Topdown and bottomup estimates of global nitrous oxide emissions to the atmosphere

Nitrous oxide is produced in 'natural' and agricultural soils almost exclusively as a result of microbial processes (see Chapter 2). The main microbial reactions involved in the production of N2O are nitrification (oxidation of ammonium to nitrite) and denitrification (reduction of nitrate to dinitrogen N2O is an obligate intermediate in this latter process). Although nitrification is basically an aerobic process and denitrification is essentially an anaerobic one, both can take place in the...

Contributors

Elizabeth Baggs is a senior lecturer at the University of Aberdeen, UK. Her research interests are in rhizosphere biogeochemistry, plant-microbe-soil interactions, and linking greenhouse gas production in soils to the underpinning microbiology. She has developed stable isotope approaches for quantifying N2O production from different microbial processes and for examining interactions between soil N and C cycles. Hermann Bange is a chemical oceanographer in the Marine Biogeochemistry Research...

References

Balasubramanian, V., Alves, B., Aulakh, M., Bekunda, M., Cai, Z., Drinkwater, L., Mugendi, D., van Kessel, C. and Oenema, O. (2004) 'Crop, environmental, and management factors affecting nitrogen use efficiency', in A. R. Mosier, J. K. Syers and J. Freney (eds) Agriculture and the Nitrogen Cycle, SCOPE 65, Island Press, Washington, DC, pp19-33 BP Global (2007) Statistical Review of World Energy 2007, www.bp.com Boyer, E. W. and Howarth, R. W. (eds) (2002) The Nitrogen Cycle at Regional to...

Nitrification

Ammonia-oxidizing bacteria (AOB) convert ammonia to nitrite in a two-step process with hydroxylamine as an intermediate (Figure 2.2). The membrane-bound ammonia mono-oxygenase enzyme (AMO) catalyses the oxidation of ammonia to hydroxylamine, and hydroxylamine is oxidized to nitrite by the periplasm-associated enzyme, hydroxylamine oxidoreductase (Hooper et al, 1997). The production of N2O occurs at this stage. Two of the four electrons derived from the oxidation of hydroxylamine to nitrite are...

What is producing nitrous oxide in soil

Soil microbial N2O production occurs via nitrification (ammonia oxidation) and nitrate dissimilation (denitrification and nitrate ammonification) pathways (Figure 2.1). These processes rarely occur in isolation, with possible competition for substrates under near-limiting conditions, and the possibility of transfer of N2O or intermediary products from one process to another depending on prevailing environmental conditions, microbial community structure and location within the soil matrix. This...

Rivers and estuaries

According to model estimates (Dumont et al, 2005), the total global load of dissolved inorganic N transported by rivers to the oceans is 25Tg yr_1, of which 16Tg N yr1 comes from anthropogenic sources, including sewage point sources (0.4Tg), diffuse agricultural emissions from mineral fertilizer (5.3Tg), biological N2 fixation (4.5Tg) and manure (3.8Tg). In addition, 12Tg organic N is transported by rivers to coastal waters (Harrison et al, 2005), plus 39Tg of particulate N (Beusen et al,...

The nitrogen cascade

Nitrogen is now known to be unusual among the elements that have had their cycles significantly perturbed by human action. The great significance of nitrogen is that it is linked to so many of the major global and regional environmental challenges that we face today ozone layer depletion, acidification of soils and surface waters, global warming, surface and groundwater pollution, biodiversity loss, and human health and vulnerability. As nitrogen moves along its biogeochemical pathway, the same...

Isotope studies

The isotope ratio 15N 14N of N2O is expressed as 815Natm relative to atmospheric N2 S15Natm (sample) ((15N 14N)sample (15N 14N)std - 1) X 1000. (3.1) In the same way, the isotope ratio 18O 16O of N2O is usually expressed as 818Ovsmow relative to Vienna standard mean ocean water (VSMOW). However, in some cases 18Oatm relative to O2 in the atmosphere is reported. 818OVSMOW can be converted to 818Oatm with the equation 18Oatm -23.0 + 18OVSMOW 1.0235 (3.2) (Kim and Craig, 1993). Mean S15Natm and...

Stable isotope approaches

Stable isotope techniques have a crucial role to play in the attribution of N2O emissions to different microbial processes. This may be done using estimation techniques (variations in natural abundance, site preference) or quantification techniques (using isotopic enrichment), which employ the 15N and 18O signatures of N2O determined by isotope ratio mass spectrometry. Here we give an outline of these approaches, but guide the reader to Baggs (2008) for theoretical details behind each of these...

Nitrous oxide from nitric acid production

Nitric acid is a key ingredient in N-based fertilizers. As a raw material, it also is used for the production of adipic acid (another important N2O source - see next section) and explosives, metal etching and in the processing of ferrous metals. Nitric acid production involves the oxidation of ammonia (NH3) using a platinum catalyst (Ostwald process). Nitrous oxide forms during the catalytic oxidation of ammonia over platinum rhodium gauzes, the major product being NO. It is estimated that...

Edited by Keith Smith

First published in 2010 by Earthscan Copyright Professor Keith Smith, 2010 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as expressly permitted by law, without the prior, written permission of the publisher. Earthscan Ltd, Dunstan House, 14a St Cross Street, London EC1N 8XA, UK Earthscan LLC, 1616 P Street, NW, Washington, DC...

Linking processes to the underpinning microbiology

Understanding how changes in the size or in the diversity of microbial communities producing or reducing N2O in response to environmental conditions or agricultural practices are related to N2O fluxes is key to understanding controls on process rates and the microbial source of N2O. However, until recently, diversity and activity of microbial communities involved in N-cycling were most often investigated in separate studies, which resulted in an artificial dichotomy between research on...

Nitrous oxide from adipic acid production

Nylon production is responsible for nitrous oxide emission through its requirement for adipic acid, (CH2)4(COOH)2, as a precursor. Adipic acid is a fine powder also used for some plastics, clothing, carpets and tyres, and in the production of dyes and insecticides. Nitrous oxide arises from adipic acid production during the oxidation of a ketone-alcohol mixture with nitric acid. It is estimated that for each kilogram of adipic acid made, around 30g of nitrous oxide is also produced. Although...

Approaches to estimating direct and indirect nitrous oxide emissions

The estimation of N2O emissions is still highly uncertain, due to their large variability in time and space. Large variability is caused by the variable rates at which the processes of nitrification and denitrification occur. These processes, in turn, are controlled by biophysical and chemical conditions in soil micro-sites, which often show strong non-linear relationships with emissions of N2O. This non-linearity makes upscaling difficult. In order to estimate direct N2O emissions from the...

Nitratereducing processes

Denitrification is the reduction of NO3 or NO2 to N2 under anaerobic conditions with N2O and NO emitted as intermediary gaseous products (Robertson and Tiedje, 1987 Bremner, 1997). The process is catalysed by the enzymes nitrate reductase, nitrite reductase, nitric oxide reductase and nitrous oxide reductase, and the transport of electrons to NO3 or other N oxides is coupled to the synthesis of ATP (adenosine triphosphate) (Hochstein and Tomlinson, 1988). The nature and regulation of the...

Nitrous oxide distribution in the water column

The shapes of N2O profiles generally fall into three categories Cat. I profiles from oceanic regions with dissolved oxygen concentrations O2 > 10pmol litre-1 throughout the water column (for example in the Atlantic Ocean, the South Indian Ocean and the central North Pacific and central South Pacific Oceans) Cat. II profiles from regions with sub-oxic environments (0 < O2 < 2-10pmol litre-1, Codispoti et al, 2005) such as found in intermediate water depths from about 200m to about 800m in...

The global problem Too much or too little nitrogen

Global Nitrogen Pool Population

Nitrogen, contained in amino acids, proteins and DNA, is necessary for life. While there is an abundance of nitrogen in nature, almost all is in an unreactive form (gaseous nitrogen, N2) that is not usable by most organisms. N compounds fall into two groups - non-reactive and reactive. Non-reactive N is N2. Reactive N (Nr) includes all biologically active, photochemically reactive, and radiatively active N compounds in the atmosphere and biosphere of the earth. Thus Nr includes inorganic...

Nitrous oxideoxygen gas relationship

The relationship between oceanic N2O production consumption and dissolved O2 concentrations is shown schematically in Figure 3.5. While the influence of O2 concentrations on the N2O production via nitrification is still lacking a mechanistic explanation, the influence of O2 on denitrification and thus N2O production results from two factors (1) the redox potential of NO3 respiration favours denitrification under reduced O2 concentrations (see for example Falkowski et al, 2008) and (2) the...

Atmospheric processes leading to nitrous oxide formation

The chemical transformation and removal of atmospheric trace gases by heterogeneous processes involving water droplets in clouds and fog, sulphuric acid and particulates is of great importance for atmospheric chemistry, since it is known that these processes can lead, for example, to major shifts in gasphase photochemistry. For the removal of atmospheric nitrogen compounds, heterogeneous reactions leading to the final end-product nitric acid (HNO3) are of special interest. However, these...

Emission factors

Upscaling of emission data is often accomplished using specific EFs. In many cases, EFs are derived from the ratio between N2O flux to the atmosphere (FN2O ) and N flux into the system (FNin). This approach can be seen as one of several concepts for deriving EFs and is thus referred to as conceptual EF 1 (CEF1) which is defined as follows This concept is used by the IPCC methodology for calculation of national inventories (Mosier et al, 1998 Groffman et al, 2002 IPCC, 2006). Indirect emissions...

Inventory methodologies

The N2O emission factor for animal excreta deposited during grazing (EF3PRP) Biological N fixation as a source of N2O (FBN) The annual amount of N input from crop residue (FCR) N sources from which the amount of leached N and subsequent indirect N2O emissions is estimated Default value for sheep and 'other IPCC (2006) animals' reduced from 0.02 to 0.01 kg C. A. M. de Klein N2O-N (kg N)-1 Remains at 0.02kg (2004, unpublished) N2O-N (kg N)-1 for cattle (dairy, non-dairy and buffalo), poultry and...

Optimizing fertilizer application with respect to nitrous oxide emission

Emissions of N2O from agricultural systems will not decrease to zero when no N fertilizer is applied, but will remain at some background level, as in any non-agricultural system. For example, when 383 non-manured, non-N-fertilized cropping systems were evaluated for N2O emissions, the average background emission was estimated at 0.55kg N2O ha-1 (Helgason et al, 2005). Natural N deposition and biological fixation, and N mineralization from soil organic Table 5.2 Global estimates of manure-N...