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Byline: Y. Ding, J. He, Q. Wu, D. Li, G. Liu, J. Liao, Y. Ma and H. Zhou Keywords: Denitrifying bacteria, Functional denitrification gene, Salt concentration, Diversity, Soil INTRODUCTION Denitrification [...]

Patterned ground is a characteristic landscape form in arid zones across the globe and is caused by the redistribution of runoff. The vegetation is concentrated in groves, which receive runoff water from the bare soil surface of the intergroves. Despite many soil chemical and physical investigations, biogeochemical cycles are not described for this landscape form. This study focuses on the distinct features of the nitrogen (N) and carbon (C) cycle in intergrove and grove areas of chenopod pattern-ground soils of the Australian rangelands. The N concentration of grove soils is low compared with the intergrove soil because of a close link between the N cycle in the topsoil and the plant primary production. In grove soils, denitrification including emission of [N.sub.2]O dominated the N cycle, whereas in intergrove soils, abiotic [N.sub.2]O uptake is the sole fate of atmospheric [N.sub.2]O. The intergrove soils appear to be generally poor in bacterial quantity and diversity, and lacking denitrification by bacteria, which has an impact on the C cycle as well. Production of C[O.sub.2] and consumption of C[H.sub.4] were substantially lower than grove soils. There was partitioning ofkcy biogeochemical processes between the intergrove and grove soils, which results in a spatially decoupled soil N and C cycle in arid chenopod, pattern-ground ecosystems. Received 24 July 2014, accepted 19 September 2014, published online 27 January 2015, Introduction Shrub-steppe covers 7.5% (451 000 [km.sup.2]) of Australia's arid and semi-arid rangelands, and is dominated by various annual and perennial species of the family Chenopodiaceae (Leigh 1972). These chenopod [...]

A set of equations governing oxygen diffusion and consumption in soils has been developed to include microbial and plant-root sinks. The dependent variable is the transformed oxygen concentration, which is the difference between the gaseous concentration and a scaled value of the aqueous oxygen concentration at the root-soil interface. The results show how, as the air-filled porosity decreases, the reduced oxygen flux causes the depth of extinction to decrease. The results also show how the depth of extinction at a particular value of soil water content decreases with increasing temperature, due to increased microbial respiration. The critical value of water content at which the oxygen concentration goes to extinction at a finite depth was compared with alternative calculations with only a microbial sink. By ignoring the feedback of oxygen concentration on root uptake, the alternative calculations yielded substantially higher critical values of water content at all temperatures. Two soil oxygen diffusion coefficient functions from the literature were compared and shown to give significantly different critical values of water content for fine-textured soils, one more realistic than the other. A single relationship between the extinction depth and the ratio of the water content to the critical value was shown to apply for all temperatures and soil textures. The oxygen profiles were used along with a function relating redox potential to oxygen concentration to generate redox potential profiles. This application of the model could be useful in explaining soil biochemical processes in soils. For one such process, denitrification, the depth at which a critical oxygen concentration is reached was calculated as a function of the air-filled porosity and temperature of the soil. The implications of the critical value of soil water content in terms of water-filled pore space and matric potential are discussed in relation to the diffusion coefficient functions and recent literature. Additional keywords: air-filled pore space, denitrification, diffusion coefficient function, oxygen transport, redox potential, soil respiration., Introduction The transport of oxygen into soil and its distribution within the profile are fundamental to the understanding of aeration, and biochemical and chemical reactions in soil. The oxygen status [...]

R. sphaeroides strain 2.4.3, when lacking the cbb3 oxidase, is unable to transition from aerobic respiration to denitrification using cellular respiration as a means of reducing oxygen levels. This is due to an inability to express nirK, the gene encoding nitrite reductase. Under certain photosynthetic conditions this strain can transition from aerobic to nitrate respiration, demonstrating that nirK expression can occur in the absence of a functional [cbb.sub.3] oxidase. If oxygen levels are reduced under non-photosynthetic conditions using low-oxygen gas mixes, nitrite reductase activity is detected at wild-type levels in the strain lacking the oxidase. In addition, co-culture experiments show that incubation of the [cbb.sub.3] deficient strain 2.4.3 with R. sphaeroides 2.4.1, which is nirK deficient but has the high-affinity [cbb.sub.3] oxidase, restores denitrification in sealed-vessel experiments. Taken together these results indicate that high end-point [O.sub.2] levels are the reason why the strain lacking the [cbb.sub.3] oxidase cannot transition from aerobic respiration to denitrification under certain conditions. The protein probably being affected by these [O.sub.2] levels is the transcriptional regulator NnrR. DOI 10.1099/mic.0.038703-0

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2010.05.009 Byline: Bonnie X. Chang, Allan H. Devol, Steven R. Emerson Keywords: Eastern tropical South Pacific; Oxygen deficient zone; Nitrogen cycle; Denitrification; Nitrate deficit; Dissolved gases Abstract: Recent studies of the nitrogen gas excess produced during water column denitrification have indicated that water column denitrification rates calculated using nitrate deficit-type methods could be a substantial underestimate. Since there are no other significant processes that produce (or consume) N.sub.2 in the oxygen deficient zone (ODZ), its excess above background can be used to estimate the amount of denitrification, avoiding assumptions made in nitrate deficit calculations of the composition of the respired organic matter and also uncertainties in the nitrogen removal pathways. Dissolved N.sub.2, Ar, and nutrient concentrations were measured at 2 stations in the ODZ of the eastern tropical South Pacific (ETSP) in order to compare the nitrogen gas excess with the dissolved inorganic nitrogen (DIN) deficit due to denitrification. In contrast with previous findings in the Arabian Sea ODZ, the shapes of the N.sub.2 excess and DIN deficit profiles were similar in the ETSP ODZ, with maxima at the top of the ODZ. Maximum DIN deficits at each station were 19 and 18[mu]M N compared to the maximum N.sub.2 excesses of 15 and 20[mu]M N, respectively. Given the same considerations of the volume and residence time for the oxygen deficient zone waters, denitrification rates for the ETSP estimated from the N.sub.2 excess would be comparable or no greater than 30% larger than the one determined using the DIN deficit. This implies that the source of the DIN removed from the ODZ is either deep sea nitrate or organic matter with an N:P ratio close to Redfield. Author Affiliation: University of Washington, School of Oceanography, Box 355351, Seattle, WA 98195, USA Article History: Received 18 June 2009; Revised 21 May 2010; Accepted 26 May 2010

The Davis Pond freshwater diversion is intended to help restore Louisiana's coastal wetlands by reintroducing Mississippi River water to Barataria Basin. We hypothesized that the high N[O.sub.3.sup.-] concentration(2.0 mg N[O.sub.3]-N [L.sup.-1]) of the Mississippi River water would control the rate of denitrification in the receiving marsh given that the soils ate saturated, anaerobic, and contain high C. Therefore, areas of high denitrification enzyme activity (DEA) in the marsh would represent soils exposed to river N[O.sub.3.sup.-] and actively involved in denitrification. Data from 88 soil samples (0-10 cm) collected throughout the marsh revealed significantly higher rates of DEA in a 715-ha area adjacent to the diversion inflow. This area of generally high DEA contained >80% of all DEA observed while representing only 19% of the total marsh area at the low discharge rate of 39.5 [m.sup.3] [s.sup.-1]. The area of high DEA coincided with the highest surface water N[O.sub.3.sup.-] and indicated that the marsh has a greater aerial capacity for N[O.sub.3-.sup.-] removal than is utilized. A laboratory experiment suggested that soils loaded with external N[O.sub.3.sup.-] typically had higher DEA rates than soils receiving no added N[O.sub.3.sup.-]. The DEA was strongly dependent on soil depth (92% of DEA occurred at 0-5 cm) and internal N cycling was substantial in this wetland soils. This study demonstrates the applicability of using soil DEA to map where denitrification activity is greatest, the aerial extent of soils involved in denitrification, and the general flow path of introduced nutrients in large wetlands where N[O.sub.3.sup.-] is the limiting factor for denitrification. Abbreviations: DEA, denitrificatiorn enzyme activity; MBC, microbial biomass carbon. doi: 10.2136/sssaj2009.0354

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2009.04.007 Byline: Daniel M. Sigman (a), Peter J. DiFiore (a), Mathis P. Hain (b), Curtis Deutsch (c), Yi Wang (a), David M. Karl (d), Angela N. Knapp (e), Moritz F. Lehmann (f), Silvio Pantoja (g) Keywords: Nitrate; Stable isotope; Biogeochemistry; Numerical model; Nutrients Abstract: We compare the output of an 18-box geochemical model of the ocean with measurements to investigate the controls on both the mean values and variation of nitrate [delta].sup.15N and [delta].sup.18O in the ocean interior. The [delta].sup.18O of nitrate is our focus because it has been explored less in previous work. Denitrification raises the [delta].sup.15N and [delta].sup.18O of mean ocean nitrate by equal amounts above their input values for N.sub.2 fixation (for [delta].sup.15N) and nitrification (for [delta].sup.18O), generating parallel gradients in the [delta].sup.15N and [delta].sup.18O of deep ocean nitrate. Partial nitrate assimilation in the photic zone also causes equivalent increases in the [delta].sup.15N and [delta].sup.18O of the residual nitrate that can be transported into the interior. However, the regeneration and nitrification of sinking N can be said to decouple the N and O isotopes of deep ocean nitrate, especially when the sinking N is produced in a low latitude region, where nitrate consumption is effectively complete. The [delta].sup.15N of the regenerated nitrate is equivalent to that originally consumed, whereas the regeneration replaces nitrate previously elevated in [delta].sup.18O due to denitrification or nitrate assimilation with nitrate having the [delta].sup.18O of nitrification. This lowers the [delta].sup.18O of mean ocean nitrate and weakens nitrate [delta].sup.18O gradients in the interior relative to those in [delta].sup.15N. This decoupling is characterized and quantified in the box model, and agreement with data shows its clear importance in the real ocean. At the same time, the model appears to generate overly strong gradients in both [delta].sup.18O and [delta].sup.15N within the ocean interior and a mean ocean nitrate [delta].sup.18O that is higher than measured. This may be due to, in the model, too strong an impact of partial nitrate assimilation in the Southern Ocean on the [delta].sup.15N and [delta].sup.18O of preformed nitrate and/or too little cycling of intermediate-depth nitrate through the low latitude photic zone. Author Affiliation: (a) Department of Geosciences, Princeton University, Princeton, NJ 08544, USA (b) Institute of Geosciences, University of Potsdam, PO Box 60 15 53, Potsdam D-14415, Germany (c) Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095, USA (d) Department of Oceanography, 1000 Pope Rd. MSB 629, University of Hawaii, Honolulu, HI 96822, USA (e) Department of Marine and Environmental Biological Sciences, University of Southern California, University of Southern California, 3616 Trousdale Parkway, AHF 108, Los Angeles, CA 90089-0371, USA (f) Institute for Environmental Geosciences, Bernoullistrasse 30, Universitat Basel, CH-4056 Basel, Switzerland (g) Department of Oceanography and Center for Oceanographic Research in the Eastern South Pacific, University of Concepcion, Casilla 160-C, Concepcion, Chile Article History: Received 21 January 2008; Revised 4 April 2009; Accepted 21 April 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2007.09.005 Byline: Thomas R. Anderson (a), Vladimir A. Ryabchenko (b), Michael J.R. Fasham (a), Victor A. Gorchakov (b) Keywords: Denitrification; Biogeochemical cycles; Ecosystem modelling; Detritus; Export flux; Arabian Sea Abstract: 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 26.2TgNyr.sup.-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 (0.73mmolNm.sup.-2 d.sup.-1) rather than from lateral transport of organic matter from elsewhere in the Arabian Sea (less than 0.01mmolNm.sup.-2 d.sup.-1). Analysis of the carbon budget in the zone of denitrification (north of 10[degrees]N and east of 55[degrees]E) indicates that the modelled vertical export flux of detritus, which is similar in magnitude to estimates from field data based on the.sup.234Th method, is sufficient to account for measured bacterial production below the euphotic zone in the Arabian Sea. Author Affiliation: (a) National Oceanography Centre, University of Southampton, Waterfront Campus, Southampton SO14 3ZH, UK (b) St. Petersburg Branch, P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, 30, Pervaya Liniya, 199053 St. Petersburg, Russia Article History: Received 6 June 2006; Revised 3 September 2007; Accepted 11 September 2007

The denitrification of human wastes by bacteria results into emission of nitrous oxide, which is a powerful pollutant. The denitrification rates are measured by nitrous oxide microprofiling in acetylene block core incubations and reactive transport modeling to measure the rate of denitrification at different depths in a macro tidal estuary.

Depth-dependent oxygen concentrations and aqueous-phase total ammonia and nitrate/nitrite ion concentrations were measured in the field during the infiltration of wastewater effluent. Measurements illustrated the dependence of nitrogen fate and transport on oxygen availability. Infiltration basins were operated by alternating wet (infiltration) and dry periods. During infiltration periods, ammonia was removed within the top few feet of sediments via adsorption. Biochemical activity rapidly eliminated residual molecular oxygen in the infiltrate, making the soil profile anoxic. During dry periods, oxygen reentered the basin profile and sorbed ammonia was converted to nitrate via nitrification. Oxygen penetrated to a depth of about 0.6 m (2 ft) within the first few days of dry periods. At greater depths, oxygen levels increased more slowly due to a combination of slow transport kinetics and biochemical (nitrogenous) oxygen demand. During normal wet/dry basin cycles consisting of about 4 wet and 4 dry days, the local vadose zone remained anoxic at depths greater than about 1.5 m (5 ft) below land surface. As a consequence, conditions for denitrificafion were satisfied in the deeper sediments. That is, the nitrate nitrogen produced in near surface sediments moved freely downward with infiltrating water where it encountered an extensive anoxic zone before reaching local monitoring or extraction wells. The relative importance of dissolved organics and sorbed ammonia as electron donors for denitrification reactions remains to be established. DOI: 10.106 l/(ASCE)0733-9372(2006) 132:10(1298) CE Database subject headings: Ground-water recharge: Nitrification: Denitrification; Oxygen: Oxidation; Wastewater management.

An innovative anaerobic--aerobic integrated bioreactor system consisting of an upflow anaerobic sludge blanket (UASB) and a jet loop reactor was developed to investigate the feasibility of combined removal of carbon and nitrogen for a low-strength wastewater at different hydraulic retention times (HRTs) and recycle ratios. Total chemical oxygen demand (COD) removal of the integrated system increased from 87 to 92%, at a combined system HRT of 44 h, when the recycle ratio was increased from 100 to 400%, respectively. Denitrification efficiency of the integrated system increased from 49 to 86%, at all HRTs, when the recycle ratio was increased from 100 to 400%. The integrated system, on average, achieved more than 78% of total nitrogen at all HRTs. Nitrogen content of the biogas produced from the UASB reactor increased with increase in recycle ratios while the methane content exhibited a reverse trend, irrespective of the HRTs. Sludge volume index of the UASB reactor increased from 15 to 42 mL/g total suspended solids at the end of the study. Specific methanogenic activity of the granular sludge decreased from 1.3 to 0.8 g C[H.sub.4]-COD/g volatile suspended solids per day at the end of the study. Nitrogen and COD mass balance of the integrated system indicated that a substantial amount of influent nitrogen and COD was lost in the effluent as dissolved form. DOI:10.1061/(ASCE)0733-9372(2006)132:6(624) CE Database subject headings. Denitrification; Nitrification; Sludge; Wastewater management; Reactors; Carbon.

Conventional agriculture has improved in crop yield but at large costs to the environment, particularly off-site pollution from mineral N fertilizers. In response to environmental concerns, organic agriculture has become an increasingly popular option. One component of organic agriculture that remains in question is whether it can reduce agricultural N losses to groundwater and the atmosphere relative to conventional agriculture. Here we report reduced N pollution from organic and integrated farming systems compared with a conventional farming system. We evaluated differences in denitrification potential and a suite of other soil biological and chemical properties in soil samples taken from organic, integrated, and conventional treatments in an experimental apple orchard. Organically farmed soils exhibited higher potential denitrification rates, greater denitrification efficiency, higher organic matter, and greater microbial activity than conventionally farmed soils. The observed differences in denitrifier function were then assessed under field conditions after fertilization. [N.sub.2]0 emissions were not significantly different among treatments; however, [N.sub.2] emissions were highest in organic plots. Annual nitrate leaching was 4.4-5.6 times higher in conventional plots than in organic plots, with the integrated plots in between. This study demonstrates that organic and integrated fertilization practices support more active and efficient denitrifier communities, shift the balance of [N.sub.2] emissions and nitrate losses, and reduce environmentally damaging nitrate losses. Although this study specifically examines a perennial orchard system, the ecological and biogeochemical processes we evaluated are present in all agroecosystems, and the reductions in nitrate loss in this study could also be achievable in other cropping systems. denitrification | nitrogen | organic agriculture | sustainable agriculture | integrated farming

Microbial N(sub 2)O release during the course of thawing of soil was investigated in model experiment focusing on denitrification, since freeze-thaw is shown to cause significant physical and biological changes in soil, including a surge of N(sub 2)O and CO(sub 2). The results support the view that the flush of N(sub 2)O and CO(sub 2) is a result of increased microbial activity during the dynamic event of freeze and thaw, instead of mere entrapment of gases due to the freeze barrier.

A study was conducted to examine the diversity and composition of denitrifying bacteria that vary across environmental gradients in both nitrate and salinity within an unconfined beach aquifer. The findings suggest that diversity in these enzymes results from adaptation to a particular environment rather than just random microheterogeneity alone.

Denitrification in constructed wetlands can be very important in the treatment of swine lagoon effluent when land application areas are limited. The objectives of this investigation were to determine (i) the denitrification enzyme activity (DEA) in the marsh sediments of marshpond-marsh (MPM) constructed wetlands, (ii) changes in DEA with additions of carbon and nitrate, and (iii) the response of DEA to different wastewater N loading rates. Swine wastewater was applied to six MPM wetlands located at North Carolina A&T State University, Greensboro, NC, at rates of 4 to 35 kg N [ha.sup.-1] [d.sup.-1]. Soil samples were obtained from the top 25 mm of the marsh sections on four dates for determination of DEA via the acetylene blockage method (blocked at [N.sub.2]O. Headspace [N.sub.2]O was measured via gas chromatography. In the control treatment, they ranged from 0.06 to 1.13 and 0.16 to 0.79 mg [N.sub.2]O-N [kg.sup.-1] soil [hr.sup.-1] in the first and second marshes, respectively. In both marshes, the DEA rate was significantly increased with the addition of nitrate but not by glucose, indicating that nitrate was a clear limiting factor for denitrification. The DEA in both the control and the amended treatments increased dramatically with increased wastewater N loading, and the increases were generally more pronounced in the first marsh. The DEA values produced in the absence of acetylene blockage did not increase with wastewater N loading rate. Denitrification enzyme activity levels in the marsh sections of the MPM were generally consistent with a highly denitrifying environment.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2005.09.009 Byline: Yuan-Hui Li (a), Laurie Menviel (a), Tsung-Hung Peng (b) Keywords: Remineralization ratios; Nitrification; Partial nitrification; Denitrification; Anammox; Nitrate deficit; Indian Ocean Abstract: The three-end-member mixing model of Li and Peng [Latitudinal change of remineralization ratios in the oceans and its implication for nutrient cycles. Global Biogeochemical Cycles 16, 1130-1145] was applied to the World Ocean Circulation Experiment (WOCE) data from Indian Ocean to obtain additional estimates on the remineralization ratios (Pas.[sup.1]Nas.[sup.1]C.sub.orgas.[sup.1]aO.sub.2) of organic matter in the oxygenated regions. The results show systematic changes of the remineralization ratios with latitude and depth in the Indian Ocean. The average remineralization ratios for Indian warm water masses (potential temperature I[cedilla][approximately equal to]10.sup.aC) are Pas.[sup.1]Nas.[sup.1]C.sub.orgas.[sup.1]aO.sub.2=1as.[sup.1](15.6[+ or -]0.7)as.[sup.1](110[+ or -]9)as.[sup.1](159[+ or -]8). These are comparable to the traditional Redfield ratios (Pas.[sup.1]Nas.[sup.1]C.sub.orgas.[sup.1]aO.sub.2=1as.[sup.1]16as.[sup.1]106as.[sup.1]138), and are in good agreement with Anderson's [On the hydrogen and oxygen content of marine phytoplankton. Deep-Sea Research I 42, 1675-1680.] values of Pas.[sup.1]Nas.[sup.1]C.sub.orgas.[sup.1]aO.sub.2=1as.[sup.1]16as.[sup.1]106as.[sup.1]150 within the given uncertainties. Separation of nitrate deficits resulting from aerobic partial nitrification (dN) and anaerobic denitrification (dNa[sup.3]) processes using empirical equations is shown to be useful and consistent with other observations. The dN maximum coincides with the phosphate and nitrate maximums, lies within the oxycline below the oxygen minimum zone, and is in contact with the continental slope sediments. The dNa[sup.3] maximum lies within the oxygen minimum zone with O.sub.2 Author Affiliation: (a) Department of Oceanography, University of Hawaii, Honolulu, Hawaii 96822 (b) NOAA/AOML, Ocean Chemistry Division, Miami, Florida 33149, USA Article History: Received 3 March 2005; Revised 12 September 2005; Accepted 19 September 2005

The long-term effects of different organic and inorganic fertilizers on activity and composition of the denitrifying and total bacterial communities in arable soil are investigated. The results have shown that the addition of different fertilizers affects both the activity and the composition of the denitrifying communities in arable soil on a lorng-term basis.

The chromium addition has less influence on the denitrification bacteria than on the nitrification bacteria. Various measures to determine the removal efficiency of carbon and nitrogen substance using lab scale sequencing batch reactors (SBR) reactor fed with untreated tannery wastewater containing a relevant amount of chromium are discussed.

Research has been conducted on the (super)15 N isotope pairing technique. The principles of this technique and the application of the (super)15 N isotope pairing in sediments are discussed.

Research has been conducted on the monoterpenes with unsaturated hydrocarbon structure. Results indicate the presence of the monoterpene degradation pathway in Alcaligenes defragrans.

Research has been conducted on the denitrifying bacteria genetic heterogeneity. The use of the single-copy genes that code for nitrite reductases as denitrifyng bacteria molecular markers is discussed.

Research has been conducted on the horizontal patchiness in microbial sediment communities. The examination of the horizontal heterogeneity for denitrifying bacteria in time and space is discussed.

Research has been conducted on the nirS gene for Paracoccus pantotrophus cytochrome cd (sub)1 nitrite reductase. The determination of the gene transcription start site and the length of nirS promoter transcripts are discussed.

Byline: Tetsuo Yanagi (1) Keywords: Box model analysis; nutrient budget; CO.sub.2 absorption; denitrification Abstract: Seasonal variations in freshwater, salt, phosphorus and nitrogen budgets of Hakata Bay, Japan were investigated from April 1993 until March 1994. The internal sink of dissolved inorganic phosphorus (DIP) and nitrogen (DIN), and the internal source of dissolved organic phosphorus (DOP) and nitrogen (DON) predominate in the bay. This means that the production of organic matter is larger than respiration, and atmospheric CO.sub.2 is absorbed in the water column of Hakata Bay. Denitrification is more dominant than nitrogen fixation in the bay. Compared to Tokyo and Mikawa Bays, Hakata Bay is harder to eutrophicate, mainly due to the shorter residence time of freshwater. Author Affiliation: (1) Research Institute for Applied Mechanics, Kyushu University, Kasuga, 816-8580, Japan Article History: Registration Date: 01/10/2004

The activity of denitrifying bacteria in the gut of Lumbricus rubellus and Ostoclasium lacteum was analyzed to determine the role of earthworms in the synthesis of VH or N2O in terrestrial ecosystems. Denitrifying activity was exhibited by 3% to 10% of the microbes isolated from earthworm gut material. The anaerobic gut homogenates also catalyzed the synthesis of N2O and N2 from nitrate after prolonged incubation. Furthermore, N2O production by earthworms was also mediated by nitrification, assimilatory nitrate reduction and dissimilatory reduction of nitrate to ammonium.

The rate of microbial denitrification in groundwater was analyzed in laboratory incubations of aquifer core materials by utilizing natural-gradient tracer test methods. Analysis of bacterial electron-accepting process of groundwater samples collected from Cape Cod, MA, indicated high levels of denitrification activity. Furthermore, the aquifer core samples exhibited a 3-4-day time lag in the rate of nitrous oxide accumulation.

A two-dimensional model of oxidant consumption in oxic sediments, in form of O2 and NO3-, in highly dynamic and diverse micro-sites indicates that few transient reaction sites mediate oxygen and nitrogen reduction. Within the sediment, oxygen content of micro-sites at a specific depth is significantly lower than the mean level at the surface. Low oxygen levels at most sites allow simultaneous denitrification leading to analogous O2 and NO3- profiles. The data is taken from shallow sediments of the Chukchi Sea, the Washington continental margin, and Puget Sound.

A study of nitrogen isotopes at three sites in the Arabian Sea indicates changes in the 15N/14N values due to climatic variations, as confirmed by the agreement of the variations with Milankovitch cycle values. This implies that subsurface nitrate level and denitrification vary with climate. These factors may have serious implications on the changes in marine biogeochemical cycles.

Sensitive mass spectrometry and denitrification bioassay studies compute (15)N abundance in nanogram pools of NO2- and NO3-, that are reduced to N2O gas by Pseudomonas aeruginosa. Samples containing low N2O gas levels are spiked with a reference N2O-containing gas of natural (15)N abundance to calculate (15)N abundance. The reduced contamination risk during N2O studies is used in isotopic analysis of inorganic N conversions by denitrifying and nitrifying bacteria.

Oxygen concentrations in overlying waters affect nitrification and denitrification, and their regulatory processes in fresh water sediment microcosms. High oxygen concentrations shift nitrification to the lower section of the oxic zone and decrease denitrification due to increased NO(sub 3) diffusion to the denitrifying regions of the anoxic sediment.

Hydrogen-oxidizing denitrifying bacterial strains isolated from nitrate-contaminated gravel and sand aquifer play a significant role in the bioremediation of nitrate-contamination in ground water. All the strains grow autotrophically on hydrogen, produce innocuous end products and are sequentially manipulated for oxygen and nitrate consumption.

The fnrA gene supports anaerobic development of nitrate-determined fnr deletion mutant of Escherichia coli. The gene possesses a 0.85 kb single transcript. Insertional mutagenesis results in mutations in fnrA, followed by gene replacement. Arginine deiminase presence and lack of fnrA transcript indicate gene replacement. The same bacterium may also contain another fnr homolog, as implied by anaerobic activation of the promoter-probe vector for transcription involving fnr.

The chemistry of azoalkanes and bicyclopentanes is stimulated by photosensitized electron transfer (PET). The intricate working of the process is determined by intramolecular trapping experiments. Derivatives such as cyclopentadienes are generated due to the possible intermediary role of the allyl cation -H+. The participation of diazenyl radical cations is examined. Rare radical cation chemistry is revealed by the 2,3-diazabicyclo(2.2.1)hept-2-ene products due to PET. 1,3-diyl radical cations use the azoalkanes as precursors in a complex manner.

A study of a pea field (Pisum sativen L.) at Blaine Lake, Saskatchewan, Canada, aimed to determine the seasonal and spatial variability of denitrification in different landform elements. N2O appears to evolve primarily due to denitrification because denitrification activity and N2O evolution were well correlated, and their temprol and landscape scale patterns resembled each other. The topography of the landscape affected the hydrologic mechanisms, which chiefly regulated the integrity of denitrification.

An evaluation of the potential denitrification rates in a shallow anaerobic groundwater system is discussed. Sediment and water samples were collected from a golf course in Tampa, Florida and were subjected to particle size analysis and calibrated acidity/dissolved oxygen meters, respectively. The rate of denitrification and the influence of acidity on the denitrifying activity was analyzed using acetylene block technique. It was found that the primary cause for the accumulation of nitrate in groundwater underlying cultivated lands is the carbon limitation in anaerobic aquifer sediments.

Thousands of gallons of JP-4 grade jet fuel contaminated the shallow aquifer in South Carolina. In relation to this, the influence of environmental factors on denitrification in sediment contaminated with JP-4 jet fuel is analyzed. Results show that denitrification at the site is NO3-N limited, and communities of denitrifiers are present throughout the sediments of the site. Moreover, the considerable variability of denitrification exhibited by the sediments is likely to be a primary determinant of the efficiency of the remediation process.

A study was conducted to identify the sources of nitric oxide and nitrous oxide in dry soils. Biological sources were activated minutesafter soil wetting. When moisture was below field capacity, nitrification appeared to be the main source of NO and N2O, with NO activity greater than N2O. Above field capacity, denitrification appeared to be the main source of N2O with N2O activity greater than NO. Acetylene was found to inhibit NO emmissions as did a combination of NO2- production and abiological reduction ofNO2- to NO.