Estimates Of Denitrification Research Articles

Estimation of Nitrification and Denitrification from Microprofiles of Oxygen and Nitrate in Model Sediment Systems

The coupling between nitrification and denitrification and the regulation of these processes by oxygen were studied in freshwater sediment microcosms with O(2) and NO(3) microsensors. Depth profiles of nitrification (indicated as NO(3) production), denitrification (indicated as NO(3) consumption), and O(2) consumption activities within the sediment were calculated from the measured concentration profiles. From the concentration profiles, it was furthermore possible to distinguish between the rate of denitrification based on the diffusional supply of NO(3) from the overlying water and the rate based on NO(3) supplied by benthic nitrification (D(w) and D(n), respectively). An increase in O(2) concentration caused a deeper O(2) penetration while a decrease in D(w) and an increase in D(n) were observed. The relative importance for total denitrification of NO(3) produced by nitrification thus increased compared with NO(3) supplied from the water phase. The decrease in D(w) at high oxygen was due to an increase in diffusion path for NO(3) from the overlying water to the denitrifying layers in the anoxic sediment. At high O(2) concentrations, nitrifying activity was restricted to the lower part of the oxic zone where there was a continuous diffusional supply of NH(4) from deeper mineralization processes, and the long diffusion path from the nitrification zone to the overlying water compared with the path to the denitrifying layers led to a stimulation in D(n).

Estimates of denitrification in soil by remote sensing of thermal infrared emission at different moisture levels

Remote sensing techniques may be one way to narrow the range of uncertainty in extrapolating N2 emissions from small-scale to large-scale terrestrial ecosystems. In the present work we investigated the correlations between denitrification activity, soil moisture, and soil thermal infrared emissions. A field experiment was performed on two different agricultural soils, one loam and one silty clay. The results indicated that thermal infrared emissions can only be used to estimate the denitrification rate in soil within a limited range of soil moisture levels. Estimates of denitrification activity based on soil texture and moisture are, however, very likely to be a fruitful approach to generating large-scale N fluxes.

Equilibrating of 15N-Gases by Electrodeless Discharge: A Method of Indirect Mass Spectrometric Analysis of 30N2 for Denitrification Studies in Soils

Abstract The estimation of denitrification in soil by the 15N tracer technique includes isotope analysis of gas samples with a nonrandom distribution of the N2 mole masses of 28, 29 and 30. In that case the emission of total 15N is underestimated by calculating 15N atom fractions from the 29N2/28N2 ratio if 30N2 is not considered. 30N2 can be measured indirectly in N2 enriched with 15N with nonrandom distribution of mole masses by mass spectrometric analysis. The nitrogen fraction of gas samples was transferred to discharge tubes. Microwaves (60 sec) generated an electrodeless discharge of the gas which caused a temporary split-up of N2 molecules and thus established an equilibrium distribution of the mole masses. The 29N2/28N2 ratio was measured in equilibrated and in untreated samples to calculate the real emission of 15N. The measurements of 15N standard gases by this method satisfactorily coincided with calculated values for 15N atom fraction above a concentration of 50 δ‰.

Denitrification and the Dinitrogen/Nitrous Oxide Ratio as Affected by Soil Water, Available Carbon, and Nitrate

Biological denitrification is affected by many environmental factors that control the amount of N₂ and N₂O entering the atmosphere. This study was conducted to measure the effect of water-filled pore space (WFPS), available C, and soil NO₃ concentration on total denitrification (N₂ + N₂O), using acetylene (C₂H₂) inhibition, and to ascertain if denitrification could be estimated from N₂O measurements in the field using an average N₂/N₂O ratio. Repacked cores of four benchmark soils were brought to 60, 75, and 90% WFPS by applying treatments of glucose-C (0, 180, and 360 kg ha⁻¹) and NO₃-N (0, 50, and 100 kg ha⁻¹). The cores were incubated at 25°C, with and without 100 mL C₂H₂ L⁻¹, for 5 d during which daily gas samples of the headspace were analyzed for N₂O and CO₂. Total N loss due to denitrification generally increased as soil texture became finer and WFPS increased. The only exception to this was the C-amended sand, where N losses up to 26 and 66% were recorded at 60 and 75% WFPS, respectively. Denitrification rates at high N concentrations were quite small in the absence of an available C source but increased with increasing available C (glucose). The N₂/N₂O ratio generally increased with time of incubation after the initial treatment application. The largest ratios (up to 549) were found at the highest available C rate and generally at the highest soil water content. The presence of high NO₃ concentrations apparently inhibited the conversion of N₂O to N₂, resulting in lower N₂/N₂O ratios. Using an average N₂/N₂O ratio for estimation of denitrification from N₂O field measurements cannot be recommended because of the variation in this ratio due to the many environmental factors altered by field management that influence denitrification and the relative production of N₂ and N₂O. Published as Paper No. 9865, Journal Series, Nebraska Agricultural Research Division, Lincoln.

Gaseous nitrogen losses from field plots grown with pea (Pisum sativum L.) or spring barley (Hordeum vulgare L.) estimated by 15N mass balance and acetylene inhibition techniques

In a mass balance of 15N-labelled nitrate added to soil grown with pea or barley, denitrification estimates using the acetylene-inhibition technique were compared with unaccounted for 15N. During the growth season of 1989, which was drier than average, N losses due to denitrification estimated by the acetylene-inhibition technique were negligible. A substantial amount of fertilizer N was unaccounted for by the 15N mass balance, especially in the pea plots. The loss took place during the period of grain-filling in which no leaching occurred, and was accompanied by a decrease in 15N content of the plants. Volatilization of ammonia from the aerial parts of the plants is a possible explanation of the observed loss. An estimation of denitrification relying only on the 15N mass balance would have resulted in an overestimation of denitrification.

Regional scale analysis of denitrification in north temperate forest soils

Large scale analyses of biogeochemical processes are necessary for understanding anthropogenic effects on global climate and environmental quality. Regional scale estimates of denitrification from forest soils in southern lower Michigan USA were produced by stratifying the region into landscape experimental units using soil texture and natural drainage classes, and extrapolating data to larger areas using a geographic information system (GIS). Previous landscape-scale research established relationships between soil texture and drainage and denitrification and quantified annual denitrification N loss in nine soil texture/drainage groups. All forest soils within the region (64 series) were assigned to one of these nine groups based on their texture and drainage characteristics and were assigned an annual denitrification N loss value. A regional estimate of denitrification was produced by multiplying the areal extent of each of the nine soil groups by their annual denitrification N loss value. Loam-textured soils underlie 47% of the regional forest and accounted for 73% of the forest denitrification. Sandy soils were found under 44% of the regional forest but produced only 5% of the regional denitrification. Clay loam soils underlie 9% of the regional forest and produced 22% of the denitrification. Annual denitrification N loss for the region was estimated as 1.4×107 kg N/yr. We used denitrification enzyme activity (DEA) as a proxy for annual denitrification N loss to determine if the relationship between denitrification and soil texture and natural drainage that we observed at the landscape scale held up at the regional scale. DEA was measured in 22 soils across the region and was strongly related to soil texture and natural drainage (r2=0.61), suggesting that extrapolation of data from the landscape to the regional scale was justified.

A TECHNIQUE FOR ESTIMATING DENITRIFICATION RATES AT DIFFERENT SOIL TEMPERATURES, WATER CONTENTS, AND NITRATE CONCENTRATIONS

Much of the mineral nitrogen loss during winter and early spring in central Alberta has been attributed to denitrification. However, the extent of this loss is site- and season-specific. In an attempt to use the results of more basic studies in the estimation of field denitrification, a simulation technique for denitrification was constructed as part of a more comprehensive agroecosystem model. As part of the larger model, the technique was fully coupled to submodels for carbon and nitrogen transformations and transport. In the technique, inter- and intra-horizon fluxes of oxygen in gaseous and soluble phases were simulated as oxygen moved from the atmosphere to sites of microbial respiration. A portion of the simulated demand for electron acceptors not met by oxygen at the microsites was met by nitrate, using a Michaelis-Menten function of rate versus nitrate concentration. The technique was tested against nitrate loss recorded under a range of controlled laboratory conditions. Recorded nitrate losses ranging from 0 to 3.0 μg N g−1 soil h−1 were reproduced by the technique across a range of temperatures, water contents, and nitrate concentrations. An interaction between temperature and water content on denitrification rate as observed elsewhere was also reproduced. However, the technique relies on an understanding of the distribution of soil organic matter among kinetic fractions in the simulated soil profile and upon the rates at which these fractions decompose. Thus, a process-based technique for the simulation of denitrification will require more detailed insight into soil carbon dynamics.

Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods

Of the biogeochemical processes, denitrification has perhaps been the most difficult to study in the field because of the inability to measure the product of the process. The last decade of research, however, has provided both acetylene and 15N based methods as well as undisturbed soil core and in situ soil cover sampling approaches to implementing these methods. All of these methods, if used appropriately, give comparable results. Thus, we now have several methods, each with advantages for particular sites or objectives, that accurately measure denitrification in nature. Because of the general usefulness of the acetylene methods, updated protocols for the following three methods are given: gas-phase recirculation soil cores; static soil cores; and the denitrifying enzyme assay also known as the phase 1 assay. Despite the availability of these and other methods, denitrification budgets remain difficult to accurately establish in most environments because of the high spatial and temporal variability inherent in denitrification. Appropriate analysis of those data includes a distribution analysis of the data, and if highly skewed as is typically the case, the most accurate method to estimate the mean and the population variance is the UMVUE method (uniformly minimum variance unbiased estimator). Geostatistical methods have also been employed to improve spatial and temporal estimates of denitrification. These have occasionally been successful for spatial analysis but in the attempt described here for temporal analysis the approach was not useful.

Nitrate requirement for acetylene inhibition of nitrous oxide reduction in marine sediments

The inhibition of nitrous oxide (N2O) reduction by acetylene (C2H2) in saltmarsh sediment was temporary; we investigated this phenomenon and possible causes. The reduction of N2O in the presence of C2H2 was biological. N2O consumption in the presence of C2H2 began when nitrate concentration became very low. The time course of N2O consumption after periods of N2O accumulation was unaffected by initial nitrate concentrations between 16 and 200μM, or C2H2 concentrations between 10 and 100% of the gas phase. Sulfide had no effect on the kinetics of N2O reduction in the presence of C2H2. In more dilute slurries of saltmarsh sediments and in estuarine sediment, N2O persisted in the presence of C2H2 unless sufficient organic carbon was added to deplete nitrate. In saltmarsh sediments, the rate of N2O consumption in the presence of C2H2 was not changed by preincubation with C2H2. Initial positive rates of N2O production in the presence of C2H2 occurred only when the block was apparently effective (i.e., at nitrate concentrations greater than about 5-10μM) and appeared to represent a valid estimate of denitrification. Conversely, and in agreement with previous studies, concentrations of NO3 (-) below these levels resulted in reduced efficiency of C2H2 blockage of N2O reductase.

Influence of soil carbon content on denitrification from fallow land during autumn

AbstractDenitrification in autumn removes nitrate from soil which may limit subsequent crop growth but also lessens the nitrate available for leaching. Autumn denitrification may therefore play a significant role in determining water quality because autumn and winter leaching of nitrate probably provides the greater part of the nitrate reaching groundwater from arable agriculture. The influence of soil carbon content on rates of denitrification during October and November 1987 was investigated in field plots of a continuous spring barley experiment which had large differences in soil organic matter content. Denitrification occurred between early autumn, when the warm soil became saturated with water, and late autumn when its temperature dropped to 6‐8°C. Gaseous N losses from plots with a low carbon content and given inorganic nitrogen were equivalent to 4.5 kg N ha−1, but those from farmyard‐manure‐treated plots with a high carbon content were 29 kg N ha−1, approximately six times greater. Measurements indicated that the high carbon content plots contained twice the denitrifying biomass of the low carbon content plots. The initial denitrification rate (Phase 1) of a laboratory measurement of potential denitrification gave a good estimate of denitrification in the field.

Denitrification in north temperate forest soils: Spatial and temporal patterns at the landscape and seasonal scales

Spatial and temporal patterns of denitrification were studied in nine forest soils of different texture and drainage classes in Michigan. Denitrification was measured using intact soil cores amended with acetylene. Sampling was done weekly during spring, and monthly at other times. To determine the factors limiting denitrification, selected cores were amended with either water or water plus nitrate. We found that activity was highest in spring and fall and was lowest during summer. Soils showed a characteristic relationship between denitrification rate and soil texture and drainage classes. Over 80% of the annual N loss to denitrification occurred during brief (3–6 week) periods of high activity in the spring and fall. Rates of denitrification during these periods exceeded 0.5kg N ha −1 d −1 in some soils. Estimates of annual N loss to denitrification ranged from < 1 kg N ha −1 yr −1 in a well-drained sand soil to over 40kg N ha −1 yr −1 in a poorly-drained clay loam soil. Lack of available NO −1 1 was the primary factor limiting denitrification in summer, but available carbon was probably occasionally limiting, especially in the well-drained soils. Marked seasonal changes were observed in the variability and frequency distributions of denitrification rates. Denitrification rates showed lower variance in spring and fall compared to summer, regardless of the magnitude of the rates. These patterns may be related to seasonal changes in soil structure, carbon availability or aeration, which create a more uniform environment in the spring an fall. The characteristic relationship between denitrification rates and soil texture and drainage over two seasons and multiple sites suggests that geomorphologically-based models using these parameters may be feasible for producing landscape- and regional-scale estimates of denitrification.

An estimate of oxygen consumption and denitrification in coastal waters of the Swedish west coast, using indirect methods

Intensive hydrographic observations during 48 h, covering an area of ca. 100 km 2 on the Swedish west coast, have been used to determine oxygen consumption at the bottom and its relation to regeneration of inorganic nitrogen and phosphorus. The results are based on measurements of salinity, O 2, PO 4 3−, NO 2 −, NO 3 −, NH 4 +, and currents in a very thin deep water layer. Oxygen concentrations decreased, corresponding to a bottom oxygen consumption of 0·27 l m −2 day −1, while the mean concentrations were about 5·5 ml l −1. Phosphate concentrations increased, corresponding to a regeneration of 0·094 mmol m −2 day −1. Inorganic nitrogen concentrations, on the other hand, decreased which was interpreted as a net effect of simultaneous remineralization, nitrification and denitrification. Denitrification was estimated to be 1·87 mmol m −2 day −1. The results indicate that high oxygen concentrations within the water (favouring rapid nitrification), in combination with a large supply of organic matter to the bottoms (resulting in oxygen depleted ‘bottoms’) are effective triggers for denitrification. The results are compared with small-scale laboratory and field experiments from similar areas, and with seasonal changes in oxygen and nutrient conditions within these waters.

Reduction of nitrous oxide (N 2O) by a bacterial isolate in the presence of sulfide and acetylene

A denitrifying bacterial isolate was isolated from soil initially amended with glucose, sodium sulfide, nitrous oxide (N 2O) and acetylene (C 2H 2). The organism was able to reduce N 2O in the presence of a C 2H 2 concentration (10%) which normally blocks the nitrous oxide reductase enzyme in the denitrification sequence. The presence of such an organism in soil may affect the usefulness of the C 2H 2 inhibition of nitrous oxide reduction as an estimate of biological denitrification if the appropriate conditions and organisms are present in the sample under investigation.

Denitrification in San Francisco Bay Intertidal Sediments

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(3) + NO(2) concentrations (</=26 muM) were below the apparent K(m) (50 muM) for nitrate. During the rainy season, when ambient NO(3) + NO(2) concentrations were higher (37 to 89 muM), an accurate estimate of the K(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(2)O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N(2)O in the presence of C(2)H(2) was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cell suspensions of a marine pseudomonad confirmed that this N(2)O loss was caused by incomplete blockage of N(2)O reductase by C(2)H(2) at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 mumol of N(2) m h (for undisturbed sediments) to 17 to 280 mumol of N(2) m h (for shaken sediment slurries).

Estimates of Denitrification and Nitrification in Coastal and Estuarine Sediments

Denitrification and nitrification in sediments of Tama Estuary and Odawa Bay, Japan, were investigated by the combined use of a continuous-flow sediment-water system and a N tracer technique. At Odawa Bay, the nitrification rate was comparable to the nitrate reduction rate, and 70% of the N(2) evolved originated from nitrogenous oxides (nitrate and nitrite) which were produced by the action of nitrifying bacteria in the sediments. At Tama Estuary, the nitrate reduction rate was 11 to 17 times higher than the nitrification rate, and nitrogenous oxides derived from ammonium accounted for only 6 to 9% of the N(2) evolution by denitrification.

Estimates of denitrification in sediments of the Bering Sea shelf

Denitrification, i.e. anaerobic reduction of nitrate or nitrite to gaseous nitrogen, in the surface sediments of the Bering Sea was estimated using a 15 N-tracer method. N 2 production is apparently controlled by the supply of nitrate and nitrite to the sediments. The average rate of N 2 production in three locations was 1.2 ng-atoms N (g dry weight of sediment) −1 h −1 . The rate of nitrate reduction estimated from the vertical distribution of nitrate in the sediments using a one-dimensional diffusion model agreed well with observed rates of N 2 production. The annual loss of combined nitrogen by denitrification in the Bering Sea shelf was estimated to be 5 × 10 11 g.

Estimates of denitrification in sediments of the Bering Sea shelf : Koike, Isao and Akihiko Hattori, 1979. Deep-Sea Res., 26(4A): 409–415

Estimates of denitrification in sediments of the Bering Sea shelf : Koike, Isao and Akihiko Hattori, 1979. Deep-Sea Res., 26(4A): 409–415