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Sample records for comparing denitrification estimates

  1. Comparing denitrification estimates for a Texas estuary by using acetylene inhibition and membrane inlet mass spectrometry.

    PubMed

    Bernot, Melody J; Dodds, Walter K; Gardner, Wayne S; McCarthy, Mark J; Sobolev, Dmitri; Tank, Jennifer L

    2003-10-01

    Characterizing denitrification rates in aquatic ecosystems is essential to understanding how systems may respond to increased nutrient loading. Thus, it is important to ensure the precision and accuracy of the methods employed for measuring denitrification rates. The acetylene (C2H2) inhibition method is a simple technique for estimating denitrification. However, potential problems, such as inhibition of nitrification and incomplete inhibition of nitrous oxide reduction, may influence rate estimates. Recently, membrane inlet mass spectrometry (MIMS) has been used to measure denitrification in aquatic systems. Comparable results were obtained with MIMS and C2H2 inhibition methods when chloramphenicol was added to C2H2 inhibition assay mixtures to inhibit new synthesis of denitrifying enzymes. Dissolved-oxygen profiles indicated that surface layers of sediment cores subjected to the MIMS flowthrough incubation remained oxic whereas cores incubated using the C2H2 inhibition methods did not. Analysis of the microbial assemblages before and after incubations indicated significant changes in the sediment surface populations during the long flowthrough incubation for MIMS analysis but not during the shorter incubation used for the C2H2 inhibition method. However, bacterial community changes were also small in MIMS cores at the oxygen transition zone where denitrification occurs. The C2H2 inhibition method with chloramphenicol addition, conducted over short incubation intervals, provides a cost-effective method for estimating denitrification, and rate estimates are comparable to those obtained by the MIMS method.

  2. 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.

  3. Estimates of sediment denitrification and its influence on the fate of nitrogen in Chesapeake Bay. Final report

    SciTech Connect

    Twilley, R.R.; Kemp, W.M.

    1987-08-01

    The variability of denitrification potentials in estuarine sediments was measured during October 15-18, 1984 at ten stations in Chesapeake Bay. Selected chemical and physical characteristics of the sediments were also measured to investigate factors that may regulate denitrification in the estuarine ecosystem. Denitrification potentials increased at higher concentrations of nitrate except for two stations. Mainstem bay stations lacked any significant denitrification potential. Estimated ranges of ambient denitrification rates suggest that they may vary as much spatially due to the kinetic nature of denitrification as seasonally due to differences in nitrate concentration.

  4. Comparing Mapped Plot Estimators

    Treesearch

    Paul C. Van Deusen

    2006-01-01

    Two alternative derivations of estimators for mean and variance from mapped plots are compared by considering the models that support the estimators and by simulation. It turns out that both models lead to the same estimator for the mean but lead to very different variance estimators. The variance estimators based on the least valid model assumptions are shown to...

  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. 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...

  7. 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.

  8. Use of Nitrogen Budgets and N2 Flux Measurements to Estimate the Role of Denitrification in Brownfield Stormwater Wetlands

    NASA Astrophysics Data System (ADS)

    Palta, M. M.; Groffman, P. M.; Findlay, S.

    2012-12-01

    Wetlands are constructed or restored in urban and agricultural areas to reduce inorganic nitrogen (N) contamination of surface water runoff. Few studies, however, have examined the performance of unrestored but highly impacted wetlands within an urban context. These wetlands tend to be the primary recipient of nitrate (NO3-)-enriched storm and rainwater due to their ubiquity in low-lying portions of the urban landscape. Wetland studies anticipate high rates of NO3- removal via the microbial process of denitrification when labile carbon (C) and NO3- are high and O2 is low. The ability to quantify and predict the role of denitrification within particular systems is limited, however, and denitrification estimates are compromised by our inability to accurately measure N2 flux. In this study, we calculated loading rates of inorganic N and used measurements of N2/Ar, O2/Ar, and NO3- flux in sediments to generate inorganic N budgets for brownfield stormwater wetland sites. Loading of inorganic N via rain and stormwater ranged from 4-533 mg N/m2/d, and large amounts of NH4+ were additionally created from mineralization of decomposing organic matter, leading to high fluxes of NH4+ out of sediment into water (2-117 mg N/m2/d). Hydrology was a strong driving force of N2 flux; lowering of the water table allowed surface sediments to oxidize, leading to production of NO3-, which fueled N2 production lower in the sediment profile. Overall, the wetlands are denitrifying NO3- at a rate of around 620-2,580 μg N/m2/day. Flux of NO3- out of sediments was higher in some cases (630-1,900 μg N/m2/day), likely due to plant uptake. These wetlands appeared to be serving as a sink for NO3-, but were net sources of NH4+; periodic drainage of the wetlands to promote oxidation of NH4+ may be a strategy for promoting higher inorganic nitrogen removal from these sites.

  9. Denitrification in Aquifer Soil and Nearshore Marine Sediments Influenced by Groundwater Nitrate

    PubMed Central

    Slater, Jennifer M.; Capone, Douglas G.

    1987-01-01

    We estimated rates of denitrification at various depths in sediments known to be affected by submarine discharge of groundwater, and also in the parent aquifer. Surface denitrification was only measured in the autumn; at 40-cm depth, where groundwater-imported nitrate has been measured, denitrification occurred consistently throughout the year, at rates from 0.14 to 2.8 ng-atom of N g−1 day−1. Denitrification consistently occurred below the zone of sulfate reduction and was sometimes comparable to it in magnitude. Denitrification occurred deep (14 to 40 cm) in the sediments along 30 km of shoreline, with highest rates occurring where groundwater input was greatest. Denitrification rates decreased with distance offshore, as does groundwater influx. Added glucose greatly stimulated denitrification at depth, but added nitrate did not. High rates of denitrification were measured in the aquifer (17 ng-atom of N g−1 day−1), and added nitrate did stimulate denitrification there. The denitrification measured was enough to remove 46% of the nitrate decrease observed between 40- and 14-cm depth in the sediment. PMID:16347361

  10. 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

  11. 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

    2016-01-01

    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.

  12. Incorporating denitrification-decomposition method to estimate field emissions for Life Cycle Assessment.

    PubMed

    Deng, Yelin; Paraskevas, Dimos; Cao, Shi-Jie

    2017-03-22

    This study focuses on a detailed Life Cycle Assessment (LCA) for flax cultivation in Northern France. Nitrogen related field emissions are derived both from a process-oriented DeNitrification-DeComposition (DNDC) method and the generic Intergovernmental Panel on Climate Change (IPCC) method. Since the IPCC method is synthesised from field measurements at sites with various soil types, climate conditions, and crops, it contains significant uncertainties. In contrast, the outputs from the DNDC method are considered as more site specific as it is built according to complex models of soil science. As it is demonstrated in this paper the emission factors from the DNDC method and the recommended values from the IPCC method exhibit significant variations for the case of flax cultivation. The DNDC based emission factor for direct N2O emission, which is a strong greenhouse gas, is 0.25-0.5%, significantly lower than the recommend 1% level derived from the IPCC method. The DNDC method leads to a reduction of 17% in the impact category of climate change per kg retted flax straw production from the level obtained from the IPCC method. Much higher reductions are recorded for particulate matter formation, terrestrial acidification, and marine eutrophication impact categories. Meanwhile, based on the DNDC and IPCC methods, a comparative LCA per kg flax straw is presented. For both methods sensitivity analysis as well as comparison of uncertainties parameterisation of the N2O estimates via Monte-Carlo analysis are performed. The DNDC method incorporates more relevant field emissions from the agricultural life cycle phase, which can also improve the quality of the Life Cycle Inventory as well as allow more precise uncertainty calibration in the LCA inventory.

  13. Evaluation of DeNitrification DeComposition Model to Estimate Ammonia Fluxes from Chemical Fertilizer Application

    NASA Astrophysics Data System (ADS)

    Balasubramanian, S.; Nelson, A. J.; Koloutsou-Vakakis, S.; Lin, J.; Myles, L.; Rood, M. J.

    2016-12-01

    Biogeochemical models such as DeNitrification DeComposition (DNDC) are used to model greenhouse and other trace gas fluxes (e.g., ammonia (NH3)) from agricultural ecosystems. NH3 is of interest to air quality because it is a precursor to ambient particulate matter. NH3 fluxes from chemical fertilizer application are uncertain due to dependence on local weather and soil properties, and farm nitrogen management practices. DNDC can be advantageously implemented to model the underlying spatial and temporal trends to support air quality modeling. However, such implementation, requires a detailed evaluation of model predictions, and model behavior. This is the first study to assess DNDC predictions of NH3 fluxes to/from the atmosphere, from chemical fertilizer application, during an entire crop growing season, in the United States. Relaxed eddy accumulation (REA) measurements over corn in Central Illinois, in year 2014, were used to evaluate magnitude and trends in modeled NH3 fluxes. DNDC was able to replicate both magnitude and trends in measured NH3 fluxes, with greater accuracy during the initial 33 days after application, when NH3 was mostly emitted to the atmosphere. However, poorer performance was observed when depositional fluxes were measured. Sensitivity analysis using Monte Carlo simulations indicated that modeled NH3 fluxes were most sensitive to input air temperature and precipitation, soil organic carbon, field capacity and pH and fertilizer loading rate, timing, and application depth and tilling date. By constraining these inputs for conditions in Central Illinois, uncertainty in annual NH3 fluxes was estimated to vary from -87% to 61%. Results from this study provides insight to further improve DNDC predictions and inform efforts for upscaling site predictions to regional scale for the development of emission inventories for air quality modeling.

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

    USDA-ARS?s Scientific Manuscript database

    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...

  15. Evaluation of DeNitrification DeComposition model for estimating ammonia fluxes from chemical fertilizer application

    USDA-ARS?s Scientific Manuscript database

    DeNitrification DeComposition (DNDC) model predictions of NH3 fluxes following chemical fertilizer application were evaluated by comparison to relaxed eddy accumulation (REA) measurements, in Central Illinois, United States, over the 2014 growing season of corn. Practical issues for evaluating closu...

  16. The challenge of denitrification

    NASA Astrophysics Data System (ADS)

    Groffman, P. M.

    2015-12-01

    Understanding the nitrogen cycle at ecosystem, landscape, regional and global scales is a great current challenge in environmental science. Large amounts of "missing nitrogen" dominate nitrogen balances at all scales and have complicated efforts to address the effects of excess reactive nitrogen pollution on tropospheric ozone levels, coastal eutrophication and drinking water quality, and to determine "critical loads" for atmospheric nitrogen deposition. Uncertainty about nitrogen balances has led to increased interest in nitrogen gas fluxes as a fate of excess nitrogen. Denitrification, the conversion of reactive nitrogen oxides such as nitrate and nitrite into nitrogen gases, is a challenging process to study in terrestrial ecosystems. This process is difficult to quantify because of problematic measurement techniques, high spatial and temporal variability, and a lack of methods for scaling point measurements to larger areas. A particular challenge is that small areas (hotspots) and brief periods (hot moments) account for a high percentage of nitrogen gas flux activity. However, recent advances have yielded new methods capable of producing well constrained estimates of denitrification at the ecosystem scale, new ideas about the occurrence of hotspots and hot moments at ecosystem and landscape scales, and powerful new tools for extrapolation and validation. Progress on the challenges of denitrification suggest that we are poised for advances more generally across the genomes-to-ecosystems cascade.

  17. Denitrification across landscapes and waterscapes: A synthesis

    USGS Publications Warehouse

    Seitzinger, S.; Harrison, J.A.; Böhlke, J.K.; Bouwman, A.F.; Lowrance, R.; Peterson, B.; Tobias, C.; Van Drecht, G.

    2006-01-01

    Denitrification is a critical process regulating the removal of bioavailable nitrogen (N) from natural and human-altered systems. While it has been extensively studied in terrestrial, freshwater, and marine systems, there has been limited communication among denitrification scientists working in these individual systems. Here, we compare rates of denitrification and controlling factors across a range of ecosystem types. We suggest that terrestrial, freshwater, and marine systems in which denitrification occurs can be organized along a continuum ranging from (1) those in which nitrification and denitrification are tightly coupled in space and time to (2) those in which nitrate production and denitrification are relatively decoupled.In aquatic ecosystems, N inputs influence denitrification rates whereas hydrology and geomorphology influence the proportion of N inputs that are denitrified. Relationships between denitrification and water residence time and N load are remarkably similar across lakes, river reaches, estuaries, and continental shelves.Spatially distributed global models of denitrification suggest that continental shelf sediments account for the largest portion (44%) of total global denitrification, followed by terrestrial soils (22%) and oceanic oxygen minimum zones (OMZs; 14%). Freshwater systems (groundwater, lakes, rivers) account for about 20% and estuaries 1% of total global denitrification. Denitrification of land-based N sources is distributed somewhat differently. Within watersheds, the amount of land-based N denitrified is generally highest in terrestrial soils, with progressively smaller amounts denitrified in groundwater, rivers, lakes and reservoirs, and estuaries. A number of regional exceptions to this general trend of decreasing denitrification in a downstream direction exist, including significant denitrification in continental shelves of N from terrestrial sources. Though terrestrial soils and groundwater are responsible for much

  18. Denitrification Hotspots: Hydrology and Biogeochemistry

    NASA Astrophysics Data System (ADS)

    Molodovskaya, M.; Singurindy, O.; Faulkner, J. W.; Zhang, W.; Richards, B. K.; Anderson, T. R.; Geohring, L. D.; Steenhuis, T. S.; Walter, M.

    2007-12-01

    Nitrogen (N) is a critical pollutant in many northeastern US watersheds and globally. Many forms of N, especially NO3, pose serious threats to coastal marine ecosystems. Agricultural land that receives fertilizers or animal manures is a principal source of anthropogenic N loading to the environment. The most effective mechanism to reduce N in streams is probably microbial denitrification, i.e., the transformation of nitrate into gaseous N2 or, in some cases, smaller amounts of N2O. Unfortunately, N2O is a greenhouse gas that may contribute to global warming. Currently, magnitudes of denitrification rates at landscape scales are "tentative" at best, largely based on watershed-scale budgets in which denitrification was estimated by difference. Denitrification and N2O net production strongly depend on both natural (temperature, soil moisture, microbial activity, soil organic matter) and anthropogenic (nitrogen fertilization, crop type, tillage) parameters. Denitrification occurs primarily under anaerobic conditions by heterotrophic microbes and is expected to be vigorous in wet soils high in organic carbon. There is good evidence that these conditions correlate strongly with hydrological sensitivity or high propensity for saturated conditions, thus by juxtaposing hydrology and biogeochemistry we can elucidate the distribution of denitrification hotspots across the landscape. Upon this hydrologic-biogeochemical framework we can ultimately develop BMPs to meet the program research priorities to improve water resource protection and promote sustainable agricultural systems that minimize environmental impact. The Cornell Soil and Water and Ecohydrology Research Groups have engaged in a variety of projects to elucidate the primary controls or quantify denitrification rates for different ecohydrological conditions including those that have been specifically designed to reduce N loading to streams. This presentation highlights recent findings of rates, controls, and spatio

  19. 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.

  20. Denitrification and Nitrogen Fixation in Alaskan Continental Shelf Sediments

    PubMed Central

    Haines, John R.; Atlas, Ronald M.; Griffiths, Robert P.; Morita, Richard Y.

    1981-01-01

    Rates of nitrogen fixation and denitrification were measured in Alaskan continental shelf sediments. In some regions, rates of nitrogen fixation and denitrification appeared to be equal; in other areas, rates were significantly different. Potential rates of denitrification were found to be limited primarily by the available nitrate substrate. Major regional differences in rates of denitrification were not statistically significant, but significant differences were found for nitrogen fixation rates in different regions of the Alaskan continental shelf. Estimated net losses of nitrogen from Bering Sea sediments were calculated as 1.8 × 1012 g of N/yr. Experimental exposure of continental shelf sediments to petroleum hydrocarbons reduced rates of nitrogen fixation and denitrification in some cases but not others. Long-term exposure was necessary before a reduction in nitrogen fixation rates was observed; unamended rates of denitrification but not potential denitrification rates (NO3− added) were depressed after exposure to hydrocarbons. PMID:16345716

  1. Vegetation Loss Decreases Salt Marsh Denitrification Capacity: Implications for Marsh Erosion.

    PubMed

    Hinshaw, Sarra E; Tatariw, Corianne; Flournoy, Nikaela; Kleinhuizen, Alice; Taylor, Caitlin; Sobecky, Patricia A; Mortazavi, Behzad

    2017-08-01

    Salt marshes play a key role in removing excess anthropogenic nitrogen (N) loads to nearshore marine ecosystems through sediment microbial processes such as denitrification. However, in the Gulf of Mexico, the loss of marsh vegetation because of human-driven disturbances such as sea level rise and oil spills can potentially reduce marsh capacity for N removal. To investigate the effect of vegetation loss on ecosystem N removal, we contrasted denitrification capacity in marsh and subtidal sediments impacted by the Deepwater Horizon oil spill using a combination of (29)N2 and (30)N2 production (isotope pairing), denitrification potential measurements (acetylene block), and quantitative polymerase chain reaction (qPCR) of functional genes in the denitrification pathway. We found that, on average, denitrification capacity was 4 times higher in vegetated sediments because of a combination of enhanced nitrification and higher organic carbon availability. The abundance of nirS-type denitrifers indicated that marsh vegetation regulates the activity, rather than the abundance, of denitrifier communities. We estimated that marsh sediments remove an average of 3.6 t N km(-2) y(-1) compared to 0.9 t N km(-2) y(-1) in unvegetated sediments. Overall, our findings indicate that marsh loss results in a substantial loss of N removal capacity in coastal ecosystems.

  2. 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.

  3. 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.

  4. Denitrification in the karstic Floridan Aquifer

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Nitrate concentrations in the karstic Floridan Aquifer have increased dramatically over the past 50 years, owing to agricultural intensification and urbanization. Due to low concentrations of organic matter and moderately oxic conditions in the Floridan Aquifer, groundwater denitrification has been assumed to be negligible. In this study, we evaluate that assumption using both existing and new data describing dissolved gases (Ne, N2, O2, Ar) and NO3- concentration and isotopic composition (δ18O- and δ15N-NO3) in the aquifer’s artesian springs. For new data, we collected samples from 33 spring vents representing a gradient of both DO and NO3- concentrations in northern Florida and used Membrane Inlet Mass Spectrometry (MIMS) to directly measure dissolved N2 and Ar. We modeled the physical processes (recharge temperature, dissolution of excess air) driving super-saturation of N2 gas using Ne and Ar where data describing Ne were available. Ar concentrations were correlated closely with recharge temperature, which ranged from 15.7 - 22.2°C, while Ne was closely correlated with excess air, which ranged from 1.05 to 2.66 mg L-1 and averaged 1.83 mg L-1. Estimates of physical mechanisms allowed calculation of expected N2 concentrations that were compared to observed N2 concentrations. Where Ne data were unavailable, we assumed excess air equal to the empirical average. Overall, observed N2 exceeded expectations based on physical processes in 33 of 47 cases; average excess N2 was 0.48 mg L-1 across all sites. In addition, excess N2 was negatively correlated with DO (r2 = 0.46); springs with low DO (<2.5 mg L-1) had an average of 0.84 mg L-1 excess N2 while springs with higher DO contain little to no excess N2 (0.04 mg L-1). In addition, excess N2 was positively correlated with δ15N-NO3-. These observations are consistent with the widespread occurrence of denitrification in the Floridan Aquifer. Low DOC concentrations indicate that alternative electron donors may fuel

  5. Distributed Denitrification in a Northeastern Agricultural Landscape

    NASA Astrophysics Data System (ADS)

    Anderson, T. R.; Groffman, P. M.; Kaushal, S. S.; Walter, M. T.

    2009-05-01

    Denitrification may be an important sink of anthropogenic nitrogen (N) in eastern US watersheds. Denitrification occurs primarily under anaerobic conditions by heterotrophic microbes, and is therefore expected to be vigorous in wet soils containing high amounts of organic carbon. Actual rates of denitrification, however, have been difficult to quantify, and remain one of the critical unresolved N processes at the landscape scale. We measured denitrification rates in situ along hydrologic flow paths and across gradients of hydroperiodicities, i.e., frequencies and durations of saturated conditions, at Cornell University's Teaching and Research Center in Harford, NY (an active dairy farm). Denitrification rates were measured monthly using the 15N push-pull method from 14 mini-piezometers arrayed along a gradient of hydroperiodicity as indicated by a soil topographic index (STI). Measured rates of denitrification were spatially variable across sites and ranged from undetectable to over 200 µg N/kg soil/day with a mean of 55.9 ± 16.4 µg N/kg soil/day. Mean rates of denitrification increased with STI, which ranged from 10 to 23. This relationship was used to estimate distributed denitrification rates across the landscape and resolve a missing piece of the N budget for the farm. We found that 16% of the farm fell into areas of STI greater than 10. Using the distributed denitrification rates, this area accounts for 15-27% of the missing N balance for the farm (9.7-17.8 Mg N/yr). Improved understanding of the distribution and magnitudes of denitrification in agricultural landscapes has good potential to facilitate new, novel, and better management practices for controlling nitrogen loading to streams and rivers. Indeed, the very areas that appear to have a propensity to harbor denitrification, i.e., areas prone to be wet, are often artificially drained as part of standard agricultural practices which effectively increase N loading to rivers and contributes to downstream

  6. Distributed denitrification in a northeastern agricultural landscape

    NASA Astrophysics Data System (ADS)

    Anderson, T. R.; Groffman, P. M.; Walter, M. T.

    2011-12-01

    Denitrification may be an important sink of anthropogenic nitrogen (N) in eastern US watersheds. Denitrification occurs primarily under anaerobic conditions by heterotrophic microbes, and is therefore expected to be vigorous in wet soils containing large amounts of organic carbon. Actual rates of denitrification, however, have been difficult to quantify, and remain one of the critical unresolved N processes at the landscape scale. We measured denitrification rates in situ along hydrologic flow paths and across gradients of hydroperiodicities, i.e., frequencies and durations of saturated conditions, at Cornell University's Teaching & Research Center in Harford, NY (an active dairy farm). Denitrification rates were measured monthly using the 15N push-pull method from 14 mini-piezometers arrayed along a gradient of hydroperiodicity as indicated by a soil topographic index (STI). Measured rates of denitrification were spatially variable across sites and ranged from undetectable to over 4500 μg N/kg soil/day with a mean of 572 ± 167 μg N/kg soil/day. Mean rates of denitrification increased with STI, which ranged from 8.7 to 23.0 across our mini-piezometer sites. This relationship was used to estimate denitrification rates across the landscape and resolve a missing piece of the N budget for the farm. Only 14% of the farm fell into areas of STI greater than 8.7; however, denitrification in these areas account for more than 60% of the missing N balance for the entire landscape. Improved understanding of the distribution and magnitudes of denitrification in agricultural landscapes has good potential to facilitate new, novel, and better management practices for controlling N loading to streams and rivers. Indeed, the very areas that appear to have a propensity to harbor denitrification, i.e., areas prone to be wet, are often artificially drained as part of standard agricultural practices which reduces the frequency that these areas are likely to be anaerobic and

  7. 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...

  8. Teasing out hydrogeomorphic controls on riparian denitrification

    NASA Astrophysics Data System (ADS)

    McPhillips, L. E.; Walter, M. T.

    2011-12-01

    . Denitrification is calculated based on N2 and N2O gases quantified from the pulled samples. Based on previous studies of denitrification in riparian areas, we anticipate denitrification rates in the range of 40-160 ug N/kg soil/day across the riparian areas studied. Comparing the observed rates to hydrogeomorphic characteristics at each site will allow us to develop predictive relationships between particular characteristics and rates of denitrification. With such a relationship, we can identify and protect riparian zones that are likely to have higher rates of denitrification and thus further reduce nitrate loading to streams in agricultural areas where this is a major issue.

  9. 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...

  10. 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...

  11. Denitrification in upland of China: Magnitude and influencing factors

    NASA Astrophysics Data System (ADS)

    Wang, Jinyang; Yan, Xiaoyuan

    2016-12-01

    A better understanding of influencing factors and accurate estimate of soil denitrification is a global concern. Here we present a synthesis of 300 observations of denitrification in Chinese upland soils from 39 field and laboratory studies using the acetylene inhibition technique. The results of a linear mixed model analysis showed that the rates of soil denitrification were significantly affected by crop type, soil organic carbon, soil pH, the measurement period, and the rate of N application. The emission factor (EF) and N2O/(N2O + N2) ratio for soil denitrification were on average 2.11 ± 0.17% and 0.508 ± 0.020, respectively. Our meta-analysis indicated that N fertilization increased soil denitrification by 311% (95% CI: 279-346%) and 112% (95% CI: 66-171%) in the field and laboratory studies, respectively. Substantial interactive effects between soil properties and N fertilization on soil denitrification were found. Although the highest values of both the rate of denitrification and the EF were found in vegetable fields, the size of the stimulating effect of N fertilization on soil denitrification was lower in vegetable fields than in maize and wheat fields. These results suggest that the crop-specific effect is important and that vegetable fields are potential hot spots of denitrification in Chinese uplands. Based on either the EF or the N2O/(N2O + N2) ratio obtained, the estimated amount of total denitrification from the upland soils was an order of magnitude lower than that from budget calculations, suggesting that the acetylene inhibition technique may significantly underestimate denitrification in Chinese upland soils.

  12. Denitrification in Sinorhizobium meliloti.

    PubMed

    Torres, María J; Rubia, María I; Bedmar, Eulogio J; Delgado, María J

    2011-12-01

    Denitrification is the complete reduction of nitrate or nitrite to N2, via the intermediates nitric oxide (NO) and nitrous oxide (N2O), and is coupled to energy conservation and growth under O2-limiting conditions. In Bradyrhizobium japonicum, this process occurs through the action of the napEDABC, nirK, norCBQD and nosRZDFYLX gene products. DNA sequences showing homology with nap, nirK, nor and nos genes have been found in the genome of the symbiotic plasmid pSymA of Sinorhizobium meliloti strain 1021. Whole-genome transcriptomic analyses have demonstrated that S. meliloti denitrification genes are induced under micro-oxic conditions. Furthermore, S. meliloti has also been shown to possess denitrifying activities in both free-living and symbiotic forms. Despite possessing and expressing the complete set of denitrification genes, S. meliloti is considered a partial denitrifier since it does not grow under anaerobic conditions with nitrate or nitrite as terminal electron acceptors. In the present paper, we show that, under micro-oxic conditions, S. meliloti is able to grow by using nitrate or nitrite as respiratory substrates, which indicates that, in contrast with anaerobic denitrifiers, O2 is necessary for denitrification by S. meliloti. Current knowledge of the regulation of S. meliloti denitrification genes is also included.

  13. 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

  14. 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. Copyright © 2015 Elsevier Ltd. All rights

  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. 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.

  17. Estimating Comparable Scores Using Surrogate Variables.

    ERIC Educational Resources Information Center

    Liou, Michelle; Cheng, Philip E.; Li, Ming-Yen

    2001-01-01

    Studied the possibility of using surrogate variables, such as school grades, test scores, or examinee background, as replacements for common terms predicting sample-selection bias between groups. Proposed a general model for estimating complete data (fitted) distributions through covariates and estimated model parameters using the EM algorithm.…

  18. 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.

  19. 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).

  20. Denitrification in San Francisco Bay intertidal sediments

    SciTech Connect

    Oremland, R.S.; Umberger, C.; Culbertson, C.W.; Smith, R.L.

    1984-05-01

    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 NO/sub 3//sup -/ + NO/sub 2//sup -/ concentrations (less than or equal to26 ..mu..M) were below the apparent K/sub m/ (50 ..mu..M) for nitrate. During the rainy season, when ambient NO/sub 3//sup -/ + NO/sub 2//sup -/ concentrations were higher (37 to 89 ..mu..M), an accurate estimate of the K/sub m/ 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 N/sub 2/O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N/sub 2/O in the presence of C/sub 2/H/sub 2/ was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cells suspensions of a marine pseudomonad confirmed that this N/sub 2/O loss was caused by incomplete blockage of N/sub 2/O reductase by C/sub 2/H/sub 2/ at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 ..mu..mol of N/sub 2/ m/sup -2/ h/sup -1/ (for undisturbed sediments) to 17 to 280 ..mu..mol of N/sub 2/ m/sup -2/ h/sup -1/ (for shaken sediment slurries). 32 references

  1. 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.

  2. 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

  3. 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.

  4. Improved interval estimation of comparative treatment effects

    NASA Astrophysics Data System (ADS)

    Van Krevelen, Ryne Christian

    Comparative experiments, in which subjects are randomized to one of two treatments, are performed often. There is no shortage of papers testing whether a treatment effect exists and providing confidence intervals for the magnitude of this effect. While it is well understood that the object and scope of inference for an experiment will depend on what assumptions are made, these entities are not always clearly presented. We have proposed one possible method, which is based on the ideas of Jerzy Neyman, that can be used for constructing confidence intervals in a comparative experiment. The resulting intervals, referred to as Neyman-type confidence intervals, can be applied in a wide range of cases. Special care is taken to note which assumptions are made and what object and scope of inference are being investigated. We have presented a notation that highlights which parts of a problem are being treated as random. This helps ensure the focus on the appropriate scope of inference. The Neyman-type confidence intervals are compared to possible alternatives in two different inference settings: one in which inference is made about the units in the sample and one in which inference is made about units in a fixed population. A third inference setting, one in which inference is made about a process distribution, is also discussed. It is stressed that certain assumptions underlying this third type of inference are unverifiable. When these assumptions are not met, the resulting confidence intervals may cover their intended target well below the desired rate. Through simulation, we demonstrate that the Neyman-type intervals have good coverage properties when inference is being made about a sample or a population. In some cases the alternative intervals are much wider than necessary on average. Therefore, we recommend that researchers consider using our Neyman-type confidence intervals when carrying out inference about a sample or a population as it may provide them with more

  5. 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.

  6. Insights into Denitrification in Methylotenera mobilis from Denitrification Pathway and Methanol Metabolism Mutants

    PubMed Central

    Mustakhimov, Ildar; Kalyuzhnaya, Marina G.; Lidstrom, Mary E.

    2013-01-01

    We investigated phenotypes of mutants of Methylotenera mobilis JLW8 with lesions in genes predicted to encode functions of the denitrification pathway, as well as mutants with mutations in methanol dehydrogenase-like structural genes xoxF1 and xoxF2, in order to obtain insights into denitrification and methanol metabolism by this bacterium. By monitoring the accumulation of nitrous oxide, we demonstrate that a periplasmic nitrate reductase, NAD(P)-linked and copper-containing nitrite reductases, and a nitric oxide reductase are involved in the denitrification pathway and that the pathway must be operational in aerobic conditions. However, only the assimilatory branch of the denitrification pathway was essential for growth on methanol in nitrate-supplemented medium. Mutants with mutations in each of the two xoxF genes maintained their ability to grow on methanol, but not the double XoxF mutant, suggesting that XoxF proteins act as methanol dehydrogenase enzymes in M. mobilis JLW8. Reduced levels of nitrous oxide accumulated by the XoxF mutants compared to the wild type suggest that these enzymes must be capable of donating electrons for denitrification. PMID:23475964

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Rates of oxygen and nitrate reduction are key factors in determining the chemical evolution of groundwater. Little is known about how these rates vary 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. Modeling denitrification in a tile-drained, corn and soybean agroecosystem of Illinois, USA

    USDA-ARS?s Scientific Manuscript database

    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...

  10. Does denitrification occur within porous carbonate sand grains?

    NASA Astrophysics Data System (ADS)

    Miall Cook, Perran Louis; Kessler, Adam John; Eyre, Bradley David

    2017-09-01

    Permeable carbonate sands form a major habitat type on coral reefs and play a major role in organic matter recycling. Nitrogen cycling within these sediments is likely to play a major role in coral reef productivity, yet it remains poorly studied. Here, we used flow-through reactors and stirred reactors to quantify potential rates of denitrification and the dependence of denitrification on oxygen concentrations in permeable carbonate sands at three sites on Heron Island, Australia. Our results showed that potential rates of denitrification fell within the range of 2-28 µmol L-1 sediment h-1 and were very low compared to oxygen consumption rates, consistent with previous studies of silicate sands. Denitrification was observed to commence at porewater oxygen concentrations as high as 50 µM in stirred reactor experiments on the coarse sediment fraction (2-10 mm) and at oxygen concentrations of 10-20 µM in flow-through and stirred reactor experiments at a site with a median sediment grain size of 0.9 mm. No denitrification was detected in sediments under oxic conditions from another site with finer sediment (median grain size: 0.7 mm). We interpret these results as confirmation that denitrification may occur within anoxic microniches present within porous carbonate sand grains. The occurrence of such microniches has the potential to enhance denitrification rates within carbonate sediments; however further work is required to elucidate the extent and ecological significance of this effect.

  11. 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.

  12. 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

  13. Denitrification in coastal Louisiana: A spatial assessment and research needs

    NASA Astrophysics Data System (ADS)

    Rivera-Monroy, Victor H.; Lenaker, Peter; Twilley, Robert R.; Delaune, Ronald D.; Lindau, Charles W.; Nuttle, William; Habib, Emad; Fulweiler, Robinson W.; Castañeda-Moya, Edward

    2010-04-01

    By transforming fixed nitrogen (N) into nitrogen gas, the biochemical processes that support denitrification provide a function critical to maintaining the integrity of ecosystems subjected to increased loading of N from anthropogenic sources. The Louisiana coastal region receives high nitrate (NO 3-) concentrations (> 100 µM) from the Mississippi-Ohio-Missouri River Basin and is also an area undergoing high rates of wetland loss. Ongoing and anticipated changes in the Louisiana coastal region promise to alter biogeochemical cycles including the net rate of denitrification by ecosystems. Projecting what these changes could mean for coastal water quality and natural resources requires an understanding of the magnitude and patterns of variation in denitrification rates and their connection to estuarine water quality at large temporal and spatial scales under current conditions. We compile and review denitrification rates reported in 32 studies conducted in a variety of habitats across coastal Louisiana during the period 1981- 2008. The acetylene inhibition and 15N flux were the preferred techniques (95%); most of the studies used sediment slurries rather than intact sediment cores. There are no estimates of denitrification rates using the N 2/Ar ratio and isotope pairing techniques, which address some of the problems and limitations of the acetylene inhibition and 15N flux techniques. These studies have shown that sediments from estuaries, lakes, marshes, forested wetlands, and the coastal shelf region are capable of high potential denitrification rates when exposed to high NO 3- concentrations (> 100 µM). Maximum potential denitrification rates in experimental and natural settings can reach values > 2500 µmol m 2 h - 1 . The lack of contemporary studies to understand the interactions among critical nitrogen transformations (e.g., organic matter mineralization, immobilization, aquatic plant assimilation, nitrification, nitrogen fixation, dissimilatory nitrate

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

    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 δ15NNO3 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 δ15NNO3 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

    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 relationships between O2 and δ15NNO3 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 δ15NNO3 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.

  16. 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.

  17. Global change, nitrification, and denitrification: A review

    NASA Astrophysics Data System (ADS)

    Barnard, Romain; Leadley, Paul W.; Hungate, Bruce A.

    2005-03-01

    We reviewed responses of nitrification, denitrification, and soil N2O efflux to elevated CO2, N availability, and temperature, based on published experimental results. We used meta-analysis to estimate the magnitude of response of soil N2O emissions, nitrifying enzyme activity (NEA), denitrifying enzyme activity (DEA), and net and gross nitrification across experiments. We found no significant overall effect of elevated CO2 on N2O fluxes. DEA and NEA significantly decreased at elevated CO2; however, gross nitrification was not modified by elevated CO2, and net nitrification increased. The negative overall response of DEA to elevated CO2 was associated with decreased soil [NO3-], suggesting that reduced availability of electron acceptors may dominate the responses of denitrification to elevated CO2. N addition significantly increased field and laboratory N2O emissions, together with gross and net nitrification, but the effect of N addition on field N2O efflux was not correlated to the amount of N added. The effects of elevated temperature on DEA, NEA, and net nitrification were not significant: The small number of studies available stress the need for more warming experiments in the field. While N addition had large effects on measurements of nitrification and denitrification, the effects of elevated CO2 were less pronounced and more variable, suggesting that increased N deposition is likely to affect belowground N cycling with a magnitude of change that is much larger than that caused by elevated CO2.

  18. 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.

  19. 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.

  20. Autotrophic denitrification for combined hydrogen sulfide removal from biogas and post-denitrification.

    PubMed

    Kleerebezem, R; Mendez, R

    2002-01-01

    In this paper we describe an alternative flow-chart for full treatment of wastewaters rich in organic substrates, ammonia (or organic nitrogen), and sulfate, such as those generated in fish cannery industries. Biogas generated during anaerobic pretreatment of these wastewaters is rich in hydrogen sulfide that needs to be removed to enable application of the biogas. Nitrogen elimination is traditionally achieved by subsequent nitrification and denitrification of the effluent of the anaerobic reactor. Alternatively, the hydrogen sulfide in the biogas can be applied as an electron donor in an autotrophic post-denitrification step. In order to study whether sufficient hydrogen sulfide containing biogas for denitrification was produced in the anaerobic reactor, the biogas composition as a function of the anaerobic reactor-pH was estimated based on a typical wastewater composition and chemical equilibrium equations. It is demonstrated that typical sulfate and nitrogen concentrations in fish cannery wastewater are highly appropriate for application of autotrophic post-denitrification. A literature review furthermore suggested that the kinetic parameters for autotrophic denitrification by Thiobacillus denitrificans represent no bottleneck for its application. Initial experimental studies in fixed-film reactors were conducted with sodium sulfide and nitrate as an electron donor-acceptor couple. The results revealed that only moderate volumetric treatment capacities (< 1 g-NO3- N l(-1) day(-1)) could be achieved. Mass balances suggested that incomplete sulfide oxidation to elemental sulfur occurred, limiting biomass retention and the treatment capacity of the reactor. Future research should clarify the questions concerning product formation from sulfide oxidation.

  1. 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.

  2. 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.

  3. 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

  4. Living oysters and their shells as sites of nitrification and denitrification.

    PubMed

    Caffrey, Jane M; Hollibaugh, James T; Mortazavi, Behzad

    2016-11-15

    Oysters provide a critical habitat, are a food resource for higher trophic levels and support important commercial fisheries throughout the world. Oyster reefs can improve water quality by removing phytoplankton. While sediment denitrification may be enhanced adjacent to oyster reefs, little is known about nitrification and denitrification associated with living oysters and their shells. We measured nitrification and denitrification in living oysters (Crassostrea virginica and Crassostrea gigas) and empty oyster shells. Nitrification was similar between live oysters and empty oyster shells, however, denitrification was enhanced significantly on living oysters compared to shells. This is the first demonstration of nitrification and denitrification associated with living oysters and their shells. Our data suggest that loss of historic oyster reefs has likely affected the resilience of estuaries to eutrophication. The additional benefit of oyster mediated denitrification should be considered in restoration of oyster reefs as a tool for managing eutrophication. Copyright © 2016 Elsevier Ltd. All rights reserved.

  5. Subsoil Denitrification experiment at KBS MSU

    NASA Astrophysics Data System (ADS)

    Shcherbak, I.; Robertson, G. P.

    2010-12-01

    Denitrification plays two important roles in the global nitrogen cycle: returning active nitrogen to inert dinitrogen form and producing potent greenhouse gas nitrous oxide as a byproduct. Effects of denitrification in the deeper layers of soil on total soil denitrification are poorly understood. The experiment will be conducted at KBS to gain a better understanding dependency of rate of subsoil denitrification and molar ratio of denitrified N2O to N2 on depth in the profile and management practice applied. Experimental setup consists of 4 soil profiles (2 tilled and 2 no-till) enclosed in stainless steel boxes with open tops providing access to the soil profile for nondestructive measurements of soil temperature, soil moisture, soil atmosphere, and soil water (6 levels of measurements). Water discharged at the bottom of the profile (~2 m) is sampled as well as gas flux from the surface of the soil to the atmosphere. Inert tracer (hexafluoride) is introduced in the profile to estimate the diffusion rates. Profiles are planted to corn fertilized at 11.1 g/m2 with 50% 15N-Ammonium Nitrate to improve accuracy of measurement and calculate a complete nitrogen balance. Preliminary results show high concentrations of nitrous oxide in the subsoil layers (up to 6 ppm) which suggest high potential contribution of subsoil denitrification to total soil flux of nitrous oxide. Simplified setup consists of gas measurements at two depths in the soil profile (7 and 70 cm) and static chamber at the top. It will be installed in duplicates at conventional tillage, no-till, reduced input, organic, and early successional treatments of Long-Term Ecological Research Site at KBS to expand the scope of findings made with more complex system. Further validation and scaling of the results is possible in terms of integrated semi-empirical models. Predictive equations developed in the study will be used together with other parts of SALUS (System Approach to Land Use Sustainability) model. This

  6. 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.

  7. 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

  8. A Comparative Study of Distribution System Parameter Estimation Methods

    SciTech Connect

    Sun, Yannan; Williams, Tess L.; Gourisetti, Sri Nikhil Gup

    2016-07-17

    In this paper, we compare two parameter estimation methods for distribution systems: residual sensitivity analysis and state-vector augmentation with a Kalman filter. These two methods were originally proposed for transmission systems, and are still the most commonly used methods for parameter estimation. Distribution systems have much lower measurement redundancy than transmission systems. Therefore, estimating parameters is much more difficult. To increase the robustness of parameter estimation, the two methods are applied with combined measurement snapshots (measurement sets taken at different points in time), so that the redundancy for computing the parameter values is increased. The advantages and disadvantages of both methods are discussed. The results of this paper show that state-vector augmentation is a better approach for parameter estimation in distribution systems. Simulation studies are done on a modified version of IEEE 13-Node Test Feeder with varying levels of measurement noise and non-zero error in the other system model parameters.

  9. 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.

  10. Comparing estimates of genetic variance across different relationship models.

    PubMed

    Legarra, Andres

    2016-02-01

    Use of relationships between individuals to estimate genetic variances and heritabilities via mixed models is standard practice in human, plant and livestock genetics. Different models or information for relationships may give different estimates of genetic variances. However, comparing these estimates across different relationship models is not straightforward as the implied base populations differ between relationship models. In this work, I present a method to compare estimates of variance components across different relationship models. I suggest referring genetic variances obtained using different relationship models to the same reference population, usually a set of individuals in the population. Expected genetic variance of this population is the estimated variance component from the mixed model times a statistic, Dk, which is the average self-relationship minus the average (self- and across-) relationship. For most typical models of relationships, Dk is close to 1. However, this is not true for very deep pedigrees, for identity-by-state relationships, or for non-parametric kernels, which tend to overestimate the genetic variance and the heritability. Using mice data, I show that heritabilities from identity-by-state and kernel-based relationships are overestimated. Weighting these estimates by Dk scales them to a base comparable to genomic or pedigree relationships, avoiding wrong comparisons, for instance, "missing heritabilities".

  11. 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

  12. 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

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

    USDA-ARS?s Scientific Manuscript database

    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...

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

    USDA-ARS?s Scientific Manuscript database

    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...

  15. Denitrification in cypress swamp within the Atchafalaya River Basin, Louisiana.

    PubMed

    Lindau, C W; Delaune, R D; Scaroni, A E; Nyman, J A

    2008-01-01

    Nitrogen has been implicated as a major cause of hypoxia in shallow water along the Louisiana/Texas, USA coasts. Excess nitrogen (mainly nitrate) from Mississippi and Atchafalaya River drainage basins may drive the onset and duration of hypoxia in the northern Gulf of Mexico. Restoring and enhancing denitrification have been proposed to reduce and control coastal hypoxia and improve water quality in the Mississippi River Basin. Sediments were collected from six baldcypress restoration sites within the Atchafalaya River Basin, Louisiana, USA. The acetylene blockage technique was used to measure background and potential sediment denitrification rates. Denitrification fluxes were measured before nitrate addition (background rates) and after nitrate addition of 100mgNl(-1) (potential denitrification) at three seasonal temperatures. Background denitrification was low across all cypress swamp sites ranging from 0.9 to 8.8, 0.6 to 28.5 and 8.8 to 47.5g N evolved ha(-1)d(-1) at water/sediment column temperatures of 8, 22 and 30 degrees C, respectively. After nitrate addition, temperature had a significant effect on sediment denitrification potential. Maximum rates measured at 8, 22 and 30 degrees C were approximately 250-260, 550 and 970gNha(-1)d(-1), respectively. Most of the added nitrate in water columns, incubated at 8 degrees C, was removed after 65d compared to 32d and 17d at 22 and 30 degrees C, respectively. These results indicate cypress swamps have the potential to assimilate and process elevated levels of floodwater nitrate with denitrification being a major removal mechanism.

  16. Methods for measuring denitrification: Diverse approaches to a difficult problem

    USGS Publications Warehouse

    Groffman, Peter M; Altabet, Mary A.; Böhlke, J.K.; Butterbach-Bahl, Klaus; David, Mary B.; Firestone, Mary K.; Giblin, Anne E.; Kana, Todd M.; Nielsen , Lars Peter; Voytek, Mary A.

    2006-01-01

    Denitrification, the reduction of the nitrogen (N) oxides, nitrate (NO3−) and nitrite (NO2−), to the gases nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2), is important to primary production, water quality, and the chemistry and physics of the atmosphere at ecosystem, landscape, regional, and global scales. Unfortunately, this process is very difficult to measure, and existing methods are problematic for different reasons in different places at different times. In this paper, we review the major approaches that have been taken to measure denitrification in terrestrial and aquatic environments and discuss the strengths, weaknesses, and future prospects for the different methods. Methodological approaches covered include (1) acetylene-based methods, (2) 15N tracers, (3) direct N2 quantification, (4) N2:Ar ratio quantification, (5) mass balance approaches, (6) stoichiometric approaches, (7) methods based on stable isotopes, (8) in situ gradients with atmospheric environmental tracers, and (9) molecular approaches. Our review makes it clear that the prospects for improved quantification of denitrification vary greatly in different environments and at different scales. While current methodology allows for the production of accurate estimates of denitrification at scales relevant to water and air quality and ecosystem fertility questions in some systems (e.g., aquatic sediments, well-defined aquifers), methodology for other systems, especially upland terrestrial areas, still needs development. Comparison of mass balance and stoichiometric approaches that constrain estimates of denitrification at large scales with point measurements (made using multiple methods), in multiple systems, is likely to propel more improvement in denitrification methods over the next few years.

  17. Temperature dependence of denitrification in phototrophic river biofilms.

    PubMed

    Boulêtreau, S; Salvo, E; Lyautey, E; Mastrorillo, S; Garabetian, F

    2012-02-01

    Denitrification is an ecosystem service of nitrogen load regulation along the terrestrial-freshwater-marine continuum. The present study documents the short-term temperature sensitivity of denitrification enzyme activity in phototrophic river biofilms as a typical microbial assemblage of this continuum. Denitrification measurements were performed using the acetylene inhibition method at four incubation temperatures: 1.1, 12.1, 21.2 and 30.9°C. For this range of temperature, N(2)O production could be fitted to an exponential function of incubation temperature, yielding mean (±standard error) activation energy of 1.42 (±0.24) eV and Q(10) of 7.0 (±1.4). This first quantification of denitrification enzyme activity temperature dependence in phototrophic river biofilms compares with previous studies performed in soils and sediments. This demonstrates the high temperature dependence of denitrification as compared to other community-level metabolisms such as respiration or photosynthesis. This result suggests that global warming can unbalance natural community metabolisms in phototrophic river biofilms and affect their biogeochemical budget.

  18. Aquatic concentrations of chemical analytes compared to ecotoxicity estimates

    USGS Publications Warehouse

    Kostich, Mitchell S.; Flick, Robert W.; Angela L. Batt,; Mash, Heath E.; Boone, J. Scott; Furlong, Edward T.; Kolpin, Dana W.; Glassmeyer, Susan T.

    2017-01-01

    We describe screening level estimates of potential aquatic toxicity posed by 227 chemical analytes that were measured in 25 ambient water samples collected as part of a joint USGS/USEPA drinking water plant study. Measured concentrations were compared to biological effect concentration (EC) estimates, including USEPA aquatic life criteria, effective plasma concentrations of pharmaceuticals, published toxicity data summarized in the USEPA ECOTOX database, and chemical structure-based predictions. Potential dietary exposures were estimated using a generic 3-tiered food web accumulation scenario. For many analytes, few or no measured effect data were found, and for some analytes, reporting limits exceeded EC estimates, limiting the scope of conclusions. Results suggest occasional occurrence above ECs for copper, aluminum, strontium, lead, uranium, and nitrate. Sparse effect data for manganese, antimony, and vanadium suggest that these analytes may occur above ECs, but additional effect data would be desirable to corroborate EC estimates. These conclusions were not affected by bioaccumulation estimates. No organic analyte concentrations were found to exceed EC estimates, but ten analytes had concentrations in excess of 1/10th of their respective EC: triclocarban, norverapamil, progesterone, atrazine, metolachlor, triclosan, para-nonylphenol, ibuprofen, venlafaxine, and amitriptyline, suggesting more detailed characterization of these analytes.

  19. Aquatic concentrations of chemical analytes compared to ecotoxicity estimates.

    PubMed

    Kostich, Mitchell S; Flick, Robert W; Batt, Angela L; Mash, Heath E; Boone, J Scott; Furlong, Edward T; Kolpin, Dana W; Glassmeyer, Susan T

    2017-02-01

    We describe screening level estimates of potential aquatic toxicity posed by 227 chemical analytes that were measured in 25 ambient water samples collected as part of a joint USGS/USEPA drinking water plant study. Measured concentrations were compared to biological effect concentration (EC) estimates, including USEPA aquatic life criteria, effective plasma concentrations of pharmaceuticals, published toxicity data summarized in the USEPA ECOTOX database, and chemical structure-based predictions. Potential dietary exposures were estimated using a generic 3-tiered food web accumulation scenario. For many analytes, few or no measured effect data were found, and for some analytes, reporting limits exceeded EC estimates, limiting the scope of conclusions. Results suggest occasional occurrence above ECs for copper, aluminum, strontium, lead, uranium, and nitrate. Sparse effect data for manganese, antimony, and vanadium suggest that these analytes may occur above ECs, but additional effect data would be desirable to corroborate EC estimates. These conclusions were not affected by bioaccumulation estimates. No organic analyte concentrations were found to exceed EC estimates, but ten analytes had concentrations in excess of 1/10th of their respective EC: triclocarban, norverapamil, progesterone, atrazine, metolachlor, triclosan, para-nonylphenol, ibuprofen, venlafaxine, and amitriptyline, suggesting more detailed characterization of these analytes. Published by Elsevier B.V.

  20. Comparative Analysis of Old-Age Mortality Estimations in Africa

    PubMed Central

    Bendavid, Eran; Seligman, Benjamin; Kubo, Jessica

    2011-01-01

    Background Survival to old ages is increasing in many African countries. While demographic tools for estimating mortality up to age 60 have improved greatly, mortality patterns above age 60 rely on models based on little or no demographic data. These estimates are important for social planning and demographic projections. We provide direct estimations of older-age mortality using survey data. Methods Since 2005, nationally representative household surveys in ten sub-Saharan countries record counts of living and recently deceased household members: Burkina Faso, Côte d'Ivoire, Ethiopia, Namibia, Nigeria, Swaziland, Tanzania, Uganda, Zambia, and Zimbabwe. After accounting for age heaping using multiple imputation, we use this information to estimate probability of death in 5-year intervals (5qx). We then compare our 5qx estimates to those provided by the World Health Organization (WHO) and the United Nations Population Division (UNPD) to estimate the differences in mortality estimates, especially among individuals older than 60 years old. Findings We obtained information on 505,827 individuals (18.4% over age 60, 1.64% deceased). WHO and UNPD mortality models match our estimates closely up to age 60 (mean difference in probability of death -1.1%). However, mortality probabilities above age 60 are lower using our estimations than either WHO or UNPD. The mean difference between our sample and the WHO is 5.9% (95% CI 3.8–7.9%) and between our sample is UNPD is 13.5% (95% CI 11.6–15.5%). Regardless of the comparator, the difference in mortality estimations rises monotonically above age 60. Interpretation Mortality estimations above age 60 in ten African countries exhibit large variations depending on the method of estimation. The observed patterns suggest the possibility that survival in some African countries among adults older than age 60 is better than previously thought. Improving the quality and coverage of vital information in developing countries will become

  1. 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.

  2. Estimating and comparing the diversity of marine actinobacteria.

    PubMed

    Stach, James E M; Bull, Alan T

    2005-01-01

    This paper reviews the application of species richness estimators to microbial diversity data and describes phylogenetic approaches to comparing microbial communities. The techniques are demonstrated using a community of marine actinobacteria. Results demonstrate that marine environments harbour massive actinobacterial diversity. Furthermore, these predictions are likely to be severe underestimates due to the use of arbitrary OTU definitions.

  3. Aquatic concentrations of chemical analytes compared to ecotoxicity estimates

    EPA Science Inventory

    We describe screening level estimates of potential aquatic toxicity posed by 227 chemical analytes that were measured in 25 ambient water samples collected as part of a joint USGS/USEPA drinking water plant study. Measured concentrations were compared to biological effect concent...

  4. Aquatic concentrations of chemical analytes compared to ecotoxicity estimates

    EPA Science Inventory

    We describe screening level estimates of potential aquatic toxicity posed by 227 chemical analytes that were measured in 25 ambient water samples collected as part of a joint USGS/USEPA drinking water plant study. Measured concentrations were compared to biological effect concent...

  5. Modeling nitrous oxide production and reduction in soil through explicit representation of denitrification enzyme kinetics.

    PubMed

    Zheng, Jianqiu; Doskey, Paul V

    2015-02-17

    An enzyme-explicit denitrification model with representations for pre- and de novo synthesized enzymes was developed to improve predictions of nitrous oxide (N2O) accumulations in soil and emissions from the surface. The metabolic model of denitrification is based on dual-substrate utilization and Monod growth kinetics. Enzyme synthesis/activation was incorporated into each sequential reduction step of denitrification to regulate dynamics of the denitrifier population and the active enzyme pool, which controlled the rate function. Parameterizations were developed from observations of the dynamics of N2O production and reduction in soil incubation experiments. The model successfully reproduced the dynamics of N2O and N2 accumulation in the incubations and revealed an important regulatory effect of denitrification enzyme kinetics on the accumulation of denitrification products. Pre-synthesized denitrification enzymes contributed 20, 13, 43, and 62% of N2O that accumulated in 48 h incubations of soil collected from depths of 0-5, 5-10, 10-15, and 15-25 cm, respectively. An enzyme activity function (E) was defined to estimate the relative concentration of active enzymes and variation in response to environmental conditions. The value of E allows for activities of pre-synthesized denitrification enzymes to be differentiated from de novo synthesized enzymes. Incorporating explicit representations of denitrification enzyme kinetics into biogeochemical models is a promising approach for accurately simulating dynamics of the production and reduction of N2O in soils.

  6. 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.

  7. 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.

  8. 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

  9. Microbial community structure and denitrification in a wetland mitigation bank.

    PubMed

    Peralta, Ariane L; Matthews, Jeffrey W; Kent, Angela D

    2010-07-01

    Wetland mitigation is implemented to replace ecosystem functions provided by wetlands; however, restoration efforts frequently fail to establish equivalent levels of ecosystem services. Delivery of microbially mediated ecosystem functions, such as denitrification, is influenced by both the structure and activity of the microbial community. The objective of this study was to compare the relationship between soil and vegetation factors and microbial community structure and function in restored and reference wetlands within a mitigation bank. Microbial community composition was assessed using terminal restriction fragment length polymorphism targeting the 16S rRNA gene (total bacteria) and the nosZ gene (denitrifiers). Comparisons of microbial function were based on potential denitrification rates. Bacterial community structures differed significantly between restored and reference wetlands; denitrifier community assemblages were similar among reference sites but highly variable among restored sites throughout the mitigation bank. Potential denitrification was highest in the reference wetland sites. These data demonstrate that wetland restoration efforts in this mitigation bank have not successfully restored denitrification and that differences in potential denitrification rates may be due to distinct microbial assemblages observed in restored and reference (natural) wetlands. Further, we have identified gradients in soil moisture and soil fertility that were associated with differences in microbial community structure. Microbial function was influenced by bacterial community composition and soil fertility. Identifying soil factors that are primary ecological drivers of soil bacterial communities, especially denitrifying populations, can potentially aid the development of predictive models for restoration of biogeochemical transformations and enhance the success of wetland restoration efforts.

  10. Enzyme diversity and mosaic gene organization in denitrification.

    PubMed

    Zumft, W G; Körner, H

    1997-02-01

    Denitrification is a main branch of the global nitrogen cycle. In the past ten years unravelling the underlying biochemistry and genetics has proceeded at an increasing pace. Fungal denitrification has become a new field. The biochemical investigation of denitrification has culminated in the description of the crystal structures of the two types of nitrite reductases. The N2O reductase shares with cytochrome c oxidase the CuA center as a structurally novel metal site. The cytochrome b subunit of NO reductase has a striking conservation of heme-binding transmembrane segments versus the subunit I of cytochrome c oxidase. Another putative denitrification gene product shows structural relation to the subunit III of the oxidase. N2O reductase and NO reductase may be ancestors of energy-conserving enzymes of the heme-copper oxidase superfamily. More than 30 genes for denitrification are located in a > 30-kb cluster in Pseudomonas stutzeri, and comparable gene clusters have been identified in Pseudomonas aeruginosa and Paracoccus denitrificans. Genes necessary for nitrite reduction and NO reduction have a mosaic arrangement with very few conserved locations within these clusters and relative to each other.

  11. Microbial Community Structure and Denitrification in a Wetland Mitigation Bank▿

    PubMed Central

    Peralta, Ariane L.; Matthews, Jeffrey W.; Kent, Angela D.

    2010-01-01

    Wetland mitigation is implemented to replace ecosystem functions provided by wetlands; however, restoration efforts frequently fail to establish equivalent levels of ecosystem services. Delivery of microbially mediated ecosystem functions, such as denitrification, is influenced by both the structure and activity of the microbial community. The objective of this study was to compare the relationship between soil and vegetation factors and microbial community structure and function in restored and reference wetlands within a mitigation bank. Microbial community composition was assessed using terminal restriction fragment length polymorphism targeting the 16S rRNA gene (total bacteria) and the nosZ gene (denitrifiers). Comparisons of microbial function were based on potential denitrification rates. Bacterial community structures differed significantly between restored and reference wetlands; denitrifier community assemblages were similar among reference sites but highly variable among restored sites throughout the mitigation bank. Potential denitrification was highest in the reference wetland sites. These data demonstrate that wetland restoration efforts in this mitigation bank have not successfully restored denitrification and that differences in potential denitrification rates may be due to distinct microbial assemblages observed in restored and reference (natural) wetlands. Further, we have identified gradients in soil moisture and soil fertility that were associated with differences in microbial community structure. Microbial function was influenced by bacterial community composition and soil fertility. Identifying soil factors that are primary ecological drivers of soil bacterial communities, especially denitrifying populations, can potentially aid the development of predictive models for restoration of biogeochemical transformations and enhance the success of wetland restoration efforts. PMID:20453124

  12. Nitrate removal with lateral flow sulphur autotrophic denitrification reactor.

    PubMed

    Lv, Xiaomei; Shao, Mingfei; Li, Ji; Xie, Chuanbo

    2014-01-01

    An innovative lateral flow sulphur autotrophic denitrification (LFSAD) reactor was developed in this study; the treatment performance was evaluated and compared with traditional sulphur/limestone autotrophic denitrification (SLAD) reactor. Results showed that nitrite accumulation in the LFSAD reactor was less than 1.0 mg/L during the whole operation. Denitrification rate increased with the increased initial alkalinity and was approaching saturation when initial alkalinity exceeded 2.5 times the theoretical value. Higher influent nitrate concentration could facilitate nitrate removal capacity. In addition, denitrification efficiency could be promoted under an appropriate reflux ratio, and the highest nitrate removal percentage was achieved under reflux ratio of 200%, increased by 23.8% than that without reflux. Running resistance was only about 1/9 of that in SLAD reactor with equal amount of nitrate removed, which was the prominent excellence of the new reactor. In short, this study indicated that the developed reactor was feasible for nitrate removal from waters with lower concentrations, including contaminated surface water, groundwater or secondary effluent of municipal wastewater treatment with fairly low running resistance. The innovation in reactor design in this study may bring forth new ideas of reactor development of sulphur autotrophic denitrification for nitrate-contaminated water treatment.

  13. 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.

  14. Denitrification Walls: Successes and Limitations.

    NASA Astrophysics Data System (ADS)

    Schipper, L. A.; Barkle, G. F.; Burgess, C. P.; Vojvodic-Vukovic, M.

    2001-05-01

    There is a need to develop practical and inexpensive approaches for removing nitrate from ground water because of its potential adverse effect on receiving aquatic environments. Denitrification walls may be one such approach for removing nitrate from shallow groundwater. In January 1996, we constructed a denitrification wall by digging a trench that intercepted groundwater and mixed the excavated soil with sawdust before the mix was returned to the trench. Sawdust provides a source of energy for denitrifying bacteria, which convert nitrate in groundwater entering the wall to nitrogen gas. For the past 5 years, nitrate concentrations in groundwater entering this wall have ranged from 5 to 16 mg N L-1 but have always been reduced to less than 2 mg N L-1 in the wall indicating nearly complete removal of nitrate from the groundwater. We showed that this nitrate removal could be accounted for by denitrification rates which ranged from 0.6 to 18.1 mg N m-3 h-1. More recently we have encountered problems with denitrification walls constructed into coarsely textured soils (such as sands) where the addition of sawdust decreased hydraulic conductivity. As a consequence groundwater flowed under rather than through the wall. We are attempting to circumvent this problem using coarser grades of carbon amendments. Particulate carbon (such as sawdust) is likely to support lower rates of nitrate removal, but for longer, than soluble carbon sources because solid carbon sources degrade more slowly.

  15. Comparing capacity value estimation techniques for photovoltaic solar power

    SciTech Connect

    Madaeni, Seyed Hossein; Sioshansi, Ramteen; Denholm, Paul

    2012-09-28

    In this paper, we estimate the capacity value of photovoltaic (PV) solar plants in the western U.S. Our results show that PV plants have capacity values that range between 52% and 93%, depending on location and sun-tracking capability. We further compare more robust but data- and computationally-intense reliability-based estimation techniques with simpler approximation methods. We show that if implemented properly, these techniques provide accurate approximations of reliability-based methods. Overall, methods that are based on the weighted capacity factor of the plant provide the most accurate estimate. As a result, we also examine the sensitivity of PV capacity value to the inclusion of sun-tracking systems.

  16. Comparing capacity value estimation techniques for photovoltaic solar power

    DOE PAGES

    Madaeni, Seyed Hossein; Sioshansi, Ramteen; Denholm, Paul

    2012-09-28

    In this paper, we estimate the capacity value of photovoltaic (PV) solar plants in the western U.S. Our results show that PV plants have capacity values that range between 52% and 93%, depending on location and sun-tracking capability. We further compare more robust but data- and computationally-intense reliability-based estimation techniques with simpler approximation methods. We show that if implemented properly, these techniques provide accurate approximations of reliability-based methods. Overall, methods that are based on the weighted capacity factor of the plant provide the most accurate estimate. As a result, we also examine the sensitivity of PV capacity value to themore » inclusion of sun-tracking systems.« less

  17. 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.

  18. Estimating Decision-Relevant Comparative Effects Using Instrumental Variables

    PubMed Central

    2011-01-01

    Instrumental variables methods (IV) are widely used in the health economics literature to adjust for hidden selection biases in observational studies when estimating treatment effects. Less attention has been paid in the applied literature to the proper use of IVs if treatment effects are heterogeneous across subjects. Such a heterogeneity in effects becomes an issue for IV estimators when individuals’ self-selected choices of treatments are correlated with expected idiosyncratic gains or losses from treatments. We present an overview of the challenges that arise with IV estimators in the presence of effect heterogeneity and self-selection and compare conventional IV analysis with alternative approaches that use IVs to directly address these challenges. Using a Medicare sample of clinically localized breast cancer patients, we study the impact of breast-conserving surgery and radiation with mastectomy on 3-year survival rates. Our results reveal the traditional IV results may have masked important heterogeneity in treatment effects. In the context of these results, we discuss the advantages and limitations of conventional and alternative IV methods in estimating mean treatment-effect parameters, the role of heterogeneity in comparative effectiveness research and the implications for diffusion of technology. PMID:22010051

  19. 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.

  20. Comparison of nutrient removal efficiency between pre- and post-denitrification wastewater treatments.

    PubMed

    Hamada, K; Kuba, T; Torrico, V; Okazaki, M; Kusuda, T

    2006-01-01

    A shortage of organic substances (COD) may cause problems for biological nutrient removal, that is, lower influent COD concentration leads to lower nutrient removal rates. Biological phosphorus removal and denitrification are reactions in which COD is indispensable. As for biological simultaneous nitrogen and phosphorus removal systems, a competition problem of COD utilisation between polyphosphate accumulating organisms (PAOs) and non-polyphosphate-accumulating denitrifiers is not avoided. From the viewpoint of effective utilisation of limited influent COD, denitrifying phosphorus-removing organisms (DN-PAOs) can be effective. In this study, DN-PAOs activities in modified UCT (pre-denitrification process) and DEPHANOX (post-denitrification process) wastewater treatments were compared. In conclusion, the post-denitrification systems can use influent COD more effectively and have higher nutrient removal efficiencies than the conventional pre-denitrification systems.

  1. Comparing Estimators of Microbiological Attributes by Random Subsamples

    NASA Astrophysics Data System (ADS)

    Li, M.; Adriaens, P.

    2005-12-01

    validation approach called bootstrapping, which randomly take a designed number of data points out of the data set, and examine the reproduction of their estimate by the rest of the data. The repeated random selection will be used to compare the M-scale model to the ordinary kriging, visualized quantitatively by quantile-quantile (Q-Q) plots and scatter plots. Estimates and uncertainties evaluated by the M-scale model will be compared using the random subsets, to examine the unbiasedness of the estimate as well as the appropriateness of the uncertainty evaluated. An additional comparison, using the dataset collected in Anacostia River, Washington D.C., can further be used to inform further applicability under sparsely sampled site. For a conclusive test, artificial datasets based on different scenario will then be generated, in order to examine the general performance and restriction of the models under different data distribution and spatial structures.

  2. beta- and gamma-Comparative dose estimates on Enewetak Atoll.

    PubMed

    Crase, K W; Gudiksen, P H; Robison, W L

    1982-05-01

    Enewetak Atoll is one of the Pacific atolls used for atmospheric testing of U.S. nuclear weapons. Beta dose and gamma-ray exposure measurements were made on two islands of the Enewetak Atoll during July-August 1976 to determine the beta and low energy gamma-contribution to the total external radiation doses to the returning Marshallese. Measurements were made at numerous locations with thermoluminescent dosimeters (TLD), pressurized ionization chambers, portable NaI detectors, and thin-window pancake GM probes. Results of the TLD measurements with and without a beta-attenuator indicate that approx. 29% of the total dose rate at 1 m in air is due to beta- or low energy gamma-contribution. The contribution at any particular site, however, is somewhat dependent on ground cover, since a minimal amount of vegetation will reduce it significantly from that over bare soil, but thick stands of vegetation have little effect on any further reductions. Integral 30-yr external shallow dose estimates for future inhabitants were made and compared with external dose estimates of a previous large scale radiological survey (En73). Integral 30-yr shallow external dose estimates are 25-50% higher than whole body estimates. Due to the low penetrating ability of the beta's or low energy gamma's, however, several remedial actions can be taken to reduce the shallow dose contribution to the total external dose.

  3. 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...

  4. 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...

  5. 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.

  6. An experiment to compare multiple methods for streamflow uncertainty estimation

    NASA Astrophysics Data System (ADS)

    Kiang, Julie; McMillan, Hilary; Gazoorian, Chris; Mason, Robert; Le Coz, Jerome; Renard, Benjamin; Mansanarez, Valentin; Westerberg, Ida; Petersen-Øverleir, Asgeir; Reitan, Trond; Sikorska, Anna; Seibert, Jan; Coxon, Gemma; Freer, Jim; Belleville, Arnaud; Hauet, Alexandre

    2017-04-01

    Stage-discharge rating curves are used to relate streamflow discharge to continuously measured river stage readings to create a continuous record of streamflow discharge. The stage-discharge relationship is estimated and refined using discrete streamflow measurements over time, during which both the discharge and stage are measured. There is uncertainty in the resulting rating curve due to multiple factors including the curve-fitting process, assumptions on the form of the model used, fluvial geomorphology of natural channels, and the approaches used to extrapolate the rating equation beyond available observations. This rating curve uncertainty leads to uncertainty in the streamflow timeseries, and therefore to uncertainty in predictive models that use the streamflow data. Many different methods have been proposed in the literature for estimating rating curve uncertainty, differing in mathematical rigor, in the assumptions made about the component errors, and in the information required to implement the method at any given site. This study describes the results of an international experiment to test and compare streamflow uncertainty estimation methods from 7 research groups across 9 institutions. The methods range from simple LOWESS fits to more complicated Bayesian methods that consider hydraulic principles directly. We evaluate these different methods when applied to three diverse gauging stations using standardized information (channel characteristics, hydrographs, and streamflow measurements). Our results quantify the resultant spread of the stage-discharge curves and compare the level of uncertainty attributed to the streamflow records by each different method. We provide insight into the sensitivity of streamflow uncertainty bounds to the choice of uncertainty estimation method, and discuss the implications for model uncertainty assessment.

  7. Small scale denitrification variability in riparian zones: Results from a high-resolution dataset

    NASA Astrophysics Data System (ADS)

    Gassen, Niklas; Knöller, Kay; Musolff, Andreas; Popp, Felix; Lüders, Tillmann; Stumpp, Christine

    2017-04-01

    Riparian zones are important compartments at the interface between groundwater and surface water where biogeochemical processes like denitrification are often enhanced. Nitrate loads of either groundwater entering a stream through the riparian zone or streamwater infiltrating into the riparian zone can be substantially reduced. These processes are spatially and temporally highly variable, making it difficult to capture solute variabilities, estimate realistic turnover rates and thus to quantify integral mass removal. A crucial step towards a more detailed characterization is to monitor solutes on a scale which adequately resemble the highly heterogeneous distribution and on a scale where processes occur. We measured biogeochemical parameters in a spatial high resolution within a riparian corridor of a German lowland river system over the course of one year. Samples were taken from three newly developed high-resolution multi-level wells with a maximum vertical resolution of 5 cm and analyzed for major ions, DOC and N-O isotopes. Sediment derived during installation of the wells was analyzed for specific denitrifying enzymes. Results showed a distinct depth zonation of hydrochemistry within the shallow alluvial aquifer, with a 1 m thick zone just below the water table with lower nitrate concentrations and EC values similar to the nearby river. Conservative parameters were consistent inbetween the three wells, but nitrate was highly variable. In addition, spots with low nitrate concentrations showed isotopic and microbial evidence for higher denitrification activities. The depth zonation was observed throughout the year, with stronger temporal variations of nitrate concentrations just below the water table compared to deeper layers. Nitrate isotopes showed a clear seasonal trend of denitrification activities (high in summer, low in winter). Our dataset gives new insight into river-groundwater exchange processes and shows the highly heterogeneous distribution of

  8. A new mechanistic model of δ18O-N2O formation by denitrification

    NASA Astrophysics Data System (ADS)

    Snider, David M.; Venkiteswaran, Jason J.; Schiff, Sherry L.; Spoelstra, John

    2013-07-01

    Anaerobic incubations of flooded and non-flooded agricultural soils and stream sediment were conducted with 18O-labelled water to investigate the stable isotope ratios (δ15N and δ18O) of nitrous oxide (N2O) produced from denitrification. The rates of N2O production and δ15N- and δ18O-N2O values were measured. The amount of oxygen exchange (O-exchange) with water, and the nitrogen and oxygen isotope effects (ɛ) were calculated. The net 15N isotope effect (NO3- → N2O) for denitrification in this study varied from -30‰ to -9‰. The net 18O isotope effect ranged between +32‰ and +60‰ and was negatively correlated to the total fraction of O-exchange, which varied between 0.40 and 0.94. This manuscript describes a new, comprehensive set of mathematical expressions that can be used to model δ18O values of N2O formed by denitrification and calculate the magnitude of O-exchange and the net 18O isotope effect for denitrification. This mathematical approach is compared to another method of approximating O-exchange (Snider et al., 2009), and we show that this older method provides a minimum estimate of O-exchange. Using this mechanistic model, we discuss how N2O consumption, open/closed systems, and variations in the N2O:N2 ratio can influence the observed δ18O-N2O. The net 18O isotope effect for denitrification in this study was partially controlled by the fractions of O-exchange and N2O reduction, which were likely influenced by the actively denitrifying microbial community and the soil moisture. We conclude that δ18O-N2O values are, in many cases, useful tracers of N2O production because they are often higher than the majority of nitrification-derived δ18O-N2O values. The usefulness of δ18O values to apportion sources must be determined on a case-by-case basis.

  9. Optimization and reconstruction technology of SCR flue gas denitrification ultra low emission in coal fired power plant

    NASA Astrophysics Data System (ADS)

    Li, Xinhao

    2017-09-01

    In recent decades, nitrogen oxides (NOx) emissions from thermal power plant increased year by year in China. A large number of nitrogen oxides (NOx) emissions caused by the growing environmental problems have been widely attached importance to people. SCR denitrification technology has the advantages of cleanliness and high efficiency. At present, it has been the major technology to control NOx emission because of its high denitrification efficiency, reliable operation, no by-products and simple structure of the device. The denitrification efficiency can be stabilized at 70%. In this paper, three different denitrification methods are compared. The factors influencing the denitrification efficiency, the system arrangement and the key factors of the denitrification system are discussed in detail. And the numerical simulation of how to use this calculation software in the SCR reactor flue, baffle, reactor, spray ammonia grille and spray ammonia, mixer, etc. are reviewed, as well as the effect of system operation control on the deoxidation performance.

  10. 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.

  11. 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).

  12. Topographic effects on denitrification in drained agricultural fields

    USDA-ARS?s Scientific Manuscript database

    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...

  13. The coefficient of error of optical fractionator population size estimates: a computer simulation comparing three estimators.

    PubMed

    Glaser, E M; Wilson, P D

    1998-11-01

    sampled disectors. There were 1000 independently simulated cell populations for each test condition, and a 'trial' was conducted for each of these cell populations. In each trial we calculated the (unique) true CE of the population size estimate and the three CE estimates obtained by applying the Scheaffer-Mendenhall-Ott (SMO) and both Gundersen-Jensen (GJ) estimators. We compared the estimated CEs with the true CEs for each population distribution. We found that the CE estimates obtained by the SMO estimator were closer to the true CEs and had less scatter than those of the nugget-modified GJ estimator. Both had small positive bias. The CE estimates obtained by the unmodified GJ estimator exhibited widely varying bias and large scatter. In all the population distributions we tested, the average true CE was very nearly proportional to 1/square root of QT, where QT is the average number of cells counted in the two-stage systematic sample.

  14. 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

  15. Co-Occurring Anammox, Denitrification, and Codenitrification in Agricultural Soils

    PubMed Central

    Long, Andrew; Heitman, Joshua; Tobias, Craig; Philips, Rebecca

    2013-01-01

    Anammox and denitrification mediated by bacteria are known to be the major microbial processes converting fixed N to N2 gas in various ecosystems. Codenitrification and denitrification by fungi are additional pathways producing N2 in soils. However, fungal codenitrification and denitrification have not been well investigated in agricultural soils. To evaluate bacterial and fungal processes contributing to N2 production, molecular and 15N isotope analyses were conducted with soil samples collected at six different agricultural fields in the United States. Denitrifying and anammox bacterial abundances were measured based on quantitative PCR (qPCR) of nitrous oxide reductase (nosZ) and hydrazine oxidase (hzo) genes, respectively, while the internal transcribed spacer (ITS) of Fusarium oxysporum was quantified to estimate the abundance of codenitrifying and denitrifying fungi. 15N tracer incubation experiments with 15NO3− or 15NH4+ addition were conducted to measure the N2 production rates from anammox, denitrification, and codenitrification. Soil incubation experiments with antibiotic treatments were also used to differentiate between fungal and bacterial N2 production rates in soil samples. Denitrifying bacteria were found to be the most abundant, followed by F. oxysporum based on the qPCR assays. The potential denitrification rates by bacteria and fungi ranged from 4.118 to 42.121 nmol N2-N g−1 day−1, while the combined potential rates of anammox and codenitrification ranged from 2.796 to 147.711 nmol N2-N g−1 day−1. Soil incubation experiments with antibiotics indicated that fungal codenitrification was the primary process contributing to N2 production in the North Carolina soil. This study clearly demonstrates the importance of fungal processes in the agricultural N cycle. PMID:23087029

  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. [Ionizing and non-ionizing radiation (comparative risk estimations)].

    PubMed

    Grigor'ev, Iu G

    2012-01-01

    The population has widely used mobile communication for already more than 15 years. It is important to note that the use of mobile communication has sharply changed the conditions of daily exposure of the population to EME We expose our brain daily for the first time in the entire civilization. The mobile phone is an open and uncontrollable source of electromagnetic radiation. The comparative risk estimation for the population of ionizing and non-ionizing radiation was carried out taking into account the real conditions of influence. Comparison of risks for the population of ionizing and non-ionizing radiation leads us to a conclusion that EMF RF exposure in conditions of wide use of mobile communication is potentially more harmful than ionizing radiation influence.

  18. 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

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

    PubMed

    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.

  20. Implication of using different carbon sources for denitrification in wastewater treatments.

    PubMed

    Cherchi, Carla; Onnis-Hayden, Annalisa; El-Shawabkeh, Ibrahim; Gu, April Z

    2009-08-01

    Application of external carbon sources for denitrification becomes necessary for wastewater treatment plants that have to meet very stringent effluent nitrogen limits (e.g., 3 to 5 mgTN/L). In this study, we evaluated and compared three carbon sources--MicroC (Environmental Operating Solutions, Bourne, Massachusetts), methanol, and acetate-in terms of their denitrification rates and kinetics, effect on overall nitrogen removal performance, and microbial community structure of carbon-specific denitrifying enrichments. Denitrification rates and kinetics were determined with both acclimated and non-acclimated biomass, obtained from laboratory-scale sequencing batch reactor systems or full-scale plants. The results demonstrate the feasibility of the use of MicroC for denitrification processes, with maximum denitrification rates (k(dmax)) of 6.4 mgN/gVSSh and an observed yield of 0.36 mgVSS/mgCOD. Comparable maximum nitrate uptake rates were found with methanol, while acetate showed a maximum denitrification rate nearly twice as high as the others. The maximum growth rates measured at 20 degrees C for MicroC and methanol were 3.7 and 1.2 day(-1), respectively. The implications resulting from the differences in the denitrification rates and kinetics of different carbon sources on the full-scale nitrogen removal performance, under various configurations and operational conditions, were assessed using Biowin (EnviroSim Associates, Ltd., Flamborough, Ontario, Canada) simulations for both pre- and post-denitrification systems. Examination of microbial population structures using Automated Ribosomal Intergenic Spacer Analysis (ARISA) throughout the study period showed dynamic temporal changes and distinct microbial community structures of different carbon-specific denitrifying cultures. The ability of a specific carbon-acclimated denitrifying population to instantly use other carbon source also was investigated, and the chemical-structure-associated behavior patterns observed

  1. 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.; 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.

  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. Comparative study on parameter estimation methods for attenuation relationships

    NASA Astrophysics Data System (ADS)

    Sedaghati, Farhad; Pezeshk, Shahram

    2016-12-01

    In this paper, the performance and advantages and disadvantages of various regression methods to derive coefficients of an attenuation relationship have been investigated. A database containing 350 records out of 85 earthquakes with moment magnitudes of 5-7.6 and Joyner-Boore distances up to 100 km in Europe and the Middle East has been considered. The functional form proposed by Ambraseys et al (2005 Bull. Earthq. Eng. 3 1-53) is selected to compare chosen regression methods. Statistical tests reveal that although the estimated parameters are different for each method, the overall results are very similar. In essence, the weighted least squares method and one-stage maximum likelihood perform better than the other considered regression methods. Moreover, using a blind weighting matrix or a weighting matrix related to the number of records would not yield in improving the performance of the results. Further, to obtain the true standard deviation, the pure error analysis is necessary. Assuming that the correlation between different records of a specific earthquake exists, the one-stage maximum likelihood considering the true variance acquired by the pure error analysis is the most preferred method to compute the coefficients of a ground motion predication equation.

  4. 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

  5. Excess cell mass as an internal carbon source for biological denitrification.

    PubMed

    Biradar, Prashant M; Roy, S B; D'Souza, S F; Pandit, A B

    2010-03-01

    Aim of the present work was to examine whether the SCOD (soluble chemical oxygen demand) released after the physical disruption of excess activated sludge can be used as an alternative carbon source for biological denitrification. In the first stage of research, we investigated the potential use of energy efficient hydrodynamic cavitation (HC) technique for the disruption of activated sludge. In a comparative study between ultrasonic cavitation (UC) and HC, it was observed that UC needs five times more energy than that of HC to release the same amount of SCOD. In the second stage of the experimental study, SCOD was successfully used as an alternative carbon source (alternative to sodium acetate) for biological denitrification. The critical weight ratio (SCOD/NO(3)-N) of seven ensured 100% removal of nitrate. Nitrate removal kinetics indicated that denitrification with SCOD as a carbon source gives higher specific denitrification rate (by approximately 200%) as compared to conventional carbon source (sodium acetate).

  6. Microseismic Network Performance Estimation: Comparing Predictions to an Earthquake Catalogue

    NASA Astrophysics Data System (ADS)

    Greig, Wesley; Ackerley, Nick

    2014-05-01

    The design of networks for monitoring induced seismicity is of critical importance as specific standards of performance are necessary. One of the difficulties involved in designing networks for monitoring induced seismicity is that it is difficult to determine whether or not the network meets these standards without first developing an earthquake catalog. We develop a tool that can assess two key measures of network performance without an earthquake catalog: location accuracy and magnitude of completeness. Site noise is measured either at existing seismic stations or as part of a noise survey. We then interpolate measured values to determine a noise map for the entire region. This information is combined with instrument noise for each station to accurately assess total ambient noise at each station. Location accuracy is evaluated according to the approach of Peters and Crosson (1972). Magnitude of completeness is computed by assuming isotropic radiation and mandating a threshold signal to noise ratio (similar to Stabile et al. 2013). We apply this tool to a seismic network in the central United States. We predict the magnitude of completeness and the location accuracy and compare predicted values with observed values generated from the existing earthquake catalog for the network. We investigate the effects of hypothetical station additions and removals to a network to simulate network expansions and station failures. We find that the addition of stations to areas of low noise results in significantly larger improvements in network performance than station additions to areas of elevated noise, particularly with respect to magnitude of completeness. Our results highlight the importance of site noise considerations in the design of a seismic network. The ability to predict hypothetical station performance allows for the optimization of seismic network design and enables the prediction of performance for a purely hypothetical seismic network. If near real

  7. Natural Denitrification in the Saturated Zone: A Review

    NASA Astrophysics Data System (ADS)

    Korom, Scott F.

    1992-06-01

    Denitrification is increasingly recognized for its ability to eliminate or reduce nitrate concentrations in groundwater. With this awareness comes a desire to predict the rate and extent of denitrification in aquifers. The limiting factor in making predictive models, however, is our limited knowledge of the physical characteristics of this process. This review synthesizes the published literature on natural aquifer denitrification. A background section discusses denitrification requirements and dissimilatory nitrate reduction to ammonium, which occurs in environments similar to those where denitrification occurs, and gives a historical perspective on denitrification. Other sections discuss denitrification with organic carbon serving as the electron donor (heterotrophic denitrification) and with reduced inorganic compounds serving as the electron donor (autotrophic denitrification). The section on heterotrophic denitrification is structured around two tables that summarize natural aquifer denitrification rates reported by laboratory studies and natural aquifer denitrification rates reported by field studies. The section on autotrophic denitrification discusses denitrification with reduced iron and reduced sulfur. Thus far, most studies only consider a single electron donor or donor type, whether heterotrophic or autotrophic. This review demonstrates, however, that multiple electron donors may be present in a given aquifer. Future research efforts are recommended to determine the factors affecting the availability of electron donors and their denitrification rates. Additional research is also suggested on how dissolved oxygen affects denitrification rates and on the factors influencing the partitioning of nitrate reduction products to nitrous oxide, a potential contributor to the destruction of the ozone layer, and to ammonium.

  8. 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.

  9. Study on enhanced denitrification using particulate organic matter in membrane bioreactor by mechanism modeling.

    PubMed

    Zheng, Min; Liu, Yan-Chen; Wang, Cheng-Wen; Xu, Kang-Ning

    2013-11-01

    Particulate organic matter (POM) in wastewater is a potential denitrification carbon source, while the optimal operational mode using denitrification mechanism with POM is still unclear in wastewater treatment plants. In this work, we investigated the denitrification rates (DNRs) in a full-scale membrane bioreactor (MBR) coupled with two-stage pre-anoxic (pre-AN), and then evaluated the POM denitrification efficiency using mechanism modeling. The results indicate that POM related fraction accounted for the majority of the obtained specific DNR of 1.39±0.46mgNg(-1) MLVSS h(-1) in the second pre-AN without available soluble carbon source. The modeling approaches with calibration and validation procedures estimated a high residual POM concentration of 0.17g COD g(-1) MLVSS in the activated sludge, which provided specific DNR of 1.14mgNg(-1) MLVSS h(-1). High POM retention time in the reactor was the result of high solid retention time used in the MBR. In particular, post-AN of high biomass concentration could provide the highest POM denitrification efficiency in MBR. The MBR process combined with additional sludge reduction technology could further enhance denitrification by POM.

  10. 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.

  11. Behavior of solid carbon sources for biological denitrification in groundwater remediation.

    PubMed

    Zhang, Jianmei; Feng, Chuanping; Hong, Siqi; Hao, Huiling; Yang, Yingnan

    2012-01-01

    The present study was conducted to compare the behavior of wheat straw, sawdust and biodegradable plastic (BP) as potential carbon sources for denitrification in groundwater remediation. The results showed that a greater amount of nitrogen compounds were released from wheat straw and sawdust than from BP in leaching experiments. In batch experiments, BP showed higher nitrate removal efficiency and longer service life than wheat straw and sawdust, which illustrated that BP is the most appropriate carbon source for stimulation of denitrification activity. In column experiments, BP was able to support complete denitrification at influent nitrate concentrations of 50, 60, 70, 80, and 90 mg NO(3)(-)-N/L, showing corresponding denitrification rates of 0.12, 0.14, 0.17, 0.19, and 0.22 mg NO(3)(-)-N.L(-1).d(-1).g(-1), respectively. These findings indicate that BP is applicable for use as a carbon source for nitrate-polluted groundwater remediation.

  12. Free nitrous acid pretreatment of wasted activated sludge to exploit internal carbon source for enhanced denitrification.

    PubMed

    Ma, Bin; Peng, Yongzhen; Wei, Yan; Li, Baikun; Bao, Peng; Wang, Yayi

    2015-03-01

    Using internal carbon source contained in waste activated sludge (WAS) is beneficial for nitrogen removal from wastewater with low carbon/nitrogen ratio, but it is usually limited by sludge disintegration. This study presented a novel strategy based on free nitrous acid (FNA) pretreatment to intensify the release of organic matters from WAS for enhanced denitrification. During FNA pretreatment, soluble chemical oxygen demand (SCOD) production kept increasing when FNA increased from 0 to 2.04 mg HNO2-N/L. Compared with untreated WAS, the internal carbon source production increased by 50% in a simultaneous fermentation and denitrification reactor fed with WAS pretreated by FNA for 24 h at 2.04 mg HNO2-N/L. This also increased denitrification efficiency by 76% and sludge reduction by 87.5%. More importantly, greenhouse gas nitrous oxide production in denitrification was alleviated since more electrons could be provided by FNA pretreated WAS.

  13. 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

  14. Denitrification coupled to pyrite oxidation and changes in groundwater quality in a shallow sandy aquifer

    NASA Astrophysics Data System (ADS)

    Zhang, Yan-Chun; Slomp, Caroline P.; Broers, Hans Peter; Passier, Hilde F.; Cappellen, Philippe Van

    2009-11-01

    This study focuses on denitrification in a sandy aquifer using geochemical analyses of both sediment and groundwater, combined with groundwater age dating ( 3H/ 3He). The study sites are located underneath cultivated fields and an adjacent forested area at Oostrum, The Netherlands. Shallow groundwater in the region has high nitrate concentrations (up to 8 mM) due to intense fertilizer application. Nitrate removal from the groundwater below cultivated fields correlates with sulfate production, and the release of dissolved Fe 2+ and pyrite-associated trace metals (e.g. As, Ni, Co and Zn). These results, and the presence of pyrite in the sediment matrix within the nitrate removal zone, indicate that denitrification coupled to pyrite oxidation is a major process in the aquifer. Significant nitrate loss coupled to sulfate production is further confirmed by comparing historical estimates of regional sulfate and nitrate loadings to age-dated groundwater sulfate and nitrate concentrations, for the period 1950-2000. However, the observed increases in sulfate concentration are about 50% lower than would be expected from complete oxidation of pyrite to sulfate, possibly due to the accumulation of intermediate oxidation state sulfur compounds, such as elemental sulfur. Pollutant concentrations (NO 3, Cl, As, Co and Ni) measured in the groundwater beneath the agricultural areas in 1996 and 2006 show systematic decreases most likely due to declining fertilizer use.

  15. 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.

  16. Determining material damping type by comparing modal frequency estimators.

    PubMed

    Anthony, D K; Simón, F; Juan, Jesús

    2009-09-01

    The accuracy of modal frequency and damping estimators for non-lightly damped single degree of freedom systems depend on the response parameter used as well as the damping mechanism. Therefore, in order to make accurate modal parameter measurements, the damping mechanism at play must be known to be either viscous or hysteretic a priori. Here, comparisons between the evaluated frequency values are used to glean this information. The damping mechanism of an experimental system (consisting of resilient layer and mass plate) is then determined using two simple modal parameter estimators and applying statistical methods.

  17. 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

  18. 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.

  19. 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

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

    USDA-ARS?s Scientific Manuscript database

    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...

  1. Comparing techniques for estimating flame temperature of prescribed fires

    Treesearch

    Deborah K. Kennard; Kenneth W. Outcalt; David Jones; Joseph J. O' Brien

    2005-01-01

    A variety of techniques that estimate temperature and/or heat output during fires are available. We assessed the predictive ability of metal and tile pyrometers, calorimeters of different sizes, and fuel consumption to time-temperature metrics derived from thick and thin thermocouples at 140 points distributed over 9 management-scale burns in a longleaf pine forest in...

  2. Denitrification by cystic fibrosis pathogens - Stenotrophomonas maltophilia is dormant in sputum.

    PubMed

    Kolpen, Mette; Kragh, Kasper Nørskov; Bjarnsholt, Thomas; Line, Laura; Hansen, Christine Rønne; Dalbøge, Christina Schjellerup; Hansen, Nana; Kühl, Michael; Høiby, Niels; Jensen, Peter Østrup

    2015-01-01

    Chronic Pseudomonas aeruginosa lung infection is the most severe complication for cystic fibrosis (CF) patients. Infected endobronchial mucus of CF patients contains anaerobic zones mainly due to the respiratory burst of polymorphonuclear leukocytes. We have recently demonstrated ongoing denitrification in sputum from patients infected with P. aeruginosa. Therefore we aimed to investigate, whether the pathogenicity of several known CF pathogens is correlated to their ability to perform denitrification. We measured denitrification with N(2)O microsensors in concert with anaerobic growth measurements by absorbance changes and colony counting in isolates from 32 CF patients chronically infected with the highly pathogenic bacteria P. aeruginosa, Achromobacter xylosoxidans, Burkholderia multivorans or the less pathogenic bacterium Stenotrophomonas maltophilia. Consumption of NO(3)(-) and NO(2)(-) was estimated by the Griess Assay. All isolates were assayed during 2 days of incubation in anaerobic LB broth with NO(3)(-) or NO(2)(-). PNA FISH staining of 16S rRNA was used to estimate the amount of ribosomes per bacterial cells and thereby the in situ growth rate of S. maltophilia in sputum. Supplemental NO(3)(-) caused increased production of N(2)O by P. aeruginosa, A. xylosoxidans and B. multivorans and increased growth for all pathogens. Growth was, however, lowest for S. maltophilia. NO(3)(-) was metabolized by all pathogens, but only P. aeruginosa was able to remove NO(2)(-). S. maltophilia had limited growth in sputum as seen by the weak PNA FISH staining. All four pathogens were able to grow anaerobically by NO(3)(-) reduction. Denitrification as demonstrated by N(2)O production was, however, not found in S. maltophilia isolates. The ability to perform denitrification may contribute to the pathogenicity of the infectious isolates since complete denitrification promotes faster anaerobic growth. The inability of S. maltophilia to proliferate by denitrification and

  3. 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.

  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.

  6. Denitrification potential in urban riparian zones.

    PubMed

    Groffman, Peter M; Crawford, Marshall Kamau

    2003-01-01

    Denitrification, the anaerobic microbial conversion of nitrate (NO3-) to nitrogen (N) gases, is an important process contributing to the ability of riparian zones to function as "sinks" for NO3- in watersheds. There has been little analysis of riparian zones in urban watersheds despite concerns about high NO3- concentrations in many urban streams. Vegetation and soils in urban ecosystems are often highly disturbed, and few studies have examined microbial processes like denitrification in these ecosystems. In this study, we measured denitrification potential and a suite of related microbial parameters (microbial biomass carbon [C] and N content, potential net N mineralization and nitrification, soil inorganic N pools) in four rural and four urban riparian zones in the Baltimore, MD metropolitan area. Two of the riparian zones were forested and two had herbaceous vegetation in each land use context. There were few differences between urban and rural and herbaceous and forest riparian zones, but variability was much higher in urban than rural sites. There were strong positive relationships between soil moisture and organic matter content and denitrification potential. Given the importance of surface runoff in urban watersheds, the high denitrification potential of the surface soils that we observed suggests that if surface runoff can be channeled through areas with high denitrification potential (e.g., stormwater detention basins with wetland vegetation), these areas could function as important NO3- sinks in urban watersheds.

  7. Aquifer Denitrification: Is it a Zero-Order or First-Order Reaction?

    NASA Astrophysics Data System (ADS)

    Korom, S. F.

    2007-12-01

    Results from a network of 16 in situ mesocosms (ISMs) used to study aquifer denitrification at 5 sites in North Dakota and 4 sites in Minnesota (with 2 more installations planned for Iowa) are considered. At the Elk Valley aquifer (EVA) site in northeastern North Dakota, denitrification rates from six denitrification experiments were all better modeled as zero-order (0.16 +/- 0.05 mg nitrate-N/L/day), as determined by squared values of the linear correlation coefficient. Denitrification experiments at the other sites showed that denitrification was either below detection (< 0.01 mg nitrate-N/L/day) or was better modeled as a first-order reaction (0.00021/day to 0.0020/day), although squared values of the linear correlation coefficients for both rate models were nearly equal for some of the experiments. Not only were denitrification rates at the EVA site highest compared to the other sites in the ISM network, but sediment concentrations of electron donors at the EVA site were also greatest [ferrous iron about 0.3%, inorganic S (as pyrite) about 0.4%, organic C about 0.4%, weight basis]. These observations support the Michaelis- Menten model for reaction rates, which indicates that reaction rates will be zero-order when the substrate (electron donor) is abundant and first-order when the substrate availability is limited.

  8. [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.

  9. 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.

  10. The use of crab-shell chitin for biological denitrification: batch and column tests.

    PubMed

    Robinson-Lora, Mary Ann; Brennan, Rachel A

    2009-01-01

    Crab-shell chitin (SC-20) was evaluated for its ability to enhance biological denitrification in bench-scale tests. In the presence of SC-20, highly reducing conditions were generated, supporting both denitrification and sulfate reduction of aerated water. Rapid degradation of protein in SC-20 was observed to cause an initial high release of ammonium and carbon, while a slower, continuous release of calcium carbonate from the crab shell maintained the pH near 9 throughout the tests. In batch tests, denitrification rates of 2.4+/-0.2 mg N/L-d were obtained. Columns receiving a continuous nitrate load of 24.5 mg N/L-d sustained complete denitrification for an average of 149 d (250 pore volumes). The denitrification rates and longevity of SC-20 chitin are comparable to, or better than, those previously reported for other polymeric substrates. This, in addition to its particle size, non-swelling nature, and ease of delivery in slurry form make SC-20 an attractive electron donor source for groundwater bio-denitrification.

  11. 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.

  12. 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

  13. 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…

  14. 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…

  15. 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

  16. Complexity of images: experimental and computational estimates compared.

    PubMed

    Chikhman, Valeriy; Bondarko, Valeriya; Danilova, Marina; Goluzina, Anna; Shelepin, Yuri

    2012-01-01

    We tested whether visual complexity can be modeled through the use of parameters relevant to known mechanisms of visual processing. In psychophysical experiments observers ranked the complexity of two groups of stimuli: 15 unfamiliar Chinese hieroglyphs and 24 outline images of well-known common objects. To predict image complexity, we considered: (i) spatial characteristics of the images, (ii) spatial-frequency characteristics, (iii) a combination of spatial and Fourier properties, and (iv) the size of the image encoded as a JPEG file. For hieroglyphs the highest correlation was obtained when complexity was calculated as the product of the squared spatial-frequency median and the image area. This measure accounts for the larger number of lines, strokes, and local periodic patterns in the hieroglyphs. For outline objects the best predictor of the experimental data was complexity estimated as the number of turns in the image, as Attneave (1957 Journal of Experimental Psychology 53 221-227) obtained for his abstract outlined images. Other predictors of complexity gave significant but lower correlations with the experimental ranking. We conclude that our modeling measures can be used to estimate the complexity of visual images but for different classes of images different measures of complexity may be required.

  17. 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.

  18. 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.

  19. 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.

  20. Environmental and Microbial Features Affecting Denitrification and Anammox Hotspots in an Estuarine Ecosystem

    NASA Astrophysics Data System (ADS)

    Lisa, J.; Song, B.; Lefcheck, J. S.; Tobias, C. R.

    2016-02-01

    Biogeochemical hotspots are characterized as a few sites that exhibit extremely high reaction rates relative to surrounding area, and often account for a high percentage of the overall reaction rates in an ecosystem. Criteria for quantitatively identifying these sites have not been well established. Further, the underlying mechanisms of hotspots have been described in terms of environmental conditions, with little attention paid to the microbial community. The objectives of this study were to establish quantitative criteria to identify denitrification and anammox hotspots, and determine the underlying microbial and environmental factors responsible for elevated N2 production. We used 15N isotope pairing incubation experiments to measure denitrification and anammox rates in the New River Estuary, NC. Quantitative PCR assays of nitrous oxide reductase (nosZ Clades I and II) and hydrazine oxidoreductase (hzo) genes were conducted to estimate denitrifier and anammox abundance. Structural Equation Modeling (SEM) was used to elucidate complex causal relationships between environmental and biological variables. Denitrification hotspots, quantitatively defined as statistical outliers, accounted for 35.6% total denitrification while comprising only 7.3% of the sites. Anammox hotspots,10.6% of the sites, accounted for 60.9% of total anammox. SEM revealed increased sediment organics at lower salinities supported higher functional gene abundance, which in turn resulted in higher N2 production. Surprisingly, denitrification rates were significantly and positively correlated with nosZ Clade II gene abundance, after accounting for the non-significant contributions of the naturally more abundant nosZ Clade I, and other environmental covariates. This is the first time that a quantitative definition of biogeochemical hotspots was put forth and used to determine the importance of anammox and denitrification hotspots in estuarine nitrogen removal capacity. Despite the low area

  1. 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.

  2. 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

  3. Comparability Of Slosson And S-B Estimates Of Intelligence

    ERIC Educational Resources Information Center

    Ritter, David; And Others

    1973-01-01

    The Slosson Intelligence Test and the Stanford-Binet Intelligence Scale (Form L-M) were administered to 44 children. A comparison of measured IQs indicated that the Slosson overestimated IQ when compared with the Stanford-Binet, for 39 of the 44 children. The results also suggest that although a high degree of correlation was attained with the…

  4. Comparability Of Slosson And S-B Estimates Of Intelligence

    ERIC Educational Resources Information Center

    Ritter, David; And Others

    1973-01-01

    The Slosson Intelligence Test and the Stanford-Binet Intelligence Scale (Form L-M) were administered to 44 children. A comparison of measured IQs indicated that the Slosson overestimated IQ when compared with the Stanford-Binet, for 39 of the 44 children. The results also suggest that although a high degree of correlation was attained with the…

  5. Comparative estimate of volcanism intensity on continents and in oceans

    SciTech Connect

    Ronov, A.B.; Khain, V.E.; Balukhovskii, A.N.

    1980-12-01

    A quantitative estimate of the volume of volcanogenic rocks and the volcanism intensity during different stages in the Earth's development indicates that the total volume of the tholeiitic basalts of Layer II of the oceans exceeds by 20 times that of the synchronous late Mesozoic-Cenozoic volcanics of the continents and is almost 5 times greater than the volume of the volcanogenic rocks of the entire Phanerozoic sequence of the continents. The absolute maxima of volcanism, determined on the basis of the area and volume of the corresponding volcanics, belong to the Late Cretaceous and Miocene intervals. Changes in the volcanic eruption areas took place synchronously in the Pacific, Atlantic, and Indian Oceans. The volcanism intensity, expressed in the volume of its products in km/sup 3/ per m.y., increases in the oceans from Late Jurassic to Pliocene time. During the Riphean and Vendian intervals, the volcanism intensity on the continents remained at an extremely low level, then increased during early Paleozoic time, and underwent a marked jump, beginning in the Devonian Period. Since Late Jurassic time, the intensity of global volcanism increased unusually sharply and reached its culmination during Neogene time.

  6. Isotopic Expression of Soil Denitrification across Gradients in Nitrogen and Carbon Availability

    NASA Astrophysics Data System (ADS)

    Walker, R.; Houlton, B. Z.; Perakis, S. S.

    2016-12-01

    Denitrification removes biologically available nitrogen (N) from ecosystems, making it an important control over the biosphere's N balance, with implications for air quality, human health and climate change. Despite its importance, estimates of the global soil denitrification flux remain highly uncertain. Major challenges lie in directly measuring the gaseous by-products of denitrification and scaling this complex microbial processes in both space and time. Process-based models constrained by empirical isotopic evidence have emerged as a method to help overcome these challenges. These models use the terrestrial 15N budget, along with soil moisture and N input data, to quantify denitrification fluxes and its gaseous forms, including NO, N2O and N2. However, the robustness of this method is limited by incomplete understanding of isotopic expression of denitrification and how it varies across known controls, such as carbon (C) and nitrate (NO3) availability. Here, we present a quantitative assessment of the isotope effect expression of in situ soil denitrification across gradients in N and C concentrations. This experiment tests the hypothesis that isotopic expression of soil denitrification (a kinetic process) increases with NO3 availability (reaction substrate) and decreases with increasing availability of organic C (electron donor). To test the impact of NO3 availability on the isotope effect of denitrification, field incubations experiments were conducted across a natural soil N gradient, ranging from 0.11 to 0.69% N. Similarly, the impact of electron donor availability was tested by conducting field incubations across a natural soil C gradient ranging from 1.94 to 11.60%. Data show that in lower N sites, the percent of NO3 consumed during the incubation was higher, while C availability neither affected the fraction of NO3 consumed nor the rate of consumption. These findings suggest that greater NO3 concentrations allow for greater isotope expression of

  7. Discerning Between Water Column and Sedimentary Denitrification in the Santa Barbara Basin Using the Nitrogen Isotopes of Nitrate

    NASA Astrophysics Data System (ADS)

    Knapp, A. N.; Sigman, D. M.; van Geen, L.; McCorkle, D. C.; Brandes, J. A.; Thunell, R. C.

    2001-05-01

    Below its sill depth, the Santa Barbara Basin (SBB) is seasonally anoxic, making the basin suitable for denitrification in both the water column and the sediments. Deviations of nitrate and phosphate concentrations from Redfield ratios provide quantitative estimates of the nitrate consumed by denitrification in the SBB. However, there are no integrative constraints on whether denitrification occurs predominantly in the water column or in the sediments. Associated with a sharp increase in the nitrate deficit across the oxic/anoxic interface within the SBB, there is an increase in the d15N of water column nitrate, as would be expected from denitrification. However, given the size of the nitrate deficit, the increase of d15N of nitrate is much smaller than would be expected from the accepted intrinsic isotope effect of denitrification of 20-30 per mil, assuming a Rayleigh model for uptake. In situations where both transport and removal are important, the Rayleigh model provides only an approximation of the actual fractionation. However, model calculations suggest that transport within the water column cannot explain the observed d15N discrepancy in the SBB. Benthic lander studies of Puget Sound sediments have demonstrated that the isotope effect of sedimentary denitrification is negligible, due to the effects of substrate diffusion in sediment porewaters (Brandes and Devol, 1997). We present new porewater measurements from the Carolina slope in the North Atlantic that confirm this conclusion for other sedimentary environments. Thus, we infer that the small magnitude of the isotopic enrichment of SBB water column nitrate is due to the importance of denitrification in the sediments relative to the water column. Assuming that water column and sedimentary denitrification have isotope effects of 25 and 0 per mil, respectively, model calculations indicate that sedimentary denitrification accounts for more than 75% of the nitrate loss within the anoxic Santa Barbara Basin.

  8. Simultaneous measurement of denitrification and nitrogen fixation using isotope pairing with membrane inlet mass spectrometry analysis.

    PubMed

    An, S; Gardner, W S; Kana, T

    2001-03-01

    A method for estimating denitrification and nitrogen fixation simultaneously in coastal sediments was developed. An isotope-pairing technique was applied to dissolved gas measurements with a membrane inlet mass spectrometer (MIMS). The relative fluxes of three N(2) gas species ((28)N(2), (29)N(2), and (30)N(2)) were monitored during incubation experiments after the addition of (15)NO(3)(-). Formulas were developed to estimate the production (denitrification) and consumption (N(2) fixation) of N(2) gas from the fluxes of the different isotopic forms of N(2). Proportions of the three isotopic forms produced from (15)NO(3)(-) and (14)NO(3)(-) agreed with expectations in a sediment slurry incubation experiment designed to optimize conditions for denitrification. Nitrogen fixation rates from an algal mat measured with intact sediment cores ranged from 32 to 390 microg-atoms of N m(-2) h(-1). They were enhanced by light and organic matter enrichment. In this environment of high nitrogen fixation, low N(2) production rates due to denitrification could be separated from high N(2) consumption rates due to nitrogen fixation. Denitrification and nitrogen fixation rates were estimated in April 2000 on sediments from a Texas sea grass bed (Laguna Madre). Denitrification rates (average, 20 microg-atoms of N m(-2) h(-1)) were lower than nitrogen fixation rates (average, 60 microg-atoms of N m(-2) h(-1)). The developed method benefits from simple and accurate dissolved-gas measurement by the MIMS system. By adding the N(2) isotope capability, it was possible to do isotope-pairing experiments with the MIMS system.

  9. Simultaneous Measurement of Denitrification and Nitrogen Fixation Using Isotope Pairing with Membrane Inlet Mass Spectrometry Analysis†

    PubMed Central

    An, Soonmo; Gardner, Wayne S.; Kana, Todd

    2001-01-01

    A method for estimating denitrification and nitrogen fixation simultaneously in coastal sediments was developed. An isotope-pairing technique was applied to dissolved gas measurements with a membrane inlet mass spectrometer (MIMS). The relative fluxes of three N2 gas species (28N2, 29N2, and 30N2) were monitored during incubation experiments after the addition of 15NO3−. Formulas were developed to estimate the production (denitrification) and consumption (N2 fixation) of N2 gas from the fluxes of the different isotopic forms of N2. Proportions of the three isotopic forms produced from 15NO3− and 14NO3− agreed with expectations in a sediment slurry incubation experiment designed to optimize conditions for denitrification. Nitrogen fixation rates from an algal mat measured with intact sediment cores ranged from 32 to 390 μg-atoms of N m−2 h−1. They were enhanced by light and organic matter enrichment. In this environment of high nitrogen fixation, low N2 production rates due to denitrification could be separated from high N2 consumption rates due to nitrogen fixation. Denitrification and nitrogen fixation rates were estimated in April 2000 on sediments from a Texas sea grass bed (Laguna Madre). Denitrification rates (average, 20 μg-atoms of N m−2 h−1) were lower than nitrogen fixation rates (average, 60 μg-atoms of N m−2 h−1). The developed method benefits from simple and accurate dissolved-gas measurement by the MIMS system. By adding the N2 isotope capability, it was possible to do isotope-pairing experiments with the MIMS system. PMID:11229907

  10. Method to identify potential phosphorus rate-limiting conditions in post-denitrification biofilm reactors within systems designed for simultaneous low-level effluent nitrogen and phosphorus concentrations.

    PubMed

    Boltz, Joshua P; Morgenroth, Eberhard; Daigger, Glen T; deBarbadillo, Christine; Murthy, Sudhir; Sørensen, Kim H; Stinson, Beverly

    2012-12-01

    Water-quality standards requiring simultaneous low level effluent N and P concentrations are increasingly common in Europe and the United States of America. Moving bed biofilm reactors (MBBRs) and biologically active filters (BAFs) have been used as post-denitrification biofilm reactors in processes designed and operated for this purpose (Boltz et al., 2010a). There is a paucity of information describing systematic design and operational protocols that will minimize the potential for phosphorus rate-limited conditions as well as a lack of information describing the interaction between these post-denitrification biofilm reactors and unit processes that substantially alter phosphorus speciation (e.g., chemically enhanced clarification). In this paper, a simple mathematical model for estimating the threshold below which P becomes rate-limiting, and the model is presented and evaluated by comparing its predictions with operational data from post-denitrification MBBRs and BAFs. Ortho-phosphorus (PO(4)-P), which is the dissolved reactive component of total phosphorus, was a primary indicator of P rate-limiting conditions in the evaluated post-denitrification biofilm reactors. The threshold below which PO(4)-P becomes the rate-limiting substrate is defined: S(PO4-P):S(NOx-N) = 0.0086 g P/g N and S(PO4-P):S(M) = 0.0013 g P/g COD. Additional analyses indicate J(NOx-N)(avg) =0.48 g/m2/d when S(PO4-P):S(NOx-N) > 0.0086, and J(NOx-N)(avg) = 0.06 g/m2/d when S(PO4-P):S(NOx-N) < 0.0086. Effluent nitrate-nitrogen plus nitrite-nitrogen concentration (S(NOx-N)) from the evaluated post-denitrification biofilm reactors began to rapidly increase when S(PO4-P):S(NOx-N) was 0.01, approximately (consistent with the rate-limitation threshold of S(PO4-P):S(NOx-N) < 0.0086 predicted by the mathematical model described in this paper). Depending on the processes used at a given WWTP, optimizing chemically enhanced clarification to increase the amount of PO(4)-P that remains in the clarifiers

  11. 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.

  12. Relative importance of time, land use and lithology on determining aquifer-scale denitrification

    NASA Astrophysics Data System (ADS)

    Kolbe, Tamara; de Dreuzy, Jean-Raynald; Abbott, Benjamin W.; Marçais, Jean; Babey, Tristan; Thomas, Zahra; Peiffer, Stefan; Aquilina, Luc; Labasque, Thierry; Laverman, Anniet; Fleckenstein, Jan; Boulvais, Philippe; Pinay, Gilles

    2017-04-01

    Unconfined shallow aquifers are commonly contaminated by nitrate in agricultural regions, because of excess fertilizer application over the last decades. Watershed studies have indicated that 1) changes in agricultural practices have caused changes in nitrate input over time, 2) denitrification occurs in localized hotspots within the aquifer, and 3) heterogeneous groundwater flow circulation has led to strong nitrate gradients in aquifers that are not yet well understood. In this study we investigated the respective influence of land use, groundwater transit time distribution, and hotspot distribution on groundwater denitrification with a particular interest on how a detailed understanding of transit time distributions could be used to upscale the point denitrification measurements to the aquifer-scale. We measured CFC-based groundwater age, oxygen, nitrate, and dinitrogen gas excess in 16 agricultural wells of an unconfined crystalline aquifer in Brittany, France. Groundwater age data was used to calibrate a mechanistic groundwater flow model of the study site. Historical nitrate inputs were reconstructed by using measured nitrate concentrations, dinitrogen gas excess and transit time distributions of the wells. Field data showed large differences in denitrification activity among wells, strongly associated with differences in transit time distribution. This suggests that knowing groundwater flow dynamics and consequent transit time distributions at the catchment-scale could be used to estimate the overall denitrification capacity of agricultural aquifers.

  13. Comparison of heterotrophic and autotrophic denitrification processes for treating nitrate-contaminated surface water.

    PubMed

    Wang, Zheng; Fei, Xiang; He, Shengbing; Huang, Jungchen; Zhou, Weili

    2017-02-01

    The goal of this study was to compare the nitrogen removal rate, effluent algal growth potential (AGP), nitrous oxide (N2O) emissions and global warming potential (GWP) between two laboratory-scale bioreactors: the autotrophic denitrification biofilter (ADBF) and heterotrophic denitrification biofilter (HDBF) for treating nitrate-contaminated surface water. The comparative study of nitrogen removal rate between ADBF and HDBF was conducted by a long-term experiment, and the comparative study of the effluent AGP, N2O emissions and GWP between ADBF and HDBF were carried out by the corresponding batch tests. The results show that the heterotrophic and autotrophic denitrification rates were close to each other. Besides, the AGP of the ADBF effluent was 2.08 times lower than that of the HDBF effluent, while the N2O concentration in off-gas emitted from HDBF was 6-8 times higher than that from ADBF. The higher N2O-N emission rate of HDBF was mainly responsible for the higher GWP of HDBF than that of ADBF. Furthermore, with a novel light-weight filtration media (NLWFM) for filtration, the autotrophic denitrification (ADN) process combined with biofilter process would be the optimal denitrification process for nitrogen removal from nitrate-contaminated surface water. The study also provided a systematic method for evaluation of biological nitrogen removal (BNR) process. Copyright © 2016. Published by Elsevier B.V.

  14. 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

  15. 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, ...

  16. 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, ...

  17. Understanding Nitrifier Denitrification: How far are we?

    NASA Astrophysics Data System (ADS)

    Wrage-Mönnig, N.

    2014-12-01

    Nitrifier denitrification is the oxidation of ammonia (NH3) via hydroxylamine (NH2OH) to nitrite (NO2-) and subsequent reduction of NO2- via nitric oxide (NO) to the greenhouse gas nitrous oxide (N2O) and possibly to dinitrogen (N2) by autotrophic nitrifiers. Especially in recent years, a lot of research has been conducted on this pathway. Under some conditions, it might dominate the N2O production from soils. Methods for studying nitrifier denitrification include selective inhibition, stable isotope and isotopomer methods, molecular and modelling approaches. They are applied from pure culture and pot studies to the field scale, trying to improve our knowledge of the conditions and factors controlling nitrifier denitrification. But how far are we? What have we learned so far and what remains to be discovered? With this contribution, I am trying to give an update of our understanding of this less well-known but important pathway.

  18. 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.

  19. Denitrification in sediments as a major nitrogen sink in the Baltic Sea: an extrapolation using sediment characteristics

    NASA Astrophysics Data System (ADS)

    Deutsch, B.; Forster, S.; Wilhelm, M.; Dippner, J. W.; Voss, M.

    2010-04-01

    Rates of denitrification in sediments were measured with the isotope pairing technique at different sites in the southern and central Baltic Sea. They varied between 0.5 μmol m-2 h-1 in sands and 28.7 μmol m-2 h-1 in muddy sediments and showed a good correlation to the organic carbon contents of the surface sediments. N-removal rates via sedimentary denitrification were estimated for the entire Baltic Sea calculating sediment specific denitrification rates and interpolating them to the whole Baltic Sea area. Another approach was carried out by using the relationship between the organic carbon content and the rate of denitrification. For the entire Baltic Sea the N-removal by denitrification in sediments varied between 426-652 kt N a-1, which is around 48-73% of the external N inputs delivered via rivers, coastal point sources and atmospheric deposition. Moreover, an expansion of the anoxic bottom areas was considered under the assumption of a rising oxycline from 100 to 80 m water depth. This leads to an increase of the area with anoxic conditions and an overall decrease in sedimentary denitrification by 14%. Overall we can show here that this type of data extrapolation is a powerful tool to estimate the nitrogen losses for a whole coastal sea and may be applicable to other coastal regions and enclosed seas, too.

  20. Denitrification in sediments as a major nitrogen sink in the Baltic Sea: an extrapolation using sediment characteristics

    NASA Astrophysics Data System (ADS)

    Deutsch, B.; Forster, S.; Wilhelm, M.; Dippner, J. W.; Voss, M.

    2010-10-01

    Rates of denitrification in sediments were measured with the isotope pairing technique at different sites in the southern and central Baltic Sea. The rates varied between 0.5 μmol N m-2 h-1 in sands and 28.7 μmol N m-2 h-1 in muddy sediments and showed a good correlation to the organic carbon contents of the surface sediments. N-removal rates via sedimentary denitrification were estimated for the entire Baltic Sea calculating sediment specific denitrification rates and interpolating them to the whole Baltic Sea area. Another approach was carried out by using the relationship between the organic carbon content and the rate of denitrification. The N-removal by denitrification in sediments varied between 426-652 kt N a-1, which is around 48-73% of the external N inputs delivered via rivers, coastal point sources, and atmospheric deposition. Moreover, an expansion of the anoxic bottom areas was considered under the assumption of a rising oxycline from 100 to 80 m water depth. This leads to an increase of the area with anoxic conditions and an overall decrease in sedimentary denitrification by 14%. Overall, we show here that this type of data extrapolation is a powerful tool to estimate the nitrogen losses for a whole coastal sea and may be applicable to other coastal regions and enclosed seas.

  1. 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

  2. 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.

  3. 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.

  4. Enhanced nitrogen loss from rivers through coupled nitrification-denitrification caused by suspended sediment.

    PubMed

    Xia, Xinghui; Liu, Ting; Yang, Zhifeng; Michalski, Greg; Liu, Shaoda; Jia, Zhimei; Zhang, Sibo

    2017-02-01

    Present-day estimations of global nitrogen loss (N-loss) are underestimated. Commonly, N-loss from rivers is thought to be caused by denitrification only in bed-sediments. However, coupled nitrification-denitrification occurring in overlying water with suspended sediments (SPS) where oxic and anoxic/low oxygen zones may coexist is ignored for N-loss in rivers. Here the Yellow and Yangtze Rivers were taken as examples to investigate the effect of SPS, which exists in many rivers of the world, on N loss through coupled nitrification-denitrification with nitrogen stable ((15)N) isotopic tracer simulation experiments and in-situ investigation. The results showed even when SPS was surrounded by oxic waters, there were redox conditions that transitioned from an oxic surface layer to anoxic layer near the particle center, enabling coupled nitrification-denitrification to occur around SPS. The production rate of (15)N2 from (15)NH4(+)-N (R15N2-production) increased with increasing SPS concentration ([SPS]) as a power function (R15N2-production=a·[SPS](b)) for both the SPS-water and bed sediment-SPS-water systems. The power-functional increase of nitrifying and denitrifying bacteria population with [SPS] accounted for the enhanced coupled nitrification-denitrification rate in overlying water. SPS also accelerated denitrification in bed-sediment due to increased NO3(-) concentration caused by SPS-mediated nitrification. For these two rivers, 1gL(-1) SPS will lead to N-loss enhancement by approximately 25-120%, and the enhancement increased with organic carbon content of SPS. Thus, we conclude that SPS in overlying water is a hot spot for nitrogen loss in river systems and current estimates of in-stream N-loss are underestimated without consideration of SPS; this may partially compensate for the current imbalance of global nitrogen inputs and sinks.

  5. 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.

  6. 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.

  7. Global trends in terrestrial denitrification and N2O emissions for the period 1900-2050

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Estimates of global terrestrial denitrification and nitrous oxide (N2O) emission are presented for the period 1900 to 2000 and scenarios for the period 2000-2050 based on the Millennium Ecosystem Assessment. Soil nitrogen (N) budgets are used in a global distributed flow-path model with 0.5 by 0.5 degree resolution, representing denitrification and N2O emissions from soils, groundwater and riparian zones. Total agricultural and natural N inputs from N fertilizers, animal manure, biological N fixation and N deposition increased from ~155 to ~345 Tg of N yr-1 (Tg = teragram; 1 Tg = 1012 g) between 1900 and 2000; depending on the scenario, inputs will further increase to ~408 to ~510 Tg of N yr-1 in 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 per year in 2050, depending on the scenario. Estimates indicate that 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 of N yr-1. The major part (70%) of global N2 and N2O-N (92%) production occurred in soils in 2000. A further increase of denitrification is foreseen to 142 Tg N2-N and 16 Tg of N2O-N yr-1 in 2050. Our results indicate that riparian buffer zones are an important source of N2O. 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. The total (temporary) storage in deep groundwater between 1900 and 2000 amounts to around 376 Tg of N. Despite the removal of N through denitrification, the N flow from diffuse sources on land to rivers increased from 38 to 65 Tg of N yr-1 between 1900 and 2000, with a further increase of up to 84 Tg of N yr-1 in 2050. The major causes of uncertainty in our estimates are the difficulties associated with measurements and models of denitrification. With the projected increase

  8. Similar temperature responses suggest future climate warming will not alter partitioning between denitrification and anammox in temperate marine sediments.

    PubMed

    Brin, Lindsay D; Giblin, Anne E; Rich, Jeremy J

    2017-01-01

    Removal of biologically available nitrogen (N) by the microbially mediated processes denitrification and anaerobic ammonium oxidation (anammox) affects ecosystem N availability. Although few studies have examined temperature responses of denitrification and anammox, previous work suggests that denitrification could become more important than anammox in response to climate warming. To test this hypothesis, we determined whether temperature responses of denitrification and anammox differed in shelf and estuarine sediments from coastal Rhode Island over a seasonal cycle. The influence of temperature and organic C availability was further assessed in a 12-week laboratory microcosm experiment. Temperature responses, as characterized by thermal optima (Topt ) and apparent activation energy (Ea ), were determined by measuring potential rates of denitrification and anammox at 31 discrete temperatures ranging from 3 to 59 °C. With a few exceptions, Topt and Ea of denitrification and anammox did not differ in Rhode Island sediments over the seasonal cycle. In microcosm sediments, Ea  was somewhat lower for anammox compared to denitrification across all treatments. However, Topt  did not differ between processes, and neither Ea  nor Topt  changed with warming or carbon addition. Thus, the two processes behaved similarly in terms of temperature responses, and these responses were not influenced by warming. This led us to reject the hypothesis that anammox is more cold-adapted than denitrification in our study system. Overall, our study suggests that temperature responses of both processes can be accurately modeled for temperate regions in the future using a single set of parameters, which are likely not to change over the next century as a result of predicted climate warming. We further conclude that climate warming will not directly alter the partitioning of N flow through anammox and denitrification. © 2016 John Wiley & Sons Ltd.

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

    PubMed

    Panno, Samuel V; Hackley, Keith C; Kelly, Walton R; Hwang, Hue-Hwa

    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 NO3- 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 NO3- 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 delta18O and delta15N also indicate that, depending on sample location and season, NO3- in the river and tile drains has undergone significant denitrification, ranging from about 0 to 55%. The majority of the denitrification appears to have occurred before discharge into the Mississippi River.

  10. 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.

  11. Can Membrane Inlet Mass Spectrometer Measure Short-term Denitrification Enzyme Activity and Denitrification Potentials of Soils?

    NASA Astrophysics Data System (ADS)

    Khalil, M. I.; Richards, K. G.

    2009-04-01

    Denitrifier population size and potential activity combined with the relevant environmental factors regulate the rates of denitrification in terrestrial and aquatic ecosystems. Due to the high atmospheric background of di-nitrogen (N2), denitrification enzyme activity (DEA) in soils is traditionally measured using the acetylene block or stable isotope techniques under non-limiting substrates and anaerobic/saturated conditions for periods from a few hours to several days so as to estimate denitrification potential (DP). This research investigated the estimation of DEA and DP by quantifying the N2/Ar ratio changes in waters/sediments using membrane inlet mass spectrometry (MIMS). Two experiments were conducted with soils of A, B and C horizons collected from grazed grassland to obtain optimal NO3- and available carbon (C) rates. In experiment 1, 30 g soil (oven dry basis) followed by helium-flushed deionized water was taken in triplicate 160 mL glass bottles and sealed with rubber stoppers without any air entrapments. Then N as potassium nitrate (0 to 120 mg NO3 - N kg-1 soil) and readily available C as glucose (0 to 240 mg glucose-C) plus 30 mg NO3 - N, kg-1 soil were amended. Laboratory incubation was performed in the dark at 21oC under water to reduce the risk of N2 contamination. After six hours, the treated water samples were transferred into 12 mL exetainers and kept under water at 4oC before analysis using MIMS. The N2/Ar ratios, representing DEA, varied between soil horizons and declined with decreasing soil depths. The maximum peak for N2/Ar ratios were observed with the 30 mg NO3 - N kg-1 soil in all soil horizons and coupled with the 60 mg glucose-C kg-1 soil for C horizon, and 120 mg glucose-C kg-1 for A and B horizons. Experiment 2 was conducted to assess simulated unsaturated and saturated subsoil (C horizon) denitrification capacity (NO3 - Nonly amendment), and DP (both C and N amendment) using the same methodology as experiment 1 and incubated for 3

  12. 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

  13. Denitrification in Agriculturally Influenced Coastal Plain Streams

    NASA Astrophysics Data System (ADS)

    McMillan, S. K.; Ensign, S. H.; Thompson, S. P.; Paerl, H. W.; Piehler, M. F.

    2005-05-01

    Agricultural runoff from coastal plain watersheds contributes nitrogen to downstream estuarine and coastal waters. Nitrogen fuels eutrophication, which has resulted in increased algal biomass, hypoxia, and fish kills in the Neuse River Estuary, North Carolina. Denitrification is the sole mechanism of permanent nitrogen removal along the riverine to estuarine continuum, but its contribution to nitrogen attenuation in this system is not well understood. Denitrification rates measured seasonally in stream bed sediments were variable but showed a distinct spring maximum, which was likely associated with rising temperatures and added nitrogen from fertilizer application (0-150 umol N m-2 h-1 during the summer, fall and winter and 150-300 umol N m-2 h-1 in the spring). Reach-scale uptake experiments showed the potential for 65-98% retention of the watershed DIN load in ephemeral drainage ditches. Results indicated that nitrogen retention was high despite low hyporheic exchange that is typically associated with channelized streams with low gradients, straight channels and homogenous stream bed sediments. Comparison of direct denitrification rate measurements to reach scale uptake rates and a watershed mass balance showed considerable potential for nitrogen removal via denitrification in agricultural stream sediments.

  14. Denitrification in a Sand and Gravel Aquifer

    PubMed Central

    Smith, Richard L.; Duff, John H.

    1988-01-01

    Denitrification was assayed by the acetylene blockage technique in slurried core material obtained from a freshwater sand and gravel aquifer. The aquifer, which has been contaminated with treated sewage for more than 50 years, had a contaminant plume greater than 3.5-km long. Near the contaminant source, groundwater nitrate concentrations were greater than 1 mM, whereas 0.25 km downgradient the central portion of the contaminant plume was anoxic and contained no detectable nitrate. Samples were obtained along the longitudinal axis of the plume (0 to 0.25 km) at several depths from four sites. Denitrification was evident at in situ nitrate concentrations at all sites tested; rates ranged from 2.3 to 260 pmol of N2O produced (g of wet sediment)−1 h−1. Rates were highest nearest the contaminant source and decreased with increasing distance downgradient. Denitrification was the predominant nitrate-reducing activity; no evidence was found for nitrate reduction to ammonium at any site. Denitrifying activity was carbon limited and not nitrate limited, except when the ambient nitrate level was less than the detection limit, in which case, even when amended with high concentrations of glucose and nitrate, the capacity to denitrify on a short-term basis was lacking. These results demonstrate that denitrification can occur in groundwater systems and, thereby, serve as a mechanism for nitrate removal from groundwater. PMID:16347621

  15. Modeling nitrate removal in a denitrification bed

    USDA-ARS?s Scientific Manuscript database

    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...

  16. 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.

  17. Biological denitrification in microbial fuel cells.

    PubMed

    Clauwaert, Peter; Rabaey, Korneel; Aelterman, Peter; de Schamphelaire, Liesje; Pham, The Hai; Boeckx, Pascal; Boon, Nico; Verstraete, Willy

    2007-05-01

    Microbial fuel cells (MFCs) that remove carbon as well as nitrogen compounds out of wastewater are of special interest for practice. We developed a MFC in which microorganisms in the cathode performed a complete denitrification by using electrons supplied by microorganisms oxidizing acetate in the anode. The MFC with a cation exchange membrane was designed as a tubular reactor with an internal cathode and was able to remove up to 0.146 kg NO(3-)-N m(-3) net cathodic compartment (NCC) d(-1) (0.080 kg NO(3-)-N m(-3) total cathodic compartment d(-1) (TCC)) at a current of 58 A m(-3) NCC (32 A m(-3) TCC) and a cell voltage of 0.075 V. The highest power output in the denitrification system was 8 W m(-3) NCC (4 W m(-3) TCC) with a cell voltage of 0.214 V and a current of 35 A m(-3) NCC. The denitrification rate and the power production was limited bythe cathodic microorganisms, which only denitrified significantly at a cathodic electrode potential below 0 V versus standard hydrogen electrode (SHE). This is, to our knowledge, the first study in which a MFC has both a biological anode and cathode performing simultaneous removal of an organic substrate, power production, and complete denitrification without relying on H2-formation or external added power.

  18. Nitric oxide in denitrification - an elusive signal molecule emitted from soil

    NASA Astrophysics Data System (ADS)

    Bakken, L. R.; Frostegard, A.

    2010-12-01

    Soils emit variable amounts of NO and N2O, with environmental consequences (atmosphere chemistry and global warming). Nitrification was for some time considered the main source of NO emission, but several investigations have indicated that denitrification may be a potent source as well. However, strong emission of NO from denitrifying organisms is in some conflict with common understanding of the role of NO in the regulation of denitrification, as based on paradigm model strains. NO appears to be an important signal molecule for denitrifying organisms by exerting a positive feedback on the expression of the genes coding for denitrification. On the other hand, a careful control of the NO concentrations at nanomolar concentrations has long been considered an essential fitness character for denitrifying organisms, since micromolar concentrations of NO is toxic to many organisms. For the same reason, organisms lacking genes encoding NO reductase (NOR) have been considered unfit for denitrification. This view is challenged by isolation of organisms whose primary product of denitrification is NO, either because they lack the genes for NO reductase, or because their synthesis of the denitrification proteome is extremely unbalanced, resulting in transient NO accumulation to micromolar concentrations when grown in pure culture. Such paralyzing NO concentrations are probably never reached in natural environments, however, due to diffusion and NO-absorption by adjacent organisms, be it by NOR or other NO scavenging enzymes. Hypothetically, the production of NO by denitrifying organisms may be an advantage by fending off nearby competitors. We have embarked on a comparative study of denitrification phenotypes regarding their denitrification gene expression and control of NO and N2O concentrations in response to anoxic spells. This includes model strains (Paracoccus denitrificans and Agrobacterium tumefaciens) and recently isolated strains within several genera. Some are found

  19. 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.

  20. 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.

  1. Enhanced Denitrification in Roadside Ditches with Bioreactors

    NASA Astrophysics Data System (ADS)

    Pluer, W.; Schneider, R.; Walter, M. T.

    2016-12-01

    Nitrate (NO3) pollution remains a water quality problem in agriculture-dominated watersheds despite decades of research and concerted efforts. Excess NO3 causes eutrophication in estuarine and marine ecosystems far downstream of the pollution source. Denitrification reduces NO3 to inert dinitrogen gas; this process occurs naturally in saturated areas of the landscape but this rate cannot keep up with the runoff rate due to fertilizer and manure applications. Researchers developed denitrifying bioreactors as a solution to encourage denitrification at the field level. Denitrifying bioreactors remove NO3 at a significantly higher rate (>2 g N m-2 d-1) than natural systems such as wetlands (<0.5 g N m-2 d-1). Most current designs of denitrifying bioreactors necessitate connection with tile drainage as the inflow source of water and NO3. It also requires a portion of farmland (typically <1% of field area is needed) which farmers can be reluctant to relinquish. Meanwhile, road ditches commonly run along agricultural fields, channeling runoff and NO3 to surface water. Because the ditches are designed to avoid flooding, they channel water rapidly and minimize time and contact with soil microbes for denitrification (denitrification rates in ditches are typically <0.1 g N m-2 d-1). Modified denitrifying bioreactors placed in road ditches could provide high NO3 removal in already marginal land, especially at baseflow conditions. A pilot study of this shows instantaneous NO3 removal rates up to 110 g N m-2 d-1 in the first year. Continued results similar to this pilot study and wider application could significantly increase ditch denitrification and help mitigate NO3 pollution.

  2. Experiments in In-Situ Aquifer Denitrification

    NASA Astrophysics Data System (ADS)

    Khan, I. A.; Spalding, R. F.

    2001-05-01

    During the past five years, denitrification experiments have been conducted in sand and gravel aquifers. Successive experiments have provided data showing both pitfalls and successes in designing sustainable injection/extraction systems for ground water denitrification. Testing has evolved from simple one-well to eight-well injection systems, commonly referred as Daisy systems. Aquifer profiles of the performance of denitrification were determined by multilevel sampling in two-foot intervals within the denitrification zone. Continuous and pulsed injection of organic carbon were tested, and in both cases the 40 mg NO3-N L-1 was reduced to below the detection limit (< 0.1 mg NO3-N L-1). Under continuous injection, accumulation of bacterial material in the vicinity of the injection well resulted in injection well clogging within 10 days. Using a dipole tool developed in the Water Sciences Laboratory, periodic cleaning was accomplished by circulating a cleaning solution (5% H2O2 and 0.02% NaOCl) in the injection well and adjacent ground water. Pulse injections, in which the carbon is separated from the nitrate, successfully alleviated the proliferation of bacterial accumulations without adversely affecting the performance of the denitrification process. Given that ethanol favored enhanced bacterial growth and increased the potential for biofouling of the equipment, acetate became the preferred carbon amendment. About 45% of the nitrate was denitrified before interception in the production well during a three-month pulsed injection experiment using the full eight-well Daisy design. Draw down of nondenitrified water from the upper two-thirds of the aquifer supplied nitrate to the production well and thus limited system performance.

  3. 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. Copyright © 2011 Elsevier Ltd. All rights reserved.

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

    USGS Publications Warehouse

    Smith, Lesley 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

  5. 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

  6. Modeling nitrous oxide production during biological nitrogen removal via nitrification and denitrification: extensions to the general ASM models.

    PubMed

    Ni, Bing-Jie; Ruscalleda, Maël; Pellicer-Nàcher, Carles; Smets, Barth F

    2011-09-15

    Nitrous oxide (N(2)O) can be formed during biological nitrogen (N) removal processes. In this work, a mathematical model is developed that describes N(2)O production and consumption during activated sludge nitrification and denitrification. The well-known ASM process models are extended to capture N(2)O dynamics during both nitrification and denitrification in biological N removal. Six additional processes and three additional reactants, all involved in known biochemical reactions, have been added. The validity and applicability of the model is demonstrated by comparing simulations with experimental data on N(2)O production from four different mixed culture nitrification and denitrification reactor study reports. Modeling results confirm that hydroxylamine oxidation by ammonium oxidizers (AOB) occurs 10 times slower when NO(2)(-) participates as final electron acceptor compared to the oxic pathway. Among the four denitrification steps, the last one (N(2)O reduction to N(2)) seems to be inhibited first when O(2) is present. Overall, N(2)O production can account for 0.1-25% of the consumed N in different nitrification and denitrification systems, which can be well simulated by the proposed model. In conclusion, we provide a modeling structure, which adequately captures N(2)O dynamics in autotrophic nitrification and heterotrophic denitrification driven biological N removal processes and which can form the basis for ongoing refinements.

  7. Performance and microbial communities of completely autotrophic denitrification in a bioelectrochemically-assisted constructed wetland system for nitrate removal.

    PubMed

    Xu, Dan; Xiao, Enrong; Xu, Peng; Zhou, Yin; He, Feng; Zhou, Qiaohong; Xu, Dong; Wu, Zhenbin

    2017-03-01

    A bioelectrochemically-assisted constructed wetland (BECW) system was used to treat nitrate-contaminated wastewater without organic carbon source. The denitrification performance and microbial community composition of a BECW in closed-circuit mode (BECW-C) was compared to a BECW in open-circuit mode (BECW-O). The highest denitrification efficiency (78.92±3.12%) was obtained in the BECW-C with an applied current of 15mA. No nitrite accumulation was observed during the autotrophic denitrification process in the BECW-C. The significantly higher denitrification efficiency of the BECW-C compared to the BECW-O suggested enhanced denitrification due to in situ generation of hydrogen. The bacterial communities in the anode, cathode and rhizosphere regions collected from the BECW-C (with 10 or 15mA) and the BECW-O were characterized using 16S rRNA pyrosequencing technology, which revealed different microbial community structures among the treatments. The results also indicated that Thiohalophilus and Clostridium sensu stricto might be responsible for autotrophic denitrification in the BECW-C. Copyright © 2016 Elsevier Ltd. All rights reserved.

  8. Genetic basis for denitrification in Ensifer meliloti.

    PubMed

    Torres, Maria J; Rubia, Maria I; de la Peña, Teodoro Coba; Pueyo, José J; Bedmar, Eulogio J; Delgado, María J

    2014-06-02

    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. 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. 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 demonstrated. The inability of E

  9. 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

  10. 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.

  11. Achieving comparable uncertainty estimates with Kalman filters or linear smoothers for bathymetry data

    NASA Astrophysics Data System (ADS)

    Bourgeois, Brian S.; Elmore, Paul A.; Avera, William E.; Zambo, Samantha J.

    2016-07-01

    This paper examines and contrasts two estimation methods, Kalman filtering and linear smoothing, for creating interpolated data products from bathymetry measurements. Using targeted examples, we demonstrate previously obscured behavior showing the dependence of linear smoothers on the spatial arrangement of the measurements, yielding markedly different estimation results than the Kalman filter. For bathymetry data, we have modified the variance estimates from both the Kalman filter and linear smoothers to obtain comparable estimators for dense data. These comparable estimators produce uncertainty estimates that have statistically insignificant differences via hypothesis testing. Achieving comparable estimation is accomplished by applying the "propagated uncertainty" concept and a numerical realization of Tobler's principle to the measurement data prior to the computation of the estimate. We show new mathematical derivations for these modifications. In addition, we show test results with (a) synthetic data and (b) gridded bathymetry in the area of the Scripps and La Jolla Canyons. Our tenfold cross-validation for case (b) shows that the modified equations create comparable uncertainty for both gridding algorithms with null hypothesis acceptance rates of greater than 99.95% of the data points. In contrast, bilinear interpolation has 10 times the amount of rejection. We then discuss how the uncertainty estimators are, in principle, applicable to interpolate geophysical data other than bathymetry.

  12. Biological denitrification of brines from membrane treatment processes using an upflow sludge blanket (USB) reactor.

    PubMed

    Beliavski, M; Meerovich, I; Tarre, S; Green, M

    2010-01-01

    This paper investigates denitrification of brines originating from membrane treatment of groundwater in an upflow sludge blanket (USB) reactor, a biofilm reactor without carrier. A simulated brine wastewater was prepared from tap water and contained a nitrate concentration of 125 mg/l as N and a total salt concentration of about 1%. In order to select for a suitable energy source for denitrification, two electron donors were compared: one promoting precipitation of calcium compounds (ethanol), while the other (acetic acid), no precipitation was expected. After extended operation to reach steady state, the sludge from the two reactors showed very different mineral contents. The VSS/TSS ratio in the ethanol fed reactor was 0.2, i.e., 80% mineral content, while the VSS/TSS ratio in the acetic acid fed reactor was 0.9, i.e., 10% mineral content. In spite of the low mineral content, the sludge from the acetic acid fed reactor showed remarkably excellent granulation and settling characteristics. Although the denitrification performance of the acetic acid fed reactor was similar to that of the ethanol fed reactor, there was a huge difference in the sludge production due to mineral precipitation, with the corresponding negative aspects including increased costs of sludge treatment and disposal and moreover, instability and difficulties in reactor operation (channeling). These arguments make acetic acid a much more suitable candidate for brine denitrification, despite previous findings observed in groundwater denitrification regarding the essential role of a relatively high sludge mineral fraction for stable and effective USB reactor operation. Based on a comparison between two denitrification reactors with and without salt addition and using acetic acid as the electron donor, it was concluded that the reason for the excellent sludge settling characteristics found in the acetic acid fed reactor is the positive effects of higher salinity on granular sludge formation.

  13. Potential sediment denitrification rates in estuaries of northern Gulf of Mexico

    SciTech Connect

    Flemer, D.A.; Lores, E.M.; Bundrick, C.M.

    1998-07-01

    The three-season average of sediment potential denitrification rates (PDRs) (i.e., NO{sub 3}{sup {minus}} saturated; acetylene blockage method) for five study areas within urban bayous and bays in the Pensacola Bay area, Florida, ranged between 43 and 223 nmol of N g{sup {minus}1} h{sup {minus}1}. Average PDRs extrapolated to a unit area basis approximated 500 to 1000 {micro}mol of N m{sup {minus}2} h{sup {minus}1} that are relatively high values but comparable to those where conditions for denitrification are favorable. A regression model, based on a larger number of measured environmental factors for the spring than fall and winter indicated that NO{sub 2}{sup {minus}} + NO{sub 3}{sup {minus}} concentrations explained most of the total variability (R{sup 2}:27%; P < 0.003) in PDRs. The NO{sub 2}{sup {minus}} + NO{sub 3}{sup {minus}} concentrations were also predictive of PDRs (R{sup 2} ranged from 0.56--0.98; all P-values <0.05) on four separate occasions for comparisons made within five study areas and three seasons. Sediment trace metal concentrations (e.g., Ni), based on published values, were high enough to cause reduction in PDRs through direct toxicity to denitrifiers at several stations. Sediment metals toxicities, based on published sediment quality guidelines, could occasionally cause a reduction in macrobenthic infaunal bioturbation and irrigation. Such a reduction could attenuate the flux of dissolved oxygen into sediments and cause a reduction in denitrification rates by limiting the coupled processes of nitrification and denitrification. Also, a reduction in the flux of NO{sub 2}{sup {minus}} or NO{sub 3}{sup {minus}}, a substrate for denitrification, into sediments can directly limit denitrification rates.

  14. 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

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

    PubMed

    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.

  16. 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

  17. Topographic and physicochemical controls on soil denitrification potential in prior converted croplands located on the Delmarva Peninsula, USA

    NASA Astrophysics Data System (ADS)

    Li, X.; Mccarty, G.; Lang, M. W.; Ducey, T.; Hunt, P.; Miller, J.

    2016-12-01

    Topography and soil physiochemical characteristics exert substantial controls on denitrification in agricultural lands. In order to depict these controls at a landscape scale for decision support applications, metrics (i.e., proxies) must be developed based on commonly available geospatial data. In this study, we analyzed the combined effects of eleven topography and soil physiochemical factors, including three topographic attributes (relief, topographic wetness index, and positive openness), two soil texture indices (sand and clay), and six soil properties (soil moisture, pH, electrical conductivity, SOC, TN, and C:N ratio), on soil denitrification potential in three actively farmed crop fields that were converted from forested wetlands before 1986 (i.e., prior converted croplands). Denitrification potential was measured using denitrification enzyme activity (DEA) assays, which employed the acetylene inhibition method under two treatments - a non-nitrate and carbon limiting treatment to measure potential denitrification and a control treatment to measure the capacity for denitrification without soil amendment. Nitrate and carbon addition led to a doubling in DEA rates compared to the control treatment. Topography explained the greatest amount of variation in potential denitrification across the three sites. The relationship between topography and DEA may partly be explained through the relatively robust relationship between topography and soil moisture, texture, and carbon content. For DEA under the control treatment, soil electrical conductivity (EC) exhibited the highest correlation with denitrification capacity (i.e., r2 = 35%). Denitrification capacity and potential were higher in a dry year with low soil moisture, relative to an average year with high soil moisture, which may be caused by the substantial increase in soil EC in the dry year. However, DEA rates were less responsive to soil EC at sandy sites which tend to have low soil moisture. Results of this

  18. Sulfur-oxidizing autotrophic and mixotrophic denitrification processes for drinking water treatment: elimination of excess sulfate production and alkalinity requirement.

    PubMed

    Sahinkaya, Erkan; Dursun, Nesrin

    2012-09-01

    This study evaluated the elimination of alkalinity need and excess sulfate generation of sulfur-based autotrophic denitrification process by stimulating simultaneous autotrophic and heterotrophic (mixotrophic) denitrification process in a column bioreactor by methanol supplementation. Also, denitrification performances of sulfur-based autotrophic and mixotrophic processes were compared. In autotrophic process, acidity produced by denitrifying sulfur-oxidizing bacteria was neutralized by the external NaHCO(3) supplementation. After stimulating mixotrophic denitrification process, the alkalinity need of the autotrophic process was satisfied by the alkalinity produced by heterotrophic denitrifiers. Decreasing and lastly eliminating the external alkalinity supplementation did not adversely affect the process performance. Complete denitrification of 75 mg L(-1) NO(3)-N under mixotrophic conditions at 4 h hydraulic retention time was achieved without external alkalinity supplementation and with effluent sulfate concentration lower than the drinking water guideline value of 250 mg L(-1). The denitrification rate of mixotrophic process (0.45 g NO(3)-N L(-1) d(-1)) was higher than that of autotrophic one (0.3 g NO(3)-N L(-1) d(-1)). Batch studies showed that the sulfur-based autotrophic nitrate reduction rate increased with increasing initial nitrate concentration and transient accumulation of nitrite was observed.

  19. 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).

  20. Comparison of combined and separated biological aerated filter (BAF) performance for pre-denitrification/nitrification of municipal wastewater.

    PubMed

    Rother, E; Cornel, P; Ante, A; Kleinert, P; Brambach, R

    2002-01-01

    The performance of two systems of semi-industrial up-flow biological aerated filters (BAF) with pre-denitrification followed by nitrification was studied and compared under various operating and loading conditions. The first system consisted of two separate reactors for the denitrification and the nitrification step, whereas in the second system the aerobic nitrification zone was packed on top of the anoxic denitrification zone in one reactor. The second system potentially offers substantial savings in investment costs and space requirements for a large scale treatment plant. Regarding the elimination of carbonaceous pollution and denitrification the systems did not show significant differences. However, nitrification in the combined system suffered from the mixing of different biocenosis by daily backwashing and was reduced to 50-70% of the separated system's performance. Factors such as oxygen concentration, raw water composition and loading rates affected both systems' nitrification rates in similar ways. Since it is impossible to optimise the nitrification and denitrification processes separately, the combined system should only be considered for large scale applications if space is very scarce and if a stable raw water composition can be expected. If strict limit values for nitrate have to be met in the effluent, a combination of pre- and post-denitrification is advantageous and advisable.

  1. 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.

  2. Comparing the Health Effects of Ambient Particulate Matter Estimated Using Ground-Based versus Remote Sensing Exposure Estimates

    PubMed Central

    Jerrett, Michael; Turner, Michelle C.; Beckerman, Bernardo S.; Pope, C. Arden; van Donkelaar, Aaron; Martin, Randall V.; Serre, Marc; Crouse, Dan; Gapstur, Susan M.; Krewski, Daniel; Diver, W. Ryan; Coogan, Patricia F.; Thurston, George D.; Burnett, Richard T.

    2016-01-01

    Background: Remote sensing (RS) is increasingly used for exposure assessment in epidemiological and burden of disease studies, including those investigating whether chronic exposure to ambient fine particulate matter (PM2.5) is associated with mortality. Objectives: We compared relative risk estimates of mortality from diseases of the circulatory system for PM2.5 modeled from RS with that for PM2.5 modeled using ground-level information. Methods: We geocoded the baseline residence of 668,629 American Cancer Society Cancer Prevention Study II (CPS-II) cohort participants followed from 1982 to 2004 and assigned PM2.5 levels to all participants using seven different exposure models. Most of the exposure models were averaged for the years 2002–2004, and one RS estimate was for a longer, contemporaneous period. We used Cox proportional hazards regression to estimate relative risks (RRs) for the association of PM2.5 with circulatory mortality and ischemic heart disease. Results: Estimates of mortality risk differed among exposure models. The smallest relative risk was observed for the RS estimates that excluded ground-based monitors for circulatory deaths [RR = 1.02, 95% confidence interval (CI): 1.00, 1.04 per 10 μg/m3 increment in PM2.5]. The largest relative risk was observed for the land-use regression model that included traffic information (RR = 1.14, 95% CI: 1.11, 1.17 per 10 μg/m3 increment in PM2.5). Conclusions: We found significant associations between PM2.5 and mortality in every model; however, relative risks estimated from exposure models using ground-based information were generally larger than those estimated using RS alone. Citation: Jerrett M, Turner MC, Beckerman BS, Pope CA III, van Donkelaar A, Martin RV, Serre M, Crouse D, Gapstur SM, Krewski D, Diver WR, Coogan PF, Thurston GD, Burnett RT. 2017. Comparing the health effects of ambient particulate matter estimated using ground-based versus remote sensing exposure estimates. Environ Health

  3. Denitrification-Efficiencies of Alternate Carbon Sources

    DTIC Science & Technology

    1984-07-01

    MUNITIONS COMPOUNDS HAZARDS CARBON HAZARDOUS MATERIALS NITRATES WASTE WATER CONTAMINATION DENITRIFICATION 20. AljThACT (Cinfbu m reveri Ohl It neffe6617 and...carbon source evaluated, while sweet whey, corn steep liquor, acid whey and soluble potato solids followed in order of decreasing efficiency. Three of...contaminated munitions process waters the use of alternate carbon sources will be needed not only for biological nitrate reduction but also for the

  4. Subsoil denitrification experiments at KBS MSU

    NASA Astrophysics Data System (ADS)

    Shcherbak, I.; Robertson, G. P.

    2011-12-01

    Denitrification is a major soil process that produces nitrous oxide (N2O), a potent greenhouse gas. Most research on denitrification has, for various reasons, concentrated on the top soil layer, ignoring depths below 10-20 cm. Although denitrification is considered to be the most active in top soil, this layer usually accounts for only 10% of the total volume of the soil profile. Our research addresses the questions: How significant is denitrification at depth in the soil profile and how does it vary with land-use? We have two field experiments at the W. K. Kellogg Biological Station (KBS) in southwest Michigan: 1) tilled versus no-tillage rainfed fertilized corn and 2) rainfed versus irrigated corn at six fertilizer levels, with N2O concentrations measured at 10 depths (3, 7, 15, 20, 25, 50, 55, 70, 75, 125 cm) and 5 depths (10, 20, 30, 50, 75 cm), respectively , along with N2O fluxes to the atmosphere in both. Soil environment data (texture, water content, temperature and nitrate content) represent a combination of measured values and simulated values using the SALUS (System Approach to Land Use Sustainability) model. We used diffusion and water balance equations that incorporated carbon dioxide concentrations and flux data collected simultaneously with N2O to determine diffusivity as a function of water content and soil temperature. We used the same diffusivity to obtain N2O production as function of moisture, temperature, and nitrate availability. Further validation of the production function was performed with data collected from the KBS Long-Term Ecological Research (LTER) site , where we also measured belowground concentrations during the 2011 growing season.

  5. Biological denitrification in a fluidized bed.

    PubMed

    Narjari, N K; Khilar, K C; Mahajan, S P

    1984-12-01

    A fluidized bed biofilm reactor using sand as the carrier particle was employed to study the effects of superficial velocity on the removal of nitrates as well as on the growth of the biofilm. Velocity was found to affect significantly both nitrate removal and biofilm growth. An analysis based on heterogenous catalysis was used to describe the denitrification process. There is good agreement between analysis and experimental measurements for startup and steady-state operating conditions.

  6. 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…

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

    USDA-ARS?s Scientific Manuscript database

    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...

  8. 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…

  9. Comparing the Health Effects of Ambient Particulate Matter Estimated Using Ground-Based versus Remote Sensing Exposure Estimates.

    PubMed

    Jerrett, Michael; Turner, Michelle C; Beckerman, Bernardo S; Pope, C Arden; van Donkelaar, Aaron; Martin, Randall V; Serre, Marc; Crouse, Dan; Gapstur, Susan M; Krewski, Daniel; Diver, W Ryan; Coogan, Patricia F; Thurston, George D; Burnett, Richard T

    2017-04-01

    Remote sensing (RS) is increasingly used for exposure assessment in epidemiological and burden of disease studies, including those investigating whether chronic exposure to ambient fine particulate matter (PM2.5) is associated with mortality. We compared relative risk estimates of mortality from diseases of the circulatory system for PM2.5 modeled from RS with that for PM2.5 modeled using ground-level information. We geocoded the baseline residence of 668,629 American Cancer Society Cancer Prevention Study II (CPS-II) cohort participants followed from 1982 to 2004 and assigned PM2.5 levels to all participants using seven different exposure models. Most of the exposure models were averaged for the years 2002-2004, and one RS estimate was for a longer, contemporaneous period. We used Cox proportional hazards regression to estimate relative risks (RRs) for the association of PM2.5 with circulatory mortality and ischemic heart disease. Estimates of mortality risk differed among exposure models. The smallest relative risk was observed for the RS estimates that excluded ground-based monitors for circulatory deaths [RR = 1.02, 95% confidence interval (CI): 1.00, 1.04 per 10 μg/m(3) increment in PM2.5]. The largest relative risk was observed for the land-use regression model that included traffic information (RR = 1.14, 95% CI: 1.11, 1.17 per 10 μg/m(3) increment in PM2.5). We found significant associations between PM2.5 and mortality in every model; however, relative risks estimated from exposure models using ground-based information were generally larger than those estimated using RS alone.

  10. 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.

  11. A Case Study on Nitrogen Uptake and Denitrification in a ...

    EPA Pesticide Factsheets

    Restoring urban infrastructure and managing the nitrogen cycle represent emerging challenges for urban water quality. We investigated whether stormwater control measures (SCMs), a form of green infrastructure, integrated into restored and degraded urban stream networks can influence watershed nitrogen loads. We hypothesized that hydrologically connected floodplains and SCMs are “hot spots” for nitrogen removal through denitrification because they have ample organic carbon, low dissolved oxygen levels, and extended hydrologic residence times. We tested this hypothesis by comparing nitrogen retention metrics in two urban stream networks (one restored and one urban degraded) that each contain SCMs, and a forested reference watershed at the Baltimore Long-Term Ecological Research site. We used an urban watershed continuum approach which included sampling over both space and time with a combination of: (1) longitudinal reach-scale mass balances of nitrogen and carbon conducted over 2 years during baseflow and storms (n = 24 sampling dates × 15 stream reaches = 360) and (2) 15N push–pull tracer experiments to measure in situ denitrification in SCMs and floodplain features (n = 72). The SCMs consisted of inline wetlands installed below a storm drain outfall at one urban site (restored Spring Branch) and a wetland/wet pond configured in an oxbow design to receive water during high flow events at another highly urbanized site (Gwynns Run). The SCMs significantly d

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

    USGS Publications Warehouse

    Bradley, P.M.; Fernandez, M.; 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. 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

  14. Dynamic interplay between microbial denitrification and antibiotic resistance under enhanced anoxic denitrification condition in soil.

    PubMed

    Sun, Mingming; Ye, Mao; Liu, Kuan; Schwab, Arthur P; Liu, Manqiang; Jiao, Jiaguo; Feng, Yanfang; Wan, Jinzhong; Tian, Da; Wu, Jun; Li, Huixin; Hu, Feng; Jiang, Xin

    2017-03-01

    Mixed contamination of nitrate and antibiotics/antibiotic-resistant genes (ARGs) is an emerging environmental risk to farmland soil. This is the first study to explore the role of excessive anthropogenic nitrate input in the anoxic dissipation of soil antibiotic/ARGs. During the initial 10 days of incubation, the presence of soil antibiotics significantly inhibited NO3(-) dissipation, N2O production rate, and denitrifying genes (DNGs) abundance in soil (p < 0.05). Between days 10 and 30, by contrast, enhanced denitrification clearly prompted the decline in antibiotic contents and ARG abundance. Significantly negative correlations were detected between DNGs and ARGs, suggesting that the higher the DNG activity, the more dramatic is the denitrification and the greater are the antibiotic dissipation and ARG abundance. This study provides crucial knowledge for understanding the mutual interaction between soil DNGs and ARGs in the enhanced anoxic denitrification condition.

  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. 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%.

  17. 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

  18. 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.

  19. 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

  20. Analysis of Antarctic Denitrification in 2003 Winter Observed by ILAS-II Onboard the ADEOS-II Satellite

    NASA Astrophysics Data System (ADS)

    Nakajima, H.; Saeki, K.; Sugita, T.

    2005-12-01

    Polar Stratospheric Clouds (PSC) play an important role in ozone destruction in both Arctic and Antarctic stratosphere in winter. They take up gas-phase nitric acid (HNO3) and grow up when temperature is below nitric acid saturation temperature (TNAT). When PSC becomes large, it starts to descend and nitric acid is removed from the air mass, resulting in denitrification. The Improved Limb Atmospheric Spectrometer-II (ILAS-II) onboard the Advanced Earth Observing Satellite-II (ADEOS-II) successfully made measurements for the whole Antarctic winter in 2003. ILAS-II measured vertical profiles of O3, HNO3, NO2, H2O, N2O, CH4, ClONO2, N2O5, etc. in addition to the aerosol extinction coefficients at 780 nm. In this study, we analyzed denitrification from ILAS-II HNO3 and N2O data in regard to temperature history on the trajectory. The quantity of denitrification was estimated from the difference between measured HNO3 and HNO3* assumed from HNO3-- N2O correlation. In this analysis, it was found that denitrification was observed only for those airmass that experienced temperature below TICE (ice saturation temperature) in late June, 2003. In late July, it was found that most airmass inside the polar vortex was denitrified regardless of temperature history. This suggests that permanent denitrification has occurred in June-July period. The transition of relationship between denitrification and airmass temperature history was discovered from the ILAS-II data. Also, major types of PSC have found to be changed from nitric acid trihydrate (NAT) in June to ice in July, from the ILAS-II data. This is considered to be due to the lack of nitric acid in the airmass due to the denitrification in July.

  1. 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.

  2. Comparing Neonatal Morbidity and Mortality Estimates across Specialty in Periviable Counseling

    PubMed Central

    Edmonds, Brownsyne Tucker; McKenzie, Fatima; Panoch, Janet; Frankel, Richard M.

    2015-01-01

    Objective To describe and compare estimates of neonatal morbidity and mortality communicated by neonatologists and obstetricians in simulated periviable counseling encounters. Methods A simulation-based study of 16 obstetricians (OBs) and 15 neonatologists counseling standardized patients portraying pregnant women with ruptured membranes at 23 weeks gestation. Two investigators tabulated all instances of numerically-described risk estimates across individuals and by specialty. Results Overall, 12/15 (80%) neonatologists utilized numeric estimates of survival; 6/16 (38%) OBs did. OBs frequently deferred the discussion of “exact numbers” to neonatologists. The twelve neonatologists provided 13 unique numeric estimates, ranging from 3% to 50% survival. Half of those neonatologists provided 2-3 different estimates in a single encounter. By comparison, six OBs provided 4 unique survival estimates (“50%”, “30-40%”, “1/3-1/2”, “<10%”). Only 2/15 (13%) neonatologists provided numeric estimates of survival without impairment. None of the neonatologists used the term ‘intact’ survival, while 5 OBs did. Three neonatologists gave numeric estimates of long-term disability and one OB did. Conclusion We found substantial variation in estimates and noteworthy omissions of discussions related to long-term morbidity. Across specialties, we noted inconsistencies in the use and meaning of terms like ‘intact survival.’ More tools and training are needed to improve the quality and consistency of periviable risk-communication. PMID:25354284

  3. 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

  4. 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

  5. Assessment of denitrification process in lower Ishikari river system, Japan.

    PubMed

    Jha, Pawan Kumar; Minagawa, Masao

    2013-11-01

    Sediment denitrification rate and its role in removal of dissolved nitrate load in lower Ishikari river system were examined. Denitrification rate were measured using acetylene inhibition technique on the sediment samples collected during August 2009-July 2010. The denitrification rate varied from 0.001 to 1.9 μg Ng(-1) DM h(-1) with an average value of 0.21 μg Ng(-1) DM h(-1) in lower Ishikari river system. Denitrification rate showed positive correlation with dissolved nitrate concentration in the river basin, indicating overlying water column supplied nitrate for the sediment denitrification processes. Nutrient enrichment experiments result showed that denitrification rate increased significantly with addition of nitrate in case of samples collected from Barato Lake however no such increase was observed in the samples collected from Ishikari river main channel and its major tributaries indicating that factors other than substrate concentration such as population of denitrifier and hydrological properties of stream channel including channel depth and flow velocity may affects the denitrification rate in lower Ishikari river system. Denitrification rate showed no significant increase with the addition of labile carbon (glucose), indicating that sediment samples had sufficient organic matter to sustain denitrification activity. The result of nutrient spiraling model indicates that in- stream denitrification process removes on an average 5%d(-1) of dissolve nitrate load in Ishikari river. This study was carried out to fill the gap present in the availability of riverine denitrification rate measurement and its role in nitrogen budget from Japanese rivers characterize by small river length and high flow rate. Copyright © 2013 Elsevier Ltd. All rights reserved.

  6. Mechanism of charged pollutants removal in an ion exchange membrane bioreactor: drinking water denitrification.

    PubMed

    Velizarov, S; Rodrigues, C M; Reis, M A; Crespo, J G

    The mechanism of anionic pollutant removal in an ion exchange membrane bioreactor (IEMB) was studied for drinking water denitrification. This hybrid process combines continuous ion exchange transport (Donnan dialysis) of nitrate and its simultaneous bioreduction to gaseous nitrogen. A nonporous mono-anion permselective membrane precludes direct contact between the polluted water and the denitrifying culture and prevents secondary pollution of the treated water with dissolved nutrients and metabolic products. Complete denitrification may be achieved without accumulation of NO3(-) and NO2(-) ions in the biocompartment. Focus was given to the effect of the concentration of co-ions, counterions, and ethanol on the IEMB performance. The nitrate overall mass transfer coefficient in this hybrid process was found to be 2.8 times higher compared to that in a pure Donnan dialysis process without denitrification. Furthermore, by adjusting the ratio of co-ions between the biocompartment and the polluted water compartment, the magnitude and direction of each individual anion flux can be easily regulated, allowing for flexible process operation and control. Synthetic groundwater containing 135-350 mg NO3(-) L(-1) was treated in the IEMB system. A surface denitrification rate of 33 g NO3(-) per square meter of membrane per day was obtained at a nitrate loading rate of 360 g NO3(-) m(-3)d(-1), resulting in a nitrate removal efficiency of 85%.

  7. 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

  8. 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

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

    USDA-ARS?s Scientific Manuscript database

    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...

  10. Investigation of fluidized-bed biological denitrification

    SciTech Connect

    Acox, T.A.

    1982-12-16

    The performance of the fluidized-bed bioreactor was modelled for denitrification using a multiple linear regression. Reasonable accuracy was obtained; however, this type of analysis did not take into account the hydraulic characteristics of the fluidized-bed. The Mulcahy and LaMotta computer program previously used to model a fluidized-bed bioreactor cannot be used in this case due to the Michaelis-Menton constant k determined in this study, which was one to two orders of magnitude lower. With some additional bioreactor study and computer program modification, this may prove to be of some benefit.

  11. Warming can boost denitrification disproportionately due to altered oxygen dynamics.

    PubMed

    Veraart, Annelies J; de Klein, Jeroen J M; Scheffer, Marten

    2011-03-31

    Global warming and the alteration of the global nitrogen cycle are major anthropogenic threats to the environment. Denitrification, the biological conversion of nitrate to gaseous nitrogen, removes a substantial fraction of the nitrogen from aquatic ecosystems, and can therefore help to reduce eutrophication effects. However, potential responses of denitrification to warming are poorly understood. Although several studies have reported increased denitrification rates with rising temperature, the impact of temperature on denitrification seems to vary widely between systems. We explored the effects of warming on denitrification rates using microcosm experiments, field measurements and a simple model approach. Our results suggest that a three degree temperature rise will double denitrification rates. By performing experiments at fixed oxygen concentrations as well as with oxygen concentrations varying freely with temperature, we demonstrate that this strong temperature dependence of denitrification can be explained by a systematic decrease of oxygen concentrations with rising temperature. Warming decreases oxygen concentrations due to reduced solubility, and more importantly, because respiration rates rise more steeply with temperature than photosynthesis. Our results show that denitrification rates in aquatic ecosystems are strongly temperature dependent, and that this is amplified by the temperature dependencies of photosynthesis and respiration. Our results illustrate the broader phenomenon that coupling of temperature dependent reactions may in some situations strongly alter overall effects of temperature on ecological processes.

  12. Warming Can Boost Denitrification Disproportionately Due to Altered Oxygen Dynamics

    PubMed Central

    Veraart, Annelies J.; de Klein, Jeroen J. M.; Scheffer, Marten

    2011-01-01

    Background Global warming and the alteration of the global nitrogen cycle are major anthropogenic threats to the environment. Denitrification, the biological conversion of nitrate to gaseous nitrogen, removes a substantial fraction of the nitrogen from aquatic ecosystems, and can therefore help to reduce eutrophication effects. However, potential responses of denitrification to warming are poorly understood. Although several studies have reported increased denitrification rates with rising temperature, the impact of temperature on denitrification seems to vary widely between systems. Methodology/Principal Findings We explored the effects of warming on denitrification rates using microcosm experiments, field measurements and a simple model approach. Our results suggest that a three degree temperature rise will double denitrification rates. By performing experiments at fixed oxygen concentrations as well as with oxygen concentrations varying freely with temperature, we demonstrate that this strong temperature dependence of denitrification can be explained by a systematic decrease of oxygen concentrations with rising temperature. Warming decreases oxygen concentrations due to reduced solubility, and more importantly, because respiration rates rise more steeply with temperature than photosynthesis. Conclusions/Significance Our results show that denitrification rates in aquatic ecosystems are strongly temperature dependent, and that this is amplified by the temperature dependencies of photosynthesis and respiration. Our results illustrate the broader phenomenon that coupling of temperature dependent reactions may in some situations strongly alter overall effects of temperature on ecological processes. PMID:21483809

  13. Short-term enhancement and long-term suppression of denitrification in estuarine sediments receiving primary- and secondary-treated paper and pulp mill discharge.

    PubMed

    Oakes, Joanne M; Eyre, Bradley D; Ross, Donald J

    2011-04-15

    To determine the role of sediment denitrification in removing inputs of primary- (PE) and secondary-treated effluent (SE) from a pulp and paper mill (PPM), organic matter (OM) associated with PE (residual wood fiber) and SE (activated sludge biomass and phytoplankton) was added to estuarine intertidal sediments and denitrification rates were measured over 27 days. Labile sludge biomass and phytoplankton initially stimulated denitrification, including for pre-existing sediment N. After 2.5 d, however, denitrification was suppressed apparently due to microbial competition for N to process the refractory (high C:N) material remaining. Wood fiber suppressed denitrification throughout the experiment due to competition for N to process the refractory OM. Ultimate long-term denitrification suppression by phytoplankton is offset by initial enhanced denitrification rates. Although nutrient release during degradation of sludge biomass and wood fiber may stimulate phytoplankton production, N equivalent to 127% of the expected daily phytoplankton load was denitrified within 24 h, allowing for permanent removal of PPM-derived N. Compared to primary treatment, secondary treatment of PPM effluent has greater potential for N removal.

  14. Distinguishing between water column and sedimentary denitrification in the Santa Barbara Basin using the stable isotopes of nitrate

    NASA Astrophysics Data System (ADS)

    Sigman, D. M.; Robinson, R.; Knapp, A. N.; van Geen, A.; McCorkle, D. C.; Brandes, J. A.; Thunell, R. C.

    2003-05-01

    Below its sill depth, the Santa Barbara Basin (SBB) is commonly suboxic ([O2] ˜ 3 μM), with only brief periods of ventilation. Associated with development of suboxia, the concentration of nitrate decreases with depth into the basin without an associated decrease in phosphate, indicating that a substantial fraction of the nitrate supplied to the basin is removed by denitrification. Coincident with the decrease in nitrate concentration across the "redoxcline" (the interface between oxic and suboxic waters) within the SBB, there is an increase in the 15N/14N of that nitrate, as would be anticipated from the isotopic fractionation associated with denitrification. However, the increase in 15N/14N of nitrate is much smaller than occurs in the open eastern tropical North Pacific (ETNP) for a comparable amount of nitrate loss. Both the concentrations of N species within the basin and measurements of nitrate 18O/16O suggest that the lower-than-expected 15N enrichment in the suboxic SBB involves denitrification, rather than being due to some unknown source of low-15N/14N N to the deep SBB. Calculations with a range of models of nitrate supply and consumption indicate that the degree of nitrate consumption in the basin is too small for differences in water circulation to explain the isotopic differences between the Santa Barbara Basin and the open ETNP. Previous studies indicate that the isotope effect of sedimentary denitrification is negligible due to nitrate diffusion in sediment pore waters. Thus we infer that the small magnitude of the isotopic enrichment of SBB water column nitrate is due to the importance of sedimentary denitrification within the basin. Assuming that water column and sedimentary denitrification have isotope effects of 25 and 1.5 per mil, respectively, our results suggest that sedimentary denitrification accounts for more than 75% of the nitrate loss within the suboxic SBB.

  15. 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.

  16. Sulfur-driven autotrophic denitrification: diversity, biochemistry, and engineering applications.

    PubMed

    Shao, Ming-Fei; Zhang, Tong; Fang, Herbert Han-Ping

    2010-11-01

    Sulfur-driven autotrophic denitrification refers to the chemolithotrophic process coupling denitrification with the oxidation of reduced inorganic sulfur compounds. Ever since 1904, when Thiobacillus denitrificans was isolated, autotrophic denitrifiers and their uncultured close relatives have been continuously identified from highly diverse ecosystems including hydrothermal vents, deep sea redox transition zones, sediments, soils, inland soda lakes, etc. Currently, 14 valid described species within α-, β-, γ-, and ε-Proteobacteria have been identified as capable of autotrophic denitrification. Autotrophic denitrification is also widely applied in environmental engineering for the removal of sulfide and nitrate from different water environments. This review summarizes recent researches on autotrophic denitrification, highlighting its diversity, metabolic traits, and engineering applications.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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)).

  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. Plant effects on soil denitrification - a review of potential mechanisms

    NASA Astrophysics Data System (ADS)

    Malique, Francois; Butterbach-Bahl, Klaus; Dannenmann, Michael

    2017-04-01

    Denitrification is a microbial process occurring in soils, both producing and consuming the potent greenhouse gas nitrous oxide (NO), competing for nitrate with plants and hydrological leaching pathways, removing nutrients and reactive nitrogen from the biosphere, and closing the global nitrogen cycle. Despite its obvious importance, denitrification remained among the least well quantified biogeochemical processes in soils. This is due to enormous methodological difficulties involved in the direct quantification of soil microbial denitrification rates (mainly with regard to the terminal product N2) and the denitrification nitrogen gas product ratios (NO:N2O:N2), Plants may affect denitrification through a myriad of mechanisms such as e.g., competition for nitrate and water, through oxygen consumption, by regulating litter quality and changing soil pH, and via the exudation of labile carbon or secondary plant compounds involved in shaping the rhizospheric microbial community. However, plant effects on denitrification so far hardly were quantified so that the actual extent of plant control on denitrification is largely unknown. Here, we summarize the current knowledge on mechanisms how plants can affect denitrification rates and N gas product ratios in soils at temporal scales from hours to days and years. We review earlier research to quantify plant effects on denitrification as well as critically discuss the limited methods currently available to quantify plant-soil-denitrifier interactions. Finally, we provide pointers to use plants as tools to manage denitrification, e.g. to improve N use efficiency in agricultural ecosystems and to minimize soil nitrous oxide emissions.

  4. Improved estimation of urinary myoglobulin by counterimmunoelectrophoresis, as compared with the double immunodiffusion technique.

    PubMed

    Hibrawi, H; Blaker, R G

    1975-05-01

    We describe a simple, sensitive, and relatively inexpensive counterimmunoelectrophoretic technique for detection and estimation of myoglobin. The test can be completed within 90 min, compared with 12-48 h required by double immunodiffusion. With the counterimmunoelectrophoretic technique we could detect myoglobin in concentrations of 2-3 mg/liter, while the detection limit by double immunodiffusion was about 9 mg/liter.

  5. 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.

  6. Comparing three sampling techniques for estimating fine woody down dead biomass

    Treesearch

    Robert E. Keane; Kathy Gray

    2013-01-01

    Designing woody fuel sampling methods that quickly, accurately and efficiently assess biomass at relevant spatial scales requires extensive knowledge of each sampling method's strengths, weaknesses and tradeoffs. In this study, we compared various modifications of three common sampling methods (planar intercept, fixed-area microplot and photoload) for estimating...

  7. Estimating Item Difficulty with Comparative Judgments. Research Report. ETS RR-14-39

    ERIC Educational Resources Information Center

    Attali, Yigal; Saldivia, Luis; Jackson, Carol; Schuppan, Fred; Wanamaker, Wilbur

    2014-01-01

    Previous investigations of the ability of content experts and test developers to estimate item difficulty have, for themost part, produced disappointing results. These investigations were based on a noncomparative method of independently rating the difficulty of items. In this article, we argue that, by eliciting comparative judgments of…

  8. Comparing self-perceived and estimated fracture risk by FRAX® of women with osteoporosis.

    PubMed

    Baji, Petra; Gulácsi, László; Horváth, Csaba; Brodszky, Valentin; Rencz, Fanni; Péntek, Márta

    2017-12-01

    In this study, we compared subjective fracture risks of Hungarian women with osteoporosis to FRAX®-based estimates. Patients with a previous fracture, parental hip fracture, low femoral T-score, higher age, and higher BMI were more likely to underestimate their risks. Patients also failed to associate risk factors with an increased risk of fractures.

  9. Estimating, Testing, and Comparing Specific Effects in Structural Equation Models: The Phantom Model Approach

    ERIC Educational Resources Information Center

    Macho, Siegfried; Ledermann, Thomas

    2011-01-01

    The phantom model approach for estimating, testing, and comparing specific effects within structural equation models (SEMs) is presented. The rationale underlying this novel method consists in representing the specific effect to be assessed as a total effect within a separate latent variable model, the phantom model that is added to the main…

  10. Estimating, Testing, and Comparing Specific Effects in Structural Equation Models: The Phantom Model Approach

    ERIC Educational Resources Information Center

    Macho, Siegfried; Ledermann, Thomas

    2011-01-01

    The phantom model approach for estimating, testing, and comparing specific effects within structural equation models (SEMs) is presented. The rationale underlying this novel method consists in representing the specific effect to be assessed as a total effect within a separate latent variable model, the phantom model that is added to the main…

  11. 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…

  12. 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…

  13. 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.

  14. Nitrification and denitrification in high-strength ammonium by Alcaligenes faecalis.

    PubMed

    Joo, Hung-Soo; Hirai, Mitsuyo; Shoda, Makoto

    2005-06-01

    Alcaligenes faecalis sp. No. 4, that has the ability of heterotrophic nitrification and aerobic denitrification in high-strength ammonium at about 1200 mg-N/l, converted about one-half of removed NH4+-N to intracellular nitrogen and nitrified only 3% of the removed NH4+. From the nitrogen balance, 40-50% of removed NH4+-N was estimated to be denitrified. Production of N2 was confirmed by GC-MS and 90% of denitrified products was N2. The maximum ammonium removal rate, 29 mg-N/l h and its denitrification rate in aerated batch experiments, were 5-40 times higher than those of other bacteria with the same ability.

  15. Sediment nitrification and denitrification rates in a Lake ...

    EPA Pesticide Factsheets

    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 spatial and depths zones and in relation to site physicochemical characteristics in the St. Louis River Estuary (SLRE) of western Lake Superior. Among vegetated habitats in 2011, NIT rates were highest in deep (>2 m) waters (249 mgN m-2 d-1) and in the upper estuary (>126). DeNIT rates were highest in deep waters and the harbor (2,111 and 274, respectively). DEA rates were similar among habitats. In 2012, we observed highest NIT (223 and 287) and DeNIT (77 and 64) rates in the harbor and from deep waters, respectively. Highest rates for NIT, DeNIT, and DEA were in July, May, and June, respectively. Individual site characteristics were weakly related to N-cycling rates, but water and sediment N-concentrations were identified as significant predictors in multiple linear regression models. NO3- was most limiting to sediment denitrification rates. The SLRE acted as a net source of NO3- to the water column, but had the potential to act as a sink. Average N2O production in 2011 was half that of 2012, with production during DEA (23-54%) being higher than DeNIT (0-41%). SLRE N-cycling rates were spatially and temporally variable, but our results give an indication of how alterations of water depth a

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

    PubMed

    Ducey, Thomas F; Shriner, Anthony D; Hunt, Patrick G

    2011-01-01

    Although anaerobic lagoons are used globally for livestock waste treatment, their detailed microbial cycling ofN is only beginning to become understood. Within this cycling, nitrification can be performed by organisms that produce the enzyme ammonia monooxygenase. For denitrification, the reduction of nitrite to nitric oxide can be catalyzed by two forms of nitrite reductases, and N,O can be reduced by nitrous oxide reductase encoded by the gene nosZ The objectives of this investigation were to (i) quantify the abundance of the amoA, nirK, nirS, and nosZ genes; (ii) evaluate the influence of environmental conditions on their abundances; and (iii) evaluate their abundance relative to denitrification enzyme activity (DEA). Samples were analyzed via real-time quantitative polymerase chain reaction and collected from eight typical, commercial anaerobic, swine wastewater lagoons located in the Carolinas. The four genes assayed in this study were present in all eight lagoons. Their abundances relative to total bacterial populations were 0.04% (amoA), 1.33% (nirS), 5.29% (nirK), and 0.27% (nosZ). When compared with lagoon chemical characteristics, amoA and nirK correlated with several measured variables. Neither nirS nor nosZ correlated with any measured environmental variables. Although no gene measured in this study correlated with actual or potential DEA, nosZ copy numbers did correlate with the disparity between actual and potential DEA. Phylogenetic analysis ofnosZdid not reveal any correlations to DEA rates. As with other investigations, analyses of these genes provide useful insight while revealing the underlying greater complexity of N cycling within swine waste lagoons.

  17. 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

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

    PubMed

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

    2014-12-15

    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 0.5m/day. NO3-(15)N and NO3-(18)O 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. Copyright © 2014 Elsevier B.V. All rights reserved.

  19. 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.

  20. 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

  1. 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).

  2. A comparative evaluation of two different approaches to estimating age at adiposity rebound.

    PubMed

    Kroke, A; Hahn, S; Buyken, A E; Liese, A D

    2006-02-01

    To compare different approaches (visual estimation of individual BMI curves with polynomial models) to estimate age at adiposity rebound (AR), as different approaches might lead to different results. AR has been suggested as a critical period between intra-uterine life and early adulthood, and recent data showed that early age at AR is associated with higher body mass later in life. Longitudinal anthropometric data from the DOrtmund Nutritional and Anthropometric Longitudinally Designed (DONALD) Study were used to obtain individual BMI growth curves. We then compared the visual estimation approach to polynomial models in three different scenarios reflected by different data sets: an idealistic, an realistic, and a realistic scenario with imputed values. In all three scenarios, the visual estimation yielded significantly higher estimates than the polynomial models of 2nd or 3rd order. Cross-tabulations of groups of age at AR (early, medium, and late) showed that truly concordant classification was low, ranging only from 51 to 63%. A closer examination of the data indicated that the differences in estimates were mainly due to differences in the underlying definitions: the polynomial models select the nadir in the growth curve as the age at AR, whereas the visual estimation deviates from this concept in those cases where there is plateau in the growth curve. In the latter instance, the turning point of the growth curve before its increase is selected as the age at rebound. Estimating AR with the visual approach appears to best reflect the physiological basis of the AR, and is also preferable, because it resulted in the lowest number of children with missing estimates for age at AR. Only when the underlying criteria for the estimation of AR with the visual approach were modified, could concordant results between the two approaches be obtained. Considering the underlying physiological basis, it became clear that approaches which determine AR by simply identifying the

  3. Comparative analysis of methods for estimating arm segment parameters and joint torques from inverse dynamics.

    PubMed

    Piovesan, Davide; Pierobon, Alberto; Dizio, Paul; Lackner, James R

    2011-03-01

    A common problem in the analyses of upper limb unfettered reaching movements is the estimation of joint torques using inverse dynamics. The inaccuracy in the estimation of joint torques can be caused by the inaccuracy in the acquisition of kinematic variables, body segment parameters (BSPs), and approximation in the biomechanical models. The effect of uncertainty in the estimation of body segment parameters can be especially important in the analysis of movements with high acceleration. A sensitivity analysis was performed to assess the relevance of different sources of inaccuracy in inverse dynamics analysis of a planar arm movement. Eight regression models and one water immersion method for the estimation of BSPs were used to quantify the influence of inertial models on the calculation of joint torques during numerical analysis of unfettered forward arm reaching movements. Thirteen subjects performed 72 forward planar reaches between two targets located on the horizontal plane and aligned with the median plane. Using a planar, double link model for the arm with a floating shoulder, we calculated the normalized joint torque peak and a normalized root mean square (rms) of torque at the shoulder and elbow joints. Statistical analyses quantified the influence of different BSP models on the kinetic variable variance for given uncertainty on the estimation of joint kinematics and biomechanical modeling errors. Our analysis revealed that the choice of BSP estimation method had a particular influence on the normalized rms of joint torques. Moreover, the normalization of kinetic variables to BSPs for a comparison among subjects showed that the interaction between the BSP estimation method and the subject specific somatotype and movement kinematics was a significant source of variance in the kinetic variables. The normalized joint torque peak and the normalized root mean square of joint torque represented valuable parameters to compare the effect of BSP estimation methods

  4. Comparative Study of Clinical and Sonographic Estimation of Foetal Weight at Term.

    PubMed

    Bakshi, L; Begum, H A; Khan, I; Dey, S K; Bhattacharjee, M; Bakshi, M K; Dey, S; Habib, A; Barman, K K

    2015-07-01

    A cross sectional comparative study was conducted at Dhaka National Medical College, Dhaka from January to June 2012, to observe the accuracy of clinical and ultrasonographic estimation of foetal weight at term in our environment. Seventy five pregnant women who fulfilled the inclusion criteria had their foetal weight estimated independently using clinical and ultrasonographic methods. Accuracy was determined by percentage error, absolute percentage error and proportion of estimates within 10% of actual birth weight (birth weight fetus of +10%). Statistical analysis was done using the paired t-test, the Wilcoxon signed-rank test, and the chi-square test. The study sample had an actual average birth weight of 2989.60 ± 408.76 (range 2310-4000 gm). Overall, the clinical method overestimated birth-weight, while ultrasound underestimated it. The mean absolute percentage error of the clinical method was more than that of the sonographic method, and the number of estimates within 10% of actual birth weight for the clinical method (41.3%) was less than for the sonographic method (57.3%); the difference was not statistically significant. In the low birth-weight (<2,500 gm) group, the mean absolute percentage error of sonographic estimates were significantly smaller. Significantly more sonographic estimates (75%) were within 10% of actual birth-weight than those of the clinical method (0%). No statistically significant difference was observed in all the measures of accuracy for the normal birth-weight range of 2,500-<4,000 gm and in the macrosomic group (≥ 4,000 gm). Clinical estimation of birth-weight is as accurate as routine ultrasonographic estimation, except in low-birth-weight babies.

  5. Comparing Oral Health Care Utilization Estimates in the United States Across Three Nationally Representative Surveys

    PubMed Central

    Macek, Mark D; Manski, Richard J; Vargas, Clemencia M; Moeller, John

    2002-01-01

    Objective To compare estimates of dental visits among adults using three national surveys. Data Sources/Study Design Cross-sectional data from the National Health Interview Survey (NHIS), National Health and Nutrition Examination Survey (NHANES), and National Health Expenditure surveys (NMCES, NMES, MEPS). Study Design This secondary data analysis assessed whether overall estimates and stratum-specific trends are different across surveys. Data Collection Dental visit data are age standardized via the direct method to the 1990 population of the United States. Point estimates, standard errors, and test statistics are generated using SUDAAN. Principal Findings Sociodemographic, stratum-specific trends are generally consistent across surveys; however, overall estimates differ (NHANES III [364-day estimate] versus 1993 NHIS: –17.5 percent difference, Z=7.27, p value < 0.001; NHANES III [365-day estimate] vs. 1993 NHIS: 5.4 percent difference, Z=–2.50, p value=0.006; MEPS vs. 1993 NHIS: –29.8 percent difference, Z=16.71, p value < 0.001). MEPS is the least susceptible to intrusion, telescoping, and social desirability. Conclusions Possible explanations for discrepancies include different reference periods, lead-in statements, question format, and social desirability of responses. Choice of survey should depend on the hypothesis. If trends are necessary, choice of survey should not matter; however, if health status or expenditure associations are necessary, then surveys that contain these variables should be used, and if accurate overall estimates are necessary, then MEPS should be used. A validation study should be conducted to establish “true” utilization estimates. PMID:12036005

  6. 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

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

    PubMed

    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."

  8. Comparative estimation of vibrational entropy changes in proteins through normal modes analysis.

    PubMed

    Carrington, Benjamin J; Mancera, Ricardo L

    2004-10-01

    We compare the vibrational entropy changes of proteins calculated using a full and a number of approximate normal modes analysis methods. The vibrational entropy differences for three conformational changes and three protein binding interactions were computed. In general, the approximate methods yield good estimates of the vibrational entropy change in a fraction of the time required by full normal modes analysis. The absolute entropies are either overestimated or greatly underestimated, but the difference is sufficiently accurate for some methods. This indicates that some of the approximate methods can give reasonable estimates of the associated vibrational entropy changes, making them suitable for inclusion in free energy calculations.

  9. Toward reliable estimates of abundance: comparing index methods to assess the abundance of a Mammalian predator.

    PubMed

    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.

  10. 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

  11. Quantification of denitrification potential in carbonaceous trickling filters.

    PubMed

    Biesterfeld, Sidney; Farmer, Greg; Figueroa, Linda; Parker, Denny; Russell, Phil

    2003-09-01

    Biofilm samples from a carbonaceous trickling filter (TF) were evaluated in bench scale reactors to determine their maximum potential denitrification rates. Intact, undisturbed biofilms were placed into 0.6 L bench-scale reactors filled with sterilized, primary clarifier effluent spiked with nitrate to a final concentration of 16-18 mg/L as N. Dissolved oxygen concentrations were maintained between 2 and 4 mg/L in the bulk aqueous phase. Nitrate loss from the reactors was monitored over a 5h period. Denitrification rates of 3.09-5.55 g-N/m(2)day were observed with no initial lag period. This suggests that the capacity for denitrification is inherent in the biofilm and that denitrification can take place even when oxygen is present in the bulk aqueous phase. There were no significant differences in denitrification rates per unit area of media (g-N/m(2)day) either between (a). experimental runs or (b). sampling locations over the trickling filter. This suggests that denitrification potentials are uniform over the entire volume of the full-scale TF. For wastewater treatment plants with TFs that currently nitrify downstream, this approach may be used to meet less stringent permitted discharge concentrations and may allow some facilities to postpone or eliminate construction of additional unit processes for denitrification.

  12. Denitrification in alluvial wetlands in an urban landscape.

    PubMed

    Harrison, Melanie D; Groffman, Peter M; Mayer, Paul M; Kaushal, Sujay S; Newcomer, Tamara A

    2011-01-01

    Riparian wetlands have been shown to be effective "sinks" for nitrate N (NO3-), minimizing the downstream export of N to streams and coastal water bodies. However, the vast majority of riparian denitrification research has been in agricultural and forested watersheds, with relatively little work on riparian wetland function in urban watersheds. We investigated the variation and magnitude of denitrification in three constructed and two relict oxbow urban wetlands, and in two forested reference wetlands in the Baltimore metropolitan area. Denitrification rates in wetland sediments were measured with a 15N-enriched NO3- "push-pull" groundwater tracer method during the summer and winter of 2008. Mean denitrification rates did not differ among the wetland types and ranged from 147 +/- 29 microg N kg soil(-1) d(-1) in constructed stormwater wetlands to 100 +/- 11 microg N kg soil(-1) d(-1) in relict oxbows to 106 +/- 32 microg N kg soil(-1) d(-1) in forested reference wetlands. High denitrification rates were observed in both summer and winter, suggesting that these wetlands are sinks for NO3- year round. Comparison of denitrification rates with NO3- standing stocks in the wetland water column and stream NO3- loads indicated that mass removal of NO3- in urban wetland sediments by denitrification could be substantial. Our results suggest that urban wetlands have the potential to reduce NO3- in urban landscapes and should be considered as a means to manage N in urban watersheds.

  13. Isotopologue data reveal denitrification as the primary source of nitrous oxide along a fertilization gradient in a temperature agricultural field

    NASA Astrophysics Data System (ADS)

    Ostrom, N. E.; Ostrom, P. H.; Gandhi, H.; Millar, N.; Robertson, G. P.

    2009-12-01

    The microbial source of nitrous oxide in terrestrial ecosystems has long been debated. Both nitrification and denitrification produce nitrous oxide but their relative importance remains uncertain. Here we apply site preference, SP, (the difference in δ15N between the central and outer N atom in nitrous oxide), to estimate production of nitrous oxide from bacterial denitrification (including nitrifier denitrification). Soil flux chambers were deployed within 3 agricultural plots planted with wheat in corn-soybean wheat rotation as part of ongoing studies at the Kellogg Biological Stations Long-Term Ecosystem Research site. Distinct levels of urea-ammonium nitrate (28%) fertilizer were applied to each plot in the spring of 2007 to obtain totals of 0, 134, and 246 kg-N ha-1. Samples for nitrous oxide flux and isotopologue composition were collected approximately 4 times per week from May through December, 2007, in each of the plots. The average annual nitrous oxide flux weighted N isotope values increased along the fertilization gradient (-14.7, -12.3 and -9.1 ‰, for the no, medium and high N additions, respectively) whereas O isotope values decreased (33.2, 28.7 and 25.3 ‰, respectively). Flux weighted SP values along the fertilization gradient (0.7, 4.0 and 3.8 ‰, respectively) were low and consistent with an origin predominantly from denitrification based on SP values found for nitrification and denitrification in pure culture studies. Consequently, we find that irregardless of the level of fertilizer applied denitrification was the predominant source of nitrous oxide.

  14. River suspended sediment estimation by climatic variables implication: Comparative study among soft computing techniques

    NASA Astrophysics Data System (ADS)

    Kisi, Ozgur; Shiri, Jalal

    2012-06-01

    Estimating sediment volume carried by a river is an important issue in water resources engineering. This paper compares the accuracy of three different soft computing methods, Artificial Neural Networks (ANNs), Adaptive Neuro-Fuzzy Inference System (ANFIS), and Gene Expression Programming (GEP), in estimating daily suspended sediment concentration on rivers by using hydro-meteorological data. The daily rainfall, streamflow and suspended sediment concentration data from Eel River near Dos Rios, at California, USA are used as a case study. The comparison results indicate that the GEP model performs better than the other models in daily suspended sediment concentration estimation for the particular data sets used in this study. Levenberg-Marquardt, conjugate gradient and gradient descent training algorithms were used for the ANN models. Out of three algorithms, the Conjugate gradient algorithm was found to be better than the others.

  15. Comparing adaptive and fixed bandwidth-based kernel density estimates in spatial cancer epidemiology.

    PubMed

    Lemke, Dorothea; Mattauch, Volkmar; Heidinger, Oliver; Pebesma, Edzer; Hense, Hans-Werner

    2015-03-31

    Monitoring spatial disease risk (e.g. identifying risk areas) is of great relevance in public health research, especially in cancer epidemiology. A common strategy uses case-control studies and estimates a spatial relative risk function (sRRF) via kernel density estimation (KDE). This study was set up to evaluate the sRRF estimation methods, comparing fixed with adaptive bandwidth-based KDE, and how they were able to detect 'risk areas' with case data from a population-based cancer registry. The sRRF were estimated within a defined area, using locational information on incident cancer cases and on a spatial sample of controls, drawn from a high-resolution population grid recognized as underestimating the resident population in urban centers. The spatial extensions of these areas with underestimated resident population were quantified with population reference data and used in this study as 'true risk areas'. Sensitivity and specificity analyses were conducted by spatial overlay of the 'true risk areas' and the significant (α=.05) p-contour lines obtained from the sRRF. We observed that the fixed bandwidth-based sRRF was distinguished by a conservative behavior in identifying these urban 'risk areas', that is, a reduced sensitivity but increased specificity due to oversmoothing as compared to the adaptive risk estimator. In contrast, the latter appeared more competitive through variance stabilization, resulting in a higher sensitivity, while the specificity was equal as compared to the fixed risk estimator. Halving the originally determined bandwidths led to a simultaneous improvement of sensitivity and specificity of the adaptive sRRF, while the specificity was reduced for the fixed estimator. The fixed risk estimator contrasts with an oversmoothing tendency in urban areas, while overestimating the risk in rural areas. The use of an adaptive bandwidth regime attenuated this pattern, but led in general to a higher false positive rate, because, in our study design

  16. 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

  17. Estimation of brood and nest survival: Comparative methods in the presence of heterogeneity

    USGS Publications Warehouse

    Manly, Bryan F.J.; Schmutz, Joel A.

    2001-01-01

    The Mayfield method has been widely used for estimating survival of nests and young animals, especially when data are collected at irregular observation intervals. However, this method assumes survival is constant throughout the study period, which often ignores biologically relevant variation and may lead to biased survival estimates. We examined the bias and accuracy of 1 modification to the Mayfield method that allows for temporal variation in survival, and we developed and similarly tested 2 additional methods. One of these 2 new methods is simply an iterative extension of Klett and Johnson's method, which we refer to as the Iterative Mayfield method and bears similarity to Kaplan-Meier methods. The other method uses maximum likelihood techniques for estimation and is best applied to survival of animals in groups or families, rather than as independent individuals. We also examined how robust these estimators are to heterogeneity in the data, which can arise from such sources as dependent survival probabilities among siblings, inherent differences among families, and adoption. Testing of estimator performance with respect to bias, accuracy, and heterogeneity was done using simulations that mimicked a study of survival of emperor goose (Chen canagica) goslings. Assuming constant survival for inappropriately long periods of time or use of Klett and Johnson's methods resulted in large bias or poor accuracy (often >5% bias or root mean square error) compared to our Iterative Mayfield or maximum likelihood methods. Overall, estimator performance was slightly better with our Iterative Mayfield than our maximum likelihood method, but the maximum likelihood method provides a more rigorous framework for testing covariates and explicity models a heterogeneity factor. We demonstrated use of all estimators with data from emperor goose goslings. We advocate that future studies use the new methods outlined here rather than the traditional Mayfield method or its previous

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

    PubMed

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

    2015-01-01

    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&new method is in the highest priority in estimation of the retired mobile phones. The result of sales&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 improve generation estimation of retired mobile phones and other WEEE.

  19. Comparing EQ-5D scores for comorbid health conditions estimated using 5 different methods.

    PubMed

    Ara, Roberta; Brazier, John

    2012-05-01

    There is currently no consensus on the most appropriate method to estimate health state utility values (HSUVs) for comorbid health conditions. The objective of the study was to assess the accuracy by applying 5 different methods to an EQ-5D dataset. EQ-5D data (n=41,174) from the Health Survey for England were used to compare HSUVs generated using the additive, multiplicative and minimum methods, the adjusted decrement estimator, and a linear regression. The additive and multiplicative methods underestimated the majority of HSUVs and the magnitude of the errors increased as the actual HSUV increased. Conversely, the minimum and adjusted decrement estimator methods overestimated the majority of HSUVs and the magnitude of errors increased as the actual HSUV decreased. Although the simple linear model produced the most accurate results, there was a tendency to underpredict higher HSUVs and overpredict lower HSUVs. The magnitude and direction of mean errors could be driven by the actual scores being estimated in addition to the technique used and the HSUVs estimated using an adjusted baseline were generally more accurate. The additive and minimum methods performed very poorly in our data. Although the simple linear model gave the most accurate results, the model requires validating in external data obtained from the EQ-5D and other preference-based measures. Based on the current evidence base, we would recommend the multiplicative method is used together with a range of univariate sensitivity analyses.

  20. Comparing potential recharge estimates from three Land Surface Models across the western US

    NASA Astrophysics Data System (ADS)

    Niraula, Rewati; Meixner, Thomas; Ajami, Hoori; Rodell, Matthew; Gochis, David; Castro, Christopher L.

    2017-02-01

    Groundwater is a major source of water in the western US. However, there are limited recharge estimates in this region due to the complexity of recharge processes and the challenge of direct observations. Land surface Models (LSMs) could be a valuable tool for estimating current recharge and projecting changes due to future climate change. In this study, simulations of three LSMs (Noah, Mosaic and VIC) obtained from the North American Land Data Assimilation System (NLDAS-2) are used to estimate potential recharge in the western US. Modeled recharge was compared with published recharge estimates for several aquifers in the region. Annual recharge to precipitation ratios across the study basins varied from 0.01% to 15% for Mosaic, 3.2% to 42% for Noah, and 6.7% to 31.8% for VIC simulations. Mosaic consistently underestimates recharge across all basins. Noah captures recharge reasonably well in wetter basins, but overestimates it in drier basins. VIC slightly overestimates recharge in drier basins and slightly underestimates it for wetter basins. While the average annual recharge values vary among the models, the models were consistent in identifying high and low recharge areas in the region. Models agree in seasonality of recharge occurring dominantly during the spring across the region. Overall, our results highlight that LSMs have the potential to capture the spatial and temporal patterns as well as seasonality of recharge at large scales. Therefore, LSMs (specifically VIC and Noah) can be used as a tool for estimating future recharge in data limited regions.

  1. 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.

  2. Comparing and combining SWE estimates from the SNOW-17 model using PRISM and SWE reconstruction

    NASA Astrophysics Data System (ADS)

    Raleigh, Mark S.; Lundquist, Jessica D.

    2012-01-01

    Snow models such as SNOW-17 may estimate past snow water equivalent (SWE) using either a forward configuration based on spatial extrapolation of measured precipitation, such as with the parameter-elevation regressions on independent slopes model (PRISM), or a reconstruction configuration based on snow disappearance timing and back-calculated snowmelt. However, little guidance exists as to which configuration is preferable. Because the two approaches theoretically have opposite sensitivities to model forcing, combining (averaging) their SWE estimates may be advantageous. Using 154 snow pillow sites located in maritime mountains of the western United States, we compared forward, reconstruction, and combined configurations of a simplified SNOW-17. We evaluated model errors in annual precipitation, peak SWE, and SWE errors during the accumulation and ablation seasons. We also conducted a separate analysis to assess the sensitivity of peak SWE to biased forcing data and model parameters. The forward model had the greatest precipitation accuracy, while the combined model had the greatest accuracy in peak SWE and SWE during the accumulation and ablation seasons. In determining peak SWE, the forward and reconstruction models demonstrated opposite sensitivities to errors in air temperature and model parameters, and the combined model minimized errors due to temperature bias and parameter uncertainty. In basins with precipitation gages, we recommend PRISM for precipitation estimation and the combined model for SWE estimation. In areas with high precipitation uncertainty, reconstruction is more viable. Accurate model parameters dramatically improved reconstruction, so more work is needed to advance parameter estimation techniques in complex terrain.

  3. 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

  4. Age estimation in fossil hominins: comparing dental development in early Homo with modern humans.

    PubMed

    Dean, M Christopher; Liversidge, Helen M

    2015-01-01

    Previous studies have used molar tooth eruption as a comparative marker of maturation in early fossil hominins. However, tooth eruption and tooth formation are independent maturational processes. To determine whether estimates of age for entering a stage of dental development in three early hominin fossils fell within the distribution of a modern human sample. This study used a comparative model of dental development to identify the stages of dental development most likely to provide information about length of the growth period in early fossil hominins. Age estimates for stages of dental development in fossils were superimposed onto a normal distribution of the same radiographically defined stages derived from a sample of 6540 children of diverse geographical origin. Both within the dentition of S7-37, from Sangiran, Java, but also for stages of two other specimens (KNM-WT 15000 from Kenya and StW 151 from South Africa), all age estimates for later stages of tooth formation fell within the modern sample range. A pattern appears to exist in early Homo where, both within and between developing dentitions, age estimates for stages of P4, M2 and M3 tooth formation fell consistently among the more advanced individuals of the modern human sample.

  5. 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 (c) 2016 APA, all rights reserved).

  6. Oxygen isotopic signature of N2O for distinguishing between bacterial and fungal denitrification

    NASA Astrophysics Data System (ADS)

    Rohe, L.; Well, R.; Lewicka-Szczebak, D.; Anderson, T. H.; Giesemann, A.

    2015-12-01

    The isotopic composition of the greenhouse gas N2O (δ15Nbulk, δ18O and 15N site preference (SP) of N2O) can be used to distinguish N2O production pathways. So far, controls of δ18O values are not sufficiently explored due to complex fractionation processes and varying extent of O-exchange with soil water. However, it can potentially serve as another isotopic parameter, beside SP values, enabling to differentiate between bacterial and fungal N2O production. In the study presented here, natural isotopic signature of N2O and O-exchange between denitrification intermediates and water for the first time was analyzed simultaneously from three bacterial and three fungal pure cultures. Anaerobic incubations with nitrite for fungi and nitrate for bacteria as electron acceptors were conducted. Treatments with three waters differing in 18O signature were used to determine O-exchange. 15N labeled electron acceptors served to determine the ongoing production pathway. After an incubation time of five, ten and 14 days gas samples were taken and analyzed with GC-IRMS. Aside from one fungus all others produced N2O by denitrification only. As expected, SP values of N2O produced by fungi were much higher compared to bacterial N2O. During fungal denitrification O-exchange was high (78 to 93%) and O isotope effects were stable over time and species and depended on O signature of water (42 to 48‰). In contrast, bacteria showed a much larger range of O-exchange (15 to 86%) with varying O isotope effects (14 to 39‰). Modelling O fractionation during denitrification revealed that O-exchange occurring by different enzymatic steps (nitrite reductase or nitric oxide reductase) could be responsible for the observed inconsistent O fractionation effects of bacteria compared to fungi. Thus, O fractionation of bacteria seems to be very complex and needs further investigation. Generally, fungal denitrification seems to be characterized by higher O fractionation effect than bacterial

  7. The Denitrification Characteristics and Microbial Community in the Cathode of an MFC with Aerobic Denitrification at High Temperatures.

    PubMed

    Zhao, Jianqiang; Wu, Jinna; Li, Xiaoling; Wang, Sha; Hu, Bo; Ding, Xiaoqian

    2017-01-01

    Microbial fuel cells (MFCs) have attracted much attention due to their ability to generate electricity while treating wastewater. The performance of a double-chamber MFC with simultaneous nitrification and denitrification (SND) in the cathode for treating synthetic high concentration ammonia wastewater was investigated at different dissolved oxygen (DO) concentrations and high temperatures. The results showed that electrode denitrification and traditional heterotrophic denitrification co-existed in the cathode chamber. Electrode denitrification by aerobic denitrification bacterium (ADB) is beneficial for achieving a higher voltage of the MFC at high DO concentrations (3.0-4.2 mg/L), while traditional heterotrophic denitrification is conducive to higher total nitrogen (TN) removal at low DO (0.5-1.0 mg/L) concentrations. Under high DO conditions, the nitrous oxide production and TN removal efficiency were higher with a 50 Ω external resistance than with a 100 Ω resistance, which demonstrated that electrode denitrification by ADB occurred in the cathode of the MFC. Sufficient electrons were inferred to be provided by the electrode to allow ADB survival at low carbon:nitrogen ratios (≤0.3). Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) results showed that increasing the DO resulted in a change of the predominant species from thermophilic autotrophic nitrifiers and facultative heterotrophic denitrifiers at low DO concentrations to thermophilic ADB at high DO concentrations. The predominant phylum changed from Firmicutes to Proteobacteria, and the predominant class changed from Bacilli to Alpha, Beta, and Gamma Proteobacteria.

  8. 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.

  9. Effect of nitrate and acetylene on nirS, cnorB, and nosZ expression and denitrification activity in Pseudomonas mandelii.

    PubMed

    Saleh-Lakha, Saleema; Shannon, Kelly E; Henderson, Sherri L; Zebarth, Bernie J; Burton, David L; Goyer, Claudia; Trevors, Jack T

    2009-08-01

    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 NO(3)(-) 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 KNO(3)/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 NO(3)(-) 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 KNO(3)/liter, indicating that there was no relationship between gene expression and denitrification activity under the conditions tested.

  10. A Comparative Study of Rotation Angle Estimation Methods Based on Complex Moments

    NASA Astrophysics Data System (ADS)

    Lee, Jong-Min; Kim, Whoi-Yul

    Determining the rotation angle between two images is essential when comparing images that may include rotational variation. While there are three representative methods that utilize the phases of Zernike moments (ZMs) to estimate rotation angles, very little work has been done to compare the performances of these methods. In this paper, we compare the performances of these three methods and propose a new, angular radial transform (ART)-based method. Our method extends Revaud et al.'s method [1] and uses the phase of angular radial transform coefficients instead of ZMs. We show that our proposed method outperforms the ZM-based method using the MPEG-7 shape dataset when computation times are compared or in terms of the root mean square error vs. coverage.

  11. 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.

  12. Impact of Groundwater Flowpaths on Subsurface Denitrification and Nutrient Loading to an Estuary

    NASA Astrophysics Data System (ADS)

    Michael, H. A.; Kroeger, K. D.; Fernandez, C.; Konikow, L. F.; Sawyer, A. H.; Russoniello, C. J.; Bratton, J. F.

    2013-12-01

    Groundwater-borne nutrient loads to Indian River Bay, Delaware, contribute to severe eutrophication. Geophysical surveys and measurements of submarine groundwater discharge (SGD) indicate that paleovalley features affect subsurface salinity distributions and discharge patterns. Site-scale variable-density numerical modeling with SEAWAT shows that groundwater flowpaths are influenced by geologic features. Fresh groundwater flowpaths extend offshore within the paleovalley--beneath a low-permeability cap-- resulting in greater mixing between fresh and saline groundwater, complex saltwater circulation patterns, and diffuse fresh discharge offshore. In contrast, away from the paleovalley in an interfluve, focused fresh discharge occurs nearshore. High-resolution groundwater sampling and measurements of biogeochemical parameters in transects across the site characterize the geochemical distribution associated with modeled flowpaths. Denitrification is indicated by quantification of excess N2 gas based on measurements of N2 and Ar. Interpretations are supported by analyses of nitrogen isotope ratios, groundwater age tracers, and long-term monitoring of groundwater recharge and temperatures. Analyses indicate that denitrification occurs along long flowpaths within the paleovalley, resulting in lower nitrate flux to the estuary. Reducing conditions and associated reduced reactants (organic carbon, Fe2+, S2-) that drive denitrification may be supplied by freshwater and marine wetlands within the paleovalley, or by subsurface sediment. In the focused discharge zone in the interfluve, little evidence of denitrification exists and high concentrations of nitrate discharge with fresh groundwater. Results have implications for estimation of groundwater-borne solute fluxes to estuaries and nutrient management, as natural or anthropogenic alterations of coastal hydrology may affect the extent to which nutrients are attenuated prior to discharge.

  13. 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

  14. 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

  15. Heterotrophic denitrification of aquaculture effluent using fluidized sand biofilters

    USDA-ARS?s Scientific Manuscript database

    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. Denitrification of groundwater with methane as sole hydrogen donor.

    PubMed

    Eisentraeger, A; Klag, P; Vansbotter, B; Heymann, E; Dott, W

    2001-06-01

    It was examined, whether methane can be used as hydrogen donor for an in situ denitrification of groundwater. It is demonstrated, that groundwater can serve as liquid medium and that the denitrification can occur at 10 degrees C. Efforts to enrich methanotrophic bacteria under anoxic conditions have not been successful. No methane oxidation occurred in the absence of oxygen. For this reason, the denitrification with methane must be performed in a two-stage process with aerobic methanotrophic bacteria producing metabolites, that are used as hydrogen donor by non-methanotrophic bacteria in anoxic areas. This kind of indirect denitrification was proved by quantifying nitrogen and nitrous oxide in enrichment cultures that were not stirred or shaken. Large numbers of non-methanotrophic bacteria being able to denitrify with methanol, acetate or proteins as sole hydrogen donor were enriched besides the methanotrophic bacteria under these conditions.

  17. 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

  18. Sample size re-estimation in paired comparative diagnostic accuracy studies with a binary response.

    PubMed

    McCray, Gareth P J; Titman, Andrew C; Ghaneh, Paula; Lancaster, Gillian A

    2017-07-14

    The sample size required to power a study to a nominal level in a paired comparative diagnostic accuracy study, i.e. studies in which the diagnostic accuracy of two testing procedures is compared relative to a gold standard, depends on the conditional dependence between the two tests - the lower the dependence the greater the sample size required. A priori, we usually do not know the dependence between the two tests and thus cannot determine the exact sample size required. One option is to use the implied sample size for the maximal negative dependence, giving the largest possible sample size. However, this is potentially wasteful of resources and unnecessarily burdensome on study participants as the study is likely to be overpowered. A more accurate estimate of the sample size can be determined at a planned interim analysis point where the sample size is re-estimated. This paper discusses a sample size estimation and re-estimation method based on the maximum likelihood estimates, under an implied multinomial model, of the observed values of conditional dependence between the two tests and, if required, prevalence, at a planned interim. The method is illustrated by comparing the accuracy of two procedures for the detection of pancreatic cancer, one procedure using the standard battery of tests, and the other using the standard battery with the addition of a PET/CT scan all relative to the gold standard of a cell biopsy. Simulation of the proposed method illustrates its robustness under various conditions. The results show that the type I error rate of the overall experiment is stable using our suggested method and that the type II error rate is close to or above nominal. Furthermore, the instances in which the type II error rate is above nominal are in the situations where the lowest sample size is required, meaning a lower impact on the actual number of participants recruited. We recommend multinomial model maximum likelihood estimation of the conditional

  19. 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.

  20. Comparing three methods for variance estimation with duplicated high density oligonucleotide arrays.

    PubMed

    Huang, Xiaohong; Pan, Wei

    2002-08-01

    Microarray experiments are being increasingly used in molecular biology. A common task is to detect genes with differential expression across two experimental conditions, such as two different tissues or the same tissue at two time points of biological development. To take proper account of statistical variability, some statistical approaches based on the t-statistic have been proposed. In constructing the t-statistic, one needs to estimate the variance of gene expression levels. With a small number of replicated array experiments, the variance estimation can be challenging. For instance, although the sample variance is unbiased, it may have large variability, leading to a large mean squared error. For duplicated array experiments, a new approach based on simple averaging has recently been proposed in the literature. Here we consider two more general approaches based on nonparametric smoothing. Our goal is to assess the performance of each method empirically. The three methods are applied to a colon cancer data set containing 2,000 genes. Using two arrays, we compare the variance estimates obtained from the three methods. We also consider their impact on the t-statistics. Our results indicate that the three methods give variance estimates close to each other. Due to its simplicity and generality, we recommend the use of the smoothed sample variance for data with a small number of replicates.

  1. Risk estimates for complex disorders: comparing personal genome testing and family history.

    PubMed

    Aiyar, Lila; Shuman, Cheryl; Hayeems, Robin; Dupuis, Annie; Pu, Shuye; Wodak, Shoshana; Chitayat, David; Velsher, Lea; Davies, Jill

    2014-03-01

    Personal genome testing allows the identification of single-nucleotide polymorphisms associated with an increased risk for common complex disorders. An area of concern in the use of personal genome testing is how risk estimates generated differ from traditional measures of risk (e.g., family history analysis). We sought to analyze the concordance of risk estimates generated by family history analysis and by personal genome testing. Risk categorizations for 20 complex conditions included in Navigenics personal genome testing were compared with risk categorization estimates derived from family history assessment using the kappa (κ) statistic. The only conditions showing slight agreement between risk assessment methods were Alzheimer disease (κ = 0.131), breast cancer (κ = 0.154), and deep vein thrombosis (κ = 0.201) in females, and colon cancer (κ = 0.124) in males. Eighty-six individuals (11.4%) were found to have additional genetic risks not assessed by personal genome testing after family and medical history assessment, including 38 individuals with family histories suggestive of hereditary cancer syndromes. Discordance between personal genome testing and family history risk estimates suggests that these methods may provide independent information that could be used in a complementary manner. Results also support that eliciting family history adds value to overall risk assessment for individuals undergoing personal genome testing.

  2. Early-Stage Capital Cost Estimation of Biorefinery Processes: A Comparative Study of Heuristic Techniques.

    PubMed

    Tsagkari, Mirela; Couturier, Jean-Luc; Kokossis, Antonis; Dubois, Jean-Luc

    2016-09-08

    Biorefineries offer a promising alternative to fossil-based processing industries and have undergone rapid development in recent years. Limited financial resources and stringent company budgets necessitate quick capital estimation of pioneering biorefinery projects at the early stages of their conception to screen process alternatives, decide on project viability, and allocate resources to the most promising cases. Biorefineries are capital-intensive projects that involve state-of-the-art technologies for which there is no prior experience or sufficient historical data. This work reviews existing rapid cost estimation practices, which can be used by researchers with no previous cost estimating experience. It also comprises a comparative study of six cost methods on three well-documented biorefinery processes to evaluate their accuracy and precision. The results illustrate discrepancies among the methods because their extrapolation on biorefinery data often violates inherent assumptions. This study recommends the most appropriate rapid cost methods and urges the development of an improved early-stage capital cost estimation tool suitable for biorefinery processes. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  3. Early‐Stage Capital Cost Estimation of Biorefinery Processes: A Comparative Study of Heuristic Techniques

    PubMed Central

    Couturier, Jean‐Luc; Kokossis, Antonis; Dubois, Jean‐Luc

    2016-01-01

    Abstract Biorefineries offer a promising alternative to fossil‐based processing industries and have undergone rapid development in recent years. Limited financial resources and stringent company budgets necessitate quick capital estimation of pioneering biorefinery projects at the early stages of their conception to screen process alternatives, decide on project viability, and allocate resources to the most promising cases. Biorefineries are capital‐intensive projects that involve state‐of‐the‐art technologies for which there is no prior experience or sufficient historical data. This work reviews existing rapid cost estimation practices, which can be used by researchers with no previous cost estimating experience. It also comprises a comparative study of six cost methods on three well‐documented biorefinery processes to evaluate their accuracy and precision. The results illustrate discrepancies among the methods because their extrapolation on biorefinery data often violates inherent assumptions. This study recommends the most appropriate rapid cost methods and urges the development of an improved early‐stage capital cost estimation tool suitable for biorefinery processes. PMID:27484398

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Toward quantitative estimation of material properties with dynamic mode atomic force microscopy: a comparative study

    NASA Astrophysics Data System (ADS)

    Ghosal, Sayan; Gannepalli, Anil; Salapaka, Murti

    2017-08-01

    In this article, we explore methods that enable estimation of material properties with the dynamic mode atomic force microscopy suitable for soft matter investigation. The article presents the viewpoint of casting the system, comprising of a flexure probe interacting with the sample, as an equivalent cantilever system and compares a steady-state analysis based method with a recursive estimation technique for determining the parameters of the equivalent cantilever system in real time. The steady-state analysis of the equivalent cantilever model, which has been implicitly assumed in studies on material property determination, is validated analytically and experimentally. We show that the steady-state based technique yields results that quantitatively agree with the recursive method in the domain of its validity. The steady-state technique is considerably simpler to implement, however, slower compared to the recursive technique. The parameters of the equivalent system are utilized to interpret storage and dissipative properties of the sample. Finally, the article identifies key pitfalls that need to be avoided toward the quantitative estimation of material properties.

  10. Comparative Study on the Estimation of Estrous Cycle in Mice by Visual and Vaginal Lavage Method

    PubMed Central

    Ekambaram, Gnanagurudasan; Joseph, Leena Dennis

    2017-01-01

    Introduction Evaluation of estrous cycle in laboratory animals can be a useful measure of the integrity of hypothalamic-pituitary-ovarian reproductive axis. Assessment of vaginal cytology is crucial to assess the milieu and compare the endocrine status of animals among the experimental groups. Aim The present study was attempted to compare the estimation of estrous cycle by visual method and non invasive vaginal lavage method. Materials and Methods Sixty healthy female swiss albino mice were used for the present study. The appearance of the vagina with respect to the opening of vagina, vaginal swellings were observed. Non-invasive method was used in vaginal lavage method in which nucleated epithelial cells, cornified squamous epithelial cells and leucocytes present in vaginal smears were used to identify the estrous stages. Results The estimation of estrous cycle by visual method coincides with the vaginal lavage method. In Vaginal lavage method, the accurate proportion of cells and the transition phases can be evaluated. Conclusion The non-invasive method reduces the risk of pseudo -pregnancy and mechanical trauma. Though, visual method is quick and reliable, for accurate estimation of the stage of the estrous, non-invasive vaginal lavage method is ideal. PMID:28273958

  11. High rates of denitrification and nitrous oxide emission in arid biological soil crusts from the Sultanate of Oman

    PubMed Central

    Abed, Raeid M M; Lam, Phyllis; de Beer, Dirk; Stief, Peter

    2013-01-01

    Using a combination of process rate determination, microsensor profiling and molecular techniques, we demonstrated that denitrification, and not anaerobic ammonium oxidation (anammox), is the major nitrogen loss process in biological soil crusts from Oman. Potential denitrification rates were 584±101 and 58±20 μmol N m−2 h−1 for cyanobacterial and lichen crust, respectively. Complete denitrification to N2 was further confirmed by an 15NO3− tracer experiment with intact crust pieces that proceeded at rates of 103±19 and 27±8 μmol N m−2 h−1 for cyanobacterial and lichen crust, respectively. Strikingly, N2O gas was emitted at very high potential rates of 387±143 and 31±6 μmol N m−2 h−1 from the cyanobacterial and lichen crust, respectively, with N2O accounting for 53–66% of the total emission of nitrogenous gases. Microsensor measurements revealed that N2O was produced in the anoxic layer and thus apparently originated from incomplete denitrification. Using quantitative PCR, denitrification genes were detected in both the crusts and were expressed either in comparable (nirS) or slightly higher (narG) numbers in the cyanobacterial crusts. Although 99% of the nirS sequences in the cyanobacterial crust were affiliated to an uncultured denitrifying bacterium, 94% of these sequences were most closely affiliated to Paracoccus denitrificans in the lichen crust. Sequences of nosZ gene formed a distinct cluster that did not branch with known denitrifying bacteria. Our results demonstrate that nitrogen loss via denitrification is a dominant process in crusts from Oman, which leads to N2O gas emission and potentially reduces desert soil fertility. PMID:23575368

  12. 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

  13. Comparative estimation of effective population sizes and temporal gene flow in two contrasting population systems.

    PubMed

    Fraser, Dylan J; Hansen, Michael M; Ostergaard, Siri; Tessier, Nathalie; Legault, Michel; Bernatchez, Louis

    2007-09-01

    Estimation of effective population sizes (N(e)) and temporal gene flow (N(e)m, m) has many implications for understanding population structure in evolutionary and conservation biology. However, comparative studies that gauge the relative performance of N(e), N(e)m or m methods are few. Using temporal genetic data from two salmonid fish population systems with disparate population structure, we (i) evaluated the congruence in estimates and precision of long- and short-term N(e), N(e)m and m from six methods; (ii) explored the effects of metapopulation structure on N(e) estimation in one system with spatiotemporally linked subpopulations, using three approaches; and (iii) determined to what degree interpopulation gene flow was asymmetric over time. We found that long-term N(e) estimates exceeded short-term N(e) within populations by 2-10 times; the two were correlated in the system with temporally stable structure (Atlantic salmon, Salmo salar) but not in the highly dynamic system (brown trout, Salmo trutta). Four temporal methods yielded short-term N(e) estimates within populations that were strongly correlated, and these were higher but more variable within salmon populations than within trout populations. In trout populations, however, these short-term N(e) estimates were always lower when assuming gene flow than when assuming no gene flow. Linkage disequilibrium data generally yielded short-term N(e) estimates of the same magnitude as temporal methods in both systems, but the two were uncorrelated. Correlations between long- and short-term geneflow estimates were inconsistent between methods, and their relative size varied up to eightfold within systems. While asymmetries in gene flow were common in both systems (58-63% of population-pair comparisons), they were only temporally stable in direction within certain salmon population pairs, suggesting that gene flow between particular populations is often intermittent and/or variable. Exploratory metapopulation N

  14. Soil physicochemical conditions, denitrification rates, and abundance in north Carolina coastal plain restored wetlands.

    PubMed

    Ducey, T F; Miller, J O; Lang, M W; Szogi, A A; Hunt, P G; Fenstermacher, D E; Rabenhorst, M C; McCarty, G W

    2015-05-01

    Over the last century, North Carolina has seen a severe reduction in the percentage of wetlands and a rise in negative environmental impacts related to this loss. To counter these effects, efforts have been enacted to mitigate wetland loss and create new wetland areas. The objective of this study was to assess the impact of hydrological restoration at several sites in the North Carolina coastal plain. Nine sites were selected for study. Hydrologically restored wetlands were compared with natural wetlands and prior converted (PC) croplands (i.e., historic wetlands under agricultural production). Each site was analyzed along a relative wetness gradient, and physicochemical properties, denitrification enzyme activity, and NO reductase gene () abundances using real-time PCR were measured. Physicochemically, restoration resulted in significantly increased levels of total C as compared with PC cropland sites. Restored wetland sites also saw pH, soil moisture, P, and NO+NO approximate levels similar to those of natural wetlands. Denitrification enzyme activity rates varied based on relative wetness within individual sites, generally increasing with increasing soil moisture. However, denitrification tended to be lower in restored wetland sites relative to natural wetlands. Gene abundances of saw statistically significant decreases in restored wetland soils. In conclusion, although analysis of restored wetlands reveals clear changes in several physicochemical characteristics and significant decreases in gene abundances, restoration efforts appear to have not significantly affected the denitrification component of the N cycle. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

  15. Linking denitrification and infiltration rates during managed groundwater recharge.

    PubMed

    Schmidt, Calla M; Fisher, Andrew T; Racz, Andrew J; Lockwood, Brian S; Huertos, Marc Los

    2011-11-15

    We quantify relations between rates of in situ denitrification and saturated infiltration through shallow, sandy soils during managed groundwater recharge. We used thermal methods to determine time series of point-specific flow rates, and chemical and isotopic methods to assess denitrification progress. Zero order denitrification rates between 3 and 300 μmol L(-1) d(-1) were measured during infiltration. Denitrification was not detected at times and locations where the infiltration rate exceeded a threshold of 0.7 ± 0.2 m d(-1). Pore water profiles of oxygen and nitrate concentration indicated a deepening of the redoxocline at high flow rates, which reduced the thickness of the zone favorable for denitrification. Denitrification rates were positively correlated with infiltration rates below the infiltration threshold, suggesting that for a given set of sediment characteristics, there is an optimal infiltration rate for achieving maximum nitrate load reduction and improvements to water supply during managed groundwater recharge. The extent to which results from this study may be extended to other managed and natural hydrologic settings remains to be determined, but the approach taken in this study should be broadly applicable, and provides a quantitative link between shallow hydrologic and biogeochemical processes.

  16. Denitrification in Marl and Peat Sediments in the Florida Everglades

    PubMed Central

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

    1986-01-01

    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 N2O 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. N2O 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 N2O amounted to only 10 to 34% of the added nitrate when 100 μM 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°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

  17. Denitrification likely catalyzed by endobionts in an allogromiid foraminifer

    PubMed Central

    Bernhard, Joan M; Edgcomb, Virginia P; Casciotti, Karen L; McIlvin, Matthew R; Beaudoin, David J

    2012-01-01

    Nitrogen can be a limiting macronutrient for carbon uptake by the marine biosphere. The process of denitrification (conversion of nitrate to gaseous compounds, including N2 (nitrogen gas)) removes bioavailable nitrogen, particularly in marine sediments, making it a key factor in the marine nitrogen budget. Benthic foraminifera reportedly perform complete denitrification, a process previously considered nearly exclusively performed by bacteria and archaea. If the ability to denitrify is widespread among these diverse and abundant protists, a paradigm shift is required for biogeochemistry and marine microbial ecology. However, to date, the mechanisms of foraminiferal denitrification are unclear, and it is possible that the ability to perform complete denitrification is because of the symbiont metabolism in some foraminiferal species. Using sequence analysis and GeneFISH, we show that for a symbiont-bearing foraminifer, the potential for denitrification resides in the endobionts. Results also identify the endobionts as denitrifying pseudomonads and show that the allogromiid accumulates nitrate intracellularly, presumably for use in denitrification. Endobionts have been observed within many foraminiferal species, and in the case of associations with denitrifying bacteria, may provide fitness for survival in anoxic conditions. These associations may have been a driving force for early foraminiferal diversification, which is thought to have occurred in the Neoproterozoic era when anoxia was widespread. PMID:22134648

  18. Denitrification likely catalyzed by endobionts in an allogromiid foraminifer.

    PubMed

    Bernhard, Joan M; Edgcomb, Virginia P; Casciotti, Karen L; McIlvin, Matthew R; Beaudoin, David J

    2012-05-01

    Nitrogen can be a limiting macronutrient for carbon uptake by the marine biosphere. The process of denitrification (conversion of nitrate to gaseous compounds, including N(2) (nitrogen gas)) removes bioavailable nitrogen, particularly in marine sediments, making it a key factor in the marine nitrogen budget. Benthic foraminifera reportedly perform complete denitrification, a process previously considered nearly exclusively performed by bacteria and archaea. If the ability to denitrify is widespread among these diverse and abundant protists, a paradigm shift is required for biogeochemistry and marine microbial ecology. However, to date, the mechanisms of foraminiferal denitrification are unclear, and it is possible that the ability to perform complete denitrification is because of the symbiont metabolism in some foraminiferal species. Using sequence analysis and GeneFISH, we show that for a symbiont-bearing foraminifer, the potential for denitrification resides in the endobionts. Results also identify the endobionts as denitrifying pseudomonads and show that the allogromiid accumulates nitrate intracellularly, presumably for use in denitrification. Endobionts have been observed within many foraminiferal species, and in the case of associations with denitrifying bacteria, may provide fitness for survival in anoxic conditions. These associations may have been a driving force for early foraminiferal diversification, which is thought to have occurred in the Neoproterozoic era when anoxia was widespread.

  19. A network biology approach to denitrification in Pseudomonas aeruginosa

    DOE PAGES

    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

  20. 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.

  1. Comparing Landsat-7 ETM+ and ASTER Imageries to Estimate Daily Evapotranspiration Within a Mediterranean Vineyard Watershed

    NASA Technical Reports Server (NTRS)

    Montes, Carlo; Jacob, Frederic

    2017-01-01

    We compared the capabilities of Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imageries for mapping daily evapotranspiration (ET) within a Mediterranean vineyard watershed. We used Landsat and ASTER data simultaneously collected on four dates in 2007 and 2008, along with the simplified surface energy balance index (S-SEBI) model. We used previously ground-validated good quality ASTER estimates as reference, and we analyzed the differences with Landsat retrievals in light of the instrumental factors and methodology. Although Landsat and ASTER retrievals of S-SEBI inputs were different, estimates of daily ET from the two imageries were similar. This is ascribed to the S-SEBI spatial differencing in temperature, and opens the path for using historical Landsat time series over vineyards.

  2. Estimating, testing, and comparing specific effects in structural equation models: the phantom model approach.

    PubMed

    Macho, Siegfried; Ledermann, Thomas

    2011-03-01

    The phantom model approach for estimating, testing, and comparing specific effects within structural equation models (SEMs) is presented. The rationale underlying this novel method consists in representing the specific effect to be assessed as a total effect within a separate latent variable model, the phantom model that is added to the main model. The following favorable features characterize the method: (a) It enables the estimation, testing, and comparison of arbitrary specific effects for recursive and nonrecursive models with latent and manifest variables; (b) it enables the bootstrapping of confidence intervals; and (c) it can be applied with all standard SEM programs permitting latent variables, the specification of equality constraints, and the bootstrapping of total effects. These features along with the fact that no manipulation of matrices and formulas is required make the approach particularly suitable for applied researchers. The method is illustrated by means of 3 examples with real data sets.

  3. Comparing estimates of climate change impacts from process-based and statistical crop models

    NASA Astrophysics Data System (ADS)

    Lobell, David B.; Asseng, Senthold

    2017-01-01

    The potential impacts of climate change on crop productivity are of widespread interest to those concerned with addressing climate change and improving global food security. Two common approaches to assess these impacts are process-based simulation models, which attempt to represent key dynamic processes affecting crop yields, and statistical models, which estimate functional relationships between historical observations of weather and yields. Examples of both approaches are increasingly found in the scientific literature, although often published in different disciplinary journals. Here we compare published sensitivities to changes in temperature, precipitation, carbon dioxide (CO2), and ozone from each approach for the subset of crops, locations, and climate scenarios for which both have been applied. Despite a common perception that statistical models are more pessimistic, we find no systematic differences between the predicted sensitivities to warming from process-based and statistical models up to +2 °C, with limited evidence at higher levels of warming. For precipitation, there are many reasons why estimates could be expected to differ, but few estimates exist to develop robust comparisons, and precipitation changes are rarely the dominant factor for predicting impacts given the prominent role of temperature, CO2, and ozone changes. A common difference between process-based and statistical studies is that the former tend to include the effects of CO2 increases that accompany warming, whereas statistical models typically do not. Major needs moving forward include incorporating CO2 effects into statistical studies, improving both approaches’ treatment of ozone, and increasing the use of both methods within the same study. At the same time, those who fund or use crop model projections should understand that in the short-term, both approaches when done well are likely to provide similar estimates of warming impacts, with statistical models generally

  4. 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

  5. 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.

  6. A comparative study of the performance of different spectral estimation methods for classification of mental tasks.

    PubMed

    Diez, Pablo F; Laciar, Eric; Mut, Vicente; Avila, Enrique; Torres, Abel

    2008-01-01

    In this paper we compare three different spectral estimation techniques for the classification of mental tasks. These techniques are the standard periodogram, the Welch periodogram and the Burg method, applied to electroencephalographic (EEG) signals. For each one of these methods we compute two parameters: the mean power and the root mean square (RMS), in various frequency bands. The classification of the mental tasks was conducted with a linear discriminate analysis. The Welch periodogram and the Burg method performed better than the standard periodogram. The use of the RMS allows better classification accuracy than the obtained with the power of EEG signals.

  7. IQ estimate smackdown: comparing IQ proxy measures to the WAIS-III.

    PubMed

    Spinks, Ruth; McKirgan, Lowell W; Arndt, Stephan; Caspers, Kristin; Yucuis, Rebecca; Pfalzgraf, Christopher J

    2009-07-01

    Brief assessments of general cognitive ability are frequently needed by neuropsychologists, and many methods of estimating intelligence quotient (IQ) have been published. While these measures typically present overall correlations with the Wechsler Adult Intelligence Scale (WAIS) Full Scale IQ, it is tacitly acknowledged that these estimates are most accurate within 1 standard deviation of the mean and that accuracy diminishes moving toward the tails of the IQ distribution. However, little work has been done to systematically characterize proxy measures at the tails of the IQ distribution. Additionally, while these measures are all correlated with the WAIS, multiple proxy measures are rarely presented in one manuscript. The current article has two goals: (1) Examine various IQ proxies against Wechsler Adult Intelligence Scale (Third Version) scores, showing the overall accuracy of each measure against the gold standard IQ measure. This comparison will assist in selecting the best proxy measure for particular clinical constraints. (2) The sample is then divided into three groups (below, average, and above-average ability), and each group is analyzed separately to characterize proxy performance at the tails of the IQ distribution. Repeated measures multivariate analysis of variance compares the different proxy measures across ability levels. All IQ estimates are represented in tables so that they can be examined side by side.

  8. Estimation of respiratory rate from photoplethysmographic imaging videos compared to pulse oximetry.

    PubMed

    Karlen, Walter; Garde, Ainara; Myers, Dorothy; Scheffer, Cornie; Ansermino, J Mark; Dumont, Guy A

    2015-07-01

    We present a study evaluating two respiratory rate estimation algorithms using videos obtained from placing a finger on the camera lens of a mobile phone. The two algorithms, based on Smart Fusion and empirical mode decomposition (EMD), consist of previously developed signal processing methods to detect features and extract respiratory induced variations in photoplethysmographic signals to estimate respiratory rate. With custom-built software on an Android phone, photoplethysmographic imaging videos were recorded from 19 healthy adults while breathing spontaneously at respiratory rates between 6 to 32 breaths/min. Signals from two pulse oximeters were simultaneously recorded to compare the algorithms' performance using mobile phone data and clinical data. Capnometry was recorded to obtain reference respiratory rates. Two hundred seventy-two recordings were analyzed. The Smart Fusion algorithm reported 39 recordings with insufficient respiratory information from the photoplethysmographic imaging data. Of the 232 remaining recordings, a root mean square error (RMSE) of 6 breaths/min was obtained. The RMSE for the pulse oximeter data was lower at 2.3 breaths/min. RMSE for the EMD method was higher throughout all data sources as, unlike the Smart Fusion, the EMD method did not screen for inconsistent results. The study showed that it is feasible to estimate respiratory rates by placing a finger on a mobile phone camera, but that it becomes increasingly challenging at respiratory rates greater than 20 breaths/min, independent of data source or algorithm tested.

  9. Body density estimates from upper-body skinfold thicknesses compared to air-displacement plethysmography.

    PubMed

    Shafer, Kimberly J; Siders, William A; Johnson, LuAnn K; Lukaski, Henry C

    2010-04-01

    Determine the accuracy of body density (Db) estimated with upper-body skinfold thickness (SFT) measurements compared to air-displacement plethysmography (ADP) and ascertain whether body mass index (BMI) impacts the accuracy of SFT to assess Db. We estimated Db with SFT and ADP in 131 healthy men and women with normal (N; 18.5-24.9kg/m(2)), overweight (OW; 25-29.9kg/m(2)), and obese (OB; 30-39.9kg/m(2)) BMI. Compared with ADP, SFT overestimated (p<0.05) Db in OW and OB females and in OB males (-0.0047, -0.0164 and -0.0119g/cc, respectively), and underestimated (p<0.05) Db in N females and males (0.0050 and 0.0068g/cc, respectively) but did not differently estimate Db in OW males. The gender by BMI group interaction was not significant. SFT underestimated (p<0.05; 0.0058g/cc) Db in the N and overestimated (p<0.05; 0.0113g/cc) Db in the OB BMI groups. The error in predicting Db did not change significantly over the range of Db within the N (r=0.239, p=0.06) and OB (r=0.160, p=0.934) BMI groups. Limits of agreement were -0.0165 to 0.0284g/cc and -0.0365 to 0.0085g/cc for the N and OB BMI groups, respectively. The error of estimating Db with SFT was correlated with mean Db in the aggregate sample (r=0.495, p<0.0001) and the OW group (r=0.394, p<0.009). The regression-based limits of agreement were +/-0.0226g/cc in the total group and +/-0.0168g/cc in the OW group. Although SFT offer practical advantages, the validity of SFT to estimate Db among individuals with N and OB BMI is adversely affected. Copyright 2009. Published by Elsevier Ltd.

  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. Comparison of two combined bioelectrochemical and sulfur autotrophic denitrification processes for drinking water treatment.

    PubMed

    Wang, Haiyan; Qu, Jiuhui

    2003-07-01

    Two combined bioelectrochemical and sulfur autotrophic denitrification (CBSAD) processes for the treatment of nitrate contaminated drinking water were studied in this article, the main difference between the two processes was whether the limestone was packed in the reactor. In these processes, the sulfur denitrification was carried out in the lower part (Sulfur Part) of the reactors while the bioelectrochemical hydrogen denitrification in the upper part (Bioelectrochemical Part). Sulfur Part of one reactor was packed with elemental sulfur and limestone while no limestone was packed in Sulfur Part of the other, the former reactor is referred to as RSL and the latter as RS. The denitrification results of the two reactors were compared under different conditions, from which it can be concluded that the minimum current of RSL was about 2 mA higher than that of RS. However, at the same hydraulic retention time (HRT) and minimum current, the nitrate removal of both reactors was higher than 90% while no nitrite was accumulated in the effluent. Ca2+ concentration in Sulfur Part effluent of RSL was increased because of the packed limestone, which led to the requirement of Ca2+ removal in Bioelectrochemical Part. The effluent sulfate concentration of RSL was higher than that of RS. When current was lower than 3 mA, the effluent pH value of RSL was about 0.6 higher than that of RS. However, the effluent pH of two parts of both reactors was about neutral under optimum operation conditions. The optimum operation condition of RSL was 1.9-4h HRT under 1.5-14 mA minimum current, while that of RSL was 1.9-5 h under 3-16.5 mA. The effluent quality of RS was better than that of RSL.

  12. Model demonstrating the potential for coupled nitrification denitrification in soil aggregates.

    PubMed

    Kremen, Arie; Bear, Jacob; Shavit, Uri; Shaviv, Avi

    2005-06-01

    A model of reactive, multi-species diffusion has been developed to describe N transformations in spherical soil aggregates, emphasizing the effects of irrigation with reclaimed wastewater. Oxygen demand for respiratory activity has been shown to promote the establishment of anaerobic conditions. Aggregate size and soil respiration rate were identified as the most significant parameters governing the existence and extent of the anaerobic volume in aggregates. The inclusion of kinetic models describing mineralization, nitrification, and denitrification facilitated the investigation of coupled nitrification/denitrification (CND), subject to O2 availability. N-transformations are shown to be affected by effluent-borne NH4+-N content, in addition to elevated BOD and pH levels. Their incremental contribution to O2 availability has been found to be secondary to respiratory activity. At the aggregate level, significant differences between apparent and gross rates of N-transformations were predicted (e.g., NH4+ oxidation and N2 formation), resulting from diffusive constraints due to aggregate size. With increasing anaerobic volume, the effective nitrification rate determined at the aggregates level decreases until its contribution to nitrification is negligible. It was found that the nitrification process was predominantly limited to aggregates <0.25 cm. Assuming that nitrification is the main source for NO3- formation, denitrification efficiency is predicted to peak in medium-sized aggregates, where aerobic and anaerobic conditions coexist, supporting CND. In effluent-irrigated soils, the predicted NO2- formation rate in small aggregates is enhanced when compared to freshwater-irrigated soils. The difference vanishes with increasing aggregate size as anaerobic NO2- consumption exceeds aerobic NO2- formation due to the coupling of nitrification and denitrification.

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

    PubMed

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

    2012-05-01

    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.

  14. 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...

  15. 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...

  16. 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...

  17. Syringe test screening of microbial gas production activity: Cases denitrification and biogas formation.

    PubMed

    Østgaard, Kjetill; Kowarz, Viktoria; Shuai, Wang; Henry, Ingrid A; Sposob, Michal; Haugen, Hildegunn Hegna; Bakke, Rune

    2017-01-01

    Mass produced plastic syringes may be applied as vessels for cheap, simple and large scale batch culture testing. As illustrated for the cases of denitrification and of biogas formation, metabolic activity was monitored by direct reading of the piston movement due to the gas volume formed. Pressure buildup due to friction was shown to be moderate. A piston pull and slide back routine can be applied before recording gas volume to minimize experimental errors due to friction. Inoculum handling and activity may be conveniently standardized as illustrated by applying biofilm carriers. A robust set of positive as well as negative controls ("blanks") should be included to ensure quality of the actual testing. The denitrification test showed saturation response at increasing amounts of inoculum in the form of adapted moving bed biofilm reactor (MBBR) carriers, with well correlated nitrate consumption vs. gas volume formed. As shown, the denitrification test efficiently screened different inocula at standardized substrates. Also, different substrates were successfully screened and compared at standardized inocula. The biogas potential test showed efficient screening of different substrates with effects of relative amounts of carbohydrate, protein, fat. A second case with CO2 capture reclaimer waste as substrate demonstrated successful use of co-feeding to support waste treatment and how temperature effects on kinetics and stoichiometry can be observed. In total, syringe test screening of microbial gas production seems highly efficient at a low cost when properly applied. Copyright © 2016 Elsevier B.V. All rights reserved.

  18. Denitrification enzyme activity of fringe salt marshes in New England (USA).

    PubMed

    Wigand, Cathleen; McKinney, Richard A; Chintala, Marnita M; Charpentier, Michael A; Groffman, Peter M

    2004-01-01

    Coastal salt marshes are a buffer between the uplands and adjacent coastal waters in New England (USA). With increasing N loads from developed watersheds, salt marshes could play an important role in the water quality maintenance of coastal waters. In this study we examined seasonal relationships between denitrification enzyme activity (DEA) in salt marshes of Narragansett Bay, Rhode Island, and watershed N loadings, land use, and terrestrial hydric soils. In a manipulative experiment, the effect of nutrient enrichment on DEA was examined in a saltmeadow cordgrass [Spartina patens (Aiton) Muhl.] marsh. In the high marsh, DEA significantly (p < 0.05) increased with watershed N loadings and decreased with the percent of hydric soils in a 200-m terrestrial buffer. In the low marsh, we found no significant relationships between DEA and watershed N loadings, residential land development, or terrestrial hydric soils. In the manipulation experiment, we measured increased DEA in N-amended treatments, but no effect in the P-amended treatments. The positive relationships between N loading and high marsh DEA support the hypothesis that salt marshes may be important buffers between the terrestrial landscape and estuaries, preventing the movement of land-derived N into coastal waters. The negative relationships between marsh DEA and the percent of hydric soils in the adjacent watershed illustrate the importance of natural buffers within the terrestrial landscape. Denitrification enzyme activity appears to be a useful index for comparing relative N exposure and the potential denitrification activity of coastal salt marshes.

  19. Ion exchange membrane textile bioreactor as a new alternative for drinking water denitrification.

    PubMed

    Berdous, Dalila; Akretche, Djamal-Eddine; Abderahmani, Ahmed; Berdous, Sakina; Meknaci, Rima

    2014-06-01

    This work enters in the optics of the denitrification of a polluted water by two membrane techniques, the Donnan dialysis (DD) and the ion exchange membrane bioreactor (IEMB), using a conventional barrier, composed by an anion exchange membrane (AEM), and a hybrid barrier, where the AEM is combined to an anion exchange textile (AET). The effects of the hydrodynamic factor and the nature of the carbon source on the transfer and the reduction of nitrate ions were studied. The study results obtained through the DD showed the effectiveness of the hybrid barrier in the recovery and concentration of nitrate ions. This was also recorded during denitrification by the hybrid process, called the ion exchange membrane textile bioreactor (IEMTB), with a significant reduction of nitrates, compared to IEMB, due to the efficiency of the Pseudomonas aeruginosa biofilm formed at the surface of the AET. Here, the permselectivity of the membrane and the good bioreduction of the pollutants are no longer major conditions to the better performance of the process. The application of IEMTB in the denitrification of groundwater, having a nitrate concentration of 96.67 ppm, shows a total reduction of nitrate ions without changing the quality of the water. Indeed, the analysis of the recovered water, or yet the treated water, shows the absence of the bacterium by-products and concentrations in the nitrates and nitrites which are, respectively, equal to 0.02±0.01 ppm, and inferiors to the detection limit (<0.02 ppm).

  20. Simultaneous nitrification and denitrification in a novel membrane bioelectrochemical reactor with low membrane fouling tendency.

    PubMed

    Li, Hui; Zuo, Wei; Tian, Yu; Zhang, Jun; Di, Shijing; Li, Lipin; Su, Xinying

    2017-02-01

    Microbial fuel cells (MFCs) can use nitrate as a cathodic electron acceptor for electrochemical denitrification, yet there is little knowledge about how to apply them into current wastewater treatment process to achieve efficient nitrogen removal. In this study, two dual-chamber MFCs were integrated with an aerobic membrane bioreactor to construct a novel membrane bioelectrochemical reactor (MBER) for simultaneous nitrification and denitrification under specific aeration. The effects of chemical oxygen demand (COD) loading rate, COD/N ratio, hydraulic retention time (HRT), and external resistance on the system performance were investigated. High effluent quality was obtained in the MBER in terms of COD and ammonium. During the operation, denitrification simultaneously occurred with nitrification at the bio-cathode of the MBER, achieving a maximal nitrogen removal efficiency of 84.3 %. A maximum power density of 1.8 W/m(3) and a current density of 8.5 A/m(3) were achieved with a coulombic efficiency of 12.1 %. Furthermore, compared to the control system, the MBER exhibited lower membrane fouling tendency due to mixed liquor volatile suspended solids (MLVSSs) and extracellular polymeric substance (EPS) reductions, EPSp/EPSc ratio decrease, and particle size increase of the sludge. These results suggest that the MBER holds potential for efficient nitrogen removal, electricity production, and membrane fouling mitigation.

  1. Sulfur-based autotrophic denitrification with eggshell for nitrate-contaminated synthetic groundwater treatment.

    PubMed

    Xu, Yaxian; Chen, Nan; Feng, Chuanping; Hao, Chunbo; Peng, Tong

    2016-12-01

    Eggshell is considered to be a waste and a significant quantity of eggshell waste is generated from food processing, baking and hatching industries. In this study, the effect of different sulfur/eggshell (w/w) ratios and temperatures was investigated to evaluate the feasibility of the sulfur-based autotrophic denitrification with eggshell (SADE) process for nitrate removal. The results showed eggshell can maintain a neutral condition in a range of pH 7.05-7.74 in the SADE process, and remove 97% of nitrate in synthetic groundwater. Compared with oyster shell and limestone, eggshell was found to be a desirable alkaline material for sulfur-based autotrophic denitrification (SAD) with no nitrite accumulation and insignificant sulfate production. Denitrification reaction was found to follow the first-order kinetic models (R(2) > .9) having nitrate removal rate constants of 0.85 and 0.93 d(-1) for raw eggshell and boiled eggshell, respectively. Sulfur/eggshell ratio of 2:3 provided the best efficiency on nitrate removal. Nitrate was removed completely by the SADE process at a low temperature of 15°C. Eggshell could be used for the SAD process due to its good effect for nitrate removal from groundwater.

  2. The Impact of Fe(II) on NO2- Isotopic Composition During Denitrification by Natural Sediment

    NASA Astrophysics Data System (ADS)

    Diaz-Etchevehere, D.; Wankel, S. D.

    2015-12-01

    The role of Fe(II) on Nitrite (NO2-) isotopic composition during denitrification was investigated in anaerobic, closed-system batch incubations of tidal marsh sediments. Fe(II) is often found in similar redox conditions and can rapidly reduce NO2- to N2 and/or nitrous oxide (N2O), a potent greenhouse gas, through a process called chemodenitrification. Microbial communities can also reduce nitrate (NO3-) to NO2- and eventually to N2O through the anaerobic process of biological denitrification. This study compared the impact on NO2- accumulation when Fe(III)-containing minerals ferrihydrite and goethite were added to natural sediments. The presence of dissolved Fe(II), presumably produced by microbial iron reduction, significantly limited the amount of NO2- accumulation, suggesting that Fe(II) may have chemically reduced NO2-. Changes in the δ15N of the intermediate NO2- pool in each bottle was measured, but the apparent isotope effects of NO2- reduction were indistinguishable among treatments, suggesting that the reaction of Fe(II) and NO2- imparts an isotope effect on the NO2- pool of a similar magnitude to that of biological NO2- reduction. The isotopic composition of N2O and its 15N site preference will be measured to determine if chemodenitrification truly occurred, and if so, the relative contributions to N2O production from biological denitrification and chemodenitrification will be determined.

  3. Enhanced heterotrophic denitrification: effect of dairy industry sludge acclimatization and operating conditions.

    PubMed

    Akbari Shahabi, Zeinab; Naeimpoor, Fereshteh

    2014-06-01

    Heterotrophic denitrification of drinking water was enhanced by selection of an anoxic sludge taken from a dairy industry among the sludges taken from various industries, and the effect of carbon sources was examined. Acclimatization to high nitrate concentration was then carried out in a five-stage process. Considering removals of both nitrate and nitrite, the sludge taken from anoxic unit of Tehran Pegah dairy industry was shown to be the superior microbial culture, with ethanol as carbon source as compared to acetate. To enhance the rate of denitrification, acclimatization to nitrate (at 100, 200, 400, 800, and 1,600 mg N-NO3/L) was carried out in sequencing batch reactors over a 3-month period under anoxic condition, and comparisons were made between the performances of acclimated and non-acclimated sludges at each stage. It was found that acclimatization up to the fourth stage enhanced the specific denitrification rate to a high value of 29.6 mg N-NO3/h/g mixed liquor suspended solids (MLSS), with no significant nitrite accumulation. Additionally, the effect of initial pH (6, 6.5, 7, and 7.5) and carbon-to-nitrogen (C/N) ratio (1, 1.5, 2, and 3) on the performance of this final acclimated sludge was assessed, where initial pH of 7 and C/N ratio of 1.5 resulted in the best performances considering both nitrate and nitrite removal.

  4. A comparative study of satellite estimation for solar insolation in Albania with ground measurements

    SciTech Connect

    Mitrushi, Driada Berberi, Pëllumb Muda, Valbona Buzra, Urim; Bërdufi, Irma; Topçiu, Daniela

    2016-03-25

    The main objective of this study is to compare data provided by Database of NASA with available ground data for regions covered by national meteorological net NASA estimates that their measurements of average daily solar radiation have a root-mean-square deviation RMSD error of 35 W/m{sup 2} (roughly 20% inaccuracy). Unfortunately valid data from meteorological stations for regions of interest are quite rare in Albania. In these cases, use of Solar Radiation Database of NASA would be a satisfactory solution for different case studies. Using a statistical method allows to determine most probable margins between to sources of data. Comparison of mean insulation data provided by NASA with ground data of mean insulation provided by meteorological stations show that ground data for mean insolation results, in all cases, to be underestimated compared with data provided by Database of NASA. Converting factor is 1.149.

  5. Comparative study of age estimation using dentinal translucency by digital and conventional methods.

    PubMed

    Bommannavar, Sushma; Kulkarni, Meena

    2015-01-01

    Estimating age using the dentition plays a significant role in identification of the individual in forensic cases. Teeth are one of the most durable and strongest structures in the human body. The morphology and arrangement of teeth vary from person-to-person and is unique to an individual as are the fingerprints. Therefore, the use of dentition is the method of choice in the identification of the unknown. Root dentin translucency is considered to be one of the best parameters for dental age estimation. Traditionally, root dentin translucency was measured using calipers. Recently, the use of custom built software programs have been proposed for the same. The present study describes a method to measure root dentin translucency on sectioned teeth using a custom built software program Adobe Photoshop 7.0 version (Adobe system Inc, Mountain View California). A total of 50 single rooted teeth were sectioned longitudinally to derive a 0.25 mm uniform thickness and the root dentin translucency was measured using digital and caliper methods and compared. The Gustafson's morphohistologic approach is used in this study. Correlation coefficients of translucency measurements to age were statistically significant for both the methods (P < 0.125) and linear regression equations derived from both methods revealed better ability of the digital method to assess age. The custom built software program used in the present study is commercially available and widely used image editing software. Furthermore, this method is easy to use and less time consuming. The measurements obtained using this method are more precise and thus help in more accurate age estimation. Considering these benefits, the present study recommends the use of digital method to assess translucency for age estimation.

  6. Comparative study of age estimation using dentinal translucency by digital and conventional methods

    PubMed Central

    Bommannavar, Sushma; Kulkarni, Meena

    2015-01-01

    Introduction: Estimating age using the dentition plays a significant role in identification of the individual in forensic cases. Teeth are one of the most durable and strongest structures in the human body. The morphology and arrangement of teeth vary from person-to-person and is unique to an individual as are the fingerprints. Therefore, the use of dentition is the method of choice in the identification of the unknown. Root dentin translucency is considered to be one of the best parameters for dental age estimation. Traditionally, root dentin translucency was measured using calipers. Recently, the use of custom built software programs have been proposed for the same. Objectives: The present study describes a method to measure root dentin translucency on sectioned teeth using a custom built software program Adobe Photoshop 7.0 version (Adobe system Inc, Mountain View California). Materials and Methods: A total of 50 single rooted teeth were sectioned longitudinally to derive a 0.25 mm uniform thickness and the root dentin translucency was measured using digital and caliper methods and compared. The Gustafson's morphohistologic approach is used in this study. Results: Correlation coefficients of translucency measurements to age were statistically significant for both the methods (P < 0.125) and linear regression equations derived from both methods revealed better ability of the digital method to assess age. Conclusion: The custom built software program used in the present study is commercially available and widely used image editing software. Furthermore, this method is easy to use and less time consuming. The measurements obtained using this method are more precise and thus help in more accurate age estimation. Considering these benefits, the present study recommends the use of digital method to assess translucency for age estimation. PMID:25709325

  7. 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.

  8. Comparing paleointensity methods: Importance of the cooling-rate effect on microwave estimates

    NASA Astrophysics Data System (ADS)

    Poletti, W.; Hartmann, G. A.; Hill, M. J.; Biggin, A. J.; Trindade, R. I.

    2013-12-01

    The strength of the past Earth's magnetic field can be inferred from the fossil magnetism of rocks and baked archeological materials. Nowadays, three techniques are used which take advantage of the proportionality between the magnetization intensity in these material and the intensity of the ambient field in which they cooled down from high temperatures - the classical Thellier-Thellier method (TT), the Triaxe method (TR) and the Microwave method (MW). In order to compare these methods, we present new MW that are compared to TT and TR paleointensity data previously obtained on well-characterized archeological bricks from Northeast Brazil, and reevaluate MW and TT paleointensity data from Southwestern Pacific islands. We note that the MW paleointensity data on both collections presented a bias towards higher fields when compared to the other double-heating paleointensity estimates. A simple theoretical approach suggests that the MW bias in NE Brazil and SW Pacific is due to a cooling-rate effect on MW estimates. We then corrected theoretically and experimentally the MW cooling-rate effects, increasing dramatically the degree of consistency between the previous and new results (reducing maximum discrepancies in NE Brazil from 25% to 8%, and in SW Pacific from 12% to 5%). Our results demonstrate the equivalence of microwave and thermal procedures despite the different ways in which the energy is transferred into the spin system (electromagnetic and lattice vibrations). Finally, our results on bricks and ceramics indicate very fast cooling-times after MW steps of less than 1 minute when compared to the several hours cooling in the oven during manufacture, highlighting the need for systematic cooling-rate corrections to be applied in MW paleointensity studies in the future.

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

    USGS Publications Warehouse

    Taggart, S. James; O'Clair, Charles E.; Shirley, Thomas C.; Mondragon, Jennifer

    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.

  10. 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

  11. 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

  12. 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).

  13. Aerobic respiration along isopycnals leads to overestimation of the isotope effect of denitrification in the ocean water column

    NASA Astrophysics Data System (ADS)

    Marconi, Dario; Kopf, Sebastian; Rafter, Patrick A.; Sigman, Daniel M.

    2017-01-01

    The nitrogen (N) isotopes provide an integrative geochemical tool for constraining the fixed N budget of the ocean. However, N isotope budgeting requires a robust estimate for the organism-scale nitrogen isotope effect of denitrification, in particular as it occurs in water column denitrification zones (εwcd). Ocean field data interpreted with the Rayleigh model have typically yielded estimates for εwcd of between 20 and 30‰. However, recent findings have raised questions about this value. In particular, culture experiments can produce a substantially lower isotope effect (∼13‰) under conditions mimicking those of ocean suboxic zones. In an effort to better understand prior field estimates of εwcd, we use a geochemical multi-box model to investigate the combined effects of denitrification, aerobic respiration, and isopycnal exchange on the δ15N of nitrate. In the context of this admittedly simplistic model, we consider three isopycnals extending from the Southern Ocean to the Eastern Tropical North Pacific (ETNP). We show that the data from the ETNP suboxic zone can be reproduced with an εwcd of 13‰, given a rate of aerobic respiration consistent with the nutrient data on these isopycnals and a plausible range in the δ15N of the sinking flux being remineralized. We discuss the limitations of our analysis, additional considerations, as well as possible data-based tests for the proposal of a lower εwcd than previously estimated. All else held constant, a lower εwcd would imply a lower global ocean rate of denitrification that is more similar to the estimated rate of N input to the global ocean, providing a major impetus for further investigation.

  14. Heterotrophic and elemental-sulfur-based autotrophic denitrification processes for simultaneous nitrate and Cr(VI) reduction.

    PubMed

    Sahinkaya, Erkan; Kilic, Adem

    2014-03-01

    Nitrate and chromate can be present together in water resources as nitrate is a common co-contaminant in surface and ground waters. This study aims at comparatively evaluating simultaneous chromate and nitrate reduction in heterotrophic and sulfur-based autotrophic denitrifying column bioreactors. In sulfur-based autotrophic denitrification process, elemental sulfur and nitrate act as an electron donor and an acceptor, respectively, without requirement of organic supplementation. Autotrophic denitrification was complete and not adversely affected by chromate up to 0.5 mg/L. Effluent chromate concentration was <50 μg/L provided that influent chromate concentration was ≤0.5 mg/L. Heterotrophic denitrification performance was not adversely affected even at 20 mg/L chromate and complete chromate reduction was attained up to 10 mg/L. Although autotrophic denitrification rate was much lower compared with heterotrophic one, it may be preferred in drinking water treatment due to the elimination of organic supplementation and the risk of treated effluent contamination.

  15. Comparison between a moving bed bioreactor and a fixed bed bioreactor for biological phosphate removal and denitrification.

    PubMed

    Choi, H J; Lee, A H; Lee, S M

    2012-01-01

    Moving bed bioreactors (MBBR) and fixed bed bioreactors (FBBR) were compared for biological phosphorus removal and denitrification. The sorption denitrification P-elimination (S-DN-P) process was selected for this study. Results indicated that all nutrients were removed by the FBBR process compared with the MBBR process: 19.8% (total COD), 35.5% (filtered COD), 27.6% (BOD(5)), 62.2% (acetate), 78.5% (PO(4)-P), and 54.2% (NO(3)-N) in MBBR; 49.7% (total COD), 54.0% (filtered COD), 63.2% (BOD(5)), 99.6% (acetate), 98.6% (PO(4)-P), and 75.9% (NO(3)-N) in FBBR. The phosphate uptake and NO(3)-N decomposition in the FBBR process during the denitrification phase were much higher than for the MBBR process despite being of shorter duration. Results obtained from this study are helpful in elucidating the practical implications of using MBBR and FBBR for the removal of bio-P and denitrification from wastewater.

  16. Evidence-based design recommendations for prevalence studies on multimorbidity: improving comparability of estimates.

    PubMed

    Holzer, Barbara M; Siebenhuener, Klarissa; Bopp, Matthias; Minder, Christoph E

    2017-03-07

    In aging populations, multimorbidity causes a disease burden of growing importance and cost. However, estimates of the prevalence of multimorbidity (prevMM) vary widely across studies, impeding valid comparisons and interpretation of differences. With this study we pursued two research objectives: (1) to identify a set of study design and demographic factors related to prevMM, and (2) based on (1), to formulate design recommendations for future studies with improved comparability of prevalence estimates. Study data were obtained through systematic review of the literature. UsingPubMed/MEDLINE, Embase, CINAHL, Web of Science, BIOSIS, and Google Scholar, we looked for articles with the terms "multimorbidity," "comorbidity," "polymorbidity," and variations of these published in English or German in the years 1990 to 2011. We selected quantitative studies of the prevalence of multimorbidity (two or more chronic medical conditions) with a minimum sample size of 50 and a study population with a majority of Caucasians. Our database consisted of prevalence estimates in 108 age groups taken from 45 studies. To assess the effects of study design variables, we used meta regression models. In 58% of the studies, there was only one age group, i.e., no stratification by age. The number of persons per age group ranged from 136 to 5.6 million. Our analyses identified the following variables as highly significant: "mean age," "number of age groups", and "data reporting quality" (all p < 0.0001). "Setting," "disease classification," and "number of diseases in the classification" were significant (0.01 < p ≤ 0.03), and "data collection period" and "data source" were non-significant. A separate analysis showed that prevMM was significantly higher in women than men (sign test, p = 0.0015). Comparable prevalence estimates are urgently needed for realistic description of the magnitude of the problem of multimorbidity. Based on the results of our analyses of variables

  17. 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

  18. 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.

  19. 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.

  20. Regime Shifts in Climate Forcing of Peru Denitrification

    NASA Astrophysics Data System (ADS)

    Altabet, M. A.; Cleaveland, L.; Tierny, J.; Herbert, T. D.

    2004-12-01

    Water column denitrification occurs in suboxic intermediate waters when bacteria transform nitrate to N2 gas, thereby removing it from the ocean's combined N inventory. Combined N availability is an important controlling factor for organic C production across much of the ocean, such that past variations in oceanic denitrification likely had repercussions for marine productivity and perhaps, at appropriate time scales, atmospheric CO2. Prior studies in the Arabian Sea and E. Tropical N. Pacific have demonstrated climatically-forced oscillations in denitrification on orbital to millennial time scales. Here we examine the Peru denitrification zone, the last of major water column denitrification zones to be studied and the only one in the S. Hemisphere. It is also the most likely to be influenced by ENSO variability. We have examined a series of high resolution cores from the upper Peru margin and developed a chronostratigraphy covering the last 60 kyr overcoming difficulties of common hiatuses and little or no preserved foraminifera. We have also examined ODP Site 1237 and associated site survey cores located in deep waters near the margin on the Nazca Ridge. A multi-proxy approach is taken including N isotopic composition to record denitrification intensity; major and minor elemental composition for sediment provenance, water column redox state, and productivity; alkenone UK37 for SST. Denitrification intensity is observed to vary at a variety of time scales. The lower resolution, 2 Ma record from site 1237 shows large orbital-scale shifts with the dominant mode shifting at the MPT. The high resolution records from the margin elucidate the nature of important forcings. The last deglaciation experienced a sharp and early rise in Peru denitrification that preceded by 2 kyr any major changes in local productivity. Forcing appears to be remote from the Peru upwelling zone, likely due to changes in either the ventilation of source intermediate waters in the Subantarctic

  1. The Denitrification Characteristics and Microbial Community in the Cathode of an MFC with Aerobic Denitrification at High Temperatures

    PubMed Central

    Zhao, Jianqiang; Wu, Jinna; Li, Xiaoling; Wang, Sha; Hu, Bo; Ding, Xiaoqian

    2017-01-01

    Microbial fuel cells (MFCs) have attracted much attention due to their ability to generate electricity while treating wastewater. The performance of a double-chamber MFC with simultaneous nitrification and denitrification (SND) in the cathode for treating synthetic high concentration ammonia wastewater was investigated at different dissolved oxygen (DO) concentrations and high temperatures. The results showed that electrode denitrification and traditional heterotrophic denitrification co-existed in the cathode chamber. Electrode denitrification by aerobic denitrification bacterium (ADB) is beneficial for achieving a higher voltage of the MFC at high DO concentrations (3.0–4.2 mg/L), while traditional heterotrophic denitrification is conducive to higher total nitrogen (TN) removal at low DO (0.5–1.0 mg/L) concentrations. Under high DO conditions, the nitrous oxide production and TN removal efficiency were higher with a 50 Ω external resistance than with a 100 Ω resistance, which demonstrated that electrode denitrification by ADB occurred in the cathode of the MFC. Sufficient electrons were inferred to be provided by the electrode to allow ADB survival at low carbon:nitrogen ratios (≤0.3). Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) results showed that increasing the DO resulted in a change of the predominant species from thermophilic autotrophic nitrifiers and facultative heterotrophic denitrifiers at low DO concentrations to thermophilic ADB at high DO concentrations. The predominant phylum changed from Firmicutes to Proteobacteria, and the predominant class changed from Bacilli to Alpha, Beta, and Gamma Proteobacteria. PMID:28154554

  2. Using measured soil water contents to estimate evapotranspiration and root water uptake profiles - a comparative study

    NASA Astrophysics Data System (ADS)

    Guderle, M.; Hildebrandt, A.

    2015-01-01

    Understanding the role of plants in soil water relations, and thus ecosystem functioning, requires information about root water uptake. We evaluated four different complex water balance methods to estimate sink term patterns and evapotranspiration directly from soil moisture measurements. We tested four methods. The first two take the difference between two measurement intervals as evapotranspiration, thus neglecting vertical flow. The third uses regression on the soil water content time series and differences between day and night to account for vertical flow. The fourth accounts for vertical flow using a numerical model and iteratively solves for the sink term. None of these methods requires any a priori information of root distribution parameters or evapotranspiration, which is an advantage compared to common root water uptake models. To test the methods, a synthetic experiment with numerical simulations for a grassland ecosystem was conducted. Additionally, the time series were perturbed to simulate common sensor errors, like those due to measurement precision and inaccurate sensor calibration. We tested each method for a range of measurement frequencies and applied performance criteria to evaluate the suitability of each method. In general, we show that methods accounting for vertical flow predict evapotranspiration and the sink term distribution more accurately than the simpler approaches. Under consideration of possible measurement uncertainties, the method based on regression and differentiating between day and night cycles leads to the best and most robust estimation of sink term patterns. It is thus an alternative to more complex inverse numerical methods. This study demonstrates that highly resolved (temporally and spatially) soil water content measurements may be used to estimate the sink term profiles when the appropriate approach is used.

  3. 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…

  4. 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…

  5. 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…

  6. 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.

  7. Evidence for biological denitrification inhibition (BDI) by plant secondary metabolites.

    PubMed

    Bardon, Clément; Piola, Florence; Bellvert, Floriant; Haichar, Feth el Zahar; Comte, Gilles; Meiffren, Guillaume; Pommier, Thomas; Puijalon, Sara; Tsafack, Noelline; Poly, Franck

    2014-11-01

    Previous studies on the effect of secondary metabolites on the functioning of rhizosphere microbial communities have often focused on aspects of the nitrogen (N) cycle but have overlooked biological denitrification inhibition (BDI), which can affect plant N-nutrition. Here, we investigated the BDI by the compounds of Fallopia spp., an invasive weed shown to be associated with a low potential denitrification of the soil. Fallopia spp. extracts were characterized by chromatographic analysis and were used to test the BDI effects on the metabolic and respiratory activities of denitrifying bacteria, under aerobic and anaerobic (denitrification) conditions. The BDI of Fallopia spp. extracts was tested on a complex soil community by measuring denitrification enzyme activity (DEA), substrate induced respiration (SIR), as well as abundances of denitrifiers and total bacteria. In 15 strains of denitrifying bacteria, extracts led to a greater BDI (92%) than respiration inhibition (50%). Anaerobic metabolic activity reduction was correlated with catechin concentrations and the BDI was dose dependent. In soil, extracts reduced the DEA/SIR ratio without affecting the denitrifiers: total bacteria ratio. We show that secondary metabolite(s) from Fallopia spp. inhibit denitrification. This provides new insight into plant-soil interactions and improves our understanding of a plant's ability to shape microbial soil functioning.

  8. Emerging complexity in the denitrification regulatory network of Bradyrhizobium japonicum.

    PubMed

    Torres, María J; Bueno, Emilio; Mesa, Socorro; Bedmar, Eulogio J; Delgado, María J

    2011-01-01

    Bradyrhizobium japonicum is a Gram-negative soil bacterium symbiotically associated with soya bean plants, which is also able to denitrify under free-living and symbiotic conditions. In B. japonicum, the napEDABC, nirK, norCBQD and nosRZDYFLX genes which encode reductases for nitrate, nitrite, nitric oxide and nitrous oxide respectively are required for denitrification. Similar to many other denitrifiers, expression of denitrification genes in B. japonicum requires both oxygen limitation and the presence of nitrate or a derived nitrogen oxide. In B. japonicum, a sophisticated regulatory network consisting of two linked regulatory cascades co-ordinates the expression of genes required for microaerobic respiration (the FixLJ/FixK2 cascade) and for nitrogen fixation (the RegSR/NifA cascade). The involvement of the FixLJ/FixK2 regulatory cascade in the microaerobic induction of the denitrification genes is well established. In addition, the FNR (fumarase and nitrate reduction regulator)/CRP(cAMP receptor protein)-type regulator NnrR expands the FixLJ/FixK2 regulatory cascade by an additional control level. A role for NifA is suggested in this process by recent experiments which have shown that it is required for full expression of denitrification genes in B. japonicum. The present review summarizes the current understanding of the regulatory network of denitrification in B. japonicum.

  9. [Identification and denitrification characteristics of a thermophilic aerobic denitrifier].

    PubMed

    Zhang, Miao; Huang, Shao-Bin

    2011-01-01

    A bacterial strain TAD1 with high nitrogen removal efficiency was isolated from biofilm of the biotrickling filter of a coal-fired power plant by thermophilic domestication. This bacterium was Gram negative, short rod, with the size of (0.67-0.89) microm x (1.03-1.41) microm. It was identified as Chelatococcus sp. according to its physiological properties and the analysis of its 16S rDNA gene. Studied on its function of aerobic denitrification at the temperature of 50 degrees C, the results showed that nitrate in the culture media was efficiently removed from 63.79 mg/L to 0.46 mg/L, and the nitrogen removal efficiency was up to 99.12% in 24 hours, and no nitrite was observed during the incubation, the major end product of the denitrification was nitrogen. During the denitrification of TAD1, the pH in the culture medium gradually increases, while the oxidation-reduction potential gradually decreases. The factors affecting aerobic denitrification by strain TAD1 were also discussed, indicating that the most suitable pH value for aerobic denitrification was 7.0-9.0, and the DO was 2.1-7.2 mg/L.

  10. Nitrogen removal from the saline sludge liquor by electrochemical denitrification.

    PubMed

    Xie, Z M; Li, X Y; Chan, K Y

    2006-01-01

    Sludge liquor from the sludge dewatering process has a high ammonia content. In the present study, a lab-scale electrochemical (EC) system with a pair of Ti electrode plates was used for treating the sludge centrate liquor of digested wastewater sludge with a NH4(+) - N content of around 500 mg/L. The sludge liquor had a high salinity due to seawater being used for toilet flushing in Hong Kong. The results show that the EC process is highly effective for denitrification of the saline sludge liquor. Complete nitrogen removal could be achieved within 1 hr or so. The rate of EC denitrification increased with the current intensity applied. The best current efficiency for nitrogen removal was obtained for a gap distance between the electrodes at 8 mm. Electro-chlorination was considered to be the major mechanism of EC denitrification. The formation of chlorination by-products (CBPs) appeared to be minimal with the total trihalomethanes (THM) detected at a level of 300 microg/L or lower. The power consumption for EC denitrification was around 23 kWh/kg N. Additional electro-flocculation with a pair of iron needle electrodes could enhance the flocculation and subsequent sedimentation of colloidal organics in the sludge liquor, increasing the organic removal from less than 30% to more than 70%. Therefore, the EC process including both electro-denitrification and electro-flocculation can be developed as the most cost-effective method for treatment of the saline sludge liquor.

  11. Microbial ecology of denitrification in biological wastewater treatment.

    PubMed

    Lu, Huijie; Chandran, Kartik; Stensel, David

    2014-11-01

    Globally, denitrification is commonly employed in biological nitrogen removal processes to enhance water quality. However, substantial knowledge gaps remain concerning the overall community structure, population dynamics and metabolism of different organic carbon sources. This systematic review provides a summary of current findings pertaining to the microbial ecology of denitrification in biological wastewater treatment processes. DNA fingerprinting-based analysis has revealed a high level of microbial diversity in denitrification reactors and highlighted the impacts of carbon sources in determining overall denitrifying community composition. Stable isotope probing, fluorescence in situ hybridization, microarrays and meta-omics further link community structure with function by identifying the functional populations and their gene regulatory patterns at the transcriptional and translational levels. This review stresses the need to integrate microbial ecology information into conventional denitrification design and operation at full-scale. Some emerging questions, from physiological mechanisms to practical solutions, for example, eliminating nitrous oxide emissions and supplementing more sustainable carbon sources than methanol, are also discussed. A combination of high-throughput approaches is next in line for thorough assessment of wastewater denitrifying community structure and function. Though denitrification is used as an example here, this synergy between microbial ecology and process engineering is applicable to other biological wastewater treatment processes. Copyright © 2014 Elsevier Ltd. All rights reserved.

  12. 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.

  13. Comparative Assessment of Environmental Flow Estimation Methods in a Mediterranean Mountain River

    NASA Astrophysics Data System (ADS)

    Papadaki, Christina; Soulis, Konstantinos; Ntoanidis, Lazaros; Zogaris, Stamatis; Dercas, Nicholas; Dimitriou, Elias

    2017-08-01

    The ecological integrity of rivers ultimately depends on flow regime. Flow degradation is especially prominent in Mediterranean systems and assessing environmental flows in modified rivers is difficult, especially in environments with poor hydrologic monitoring and data availability. In many Mediterranean countries, which are characterized by pronounced natural variability and low summer flows, water management actions usually focus on prescribing minimum acceptable flows estimated by hydrologic methods. In this study, a comparative assessment of environmental flow estimation methods is developed in a river with poorly monitored flows and limited understanding of past reference conditions. This assessment incorporates both a hydrologic and a fish habitat simulation effort that takes into consideration hydrologic seasonality in a Greek mountainous river. The results of this study indicate that especially in data scarce regions the utilization of biotic indicators through habitat models, may provide valuable information, beyond that achievable with hydrologic methods, for developing regional environmental flow criteria. Despite the widespread use of the method, challenges in transferability of fish habitat simulation provide undefined levels of uncertainty and may require the concurrent use of different assessment tools and site-specific study.

  14. Comparative analysis of UVB exposure between Nimbus 7/TOMS satellite estimates and ground-based measurements

    NASA Astrophysics Data System (ADS)

    Gao, Zhiqiang; Gao, Wei

    2010-08-01

    This study describes the patterns of variation in ultraviolet (UV) exposure across time and space using two continental scale data sets on UV radiation and conducts a comparative analysis of two sources of noontime UV-B exposure data across the continental US. One dataset was collected from 37 ground-based stations equipped with broadband UV-B-1 Pyranometers across North America whereas the other dataset was of synchronous satellite data collected from the Nimbus-7/TOMS sensor. Comparisons of these datasets confirmed agreement between the ground-based measurements and the TOMS satellite estimates with correlation coefficients of 0.87 and 0.95 for daily and monthly UV Index time series (i.e., a common metric of UV radiation exposure), respectively.

  15. 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

  16. 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)).

  17. Fate and impact of organics in an immersed membrane bioreactor applied to brine denitrification and ion exchange regeneration.

    PubMed

    McAdam, Ewan J; Pawlett, Mark; Judd, Simon J

    2010-01-01

    The application of membrane bioreactors (MBRs) to brine denitrification for ion exchange regeneration has been studied. The developed culture was capable of complete brine denitrification at 50 gNaCl.l(-1). Denitrification reduced to c.60% and c.70% when salinity was respectively increased to 75 and 100g.l(-1), presumed to be due to reduced growth rate and the low imposed solids retention time (10 days). Polysaccharide secretion was not induced by stressed cells following salt shocking, implying that cell lysis did not occur. Fouling propensity, monitored by critical flux, was steady at 12-15l.m(-2).h(-1) during salinity shocking and after brine recirculation, indicating that the system was stable following perturbation. Low molecular weight polysaccharide physically adsorbed onto the nitrate selective anion exchange resin during regeneration reducing exchange capacity by c.6.5% when operating up to complete exhaustion. However, based on a breakthrough threshold of 10 mgNO(3)(-)-N.l(-1) the exchange capacity was comparative to that determined when using freshly produced brine for regeneration. It was concluded that a denitrification MBR was an appropriate technology for IEX spent brine recovery and reuse.

  18. 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

  19. 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.

  20. Comparing simple methods for predictive uncertainty estimation over 1000 French catchments

    NASA Astrophysics Data System (ADS)

    Bourgin, F.; Andréassian, V.; Perrin, C.

    2012-04-01

    Proper quantification of uncertainty in hydrological modelling is a challenging task, for which various techniques, based on different philosophies and approaches, have been proposed over the last 20 years. The choice of a suitable framework to properly estimate uncertainty in hydrology is still controversial, especially regarding the differences between formal Bayesian methods and informal methods such as the GLUE and GLUE-like methods. While these two groups of methods are strongly related to the inference problem, several alternative methods aim at estimating the total predictive uncertainty of a calibrated model in an aggregated way. Those methods are especially attractive in a forecasting context, where they can be used as hydrological uncertainty processors (Krzysztofowicz and Kelly, 2000). In this study, we compare three of the recently proposed techniques, namely the meta-Gaussian approach (Montanari and Brath, 2004; Montanari and Grossi, 2008), the Quantile Regression technique (Weerts et al., 2011) and the Model Conditional Processor (Coccia and Todini, 2011). We also introduce, as a benchmark, a distribution-free approach based on conditional quantile estimation. All these methods involve statistical learning (i.e. using training data to characterize a relationship between variables of interest to predict future behaviour) but differ in their hypotheses and the regression techniques they use. To evaluate uncertainty estimates, we focus on the reliability and the sharpness of the predictive runoff distributions, since uncertainty analysis should provide prediction intervals as reliable and narrow as possible. Discharge predictions are given by the GRP model (Berthet et al., 2009), an operational forecasting lumped model widely used in France. To overcome the limitations of past comparisons carried out on very few catchments, a large dataset of French catchments is used to evaluate the robustness of the tested methods. This will provide more general

  1. 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

  2. Assessment of the denitrification process in alluvial wetlands at floodplain scale using the SWAT model

    USDA-ARS?s Scientific Manuscript database

    As alluvial plains support intensive agricultural activities, they often suffer from groundwater nitrate pollution. Denitrification is recognized as an important process in nitrate pollution control in riparian zones. In shallow aquifer zones influenced by recharged surface water, denitrification ...

  3. 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.

  4. 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.

  5. Urbanization and agricultural land loss in India: comparing satellite estimates with census data.

    PubMed

    Pandey, Bhartendu; Seto, Karen C

    2015-01-15

    We examine the impacts of urbanization on agricultural land loss in India from 2001 to 2010. We combined a hierarchical classification approach with econometric time series analysis to reconstruct land-cover change histories using time series MODIS 250 m VI images composited at 16-day intervals and night time lights (NTL) data. We compared estimates of agricultural land loss using satellite data with agricultural census data. Our analysis highlights six key results. First, agricultural land loss is occurring around smaller cities more than around bigger cities. Second, from 2001 to 2010, each state lost less than 1% of its total geographical area due to agriculture to urban expansion. Third, the northeastern states experienced the least amount of agricultural land loss. Fourth, agricultural land loss is largely in states and districts which have a larger number of operational or approved SEZs. Fifth, urban conversion of agricultural land is concentrated in a few districts and states with high rates of economic growth. Sixth, agricultural land loss is predominantly in states with higher agricultural land suitability compared to other states. Although the total area of agricultural land lost to urban expansion has been relatively low, our results show that since 2006, the amount of agricultural land converted has been increasing steadily. Given that the preponderance of India's urban population growth has yet to occur, the results suggest an increase in the conversion of agricultural land going into the future. Copyright © 2014 Elsevier Ltd. All rights reserved.

  6. Methods for estimating and comparing VA outpatient drug benefits with the private sector.

    PubMed

    Render, Marta L; Nowak, John; Hammond, Emmett K; Roselle, Gary

    2003-06-01

    To estimate and compare Veterans Health Administration (VA) expenditures for outpatient pharmaceuticals for veterans at six VA facilities with hypothetical private sector costs. Using the VA Pharmacy Benefits Management Strategic Health Care Group (PBM) database, we extracted data for all dispensed outpatient prescriptions from the six study sites over federal fiscal year 1999. After extensive data validation, we converted prescriptions to the same units and merged relevant VA pricing information by National Drug Code to Redbook listed average wholesale price and the Medicaid maximal allowable charge, where available. We added total VA drug expenditures to personnel cost from the pharmacy portion of that medical center's cost distribution report. Hypothetical private sector payments were $200.8 million compared with an aggregate VA budget of $118.8 million. Using National Drug Code numbers, 97% of all items dispensed from the six facilities were matched to private sector price data. Nonmatched pharmaceuticals were largely generic over-the-counter pain relievers and commodities like alcohol swabs. The most commonly prescribed medications reflect the diseases and complaints of an older male population: pain, cardiovascular problems, diabetes, and depression or other psychiatric disorders. Use of the VA PBM database permits researchers to merge expenditure and prescription data to patient diagnoses and sentinel events. A critical element in its use is creating similar units among the systems. Such data sets permit a deeper view of the variability in drug expenditures, an important sector of health care whose inflation has been disproportionate to that of the economy and even health care.

  7. 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.

  8. 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.

  9. 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.

  10. Effect of atrazine on potential denitrification in aquifer sediments

    USGS Publications Warehouse

    Bradley, P.M.; Chapelle, F.H.; Jagucki, M.L.; McMahon, P.B.

    1994-01-01

    Agriculturaf use of fertilizers and herbicides has often resulted in nitrate and atrazine contamination of the shallow aquifers that underlay cultivated fields. In several cases, the concentrations of atrazine and nitrate dissolved in ground water are positively correlated (Spalding ef al., 1979; Chen and Druliner, 1987; Spalding et al., 1989). Because simultaneous application of nitrate fertilizers and the herbicide, atrazine, is common, the co-occurrence of these contaminants in ground water is not entirely unexpected. However, the possibility also exists that this co-occurrence may ret&t interactions of atrazine with nitrate in the subsurface environment. R&ton and Cervelh (1980), McElhannon ei al. (1984) and Mills (1984) have reported that atrazine inhibits denitrification in‘soil’lf this i‘s indeed the case, atrazine contamination may contribute to nitrate preservation and accumulation in anaerobic aquifers by inhibiting denitrification, the principal mechanism for nitrate removal in anaerobic systems. Huwever, the effect of atrazine on the rate of denit~ficat~on in soils remains controversial, because atrazine has been reported variously to enhance denitrification (Cervelli and Ralston, 1983) or to have no effect on denitrification in soils (Bollag and Henninger, 1976; Yeomans and Bremner, IQ85, 1987). Moreover, the effect of dissolved atrazine concentrations on the rate of denitrification in aquifer sediments has not been reported. Our purpose was to determine the elects of dissolved atrazine concentrations on potential rates ofdenitri~~t~on in aquifer sediments from two different agricultural areas to evaluate the hypothesis that, by inhibiting denitrification, atrazine contributes to nitrate preservation in anaerobic aquifer systems.

  11. Subpixel urban land cover estimation: comparing cubist, random forests, and support vector regression

    Treesearch

    Jeffrey T. Walton

    2008-01-01

    Three machine learning subpixel estimation methods (Cubist, Random Forests, and support vector regression) were applied to estimate urban cover. Urban forest canopy cover and impervious surface cover were estimated from Landsat-7 ETM+ imagery using a higher resolution cover map resampled to 30 m as training and reference data. Three different band combinations (...

  12. Disease severity estimates - effects of rater accuracy and assessments methods for comparing treatments

    USDA-ARS?s Scientific Manuscript database

    Assessment of disease is fundamental to the discipline of plant pathology, and estimates of severity are often made visually. However, it is established that visual estimates can be inaccurate and unreliable. In this study estimates of Septoria leaf blotch on leaves of winter wheat from non-treated ...

  13. Comparing acid steatocrit and faecal elastase estimations for use in M-ANNHEIM staging for pancreatitis

    PubMed Central

    Kamath, M Ganesh; Pai, C Ganesh; Kamath, Asha; Kurien, Annamma

    2017-01-01

    AIM To compare two tests for exocrine pancreatic function (EPF) for use in M-ANNHEIM staging for pancreatitis. METHODS One hundred and ninety four consecutive patients with acute pancreatitis (AP; n = 13), recurrent acute pancreatitis (RAP; n = 65) and chronic pancreatitis (CP; n = 116) were enrolled. EPF was assessed by faecal elastase-1 (FE-1) estimation and stool fat excretion by the acid steatocrit method. Patients were classified as per M-ANNHEIM stages separately based on the results of the two tests for comparison. Independent Student’s t-test, χ2 test, Kruskal-Wallis test, Mann-Whitney U test and McNemar’s test were used as appropriate. RESULTS Sixty-one (52.5%) patients with CP had steatorrhoea when assessed by the acid steatocrit method; 79 (68.1%) with CP had exocrine insufficiency by the FE-1 test (χ2 test, P < 0.001). The results of acid steatocrit and FE-1 showed a significant negative correlation (Spearman’s rho = -0.376, P < 0.001). A statistically significant difference was seen between the M-ANNHEIM stages as classified separately by acid steatocrit and the FE-1. Thirteen (6.7%), 87 (44.8%), 89 (45.8%) and 5 (2.5%) patients were placed in M-ANNHEIM stages 0, I, II, and III respectively, with the use of acid steatocrit as against 13 (6.7%), 85 (43.8%), 75 (38.6%), and 21 (10.8%) respectively by FE-1 in stages 0, I, II, and III thereby altering the stage in 28 (14.4%) patients (P < 0.001, McNemar’s test). CONCLUSION FE-1 estimation performed better than the acid steatocrit test for use in the staging of pancreatitis by the M-ANNHEIM classification since it diagnosed a higher proportion of patients with exocrine insufficiency. PMID:28405150

  14. Granulation of sulfur-oxidizing bacteria for autotrophic denitrification.

    PubMed

    Yang, Weiming; Lu, Hui; Khanal, Samir K; Zhao, Qing; Meng, Liao; Chen, Guang-Hao

    2016-11-01

    Sulfur-oxidizing bacteria (SOB) was successfully employed for effective autotrophic denitrification and sludge minimization in a full-scale application of saline sewage treatment in Hong Kong. In this study, a Granular Sludge Autotrophic Denitrification (GSAD) reactor was continuously operated over 600 days for SOB granulation, and to evaluate the long-term stability of SOB granules, microbial communities and denitrification efficacy. Sludge granulation initiated within the first 40 days of start-up with an average particle size of 186.4 μm and sludge volume index (SVI5) of 40 mL/g in 5 min. The sludge granules continued to grow reaching a nearly uniform size of mean diameter 1380 ± 20 μm with SVI5 of 30 mL/g during 600 days of GSAD reactor operation at hydraulic retention time of 5 h and nitrate loading rate of 0.33 kg-N/m(3)/d. The GSAD reactor with SOB granular sludge achieved 93.7 ± 2.1% nitrogen and complete sulfide removal with low sludge yield of 0.15 g-volatile suspended solids (VSS)/g-N, and much lower nitrous oxide (N2O) emission than the heterotrophic denitrifying process. Microbial community analysis using fluorescence in situ hybridization (FISH) technique revealed that granules were enriched with SOB contributing to autotrophic denitrification. Furthermore, 16S rRNA analysis showed diverse autotrophic denitrification related genera, namely Thiobacillus (32.6%), Sulfurimonas (31.3%), and Arcobacter (0.01%), accounting for 63.9% of total operational taxonomic units at the generic level. No heterotrophic denitrification related genera were detected. The results from this study could provide useful design and operating conditions with respect to SOB sludge granulation and its subsequent application in a full-scale autotrophic denitrification in the Sulfate reduction-Autotrophic denitrification-Nitrification Integrated (SANI) process. Copyright © 2016 Elsevier Ltd. All rights reserved.

  15. 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.

  16. 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

  17. Implications of non-equilibrium transport in heterogeneous reactive barrier systems: evidence from laboratory denitrification experiments.

    PubMed

    Herbert, Roger B

    2011-04-01

    Organic substrates in reactive barrier systems are often heterogeneous material mixtures with relatively large contrasts in hydraulic conductivity and porosity over short distances. These short-range variations in material properties imply that preferential flow paths and diffusion between regions of higher and lower hydraulic conductivity may be important for treatment efficiency. This paper presents the results of a laboratory column experiment where denitrification is investigated using a heterogeneous reactive substrate (sawdust mixed with sewage sludge). Displacement experiments with a non-reactive solute at three different flow rates are used to estimate transport parameters using a dual porosity non-equilibrium model. Parameter estimation from breakthrough curves produced relatively consistent values for the fraction of the porosity consisting of mobile water (β) and the mass transfer coefficient (α), with average values of 0.27 and 0.42 d(-1), respectively. The column system removes >95% of the influent nitrate at low and medium flow, but only 50-75% of the influent nitrate at high flow, suggesting that denitrification kinetics and diffusive mass transfer rates are limiting the degree of treatment at lower hydraulic residence times. Reactive barrier systems containing dual porosity media must therefore consider mass transfer times in their design; this is often most easily accommodated by adjusting flowpath length. Copyright © 2010 Elsevier B.V. All rights reserved.

  18. Implications of non-equilibrium transport in heterogeneous reactive barrier systems: Evidence from laboratory denitrification experiments

    NASA Astrophysics Data System (ADS)

    Herbert, Roger B., Jr.

    2011-04-01

    Organic substrates in reactive barrier systems are often heterogeneous material mixtures with relatively large contrasts in hydraulic conductivity and porosity over short distances. These short-range variations in material properties imply that preferential flow paths and diffusion between regions of higher and lower hydraulic conductivity may be important for treatment efficiency. This paper presents the results of a laboratory column experiment where denitrification is investigated using a heterogeneous reactive substrate (sawdust mixed with sewage sludge). Displacement experiments with a non-reactive solute at three different flow rates are used to estimate transport parameters using a dual porosity non-equilibrium model. Parameter estimation from breakthrough curves produced relatively consistent values for the fraction of the porosity consisting of mobile water (β) and the mass transfer coefficient (α), with average values of 0.27 and 0.42 d - 1 , respectively. The column system removes > 95% of the influent nitrate at low and medium flow, but only 50-75% of the influent nitrate at high flow, suggesting that denitrification kinetics and diffusive mass transfer rates are limiting the degree of treatment at lower hydraulic residence times. Reactive barrier systems containing dual porosity media must therefore consider mass transfer times in their design; this is often most easily accommodated by adjusting flowpath length.

  19. Effect of electromagnetic fields on the denitrification activity of Paracoccus denitrificans.

    PubMed

    Fojt, Lukás; Strasák, Ludek; Vetterl, Vladimír

    2007-01-01

    Enzymatic activity (denitrification) of Paracoccus denitrificans was estimated electrochemically by reduction of duroquinone (DQ). Graphite electrodes covered with whole bacterial cells behind a dialysis membrane were used for measurement. P. denitrificans reduce nitrate and/or nitrite under anaerobic conditions to nitrogen gas. DQ acts as an electron mediator. After donation of the electrons to the respiratory system of the bacteria, produced DQ is reduced to durohydroquinone on the electrode surface electrocatalytically. P. denitrificans were exposed to low-frequency magnetic field (10 mT, 50 Hz) for 24 min. In comparison with the control samples, the reduction peak of I-E curves that represent denitrification activity of the cells decreased significantly after magnetic field exposure. The decrease of the peak current was about 20%. The CFU-colony forming units-method was used to estimate the number of surviving bacteria. After 24 min exposure of 10 mT magnetic field P. denitrificans culture on electrode indicates 21% bacterial death.

  20. 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

  1. Reduced models of atmospheric low-frequency variability: Parameter estimation and comparative performance

    NASA Astrophysics Data System (ADS)

    Strounine, K.; Kravtsov, S.; Kondrashov, D.; Ghil, M.

    2010-02-01

    Low-frequency variability (LFV) of the atmosphere refers to its behavior on time scales of 10-100 days, longer than the life cycle of a mid-latitude cyclone but shorter than a season. This behavior is still poorly understood and hard to predict. The present study compares various model reduction strategies that help in deriving simplified models of LFV. Three distinct strategies are applied here to reduce a fairly realistic, high-dimensional, quasi-geostrophic, 3-level (QG3) atmospheric model to lower dimensions: (i) an empirical-dynamical method, which retains only a few components in the projection of the full QG3 model equations onto a specified basis, and finds the linear deterministic and the stochastic corrections empirically as in Selten (1995) [5]; (ii) a purely dynamics-based technique, employing the stochastic mode reduction strategy of Majda et al. (2001) [62]; and (iii) a purely empirical, multi-level regression procedure, which specifies the functional form of the reduced model and finds the model coefficients by multiple polynomial regression as in Kravtsov et al. (2005) [3]. The empirical-dynamical and dynamical reduced models were further improved by sequential parameter estimation and benchmarked against multi-level regression models; the extended Kalman filter was used for the parameter estimation. Overall, the reduced models perform better when more statistical information is used in the model construction. Thus, the purely empirical stochastic models with quadratic nonlinearity and additive noise reproduce very well the linear properties of the full QG3 model’s LFV, i.e. its autocorrelations and spectra, as well as the nonlinear properties, i.e. the persistent flow regimes that induce non-Gaussian features in the model’s probability density function. The empirical-dynamical models capture the basic statistical properties of the full model’s LFV, such as the variance and integral correlation time scales of the leading LFV modes, as well as

  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. Use of models in large-area forest surveys: comparing model-assisted, model-based and hybrid estimation

    Treesearch

    Goran Stahl; Svetlana Saarela; Sebastian Schnell; Soren Holm; Johannes Breidenbach; Sean P. Healey; Paul L. Patterson; Steen Magnussen; Erik Naesset; Ronald E. McRoberts; Timothy G. Gregoire

    2016-01-01

    This paper focuses on the use of models for increasing the precision of estimators in large-area forest surveys. It is motivated by the increasing availability of remotely sensed data, which facilitates the development of models predicting the variables of interest in forest surveys. We present, review and compare three different estimation frameworks where...

  4. 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

  5. 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.

  6. An integrated process of three-dimensional biofilm-electrode with sulfur autotrophic denitrification (3DBER-SAD) for wastewater reclamation.

    PubMed

    Hao, Ruixia; Meng, Chengcheng; Li, Jianbing

    2016-08-01

    A three-dimensional biofilm-electrode reactor (3DBER) was integrated with sulfur autotrophic denitrification (SAD) to improve nitrogen removal performance for wastewater reclamation. The impacts of influent carbon/nitrogen (C/N) ratio, electric current, and hydraulic retention time (HRT) were evaluated. The new process, abbreviated as 3DBER-SAD, achieved a more stable denitrification compared to the recently studied 3DBER in literature. Its nitrogen removal improved by about 45 % as compared to 3DBER, especially under low C/N ratio conditions. The results also revealed that the biofilm bacteria community of 3DBER-SAD contained 21.1 % of the genus Thauera, 19.3 % of the genus Thiobacillus and Sulfuricella, as well as 5.3 % of the genus Alicycliphilus, Pseudomonas, and Paracoccus. The synergy between these heterotrophic, sulfur autotrophic, and hydrogenotrophic denitrification bacteria was believed to cause the high and stable nitrogen removal performance under various operating conditions.

  7. Field methods in medical record abstraction: assessing the properties of comparative effectiveness estimates.

    PubMed

    Cook, Elizabeth A; Schneider, Kathleen M; Robinson, Jennifer; Wilwert, June; Chrischilles, Elizabeth; Pendergast, Jane; Brooks, John

    2014-09-15

    Comparative effectiveness studies using Medicare claims data are vulnerable to treatment selection biases and supplemental data from a sample of patients has been recommended for examining the magnitude of this bias. Previous research using nationwide Medicare claims data has typically relied on the Medicare Current Beneficiary Survey (MCBS) for supplemental data. Because many important clinical variables for our specific research question are not available in the MCBS, we collected medical record data from a subsample of patients to assess the validity of assumptions and to aid in the interpretation of our estimates. This paper seeks to describe and document the process used to collect and validate this supplemental information. Medicare claims data files for all patients with fee-for-service Medicare benefits who had an acute myocardial infarction (AMI) in 2007 or 2008 were obtained. Medical records were obtained and abstracted for a stratified subsample of 1,601 of these patients, using strata defined by claims-based measures of physician prescribing practices and drug treatment combinations. The abstraction tool was developed collaboratively by study clinicians and researchers, leveraging important elements from previously validated tools. Records for 2,707 AMI patients were requested from the admitting hospitals and 1,751 were received for an overall response rate of 65%; 1,601 cases were abstracted by trained personnel at a contracted firm. Data were collected with overall 96% inter-abstractor agreement across all variables. Some non-response bias was detected at the patient and facility level. Although Medicare claims data are a potentially powerful resource for conducting comparative effectiveness analyses, observational databases are vulnerable to treatment selection biases. This study demonstrates that it is feasible to abstract medical records for Medicare patients nationwide and collect high quality data, to design the sampling purposively to address

  8. A Comparative Study Of Motion Estimation Techniques For Application To Sub-Sea Robotics

    NASA Astrophysics Data System (ADS)

    Russell, George T.; Wells, Stuart C.

    1984-02-01

    As the complexity of sub-sea maintenance and inspection tasks increases, and the search for further reserves of offshore oil goes into deeper and more hazardous environmental conditions, the need for autonomous working submersibles is increased. The total free swimming submersible system requires a scope that embraces the guidance and control of the vehicle and associated payload, the acquisition and processing of information, and the communication of that information between the vehicle and the surface operator. This paper describes an important aspect of the total system, namely, the technique employed in reducing the required bandwidth for the transmission of television pictures, through an acoustic communication link. In particular, the estimation of motion within an image sequence has been shown to offer a further refinement in bandwidth reduction when used in conjunction with interframe hybrid coding. Many competing techniques have been proposed in the literature. The objective of this study has been to compare a range of fundamental techniques, in order to optimise the communication system design for this particular application. An essential by-product of this investigation has been the development of a general image processing system that incorporates a set of interactive image processing modules and provides a real-time colour picture capture and display facility.

  9. 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.

  10. 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.

  11. 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).

  12. 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...

  13. Denitrification in Wood Chip Bioreactors at Different Water Flows

    USDA-ARS?s Scientific Manuscript database

    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....

  14. 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

  15. 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 ...

  16. 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...

  17. Internal hydraulics of an agricultural drainage denitrification bioreactor

    USDA-ARS?s Scientific Manuscript database

    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...

  18. 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 ...

  19. 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...

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

    Treesearch

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

    2011-01-01

    Nitrous oxide (N20) 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 N20 via microbial denitrification that converts N to N20 and dinitrogen (N2...

  1. Labile dissolved organic carbon supply limits hyporheic denitrification

    Treesearch

    Jay P. Zarnetske; Roy Haggerty; Steven M. Wondzell; Michelle A. Baker

    2012-01-01

    We used an in situ steady state 15N-labeled nitrate and acetate well-to-wells injection experiment to determine how the availability of labile dissolved organic carbon as acetate influences microbial denitrification in the hyporheic zone of an upland (third-order) agricultural stream.

  2. 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

    2015-02-03

    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.

  3. 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...

  4. Comparing Minnesota land cover/use area estimates using NRI and FIA data

    Treesearch

    Veronica C. Lessard; Mark H. Hansen; Mark D. Nelson

    2002-01-01

    Areas for land cover/use categories on non-Federal land in Minnesota were estimated from Forest Inventory and Analysis (FIA) data and National Resources Inventory (NRI) data. Six common land cover/use categories were defined, and the NRI and FIA land cover/use categories were assigned to them. Area estimates for these categories were calculated from the FIA and NRI...

  5. Comparing Four Estimates of the Criterion-Referenced Standard for a Written Test.

    ERIC Educational Resources Information Center

    Hughes, Francis P.

    Four procedures were used to estimate a criterion-referenced standard for a multiple-choice examination developed by the National Board of Medical Examiners (NBME). Two experimental procedures, the NBME method and a modification of the Guerin method, and the Angoff and Ebel procedures were evaluated on the consistency of the estimates they…

  6. Comparing methods to estimate Reineke’s maximum size-density relationship species boundary line slope

    Treesearch

    Curtis L. VanderSchaaf; Harold E. Burkhart

    2010-01-01

    Maximum size-density relationships (MSDR) provide natural resource managers useful information about the relationship between tree density and average tree size. Obtaining a valid estimate of how maximum tree density changes as average tree size changes is necessary to accurately describe these relationships. This paper examines three methods to estimate the slope of...

  7. Comparing algorithms for estimating foliar biomass of conifers in the Pacific Northwest

    Treesearch

    Crystal L. Raymond; Donald. McKenzie

    2013-01-01

    Accurate estimates of foliar biomass (FB) are important for quantifying carbon storage in forest ecosystems, but FB is not always reported in regional or national inventories. Foliar biomass also drives key ecological processes in ecosystem models. Published algorithms for estimating FB in conifer species of the Pacific Northwest can yield signifi cantly different...

  8. 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

  9. 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.

  10. 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.

  11. Isotopic and Reporter Techniques to Verify Links Between Plant C Flow and Denitrification

    NASA Astrophysics Data System (ADS)

    Killham, K.; Prendergast, M.; Baggs, E.

    2007-12-01

    The availability of organic C is considered paramount for the production and reduction of the greenhouse gas nitrous oxide (N2O) during denitrification in the rhizosphere. Despite this, the role of organic C in the regulation of N2O- and N2-genic enzymes is poorly understood. Stable isotopes are fundamental in resolving this. Here we will present selected results from experiments in which we have applied isotopic and reporter techniques to verify the effect of plant C in driving denitrification, and the potential feedbacks of this on climate change. Changes in C input to soil, such as under elevated atmospheric CO2, is significant for N2O production and reduction. Following application of 15N-labelled fertiliser to Lolium perenne swards we showed increased denitrifier-N2O and N2 production under elevated pCO2 (60 Pa) in the Swiss FACE experiment. This was attributed to greater below ground C allocation providing the energy for denitrification, and emissions were strongly positively correlated with TOC. By converting all rhizosphere soil to Redox conditions conducive to denitrification, rhizosphere C flow was quantified via N2O flux, and estimates agreed with measurements using 13C and 14C approaches. Little is known about the effect of different C substrates in regulating N2O and N2 production nor their effects on community structure, activity or species selection of denitrifying bacteria in the rhizosphere. We provide the first evidence for differences in N2O and N2 production with different C compounds typically present in root exudate, which suggest differences in regulation of the NO and N2O reductases, or preference for different C compounds in the rhizosphere denitrifier community. Such differences in gaseous N production are being related to the function and activity of the denitrifier community associated with this root C flow, with the link between C flow and denitrifier activity being verified by stable isotope probing and NanoSIMS imaging. Further

  12. 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