLP) of nitrous oxide reductase genes (nosZ). Chloride significantly (p < 0.05) inhibited denitrification in forested wetlands at a Cl(-) dosage of 2500 or 5000 mg L(-1), but the decrease in denitrification rates was less and not significant for the roadside wetlands historically exposed to elevated concentrations of Cl(-). The difference could not be attributed to other significant changes in conditions, such as DOC concentrations, N species concentrations, or pH levels. Denitrifying communities, as measured by T-RFs of the nosZ gene, in the roadside wetlands with elevated concentration of Cl(-) were distinctly different and more diverse compared to forested wetlands, and also different in roadside wetlands after 96 h exposures to Cl(-). The shifts in denitrifying communities seem to minimize the decrease in denitrification rates in the wetlands previously exposed to Cl. As development results in more Cl(-) use and exposure to a broad range of natural or manmade wetland structures, an understanding of the seasonal effect of Cl on denitrification processes in these systems would aid in design or mitigation of the effects on N removal

  6. Remediation of nitrate-contaminated water by solid-phase denitrification process-a review.

    PubMed

    Ashok, Vaishali; Hait, Subrata

    2015-06-01

    The paper presents a compilation of various autotrophic and heterotrophic ways of solid-phase denitrification. It covers a complete understanding of various pathways followed during denitrification process. The paper gives a brief review on various governing factors on which the process depends. It focuses mainly on the solid-phase denitrification process, its applicability, efficiency, and disadvantages associated. It presents a critical review on various methodologies associated with denitrification process reported in past years. A comparative study has also been carried out to have a better understanding of advantages and disadvantages of a particular method. We summarize the various organic and inorganic substances and various techniques that have been used for enhancing denitrification process and suggest possible gaps in the research areas whi'ch are worthy of future research. PMID:25787220

  7. Nitrate removal and denitrification affected by soil characteristics in nitrate treatment wetlands.

    PubMed

    Lin, Ying-Feng; Jing, Shuh-Ren; Lee, Der-Yuan; Chang, Yih-Feng; Shih, Kai-Chung

    2007-03-01

    Several small-scale surface flow constructed wetlands unplanted and planted (monoculture) with various macrophytes (Phragmites australis, Typha orientalis, Pennisetum purpureum, Ipomoea aquatica, and Pistia stratiotes) were established to continuously receive nitrate-contaminated groundwater. Soil characteristics and their effects on nitrate removal and soil denitrification were investigated. The results showed that planted wetland cells exhibited significantly higher (P < 0.05) nitrate removal efficiencies (70-99%) and soil denitrification rates (3.78-15.02 microg N2O-N/g dry soil/h) than an unplanted covered wetland cell (1%, 0.11 microg N2O-N/g/h). However, the unplanted uncovered wetland cell showed a nitrate removal efficiency (55%) lower than but a soil denitrification rate (9.12 microg N2O-N/g/h) comparable to the planted cells. The nitrate removal rate correlated closely and positively with the soil denitrification rate for the planted cells, indicating that soil denitrification is an important process for removing nitrate in constructed wetlands. The results of nitrogen budget revealed that around 68.9-90.7% of the overall nitrogen removal could be attributed to the total denitrification. The soil denitrification rate was found to correlate significantly (P < 0.01) with the extractable organic carbon, organic matter, and in situ-measured redox potential of wetland soil, which accordingly were concluded as suitable indicators of soil denitrification rate and nitrate removal rate in nitrate treatment wetlands. PMID:17365317

  8. Sediment nitrification and denitrification rates in a Lake Superior estuary

    EPA Science Inventory

    Microbially-mediated nitrogen (N) cycling in aquatic sediments has been recognized as an ecosystem service due to mitigation of N-transport to receiving waters. In 2011 and 2012, we compared nitrification (NIT), unamended (DeNIT) and amended (DEA) denitrification rates among spat...

  9. Searching for hot spots and hot moments of soil denitrification in northern hardwood forests

    NASA Astrophysics Data System (ADS)

    Morse, J. L.; Duran, J.; Morillas, L.; Roales, J.; Bailey, S. W.; McGuire, K. J.; Groffman, P. M.

    2014-12-01

    Denitrification is a key biogeochemical process that affects nitrogen (N) availability, N losses to aquatic systems, and atmospheric chemistry. In upland forests, denitrification has not been thought to be a major N pathway because it is an anaerobic microbial process that requires nitrate, labile carbon (C), and low oxygen (O2) conditions, which do not occur broadly or consistently throughout forest soils. However, there may be enough spatial and temporal heterogeneity at fine scales to support denitrification rates that are relevant at the landscape scale. To quantify the importance of spatial and temporal variability in soil denitrification in northern hardwood forests at the Hubbard Brook Experimental Forest (HBEF; New Hampshire, USA), we developed two related projects: 1) we sought to identify hot spots of biogeochemical activity, including soil denitrification potential, based on hydropedologic settings and flowpaths in a catchment during the growing season; and 2) we investigated the influence of simulated rainfall events on soil O2 and nitrous oxide concentrations, denitrification rates, and soil respiration during different seasons at HBEF. In the first study, we expected to find that sites dominated by soils with thick Bh horizons (zones of C accumulation) would have the highest denitrification rates. However, despite the variation among soil profiles found in different hydropedologic settings, we did not find significant differences in denitrification potential. Rather, when areal coverage and horizon thickness for the contrasting hydropedologic settings were accounted for, catchment-scale estimates of denitrification potential were about 1/3 higher than conventionally calculated estimates. In the second study, soil O2 in surface horizons only decreased following additions of labile C. Responses of soil respiration and denitrification to simulated rainfall were also influenced by season. While these studies highlight the complex heterogeneity in forest

  10. Is pre-conditioning required for the measurement of in situ denitrification rates with push-pull 15N-tracer tests?

    NASA Astrophysics Data System (ADS)

    Eschenbach, Wolfram; Well, Reinhard

    2013-04-01

    Diffuse NO3 emissions derived from agricultural N surpluses are the main cause of NO3 pollution of aquifers and open water bodies. Denitrification is the key process for the attenuation of this anthropogenic NO3 in groundwater. Knowledge about the spatial variability denitrification rates in nitrate-contaminated aquifers is crucial to predict the development of groundwater quality. However, the spatial distribution and intensity of denitrification in aquifers is difficult to predict. But precisely this knowledge is important for an effective implementation of measures for the reduction of agricultural N-surpluses to gain a good chemical status of groundwater bodies. Push-pull tests have proven to be a relatively low-cost instrument to obtain quantitative information about aquifer properties and microbial activities in aquifers. These tests have been already successfully used for the measurement of in situ denitrification rates (Dr(in situ); Well and Myrold, 2002;Konrad, 2007). We conducted 28 push-pull tracer tests in the Großen Kneten (GKA) and the Furberger Feld aquifer (FFA), two Pleistocene sandy aquifers in Lower Saxony (Germany) to measure Dr(in situ) and to derive an estimate on the stock of reactive compounds. In the deeper NO3-free zone of the aquifer, Dr(in situ) was relatively low despite the high abundance of reductants. Our aim was to check whether pre-conditioning by repeated NO3-injections would stimulate indigenous denitrifiers and thus lead to increased reduction rates of NO3 corresponding to the stock of reductants. Pre-conditioning by the injection of the electron acceptor NO3 prior to subsequent push-pull tracer tests with 15N labelled NO3 was performed at 4 depths in the NO3-free groundwater zone in the Fuhrberger Feld aquifer. We compared unconditioned and pre-conditioned in situ denitrification rates with laboratory denitrification rates measured during one year laboratory incubations with corresponding aquifer material (Dr(365)). Our

  11. Denitrification in the Antarctic stratosphere

    NASA Technical Reports Server (NTRS)

    Salawitch, R. J.; Gobbi, G. P.; Wofsy, S. C.; Mcelroy, M. B.

    1989-01-01

    Rapid loss of ozone over Antarctica in spring requires that the abundance of gaseous nitric acid be very low. Precipitation of particulate nitric acid has been assumed to occur in association with large ice crystals, requiring significant removal of H2O and temperatures well below the frost point. However, stratospheric clouds exhibit a bimodal size distribution in the Antarctic atmosphere, with most of the nitrate concentrated in particles with radii of 1 micron or greater. It is argued here that the bimodal size distribution sets the stage for efficient denitrification, with nitrate particles either falling on their own or serving as nuclei for the condensation of ice. Denitrification can therefore occur without significant dehydration, and it is unnecessary for temperatures to drop significantly below the frost point.

  12. Denitrification and the denitrifier community in coastal microbial mats.

    PubMed

    Fan, Haoxin; Bolhuis, Henk; Stal, Lucas J

    2015-03-01

    Denitrification was measured in three structurally different coastal microbial mats by using the stable isotope technique. The composition of the denitrifying community was determined by analyzing the nitrite reductase (nirS and nirK) genes using clone libraries and the GeoChip. The highest potential rate of denitrification (7.0 ± 1.0 mmol N m(-2) d(-1)) was observed during summer at station 1 (supra-littoral). The rates of denitrification were much lower in the stations 2 (marine) and 3 (intermediate) (respectively 0.1 ± 0.05 and 0.7 ± 0.2 mmol N m(-2) d(-1)) and showed less seasonality when compared to station 1. The denitrifying community at station 1 was also more diverse than that at station 2 and 3, which were more similar to each other than either of these stations to station 1. In all three stations, the diversity of both nirS and nirK denitrifiers was higher in summer when compared to winter. The location along the tidal gradient seems to determine the composition, diversity and activity of the denitrifier community, which may be driven by salinity, nitrate/nitrite and organic carbon. Both nirS and nirK denitrifiers are equally present and therefore they are likely to play a role in the denitrification of the microbial mats studied. PMID:25764561

  13. N₂O accumulation from denitrification under different temperatures.

    PubMed

    Poh, Leong Soon; Jiang, Xie; Zhang, Zhongbo; Liu, Yu; Ng, Wun Jern; Zhou, Yan

    2015-11-01

    The effects of temperature on nitrous oxide (N2O) accumulation during denitrification and denitritation were investigated. Batch experiments were performed to measure N2O accumulation at 25 and 35 °C. More N2O accumulation was observed during denitritation at the higher temperature as compared with full denitrification and low temperature tests. The highest nitrite concentration tested in this study (25 mg/L NO2 (-)N and pH 8.0) did not show inhibitory effect on N2O reduction. It was found that the major cause of more N2O accumulation during denitrification at higher temperature was due to higher N2O production rate and lower N2O solubility. Specific nitrate, nitrite, and N2O reduction rates increased 62, 61, and 41 %, respectively, when temperature rose from 25 to 35 °C. The decrease of N2O solubility in mixed liquor at 35 °C (when compared to 25 °C) resulted in faster diffusing rate of N2O from liquid to gas phase. It was also more difficult for gas phase N2O to be re-dissolved. The diffused N2O was then accumulated in the headspace, which was not available for denitrification by denitrifiers. The results of this study suggest higher temperature may worsen N2O emission from wastewater treatment plants (WWTPs). PMID:26129949

  14. Sediment, water column, and open-channel denitrification in rivers measured using membrane-inlet mass spectrometry

    NASA Astrophysics Data System (ADS)

    Reisinger, Alexander J.; Tank, Jennifer L.; Hoellein, Timothy J.; Hall, Robert O.

    2016-05-01

    Riverine biogeochemical processes are understudied relative to headwaters, and reach-scale processes in rivers reflect both the water column and sediment. Denitrification in streams is difficult to measure, and is often assumed to occur only in sediment, but the water column is potentially important in rivers. Dissolved nitrogen (N) gas flux (as dinitrogen (N2)) and open-channel N2 exchange methods avoid many of the artificial conditions and expenses of common denitrification methods like acetylene block and 15N-tracer techniques. We used membrane-inlet mass spectrometry and microcosm incubations to quantify net N2 and oxygen flux from the sediment and water column of five Midwestern rivers spanning a land use gradient. Sediment and water column denitrification ranged from below detection to 1.8 mg N m-2 h-1 and from below detection to 4.9 mg N m-2 h-1, respectively. Water column activity was variable across rivers, accounting for 0-85% of combined microcosm denitrification and 39-85% of combined microcosm respiration. Finally, we estimated reach-scale denitrification at one Midwestern river using a diel, open-channel N2 exchange approach based on reach-scale metabolism methods, providing an integrative estimate of riverine denitrification. Reach-scale denitrification was 8.8 mg N m-2 h-1 (95% credible interval: 7.8-9.7 mg N m-2 h-1), higher than combined sediment and water column microcosm estimates from the same river (4.3 mg N m-2 h-1) and other estimates of reach-scale denitrification from streams. Our denitrification estimates, which span habitats and spatial scales, suggest that rivers can remove N via denitrification at equivalent or higher rates than headwater streams.

  15. Evapotranspiration: Mass balance measurements compared with flux estimation methods

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Evapotranspiration (ET) may be measured by mass balance methods and estimated by flux sensing methods. The mass balance methods are typically restricted in terms of the area that can be represented (e.g., surface area of weighing lysimeter (LYS) or equivalent representative area of neutron probe (NP...

  16. Influence of biochar on soil pore structure and denitrification

    NASA Astrophysics Data System (ADS)

    Maenhout, Peter; Sleutel, Steven; Ameloot, Nele; De Neve, Stefaan

    2014-05-01

    Incorporation of biochar into soils has frequently been found to reduce soil emission of the greenhouse gas N2O, formed as an intermediate during microbial denitrification. The exact mechanism that regulates N2O emission reduction after biochar incorporation is still unknown and diverse hypotheses on either chemical, physical or biological controls over soil denitrification exist. The porous structure of biochar may directly and indirectly influence the soil pore structure upon its incorporation. Firstly biochar may increase soil aeration and thereby reduce denitrification which requires an anaerobic atmosphere to continue. In order to investigate this hypothesis we incorporated 4 biochar types in a sandy loam soil and collected undisturbed soil cores after 8 months of field incorporation. We then crushed half of the soil cores and replaced them. We followed N2O emissions from undisturbed and disturbed biochar amended soil cores by GC headspace analysis. From the disturbed soil cores no emission reduction was expected because soil pore structure was severely disrupted. However, both disturbed and undisturbed soil cores showed emission reductions when compared to the soil cores without biochar amendment. This allowed us to reject the hypothesis that biochar would affect soil denitrification through increased soil aeration. We moved to investigate a second hypothesis, viz. 'Through the retention of water in its finer pores, biochar could create local anaerobic 'denitrification hot spots' in soils. It could be hypothesized that the final further reduction of N2O into N2 is stimulated. We tested this hypothesis by comparing N2+N2O (acetylene inhibition) and N2O emissions from undisturbed soil cores with or without biochar amended, at 70 and 90 % WFPS. At 70% WFPS we expected higher N2 emissions in biochar amended soils compared to the unamended control cores, through the action of anaerobic hot spots in biochar. In contrast, at 90% WFPS anaerobicity would be general in

  17. Topographic effects on denitrification in drained agricultural fields

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Denitrification is affected by soil moisture, while soil moisture can be affected by topography. Therefore, denitrification can be spatially correlated to topographic gradients. Three prior converted fields on the Delmarva Peninsula were sampled spatially for denitrification enzyme activity. The up...

  18. Predicting the denitrification capacity of sandy aquifers from shorter-term incubation experiments and sediment properties

    NASA Astrophysics Data System (ADS)

    Eschenbach, W.; Well, R.

    2013-02-01

    Knowledge about the spatial variability of denitrification rates and the lifetime of denitrification in nitrate-contaminated aquifers is crucial to predict the development of groundwater quality. Therefore, regression models were derived to estimate the measured cumulative denitrification of aquifer sediments after one year of incubation from initial denitrification rates and several sediment parameters, namely total sulphur, total organic carbon, extractable sulphate, extractable dissolved organic carbon, hot water soluble organic carbon and potassium permanganate labile organic carbon. For this purpose, we incubated aquifer material from two sandy Pleistocene aquifers in Northern Germany under anaerobic conditions in the laboratory using the 15N tracer technique. The measured amount of denitrification ranged from 0.19 to 56.2 mg N kg-1 yr-1. The laboratory incubations exhibited high differences between non-sulphidic and sulphidic aquifer material in both aquifers with respect to all investigated sediment parameters. Denitrification rates and the estimated lifetime of denitrification were higher in the sulphidic samples. For these samples, the cumulative denitrification measured during one year of incubation (Dcum(365)) exhibited distinct linear regressions with the stock of reduced compounds in the investigated aquifer samples. Dcum(365) was predictable from sediment variables within a range of uncertainty of 0.5 to 2 (calculated Dcum(365)/measured Dcum(365)) for aquifer material with a Dcum(365) > 20 mg N kg-1 yr-1. Predictions were poor for samples with lower Dcum(365), such as samples from the NO3- bearing groundwater zone, which includes the non-sulphidic samples, from the upper part of both aquifers where denitrification is not sufficient to protect groundwater from anthropogenic NO3- input. Calculation of Dcum(365) from initial denitrification rates was only successful for samples from the NO3--bearing zone, whereas a lag-phase of denitrification in samples

  19. Comparative evaluation of workload estimation techniques in piloting tasks

    NASA Technical Reports Server (NTRS)

    Wierwille, W. W.

    1983-01-01

    Techniques to measure operator workload in a wide range of situations and tasks were examined. The sensitivity and intrusion of a wide variety of workload assessment techniques in simulated piloting tasks were investigated. Four different piloting tasks, psychomotor, perceptual, mediational, and communication aspects of piloting behavior were selected. Techniques to determine relative sensitivity and intrusion were applied. Sensitivity is the relative ability of a workload estimation technique to discriminate statistically significant differences in operator loading. High sensitivity requires discriminable changes in score means as a function of load level and low variation of the scores about the means. Intrusion is an undesirable change in the task for which workload is measured, resulting from the introduction of the workload estimation technique or apparatus.

  20. Comparison of Simultaneous Nitrification and Denitrification for Three Different Reactors

    PubMed Central

    Khanitchaidecha, W.; Nakaruk, A.; Koshy, P.; Futaba, K.

    2015-01-01

    Discharge of high NH4-N containing wastewater into water bodies has become a critical and serious issue due to its negative impact on water and environmental quality. In this research, the performance of three different reactors was assessed and compared with regard to the removal of NH4-N from wastewater. The highest nitrogen removal efficiency of 98.3% was found when the entrapped sludge reactor (ESR), in which the sludge was entrapped in polyethylene glycol polymer, was used. Under intermittent aeration, nitrification and denitrification occurred simultaneously in the aerobic and anaerobic periods. Moreover, internal carbon was consumed efficiently for denitrification. On the other hand, internal carbon consumption was not found to occur in the suspended sludge reactor (SSR) and the mixed sludge reactor (MSR) and this resulted in nitrogen removal efficiencies of SSR and MSR being 64.7 and 45.1%, respectively. Nitrification and denitrification were the main nitrogen removal processes in the aerobic and anaerobic periods, respectively. However, due to the absence of sufficient organic carbon, denitrification was uncompleted resulting in high NO3-N contents in the effluent. PMID:26380304

  1. Autotrophic denitrification of nitrate and nitrite using thiosulfate as an electron donor.

    PubMed

    Chung, Jinwook; Amin, Khurram; Kim, Seungjin; Yoon, Seungjoon; Kwon, Kiwook; Bae, Wookeun

    2014-07-01

    This study was carried out to determine the possibility of autotrophic denitritation using thiosulfate as an electron donor, compare the kinetics of autotrophic denitrification and denitritation, and to study the effects of pH and sulfur/nitrogen (S/N) ratio on the denitrification rate of nitrite. Both nitrate and nitrite were removed by autotrophic denitrification using thiosulfate as an electron donor at concentrations up to 800 mg-N/L. Denitrification required a S/N ratio of 5.1 for complete denitrification, but denitritation was complete at a S/N ratio of 2.5, which indicated an electron donor cost savings of 50%. Also, pH during denitrification decreased but increased with nitrite, implying additional alkalinity savings. Finally, the highest specific substrate utilization rate of nitrite was slightly higher than that of nitrate reduction, and biomass yield for denitrification was relatively higher than that of denitritation, showing less sludge production and resulting in lower sludge handling costs. PMID:24755301

  2. Nitrous oxide emission from denitrification in stream and river networks

    PubMed Central

    Beaulieu, Jake J.; Tank, Jennifer L.; Hamilton, Stephen K.; Wollheim, Wilfred M.; Hall, Robert O.; Mulholland, Patrick J.; Peterson, Bruce J.; Ashkenas, Linda R.; Cooper, Lee W.; Dahm, Clifford N.; Dodds, Walter K.; Grimm, Nancy B.; Johnson, Sherri L.; McDowell, William H.; Poole, Geoffrey C.; Valett, H. Maurice; Arango, Clay P.; Bernot, Melody J.; Burgin, Amy J.; Crenshaw, Chelsea L.; Helton, Ashley M.; Johnson, Laura T.; O'Brien, Jonathan M.; Potter, Jody D.; Sheibley, Richard W.; Sobota, Daniel J.; Thomas, Suzanne M.

    2011-01-01

    Nitrous oxide (N2O) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Anthropogenic nitrogen (N) loading to river networks is a potentially important source of N2O via microbial denitrification that converts N to N2O and dinitrogen (N2). The fraction of denitrified N that escapes as N2O rather than N2 (i.e., the N2O yield) is an important determinant of how much N2O is produced by river networks, but little is known about the N2O yield in flowing waters. Here, we present the results of whole-stream 15N-tracer additions conducted in 72 headwater streams draining multiple land-use types across the United States. We found that stream denitrification produces N2O at rates that increase with stream water nitrate (NO3−) concentrations, but that <1% of denitrified N is converted to N2O. Unlike some previous studies, we found no relationship between the N2O yield and stream water NO3−. We suggest that increased stream NO3− loading stimulates denitrification and concomitant N2O production, but does not increase the N2O yield. In our study, most streams were sources of N2O to the atmosphere and the highest emission rates were observed in streams draining urban basins. Using a global river network model, we estimate that microbial N transformations (e.g., denitrification and nitrification) convert at least 0.68 Tg·y−1 of anthropogenic N inputs to N2O in river networks, equivalent to 10% of the global anthropogenic N2O emission rate. This estimate of stream and river N2O emissions is three times greater than estimated by the Intergovernmental Panel on Climate Change. PMID:21173258

  3. Nitrous oxide emission from denitrification in stream and river networks

    USGS Publications Warehouse

    Beaulieu, J.J.; Tank, J.L.; Hamilton, S.K.; Wollheim, W.M.; Hall, R.O., Jr.; Mulholland, P.J.; Peterson, B.J.; Ashkenas, L.R.; Cooper, L.W.; Dahm, Clifford N.; Dodds, W.K.; Grimm, N. B.; Johnson, S.L.; McDowell, W.H.; Poole, G.C.; Maurice, Valett H.; Arango, C.P.; Bernot, M.J.; Burgin, A.J.; Crenshaw, C.L.; Helton, A.M.; Johnson, L.T.; O'Brien, J. M.; Potter, J.D.; Sheibley, R.W.; Sobota, D.J.; Thomas, S.M.

    2011-01-01

    Nitrous oxide (N2O) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Anthropogenic nitrogen (N) loading to river networks is a potentially important source of N 2O via microbial denitrification that converts N to N2O and dinitrogen (N2). The fraction of denitrified N that escapes as N2O rather than N2 (i.e., the N2O yield) is an important determinant of how much N2O is produced by river networks, but little is known about the N2O yield in flowing waters. Here, we present the results of whole-stream 15N-tracer additions conducted in 72 headwater streams draining multiple land-use types across the United States. We found that stream denitrification produces N2O at rates that increase with stream water nitrate (NO3-) concentrations, but that <1% of denitrified N is converted to N2O. Unlike some previous studies, we found no relationship between the N2O yield and stream water NO3-. We suggest that increased stream NO3- loading stimulates denitrification and concomitant N2O production, but does not increase the N2O yield. In our study, most streams were sources of N2O to the atmosphere and the highest emission rates were observed in streams draining urban basins. Using a global river network model, we estimate that microbial N transformations (e.g., denitrification and nitrification) convert at least 0.68 Tg??y -1 of anthropogenic N inputs to N2O in river networks, equivalent to 10% of the global anthropogenic N2O emission rate. This estimate of stream and river N2O emissions is three times greater than estimated by the Intergovernmental Panel on Climate Change.

  4. Software Effort Estimation Accuracy: A Comparative Study of Estimations Based on Software Sizing and Development Methods

    ERIC Educational Resources Information Center

    Lafferty, Mark T.

    2010-01-01

    The number of project failures and those projects completed over cost and over schedule has been a significant issue for software project managers. Among the many reasons for failure, inaccuracy in software estimation--the basis for project bidding, budgeting, planning, and probability estimates--has been identified as a root cause of a high…

  5. Denitrification and nitrous oxide in the North Sea

    NASA Astrophysics Data System (ADS)

    Law, C. S.; Owens, N. J. P.

    In situ sediment denitrification rates were determined in the major areas of deposition of the North Sea, using the acetylene block technique. In addition, nitrous oxide profiles of the water column were determined. Nitrous oxide production generally occurred in the photic zone possibly due to nitrification; and throughout the water column in the German Bight region. Consumption at depth was possibly due to reduction in the anoxic microzones of faecal pellets, concentrated at the thermocline. Saturation of surface waters was 102.2% compared to 130.3% in the German Bight region. Calculated flux of nitrous oxide to the atmosphere was 9.5 × 10 6 kg yr -1, over half of which was produced in the German Bight. Sediment denitrification rates varied through three orders of magnitude; the highest value of 150 μmol m -2 d -1 was recorded in the Norwegian Trench. Nitrous oxide production by the sediments was low (1.1 μmol m -2 d -1 max.), and was undetectable at half of the sites. Sediment nutrient profiles exhibited porewater nitrate concentrations exceeding that of the overlying water suggesting that denitrification was fuelled by nitrification, which, in turn was related to other environmental variables. A significant positive relationship existed between in situ denitrification rate and the nitrate content of the upper sediment. Extrapolation of the rate to the total area of deposition in the North Sea suggests that denitrification is responsible for a minimum loss of 7.5-12% of the total annual nitrogen contaminant input.

  6. Predicting long-term denitrification capacity of sandy aquifers from incubation experiments and sediment properties

    NASA Astrophysics Data System (ADS)

    Eschenbach, W.; Well, R.

    2012-07-01

    Knowledge about the spatial variability of denitrification rates and the lifetime of denitrification in nitrate-contaminated aquifers is crucial to predict the development of groundwater quality. Therefore, regression models were derived to estimate the measured denitrification capacity of incubated aquifer sediments from initial denitrification rates and several sediment parameters, namely total sulphur, total organic carbon, extractable sulfate, extractable dissolved organic carbon, hot water soluble organic carbon and potassium permanganate labile organic carbon. For this purpose, we incubated aquifer material from two sandy Pleistocene aquifers in Northern Germany under anaerobic conditions in the laboratory using the 15N tracer technique. The measured long-term denitrification capacities ranged from 0.18 to 56.2 mg N kg-1 yr-1. The laboratory incubations exhibited high differences between non-sulphidic and sulphidic aquifer material in both aquifers with respect to all investigated sediment parameters. Denitrification rates and the estimated lifetime of denitrification were higher in the sulphidic samples. Denitrification capacity measured during one year of incubation (Dcap) was predictable from sediment variables within a range of uncertainty of 0.5 to 2 (calculated Dcap/measured Dcap) for aquifer material with a Dcap > 20 mg N kg-1 yr-1. Predictions were poor for samples with lower Dcap like samples from the NO3--bearing groundwater zone, which includes the non-sulphidic samples, from the upper part of both aquifers where Dcap is not sufficient to protect groundwater from anthropogenic NO3- input. Calculation of Dcap from initial denitrification rates was only successful for samples from the NO3--bearing zone, whereas a lag-phase of denitrification in samples from deeper zones of NO3- free groundwater caused imprecise predictions. Our results thus show that Dcap of sandy Pleistocene aquifers can be predicted using a combination of short-term incubation and

  7. Sulfur-based denitrification: Effect of biofilm development on denitrification fluxes.

    PubMed

    Wang, Yue; Bott, Charles; Nerenberg, Robert

    2016-09-01

    Elemental sulfur (S(o)) can serve as an electron donor for denitrification. However, the mechanisms and rates of S(o)-based denitrification, which depend on a biofilm development on a solid S(o) surface, are not well understood. We used completely-mixed reactors packed with S(o) chips to systematically explore the behavior of S(o)-based denitrification as a function of the bulk nitrate (NO3(-)) concentration and biofilm development. High-purity (99.5%) and agricultural-grade (90% purity) S(o) chips were tested to explore differences in performance. NO3(-) fluxes followed a Monod-type relationship with the bulk NO3(-) concentration. For high-purity S(o), the maximum NO3(-) flux increased from 0.4 gN/m(2)-d at 21 days to 0.9 g N/m(2)-d at around 100 days, but then decreased to 0.65 gN/m(2)-d at 161 days. The apparent (extant) half-saturation constant for NO3(-) KSapp, based on the bulk NO3(-) concentration and NO3(-) fluxes into the biofilm, increased from 0.1 mgN/L at 21 days to 0.8 mgN/L at 161 days, reflecting the increasing mass transfer resistance as the biofilm thickness increased. Nitrite (NO2(-)) accumulation became significant at bulk NO3(-) concentration above 0.2 mgN/L. The behavior of the agricultural-grade S(o) was very similar to the high-purity S(o). The kinetic behavior of S(o)-based denitrification was consistent with substrate counter-diffusion, where the soluble sulfur species diffuse from the S(o) particle into the base of the biofilm, while NO3(-) diffuses into the biofilm from the bulk. Initially, the fluxes were low due to biomass limitation (thin biofilms). As the biofilm thickness increased with time, the fluxes first increased, stabilized, and then decreased. The decrease was probably due to increasing diffusional resistance in the thick biofilm. Results suggest that fluxes comparable to heterotrophic biofilm processes can be achieved, but careful management of biofilm accumulation is important to maintain high fluxes. PMID:27187050

  8. Comparative evaluation of two quantitative precipitation estimation methods in Korea

    NASA Astrophysics Data System (ADS)

    Ko, H.; Nam, K.; Jung, H.

    2013-12-01

    The spatial distribution and intensity of rainfall is necessary for hydrological model, particularly, grid based distributed model. The weather radar is much higher spatial resolution (1kmx1km) than rain gauges (~13km) although radar is indirect measurement of rainfall and rain gauges are directly observed it. And also, radar is provided areal and gridded rainfall information while rain gauges are provided point data. Therefore, radar rainfall data can be useful for input data on the hydrological model. In this study, we compared two QPE schemes to produce radar rainfall for hydrological utilization. The two methods are 1) spatial adjustment and 2) real-time Z-R relationship adjustment (hereafter RAR; Radar-Aws Rain rate). We computed and analyzed the statistics such as ME (Mean Error), RMSE (Root mean square Error), and correlation using cross-validation method (here, leave-one-out method).

  9. Spatial trends of potential denitrification below the root zone in an agricultural setting, San Joaquin Valley, California, USA

    NASA Astrophysics Data System (ADS)

    Green, C. T.; Duff, J. H.; Bekins, B. A.

    2004-05-01

    Contamination of groundwater by nitrate is a major problem worldwide. Under anaerobic conditions in the subsurface, reduction of nitrate to nitrogen gas via denitrification may mitigate the problem. Denitrification has been studied extensively in the shallow subsurface, but few studies have been done to examine the potential for denitrification below the root zone. In this study, we examined spatial trends in potential denitrification rates in the sub-root unsaturated and saturated zones. Sediment samples were collected from bore holes located in the San Joaquin Valley near Merced, California. Samples were analyzed for potential denitrification rates using acetylene block enzyme assays. Maximum denitrification rates, microbial growth, and lag coefficients were calculated by calibrating a numerical model of microbial growth and substrate consumption to the experimental data. The rate coefficients were compared to hydrologic regime, depth, grain size, and organic carbon content of the sediment samples. Preliminary results show complex spatial trends in potential denitrification rates. In samples taken from near the water table and near the ground surface, rates were comparable. In the unsaturated zone and deep saturated zone, rates were orders of magnitude lower. Variability between sites and hydrologic regimes could be explained in part by abundance of organic carbon. We speculate that limitations on microbial growth and transport by sediment properties and hydrologic regime also control the ability of subsurface microbial communities to carry out denitrification.

  10. Temporal variability of denitrification in estuarine sediments

    NASA Astrophysics Data System (ADS)

    Law, C. S.; Rees, A. P.; Owens, N. J. P.

    1991-07-01

    Sediment denitrification rates and fluxes of nitrous oxide, nitrate, nitrite and ammonium were determined at two intertidal sites in the Tamar estuary (S.W. England). High sediment nitrate uptake rates were recorded throughout the year, whereas the nitrite and ammonium fluxes were positive (from sediment to water column), with the former resulting from nitrification. Nitrous oxide flux was also positive, being largely attributable to denitrification with some contribution from nitrification or nitrification-denitrification coupling. No relationship was apparent between denitrification rate and nitrate concentration in the overlying water, invalidating the notion that denitrification automatically regulates nitrate during periods of elevated ambient concentration. However, denitrification exhibited a strong covariance with the degree of sediment bioturbation ( Nereis diversicolor), which was considered to be attributable to increased transport and supply of nitrate via Nereis burrows. Denitrification accounted for 8·5% of the annual total nitrate loading to the Tamar estuary, although a maximum of 100% was observed in summer when the phytoplankton nutrient requirement would also be highest.

  11. Expansion of denitrification and anoxia in the eastern tropical North Pacific from 1972 to 2012

    NASA Astrophysics Data System (ADS)

    Horak, Rachel E. A.; Ruef, Wendi; Ward, Bess B.; Devol, Allan H.

    2016-05-01

    The eastern tropical North Pacific (ETNP) is a large region of anoxic water that hosts widespread water column N loss (denitrification). There is some disagreement about the long-term trends of denitrification and anoxia and long-term studies of water column denitrification within the anoxic zone are lacking. In this study, we compared ETNP water column nitrite, N*, and O2 data along the same transect for four studies ranging from 1972 to 2012. Anoxic water volume increased, and low-oxygen conditions expanded into shallower isopycnals from 1972 to 2012. A geochemical marker for cumulative N loss indicates that denitrification was highest in 2012 and the upper oxygen-deficient zone (ODZ) experienced the most change. Oxygen and N loss changes in the world's largest ODZ for 2012 could not be explained by the Pacific Decadal Oscillation, and decreased O2 in supply currents and increased wind-driven upwelling are likely mechanisms contributing to increased N loss and anoxia.

  12. Denitrification in marine shales in northeastern Colorado

    USGS Publications Warehouse

    McMahon, P.B.; Böhlke, J.K.; Bruce, B.W.

    1999-01-01

    Parts of the South Platte River alluvial aquifer in northeastern Colorado are underlain by the Pierre Shale, a marine deposit of Late Cretaceous age that is <1000 m thick. Ground water in the aquifer is contaminated with NO3/-, and the shale contains abundant potential electron donors for denitrification in the forms of organic carbon and sulfide minerals. Nested piezometers were sampled, pore water was squeezed from cores of shale, and an injection test was conducted to determine if denitrification in the shale was a sink for alluvial NO3/- and to measure denitrification rates in the shale. Measured values of NO3/-, N2, NH4/+, ??15[NO3/-], ??15N[N2], and ??15N[NH4/+] in the alluvial and shale pore water indicated that denitrification in the shale was a sink for alluvial NO3/-. Chemical gradients, reaction rate constants, and hydraulic head data indicated that denitrification in the shale was limited by the slow rate of NO3/- transport (possibly by diffusion) into the shale. The apparent in situ first-order rate constant for denitrification in the shale based on diffusion calculations was of the order of 0.04-0.4 yr-1, whereas the potential rate constant in the shale based on injection tests was of the order of 60 yr-1. Chemical data and mass balance calculations indicate that organic carbon was the primary electron donor for denitrification in the shale during the injection test, and ferrous iron was a minor electron donor in the process. Flux calculations for the conditions encountered at the site indicate that denitrification in the shale could remove only a small fraction of the annual agricultural NO3/- input to the alluvial aquifer. However, the relatively large potential first-order rate constant for denitrification in the shale indicated that the percentage of NO3/- uptake by the shale could be considerably larger in areas where NO3/- is transported more rapidly into the shale by advection.

  13. The kinetics of denitrification in permeable sediments

    NASA Astrophysics Data System (ADS)

    Evrard, Victor; Glud, Ronnie N.; Cook, Perran L. M.

    2013-04-01

    Permeable sediments comprise the majority of shelf sediments, yet the rates of denitrification remain highly uncertain in these environments. Computational models are increasingly being used to understand the dynamics of denitrification in permeable sediments, which are complex environments to study experimentally. The realistic implementation of such models requires reliable experimentally derived data on the kinetics of denitrification. Here we undertook measurements of denitrification kinetics as a function of nitrate concentration and in the presence and absence of oxygen, in carefully controlled flow through reactor experiments on sediments taken from six shallow coastal sites in Port Phillip Bay, Victoria, Australia. The results showed that denitrification commenced rapidly (within 30 min) after the onset of anoxia and the kinetics could be well described by Michaelis-Menten kinetics with half saturation constants (apparent Km) ranging between 1.5 and 19.8 μM, and maximum denitrification rate (Vmax) were in the range of 0.9-7.5 nmol mL-1 h-1. The production of N2 through anaerobic ammonium oxidation (anammox) was generally found to be less than 10% that of denitrification. Vmax were in the same range as previously reported in cohesive sediments despite organic carbon contents one order of magnitude lower for the sediments studied here. The ratio of sediment O2 consumption to Vmax was in the range of 0.02-0.09, and was on average much lower than the theoretical ratio of 0.8. The most likely explanation for this is that the microbial community is not able to instantaneously shift or optimally use a particular electron acceptor in the highly dynamic redox environment experienced in permeable sediments. Consistent with this explanation, subsequent longer-term experiments over 5 days showed that denitrification rates increased by a factor of 10 within 3 days of the permanent onset of anoxia. In contrast to previous studies, we did not observe any significant

  14. The effect of floating vegetation on denitrification and greenhouse gas production in wetland mesocosms

    NASA Astrophysics Data System (ADS)

    Jacobs, A. E.; Harrison, J. A.

    2012-12-01

    compared to inflow water, and calculated denitrification was statistically higher in the floating vegetation treatments compared to the other treatments. Greenhouse gas production, measured in CO2 equivalents for N2O and CH4, was highly variable and not statistically different between the treatments. Denitrification in the tarp covered mesocosms was similar to the no-cover treatment, indicating that biotic effects in the floating vegetation treatment may be important in lowering water column oxygen levels and increasing denitrification. Understanding how floating vegetation affects total nitrogen loss, denitrification, and greenhouse gas production can be used to weigh ecological costs and benefits of different vegetation types, especially in constructed and managed wetlands.

  15. [Denitrification performance of PBS as a solid carbon source of denitrification].

    PubMed

    Liu, Jia; Shen, Zhi-Qiang; Zhou, Yue-Xi; Cao, Rong; Li, Yuan-Zhi

    2014-07-01

    Poly-butylenes succinate (PBS) was used as solid denitrification carbon source and biofilm carrier, to investigate the denitrification performance and the influence of adding inert carrier. The experimental results showed that PBS could serve as solid carbon source for denitrification of low C/N ratio wastewater, but the startup time was longer, about 33 d. There was no accumulation of nitrite nitrogen in the process of denitrification, but it produced less than 0.8 mg x L(-1) ammonia nitrogen. Increasing the amount of biofilm in PBS supported denitrification system by adding the inert carrier could improve the denitrification rate. The denitrification rates of PBS, PBS + 30 g gravel, PBS + 60 g gravel and PBS +90 g gravel systems were 5.33, 7.04, 10.05 and 6.93 mg x (L x h)(-1), respectively, and all reactions were zero order. During the denitrification process (0-9 h), DOC increased before it was reduced. At the end of the denitrification reaction (24 h), DOC of the denitrification system with inert carrier 60 g gravel and 90 g gravel was 16.34 mg x L(-1) and 19.22 mg x L(-1), respectively, higher than that without gravel of 13.48 mg x L(-1). The pH of all denitrification systems were lower than the initial value, which was the result of comprehensive function of acidic substances and alkalinity produced in the process of degradation of solid carbon source and denitrification, respectively. PMID:25244849

  16. Isotopologue fractionation during N(2)O production by fungal denitrification.

    PubMed

    Sutka, Robin L; Adams, Gerard C; Ostrom, Nathaniel E; Ostrom, Peggy H

    2008-12-01

    Identifying the importance of fungi to nitrous oxide (N2O) production requires a non-intrusive method for differentiating between fungal and bacterial N2O production such as natural abundance stable isotopes. We compare the isotopologue composition of N2O produced during nitrite reduction by the fungal denitrifiers Fusarium oxysporum and Cylindrocarpon tonkinense with published data for N2O production during bacterial nitrification and denitrification. The fractionation factors for bulk nitrogen isotope values for fungal denitrification were in the range -74.7 to -6.6 per thousand. There was an inverse relationship between the absolute value of the fractionation factors and the reaction rate constant. We interpret this in terms of variation in the relative importance of the rate constants for diffusion and enzymatic reduction in controlling the net isotope effect for N2O production during fungal denitrification. Over the course of nitrite reduction, the delta(18)O values for N2O remained constant and did not exhibit a relationship with the concentration characteristic of an isotope effect. This probably reflects isotopic exchange with water. Similar to the delta(18)O data, the site preference (SP; the difference in delta(15)N between the central and outer N atoms in N2O) was unrelated to concentration during nitrite reduction and, therefore, has the potential to act as a conservative tracer of production from fungal denitrification. The SP values of N2O produced by F. oxysporum and C. tonkinense were 37.1 +/- 2.5 per thousand and 36.9 +/- 2.8 per thousand, respectively. These SP values are similar to those obtained in pure culture studies of bacterial nitrification but quite distinct from SP values for bacterial denitrification. The large magnitude of the bulk nitrogen isotope fractionation and the delta(18)O values associated with fungal denitrification are distinct from bacterial production pathways; thus multiple isotopologue data holds much promise for

  17. Biological denitrification of high concentration nitrate waste

    DOEpatents

    Francis, Chester W.; Brinkley, Frank S.

    1977-01-01

    Biological denitrification of nitrate solutions at concentrations of greater than one kilogram nitrate per cubic meter is accomplished anaerobically in an upflow column having as a packing material a support for denitrifying bacteria.

  18. Meiofauna increases bacterial denitrification in marine sediments

    PubMed Central

    Bonaglia, S.; Nascimento, F. J. A; Bartoli, M.; Klawonn, I.; Brüchert, V.

    2014-01-01

    Denitrification is a critical process that can alleviate the effects of excessive nitrogen availability in aquatic ecosystems subject to eutrophication. An important part of denitrification occurs in benthic systems where bioturbation by meiofauna (invertebrates <1 mm) and its effect on element cycling are still not well understood. Here we study the quantitative impact of meiofauna populations of different abundance and diversity, in the presence and absence of macrofauna, on nitrate reduction, carbon mineralization and methane fluxes. In sediments with abundant and diverse meiofauna, denitrification is double that in sediments with low meiofauna, suggesting that meiofauna bioturbation has a stimulating effect on nitrifying and denitrifying bacteria. However, high meiofauna densities in the presence of bivalves do not stimulate denitrification, while dissimilatory nitrate reduction to ammonium rate and methane efflux are significantly enhanced. We demonstrate that the ecological interactions between meio-, macrofauna and bacteria are important in regulating nitrogen cycling in soft-sediment ecosystems. PMID:25318852

  19. Meiofauna increases bacterial denitrification in marine sediments.

    PubMed

    Bonaglia, S; Nascimento, F J A; Bartoli, M; Klawonn, I; Brüchert, V

    2014-01-01

    Denitrification is a critical process that can alleviate the effects of excessive nitrogen availability in aquatic ecosystems subject to eutrophication. An important part of denitrification occurs in benthic systems where bioturbation by meiofauna (invertebrates <1 mm) and its effect on element cycling are still not well understood. Here we study the quantitative impact of meiofauna populations of different abundance and diversity, in the presence and absence of macrofauna, on nitrate reduction, carbon mineralization and methane fluxes. In sediments with abundant and diverse meiofauna, denitrification is double that in sediments with low meiofauna, suggesting that meiofauna bioturbation has a stimulating effect on nitrifying and denitrifying bacteria. However, high meiofauna densities in the presence of bivalves do not stimulate denitrification, while dissimilatory nitrate reduction to ammonium rate and methane efflux are significantly enhanced. We demonstrate that the ecological interactions between meio-, macrofauna and bacteria are important in regulating nitrogen cycling in soft-sediment ecosystems. PMID:25318852

  20. Hyporheic zone denitrification: Controls on effective reaction depth and contribution to whole-stream mass balance

    NASA Astrophysics Data System (ADS)

    Harvey, Judson W.; Böhlke, J. K.; Voytek, Mary A.; Scott, Durelle; Tobias, Craig R.

    2013-10-01

    Stream denitrification is thought to be enhanced by hyporheic transport but there is little direct evidence from the field. To investigate at a field site, we injected 15NO3-, Br (conservative tracer), and SF6 (gas exchange tracer) and compared measured whole-stream denitrification with in situ hyporheic denitrification in shallow and deeper flow paths of contrasting geomorphic units. Hyporheic denitrification accounted for between 1 and 200% of whole-stream denitrification. The reaction rate constant was positively related to hyporheic exchange rate (greater substrate delivery), concentrations of substrates DOC and nitrate, microbial denitrifier abundance (nirS), and measures of granular surface area and presence of anoxic microzones. The dimensionless product of the reaction rate constant and hyporheic residence time, λhzτhz define a Damköhler number, Daden-hz that was optimal in the subset of hyporheic flow paths where Daden-hz ≈ 1. Optimal conditions exclude inefficient deep pathways where substrates are used up and also exclude inefficient shallow pathways that require repeated hyporheic entries and exits to complete the reaction. The whole-stream reaction significance, Rs (dimensionless), was quantified by multiplying Daden-hz by the proportion of stream discharge passing through the hyporheic zone. Together these two dimensionless metrics, one flow-path scale and the other reach-scale, quantify the whole-stream significance of hyporheic denitrification. One consequence is that the effective zone of significant denitrification often differs from the full depth of the hyporheic zone, which is one reason why whole-stream denitrification rates have not previously been explained based on total hyporheic-zone metrics such as hyporheic-zone size or residence time.

  1. Hyporheic zone denitrification: controls on effective reaction depth and contribution to whole-stream mass balance

    USGS Publications Warehouse

    Harvey, Judson W.; Böhlke, John Karl; Voytek, Mary A.; Scott, Durelle; Tobias, Craig R.

    2013-01-01

    Stream denitrification is thought to be enhanced by hyporheic transport but there is little direct evidence from the field. To demonstrate at a field site, we injected 15NO3−, Br (conservative tracer), and SF6 (gas exchange tracer) and compared measured whole-stream denitrification with in situ hyporheic denitrification in shallow and deeper flow paths of contrasting geomorphic units. Hyporheic denitrification accounted for between 1 and 200% of whole-stream denitrification. The reaction rate constant was positively related to hyporheic exchange rate (greater substrate delivery), concentrations of substrates DOC and nitrate, microbial denitrifier abundance (nirS), and measures of granular surface area and presence of anoxic microzones. The dimensionless product of the reaction rate constant and hyporheic residence time, λhzτhz define a Damköhler number, Daden-hz that was optimal in the subset of hyporheic flow paths where Daden-hz ≈ 1. Optimal conditions exclude inefficient deep pathways transport where substrates are used up and also exclude inefficient shallow pathways that require repeated hyporheic entries and exits to complete the reaction. The whole-stream reaction significance, Rs (dimensionless), was quantified by multiplying Daden-hz by the proportion of stream discharge passing through the hyporheic zone. Together these two dimensionless metrics, one flow-path scale and the other reach-scale, quantify the whole-stream significance of hyporheic denitrification. One consequence is that the effective zone of significant denitrification often differs from the full depth of the hyporheic zone, which is one reason why whole-stream denitrification rates have not previously been explained based on total hyporheic-zone metrics such as hyporheic-zone size or residence time.

  2. Denitrification and N2O emission from forested and cultivated alluvial clay soil

    USGS Publications Warehouse

    Ullah, S.; Breitenbeck, G.A.; Faulkner, S.P.

    2005-01-01

    Restored forested wetlands reduce N loads in surface discharge through plant uptake and denitrification. While removal of reactive N reduces impact on receiving waters, it is unclear whether enhanced denitrification also enhances emissions of the greenhouse gas N2O, thus compromising the water-quality benefits of restoration. This study compares denitrification rates and N2O:N2 emission ratios from Sharkey clay soil in a mature bottomland forest to those from an adjacent cultivated site in the Lower Mississippi Alluvial Valley. Potential denitrification of forested soil was 2.4 times of cultivated soil. Using intact soil cores, denitrification rates of forested soil were 5.2, 6.6 and 2.0 times those of cultivated soil at 70, 85 and 100% water-filled pore space (WFPS), respectively. When NO3 was added, N2O emissions from forested soil were 2.2 times those of cultivated soil at 70% WFPS. At 85 and 100% WFPS, N2O emissions were not significantly different despite much greater denitrification rates in the forested soil because N2O:N2 emission ratios declined more rapidly in forested soil as WFPS increased. These findings suggest that restoration of forested wetlands to reduce NO3 in surface discharge will not contribute significantly to the atmospheric burden of N2O. ?? Springer 2005.

  3. [Feasibility and Economic Analysis of Denitrification of Photovoltaic Wastewater Containing High Fluorine].

    PubMed

    Li, Xiang; Zhu, Liang; Huang, Yong; Yang, Peng-bing; Cui, Jian-hong; Ma, Hang

    2016-04-15

    In order to reduce acid and alkali dosing in wastewater treatment process of polycrystalline silicon by using denitrification after fluoride removal. This experiment studied the feasibility of first removing nitrogen using the denitrification process by start-up denitrifying reactor before fluoride removal. The results showed that the F⁻ concentration in the waste water to had a certain influence on the denitrification. When the concentration of F⁻ was controlled to about 750 mg · L⁻¹, the activity of denitrifying bacteria was not significantly influenced; when the concentration of F⁻ continued to increase, the denitrification efficiency of denitrifying sludge gradually reduced. In wastewater treatment of polycrystalline silicon, if the concentration of F⁻ was kept below 800 mg · L⁻¹, the denitrification performance of denitrifying sludge was not obviously affected. After 93 d operation, the total nitrogen in effluent was stabilized below 50 mg · L⁻¹, the total nitrogen removal efficiency reached 90%, and the removal rate reached 5 kg · (m³ · d)⁻¹. The calculation result showed, compared with the conventional denitrification process after fluoride removal, the proposed process could save about 70% of acid and 100% of alkali dosing, greatly reducing the cost of wastewater treatment. PMID:27548970

  4. Monitoring induced denitrification in an artificial aquifer recharge system.

    NASA Astrophysics Data System (ADS)

    Grau-Martinez, Alba; Torrentó, Clara; Folch, Albert; Domènech, Cristina; Otero, Neus; Soler, Albert

    2014-05-01

    literature ɛN values of -4o and -22o respectively (Aravena and Robertson, 1998; Pauwels et al., 2000). Ongoing denitrification batch experiments will allow us to determine the specific nitrogen and oxygen isotopic fractionation induced by the organic reactive layer, in order to estimate more precisely the extent of denitrification during artificial aquifer recharge. These results confirmed that the reactive layer induces denitrification in the recharge ponds area, proving the usefulness of an isotopic approach to characterize water quality improvement occurring during artificial aquifer recharge. References 1. Aravena, R., Robertson, W.D., 1998. Use of multiple isotope tracers to evaluate denitrification in ground water: Study of nitrate from a large-flux septic system plume. Ground Water, 36(6): 975-982. 2. Pauwels, H., J.C., Kloppmann, W., 2000. Denitrification and mixing in a schist aquifer: Influence on water chemistry and isotopes. Chemical Geology, 168(3-4): 307-324. Acknowledgment This study was supported by the projects CGL2011-29975-C04-01 from the Spanish Government, 2009SGR-00103 from the Catalan Government and ENPI/2011/280-008 from the European Commission. Please fill in your abstract text.

  5. Modeling nitrate removal in a denitrification bed.

    PubMed

    Ghane, Ehsan; Fausey, Norman R; Brown, Larry C

    2015-03-15

    Denitrification beds are promoted to reduce nitrate load in agricultural subsurface drainage water to alleviate the adverse environmental effects associated with nitrate pollution of surface water. In this system, drainage water flows through a trench filled with a carbon media where nitrate is transformed into nitrogen gas under anaerobic conditions. The main objectives of this study were to model a denitrification bed treating drainage water and evaluate its adverse greenhouse gas emissions. Field experiments were conducted at an existing denitrification bed. Evaluations showed very low greenhouse gas emissions (mean N2O emission of 0.12 μg N m(-2) min(-1)) from the denitrification bed surface. Field experiments indicated that nitrate removal rate was described by Michaelis-Menten kinetics with the Michaelis-Menten constant of 7.2 mg N L(-1). We developed a novel denitrification bed model based on the governing equations for water flow and nitrate removal kinetics. The model evaluation statistics showed satisfactory prediction of bed outflow nitrate concentration during subsurface drainage flow. The model can be used to design denitrification beds with efficient nitrate removal which in turn leads to enhanced drainage water quality. PMID:25638338

  6. Denitrification in the shallow ground water of a tile-drained, agricultural watershed

    USGS Publications Warehouse

    Mehnert, E.; Hwang, H.-H.; Johnson, T.M.; Sanford, R.A.; Beaumont, W.C.; Holm, T.R.

    2007-01-01

    Nonpoint-source pollution of surface water by N is considered a major cause of hypoxia. Because Corn Belt watersheds have been identified as major sources of N in the Mississippi River basin, the fate and transport of N from midwestern agricultural watersheds have received considerable interest. The fate and transport of N in the shallow ground water of these watersheds still needs additional research. Our purpose was to estimate denitrification in the shallow ground water of a tile-drained, Corn Belt watershed with fine-grained soils. Over a 3-yr period, N was monitored in the surface and ground water of an agricultural watershed in central Illinois. A significant amount of N was transported past the tile drains and into shallow ground water. The ground water nitrate was isotopically heavier than tile drain nitrate, which can be explained by denitrification in the subsurface. Denitrifying bacteria were found at depths to 10 m throughout the watershed. Laboratory and push-pull tests showed that a significant fraction of nitrate could be denitrified rapidly. We estimated that the N denitrified in shallow ground water was equivalent to 0.3 to 6.4% of the applied N or 9 to 27% of N exported via surface water. These estimates varied by water year and peaked in a year of normal precipitation after 2 yr of below average precipitation. Three years of monitoring data indicate that shallow ground water in watersheds with fine-grained soils may be a significant N sink compared with N exported via surface water. ?? ASA, CSSA, SSSA.

  7. Comparison of denitrification activity measurements in groundwater using cores and natural-gradient tracer tests

    USGS Publications Warehouse

    Smith, R.L.; Garabedian, S.P.; Brooks, M.H.

    1996-01-01

    The transport of many solutes in groundwater is dependent upon the relative rates of physical flow and microbial metabolism. Quantifying rates of microbial processes under subsurface conditions is difficult and is most commonly approximated using laboratory studies with aquifer materials. In this study, we measured in situ rates of denitrification in a nitrate- contaminated aquifer using small-scale, natural-gradient tracer tests and compared the results with rates obtained from laboratory incubations with aquifer core material. Activity was measured using the acetylene block technique. For the tracer tests, co-injection of acetylene and bromide into the aquifer produced a 30 ??M increase in nitrous oxide after 10 m of transport (23-30 days). An advection-dispersion transport model was modified to include an acetylene-dependent nitrous oxide production term and used to simulate the tracer breakthrough curves. The model required a 4-day lag period and a relatively low sensitivity to acetylene to match the narrow nitrous oxide breakthrough curves. Estimates of in situ denitrification rates were 0.60 and 1.51 nmol of N2O produced cm-3 aquifer day-1 for two successive tests. Aquifer core material collected from the tracer test site and incubated as mixed slurries in flasks and as intact cores yielded rates that were 1.2-26 times higher than the tracer test rate estimates. Results with the coring-dependent techniques were variable and subject to the small- scale heterogeneity within the aquifer, while the tracer tests integrated the heterogeneity along a flow path, giving a rate estimate that is more applicable to transport at the scale of the aquifer.

  8. Denitrification and availability of carbon and nitrogen in a well-drained pasture soil amended with particulate organic carbon.

    PubMed

    Stevenson, Bryan A; Schipper, Louis A; McGill, Alexandra; Clark, Dave

    2011-01-01

    A well-drained soil in N-fertilized dairy pasture was amended with particulate organic carbon (POC), either sawdust or coarse woody mulch, and sampled every 4 wk for a year to test the hypothesis that the addition of POC would increase denitrification activity by increasing the number of microsites where denitrification occurred. Overall mean denitrifying enzyme activity (DEA), on a gravimetric basis, was 100% greater for the woody mulch treatment and 50% greater for the sawdust treatment compared with controls, indicating the denitrifying potential of the soil was enhanced. Despite differences in DEA, no difference in denitrification rate, as measured by the acetylene block technique, was detected among treatments, with an average annual N loss of ∼22 kg N ha yr Soil water content overall was driving denitrification in this well-drained soil as regression of the natural log of volumetric soil water content (VWC) against denitrification rate was highly significant ( = 0.74, < 0.001). Addition of the amendments, however, had significant effects on the availability of both C and N. An additional 20 to 40 kg N ha was stored in POC-amended treatments as a result of increases in the microbial biomass. Basal respiration, as a measure of available C, was 400% greater than controls in the sawdust treatment and 250% greater than controls in the mulch. Net N mineralization, however, was significantly lower in the sawdust treatment, resulting in significantly lower nitrate N levels than in the control. We attribute the lack of measured response in denitrification rate to the high temporal variability in denitrification and suggest that diffusion of nitrate may ultimately have limited denitrification in the amended treatments. Our data indicate that manipulation of denitrification by addition of POC may be possible, particularly when nitrate levels are high, but quantifying differences in the rate of denitrification is difficult because of the temporal nature of the process

  9. Confirmation of co-denitrification in grazed grassland

    NASA Astrophysics Data System (ADS)

    Selbie, Diana R.; Lanigan, Gary J.; Laughlin, Ronald J.; di, Hong J.; Moir, James L.; Cameron, Keith C.; Clough, Tim J.; Watson, Catherine J.; Grant, James; Somers, Cathal; Richards, Karl G.

    2015-11-01

    Pasture-based livestock systems are often associated with losses of reactive forms of nitrogen (N) to the environment. Research has focused on losses to air and water due to the health, economic and environmental impacts of reactive N. Di-nitrogen (N2) emissions are still poorly characterized, both in terms of the processes involved and their magnitude, due to financial and methodological constraints. Relatively few studies have focused on quantifying N2 losses in vivo and fewer still have examined the relative contribution of the different N2 emission processes, particularly in grazed pastures. We used a combination of a high 15N isotopic enrichment of applied N with a high precision of determination of 15N isotopic enrichment by isotope-ratio mass spectrometry to measure N2 emissions in the field. We report that 55.8 g N m-2 (95%, CI 38 to 77 g m-2) was emitted as N2 by the process of co-denitrification in pastoral soils over 123 days following urine deposition (100 g N m-2), compared to only 1.1 g N m-2 (0.4 to 2.8 g m-2) from denitrification. This study provides strong evidence for co-denitrification as a major N2 production pathway, which has significant implications for understanding the N budgets of pastoral ecosystems.

  10. Confirmation of co-denitrification in grazed grassland

    PubMed Central

    Selbie, Diana R.; Lanigan, Gary J.; Laughlin, Ronald J.; Di, Hong J.; Moir, James L.; Cameron, Keith C.; Clough, Tim J.; Watson, Catherine J.; Grant, James; Somers, Cathal; Richards, Karl G.

    2015-01-01

    Pasture-based livestock systems are often associated with losses of reactive forms of nitrogen (N) to the environment. Research has focused on losses to air and water due to the health, economic and environmental impacts of reactive N. Di-nitrogen (N2) emissions are still poorly characterized, both in terms of the processes involved and their magnitude, due to financial and methodological constraints. Relatively few studies have focused on quantifying N2 losses in vivo and fewer still have examined the relative contribution of the different N2 emission processes, particularly in grazed pastures. We used a combination of a high 15N isotopic enrichment of applied N with a high precision of determination of 15N isotopic enrichment by isotope-ratio mass spectrometry to measure N2 emissions in the field. We report that 55.8 g N m−2 (95%, CI 38 to 77 g m−2) was emitted as N2 by the process of co-denitrification in pastoral soils over 123 days following urine deposition (100 g N m−2), compared to only 1.1 g N m−2 (0.4 to 2.8 g m−2) from denitrification. This study provides strong evidence for co-denitrification as a major N2 production pathway, which has significant implications for understanding the N budgets of pastoral ecosystems. PMID:26615911

  11. Confirmation of co-denitrification in grazed grassland.

    PubMed

    Selbie, Diana R; Lanigan, Gary J; Laughlin, Ronald J; Di, Hong J; Moir, James L; Cameron, Keith C; Clough, Tim J; Watson, Catherine J; Grant, James; Somers, Cathal; Richards, Karl G

    2015-01-01

    Pasture-based livestock systems are often associated with losses of reactive forms of nitrogen (N) to the environment. Research has focused on losses to air and water due to the health, economic and environmental impacts of reactive N. Di-nitrogen (N2) emissions are still poorly characterized, both in terms of the processes involved and their magnitude, due to financial and methodological constraints. Relatively few studies have focused on quantifying N2 losses in vivo and fewer still have examined the relative contribution of the different N2 emission processes, particularly in grazed pastures. We used a combination of a high (15)N isotopic enrichment of applied N with a high precision of determination of (15)N isotopic enrichment by isotope-ratio mass spectrometry to measure N2 emissions in the field. We report that 55.8 g N m(-2) (95%, CI 38 to 77 g m(-2)) was emitted as N2 by the process of co-denitrification in pastoral soils over 123 days following urine deposition (100 g N m(-2)), compared to only 1.1 g N m(-2) (0.4 to 2.8 g m(-2)) from denitrification. This study provides strong evidence for co-denitrification as a major N2 production pathway, which has significant implications for understanding the N budgets of pastoral ecosystems. PMID:26615911

  12. Comparing the estimation methods of stable distributions with respect to robustness properties

    NASA Astrophysics Data System (ADS)

    Celik, Nuri; Erden, Samet; Sarikaya, M. Zeki

    2016-04-01

    In statistical applications, some data set may exhibit the features like high skewness and kurtosis and heavy tailness that are incompatible with the normality assumption especially in finance and engineering. For these reason, the modeling of the data sets with α stable distributions will be reasonable approach. The stable distributions have four parameters. In literature, the estimation methods have been studied in order to estimate these unknown model parameters. In this study, we give small information about these proposed estimation methods and we compare these estimators with respect to robustness properties with a comprehensive simulation study, since the robustness property of an estimator has been an important tool for an appropriate modeling.

  13. Mechanism and rate of denitrification in an agricultural watershed: Electron and mass balance along groundwater flow paths

    USGS Publications Warehouse

    Tesoriero, A.J.; Liebscher, H.; Cox, S.E.

    2000-01-01

    The rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer. Intensive agricultural activity in this area has resulted in nitrate concentrations in groundwater often exceeding drinking water standards. Both the extent and rate of denitrification varied depending on the groundwater flow path. While little or no denitrification occurred in much of the upland portions of the aquifer, a gradual redox gradient is observed as aerobic upland groundwater moves deeper in the aquifer. In contrast, a sharp shallow redox gradient is observed adjacent to a third-order stream as aerobic groundwater enters reduced sediments. An essentially complete loss of nitrate concurrent with increases in excess N2 provide evidence that denitrification occurs as groundwater enters this zone. Electron and mass balance calculations suggest that iron sulfide (e.g., pyrite) oxidation is the primary source of electrons for denitrification. Denitrification rate estimates were based on mass balance calculations using nitrate and excess N2 coupled with groundwater travel times. Travel times were determined using a groundwater flow model and were constrained by chlorofluorocarbon-based age dates. Denitrification rates were found to vary considerably between the two areas where denitrification occurs. Denitrification rates in the deep, upland portions of the aquifer were found to range from < 0.01 to 0.14 mM of N per year; rates at the redoxcline along the shallow flow path range from 1.0 to 2.7 mM of N per year. Potential denitrification rates in groundwater adjacent to the stream may be much faster, with rates up to 140 mM per year based on an in situ experiment conducted in this zone.The rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer. Intensive

  14. Seasonal variability of denitrification efficiency in northern salt marshes: an example from the St. Lawrence Estuary.

    PubMed

    Poulin, Patrick; Pelletier, Emilien; Saint-Louis, Richard

    2007-06-01

    In coastal ecosystems, denitrification is a key process in removing excess dissolved nitrogen oxides and participating in the control of eutrophication process. Little is known about the role of salt marshes on nitrogen budgets in cold weather coastal areas. Although coastal salt marshes are important sites for organic matter degradation and nutrient regeneration, bacterial-mediated nitrogen cycling processes, such as denitrification, remain unknown in northern and sub-arctic regions, especially under winter conditions. Using labelled nitrogen (15N), denitrification rates were measured in an eastern Canadian salt marsh in August, October and December 2005. Freshly sampled undisturbed sediment cores were incubated over 8h and maintained at their sampling temperatures to evaluate the influence of low temperatures on the denitrification rate. From 2 to 12 degrees C, average denitrification rate and dissolved oxygen consumption increased from 9.6 to 25.5 micromol N2 m-2 h-1 and from 1.3 to 1.8 mmol O2 m-2 h-1, respectively, with no statistical dependence of temperature (p>0.05). Nitrification has been identified as the major nitrate source for denitrification, supplying more than 80% of the nitrate demand. Because no more than 31% of the nitrate removed by sediment is estimated to be denitrified, the presence of a major nitrate sink in sediment is suspected. Among possible nitrate consumption mechanisms, dissimilatory reduction of nitrate to ammonium, metal and organic matter oxidation processes are discussed. Providing the first measurements of denitrification rate in a St. Lawrence Estuary salt marsh, this study evidences the necessity of preserving and restoring marshes. They constitute an efficient geochemical filter against an excess of nitrate dispersion to coastal waters even under cold northern conditions. PMID:17276505

  15. Denitrification of agricultural drainage line water via immobilized denitrification sludge.

    PubMed

    Hunt, Patrick G; Matheny, Terry A; Ro, Kyoung S; Stone, Kenneth C; Vanotti, Matias B

    2008-07-15

    Nonpoint source nitrogen is recognized as a significant water pollutant worldwide. One of the major contributors is agricultural drainage line water. A potential method of reducing this nitrogen discharge to water bodies is the use of immobilized denitrifying sludge (IDS). Our objectives were to (1) produce an effective IDS, (2) determine the IDS reaction kinetics in laboratory column bioreactors, and (3) test a field bioreactor for nitrogen removal from agricultural drainage line water. We developed a mixed liquor suspended solid (MLSS) denitrifying sludge using inoculant from an overland flow treatment system. It had a specific denitrification rate of 11.4 mg NO(3)-N g(-1) MLSS h(-1). We used polyvinyl alcohol (PVA) to immobilize this sludge and form IDS pellets. When placed in a 3.8-L column bioreactor, the IDS had a maximum removal rate (K(MAX)) of 3.64 mg NO(3)-N g(-1) pellet d(-1). In a field test with drainage water containing 7.8 mg NO(3)-N L(-1), 50% nitrogen removal was obtained with a 1 hr hydraulic retention time. Expressed as a 1 m(3) cubically-shaped bioreactor, the nitrogen removal rate would be 94 g NO(3)-N m(-2)d(-1), which is dramatically higher than treatment wetlands or passive carbonaceous bioreactors. IDS bioreactors offer potential for reducing nitrogen discharge from agricultural drainage lines. More research is needed to develop the bioreactors for agricultural use and to devise effective strategies for their implementation with other emerging technologies for improved water quality on both watershed and basin scales. PMID:18569323

  16. Groundwater denitrification and denitrifer gene abundances at varying hydrogeological settings in Ireland

    NASA Astrophysics Data System (ADS)

    Jahangir, M. M.; Barrett, M.; Johnston, P.; O'Flaherty, V.; Khalil, M. I.; Richards, K.

    2010-12-01

    Biological denitrification is an important mechanism for the reduction of nitrate in the terrestrial and aquatic environments and contributing to the global nitrogen balance. This study focuses on the abundance of denitrifier functional genes and dissolved gases (N2O and denitrified N2, called excess N2) in groundwater. Multilevel piezometers (36) installed to target three groundwater zones were: subsoil (5 m bgl, below ground level); bedrock interface (10 m bgl) and bedrock (20 m bgl) at three agricultural sites (Johnstown Castle, Solohead, Oak Park) and in bedrock at a further site (Dairy Gold). Low flow sampling procedures were used to collect groundwater monthly from February 2009 and January 2010. Dissolved N2 and Ar, measured using Membrane Inlet Mass Spectrometry, were used to estimate excess N2. Dissolved N2O was extracted using a helium headspace method. Ten litres groundwater were sampled from each well in May 2010 and DNA was concentrated by vacuum filter in 0.2 µm filter paper. Functional gene abundances were quantified using real-time PCR assays targeting the nitrite reductase (nir) and nitrous oxide reductase (nos) genes. Mean water table (WT) depth varied seasonally and was the shallowest in November and the deepest in June across all sites. Groundwater properties varied across sites and depths, with ranges of dissolved oxygen (DO) from 1.0-9.0 mg L-1, redox potential (Eh) -0.80-191, and aquifer permeability (Ksat) from 0.003-1.04 m d-1. Dissolved organic C (DOC), decreased with increasing depth ranged from 1.0-4.0, 0.9-2.4 and 0.8-2.4 respectively in subsoil, interface and bedrock, lowest in Oak Park and highest in Johnstown Castle. Total bacterial abundances were higher in subsoil (2.9 x 104 genes L-1) than in interface (6.7 x 104 genes L-1). The most abundant denitrifying functional genes were nirS, ranged from 1.4 x 103 genes L-1 in subsoil to 2.0 x 104 genes L-1 in bedrock followed by nosZ, varied from 2.56 x 102 genes L-1 in bedrock to 1.9 x

  17. Denitrification mechanism in combustion of biocoal briquettes.

    PubMed

    Kim, Heejoon; Li, Tianji

    2005-02-15

    Pulp black liquor (PBL), an industrial waste from paper production, has been previously shown to be an effective binder and denitrification agent for coal briquettes. This study investigated the denitrification mechanism of PBL in both the volatile combustion and char combustion stages of coal briquettes. X-ray diffraction and ion chromatography were used to analyze the residual ashes of combustion. The exhaust gas was analyzed by a flue gas analysis system and a Q-mass spectrometry system. The denitrification mechanism of PBL in the volatile combustion stage was found to result from the emission of NH3. The denitrification of PBL in the char combustion stage was associated with the NaOH contained in PBL. The direct reaction of NaOH with NO gas was examined, and some interesting phenomena were observed. Pure carbon or pure NaOH showed only limited reaction with NO. However, the mixture of NaOH and carbon (NaOH + C) significantly enhanced the reaction. This mixture increased the NO removal up to 100%. Subsequently, denitrification lasted for a long time period, with about 25% of NO removal. The pyrolysis characteristic of NaNO3, a compound resulting from denitrification, was also affected by the presence of carbon. In the presence of carbon, the NOx emission resulting from the pyrolysis of NaNO3 was reduced by a factor of 6. Since the denitrification phenomena appeared only in the absence of oxygen, a model of oxygen distribution in a burning coal briquette was employed to explain the reactions occurring in real combustion of coal briquettes. PMID:15773493

  18. Beyond Self-Report: Tools to Compare Estimated and Real-World Smartphone Use

    PubMed Central

    Andrews, Sally; Ellis, David A.; Shaw, Heather; Piwek, Lukasz

    2015-01-01

    Psychologists typically rely on self-report data when quantifying mobile phone usage, despite little evidence of its validity. In this paper we explore the accuracy of using self-reported estimates when compared with actual smartphone use. We also include source code to process and visualise these data. We compared 23 participants’ actual smartphone use over a two-week period with self-reported estimates and the Mobile Phone Problem Use Scale. Our results indicate that estimated time spent using a smartphone may be an adequate measure of use, unless a greater resolution of data are required. Estimates concerning the number of times an individual used their phone across a typical day did not correlate with actual smartphone use. Neither estimated duration nor number of uses correlated with the Mobile Phone Problem Use Scale. We conclude that estimated smartphone use should be interpreted with caution in psychological research. PMID:26509895

  19. Denitrification, anammox and fixed nitrogen removal in the water column of a tropical great lake

    NASA Astrophysics Data System (ADS)

    Darchambeau, François; Roland, Fleur; Crowe, Sean A.; De Brabandere, Loreto; Llirós, Marc; Garcia-Armisen, Tamara; Inceoglu, Ozgul; Michiels, Céline; Servais, Pierre; Morana, Cédric D. T.; Bouillon, Steven; Meysman, Filip; Veuger, Bart; Masilya, Pascal M.; Descy, Jean-Pierre; Borges, Alberto V.

    2013-04-01

    If rates of microbial denitrification in aquatic systems are poorly constrained, it is much more the case for tropical water bodies. Lake Kivu [2.50° S 1.59° S, 29.37° E 28.83° E] is one of the great lakes of the East African Rift. It is an oligotrophic lake characterized by anoxic deep waters rich in dissolved gases (methane and carbon dioxide) and nutrients, and by well oxygenated and nutrient-depleted surface waters. During the seasonally stratified rainy season (October to May), a nitrogenous zone characterized by the accumulation of nitrite (NO2-) and nitrate (NO3-) is often observed in the lower layer of the mixolimnion. It results from nitrification of ammonium released by decaying organic matter. With the seasonal uplift of the oxygen minimum zone, the nitrogenous zone becomes anoxic and might be the most preferential area for fixed nitrogen (N) removal in Lake Kivu. Our work aimed at identifying and quantifying the processes of N losses by denitrification and/or anammox in the nitrogenous zone of the Lake Kivu water column. During 5 sampling campaigns (March 2010, October 2010, June 2011, February 2012 and September 2012), isotopic labelling experiments were used to quantify denitrification and anammox rates along vertical profiles at two pelagic stations of the main lake. Moreover, N2:Ar ratios were estimated during the September 2012 campaign, and 16S rDNA pyrosequencing was used to describe bacterial community composition during the last 2 campaigns. No bacteria related to organisms performing anammox was observed and labelling experiments failed to detect anammox at any locations and any depths. In Lake Kivu, denitrifying bacteria were mainly related to Denitratisoma and Thiobacillus genus. Significant denitrification rates were observed at several occasions, especially under the oxic-anoxic interface in the bottom of the nitracline. The annual average denitrification rate was estimated at ~150 μmoles N m-2 d-1. Denitrification was not the only

  20. Body Density Estimates from Upper-Body Skinfold Thicknesses Compared to Air-Displacement Plethysmography

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Technical Summary Objectives: Determine the effect of body mass index (BMI) on the accuracy of body density (Db) estimated with skinfold thickness (SFT) measurements compared to air displacement plethysmography (ADP) in adults. Subjects/Methods: We estimated Db with SFT and ADP in 131 healthy men an...

  1. Radiologists’ ability to accurately estimate and compare their own interpretative mammography performance to their peers

    PubMed Central

    Cook, Andrea J.; Elmore, Joann G.; Zhu, Weiwei; Jackson, Sara L.; Carney, Patricia A.; Flowers, Chris; Onega, Tracy; Geller, Berta; Rosenberg, Robert D.; Miglioretti, Diana L.

    2013-01-01

    Objective To determine if U.S. radiologists accurately estimate their own interpretive performance of screening mammography and how they compare their performance to their peers’. Materials and Methods 174 radiologists from six Breast Cancer Surveillance Consortium (BCSC) registries completed a mailed survey between 2005 and 2006. Radiologists’ estimated and actual recall, false positive, and cancer detection rates and positive predictive value of biopsy recommendation (PPV2) for screening mammography were compared. Radiologists’ ratings of their performance as lower, similar, or higher than their peers were compared to their actual performance. Associations with radiologist characteristics were estimated using weighted generalized linear models. The study was approved by the institutional review boards of the participating sites, informed consent was obtained from radiologists, and procedures were HIPAA compliant. Results While most radiologists accurately estimated their cancer detection and recall rates (74% and 78% of radiologists), fewer accurately estimated their false positive rate and PPV2 (19% and 26%). Radiologists reported having similar (43%) or lower (31%) recall rates and similar (52%) or lower (33%) false positive rates compared to their peers, and similar (72%) or higher (23%) cancer detection rates and similar (72%) or higher (38%) PPV2. Estimation accuracy did not differ by radiologists’ characteristics except radiologists who interpret ≤1,000 mammograms annually were less accurate at estimating their recall rates. Conclusion Radiologists perceive their performance to be better than it actually is and at least as good as their peers. Radiologists have particular difficulty estimating their false positive rates and PPV2. PMID:22915414

  2. Factor Analysis with Ordinal Indicators: A Monte Carlo Study Comparing DWLS and ULS Estimation

    ERIC Educational Resources Information Center

    Forero, Carlos G.; Maydeu-Olivares, Alberto; Gallardo-Pujol, David

    2009-01-01

    Factor analysis models with ordinal indicators are often estimated using a 3-stage procedure where the last stage involves obtaining parameter estimates by least squares from the sample polychoric correlations. A simulation study involving 324 conditions (1,000 replications per condition) was performed to compare the performance of diagonally…

  3. Inhibition of denitrification by ultraviolet radiation

    NASA Astrophysics Data System (ADS)

    Mancinelli, R. L.; White, M. R.

    It has been shown that UV-A (λ = 320- 400 nm) and UV-B (λ = 280 - 320 nm) inhibit photosynthesis, nitrogen fixation and nitrification. The purpose of this study was to determine the effects, if any, on denitrification in a microbial community inhabiting the intertidal. The community studied is the microbial mat consisting primarily of Lyngbya that inhabits the Pacific marine intertidal, Baja California, Mexico. Rates of denitrification were determined using the acetylene blockage technique. Pseudomonas fluorescens (ATCC # 17400) was used as a control organism, and treated similarly to the mat samples. Samples were incubated either beneath a PAR transparent, UV opaque screen (OP3), or a mylar screen to block UV-B, or a UV transparent screen (UVT) for 2 to 3 hours. Sets of samples were also treated with nitrapyrin to inhibit nitrification, or DCMU to inhibit photosynthesis and treated similarly. Denitrification rates were greater in the UV protected samples than in the UV exposed samples the mat samples as well as for the Ps. fluorescens cultures. Killed controls exhibited no activity. In the DCMU and nitrapyrin treated samples denitrification rates were the same as in the untreated samples. These data indicate that denitrification is directly inhibited by UV radiation.

  4. Inhibition of denitrification by ultraviolet radiation.

    PubMed

    Mancinelli, R L; White, M R

    2000-01-01

    It has been shown that UV-A (lambda=320-400 nm) and UV-B (lambda=280-320 nm) inhibit photosynthesis, nitrogen fixation and nitrification. The purpose of this study was to determine the effects, if any, on denitrification in a microbial community inhabiting the intertidal. The community studied is the microbial mat consisting primarily of Lyngbya that inhabits the Pacific marine intertidal, Baja California, Mexico. Rates of denitrification were determined using the acetylene blockage technique. Pseudomonas fluorescens (ATCC #17400) was used as a control organism, and treated similarly to the mat samples. Samples were incubated either beneath a PAR transparent, UV opaque screen (OP3), or a mylar screen to block UV-B, or a UV transparent screen (UVT) for 2 to 3 hours. Sets of samples were also treated with nitrapyrin to inhibit nitrification, or DCMU to inhibit photosynthesis and treated similarly. Denitrification rates were greater in the UV protected samples than in the UV exposed samples the mat samples as well as for the Ps fluorescens cultures. Killed controls exhibited no activity. In the DCMU and nitrapyrin treated samples denitrification rates were the same as in the untreated samples. These data indicate that denitrification is directly inhibited by UV radiation. PMID:12038490

  5. Nitrous oxide emission from denitrification in stream and river networks

    SciTech Connect

    Beaulieu, Jake; Tank, Jennifer; Hamilton, Stephen; Wollheim, Wilfred; Hall, Robert; Mulholland, Patrick J; Peterson, Bruce; Ashkenas, Linda; Cooper, Lee W; Dahm, Cliff; Dodds, Walter; Grimm, Nancy; Johnson, Sherri; McDowell, William; Poole, Geoffrey C.; Valett, H. Maurice; Arango, Clay; Bernot, Melody; Burgin, Amy; Crenshaw, Chelsea; Helton, Ashley; Johnson, Laura; O'Brien, Jon; Potter, Jody; Sheibley, Rich; Sobota, Daniel; Thomas, Suzanne

    2011-01-01

    Nitrous oxide (N{sub 2}O) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Anthropogenic nitrogen (N) loading to river networks is a potentially important source of N{sub 2}O via microbial denitrification that converts N to N{sub 2}O and dinitrogen (N{sub 2}). The fraction of denitrified N that escapes as N{sub 2}O rather than N{sub 2} (i.e., the N{sub 2}O yield) is an important determinant of how much N{sub 2}O is produced by river networks, but little is known about the N{sub 2}O yield in flowing waters. Here, we present the results of whole-stream {sup 15}N-tracer additions conducted in 72 headwater streams draining multiple land-use types across the United States. We found that stream denitrification produces N{sub 2}O at rates that increase with stream water nitrate (NO{sub 3}{sup -}) concentrations, but that <1% of denitrified N is converted to N{sub 2}O. Unlike some previous studies, we found no relationship between the N{sub 2}O yield and stream water NO{sub 3}{sup -}. We suggest that increased stream NO{sub 3}{sup -} loading stimulates denitrification and concomitant N{sub 2}O production, but does not increase the N{sub 2}O yield. In our study, most streams were sources of N{sub 2}O to the atmosphere and the highest emission rates were observed in streams draining urban basins. Using a global river network model, we estimate that microbial N transformations (e.g., denitrification and nitrification) convert at least 0.68 Tg {center_dot} y{sup -1} of anthropogenic N inputs to N{sub 2}O in river networks, equivalent to 10% of the global anthropogenic N{sub 2}O emission rate. This estimate of stream and river N{sub 2}O emissions is three times greater than estimated by the Intergovernmental Panel on Climate Change.

  6. Enhanced denitrification of Pseudomonas stutzeri by a bioelectrochemical system assisted with solid-phase humin.

    PubMed

    Xiao, Zhixing; Awata, Takanori; Zhang, Dongdong; Zhang, Chunfang; Li, Zhiling; Katayama, Arata

    2016-07-01

    The denitrification reactions performed by Pseudomonas stutzeri JCM20778 were enhanced electrochemically with the use of solid-phase humin, although P. stutzeri itself was incapable of receiving electrons directly from the graphite electrode. Electrochemically reduced humin enhanced the microbial, but not abiotic, denitrification reactions. Electric current and cyclic voltammetry analyses suggested that the solid-phase humin functioned as an electron donor for the denitrification reactions of P. stutzeri. Nitrogen balance study and the estimation of the first-order rate constants of the consecutive denitrification reactions suggested that the solid-phase humin enhanced all reducing reactions from nitrate to nitrogen gas. Considering the wide distribution of humin in the environment, the findings that solid-phase humin can assist in electron transfer, from the electrode to a denitrifying bacterium that has little ability to directly utilize external electrons, has important implications for the widespread application of bioelectrochemical systems assisted by solid-phase humin for enhancing microbial denitrification. PMID:26905325

  7. Denitrification 'hot spots' in soil following surface residue application

    NASA Astrophysics Data System (ADS)

    Kuntz, Marianne; Morley, Nicholas J.; Hallett, Paul D.; Watson, Christine; Baggs, Elizabeth M.

    2015-04-01

    The availability of organic C is an important driver for the production and reduction of the greenhouse gas nitrous oxide (N2O) during denitrification. Denitrification as a response to plant residue amendments to soil surfaces has been extensively researched. However, the nature of hotspot sites of N2O production and reduction within the soil profile, especially in relation to the location of applied residues, is unknown. In a laboratory experiment we investigated the relationship between denitrifier N2O surface fluxes and N2O production and reduction sites. Probes which equilibrate with the soil gas phase by diffusion were developed to quantify denitrification products and product ratios at 1-2 cm, 4.5-5.5 cm or 8-9 cm from the surface. 13C labelled barley straw was incorporated at rates of 0, 2 and 4 t ha-1 into the top 3 cm of soil and subsequently amended with 14NH415NO3. In a three week experiment the soil gas phase at the three depths was analysed for 15N-N2O, 15N-N2, 13C-CO2 and O2 concentrations. Additionally, cores were destructively sampled for mineral 15N as well as microbial C and dissolved C in the respective depths. 15N-N2O and CO2 surface fluxes peaked one day after N application, with residue application resulting in significantly higher 15N-N2O emission rates compared to the non-amended control. The timing of the 15N-N2O surface flux on day 1 was related to maximum 15N-N2O concentrations of 36.6 μg 15N L-1 within the pore space at 5 cm depth. Three days after fertilizer application 15N-N2O pore space concentrations had significantly increased to 193 μg 15N L-1 at 9 cm depth indicating denitrifier activity at greater depth. Denitrification below the soil surface could be explained by increased microbial activity, oxygen depletion with increasing depth and progressive downwards diffusion of fertilizer NO3-. However, C availability appeared to only affect denitrification in the surface layer in which the residue was incorporated. Our results provide

  8. Linking hydrology and denitrification kinetics in treatment wetlands

    NASA Astrophysics Data System (ADS)

    Kjellin, J.; Wörman, A.; Hallin, S.

    2007-12-01

    A number of factors control the kinetics of denitrification in natural environments, particularly, in treatment wetlands. In order to understand and, in some sense, optimize nitrogen removal in wetlands we must link hydrological and geochemical processes. Based on a two-dimensional flow model we found that topography and vegetation distribution as well as density of vegetation are crucial reproducing the residence time distribution from a tracer test experiment. The tracer test used simultaneous injection of three labelled isotopes; H2O-3, PO4- 32 and NO3-15. Not only are the reactions constrained by the circulation patterns and water residence time, but there are essential links between vegetation as friction causing objects for the water flow and vegetation as host medium for biofilms in which denitrification can occur. This study has illuminated the importance for the treatment efficiency of the various time-scales involved in the denitrification occurring in wetlands used for treating municipal wastewater. Sampling of bed sediments in Ekeby Wetland, Eskilstuna, Sweden, were used as a basis for laboratory measurements of potential denitrification activity (PDA), evaluation of the Michaelis-Menten kinetics and denaturing gel electrophoreses (DGGE) patterns of nosZ genes, which represent the denitrifying bacterial community structure in various locations. A most essential contribution of the study is to translate such basic microbiological entities into a system response model that considers both water flow and mixing as well as microbiological reactions. The behaviour of this system model was also compared with the tracer test bfreakthrough curves. The structure and placement of vegetation is found to be of utmost importance for the contact between biofilms and nitrate-polluted wastewater and, thus, for the treatment efficiency. Erroneously placed vegetation can cause flow channelling with little utilisation of the entire wetland volume and little availability of

  9. Using soil isotopes as an indicator of denitrification in weetlands

    EPA Science Inventory

    Denitrification is an important ecosystem service provided by wetlands, which results in removal of excess nitrogen that can threaten aquatic systems. Unfortunately, direct measurement of denitrification has traditionally been expensive, time intensive, and difficult. However, ...

  10. Hyporheic Zone Denitrification: Flow Path Controls and Scaling Consequences for N budgets for the Whole Stream

    NASA Astrophysics Data System (ADS)

    Harvey, J. W.; Bohlke, J. K.; Voytek, M. A.; Scott, D.; Tobias, C. R.

    2013-12-01

    Denitrification is thought to be enhanced by hyporheic transport but there is little direct evidence from the field that relates controlling processes to whole-stream consequences for N budgets. To demonstrate at a field site we injected 15 NO3-, Br (conservative tracer) and SF6 (gas exchange tracer) and compared measures of whole-stream denitrification with in situ hyporheic denitrification measurements in both shallow and deeper flow paths of contrasting geomorphic units such as channel thalwegs and side cavities. Hyporheic denitrification accounted for between a few percent and 200% of whole-stream denitrification. The reaction rate constant was positively related to hyporheic exchange rate (which increases substrate delivery), concentrations of substrates DOC and nitrate, microbial denitrifier abundance as indicated by nirS, and measures related to granular surface area and presence of anoxic microzones in otherwise suboxic porewater. Reaction efficiency in individual hyporheic flow paths was quantified as the dimensionless product of reaction rate constant and hyporheic residence time, λhzτhz (also defined as a Damköhler number, Daden-hz). At the stream reach scale the reaction significance was quantified by a dimensionless index Rs that combines the product of Da hz and the proportion of stream discharge passing through the hyporheic zone. Reaction progress was optimal in the subset of hyporheic flow paths where Da den-hz ~ 1, which avoids inefficient transport through very long flow paths after substrates have been used up but also avoids inefficient pathways that require repeated entries and exits through very short hyporheic flow paths to complete the reaction. We conclude that the zone of significant denitrification in the streambed can be substantially less than the full depth of the hyporheic zone, which is one reason previous researchers were not able to explain whole-stream denitrification rates based on total hyporheic-zone metrics such as

  11. Incorporating spatial variation of nitrification and denitrification rates into whole-lake nitrogen dynamics

    NASA Astrophysics Data System (ADS)

    Bruesewitz, Denise A.; Tank, Jennifer L.; Hamilton, Stephen K.

    2012-09-01

    Despite dramatic increases in nitrogen (N) loading to fresh waters and growing scientific attention on the changing N cycle, measurements of nitrification and denitrification rates in lakes are lacking. In particular, we know little about how these processes vary spatially within a lake, and how this potential spatial variation contributes to a lake's N dynamics. We measured sediment nitrification and denitrification rates at 40 sites in Gull Lake, Michigan (USA), and found that the shallow edge sediments (<2 m deep) of the lake were hot spots of N transformation. Nitrification rates were comparable in sediments at all depths, while sediment denitrification rates were highest in the shallow edge habitat, and lowest in the profundal sediments (<2 m and >10 m deep, respectively). We scaled-up our sediment transformation rates across the lake to illustrate spatial variability in nitrification and denitrification. For whole-lake nitrification, the contribution of shallow edge, littoral, and profundal sediments followed in proportion to lake surface area of each habitat. In contrast, the contribution of each of these areas to whole-lake denitrification was not proportional to their respective surface areas, and instead was equal across the 3 habitat types, with each area contributing roughly 30% of the total N loss via denitrification. Spatially representative characterization of nitrification and denitrification in lentic ecosystems requires incorporation of the spatial variation in these transformations with a particular focus on littoral sediments, and this is often overlooked in studies of lentic N cycling. Furthermore, anthropogenic changes to lake shorelines that influence N cycling in littoral sediments may have a disproportionate effect on whole-lake ecosystem function.

  12. Denitrification potential in stormwater control structures and natural riparian zones in an urban landscape.

    PubMed

    Bettez, Neil D; Groffman, Peter M

    2012-10-16

    Humans have significantly altered urban landscapes, creating impervious surfaces, and changing drainage patterns that increase volume and velocity as well as frequency and timing of runoff following precipitation events. These changes in runoff have impaired streams and riparian areas that previously reduced watershed nitrogen (N) flux through uptake and denitrification. Stormwater control measures (SCM) are used most frequently to mitigate these hydrologic impacts. While SCM control runoff, their ability to remove N compared to natural riparian areas is not well-known. In this study we compared potential denitrification [as denitrification enzyme activity (DEA)] in five types of SCM (wet ponds, dry detention ponds, dry extended detention, infiltration basin, and filtering practices) and forested and herbaceous riparian areas in Baltimore, MD. DEA was higher in SCM (1.2 mg N kg(-1) hr(-1)) than in riparian areas (0.4 mg N kg(-1) hr(-1)). While DEA was highly correlated with soil moisture, organic matter, microbial biomass, and soil respiration areas across sites, it was always higher in SCM at equivalent levels of these variables. SCM appear to function as denitrification hotspots and, despite having similar microbial biomass, have higher potential denitrification than natural riparian areas. PMID:22963127

  13. Enhanced biological nitrogen removal in MLE combined with post-denitrification process and EF clarifier.

    PubMed

    Chung, C M; Cho, K W; Kim, Y J; Yamamoto, K; Chung, T H

    2012-05-01

    A modified ludzack ettinger reactor (MLE) combined with a post-denitrification reactor (PDMLE) using electroflotation (EF) as a secondary clarifier was investigated on its feasibility and process performance. Results indicated that higher mixed liquor suspended solids (MLSS) concentrations in bioreactor (5,350 ± 352 mg L(-1)) were maintained via the highly concentrated return sludge (16,771 ± 991 mg L(-1)) from the EF clarifier and the effluent suspended solids (SS) concentrations continued relatively low, representing effluent SS concentration of 1.71 ± 1.16 mg L(-1), compared with GS-A2O process during the operation of four months. The denitrification was improved by combining MLE process with post-denitrification based on endogenous decay (i.e. no additional carbon source was added), resulting in the removal efficiencies of TN were about 91 and 59% for the influent C/N ratio of 10 and 5, respectively, revealing relatively high nitrogen removal as compared with EF-A2O and gravity settling (GS)-A2O processes as a control. The nitrogen balance analysis indicates that pre-denitrification and post-denitrification contributed to 78 and 22% of TN removed, respectively. PMID:21947625

  14. Low Probability of Initiating nirS Transcription Explains Observed Gas Kinetics and Growth of Bacteria Switching from Aerobic Respiration to Denitrification

    PubMed Central

    Hassan, Junaid; Bergaust, Linda L.; Wheat, I. David; Bakken, Lars R.

    2014-01-01

    In response to impending anoxic conditions, denitrifying bacteria sustain respiratory metabolism by producing enzymes for reducing nitrogen oxyanions/-oxides (NOx) to N2 (denitrification). Since denitrifying bacteria are non-fermentative, the initial production of denitrification proteome depends on energy from aerobic respiration. Thus, if a cell fails to synthesise a minimum of denitrification proteome before O2 is completely exhausted, it will be unable to produce it later due to energy-limitation. Such entrapment in anoxia is recently claimed to be a major phenomenon in batch cultures of the model organism Paracoccus denitrificans on the basis of measured e−-flow rates to O2 and NOx. Here we constructed a dynamic model and explicitly simulated actual kinetics of recruitment of the cells to denitrification to directly and more accurately estimate the recruited fraction (). Transcription of nirS is pivotal for denitrification, for it triggers a cascade of events leading to the synthesis of a full-fledged denitrification proteome. The model is based on the hypothesis that nirS has a low probability (, h−1) of initial transcription, but once initiated, the transcription is greatly enhanced through positive feedback by NO, resulting in the recruitment of the transcribing cell to denitrification. We assume that the recruitment is initiated as [O2] falls below a critical threshold and terminates (assuming energy-limitation) as [O2] exhausts. With  = 0.005 h−1, the model robustly simulates observed denitrification kinetics for a range of culture conditions. The resulting (fraction of the cells recruited to denitrification) falls within 0.038–0.161. In contrast, if the recruitment of the entire population is assumed, the simulated denitrification kinetics deviate grossly from those observed. The phenomenon can be understood as a ‘bet-hedging strategy’: switching to denitrification is a gain if anoxic spell lasts long but is a waste of energy if anoxia

  15. Comparing the estimation of postpartum hemorrhage using the weighting method and National Guideline with the postpartum hemorrhage estimation by midwives

    PubMed Central

    Golmakani, Nahid; Khaleghinezhad, Khosheh; Dadgar, Selmeh; Hashempor, Majid; Baharian, Nosrat

    2015-01-01

    Introduction: In developing countries, hemorrhage accounts for 30% of the maternal deaths. Postpartum hemorrhage has been defined as blood loss of around 500 ml or more, after completing the third phase of labor. Most cases of postpartum hemorrhage occur during the first hour after birth. The most common reason for bleeding in the early hours after childbirth is uterine atony. Bleeding during delivery is usually a visual estimate that is measured by the midwife. It has a high error rate. However, studies have shown that the use of a standard can improve the estimation. The aim of the research is to compare the estimation of postpartum hemorrhage using the weighting method and the National Guideline for postpartum hemorrhage estimation. Materials and Methods: This descriptive study was conducted on 112 females in the Omolbanin Maternity Department of Mashhad, for a six-month period, from November 2012 to May 2013. The accessible method was used for sampling. The data collection tools were case selection, observation and interview forms. For postpartum hemorrhage estimation, after the third section of labor was complete, the quantity of bleeding was estimated in the first and second hours after delivery, by the midwife in charge, using the National Guideline for vaginal delivery, provided by the Maternal Health Office. Also, after visual estimation by using the National Guideline, the sheets under parturient in first and second hours after delivery were exchanged and weighted. The data were analyzed using descriptive statistics and the t-test. Results: According to the results, a significant difference was found between the estimated blood loss based on the weighting methods and that using the National Guideline (weighting method 62.68 ± 16.858 cc vs. National Guideline 45.31 ± 13.484 cc in the first hour after delivery) (P = 0.000) and (weighting method 41.26 ± 10.518 vs. National Guideline 30.24 ± 8.439 in second hour after delivery) (P = 0.000). Conclusions

  16. Stratospheric Polar Freezing Belt Causes Denitrification

    NASA Technical Reports Server (NTRS)

    Tabazadeh, A.; Jensen, E. J.; Toon, O. B.; Drdla, K.; Schoeberl, M. R.; Gore, Warren J. (Technical Monitor)

    2001-01-01

    Trajectory cloud model calculations are presented to show that homogeneous freezing of nitric acid hydrates can produce a polar freezing belt in both hemispheres that can cause denitrification. While hydrate cloud microphysical properties are similar over both poles, the shorter persistence of clouds in the Arctic prevents the depth of the denitrified layers from growing beyond a few kilometers. The 1999-2000 Arctic winter is unique in showing a distinct denitrification profile with a depth of approx. 4.5 km that is nearly half as deep as that computed for a typical Antarctic winter.

  17. Cell biology and molecular basis of denitrification.

    PubMed Central

    Zumft, W G

    1997-01-01

    Denitrification is a distinct means of energy conservation, making use of N oxides as terminal electron acceptors for cellular bioenergetics under anaerobic, microaerophilic, and occasionally aerobic conditions. The process is an essential branch of the global N cycle, reversing dinitrogen fixation, and is associated with chemolithotrophic, phototrophic, diazotrophic, or organotrophic metabolism but generally not with obligately anaerobic life. Discovered more than a century ago and believed to be exclusively a bacterial trait, denitrification has now been found in halophilic and hyperthermophilic archaea and in the mitochondria of fungi, raising evolutionarily intriguing vistas. Important advances in the biochemical characterization of denitrification and the underlying genetics have been achieved with Pseudomonas stutzeri, Pseudomonas aeruginosa, Paracoccus denitrificans, Ralstonia eutropha, and Rhodobacter sphaeroides. Pseudomonads represent one of the largest assemblies of the denitrifying bacteria within a single genus, favoring their use as model organisms. Around 50 genes are required within a single bacterium to encode the core structures of the denitrification apparatus. Much of the denitrification process of gram-negative bacteria has been found confined to the periplasm, whereas the topology and enzymology of the gram-positive bacteria are less well established. The activation and enzymatic transformation of N oxides is based on the redox chemistry of Fe, Cu, and Mo. Biochemical breakthroughs have included the X-ray structures of the two types of respiratory nitrite reductases and the isolation of the novel enzymes nitric oxide reductase and nitrous oxide reductase, as well as their structural characterization by indirect spectroscopic means. This revealed unexpected relationships among denitrification enzymes and respiratory oxygen reductases. Denitrification is intimately related to fundamental cellular processes that include primary and secondary

  18. Enhancing denitrification using a carbon supplement generated from the wet oxidation of waste activated sludge.

    PubMed

    Strong, P J; McDonald, B; Gapes, D J

    2011-05-01

    This study compared the effect of four pure carbon supplements on biological denitrification to a liquor derived as a by-product from the wet oxidation (WO) of waste activated sludge. Sequencing batch reactors were used to acclimate sludge biomass, which was used in batch assays. Acetate, WO liquor and ethanol-supplementation generated the fastest denitrification rates. Acetate and WO liquor were efficiently utilised by all acclimated biomass types, while poor rates were achieved with methanol and formate. When comparing an inoculum from an ethanol-supplemented and non-supplemented wastewater treatment plant (WWTP), the ethanol-acclimated sludge obtained superior denitrification rates when supplemented with ethanol. Similarly high nitrate removal rates were achieved with both sludge types with acetate and WO liquor supplementation, indicating that WO liquors could achieve excellent rates of nitrate removal. The performance of the WO liquor was attributed to the variety of organic carbon substrates (particularly acetic acid) present within the liquor. PMID:21196117

  19. Denitrification in bottomland hardwood wetland soils of the Cache River

    USGS Publications Warehouse

    DeLaune, R.D.; Boar, R.R.; Lindau, C.W.; Kleiss, B.A.

    1996-01-01

    Denitrification rates were quantified in bottomland hardwood wetland soils of the Cache River. N15 labeled nitrate was added to columns containing wetland soils and river water. Over 40 days, nitrate-N in floodwater (approximately 9 mg N L-1) decreased by between 82% and 59%, which gave estimates of N export from the water column of between 11.5 mg N m-2 day-1 and 7.5 mg N m-2 day-1. These values correlated directly with organic content of surface sediment, which included forest litter. Added glucose doubled rates of nitrate loss in these soils, which indicated that the process was carbon limited. Nitrification occurring simultaneously with denitrification was determined using isotopic dilution techniques. Contributions of nitrate to water from nitrification were estimated at between 5% and 12% of the total nitrate reduced. Rates of nitrogen transformation in these forest soils were likely limited by available soil carbon from tree litter and perhaps canopy leachate, rather than by nitrate concentration in inflowing floodwater.

  20. Body mass estimates of an exceptionally complete Stegosaurus (Ornithischia: Thyreophora): comparing volumetric and linear bivariate mass estimation methods

    PubMed Central

    Brassey, Charlotte A.; Maidment, Susannah C. R.; Barrett, Paul M.

    2015-01-01

    Body mass is a key biological variable, but difficult to assess from fossils. Various techniques exist for estimating body mass from skeletal parameters, but few studies have compared outputs from different methods. Here, we apply several mass estimation methods to an exceptionally complete skeleton of the dinosaur Stegosaurus. Applying a volumetric convex-hulling technique to a digital model of Stegosaurus, we estimate a mass of 1560 kg (95% prediction interval 1082–2256 kg) for this individual. By contrast, bivariate equations based on limb dimensions predict values between 2355 and 3751 kg and require implausible amounts of soft tissue and/or high body densities. When corrected for ontogenetic scaling, however, volumetric and linear equations are brought into close agreement. Our results raise concerns regarding the application of predictive equations to extinct taxa with no living analogues in terms of overall morphology and highlight the sensitivity of bivariate predictive equations to the ontogenetic status of the specimen. We emphasize the significance of rare, complete fossil skeletons in validating widely applied mass estimation equations based on incomplete skeletal material and stress the importance of accurately determining specimen age prior to further analyses. PMID:25740841

  1. Body mass estimates of an exceptionally complete Stegosaurus (Ornithischia: Thyreophora): comparing volumetric and linear bivariate mass estimation methods.

    PubMed

    Brassey, Charlotte A; Maidment, Susannah C R; Barrett, Paul M

    2015-03-01

    Body mass is a key biological variable, but difficult to assess from fossils. Various techniques exist for estimating body mass from skeletal parameters, but few studies have compared outputs from different methods. Here, we apply several mass estimation methods to an exceptionally complete skeleton of the dinosaur Stegosaurus. Applying a volumetric convex-hulling technique to a digital model of Stegosaurus, we estimate a mass of 1560 kg (95% prediction interval 1082-2256 kg) for this individual. By contrast, bivariate equations based on limb dimensions predict values between 2355 and 3751 kg and require implausible amounts of soft tissue and/or high body densities. When corrected for ontogenetic scaling, however, volumetric and linear equations are brought into close agreement. Our results raise concerns regarding the application of predictive equations to extinct taxa with no living analogues in terms of overall morphology and highlight the sensitivity of bivariate predictive equations to the ontogenetic status of the specimen. We emphasize the significance of rare, complete fossil skeletons in validating widely applied mass estimation equations based on incomplete skeletal material and stress the importance of accurately determining specimen age prior to further analyses. PMID:25740841

  2. Isotopic evidence of nitrate sources and denitrification in the Mississippi River, Illinois

    USGS Publications Warehouse

    Panno, S.V.; Hackley, Keith C.; Kelly, W.R.; Hwang, H.-H.

    2006-01-01

    Anthropogenic nitrate (NO3-) within the Mississippi-Atchafalaya River basin and discharge to the Gulf of Mexico has been linked to serious environmental problems. The sources of this NO 3- have been estimated by others using mass balance methods; however, there is considerable uncertainty in these estimates. Part of the uncertainty is the degree of denitrification that the NO3- has undergone. The isotopic composition of NO3- in the Mississippi River adjacent to Illinois and tile drain (subsurface drain) discharge in agricultural areas of east-central Illinois was examined using N and O isotopes to help identify the major sources of NO 3- and assess the degree of denitrification in the samples. The isotopic evidence suggests that most of the NO3- in the river is primarily derived from synthetic fertilizers and soil organic N, which is consistent with published estimates of N inputs to the Mississippi River. The 1:2 relationship between ??18O and ??15N also indicate that, depending on sample location and season, NO3- in the river and tile drains lias undergone significant denitrification, ranging from about 0 to 55%. The majority of the denitrification appears to have occurred before discharge into the Mississippi River. ?? ASA, CSSA, SSSA.

  3. Estimating and comparing microbial diversity in the presence of sequencing errors

    PubMed Central

    Chiu, Chun-Huo

    2016-01-01

    Estimating and comparing microbial diversity are statistically challenging due to limited sampling and possible sequencing errors for low-frequency counts, producing spurious singletons. The inflated singleton count seriously affects statistical analysis and inferences about microbial diversity. Previous statistical approaches to tackle the sequencing errors generally require different parametric assumptions about the sampling model or about the functional form of frequency counts. Different parametric assumptions may lead to drastically different diversity estimates. We focus on nonparametric methods which are universally valid for all parametric assumptions and can be used to compare diversity across communities. We develop here a nonparametric estimator of the true singleton count to replace the spurious singleton count in all methods/approaches. Our estimator of the true singleton count is in terms of the frequency counts of doubletons, tripletons and quadrupletons, provided these three frequency counts are reliable. To quantify microbial alpha diversity for an individual community, we adopt the measure of Hill numbers (effective number of taxa) under a nonparametric framework. Hill numbers, parameterized by an order q that determines the measures’ emphasis on rare or common species, include taxa richness (q = 0), Shannon diversity (q = 1, the exponential of Shannon entropy), and Simpson diversity (q = 2, the inverse of Simpson index). A diversity profile which depicts the Hill number as a function of order q conveys all information contained in a taxa abundance distribution. Based on the estimated singleton count and the original non-singleton frequency counts, two statistical approaches (non-asymptotic and asymptotic) are developed to compare microbial diversity for multiple communities. (1) A non-asymptotic approach refers to the comparison of estimated diversities of standardized samples with a common finite sample size or sample completeness. This

  4. Estimating and comparing microbial diversity in the presence of sequencing errors.

    PubMed

    Chiu, Chun-Huo; Chao, Anne

    2016-01-01

    Estimating and comparing microbial diversity are statistically challenging due to limited sampling and possible sequencing errors for low-frequency counts, producing spurious singletons. The inflated singleton count seriously affects statistical analysis and inferences about microbial diversity. Previous statistical approaches to tackle the sequencing errors generally require different parametric assumptions about the sampling model or about the functional form of frequency counts. Different parametric assumptions may lead to drastically different diversity estimates. We focus on nonparametric methods which are universally valid for all parametric assumptions and can be used to compare diversity across communities. We develop here a nonparametric estimator of the true singleton count to replace the spurious singleton count in all methods/approaches. Our estimator of the true singleton count is in terms of the frequency counts of doubletons, tripletons and quadrupletons, provided these three frequency counts are reliable. To quantify microbial alpha diversity for an individual community, we adopt the measure of Hill numbers (effective number of taxa) under a nonparametric framework. Hill numbers, parameterized by an order q that determines the measures' emphasis on rare or common species, include taxa richness (q = 0), Shannon diversity (q = 1, the exponential of Shannon entropy), and Simpson diversity (q = 2, the inverse of Simpson index). A diversity profile which depicts the Hill number as a function of order q conveys all information contained in a taxa abundance distribution. Based on the estimated singleton count and the original non-singleton frequency counts, two statistical approaches (non-asymptotic and asymptotic) are developed to compare microbial diversity for multiple communities. (1) A non-asymptotic approach refers to the comparison of estimated diversities of standardized samples with a common finite sample size or sample completeness. This approach

  5. Comparing NASA and ESA Cost Estimating Methods for Human Missions to Mars

    NASA Technical Reports Server (NTRS)

    Hunt, Charles D.; vanPelt, Michel O.

    2004-01-01

    To compare working methodologies between the cost engineering functions in NASA Marshall Space Flight Center (MSFC) and ESA European Space Research and Technology Centre (ESTEC), as well as to set-up cost engineering capabilities for future manned Mars projects and other studies which involve similar subsystem technologies in MSFC and ESTEC, a demonstration cost estimate exercise was organized. This exercise was a direct way of enhancing not only cooperation between agencies but also both agencies commitment to credible cost analyses. Cost engineers in MSFC and ESTEC independently prepared life-cycle cost estimates for a reference human Mars project and subsequently compared the results and estimate methods in detail. As a non-sensitive, public domain reference case for human Mars projects, the Mars Direct concept was chosen. In this paper the results of the exercise are shown; the differences and similarities in estimate methodologies, philosophies, and databases between MSFC and ESTEC, as well as the estimate results for the Mars Direct concept. The most significant differences are explained and possible estimate improvements identified. In addition, the Mars Direct plan and the extensive cost breakdown structure jointly set-up by MSFC and ESTEC for this concept are presented. It was found that NASA applied estimate models mainly based on historic Apollo and Space Shuttle cost data, taking into account the changes in technology since then. ESA used models mostly based on European satellite and launcher cost data, taking into account the higher equipment and testing standards for human space flight. Most of NASA's and ESA s estimates for the Mars Direct case are comparable, but there are some important, consistent differences in the estimates for: 1) Large Structures and Thermal Control subsystems; 2) System Level Management, Engineering, Product Assurance and Assembly, Integration and Test/Verification activities; 3) Mission Control; 4) Space Agency Program Level

  6. A Bayesian Estimation Framework for Pharmacogenomics Driven Warfarin Dosing: A Comparative Study.

    PubMed

    Öztaner, Serdar Murat; Temizel, Tuğba Taşkaya; Erdem, S Remzi; Özer, Mahmut

    2015-09-01

    The incorporation of pharmacogenomics information into the drug dosing estimation formulations has been shown to increase the accuracy in drug dosing and decrease the frequency of adverse drug effects in many studies in the literature. In this paper, an estimation framework based on the Bayesian structural equation modeling, which is driven by pharmacogenomics, is proposed. The results show that the model compares favorably with the linear models in terms of prediction and explaining the variations in warfarin dosing. PMID:25020183

  7. Physicochemical properties influencing denitrification rate and microbial activity in denitrification bioreactors

    NASA Astrophysics Data System (ADS)

    Schmidt, C. A.

    2012-12-01

    The use of N-based fertilizer will need to increase to meet future demands, yet existing applications have been implicated as the main source of coastal eutrophication and hypoxic zones. Producing sufficient crops to feed a growing planet will require efficient production in combination with sustainable treatment solutions. The long-term success of denitrification bioreactors to effectively remove nitrate (NO¬3), indicates this technology is a feasible treatment option. Assessing and quantifying the media properties that affect NO¬3 removal rate and microbial activity can improve predictions on bioreactor performance. It was hypothesized that denitrification rates and microbial biomass would be correlated with total C, NO¬3 concentration, metrics of organic matter quality, media surface area and laboratory measures of potential denitrification rate. NO¬3 removal rates and microbial biomass were evaluated in mesocosms filled with different wood treatments and the unique influence of these predictor variables was determined using a multiple linear regression analysis. NO3 reduction rates were independent of NO¬3 concentration indicating zero order reaction kinetics. Temperature was strongly correlated with denitrification rate (r2=0.87; Q10=4.7), indicating the variability of bioreactor performance in differing climates. Fiber quality, and media surface area were strong (R>0.50), unique predictors of rates and microbial biomass, although C:N ratio and potential denitrification rate did not predict actual denitrification rate or microbial biomass. Utilizing a stepwise multiple linear regression, indicates that the denitrification rate can be effectively (r2=0.56;p<0.0001) predicted if the groundwater temperature, neutral detergent fiber and surface area alone are quantified. These results will assist with the widespread implementation of denitrification bioreactors to achieve significant N load reductions in large watersheds. The nitrate reduction rate as a

  8. Modeling nitrate removal in a denitrification bed

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Denitrification beds are being promoted to reduce nitrate concentrations in agricultural drainage water to alleviate the adverse environmental effects associated with nitrate pollution in surface water. In this system, water flows through a trench filled with a carbon media where nitrate is transfor...

  9. Nitrite inhibition of denitrification by Pseudomonas fluorescens

    SciTech Connect

    Almeida, J.S.; Julio, S.M.; Reis, M.A.M. |

    1995-05-05

    Using a pure culture of Pseudomonas fluorescens as a model system nitrite inhibition of denitrification was studied. A mineral media with acetate and nitrate as sole electron donor and acceptor, respectively, was used. Results obtained in continuous stirred-tank reactors (CSTR) operated at pH values between 6.6 and 7.8 showed that growth inhibition depended only on the nitrite undissociated fraction concentration (nitrous acid). A mathematical model to describe this dependence is put forward. The maximum nitrous acid concentration compatible with cell growth and denitrification activity was found to be 66 {mu}g N/L. Denitrification activity was partially associated with growth, as described by the Luedeking-Piret equation. However, when the freshly inoculated reactor was operated discontinuously, nitrite accumulation caused growth uncoupling from denitrification activity. The authors suggest that these results can be interpreted considering that (a) nitrous acid acts as a proton uncoupler; and (b) cultures continuously exposed to nitrous acid prevent the uncoupling effect but not the growth inhibition. Examination of the growth dependence on nitrite concentration at pH 7.0 showed that adapted cultures (growth on CSTR) are less sensitive to nitrous acid inhibition than the ones cultivated in batch.

  10. Denitrification in frozen agricultural soil. A review

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Nitrogen (N) in agricultural fertilizers is denitrified by soil bacteria when oxygen is limited, which effectively removes plant-available N from the soil to the atmosphere. Reported denitrification rates range from 0 to 239 kg N ha-1 yr-1 and may reduce the amount of N available for crop growth by...

  11. [Heterotrophic Nitrification and Aerobic Denitrification of the Hypothermia Aerobic Denitrification Bacterium: Arthrobacter arilaitensis].

    PubMed

    He, Teng-xia; Ni, Jiu-pai; Li, Zhen-lun; Sun, Quan; Ye Qing; Xu, Yi

    2016-03-15

    High concentrations of ammonium, nitrate and nitrite nitrogen were employed to clarify the abilities of heterotrophic nitrification and aerobic denitrification of Arthrobacter arilaitensis strain Y-10. Meanwhile, by means of inoculating the strain suspension into the mixed ammonium and nitrate, ammonium and nitrite nitrogen simulated wastewater, we studied the simultaneous nitrification and denitrification ability of Arthrobacter arilaitensis strain Y-10. In addition, cell optical density was assayed in each nitrogen removal process to analyze the relationship of cell growth and nitrogen removal efficiency. The results showed that the hypothermia denitrification strain Arthrobacter arilaitensis Y-10 exhibited high nitrogen removal efficiency during heterotrophic nitrification and aerobic denitrification. The ammonium, nitrate and nitrite removal rates were 65.0%, 100% and 61.2% respectively when strain Y-10 was cultivated for 4 d at 15°C with initial ammonium, nitrate and nitrite nitrogen concentrations of 208.43 mg · L⁻¹, 201.16 mg · L⁻¹ and 194.33 mg · L⁻¹ and initial pH of 7.2. Nitrite nitrogen could only be accumulated in the medium containing nitrate nitrogen during heterotrophic nitrification and aerobic denitrification process. Additionally, the ammonium nitrogen was mainly removed in the inorganic nitrogen mixed synthetic wastewater. In short, Arthrobacter arilaitensis Y-10 could conduct nitrification and denitrification effectively under aerobic condition and the ammonium nitrogen removal rate was more than 80.0% in the inorganic nitrogen mixed synthetic wastewater. PMID:27337904

  12. Aquifer denitrification and in situ mesocosms: Modeling electron donor contributions and measuring rates

    NASA Astrophysics Data System (ADS)

    Korom, Scott F.; Schuh, William M.; Tesfay, Tedros; Spencer, Eben J.

    2012-04-01

    SummaryIn situ denitrification rates were measured in a shallow unconfined glaciofluvial aquifer that had undergone large-scale nitrate contamination. Denitrification rates and isotopic enrichment factors, ɛ, were measured using three tracer tests in two aquifer in situ mesocosms (ISMs). Denitrification rates were also measured using a mass balance method using water samples from multiport samplers. First-order kinetic rates (k) best described the denitrification rates measured. ISM kinetic rates ranged from 0.00049/d to 0.0031/d and ɛ values ranged from -4.86‰ to -9.34‰; a linear relationship between k and ɛ values showed greater fractionation (more negative ɛ values) associated with higher rates. For the mass balance method, k values ranged from 0.0028/d to 0.0041/d. Combined mineralogical analysis, water quality data from the ISMs, and geochemical models using PHREEQC indicated that contributions of major electron donors to denitrification were 43-92% by organic carbon, 4-18% by pyrite, and 2-43% by non-pyritic ferrous iron, depending on the sample date and the type of amphibole used as the electron donor for ferrous iron. ISMs show promise as a tool for hydrogeochemical investigations. They are large enough to allow long-term sampling of aquifer denitrification tracer tests (>2 years), they may be used, with the modeling methodology shown herein, to estimate relative e- donor contributions, and they limit the influence of advection and mechanical dispersion on the amended water within the chamber.

  13. Denitrification in the Arabian Sea: A 3D ecosystem modelling study

    NASA Astrophysics Data System (ADS)

    Anderson, Thomas R.; Ryabchenko, Vladimir A.; Fasham, Michael J. R.; Gorchakov, Victor A.

    2007-12-01

    A three-dimensional hydrodynamic-ecosystem model was used to examine the factors determining the spatio-temporal distribution of denitrification in the Arabian Sea. The ecosystem model includes carbon and nitrogen as currencies, cycling of organic matter via detritus and dissolved organic matter, and both remineralization and denitrification as sinks for material exported below the euphotic zone. Model results captured the marked seasonality in plankton dynamics of the region, with characteristic blooms of chlorophyll in the coastal upwelling regions and central Arabian Sea during the southwest monsoon, and also in the northern Arabian Sea during the northeast monsoon as the mixed layer shoals. Predicted denitrification was 26.2 Tg N yr -1,the greatest seasonal contribution being during the northeast monsoon when primary production is co-located with the zone of anoxia. Detritus was the primary organic substrate consumed in denitrification (97%), with a small (3%) contribution by dissolved organic matter. Denitrification in the oxygen minimum zone was predicted to be fuelled almost entirely by organic matter supplied by particles sinking vertically from the euphotic zone above (0.73 mmol N m -2 d -1) rather than from lateral transport of organic matter from elsewhere in the Arabian Sea (less than 0.01 mmol N m -2 d -1). Analysis of the carbon budget in the zone of denitrification (north of 10°N and east of 55°E) indicates that the modelled vertical export flux of detritus, which is similar in magnitude to estimates from field data based on the 234Th method, is sufficient to account for measured bacterial production below the euphotic zone in the Arabian Sea.

  14. Mustard catch crop enhances denitrification in shallow groundwater beneath a spring barley field.

    PubMed

    Jahangir, M M R; Minet, E P; Johnston, P; Premrov, A; Coxon, C E; Hackett, R; Richards, K G

    2014-05-01

    Over-winter green cover crops have been reported to increase dissolved organic carbon (DOC) concentrations in groundwater, which can be used as an energy source for denitrifiers. This study investigates the impact of a mustard catch crop on in situ denitrification and nitrous oxide (N2O) emissions from an aquifer overlain by arable land. Denitrification rates and N2O-N/(N2O-N+N2-N) mole fractions were measured in situ with a push-pull method in shallow groundwater under a spring barley system in experimental plots with and without a mustard cover crop. The results suggest that a mustard cover crop could substantially enhance reduction of groundwater nitrate NO3--N via denitrification without significantly increasing N2O emissions. Mean total denitrification (TDN) rates below mustard cover crop and no cover crop were 7.61 and 0.002 μg kg(-1) d(-1), respectively. Estimated N2O-N/(N2O-N+N2-N) ratios, being 0.001 and 1.0 below mustard cover crop and no cover crop respectively, indicate that denitrification below mustard cover crop reduces N2O to N2, unlike the plot with no cover crop. The observed enhanced denitrification under the mustard cover crop may result from the higher groundwater DOC under mustard cover crop (1.53 mg L(-1)) than no cover crop (0.90 mg L(-1)) being added by the root exudates and root masses of mustard. This study gives insights into the missing piece in agricultural nitrogen (N) balance and groundwater derived N2O emissions under arable land and thus helps minimise the uncertainty in agricultural N and N2O-N balances. PMID:24374183

  15. Effect of sludge age on simultaneous nitrification and denitrification in membrane bioreactor.

    PubMed

    Hocaoglu, S Murat; Insel, G; Cokgor, E Ubay; Orhon, D

    2011-06-01

    This study evaluated the effect of sludge age on simultaneous nitrification and denitrification in a membrane bioreactor treating black water. A membrane bioreactor with no separate anoxic volume was operated at a sludge age of 20 days under low dissolved oxygen concentration of 0.1-0.2mg/L. Its performance was compared with the period when the sludge age was adjusted to 60 days. Floc size distribution, apparent viscosity, and nitrogen removal differed significantly, together with different biomass concentrations: nitrification was reduced to 40% while denitrification was almost complete. Modelling indicated that both nitrification and denitrification kinetics varied as a function of the sludge age. Calibrated values of half saturation coefficients were reduced when the sludge age was lowered to 20 days. Model simulation confirmed the validity of variable process kinetics for nitrogen removal, specifically set by the selected sludge age. PMID:21507621

  16. Modeling Non-Steady Isotopic Effects Caused by Biological Kinetic Transient Complexation During Denitrification in Soils

    NASA Astrophysics Data System (ADS)

    Maggi, F.; Riley, W. J.

    2008-12-01

    The composition and location of 15N atoms on N2O molecules has been used to characterize soil biological N cycling and N2O surface emissions. Besides the complexity of the processes related to N2O transformations and movements (e.g., chain-like denitrification reaction, soil moisture and temperature dynamics, aqueous and gaseous advection and diffusion) which make interpretation of the isotopic N2O composition very difficult, a theoretical aspect has been overlooked. The theoretical formulation of biological kinetic reactions in isotopic applications makes common use of first-order and quasi steady-state assumptions, according to which the rates of change of the concentration of intermediate complexes can be neglected. When isotopically-labeled reactants are used, these assumptions are not necessarily accurate since isotopic effects during complexation occur at orders of magnitude that compare with the truncation used under first-order and quasi steady-state conditions. Both assumptions, in fact, always lead to a constant fractionation factor and may therefore yield incorrect estimates of the isotopic effect and a misleading interpretation of the reaction signature. We have analyzed the isotopic signature of denitrification in biogeochemical soil systems reported by Menyailo and Hungate (2006), where high 15N2O enrichment during N2O production and inverse isotope fractionation during N2O consumption could not be explained with first-order kinetics and the Rayleigh equation, or with quasi steady-state Monod kinetics. When the quasi steady-state assumption was relaxed, transient Monod kinetics accounting for isotopic effect occurring at the complexes accurately reproduced the observations and aided in interpretation of experimental isotopic signatures. These results may imply a substantial revision in using the Rayleigh equation for interpretation and in modeling biological kinetic isotope fractionation with first-order kinetics or quasi steady state Monod kinetics.

  17. [Research progress in microbial methane oxidation coupled to denitrification].

    PubMed

    Zhu, Jing; Yuan, Meng-Dong; Liu, Jing-Jing; Huang, Xiao-Xiao; Wu, Wei-Xiang

    2013-12-01

    Methane oxidation coupled to denitrification is an essential bond to connect carbon- and nitrogen cycling. To deeply research this process will improve our understanding on the biochemical cycling of global carbon and nitrogen. As an exogenous gaseous carbon source of denitrification, methane can both regulate the balance of atmospheric methane to effectively mitigate the greenhouse effect caused by methane, and reduce the cost of exogenous carbon source input in traditional wastewater denitrification treatment process. As a result, great attention has being paid to the mechanical study of the process. This paper mainly discussed the two types of methane oxidation coupled to denitrification, i. e., aerobic methane oxidation coupled to denitrification (AME-D) and anaerobic methane oxidation coupled to denitrification (ANME-D), with the focus on the microbiological coupling mechanisms and related affecting factors. The existing problems in the engineering application of methane oxidation coupled to denitrification were pointed out, and the application prospects were approached. PMID:24697087

  18. Theoretical and practical limitations of the acetylene inhibition technique to determine total denitrification losses

    NASA Astrophysics Data System (ADS)

    Felber, R.; Conen, F.; Flechard, C. R.; Neftel, A.

    2012-10-01

    The loss of N2 from intensively managed agro-ecosystems is an important part of the N budget. Flux monitoring of N2 emissions at the field scale, e.g., by eddy correlation or aerodynamic gradient method, is impossible due to the large atmospheric N2 background (78%). The acetylene (C2H2) inhibition technique (AIT) is a rather simple and frequently used, albeit imperfect, method to determine N2 losses from intact soil cores. In principle, AIT allows an estimation of total denitrification at high temporal resolution and on small spatial scales, with limited workload and costs involved. To investigate its potential and limitations, a laboratory system with two different detection systems (photoacoustic IR spectroscopy and gas chromatography) is presented, which allowed simultaneous measurements of up to 7 intact soil cores in air-tight glass tubes in a temperature controlled cabinet (adjusted to field conditions) with automated C2H2 injection. A survey of total denitrification losses (N2 + N2O) over 1.5 yr in soil cores from an intensively managed, cut grassland system in central Switzerland supports previous reports on severe limitations of the AIT, which precluded reliable estimates of total denitrification losses. Further, the unavoidable sampling and transfer of soil samples to the laboratory causes unpredictable deviations from the denitrification activity in the field.

  19. Denitrification in nitrate-rich streams: Application of N2:Ar and 15N-tracer methods in intact cores

    USGS Publications Warehouse

    Smith, L.K.; Voytek, M.A.; Böhlke, J.K.; Harvey, J.W.

    2006-01-01

    Rates of benthic denitrification were measured using two techniques, membrane inlet mass spectrometry (MIMS) and isotope ratio mass spectrometry (IRMS), applied to sediment cores from two NO3--rich streams draining agricultural land in the upper Mississippi River Basin. Denitrification was estimated simultaneously from measurements of N 2:Ar (MIMS) and 15N[N2] (IRMS) after the addition of low-level 15NO3- tracer ( 15N:N = 0.03-0.08) in stream water overlying intact sediment cores. Denitrification rates ranged from about 0 to 4400 lmol N??m -2??h-1 in Sugar Creek and from 0 to 1300 ??mol N??m-2??h-1 in Iroquois River, the latter of which possesses greater streamflow discharge and a more homogeneous streambed and water column. Within the uncertainties of the two techniques, there is good agreement between the MIMS and IRMS results, which indicates that the production of N2 by the coupled process of nitrification/denitrification was relatively unimportant and surface-water NO3- was the dominant source of NO3- for benthic denitrification in these streams. Variation in stream NO3- concentration (from about 20 ??mol/L during low discharge to 1000 ??mol/L during high discharge) was a significant control of benthic denitrification rates, judging from the more abundant MIMS data. The interpretation that NO3- concentration directly affects denitrification rate was corroborated by increased rates of denitrification in cores amended with NO 3-. Denitrification in Sugar Creek removed ???11% per day of the instream NO3- in late spring and removed roughly 15-20% in late summer. The fraction of NO3- removed in Iroquois River was less than that of Sugar Creek. Although benthic denitrification rates were relatively high during periods of high stream flow, when NO3 concentrations were also high, the increase in benthic denitrification could not compensate for the much larger increase in stream NO3- fluxes during high flow. Consequently, fractional NO3- losses were relatively low

  20. Comparative assessment of techniques for initial pose estimation using monocular vision

    NASA Astrophysics Data System (ADS)

    Sharma, Sumant; D`Amico, Simone

    2016-06-01

    This work addresses the comparative assessment of initial pose estimation techniques for monocular navigation to enable formation-flying and on-orbit servicing missions. Monocular navigation relies on finding an initial pose, i.e., a coarse estimate of the attitude and position of the space resident object with respect to the camera, based on a minimum number of features from a three dimensional computer model and a single two dimensional image. The initial pose is estimated without the use of fiducial markers, without any range measurements or any apriori relative motion information. Prior work has been done to compare different pose estimators for terrestrial applications, but there is a lack of functional and performance characterization of such algorithms in the context of missions involving rendezvous operations in the space environment. Use of state-of-the-art pose estimation algorithms designed for terrestrial applications is challenging in space due to factors such as limited on-board processing power, low carrier to noise ratio, and high image contrasts. This paper focuses on performance characterization of three initial pose estimation algorithms in the context of such missions and suggests improvements.

  1. Estimating and Interpreting Variance Components in International Comparative Studies in Education

    ERIC Educational Resources Information Center

    Foy, Pierre

    2005-01-01

    Data from international comparative studies in education are generally derived from complex, multi-stage sample designs and rotated assessments. Consequently, care must be taken not only in estimating variance components but also in interpreting them. Target population definitions, the nature of the sampling stages and their sampling units, and…

  2. Comparative estimate of the effectiveness of different algorithms for the radar classification of thunderstorms and showers

    NASA Technical Reports Server (NTRS)

    Linev, A. G.; Oprishko, V. S.; Popova, N. D.; Salman, Y. M.

    1975-01-01

    Several schemes for discriminating severe weather phenomena with the aid of different algorithms are examined. The schemes were tested on the same sample. A comparative estimate of the effectiveness of the different algorithms for classifying thunderstorms and showers is carried out.

  3. Soil Texture Estimates: A Tool to Compare Texture-by-Feel and Lab Data

    ERIC Educational Resources Information Center

    Franzmeier, D.P.; Owens, P.R.

    2008-01-01

    Soil texture is a fundamental soil property that impacts agricultural and engineering land-use. Comparing texture estimates-by-feel to laboratory-known values to calibrate fingers is a common practice. As educators, it is difficult to assess this field skill consistently and fairly. The instructor may give full credit for the correct texture class…

  4. Comparing One-Step M-Estimators of Location When There Are More than Two Groups.

    ERIC Educational Resources Information Center

    Wilcox, Rand R.

    1993-01-01

    Modifications are proposed to the recently developed method of comparing one-step M-estimators of location corresponding to two independent groups that provides good control over the probability of Type I error even for unequal sample size, unequal variances, and different shaped distributions. Simulation results reveal cautions required. (SLD)

  5. Comparing One-Step M-Estimators of Location Corresponding to Two Independent Groups.

    ERIC Educational Resources Information Center

    Wilcox, Rand R.

    1992-01-01

    A method of comparing one-step M-estimates of location for heavy tailed distributions is proposed and investigated. Simulations indicate that the new procedure provides good control over Type I errors and has more power than do some other methods for dealing with heavy tailed distributions. (SLD)

  6. The mechanism of oxygen isotopic fractionation during fungal denitrification - A pure culture study

    NASA Astrophysics Data System (ADS)

    Wrage-Moennig, Nicole; Rohe, Lena; Anderson, Traute-Heidi; Braker, Gesche; Flessa, Heinz; Giesemann, Annette; Lewicka-Szczebak, Dominika; Well, Reinhard

    2014-05-01

    Nitrous oxide (N2O) from soil denitrification originates from bacteria and - to an unknown extent - also from fungi. During fungal denitrification, oxygen (O) exchange takes place between H2O and intermediates of the denitrification process as in bacterial exchange[1,2]. However, information about enzymes involved in fungal O exchanges and the associated fractionation effects is lacking. The objectives of this study were to estimate the O fractionation and O exchange during the fungal denitrifying steps using a conceptual model[2] adapted from concepts for bacterial denitrification[3], implementing controls of O exchange proposed by Aerssens, et al.[4] and using fractionation models by Snider et al.[5] Six different pure fungal cultures (five Hypocreales, one Sordariales) known to be capable of denitrification were incubated under anaerobic conditions, either with nitrite or nitrate. Gas samples were analyzed for N2O concentration and its isotopic signatures (SP, average δ15N, δ18O). To investigate O exchange, both treatments were also established with 18O-labelled water as a tracer in the medium. The Hypocreales strains showed O exchange mainly at NO2- reductase (Nir) with NO2- as electron acceptor and no additional O exchange at NO3- reductase (Nar) with NO3- as electron acceptor. The only Hypocreales species having higher O exchange with NO3- than with NO2- also showed O exchange at Nar. The Sordariales species tested seems capable of O exchange at NO reductase (Nor) additionally to O exchange at Nir with NO2-. The data will help to better interpret stable isotope values of N2O from soils. .[1] D. M. Kool, N. Wrage, O. Oenema, J. Dolfing, J. W. Van Groenigen. Oxygen exchange between (de)nitrification intermediates and H2O and its implications for source determination of NO?3- and N2O: a review. Rapid Commun. Mass Spec. 2007, 21, 3569. [2] L. Rohe, T.-H. Anderson, B. Braker, H. Flessa, A. Giesemann, N. Wrage-Mönnig, R. Well. Fungal Oxygen Exchange between

  7. Dissolved gas and isotopic tracers of denitrification

    SciTech Connect

    Singleton, M J; Moran, J E; Esser, B K; McNab, W W; Carle, S F; Cey, B D

    2008-02-28

    We present results from field studies in California (USA) where tritium-helium age dating is used in conjunction with major gases (N{sub 2}, O{sub 2}, CH{sub 4}, CO{sub 2}), noble gases (He, Ne, Ar, Kr, Xe), and stable isotopes ({sup 15}N/{sup 14}N, {sup 18}O/{sup 16}O) in order to document nitrate loading and denitrification associated with confined animal agricultural operations and septic systems. Preliminary results show that in-field extraction of the full suite of dissolved gases will be possible using a new Gas Extraction System under development to augment the current Noble Gas Mass Spectrometry and Membrane Inlet Mass Spectrometry techniques. Ascribing observed groundwater nitrate levels to specific current and past land use practices is often complicated by uncertainty in groundwater age and the degree and locus of dentrification. Groundwater age dating at dairy field sites using the {sup 3}H-{sup 3}He method indicates that the highest nitrate concentrations (150-260 mg/L-NO3) occur in waters with apparent ages of <5 yrs, whereas older waters contain excess N{sub 2} from saturated zone denitrification [1]. At a residential septic system site in Livermore, CA, waters with young apparent ages (<1 yr) proximal to leach line drainage have lower nitrate concentrations and elevated nitrate {delta}{sup 15}N and {delta}{sup 18}O values consistent with denitrification, but little evidence for excess N{sub 2}, indicating that denitrification is occurring in the unsaturated zone. Degassing of groundwater can complicate efforts to calculate travel times [2] and to quantify denitrification. Degassed groundwater underlying dairy operations is formed by two distinct mechanisms: (1) recharge of manure lagoon water affected by biogenic gas ebullition [3] and (2) saturated zone denitrification producing N{sub 2} gas above solubility in groundwater. Gas loss due to both mechanisms is evident in the concentrations of noble gases and major gases in dairy groundwater samples.

  8. Genetic basis for denitrification in Ensifer meliloti

    PubMed Central

    2014-01-01

    Background Denitrification is defined as the dissimilatory reduction of nitrate or nitrite to nitric oxide (NO), nitrous oxide (N2O), or dinitrogen gas (N2). N2O is a powerful atmospheric greenhouse gas and cause of ozone layer depletion. Legume crops might contribute to N2O production by providing nitrogen-rich residues for decomposition or by associating with rhizobia that are able to denitrify under free-living and symbiotic conditions. However, there are limited direct empirical data concerning N2O production by endosymbiotic bacteria associated with legume crops. Analysis of the Ensifer meliloti 1021 genome sequence revealed the presence of the napEFDABC, nirK, norECBQD and nosRZDFYLX denitrification genes. It was recently reported that this bacterium is able to grow using nitrate respiration when cells are incubated with an initial O2 concentration of 2%; however, these cells were unable to use nitrate respiration when initially incubated anoxically. The involvement of the nap, nirK, nor and nos genes in E. meliloti denitrification has not been reported. Results E. meliloti nap, nirK and norC mutant strains exhibited defects in their ability to grow using nitrate as a respiratory substrate. However, E meliloti nosZ was not essential for growth under these conditions. The E. meliloti napA, nirK, norC and nosZ genes encode corresponding nitrate, nitrite, nitric oxide and nitrous oxide reductases, respectively. The NorC component of the E. meliloti nitric oxide reductase has been identified as a c-type cytochrome that is 16 kDa in size. Herein, we also show that maximal expression of the E. meliloti napA, nirK, norC and nosZ genes occurred when cells were initially incubated anoxically with nitrate. Conclusion The E. meliloti napA, nirK, norC and nosZ genes are involved in nitrate respiration and in the expression of denitrification enzymes in this bacterium. Our findings expand the short list of rhizobia for which denitrification gene function has been

  9. Evaluating two concepts for the modelling of intermediates accumulation during biological denitrification in wastewater treatment.

    PubMed

    Pan, Yuting; Ni, Bing-Jie; Lu, Huijie; Chandran, Kartik; Richardson, David; Yuan, Zhiguo

    2015-03-15

    The accumulation of the denitrification intermediates in wastewater treatment systems is highly undesirable, since both nitrite and nitric oxide (NO) are known to be toxic to bacteria, and nitrous oxide (N2O) is a potent greenhouse gas and an ozone depleting substance. To date, two distinct concepts for the modelling of denitrification have been proposed, which are represented by the Activated Sludge Model for Nitrogen (ASMN) and the Activated Sludge Model with Indirect Coupling of Electrons (ASM-ICE), respectively. The two models are fundamentally different in describing the electron allocation among different steps of denitrification. In this study, the two models were examined and compared in their ability to predict the accumulation of denitrification intermediates reported in four different experimental datasets in literature. The N-oxide accumulation predicted by the ASM-ICE model was in good agreement with values measured in all four cases, while the ASMN model was only able to reproduce one of the four cases. The better performance of the ASM-ICE model is due to that it adopts an "indirect coupling" modelling concept through electron carriers to link the carbon oxidation and the nitrogen reduction processes, which describes the electron competition well. The ASMN model, on the other hand, is inherently limited by its structural deficiency in assuming that carbon oxidation is always able to meet the electron demand by all denitrification steps, therefore discounting electron competition among these steps. ASM-ICE therefore offers a better tool for predicting and understanding intermediates accumulation in biological denitrification. PMID:25577690

  10. Estimation of retired mobile phones generation in China: A comparative study on methodology

    SciTech Connect

    Li, Bo; Yang, Jianxin; Lu, Bin; Song, Xiaolong

    2015-01-15

    Highlights: • The sales data of mobile phones in China was revised by considering the amount of smuggled and counterfeit mobile phones. • The estimation of retired mobile phones in China was made by comparing some relevant methods. • The advanced result of estimation can help improve the policy-making. • The method suggested in this paper can be also used in other countries. • Some discussions on methodology are also conducted in order for the improvement. - Abstract: Due to the rapid development of economy and technology, China has the biggest production and possession of mobile phones around the world. In general, mobile phones have relatively short life time because the majority of users replace their mobile phones frequently. Retired mobile phones represent the most valuable electrical and electronic equipment (EEE) in the main waste stream because of such characteristics as large quantity, high reuse/recovery value and fast replacement frequency. Consequently, the huge amount of retired mobile phones in China calls for a sustainable management system. The generation estimation can provide fundamental information to construct the sustainable management system of retired mobile phones and other waste electrical and electronic equipment (WEEE). However, the reliable estimation result is difficult to get and verify. The priority aim of this paper is to provide proper estimation approach for the generation of retired mobile phones in China, by comparing some relevant methods. The results show that the sales and new method is in the highest priority in estimation of the retired mobile phones. The result of sales and new method shows that there are 47.92 million mobile phones retired in 2002, and it reached to 739.98 million in China in 2012. It presents an increasing tendency with some fluctuations clearly. Furthermore, some discussions on methodology, such as the selection of improper approach and error in the input data, are also conducted in order to

  11. Denitrification and Nitrogen Fixation Dynamics in the Area Surrounding an Individual Ghost Shrimp (Neotrypaea californiensis) Burrow System

    PubMed Central

    Bertics, Victoria J.; Sohm, Jill A.; Magnabosco, Cara

    2012-01-01

    Bioturbated sediments are thought of as areas of increased denitrification or fixed-nitrogen (N) loss; however, recent studies have suggested that not all N may be lost from these environments, with some N returning to the system via microbial dinitrogen (N2) fixation. We investigated denitrification and N2 fixation in an intertidal lagoon (Catalina Harbor, CA), an environment characterized by bioturbation by thalassinidean shrimp (Neotrypaea californiensis). Field studies were combined with detailed measurements of denitrification and N2 fixation surrounding a single ghost shrimp burrow system in a narrow aquarium (15 cm by 20 cm by 5 cm). Simultaneous measurements of both activities were performed on samples taken within a 1.5-cm grid for a two-dimensional illustration of their intensity and distribution. These findings were then compared with rate measurements performed on bulk environmental sediment samples collected from the lagoon. Results for the aquarium indicated that both denitrification and N2 fixation have a patchy distribution surrounding the burrow, with no clear correlation to each other, sediment depth, or distance from the burrow. Field denitrification rates were, on average, lower in a bioturbated region than in a seemingly nonbioturbated region; however, replicates showed very high variability. A comparison of denitrification field results with previously reported N2 fixation rates from the same lagoon showed that in the nonbioturbated region, depth-integrated (10 cm) denitrification rates were higher than integrated N2 fixation rates (∼9 to 50 times). In contrast, in the bioturbated sediments, depending on the year and bioturbation intensity, some (∼6.2%) to all of the N lost via denitrification might be accounted for via N2 fixation. PMID:22447588

  12. Toward Reliable Estimates of Abundance: Comparing Index Methods to Assess the Abundance of a Mammalian Predator

    PubMed Central

    Güthlin, Denise; Storch, Ilse; Küchenhoff, Helmut

    2014-01-01

    Due to time and financial constraints indices are often used to obtain landscape-scale estimates of relative species abundance. Using two different field methods and comparing the results can help to detect possible bias or a non monotonic relationship between the index and the true abundance, providing more reliable results. We used data obtained from camera traps and feces counts to independently estimate relative abundance of red foxes in the Black Forest, a forested landscape in southern Germany. Applying negative binomial regression models, we identified landscape parameters that influence red fox abundance, which we then used to predict relative red fox abundance. We compared the estimated regression coefficients of the landscape parameters and the predicted abundance of the two methods. Further, we compared the costs and the precision of the two field methods. The predicted relative abundances were similar between the two methods, suggesting that the two indices were closely related to the true abundance of red foxes. For both methods, landscape diversity and edge density best described differences in the indices and had positive estimated effects on the relative fox abundance. In our study the costs of each method were of similar magnitude, but the sample size obtained from the feces counts (262 transects) was larger than the camera trap sample size (88 camera locations). The precision of the camera traps was lower than the precision of the feces counts. The approach we applied can be used as a framework to compare and combine the results of two or more different field methods to estimate abundance and by this enhance the reliability of the result. PMID:24743565

  13. Numerical modeling of coupled nitrification-denitrification in sediment perfusion cores from the hyporheic zone of the Shingobee River, MN

    USGS Publications Warehouse

    Sheibley, R.W.; Jackman, A.P.; Duff, J.H.; Triska, F.J.

    2003-01-01

    Nitrification and denitrification kinetics in sediment perfusion cores were numerically modeled and compared to experiments on cores from the Shingobee River MN, USA. The experimental design incorporated mixing groundwater discharge with stream water penetration into the cores, which provided a well-defined, one-dimensional simulation of in situ hydrologic conditions. Ammonium (NH+4) and nitrate (NO-3) concentration gradients suggested the upper region of the cores supported coupled nitrification-denitrification, where groundwater-derived NH+4 was first oxidized to NO-3 then subsequently reduced via denitrification to N2. Nitrification and denitrification were modeled using a Crank-Nicolson finite difference approximation to a one-dimensional advection-dispersion equation. Both processes were modeled using first-order reaction kinetics because substrate concentrations (NH+4 and NO-3) were much smaller than published Michaelis constants. Rate coefficients for nitrification and denitrification ranged from 0.2 to 15.8 h-1 and 0.02 to 8.0 h-1, respectively. The rate constants followed an Arrhenius relationship between 7.5 and 22 ??C. Activation energies for nitrification and denitrification were 162 and 97.3 kJ/mol, respectively. Seasonal NH+4 concentration patterns in the Shingobee River were accurately simulated from the relationship between perfusion core temperature and NH+4 flux to the overlying water. The simulations suggest that NH+4 in groundwater discharge is controlled by sediment nitrification that, consistent with its activation energy, is strongly temperature dependent. ?? 2003 Elsevier Ltd. All rights reserved.

  14. Pilot and full scale applications of sulfur-based autotrophic denitrification process for nitrate removal from activated sludge process effluent.

    PubMed

    Sahinkaya, Erkan; Kilic, Adem; Duygulu, Bahadir

    2014-09-01

    Sulfur-based autotrophic denitrification of nitrified activated sludge process effluent was studied in pilot and full scale column bioreactors. Three identical pilot scale column bioreactors packed with varying sulfur/lime-stone ratios (1/1-3/1) were setup in a local wastewater treatment plant and the performances were compared under varying loading conditions for long-term operation. Complete denitrification was obtained in all pilot bioreactors even at nitrate loading of 10 mg NO3(-)-N/(L.h). When the temperature decreased to 10 °C during the winter time at loading of 18 mg NO3(-)-N/(L.h), denitrification efficiency decreased to 60-70% and the bioreactor with S/L ratio of 1/1 gave slightly better performance. A full scale sulfur-based autotrophic denitrification process with a S/L ratio of 1/1 was set up for the denitrification of an activated sludge process effluent with a flow rate of 40 m(3)/d. Almost complete denitrification was attained with a nitrate loading rate of 6.25 mg NO3(-)-N/(L.h). PMID:24862952

  15. Probe Region Expression Estimation for RNA-Seq Data for Improved Microarray Comparability

    PubMed Central

    Uziela, Karolis; Honkela, Antti

    2015-01-01

    Rapidly growing public gene expression databases contain a wealth of data for building an unprecedentedly detailed picture of human biology and disease. This data comes from many diverse measurement platforms that make integrating it all difficult. Although RNA-sequencing (RNA-seq) is attracting the most attention, at present, the rate of new microarray studies submitted to public databases far exceeds the rate of new RNA-seq studies. There is clearly a need for methods that make it easier to combine data from different technologies. In this paper, we propose a new method for processing RNA-seq data that yields gene expression estimates that are much more similar to corresponding estimates from microarray data, hence greatly improving cross-platform comparability. The method we call PREBS is based on estimating the expression from RNA-seq reads overlapping the microarray probe regions, and processing these estimates with standard microarray summarisation algorithms. Using paired microarray and RNA-seq samples from TCGA LAML data set we show that PREBS expression estimates derived from RNA-seq are more similar to microarray-based expression estimates than those from other RNA-seq processing methods. In an experiment to retrieve paired microarray samples from a database using an RNA-seq query sample, gene signatures defined based on PREBS expression estimates were found to be much more accurate than those from other methods. PREBS also allows new ways of using RNA-seq data, such as expression estimation for microarray probe sets. An implementation of the proposed method is available in the Bioconductor package “prebs.” PMID:25966034

  16. Impact of Aquifer Heterogeneities on Autotrophic Denitrification.

    NASA Astrophysics Data System (ADS)

    McCarthy, A.; Roques, C.; Selker, J. S.; Istok, J. D.; Pett-Ridge, J. C.

    2015-12-01

    Nitrate contamination in groundwater is a big challenge that will need to be addressed by hydrogeologists throughout the world. With a drinking water standard of 10mg/L of NO3-, innovative techniques will need to be pursued to ensure a decrease in drinking water nitrate concentration. At the pumping site scale, the influence and relationship between heterogeneous flow, mixing, and reactivity is not well understood. The purpose of this project is to incorporate both physical and chemical modeling techniques to better understand the effect of aquifer heterogeneities on autotrophic denitrification. We will investigate the link between heterogeneous hydraulic properties, transport, and the rate of autotrophic denitrification. Data collected in previous studies in laboratory experiments and pumping site scale experiments will be used to validate the models. The ultimate objective of this project is to develop a model in which such coupled processes are better understood resulting in best management practices of groundwater.

  17. Quantifying denitrification losses from a sub-tropical pasture in Queensland/Australia - use of the 15N gas flux method

    NASA Astrophysics Data System (ADS)

    Friedl, Johannes; Scheer, Clemens; Warner, Daniel; Grace, Peter

    2014-05-01

    The microbial mediated production of nitrous oxide (N2O) and its reduction to dinitrogen (N2) via denitrification represents a loss of nitrogen (N) from fertilised agro ecosystems to the atmosphere. Although denitrification remains a major uncertainty in estimating N losses from soils, the magnitude of N2 losses and related N2:N2O ratios from soils are largely unknown due to difficulties measuring N2 against a high atmospheric background. In order to address this lack of data, this study investigated the influence of different soil moisture contents on N2 and N2O emissions from a sub-tropical pasture in Queensland/Australia using the 15N gas flux method. Intact soil cores were incubated over 14 days at 80% and 100% water filled pore space (WFPS). Gas samples were taken up to six times per day after application of 15N labelled nitrate, equivalent to 50 kg N ha-1 and analysed for N2 and N2O by isotope ratio mass spectrometry. Fluxes were calculated assuming non-random 15N distribution in the headspace according to Mulvaney and Kurtz (1984) using the labelled pool of nitrate estimated from N2O measurements (Stevens and Laughlin 2001). The main product of denitrification in both treatments was N2. N2 emissions exceeded N2O emissions by a factor of 1.3 ± 0.3 at 80% WFPS and a factor of 3 ± 0.8 at 100% WFPS. The total amount of N-N2 lost over the incubation period was 13.5±1.0 kg N ha-1 at 80% WFPS and 21.8±1.8 kg ha-1 at 100% WFPS respectively. Over the entire incubation period, N2 emissions remained elevated at 100% WFPS, showing high variation between soil cores, while related N2O emissions decreased. At 80% WFPS, N2 emissions increased constantly over time showing significantly higher values after day five. At the same time, N2O fluxes declined. Consequently, N2:N2O ratios rose over the incubation period in both treatments. Overall denitrification rates and related N2:N2O ratios were higher at 100% WFPS compared to 80% WFPS, confirming WFPS as a major driver of

  18. Sources of bias in peoples' social-comparative estimates of food consumption.

    PubMed

    Scherer, Aaron M; Bruchmann, Kathryn; Windschitl, Paul D; Rose, Jason P; Smith, Andrew R; Koestner, Bryan; Snetselaar, Linda; Suls, Jerry

    2016-06-01

    Understanding how healthfully people think they eat compared to others has implications for their motivation to engage in dietary change and the adoption of health recommendations. Our goal was to investigate the scope, sources, and measurements of bias in comparative food consumption beliefs. Across 4 experiments, participants made direct comparisons of how their consumption compared to their peers' consumption and/or estimated their personal consumption of various foods/nutrients and the consumption by peers, allowing the measurement of indirect comparisons. Critically, the healthiness and commonness of the foods varied. When the commonness and healthiness of foods both varied, indirect comparative estimates were more affected by the healthiness of the food, suggesting a role for self-serving motivations, while direct comparisons were more affected by the commonness of the food, suggesting egocentrism as a nonmotivated source of comparative bias. When commonness did not vary, the healthiness of the foods impacted both direct and indirect comparisons, with a greater influence on indirect comparisons. These results suggest that both motivated and nonmotivated sources of bias should be taken into account when creating interventions aimed at improving eating habits and highlights the need for researchers to be sensitive to how they measure perceptions of comparative eating habits. (PsycINFO Database Record PMID:27054551

  19. Denitrification using a membrane-immobilized biofilm

    SciTech Connect

    McCleaf, P.R. ); Schroeder, E.D. . Dept. of Civil and Environmental Engineering)

    1995-03-01

    Immobilized bacterial cell technology was applied, on a bench scale, to the selective removal of nitrate from contaminated water, together with the segregation of denitrifying bacteria and the carbon energy source from the treated water. The two-chambered reactor, with a microporous membrane for bacterial cell immobilization, performed at an average denitrification rate of 5,800 mg nitrate-nitrogen (NO[sub 3][sup [minus

  20. Sedimentary denitrification in the eastern tropical North Pacific in the last 2000 years

    NASA Astrophysics Data System (ADS)

    Juarez, M.; Sanchez, A.; Gonzalez-Yajimovich, O.

    2013-05-01

    The southwestern margin of the Baja California peninsula display intense coastal upwelling, which promotes high primary productivity and the settling of a great amount of organic matter. The oxidation of this organic matter consumes oxygen at a rate that exceeds supply. This condition and the presence of an oxygen minimum zone (OMZ) help to conserve the exported organic matter and can be used to infer changes in productivity. Here we present results of a study based on records of biogenic opal and δ15N to estimate changes in sedimentary denitrification in the eastern tropical North Pacific in the last 2000 years. A multicore (MAGD-MC02) was recovered during the LONO-09 cruise off the Magdalena margin, western Baja California Sur. This site was located within the eastern North Pacific OMZ at a depth of 680 m. The biogenic opal record showed little variability in the last 2000 years, but increased gradually towards the present. The records showed the same variability during the Medieval Warm Period, while denitrification decreased during the Little Ice Age, suggesting that denitrification in the Medieval Warm Period was synchronous with primary productivity, but during the Little Ice Age, the water column showed intensification in ventilation at intermediate depth without change in primary productivity. Keywords: Denitrification, Oxygen Minimum Zone, Ventilation, Primary Productivity, Medieval Warm Period, Little Ice Age.

  1. Progress in Quantifying Rates and Product Ratios of Microbial Denitrification Using Stable Isotope Approaches

    NASA Astrophysics Data System (ADS)

    Well, R.; Braker, G.; Buchen, C.; Giesemann, A.; Lewicka-Szczebak, D.; Rohe, L.; Flessa, H.

    2014-12-01

    Although it is known since long that microbial denitrification plays a central role in N cycling in soils due to loss of nutrient N, emissions of N2O and lowering of N leaching, few data at the field scale are available due to the difficulty in measurement. In recent years, stable isotope signatures of N2O such as d18O, average d15N (d15Nbulk) and 15N site preference (SP = difference in d15N between the central and peripheral N positions of the asymmetric N2O molecule) have been used to constrain the atmospheric N2O budget and to characterize N2O turnover processes including N2O production and reduction by microbial denitrification. However, the use of this approach to study N2O dynamics in soils requires knowledge of isotope fractionation factors for the various partial processes involved, e.g. N2O production by nitrification or fungal/bacterial denitrification, and N2O reduction by bacterial denitrification. Here we present recent progress on the principles of isotope fractionation modeling to estimate N2O reduction and on the role of microbial groups and their specific impact on isotope values. Moreover, we report and discuss approaches to determine isotope values of produced N2O prior to its reduction as well as enrichment factors of N2O reduction. Finally, a variety of results from lab and field studies will be shown were N2O reduction estimates by isotope fractionation modeling are validated by independent measurements using 15N tracing or He/O2 incubations. Methodical improvements to increase sensitivity of the 15N tracing approach will be briefly addressed. We conclude that up to now SP of soil-emitted N2O proved to be suitable to constrain the product ratio of denitrification if N2O fluxes are dominated by bacterial denitrification. Although this approach is not yet precise enough for robust quantification of N2 fluxes, improved precision can be obtained in future, if further progress in understanding the control of fractionation factors of production and

  2. A comparative study of iron abundance estimation methods: Application to the western nearside of the Moon

    NASA Astrophysics Data System (ADS)

    Bhatt, Megha; Mall, Urs; Wöhler, Christian; Grumpe, Arne; Bugiolacchi, Roberto

    2015-03-01

    The FeO weight percentage (wt.%) abundance of the Moon's western nearside (55°S-55°N and 5°E-40°W) is estimated using data from the InfraRed Spectrometer-2 (SIR-2) and the Moon Mineralogy Mapper (M3). In this study, we modified an FeO abundance estimation algorithm (Bhatt, M., Mall, U., Bugiolacchi, R., McKenna-Lawlor, S., Banaszkiewicz, M., Nathues, A., Ullaland, K. [2012]. Icarus 220, 51-64) which relies exclusively on the 2-μm absorption band parameters. The modified FeO abundance estimation algorithm and the regression-based elemental abundance estimation algorithm (Wöhler, C., Grumpe, A., Berezhnoy, A., Bhatt, M.U., Mall, U. [2014]. Icarus 235, 86-122) which is based on the 1-μm and 2-μm absorption band parameters is applied to the M3 data. We have compared results obtained from these two modified algorithms with a previously published Clementine's FeO wt.% map (Lucey, P.G., Blewett, D.T., Jolliff, B.L. [2000]. J. Geophys. Res. 105, 20297-20306). The effects of topography and space weathering on FeO wt.% estimates have been successfully minimized using the modified algorithm based on the 2-μm absorption band parameters. Thus, this algorithm can be successfully applied at middle to high latitudes. Furthermore, a correction for TiO2 is applied to the FeO abundance estimation algorithm based on the 2-μm absorption band parameters using the M3 data. Our comparative study shows a good correspondence between the three algorithms discussed. There are two locations: the crater Tycho and the region around Rima Bode which show major discrepancies. Our modified algorithm based on the 2-μm absorption parameters predicts 3-4 wt.% less FeO for the ray system of Tycho than for the surrounding region. The average iron abundance for the lunar highlands is about 6 wt.% and for the mare regions is about 16 wt.% using the regression-based elemental abundance estimation algorithm and the algorithm based on the 2-μm absorption parameters. This result is consistent with

  3. Evapotranspiration Measurement and Estimation: Weighing Lysimeter and Neutron Probe Based Methods Compared with Eddy Covariance

    NASA Astrophysics Data System (ADS)

    Evett, S. R.; Gowda, P. H.; Marek, G. W.; Alfieri, J. G.; Kustas, W. P.; Brauer, D. K.

    2014-12-01

    Evapotranspiration (ET) may be measured by mass balance methods and estimated by flux sensing methods. The mass balance methods are typically restricted in terms of the area that can be represented (e.g., surface area of weighing lysimeter (LYS) or equivalent representative area of neutron probe (NP) and soil core sampling techniques), and can be biased with respect to ET from the surrounding area. The area represented by flux sensing methods such as eddy covariance (EC) is typically estimated with a flux footprint/source area model. The dimension, position of, and relative contribution of upwind areas within the source area are mainly influenced by sensor height, wind speed, atmospheric stability and wind direction. Footprints for EC sensors positioned several meters above the canopy are often larger than can be economically covered by mass balance methods. Moreover, footprints move with atmospheric conditions and wind direction to cover different field areas over time while mass balance methods are static in space. Thus, EC systems typically sample a much greater field area over time compared with mass balance methods. Spatial variability of surface cover can thus complicate interpretation of flux estimates from EC systems. The most commonly used flux estimation method is EC; and EC estimates of latent heat energy (representing ET) and sensible heat fluxes combined are typically smaller than the available energy from net radiation and soil heat flux (commonly referred to as lack of energy balance closure). Reasons for this are the subject of ongoing research. We compare ET from LYS, NP and EC methods applied to field crops for three years at Bushland, Texas (35° 11' N, 102° 06' W, 1170 m elevation above MSL) to illustrate the potential problems with and comparative advantages of all three methods. In particular, we examine how networks of neutron probe access tubes can be representative of field areas large enough to be equivalent in size to EC footprints, and

  4. Saturated Zone Denitrification at California Dairies

    SciTech Connect

    Singleton, M J; Esser, B K; Moran, J E; McNab, W W; Beller, H R

    2006-02-27

    Denitrification can effectively mitigate the problem of high nitrate concentrations in groundwater under dairy operations by reducing nitrate to N{sub 2} gas, at sites where biogeochemical conditions are favorable. We present results from field studies at central California dairies that document the occurrence of saturated-zone denitrification in shallow groundwater using biomolecular indicators, stable isotope compositions of nitrate, and measurements of dissolved excess N{sub 2} gas. Excess N{sub 2} concentrations provide a measure of the extent to which nitrate in groundwater has been partially or completely denitrified. Abundant excess N{sub 2} and young {sup 3}H/{sup 3}He apparent groundwater ages indicate high denitrification rates near manure lagoons where multiple lines of evidence indicate seepage of lagoon water into the groundwater system. Natural tracers of lagoon water include high chloride and dissolved organic carbon concentrations, distinctive trace organic compounds, and high groundwater {delta}{sup 18}O values (relative to other recharge sources). Proximal to the lagoons, NH{sub 4}{sup +} may be present in groundwater, but is strongly adsorbed on to sediment particles. Bubble formation in the lagoons causes the exsolution of other gases (N{sub 2}, Ar, Ne, He, etc.), which partition into the gas phase and strip the lagoon water of its dissolved gas load, providing a unique tracer of lagoon seepage in groundwater.

  5. Floodplain denitrification within contrasting hydrologic environments

    NASA Astrophysics Data System (ADS)

    Scott, D.; Harvey, J. W.; Noe, G. B.; Bohlke, J. K.

    2012-12-01

    Forested wetlands are an important ecosystem across the southern US. During high-water, the adjacent river actively exchanges dissolved and particulate materials including nutrients (e.g., nitrogen) and suspended sediment with extensive floodplains that are inundated at any time of year during significant storms. Here, we examined the fate of nitrate during active inundation of the floodplain to determine denitrification rates and variation in those rates caused by the influence of hydrologic fluxes across the water-sediment interface. A ^{15}NO_{3}^{-} and Br^{-} addition experiment was carried out during the recession limb of the flood within two adjacent floodplain sloughs that were similar in size and connectivity with the river but differed in their ground surface elevation. Relative elevation of floodplain sloughs influenced the extent to which water flowed into floodplain sediment (i.e. recharge) or flowed out of sediment (discharge). Hydrologic measurements confirmed that the 2 sloughs were distinct - the higher elevation slough was actively recharging, versus in the second slough where exchange across the sediment water interface was absent. Measured rates of denitrification were higher in the recharging slough, and nitrification was only detected in this slough. Collectively, our results suggest that denitrification was important throughout the floodplain of this southeastern U.S. river, however recharging zones on the floodplain have greater nitrogen transformation rates and ultimately higher net nitrogen removal.

  6. Icehouse-greenhouse variations in marine denitrification

    NASA Astrophysics Data System (ADS)

    Algeo, T. J.; Meyers, P. A.; Robinson, R. S.; Rowe, H.; Jiang, G. Q.

    2014-02-01

    Long-term secular variation in the isotopic composition of seawater fixed nitrogen (N) is poorly known. Here, we document variation in the N-isotopic composition of marine sediments (δ15Nsed) since 660 Ma (million years ago) in order to understand major changes in the marine N cycle through time and their relationship to first-order climate variation. During the Phanerozoic, greenhouse climate modes were characterized by low δ15Nsed (˜-2 to +2‰) and icehouse climate modes by high δ15Nsed (˜+4 to +8‰). Shifts toward higher δ15Nsed occurred rapidly during the early stages of icehouse modes, prior to the development of major continental glaciation, suggesting a potentially important role for the marine N cycle in long-term climate change. Reservoir box modeling of the marine N cycle demonstrates that secular variation in δ15Nsed was likely due to changes in the dominant locus of denitrification, with a shift in favor of sedimentary denitrification during greenhouse modes owing to higher eustatic (global sea-level) elevations and greater on-shelf burial of organic matter, and a shift in favor of water-column denitrification during icehouse modes owing to lower eustatic elevations, enhanced organic carbon sinking fluxes, and expanded oceanic oxygen-minimum zones. The results of this study provide new insights into operation of the marine N cycle, its relationship to the global carbon cycle, and its potential role in modulating climate change at multimillion-year timescales.

  7. A Comparative Approach to Hand Force Estimation using Artificial Neural Networks

    PubMed Central

    Mobasser, Farid; Hashtrudi-Zaad, Keyvan

    2012-01-01

    In many applications that include direct human involvement such as control of prosthetic arms, athletic training, and studying muscle physiology, hand force is needed for control, modeling and monitoring purposes. The use of inexpensive and easily portable active electromyography (EMG) electrodes and position sensors would be advantageous in these applications compared to the use of force sensors which are often very expensive and require bulky frames. Among non-model-based estimation methods, Multilayer Perceptron Artificial Neural Networks (MLPANN) has widely been used to estimate muscle force or joint torque from different anatomical features in humans or animals. This paper investigates the use of Radial Basis Function (RBF) ANN and MLPANN for force estimation and experimentally compares the performance of the two methodologies for the same human anatomy, ie, hand force estimation, under an ensemble of operational conditions. In this unified study, the EMG signal readings from upper-arm muscles involved in elbow joint movement and elbow angular position and velocity are utilized as inputs to the ANNs. In addition, the use of the elbow angular acceleration signal as an input for the ANNs is also investigated. PMID:25288896

  8. A Comparative Approach to Hand Force Estimation using Artificial Neural Networks.

    PubMed

    Mobasser, Farid; Hashtrudi-Zaad, Keyvan

    2012-01-01

    In many applications that include direct human involvement such as control of prosthetic arms, athletic training, and studying muscle physiology, hand force is needed for control, modeling and monitoring purposes. The use of inexpensive and easily portable active electromyography (EMG) electrodes and position sensors would be advantageous in these applications compared to the use of force sensors which are often very expensive and require bulky frames. Among non-model-based estimation methods, Multilayer Perceptron Artificial Neural Networks (MLPANN) has widely been used to estimate muscle force or joint torque from different anatomical features in humans or animals. This paper investigates the use of Radial Basis Function (RBF) ANN and MLPANN for force estimation and experimentally compares the performance of the two methodologies for the same human anatomy, ie, hand force estimation, under an ensemble of operational conditions. In this unified study, the EMG signal readings from upper-arm muscles involved in elbow joint movement and elbow angular position and velocity are utilized as inputs to the ANNs. In addition, the use of the elbow angular acceleration signal as an input for the ANNs is also investigated. PMID:25288896

  9. Comparing the effects of climate and impact model uncertainty on climate impacts estimates for grain maize

    NASA Astrophysics Data System (ADS)

    Holzkämper, Annelie; Honti, Mark; Fuhrer, Jürg

    2015-04-01

    Crop models are commonly applied to estimate impacts of projected climate change and to anticipate suitable adaptation measures. Thereby, uncertainties from global climate models, regional climate models, and impacts models cascade down to impact estimates. It is essential to quantify and understand uncertainties in impact assessments in order to provide informed guidance for decision making in adaptation planning. A question that has hardly been investigated in this context is how sensitive climate impact estimates are to the choice of the impact model approach. In a case study for Switzerland we compare results of three different crop modelling approaches to assess the relevance of impact model choice in relation to other uncertainty sources. The three approaches include an expert-based, a statistical and a process-based model. With each approach impact model parameter uncertainty and climate model uncertainty (originating from climate model chain and downscaling approach) are accounted for. ANOVA-based uncertainty partitioning is performed to quantify the relative importance of different uncertainty sources. Results suggest that uncertainty in estimated yield changes originating from the choice of the crop modelling approach can be greater than uncertainty from climate model chains. The uncertainty originating from crop model parameterization is small in comparison. While estimates of yield changes are highly uncertain, the directions of estimated changes in climatic limitations are largely consistent. This leads us to the conclusion that by focusing on estimated changes in climate limitations, more meaningful information can be provided to support decision making in adaptation planning - especially in cases where yield changes are highly uncertain.

  10. A comparative study for the estimation of geodetic point velocity by artificial neural networks

    NASA Astrophysics Data System (ADS)

    Yilmaz, M.; Gullu, M.

    2014-06-01

    Space geodesy era provides velocity information which results in the positioning of geodetic points by considering the time evolution. The geodetic point positions on the Earth's surface change over time due to plate tectonics, and these changes have to be accounted for geodetic purposes. The velocity field of geodetic network is determined from GPS sessions. Velocities of the new structured geodetic points within the geodetic network are estimated from this velocity field by the interpolation methods. In this study, the utility of Artificial Neural Networks (ANN) widely applied in diverse fields of science is investigated in order to estimate the geodetic point velocities. Back Propagation Artificial Neural Network (BPANN) and Radial Basis Function Neural Network (RBFNN) are used to estimate the geodetic point velocities. In order to evaluate the performance of ANNs, the velocities are also interpolated by Kriging (KRIG) method. The results are compared in terms of the root mean square error (RMSE) over five different geodetic networks. It was concluded that the estimation of geodetic point velocity by BPANN is more effective and accurate than by KRIG when the points to be estimated are more than the points known.

  11. Comparing geophysical measurements to theoretical estimates for soil mixtures at low pressures

    SciTech Connect

    Wildenschild, D; Berge, P A; Berryman, K G; Bonner, B P; Roberts, J J

    1999-01-15

    The authors obtained good estimates of measured velocities of sand-peat samples at low pressures by using a theoretical method, the self-consistent theory of Berryman (1980), using sand and porous peat to represent the microstructure of the mixture. They were unable to obtain useful estimates with several other theoretical approaches, because the properties of the quartz, air and peat components of the samples vary over several orders of magnitude. Methods that are useful for consolidated rock cannot be applied directly to unconsolidated materials. Instead, careful consideration of microstructure is necessary to adapt the methods successfully. Future work includes comparison of the measured velocity values to additional theoretical estimates, investigation of Vp/Vs ratios and wave amplitudes, as well as modeling of dry and saturated sand-clay mixtures (e.g., Bonner et al., 1997, 1998). The results suggest that field data can be interpreted by comparing laboratory measurements of soil velocities to theoretical estimates of velocities in order to establish a systematic method for predicting velocities for a full range of sand-organic material mixtures at various pressures. Once the theoretical relationship is obtained, it can be used to estimate the soil composition at various depths from field measurements of seismic velocities. Additional refining of the method for relating velocities to soil characteristics is useful for development inversion algorithms.

  12. Carbon limitation of denitrification rates in an anaerobic groundwater system

    USGS Publications Warehouse

    Bradley, P.M.; Fernandez, M., Jr.; Chapelle, F.H.

    1992-01-01

    Rates of potential denitrification were determined for anaerobic aquifer sediments collected at a site where groundwater NO3 concentrations ranged from 0.7 ??M to 8.6 mM. A significant relation (p = 0.046) was observed between denitrification rates and the in situ concentration of NO3, but NO3 concentration only accounted for approximately 34% (r2) of the variation in activity. The highly significant relation (p < 0.001; r2 = 0.80) between potential denitrification and sediment total organic content and the enhanced activity of sediments amended with glucose indicated that denitrification rates in this aquifer system were carbon limited. No significant relation was observed between denitrification and the in situ groundwater pH, but short-term variations in pH influenced both the magnitude and the end products of denitrification. ?? 1992 American Chemical Society.

  13. A comparative study of shear wave speed estimation techniques in optical coherence elastography applications

    NASA Astrophysics Data System (ADS)

    Zvietcovich, Fernando; Yao, Jianing; Chu, Ying-Ju; Meemon, Panomsak; Rolland, Jannick P.; Parker, Kevin J.

    2016-03-01

    Optical Coherence Elastography (OCE) is a widely investigated noninvasive technique for estimating the mechanical properties of tissue. In particular, vibrational OCE methods aim to estimate the shear wave velocity generated by an external stimulus in order to calculate the elastic modulus of tissue. In this study, we compare the performance of five acquisition and processing techniques for estimating the shear wave speed in simulations and experiments using tissue-mimicking phantoms. Accuracy, contrast-to-noise ratio, and resolution are measured for all cases. The first two techniques make the use of one piezoelectric actuator for generating a continuous shear wave propagation (SWP) and a tone-burst propagation (TBP) of 400 Hz over the gelatin phantom. The other techniques make use of one additional actuator located on the opposite side of the region of interest in order to create an interference pattern. When both actuators have the same frequency, a standing wave (SW) pattern is generated. Otherwise, when there is a frequency difference df between both actuators, a crawling wave (CrW) pattern is generated and propagates with less speed than a shear wave, which makes it suitable for being detected by the 2D cross-sectional OCE imaging. If df is not small compared to the operational frequency, the CrW travels faster and a sampled version of it (SCrW) is acquired by the system. Preliminary results suggest that TBP (error < 4.1%) and SWP (error < 6%) techniques are more accurate when compared to mechanical measurement test results.

  14. Quantitative Estimates of Sequence Divergence for Comparative Analyses of Mammalian Genomes

    PubMed Central

    Cooper, Gregory M.; Brudno, Michael; Program, NISC Comparative Sequencing; Green, Eric D.; Batzoglou, Serafim; Sidow, Arend

    2003-01-01

    Comparative sequence analyses on a collection of carefully chosen mammalian genomes could facilitate identification of functional elements within the human genome and allow quantification of evolutionary constraint at the single nucleotide level. High-resolution quantification would be informative for determining the distribution of important positions within functional elements and for evaluating the relative importance of nucleotide sites that carry single nucleotide polymorphisms (SNPs). Because the level of resolution in comparative sequence analyses is a direct function of sequence diversity, we propose that the information content of a candidate mammalian genome be defined as the sequence divergence it would add relative to already-sequenced genomes. We show that reliable estimates of genomic sequence divergence can be obtained from small genomic regions. On the basis of a multiple sequence alignment of ∼1.4 megabases each from eight mammals, we generate such estimates for five unsequenced mammals. Estimates of the neutral divergence in these data suggest that a small number of diverse mammalian genomes in addition to human, mouse, and rat would allow single nucleotide resolution in comparative sequence analyses. [The multiple sequence alignment of the CFTR region and a spreadsheet with the calculations performed, will be available as supplementary information online at www.genome.org.] PMID:12727901

  15. Comparing Denitrification Rates and Carbon Sources in Commercial Scale Upflow Denitrification Biological Filters in Aquaculture

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aerobic biological filtration systems employing nitrifying bacteria to remediate excess ammonia and nitrite concentrations are common components of recirculating aquaculture systems (RAS). However, significant water exchange may still be necessary to reduce nitrate concentrations to acceptable leve...

  16. Comparative soil CO2 flux measurements and geostatistical estimation methods on Masaya volcano, Nicaragua

    USGS Publications Warehouse

    Lewicki, J.L.; Bergfeld, D.; Cardellini, C.; Chiodini, G.; Granieri, D.; Varley, N.; Werner, C.

    2005-01-01

    We present a comparative study of soil CO2 flux (FCO2) measured by five groups (Groups 1-5) at the IAVCEI-CCVG Eighth Workshop on Volcanic Gases on Masaya volcano, Nicaragua. Groups 1-5 measured (FCO2) using the accumulation chamber method at 5-m spacing within a 900 m2 grid during a morning (AM) period. These measurements were repeated by Groups 1-3 during an afternoon (PM) period. Measured (FCO2 ranged from 218 to 14,719 g m-2 day-1. The variability of the five measurements made at each grid point ranged from ??5 to 167%. However, the arithmetic means of fluxes measured over the entire grid and associated total CO2 emission rate estimates varied between groups by only ??22%. All three groups that made PM measurements reported an 8-19% increase in total emissions over the AM results. Based on a comparison of measurements made during AM and PM times, we argue that this change is due in large part to natural temporal variability of gas flow, rather than to measurement error. In order to estimate the mean and associated CO2 emission rate of one data set and to map the spatial FCO2 distribution, we compared six geostatistical methods: Arithmetic and minimum variance unbiased estimator means of uninterpolated data, and arithmetic means of data interpolated by the multiquadric radial basis function, ordinary kriging, multi-Gaussian kriging, and sequential Gaussian simulation methods. While the total CO2 emission rates estimated using the different techniques only varied by ??4.4%, the FCO2 maps showed important differences. We suggest that the sequential Gaussian simulation method yields the most realistic representation of the spatial distribution of FCO2, but a variety of geostatistical methods are appropriate to estimate the total CO2 emission rate from a study area, which is a primary goal in volcano monitoring research. ?? Springer-Verlag 2005.

  17. COMPARING SINGLE-EPOCH VIRIAL BLACK HOLE MASS ESTIMATORS FOR LUMINOUS QUASARS

    SciTech Connect

    Shen Yue; Liu Xin

    2012-07-10

    Single-epoch virial black hole (BH) mass estimators utilizing broad emission lines have been routinely applied to high-redshift quasars to estimate their BH masses. Depending on the redshift, different line estimators (H{alpha}, H{beta}, Mg II {lambda}2798, C IV {lambda}1549) are often used with optical/near-infrared spectroscopy. Here, we use a homogeneous sample of 60 intermediate-redshift (z {approx} 1.5-2.2) Sloan Digital Sky Survey quasars with optical and near-infrared spectra covering C IV through H{alpha} to investigate the consistency between different single-epoch virial BH mass estimators. We critically compare rest-frame UV line estimators (C IV {lambda}1549, C III] {lambda}1908, and Mg II {lambda}2798) with optical estimators (H{beta} and H{alpha}) in terms of correlations between line widths and between continuum/line luminosities, for the high-luminosity regime (L{sub 5100} > 10{sup 45.4} erg s{sup -1}) probed by our sample. The continuum luminosities of L{sub 1350} and L{sub 3000}, and the broad-line luminosities are well correlated with L{sub 5100}, reflecting the homogeneity of quasar spectra in the rest-frame UV-optical, among which L{sub 1350} and the line luminosities for C IV and C III] have the largest scatter in the correlation with L{sub 5100}. We found that the Mg II FWHM correlates well with the FWHMs of the Balmer lines and that the Mg II line estimator can be calibrated to yield consistent virial mass estimates with those based on the H{beta}/H{alpha} estimators, thus extending earlier results on less luminous objects. The C IV FWHM is poorly correlated with the Balmer line FWHMs, and the scatter between the C IV and H{beta} FWHMs consists of an irreducible part ({approx}0.12 dex), and a part that correlates with the blueshift of the C IV centroid relative to that of H{beta}, similar to earlier studies comparing C IV with Mg II. The C III] FWHM is found to correlate with the C IV FWHM, and hence is also poorly correlated with the H

  18. Progress in quantifying rates and product ratios of microbial denitrification using stable isotope approaches

    NASA Astrophysics Data System (ADS)

    Well, Reinhard; Buchen, Caroline; Giesemann, Anette; Lewicka-Szczebak, Dominika; Rohe, Lena; Flessa, Heinz

    2015-04-01

    Although it is known since long that microbial denitrification plays a central role in N cycling in soils due to loss of nutrient N, emissions of N2O and lowering of N leaching, few data at the field scale are available due to the difficulty in measurement. In recent years, stable isotope signatures of N2O such as δ18O, average δ15N (δ15Nbulk) and 15N site preference (SP = difference in δ15N between the central and peripheral N positions of the asymmetric N2O molecule) have been used to constrain the atmospheric N2O budget and to characterize N2O turnover processes including N2O production and reduction by microbial denitrification. However, the use of this approach to study N2O dynamics in soils requires knowledge of isotope fractionation factors for the various partial processes involved, e.g. N2O production by nitrification or fungal/bacterial denitrification, and N2O reduction by bacterial denitrification. Here we present recent progress on the principles of isotope fractionation modeling to estimate N2O reduction and on the role of microbial groups and their specific impact on isotope values. Moreover, we report and discuss approaches to determine isotope values of produced N2O prior to its reduction as well as enrichment factors of N2O reduction. Finally, a variety of results from lab and field studies will be shown were N2O reduction estimates by isotope fractionation modeling are validated by independent measurements using 15N tracing or He/O2 incubations. Methodical improvements to increase sensitivity of the 15N tracing approach will be briefly addressed. We conclude that up to now SP of soil-emitted N2O proved to be suitable to constrain the product ratio of denitrification if N2O fluxes are dominated by bacterial denitrification. Although this approach is not yet precise enough for robust quantification of N2 fluxes, improved precision can be obtained in future, if further progress in understanding the control of fractionation factors of production

  19. Quantifying Denitrification and Its Effect on Ozone Recovery

    NASA Technical Reports Server (NTRS)

    Tabazadeh, A.; Santee, M. L.; Danilin, M. Y.; Pumphrey, H. C.; Newman, P. A.; Hamill, P. J.; Mergenthaler, J. L.; Gore, Warren J. (Technical Monitor)

    2000-01-01

    Upper Atmosphere Research Satellite observations indicate that extensive denitrification, without significant dehydration, currently occurs only in the Antarctic during mid to late June. The fact that denitrification occurs in a relatively warm month in the Antarctic raises concern about the likelihood of its occurrence, and associated effects on ozone recovery, in a future colder and possibly more humid Arctic lower stratosphere. Polar stratospheric cloud lifetimes required for Arctic denitrification to occur in the future are presented and contrasted against the current Antarctic cloud lifetimes. Model calculations show widespread severe denitrification could enhance future Arctic ozone loss by up to 30%.

  20. Optimal Scales for Comparing Satellite and Rain-Gauge Rainfall Estimates for Verification Purposes

    NASA Technical Reports Server (NTRS)

    Bell, Thomas L.; Kundu, Prasun K.

    1999-01-01

    In spite of all their problems, rain gauges measure rainfall in such a direct way when compared with other methods of estimating rainfall that comparing their totals to satellite estimates remains an essential tool in the validation of satellite products. Some disagreement between averages of satellite data and rain-gauge data is expected because of the very different sampling patterns of the two systems--the satellite provides only occasional snapshots of large areas, whereas rain gauges provide continuous measurements over very small areas. The comparison of the two requires that some quantitative measure be supplied for the amount of disagreement that can be tolerated due to the differences in sampling. As part of an effort to determine the sampling error of satellite averages, a space-time model for rainfall statistics was developed and its parameters fit to radar data from a field experiment conducted near the Inter-Tropical Convergence Zone (ITCZ) in the eastern Atlantic (GATE). Although the model was intended to represent the statistics of relatively large scale fluctuations of rain, it is surprisingly consistent with the very different scales on which rain gauges observe. It can therefore be used to study some of the issues involved with comparing rain-gauge averages to satellite averages. Its implications for the best time and space scales for comparing the two will be discussed.

  1. Age estimation in Indian children and adolescents in the NCR region of Haryana: A comparative study

    PubMed Central

    Gupta, Swati; Mehendiratta, Monica; Rehani, Shweta; Kumra, Madhumani; Nagpal, Ruchi; Gupta, Ramakant

    2015-01-01

    Introduction: Age estimation is a preliminary step in the identification of an individual. It is a crucial and often most critical step for forensic experts. The assessment has been standardized utilizing common dental diagnostic x-rays, but most such age-estimating systems are European population-based and their applicability has not been determined in the context of the Indian population. Aims and Objectives: To assess the applicability and to compare the methods of dental age estimation by Demirjian's method and the same method as modified by Willems (i.e. the Willems method) in Indian children of the National Capital Region (NCR). Also, to find a correlation among skeletal maturity using the Cervical vertebrae maturation index (CVMI), dental maturity, and chronological age in the same population. Materials and Methods: This cross-sectional study was conducted using dental radiographs of 70 orthodontic patients (37 males, 33 females) in the age range 9-16 years selected by simple random sampling. pantomogram were used to estimate dental age by Demirjian's method and the Willems method using their scoring tables. Lateral cephalograms were used to estimate skeletal maturity using CVMI. The latter was compared with Demirjian's stage for mandibular left second molar. Results: Overestimation of age among males by 0.856 years and 0.496 years was found by Demirjian's and the Willems methods, respectively. Among females, both the methods underestimated the age by 0.31 years and 0.45 years, respectively. Demirjian's stage G corresponded to CVMI stage 3 in males and stage 2 in females. Conclusion: In our study, the Willems method has proved to be more accurate for age estimation among Indian males, and Demirjian's method for Indian females. A statistically significant association appeared between Demirjian's stages and CVMI among both males and females. Our study recommends the derivation of a regression formula by studying a larger section of the Indian population

  2. Effort estimation for enterprise resource planning implementation projects using social choice - a comparative study

    NASA Astrophysics Data System (ADS)

    Koch, Stefan; Mitlöhner, Johann

    2010-08-01

    ERP implementation projects have received enormous attention in the last years, due to their importance for organisations, as well as the costs and risks involved. The estimation of effort and costs associated with new projects therefore is an important topic. Unfortunately, there is still a lack of models that can cope with the special characteristics of these projects. As the main focus lies in adapting and customising a complex system, and even changing the organisation, traditional models like COCOMO can not easily be applied. In this article, we will apply effort estimation based on social choice in this context. Social choice deals with aggregating the preferences of a number of voters into a collective preference, and we will apply this idea by substituting the voters by project attributes. Therefore, instead of supplying numeric values for various project attributes, a new project only needs to be placed into rankings per attribute, necessitating only ordinal values, and the resulting aggregate ranking can be used to derive an estimation. We will describe the estimation process using a data set of 39 projects, and compare the results to other approaches proposed in the literature.

  3. Denitrification in continental shelf sediments has major impact on the oceanic nitrogen budget

    NASA Astrophysics Data System (ADS)

    Christensen, John P.; Murray, James W.; Devol, Allan H.; Codispoti, Louis A.

    1987-06-01

    Denitrification rates in sediments within the oxygen deficient waters off Mexico and from the Gulf of Maine were investigated on the basis of interstitial nutrient profiles. Nitrate fluxes into the sediments were calculated from gradients across the sediment-water interface and vertical molecular diffusion coefficients and averaged 0.151 (Mexico) and 0.0920 (Gulf of Maine) pmol NO-3 cm-2 s-1. These are minimum values, since these gradients may have been underestimated. In the Gulf of Maine, bottom water irrigation by macrobenthos increases the nitrate supply well above this estimate. In addition, only 15-22% of the expected ammonium is present in Gulf of Maine sediments perhaps because of removal by a rapid coupling of nitrification with denitrification. This large apparent loss of the regenerated ammonium appears to be ubiquitous in shelf sediments with oxygenated bottom water. The global denitrification rate in continental shelf sediments was reassessed to be >50 Tg N yr-1 (1 Tg = 1012 g), demonstrating that sediments are an important sink for oceanic nitrogen. Globally, current nitrogen losses from the oceans may exceed inputs by 60-90 Tg N yr-1. Over the glacial-interglacial cycle the global sedimentary denitrification rate probably varied commensurately with the changing continental shelf area. An oscillating oceanic nitrogen budget over these time scales could occur given the sequence of (1) scouring and dumping of terrestrial nitrogen into the oceans during glacial advance, (2) removal of oceanic combined nitrogen to the atmosphere by denitrification following glacial retreat, and (3) reincorporation of this N into terrestrial biomass during the interglacial period.

  4. A comparative study of commercial lithium ion battery cycle life in electric vehicle: Capacity loss estimation

    NASA Astrophysics Data System (ADS)

    Han, Xuebing; Ouyang, Minggao; Lu, Languang; Li, Jianqiu

    2014-12-01

    Now the lithium ion batteries are widely used in electric vehicles (EV). The cycle life is among the most important characteristics of the power battery in EV. In this report, the battery cycle life experiment is designed according to the actual working condition in EV. Five different commercial lithium ion cells are cycled alternatively under 45 °C and 5 °C and the test results are compared. Based on the cycle life experiment results and the identified battery aging mechanism, the battery cycle life models are built and fitted by the genetic algorithm. The capacity loss follows a power law relation with the cycle times and an Arrhenius law relation with the temperature. For automotive application, to save the cost and the testing time, a battery SOH (state of health) estimation method combined the on-line model based capacity estimation and regular calibration is proposed.

  5. Denitrification and Nitrate-Dependent Fe(II) Oxidation in Various Pseudogulbenkiania Strains

    PubMed Central

    Ishii, Satoshi; Joikai, Kazuki; Otsuka, Shigeto; Senoo, Keishi; Okabe, Satoshi

    2016-01-01

    Pseudogulbenkiania is a relatively recently characterized genus within the order Neisseriales, class Betaproteobacteria. This genus contains several strains that are capable of anaerobic, nitrate-dependent Fe(II) oxidation (NDFO), a geochemically important reaction for nitrogen and iron cycles. In the present study, we examined denitrification functional gene diversities within this genus, and clarified whether other Pseudogulbenkiania sp. strains perform denitrification and NDFO. Seventy strains were analyzed, including two type strains, a well-characterized NDFO strain, and 67 denitrifying strains isolated from various rice paddy fields and rice-soybean rotation fields in Japan. We also attempted to identify the genes responsible for NDFO by mutagenesis. Our comprehensive analysis showed that all Pseudogulbenkiania strains tested performed denitrification and NDFO; however, we were unable to obtain NDFO-deficient denitrifying mutants in our mutagenesis experiment. This result suggests that Fe(II) oxidation in these strains is not enzymatic, but is caused by reactive N-species that are formed during nitrate reduction. Based on the results of the comparative genome analysis among Pseudogulbenkiania sp. strains, we identified low sequence similarity within the nos gene as well as different gene arrangements within the nos gene cluster, suggesting that nos genes were horizontally transferred. Since Pseudogulbenkiania sp. strains have been isolated from various locations around the world, their denitrification and NDFO abilities may contribute significantly to nitrogen and iron biogeochemical cycles. PMID:27431373

  6. Prophylactic radiotherapy against heterotopic ossification following internal fixation of acetabular fractures: a comparative estimate of risk

    PubMed Central

    Nasr, P; Yip, G; Scaife, J E; House, T; Thomas, S J; Harris, F; Owen, P J; Hull, P

    2014-01-01

    Objective: Radiotherapy (RT) is effective in preventing heterotopic ossification (HO) around acetabular fractures requiring surgical reconstruction. We audited outcomes and estimated risks from RT prophylaxis, and alternatives of indometacin or no prophylaxis. Methods: 34 patients underwent reconstruction of acetabular fractures through a posterior approach, followed by a 8-Gy single fraction. The mean age was 44 years. The mean time from surgery to RT was 1.1 days. The major RT risk is radiation-induced fatal cancer. The International Commission on Radiological Protection (ICRP) method was used to estimate risk, and compared with a method (Trott and Kemprad) specifically for estimating RT risk for benign disease. These were compared with risks associated with indometacin and no prophylaxis. Results: 28 patients (82%) developed no HO; 6 developed Brooker Class I; and none developed Class II–IV HO. The ICRP method suggests a risk of fatal cancer in the range of 1 in 1000 to 1 in 10,000; the Trott and Kemprad method suggests 1 in 3000. For younger patients, this may rise to 1 in 2000; and for elderly patients, it may fall to 1 in 6000. The risk of death from gastric bleeding or perforation from indometacin is 1 in 180 to 1 in 900 in older patients. Without prophylaxis risk of death from reoperation to remove HO is 1 in 4000 to 1 in 30,000. Conclusion: These results are encouraging, consistent with much larger series and endorse our multidisciplinary management. Risk estimates can be used in discussion with patients. Advances in knowledge: The risk from RT prophylaxis is small, it is safer than indometacin and substantially overlaps with the range for no prophylaxis. PMID:25089852

  7. [Denitrification potential and CO2 emission in the northern forest soils of the Enisei meridian (the Siberian IGBP transect)].

    PubMed

    Meniaĭlo, O V; Krasnoshchekov, Iu N

    2003-01-01

    To estimate the probable contribution of northern forest soils to the global budget of greenhouse microgases, the cryogenic soils along the Yenisei meridian have been studied with respect to their potential denitrification and carbon mineralization activities. It is shown that the forest soils of the boreal zone have a high denitrification potential and, under conditions of a high nitrate nitrogen content, may be a source of nitrogen oxide emission. A significant correlation is observed between N2O and CO2 emissions (r = 0.85, p < 0.001). PMID:12816071

  8. Comparative analysis of monetary estimates of external environmental costs associated with combustion of fossil fuels

    SciTech Connect

    Koomey, J.

    1990-07-01

    Public utility commissions in a number of states have begun to explicitly treat costs of environmental externalities in the resource planning and acquisition process (Cohen et al. 1990). This paper compares ten different estimates and regulatory determinations of external environmental costs associated with fossil fuel combustion, using consistent assumptions about combustion efficiency, emissions factors, and resource costs. This consistent comparison is useful because it makes explicit the effects of various assumptions. This paper uses the results of the comparison to illustrate pitfalls in calculation of external environmental costs, and to derive lessons for design of policies to incorporate these externalities into resource planning. 38 refs., 2 figs., 10 tabs.

  9. Denitrification Genes Regulate Brucella Virulence in Mice

    PubMed Central

    Baek, Seung-Hun; Rajashekara, Gireesh; Splitter, Gary A.; Shapleigh, James P.

    2004-01-01

    Brucella is the causative agent of the zoonotic disease brucellosis, which is endemic in many parts of the world. Genome sequencing of B. suis and B. melitensis revealed that both are complete denitrifiers. To learn more about the role of denitrification in these animal pathogens, a study of the role of denitrification in the closely related B. neotomae was undertaken. In contrast to B. suis and B. melitensis, it was found that B. neotomae is a partial denitrifier that can reduce nitrate to nitrite but no further. Examination of the B. neotomae genome showed that a deletion in the denitrification gene cluster resulted in complete loss of nirV and the partial deletion of nirK and nnrA. Even though the nor operon is intact, a norC-lacZ promoter fusion was not expressed in B. neotomae. However, the norC-lacZ fusion was expressed in the related denitrifier Agrobacterium tumefaciens, suggesting that the lack of expression in B. neotomae is due to inactivation of NnrA. A narK-lacZ promoter fusion was found to exhibit nitrate-dependent expression consistent with the partial denitrifier phenotype. Complementation of the deleted region in B. neotomae by using nirK, nirV, and nnrA from B. melitensis restored the ability of B. neotomae to reduce nitrite. There was a significant difference in the death of IRF-1−/− mice when infected with B. neotomae containing nirK, nirV, and nnrA and those infected with wild-type B. neotomae. The wild-type strain killed all the infected mice, whereas most of the mice infected with B. neotomae containing nirK, nirV, and nnrA survived. PMID:15342571

  10. Optimization and evaluation of a bottom substrate denitrification tank for nitrate removal from a recirculating aquaculture system.

    PubMed

    Pungrasmi, Wiboonluk; Playchoom, Cholticha; Powtongsook, Sorawit

    2013-08-01

    A bottom substrate denitrification tank for a recirculating aquaculture system was developed. The laboratory scale denitrification tank was an 8 L tank (0.04 m2 tank surface area), packed to a depth of 5 cm with a bottom substrate for natural denitrifying bacteria. An aquarium pump was used for gentle water mixing in the tank; the dissolved oxygen in the water was maintained in aerobic conditions (e.g. > 2 mg/L) while anoxic conditions predominated only at the bottom substrate layer. The results showed that, among the four substrates tested (soil, sand, pumice stone and vermiculite), pumice was the most preferable material. Comparing carbon supplementation using methanol and molasses, methanol was chosen as the carbon source because it provided a higher denitrification rate than molasses. When methanol was applied at the optimal COD:N ratio of 5:1, a nitrate removal rate of 4591 +/- 133 mg-N/m2 tank bottom area/day was achieved. Finally, nitrate removal using an 80 L denitrification tank was evaluated with a 610 L recirculating tilapia culture system. Nitrate treatment was performed by batch transferring high nitrate water from the nitrification tank into the denitrification tank and mixing with methanol at a COD:N ratio of 5:1. The results from five batches of nitrate treatment revealed that nitrate was successfully removed from water without the accumulation of nitrite and ammonia. The average nitrate removal efficiency was 85.17% and the average denitrification rate of the denitrification tank was 6311 +/- 945 mg-N/m2 tank bottom area/day or 126 +/- 18 mg-N/L of pumice packing volume/day. PMID:24520693

  11. The metric comparability of meta-analytic effect-size estimators from factorial designs.

    PubMed

    Gillett, Raphael

    2003-12-01

    The primary studies in a meta-analysis of standardized mean differences generally include a mixture of single-factor t tests and multifactor analysis of variance designs. Accordingly, there is a need for effect-size measures in multifactor designs that are metrically comparable with measures in single-factor t tests. Two models, the variance-preservation model and the variance-reduction model, provide a formal description of the 2 principal routes by which a single-factor design may evolve into a higher order factorial design. New metrically comparable effect-size measures and estimators are developed for designs that contain variance-preservation factors, variance-reduction factors, or a mixture of both types of factors. A statistical test for checking the validity of model assumptions is presented. PMID:14664680

  12. N fertilization effects on denitrification and N cycling in an aggrading forest.

    PubMed

    Wallenstein, Matthew D; Peterjohn, William T; Schlesinger, William H

    2006-12-01

    We investigated N cycling and denitrification rates following five years of N and dolomite amendments to whole-tree harvested forest plots at the long-term soil productivity experiment in the Fernow Experimental Forest in West Virginia, USA. We hypothesized that changes in soil chemistry and nutrient cycling induced by N fertilization would increase denitrification rates and the N2O:N2 ratio. Soils from the fertilized plots had a lower pH (2.96) than control plots (3.22) and plots that received fertilizer and dolomite (3.41). There were no significant differences in soil %C or %N between treatments. Chloroform-labile microbial biomass carbon was lower in fertilized plots compared to control plots, though this trend was not significant. Extractable soil NO3- was elevated in fertilized plots on each sample date. Soil-extractable NH4+, NO3-, pH, microbial biomass carbon, and %C varied significantly by sample date suggesting important seasonal patterns in soil chemistry and N cycling. In particular, the steep decline in extractable NH4+ during the growing season is consistent with the high N demands of a regenerating forest. Net N mineralization and nitrification also varied by date but were not affected by the fertilization and dolomite treatments. In a laboratory experiment, denitrification was stimulated by NO3- additions in soils collected from all field plots, but this effect was stronger in soils from the unfertilized control plots, suggesting that chronic N fertilization has partially alleviated a NO3- limitation on denitrification rates. Dextrose stimulated denitrification only in the whole-tree-harvest soils. Denitrification enzyme activity varied by sample date and was elevated in fertilized plots for soil collected in July 2000 and June 2001. There were no detectable treatment effects on N2O or N2 flux from soils under anaerobic conditions, though there was strong temporal variation. These results suggest that whole-tree harvesting has altered the N status

  13. Estimate of safe human exposure levels for lunar dust based on comparative benchmark dose modeling.

    PubMed

    James, John T; Lam, Chiu-Wing; Santana, Patricia A; Scully, Robert R

    2013-04-01

    Brief exposures of Apollo astronauts to lunar dust occasionally elicited upper respiratory irritation; however, no limits were ever set for prolonged exposure to lunar dust. The United States and other space faring nations intend to return to the moon for extensive exploration within a few decades. In the meantime, habitats for that exploration, whether mobile or fixed, must be designed to limit human exposure to lunar dust to safe levels. Herein we estimate safe exposure limits for lunar dust collected during the Apollo 14 mission. We instilled three respirable-sized (∼2 μ mass median diameter) lunar dusts (two ground and one unground) and two standard dusts of widely different toxicities (quartz and TiO₂) into the respiratory system of rats. Rats in groups of six were given 0, 1, 2.5 or 7.5 mg of the test dust in a saline-Survanta® vehicle, and biochemical and cellular biomarkers of toxicity in lung lavage fluid were assayed 1 week and one month after instillation. By comparing the dose--response curves of sensitive biomarkers, we estimated safe exposure levels for astronauts and concluded that unground lunar dust and dust ground by two different methods were not toxicologically distinguishable. The safe exposure estimates were 1.3 ± 0.4 mg/m³ (jet-milled dust), 1.0 ± 0.5 mg/m³ (ball-milled dust) and 0.9 ± 0.3 mg/m³ (unground, natural dust). We estimate that 0.5-1 mg/m³ of lunar dust is safe for periodic human exposures during long stays in habitats on the lunar surface. PMID:23614726

  14. Estimating Dungeness crab (Cancer magister) abundance: Crab pots and dive transects compared

    USGS Publications Warehouse

    Taggart, S.J.; O'Clair, C. E.; Shirley, T.C.; Mondragon, J.

    2004-01-01

    Dungeness crabs (Cancer magister) were sampled with commercial pots and counted by scuba divers on benthic transects at eight sites near Glacier Bay, Alaska. Catch per unit of effort (CPUE) from pots was compared to the density estimates from dives to evaluate the bias and power of the two techniques. Yearly sampling was conducted in two seasons: April and September, from 1992 to 2000. Male CPUE estimates from pots were significantly lower in April than in the following September; a step-wise regression demonstrated that season accounted for more of the variation in male CPUE than did temperature. In both April and September, pot sampling was significantly biased against females. When females were categorized as ovigerous and nonovigerous, it was clear that ovigerous females accounted for the majority of the bias because pots were not biased against nonovigerous females. We compared the power of pots and dive transects in detecting trends in populations and found that pots had much higher power than dive transects. Despite their low power, the dive transects were very useful for detecting bias in our pot sampling and in identifying the optimal times of year to sample so that pot bias could be avoided.

  15. Use of microbial analysis to evaluate denitrification in the karstic aquifer of Okinawa, Japan

    NASA Astrophysics Data System (ADS)

    Yasumoto, J.

    2014-12-01

    Denitrification, a microbial process in the nitrogen cycle, is a facultative respiratory pathway in which nitrate (NO3-), nitrite (NO2-), nitric oxide (NO), and nitrous oxide (N2O), successively, are reduced to nitrogen gas (N2). This study explores the use of microbial analysis to evaluate the processes involved in nitrate attenuation in groundwater. Polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) is used to identify denitrifiers based only on their 16SrRNA gene sequences, and Real-Time PCR analysis is used to quantify nitrite reducing genes (nirK and nirS), this suggest that a new methods for detecting denitrification activity by comparing the gene dosage that has been detected by RT-PCR and the value of the δ15NNO3- and δ18ONO3-. This study focuses on a zone of significant NO3- attenuation occurring at underground dam catchment area in the karstic Ryukyu limestone aquifer, which is located southern part of Okinawa, Japan. As a result of microbial analysis, the bacteria were detected at all observation points which have been reported to have denitrification ability. And it has been confirmed that the bacteria has a gene nirS which is related to denitrification. In addition, many bacteria related to denitrification have been extracted from suspended solids more than from groundwater in the aquifer. And, the correlation was high between nirK /nirS gene dosage that has been detected by RT-PCR and the value of the δ15N and δ18O; therefore, this study demonstrates the effectiveness of using Real-Time PCR analysis for providing insights into the processes affecting nitrate attenuation in ground water.

  16. Barometric process separation: New method for quantifying nitrification, denitrification, and nitrous oxide sources in soils

    SciTech Connect

    Ingwersen, J.; Butterbach-Bahl, K.; Gasche, R.; Papen, H.; Richter, O.

    1999-01-01

    A method, Barometric Process Separation (BaPS), was developed for the quantification of gross nitrification rates and denitrification rates in oxic soil using intact soil cores incubated in an isothermal gas tight system. Gross nitrification rates and denitrification rates are derived from measurements of changes (i) in air pressure within the closed system, which are primarily the result of the activities of nitrification, denitrification, and respiration, and (2) of O{sub 2} and CO{sub 2} concentrations in the system. Besides these biological processes, the contribution of physicochemical dissolution of produced CO{sub 2} in soil water to the pressure changes observed is to be considered. The method allows collection of additional information about the contribution of nitrification and denitrification to N{sub 2}O emission from soil, provided simultaneous measurements of N{sub 2}O emission are performed. Furthermore, BaPS can be used to quantify the percentage of N{sub 2}O lost from nitrification. The advantage of BaPS is that disturbance of the soil system is minimized compared with other methods such as the use of gaseous inhibitors (e.g., acetylene) or application of {sup 15}N compounds to the soil. The authors present the theoretical considerations of BaPS, results for nitrification rates, denitrification rates, and identification of soil N{sub 2}O sources in a well-aerated coniferous forest soil using BaPS. The suitability of BaPS as a method for determination of gross nitrification is demonstrated by validation experiments using the {sup 15}N-pool dilution technique.

  17. AN EVALUATION OF TWO GROUND-BASED CROWN CLOSURE ESTIMATION TECHNIQUES COMPARED TO CROWN CLOSURE ESTIMATES DERIVED FROM HIGH RESOLUTION IMAGERY

    EPA Science Inventory

    Two ground-based canopy closure estimation techniques, the Spherical Densitometer (SD) and the Vertical Tube (VT), were compared for the effect of deciduous understory on dominant/co-dominant crown closure estimates in even-aged loblolly (Pinus taeda) pine stands located in the N...

  18. AN EVALUATION OF TWO GROUND-BASED CROWN CLOSURE ESTIMATION TECHNIQUES COMPARED TO CROWN CLOSURE ESTIMATES DERIVED FROM HIGH RESOLUTION IMAGERY

    EPA Science Inventory

    Two ground-based canopy closure estimation techniques, the Spherical Densitometer (SD) and the Vertical Tube (VT), were compared for the effect of deciduous understory on dominantlco-dominant crown closure estimates in even-aged loblolly (Pinus taeda) pine stands located in the N...

  19. A PRELIMINARY EXPERIMENT ON DENITRIFICATION OF WASTE LANDFILL LEACHATE

    NASA Astrophysics Data System (ADS)

    Wada, Nariaki; Nakamichi, Tamihiro; Yagi, Masahiro; Matsumoto, Toshihide; Kugimiya, Akikazu; Michioku, Kohji

    A laboratory experiment on denitrification was carried out in order to reduce nitrogen load from municipal landfill leachate. Nitrogen was efficiently removed by feeding sludge of the leachate pond into the tanks, which could activate denitrification bacteria. Although inorganic reducing agent such as iron powder was not able to make the whole water mass anoxic, denitrification took place by supplying organic matters such as methanol, hydrogen feeding agent, etc.. It is considered that small amount of anoxic water film produced on surfaces of container and carriers might contribute to denitrification, although the bulk water is kept aerobic. It is found that organic matters contained in the leachate is so insufficient that nitrification liquid circulation does not work well for denitrification.

  20. Comparing the accuracy of experimental estimates to guessing: a new perspective on replication and the "Crisis of Confidence" in psychology.

    PubMed

    Davis-Stober, Clintin P; Dana, Jason

    2014-03-01

    We develop a general measure of estimation accuracy for fundamental research designs, called v. The v measure compares the estimation accuracy of the ubiquitous ordinary least squares (OLS) estimator, which includes sample means as a special case, with a benchmark estimator that randomizes the direction of treatment effects. For sample and effect sizes common to experimental psychology, v suggests that OLS produces estimates that are insufficiently accurate for the type of hypotheses being tested. We demonstrate how v can be used to determine sample sizes to obtain minimum acceptable estimation accuracy. Software for calculating v is included as online supplemental material (R Core Team, 2012). PMID:23661222

  1. Comparing an estimate of seabirds at risk to a mortality estimate from the November 2004 Terra Nova FPSO oil spill.

    PubMed

    Wilhelm, Sabina I; Robertson, Gregory J; Ryan, Pierre C; Schneider, David C

    2007-05-01

    On 21 November 2004, about 1000 barrels of crude oil were accidentally released from the Terra Nova FPSO (floating production, storage and offloading) onto the Grand Banks, approximately 340 km east-southeast of St. John's, Newfoundland. We estimated the number of vulnerable seabirds (murres (Uria spp.) and dovekies (Alle alle)) at risk from this incident by multiplying observed densities of seabirds with the total area covered by the slick, estimated at 793 km(2). A mean density of 3.46 murres/km(2) and 1.07 dovekies/km(2) on the sea surface was recorded during vessel-based surveys on 28 and 29 November 2004, with a mean density of 6.90 murres/km(2) and 13.43 dovekies/km(2) combining those on the sea and in flight. We calculated a mean of 9858 murres and dovekies were at risk of being oiled, with estimates ranging from 3593 to 16,122 depending on what portion of birds in flight were assumed to be at risk. A mortality model based on spill volume was derived independently of the risk model, and estimated that 4688 (CI 95%: 1905-12,480) birds were killed during this incident. A low mortality estimate based strictly on spill volume would be expected for this incident, which occurred in an area of relatively high seabird densities. Given that the risk and mortality estimates are statistically indistinguishable, we estimate that on the order of 10,000 birds were killed by the Terra Nova spill. PMID:17328926

  2. Denitrification as a Model Chemical Process

    NASA Astrophysics Data System (ADS)

    Grguric, Gordan

    2002-02-01

    Bacterial denitrification in seawater facilities such as aquaria and mariculture systems is a process particularly well suited for illustrating important concepts in chemistry to undergraduates. Students can gain firsthand experience related to these concepts, for example by (i) analyzing and quantifying chemical reactions based on empirical data, (ii) employing stoichiometry and mass balance to determine the amounts of reactants required and products produced in a chemical reaction, and (iii) using acid-base speciation diagrams and other information to quantify the changes in pH and carbonic acid speciation in an aqueous medium. At the Richard Stockton College of New Jersey, we have utilized actual data from several seawater systems to discuss topics such as stoichiometry, mass and charge balance, and limiting reagents. This paper describes denitrification in closed seawater systems and how the process can be used to enhance undergraduate chemistry education. A number of possible student exercises are described that can be used as practical tools to enhance the students' quantitative understanding of chemical reactions.

  3. Modeling enhanced in situ denitrification in groundwater

    USGS Publications Warehouse

    Killingstad, M.W.; Widdowson, M.A.; Smith, R.L.

    2002-01-01

    A two-dimensional numerical solute transport model was developed for simulating an enhanced in situ denitrification experiment performed in a nitrate-contaminated aquifer on Cape Cod, Massachusetts. In this experiment, formate (HCOO-) was injected for a period of 26 days into the carbon-limited aquifer to stimulate denitrification. Calibration of the vertical-profile site model was demonstrated through error analysis and comparison with formate, nitrate, and nitrite concentration data monitored along a transect of three multilevel groundwater sampling wells for 75 days after initial injection. Formate utilization rates were approximately 142 and 38 ??M/day for nitrate and nitrite reduction, respectively. Nitrate and nitrite utilization rates were approximately 29 and 8 ??M/day, respectively. Nitrate utilization rates under enhanced conditions were 1 order of magnitude greater than previously reported naturally occurring rates. The nitrite production rate was approximately 29 ??M/day. Persistence of nitrite was attributed to a combination of factors, including electron donor (formate) limitation late in the experiment, preferential utilization of nitrate as an electron acceptor, and greater nitrite production relative to nitrite utilization.

  4. Denitrification in USB reactor with granulated biomass.

    PubMed

    Pagácová, P; Galbová, K; Drtil, M; Jonatová, I

    2010-01-01

    Denitrification of low concentrations of NO(3)-N (20 mg L(-1)), with methanol as an organic carbon source (COD:NO(3)-N=6) in laboratory upflow sludge bed reactor (USB), was tested as a possibility for wastewater post-treatment. By gradual increase of volumetric loading (Bv) and hydraulic loading (gamma), anoxic biomass spontaneously granulated out even from flocculate activated sludge and from anaerobic granulated sludge as well. Anaerobic granulated biomass derived from high-rate anaerobic IC reactor was a far better inoculum for anoxic granulation and for denitrification in the USB reactor. The maximum level of Bv and gamma was remarkably higher with the use of anaerobic granulated inoculum, (19-22 kg COD m(-3)d(-1); 3.2-3.7 kg NO(3)-Nm(-3)d(-1); 2.8-3.2m(3)m(-2)h(-1); SVI=15 mL g(-1)) in comparison to inoculum from flocculate activated sludge (4.2-8.1 kg CO Dm(-3)d(-1); 0.7-1.4 kg NO(3)-Nm(-3)d(-1); 0.7-1.15m(3)m(-2)h(-1); SVI=40-95 mL g(-1)). PMID:19716692

  5. N2O production by nitrifier denitrification in the Benguela Upwelling System

    NASA Astrophysics Data System (ADS)

    Frame, C. H.; Hou, L.; Lehmann, M. F.

    2014-12-01

    The Benguela upwelling system off the coast of southwestern Africa is an important zone of marine N2O production whose upwelling rates vary seasonally. Here we present N2O stable isotopic and isotopomeric data collected during a period of high upwelling (September 2013) and low upwelling (January 2014). During both periods, 15N-nitrite and 15N-ammonium tracer inucbation experiments were used to investigate N2O production by ammonia oxidizing microorganisms in the top 150m of the water column. N2O production from 15N-ammonium was not measurable during these incubations. However, we detected N2O production from 15N-nitrite, suggesting that nitrifier denitrification is a source of shallow N2O in this region. Furthermore, decreasing the pH of the incubation water enhanced the amount of N2O produced, suggesting that upwelling of CO2-rich/low-pH deep water may enhance N2O production in this region. Finally, we present our incubation data in the larger context of the N2O and nitrite isotopic and concentration profiles, with an eye toward comparing incubation-based N2O production rates with profile-based estimates.

  6. Differential effects of crude oil on denitrification and anammox, and the impact on N2O production.

    PubMed

    Ribeiro, Hugo; Mucha, Ana P; Azevedo, Isabel; Salgado, Paula; Teixeira, Catarina; Almeida, C Marisa R; Joye, Samantha B; Magalhães, Catarina

    2016-09-01

    Denitrification and anammox are key processes for reducing the external nitrogen loads delivered to coastal ecosystems, and these processes can be affected by pollutants. In this study, we investigated the effect of crude oil on denitrification and anammox. Controlled laboratory experiments were performed using sediment slurries from the Lima Estuary (NW Portugal). Anammox and denitrification rates were measured using (15)N-labeled NO3(-), and the production of (29)N2 and (30)N2 quantified by membrane inlet mass spectrometry. Results revealed that while denitrification rates were stimulated between 10 and 25 000 times after crude oil amendment, anammox activity was partially (between 2 and 5 times) or completely inhibited by the addition of crude oil when comparing to rates in unamended controls. Similar results were observed across four estuarine sediment types, despite their different physical-chemical characteristics. Moreover, N2O production was reduced by 2-36 times following crude oil addition. Further work is required to fully understand the mechanism(s) of the observed reduction in N2O production. This study represents one of the first contributions to the understanding of the impact of crude oil pollution on denitrification and anammox, with profound implications for the management of aquatic ecosystems regarding eutrophication (N-removal). PMID:27395442

  7. High-Resolution Denitrification Kinetics in Pasture Soils Link N2O Emissions to pH, and Denitrification to C Mineralization

    PubMed Central

    Samad, Md Sainur; Bakken, Lars R.; Nadeem, Shahid; Clough, Timothy J.; de Klein, Cecile A. M.; Richards, Karl G.; Lanigan, Gary J.; Morales, Sergio E.

    2016-01-01

    Denitrification in pasture soils is mediated by microbial and physicochemical processes leading to nitrogen loss through the emission of N2O and N2. It is known that N2O reduction to N2 is impaired by low soil pH yet controversy remains as inconsistent use of soil pH measurement methods by researchers, and differences in analytical methods between studies, undermine direct comparison of results. In addition, the link between denitrification and N2O emissions in response to carbon (C) mineralization and pH in different pasture soils is still not well described. We hypothesized that potential denitrification rate and aerobic respiration rate would be positively associated with soils. This relationship was predicted to be more robust when a high resolution analysis is performed as opposed to a single time point comparison. We tested this by characterizing 13 different temperate pasture soils from northern and southern hemispheres sites (Ireland and New Zealand) using a fully automated-high-resolution GC detection system that allowed us to detect a wide range of gas emissions simultaneously. We also compared the impact of using different extractants for determining pH on our conclusions. In all pH measurements, soil pH was strongly and negatively associated with both N2O production index (IN2O) and N2O/(N2O+N2) product ratio. Furthermore, emission kinetics across all soils revealed that the denitrification rates under anoxic conditions (NO+N2O+N2 μmol N/h/vial) were significantly associated with C mineralization (CO2 μmol/h/vial) measured both under oxic (r2 = 0.62, p = 0.0015) and anoxic (r2 = 0.89, p<0.0001) conditions. PMID:26990862

  8. High-Resolution Denitrification Kinetics in Pasture Soils Link N2O Emissions to pH, and Denitrification to C Mineralization.

    PubMed

    Samad, Md Sainur; Bakken, Lars R; Nadeem, Shahid; Clough, Timothy J; de Klein, Cecile A M; Richards, Karl G; Lanigan, Gary J; Morales, Sergio E

    2016-01-01

    Denitrification in pasture soils is mediated by microbial and physicochemical processes leading to nitrogen loss through the emission of N2O and N2. It is known that N2O reduction to N2 is impaired by low soil pH yet controversy remains as inconsistent use of soil pH measurement methods by researchers, and differences in analytical methods between studies, undermine direct comparison of results. In addition, the link between denitrification and N2O emissions in response to carbon (C) mineralization and pH in different pasture soils is still not well described. We hypothesized that potential denitrification rate and aerobic respiration rate would be positively associated with soils. This relationship was predicted to be more robust when a high resolution analysis is performed as opposed to a single time point comparison. We tested this by characterizing 13 different temperate pasture soils from northern and southern hemispheres sites (Ireland and New Zealand) using a fully automated-high-resolution GC detection system that allowed us to detect a wide range of gas emissions simultaneously. We also compared the impact of using different extractants for determining pH on our conclusions. In all pH measurements, soil pH was strongly and negatively associated with both N2O production index (IN2O) and N2O/(N2O+N2) product ratio. Furthermore, emission kinetics across all soils revealed that the denitrification rates under anoxic conditions (NO+N2O+N2 μmol N/h/vial) were significantly associated with C mineralization (CO2 μmol/h/vial) measured both under oxic (r2 = 0.62, p = 0.0015) and anoxic (r2 = 0.89, p<0.0001) conditions. PMID:26990862

  9. Comparability of National Estimates for Traumatic Brain Injury-Related Medical Encounters

    PubMed Central

    Taylor, Christopher A.; Greenspan, Arlene I.; Xu, Likang; Kresnow, Marcie-jo

    2015-01-01

    Objective To describe similarities and differences in the number of civilian traumatic brain injury (TBI)-related hospitalizations and emergency department visits between national databases that capture US hospital data. Participants TBI-related hospitalizations included in the National Hospital Discharge Survey (NHDS) and Healthcare Cost and Utilization Project Nationwide Inpatient Sample (HCUP-NIS) and emergency department visits in the National Hospital Ambulatory Medical Care Survey (NHAMCS) and HCUP Nationwide Emergency Department Sample (HCUP-NEDS) for 2006–2010. Design Cross-sectional design. Main Measures Nationwide counts of TBI-related medical encounters. Results Overall, the frequency of TBI is comparable when comparing NHDS with HCUP-NIS and NHAMCS with HCUP-NEDS. However, annual counts in both NHDS and NHAMCS are consistently unstable when examined in smaller subgroups, such as by age group and injury mechanism. Injury mechanism is consistently missing from many more records in NHDS compared with HCUP-NIS. Conclusion Given the large sample size of HCUP-NIS and HCUP-NEDS, these data can offer a valuable resource for examining TBI-related hospitalization and emergency department visits, especially by subgroup. These data hold promise for future examinations of annual TBI counts, but ongoing comparisons with national probability samples will be necessary to ensure that HCUP continues to track with estimates from these data. PMID:25955702

  10. Stimulating in situ denitrification in an aerobic, highly permeable municipal drinking water aquifer

    NASA Astrophysics Data System (ADS)

    Critchley, K.; Rudolph, D. L.; Devlin, J. F.; Schillig, P. C.

    2014-12-01

    A preliminary trial of a cross-injection system (CIS) was designed to stimulate in situ denitrification in an aquifer servicing an urban community in southern Ontario. It was hypothesized that this remedial strategy could be used to reduce groundwater nitrate in the aquifer such that it could remain in use as a municipal supply until the beneficial effects of local reduced nutrient loadings lead to long-term water quality improvement at the wellfield. The CIS application involved injecting a carbon source (acetate) into the subsurface using an injection-extraction well pair positioned perpendicular to the regional flow direction, up-gradient of the water supply wells, with the objective of stimulating native denitrifying bacteria. The pilot remedial strategy was targeted in a high nitrate flux zone within an aerobic and heterogeneous section of the glacial sand and gravel aquifer. Acetate injections were performed at intervals ranging from daily to bi-daily. The carbon additions led to general declines in dissolved oxygen concentrations; decreases in nitrate concentration were localized in aquifer layers where velocities were estimated to be less than 0.5 m/day. NO3-15N and NO3-18O isotope data indicated the nitrate losses were due to denitrification. Relatively little nitrate was removed from groundwater in the more permeable strata, where velocities were estimated to be on the order of 18 m/day or greater. Overall, about 11 percent of the nitrate mass passing through the treatment zone was removed. This work demonstrates that stimulating in situ denitrification in an aerobic, highly conductive aquifer is challenging but achievable. Further work is needed to increase rates of denitrification in the most permeable units of the aquifer.

  11. Comparing population exposure to multiple Washington earthquake scenarios for prioritizing loss estimation studies

    USGS Publications Warehouse

    Wood, Nathan J.; Ratliff, Jamie L.; Schelling, John; Weaver, Craig S.

    2014-01-01

    Scenario-based, loss-estimation studies are useful for gauging potential societal impacts from earthquakes but can be challenging to undertake in areas with multiple scenarios and jurisdictions. We present a geospatial approach using various population data for comparing earthquake scenarios and jurisdictions to help emergency managers prioritize where to focus limited resources on data development and loss-estimation studies. Using 20 earthquake scenarios developed for the State of Washington (USA), we demonstrate how a population-exposure analysis across multiple jurisdictions based on Modified Mercalli Intensity (MMI) classes helps emergency managers understand and communicate where potential loss of life may be concentrated and where impacts may be more related to quality of life. Results indicate that certain well-known scenarios may directly impact the greatest number of people, whereas other, potentially lesser-known, scenarios impact fewer people but consequences could be more severe. The use of economic data to profile each jurisdiction’s workforce in earthquake hazard zones also provides additional insight on at-risk populations. This approach can serve as a first step in understanding societal impacts of earthquakes and helping practitioners to efficiently use their limited risk-reduction resources.

  12. Comparative Evaluation of Inversion Approaches of the Radiative Transfer Model for Estimation of Crop Biophysical Parameters

    NASA Astrophysics Data System (ADS)

    Mridha, Nilimesh; Sahoo, Rabi N.; Sehgal, Vinay K.; Krishna, Gopal; Pargal, Sourabh; Pradhan, Sanatan; Gupta, Vinod K.; Kumar, Dasika Nagesh

    2015-04-01

    The inversion of canopy reflectance models is widely used for the retrieval of vegetation properties from remote sensing. This study evaluates the retrieval of soybean biophysical variables of leaf area index, leaf chlorophyll content, canopy chlorophyll content, and equivalent leaf water thickness from proximal reflectance data integrated broadbands corresponding to moderate resolution imaging spectroradiometer, thematic mapper, and linear imaging self scanning sensors through inversion of the canopy radiative transfer model, PROSAIL. Three different inversion approaches namely the look-up table, genetic algorithm, and artificial neural network were used and performances were evaluated. Application of the genetic algorithm for crop parameter retrieval is a new attempt among the variety of optimization problems in remote sensing which have been successfully demonstrated in the present study. Its performance was as good as that of the look-up table approach and the artificial neural network was a poor performer. The general order of estimation accuracy for parameters irrespective of inversion approaches was leaf area index > canopy chlorophyll content > leaf chlorophyll content > equivalent leaf water thickness. Performance of inversion was comparable for broadband reflectances of all three sensors in the optical region with insignificant differences in estimation accuracy among them.

  13. Comparing Three Estimation Methods for the Three-Parameter Logistic IRT Model

    ERIC Educational Resources Information Center

    Lamsal, Sunil

    2015-01-01

    Different estimation procedures have been developed for the unidimensional three-parameter item response theory (IRT) model. These techniques include the marginal maximum likelihood estimation, the fully Bayesian estimation using Markov chain Monte Carlo simulation techniques, and the Metropolis-Hastings Robbin-Monro estimation. With each…

  14. The mechanism of oxygen isotope fractionation during N2O production by denitrification

    NASA Astrophysics Data System (ADS)

    Lewicka-Szczebak, D.; Dyckmans, J.; Kaiser, J.; Marca, A.; Augustin, J.; Well, R.

    2015-10-01

    The isotopic composition of soil-derived N2O can help differentiate between N2O production pathways and estimate the fraction of N2O reduced to N2. Until now, δ18O of N2O has been rarely used in the interpretation of N2O isotopic signatures because of the rather complex oxygen isotope fractionations during N2O production by denitrification. The latter process involves nitrate reduction mediated through the following three enzymes: nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR). Each step removes one oxygen atom as water (H2O), which gives rise to a branching isotope effect. Moreover, denitrification intermediates may partially or fully exchange oxygen isotopes with ambient water, which is associated with an exchange isotope effect. The main objective of this study was to decipher the mechanism of oxygen isotope fractionation during N2O production by denitrification and, in particular, to investigate the relationship between the extent of oxygen isotope exchange with soil water and the δ18O values of the produced N2O. We performed several soil incubation experiments. For the first time, Δ17O isotope tracing was applied to simultaneously determine the extent of oxygen isotope exchange and any associated oxygen isotope effect. We found bacterial denitrification to be typically associated with almost complete oxygen isotope exchange and a stable difference in δ18O between soil water and the produced N2O of δ18O(N2O / H2O) = (17.5 ± 1.2) ‰. However, some experimental setups yielded oxygen isotope exchange as low as 56 % and a higher δ18O(N2O / H2O) of up to 37 ‰. The extent of isotope exchange and δ18O(N2O / H2O) showed a very significant correlation (R2 = 0.70, p < 0.00001). We hypothesise that this observation was due to the contribution of N2O from another production process, most probably fungal denitrification. An oxygen isotope fractionation model was used to test various scenarios with different magnitudes of

  15. Comparative biomass structure and estimated carbon flow in food webs in the deep Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Rowe, Gilbert T.; Wei, Chihlin; Nunnally, Clifton; Haedrich, Richard; Montagna, Paul; Baguley, Jeffrey G.; Bernhard, Joan M.; Wicksten, Mary; Ammons, Archie; Briones, Elva Escobar; Soliman, Yousra; Deming, Jody W.

    2008-12-01

    A budget of the standing stocks and cycling of organic carbon associated with the sea floor has been generated for seven sites across a 3-km depth gradient in the NE Gulf of Mexico, based on a series of reports by co-authors on specific biotic groups or processes. The standing stocks measured at each site were bacteria, Foraminifera, metazoan meiofauna, macrofauna, invertebrate megafauna, and demersal fishes. Sediment community oxygen consumption (SCOC) by the sediment-dwelling organisms was measured at each site using a remotely deployed benthic lander, profiles of oxygen concentration in the sediment pore water of recovered cores and ship-board core incubations. The long-term incorporation and burial of organic carbon into the sediments has been estimated using profiles of a combination of stable and radiocarbon isotopes. The total stock estimates, carbon burial, and the SCOC allowed estimates of living and detrital carbon residence time within the sediments, illustrating that the total biota turns over on time scales of months on the upper continental slope but this is extended to years on the abyssal plain at 3.6 km depth. The detrital carbon turnover is many times longer, however, over the same depths. A composite carbon budget illustrates that total carbon biomass and associated fluxes declined precipitously with increasing depth. Imbalances in the carbon budgets suggest that organic detritus is exported from the upper continental slope to greater depths offshore. The respiration of each individual "size" or functional group within the community has been estimated from allometric models, supplemented by direct measurements in the laboratory. The respiration and standing stocks were incorporated into budgets of carbon flow through and between the different size groups in hypothetical food webs. The decline in stocks and respiration with depth were more abrupt in the larger forms (fishes and megafauna), resulting in an increase in the relative predominance of

  16. Comparing estimation approaches for the illness-death model under left truncation and right censoring.

    PubMed

    Vakulenko-Lagun, Bella; Mandel, Micha

    2016-04-30

    Left-truncated data arise when lifetimes are observed only if they are larger than independent truncation times. For example, in a cross-sectional sampling, only individuals who live long enough to be present on the sampling day are observed. There are several ways to perform statistical inference under this setting. One can do the following: (i) use an unconditional approach, (ii) condition on the value of the truncation variable, or (iii) condition on all the history up to the time of truncation. The latter two approaches are equivalent when analyzing univariate survival outcomes but differ under the multi-state framework. In this paper, we consider the illness-death model and compare between the three estimation approaches in a parametric regression framework. We show that approach (ii) is more efficient than the standard approach (iii), although it requires more computational effort. Approach (i) is the most efficient approach, but it requires knowledge on the distribution of the truncation variable and hence is less robust. The methods are compared using a theoretical example and simulations and are applied to intensive care units data collected in a cross-sectional design, where the illness state corresponds to a bloodstream infection. Copyright © 2015 John Wiley & Sons, Ltd. PMID:26553433

  17. Comparing GOSAT observations of localized CO2 enhancements by large emitters with inventory-based estimates

    NASA Astrophysics Data System (ADS)

    Janardanan, Rajesh; Maksyutov, Shamil; Oda, Tomohiro; Saito, Makoto; Kaiser, Johannes W.; Ganshin, Alexander; Stohl, Andreas; Matsunaga, Tsuneo; Yoshida, Yukio; Yokota, Tatsuya

    2016-04-01

    We employed an atmospheric transport model to attribute column-averaged CO2 mixing ratios (XCO2) observed by Greenhouse gases Observing SATellite (GOSAT) to emissions due to large sources such as megacities and power plants. XCO2 enhancements estimated from observations were compared to model simulations implemented at the spatial resolution of the satellite observation footprint (0.1° × 0.1°). We found that the simulated XCO2 enhancements agree with the observed over several continental regions across the globe, for example, for North America with an observation to simulation ratio of 1.05 ± 0.38 (p < 0.1), but with a larger ratio over East Asia (1.22 ± 0.32; p < 0.05). The obtained observation-model discrepancy (22%) for East Asia is comparable to the uncertainties in Chinese emission inventories (~15%) suggested by recent reports. Our results suggest that by increasing the number of observations around emission sources, satellite instruments like GOSAT can provide a tool for detecting biases in reported emission inventories.

  18. Comparing GOSAT Observations of Localized CO2 Enhancements by Large Emitters with Inventory-Based Estimates

    NASA Technical Reports Server (NTRS)

    Janardanan, Rajesh; Maksyutov, Shamil; Oda, Tomohiro; Saito, Makoto; Kaiser, Johannes W.; Ganshin, Alexander; Stohl, Andreas; Matsunaga, Tsuneo; Yoshida, Yukio; Yokota, Tatsuya

    2016-01-01

    We employed an atmospheric transport model to attribute column-averaged CO2 mixing ratios (XCO2) observed by Greenhouse gases Observing SATellite (GOSAT) to emissions due to large sources such as megacities and power plants. XCO2 enhancements estimated from observations were compared to model simulations implemented at the spatial resolution of the satellite observation footprint (0.1deg × 0.1deg). We found that the simulated XCO2 enhancements agree with the observed over several continental regions across the globe, for example, for North America with an observation to simulation ratio of 1.05 +/- 0.38 (p<0.1), but with a larger ratio over East Asia (1.22 +/- 0.32; p<0.05). The obtained observation-model discrepancy (22%) for East Asia is comparable to the uncertainties in Chinese emission inventories (approx.15%) suggested by recent reports. Our results suggest that by increasing the number of observations around emission sources, satellite instruments like GOSAT can provide a tool for detecting biases in reported emission inventories.

  19. QED Estimates of the 1990-91 Schools and Staffing Survey: Deriving and Comparing QED School Estimates with CCD Estimates. Working Paper Series.

    ERIC Educational Resources Information Center

    Holt, Albert; Scanlon, Brian R.

    This study examines the magnitude of the difference between estimates from the 1990-91 Schools and Staffing Survey (SASS) using a Common Core of Data (CCD) definition of a school and a Quality Education Data (QED) definition of a school. The 1990-91 SASS sample design allows for the development of school and administrator estimates using either…

  20. Vertical Distribution of Denitrification in an Estuarine Sediment: Integrating Sediment Flowthrough Reactor Experiments and Microprofiling via Reactive Transport Modeling▿

    PubMed Central

    Laverman, Anniet M.; Meile, Christof; Van Cappellen, Philippe; Wieringa, Elze B. A.

    2007-01-01

    Denitrifying activity in a sediment from the freshwater part of a polluted estuary in northwest Europe was quantified using two independent approaches. High-resolution N2O microprofiles were recorded in sediment cores to which acetylene was added to the overlying water and injected laterally into the sediment. The vertical distribution of the rate of denitrification supported by nitrate uptake from the overlying water was then derived from the time series N2O concentration profiles. The rates obtained for the core incubations were compared to the rates predicted by a forward reactive transport model, which included rate expression for denitrification calibrated with potential rate measurements obtained in flowthrough reactors containing undisturbed, 1-cm-thick sediment slices. The two approaches yielded comparable rate profiles, with a near-surface, 2- to 3-mm narrow zone of denitrification and maximum in situ rates on the order of 200 to 300 nmol cm−3 h−1. The maximum in situ rates were about twofold lower than the maximum potential rate for the 0- to 1-cm depth interval of the sediment, indicating that in situ denitrification was nitrate limited. The experimentally and model-derived rates of denitrification implied that there was nitrate uptake by the sediment at a rate that was on the order of 50 (± 10) nmol cm−2 h−1, which agreed well with direct nitrate flux measurements for core incubations. Reactive transport model calculations showed that benthic uptake of nitrate at the site is particularly sensitive to the nitrate concentration in the overlying water and the maximum potential rate of denitrification in the sediment. PMID:17071796

  1. Nitrogen removal capability through simultaneous heterotrophic nitrification and aerobic denitrification by Bacillus sp. LY.

    PubMed

    Zhao, Bin; He, Yi Liang; Zhang, Xiao Fan

    2010-04-01

    The heterotrophic nitrification and aerobic denitrification capabilities of Bacillus sp. LY were investigated under the aerobic condition. The results indicate that Bacillus sp. LY is not only a heterotrophic nitrifier, but also an aerobic denitrifier. Experiments were carried out in an attempt to determine and quantify the contribution of heterotrophic nitrification and aerobic denitrification to total N removal. By taking the nitrogen balance under the culture condition of 41.1 mg/L of initial NH(4+)-N at a C/N ratio of 15 in 96 h, 8.0% of the initial NH(4)+-N still remained in the medium in the forms of hydroxylamine, nitrite, nitrate and organic N; 40.5% of NH(4+)-N was converted to biomass and 45.9% of NH(4+)-N was estimated to be finally removed in the formation of N2. This conversion of ammonium to N2 with the intermediate formation of N2O under the aerobic condition was confirmed by gas chromatography. Single step nitrogen removal by simultaneous heterotrophic nitrification and aerobic denitrification has great potential in wastewater treatment. PMID:20450115

  2. A comparative experimental evaluation of uncertainty estimation methods for two-component PIV

    NASA Astrophysics Data System (ADS)

    Boomsma, Aaron; Bhattacharya, Sayantan; Troolin, Dan; Pothos, Stamatios; Vlachos, Pavlos

    2016-09-01

    Uncertainty quantification in planar particle image velocimetry (PIV) measurement is critical for proper assessment of the quality and significance of reported results. New uncertainty estimation methods have been recently introduced generating interest about their applicability and utility. The present study compares and contrasts current methods, across two separate experiments and three software packages in order to provide a diversified assessment of the methods. We evaluated the performance of four uncertainty estimation methods, primary peak ratio (PPR), mutual information (MI), image matching (IM) and correlation statistics (CS). The PPR method was implemented and tested in two processing codes, using in-house open source PIV processing software (PRANA, Purdue University) and Insight4G (TSI, Inc.). The MI method was evaluated in PRANA, as was the IM method. The CS method was evaluated using DaVis (LaVision, GmbH). Utilizing two PIV systems for high and low-resolution measurements and a laser doppler velocimetry (LDV) system, data were acquired in a total of three cases: a jet flow and a cylinder in cross flow at two Reynolds numbers. LDV measurements were used to establish a point validation against which the high-resolution PIV measurements were validated. Subsequently, the high-resolution PIV measurements were used as a reference against which the low-resolution PIV data were assessed for error and uncertainty. We compared error and uncertainty distributions, spatially varying RMS error and RMS uncertainty, and standard uncertainty coverages. We observed that qualitatively, each method responded to spatially varying error (i.e. higher error regions resulted in higher uncertainty predictions in that region). However, the PPR and MI methods demonstrated reduced uncertainty dynamic range response. In contrast, the IM and CS methods showed better response, but under-predicted the uncertainty ranges. The standard coverages (68% confidence interval) ranged from

  3. Estimation of Salivary and Serum Biomarkers in Diabetic and Non Diabetic Patients - A Comparative Study

    PubMed Central

    Ladgotra, Amit; Raj, Seetharamaiah Sunder

    2016-01-01

    Introduction Blood is the gold standard body fluid for diagnosis of Diabetes Mellitus (DM) but saliva offers an alternative to serum as a biological fluid for diagnostic purposes because it contains serum constituents. Aim The study was conducted to estimate and compare serum and salivary glucose, amylase, proteins, calcium and phosphorus levels in DM and healthy subjects and to evaluate whether saliva can be used as a diagnostic fluid in DM patients. Materials and Methods Study consisted of 120 subjects from OPD of Surendera Dental College, Sriganganagar, Rajasthan, India. The study groups were divided into Group I-60 DM patients (Type I & II) and Group II-60 healthy subjects. The saliva and serum samples were collected from each subject and levels of different biochemical parameters were estimated. Results Mean serum level of glucose (211.50 ± 43.82), amylase (79.86 ± 16.23), total proteins (6.65 ± 0.84), calcium (7.17 ± 0.91) and phosphorus (3.68±0.65) as observed in Group I while in Group II, glucose (88.81±11.29), amylase (77.67±14.88), total proteins (6.35±0.76), calcium (7.52±0.97) and phosphorus (3.96 ± 0.91) were noted. Mean salivary level of glucose (14.10±6.99), amylase (1671.42±569.86), total proteins (1.33±1.11), calcium (10.06±2.76) and phosphorus (13.75±4.45) as observed in Group I while in Group II, glucose (5.87± 2.42), amylase (1397.59 ±415.97), total proteins (1.36±0.81), calcium (7.73±2.78) and phosphorus (8.39 ± 1.95) were noted. On comparing values in saliva and serum, among two groups, an insignificant difference (p>0.005) was found between few of them. Conclusion Values regarding blood and salivary biochemical parameters were distinctly different between two groups suggesting salivary parameters can be used as a diagnostic alternative to blood parameters for diabetes mellitus. PMID:27504412

  4. Nitrogen speciation and trends, and prediction of denitrification extent, in shallow US groundwater

    NASA Astrophysics Data System (ADS)

    Hinkle, Stephen R.; Tesoriero, Anthony J.

    2014-02-01

    Uncertainties surrounding nitrogen cycling complicate assessments of the environmental effects of nitrogen use and our understanding of the global carbon-nitrogen cycle. In this paper, we synthesize data from 877 ambient-monitoring wells across the US to frame broad patterns of nitrogen speciation and trends. At these sites, groundwater frequently contains substantial co-occurring NO3- and XSN2 (N2 from denitrification), reflecting active/ongoing denitrification and/or a mixture of undenitrified and denitrified groundwater. NO3- and NH4+ essentially do not co-occur, indicating that the dominant source of NH4+ at these sites likely is not dissimilatory reduction of NO3- to NH4+. Positive correlations of NH4+ with apparent age, CH4, dissolved organic carbon, and indicators of reduced conditions are consistent with NH4+ mobilization from degradation of aquifer organic matter and contraindicate an anthropogenic source of NH4+ for most sites. Glacial aquifers and eastern sand and gravel aquifers generally have lower proportions of NO3- and greater proportions of XSN2 than do fractured rock and karst aquifers and western sand and gravel aquifers. NO3- dominates in the youngest groundwater, but XSN2 increases as residence time increases. Temporal patterns of nitrogen speciation and concentration reflect (1) changing NO3- loads over time, (2) groundwater residence-time controls on NH4+ mobilization from solid phases, and (3) groundwater residence-time controls on denitrification. A simple classification tree using readily available variables (a national coverage of soil water depth, generalized geology) or variables reasonably estimated in many aquifers (residence time) identifies categorical denitrification extent (<10%, 10-50%, and >50%) with 79% accuracy in an independent testing set, demonstrating a predictive application based on the interconnected effects of redox, geology, and residence time.

  5. Submerged bed versus unsaturated flow reactor: A pressurized hydrogenotrophic denitrification reactor as a case study.

    PubMed

    Epsztein, Razi; Beliavski, Michael; Tarre, Sheldon; Green, Michal

    2016-10-01

    The paper compares the main features of a submerged bed reactor (SuBR) with bubbling and recirculation of gas to those of an unsaturated flow reactor (uSFR) with liquid recirculation. A novel pressurized closed-headspace hydrogenotrophic denitrification system characterized by safe and economic utilization of H2 gas was used for the comparison. Under similar conditions, denitrification rates were lower in the SuBR as a result of a lower effective biofilm surface area and overall gas-liquid mass transfer coefficient kLa. Similar values of effluent DOC were achieved for both reactors, although effluent suspended solids concentration of the SuBR were substantially higher. On the other hand, the required cleaning frequency in the SuBR was 2.5 times lower. Moreover, the SuBR is expected to reduce the recirculation energy consumption by 0.35 kWh/m(3) treated. PMID:27424057

  6. Dynamics of methane production, sulfate reduction, and denitrification in a permanently waterlogged alder swamp

    SciTech Connect

    Westermann, P.; Ahring, B.K.

    1987-10-01

    The dynamics of sulfate reduction, methane production, and denitrification were investigated in a permanently waterlogged alder swamp. Molybdate, an inhibitor of sulfate reduction, stimulated methane production in soil slurries, thus suggesting competition for common substrates between sulfate-reducing and methane-producing bacteria. Acetate, hydrogen, and methanol were found to stimulate both sulfate reduction and methane production, while trimethylamine mainly stimulated methane production. Nitrate addition reduced both methane production and sulfate reduction, either as a consequence of competition of poisoning of the bacteria. Sulfate-reducing bacteria were only slightly limited by the availability of electron acceptors, while denitrifying bacteria were seriously limited by low nitrate concentrations. Arrhenius plots of the three processes revealed different responses to temperature changes in the slurries. Methane production was most sensitive to temperature changes, followed by denitrification and sulfate reduction. No significant differences between slope patterns were observed when comparing summer and winter measurements, indicating similar populations regarding temperature responses.

  7. Enhancement of bacterial denitrification for nitrate removal in groundwater with electrical stimulation from microbial fuel cells

    NASA Astrophysics Data System (ADS)

    Zhang, Baogang; Liu, Ye; Tong, Shuang; Zheng, Maosheng; Zhao, Yinxin; Tian, Caixing; Liu, Hengyuan; Feng, Chuanping

    2014-12-01

    Electricity generated from the microbial fuel cell (MFC) is applied to the bioelectrical reactor (BER) directly as electrical stimulation means for enhancement of bacterial denitrification to remove nitrate effectively from groundwater. With maximum power density of 502.5 mW m-2 and voltage outputs ranging from 500 mV to 700 mV, the nitrate removal is accelerated, with less intermediates accumulation, compared with control sets without electrical stimulation. Denitrification bacteria proliferations and activities are promoted as its number and Adenosine-5'-triphosphate (ATP) concentration increased one order of magnitude (3.5 × 107 in per milliliter biofilm solution) and about 1.5 folds, respectively. Effects of electricity from MFCs on enhancement of bacterial behaviors are demonstrated for the first time. These results indicate that MFCs can be applied in the in-situ bioremediation of nitrate polluted groundwater for efficiency improvement.

  8. Dynamics of Methane Production, Sulfate Reduction, and Denitrification in a Permanently Waterlogged Alder Swamp

    PubMed Central

    Westermann, Peter; Ahring, Birgitte Kiær

    1987-01-01

    The dynamics of sulfate reduction, methane production, and denitrification were investigated in a permanently waterlogged alder swamp. Molybdate, an inhibitor of sulfate reduction, stimulated methane production in soil slurries, thus suggesting competition for common substrates between sulfate-reducing and methane-producing bacteria. Acetate, hydrogen, and methanol were found to stimulate both sulfate reduction and methane production, while trimethylamine mainly stimulated methane production. Nitrate addition reduced both methane production and sulfate reduction, either as a consequence of competition or poisoning of the bacteria. Sulfate-reducing bacteria were only slightly limited by the availability of electron acceptors, while denitrifying bacteria were seriously limited by low nitrate concentrations. Arrhenius plots of the three processes revealed different responses to temperature changes in the slurries. Methane production was most sensitive to temperature changes, followed by denitrification and sulfate reduction. No significant differences between slope patterns were observed when comparing summer and winter measurements, indicating similar populations regarding temperature responses. PMID:16347472

  9. Influence of flow velocity and experimental setup on denitrification processes at the laboratory scale

    NASA Astrophysics Data System (ADS)

    Boisson, A.; Aquilina, L.; Bour, O.; De Ridder, J.

    2009-04-01

    In fractured media, physical heterogeneities lead to a large distribution of flow velocities that can partly control chemical reactions involving microbial activity. The aim of this project is to assess influence of fluid flow velocity on chemical reactivity at the laboratory scale. The experimental setup tries to reproduce autotrophic denitrification observed in a cristaline aquifer (Ploemeur; France) where denitrification seems to be enhanced by the exploitation of the aquifer. The experimental setup is based on a column filled with crushed granite from the Ploemeur site. Nitrate-rich water (C=40mg/l) is injected through the column under controlled flow conditions. Nitrate degradation is measured at the outlet and at different sampling plots along the column. These experiments use natural field water without treatment in order to use total available communities instead of one known bacterial community. Typically, the experiments are made during ten days at fluid flow velocities ranging from 0.5 to 5 cm/h. The first point is that the use of uncontrolled bacterial communities in experimental setup can lead to important evolution of the bacterial activity and competition. Results show that this competition is not only related to the experimental conditions but also to the experimental apparatus equipment. Batch experiments show that commonly used polymers (PVC, Tygon, Teflon) can react with nitrates via heterotrophic denitrification within the same time scale as the rock reactivity. Such reactions can even overwhelm the studied reaction. To assess the role of the experimental conditions, we control materials reactivity compared to the relevant time scale of the experiments. The first set of experiments exhibit autotrophic denitrification along the column with variations of the location of the reactive zone during the experiments. Reactivity arises all along the experiments in the first hours but becomes highly localized at the inlet of the column in the following

  10. Anoxia over the western continental shelf of India: bacterial indications of intrinsic nitrification feeding denitrification.

    PubMed

    Krishnan, K P; Fernandes, Sheryl O; Loka Bharathi, P A; Krishna Kumari, L; Nair, Shanta; Pratihary, Anil K; Rao, B Ramalingeswara

    2008-06-01

    Studies on the Arabian Sea coastal anoxia have been of immense interest, but despite its ecological significance there is sparse understanding of the microbes involved. Hence, observations were carried out off Goa (15 degrees 30'N, 72 degrees 40'E to 15 degrees 30'N, 72 degrees 59'E) to understand the processes that mediate the changes in various inorganic nitrogen species in the water column during anoxia. Water column chemistry showed a clear distinct oxic environment in the month of April and anoxic condition in October. Our study based on microbial signatures indicated that oxygen deficit appeared as a well-defined nucleus almost 40 km away from the coast during the oxic period (April) and spreads there after to the entire water column synchronizing with the water chemistry. Striking results of net changes in inorganic nitrogen species in nitrification blocked and unblocked experimental systems show that denitrification is the predominant process in the water column consuming available nitrate ( approximately 0.5 microM) to near zero levels within approximately 72 h of incubation. These observations have been supported by concomitant increase in nitrite concentration ( approximately 4 microM). Similar studies on denitrification-blocked incubations, demonstrate the potential of nitrification to feed denitrification. Nitrification could contribute almost 4.5 microM to the total nitrate pool. It was found that the relation between ammonium and total dissolved inorganic nitrogen (DIN) pool (r=0.98, p<0.001, n=122) was significant compared to the latter with nitrite and nitrate. The occurrence of high ammonium under low phosphate conditions corroborates our observations that ammonium does not appear to be locked under low oxygen regimes. It is suggested that ammonium actively produced by detrital breakdown (ammonification) is efficiently consumed through nitrification process. The three processes in concert viz. ammonification, nitrification and denitrification

  11. Co-denitrification an important process in urine amended grassland soil

    NASA Astrophysics Data System (ADS)

    Selbie, Diana R.; Lanigan, Gary J.; Laughlin, Ronald J.; Di, Hong J.; Moir, James L.; Cameron, Keith C.; Clough, Tim J.; Watson, Catherine J.; Grant, James; Somers, Cathal; Richards, Karl G.

    2016-04-01

    Grazed grassland livestock systems are often associated with considerable losses of reactive forms of nitrogen (N) to the environment such as nitrate leaching, ammonia and nitrous oxide (N2O) emissions. Previous research has focused on losses to air and water due to the health, economic and environmental impacts of reactive N. Di-nitrogen (N2) emissions from soils are still poorly characterized, both in terms of the processes involved and their magnitude, due to methodological constraints. There have been relatively few studies on N2 losses in vivo and even fewer have examined the relative contribution of the different N2 emission pathways. Cow urine was amended with 98 atom% 15N-labelled urea resulting in a urine N concentration of 10 g N L-1 and a 15N enrichment of 45 atom% excess. Two litres of urine was applied to replicated monolith lysimeters at a rate of 100 g N m-2 and N2 and N2O emissions were measured over 123 days using the static chamber technique. Headspace N2 and N2O samples were analyzed for 15N by isotope ratio mass spectrometry in the UC Davis Stable Isotope Facility. Contributions of true denitrification and co-denitrification to N2 emissions were calculated using the 15N flux method. The study found that N2 emissions accounted for 95% of gaseous N loss, with 55.8 g N m-2 emitted as N2 by the process of co-denitrification, compared to only 1.1 g N m-2 from conventional denitrification. This study highlights the large N2 fluxes and the importance of co-denitrification in contributing to N dynamics in urine amended grassland soil. Reference Selbie D.R., Lanigan G.J., Laughlin R.J., Di H.J., Moir J.L., Cameron K.C., Clough T.J., Watson C.J., Grant J., Sommers C. & Richards K.G. (2015) Confirmation of co-denitrification in grazed grassland, Scientific Reports 5:17361 1-5

  12. Estimated performance of solar PV and wind turbine systems compared to coincident electrical demand in Minnesota

    SciTech Connect

    Artig, R.

    1995-10-01

    The Minnesota Department of Public Service (department), with the cooperation of Northern States Power (NSP) and US Department of Energy, is making a detailed study of wind and solar resources in the Buffalo Ridge area of southwestern Minnesota. The purpose of the study is to determine the viability of using a combination of wind and solar generation facilities to help meet electrical demand in the region. Through the Solar/Wind Study, five monitoring sites have been established to collect solar radiation and temperature data as well as to record wind speed and direction information at multiple elevations. In this paper, the data from the first year of the Solar/Wind Study are used to directly compare the projected hourly production of electricity from the wind and solar resources to hourly electrical demand. This study compares the potential electrical production from these renewable resources concurrent with peak or near peak occurrences in electrical demand. The electrical demand information used in this study is from two utilities: NSP, a utility that supplies electricity to a combination of urban residential, commercial, and industrial customers; and Cooperative Power (CP), which provides power primarily to suburban and rural residential customers. Estimates of the performance of solar PV systems were made using PVFORM, a simulation program from Sandia National Laboratories. Analysis of first year data indicates that the availability of electricity generated from a combination of solar and wind resources matches period of high peak demand for Northern States Power. The value of adding wind and solar generated electricity to the utility`s resource mix merits further investigation. The match between solar and wind power availability and Cooperative Power`s peak demand period is not apparent, but here, too, further study is needed.

  13. Comparing and evaluating model estimates of background ozone in surface air over North America

    NASA Astrophysics Data System (ADS)

    Oberman, J.; Fiore, A. M.; Lin, M.; Zhang, L.; Jacob, D. J.; Naik, V.; Horowitz, L. W.

    2011-12-01

    Tropospheric ozone adversely affects human health and vegetation, and is thus a criteria pollutant regulated by the U.S. Environmental Protection Agency (EPA) under the National Ambient Air Quality Standard (NAAQS). Ozone is produced in the atmosphere via photo-oxidation of volatile organic compounds (VOCs) and carbon monoxide (CO) in the presence of nitrogen oxides (NOx). The present EPA approach considers health risks associated with exposure to ozone enhancement above the policy-relevant background (PRB), which is currently defined as the surface concentration of ozone that would exist without North American anthropogenic emissions. PRB thus includes production by natural precursors, production by precursors emitted on foreign continents, and transport of stratospheric ozone into surface air. As PRB is not an observable quantity, it must be estimated using numerical models. We compare PRB estimates for the year 2006 from the GFDL Atmospheric Model 3 (AM3) chemistry-climate model (CCM) and the GEOS-Chem (GC) chemical transport model (CTM). We evaluate the skill of the models in reproducing total surface ozone observed at the U.S. Clean Air Status and Trends Network (CASTNet), dividing the stations into low-elevation (< 1.5 km in altitude, primarily eastern) and high-elevation (> 1.5 km in altitude, all western) subgroups. At the low-elevation sites AM3 estimates of PRB (38±9 ppbv in spring, 27±9 ppbv in summer) are higher than GC (27±7 ppbv in spring, 21±8 ppbv in summer) in both seasons. Analysis at these sites is complicated by a positive bias in AM3 total ozone with respect to the observed total ozone, the source of which is yet unclear. At high-elevation sites, AM3 PRB is higher in the spring (47±8 ppbv) than in the summer (33±8 ppbv). In contrast, GC simulates little seasonal variation at high elevation sites (39±5 ppbv in spring vs. 38±7 ppbv in summer). Seasonal average total ozone at these sites was within 4 ppbv of the observations for both

  14. Estimation of AM fungal colonization - Comparability and reliability of classical methods.

    PubMed

    Füzy, Anna; Biró, Ibolya; Kovács, Ramóna; Takács, Tünde

    2015-12-01

    The characterization of mycorrhizal status in hosts can be a good indicator of symbiotic associations in inoculation experiments or in ecological research. The most common microscopic-based observation methods, such as (i) the gridline intersect method, (ii) the magnified intersections method and (iii) the five-class system of Trouvelot were tested to find the most simple, easily executable, effective and objective ones and their appropriate parameters for characterization of mycorrhizal status. In a pot experiment, white clover (Trifolium repens L.) host plant was inoculated with 6 (BEG144; syn. Rhizophagus intradices) in pumice substrate to monitor the AMF colonization properties during host growth. Eleven (seven classical and four new) colonization parameters were estimated by three researchers in twelve sampling times during plant growth. Variations among methods, observers, parallels, or individual plants were determined and analysed to select the most appropriate parameters and sampling times for monitoring. The comparability of the parameters of the three methods was also tested. As a result of the experiment classical parameters were selected for hyphal colonization: colonization frequency in the first stage or colonization density in the later period, and arbuscular richness of roots. A new parameter was recommended to determine vesicule and spore content of colonized roots at later stages of symbiosis. PMID:26689879

  15. Heterotrophic denitrification of aquaculture effluent using fluidized sand biofilters

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The ability to consistently and cost-effectively reduce nitrate-nitrogen loads in effluent from recirculating aquaculture systems would enhance the industry's environmental stewardship and allow improved facility proximity to large markets in sensitive watersheds. Heterotrophic denitrification techn...

  16. Nitrification and denitrification gene abundances in swine wastewater anaerobic lagoons

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Although anaerobic lagoons are used globally for livestock waste treatment, their detailed microbial cycling of nitrogen is only beginning to become understood. Within this cycling, nitrification can be performed by organisms which produce the enzyme ammonia monooxygenase (AMO). For denitrification,...

  17. Evidence of anoxic methane oxidation coupled to denitrification.

    PubMed

    Islas-Lima, S; Thalasso, F; Gómez-Hernandez, J

    2004-01-01

    Denitrification using methane as sole electron donor under anoxic condition was investigated. Sludge produced by a denitrifying reactor using acetate as electron donor was put in contact with methane at partial pressures from 1.8 to 35.7kPa. Nitrate depletion and gaseous nitrogen production were measured. The denitrification rate was independent of the methane partial pressure when superior or equal to 8.8kPa. The nitrate depletion was asymptotic. A denitrification rate of 0.25g NO(3)(-)-Ng(-1) VSSd(-1) was observed at the onset of culturing, followed by a slower and lineal denitrification rate of 4.9x10(-3)g NO(3)(-)-Ng(-1) VSSd(-1). Abiotic nitrate removal or the availability of another carbon source were discarded from control experiments made in the absence of methane or using sterilized inoculum. PMID:14630098

  18. Denitrification in Gram-positive bacteria: an underexplored trait.

    PubMed

    Verbaendert, Ines; De Vos, Paul; Boon, Nico; Heylen, Kim

    2011-01-01

    Denitrifying organisms are essential in removing fixed nitrogen pollutants from ecosystems (e.g. sewage sludge). They can be detrimental (e.g. for agricultural soil) and can also produce the greenhouse gas N2O (nitrous oxide). Therefore a more comprehensive understanding of this process has become increasingly important regarding its global environmental impact. Even though bacterial genome sequencing projects may reveal new data, to date the denitrification abilities and features in Gram-positive bacteria are still poorly studied and understood. The present review evaluates current knowledge on the denitrification trait in Gram-positive bacteria and addresses the likely existence of unknown denitrification genes. In addition, current molecular tools to study denitrification gene diversity in pure cultures and environmental samples seem to be highly biased, and additional novel approaches for the detection of denitrifying (Gram-positive) bacteria appear to be crucial in re-assessing the real diversity of denitrifiers. PMID:21265783

  19. One method is not enough to determine denitrification in a Histic Gleysol following different grassland renovation techniques in Northwest Germany

    NASA Astrophysics Data System (ADS)

    Well, Reinhard; Buchen, Caroline; Eschenbach, Wolfram; Lewicka-Szczebak, Dominika; Helfrich, Mirjam; Gensior, Andreas; Flessa, Heinz

    2014-05-01

    Grassland renovation by reseeding is a common practices to improve productivity, but knowledge on enhanced nitrate leaching and N2O emission due to disturbance during associated soil tillage is scarce. Denitrification in hydromorphic soils under agricultural management is potentially extremely high due to the coincidence of high nitrate concentrations, labile organic carbon and oxygen depletion during extended periods of water saturation close to the soil surface (Well et al. 2003; Well et al. 2005). We investigated the impact of grassland renewal or conversion to arable land on greenhouse gas fluxes and N losses in field plot experiments. One of the two sites is a hydromorphic soil (Histic Gleysol) rich in organic C, with groundwater level always within the rooting zone and close to the surface during winter. Assessment of the N budget to estimate enhanced N mineralization following grassland renewal as well as associated N leaching is complicated by potentially complete NO3- consumption via denitrification. Robust estimation on denitrification losses at this site is crucial to assess the impact of grassland renewal on its N dynamics and budget. One aim of this study is to determine denitrification in the surface and subsoil in order to close the N budget. We apply five approaches to investigate spatial and temporal dynamics of denitrification and will report first results. (1) N balance approach: The N budget is obtained by weekly measurement of N2O fluxes and mineral N in the top soil, mineral N twice a year at 0 to 90 cm depth, N uptake, N fertilization and modeling N leaching based on mineral N and hydrological model data. Unaccounted N is attributed to possible denitrification. (2) Isotopologue approach: δ18O, average δ15N and 15N site preference of N2O as well as δ15N and δ18O of NO3- are measured at times to estimate N2O reduction to N2 in the topsoil during periods of unsaturated conditions using the N2O isotope fractionation approach (Lewicka

  20. Denitrification and a nitrogen budget of created riparian wetlands.

    PubMed

    Batson, Jacqulyn A; Mander, Ulo; Mitsch, William J

    2012-01-01

    Riparian wetland creation and restoration have been proposed to mediate nitrate-nitrogen (NO-N) pollution from nonpoint agricultural runoff. Denitrification by anaerobic microbial communities in wetland soils is believed to be one of the main sinks for NO-N as it flows through wetlands. Denitrification rates were quantified using an in situ acetylene inhibition technique at 12 locations in three wetland/riverine sites at the Olentangy River Wetland Research Park, Columbus, Ohio for 1 yr. Sites included two created flow-through experimental wetlands and one bottomland forest/river-edge site. Points were spatially distributed at inflows, center, and outflows of the two wetlands to include permanently flooded open water, intermittently flooded transitions, and upland. Annual denitrification rates (median [mean]) were significantly higher ( < 0.001) in permanently flooded zones of the wetlands (266 [415] μg NO-N m h) than in shallower transition zones (58 [37.5] μg NO-N m h). Median wetland transition zone denitrification rates did not differ significantly ( ≥ 0.05) from riverside or upland sites. Denitrification rates peaked in spring; for the months of April through June, median denitrification rates ranged from 240 to 1010 μg NO-N m h in the permanently flooded zones. A N mass balance analysis showed that surface water flux of N was reduced by 57% as water flowed through the wetland, but only about 3.5% of the N inflow was permanently removed through denitrification. Most N was probably lost through groundwater seepage. Comparison with denitrification rates measured previously in these wetlands suggests that these rates have remained steady over the past 4 to 5 yr. PMID:23128759

  1. Oxygen isotope fractionation during N2O production by soil denitrification

    NASA Astrophysics Data System (ADS)

    Lewicka-Szczebak, Dominika; Dyckmans, Jens; Kaiser, Jan; Marca, Alina; Augustin, Jürgen; Well, Reinhard

    2016-02-01

    The isotopic composition of soil-derived N2O can help differentiate between N2O production pathways and estimate the fraction of N2O reduced to N2. Until now, δ18O of N2O has been rarely used in the interpretation of N2O isotopic signatures because of the rather complex oxygen isotope fractionations during N2O production by denitrification. The latter process involves nitrate reduction mediated through the following three enzymes: nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR). Each step removes one oxygen atom as water (H2O), which gives rise to a branching isotope effect. Moreover, denitrification intermediates may partially or fully exchange oxygen isotopes with ambient water, which is associated with an exchange isotope effect. The main objective of this study was to decipher the mechanism of oxygen isotope fractionation during N2O production by soil denitrification and, in particular, to investigate the relationship between the extent of oxygen isotope exchange with soil water and the δ18O values of the produced N2O. In our soil incubation experiments Δ17O isotope tracing was applied for the first time to simultaneously determine the extent of oxygen isotope exchange and any associated oxygen isotope effect. We found that N2O formation in static anoxic incubation experiments was typically associated with oxygen isotope exchange close to 100 % and a stable difference between the 18O / 16O ratio of soil water and the N2O product of δ18O(N2O / H2O) = (17.5 ± 1.2) ‰. However, flow-through experiments gave lower oxygen isotope exchange down to 56 % and a higher δ18O(N2O / H2O) of up to 37 ‰. The extent of isotope exchange and δ18O(N2O / H2O) showed a significant correlation (R2 = 0.70, p < 0.00001). We hypothesize that this observation was due to the contribution of N2O from another production process, most probably fungal denitrification. An oxygen isotope fractionation model was used to test various scenarios with

  2. A network biology approach to denitrification in Pseudomonas aeruginosa

    DOE PAGESBeta

    Arat, Seda; Bullerjahn, George S.; Laubenbacher, Reinhard

    2015-02-23

    Pseudomonas aeruginosa is a metabolically flexible member of the Gammaproteobacteria. Under anaerobic conditions and the presence of nitrate, P. aeruginosa can perform (complete) denitrification, a respiratory process of dissimilatory nitrate reduction to nitrogen gas via nitrite (NO₂), nitric oxide (NO) and nitrous oxide (N₂O). This study focuses on understanding the influence of environmental conditions on bacterial denitrification performance, using a mathematical model of a metabolic network in P. aeruginosa. To our knowledge, this is the first mathematical model of denitrification for this bacterium. Analysis of the long-term behavior of the network under changing concentration levels of oxygen (O₂), nitrate (NO₃),more » and phosphate (PO₄) suggests that PO₄ concentration strongly affects denitrification performance. The model provides three predictions on denitrification activity of P. aeruginosa under various environmental conditions, and these predictions are either experimentally validated or supported by pertinent biological literature. One motivation for this study is to capture the effect of PO₄ on a denitrification metabolic network of P. aeruginosa in order to shed light on mechanisms for greenhouse gas N₂O accumulation during seasonal oxygen depletion in aquatic environments such as Lake Erie (Laurentian Great Lakes, USA). Simulating the microbial production of greenhouse gases in anaerobic aquatic systems such as Lake Erie allows a deeper understanding of the contributing environmental effects that will inform studies on, and remediation strategies for, other hypoxic sites worldwide.« less

  3. A Network Biology Approach to Denitrification in Pseudomonas aeruginosa

    PubMed Central

    Arat, Seda; Bullerjahn, George S.; Laubenbacher, Reinhard

    2015-01-01

    Pseudomonas aeruginosa is a metabolically flexible member of the Gammaproteobacteria. Under anaerobic conditions and the presence of nitrate, P. aeruginosa can perform (complete) denitrification, a respiratory process of dissimilatory nitrate reduction to nitrogen gas via nitrite (NO2), nitric oxide (NO) and nitrous oxide (N2O). This study focuses on understanding the influence of environmental conditions on bacterial denitrification performance, using a mathematical model of a metabolic network in P. aeruginosa. To our knowledge, this is the first mathematical model of denitrification for this bacterium. Analysis of the long-term behavior of the network under changing concentration levels of oxygen (O2), nitrate (NO3), and phosphate (PO4) suggests that PO4 concentration strongly affects denitrification performance. The model provides three predictions on denitrification activity of P. aeruginosa under various environmental conditions, and these predictions are either experimentally validated or supported by pertinent biological literature. One motivation for this study is to capture the effect of PO4 on a denitrification metabolic network of P. aeruginosa in order to shed light on mechanisms for greenhouse gas N2O accumulation during seasonal oxygen depletion in aquatic environments such as Lake Erie (Laurentian Great Lakes, USA). Simulating the microbial production of greenhouse gases in anaerobic aquatic systems such as Lake Erie allows a deeper understanding of the contributing environmental effects that will inform studies on, and remediation strategies for, other hypoxic sites worldwide. PMID:25706405

  4. Denitrification in marl and peat sediments in the Florida everglades.

    PubMed

    Gordon, A S; Cooper, W J; Scheidt, D J

    1986-11-01

    The potential for denitrification in marl and peat sediments in the Shark River Slough in the Everglades National Park was determined by the acetylene blockage assay. The influence of nitrate concentration on denitrification rate and N(2)O yield from added nitrate was examined. The effects of added glucose and phosphate and of temperature on the denitrification potential were determined. The sediments readily denitrified added nitrate. N(2)O was released from the sediments both with and without added acetylene. The marl sediments had higher rates than the peat on every date sampled. Denitrification was nitrate limited; however, the yields of N(2)O amounted to only 10 to 34% of the added nitrate when 100 muM nitrate was added. On the basis of measured increases in ammonium concentration, it appears that the balance of added nitrate may be converted to ammonium in the marl sediment. The sediment temperature at the time of sampling greatly influenced the denitrification potential (15-fold rate change) at the marl site, indicating that either the number or the specific activity of the denitrifiers changed in response to temperature fluctuations (9 to 25 degrees C) in the sediment. It is apparent from this study that denitrification in Everglades sediments is not an effective means of removing excess nitrogen which may be introduced as nitrate into the ecosystem with supply water from the South Florida watershed and that sporadic addition of nitrate-rich water may lead to nitrous oxide release from these wetlands. PMID:16347228

  5. A network biology approach to denitrification in Pseudomonas aeruginosa.

    PubMed

    Arat, Seda; Bullerjahn, George S; Laubenbacher, Reinhard

    2015-01-01

    Pseudomonas aeruginosa is a metabolically flexible member of the Gammaproteobacteria. Under anaerobic conditions and the presence of nitrate, P. aeruginosa can perform (complete) denitrification, a respiratory process of dissimilatory nitrate reduction to nitrogen gas via nitrite (NO2), nitric oxide (NO) and nitrous oxide (N2O). This study focuses on understanding the influence of environmental conditions on bacterial denitrification performance, using a mathematical model of a metabolic network in P. aeruginosa. To our knowledge, this is the first mathematical model of denitrification for this bacterium. Analysis of the long-term behavior of the network under changing concentration levels of oxygen (O2), nitrate (NO3), and phosphate (PO4) suggests that PO4 concentration strongly affects denitrification performance. The model provides three predictions on denitrification activity of P. aeruginosa under various environmental conditions, and these predictions are either experimentally validated or supported by pertinent biological literature. One motivation for this study is to capture the effect of PO4 on a denitrification metabolic network of P. aeruginosa in order to shed light on mechanisms for greenhouse gas N2O accumulation during seasonal oxygen depletion in aquatic environments such as Lake Erie (Laurentian Great Lakes, USA). Simulating the microbial production of greenhouse gases in anaerobic aquatic systems such as Lake Erie allows a deeper understanding of the contributing environmental effects that will inform studies on, and remediation strategies for, other hypoxic sites worldwide. PMID:25706405

  6. Comparing new and conventional methods to estimate benthic algal biomass and composition in freshwaters.

    PubMed

    Kahlert, Maria; McKie, Brendan G

    2014-11-01

    We compared conventional microscope-based methods for quantifying biomass and community composition of stream benthic algae with output obtained for these parameters from a new instrument (the BenthoTorch), which measures fluorescence of algal pigments in situ. Benthic algae were studied in 24 subarctic oligotrophic (1.7-26.9, median 7.2 μg total phosphorus L(-1)) streams in Northern Sweden. Readings for biomass of the total algal mat, quantified as chlorophyll a, did not differ significantly between the BenthoTorch (median 0.52 μg chlorophyll a cm(-2)) and the conventional method (median 0.53 μg chlorophyll a cm(-2)). However, quantification of community composition of the benthic algal mat obtained using the BenthoTorch did not match those obtained from conventional methods. The BenthoTorch indicated a dominance of diatoms, whereas microscope observations showed a fairly even distribution between diatoms, blue-green algae (mostly nitrogen-fixing) and green algae (mostly large filamentous), and also detected substantial biovolumes of red algae in some streams. These results most likely reflect differences in the exact parameters quantified by the two methods, as the BenthoTorch does not account for variability in cell size and the presence of non-chlorophyll bearing biomass in estimating the proportion of different algal groups, and does not distinguish red algal chlorophyll from that of other algal groups. Our findings suggest that the BenthoTorch has utility in quantifying biomass expressed as μg chlorophyll a cm(-2), but its output for the relative contribution of different algal groups to benthic algal biomass should be used with caution. PMID:25277172

  7. Comparing Parameter Estimation Techniques for an Electrical Power Transformer Oil Temperature Prediction Model

    NASA Technical Reports Server (NTRS)

    Morris, A. Terry

    1999-01-01

    This paper examines various sources of error in MIT's improved top oil temperature rise over ambient temperature model and estimation process. The sources of error are the current parameter estimation technique, quantization noise, and post-processing of the transformer data. Results from this paper will show that an output error parameter estimation technique should be selected to replace the current least squares estimation technique. The output error technique obtained accurate predictions of transformer behavior, revealed the best error covariance, obtained consistent parameter estimates, and provided for valid and sensible parameters. This paper will also show that the output error technique should be used to minimize errors attributed to post-processing (decimation) of the transformer data. Models used in this paper are validated using data from a large transformer in service.

  8. Nonparametric estimation of the survival function for ordered multivariate failure time data: A comparative study.

    PubMed

    Meira-Machado, Luís; Sestelo, Marta; Gonçalves, Andreia

    2016-05-01

    In longitudinal studies of disease, patients may experience several events through a follow-up period. In these studies, the sequentially ordered events are often of interest and lead to problems that have received much attention recently. Issues of interest include the estimation of bivariate survival, marginal distributions, and the conditional distribution of gap times. In this work, we consider the estimation of the survival function conditional to a previous event. Different nonparametric approaches will be considered for estimating these quantities, all based on the Kaplan-Meier estimator of the survival function. We explore the finite sample behavior of the estimators through simulations. The different methods proposed in this article are applied to a dataset from a German Breast Cancer Study. The methods are used to obtain predictors for the conditional survival probabilities as well as to study the influence of recurrence in overall survival. PMID:26455826

  9. The effects of fulvic acid on microbial denitrification: promotion of NADH generation, electron transfer, and consumption.

    PubMed

    Li, Mu; Su, Yinglong; Chen, Yinguang; Wan, Rui; Zheng, Xiong; Liu, Kun

    2016-06-01

    The heterotrophic denitrification requires the participation of electrons which are derived from direct electron donor (usually nicotinamide adenine dinucleotide (NADH)), and the electrons are transferred via electron transport system in denitrifiers and then consumed by denitrifying enzymes. Despite the reported electron transfer ability of humic substances (HS), the influences of fulvic acid (FA), an ubiquitous major component of HS, on promoting NADH generation, electron transfer, and consumption in denitrification process have never been reported. The presence of FA, compared with the control, was found not only significantly improved the total nitrogen (TN) removal efficiency (99.9 % versus 74.8 %) but remarkably reduced the nitrite accumulation (0.2 against 43.8 mg/L) and N2O emission (0.003 against 0.240 mg nitrogen/mg TN removed). The mechanisms study showed that FA increased the metabolism of carbon source via glycolysis and tricarboxylic acid (TCA) cycle pathways to produce more available NADH. FA also facilitated the electron transfer activities from NADH to denitrifying enzymes via complex I and complex III in electron transport system, which improved the reduction of nitrate and accelerated the transformations of nitrite and N2O, and lower nitrite and N2O accumulations were therefore observed. In addition, the consumption of electrons in denitrification was enhanced due to FA stimulating the synthesis and the catalytic activity of key denitrifying enzymes, especially nitrite reductase and N2O reductase. It will provide an important new insight into the potential effect of FA on microbial denitrification metabolism process and even nitrogen cycle in nature niches. PMID:26894403

  10. Large-scale controls on potential respiration and denitrification in riverine floodplains

    PubMed Central

    Welti, Nina; Bondar-Kunze, Elisabeth; Singer, Gabriel; Tritthart, Michael; Zechmeister-Boltenstern, Sophie; Hein, Thomas; Pinay, Gilles

    2012-01-01

    Restoration measures of deteriorated river ecosystems generally aim at increasing the spatial heterogeneity and connectivity of these systems in order to increase biodiversity and ecosystem stability. While this is believed to benefit overall ecological integrity, consequences of such restoration projects on biogeochemical processes per se (i.e. ecosystem functioning) in fluvial systems are rarely considered. We address these issues by evaluating the characteristics of surface water connection between side arms and the main river channel in a former braided river section and the role and degree of connectivity (i.e. duration of surface water connection) on the sediment biogeochemistry. We hypothesized that potential respiration and denitrification would be controlled by the degree of hydrological connectivity, which was increased after floodplain restoration. We measured potential microbial respiration (SIR) and denitrification (DEA) and compared a degraded floodplain section of the Danube River with a reconnected and restored floodplain in the same river section. Re-establishing surface water connection altered the controls on sediment microbial respiration and denitrification ultimately impacting potential microbial activities. Meta-variables were created to characterize the effects of hydrology, morphology, and the available carbon and nutrient pools on potential microbial processing. Mantel statistics and path analysis were performed and demonstrate a hierarchy where the effects of hydrology on the available substrates and microbial processing are mediated by the morphology of the floodplain. In addition, these processes are highest in the least connected sites. Surface water connection, mediated by morphology regulates the potential denitrification rate and the ratio of N2O to N2 emissions, demonstrating the effects of restoration in floodplain systems. PMID:23565037

  11. An additional simple denitrification bioreactor using packed gel envelopes applicable to industrial wastewater treatment.

    PubMed

    Morita, Masahiko; Uemoto, Hiroaki; Watanabe, Atsushi

    2007-08-15

    A simple denitrification bioreactor for nitrate-containing wastewater without organic compounds was developed. This bioreactor consisted of packed gel envelopes in a single tank. Each envelope comprised two plates of gels containing Paracoccus denitrificans cells with an internal space between the plates. As an electron donor for denitrification, ethanol was injected into the internal space and not directly into the wastewater. P. denitrificans cells in the gel reduced nitrate to nitrogen gas by using the injected ethanol. Nitrate-containing desulfurization wastewater derived from a coal-fired thermal power plant was continuously treated with 20 packed gel envelopes (size, 1,000 x 900 x 12 mm; surface area, 1.44 m(2)) in a reactor tank (volume 1.5 m(3)). When the total nitrogen concentration in the inflow was around 150 mg-N x L(-1), the envelopes removed approximately 60-80% of the total nitrogen, and the maximum nitrogen removal rate was 5.0 g-N x day(-1) per square meter of the gel surface. This value corresponded to the volumetric nitrogen removal performance of 0.109 kg-N x m(-3) x day(-1). In each envelope, a high utilization efficiency of the electron donor was attained, although more than the double amount of the electron donor was empirically injected in the present activated sludge system to achieve denitrification when compared with the theoretical value. The bioreactor using the envelopes would be extremely effective as an additional denitrification system because these envelopes can be easily installed in the vacant spaces of preinstalled water treatment systems, without requiring additional facilities for removing surplus ethanol and sludge. PMID:17252606

  12. Biological denitrification of brine: the effect of compatible solutes on enzyme activities and fatty acid degradation.

    PubMed

    Cyplik, Paweł; Piotrowska-Cyplik, Agnieszka; Marecik, Roman; Czarny, Jakub; Drozdzyńska, Agnieszka; Chrzanowski, Łukasz

    2012-09-01

    The effect of the addition of compatible solutes (ectoine and trehalose) on the denitrification process of saline wastewater was studied. In saline wastewater, it was observed that the initial concentration of nitrates was 500 mg N l⁻¹. A fatty substance isolated from oiled bleaching earth (waste of vegetable oil refining process) was used as a source of carbon.The consortium, which was responsible for the denitrification process originated from the wastewater of the vegetable oil industry. The consortium of microorganisms was identified by the use of restriction fragment length polymorphism of 16S rRNA gene amplicons and sequencing techniques. It was noted that ectoine affects significantly the activity of lipase and nitrate reductase, and resulted in faster denitrification compared to saline wastewater with the addition of trehalose or control saline wastewater (without compatible solutes). It was observed that relative enzyme activities of lipase and nitrate reductase increased by 32 and 35%, respectively, in the presence of 1 mM ectoine. This resulted in an increase in specific nitrate reduction rate in the presence of 1 mM ectoine to 5.7 mg N g⁻¹ VSS h⁻¹, which was higher than in the absence of ectoine (3.2 mg N g⁻¹ VSS h⁻¹). The addition of trehalose did not have an effect on nitrate removals. Moreover, it was found that trehalose was used up completely by bacteria as a source of carbon in the denitrification process. The fatty acids were biodegraded by 74% in the presence of 1 mM ectoine. PMID:22286267

  13. [Effect of C/N ratio on nitrous oxide production during denitrification with different electron acceptors].

    PubMed

    Shang, Hui-Lai; Peng, Yong-Zhen; Zhang, Jing-Rong; Wang, Shu-Ying

    2009-07-15

    The experiment investigated the nitrous oxide production under different C/N ratios during denitrification, taking nitrate and nitrite as electron acceptor respectively. Ethanol was selected as carbon source. The C/N ratios were 0, 1.2, 2.4, 3.5, 5.0 and 20 when nitrate was taken as electron acceptor and C/N ratios 0, 1.8, 2.4, 3.0, 4.3, 5.2, 6.6, 20.6 when electron acceptor was nitrite. The results indicated that: the optimum C/N ratio was 3.0 taking nitrite as electron acceptor and the N2O production was 0.044 mg x L(-1); the optimum C/N ratio was 5.0 taking nitrate as electron acceptor and the N2O production was 0.135 mg x L(-1) which was 3 times higher than that of nitrite as electron acceptor. Though the electron acceptor changed, the trend of N2O production was similar: when carbon source was badly insufficient, the production of N2O and denitrification rate were both quite small; the N2O production increased with the increasing of the quantity of carbon source; when the carbon source was excessive, the N2O production sharply raised. Consequently, compared to complete nitrification and denitrification, short-cut nitrification and denitrification could save 40% carbon source. Moreover, controlling C/N = 3 could reduce the production of N2O in short-cut nitrification. PMID:19775000

  14. Stimulation of Autotrophic Denitrification by Intrusions of the Bosporus Plume into the Anoxic Black Sea

    PubMed Central

    Fuchsman, Clara A.; Murray, James W.; Staley, James T.

    2012-01-01

    Autotrophic denitrification was measured in the southwestern coastal Black Sea, where the Bosporus Plume injects oxidized chemical species (especially O2 and NO3−) into the oxic, suboxic, and anoxic layers. Prominent oxygen intrusions caused an overlap of NOx− and sulfide at the same station where autotrophic denitrification activity was detected with incubation experiments. Several bacteria that have been proposed to oxidize sulfide in other low oxygen environments were found in the Black Sea including SUP05, Sulfurimonas, Arcobacter, and BS-GSO2. Comparison of TRFLP profiles from this mixing zone station and the Western Gyre (a station not affected by the Bosporus Plume) indicate the greatest relative abundance of Sulfurimonas and Arcobacter at the appropriate depths at the mixing zone station. The autotrophic gammaproteobacterium BS-GSO2 correlated with ammonium fluxes rather than with sulfide fluxes and the maximum in SUP05 peak height was shallower than the depths where autotrophic denitrification was detected. Notably, anammox activity was not detected at the mixing zone station, though low levels of DNA from the anammox bacteria Candidatus Scalindua were present. These results provide evidence for a modified ecosystem with different N2 production pathways in the southwest coastal region compared to that found in the rest of the Black Sea. Moreover, the same Sulfurimonas phylotype (BS139) was previously detected on >30 μm particles in the suboxic zone of the Western Gyre along with DNA of potential sulfate reducers, so it is possible that particle-attached autotrophic denitrification may be an overlooked N2 production pathway in the central Black Sea as well. PMID:22826706

  15. [Advanced nitrogen removal using innovative denitrification biofilter with sustained-release carbon source material].

    PubMed

    Tang, Lei; Li, Peng; Zuo, Jian-e; Yuan, Lin; Li, Zai-xing

    2013-09-01

    An innovative denitrification biofilter was developed with polycaprolactone (PCL) as the carbon source and biofilm carrier. The performance of nitrogen removal was investigated with biologically treated effluent from secondary clarifier, and the results indicated that a maximum TN removal efficiency of 98.9% was achieved under the following conditions: influent total nitrogen (TN) concentration 30.0 mg x L(-1), denitrification load 54.0 mg (L x h)(-1), operating temperature 20. 1-22.0 degrees C, hydraulic retention time 0. 5 h; the total organic carbon (TOC) in effluent was 6.5-8.4 mg x L(-1), which was increased by 2.0-3.0 mg x L(-1) compared with that in the influent; the suspended solids (SS) concentration was less than 4.0 mg x L(-1) during operation; nearly 84.2% of the total released organic carbon which was used as electron donor in the denitrification process, was derived in the presence of microbes. The surface of the PCL pellets was observed by scanning electron microscope (SEM), it was shown that thick biofilm was formed on the surface of pellets, and the main microbial species were Bacillus and Trichobacteria. PMID:24289000

  16. Comparative analysis of numerical estimation methods of epithelial nerve fibers using tissue sections.

    PubMed

    Hilliges, M; Johansson, O

    1999-01-01

    The proper assessment of neuron numbers in the nervous system during physiological and pathological conditions, as well as following various treatments, has always been an important part of neuroscience. The present paper evaluates three methods for numerical estimates of nerves in epithelium: I) unbiased nerve fiber profile and nerve fiber fragment estimation methods, II) the traditional method of counting whole nerve fibers, and III) the nerve fiber estimation method. In addition, an unbiased nerve length estimation method was evaluated. Of these four methods, the nerve length per volume method was theoretically optimal, but more time-consuming than the others. The numbers obtained with the methods of nerve fiber profile, nerve fragment and nerve fiber estimation are dependent on the thickness of the epithelium and the sections as well as certain shape factors of the counted fiber. However for those, the actual counting can readily be performed in the microscope and is consequently quick and relatively inexpensive. The statistical analysis showed a very good correlation (R > 0.96) between the three numerical methods, meaning that basically any method could be used. However, dependent on theoretical and practical considerations and the correlation statistics, it may be concluded that the nerve fiber profile or fragment estimation methods should be employed if differences in epithelial and section thickness and the nerve fibers shape factors can be controlled. Such drawbacks are not inherent in the nerve length estimation method and, thus, it can generally be applied. PMID:10197065

  17. Controls on Mixing-Dependent Denitrification in Hyporheic Zones

    NASA Astrophysics Data System (ADS)

    Hester, E. T.; Young, K. I.; Widdowson, M. A.

    2013-12-01

    Interaction of surface water and groundwater in hyporheic sediments of river systems is known to create unique biogeochemical conditions that can attenuate contaminants flowing downstream. Oxygen, carbon, and the contaminants themselves (e.g., excess nitrate) often advect together through the hyporheic zone from sources in surface water. However, the ability of the hyporheic zone to attenuate contaminants in upwelling groundwater plumes as they exit to rivers is less known. Such reactions may be more dependent on mixing of carbon and oxygen sources from surface water with contaminants from deeper groundwater. We simulated hyporheic flow cells and upwelling groundwater together with mixing-dependent denitrification of an upwelling nitrate plume in shallow riverbed sediments using MODFLOW and SEAM3D. For our first set of model scenarios, we set biogeochemical boundary conditions to be consistent with situations where only mixing-dependent denitrification occurred within the model domain. This occurred where dissolved organic carbon (DOC) advecting from surface water through hyporheic flow cells meets nitrate upwelling from deeper groundwater. This would be common where groundwater is affected by septic systems which contribute nitrate that upwells into streams that do not have significant nitrate sources from upstream. We conducted a sensitivity analysis that showed that mixing-dependent denitrification increased with parameters that increase mixing itself, such as the degree of heterogeneity of sediment hydraulic conductivity (K). Mixing-dependent denitrification also increased with certain biogeochemical boundary concentrations such as increasing DOC or decreasing dissolved oxygen (DO) advecting from surface water. For our second set of model scenarios, we set biogeochemical boundary conditions to be consistent with common situations where non-mixing-dependent denitrification also occurred within the model domain. For example, when nitrate concentrations are

  18. Predicting the denitrification capacity of sandy aquifers from in situ measurements using push-pull 15N tracer tests

    NASA Astrophysics Data System (ADS)

    Eschenbach, W.; Well, R.; Walther, W.

    2015-04-01

    Knowledge about the spatial variability of in situ denitrification rates (Dr(in situ)) and their relation to the denitrification capacity in nitrate-contaminated aquifers is crucial to predict the development of groundwater quality. Therefore, 28 push-pull 15N tracer tests for the measurement of in situ denitrification rates were conducted in two sandy Pleistocene aquifers in northern Germany. The 15N analysis of denitrification-derived 15N-labelled N2 and N2O dissolved in water samples collected during the push-pull 15N tracer tests was performed using isotope ratio mass spectrometry (IRMS) in the lab and additionally for some tracer tests online in the field with a quadrupole membrane inlet mass spectrometer (MIMS) in order to test the feasibility of on-site real-time 15N analysis. Aquifer material from the same locations and depths as the push-pull injection points was incubated, and the initial and cumulative denitrification after 1 year of incubation (Dcum(365)) as well as the stock of reduced compounds (SRC) was compared with in situ measurements of denitrification. This was done to derive transfer functions suitable to predict Dcum(365) and SRC from Dr(in situ). Dr(in situ) ranged from 0 to 51.5 μg N kg-1 d-1. Denitrification rates derived from on-site isotope analysis using MIMS satisfactorily coincided with laboratory analysis by conventional IRMS, thus proving the feasibility of in situ analysis. Dr(in situ) was significantly higher in the sulfidic zone of both aquifers compared to the zone of non-sulfidic aquifer material. Overall, regressions between the Dcum(365) and SRC of the tested aquifer material with Dr(in situ) exhibited only a modest linear correlation for the full data set. However, the predictability of Dcum(365) and SRC from Dr(in situ) data clearly increased for aquifer samples from the zone of NO3--bearing groundwater. In the NO3--free aquifer zone, a lag phase of denitrification after NO3- injections was observed, which confounded the

  19. Predicting the denitrification capacity of sandy aquifers from in situ measurements using push-pull 15N tracer tests

    NASA Astrophysics Data System (ADS)

    Eschenbach, W.; Well, R.; Walther, W.

    2014-12-01

    Knowledge about the spatial variability of in situ denitrification rates (Dr(in situ)) and their relation to the denitrification capacity in nitrate-contaminated aquifers is crucial to predict the development of groundwater quality. Therefore, 28 push-pull 15N tracer tests for the measurement of in situ denitrification rates were conducted in two sandy Pleistocene aquifers in Northern Germany. The 15N analysis of denitrification derived 15N labelled N2 and N2O dissolved in water samples collected during the push-pull 15N tracer tests was performed by isotope ratio mass spectrometry (IRMS) in the lab and additionally for some tracer tests online in the field with a quadrupole membrane inlet mass spectrometer (MIMS), in order to test the feasibility of on-site real-time 15N analysis. Aquifer material from the same locations and depths as the push-pull injection points was incubated and the initial and cumulative denitrification after one year of incubation (Dcum(365)) as well as the stock of reduced compounds (SRC) was compared with in situ measurements of denitrification. This was done to derive transfer functions suitable to predict Dcum(365) and SRC from Dr(in situ). Dr(in situ) ranged from 0 to 51.5 μg N kg-1 d-1. Denitrification rates derived from on-site isotope analysis using membrane-inlet mass spectrometry satisfactorily coincided with laboratory analysis by conventional isotope ratio mass spectrometry, thus proving the feasibility of in situ analysis. Dr(in situ) was significantly higher in the sulphidic zone of both aquifers compared to the zone of non-sulphidic aquifer material. Overall, regressions between the Dcum(365) and SRC of the tested aquifer material with Dr(in situ) exhibited only a modest linear correlation for the full data set. But the predictability of Dcum(365) and SRC from Dr(in situ) data clearly increased for aquifer samples from the zone of NO3--bearing groundwater. In the NO3--free aquifer zone a lag phase of denitrification after NO3

  20. Biogas desulfurization using autotrophic denitrification process.

    PubMed

    Bayrakdar, Alper; Tilahun, Ebrahim; Calli, Baris

    2016-01-01

    The aim of this study was to evaluate the performance of an autotrophic denitrification process for desulfurization of biogas produced from a chicken manure digester. A laboratory scale upflow fixed bed reactor (UFBR) was operated for 105 days and fed with sodium sulfide or H2S scrubbed from the biogas and nitrate as electron donor and acceptor, respectively. The S/N ratio (2.5 mol/mol) of the feed solution was kept constant throughout the study. When the UFBR was fed with sodium sulfide solution with an influent pH of 7.7, about 95 % sulfide and 90 % nitrate removal efficiencies were achieved. However, the inlet of the UFBR was clogged several times due to the accumulation of biologically produced elemental sulfur particles and the clogging resulted in operational problems. When the UFBR was fed with the H2S absorbed from the biogas and operated with an influent pH of 8-9, around 98 % sulfide and 97 % nitrate removal efficiencies were obtained. In this way, above 95 % of the H2S in the biogas was removed as elemental sulfur and the reactor effluent was reused as scrubbing liquid without any clogging problem. PMID:26428238

  1. Comparative study of vehicle tyre-road friction coefficient estimation with a novel cost-effective method

    NASA Astrophysics Data System (ADS)

    Li, Boyuan; Du, Haiping; Li, Weihua

    2014-08-01

    This paper qualitatively and quantitatively reviews and compares three typical tyre-road friction coefficient estimation methods, which are the slip slope method, individual tyre force estimation method and extended Kalman filter method, and then presents a new cost-effective tyre-road friction coefficient estimation method. Based on the qualitative analysis and the numerical comparisons, it is found that all of the three typical methods can successfully estimate the tyre force and friction coefficient in most of the test conditions, but the estimation performance is compromised for some of the methods during different simulation scenarios. In addition, all of these three methods need global positioning system (GPS) to measure the absolute velocity of a vehicle. To overcome the above-mentioned problem, a novel cost-effective estimation method is proposed in this paper. This method requires only the inputs of wheel angular velocity, traction/brake torque and longitudinal acceleration, which are all easy to be measured using available sensors installed in passenger vehicles. By using this method, the vehicle absolute velocity and slip ratio can be estimated by an improved nonlinear observer without using GPS, and the friction force and tyre-road friction coefficient can be obtained from the estimated vehicle velocity and slip ratio. Simulations are used to validate the effectiveness of the proposed estimation method.

  2. Cross-national comparability of burden of disease estimates: the European Disability Weights Project.

    PubMed Central

    Essink-Bot, Marie-Louise; Pereira, Joaquin; Packer, Claire; Schwarzinger, Michael; Burstrom, Kristina

    2002-01-01

    OBJECTIVE: To investigate the sources of cross-national variation in disability-adjusted life-years (DALYs) in the European Disability Weights Project. METHODS: Disability weights for 15 disease stages were derived empirically in five countries by means of a standardized procedure and the cross-national differences in visual analogue scale (VAS) scores were analysed. For each country the burden of dementia in women, used as an illustrative example, was estimated in DALYs. An analysis was performed of the relative effects of cross-national variations in demography, epidemiology and disability weights on DALY estimates. FINDINGS: Cross-national comparison of VAS scores showed almost identical ranking orders. After standardization for population size and age structure of the populations, the DALY rates per 100000 women ranged from 1050 in France to 1404 in the Netherlands. Because of uncertainties in the epidemiological data, the extent to which these differences reflected true variation between countries was difficult to estimate. The use of European rather than country-specific disability weights did not lead to a significant change in the burden of disease estimates for dementia. CONCLUSIONS: Sound epidemiological data are the first requirement for burden of disease estimation and relevant between-countries comparisons. DALY estimates for dementia were relatively insensitive to differences in disability weights between European countries. PMID:12219156

  3. How deep, how hot: comparing pressure and temperature estimates from amphibole and rhyolite-MELTS thermobarometry

    NASA Astrophysics Data System (ADS)

    Pamukcu, A. S.; Gualda, G. A.

    2013-12-01

    Accurately constraining the pressure and temperature of magma residence is problematic, but it is key to understanding the structure and evolution of magmatic systems. Various thermometers exist (Fe-Ti oxides, Ti-in-zircon, Zr-in-sphene, etc.), but there are fewer barometers that can be applied to volcanic rocks. Most barometers capitalize on amphibole, a relatively common mineral whose composition is sensitive to pressure and temperature changes. Glass composition is a function of pressure for magmas saturated in quartz and feldspar, and a new thermobarometer based on rhyolite-MELTS simulations using glass (matrix glass and crystal-hosted glass inclusions) compositions has been recently proposed. We compare results from amphibole and matrix glass thermobarometry. We focus on outflow high-silica rhyolite pumice from the Peach Spring Tuff (CA-NV-AZ, USA), which are characterized by sanidine+plagioclase×quartz+amphibole+sphene in a high-silica rhyolite glass matrix. Compositional variations in amphibole are slight and described by edenite and Ti-Tschermak substitution, with little Al-Tschermak substitution, suggesting small changes in temperature but not in pressure. Plagioclase compositions are also nearly homogeneous. Thus, we expect thermobarometry results to cluster around a single pressure and temperature, making these samples excellent candidates for comparing thermobarometers. Amphibole×plagioclase thermobarometry reveals: - Amphibole-plagioclase: results vary widely depending on the calibration (e.g. 150-420 MPa, 520-730 °C); combined Anderson & Smith (1995) barometer with Holland & Blundy (1990) thermometer is most consistent, suggesting crystallization at 230 MPa, 680 °C. - Amphibole-only: calibrations give significantly different results (75-115 MPa, 770-960 °C [Ridolfi et al. 2010]; 400-950 MPa, 800-950°C [Ridolfi & Renzulli 2012]). Results suggest the recent re-calibration is particularly unreliable for these rocks, and the earlier calibration is

  4. Importance of denitrification to the efficiency of waste-water treatment in forested wetlands. Project completion report

    SciTech Connect

    Twilley, R.R.; Boustany, R.G.

    1990-09-01

    Wastewater, even after secondary treatment, typically contains high concentrations of nutrients that can cause eutrophication of receiving waters and deterioration of water quality. Therefore, there has been much interest in the use of natural wetlands as a simple and energy-efficient means of removing nutrients from wastewater and improving water quality. The utilization of a wetland for tertiary treatment of wastewater is based on the ability of the wetland to act as a nutrient sink. One of the most important processes in wetland ecosystems that influences their capacity as a nitrogen sink is the gaseous exchange of nitrogen with the atmosphere known as denitrification. Since denitrification represents a loss of nitrogen to the atmosphere, the mechanism tends to be most favorable for the removal of nitrogen. The objectives of the research project were to (1) determine the temporal and spatial ambient rates of denitrification and compare these rates to those of sediments amended with increased concentrations of nitrate comparable to concentrations of total nitrogen in the sewage effluent to be discharged; and (2) determine the proportion of total denitrification that can be attributed to direct utilization of nitrate loaded into the wetland, as compared to nitrate produced via nitrification within the wetland. Although nitrate is readily denitrified, short-term incubation rates are relatively low which is attributed to the presently low nitrate concentrations and subsequent reduced denitrifying microbial population in the wetland sediments. Nitrate concentrations varied seasonally associated with increased flooding during spring. Rates of nitrification coupled with denitrification were investigated with nitrogen-15 isotopes. Nitrification is limited in the wetland sedments; therefore, controls the rate of total nitrogen loss from the system.

  5. Comparing AMSR-E soil moisture estimates to the extended record of the U.S. Climate Reference Network (USCRN)

    NASA Astrophysics Data System (ADS)

    Coopersmith, Evan J.; Cosh, Michael H.; Bindlish, Rajat; Bell, Jesse

    2015-11-01

    Soil moisture plays an integral role in multi-scale hydrologic modeling, agricultural decision analysis, climate change assessments, and drought prediction/prevention. The broad availability of soil moisture estimates has only occurred within the past decade through a combination of in situ networks and satellite-driven remote sensing. The U.S. Climate Reference Network (USCRN) has provided a nationwide in situ resource since 2009. The Advanced Microwave Scanning Radiometer (AMSR-E), launched in 2002, is one of the satellite products available for comparison, but there are a limited number of years where the data records overlap. This study compares the results of modeled historical soil moisture estimates derived using USCRN precipitation data to the remotely sensed estimates provided by the AMSR-E satellite between 2002 and 2011. First, this work assesses the calibrated model's similarity to in situ estimates. Next, the model estimates and in situ measurements are shown to perform comparably well against the AMSR-E satellite product, suggesting that it may be possible to utilize modeled estimates at times and locations where satellite estimates are unavailable and further extend the soil moisture record spatially and temporally.

  6. Using Pure Cultures to Define the Site Preference of Nitrous Oxide Produced by Microbial Nitrification and Denitrification

    NASA Astrophysics Data System (ADS)

    Sutka, R. L.; Breznak, J. A.; Ostrom, N. E.; Ostrom, P. H.; Gandhi, H.

    2004-12-01

    Defining the site preference of nitrous oxide (N2O) produced in pure culture studies is crucial to interpreting field data. We have previously demonstrated that the intramolecular distribution of nitrogen isotopes (isotopomers) can be used to differentiate N2O produced by nitrifier denitrification and nitrification in cultures of Nitrosomonas europaea. Here, we have expanded on our initial results and evaluated the isotopomeric composition of N2O produced during nitrification and nitrifier denitrification with cultures of Nitrosospira multiformis. In addition, we have analyzed N2O produced during methanotrophic nitrification, denitrification, and fungal denitrification. To evaluate N2O production during nitrification and nitrifier denitrification, we compared the site preference of N2O formed as a result of nitrite reduction and hydroxylamine oxidation with Nitrosomonas europaea and Nitrosospira multiformis. The average site preference of N2O produced by hydroxylamine oxidation was similar for Nitrosomonas europaea (33.0 ± 3.5 ‰ ) and Nitrosospira multiformis (33.1 ± 4.2 ‰ ). Nitrous oxide produced by nitrifier-denitrification by Nitrosomonas europaea and Nitrosospira multiformis had a similar site preference of - 1.4 ± 4.4 ‰ and - 1.1 ± 2.6 ‰ respectively. The results indicate that it is possible to differentiate between N2O produced by nitrite reduction and hydroxylamine oxidation by ammonia oxidizing bacteria. Methanotrophic nitrification was evaluated by analyzing the N2O produced during hydroxylamine oxidation in concentrated cell suspensions of two methane oxidizing bacteria. The site preference of N2O produced by the two methane oxidizers, Methylococcus capsulatus Bath and Methylosinus trichosporium was 31.8 ± 4.7 ‰ and 33.0 ± 4.5 ‰ respectively. The results indicate that a site preference of 33 ‰ is applicable for nitrification regardless of whether a methane oxidizer or ammonia oxidizer is involved in the reaction. To determine the site

  7. Comparing C- and L-band SAR images for sea ice motion estimation

    NASA Astrophysics Data System (ADS)

    Lehtiranta, J.; Siiriä, S.; Karvonen, J.

    2015-02-01

    Pairs of consecutive C-band synthetic-aperture radar (SAR) images are routinely used for sea ice motion estimation. The L-band radar has a fundamentally different character, as its longer wavelength penetrates deeper into sea ice. L-band SAR provides information on the seasonal sea ice inner structure in addition to the surface roughness that dominates C-band images. This is especially useful in the Baltic Sea, which lacks multiyear ice and icebergs, known to be confusing targets for L-band sea ice classification. In this work, L-band SAR images are investigated for sea ice motion estimation using the well-established maximal cross-correlation (MCC) approach. This work provides the first comparison of L-band and C-band SAR images for the purpose of motion estimation. The cross-correlation calculations are hardware accelerated using new OpenCL-based source code, which is made available through the author's web site. It is found that L-band images are preferable for motion estimation over C-band images. It is also shown that motion estimation is possible between a C-band and an L-band image using the maximal cross-correlation technique.

  8. Pore Size Distribution Estimates Compared: Available software applied to soil CT and synthetic images.

    NASA Astrophysics Data System (ADS)

    Houston, Alasdair N.; Falconer, Ruth E.; Otten, Wilfred; Hapca, Simona M.

    2015-04-01

    The Pore Size Distribution (PSD) has been widely used as a means of characterising porous media and, in conjunction with knowledge of pore space connectivity, has been used to infer hydrological properties. There exist various strategies to estimate PSD from a segmented image and each strategy typically involves a sequence of algorithms that transform image information. Some of these algorithms may be explicitly parameterised, requiring decisions by a knowledgeable operator. As a result PSD estimates may be quite variable between software applications and operators. In order to better understand these differences, a constrained boolean model was used to construct synthetic images whose pore structure is without ambiguity and whose properties can be analytically determined. Applying to such images a selection of analysis procedures in the form of readily available software applications, reveals differences between PSD estimates and analytic information. In some cases it is possible to attribute these differences to artifacts visible within map images generated by the analysis procedures, permitting correction procedures to be devised. In the case of soil CT images which exhibit complex interconnected pore structure, differences in the PSD estimate between analysis procedures are very great in some cases. Inspection of map images can again help in identifying the cause of such problems, but this may result from a fundamental property of the procedure with respect to complex pore structure. Based on the evidence presented, we conclude that some readily available software will produce PSD estimates that can usefully characterise geomaterials.

  9. Direct contribution of clams (Ruditapes philippinarum) to benthic fluxes, nitrification, denitrification and nitrous oxide emission in a farmed sediment

    NASA Astrophysics Data System (ADS)

    Welsh, David T.; Nizzoli, Daniele; Fano, Elisa A.; Viaroli, Pierluigi

    2015-03-01

    The influence of the manila clam (Ruditapes philippinarum) on N-cycle processes, and oxygen and nutrient fluxes in a farmed sediment was investigated using a multiple core incubation approach and parallel incubations of individual clams. Clam population/biomass density varied ∼8-fold between cores and all sediment-water column solute (O2. N2, N2O, NH4+, NOX and DIN) fluxes and benthic process (N-regeneration, nitrification and denitrification) rates were strongly and significantly correlated with clam density/biomass. Isolated clams exhibited high rates of respiration, N-excretion, nitrification and denitrification of 2050 ± 70, 395 ± 49, 201 ± 42 and 235 ± 40 nmol individual-1 h-1, respectively. The direct contribution of the clams and their associated microbiota to benthic processes was estimated by multiplying the per individual rates by the number of clams in each incubated core. The clams on average directly accounted for 64-133% of total rates of sediment oxygen demand, N-regeneration, nitrification and denitrification, indicating that they regulated processes primarily through their own metabolic activity and that of bacteria that colonise them. Clams and the farmed sediments were significant sources of the greenhouse gas N2O, but this was primarily due to their high nitrification and denitrification rates, rather than high specific N2O yields, as N2O emissions represented <1% of total N2O + N2 production. The clam-farmed sediments had a high denitrification efficiency of 67 ± 10%, but this ecosystem service came at the environmental cost of increased N-regeneration and N2O emission rates. The measured N2O emissions indicate that bivalve aquaculture may be a significant source of N2O. It is therefore recommended that N2O emissions should be included in the impact assessments of current and future bivalve-farming projects.

  10. Autoxidation and acetylene-accelerated oxidation of NO in a 2-phase system; implications for the expression of denitrification in ex situ experiments

    NASA Astrophysics Data System (ADS)

    Nadeem, Shahid; Dörsch, Peter; Bakken, Lars

    2013-04-01

    flasks (with and without C2H2), and monitored for O2, NO, N2O and N2 production while depleting the oxygen and switching to anoxic respiration. Acetylene effectively scavenged NO from the cultures until oxygen concentration reached below ~0.19 mL L-1, and the estimated rate of acetylene-accelerated NO oxidation was more than sufficient to explain an observed reduction of the N2O production induced by acetylene. When [O2] reached below 0.19 mL L-1, the NO concentrations increased and stabilized at the same level as in the treatments without acetylene, but the rate of denitrification was much lower than without acetylene. The results indicate that the early accumulation of 10-20 nM NO during oxygen depletion has a significant effect on the expression of denitrification in soil communities. This warrants a greater interest in NO as a regulator of denitrification in soils and shows that the acetylene inhibition method may be problematic even for intentionally anoxic incubations, unless precautions are taken to secure initial O2-concentrations below 0.19 mL O2 L-1.

  11. Optimization of nitrate removal from wastewater with a low C/N ratio using solid-phase denitrification.

    PubMed

    Zhang, Qian; Ji, Fangying; Xu, Xiaoyi

    2016-01-01

    In this study, the optimization of nitrate removal from wastewater with a low C/N ratio using solid-phase denitrification was investigated. Biodegradable polymer, an attractive alternative to liquid carbon sources for biological denitrification, was used as a carbon source and biofilm support for nitrate removal. An experiment was conducted based on a central composite design (CCD) with response surface methodology (RSM). A secondary polynomial regression with nitrate removal efficiency as response value was developed. Based on statistical analysis, the nitrate removal model was highly significant with very low probability values (<0.0001). At the optimal conditions for nitrate removal (hydraulic retention time (HRT), 3.5 h; influent NO3 (-)-N concentration, 14.73 mg/L; and influent CODCr concentration, 15.00 mg/L), the nitrate removal efficiency was 99.23 %. The results of an ANOVA and response surface analysis showed that HRT, influent NO3 (-)-N concentration, influent CODCr concentration, and the interaction between the HRT and influent CODCr concentration significantly affected the nitrate removal efficiency (P < 0.05). In solid-phase denitrification process, electron donor for denitrification could be obtained by biological degradation of biodegradable polymer. Therefore, the influent CODCr concentration has no major effect on nitrate removal efficiency compared with that of HRT and influent NO3 (-)-N concentration. PMID:26335529

  12. Effect of fermentation liquid from food waste as a carbon source for enhancing denitrification in wastewater treatment.

    PubMed

    Zhang, Yongmei; Wang, Xiaochang C; Cheng, Zhe; Li, Yuyou; Tang, Jialing

    2016-02-01

    Food wastes were used for anaerobic fermentation to prepare carbon sources for enhancing nitrogen removal in wastewater treatment. Under anaerobic conditions without pH adjustment, the fermentation liquid from food wastes (FLFW) with a high organic acid content was produced at room temperature (25 °C) and initial solid concentration of 13%. Using FLFW as the sole carbon source of artificial wastewater for biological treatment by sequence batch operation, maximized denitrification (with a denitrification rate of V(DN) = 12.89 mg/gVSS h and a denitrification potential of P(DN) = 0.174 gN/gCOD) could be achieved at a COD/TN ratio of 6. The readily biodegradable fraction in the FLFW was evaluated as 58.35%. By comparing FLFW with glucose and sodium acetate, two commonly used chemical carbon sources, FLFW showed a denitrification result similar to sodium acetate but much better than glucose in terms of total nitrogen removal, V(DN), P(DN), organic matter consumption rate (V(COD)) and heterotrophy anoxic yield coefficient (Y(H)). PMID:26408975

  13. Global trends and uncertainties in terrestrial denitrification and N2O emissions

    PubMed Central

    Bouwman, A. F.; Beusen, A. H. W.; Griffioen, J.; Van Groenigen, J. W.; Hefting, M. M.; Oenema, O.; Van Puijenbroek, P. J. T. M.; Seitzinger, S.; Slomp, C. P.; Stehfest, E.

    2013-01-01

    Soil nitrogen (N) budgets are used in a global, distributed flow-path model with 0.5° × 0.5° resolution, representing denitrification and N2O emissions from soils, groundwater and riparian zones for the period 1900–2000 and scenarios for the period 2000–2050 based on the Millennium Ecosystem Assessment. Total agricultural and natural N inputs from N fertilizers, animal manure, biological N2 fixation and atmospheric N deposition increased from 155 to 345 Tg N yr−1 (Tg = teragram; 1 Tg = 1012 g) between 1900 and 2000. Depending on the scenario, inputs are estimated to further increase to 408–510 Tg N yr−1 by 2050. In the period 1900–2000, the soil N budget surplus (inputs minus withdrawal by plants) increased from 118 to 202 Tg yr−1, and this may remain stable or further increase to 275 Tg yr−1 by 2050, depending on the scenario. N2 production from denitrification increased from 52 to 96 Tg yr−1 between 1900 and 2000, and N2O–N emissions from 10 to 12 Tg N yr−1. The scenarios foresee a further increase to 142 Tg N2–N and 16 Tg N2O–N yr−1 by 2050. Our results indicate that riparian buffer zones are an important source of N2O contributing an estimated 0.9 Tg N2O–N yr−1 in 2000. Soils are key sites for denitrification and are much more important than groundwater and riparian zones in controlling the N flow to rivers and the oceans. PMID:23713114

  14. The kinetic and isotopic competence of nitric oxide as an intermediate in denitrification.

    PubMed

    Goretski, J; Hollocher, T C

    1990-01-15

    Rates of NO uptake by five denitrifying bacteria were estimated by NO-electrode and gas chromatography methods under conditions of rather low cell densities and [NOaq]. The rates so measured, VmaxNO, represent lower limits for the true value of that parameter, but nevertheless exceed Vmax for nitrite uptake, VmaxNi, by a factor of two typically. Previous estimates under suboptimal conditions had placed VmaxNO at 0.3-0.5 of VmaxNi (St. John, R. T., and Hollocher, T. C. (1977) J. Biol. Chem. 252, 212-218; Garber, E. A. E., and Hollocher, T.C. (1981) J. Biol. Chem. 256, 5459-5465). The steady-state [NOaq] during denitrification of nitrite by nitrate-grown cells was less than or equal to 1 microM. The above observations, taken with a recent direct estimate for the KmNO for NO uptake of 0.4 microM (Zafiriou, O. C., Hanley, Q. S., and Snyder, G. (1989) J. Biol. Chem. 264, 5694-5699), would allow NO to be a free intermediate between nitrite and N2O with steady-state concentrations of less than or equal to 0.4 microM. As the result of special conditions during cell growth or differential inhibition by azide, it was possible to establish systems that accumulated NO during denitrification of nitrite. In all such cases, VmaxNO less than VmaxNi, and the time required to reach the maximum [NOaq] corresponded closely to the time needed to exhaust the nitrite. A semiquantitative isotope experiment with Paracoccus denitrificans demonstrated the trapping of 15NO from 15NO2- in a pool of NOaq. A quantitative isotope method using low densities of the same bacterium showed that 15N from 15NO2- and 14N from NOg combine randomly to form N2O during the simultaneous denitrification of 15NO2- and NO. The result requires that the pathways from nitrite and NO share a common mononitrogen intermediate. Results to the contrary obtained at high cell densities (first two references cited above) are now believed to have been due to technical artifacts. The present results are consistent with the

  15. Models of Quantitative Estimations: Rule-Based and Exemplar-Based Processes Compared

    ERIC Educational Resources Information Center

    von Helversen, Bettina; Rieskamp, Jorg

    2009-01-01

    The cognitive processes underlying quantitative estimations vary. Past research has identified task-contingent changes between rule-based and exemplar-based processes (P. Juslin, L. Karlsson, & H. Olsson, 2008). B. von Helversen and J. Rieskamp (2008), however, proposed a simple rule-based model--the mapping model--that outperformed the exemplar…

  16. Comparing Accuracy of Parameter Estimation Using IRT Models in the Presence of Guessing

    ERIC Educational Resources Information Center

    Fu, Qiong

    2010-01-01

    This research investigated how the accuracy of person ability and item difficulty parameter estimation varied across five IRT models with respect to the presence of guessing, targeting, and varied combinations of sample sizes and test lengths. The data were simulated with 50 replications under each of the 18 combined conditions. Five IRT models…

  17. A comparative study of frequency offset estimations in real and complex OFDM systems using different algorithms

    NASA Astrophysics Data System (ADS)

    Sahu, Swagatika; Mohanty, Saumendra; Srivastav, Richa

    2013-01-01

    Orthogonal Frequency Division Multiplexing (OFDM) is an emerging multi-carrier modulation scheme, which has been adopted for several wireless standards such as IEEE 802.11a and HiperLAN2, etc. A well-known problem of OFDM is its sensitivity to frequency offset between the transmitted and received carrier frequencies. In (OFDM) system Carrier frequency offsets (CFOs) between the transmitter and the receiver destroy the orthogonality between carriers and degrade the system performance significantly. The main problem with frequency offset is that it introduces interference among the multiplicity of carriers in the OFDM signal.The conventional algorithms given by P. Moose and Schmidl describes how carrier frequency offset of an OFDM system can be estimated using training sequences. Simulation results show that the improved carrier frequency offset estimation algorithm which uses a complex training sequence for frequency offset estimation, performs better than conventional P. Moose and Schmidl algorithm, which can effectively improve the frequency estimation accuracy and provides a wide acquisition range for the carrier frequency offset with low complexity. This paper introduces the BER comparisons of different algorithms with the Improved Algorithms for different Real and Complex modulations schemes, considering random carrier offsets . This paper also introduces the BER performances with different CFOs for different Real and Complex modulation schemes for the Improved algorithm.

  18. Comparative Evaluation of Two Methods to Estimate Natural Gas Production in Texas

    EIA Publications

    2003-01-01

    This report describes an evaluation conducted by the Energy Information Administration (EIA) in August 2003 of two methods that estimate natural gas production in Texas. The first method (parametric method) was used by EIA from February through August 2003 and the second method (multinomial method) replaced it starting in September 2003, based on the results of this evaluation.

  19. Comparing Participants' Rating and Compendium Coding to Estimate Physical Activity Intensities

    ERIC Educational Resources Information Center

    Masse, Louise C.; Eason, Karen E.; Tortolero, Susan R.; Kelder, Steven H.

    2005-01-01

    This study assessed agreement between participants' rating (PMET) and compendium coding (CMET) of estimating physical activity intensity in a population of older minority women. As part of the Women on the Move study, 224 women completed a 7-day activity diary and wore an accelerometer for 7 days. All activities recorded were coded using PMET and…

  20. Comparing LAI estimates of corn and soybean from vegetation indices of multi-resolution satellite images

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Leaf area index (LAI) is important in explaining the ability of the crop to intercept solar energy for biomass production and in understanding the impact of crop management practices. This paper describes a procedure for estimating LAI as a function of image-derived vegetation indices from temporal ...

  1. Comparative study of methods used to estimate ionic diffusion coefficients using migration tests

    SciTech Connect

    Narsilio, G.A. Li, R. Pivonka, P. Smith, D.W.

    2007-08-15

    Ionic diffusion coefficients are estimated rapidly using electromigration tests. In this paper, electromigration tests are accurately simulated by numerically solving the Nernst-Planck (NP) equation (coupled with the electroneutrality condition (EN)) using the finite element method. Numerical simulations are validated against experimental data obtained elsewhere [E. Samson, J. Marchand, K.A. Snyder, Calculation of ionic diffusion coefficients on the basis of migration test results, Materials and Structures/Materiaux et Constructions 36 (257) (2003) 156-165., H. Friedmann, O. Amiri, A. Ait-Mokhtar, A direct method for determining chloride diffusion coefficient by using migration test, Cement and Concrete Research 34 (11) (2004) 1967-1973.]. It is shown that migration due to the non-linear electric potential completely overwhelms diffusion due to concentration gradients. The effects of different applied voltage differences and chloride source concentrations on estimations of chloride diffusion coefficients are explored. We show that the pore fluid within concrete and mortar specimens generally differs from the curing solution, lowering the apparent diffusion coefficient, primarily due to interactions of chloride ions with other ions in the pore fluid. We show that the variation of source chloride concentration strongly affects the estimation of diffusion coefficients in non-steady-state tests; however this effect vanishes under steady-state conditions. Most importantly, a comparison of diffusion coefficients obtained from sophisticated analyses (i.e., NP-EN) and a variety of commonly used simplifying methods to estimate chloride diffusion coefficients allows us to identify those methods and experimental conditions where both approaches deliver good estimates for chloride diffusion coefficients. Finally, we demonstrate why simultaneous use and monitoring of current density and fluxes are recommended for both the non-steady and steady-state migration tests.

  2. Denitrification rates in marsh soils and hydrologic and water quality data for Northeast Creek and Bass Harbor Marsh watersheds, Mount Desert Island, Maine

    USGS Publications Warehouse

    Huntington, Thomas G.; Culbertson, Charles W.; Duff, John H.

    2011-01-01

    Nutrient enrichment from atmospheric deposition, agricultural activities, wildlife, and domestic sources is a concern at Acadia National Park because of the potential problem of water-quality degradation and eutrophication in estuaries. Water-quality degradation has been observed at the park's Bass Harbor Marsh estuary but minimal degradation is observed in Northeast Creek estuary. Previous studies at Acadia National Park have estimated nutrient inputs to estuaries from atmospheric deposition and surface-water runoff, and have identified shallow groundwater as an additional potential nutrient source. Previous studies at Acadia National Park have assumed that a certain fraction of the nitrogen input was removed through microbial denitrification, but rates of denitrification (natural or maximum potential) in marsh soils have not been determined. The U.S. Geological Survey, in cooperation with Acadia National Park, measured in situ denitrification rates in marsh soils in Northeast Creek and Bass Harbor Marsh watersheds during the summer seasons of 2008 and 2009. Denitrification was measured under ambient conditions and following inorganic nitrogen and glucose additions. Laboratory incubations of marsh soils with and without acetylene were conducted to determine average ratios of nitrous oxide (N2O) to nitrogen (N2) produced during denitrification. Surface water and groundwater samples were analyzed for nutrients, specific conductance, temperature, and dissolved oxygen. Water level was recorded continuously during the growing season in Fresh Meadow Marsh in the Northeast Creek Watershed.

  3. Effects of N and C Distribution on N-Emissions during Denitrification

    NASA Astrophysics Data System (ADS)

    Loick, Nadine; Dixon, Liz; Abalos, Diego; Vallejo, Antonio; Watson, Catherine; McGeough, Karen; Matthews, Peter; Cardenas, Laura

    2015-04-01

    Agricultural soils are a major source of nitric- (NO) and nitrous oxide (N2O) which are produced and consumed by biotic and abiotic soil processes. The dominant sources of NO and N2O are microbial nitrification and denitrification. Which process dominates depends on environmental conditions such as pH and water filled pore space (WFPS) as well as substrate availability which is seldom homogeneous across the whole field. N2O emissions have been attributed to both processes whereas NO emissions are thought to predominantly derive from nitrification. Recent findings challenge the latter assumption indicating denitrification to be a significant source of NO. The present study investigated the impact that N and C application hot spots have on emissions of NO and N2O as well as the significance of denitrification as a source of NO emissions. This study used the gas-flow-soil-core technique (Cardenas et al 2003) to simultaneously measure three nitrogen-gases (NO, N2O, N2) and CO2. This was combined with 15N labelled isotopic techniques to determine the source of N-emissions. A nutrient solution containing KNO3 with 15N at 5 atom% and glucose was applied at a rate of 75 kg N ha-1 and 400 kg C ha-1 to vessels containing three repacked grassland soil cores, where the amendment was either split and applied equally to the three cores or the full rate was applied to only one of the cores, mimicking heterogeneous fertiliser application. Under field conditions nutrient/fertiliser application is seldom homogeneous across the whole field and our results show a clear effect of the heterogeneous application of nutrients. NO emissions were significantly lower when a high concentration of nutrients was applied to a single core compared to an even distribution over multiple cores. Total emissions of N2O, N2 and CO2, however, were not affected by application heterogeneity but showed a delay in the occurrence of the peak of all three gases when the nutrients were applied to only one core

  4. [N2O emission and control in shortcut nitrification and denitrification and simultaneous nitrification and denitrification biological nitrogen removal systems].

    PubMed

    Zhang, Jing-rong; Wang, Shu-ying; Shang, Hui-lai; Peng, Yong-zhen

    2009-12-01

    SBR reactors were used to investigate the N2O emission in shortcut nitrification and simultaneous nitrification and denitrification (SND). Shortcut nitrification with nitrosation rate above 90% was realized by real-time control strategy. The N2O emission and variation of nitrosation rate were investigated under 4 DO levels (0.5, 1.0, 1.5, 2.0 mg/L). The results turned out that the optimal DO to maintain high nitrosation rate and minimum N2O emission was 1.5 mg/L and the N4O emission was 0.06 g per ammonium removed. The SBR filled with carbon fiber performed under low DO and pulse feeding. The SND rate was over 79% during the experiment. The N2O emission was studied under DO 0.2, 0.4, 1.0 and 1.5 mg/L. It turned out that the optimal DO was 1.0 mg/L and the N2O emission was 0.021 g per ammonium removed. Compared to the shortcut nitrification, the N2O emission of SND was 1/3 of the short-cut nitrification under optimal DO. PMID:20187398

  5. A comparative study of soft sensor design for lipid estimation of microalgal photobioreactor system with experimental validation.

    PubMed

    Yoo, Sung Jin; Jung, Dong Hwi; Kim, Jung Hun; Lee, Jong Min

    2015-03-01

    This study examines the applicability of various nonlinear estimators for online estimation of the lipid concentration in microalgae cultivation system. Lipid is a useful bio-product that has many applications including biofuels and bioactives. However, the improvement of lipid productivity using real-time monitoring and control with experimental validation is limited because measurement of lipid in microalgae is a difficult and time-consuming task. In this study, estimation of lipid concentration from other measurable sources such as biomass or glucose sensor was studied. Extended Kalman filter (EKF), unscented Kalman filter (UKF), and particle filter (PF) were compared in various cases for their applicability to photobioreactor systems. Furthermore, simulation studies to identify appropriate types of sensors for estimating lipid were also performed. Based on the case studies, the most effective case was validated with experimental data and found that UKF and PF with time-varying system noise covariance is effective for microalgal photobioreactor system. PMID:25545097

  6. Comparing distance metrics for rotation using the k-nearest neighbors algorithm for entropy estimation.

    PubMed

    Huggins, David J

    2014-02-15

    Distance metrics facilitate a number of methods for statistical analysis. For statistical mechanical applications, it is useful to be able to compute the distance between two different orientations of a molecule. However, a number of distance metrics for rotation have been employed, and in this study, we consider different distance metrics and their utility in entropy estimation using the k-nearest neighbors (KNN) algorithm. This approach shows a number of advantages over entropy estimation using a histogram method, and the different approaches are assessed using uniform randomly generated data, biased randomly generated data, and data from a molecular dynamics (MD) simulation of bulk water. The results identify quaternion metrics as superior to a metric based on the Euler angles. However, it is demonstrated that samples from MD simulation must be independent for effective use of the KNN algorithm and this finding impacts any application to time series data. PMID:24311273

  7. Probability estimates of seismic event occurrence compared to health hazards - Forecasting Taipei's Earthquakes

    NASA Astrophysics Data System (ADS)

    Fung, D. C. N.; Wang, J. P.; Chang, S. H.; Chang, S. C.

    2014-12-01

    Using a revised statistical model built on past seismic probability models, the probability of different magnitude earthquakes occurring within variable timespans can be estimated. The revised model is based on Poisson distribution and includes the use of best-estimate values of the probability distribution of different magnitude earthquakes recurring from a fault from literature sources. Our study aims to apply this model to the Taipei metropolitan area with a population of 7 million, which lies in the Taipei Basin and is bounded by two normal faults: the Sanchaio and Taipei faults. The Sanchaio fault is suggested to be responsible for previous large magnitude earthquakes, such as the 1694 magnitude 7 earthquake in northwestern Taipei (Cheng et. al., 2010). Based on a magnitude 7 earthquake return period of 543 years, the model predicts the occurrence of a magnitude 7 earthquake within 20 years at 1.81%, within 79 years at 6.77% and within 300 years at 21.22%. These estimates increase significantly when considering a magnitude 6 earthquake; the chance of one occurring within the next 20 years is estimated to be 3.61%, 79 years at 13.54% and 300 years at 42.45%. The 79 year period represents the average lifespan of the Taiwan population. In contrast, based on data from 2013, the probability of Taiwan residents experiencing heart disease or malignant neoplasm is 11.5% and 29%. The inference of this study is that the calculated risk that the Taipei population is at from a potentially damaging magnitude 6 or greater earthquake occurring within their lifetime is just as great as of suffering from a heart attack or other health ailments.

  8. Comparing methods for estimating R0 from the size distribution of subcritical transmission chains

    PubMed Central

    Blumberg, S.; Lloyd-Smith, J.O.

    2013-01-01

    Many diseases exhibit subcritical transmission (i.e. 0 < R0 < 1) so that infections occur as self-limited ‘stuttering chains’. Given an ensemble of stuttering chains, information about the number of cases in each chain can be used to infer R0, which is of crucial importance for monitoring the risk that a disease will emerge to establish endemic circulation. However, the challenge of imperfect case detection has led authors to adopt a variety of work-around measures when inferring R0, such as discarding data on isolated cases or aggregating intermediate-sized chains together. Each of these methods has the potential to introduce bias, but a quantitative comparison of these approaches has not been reported. By adapting a model based on a negative binomial offspring distribution that permits a variable degree of transmission heterogeneity, we present a unified analysis of existing R0 estimation methods. Simulation studies show that the degree of transmission heterogeneity, when improperly modeled, can significantly impact the bias of R0 estimation methods designed for imperfect observation. These studies also highlight the importance of isolated cases in assessing whether an estimation technique is consistent with observed data. Analysis of data from measles outbreaks shows that likelihood scores are highest for models that allow a flexible degree of transmission heterogeneity. Aggregating intermediate sized chains often has similar performance to analyzing a complete chain size distribution. However, truncating isolated cases is beneficial only when surveillance systems clearly favor full observation of large chains but not small chains. Meanwhile, if data on the type and proportion of cases that are unobserved were known, we demonstrate that maximum likelihood inference of R0 could be adjusted accordingly. This motivates the need for future empirical and theoretical work to quantify observation error and incorporate relevant mechanisms into stuttering chain

  9. A Unified Framework for Estimating Minimum Detectable Effects for Comparative Short Interrupted Time Series Designs

    ERIC Educational Resources Information Center

    Price, Cristofer; Unlu, Fatih

    2014-01-01

    The Comparative Short Interrupted Time Series (C-SITS) design is a frequently employed quasi-experimental method, in which the pre- and post-intervention changes observed in the outcome levels of a treatment group is compared with those of a comparison group where the difference between the former and the latter is attributed to the treatment. The…

  10. COMPARING A NEW ALGORITHM WITH THE CLASSIC METHODS FOR ESTIMATING THE NUMBER OF FACTORS. (R826238)

    EPA Science Inventory

    This paper presents and compares a new algorithm for finding the number of factors in a data analytic model. After we describe the new method, called NUMFACT, we compare it with standard methods for finding the number of factors to use in a model. The standard methods that we ...

  11. COMPARING A NEW ALGORITHM WITH THE CLASSIC METHODS FOR ESTIMATING THE NUMBER OF FACTORS. (R825173)

    EPA Science Inventory

    Abstract

    This paper presents and compares a new algorithm for finding the number of factors in a data analytic model. After we describe the new method, called NUMFACT, we compare it with standard methods for finding the number of factors to use in a model. The standard...

  12. Comparing Satellite Rainfall Estimates with Rain-Gauge Data: Optimal Strategies Suggested by a Spectral Model

    NASA Technical Reports Server (NTRS)

    Bell, Thomas L.; Kundu, Prasun K.; Lau, William K. M. (Technical Monitor)

    2002-01-01

    Validation of satellite remote-sensing methods for estimating rainfall against rain-gauge data is attractive because of the direct nature of the rain-gauge measurements. Comparisons of satellite estimates to rain-gauge data are difficult, however, because of the extreme variability of rain and the fact that satellites view large areas over a short time while rain gauges monitor small areas continuously. In this paper, a statistical model of rainfall variability developed for studies of sampling error in averages of satellite data is used to examine the impact of spatial and temporal averaging of satellite and gauge data on intercomparison results. The model parameters were derived from radar observations of rain, but the model appears to capture many of the characteristics of rain-gauge data as well. The model predicts that many months of data from areas containing a few gauges are required to validate satellite estimates over the areas, and that the areas should be of the order of several hundred km in diameter. Over gauge arrays of sufficiently high density, the optimal areas and averaging times are reduced. The possibility of using time-weighted averages of gauge data is explored.

  13. Determining the nitrogen and oxygen isotope effects of microbial denitrification

    NASA Astrophysics Data System (ADS)

    Philp, C.; Martin, T. S.; Casciotti, K. L.

    2013-12-01

    The nitrogen cycle describes how nitrogen, a critical nutrient for life, moves throughout the ground, oceans, and atmosphere. An essential component of the nitrogen cycle is denitrification, in which bioavailable nitrogen is transformed into nitrous oxide and nitrogen gas and can no longer be harnessed by most organisms. We can further understand the importance of this nitrogen cycle process by examining the N and O isotope effects of microbial denitrification. We have cultured four denitrifying bacteria: P. stutzeri, P. putida, P. aureofaciens, and P. aeruginosa. After providing them with an initial amount of nitrite we tracked the rate at which each type of bacteria consumed the nitrite through a time series experiment. We then measured the N and O isotope ratios of the nitrite at each time point using a gas-source isotope ratio mass spectrometer. The subsequent isotope effects calculated using the Rayleigh equation provide an important tool for modeling denitrification in the environment.

  14. Denitrification 'Woodchip' Bioreactors for Productive and Sustainable Agricultural Systems

    NASA Astrophysics Data System (ADS)

    Christianson, L. E.; Summerfelt, S.; Sharrer, K.; Lepine, C.; Helmers, M. J.

    2014-12-01

    Growing alarm about negative cascading effects of reactive nitrogen in the environment has led to multifaceted efforts to address elevated nitrate-nitrogen levels in water bodies worldwide. The best way to mitigate N-related impacts, such as hypoxic zones and human health concerns, is to convert nitrate to stable, non-reactive dinitrogen gas through the natural process of denitrification. This means denitrification technologies need to be one of our major strategies for tackling the grand challenge of managing human-induced changes to our global nitrogen cycle. While denitrification technologies have historically been focused on wastewater treatment, there is great interest in new lower-tech options for treating effluent and drainage water from one of our largest reactive nitrogen emitters -- agriculture. Denitrification 'woodchip' bioreactors are able to enhance this natural N-conversion via addition of a solid carbon source (e.g., woodchips) and through designs that facilitate development of anoxic conditions required for denitrification. Wood-based denitrification technologies such as woodchip bioreactors and 'sawdust' walls for groundwater have been shown to be effective at reducing nitrate loads in agricultural settings around the world. Designing these systems to be low-maintenance and to avoid removing land from agricultural production has been a primary focus of this "farmer-friendly" technology. This presentation provides a background on woodchip bioreactors including design considerations, N-removal performance, and current research worldwide. Woodchip bioreactors for the agricultural sector are an accessible new option to address society's interest in improving water quality while simultaneously allowing highly productive agricultural systems to continue to provide food in the face of increasing demand, changing global diets, and fluctuating weather.

  15. In-Situ Denitrification and N2O Emission from Natural and Semi-natural Land Use Types in two UK Catchments

    NASA Astrophysics Data System (ADS)

    Sgouridis, F.; Ullah, S.

    2014-12-01

    Whilst data and understanding of the controls of denitrification process and the subsequent emission of N2O at microbial and plot scale exist, quantification of in situ annual denitrification rates at catchment scales is scarce due to methodological constraints in measuring in situ denitrification in large temporal and spatial scales. In situ denitrification (DNT) was measured monthly (April 2013 - October 2014) in organic (peat bog, heathland, acid grassland), forest (mixed and deciduous), and grassland (improved and semi-improved) land use types in the Ribble-Wyre and Conwy River catchments in the UK. A static chamber technique according to the 15N-Gas Flux method1 was employed for quantifying the fluxes of 15N-N2 and 15N-N2O gases after labelling the soil with 98 at% K15NO3- at tracer level amounts (10% of the ambient nitrate concentration) and sampling the chamber headspace at 0, 1, 2 and 20 hour intervals. The DNT rates ranged between 0 and 2.3 mg N m-2 h-1 and were significantly influenced by land use type (p<0.05). The annual denitrification rate of organic and forest soils (4 kg N ha-1 y-1) was 3 and 6 times less than that of semi-improved (12 kg N ha-1 y-1) and improved (23 kg N ha-1 y-1) grassland soils, respectively. The N2O emission, due to denitrification, followed a similar trend with lower fluxes from organic and higher from improved grassland soils (range: 0 - 0.04 mg N m-2 h-1), whilst the N2O:N2 ratio ranged between 0.2 and 4%. The relative contribution of denitrification to net N2O flux varied temporally and across the different land use types and ranged from 0.2 to 75%. The 15N-Gas Flux method can be successfully applied in a variety of land use types for relatively high temporal and spatial resolution measurement of in situ denitrification and the simultaneous quantification of N2 and N2O fluxes due to denitrification. Therefore the ratio of N2O:N2 and also the source apportionment for N2O can be estimated more accurately. The results suggested

  16. Groundwater denitrification in two agricultural river catchments: influence of hydro-geological setting and aquifer geochemistry

    NASA Astrophysics Data System (ADS)

    McAleer, Eoin; Mellander, Per-Erik; Coxon, Catherine; Richards, Karl G.; Jahangir, Mohammad M. R.

    2015-04-01

    products (excess N2 mean: 1.57 mg/l, N2O mean: 1.61µg/l). Groundwater in the sandstone catchment had a comparable mean NO3--N concentration to that of the slate site (6.24mg/l) and while temporal variation was low (SD: 0.9 mg/l), spatial variation was substantially greater (SD: 3.63 mg/l). The accumulation of denitrification products in the sandstone catchment showed a large contrast to that of the slate with excess N2 ranging from 0.16-8.77 mg/l and N2O from 0.07-66.42 µg/l. Mean dissolved oxygen concentration and redox potential were 5.6mg/l and 67.5mV respectively. The near stream zones in particular were marked by favourable denitrifying conditions: hydraulic conductivity (<2m/day), Eh (<50mV) and DO (<5mg/l). Winter recharge had a diluting effect, increasing the concentration of DO and Eh with a concurrent decrease in excess N2 and N2O. The evolution of groundwater geochemistry along a subsurface flow path is a function of residence time. While both catchments are characterised as permeable, the slate catchment exhibits greater hydraulic conductivity values, particularly at depth, with groundwater geochemistry in all horizons reflective of recently recharged water. The deeper groundwater pathways and near stream zones in the sandstone catchment have a lower hydraulic conductivity. As such, dissolved oxygen and redox gradients occur with depth, causing the development of NO3- reducing zones.

  17. Probability weighted moments compared with some traditional techniques in estimating Gumbel parameters and quantiles.

    USGS Publications Warehouse

    Landwehr, J.M.; Matalas, N.C.; Wallis, J.R.

    1979-01-01

    Results were derived from Monte Carlo experiments by using both independent and serially correlated Gumbel numbers. The method of probability weighted moments was seen to compare favourably with two other techniques. -Authors

  18. Comparing measured and modelled PFOS concentrations in a UK freshwater catchment and estimating emission rates.

    PubMed

    Earnshaw, Mark R; Paul, Alexander G; Loos, Robert; Tavazzi, Simona; Paracchini, Bruno; Scheringer, Martin; Hungerbühler, Konrad; Jones, Kevin C; Sweetman, Andrew J

    2014-09-01

    The lifecycle, sources and fate of perfluorooctane sulfonate (PFOS) continue to generate scientific and political interest, particularly since PFOS was listed by the Stockholm Convention and largely restricted in Europe. It continues to be detected in aquatic environments, with only limited studies into the on-going sources. This paper explores PFOS emissions discharged by the general population into a small catchment comprising two rivers in the UK. A sampling campaign was undertaken to improve our understanding of population-derived PFOS sources from sewage treatment plants (STPs) and in rivers. A corresponding modelling exercise allowed an emission estimate of 13μg/day/per capita to be derived for the Aire and Calder rivers. PFOS emission was linked to STP discharges bylinear regression of measured and modelled concntrations (R(2)=0.49-0.85). The model was able to accurately estimate the spatial trends of PFOS in the rivers, while predicted concentrations were within a factor of three based on per capita emission values taken from the literature. Measured PFOS concentrations in rivers suggested that emissions from STPs are partially dependent on treatment type, where plants with secondary or tertiary treatment such as activated sludge processes emit less PFOS, possibly due to increased partitioning and retention. With refinements based on the type of treatment at each STP, predictions were further improved. The total PFOS mass discharged annually via rivers from the UK has been estimated to be between 215 and 310kg, based on the per capita emission range derived in this study. PMID:24879369

  19. Denitrification by a marine bacterium Pseudomonas nautica strain 617.

    PubMed

    Bonin, P; Gilewicz, M; Bertrand, J C

    1987-01-01

    A bacterial strain was isolated from a marine sediment highly contaminated by hydrocarbons. From taxonomic tests, it was identified as Pseudomonas nautica. This marine strain was able to grow on nitrate, nitrite and nitrous oxide as an electron acceptor. The terminal product from the denitrification was dinitrogen. Thus, P. nautica was a denitrifier. The kinetics of each step of denitrification was examined in resting cell suspensions. The relative rates of nitrate and nitrite reduction and of nitrite reduction and nitrous oxide production explain, respectively, the presence of accumulated nitrite and that of compound intermediate between nitrite and nitrous oxide. PMID:3620203

  20. Observations of denitrification and dehydration in the winter polar stratospheres

    NASA Technical Reports Server (NTRS)

    Fahey, D. W.; Kelly, K. K.; Kawa, S. R.; Tuck, A. F.; Loewenstein, M.

    1990-01-01

    It is argued that denitrification of the Arctic stratosphere can be explained by the selective growth and sedimentation of aerosol particles rich in nitric acid. Because reactive nitrogen species moderate the destruction of ozone by chlorine-catalyzed reactions by sequestering chlorine in reservoir species such as ClONO2, the possibility of the removal of reactive nitrogen without dehydration should be allowed for in attempts to model ozone depletion in the Arctic. Indeed, denitrification along with elevated concentrations of reactive chlorine observed in 1989 indicate that the Arctic was chemically primed for ozone destruction without an extended period of temperatures below the frost point, as is characteristic of the Antarctic.

  1. Comparative assessment of bone pose estimation using Point Cluster Technique and OpenSim.

    PubMed

    Lathrop, Rebecca L; Chaudhari, Ajit M W; Siston, Robert A

    2011-11-01

    Estimating the position of the bones from optical motion capture data is a challenge associated with human movement analysis. Bone pose estimation techniques such as the Point Cluster Technique (PCT) and simulations of movement through software packages such as OpenSim are used to minimize soft tissue artifact and estimate skeletal position; however, using different methods for analysis may produce differing kinematic results which could lead to differences in clinical interpretation such as a misclassification of normal or pathological gait. This study evaluated the differences present in knee joint kinematics as a result of calculating joint angles using various techniques. We calculated knee joint kinematics from experimental gait data using the standard PCT, the least squares approach in OpenSim applied to experimental marker data, and the least squares approach in OpenSim applied to the results of the PCT algorithm. Maximum and resultant RMS differences in knee angles were calculated between all techniques. We observed differences in flexion/extension, varus/valgus, and internal/external rotation angles between all approaches. The largest differences were between the PCT results and all results calculated using OpenSim. The RMS differences averaged nearly 5° for flexion/extension angles with maximum differences exceeding 15°. Average RMS differences were relatively small (< 1.08°) between results calculated within OpenSim, suggesting that the choice of marker weighting is not critical to the results of the least squares inverse kinematics calculations. The largest difference between techniques appeared to be a constant offset between the PCT and all OpenSim results, which may be due to differences in the definition of anatomical reference frames, scaling of musculoskeletal models, and/or placement of virtual markers within OpenSim. Different methods for data analysis can produce largely different kinematic results, which could lead to the misclassification

  2. Estimation of age based on tooth cementum annulations: A comparative study using light, polarized, and phase contrast microscopy

    PubMed Central

    Kaur, Prabhpreet; Astekar, Madhusudan; Singh, Jappreet; Arora, Karandeep Singh; Bhalla, Gagandeep

    2015-01-01

    Context: The identification of living or deceased persons using unique traits and characteristics of the teeth and jaws is a cornerstone of forensic science. Teeth have been used to estimate age both in the young and old, as well as in the living and dead. Gradual structural changes in teeth throughout life are the basis for age estimation. Tooth cementum annulation (TCA) is a microscopic method for the determination of an individual's age based on the analysis of incremental lines of cementum. Aim: To compare ages estimated using incremental lines of cementum as visualized by bright field microscopy, polarized microscopy, and phase contrast microscopy with the actual age of subject and to determine accuracy and feasibility of the method used. Materials and Methods: Cementum annulations of 60 permanent teeth were analyzed after longitudinal ground sections were made in the mesiodistal plane. The incremental lines were counted manually using a light, polarized and phase contrast microscopy. Ages were estimated and then compared with the actual age of individual. Statistical Analysis: Analysis of variance (ANOVA), Student's t-test, the Pearson product-moment corre (PPMCC) and regression analysis were performed. Results: PPMCC value r = 0.347, 0.542 and 0.989 were obtained using light, polarized and phase contrast microscopy methods respectively. Conclusion: It was concluded that incremental lines of cementum were most clearly visible under a phase contrast microscope, followed by a polarized microscope, and then a light microscope when used for age estimation. PMID:26816462

  3. Global rates of water-column denitrification derived from nitrogen gas measurements

    NASA Astrophysics Data System (ADS)

    Devries, Tim; Deutsch, Curtis; Primeau, François; Chang, Bonnie; Devol, Allan

    2012-08-01

    Biologically available nitrogen (N) limits phytoplankton growth over much of the ocean. The rate at which N is removed from the contemporary ocean by denitrifying bacteria is highly uncertain. Some studies suggest that N losses exceed inputs; others argue for a balanced budget. Here, we use a global ocean circulation model to simulate the distribution of N2 gas produced by denitrifying bacteria in the three main suboxic zones in the open ocean. By fitting the model to measured N2 gas concentrations, we infer a globally integrated rate of water-column denitrification of 66+/-6TgNyr-1. Taking into account isotopic constraints on the fraction of denitrification occurring in the water column versus marine sediments, we estimate that the global rate of N loss from marine sediments and the oceanic water column combined amounts to around 230+/-60TgNyr-1. Given present estimates of N input rates, our findings imply a net loss of around 20+/-70Tg of N from the global ocean each year, indistinguishable from a balanced budget. A balanced N budget, in turn, implies that the marine N cycle is governed by strong regulatory feedbacks.

  4. The logic of comparative life history studies for estimating key parameters, with a focus on natural mortality rate

    USGS Publications Warehouse

    Hoenig, John M; Then, Amy Y.-H.; Babcock, Elizabeth A.; Hall, Norman G.; Hewitt, David A.; Hesp, Sybrand A.

    2016-01-01

    There are a number of key parameters in population dynamics that are difficult to estimate, such as natural mortality rate, intrinsic rate of population growth, and stock-recruitment relationships. Often, these parameters of a stock are, or can be, estimated indirectly on the basis of comparative life history studies. That is, the relationship between a difficult to estimate parameter and life history correlates is examined over a wide variety of species in order to develop predictive equations. The form of these equations may be derived from life history theory or simply be suggested by exploratory data analysis. Similarly, population characteristics such as potential yield can be estimated by making use of a relationship between the population parameter and bio-chemico–physical characteristics of the ecosystem. Surprisingly, little work has been done to evaluate how well these indirect estimators work and, in fact, there is little guidance on how to conduct comparative life history studies and how to evaluate them. We consider five issues arising in such studies: (i) the parameters of interest may be ill-defined idealizations of the real world, (ii) true values of the parameters are not known for any species, (iii) selecting data based on the quality of the estimates can introduce a host of problems, (iv) the estimates that are available for comparison constitute a non-random sample of species from an ill-defined population of species of interest, and (v) the hierarchical nature of the data (e.g. stocks within species within genera within families, etc., with multiple observations at each level) warrants consideration. We discuss how these issues can be handled and how they shape the kinds of questions that can be asked of a database of life history studies.

  5. InterVA versus Spectrum: how comparable are they in estimating AIDS mortality patterns in Nairobi's informal settlements?

    PubMed Central

    Oti, Samuel Oji; Wamukoya, Marilyn; Mahy, Mary; Kyobutungi, Catherine

    2013-01-01

    Background The Spectrum computer package is used to generate national AIDS mortality estimates in settings where vital registration systems are lacking. Similarly, InterVA-4 (the latest version of the InterVA programme) is used to estimate cause-of-mortality data in countries where cause-specific mortality data are not available. Objective This study aims to compare trends in adult AIDS-related mortality estimated by Spectrum with trends from the InterVA-4 programme applied to data from a Health and Demographic Surveillance System (HDSS) in Nairobi, Kenya. Design A Spectrum model was generated for the city of Nairobi based on HIV prevalence data for Nairobi and national antiretroviral therapy coverage, underlying mortality, and migration assumptions. We then used data, generated through verbal autopsies, on 1,799 deaths that occurred in the HDSS area from 2003 to 2010 among adults aged 15–59. These data were then entered into InterVA-4 to estimate causes of death using probabilistic modelling. Estimates of AIDS-related mortality rates and all-cause mortality rates from Spectrum and InterVA-4 were compared and presented as annualised trends. Results Spectrum estimated that HIV prevalence in Nairobi was 7%, while the HDSS site measured 12% in 2010. Despite this difference, Spectrum estimated higher levels of AIDS-related mortality. Between 2003 and 2010, the proportion of AIDS-related mortality in Nairobi decreased from 63 to 40% according to Spectrum and from 25 to 16% according to InterVA. The net AIDS-related mortality in Spectrum was closer to the combined mortality rates when AIDS and tuberculosis (TB) deaths were included for InterVA-4. Conclusion Overall trends in AIDS-related deaths from both methods were similar, although the values were closer when TB deaths were included in InterVA. InterVA-4 might not accurately differentiate between TB and AIDS deaths. PMID:24160914

  6. [Comparative analysis of modern approaches to risk estimation from artificially created nanoparticles and nanomaterials].

    PubMed

    Kazak, A A; Stepanov, E G; Gmoshinskiĭ, I V; Khotimchenko, S A

    2012-01-01

    The article represents a review of modern approaches to problem of nanotechnologies and nanomaterials risk estimation for human health and environment that were elaborated in EU, USA and some international authorities. Submitted data suggests that there is a significant coincidence with approaches being developed and introduced in Russian Federation under the guidance of Rospotrebnadzor. Particularly criteria being used in Russian Federation and EU for classification of nanotechnologies and nanoindustry production are mainly similar. They include a) identification of nanomaterials in production, b) establishment of production disintegration possibility with concomitant migration of free nanoparticles, c) possibility of nanoparticles emission/migration both in normal conditions of utilization and in possible emergency conditions, d) degree of proximity of particular kind of production to it's consumer that means the possibility of exposition being from closely to zero (in conditions of unhabitated exploitation) up to approximately 100% (in case of medicine, food and cosmetics), e) biological examination of potential danger of nanomaterials according to current volume of scientific information. As applied to nanotechnology plants there are such criteria in use as a) nanomaterial identification, b) personnel exhibiting possibility, c) potential toxicity of stuff in aerosol nano-form, d) characteristics of biological action. Thus applied in Russia principles for nanomaterials safety estimation do not contradict to concepts of foreign authorities that builds up a possibility of said approaches harmonization to internationally recognized norms. PMID:23156045

  7. Ecosystem Modeling of College Drinking: Parameter Estimation and Comparing Models to Data*

    PubMed Central

    Ackleh, Azmy S.; Fitzpatrick, Ben G.; Scribner, Richard; Simonsen, Neal; Thibodeaux, Jeremy J.

    2009-01-01

    Recently we developed a model composed of five impulsive differential equations that describes the changes in drinking patterns (that persist at epidemic level) amongst college students. Many of the model parameters cannot be measured directly from data; thus, an inverse problem approach, which chooses the set of parameters that results in the “best” model to data fit, is crucial for using this model as a predictive tool. The purpose of this paper is to present the procedure and results of an unconventional approach to parameter estimation that we developed after more common approaches were unsuccessful for our specific problem. The results show that our model provides a good fit to survey data for 32 campuses. Using these parameter estimates, we examined the effect of two hypothetical intervention policies: 1) reducing environmental wetness, and 2) penalizing students who are caught drinking. The results suggest that reducing campus wetness may be a very effective way of reducing heavy episodic (binge) drinking on a college campus, while a policy that penalizes students who drink is not nearly as effective. PMID:20161275

  8. Estimation of staff lens doses during interventional procedures. Comparing cardiology, neuroradiology and interventional radiology.

    PubMed

    Vano, E; Sanchez, R M; Fernandez, J M

    2015-07-01

    The purpose of this article is to estimate lens doses using over apron active personal dosemeters in interventional catheterisation laboratories (cardiology IC, neuroradiology IN and radiology IR) and to investigate correlations between occupational lens doses and patient doses. Active electronic personal dosemeters placed over the lead apron were used on a sample of 204 IC procedures, 274 IN and 220 IR (all performed at the same university hospital). Patient dose values (kerma area product) were also recorded to evaluate correlations with occupational doses. Operators used the ceiling-suspended screen in most cases. The median and third quartile values of equivalent dose Hp(10) per procedure measured over the apron for IC, IN and IR resulted, respectively, in 21/67, 19/44 and 24/54 µSv. Patient dose values (median/third quartile) were 75/128, 83/176 and 61/159 Gy cm(2), respectively. The median ratios for dosemeters worn over the apron by operators (protected by the ceiling-suspended screen) and patient doses were 0.36; 0.21 and 0.46 µSv Gy(-1) cm(-2), respectively. With the conservative approach used (lens doses estimated from the over apron chest dosemeter) we came to the conclusion that more than 800 procedures y(-1) and per operator were necessary to reach the new lens dose limit for the three interventional specialties. PMID:25848117

  9. Microphytobenthic potential productivity estimated in three tidal embayments of the San Francisco Bay: A comparative study

    USGS Publications Warehouse

    Guarini, J.-M.; Cloern, James E.; Edmunds, J.

    2002-01-01

    In this paper we describe a three-step procedure to infer the spatial heterogeneity in microphytobenthos primary productivity at the scale of tidal estuaries and embayments. The first step involves local measurement of the carbon assimilation rate of benthic microalgae to determine the parameters of the photosynthesis-irradiance (P-E) curves (using non-linear optimization methods). In the next step, a resampling technique is used to rebuild pseudo-sampling distributions of the local productivity estimates; these provide error estimates for determining the significance level of differences between sites. The third step combines the previous results with deterministic models of tidal elevation and solar irradiance to compute mean and variance of the daily areal primary productivity over an entire intertidal mudflat area within each embayment. This scheme was applied on three different intertidal mudflat regions of the San Francisco Bay estuary during autumn 1998. Microphytobenthos productivity exhibits strong (ca. 3-fold) significant differences among the major sub-basins of San Francisco Bay. This spatial heterogeneity is attributed to two main causes: significant differences in the photosynthetic competence (P-E parameters) of the microphytobenthos in the different sub-basins, and spatial differences in the phase shifts between the tidal and solar cycles controlling the exposure of intertidal areas to sunlight. The procedure is general and can be used in other estuaries to assess the magnitude and patterns of spatial variability of microphytobenthos productivity at the level of the ecosystems.

  10. Full Bayes Poisson gamma, Poisson lognormal, and zero inflated random effects models: Comparing the precision of crash frequency estimates.

    PubMed

    Aguero-Valverde, Jonathan

    2013-01-01

    In recent years, complex statistical modeling approaches have being proposed to handle the unobserved heterogeneity and the excess of zeros frequently found in crash data, including random effects and zero inflated models. This research compares random effects, zero inflated, and zero inflated random effects models using a full Bayes hierarchical approach. The models are compared not just in terms of goodness-of-fit measures but also in terms of precision of posterior crash frequency estimates since the precision of these estimates is vital for ranking of sites for engineering improvement. Fixed-over-time random effects models are also compared to independent-over-time random effects models. For the crash dataset being analyzed, it was found that once the random effects are included in the zero inflated models, the probability of being in the zero state is drastically reduced, and the zero inflated models degenerate to their non zero inflated counterparts. Also by fixing the random effects over time the fit of the models and the precision of the crash frequency estimates are significantly increased. It was found that the rankings of the fixed-over-time random effects models are very consistent among them. In addition, the results show that by fixing the random effects over time, the standard errors of the crash frequency estimates are significantly reduced for the majority of the segments on the top of the ranking. PMID:22633143

  11. A Method for Making Cross-Comparable Estimates of the Benefits of Decision Support Technologies for Air Traffic Management

    NASA Technical Reports Server (NTRS)

    Lee, David; Long, Dou; Etheridge, Mel; Plugge, Joana; Johnson, Jesse; Kostiuk, Peter

    1998-01-01

    We present a general method for making cross comparable estimates of the benefits of NASA-developed decision support technologies for air traffic management, and we apply a specific implementation of the method to estimate benefits of three decision support tools (DSTs) under development in NASA's advanced Air Transportation Technologies Program: Active Final Approach Spacing Tool (A-FAST), Expedite Departure Path (EDP), and Conflict Probe and Trial Planning Tool (CPTP). The report also reviews data about the present operation of the national airspace system (NAS) to identify opportunities for DST's to reduce delays and inefficiencies.

  12. Soil denitrification fluxes from three northeastern North American forests across a range of nitrogen deposition.

    PubMed

    Morse, Jennifer L; Durán, Jorge; Beall, Fred; Enanga, Eric M; Creed, Irena F; Fernandez, Ivan; Groffman, Peter M

    2015-01-01

    In northern forests, large amounts of missing N that dominate N balances at scales ranging from small watersheds to large regional drainage basins may be related to N-gas production by soil microbes. We measured denitrification rates in forest soils in northeastern North America along a N deposition gradient to determine whether N-gas fluxes were a significant fate for atmospheric N inputs and whether denitrification rates were correlated with N availability, soil O2 status, or forest type. We quantified N2 and N2O fluxes in the laboratory with an intact-core method and monitored soil O2, temperature and moisture in three forests differing in natural and anthropogenic N enrichment: Turkey Lakes Watershed, Ontario; Hubbard Brook Experimental Forest, New Hampshire; and Bear Brook Watershed, Maine (fertilized and reference plots in hardwood and softwood stands). Total N-gas flux estimates ranged from <1 in fertilized hardwood uplands at Bear Brook to >100 kg N ha(-1) year(-1) in hardwood wetlands at Turkey Lakes. N-gas flux increased systematically with natural N enrichment from soils with high nitrification rates (Bear Brook < Hubbard Brook < Turkey Lakes) but did not increase in the site where N fertilizer has been added since 1989 (Bear Brook). Our results show that denitrification is an important and underestimated term (1-24% of atmospheric N inputs) in N budgets of upland forests in northeastern North America, but it does not appear to be an important sink for elevated anthropogenic atmospheric N deposition in this region. PMID:25407616

  13. Comparing conservative and nonconservative tracers in karst and using them to estimate flow path geometry

    NASA Astrophysics Data System (ADS)

    Luhmann, Andrew J.; Covington, Matthew D.; Alexander, Scott C.; Chai, Su Yi; Schwartz, Benjamin F.; Groten, Joel T.; Alexander, E. Calvin

    2012-07-01

    SummaryA controlled recharge event was conducted with multiple tracers in a karst aquifer in southeastern Minnesota. A pool adjacent to a sinkhole was filled with approximately 13,000 L of water. After tracers were added and thoroughly mixed, the pool was emptied into the sinkhole. Data were collected at Freiheit Spring approximately 95 m north of the sinkhole to monitor spring responses. Flow peaked first at the spring, and suspended sediment peaked next. Then nearly identical uranine, chloride, and δD peaks occurred. Temperature was the last of the tracers to peak. The initial increase in flow at the spring recorded the time at which the water reached a submerged conduit, sending a pressure pulse to the spring at approximately the speed of sound in open water. The initial increase in uranine, chloride, and δD at the spring recorded the arrival of the recharge water. The initial change in temperature and its peak occurred later than the same features in the uranine, chloride, and δD breakthrough curves. As water flowed along this flow path, water exchanged heat with the aquifer, producing a lagged, damped thermal peak at the spring. The combination of hydraulic response and conservative and nonconservative tracers illustrates unique pressure, advective, and nonconservative processes. Geometrical properties of the flow system may be estimated using these tracers. By summing discharge between the time of the initial increase in stage produced by a pressure pulse in a fully phreatic flow path and the time of the chloride peak, the conduit volume is estimated as 47 ± 10% m3. Heat transport simulations were used to reproduce the modified thermal signal, and simulations with planar flow paths and hydraulic diameters of 7 and 8 cm produced the best fits to the observed temperature breakthrough curve. These volume and hydraulic diameter estimates together predict a bedding plane flow path that is 3.5 cm high by 9 m wide or 4 cm high by 8 m wide. The different tracers

  14. A comparative study on defect estimation using XPS and Raman spectroscopy in few layer nanographitic structures.

    PubMed

    Ganesan, K; Ghosh, Subrata; Gopala Krishna, Nanda; Ilango, S; Kamruddin, M; Tyagi, A K

    2016-08-10

    Defects in planar and vertically oriented nanographitic structures (NGSs) synthesized by plasma enhanced chemical vapor deposition (PECVD) have been investigated using Raman and X-ray photoelectron spectroscopy. While Raman spectra reveal the dominance of vacancy and boundary type defects respectively in vertical and planar NGSs, XPS provides additional information on vacancy related defect peaks in the C 1s spectrum, which originate from non-conjugated carbon atoms in the hexagonal lattice. Although an excellent correlation prevails between these two techniques, our results show that estimation of surface defects by XPS is more accurate than Raman analysis. Nuances of these techniques are discussed in the context of assessing defects in nanographitic structures. PMID:27445041

  15. [Comparative Research on Estimating the Severity of Yellow Rust in Winter Wheat].

    PubMed

    Wang, Jing; Jing, Yuan-shu; Huang, Wen-jiang; Zhang, Jing-cheng; Zhao, Juan; Zhang, Qing; Wang, Li

    2015-06-01

    In order to improve the accuracy of wheat yellow rust disease severity using remote sensing and to find the optimum inversion model of wheat diseases, the canopy reflectance and disease index (DI) of winter wheat under different severity stripe rust were acquired. The three models of PLS (Partial Least Square), BP neural network using seven hyperspectral vegetation indices which have significant relationship with the occurrence of disease and vegetation index (PRI) were adopted to build a feasible regression model for detecting the disease severity. The results showed that PLS performed much better. The inversion accuracy of PLS method is best than of the VI (PRI, Photochemical Reflectance Index) and BP neural network models. The coefficients of determination (R2) of three methods to estimate disease severity between predicted and measured values are 0.936, 0.918 and 0.767 respectively. Evaluation was made between the estimated DI and the measured DI, indicating that the model based on PLS is suitable for monitoring wheat disease. In addition, to explore the different contributions of diverse types of vegetation index to the models, the paper attempts to use NDVI, GNDVI and MSR which on behalf of vegetation greenness and NDWI and MSI that represents the moisture content to be input variables of PLS model. The results showed that, for the wheat yellow rust disease, changes in chlorophyll content is more sensitive to the disease severity than the changes in water content of the canopy. However, the accuracy of the two models are both lower than predicted when participating in all seven vegetation indices, namely using several species of vegetation indices tends to be more accurate than that using single category. It indicated that it has great potential for evaluating wheat disease severity by using hyper-spectral remote sensing. PMID:26601384

  16. Comparing Regression Coefficients between Nested Linear Models for Clustered Data with Generalized Estimating Equations

    ERIC Educational Resources Information Center

    Yan, Jun; Aseltine, Robert H., Jr.; Harel, Ofer

    2013-01-01

    Comparing regression coefficients between models when one model is nested within another is of great practical interest when two explanations of a given phenomenon are specified as linear models. The statistical problem is whether the coefficients associated with a given set of covariates change significantly when other covariates are added into…

  17. Estimation of VO2 Max: A Comparative Analysis of Five Exercise Tests.

    ERIC Educational Resources Information Center

    Zwiren, Linda D.; And Others

    1991-01-01

    Thirty-eight healthy females measured maximal oxygen uptake (VO2max) on the cycle ergometer and treadmill to compare five exercise tests (run, walk, step, and two tests using heart-rate response on the bicycle ergometer) in predicting VO2max. Results indicate that walk and run tests are satisfactory predictors of VO2max in 30- to 39-year-old…

  18. Comparative analysis of forest lands cadastral appraisal estimated with regards to wood and food resources

    NASA Astrophysics Data System (ADS)

    Kovyazin, V.; Romanchikov, A.; Pasko, O.

    2015-11-01

    Cadastral appraisal of forest fund is one of the topical challenges of modern natural resource management. The paper delivers comparison of different approaches to cadastral appraisal of forest lands. The authors suggest a uniformed model to compare objectively and choose the most effective use of parcels.

  19. A Comparative Study of Information-Based Source Number Estimation Methods and Experimental Validations on Mechanical Systems

    PubMed Central

    Cheng, Wei; Zhang, Zhousuo; Cao, Hongrui; He, Zhengjia; Zhu, Guanwen

    2014-01-01

    This paper investigates one eigenvalue decomposition-based source number estimation method, and three information-based source number estimation methods, namely the Akaike Information Criterion (AIC), Minimum Description Length (MDL) and Bayesian Information Criterion (BIC), and improves BIC as Improved BIC (IBIC) to make it more efficient and easier for calculation. The performances of the abovementioned source number estimation methods are studied comparatively with numerical case studies, which contain a linear superposition case and a both linear superposition and nonlinear modulation mixing case. A test bed with three sound sources is constructed to test the performances of these methods on mechanical systems, and source separation is carried out to validate the effectiveness of the experimental studies. This work can benefit model order selection, complexity analysis of a system, and applications of source separation to mechanical systems for condition monitoring and fault diagnosis purposes. PMID:24776935

  20. Fungal and bacterial mediated denitrification in wetlands: influence of sediment redox condition.

    PubMed

    Seo, Dong Cheol; DeLaune, R D

    2010-04-01

    Fungal and bacterial denitrification rates were determined under a range of redox conditions in sediment from a Louisiana swamp forest used for wastewater treatment. Sediment was incubated in microcosms at 6 Eh levels (-200, -100, 0, +100, +250 and +400 mV) ranging from strongly reducing to moderately oxidizing conditions. Denitrification was determined using the substrate-induced respiration (SIR) inhibition and acetylene inhibition methods. Cycloheximide (C15H23NO4) was used as the fungal inhibitor and streptomycin (C21H39N7O12) as the bacterial inhibitor. At Eh values of +250 mV and +400 mV, denitrification rates by fungi and bacteria were 34.3-35.1% and 1.46-1.59% of total denitrification, respectively, indicating that fungi were responsible for most of the denitrification under aerobic or weakly reducing conditions. On the other hand, at Eh -200 mV, denitrification rates of fungi and bacteria were 17.6% and 64.9% of total denitrification, respectively, indicating that bacteria were responsible for most of the denitrification under strongly reducing conditions. Results show fungal denitrification was dominant under moderately reducing to weakly oxidizing conditions (Eh>+250 mV), whereas bacterial denitrification was dominant under strongly reducing condition (Eh<-100 mV). At Eh values between -100 to +100 mV, denitrification by fungi and bacteria were 37.9-43.2% and 53.0-51.1% of total denitrification, respectively, indicating that both bacteria and fungi contributed significantly to denitrification under these redox conditions. Because N2O is an important gaseous denitrification product in sediment, fungal denitrification could be of greater ecological significance under aerobic or moderately reducing conditions contributing to greenhouse gas emission and global warming potential (GWP). PMID:20122708

  1. Summer nitrate uptake and denitrification in an upper Mississippi River backwater lake: The role of rooted aquatic vegetation

    USGS Publications Warehouse

    Kreiling, Rebecca M.; Richardson, W.B.; Cavanaugh, J.C.; Bartsch, L.A.

    2011-01-01

    In-stream nitrogen processing in the Mississippi River has been suggested as one mechanism to reduce coastal eutrophication in the Gulf of Mexico. Aquatic macrophytes in river channels and flood plain lakes have the potential to temporarily remove large quantities of nitrogen through assimilation both by themselves and by the attached epiphyton. In addition, rooted macrophytes act as oxygen pumps, creating aerobic microsites around their roots where coupled nitrification-denitrification can occur. We used in situ 15N-NO3- tracer mesocosm experiments to measure nitrate assimilation rates for macrophytes, epiphyton, and microbial fauna in the sediment in Third Lake, a backwater lake of the upper Mississippi River during June and July 2005. We measured assimilation over a range of nitrate concentrations and estimated a nitrate mass balance for Third Lake. Macrophytes assimilated the most nitrate (29.5 mg N m-2 d-1) followed by sediment microbes (14.4 mg N m-2 d-1) and epiphytes (5.7 mg N m-2d-1. Assimilation accounted for 6.8% in June and 18.6% in July of total nitrate loss in the control chambers. However, denitrification (292.4 mg N m-2 d-1) is estimated to account for the majority (82%) of the nitrate loss. Assimilation and denitrification rates generally increased with increasing nitrate concentration but denitrification rates plateaued at about 5 mg N L-1. This suggests that backwaters have the potential to remove a relatively high amount of nitrate but will likely become saturated if the load becomes too large. ?? 2010 US Government.

  2. Comparative estimates of transpiration of ash and beech forest at a chalk site in southern Britain

    NASA Astrophysics Data System (ADS)

    Roberts, John; Rosier, Paul T. W.

    1994-11-01

    (1) During the dry summer of 1989 stomatal conductance ( gs), boundary-layer conductance ( ga), leaf water and osmotic potentials ( ψ1, ψπ) and leaf area index ( L∗) measurements were made in mature ash and beech stands growing on shallow soil over chalk near Winchester, Hampshire, UK. In addition measurements of gs and L∗ were made in the understorey layer in the ash stand, comprised mainly of dog's mercury, hazel and bramble. Automatic weather stations located (i) above the beech stand and (ii) at the understorey level (within the ash stand) provided hourly averages of weather variables. Changes in soil moisture deficit in both stands were determined from regular measurements made with a neutron probe. (2) Maximum values of gs (up to 0.3 mol m -2 s -1) were found at the top of the ash and beech canopies at the start of the day, while at the canopy base gs was about half of these values. At all canopy levels the value of gs was more closely associated with specific humidity deficit (at the time of measurement) than with any other weather variable, and there was no relationship between gs and soil mositure deficit or leaf water status, described by ψ1 and ψπ on the day of measurement. (3) Values of gs of the understorey plants were only half those of the tree species and changed less during the day. However, seasonal changes in gs of dog's mercury did seem to be associated with increased soil moisture deficit. (4) Estimates of L∗ in the ash and beech stands were made from leaf litter collections and partitioned into canopy layers using ratios determined by destructive sampling. L∗ of the beech stand was 5.3 and for the ash stand 2.7. L∗ of the understorey varied seasonally and rose to a peak of 3 in June falling gradually for the remainder of the summer period. (5) Hourly values of gs and ga in each stand for each canopy layer were scaled up to the canopy by using L∗ of the individual canopy layers (including the understorey level in the ash stand

  3. Health risks in wastewater irrigation: comparing estimates from quantitative microbial risk analyses and epidemiological studies.

    PubMed

    Mara, D D; Sleigh, P A; Blumenthal, U J; Carr, R M

    2007-03-01

    The combination of standard quantitative microbial risk analysis (QMRA) techniques and 10,000-trial Monte Carlo risk simulations was used to estimate the human health risks associated with the use of wastewater for unrestricted and restricted crop irrigation. A risk of rotavirus infection of 10(-2) per person per year (pppy) was used as the reference level of acceptable risk. Using the model scenario of involuntary soil ingestion for restricted irrigation, the risk of rotavirus infection is approximately 10(-2) pppy when the wastewater contains < or =10(6) Escherichia coli per 100ml and when local agricultural practices are highly mechanised. For labour-intensive agriculture the risk of rotavirus infection is approximately 10(-2) pppy when the wastewater contains < or = 10(5) E. coli per 100ml; however, the wastewater quality should be < or = 10(4) E. coli per 100ml when children under 15 are exposed. With the model scenario of lettuce consumption for unrestricted irrigation, the use of wastewaters containing < or =10(4) E. coli per 100ml results in a rotavirus infection risk of approximately 10(-2) pppy; however, again based on epidemiological evidence from Mexico, the current WHO guideline level of < or =1,000 E. coli per 100ml should be retained for root crops eaten raw. PMID:17402278

  4. Comparing ensemble projections of flooding against flood estimation by continuous simulation

    NASA Astrophysics Data System (ADS)

    Smith, Andrew; Freer, Jim; Bates, Paul; Sampson, Christopher

    2014-04-01

    Climate impact studies focused on the projection of changing flood risk are increasingly utilized to inform future flood risk policy. These studies typically use the output from global (GCMs) and regional climate models (RCMs). However the direct application of GCM/RCM output is controversial as often significant biases exist in predicted rainfall; instead a number of alternative 'correction' approaches have emerged. In this study an ensemble of RCMs from the ENSEMBLES and UKCP09 projects are applied, via a number of application techniques, to explore the possible impacts of climate change on flooding in the Avon catchment, in the UK. The analysis is conducted under a continuous simulation methodology, using a stochastic rainfall generator to drive the HBV-light rainfall run-off model under a parameter uncertainty framework. This permitted a comparison between the projections produced by differing application approaches, whilst also considering the uncertainty associated with flood risk projections under observed conditions. The results from each of the application approaches project an increase in annual maximum flows under the future (2061-2099) climate scenario. However the magnitude and spread of the projected changes varied significantly. These findings highlight the need to incorporate multiple approaches in climate impact studies focusing on flood risk. Additionally these results outline the significant uncertainties associated with return period estimates under current climate conditions, suggesting that uncertainty over this observed record already poses a challenge to develop robust risk management plans.

  5. Modeling Groundwater-Quality Data from In-Situ Mesocosms Using PHREEQC to Provide Insights into the Electron Donors Involved in Denitrification in the Karlsruhe Aquifer, ND

    NASA Astrophysics Data System (ADS)

    Korom, S. F.; Tesfay, T.

    2009-12-01

    results were compared to actual results to determine which reactions with nitrate best explained the natural evolution of the water quality in the ISMs. Denitrification in the KG ISM was < 0.5 mM after two years; denitrification by pyrite was evident - explaining 16 to 88% of the denitrification, depending on the sampling date, but the denitrification rate was apparently too low for the modeling methodology to provide information on how much ferrous iron and OC were involved. Two tracer tests were done at the KS ISM. The modeling results suggest that during the first test pyrite accounted for 14 to 30% of the denitrification measured, with OC causing the majority of the denitrification remaining. For the second test OC accounted for nearly all of the denitrification.

  6. The negligible effect of bed form migration on denitrification in hyporheic zones of permeable sediments

    NASA Astrophysics Data System (ADS)

    Kessler, Adam J.; Cardenas, M. Bayani; Cook, Perran L. M.

    2015-03-01

    Bed form celerity, the migration rate of ripples along a sediment bed, has previously been shown to have dramatic effects on oxygen distribution and transport within the hyporheic zone of permeable sediments. This has the potential to influence denitrification rates—in particular by increasing the coupling of nitrification and denitrification. To further understand this, we numerically modeled nitrogen cycling under migrating ripples. While the simulated oxygen profiles match with expected behavior, almost no effect on denitrification or coupled nitrification-denitrification was observed with increasing celerity. Instead, denitrification rates were dominantly controlled by the flow velocity of water overlying the sediment.

  7. Denitrification in Wood Chip Bioreactors at Different Water Flows

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Subsurface drainage in agricultural watersheds exports a large quantity of nitrate-nitrogen (NO3-N) and concentrations frequently exceed 10 mg L-1. A laboratory column study was conducted to investigate the ability of a wood chip biofilter to promote denitrification under mean water flow rates of 2....

  8. Denitrification in Alluvial Wetlands in an Urban Landscape

    EPA Science Inventory

    Riparian wetlands have been shown to be particularly effective “sinks” for nitrate-N (NO3-), minimizing the downstream export of nitrogen (N) to streams and coastal water bodies. However, the vast majority of riparian denitrification research has been in agricultural and forested...

  9. Denitrification Rates in a Lake Superior Coastal Wetland

    EPA Science Inventory

    In recent years, nitrogen has increased substantially in the Nation’s aquatic ecosystems mainly due to the increased use of fertilizers and land use practices. Denitrification is a process that can potentially mitigate this increased influx of fixed nitrate. Coastal wetlands are ...

  10. Microbial denitrification dominates nitrate losses from forest ecosystems.

    PubMed

    Fang, Yunting; Koba, Keisuke; Makabe, Akiko; Takahashi, Chieko; Zhu, Weixing; Hayashi, Takahiro; Hokari, Azusa A; Urakawa, Rieko; Bai, Edith; Houlton, Benjamin Z; Xi, Dan; Zhang, Shasha; Matsushita, Kayo; Tu, Ying; Liu, Dongwei; Zhu, Feifei; Wang, Zhenyu; Zhou, Guoyi; Chen, Dexiang; Makita, Tomoko; Toda, Hiroto; Liu, Xueyan; Chen, Quansheng; Zhang, Deqiang; Li, Yide; Yoh, Muneoki

    2015-02-01

    Denitrification removes fixed nitrogen (N) from the biosphere, thereby restricting the availability of this key limiting nutrient for terrestrial plant productivity. This microbially driven process has been exceedingly difficult to measure, however, given the large background of nitrogen gas (N2) in the atmosphere and vexing scaling issues associated with heterogeneous soil systems. Here, we use natural abundance of N and oxygen isotopes in nitrate (NO3 (-)) to examine dentrification rates across six forest sites in southern China and central Japan, which span temperate to tropical climates, as well as various stand ages and N deposition regimes. Our multiple stable isotope approach across soil to watershed scales shows that traditional techniques underestimate terrestrial denitrification fluxes by up to 98%, with annual losses of 5.6-30.1 kg of N per hectare via this gaseous pathway. These N export fluxes are up to sixfold higher than NO3 (-) leaching, pointing to widespread dominance of denitrification in removing NO3 (-) from forest ecosystems across a range of conditions. Further, we report that the loss of NO3 (-) to denitrification decreased in comparison to leaching pathways in sites with the highest rates of anthropogenic N deposition. PMID:25605898

  11. Internal hydraulics of an agricultural drainage denitrification bioreactor

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Denitrification bioreactors to reduce the amount of nitrate-nitrogen in agricultural drainage are now being deployed across the U.S. Midwest. However, there are still many unknowns regarding internal hydraulic-driven processes in these "black box" engineered treatment systems. To improve this unders...

  12. Nitrous oxide emission from denitrification in stream and river networks

    EPA Science Inventory

    Nitrous oxide (N2O) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Anthropogenic nitrogen (N) loading to river networks is a potentially important source of N2O via microbial denitrification which converts N to N2O and dinitrog...

  13. Denitrification in anaerobic digesters: A review of recent studies

    SciTech Connect

    Akunna, J.C.

    1996-11-01

    Wastewaters from food processing industries (and domestic activities) are usually treated principally for organic carbon removal. But recent standards have generated interests in nitrogen and phosphorus removal. This has led to the addition of nitrification, denitrification and phosphorus removal units in the existing treatment plants, thus increasing the cost of treatment operations. The need to reduce treatment costs has led to research on ways to carry out many treatment processes in a single system. One of these systems consists of anaerobic and aerobic units in series with effluent recycle. In the anaerobic unit, anaerobic digestion and denitrification take place simultaneously producing methane and nitrogen gas while in the aerobic unit, ammonia oxidation to nitrate (nitrification) takes place. This process configuration appears to give lesser problems associated with operations such as the addition of raw wastewater or external organic carbon to ensure complete denitrification. In this paper a review of the results of recent studies are presented, with special emphasis on the factors affecting treatment efficiencies (i.e., denitrification, ammonia production from nitrate, and methane production efficiencies).

  14. Denitrification in anaerobic lagoons used to treat swine wastewater.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Anaerobic lagoons are commonly used for treatment of swine wastewater. Although these lagoons were once thought to be relatively simple; their physical, chemical, and biological processes are actually very complex. This study of anaerobic lagoons had twofold objectives: 1] quantify denitrification e...

  15. Microbial denitrification dominates nitrate losses from forest ecosystems

    PubMed Central

    Fang, Yunting; Koba, Keisuke; Makabe, Akiko; Takahashi, Chieko; Zhu, Weixing; Hayashi, Takahiro; Hokari, Azusa A.; Urakawa, Rieko; Bai, Edith; Houlton, Benjamin Z.; Xi, Dan; Zhang, Shasha; Matsushita, Kayo; Tu, Ying; Liu, Dongwei; Zhu, Feifei; Wang, Zhenyu; Zhou, Guoyi; Chen, Dexiang; Makita, Tomoko; Toda, Hiroto; Liu, Xueyan; Chen, Quansheng; Zhang, Deqiang; Li, Yide; Yoh, Muneoki

    2015-01-01

    Denitrification removes fixed nitrogen (N) from the biosphere, thereby restricting the availability of this key limiting nutrient for terrestrial plant productivity. This microbially driven process has been exceedingly difficult to measure, however, given the large background of nitrogen gas (N2) in the atmosphere and vexing scaling issues associated with heterogeneous soil systems. Here, we use natural abundance of N and oxygen isotopes in nitrate (NO3−) to examine dentrification rates across six forest sites in southern China and central Japan, which span temperate to tropical climates, as well as various stand ages and N deposition regimes. Our multiple stable isotope approach across soil to watershed scales shows that traditional techniques underestimate terrestrial denitrification fluxes by up to 98%, with annual losses of 5.6–30.1 kg of N per hectare via this gaseous pathway. These N export fluxes are up to sixfold higher than NO3− leaching, pointing to widespread dominance of denitrification in removing NO3− from forest ecosystems across a range of conditions. Further, we report that the loss of NO3− to denitrification decreased in comparison to leaching pathways in sites with the highest rates of anthropogenic N deposition. PMID:25605898

  16. Model evaluation of denitrification under rapid infiltration basin systems

    NASA Astrophysics Data System (ADS)

    Akhavan, Maryam; Imhoff, Paul T.; Andres, A. Scott; Finsterle, Stefan

    2013-09-01

    Rapid Infiltration Basin Systems (RIBS) are used for disposing reclaimed wastewater into soil to achieve additional treatment before it recharges groundwater. Effluent from most new sequenced batch reactor wastewater treatment plants is completely nitrified, and denitrification (DNF) is the main reaction for N removal. To characterize effects of complex surface and subsurface flow patterns caused by non-uniform flooding on DNF, a coupled overland flow-vadose zone model is implemented in the multiphase flow and reactive transport simulator TOUGHREACT. DNF is simulated in two representative soils varying the application cycle, hydraulic loading rate, wastewater quality, water table depth, and subsurface heterogeneity. Simulations using the conventional specified flux boundary condition under-predict DNF by as much as 450% in sand and 230% in loamy sand compared to predictions from the coupled overland flow-vadose zone model, indicating that simulating coupled flow is critical for predicting DNF in cases where hydraulic loading rates are not sufficient to spread the wastewater over the whole basin. Smaller ratios of wetting to drying time and larger hydraulic loading rates result in greater water saturations, more anoxic conditions, and faster water transport in the vadose zone, leading to greater DNF. These results in combination with those from different water table depths explain why reported DNF varied with soil type and water table depth in previous field investigations. Across all simulations, cumulative percent DNF varies between 2 and 49%, indicating that NO3 removal in RIBS may vary widely depending on operational procedures and subsurface conditions. These modeling results improve understanding of DNF in RIBS and suggest operational procedures that may improve NO3 removal.

  17. Model evaluation of denitrification under rapid infiltration basin systems.

    PubMed

    Akhavan, Maryam; Imhoff, Paul T; Andres, A Scott; Finsterle, Stefan

    2013-09-01

    Rapid Infiltration Basin Systems (RIBS) are used for disposing reclaimed wastewater into soil to achieve additional treatment before it recharges groundwater. Effluent from most new sequenced batch reactor wastewater treatment plants is completely nitrified, and denitrification (DNF) is the main reaction for N removal. To characterize effects of complex surface and subsurface flow patterns caused by non-uniform flooding on DNF, a coupled overland flow-vadose zone model is implemented in the multiphase flow and reactive transport simulator TOUGHREACT. DNF is simulated in two representative soils varying the application cycle, hydraulic loading rate, wastewater quality, water table depth, and subsurface heterogeneity. Simulations using the conventional specified flux boundary condition under-predict DNF by as much as 450% in sand and 230% in loamy sand compared to predictions from the coupled overland flow-vadose zone model, indicating that simulating coupled flow is critical for predicting DNF in cases where hydraulic loading rates are not sufficient to spread the wastewater over the whole basin. Smaller ratios of wetting to drying time and larger hydraulic loading rates result in greater water saturations, more anoxic conditions, and faster water transport in the vadose zone, leading to greater DNF. These results in combination with those from different water table depths explain why reported DNF varied with soil type and water table depth in previous field investigations. Across all simulations, cumulative percent DNF varies between 2 and 49%, indicating that NO₃ removal in RIBS may vary widely depending on operational procedures and subsurface conditions. These modeling results improve understanding of DNF in RIBS and suggest operational procedures that may improve NO₃ removal. PMID:23835290

  18. Comparative Benchmark Dose Modeling as a Tool to Make the First Estimate of Safe Human Exposure Levels to Lunar Dust

    NASA Technical Reports Server (NTRS)

    James, John T.; Lam, Chiu-wing; Scully, Robert R.

    2013-01-01

    Brief exposures of Apollo Astronauts to lunar dust occasionally elicited upper respiratory irritation; however, no limits were ever set for prolonged exposure ot lunar dust. Habitats for exploration, whether mobile of fixed must be designed to limit human exposure to lunar dust to safe levels. We have used a new technique we call Comparative Benchmark Dose Modeling to estimate safe exposure limits for lunar dust collected during the Apollo 14 mission.

  19. Nitrogen speciation and trends, and prediction of denitrification extent, in shallow US groundwater

    USGS Publications Warehouse

    Hinkle, Stephen R.; Tesoriero, Anthony J.

    2014-01-01

    Uncertainties surrounding nitrogen cycling complicate assessments of the environmental effects of nitrogen use and our understanding of the global carbon–nitrogen cycle. In this paper, we synthesize data from 877 ambient-monitoring wells across the US to frame broad patterns of nitrogen speciation and trends. At these sites, groundwater frequently contains substantial co-occurring NO3− and XSN2 (N2 from denitrification), reflecting active/ongoing denitrification and/or a mixture of undenitrified and denitrified groundwater. NO3− and NH4+ essentially do not co-occur, indicating that the dominant source of NH4+ at these sites likely is not dissimilatory reduction of NO3− to NH4+. Positive correlations of NH4+ with apparent age, CH4, dissolved organic carbon, and indicators of reduced conditions are consistent with NH4+ mobilization from degradation of aquifer organic matter and contraindicate an anthropogenic source of NH4+ for most sites. Glacial aquifers and eastern sand and gravel aquifers generally have lower proportions of NO3− and greater proportions of XSN2 than do fractured rock and karst aquifers and western sand and gravel aquifers. NO3− dominates in the youngest groundwater, but XSN2 increases as residence time increases. Temporal patterns of nitrogen speciation and concentration reflect (1) changing NO3− loads over time, (2) groundwater residence-time controls on NH4+ mobilization from solid phases, and (3) groundwater residence-time controls on denitrification. A simple classification tree using readily available variables (a national coverage of soil water depth, generalized geology) or variables reasonably estimated in many aquifers (residence time) identifies categorical denitrification extent (<10%, 10–50%, and >50%) with 79% accuracy in an independent testing set, demonstrating a predictive application based on the interconnected effects of redox, geology, and residence time.

  20. Hydrological controls on denitrification in riparian zone of forested headwater catchment: Soil physical properties make difference in reduced environment

    NASA Astrophysics Data System (ADS)

    Ohte, N.; Watanabe, Y.; Oda, T.; Osaka, K.

    2010-12-01

    Riparian zone near stream plays important roles to control the solute discharge from hillslope to stream. Supply of inorganic nitrogen as an essential nutrient of aquatic primary producers is generally regulated by hydrological and biogeochemical processes such as denitrification in this unique landscape unit in headwaters. To elucidate how the denitrification is controlled by hydrological properties of riparian groundwater aquifer, we investigated two similar scaled forested headwater catchments with different soil physical properties in Japan. The Kiryu- Matsuzawa catchment (KEW, 0.6 ha) has weathered granitic bedrock, and its soils in riparian zones are sandy, while the Fukuroyama-sawa catchment (FEW, 1.1 ha) has Tertiary sedimentary bedrock, and has clayey soils. Concentrations, δ15N and δ18O of NO3- in soil water, groundwater and streamwater were monitored during 2007 - 2009. Enrichment in δ15N-NO3- was found in the perennial groundwater bodies both in KEW and FEW, indicating active denitrification occurred (Fig 1). In the same time, however, increase in δ18O-NO3- of KEW groundwater was unclear, while that of FEW was found clearly indicating the denitrification under a closed system without significant dissolved O2 (DO) and new NO3- supply. It was also suggested that the denitrification in the KEW groundwater occurred under condition with relatively high DO, and new NO3- recharge by lateral groundwater movement. These differences were explainable by hydrological features of soils holding groundwater: The mean residence time (MRT) of the groundwater in FEW was estimated as three times longer (>1000 days) than that in KEW (<300 days). Moreover, this difference in MRT of groundwater aquifer is essentially caused by difference in the soil water retention characteristics between sandy soil in KEW and clayey soil in FEW. Those indicated the possibility that the difference of soil physical properties can be reflected strongly on inorganic nitrogen discharge from

  1. Elucidation of denitrification mechanism in karstic Ryukyu limestone aquifer

    NASA Astrophysics Data System (ADS)

    Hijikawa, K.

    2014-12-01

    Nitrate (NO3-) concentrations in public water supplies have risen above acceptable levels in many areas of the world including Japan, largely as a result of contamination by human and animal waste and overuse of fertilizers. A previous study has characterized nitrate concentrations in groundwater in this area is a higher than the upper value (44mgL-1) of environmental quality criteria on one hands. On the other hand, there exists points where the concentration of nitric acid is not detected, which suggests the possibility of denitrification. During early 2000, a new analytical procedure for nitrate isotopic measurement, termed the "denitrifier method", was established. With the development of the nitrate isotope tracer method, much research has been reported detailing sources of groundwater nitrate and denitrification mechanisms. This study presents a pilot case study (in the southern part of Okinawa Main Island, Japan, where Ryukyu limestone is extensively distributed) using the combined stable isotope ratios of major elements (C, N and S) as net recorders of the biogeochemical reactions with the aim of elucidation of denitrification mechanism in Ryukyu limestone aquifer. As a result, significant decreases in nitrate concentrations due to denitrification were observed in groundwater at some locations, which induced increases in isotope ratios up to 59.7‰ for δ15NNO3. These points of groundwater were located above the cutoff wall of the underground dam and near the fault. It is considered that the residence time of the groundwater is longer than the other points at these denitrification points, and that reduction condition tends to be formed in the groundwater. However, the rapid rise of the groundwater level due to rainfall is likely to occur in the Ryukyu limestone aquifer, where the ground water was found to have changed dynamically from the reduction condition to the oxidation condition which a denitrification (has not occured)does not occur. Moreover, the

  2. The impact of relict organic materials on the denitrification capacity in the unsaturated-saturated zone continuum of three volcanic profiles.

    PubMed

    Clague, J C; Stenger, R; Clough, T J

    2013-01-01

    The denitrification capacity of wetlands, riparian zones, and aquifers in glacial outwash areas is well documented, but little or no information exists for volcanic profiles, particularly those containing relict organic matter contained in or on top of paleosols (old soils buried by volcanic deposits) below the groundwater table. Relict carbon contained in these layers could provide the necessary electrons to fuel heterotrophic denitrification. To the best of our knowledge, this is the first study investigating the denitrification capacity in both the unsaturated and saturated zone of volcanic profiles. Samples from three profile types with differing organic matter distribution were amended with N-enriched nitrate (NO-) and incubated in the laboratory under anaerobic conditions. Dinitrogen (N) dominated the N gas fluxes; averaged across all samples, it accounted for 96% of the total N (nitrous oxide [NO] and N) gas fluxes. Dinitrogen fluxes were generally highest in the A horizon samples (4.1-6.2 nmol N g h), but substantial fluxes were also observed in some paleosol layers (up to 0.72 nmol N g h). A significant correlation ( < 0.001) was found between the concentration of extractable dissolved organic carbon and the total N gas flux produced in samples from below the A horizon, suggesting that heterotrophic denitrification was the dominant NO attenuation process in this study. Extrapolation of lab-derived denitrification capacities to field conditions suggests that the denitrification capacity of profiles containing relict soil organic matter in the saturated zone exceeds the estimated N leaching from the root zone. PMID:23673749

  3. Comparing writing style feature-based classification methods for estimating user reputations in social media.

    PubMed

    Suh, Jong Hwan

    2016-01-01

    In recent years, the anonymous nature of the Internet has made it difficult to detect manipulated user reputations in social media, as well as to ensure the qualities of users and their posts. To deal with this, this study designs and examines an automatic approach that adopts writing style features to estimate user reputations in social media. Under varying ways of defining Good and Bad classes of user reputations based on the collected data, it evaluates the classification performance of the state-of-art methods: four writing style features, i.e. lexical, syntactic, structural, and content-specific, and eight classification techniques, i.e. four base learners-C4.5, Neural Network (NN), Support Vector Machine (SVM), and Naïve Bayes (NB)-and four Random Subspace (RS) ensemble methods based on the four base learners. When South Korea's Web forum, Daum Agora, was selected as a test bed, the experimental results show that the configuration of the full feature set containing content-specific features and RS-SVM combining RS and SVM gives the best accuracy for classification if the test bed poster reputations are segmented strictly into Good and Bad classes by portfolio approach. Pairwise t tests on accuracy confirm two expectations coming from the literature reviews: first, the feature set adding content-specific features outperform the others; second, ensemble learning methods are more viable than base learners. Moreover, among the four ways on defining the classes of user reputations, i.e. like, dislike, sum, and portfolio, the results show that the portfolio approach gives the highest accuracy. PMID:27006870

  4. O 2 reduction and denitrification rates in shallow aquifers

    USGS Publications Warehouse

    Tesoriero, A.J.; Puckett, L.J.

    2011-01-01

    O 2 reduction and denitrification rates were determined in shallow aquifers of 12 study areas representing a wide range in sedimentary environments and climatic conditions. Zero-and first-order rates were determined by relating reactant or product concentrations to apparent groundwater age. O 2 reduction rates varied widely within and between sites, with zero-order rates ranging from <3 ??mol L -1 yr -1 to more than 140 ??mol L -1 yr -1 and first-order rates ranging from 0.02 to 0.27 yr -1. Moderate denitrification rates (10-100 ??mol N L -1 yr -1; 0.06-0.30 yr -1) were observed in most areas with O 2 concentrations below 60 mol L -1, while higher rates (>100 mol N L -1 yr -1; >0.36 yr -1) occur when changes in lithology result in a sharp increase in the supply of electron donors. Denitrification lag times (i.e., groundwater travel times prior to the onset of denitrification) ranged from <20 yr to >80 yr. The availability of electron donors is indicated as the primary factor affecting O 2 reduction rates. Concentrations of dissolved organic carbon (DOC) and/or sulfate (an indicator of sulfide oxidation) were positively correlated with groundwater age at sites with high O 2 reduction rates and negatively correlated at sites with lower rates. Furthermore, electron donors from recharging DOC are not sufficient to account for appreciable O 2 and nitrate reduction. These relations suggest that lithologic sources of DOC and sulfides are important sources of electrons at these sites but surface-derived sources of DOC are not. A review of published rates suggests that denitrification tends to occur more quickly when linked with sulfide oxidation than with carbon oxidation. copyright 2011 by the American Geophysical Union.

  5. O2 reduction and denitrification rates in shallow aquifers

    NASA Astrophysics Data System (ADS)

    Tesoriero, Anthony J.; Puckett, Larry J.

    2011-12-01

    O2 reduction and denitrification rates were determined in shallow aquifers of 12 study areas representing a wide range in sedimentary environments and climatic conditions. Zero- and first-order rates were determined by relating reactant or product concentrations to apparent groundwater age. O2 reduction rates varied widely within and between sites, with zero-order rates ranging from <3 μmol L-1 yr-1 to more than 140 μmol L-1 yr-1 and first-order rates ranging from 0.02 to 0.27 yr-1. Moderate denitrification rates (10-100 μmol N L-1 yr-1; 0.06-0.30 yr-1) were observed in most areas with O2 concentrations below 60 μmol L-1, while higher rates (>100 μmol N L-1 yr-1; >0.36 yr-1) occur when changes in lithology result in a sharp increase in the supply of electron donors. Denitrification lag times (i.e., groundwater travel times prior to the onset of denitrification) ranged from <20 yr to >80 yr. The availability of electron donors is indicated as the primary factor affecting O2 reduction rates. Concentrations of dissolved organic carbon (DOC) and/or sulfate (an indicator of sulfide oxidation) were positively correlated with groundwater age at sites with high O2 reduction rates and negatively correlated at sites with lower rates. Furthermore, electron donors from recharging DOC are not sufficient to account for appreciable O2 and nitrate reduction. These relations suggest that lithologic sources of DOC and sulfides are important sources of electrons at these sites but surface-derived sources of DOC are not. A review of published rates suggests that denitrification tends to occur more quickly when linked with sulfide oxidation than with carbon oxidation.

  6. Denitrification gene expression in clay-soil bacterial community

    NASA Astrophysics Data System (ADS)

    Pastorelli, R.; Landi, S.

    2009-04-01

    Our contribution in the Italian research project SOILSINK was focused on microbial denitrification gene expression in Mediterranean agricultural soils. In ecosystems with high inputs of nitrogen, such as agricultural soils, denitrification causes a net loss of nitrogen since nitrate is reduced to gaseous forms, which are released into the atmosphere. Moreover, incomplete denitrification can lead to emission of nitrous oxide, a potent greenhouse gas which contributes to global warming and destruction of ozone layer. A critical role in denitrification is played by microorganisms and the ability to denitrify is widespread among a variety of phylogenetically unrelated organisms. Data reported here are referred to wheat cultivation in a clay-rich soil under different environmental impact management (Agugliano, AN, Italy). We analysed the RNA directly extracted from soil to provide information on in situ activities of specific populations. The expression of genes coding for two nitrate reductases (narG and napA), two nitrite reductases (nirS and nirK), two nitric oxide reductases (cnorB and qnorB) and nitrous oxide reductase (nosZ) was analyzed by reverse transcription (RT)-nested PCR. Only napA, nirS, nirK, qnorB and nosZ were detected and fragments sequenced showed high similarity with the corresponding gene sequences deposited in GenBank database. These results suggest the suitability of the method for the qualitative detection of denitrifying bacteria in environmental samples and they offered us the possibility to perform the denaturing gradient gel electrophoresis (DGGE) analyzes for denitrification genes.. Earlier conclusions showed nirK gene is more widely distributed in soil environment than nirS gene. The results concerning the nosZ expression indicated that microbial activity was clearly present only in no-tilled and no-fertilized soils.

  7. Complete autotrophic denitrification in a single reactor using nitritation and anammox gel carriers.

    PubMed

    Isaka, Kazuichi; Kimura, Yuya; Yamamoto, Tomoko; Osaka, Toshifumi; Tsuneda, Satoshi

    2013-11-01

    A novel aerobic denitrification reactor, aerobic denitrification using nitrifying and anoxic ammonium-oxidizing (anammox) bacteria immobilized on gel carriers in a single stage (AIGES), was developed. Two types of gel carriers, a nitritation gel carrier and an anammox gel carrier, were installed in single reactor, and the denitrification performance of simultaneous nitritation and anammox was evaluated. The denitrification performance increased gradually with increased aeration rate, reaching a denitrification rate of 1.4 kg N m(-3) d(-1) 2 weeks after the nitritation and anammox gel carriers were mixed. A high average denitrification efficiency of 82% was confirmed. Stable aerobic denitrification performance was observed for more than half a year. In the startup period of AIGES operation, ammonia-oxidizing bacteria were shown by fluorescence in situ hybridization analysis to grow on the surface layer of anammox gel cubes. These results indicated that anammox gel carriers promptly adapted to an aerobic environment by altering the microbial ecosystem. PMID:23994309

  8. Catalyzing denitrification of Paracoccus versutus by immobilized 1,5-dichloroanthraquinone.

    PubMed

    Liu, Huijuan; Guo, Jianbo; Qu, Jiuhui; Lian, Jing; Jefferson, William; Yang, Jingliang; Li, Haibo

    2012-06-01

    The accelerating effect of non-dissolved redox mediator (1,5-dichloroanthraquinone) on the biological denitrification was investigated in this paper using 1,5-dichloroanthraquinone immobilized by calcium alginate (CA) and a heterotrophic denitrification bacterium of Paracoccus versutus (GU111570). The results suggested that the denitrification rate was enhanced 2.1 fold by 25 mmol l(-1) 1,5-dichloroanthraquinone of this study, and a positive correlation was found for the denitrification rate and 1,5-dichloroanthraquinone concentrations from 0 to 25 mmol l(-1). According to the change characteristic of NO(3) (-) and NO(2) (-) during the denitrification process, the tentative accelerating mechanism of the denitrification by redox mediators was put forward, and redox mediator might play the role of reduced cofactors like NADH, N(A)DH and SDH, or the similar ubiquinol/ubiquinone (Q/QH(2)) role during the denitrification process. PMID:22086549

  9. Comparing Two Different Methods to Evaluate Convariance-Matrix of Debris Orbit State in Collision Probability Estimation

    NASA Astrophysics Data System (ADS)

    Cheng, Haowen; Liu, Jing; Xu, Yang

    The evaluation of convariance-matrix is an inevitable step when estimating collision probability based on the theory. Generally, there are two different methods to compute convariance-matrix. One is so-called Tracking-Delta-Fitting method, first introduced when estimating the collision probability using TLE catalogue data, in which convariance-matrix is evaluated by fitting series of differences between propagated orbits of formal data and updated orbit data. In the second method, convariance-matrix is evaluated in the process of orbit determination. Both of the methods has there difficulties when introduced in collision probability estimation. In the first method, the value of convariance-matrix is evaluated based only on historical orbit data, ignoring information of latest orbit determination. As a result, the accuracy of the method strongly depends on the stability of convariance-matrix of latest updated orbit. In the second method, the evaluation of convariance-matrix is acceptable when the determined orbit satisfies weighted-least-square estimation, depending on the accuracy of observation error convariance, which is hard to obtain in real application, evaluated by analyzing the residuals of orbit determination in our research. In this paper we provided numerical tests to compare these two methods. A simulation of cataloguing objects in LEO, MEO and GEO regions has been carried out for a time span of 3 months. The influence of orbit maneuver has been included in GEO objects cataloguing simulation. For LEO objects cataloguing, the effect of atmospheric density variation has also been considered. At the end of the paper accuracies of evaluated convariance-matrix and estimated collision probability have been tested and compared.

  10. Stark Contrast in Denitrification and Anammox across the Deep Norwegian Trench in the Skagerrak

    PubMed Central

    Engström, Pia; Thamdrup, Bo

    2013-01-01

    Environmental anaerobic ammonium oxidation (anammox) was demonstrated for the first time in 2002, using 15N labeling, in homogenized sediment from the Skagerrak, where it accounted for up to 67% of N2 production. We returned to some of these original sites in 2010 to make measurements of nitrogen and carbon cycling under conditions more representative of those in situ, quantifying anammox and denitrification, together with oxygen penetration and consumption, in intact sediment cores. Overall, oxygen consumption and N2 production decayed with water depth, as expected, but the drop in N2 production was relatively more pronounced. Whereas we confirmed the dominance of N2 production by anammox (72% and 77%) at the two deepest sites (∼700 m of water), anammox was conspicuously absent from two shallower sites (∼200 m and 400 m). At the shallower sites, we could measure no anammox activity with either intact or homogeneous sediment, and quantitative PCR (16S rRNA) gave a negligible abundance of anammox bacteria in the anoxic layers. Such an absence of anammox, especially at one locale where it was originally demonstrated, is hard to reconcile. Despite the dominance of anammox at the deepest sites, anammox activity could not make up for the drop in denitrification, and assuming Redfield ratios for the organic matter being mineralized, the estimated retention of fixed N actually increased to 90% to 97% of that mineralized, whereas it was 80% to 86% at the shallower sites. PMID:24056465

  11. Effect of Nitrate and Acetylene on nirS, cnorB, and nosZ Expression and Denitrification Activity in Pseudomonas mandelii▿

    PubMed Central

    Saleh-Lakha, Saleema; Shannon, Kelly E.; Henderson, Sherri L.; Zebarth, Bernie J.; Burton, David L.; Goyer, Claudia; Trevors, Jack T.

    2009-01-01

    Nitrate acts as an electron acceptor in the denitrification process. The effect of nitrate in the range of 0 to 1,000 mg/liter on Pseudomonas mandelii nirS, cnorB, and nosZ gene expression was studied, using quantitative reverse transcription-quantitative PCR. Denitrification activity was measured by using the acetylene blockage method and gas chromatography. The effect of acetylene on gene expression was assessed by comparing denitrification gene expression in P. mandelii culture grown in the presence or absence of acetylene. The higher the amount of NO3− present, the greater the induction and the longer the denitrification genes remained expressed. nirS gene expression reached a maximum at 2, 4, 4, and 6 h in cultures grown in the presence of 0, 10, 100, and 1,000 mg of KNO3/liter, respectively, while induction of nirS gene ranged from 12- to 225-fold compared to time zero. cnorB gene expression also followed a similar trend. nosZ gene expression did not respond to NO3− treatment under the conditions tested. Acetylene decreased nosZ gene expression but did not affect nirS or cnorB gene expression. These results showed that nirS and cnorB responded to nitrate concentrations; however, significant denitrification activity was only observed in culture with 1,000 mg of KNO3/liter, indicating that there was no relationship between gene expression and denitrification activity under the conditions tested. PMID:19525277

  12. Comparability of Weighed Dietary Records and a Self-Administered Diet History Questionnaire for Estimating Monetary Cost of Dietary Energy

    PubMed Central

    Murakami, Kentaro; Sasaki, Satoshi; Takahashi, Yoshiko; Okubo, Hitomi; Hirota, Naoko; Notsu, Akiko; Fukui, Mitsuru; Date, Chigusa

    2008-01-01

    An increasing number of studies have estimated monetary diet cost using various dietary assessment methods, based on databases on retail food prices, for investigating its association with dietary intake and health outcomes. However, information regarding the comparability of monetary diet cost across dietary assessment methods is absolutely lacking. This study compared monetary cost of dietary energy estimated from weighed dietary records (DRs) with that estimated from a self-administered diet history questionnaire (DHQ). The subjects were 92 Japanese women aged 31–69 years and 92 Japanese men aged 32–76 years. The DHQ (assessing diet during the preceding month) and 4-day DRs (one weekend day and three weekdays) were completed in each season over a 1-year period (DHQs1-4 and DRs1-4, respectively). An additional DHQ was completed at one year after completing DHQ1 (DHQ5). Monetary cost of dietary energy (Japanese yen/4184 kJ) was calculated using food intake information derived from each dietary assessment method, based on retail food prices. Pearson correlation between the mean of DRs1-4 and mean of DHQs1-4 was 0.64 for women and 0.69 for men. Pearson correlation between the mean of DRs1-4 and DHQ1 was 0.60 for women and 0.52 for men, while intraclass correlation between DHQ1 and DHQ5 was 0.64 for women and 0.51 for men. These data indicate reasonable comparability of monetary cost of dietary energy across DR and a DHQ as well as usefulness of a single administration of the DHQ for estimating monetary cost of dietary energy. PMID:21572846

  13. Rate of denitrification and the accumulation of intermediates in a denitrifying bioreactor

    NASA Astrophysics Data System (ADS)

    Parsignault, D. R.; Gursky, H.; Kellogg, E. M.; Matilsky, T.; Murray, S.; Schreier, E.; Tananbaum, H.; Giacconi, R.; Brinkman, A. C.

    2012-12-01

    Denitrifying bioreactors (DNBRs) are an emerging mechanism to mitigate the impact of excess reactive nitrogen by harnessing the activity of ubiquitous denitrifying soil microbes. DNBRs fundamentally consist of an organic carbon energy source sufficiently saturated to develop anaerobic conditions and support heterotrophic reduction of nitrate to dinitrogen. Although recent research has well established achievable nitrate removal in DNBRs upwards of 90%, few studies experimentally determine the fate of nitrogen in these systems. This study differentiates between denitrification to inert nitrogen gas, which permanently removes reactive nitrogen from an enriched ecosystem, and transformation of nitrate to another bioavailable form (such as N2O or NOX, powerful greenhouse gases). Previous research has failed to make this distinction and as both are perceived as a reduction in nitrate concentration at the outlet, the utility of DNBRs in reducing downstream reactive nitrogen has not been sufficiently established. In order to quantify the rate of nitrate removal and the products produced, dissolved gas samples are collected from the DNBR with passive diffusion gas samplers while the influent and effluent nitrate concentration and chemical oxygen demand are monitored in real time with spectrometer probes. Nitrate removal is compared with the denitrification rate and the ratio of dinitrogen to nitrous oxide is reported. Denitrification is quantified from the proportion of nitrogen gas products produced from the nitrate pool, indicated by the negative congruence of the regression of 15N enrichment in the nitrate pool and temporal depletion in the gaseous products. The proportion of nitrous oxide to dinitrogen is examined with respect to saturation and redox potential. This research informs the interpretation of previous studies as well as advises the focus of long-term system level monitoring that will provide further information on the design and application of DNBRs to

  14. Denitrification potential of different land-use types in an agricultural watershed, lower Mississippi valley

    USGS Publications Warehouse

    Ullah, S.; Faulkner, S.P.

    2006-01-01

    Expansion of agricultural land and excessive nitrogen (N) fertilizer use in the Mississippi River watershed has resulted in a three-fold increase in the nitrate load of the river since the early 1950s. One way to reduce this nitrate load is to restore wetlands at suitable locations between croplands and receiving waters to remove run-off nitrate through denitrification. This research investigated denitrification potential (DP) of different land uses and its controlling factors in an agricultural watershed in the lower Mississippi valley (LMV) to help identify sites with high DP for reducing run-off nitrate. Soil samples collected from seven land-use types of an agricultural watershed during spring, summer, fall and winter were incubated in the laboratory for DP determination. Low-elevation clay soils in wetlands exhibited 6.3 and 2.5 times greater DP compared to high-elevation silt loam and low-elevation clay soils in croplands, respectively. DP of vegetated-ditches was 1.3 and 4.2 times that of un-vegetated ditches and cultivated soils, respectively. Soil carbon and nitrogen availability, bulk density, and soil moisture significantly affected DP. These factors were significantly influenced in turn by landscape position and land-use type of the watershed. It is evident from these results that low-elevation, fine-textured soils under natural wetlands are the best locations for mediating nitrate loss from agricultural watersheds in the LMV. Landscape position and land-use types can be used as indices for the assessment/modeling of denitrification potential and identification of sites for restoration for nitrate removal in agricultural watersheds. ?? 2006 Elsevier B.V. All rights reserved.

  15. Comparison of the MBBR denitrification carriers for advanced nitrogen removal of wastewater treatment plant effluent.

    PubMed

    Yuan, Quan; Wang, Haiyan; Hang, Qianyu; Deng, Yangfan; Liu, Kai; Li, Chunmei; Zheng, Shengzhi

    2015-09-01

    The moving bed biofilm reactors (MBBRs) were used to remove the residual NO3(-)-N of wastewater treatment plant (WWTP) effluent, and the MBBR carriers for denitrification were compared. The results showed that high denitrification efficiency can be achieved with polyethylene, polypropylene, polyurethane foam, and haydite carriers under following conditions: 7.2 to 8.0 pH, 24 to 26 °C temperature, 12 h hydraulic retention time (HRT), and 25.5 mg L(-1) external methanol dosage, while the WWTP effluent total nitrogen (TN) was between 2.6 and 15.4 mg L(-1) and NO3(-)-N was between 0.2 and 12.6 mg L(-1). The MBBR filled with polyethylene carriers had higher TN and NO3(-)-N removal rate (44.9 ± 19.1 and 83.4 ± 13.0%, respectively) than those with other carriers. The minimum effluent TN and NO3(-)-N of polyethylene MBBR were 1.6 and 0.1 mg L(-1), respectively, and the maximum denitrification rate reached 23.0 g m(-2) day(-1). When chemical oxygen demand (COD)/TN ratio dropped from 6 to 4, the NO3(-)- N and TN removal efficiency decreased significantly in all reactors except for that filled with polyethylene, which indicated that the polyethylene MBBR can resist influent fluctuation much better. The three-dimensional excitation-emission matrix analysis showed that all the influent and effluent of MBBRs contain soluble microbial products (SMPs)-like organics and biochemical oxygen demand (BOD), which can be removed better by MBBRs filled with haydite and polyethylene carriers. The nitrous oxide reductase (nosZ)-based terminal restriction fragment length polymorphism (T-RFLP) analysis suggested that the dominant bacteria in polyethylene MBBR are the key denitrificans. PMID:25953607

  16. Nitrous oxide emissions and denitrification rates: A blueprint for smart management and remediation of agricultural landscapes.

    NASA Astrophysics Data System (ADS)

    Tomasek, A.; Hondzo, M.; Kozarek, J. L.

    2015-12-01

    Anthropogenic activities have greatly altered the global nitrogen cycle, especially in the agriculturally dominated Midwest, with severe consequences on human and aquatic health. Complete microbial denitrification can be viewed as a nitrogen sink, converting soluble nitrate into inert nitrogen gas. This research aims to quantify and correlate the driving parameters in microbial denitrification and explore the relationship to the abundance of denitrifying genes and the microbial communities at these sites. Denitrifying genes for each step in the denitrification process have been quantified. Data from a field site in Southern Minnesota has been collected throughout the season for two years enabling investigation into the temporal variability of denitrification. Data was collected at two cross-sections across the channel to determine the effect of bank location and moisture content on denitrification. Data were collected in an experimental basin in the summer of 2015 to determine the effect of flooding and benthic organic matter content and quality on microbial denitrification and nitrous oxide production. Four sediment types were investigated in three different flood regimes. After each raising or lowering of the water level, soil cores were taken to determine soil characteristics, the potential denitrification using the denitrification enzyme activity method, nitrous oxide production using a static core method, and the denitrifying gene abundance. Chambers were also deployed over each soil amendment in each flood regime to determine the nitrous oxide production over time. Results from these studies will convey a more complete explanation of denitrification and nitrous oxide production under varying environmental conditions. By determining the driving parameters for microbial denitrification, denitrification hot spots and hot moments can be created and enhanced. One potential consequence of increased denitrification is the possibility of incomplete denitrification

  17. Comparing the model-simulated global warming signal to observations using empirical estimates of unforced noise

    PubMed Central

    Brown, Patrick T.; Li, Wenhong; Cordero, Eugene C.; Mauget, Steven A.

    2015-01-01

    The comparison of observed global mean surface air temperature (GMT) change to the mean change simulated by climate models has received much public and scientific attention. For a given global warming signal produced by a climate model ensemble, there exists an envelope of GMT values representing the range of possible unforced states of the climate system (the Envelope of Unforced Noise; EUN). Typically, the EUN is derived from climate models themselves, but climate models might not accurately simulate the correct characteristics of unforced GMT variability. Here, we simulate a new, empirical, EUN that is based on instrumental and reconstructed surface temperature records. We compare the forced GMT signal produced by climate models to observations while noting the range of GMT values provided by the empirical EUN. We find that the empirical EUN is wide enough so that the interdecadal variability in the rate of global warming over the 20th century does not necessarily require corresponding variability in the rate-of-increase of the forced signal. The empirical EUN also indicates that the reduced GMT warming over the past decade or so is still consistent with a middle emission scenario's forced signal, but is likely inconsistent with the steepest emission scenario's forced signal. PMID:25898351

  18. Comparing the model-simulated global warming signal to observations using empirical estimates of unforced noise.

    PubMed

    Brown, Patrick T; Li, Wenhong; Cordero, Eugene C; Mauget, Steven A

    2015-01-01

    The comparison of observed global mean surface air temperature (GMT) change to the mean change simulated by climate models has received much public and scientific attention. For a given global warming signal produced by a climate model ensemble, there exists an envelope of GMT values representing the range of possible unforced states of the climate system (the Envelope of Unforced Noise; EUN). Typically, the EUN is derived from climate models themselves, but climate models might not accurately simulate the correct characteristics of unforced GMT variability. Here, we simulate a new, empirical, EUN that is based on instrumental and reconstructed surface temperature records. We compare the forced GMT signal produced by climate models to observations while noting the range of GMT values provided by the empirical EUN. We find that the empirical EUN is wide enough so that the interdecadal variability in the rate of global warming over the 20(th) century does not necessarily require corresponding variability in the rate-of-increase of the forced signal. The empirical EUN also indicates that the reduced GMT warming over the past decade or so is still consistent with a middle emission scenario's forced signal, but is likely inconsistent with the steepest emission scenario's forced signal. PMID:25898351

  19. Comparing different algorithms for estimating satellite-based vertically integrated water vapor for Central/Eastern Europe

    NASA Astrophysics Data System (ADS)

    Kern, A.; Bartholy, J.; Gelybó, G. Y.; Pongrácz, R.; Barcza, Z.; Borbás, E.; Woolf, H. M.; Ferencz, C. S.

    There is a growing need in the meteorologist community for high spatial and temporal resolution atmospheric water vapor data since it is essential to understand the hydrological cycle aerosol properties aerosol-cloud interactions energy budget the greenhouse effect and the climate system Atmospheric water vapor is estimated in several places worldwide using the signal of the GPS Global Positional System satellites measured in a network of ground-based meteorological stations and also in a sparse network of radiosondes Remote sensing provides an alternative method to estimate the water vapor content of the atmosphere in high spatial resolution Many techniques have been proposed to estimate atmospheric water vapor content using satellite data primarily in the form of total column precipitable water using a variety of electromagnetic spectrum In this poster we compare different estimation techniques of the vertically integrated water vapor VIWV for Hungary located in Central Eastern Europe using remotely sensed data One of the applications of VIWV data is also presented namely an atmospheric correction algorithm the so-called SMAC method Simplified Method for the Atmospheric Correction In order to determine the VIWV observations of the AVHRR Advanced Very High Resolution Radiometer the ATOVS Advanced TIROS Operational Vertical Sounder onboard the NOAA meteorological satellites and measurements of the MODIS Moderate Resolution Imaging Spectroradiometer onboard the satellites Terra and Aqua are used Our comparisonal study is based on the

  20. Nitrification and denitrification in two-chamber microbial fuel cells for treatment of wastewater containing high concentrations of ammonia nitrogen.

    PubMed

    Du, Haixia; Li, Fusheng; Yu, Zaiji; Feng, Chunhua; Li, Wenhan

    2016-05-01

    Simultaneous nitrification and denitrification in the aerated cathode chamber of microbial fuel cells (MFCs) inoculated with nitrifying bacteria were investigated using two-chamber MFCs. Based on the variations of [Formula: see text], [Formula: see text] and [Formula: see text] in the cathode chamber of four MFCs added with different concentrations of [Formula: see text] (50, 65, 130 and 230 mg/L), the occurrence of simultaneous nitrification and denitrification leading to effective removal of nitrogen was confirmed. Electrochemical reaction with electrons transferred from the anode chamber was found to be the major mechanism responsible for the removal of [Formula: see text] in the cathode chamber. The estimated values of the first-order rate constant for nitrification and denitrification varied in the range of 0.3-1.7 day(-1) and 0.2-0.9 day(-1), revealing a decreasing trend with increases in the initial [Formula: see text] concentrations and the detected maximum concentration of the nitrification product of [Formula: see text] in the cathode chamber, respectively. PMID:26507121

  1. Inorganic nitrogen control in wastewater treatment ponds from a fish farm (Orbetello, Italy): denitrification versus Ulva uptake.

    PubMed

    Bartoli, Marco; Nizzoli, Daniele; Naldi, Mariachiara; Vezzulli, Luigi; Porrello, Salvatore; Lenzi, Mauro; Viaroli, Pierluigi

    2005-11-01

    The aim of this study was to quantify the N removal efficiency of an Ulva-based phytotreatment system receiving wastewaters from a land-based fish farm (Orbetello, Italy), to identify the main biogeochemical pathways involved and to provide basic guidelines for treatment implementation and management. Fluxes of O2 and nutrients in bare and in Ulva colonised sediments were assessed by light/dark core incubations; denitrification by the isotope pairing technique and Ulva growth by in situ incubation of macroalgal disks in cages. O2 and nutrient budgets were estimated as sum of individual processes and further verified by 24-h investigations of overall inlet and outlet loads. Ulva uptake (up to 7.8 mmol Nm(-2) h(-1)) represented a net sink for water column and regenerated NH4+ whilst N removal via denitrification (10-170 micromol Nm(-2) h(-1)) accounted for a small percentage of inorganic nitrogen load (<5%). Laboratory experiments demonstrated a high potential for denitrification (over 800 microM Nm(-2) h(-1)) indicating that N loss could be enhanced. The control of Ulva standing stocks by optimised harvesting of surplus biomass may represent an effective strategy to maximise DIN removal and could result in the assimilation of approximately 50% of produced inorganic nitrogen. PMID:16045942

  2. The acetylene inhibition technique to determine total denitrification (N2 + N2O) losses from soil samples: potentials and limitations

    NASA Astrophysics Data System (ADS)

    Felber, R.; Conen, F.; Flechard, C. R.; Neftel, A.

    2012-03-01

    The loss of N2 from intensively managed agro-ecosystems is an important part of the N budget. The monitoring of N2 emissions at the field scale is impossible due to the high atmospheric background of 78%, which precludes the measurement of fluxes. The acetylene (C2H2) inhibition technique is a rather simple, albeit imperfect, method to determine N2 losses from entire soil cores. Despites serious limitations it is one among very few methodological options to estimate total denitrification at high temporal resolution and on small spatial scale, with limited workload and costs involved. A laboratory system with two different detection systems (photoacoustic IR spectroscopy and gas chromatography) is presented, which allowed parallel measurements of up to 7 intact soil cores in air-tight glass tubes in a temperature controlled cabinet (adjusted to field conditions) with an automated C2H2 injection. A survey of total denitrification losses (N2 + N2O) over 1.5 yr in soil from an intensively managed, cut grassland system in central Switzerland showed a lower bound loss in the range of 6 to 25 kg N ha-1 yr-1 (3-13% of added N), roughly 3.4 times higher than the N2O loss. However, several drawbacks of the C2H2 inhibition technique preclude a more precise determination of the total denitrification loss.

  3. Incidence of childhood pneumonia: facility-based surveillance estimate compared to measured incidence in a South African birth cohort study

    PubMed Central

    le Roux, David M; Myer, Landon; Nicol, Mark P; Zar, Heather J

    2015-01-01

    Background Pneumonia is the leading cause of childhood mortality and a major contributor to childhood morbidity, but accurate measurement of pneumonia incidence is challenging. We compared pneumonia incidence using a facility-based surveillance system to estimates from a cohort study conducted contemporaneously in the same community in Cape Town, South Africa. Methods A surveillance system was developed in six public sector primary care clinics and in a regional referral hospital, to detect childhood pneumonia cases. Nurses recorded all children presenting to facilities who met WHO case definitions of pneumonia, and hospital records were reviewed. Estimates of pneumonia incidence and severity were compared with incidence rates based on active surveillance in the Drakenstein Child Health Study. Results From June 2012 until September 2013, the surveillance system detected 306 pneumonia episodes in children under 1 year of age, an incidence of 0.20 episodes/child-year (e/cy) (95% CI 0.17 to 0.22 e/cy). The incidence in the cohort study from the same period was 0.27 e/cy (95% CI 0.23 to 0.32 e/cy). Pneumonia incidence in the surveillance system was almost 30% lower than in the birth cohort; incidence rate ratio 0.72 (95% CI 0.58 to 0.89). In the surveillance system, 18% were severe pneumonia cases, compared to 23% in the birth cohort, rate ratio 0.81 (95% CI 0.55 to 1.18). Conclusions In this setting, facility-based pneumonia surveillance detected fewer cases of pneumonia, and fewer severe cases, compared to the corresponding cohort study. Facility pneumonia surveillance using data collected by local healthcare workers provides a useful estimate of the epidemiology of childhood pneumonia but may underestimate incidence and severity. PMID:26685027

  4. Paracoccus denitrificans for the effluent recycling during continuous denitrification of liquid food.

    PubMed

    Tippkötter, Nils; Roikaew, Wipa; Ulber, Roland; Hoffmann, Alexander; Denzler, Hans-Jörg; Buchholz, Heinrich

    2010-01-01

    Nitrate is an undesirable component of several foods. A typical case of contamination with high nitrate contents is whey concentrate, containing nitrate in concentrations up to 25 l. The microbiological removal of nitrate by Paracoccus denitrificans under formation of harmless nitrogen in combination with a cell retention reactor is described here. Focus lies on the resource-conserving design of a microbal denitrification process. Two methods are compared. The application of polyvinyl alcohol-immobilized cells, which can be applied several times in whey feed, is compared with the implementation of a two step denitrification system. First, the whey concentrate's nitrate is removed by ion exchange and subsequently the eluent regenerated by microorganisms under their retention by crossflow filtration. Nitrite and nitrate concentrations were determined by reflectometric color measurement with a commercially available Reflectoquant device. Correction factors for these media had to be determined. During the pilot development, bioreactors from 4 to 250 mg x L(-1) and crossflow units with membrane areas from 0.02 to 0.80 m(2) were examined. Based on the results of the pilot plants, a scaling for the exemplary process of denitrifying 1,000 tons per day is discussed. PMID:20187124

  5. Technical Note: Alternative in-stream denitrification equation for the INCA-N model

    NASA Astrophysics Data System (ADS)

    Etheridge, J. R.; Birgand, F.; Burchell, M. R., II; Lepistö, A.; Rankinen, K.; Granlund, K.

    2014-04-01

    The Integrated Catchment model for Nitrogen (INCA-N) is a semi-distributed, process based model that has been used to model the impacts of land use, climate, and land management changes on hydrology and nitrogen loading. An observed problem with the INCA-N model is reproducing low nitrate-nitrogen concentrations during the summer growing season in some catchments. In this study, the current equation used to simulate the rate of in-stream denitrification was replaced with an alternate equation that uses a mass transfer coefficient and the stream bottom area. The results of simulating in-stream denitrification using the two different methods were compared for a one year simulation period of the Yläneenjoki catchment in Finland. The alternate equation (Nash-Sutcliffe efficiency = 0.61) simulated concentrations during the periods of the growing season with the lowest flow that were closer to the observed concentrations than the current equation (Nash-Sutcliffe efficiency = 0.60), but the results were mixed during other portions of the year. The results of the calibration and validation of the model using the two equations show that the alternate equation will simulate lower nitrate-nitrogen concentrations during the growing season when compared to the current equation, but promote investigation into other errors in the model that may be causing inaccuracies in the modeled concentrations.

  6. Microbiology and potential applications of aerobic methane oxidation coupled to denitrification (AME-D) process: A review.

    PubMed

    Zhu, Jing; Wang, Qian; Yuan, Mengdong; Tan, Giin-Yu Amy; Sun, Faqian; Wang, Cheng; Wu, Weixiang; Lee, Po-Heng

    2016-03-01

    Aerobic methane oxidation coupled to denitrification (AME-D) is an important link between the global methane and nitrogen cycles. This mini-review updates discoveries regarding aerobic methanotrophs and denitrifiers, as a prelude to spotlight the microbial mechanism and the potential applications of AME-D. Until recently, AME-D was thought to be accomplished by a microbial consortium where denitrifying bacteria utilize carbon intermediates, which are excreted by aerobic methanotrophs, as energy and carbon sources. Potential carbon intermediates include methanol, citrate and acetate. This mini-review presents microbial thermodynamic estimations and postulates that methanol is the ideal electron donor for denitrification, and may serve as a trophic link between methanotrophic bacteria and denitrifiers. More excitingly, new discoveries have revealed that AME-D is not only confined to the conventional synergism between methanotrophic bacteria and denitrifiers. Specifically, an obligate aerobic methanotrophic bacterium, Methylomonas denitrificans FJG1, has been demonstrated to couple partial denitrification with methane oxidation, under hypoxia conditions, releasing nitrous oxide as a terminal product. This finding not only substantially advances the understanding of AME-D mechanism, but also implies an important but unknown role of aerobic methanotrophs in global climate change through their influence on both the methane and nitrogen cycles in ecosystems. Hence, further investigation on AME-D microbiology and mechanism is essential to better understand global climate issues and to develop niche biotechnological solutions. This mini-review also presents traditional microbial techniques, such as pure cultivation and stable isotope probing, and powerful microbial techniques, such as (meta-) genomics and (meta-) transcriptomics, for deciphering linked methane oxidation and denitrification. Although AME-D has immense potential for nitrogen removal from wastewater, drinking

  7. Denitrification and nitrogen transport in a coastal aquifer receiving wastewater discharge

    USGS Publications Warehouse

    DeSimone, L.A.; Howes, B.L.

    1996-01-01

    Denitrification and nitrogen transport were quantified in a sandy glacial aquifer receiving wastewater from a septage-treatment facility on Cape Cod, MA. The resulting groundwater plume contained high concentrations of NO3- (32 mg of NL-1), total dissolved nitrogen (40.5 mg of N L-1), and dissolved organic carbon (1.9 mg of C L-1) and developed a central anoxic zone after 17 months of effluent discharge. Denitrifying activity was measured using four approaches throughout the major biogeochemical zones of the plume. Three approaches that maintained the structure of aquifer materials yielded comparable rates: acetylene block in intact sediment cores, 9.6 ng of N cm-3 d-1 (n = 61); in situ N2 production, 3.0 ng of N cm-3 d-1 (n = 11); and in situ NO3- depletion, 7.1 ng of N cm-3 d-1 (n = 3). In contrast, the mixing of aquifer materials using a standard slurry method yielded rates that were more than 15-fold higher (150 ng of N cm-3 d-1, n = 16) than other methods. Concentrations and ??15N of groundwater and effluent N2, NO3-, and NH4+ were consistent with the lower rates of denitrification determined by the intact-core or in situ methods. These methods and a plumewide survey of excess N2 indicate that 2-9% of the total mass of fixed nitrogen recharged to the anoxic zone of the plume was denitrified during the 34-month study period. Denitrification was limited by organic carbon (not NO3-) concentrations, as evidenced by a nitrate and carbon addition experiment, the correlation of denitrifying activity with in situ concentrations of dissolved organic carbon, and the assessments of available organic carbon in plume sediments. Carbon limitation is consistent with the observed conservative transport of 85-96% of the nitrate in the anoxic zone. Although denitrifying activity removed a significant amount (46250 kg) of fixed nitrogen during transport, the effects of aquifer denitrification on the nitrogen load to receiving ecosystems are likely to be small (<10%).

  8. Effect of Solids Retention Time on the Denitrification Potential of Anaerobically Digested Swine Waste

    NASA Astrophysics Data System (ADS)

    Kinyua, Maureen Njoki

    Three continuously stirred tank reactors (CSTR) were operated in semi continuous mode treating swine waste using anaerobic digestion. The reactors were used to test the effect of solid retention time (SRT) on CH4 yield, total ammonia nitrogen (TAN) concentrations, % volatile solids (VS), chemical oxygen demand (COD) and volatile fatty acids (VFA) removal, readily biodegradable COD concentration and the denitrification potential for the effluent in a biological nutrient removal (BNR) system. During Phase I of the study, the three reactors were operated at the same 28 day SRT for 16 weeks. SRTs were then changed during the 12 week Phase II period. The SRTs studied were 14, 21 and 28 days, with the same organic loading rate (OLR) of 1.88 ± 0.2 kg VS/ m3-day. The reactor with the lowest SRT (14 days) had the highest VS and VFA removal at 73.6 and 67.6% and lowest TAN concentration at 0.78 g NH4+-N/L, followed by the 21 day and 28 day reactors. This was likely due to the fast microbial growth rates and substrate utilization rates in this reactor compared with the other two. The 14 day reactor had the highest CH4 yield at 0.33 m3CH 4/kg VS added and readily biodegradable COD concentration at 0.93 COD/L. The variations in CH4 yield and readily biodegradable COD concentrations between the three reactors were not statistically significant. Denitrification potential for the reactors was 1.20, 0.73 and 0.56 g COD/g N for 14, 21 and 28 day reactors, respectively, and the differences were statistically significant. None of the reactors achieved a denitrification potential of 5 g COD/g N, the amount required to use effluent of anaerobically digested swine waste as an internal carbon source in a BNR. This was attributed to operating conditions such as freezing and thawing of the raw swine waste that maximized CH4 yield and lowered the readily biodegradable COD concentration. In addition the 14 day reactor had low TAN concentrations thus increasing the denitrification potential

  9. Denitrification potential of organic, forest and grassland soils in the Ribble-Wyre and Conwy River catchments, UK.

    PubMed

    Sgouridis, Fotis; Ullah, Sami

    2014-07-01

    Soil denitrification activity can be highly variable due to the effects of varied land use management practices within catchments on the biogeochemical regulators of denitrification. To test this assumption in the context of mixed-use rural catchments, it was hypothesised that the relative magnitude of denitrification activity may be regulated, among others, by a gradient of soil nitrate (low to high) between organic (peat bog, heathland, and acid grassland), forest (coniferous and deciduous), and grassland (improved and semi-improved) rural land use types. The denitrification potential (DP) of organic, forest and grassland soils, in two UK catchments was measured in the laboratory. Land use type significantly (p < 0.05) influenced the DP, which ranged between 0.02 and 63.3 mg N m(-2) h(-1). The averaged DP of organic and forest soils (1.08 mg N m(-2) h(-1)) was 3 and 10 times less than the DP of semi-improved (4.06 mg N m(-2) h(-1)) and improved (12.09 mg N m(-2) h(-1)) grassland soils, respectively; and among others, nitrate correlated positively (p < 0.05) with the DP. The results indicated that the difference in soil nitrate concentration between organic (naturally low in nitrate availability) and grassland soils (nitrate enriched due to land management) partially regulated the extent of DP. In the absence of N fertilisation, except for the atmospheric N deposition, the relatively low net nitrification potential (as a source of nitrate for denitrifiers) of organic and forest soils alone seem to have resulted in lower denitrifier's activity compared to grassland soils. Moreover, the interactions between soil organic carbon, pH, bulk density, water filled pore space, and texture, as these are influenced by the relative degree of land management, exerted additional controls on the DP. The results suggest that land management can have significant effects on denitrification, and thus needs to be considered when modelling and/or predicting the response of

  10. Forest Cover Estimation in Ireland Using Radar Remote Sensing: A Comparative Analysis of Forest Cover Assessment Methodologies.

    PubMed

    Devaney, John; Barrett, Brian; Barrett, Frank; Redmond, John; O Halloran, John

    2015-01-01

    Quantification of spatial and temporal changes in forest cover is an essential component of forest monitoring programs. Due to its cloud free capability, Synthetic Aperture Radar (SAR) is an ideal source of information on forest dynamics in countries with near-constant cloud-cover. However, few studies have investigated the use of SAR for forest cover estimation in landscapes with highly sparse and fragmented forest cover. In this study, the potential use of L-band SAR for forest cover estimation in two regions (Longford and Sligo) in Ireland is investigated and compared to forest cover estimates derived from three national (Forestry2010, Prime2, National Forest Inventory), one pan-European (Forest Map 2006) and one global forest cover (Global Forest Change) product. Two machine-learning approaches (Random Forests and Extremely Randomised Trees) are evaluated. Both Random Forests and Extremely Randomised Trees classification accuracies were high (98.1-98.5%), with differences between the two classifiers being minimal (<0.5%). Increasing levels of post classification filtering led to a decrease in estimated forest area and an increase in overall accuracy of SAR-derived forest cover maps. All forest cover products were evaluated using an independent validation dataset. For the Longford region, the highest overall accuracy was recorded with the Forestry2010 dataset (97.42%) whereas in Sligo, highest overall accuracy was obtained for the Prime2 dataset (97.43%), although accuracies of SAR-derived forest maps were comparable. Our findings indicate that spaceborne radar could aid inventories in regions with low levels of forest cover in fragmented landscapes. The reduced accuracies observed for the global and pan-continental forest cover maps in comparison to national and SAR-derived forest maps indicate that caution should be exercised when applying these datasets for national reporting. PMID:26262681

  11. Forest Cover Estimation in Ireland Using Radar Remote Sensing: A Comparative Analysis of Forest Cover Assessment Methodologies

    PubMed Central

    Devaney, John; Barrett, Brian; Barrett, Frank; Redmond, John; O`Halloran, John

    2015-01-01

    Quantification of spatial and temporal changes in forest cover is an essential component of forest monitoring programs. Due to its cloud free capability, Synthetic Aperture Radar (SAR) is an ideal source of information on forest dynamics in countries with near-constant cloud-cover. However, few studies have investigated the use of SAR for forest cover estimation in landscapes with highly sparse and fragmented forest cover. In this study, the potential use of L-band SAR for forest cover estimation in two regions (Longford and Sligo) in Ireland is investigated and compared to forest cover estimates derived from three national (Forestry2010, Prime2, National Forest Inventory), one pan-European (Forest Map 2006) and one global forest cover (Global Forest Change) product. Two machine-learning approaches (Random Forests and Extremely Randomised Trees) are evaluated. Both Random Forests and Extremely Randomised Trees classification accuracies were high (98.1–98.5%), with differences between the two classifiers being minimal (<0.5%). Increasing levels of post classification filtering led to a decrease in estimated forest area and an increase in overall accuracy of SAR-derived forest cover maps. All forest cover products were evaluated using an independent validation dataset. For the Longford region, the highest overall accuracy was recorded with the Forestry2010 dataset (97.42%) whereas in Sligo, highest overall accuracy was obtained for the Prime2 dataset (97.43%), although accuracies of SAR-derived forest maps were comparable. Our findings indicate that spaceborne radar could aid inventories in regions with low levels of forest cover in fragmented landscapes. The reduced accuracies observed for the global and pan-continental forest cover maps in comparison to national and SAR-derived forest maps indicate that caution should be exercised when applying these datasets for national reporting. PMID:26262681

  12. Building a Probabilistic Denitrification Model for an Oregon Salt Marsh

    NASA Astrophysics Data System (ADS)

    Moon, J. B.; Stecher, H. A.; DeWitt, T.; Nahlik, A.; Regutti, R.; Michael, L.; Fennessy, M. S.; Brown, L.; Mckane, R.; Naithani, K. J.

    2015-12-01

    Despite abundant work starting in the 1950s on the drivers of denitrification (DeN), mechanistic complexity and methodological challenges of direct DeN measurements have resulted in a lack of reliable rate estimates across landscapes, and a lack of operationally valid, robust models. Measuring and modeling DeN are particularly challenging in tidal systems, which play a vital role in buffering adjacent coastal waters from nitrogen inputs. These systems are hydrologically and biogeochemically complex, varying on fine temporal and spatial scales. We assessed the spatial and temporal variability of soil nitrate (NO3-) levels and O2 availability, two primary drivers of DeN, in surface soils of Winant salt marsh located in Yaquina estuary, OR during the summers of 2013 and 2014. We found low temporal variability in soil NO3- concentrations across years, tide series, and tide cycles, but high spatial variability linked to elevation gradients (i.e., habitat types); spatial variability within the high marsh habitat (0 - 68 μg N g-1 dry soil) was correlated with distance to major tide creek channels and connectivity to upslope N-fixing red alder. Soil O2 measurements collected at 5 cm below ground across three locations on two spring tide series showed that O2 drawdown rates were also spatially variable. Depending on the marsh location, O2 draw down ranged from sub-optimal for DeN (> 80 % O2 saturation) across an entire tide series (i.e., across days) to optimum (i.e., ~ 0 % O2 saturation) within one overtopping tide event (i.e., within hours). We are using these results, along with empirical relationships created between DeN and soil NO3- concentrations for Winant to improve on a pre-existing tidal DeN model. We will develop the first version of a fully probabilistic hierarchical Bayesian tidal DeN model to quantify parameter and prediction uncertainties, which are as important as determining mean predictions in order to distinguish measurable differences across the marsh.

  13. Reduced isotope fractionation by denitrification under conditions relevant to the ocean

    NASA Astrophysics Data System (ADS)

    Kritee, K.; Sigman, Daniel M.; Granger, Julie; Ward, Bess B.; Jayakumar, Amal; Deutsch, Curtis

    2012-09-01

    Experiments with two well-studied denitrifiers and one recently isolated marine suboxic zone denitrifier show that the cellular-level denitrification N isotope effect (15ɛ) is typically lower than the canonical value of ˜25‰ under many conditions prevalent in the ocean. Across all three strains, 15ɛ is 10-15‰ at cellular nitrate reduction rates that are more representative of the environment than the very high rates under which we and previous investigators measure 15ɛ to be 20-30‰. A sharp decrease in 15ɛ is also observed in individual nitrate drawdown assays as the extracellular nitrate concentrations approach 2-35 μM and nitrate uptake becomes the rate-limiting step. On an apparently strain-specific basis, lower values of 15ɛ are observed under diverse conditions common in the natural environment: less reduced carbon sources, small inputs of oxygen, nutrient availability, agitation, and age of starter culture (i.e., initiation of assays with cells that had recently depleted a large previous nitrate amendment or were more recently in the exponential growth ("bloom") phase). A conserved oxygen-to-nitrogen isotope relationship across the experiments for all three denitrifiers (18ɛ/15ɛ = 0.93 ± 0.06 (1SD)) supports the interpretation that fractionation is imparted solely by the internal respiratory nitrate reductase, with the amplitude of 15ɛ varying with the proportional importance of cellular nitrate efflux relative to uptake. Aspects of the 15ɛ variation are unexpected; nevertheless, the occurrence of lower 15ɛ is robust. It is uncertain if our lower 15ɛ estimates apply to oceanic water column denitrification because field studies have generally yielded 15ɛwc between 20-30‰, more similar to previous culture estimates and our estimates at high cell specific nitrate reduction rates. If denitrification in the ocean's major suboxic zones does have an 15ɛ of ˜10-15‰, it would remove an apparent imbalance between global ocean N inputs and

  14. Extended Kalman Filter-Based Methods for Pose Estimation Using Visual, Inertial and Magnetic Sensors: Comparative Analysis and Performance Evaluation

    PubMed Central

    Ligorio, Gabriele; Sabatini, Angelo Maria

    2013-01-01

    In this paper measurements from a monocular vision system are fused with inertial/magnetic measurements from an Inertial Measurement Unit (IMU) rigidly connected to the camera. Two Extended Kalman filters (EKFs) were developed to estimate the pose of the IMU/camera sensor moving relative to a rigid scene (ego-motion), based on a set of fiducials. The two filters were identical as for the state equation and the measurement equations of the inertial/magnetic sensors. The DLT-based EKF exploited visual estimates of the ego-motion using a variant of the Direct Linear Transformation (DLT) method; the error-driven EKF exploited pseudo-measurements based on the projection errors from measured two-dimensional point features to the corresponding three-dimensional fiducials. The two filters were off-line analyzed in different experimental conditions and compared to a purely IMU-based EKF used for estimating the orientation of the IMU/camera sensor. The DLT-based EKF was more accurate than the error-driven EKF, less robust against loss of visual features, and equivalent in terms of computational complexity. Orientation root mean square errors (RMSEs) of 1° (1.5°), and position RMSEs of 3.5 mm (10 mm) were achieved in our experiments by the DLT-based EKF (error-driven EKF); by contrast, orientation RMSEs of 1.6° were achieved by the purely IMU-based EKF. PMID:23385409

  15. A simple smoother based on continuous wavelet transform: Comparative evaluation based on the fidelity, smoothness and efficiency in phenological estimation

    NASA Astrophysics Data System (ADS)

    Qiu, Bingwen; Feng, Min; Tang, Zhenghong

    2016-05-01

    This study proposed a simple Smoother without any local adjustments based on Continuous Wavelet Transform (SCWT). And then it evaluated its performance together with other commonly applied techniques in phenological estimation. These noise reduction methods included Savitzky-Golay filter (SG), Double Logistic function (DL), Asymmetric Gaussian function (AG), Whittaker Smoother (WS) and Harmonic Analysis of Time-Series (HANTS). They were evaluated based on fidelity and smoothness, and their efficiencies in deriving phenological parameters through the inflexion point-based method with the 8-day composite Moderate Resolution Imaging Spectroradiometer (MODIS) 2-band Enhanced Vegetation Index (EVI2) in 2013 in China. The following conclusions were drawn: (1) The SG method exhibited strong fidelity, but weak smoothness and spatial continuity. (2) The HANTS method had very robust smoothness but weak fidelity. (3) The AG and DL methods performed weakly for vegetation with more than one growth cycle (i.e., multiple crops). (4) The WS and SCWT smoothers outperformed others with combined considerations of fidelity and smoothness, and consistent phenological patterns (correlation coefficients greater than 0.8 except evergreen broadleaf forests (0.68)). (5) Compared with WS methods, the SCWT smoother was capable in preservation of real local minima and maxima with fewer inflexions. (6) Large discrepancy was examined from the estimated phenological dates with SG and HANTS methods, particularly in evergreen forests and multiple cropping regions (the absolute mean deviation rates were 6.2-17.5 days and correlation coefficients less than 0.34 for estimated start dates).

  16. A comparative study of prevalence-based incidence estimation techniques with application to dementia data in Germany.

    PubMed

    Landwehr, Sandra; Brinks, Ralph

    2016-02-28

    Dementia is becoming a major health burden, which is mainly due to the increasing life expectancy in many developed countries. To describe the disease progression of individuals, multistate models are generally appropriate tools. These models allow the individuals to move along a path consisting of a finite number of disease states. We consider a simplifying illness-death model in which the subjects progress through the states healthy, diseased and dead. We use this model to study analytic relationships between the prevalence, incidence and mortality rates of irreversible diseases that have been applied in the past. One of these approaches is a rather recently proposed technique based on an ordinary differential equation (ODE). We conduct a simulation study to compare the performance of two suggested numerical approximations of this ODE with three alternative techniques, the common goal of which is to estimate age-specific incidence from cross-sectional information. The quality of the estimation methods is further explored using data on dementia in Germany. In the simulation scenarios as well as in the dementia data setting, the ODE method turns out to be the predominant technique with regard to the quality of the estimation of the known incidence regimes. PMID:26376995

  17. Comparative evaluation of different satellite rainfall estimation products and bias correction in the Upper Blue Nile (UBN) basin

    NASA Astrophysics Data System (ADS)

    Abera, Wuletawu; Brocca, Luca; Rigon, Riccardo

    2016-09-01

    In a region where ground-based gauge data are scarce, satellite rainfall estimates (SREs) are a viable option for proper space-time rainfall characterization. However, their accuracy and performances vary from region to region, and must be assessed. In this study, five high resolution satellite products (3B42V7, CMORPH, TAMSAT, SM2R-CCI, and CFSR) are compared and analyzed using the available rain gauge data in one of the most topographically and climatologically complex basin of Africa, the Upper Blue Nile basin (UBN). The basin rainfall is investigated systematically, and it is found that, at some locations, the difference in mean annual rainfall estimates between these SREs could be as much as about 2700 mm. Considering three goodness-of-fit indexes, correlation, bias and root mean square error (RMSE) between the SREs and ground-based gauge rainfall, CMORPH, TAMSAT and SM2R-CCI outperform the other two. Furthermore, a confusion matrix is used to investigate the detection ability of satellite rainfall products for different rainfall intensities. TAMSAT has the highest (91%) detection skill for dry days, followed by CFSR (77%). On the contrary, SM2R-CCI has the highest accuracy index for medium rainfall ranges (10-20 mm). The empirical cumulative distribution (ecdf) mapping technique is used to correct the intensities distribution givenby the SREs. This method provides a means to improve the rainfall estimation of all SREs, and the highest improvement is obtained for CMORPH (bias reduction from - 72% to - 1%).

  18. Soil infiltration bioreactor incorporated with pyrite-based (mixotrophic) denitrification for domestic wastewater treatment.

    PubMed

    Kong, Zhe; Li, Lu; Feng, Chuanping; Chen, Nan; Dong, Shanshan; Hu, Weiwu

    2015-01-01

    In this study, an integrated two-stage soil infiltration bioreactor incorporated with pyrite-based (mixotrophic) denitrification (SIBPD) was designed for domestic wastewater treatment. Benefited from excellent adsorption ability and water-permeability, soil infiltration could avoid clogging, shorten operating time and lower maintenance cost. Respiration and nitrification were mostly engaged in aerobic stage (AES), while nitrate was majorly removed by pyrite-based mixotrophic denitrification mainly occurred in anaerobic stage (ANS). Fed with synthetic and real wastewater for 120days at 1.5h HRT, SIBPD demonstrated good removal performance showing 87.14% for COD, 92.84% for NH4(+)-N and 82.58% for TP along with 80.72% of nitrate removed by ANS. TN removal efficiency was 83.74% when conducting real wastewater. Compared with sulfur-based process, the effluent pH of SIBPD was maintained at 6.99-7.34 and the highest SO4(2-) concentration was only 64.63mgL(-1). This study revealed a promising and feasible application prospect for on-site domestic wastewater treatment. PMID:25827248

  19. Use of cotton gin trash to enhance denitrification in restored forested wetlands

    USGS Publications Warehouse

    Ullah, S.; Faulkner, S.P.

    2006-01-01

    Lower Mississippi Valley (LMV) has lost about 80% bottomland hardwood forests, mainly to agriculture. This landscape scale alteration of the LMV resulted in the loss of nitrate (NO3) removal capacity of the valley, contributing to nitrogen (N)-enhanced eutrophication and potentially hypoxia in the northern Gulf of Mexico. Restoration of hardwood forests in the LMV is a highly recommended practice to reduce NO3 load of the Mississippi River. However, restored bottomland forests take decades to develop characteristic ecological functions including denitrifier activity. One way to enhance denitrifier activity in restored wetland forests is to amend the soils with an available carbon (C) source. This research investigated the effects of cotton gin trash (CGT) amendment on denitrification rate and N2O:N2 emission ratio from a restored bottomland forest soils and compared it to those from an adjacent unamended natural forest soils. CGT amendment increased denitrification rates in the restored forest soils to the level of the natural forest soils. N2O:N2 emission ratios from the restored and natural forest soils were highly variable and were not significantly different from each other. These findings suggest that restoration of bottomland hardwood forests in the LMV will require organic carbon amendment to achieve enhanced denitrifier activity for NO3 removal while the restored forest is developing into a mature state over time. ?? 2006 Elsevier B.V. All rights reserved.

  20. [Simultaneous desulfurization and denitrification by TiO2/ACF under different irradiation].

    PubMed

    Han, Jing; Zhao, Yi

    2009-04-15

    The supported TiO2 photocatalysts were prepared in laboratory, and the experiments of simultaneous desulfurization and denitrification were carried out by self-designed photocatalysis reactor. The optimal experimental conditions were achieved, and the efficiencies of simultaneous desulfurization and denitrification under two different light sources were compared. The results show that the oxygen content of flue gas, reaction temperature, flue gas humidity and irradiation intensity are most essential factors to photocatalysis. For TiO2/ACF, the removal efficiencies of 99.7% for SO2 and 64.3% for NO are obtained respectively at optimal experimental conditions under UV irradiation. For TiO2/ACF, the removal efficiencies of 97.5% for SO2 and 49.6% for NO are achieved respectively at optimal experimental conditions under the visible light irradiation. The results of five times parallel experiments indicate standard deviation S of parallel data is little. The mechanism of removal for SO2 and NO is proposed under two light sources by ion chromatography analysis of the absorption liquid. PMID:19544996

  1. Laboratory study of nitrification, denitrification and anammox processes in membrane bioreactors considering periodic aeration.

    PubMed

    Abbassi, Rouzbeh; Yadav, Asheesh Kumar; Huang, Shan; Jaffé, Peter R

    2014-09-01

    The possibility of using membrane bioreactors (MBRs) in simultaneous nitrification-anammox-denitrification (SNAD) by considering periodic aeration cycles was investigated. Two separate reactors were operated to investigate the effect of different anammox biomass in the presence of nitrifying and denitrifying biomass on the final nitrogen removal efficiency. The results illustrated that the reactor with higher anammox biomass was more robust to oxygen cycling. Around 98% Total Nitrogen (TN) and 83% Total Organic Carbon (TOC) removal efficiencies were observed by applying one hour aeration over a four-hour cycle. Decreasing the aeration time to 30, 15, and 2 min during a four-hour cycle affected the final TN removal efficiencies. However, the effect of decreasing aeration on the TN removal efficiencies in the reactor with higher anammox biomass was much lower compared to the regular reactor. The nitrous oxide (N2O) emission was a function of aeration as well, and was lower in the reactor with higher anammox biomass. The results of q-PCR analysis confirmed the simultaneous co-existence of nitrifiers, anammox, and denitrifiers in both of the reactors. To simulate the TN removal in these reactors as a function of the aeration time, a new model, based on first order reaction kinetics for both denitrification and anammox was developed and yielded a good agreement with the experimental observations. PMID:24814548

  2. Technical Note: Alternative in-stream denitrification equation for the INCA-N model

    NASA Astrophysics Data System (ADS)

    Etheridge, J. R.; Birgand, F.; Burchell, M. R., II; Lepistö, A.; Rankinen, K.; Granlund, K.

    2013-11-01

    The Integrated Catchment model for Nitrogen (INCA-N) is a semi-distributed, process based model that has been used to model the impacts of land use, climate, and land management changes on hydrology and nitrogen loading. An observed problem with the INCA-N model is reproducing low nitrate-nitrogen concentrations during the summer growing season in some catchments. In this study, the current equation used to simulate the rate of in-stream denitrification was replaced with an alternate equation that uses a mass transfer coefficient and the stream bottom area. The results of simulating in-stream denitrification using the two different methods were compared for a 9 month simulation period of the Yläneenjoki catchment in Finland. The alternate equation (Nash-Sutcliffe efficiency = 0.59) simulated concentrations during the growing season that were closer to the observed concentrations than the current equation (Nash-Sutcliffe efficiency = 0.47). The results of this work promote the incorporation of the alternate equation into the model for further testing.

  3. Physiological levels of nitrate support anoxic growth by denitrification of Pseudomonas aeruginosa at growth rates reported in cystic fibrosis lungs and sputum

    PubMed Central

    Line, Laura; Alhede, Morten; Kolpen, Mette; Kühl, Michael; Ciofu, Oana; Bjarnsholt, Thomas; Moser, Claus; Toyofuku, Masanori; Nomura, Nobuhiko; Høiby, Niels; Jensen, Peter Ø.

    2014-01-01

    Chronic Pseudomonas aeruginosa lung infection is the most severe complication in patients with cystic fibrosis (CF). The infection is characterized by the formation of biofilm surrounded by numerous polymorphonuclear leukocytes (PMNs) and strong O2 depletion in the endobronchial mucus. We have reported that O2 is mainly consumed by the activated PMNs, while O2 consumption by aerobic respiration is diminutive and nitrous oxide (N2O) is produced in infected CF sputum. This suggests that the reported growth rates of P. aeruginosa in lungs and sputum may result from anaerobic respiration using denitrification. The growth rate of P. aeruginosa achieved by denitrification at physiological levels (~400 μM) of nitrate (NO−3) is however, not known. Therefore, we have measured growth rates of anoxic cultures of PAO1 and clinical isolates (n = 12) in LB media supplemented with NO−3 and found a significant increase of growth when supplementing PAO1 and clinical isolates with ≥150 μM NO−3 and 100 μM NO−3, respectively. An essential contribution to growth by denitrification was demonstrated by the inability to establish a significantly increased growth rate by a denitrification deficient ΔnirS-N mutant at <1 mM of NO−3. Activation of denitrification could be achieved by supplementation with as little as 62.5 μM of NO−3 according to the significant production of N2O by the nitrous oxide reductase deficient ΔnosZ mutant. Studies of the promoter activity, gene transcripts, and enzyme activity of the four N-oxide reductases in PAO1 (Nar, Nir, Nor, Nos) further verified the engagement of denitrification, showing a transient increase in activation and expression and rapid consumption of NO−3 followed by a transient increase of NO−2. Growth rates obtained by denitrification in this study were comparable to our reported growth rates in the majority of P. aeruginosa cells in CF lungs and sputum. Thus, we have demonstrated that denitrification is required for P

  4. A comparative evaluation of piezoelectric sensors for acoustic emission-based impact location estimation and damage classification in composite structures

    NASA Astrophysics Data System (ADS)

    Uprety, Bibhisha; Kim, Sungwon; Mathews, V. John; Adams, Daniel O.

    2015-03-01

    Acoustic Emission (AE) based Structural Health Monitoring (SHM) is of great interest for detecting impact damage in composite structures. Within the aerospace industry the need to detect and locate these events, even when no visible damage is present, is important both from the maintenance and design perspectives. In this investigation, four commercially available piezoelectric sensors were evaluated for usage in an AE-based SHM system. Of particular interest was comparing the acoustic response of the candidate piezoelectric sensors for impact location estimations as well as damage classification resulting from the impact in fiber-reinforced composite structures. Sensor assessment was performed based on response signal characterization and performance for active testing at 300 kHz and steel-ball drop testing using both aluminum and carbon/epoxy composite plates. Wave mode velocities calculated from the measured arrival times were found to be in good agreement with predictions obtained using both the Disperse code and finite element analysis. Differences in the relative strength of the received wave modes, the overall signal strengths and signal-to-noise ratios were observed through the use of both active testing as well as passive steel-ball drop testing. Further comparative is focusing on assessing AE sensor performance for use in impact location estimation algorithms as well as detecting and classifying damage produced in composite structures due to impact events.

  5. A Comparative Study of the Applied Methods for Estimating Deflection of the Vertical in Terrestrial Geodetic Measurements.

    PubMed

    Vittuari, Luca; Tini, Maria Alessandra; Sarti, Pierguido; Serantoni, Eugenio; Borghi, Alessandra; Negusini, Monia; Guillaume, Sébastien

    2016-01-01

    This paper compares three different methods capable of estimating the deflection of the vertical (DoV): one is based on the joint use of high precision spirit leveling and Global Navigation Satellite Systems (GNSS), a second uses astro-geodetic measurements and the third gravimetric geoid models. The working data sets refer to the geodetic International Terrestrial Reference Frame (ITRF) co-location sites of Medicina (Northern, Italy) and Noto (Sicily), these latter being excellent test beds for our investigations. The measurements were planned and realized to estimate the DoV with a level of precision comparable to the angular accuracy achievable in high precision network measured by modern high-end total stations. The three methods are in excellent agreement, with an operational supremacy of the astro-geodetic method, being faster and more precise than the others. The method that combines leveling and GNSS has slightly larger standard deviations; although well within the 1 arcsec level, which was assumed as threshold. Finally, the geoid model based method, whose 2.5 arcsec standard deviations exceed this threshold, is also statistically consistent with the others and should be used to determine the DoV components where local ad hoc measurements are lacking. PMID:27104544

  6. A Comparative Study of the Applied Methods for Estimating Deflection of the Vertical in Terrestrial Geodetic Measurements

    PubMed Central

    Vittuari, Luca; Tini, Maria Alessandra; Sarti, Pierguido; Serantoni, Eugenio; Borghi, Alessandra; Negusini, Monia; Guillaume, Sébastien

    2016-01-01

    This paper compares three different methods capable of estimating the deflection of the vertical (DoV): one is based on the joint use of high precision spirit leveling and Global Navigation Satellite Systems (GNSS), a second uses astro-geodetic measurements and the third gravimetric geoid models. The working data sets refer to the geodetic International Terrestrial Reference Frame (ITRF) co-location sites of Medicina (Northern, Italy) and Noto (Sicily), these latter being excellent test beds for our investigations. The measurements were planned and realized to estimate the DoV with a level of precision comparable to the angular accuracy achievable in high precision network measured by modern high-end total stations. The three methods are in excellent agreement, with an operational supremacy of the astro-geodetic method, being faster and more precise than the others. The method that combines leveling and GNSS has slightly larger standard deviations; although well within the 1 arcsec level, which was assumed as threshold. Finally, the geoid model based method, whose 2.5 arcsec standard deviations exceed this threshold, is also statistically consistent with the others and should be used to determine the DoV components where local ad hoc measurements are lacking. PMID:27104544

  7. Biological Denitrification Treatment of Wastewater Using Wood Chips

    NASA Astrophysics Data System (ADS)

    Mizoguchi, Tadaaki; Koremura, Nao; Sato, Aya; Yoshioka, Toshiaki

    A novel method for removing nitrate in waste water which uses wood chips as a reduction agent and growth support mechanism for denitrification bacteria is studied in this report. A higher denitrification rate was obtained when a portion of the wood chips packed in a column were exposed to air than when all of the wood chips were entirely immersed in solution. Cherry tree chips were more effective than cedar chips, as almost a 100% denitirification rate was maintained for at least 69 days at an inlet concentration of 20mg-N/L and HRT of 20 hr. The denitrification rate decreased significantly when the initial nitrate concentration was increased from 21mg-N/L to 46 mg-N/L. It was possible to use wood chips exclusively as a supply source of organic compounds. An excess amount of organic compounds which is discharged from the reactor can be reduced by passing the solution through a column packed with activated carbon. Cedar chips prepared from a fresh log shortly after cutting were used as a supporting material for denitirification bacteria. A satisfactorily high degree of denitirifation was obtained at HRT of 0.76 hr by adding ethanol as a reduction agent for nitrate.

  8. Effect of tourmaline on denitrification characteristics of hydrogenotrophic bacteria.

    PubMed

    Wang, Wei; Jiang, Hongyan; Zhu, Guangquan; Song, Xueying; Liu, Xingyu; Qiao, Ya

    2016-03-01

    To improve the denitrification characteristics of anaerobic denitrifying bacteria and obviate the disadvantage of use of explosive hydrogen gas, tourmaline, a polar mineral, was added to the hydrogenotrophic denitrification system in this study. Microbial reduction of nitrate in the presence of tourmaline was evaluated to assess the promotion effect of tourmaline on nitrate biodegradation. The experiment results demonstrated that tourmaline speeded up the cultivation process of bacteria from 65 to 36 days. After domestication of the bacteria, nitrate (50 mg NO3 (-)-N L(-1)) was completely removed within 3 days in the combined tourmaline-bacteria system, and the generated nitrite was also removed within 8 days. The reduction rate in this system is higher relative to that in the bacteria system alone. Efficient removal of nitrate by tourmaline-supported anaerobic bacteria (without external hydrogen input) indicated that tourmaline might act as the sole hydrogen donor to sustain autotrophic denitrification. Besides the production of hydrogen, the promoted activity of anaerobic denitrifying bacteria might be caused by the change of water properties, e.g., the pH of aqueous solutions was altered to about 8.0 and the oxidation-reduction potential decreased by 62 % in the tourmaline system. The distinctive effects of tourmaline on bacteria were related to its electric properties. PMID:26545889

  9. Design of fluidized-bed, biological denitrification systems

    SciTech Connect

    Patton, B.D.; Hancher, C.W.; Pitt, W.W.; Walker, J.F.

    1982-01-01

    Many commercial processes yield nitrate-containing wastewaters that are being discharged to the environment because traditional recovery or disposal methods are economically unacceptable. The anticipated discharge limits (i.e., 10 to 20 g (NO/sub 3//sup -/)/m/sup 3/) being considered by many states will not allow continued release of these wastewaters. The new discharge standards can be met economically by use of the fluidizied-bed, biological denitrification process. Research and development studies were conducted with 0.05-, 0.10-, 0.20-, and 0.50-m-diam fluidized-bed bioreactor systems. Feed nitrate concentrations were in the 0 to 10,000 g (NO/sub 3//sup -/)/m/sup 3/ range. Using the data from these studies, rate expressions were developed for the destruction of nitrate as a function of nitrate concentration. Methods were also developed for sizing bioreactors and biomass control systems. The sizing methods for fluidized-bed denitrification systems are described, and support systems such as sampling and analysis, instrumentation and controls, utilities, and bacteria storage are discussed. Operation of the process is also briefly discussed to aid the designer. Using the methods presented in this report, fluidized-bed, biological denitrification systems can be designed to treat nitrate wastewater streams.

  10. Evaluating simultaneous chromate and nitrate reduction during microbial denitrification processes.

    PubMed

    Peng, Lai; Liu, Yiwen; Gao, Shu-Hong; Chen, Xueming; Ni, Bing-Jie

    2016-02-01

    Sulfur-based autotrophic denitrification and heterotrophic denitrification have been demonstrated to be promising technological processes for simultaneous removal of nitrate NO3(-) and chromate (Cr (VI)), two common contaminants in surface and ground waters. In this work, a mathematical model was developed to describe and evaluate the microbial and substrate interactions among sulfur oxidizing denitrifying organism, methanol-based heterotrophic denitrifiers and chromate reducing bacteria in the biofilm systems for simultaneous nitrate and chromate removal. The concomitant multiple chromate reduction pathways by these microbes were taken into account in this model. The validity of the model was tested using experimental data from three independent biofilm reactors under autotrophic, heterotrophic and mixotrophic conditions. The model sufficiently described the nitrate, chromate, methanol, and sulfate dynamics under varying conditions. The modeling results demonstrated the coexistence of sulfur-oxidizing denitrifying bacteria and heterotrophic denitrifying bacteria in the biofilm under mixotrophic conditions, with chromate reducing bacteria being outcompeted. The sulfur-oxidizing denitrifying bacteria substantially contributed to both nitrate and chromate reductions although heterotrophic denitrifying bacteria dominated in the biofilm. The mixotrophic denitrification could improve the tolerance of autotrophic denitrifying bacteria to Cr (VI) toxicity. Furthermore, HRT would play an important role in affecting the microbial distribution and system performance, with HRT of higher than 0.15 day being critical for a high level removal of nitrate and chromate (over 90%). PMID:26619398

  11. Simulation of three-phase fluidized bioreactors for denitrification

    SciTech Connect

    Hamza, A.V.; Dolan, J.F.; Wong, E.W.

    1981-03-01

    Fluidized-bed bioreactors were developed and operated at three scales (diameters of 0.1, 0.2, and 0.5 m) by the Chemical Technology Division. The performance of these reactors in denitrification was simulated using the following modified form of Monod kinetics to describe the reaction kinetics: rate = V/sub max/ (NO/sub 3//sup -//K/sub s/ + NO/sub 3//sup -/) (% biomass). In the fluids-movement portion of the simulation the tanks-in-series approximation to backmixing was used. This approach yielded a V/sub max/ of 3.5 g/m/sup 3/-min (% biomass) and a K/sub s/ of 163 g/m/sup 3/ for the 0.5-m bioreactor. Values of V/sub max/ and K/sub s/ were also determined for data derived from the 0.1-m bioreactor, but inadequate RTD data reduced the confidence level in these results. A complication in denitrification is the multi-step nature of the reduction from nitrate to nitrite to hyponitrite and finally to nitrogen. An experimental study of the effect of biomass loading upon denitrification was begun. It is recommended that the experimental work be continued.

  12. Transport zonation limits coupled nitrification-denitrification in permeable sediments.

    PubMed

    Kessler, Adam J; Glud, Ronnie N; Cardenas, M Bayani; Cook, Perran L M

    2013-01-01

    Measurement of biogeochemical processes in permeable sediments (including the hyporheic zone) is difficult because of complex multidimensional advective transport. This is especially the case for nitrogen cycling, which involves several coupled redox-sensitive reactions. To provide detailed insight into the coupling between ammonification, nitrification and denitrification in stationary sand ripples, we combined the diffusion equilibrium thin layer (DET) gel technique with a computational reactive transport biogeochemical model. The former approach provided high-resolution two-dimensional distributions of NO3(-) and (15)N-N2 gas. The measured two-dimensional profiles correlate with computational model simulations, showing a deep pool of N2 gas forming, and being advected to the surface below ripple peaks. Further isotope pairing calculations on these data indicate that coupled nitrification-denitrification is severely limited in permeable sediments because the flow and transport field limits interaction between oxic and anoxic pore water. The approach allowed for new detailed insight into subsurface denitrification zones in complex permeable sediments. PMID:24224741

  13. Influence of mixed liquor recycle ratio and dissolved oxygen on performance of pre-denitrification submerged membrane bioreactors.

    PubMed

    Tan, Teck Wee; Ng, How Yong

    2008-02-01

    The conflicting influence of mixed liquor recycle ratio and dissolved oxygen on nitrogen removal and membrane fouling of a pre-denitrification submerged MBR was investigated in this study. It was found that a high aeration rate of 10 L air/min was able to minimize membrane fouling as compared with lower aeration rates of 5 and 2.5L air/min in this study. Faster fouling at lower aeration rate was due to the decrease in cross-flow velocity across the membrane surface. However, high DO concentration (average of 5.1+/-0.5mg O2/L) present in the recycle mixed liquor at an aeration rate of 10 L air/min deteriorated the TN removal efficiency when operating at a recycle ratio of more than 3. A lower aeration rate of 5L air/min, resulting in an average DO concentration of 3.4+/-0.7 mg O2/L in the recycle mixed liquor, led to an improvement in TN removal efficiency: 63%, 80%, 84% and 89% for mixed liquor recycle ratio of 1, 3, 5 and 10, respectively. Further decrease in aeration rate to 2.5L air/min, resulting in an average DO concentration of 1.9+/-0.8 mg O2/L, did not improve the TN removal efficiency. Using a newly developed simplified nitrification-denitrification model, it was calculated that the COD/NO3(-)-N required for denitrification at 10 L air/min aeration rate was higher than those associated with 5 and 2.5L air/min aeration rates. The model also revealed that denitrification at an aeration rate of 10 L air/min was limited by COD concentration present in the wastewater when operating at a mixed liquor recycle ratio of 3 and higher. PMID:17905406

  14. [Cultivation of Aerobic Granular Sludge with Real Low Concentration Domestic Wastewater and Its Denitrification Performances Under the Continuous Flow].

    PubMed

    Yao, Li; Xin, Xin; Lu, Hang; Zhu, Liao-dong; Xie, Si-jian

    2015-07-01

    The COD, ammonia and total nitrogen removal efficiency, as well as the physical properties of aerobic granular sludge (AGS) and its denitrification kinetics were studied in the continuous flow reactor. The experimental results showed that the AGS was successfully cultivated in the continuous flow system within 40 days. The nitrogen and carbon removal efficiencies were gradually improved with the improvement of sludge granulation. In the running stage of 41 - 60 days, the COD, ammonia and TN removal efficiency could reach 85. 54% , 95. 5% and 65. 56%, respectively. And the nitrate and nitrite nitrogen accumulation was not high in the reaction process. Mature AGS had more void structure and a large number of extracellular polymeric substances. It had significant advantages compared with the seed sludge in the aspects of moisture content, wet density, sedimentation rate, mechanical strength, and SVI values. The simultaneous nitrification and denitrification efficiency was 81. 69% , the nitrification rate and denitrification rate were 5.78 mg . (L.h) -1 and 4. 90 mg . (L.h) -1, respectively. PMID:26489334

  15. Effect of low dissolved oxygen on simultaneous nitrification and denitrification in a membrane bioreactor treating black water.

    PubMed

    Hocaoglu, S Murat; Insel, G; Cokgor, E Ubay; Orhon, D

    2011-03-01

    Effect of low dissolved oxygen on simultaneous nitrification and denitrification was evaluated in a membrane bioreactor treating black water. A fully aerobic membrane bioreactor was operated at a sludge age of 60 days under three low dissolved oxygen (DO) levels below 0.5mg/L. It sustained effective simultaneous nitrification/denitrification for the entire observation period. Nitrification was incomplete due to adverse effects of a number of factors such as low DO level, SMPs inhibition, alkalinity limitation, etc. DO impact was more significant on denitrification: Nitrate was fully removed at low DO level but the removal was gradually reduced as DO was increased to 0.5mg/L. Nitrogen removal remained optimal within the DO range of 0.15-0.35 mg/L. Experimental results were calibrated and simulated by model evaluation with the same model coefficients. The model defined improved mass transfer with lower affinity coefficients for oxygen and nitrate as compared to conventional activated sludge. PMID:21239168

  16. Simultaneous nitrification, denitrification and phosphorus removal (SNDPR) in a full-scale water reclamation plant located in warm climate.

    PubMed

    Yang, Qin; Shen, Nan; Lee, Zarraz M-P; Xu, Guangjing; Cao, Yeshi; Kwok, Beehong; Lay, Winson; Liu, Yu; Zhou, Yan

    2016-01-01

    The combination of simultaneous nitrification-denitrification (SND) with enhanced biological phosphorus removal (EBPR) provides a more efficient and economically viable option for nutrient removal from municipal wastewater compared to conventional two-step nitrification-denitrification. This study analyzed the nutrients (N and P) profiles in a full-scale municipal wastewater reclamation plant (WRP) located in the tropical region, in which more than 90% of nitrogen was removed. Interestingly, average SND efficiency in aerobic zones was found to be up to 50%, whereas phosphorus profile displayed a clear cyclic release and uptake pattern with a phosphorus removal efficiency of up to 76%. The capability of sludge to perform SND and EBPR was further confirmed through a series of batch experiments. Microbial analysis revealed the presence of Accumulibacter and Tetrasphaera phosphate accumulating organisms in the plant, while few glycogen accumulating organisms (GAO) was observed. This study showed the significant occurrence of combined SND and EBPR, known as simultaneous nitrification, denitrification and phosphorus removal (SNDPR), in the studied WRP under warm climate. The possible causes behind the observed SNDPR were also discussed. PMID:27438250

  17. Nutrient Fluxes, Porewater Profiles and Denitrification in Sediment Influenced by Algal Sedimentation and Bioturbation by Monoporeia affinis

    NASA Astrophysics Data System (ADS)

    Tuominen, L.; Mäkelä, K.; Lehtonen, K. K.; Haahti, H.; Hietanen, S.; Kuparinen, J.

    1999-07-01

    The effects of addition of algae (340 mg C m-2) and of the amphipod Monoporeia affinis (1500 ind m-2) on denitrification; porewater nutrient profiles; nutrient fluxes between sediment and water; and bacterial production were studied. A laboratory experiment was conducted using cores filled with sediment from the Gulf of Finland (Baltic Sea). Denitrification (isotope pairing method) was dramatically reduced in the cores enriched with algae (from 200-300 to 10-20 μmol N m-2 day-1). However, the addition of M. affinis together with algae negated this effect. Monoporeia affinis alone increased the coupled nitrification-denitrification as compared to the control cores. Bioturbation by the amphipods oxidised the sediment surface layers and consequently, PO43-concentration in the porewater decreased. In the cores enriched with algae, the loss of N from the sediment porewater was dominated by the efflux of NH4+which formed 90% of the loss. In the M. affinis enriched cores, the share of the NH4+efflux was 60% of which the excretion by M. affinis was 5-10%. The effects of M. affinis were found to be caused mainly by the improved O2conditions in the sediment.

  18. Sulfide-based mixotrophic denitrification for treatment of sulfur, nitrogen and carbon-contaminated wastewater.

    PubMed

    Wei, Li; Xiao, Liang; Lei, Liu; Jianguo, Lin

    2015-07-01

    Wastewater contaminated by sulfur, nitrogen and carbon compounds was treated by sulfide-based denitrification process in an expanded granular sludge bed packed with porous sponge. In influent, nitrate and nitrite served as electron acceptors, while sulfide and organic carbon served as electron donors. Both sulfide-based autotrophic denitrification and heterotrophic denitrification were found in the bioreactor. The percentage of heterotrophic denitrification was 36.5%, and the removal rates of sulfide, nitrate, nitrite and organic carbon were 99%, 99%, 95.5% and 80% respectively, which actualized the simultaneous mixotrophic denitrification and desulfurization. The effect factors such as organic carbon category, organic carbon loading rate and nitrite loading rate were also investigated. The 50 mg Cl(-1)d(-1) of glucose and 25 mg Cl(-1) d(-1) acetate sodium were found good for sulfide-based denitrification, while the suitable loading rate of nitrite was 50 mg Nl(-1)d(-1). PMID:26387356

  19. Denitrification in a BTEX Contaminated Aquifer Containing Reduced Sulfur

    NASA Astrophysics Data System (ADS)

    Eckert, P.; Appelo, C.; Wisotzky, F.; Obermann, P.

    2001-05-01

    At a former gasworks plant in Duesseldorf (Germany) a massive soil and groundwater contamination with BTEX (up to 100 mg/l) and to a minor extent with PAH (up to 10 mg/l) were detected. Mainly due to sulfate and iron-(III) reduction, a natural biodegradation has occurred and restricted the length of the contaminant plume in the direction of groundwater flow to only 600 m. The active remediation strategy at this site includes nitrate-enhanced in-situ bioremediation of the remaining contaminants in the plume. Nitrate was infiltrated in the contaminated aquifer during a field test to study the efficacy of enhanced natural attenuation. Degradation of hydrocarbons under denitrifying has been proved by numerous laboratory and field studies. However, at this site the competing reaction of nitrate with hydrocarbons and reduced sulfur components has to be considered. The oxidation of pyrite by nitrate in pristine aquifers is well known. The Duesseldorf aquifer contains FeS, pyrite and Fe-calcite precipitated during over 50 years of natural attenuation. The hydrogeochemical transport model PHREEQC-2 is used to simulate the distribution of chemical species and reaction rates along the flow path between the infiltration well and two multilevel wells . The complicated suite of reactions caused by the reduction of nitrate is evaluated by the comparison of modeled and measured data. At the Duesseldorf site the concomitant presence of nitrate, Fe(II) and BTEX/PAHs showed that the reactions did not evolve to thermodynamic equilibrium and were controlled by kinetics. The very good fit of observed and model calculations illustrates that the inorganic chemical reactions during the field test are generally well understood. The kinetic reactions could be modelled with rate equations from the literature based on oxygen, and which were extended with nitrate. Denitrification rates with BTEX compounds and with FeS were found to be comparable, but the oxidation of Fe(II) and FeS occurred

  20. Comparing integrated stable isotope and eddy covariance estimates of water-use efficiency on a Mediterranean successional sequence.

    PubMed

    Scartazza, Andrea; Vaccari, Francesco Primo; Bertolini, Teresa; Di Tommasi, Paul; Lauteri, Marco; Miglietta, Franco; Brugnoli, Enrico

    2014-10-01

    Water-use efficiency (WUE), thought to be a relevant trait for productivity and adaptation to water-limited environments, was estimated for three different ecosystems on the Mediterranean island of Pianosa: Mediterranean macchia (SMM), transition (S(TR)) and abandoned agricultural (SAA) ecosystems, representing a successional series. Three independent approaches were used to study WUE: eddy covariance measurements, C isotope composition of ecosystem respired CO2, and C isotope discrimination (Δ) of leaf material (dry matter and soluble sugars). Seasonal variations in C-water relations and energy fluxes, compared in S(MM) and in SAA, were primarily dependent on the specific composition of each plant community. WUE of gross primary productivity was higher in SMM than in SAA at the beginning of the dry season. Both structural and fast-turnover leaf material were, on average, more enriched in (13)C in S(MM) than SAA, indicating relatively higher stomatal control and WUE for the long-lived macchia species. This pattern corresponded to (13)C-enriched respired CO2 in SMM compared to the other ecosystems. Conversely, most of the annual herbaceous SAA species (terophytes) showed a drought-escaping strategy, with relatively high stomatal conductance and low WUE. An ecosystem-integrated Δ value was weighted for each ecosystem on the abundance of different life forms, classified according to Raunkiar's system. Agreement was found between ecosystem WUE calculated using eddy covariance and those estimated using integrated Δ approaches. Comparing the isotopic methods, Δ of leaf soluble sugars provided the most reliable proxy for short-term changes in photosynthetic discrimination and associated shifts in integrated canopy-level WUE along the successional series. PMID:25085444

  1. Nitrogen, carbon, and sulfur isotopic change during heterotrophic (Pseudomonas aureofaciens) and autotrophic (Thiobacillus denitrificans) denitrification reactions.

    PubMed

    Hosono, Takahiro; Alvarez, Kelly; Lin, In-Tian; Shimada, Jun

    2015-12-01

    In batch culture experiments, we examined the isotopic change of nitrogen in nitrate (δ(15)NNO3), carbon in dissolved inorganic carbon (δ(13)CDIC), and sulfur in sulfate (δ(34)SSO4) during heterotrophic and autotrophic denitrification of two bacterial strains (Pseudomonas aureofaciens and Thiobacillus denitrificans). Heterotrophic denitrification (HD) experiments were conducted with trisodium citrate as electron donor, and autotrophic denitrification (AD) experiments were carried out with iron disulfide (FeS2) as electron donor. For heterotrophic denitrification experiments, a complete nitrate reduction was accomplished, however bacterial denitrification with T. denitrificans is a slow process in which, after seventy days nitrate was reduced to 40% of the initial concentration by denitrification. In the HD experiment, systematic change of δ(13)CDIC (from -7.7‰ to -12.2‰) with increase of DIC was observed during denitrification (enrichment factor εN was -4.7‰), suggesting the contribution of C of trisodium citrate (δ(13)C=-12.4‰). No SO4(2-) and δ(34)SSO4 changes were observed. In the AD experiment, clear fractionation of δ(13)CDIC during DIC consumption (εC=-7.8‰) and δ(34)SSO4 during sulfur use of FeS2-S (around 2‰), were confirmed through denitrification (εN=-12.5‰). Different pattern in isotopic change between HD and AD obtained on laboratory-scale are useful to recognize the type of denitrification occurring in the field. PMID:26529303

  2. Denitrification of the polar winter stratosphere - Implications of SAM II cloud formation temperatures

    NASA Technical Reports Server (NTRS)

    Hamill, Patrick; Toon, O. B.

    1990-01-01

    The SAM II extinction profiles and the associated temperature profiles are used to determine the amount of denitrification of the winter polar stratospheres. Clear evidence of the denitrification process in the Antarctic data is seen. There are indications in the Arctic data that denitrification mechanisms may be at work there also. At the latitudes observed by the SAM II satellite system, denitrification begins before the formation of extensive ice clouds and may be due to sedimentation of nitric acid particles. However, the possibility of dinitrification by type II PSCs at latitudes not observed by SAM II cannot be excluded.

  3. Nitrogen, carbon, and sulfur isotopic change during heterotrophic (Pseudomonas aureofaciens) and autotrophic (Thiobacillus denitrificans) denitrification reactions

    NASA Astrophysics Data System (ADS)

    Hosono, Takahiro; Alvarez, Kelly; Lin, In-Tian; Shimada, Jun

    2015-12-01

    In batch culture experiments, we examined the isotopic change of nitrogen in nitrate (δ15NNO3), carbon in dissolved inorganic carbon (δ13CDIC), and sulfur in sulfate (δ34SSO4) during heterotrophic and autotrophic denitrification of two bacterial strains (Pseudomonas aureofaciens and Thiobacillus denitrificans). Heterotrophic denitrification (HD) experiments were conducted with trisodium citrate as electron donor, and autotrophic denitrification (AD) experiments were carried out with iron disulfide (FeS2) as electron donor. For heterotrophic denitrification experiments, a complete nitrate reduction was accomplished, however bacterial denitrification with T. denitrificans is a slow process in which, after seventy days nitrate was reduced to 40% of the initial concentration by denitrification. In the HD experiment, systematic change of δ13CDIC (from - 7.7‰ to - 12.2‰) with increase of DIC was observed during denitrification (enrichment factor εN was - 4.7‰), suggesting the contribution of C of trisodium citrate (δ13C = - 12.4‰). No SO42 - and δ34SSO4 changes were observed. In the AD experiment, clear fractionation of δ13CDIC during DIC consumption (εC = - 7.8‰) and δ34SSO4 during sulfur use of FeS2-S (around 2‰), were confirmed through denitrification (εN = - 12.5‰). Different pattern in isotopic change between HD and AD obtained on laboratory-scale are useful to recognize the type of denitrification occurring in the field.

  4. Estimating heritabilities and genetic correlations: comparing the 'animal model' with parent-offspring regression using data from a natural population.

    PubMed

    Akesson, Mikael; Bensch, Staffan; Hasselquist, Dennis; Tarka, Maja; Hansson, Bengt

    2008-01-01

    Quantitative genetic parameters are nowadays more frequently estimated with restricted maximum likelihood using the 'animal model' than with traditional methods such as parent-offspring regressions. These methods have however rarely been evaluated using equivalent data sets. We compare heritabilities and genetic correlations from animal model and parent-offspring analyses, respectively, using data on eight morphological traits in the great reed warbler (Acrocephalus arundinaceus). Animal models were run using either mean trait values or individual repeated measurements to be able to separate between effects of including more extended pedigree information and effects of replicated sampling from the same individuals. We show that the inclusion of more pedigree information by the use of mean traits animal models had limited effect on the standard error and magnitude of heritabilities. In contrast, the use of repeated measures animal model generally had a positive effect on the sampling accuracy and resulted in lower heritabilities; the latter due to lower additive variance and higher phenotypic variance. For most trait combinations, both animal model methods gave genetic correlations that were lower than the parent-offspring estimates, whereas the standard errors were lower only for the mean traits animal model. We conclude that differences in heritabilities between the animal model and parent-offspring regressions were mostly due to the inclusion of individual replicates to the animal model rather than the inclusion of more extended pedigree information. Genetic correlations were, on the other hand, primarily affected by the inclusion of more pedigree information. This study is to our knowledge the most comprehensive empirical evaluation of the performance of the animal model in relation to parent-offspring regressions in a wild population. Our conclusions should be valuable for reconciliation of data obtained in earlier studies as well as for future meta

  5. A comparative pharmacokinetic estimate of mercury in U.S. Infants following yearly exposures to inactivated influenza vaccines containing thimerosal.

    PubMed

    Mitkus, Robert J; King, David B; Walderhaug, Mark O; Forshee, Richard A

    2014-04-01

    The use of thimerosal preservative in childhood vaccines has been largely eliminated over the past decade in the United States because vaccines have been reformulated in single-dose vials that do not require preservative. An exception is the inactivated influenza vaccines, which are formulated in both multidose vials requiring preservative and preservative-free single-dose vials. As part of an ongoing evaluation by USFDA of the safety of biologics throughout their lifecycle, the infant body burden of mercury following scheduled exposures to thimerosal preservative in inactivated influenza vaccines in the United States was estimated and compared to the infant body burden of mercury following daily exposures to dietary methylmercury at the reference dose established by the USEPA. Body burdens were estimated using kinetic parameters derived from experiments conducted in infant monkeys that were exposed episodically to thimerosal or MeHg at identical doses. We found that the body burden of mercury (AUC) in infants (including low birth weight) over the first 4.5 years of life following yearly exposures to thimerosal was two orders of magnitude lower than that estimated for exposures to the lowest regulatory threshold for MeHg over the same time period. In addition, peak body burdens of mercury following episodic exposures to thimerosal in this worst-case analysis did not exceed the corresponding safe body burden of mercury from methylmercury at any time, even for low-birth-weight infants. Our pharmacokinetic analysis supports the acknowledged safety of thimerosal when used as a preservative at current levels in certain multidose infant vaccines in the United States. PMID:24117921

  6. Carbohydrate Estimation by a Mobile Phone-Based System Versus Self-Estimations of Individuals With Type 1 Diabetes Mellitus: A Comparative Study

    PubMed Central

    Dehais, Joachim; Anthimopoulos, Marios; Shevchik, Sergey; Botwey, Ransford Henry; Duke, David; Stettler, Christoph; Diem, Peter

    2016-01-01

    Background Diabetes mellitus is spreading throughout the world and diabetic individuals have been shown to often assess their food intake inaccurately; therefore, it is a matter of urgency to develop automated diet assessment tools. The recent availability of mobile phones with enhanced capabilities, together with the advances in computer vision, have permitted the development of image analysis apps for the automated assessment of meals. GoCARB is a mobile phone-based system designed to support individuals with type 1 diabetes during daily carbohydrate estimation. In a typical scenario, the user places a reference card next to the dish and acquires two images using a mobile phone. A series of computer vision modules detect the plate and automatically segment and recognize the different food items, while their 3D shape is reconstructed. Finally, the carbohydrate content is calculated by combining the volume of each food item with the nutritional information provided by the USDA Nutrient Database for Standard Reference. Objective The main objective of this study is to assess the accuracy of the GoCARB prototype when used by individuals with type 1 diabetes and to compare it to their own performance in carbohydrate counting. In addition, the user experience and usability of the system is evaluated by questionnaires. Methods The study was conducted at the Bern University Hospital, “Inselspital” (Bern, Switzerland) and involved 19 adult volunteers with type 1 diabetes, each participating once. Each study day, a total of six meals of broad diversity were taken from the hospital’s restaurant and presented to the participants. The food items were weighed on a standard balance and the true amount of carbohydrate was calculated from the USDA nutrient database. Participants were asked to count the carbohydrate content of each meal independently and then by using GoCARB. At the end of each session, a questionnaire was completed to assess the user’s experience with Go

  7. Validity of Electronic Diet Recording Nutrient Estimates Compared to Dietitian Analysis of Diet Records: Randomized Controlled Trial

    PubMed Central

    Scheett, Angela J; Johnson, LuAnn K; Jahns, Lisa

    2015-01-01

    Background Dietary intake assessment with diet records (DR) is a standard research and practice tool in nutrition. Manual entry and analysis of DR is time-consuming and expensive. New electronic tools for diet entry by clients and research participants may reduce the cost and effort of nutrient intake estimation. Objective To determine the validity of electronic diet recording, we compared responses to 3-day DR kept by Tap & Track software for the Apple iPod Touch and records kept on the Nutrihand website to DR coded and analyzed by a research dietitian into a customized US Department of Agriculture (USDA) nutrient analysis program, entitled GRAND (Grand Forks Research Analysis of Nutrient Data). Methods Adult participants (n=19) enrolled in a crossover-designed clinical trial. During each of two washout periods, participants kept a written 3-day DR. In addition, they were randomly assigned to enter their DR in a Web-based dietary analysis program (Nutrihand) or a handheld electronic device (Tap & Track). They completed an additional 3-day DR and the alternate electronic diet recording methods during the second washout. Entries resulted in 228 daily diet records or 12 for each of 19 participants. Means of nutrient intake were calculated for each method. Concordance of the intake estimates were determined by Bland-Altman plots. Coefficients of determination (R 2) were calculated for each comparison to assess the strength of the linear relationship between methods. Results No significant differences were observed between the mean nutrient values for energy, carbohydrate, protein, fat, saturated fatty acids, total fiber, or sodium between the recorded DR analyzed in GRAND and either Nutrihand or Tap & Track, or for total sugars comparing GRAND and Tap & Track. Reported values for total sugars were significantly reduced (P<.05) comparing Nutrihand to GRAND. Coefficients of determination (R 2) for Nutrihand and Tap & Track compared to DR entries into GRAND, respectively

  8. A comparative study for the concrete compressive strength estimation using neural network and neuro-fuzzy modelling approaches

    NASA Astrophysics Data System (ADS)

    Bilgehan, Mahmut

    2011-03-01

    In this paper, adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN) model have been successfully used for the evaluation of relationships between concrete compressive strength and ultrasonic pulse velocity (UPV) values using the experimental data obtained from many cores taken from different reinforced concrete structures having different ages and unknown ratios of concrete mixtures. A comparative study is made using the neural nets and neuro-fuzzy (NF) techniques. Statistic measures were used to evaluate the performance of the models. Comparing of the results, it is found that the proposed ANFIS architecture with Gaussian membership function is found to perform better than the multilayer feed-forward ANN learning by backpropagation algorithm. The final results show that especially the ANFIS modelling may constitute an efficient tool for prediction of the concrete compressive strength. Architectures of the ANFIS and neural network established in the current study perform sufficiently in the estimation of concrete compressive strength, and particularly ANFIS model estimates closely follow the desired values. Both ANFIS and ANN techniques can be used in conditions where too many structures are to be examined in a restricted time. The presented approaches enable to practically find concrete strengths in the existing reinforced concrete structures, whose records of concrete mixture ratios are not available or present. Thus, researchers can easily evaluate the compressive strength of concrete specimens using UPV and density values. These methods also contribute to a remarkable reduction in the computational time without any significant loss of accuracy. A comparison of the results clearly shows that particularly the NF approach can be used effectively to predict the compressive strength of concrete using UPV and density values. In addition, these model architectures can be used as a nondestructive procedure for health monitoring of

  9. A New Approach for Validating Satellite Estimates of Soil Moisture Using Large-Scale Precipitation: Comparing AMSR-E Products

    NASA Astrophysics Data System (ADS)

    Tuttle, S. E.; Salvucci, G.

    2012-12-01

    Soil moisture influences many hydrological processes in the water and energy cycles, such as runoff generation, groundwater recharge, and evapotranspiration, and thus is important for climate modeling, water resources management, agriculture, and civil engineering. Large-scale estimates of soil moisture are produced almost exclusively from remote sensing, while validation of remotely sensed soil moisture has relied heavily on ground truthing, which is at an inherently smaller scale. Here we present a complementary method to determine the information content in different soil moisture products using only large-scale precipitation data (i.e. without modeling). This study builds on the work of Salvucci [2001], Saleem and Salvucci [2002], and Sun et al. [2011], in which precipitation was conditionally averaged according to soil moisture level, resulting in moisture-outflow curves that estimate the dependence of drainage, runoff, and evapotranspiration on soil moisture (i.e. sigmoidal relations that reflect stressed evapotranspiration for dry soils, roughly constant flux equal to potential evaporation minus capillary rise for moderately dry soils, and rapid drainage for very wet soils). We postulate that high quality satellite estimates of soil moisture, using large-scale precipitation data, will yield similar sigmoidal moisture-outflow curves to those that have been observed at field sites, while poor quality estimates will yield flatter, less informative curves that explain less of the precipitation variability. Following this logic, gridded ¼ degree NLDAS precipitation data were compared to three AMSR-E derived soil moisture products (VUA-NASA, or LPRM [Owe et al., 2001], NSIDC [Njoku et al., 2003], and NSIDC-LSP [Jones & Kimball, 2011]) for a period of nine years (2001-2010) across the contiguous United States. Gaps in the daily soil moisture data were filled using a multiple regression model reliant on past and future soil moisture and precipitation, and soil

  10. Quantitative importance of denitrification and N2O emission in an N-saturated subtropical forest catchment, southwest China

    NASA Astrophysics Data System (ADS)

    Zhu, J.; Dörsch, P.; Mulder, J.

    2009-04-01

    Anthropogenic emission of nitrogen in the environment has increased rapidly, due to fast economic growth. This has resulted in increased deposition rates of reactive nitrogen, primarily as NOx (from fossil fuel combustion) and NH3 (from fertilizer production and animal husbandry). In response, temperate and boreal forests may develop nitrogen saturation, characterized by increased leaching of nitrate. In addition, elevated emission of N2 and N2O, due to nitrification and denitrification, may occur. To date, few studies exist quantifying the nitrogen balance, including N2 and N2O production, in nitrogen-saturated, monsoonal, sub-tropical forest ecosystems in south-west China. Since nitrate contributes to the eutrophication of stream water, and N2O is a potent greenhouse gas, it is important to quantitatively understand the role of nitrification and denitrification in the nitrogen cycle. Several subtropical forests in southwest China, receiving elevated nitrogen deposition (30-73 kg N ha-1 a-1; Zhang. et al., 2008), are characterized by high temperature and soil moisture content in much of the growing season. This may cause a much stronger intensity of denitrification compared with that in temperate and boreal forests. In turn this may lead to decreased nitrate leaching and a higher potential of N2O emission. In my PhD project, I will investigate the nitrogen cycle in a forest catchment (TieShanPing; TSP), which is near one of the biggest cities, Chongqing, in southwest China. Previous research suggests high nitrogen deposition (3.52 gN m-2 a-1), but low nitrogen flux (0.57 gN m-2 a-1) in runoff (Chen & Mulder, 2007). Tree growth, and thus plant N uptake, is limited and nitrate fluxes below the root zone are relatively large, suggesting ‘N-saturation'. Based on this, we hypothesize that significant amounts of nitrogen are emitted as gases, with denitrification playing an important role, and N2 and N2O (especially N2) being major components of the emitted gases

  11. Numerical evaluation of subsoil diffusion of (15) N labelled denitrification products during employment of the (15) N gas flux method in the field

    NASA Astrophysics Data System (ADS)

    Well, Reinhard; Buchen, Caroline; Lewicka-Szczebak, Dominika; Ruoss, Nicolas

    2016-04-01

    Common methods for measuring soil denitrification in situ include monitoring the accumulation of 15N labelled N2 and N2O evolved from 15N labelled soil nitrate pool in soil surface chambers. Gas diffusion is considered to be the main accumulation process. Because accumulation of the gases decreases concentration gradients between soil and chamber over time, gas production rates are underestimated if calculated from chamber concentrations. Moreover, concentration gradients to the non-labelled subsoil exist, inevitably causing downward diffusion of 15N labelled denitrification products. A numerical model for simulating gas diffusion in soil was used in order to determine the significance of this source of error. Results show that subsoil diffusion of 15N labelled N2 and N2O - and thus potential underestimation of denitrification derived from chamber fluxes - increases with cover closure time as well as with increasing diffusivity. Simulations based on the range of typical gas diffusivities of unsaturated soils show that the fraction of subsoil diffusion after chamber closure for 1 hour is always significant with values up to >30 % of total production of 15N labelled N2 and N2O. Field experiments for measuring denitrification with the 15N gas flux method were conducted. The ability of the model to predict the time pattern of gas accumulation was evaluated by comparing measured 15N2 concentrations and simulated values.

  12. The use of fermentation liquid of wastewater primary sedimentation sludge as supplemental carbon source for denitrification based on enhanced anaerobic fermentation.

    PubMed

    Liu, Feng; Tian, Yu; Ding, Yi; Li, Zhipeng

    2016-11-01

    Wastewater primary sedimentation sludge was prepared into fermentation liquid as denitrification carbon source, and the main components of fermentation liquid was short-chain volatile fatty acids. Meanwhile, the acetic acid and propionic acid respectively accounted for about 29.36% and 26.56% in short-chain volatile fatty acids. The performance of fermentation liquid, methanol, acetic acid, propionic acid and glucose used as sole carbon source were compared. It was found that the denitrification rate with fermentation liquid as carbon source was 0.17mgNO3(-)-N/mg mixed liquor suspended solid d, faster than that with methanol, acetic acid, and propionic acid as sole carbon source, and lower than that with glucose as sole carbon source. For the fermentation liquid as carbon source, the transient accumulation of nitrite was insignificantly under different initial total nitrogen concentration. Therefore, the use of fermentation liquid for nitrogen removal could improve denitrification rate, and reduce nitrite accumulation in denitrification process. PMID:27472748

  13. Long-term Effects of Ethanol Addition on Denitrification At The Uranium Mill Tailing Site In Monument Valley, Arizona

    NASA Astrophysics Data System (ADS)

    McMillan, A. L.; Borden, A. K.; Brusseau, M. L.; Carroll, K. C.; Akyol, N. H.; Berkompas, J. L.; Miao, Z.; Jordan, F.; Tick, G. R.; Waugh, J.; Glenn, E. P.

    2011-12-01

    Due to mining and processing of uranium at a site near Monument Valley, AZ, an extensive nitrate plume was produced in a shallow alluvial aquifer. Two pilot tests were conducted to evaluate the addition of ethanol as a carbon substrate to enhance natural denitrification. Aqueous geochemistry was characterized based upon groundwater samples collected before and after the addition of ethanol. Compound specific stable isotope analysis was also conducted. The results of the field tests showed that the concentration of nitrate decreased, while the concentration of nitrous oxide (a product of denitrification) increased. In addition, changes in aqueous concentrations of sulfate, iron, and manganese indicated that the ethanol amendment caused a change in prevailing redox conditions. The results of compound-specific stable isotope analysis for nitrate-nitrogen indicated that the nitrate concentration reductions were biologically mediated. Denitrification rate coefficients estimated for the pilot tests were approximately 50 times larger than resident-condition (non-enhanced) values obtained from prior characterization studies conducted at the site. Using the time at which nitrate concentrations began to decline for downgradient monitoring wells, and the associated inter-well distances, rough estimates of approximately 0.1-0.17 m/day were obtained for the effective reactive-front velocity. These values are within the range of mean pore-water velocities expected for the measured hydraulic conductivities and gradient. The nitrate concentrations in the injection zone have remained at levels three orders of magnitude below the initial values for many months, indicating that the ethanol amendments had a long-term impact on the local subsurface environment.

  14. The influence of N-fertilization regimes on N2O emissions and denitrification in rain-fed cropland during the rainy season.

    PubMed

    Dong, Zhixin; Zhu, Bo; Zeng, Zebin

    2014-11-01

    The effects of nitrogen fertilization regimes on N2O emissions and denitrification rates were evaluated by in situ field incubation experiments with intact soil cores and the acetylene block technique. Intact soil cores were collected from long-term field experiments involving several N fertilization regimes, including single synthetic N fertilizer (N), organic manure (OM), synthetic N, P, K fertilizer (NPK), organic manure with synthetic fertilizer (OMNPK), crop straw residue with synthetic fertilizer (SRNPK) and no nitrogen fertilizer (NF). N2O was sampled from the head space of the cylinders to determine the daily N2O emission and denitrification rate. The results showed that the N2O emissions were greatly influenced by the specific fertilization regime even when the same nitrogen rate was applied. The mean N2O emissions and denitrification rates from the N, OM, NPK, OMNPK and SRNPK treatment were 2.22, 2.66, 1.94, 2.53, 1.67 and 4.63, 5.96, 4.15, 5.41, 3.65 mg per m(2) per day, respectively. The application of OM significantly increased the N2O emission and denitrification compared to the application of NPK because of the high soil organic carbon (SOC) content of OM. However, SRNPK increased the SOC content and decreased the N2O emissions significantly compared to the OM and OMNPK treatments because the addition of crop straw with a high C/N ratio to soil with a low inorganic N content induced N immobilization. The contents of soil nitrate and ammonium were the main limiting factors for N2O emissions in a positive regression as follows: Ln (N2O) = 2.511 + 1.258 × Ln ([NH4(+)] + [NO3(-)]). Crop straw residue combined with synthetic fertilizer is recommended as an optimal strategy for mitigating N2O emissions and denitrification-induced N loss in rain-fed croplands. PMID:25220444

  15. Comparative Dosimetric Estimates of a 25 keV Electron Micro-beam with three Monte Carlo Codes

    SciTech Connect

    Mainardi, Enrico; Donahue, Richard J.; Blakely, Eleanor A.

    2002-09-11

    The calculations presented compare the different performances of the three Monte Carlo codes PENELOPE-1999, MCNP-4C and PITS, for the evaluation of Dose profiles from a 25 keV electron micro-beam traversing individual cells. The overall model of a cell is a water cylinder equivalent for the three codes but with a different internal scoring geometry: hollow cylinders for PENELOPE and MCNP, whereas spheres are used for the PITS code. A cylindrical cell geometry with scoring volumes with the shape of hollow cylinders was initially selected for PENELOPE and MCNP because of its superior simulation of the actual shape and dimensions of a cell and for its improved computer-time efficiency if compared to spherical internal volumes. Some of the transfer points and energy transfer that constitute a radiation track may actually fall in the space between spheres, that would be outside the spherical scoring volume. This internal geometry, along with the PENELOPE algorithm, drastically reduced the computer time when using this code if comparing with event-by-event Monte Carlo codes like PITS. This preliminary work has been important to address dosimetric estimates at low electron energies. It demonstrates that codes like PENELOPE can be used for Dose evaluation, even with such small geometries and energies involved, which are far below the normal use for which the code was created. Further work (initiated in Summer 2002) is still needed however, to create a user-code for PENELOPE that allows uniform comparison of exact cell geometries, integral volumes and also microdosimetric scoring quantities, a field where track-structure codes like PITS, written for this purpose, are believed to be superior.

  16. Using stable isotopes to estimate and compare mean residence times in contrasting geologic catchments (Attert River, NW Luxembourg)

    NASA Astrophysics Data System (ADS)

    Martínez-Carreras, N.; Fenicia, F.; Frentress, J.; Wrede, S.; Pfister, L.

    2012-04-01

    In recent years, stable isotopes have been increasingly used to characterize important aspects of catchment hydrological functioning, such as water storage dynamics, flow pathways and water sources. These characteristics are often synthesized by the Mean Residence Time (MRT), which is a simple catchment descriptor that employ the relation of distinct stable isotopic signatures in the rainfall input and streamflow output of a catchment that are significantly dampened through sub-surface propagation. In this preliminary study, MRT was estimated in the Attert River catchment (NW Luxembourg), where previous studies have shown that lithology exerts a major control on runoff generation. The Attert catchment lies at the transition zone of contrasting bedrock lithology: the Northern part is characterized by Devonian schist of the Ardennes massif, while sedimentary deposits of sandstone and marls dominate in the south of the catchment. As a consequence of differing lithologic characteristics, hydrological processes change across scales. The schistose catchments exhibit a delayed shallow groundwater component, sandstone catchments have slow-responding year-round groundwater component, whereas flashy runoff regimes prevails in the marly catchments. Under these circumstances, the MRTs are expected to vary significantly according to lithology, and provide additional understanding in internal catchment processes and their scale dependencies. In order to test this, bi-weekly monitoring of rainfall and discharge stable water isotope composition (oxygen-18 and deuterium) has been carried out since 2007 in 10 nested sub-catchments ranging in size from 0.4 to 247 km2 in the Attert catchment. MRT was estimated using different lumped convolution integral models and sine wave functions with varying transit times distributions (TTDs). TTDs were evaluated through calibration. Further research efforts will deal with the application of conceptual models to simulate and compare TTD, using

  17. [Hydrogenotrophic denitrification for the removal of nitrate in drinking water].

    PubMed

    Lu, Cai-Xia; Gu, Ping

    2008-03-01

    Autotrophic denitrification with hydrogen as the electron donor for the removal of nitrate in drinking water was investigated by using a bench-scale sequencing batch reactor in an attached growth system. Gas permeable membrane was employed as the hydrogen diffuser to improve the hydrogen mass transfer and decrease the explosion risk. The results showed that nitrate could be removed efficiently with this technology. The removal rates of NO3(-)-N and TN could achieve 6.45 mg/(L h) and 4.89 mg/(L h) respectively, with the highest accumulation of NO2(-)-N 11.58 mg/L. pH increased to 10.56 and DOC increased 0.91 mg/L. A zero order kinetic model was proposed for NO3(-) and NO2(-) reduction, with the kinetic coefficients in the ranges of 0.33 - 0.60 g/(g d) and 0.37 - 0.45 g/(g d) respectively, The removal rates of NO3(-)-N and TN were not affected with the hydrogen pressure higher than 40 kPa, with the values (5.97 +/- 0.08) mg/(L h) and (4.25 +/- 0.04) mg/(L h) respectively, while decreased remarkably when the hydrogen pressure was 25 kPa. The denitrification reaction was inhibited at pH 6 with the removal rate of NO3(-)-N 1.83 mg/( L h); pH higher than 8 was the favorable condition for denitrification with the removal rate of NO3(-)-N 3.13 mg/(L h). PMID:18649526

  18. The occurrence of denitrification in extremely halophilic bacteria

    NASA Technical Reports Server (NTRS)

    Mancinelli, R. L.; Hochstein, L. I.

    1986-01-01

    The ability of Halobacterium vallismortis, Halobacterium mediterranei and Halobacterium marismortui (Ginzburg strain) to grow anaerobically and denitrify was determined. Each organism grew anaerobically only in the presence of nitrate. H. marismortui produced nitrite and dinitrogen from nitrate during exponential growth. However, as the culture entered stationary phase, dinitrogen production ceased and nitrous oxide was detected. H. vallismortis produced nitrous oxide and dinitrogen during exponential growth, with dinitrogen production ceasing at the onset of stationary phase. H. mediterranei produced dinitrogen during exponential growth and did not produce nitrous oxide. These results confirm the occurrence of denitrification in the halobacteria.

  19. A diagnostic for denitrification in the winter polar stratospheres

    NASA Technical Reports Server (NTRS)

    Fahey, D. W.; Solomon, S.; Kawa, S. R.; Loewenstein, M.; Podolske, J. R.; Strahan, S. E.; Chan, K. R.

    1990-01-01

    The pairwise correlation of NO(y) and N2O data from the Southern and Northern Hemispheres is presented. Both data sets show a linear correlation region, defined as a reference state, and regions of denitrification where the correlation breaks down. Using two-dimensional photochemical model simulations of the atmosphere, a similar linear correlation is found between NO(y) and N2O, thereby establishing a theoretical framework for the reference state. This general approach, which can be extended to other pairs of molecules, should prove to be powerful in further comparisons of aircraft data with numerical models.

  20. Carbonate precipitation under pressure for bioengineering in the anaerobic subsurface via denitrification.

    PubMed

    Martin, Derek; Dodds, Kevin; Butler, Ian B; Ngwenya, Bryne T

    2013-08-01

    A number of bioengineering techniques are being developed using microbially catalyzed hydrolysis of urea to precipitate calcium carbonate for soil and sand strengthening in the subsurface. In this study, we evaluate denitrification as an alternative microbial metabolism to induce carbonate precipitation for bioengineering under anaerobic conditions and at high pressure. In anaerobic batch culture, the halophile Halomonas halodenitrificans is shown to be able to precipitate calcium carbonate at high salinity and at a pressure of 8 MPa, with results comparable to those observed when grown at ambient pressure. A larger scale proof-of-concept experiment shows that, as well as sand, coarse gravel can also be cemented with calcium carbonate using this technique. Possible practical applications in the subsurface are discussed, including sealing of improperly abandoned wells and remediation of hydraulic fracturing during shale gas extraction. PMID:23837893

  1. Denitrification and N20 emissions from Carolina Bays receiving poultry runoff

    Technology Transfer Automated Retrieval System (TEKTRAN)

    On the southeastern Coastal Plain, there are depressional wetlands known as Carolina Bays that may receive runoff from agricultural land. Little is known about denitrification and gas emission within these isolated wetlands. Three forested Carolina Bays were selected to observe denitrification enzym...

  2. Large differences in potential denitrification and sediment microbial communities across the Laurentian great lakes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Lakes can be important sites for removal of reactive nitrogen (N) through denitrification, but spatial heterogeneity in denitrification rates can be high, and our understanding of factors controlling the capacity of lakes to remove excess N is incomplete. In oligotrophic Lake Superior, a century-lon...

  3. Modeling Denitrification in Terrestrial and Aquatic Ecosystems at Regional Scalles. Ecological Applications.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Quantifying where, when, and how much denitrification occurs on the basis of measurements alone remains particularly vexing at virtually all spatial scales. As a result, models have become essential tools for integrating current understanding of the processes that control denitrification with measur...

  4. Denitrification gene density across a wastewater-impacted riparian buffer zone

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Riparian buffers are a best management practice used extensively to protect water bodies from agriculturally-generated nitrate pollution. In particular, the biological process of denitrification has been shown to be a sink for this nitrate. Denitrification results in the reduction of nitrate under a...

  5. Linkages between denitrification and dissolved organic matter quality, Boulder Creek watershed, Colorado

    NASA Astrophysics Data System (ADS)

    Barnes, Rebecca T.; Smith, Richard L.; Aiken, George R.

    2012-03-01

    Dissolved organic matter (DOM) fuels the majority of in-stream microbial processes, including the removal of nitrate via denitrification. However, little is known about how the chemical composition of DOM influences denitrification rates. Water and sediment samples were collected across an ecosystem gradient, spanning the alpine to plains, in central Colorado to determine whether the chemical composition of DOM was related to denitrification rates. Laboratory bioassays measured denitrification potentials using the acetylene block technique and carbon mineralization via aerobic bioassays, while organic matter characteristics were evaluated using spectroscopic and fractionation methods. Denitrification potentials under ambient and elevated nitrate concentrations were strongly correlated with aerobic respiration rates and the percent mineralized carbon, suggesting that information about the aerobic metabolism of a system can provide valuable insight regarding the ability of the system to additionally reduce nitrate. Multiple linear regressions (MLR) revealed that under elevated nitrate concentrations denitrification potentials were positively related to the presence of protein-like fluorophores and negatively related to more aromatic and oxidized fractions of the DOM pool. Using MLR, the chemical composition of DOM, carbon, and nitrate concentrations explained 70% and 78% of the observed variability in denitrification potential under elevated and ambient nitrate conditions, respectively. Thus, it seems likely that DOM optical properties could help to improve predictions of nitrate removal in the environment. Finally, fluorescence measurements revealed that bacteria used both protein and humic-like organic molecules during denitrification providing further evidence that larger, more aromatic molecules are not necessarily recalcitrant in the environment.

  6. Enhanced Alcaligenes faecalis Denitrification Rate with Electrodes as the Electron Donor

    PubMed Central

    Wang, Xin; Yu, Ping; Zeng, Cuiping; Ding, Hongrui; Wang, Changqiu

    2015-01-01

    The utilization by Alcaligenes faecalis of electrodes as the electron donor for denitrification was investigated in this study. The denitrification rate of A. faecalis with a poised potential was greatly enhanced compared with that of the controls without poised potentials. For nitrate reduction, although A. faecalis could not reduce nitrate, at three poised potentials of +0.06, −0.06, and −0.15 V (versus normal hydrogen electrode [NHE]), the nitrate was partially reduced with −0.15- and −0.06-V potentials at rates of 17.3 and 28.5 mg/liter/day, respectively. The percentages of reduction for −0.15 and −0.06 V were 52.4 and 30.4%, respectively. Meanwhile, for nitrite reduction, the poised potentials greatly enhanced the nitrite reduction. The nitrite reduction rates for three poised potentials (−0.06, −0.15, and −0.30 V) were 1.98, 4.37, and 3.91 mg/liter/h, respectively. When the potentials were cut off, the nitrite reduction rate was maintained for 1.5 h (from 2.3 to 2.25 mg/liter/h) and then greatly decreased, and the reduction rate (0.38 mg/liter/h) was about 1/6 compared with the rate (2.3 mg/liter/h) when potential was on. Then the potentials resumed, but the reduction rate did not resume and was only 2 times higher than the rate when the potential was off. PMID:26048940

  7. Enhanced Alcaligenes faecalis Denitrification Rate with Electrodes as the Electron Donor.

    PubMed

    Wang, Xin; Yu, Ping; Zeng, Cuiping; Ding, Hongrui; Li, Yan; Wang, Changqiu; Lu, Anhuai

    2015-08-15

    The utilization by Alcaligenes faecalis of electrodes as the electron donor for denitrification was investigated in this study. The denitrification rate of A. faecalis with a poised potential was greatly enhanced compared with that of the controls without poised potentials. For nitrate reduction, although A. faecalis could not reduce nitrate, at three poised potentials of +0.06, -0.06, and -0.15 V (versus normal hydrogen electrode [NHE]), the nitrate was partially reduced with -0.15- and -0.06-V potentials at rates of 17.3 and 28.5 mg/liter/day, respectively. The percentages of reduction for -0.15 and -0.06 V were 52.4 and 30.4%, respectively. Meanwhile, for nitrite reduction, the poised potentials greatly enhanced the nitrite reduction. The nitrite reduction rates for three poised potentials (-0.06, -0.15, and -0.30 V) were 1.98, 4.37, and 3.91 mg/liter/h, respectively. When the potentials were cut off, the nitrite reduction rate was maintained for 1.5 h (from 2.3 to 2.25 mg/liter/h) and then greatly decreased, and the reduction rate (0.38 mg/liter/h) was about 1/6 compared with the rate (2.3 mg/liter/h) when potential was on. Then the potentials resumed, but the reduction rate did not resume and was only 2 times higher than the rate when the potential was off. PMID:26048940

  8. Trade-off between mesophilic and thermophilic denitrification: rates vs. sludge production, settleability and stability.

    PubMed

    Courtens, Emilie N P; Vlaeminck, Siegfried E; Vilchez-Vargas, Ramiro; Verliefde, Arne; Jauregui, Ruy; Pieper, Dietmar H; Boon, Nico

    2014-10-15

    The development of thermophilic nitrogen removal strategies will facilitate sustainable biological treatment of warm nitrogenous wastewaters. Thermophilic denitrification was extensively compared to mesophilic denitrification for the first time in this study. Two sequential batch reactors (SBR) at 34 °C and 55 °C were inoculated with mesophilic activated sludge (26 °C), fed with synthetic influent in a first phase. Subsequently, the carbon source was switched from acetate to molasses, whereas in a third phase, the nitrate source was fertilizer industry wastewater. The denitrifying sludge maintained its activity at 55 °C, resulting in an immediate process start-up, obtaining nitrogen removal rates higher than 500 mg N g(-1) VSS d(-1) in less than one week. Although the mesophilic SBR showed twice as high specific nitrogen removal rates, the maximum thermophilic denitrifying activity in this study was nearly 10 times higher than the activities reported thus far. The thermophilic SBR moreover had a 73% lower sludge volume index, a 45% lower sludge production and a higher resilience towards a change in carbon source compared with the mesophilic SBR. The higher resilience was potentially related to a higher microbial diversity and evenness of the thermophilic community at the end of the synthetic feeding period. The thermophilic microbial community showed a higher similarity over the different feeding periods implying a more stable community. Overall, this study showed the capability of mesophilic denitrifiers to maintain their activity after a large temperature increase. Existing mesophilic process systems with cooling for the treatment of warm wastewaters could thus efficiently be converted to thermophilic systems with low sludge production and good settling properties. PMID:25007305

  9. Nonparametric estimation of transition probabilities in the non-Markov illness-death model: A comparative study.

    PubMed

    de Uña-Álvarez, Jacobo; Meira-Machado, Luís

    2015-06-01

    Multi-state models are often used for modeling complex event history data. In these models the estimation of the transition probabilities is of particular interest, since they allow for long-term predictions of the process. These quantities have been traditionally estimated by the Aalen-Johansen estimator, which is consistent if the process is Markov. Several non-Markov estimators have been proposed in the recent literature, and their superiority with respect to the Aalen-Johansen estimator has been proved in situations in which the Markov condition is strongly violated. However, the existing estimators have the drawback of requiring that the support of the censoring distribution contains the support of the lifetime distribution, which is not often the case. In this article, we propose two new methods for estimating the transition probabilities in the progressive illness-death model. Some asymptotic results are derived. The proposed estimators are consistent regardless the Markov condition and the referred assumption about the censoring support. We explore the finite sample behavior of the estimators through simulations. The main conclusion of this piece of research is that the proposed estimators are much more efficient than the existing non-Markov estimators in most cases. An application to a clinical trial on colon cancer is included. Extensions to progressive processes beyond the three-state illness-death model are discussed. PMID:25735883

  10. Estimating the global oceanic net freshwater flux from Argo and comparing it with satellite-based freshwater flux products

    NASA Astrophysics Data System (ADS)

    Ren, Li; Hackert, Eric; Arkin, Phillip; Busalacchi, Antonio J.

    2014-11-01

    Following the idea that analysis of in situ information in the salt budget could be used as a surrogate for global "ocean rain gauge," the annual mean oceanic net freshwater flux (E-P) was estimated from the Argo profiles and the wind stress data on a global scale. The comparison between the independent E-P estimation from Argo and the E-P product sets, including the combination of precipitation from TRMM, GPCP, CMAP and evaporation from OAFlux, GSSTF3 and IFREMER and E-P set from NEWS formed from satellite, generally show similar spatial patterns, particularly on the large scale. However, there are differences among the different satellite-based E-P estimates and between satellite estimates and independent in situ estimates. Based on the pattern correlation and the RMSD, the evaporation and precipitation from OAFlux and TRMM agrees best with the E-P estimated from the independent Argo-based estimates.

  11. Particulate Pyrite Autotrophic Denitrification (PPAD) for Remediation of Nitrate-contaminated Groundwater

    NASA Astrophysics Data System (ADS)

    Tong, S.; Rodriguez-Gonzalez, L. C.; Henderson, M.; Feng, C.; Ergas, S. J.

    2015-12-01

    The rapid movement of human civilization towards urbanization, industrialization, and increased agricultural activities has introduced a large amount of nitrate into groundwater. Nitrate is a toxic substance discharged from groundwater to rivers and leads to decreased dissolved oxygen and eutrophication. For this experiment, an electron donor is needed to convert nitrate into non-toxic nitrogen gas. Pyrite is one of the most abundant minerals in the earth's crust making it an ideal candidate as an electron donor. The overall goal of this research was to investigate the potential for pyrite to be utilized as an electron donor for autotrophic denitrification of nitrate-contaminated groundwater. Batch studies of particulate pyrite autotrophic denitrification (PPAD) of synthetic groundwater (100 mg NO3--N L-1) were set up with varying biomass concentration, pyrite dose, and pyrite particle size. Reactors were seeded with mixed liquor volatile suspended solids (VSS) from a biological nitrogen removal wastewater treatment facility. PPAD using small pyrite particles (<0.45mm) resulted in a favorable nitrate removal. The nitrate removal rate increased from 0.26 to 0.34 mg L-1h-1 and then to 0.86 mg L-1h-1, approaching that of the sulfur oxidizing denitrification (SOD) rate of 1.19 mg L-1h-1. Based on Box-Behnken design (BBD) and response surface methodology (RSM), the optimal amount of biomass concentration, pyrite dose, and pyrite particle size were 1,250 mg VSS L-1, 125 g L-1, and 0.815-1.015 mm, respectively. PPAD exhibited substantial nitrate removal rate, lower sulfate accumulation (5.46 mg SO42-/mg NO3--N) and lower alkalinity consumption (1.70 mg CaCO3/mg NO3--N) when compared to SOD (7.54 mg SO42-/mg NO3--N, 4.57 mg CaCO3/mg NO3--N based on stoichiometric calculation). This research revealed that the PPAD process is a promising technique for nitrate-contaminated groundwater treatment and promoted the utilization of pyrite in the field of environmental remediation.

  12. [Effects of saltwater incursion on the microbiological characteristics and denitrification in a riparian rhizosphere soil in Chongming Island of Shanghai, East China].

    PubMed

    Yang, Chang-Ming; Cai, Wen-Juan; Li, Jian-Hua

    2012-04-01

    A simulation test was conducted to study the effects of saltwater incursion on the microbiological characteristics and denitrification in the riparian rhizosphere soils vegetated with different plants in Chongming Island of Shanghai. Saltwater incursion changed the microflora in the rhizospheric soils. Except for actinomycete whose quantity had slight increase, the quantities of bacteria, fungi, nitrifiers, and denitrifiers all decreased to some extent by saltwater incursion, with the denitrifiers decreased by 51.8%, suggesting that the riparian soil microflora responded differentially to saltwater incursion. The activities of soil nitrogen-transforming enzymes were significantly inhibited by saltwater incursion, and the inhibitory effects differed with the enzymes. Nitrite reductase activity was most sensitive to saltwater incursion, with an inhibition rate of 43.5%, followed by urease activity, with 37.4% inhibition, and by dehydrogenase (29.5% inhibition). Saltwater incursion inhibited the denitrification, with the average denitrification rate decreased by 34.9%. There existed significant differences in the eco-physiological responses of the microbes in the rhizosphere soils vegetated with different plants to the saltwater incursion. The microbial quantities and enzyme activities showed the highest inhibition percentages in the rhizosphere soil of Zizania aquatica, followed by in the rhizosphere soils of Acorus calamus and Phragmites australis. Under saltwater incursion, the inhibition percentages of microbial quantities, enzyme activities, and denitrification rate in the rhizosphere soil of A. calamus-P. australis were significantly lower, as compared with those in the rhizosphere soils vegetated with Z. aquatica, A. calamus, and P. australis, respectively, suggesting that mixed vegetation showed a better buffer effect on the responses of riparian rhizosphere soil microbiological processes and denitrification to saltwater incursion. PMID:22803478

  13. A Quantitative Method for Comparing the Brightness of Antibody-dye Reagents and Estimating Antibodies Bound per Cell.

    PubMed

    Kantor, Aaron B; Moore, Wayne A; Meehan, Stephen; Parks, David R

    2016-01-01

    We present a quantitative method for comparing the brightness of antibody-dye reagents and estimating antibodies bound per cell. The method is based on complementary binding of test and fill reagents to antibody capture microspheres. Several aliquots of antibody capture beads are stained with varying amounts of the test conjugate. The remaining binding sites on the beads are then filled with a second conjugate containing a different fluorophore. Finally, the fluorescence of the test conjugate compared to the fill conjugate is used to measure the relative brightness of the test conjugate. The fundamental assumption of the test-fill method is that if it takes X molecules of one test antibody to lower the fill signal by Y units, it will take the same X molecules of any other test antibody to give the same effect. We apply a quadratic fit to evaluate the test-fill signal relationship across different amounts of test reagent. If the fit is close to linear, we consider the test reagent to be suitable for quantitative evaluation of antibody binding. To calibrate the antibodies bound per bead, a PE conjugate with 1 PE molecule per antibody is used as a test reagent and the fluorescence scale is calibrated with Quantibrite PE beads. When the fluorescence per antibody molecule has been determined for a particular conjugate, that conjugate can be used for measurement of antibodies bound per cell. This provides comparisons of the brightness of different conjugates when conducted on an instrument whose statistical photoelectron (Spe) scales are known. © 2016 by John Wiley & Sons, Inc. PMID:27367287

  14. Cheatgrass percent cover change: Comparing recent estimates to climate change − Driven predictions in the Northern Great Basin

    USGS Publications Warehouse

    Boyte, Stephen P.; Wylie, Bruce K.; Major, Donald J.

    2016-01-01

    Cheatgrass (Bromus tectorum L.) is a highly invasive species in the Northern Great Basin that helps decrease fire return intervals. Fire fragments the shrub steppe and reduces its capacity to provide forage for livestock and wildlife and habitat critical to sagebrush obligates. Of particular interest is the greater sage grouse (Centrocercus urophasianus), an obligate whose populations have declined so severely due, in part, to increases in cheatgrass and fires that it was considered for inclusion as an endangered species. Remote sensing technologies and satellite archives help scientists monitor terrestrial vegetation globally, including cheatgrass in the Northern Great Basin. Along with geospatial analysis and advanced spatial modeling, these data and technologies can identify areas susceptible to increased cheatgrass cover and compare these with greater sage grouse priority areas for conservation (PAC). Future climate models forecast a warmer and wetter climate for the Northern Great Basin, which likely will force changing cheatgrass dynamics. Therefore, we examine potential climate-caused changes to cheatgrass. Our results indicate that future cheatgrass percent cover will remain stable over more than 80% of the study area when compared with recent estimates, and higher overall cheatgrass cover will occur with slightly more spatial variability. The land area projected to increase or decrease in cheatgrass cover equals 18% and 1%, respectively, making an increase in fire disturbances in greater sage grouse habitat likely. Relative susceptibility measures, created by integrating cheatgrass percent cover and temporal standard deviation datasets, show that potential increases in future cheatgrass cover match future projections. This discovery indicates that some greater sage grouse PACs for conservation could be at heightened risk of fire disturbance. Multiple factors will affect future cheatgrass cover including changes in precipitation timing and totals and

  15. Increased nitrous oxide accumulation by bioelectrochemical denitrification under autotrophic conditions: kinetics and expression of denitrification pathway genes.

    PubMed

    Van Doan, Tuan; Lee, Tae Kwon; Shukla, Sudheer Kumar; Tiedje, James M; Park, Joonhong

    2013-12-01

    Under autotrophic conditions, we investigated the effects of different current densities on bioelectrochemical denitrification (BED). In this study, nitrate consumption and nitrous oxide (N2O) production, microbial diversity and population dynamics, and denitrification pathway gene expressions were explored in continuous flow BED reactors at different current densities (0.2, 1, 5, 10 and 20 A/m(2)). We found that, under the autotrophic conditions, N2O accumulation was increased with increase in current density. The maximum rate of denitrification was 1.65 NO3(-)-N (g/NCCm(3).h), and approximately 70% of the reduced N was accumulated as N2O. After each current density was applied, pyrosequencing of the expressed 16S rRNA genes amplified from the cathodic biofilms revealed that that 16 genera were active and in common at all currents, and that eight of those showed a statistically significant correlation with particular current densities. The relative expression of napA and narG was highest, whereas nosZ was low relative to its level in the inoculum suggesting that this could have contributed the high N2O accumulation. Kinetic analysis of nitrate reduction and N2O accumulation followed Michaelis-Menten kinetics. The Vmax for nitrate consumption and N2O accumulation were similar, however the Km values determined as A/m(2) were not. This study provides better understanding of the community and kinetics of a current-fed, autotrophic, cathodic biofilm for evaluating its potential for scale-up and for N2O recovery. PMID:24210359

  16. Estimating and comparing time-dependent areas under receiver operating characteristic curves for censored event times with competing risks.

    PubMed

    Blanche, Paul; Dartigues, Jean-François; Jacqmin-Gadda, Hélène

    2013-12-30

    The area under the time-dependent ROC curve (AUC) may be used to quantify the ability of a marker to predict the onset of a clinical outcome in the future. For survival analysis with competing risks, two alternative definitions of the specificity may be proposed depending of the way to deal with subjects who undergo the competing events. In this work, we propose nonparametric inverse probability of censoring weighting estimators of the AUC corresponding to these two definitions, and we study their asymptotic properties. We derive confidence intervals and test statistics for the equality of the AUCs obtained with two markers measured on the same subjects. A simulation study is performed to investigate the finite sample behaviour of the test and the confidence intervals. The method is applied to the French cohort PAQUID to compare the abilities of two psychometric tests to predict dementia onset in the elderly accounting for death without dementia competing risk. The 'timeROC' R package is provided to make the methodology easily usable. PMID:24027076

  17. Continuous fermentation of food waste leachate for the production of volatile fatty acids and potential as a denitrification carbon source.

    PubMed

    Kim, Hakchan; Kim, Jaai; Shin, Seung Gu; Hwang, Seokhwan; Lee, Changsoo

    2016-05-01

    This study investigated the simultaneous effects of hydraulic retention time (HRT) and pH on the continuous production of VFAs from food waste leachate using response surface analysis. The response surface approximations (R(2)=0.895, p<0.05) revealed that pH has a dominant effect on the specific VFA production (PTVFA) within the explored space (1-4-day HRT, pH 4.5-6.5). The estimated maximum PTVFA was 0.26g total VFAs/g CODf at 2.14-day HRT and pH 6.44, and the approximation was experimentally validated by running triplicate reactors under the estimated optimum conditions. The mixture of the filtrates recovered from these reactors was tested as a denitrification carbon source and demonstrated superior performance in terms of reaction rate and lag length relative to other chemicals, including acetate and methanol. The overall results provide helpful information for better design and control of continuous fermentation for producing waste-derived VFAs, an alternative carbon source for denitrification. PMID:26922002

  18. Acetylene inhibition of N2O reduction in laboratory soil and groundwater denitrification assays: evaluation by 15N tracer and 15N site preference of N2O

    NASA Astrophysics Data System (ADS)

    Weymann, Daniel; Well, Reinhard; Lewicka-Szczebak, Dominika; Lena, Rohe

    2013-04-01

    The measurement of denitrification in soils and aquifers is still challenging and often enough associated with considerable experimental effort and high costs. Against this background, the acetylene inhibition technique (AIT) applied in laboratory soil and groundwater denitrification assays is by far the most effective approach. However, this method has been largely criticized, as it is susceptible to underestimate denitrification rates and adds an additional carbon source to the substrates to be investigated. Here we provide evidence that the AIT is not necessarily an inappropriate approach to measure denitrification, that its reliability depends on the drivers governing the process, and that the 15N site preference of N2O (SP) may serve as a tool to assess this reliability. Two laboratory batch experiments were conducted, where sandy aquifer material and a peat soil were incubated as slurries. We established (i) a standard anaerobic treatment by adding KNO3 (10 mg N L-1), (ii) an oxygen treatment by adding KNO3 and O2 (5 mg L-1), and (iii) a glucose treatment by adding KNO3 supplemented with glucose (200 mg C L-1). Both experiments were run under 10 % (v/v) acetylene atmosphere and as 15N tracer treatments using labeled K15NO3 (60 atom % 15N). In the case of the standard anaerobic treatments, we found a very good agreement of denitrification potential obtained by the AIT and 15N tracer methods. SP of N2O of the AIT samples from this treatment ranged between -4.8 and 2.6 ‰ which is indicative for N2O production during bacterial denitrification but not for N2O reduction to N2. In contrast, we observed substantial underestimation of denitrification by AIT for the glucose treatments compared to the 15N method, i.e. denitrification was underestimated by 36 % (sandy aquifer material) and 47 % (peat soil). SP of N2O of the AIT samples from this treatment ranged between 4.5 and 9.6 ‰, which suggests occurrence of bacterial N2O reduction. In the case of the oxygen

  19. Denitrification characteristics of a marine origin psychrophilic aerobic denitrifying bacterium.

    PubMed

    Zheng, Haiyan; Liu, Ying; Sun, Guangdong; Gao, Xiyan; Zhang, Qingling; Liu, Zhipei

    2011-01-01

    A psychrophilic aerobic denitrifying bacterium, strain S1-1, was isolated from a biological aerated filter conducted for treatment of recirculating water in a marine aquaculture system. Strain S1-1 was preliminarily identified as Psychrobacter sp. based on the analysis of its 16S rRNA gene sequence, which showed 100% sequence similarity to that of Psychrobacter sp. TSBY-70. Strain S1-1 grew well either in high nitrate or high nitrite conditions with a removal of 100% nitrate or 63.50% nitrite, and the total nitrogen removal rates could reach to 46.48% and 31.89%, respectively. The results indicated that nitrate was mainly reduced in its logarithmic growth phase with a very low level accumulation of nitrite, suggesting that the aerobic denitrification process of strain S1-1 occurred mainly in this phase. The GC-MS results showed that N2O was formed as the major intermediate during the aerobic denitrifying process of strain S1-1. Finally, factors affecting the growth of strain S1-1 and its aerobic denitrifying ability were also investigated. Results showed that the optimum aerobic denitrification conditions for strain S1-1 were sodium succinate as carbon source, C/N ratio15, salinity 10 g/L NaCl, incubation temperature 20 degrees C and initial pH 6.5. PMID:22432315

  20. Examining thiosulfate-driven autotrophic denitrification through respirometry.

    PubMed

    Mora, Mabel; Guisasola, Albert; Gamisans, Xavier; Gabriel, David

    2014-10-01

    Anoxic respirometry was applied to characterize a sulfide-oxidizing nitrate-reducing (SO-NR) culture obtained from an anoxic biogas desulfurizing biotrickling filter treating high loads of H2S. Immobilized biomass extracted from the biotrickling filter was grown in a suspended culture with thiosulfate as electron donor to obtain the biomass growth yield and the S2O3(2)(-)/NO3(-) consumed ratio. Afterward, respirometry was applied to describe thiosulfate oxidation under anoxic conditions. A pure culture of Thiobacillus denitrificans was also used as a control culture in order to validate the procedure proposed in this work to characterize the SO-NR biomass. Respirometric profiles obtained with this microbial culture showed that nitrite was formed as intermediate during nitrate reduction and revealed that no competitive inhibition appeared when both electron acceptors were present in the medium. Although final bioreaction products depended on the initial S2O3(2)(-)/NO3(-) ratio, such ratio did not affect thiosulfate oxidation or denitrification rates. Moreover, respirometric profiles showed that the specific nitrite uptake rate depended on the biomass characteristics being that of a SO-NR mixed culture (39.8mgNg(-1) VSSh(-1)) higher than that obtained from a pure culture of T. denitrificans (19.7mgNg(-1) VSSh(-1)). For the first time, the stoichiometry of the two-step denitrification mechanism with thiosulfate oxidation and biomass growth associated was solved for both reactions. PMID:25065782

  1. Transformations of halogenated organic compounds under denitrification conditions.

    PubMed Central

    Bouwer, E J; McCarty, P L

    1983-01-01

    Trihalomethanes, carbon tetrachloride, 1,1,1-trichloroethane, 1,2-dibromoethane, chlorinated benzenes, ethylbenzene, and naphthalene at concentrations commonly found in surface and groundwater were incubated under anoxic conditions to study their transformability in the presence of denitrifying bacteria. None of the aromatic compounds showed significant utilization relative to sterile controls at initial concentrations from 41 to 114 micrograms/liter after 11 weeks of incubation. Of the halogenated aliphatic compounds studied, transformations of carbon tetrachloride and brominated trihalomethanes were observed after 8 weeks in batch denitrification cultures. Carbon from the decomposition of carbon tetrachloride was both assimilated into cell material and mineralized to carbon dioxide. How this was possible remains unexplained, since carbon tetrachloride is transformed to CO2 by hydrolysis and not by oxidation-reduction. Chloroform was detected in bacterial cultures with carbon tetrachloride initially present, indicating that reductive dechlorination had occurred in addition to hydrolysis. The data suggest that transformations of certain halogenated aliphatic compounds are likely to occur under denitrification conditions in the environment. PMID:6859850

  2. Denitrification of nitrate by the fungus Cylindrocarpon tonkinense.

    PubMed

    Watsuji, Tomo-o; Takaya, Naoki; Nakamura, Akira; Shoun, Hirofumi

    2003-05-01

    The denitrifying fungus Cylindrocarpon tonkinense was thought to be able to denitrify only nitrite (NO2-) but not nitrate (NO3-) to form nitrous oxide (N2O). Here we found, however, that C. tonkinense can denitrify NO3- under certain conditions. Presence of ammonium (NH3+) in addition to NO3- and the use of a fermentable sugar as an electron donor were key conditions for inducing the denitrifying activity. Such induction accompanied a remarkable increase in the intracellular level of the enzyme activities related to NO3- metabolism. These activities contained assimilatory type NADPH (or NADH)-dependent NO3- reductase (aNar), dissimilatory nitrite reductase (dNir), and nitric oxide reductase (P450nor), but did not contain ubiquinol-dependent, dissimilatory NO3- reductase (dNar). The denitrification was inhibited by tungstate, an inhibitor of Nar. These results demonstrated occurrence of a novel type of denitrification in C. tonkinense, in which assimilatory type Nar is possibly involved. PMID:12834290

  3. Cocurrent biological nitrification and denitrification in wastewater treatment

    SciTech Connect

    Spector, M.

    1998-11-01

    Repetitive conditioning of recycle activated sludge (RAS) under strict anaerobic conditions gradually changes the products of ammonia oxidation from nitrite and nitrate to nitrous oxide (N{sub 2}O) and nitrogen (N{sub 2}). Nitrite inhibits oxygen respiration of anaerobically conditioned sludge; biochemical oxygen demand (BOD) is then oxidized by nitrite, which is reduce to N{sub 2}O and N{sub 2}. When anaerobic RAS conditioning is initially imposed on a nitrifying system, Nitrobacter species continue to oxidize nitrite to nitrate and thus reduce the nitrite available to oxidize BOD. However, Nitrobacter in the mixed liquor gradually tend to wash out because the sole source of Nictrobacter energy, the oxidation of nitrite to nitrate, is diminished to the extent that nitrite is reduced. Incorporation of an RAS conditioning zone to the activate-sludge process results in evolution of a nonfilamentous biomass, which affects both cocurrent biological nitrification and denitrification (CBND) and biological phosphorus removal (BPR). The initial feed zone may be either aerobic or anaerobic. A final anoxic denitrification zone is desirable for removal of residual nitrite plus nitrate (NO{sub x}) from aeration effluent. Nitrous oxide, the main reaction product of CBND, promotes both global warming and destruction of the stratospheric ozone layer.

  4. Nitrate removal with sulfur-limestone autotrophic denitrification processes

    SciTech Connect

    Flere, J.M.; Zhang, T.C.

    1999-08-01

    Nitrate removal using sulfur and limestone autotrophic denitrificatio