Denitrification measurements

Figure 18.11 Frequency distribution of denitrification measurements from a variety of estuarine ecosystems. The inset is a frequency histogram using denitrification measurements from all aquatic systems. Both figures used data from the denitrification summary developed by Greene...

Hamersley, M. R., and Howes, B. L. (2005). Couple nitrification-denitrification measured in situ in a Spartina alternijlora marsh with a (NH4+)-N-15 tracer. Mar. Ecol. Prog. Ser. 299, 123-135. 

Seitzinger S. P., Nielsen L. P., Caffrey J., and Christensen P. B. (1993) Denitrification measurements in aquatic sediments a comparison of three methods. Biogeochemistry 23, 147-167. 

NO emissions did not exceed 2 ng Nm s and their measurement was only possible by chamber methods. The low NO emissions but high NjO emissions show that denitrification was the main source of NjO at this site. The discrepancies between the chamber and micrometeorological methods illustrated the need to define the flux-footprint of a micrometeorological measurement very carefully, and to use this information in the field to choose the locations in which chambers are placed. Without such an approach, the integration of results from chambers into estimates of field-scale emission remains an uncertain method. 

Fig. 2 Longitudinal changes in nutrient concentrations below the effluent input of a WWTP without tertiary treatment in La Tordera Stream. Values are the average ( SEM) of monthly measurements done over a year (see more details in [47]). In the left panel, note the net decline of ammonium concentration with concomitant net increases in nitrate concentration, suggesting a potential hot spot for nitriflcation. However, in the latest meters downstream, dissolved inorganic nitrogen (DIN) tends to decrease, which indicates net lost of DIN possibly due to denitrification. The right panel shows net changes in phosphate and dissolved organic carbon (DOC) concentrations. While phosphate does not exhibit any clear trend on an annual basis, DOC seems to decline similarly to DIN, which supports the relative dominance of denitrification...

Sigman et al. [134] have described a bacterial method for measuring the isotopic composition of seawater nitrate at the natural-abundance level. The method is based on the analysis of nitrous oxide gas (N2O) produced quantitatively from nitrate by denitrifying bacteria. The classical denitrification pathway consists of the stepwise reduction of nitrate (NOp to nitrite (N02), nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2) ... 

Bouwman AF, Boumans LJM, Batjes NH (2002) Emissions of N20 and NO from fertilised fields summary of available measurement data. Glob Biogeochem Cycles 16 1058 Christensen S, Simkins S, Tiedje JM (1990) Spatial variation in denitrification dependency of activity centers on the soil environment. Soil Sci Soc Am J 54 1608-1613 CONCAWE (2006) Well-to-wheels analyses of future automotive fuels and powertrains in the European context. Study of European Council for Automotive R D, EUCAR, European Commission, Brussels... 

Denitrification, a dissimilatory pathway of nitrate reduction (see Section 3.3 also) into nitrogen oxides, N2O, and dinitrogen, N2, is performed by a wide variety of microorganisms in the forest ecosystems. Measurable rates of N20 production have been observed in many forest soils. The values from 2.1 to 4.0 kg/ha/yr are typical for forest soils in various places of Boreal and Sub-Boreal Forest ecosystems. All in situ studies (field monitoring) of denitrification in forest soils have shown large spatial and temporal variability in response to varying soils characteristics such as acidity, temperature, moisture, oxygen, ambient nitrate and available carbon. 

Nitrate can be used to delay a return to fermentation after treatment. In this case the nitrate concentration needs to be measured. It is important to realise that nitrate can be lost through denitrification within 20 minutes of removing the sample from the reactor. 

Sexstone AJ, Revsbech NP, Parkin TB, Tiedje JM. 1985. Direct measurement of oxygen profiles and denitrification rates in soil aggregates. Soil Sci Soc Am 1 49 645-51. 

At this site in the eastern tropical North Pacific, denitrification is responsible fiar the midwater loss of nitrate and production of nitrite. The size of the secondary nitrite maximum is dependent on the relative rates of its production from NO3 and its loss via dissimilatory reduction to N2. The amount of nitrate lost to denitrification is shown as the difference between the measured nitrate and the calculated nitrate. The latter was estimated by multiplying the observed phosphate concentrations by the average nitrate-to-phosphate ratio in the three deepest samples (11.9 1.6pmolN/L). Note that the zone of denitrification is restricted to mid-depths, i.e., the depths of the OMZ at this site. 

These general features of NOs reduction in submerged rice soils are bom out by field observations. Buresh et al. (1993b) found that from 60 to 75 % of N-labelled NOs" applied on the surface of flooded ricefields was lost by denitrification over 2-3 weeks, as measured by the not recovered in the soil, floodwater and plants. The recovery of (N2 + N20)- N in chambers placed over the floodwater was less than the estimated denitrification loss because gas bubbles became entrapped in the soil. More N2 + N2O was recovered when the chambers were placed over the rice plants showing that some of the gas escaped through the plants. The not lost by denitrification was presumed to have... 

Effluent waters from denitrification reactors, while free of nitrate, may have other water quality problems. During bench-scale testing, it was found that process effluent contained high chemical oxygen demand (COD), total suspended solids (TSS), and turbidity. Dissolved oxygen (DO) levels were low, and odor was caused by the presence of measurable amounts of hydrogen sulfide. 

While there is a variety of evidence from these and other measurements (e.g., see Notholt, 1994) that denitrification is more episodic and less widespread in the Arctic compared to the Antarctic, it does not mean that it does not occur. Indeed, there is good evidence for denitrification of the Arctic polar vortex under some conditions (e.g., see Schlager et al., 1990 Kondo et al., 1992 Wilson et al., 1992 Dye et al., 1992 Pueschel et al., 1992b Tuck et al., 1994 and Hopfner et al., 1996). For example, direct measurements of stratospheric water and NO>. at the edge of the Arctic polar vortex in one study showed that in that case, both dehydration and denitrification had occurred (Hintsa et al., 1998a). 

Thus, in order to balance the electrons, 1 mM e have to be consumed by denitrification. Hence, the calculated consumption of nitrate is 1 mM e = 0.2 mM NO = 2.8 mg N-L 1, which is more than is present in the river water. Note, however, that reaction (ii) produces 0.15 mM = 2.1 mg N L 1 nitrate. Thus, one would expect a net decrease in nitrate of only 0.7 mg N L 1, which compares well with the observed 0.5 mg N L"1 decrease. The measured concentration changes of the four water constituents are, therefore, reasonable. 

Measured ammonification, nitrification, and denitrification of the soil in GEM, and its nonrecombinant parent. 

The understanding of four aspects of the lower stratosphere must be improved. The first is the processes of heterogeneous conversion. Does it occur in three hours or in three days Which type of aerosols or particles are most favorable for conversion and what are the conditions required for their formation How do the particles form, and what are their compositions and structures What are the most important mechanisms for denitrification These issues can be settled only by a combination of laboratory and stratospheric measurements. 

Small enrichments of stable isotopes can be used for detailed studies of specific processes such as denitrification. If these processes are important in the flux of material in the ecosystem from an isotopic mass-balance standpoint, then process rates and associated isotopic fractionations must be measured independently. Alternatively, sufficient isotope must be added to enrich the pool of interest to a level at which the magnitude of fractionation effects is negligible. For example, an enrichment of ammonium by 1 order... 

The Henry s law solubility of trace species such as HNO, HC1, HBr and HOC1 in sulfuric acid solutions is an important issue. Reactions (1) to (4) generate HNO, and its solubility determines whether the product dissolves or is released into the gas phase. As expected from Van t Hoff law, the solubilities of HNO, and HC1 have found to increase with decreasing temperature. In addition, the solubilities for both HC1 and HNO, increase as the concentration of sulfuric acid decreases [49,80]. Both of these factors will work together to predict that the highest solubilities for HC1 and HNO, in stratospheric sulfate aerosols will occur at low temperatures, where the sulfate particles will be most dilute. The measured solubility of HNO, in sulfuric acid is small enough that most of the stratospheric nitric acid will be in the gas phase. Thus the denitrification, which contributes to polar ozone depletion, will not occur on the global sulfate aerosol. 

Seitzinger (1987) TN, Seitzinger, unpublished measurements 7, TN compiled in Nixon et al. (1996) DIN estimated assuming DIN = 50% TN (Graneli et al., 1990) denitrification range from Shaffer and Ronner (1984) (measurements of deep Baltic water) and Nixon et al. 

Laursen, A.E., and Seitzinger, S.R (2002) Measurement of denitrification in rivers an integrated, whole reach approach. Hydrobiologia 485, 67-81. 

Nowicki, B.L. (1994) The effect of temperature, oxygen, salinity, and nutrient enrichment on estuarine denitrification rates measured with a modified nitrogen gas flux technique. Estuar. Coastal Shelf Sci. 38, 137-156. 

Rysgaard, S., Risgaard-Petersen, N., Nielsen, L.P., and Revsbech, N.P. (1993) Nitrification and denitrification in lake and estuarine sediments measured by the 15 N dilution technique and isotope pairing. Appl. Environ. Microbiol. 59 2093-2098. 

Seitzinger, S.P. (2000) Scaling up Site-specific measurements to global estimates of denitrification. In Estuarine Science A Synthetic Approach to Research and Practice (Hobbie, J.E., ed.), pp. 211-240, Island Press, Washington, DC. 

Sprensen, J. (1978) Denitrification rates in a marine sediment measured by the acetylene inhibition technique. Appl. Environ. Microbiol. 36 139-143. 

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