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Australian Journal of Experimental Agriculture, 2008, 48, 213–218

Emissions of the indirect greenhouse gases NH3 and NOx from Australian beef cattle feedlots O. T. DenmeadA,B,D , D. ChenB , D. W. T. GriffithC , Z. M. LohB , M. BaiC and T. NaylorC A

CSIRO Land and Water, GPO Box 1666, Canberra, ACT 2601, Australia. Faculty of Land and Food Resources, University of Melbourne, Vic. 3010, Australia. C Department of Chemistry, University of Wollongong, NSW 2522, Australia. D Corresponding author. Email: [email protected] B

Abstract. Emissions of indirect greenhouse gases, notably the nitrogen gases ammonia (NH3 ) and the odd oxides of nitrogen (NOx ), play important roles in the greenhouse story. Feedlots are intense, but poorly quantified, sources of atmospheric NH3 and although production of NOx is to be expected in feedlots, rates of NOx emission are virtually unknown. In the atmosphere, these gases are involved in several transformations, but eventually return to the earth in gaseous or liquid form and can then undergo further transformations involving the formation and emission of the direct greenhouse gas nitrous oxide (N2 O). The IPCC Phase II guidelines estimate that indirect N2 O emissions due to atmospheric deposition of N compounds formed from NH3 and NOx could be ∼14% of the direct emissions from agricultural soils or from animal production systems. IPCC recommends that these indirect emissions be accounted for in making inventory estimates of N2 O emission. This paper is a preliminary report of emissions of NH3 and NOx from two Australian feedlots determined with micrometeorological techniques. Emissions of nitrogen gases from both feedlots were dominated by emissions of NH3 . The average NH3 emission rate over both feedlots in winter was 46 g N/animal.day, while that of NOx was less than 1% of that rate at 0.36 g N/animal.day. It was apparent that NH3 release was governed by the wetness of the surface. Rates of emission from the feedlot with the wetter surface were almost three times those from the other. The IPCC default emission factor for the combined emission of NH3 and NOx from livestock is 0.2 kg N/kg N excreted, but in our work, the emission factor was 0.59 kg N/kg N excreted. Potential emissions of N2 O due to NH3 and NOx deposition were estimated to be of the same magnitude as the direct N2 O emissions, the sum of direct and potential indirect amounting to ∼3 g N2 O-N/animal.day. If applied nationally, this would represent a contribution of N2 O from Australian feedlots of 533Gg CO2 -e or 2.2% of all Australian N2 O emissions.

Introduction It is increasingly evident that emissions of indirect greenhouse gases, notably the nitrogen gases, ammonia (NH3 ) and the odd oxides of nitrogen, nitric oxide (NO) and nitrogen dioxide (NO2 ), known collectively as NOx , play important roles in the greenhouse story. Ammonia emitted to the atmosphere affects the earth’s radiation balance and the greenhouse effect through aerosol formation and cloud-forming processes. It eventually returns to the earth as gas or dissolved in rain or as rained-out aerosols. Much of it then undergoes nitrification and denitrification with the consequent formation of nitrous oxide (N2 O). NOx in the atmosphere take part in the production and/or consumption of atmospheric oxidants such as ozone and hydroxyl radicals and are removed from the atmosphere through the formation and deposition of nitric acid. It has been suggested that the return of NOx from the atmosphere to the land results in substantial redistribution of N over the landscape and the formation of more N2 O. Because NO is rapidly oxidised by ambient ozone to NO2 , the net emission of both gases is usually calculated from measurements of the flux of NOx . The source of NH3 and NOx in feedlots is the nitrogen voided in urine and faeces by the cattle. Microbial breakdown of the wastes leads to the production of NH3 and the formation © CSIRO 2008

of nitrate accompanied by the production of NOx and N2 O. Rates of NH3 volatilisation from feedlots have been studied most in North America. Reported losses range from 0.05 to 0.12 kg N/animal.day (Hutchinson et al. 1982; Flesch et al. 2007). Loh et al. (2008) report measurements for Australian feedlots in a companion paper in this issue. Rates of NOx emission from feedlots have not been quantified so far. In a revision of IPCC guidelines, Mosier et al. (1998) suggest an emission factor for NH3 plus NOx of 0.2 kg N/kg N excreted by livestock. They estimate that indirect N2 O emissions due to atmospheric deposition of N compounds formed from NH3 and NOx could be around 14% of the direct N2 O emissions from soils or animal production systems. IPCC recommends that these indirect emissions be accounted for in making inventory estimates of N2 O emission. The work reported here is part of a project (funded by Meat and Livestock Australia and the Australian Greenhouse Office) to measure emissions of direct and indirect greenhouse gases (CH4 , N2 O, NH3 and NOx ) from two beef cattle feedlots representative of Australian production systems. The information can then be used to update the current livestock emission accounting system and develop mitigation strategies. The feedlots are located in the southern state of Victoria and

10.1071/EA07276

0816-1089/08/020213

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Australian Journal of Experimental Agriculture

O. T. Denmead et al.

the northern state of Queensland and measurements are being made in winter and summer at each location in each of 2 years. This paper is a preliminary report of emissions of NH3 and NOx determined during the first winter with micrometeorological techniques employing closed-path gas analysers. Two other papers in this journal issue report measurements of emissions of CH4 , NH3 and N2 O, made at the same locations with the use of open-path gas analysers (Loh et al. 2008; McGinn et al. 2008).

(commonly 50 000), and w0 is the vertical velocity of particles at touchdown. Then: Q = (C − Cbackground )/(C/Q)sim Cbackground being the upwind gas concentration outside the source area. A computer package WindTrax (Thunder Beach Scientific, Nanaimo, Canada) was used to make the calculations of emission rate using micrometeorological measurements to generate particle trajectories and closed-path gas analysers to measure gas concentrations at two heights downwind. The measurement heights were 1.6 and 3.2 m at the Victorian site, and 2.1 and 3.2 m at the Queensland site. The layout of the Queensland feedlot is in Fig. 1. Note that it is not possible to calculate the separate emissions from the pens and manure storages using the instrument configuration employed here. However, at both locations, very few of the simulated particle trajectories had touchdowns in the manure piles or effluent ponds so that effectively, our results represent emissions from the pens. The near central location of the trace gas station permitted flux measurements to be made for winds from a wide range of compass directions, whereas the open-path measurements described by Loh et al. (2008) were more restricted in that respect. However, the latter measurements were representative of much larger source areas since the paths were usually between 100 and 200 m long and the touchdown regions correspondingly wider. The trace gas station (Ecotech Pty Ltd) comprises a CH4 /nonCH4 hydrocarbon analyser, an NH3 chemiluminescence analyser, a pulsed fluorescence SO2 /H2 S analyser and an NO/NO2 /NOx chemiluminescence analyser all rack-mounted in an air conditioned cabinet, an automatic gas calibrator and a zero air supply, sample and exhaust manifolds, and a data

Materials and methods Measurements were made in late winter at both sites: from 4 August to 17 August 2006 at the Victorian site and from 24 August to 9 September 2006 at the Queensland site. At the times of measurement, 17 700 cattle were penned in an area of 22 ha at the Victorian site, and 16 800 cattle in an area of 38 ha at the Queensland site. Pen-cleaning practices were different at the two sites. At the Victorian site, pens were cleaned at intervals of 6 to 8 weeks, whereas at the Queensland site, the dung was mounded in the middle of the pen at intervals of a few days, and removed later. A backward Lagrangian stochastic (bLs) dispersion technique (Flesch et al. 2007) was used to infer fluxes of several trace gases from the feedlots. In brief, the bLs model calculates emissions from a delineated source area by tracing particles arriving at the point of measurement backwards to their touchdowns inside and outside the source area. From some thousands of simulations of particle trajectories, the surface emission rate is calculated from the relationship (C/Q)sim = (1/N)|2/w 0 | where C is the measured downwind gas concentration, Q is its surface emission rate, N is the number of trajectory simulations

N

end C

Effluent ponds

start

T P

Pens

Dung piles

Fig. 1. WindTrax map of the Queensland site, Australia, showing the pen areas (light shading) with dung piles and effluent ponds and the instrument tower for meteorological and trace gas concentration measurements (near the centre of the penned area). Paths used to obtain line-averaged concentrations, as described in Loh et al. (2008), are shown on the northern side of the pens.

Emissions of NH3 and NOx from feedlots


Results and discussion Concentrations of greenhouse gases Figure 2 shows representative concentrations of NH3 and NOx over 3 days at the Queensland site when, for the most part, winds were light to moderate (2–4 m/s) and wind directions favourable (SE to NE). The average concentrations for all periods when the fetch was over the feedlots are in Table 1. There was virtually no correlation between the highs and lows of the two gases, which is perhaps to be expected since the gases are formed by different processes. NH3 volatilisation is a physicochemical process which would occur quickly after deposition of animal wastes on the surface, whereas NO and NO2 are formed by biochemical processes during episodes of nitrification and denitrification, which lag behind NH3 deposition. Background concentrations of NH3 and NOx in rural air are variable, but Conrad and Dentener (1999) give typical values of 0.1–13 ppb for NH3 and 0.1–24 ppb for NOx . Our own measurements of background concentrations at the measurement sites, made in situations

where the air had not passed over the feedlots, were in the range 4–10 ppb for NH3 and 0.4–1.4 ppb for NOx . Concentrations of NH3 in air that had passed over the feedlots were 50 to 100-times background (Table 1), and NOx concentrations were about twice background. However, as noted above, with concentration measurements at two heights, it is not necessary to know the background in order to calculate the flux from the source area. Emissions of greenhouse gases Ensemble averages of hourly emission rates for both gases and both sites are in Fig. 3a, b. The averages are formed from all those data meeting the micrometeorological criteria defined in Loh et al. (2008). It is evident that emission rates exhibited a diurnal cycle with maximum emissions occurring in the afternoon and minimum emissions between midnight and midday. The pattern Table 1. Mean (± s.e.) daily concentrations and emission rates for NH3 and NOx and climatic conditions at Victorian and Queensland sites, Australia

No. of acceptable days Mean daily NH3 concentration (ppb) Mean daily NOx concentration (ppb) Mean daily NH3 emission rate (g N/animal.day) Mean daily NOx emission rate (g N/animal.day) Mean daily evaporation rate (mm/day) Mean daily temperature (◦ C) Mean daily wind speed (m/s)

Victorian site

Queensland site

4 490 ± 118 1.70 ± 0.14 69 ± 22

9 336 ± 35 1.93 ± 0.14 24 ± 3

0.20 ± 0.09

0.53 ± 0.31

1.12 ± 0.12 11.1 ± 0.8 2.6 ± 0.7

1.05 ± 0.08 19.7 ± 0.6 2.8 ± 0.3

200

NH3-N emission rate (g/animal.day)

acquisition and control system. Only results for the nitrogen species are reported here. Air was drawn continuously from each of the measuring heights through 10 m of Teflon tubing and was diverted through each of the gas analysers by solenoid valves operating under computer control. The valves were switched at intervals of 7.5 min. The analysers returned 1-min averages of gas concentrations, but readings during the first 2 min of each sampling period were discarded to allow for equilibration with the new air stream. The final concentrations were combined with 15-min averages of the relevant micrometeorological parameters for bLs analysis. The latter were made with a 3-dimensional sonic anemometer (Campbell Scientific CSAT-3) and included wind speeds in three directions, wind direction, turbulence levels and conditions of atmospheric stability. Periods with unfavourable wind directions, low wind speeds and extreme stabilities were excluded from the analysis following procedures defined in Loh et al. (2008). The inclusion of simultaneous gas concentrations from two heights allows determination of both the surface flux and the background concentration. Ancillary micrometeorological measurements included evaporation rate determined by eddy covariance using the CSAT-3 and a Krypton hygrometer, net radiation, and air temperature and humidity.

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(a)

Victoria

Queensland

Victoria

Queensland

150

100

50 0

8

1500

6

1000

4

500

2

NOx-N emission rate (g/animal.day)

NH3 NOx

NOx (ppb)

NH3 (ppb)

2000

3

10

2500

(b)

2

1

0 0000 0600 1200 0 4 Sept.

5 Sept.

6 Sept.

0 7 Sept.

Fig. 2. Representative atmospheric concentrations of NH3 and NOx at 2.1 m at the Queensland feedlot, Australia.

1800 2400 0000

0600 1200 1800 2400

Time Fig. 3. Ensemble averages of hourly emission rates for (a) NH3 and (b) NOx at Victorian and Queensland feedlots, Australia, in 2006.

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for NH3 is very similar to those observed by Flesch et al. (2007) at a beef cattle feedlot in the USA and Loh et al. (2008) at the Queensland site in summer. The scales in Fig. 3a, b indicate the relative magnitudes of emissions of NH3 and NOx : NH3 emission rates were around 100 times those of NOx at both sites. Daily emission rates for NH3 and NOx for each of the study days at both sites are in Fig. 4a, b and means for each site are in Table 1. Only those days where acceptable weather conditions occurred for most of the day are included in Table 1. There were four such days at the Victorian site and nine at the Queensland site. The data analysed are too few to draw definite conclusions about annual emissions from either feedlot, and the results

NH3-N emission rate (g/animal.day)

160

(a)

Victoria

Queensland

(b)

Victoria

Queensland

120

80

40

0

NOx-N emission rate (g/animal.day)

5 4 3 2 1 0 5 Aug.

10 Aug. 15 Aug.

25 Aug. 30 Aug. 4 Sept.

Date

Daily evaporation rates or available energy supply (W/m2)

Fig. 4. Daily emissions of (a) NH3 and (b) NOx from Victorian and Queensland feedlots, Australia, in 2006.


should be regarded as indicative only. However, we can make the following observations. There were large differences between the two feedlots in emissions of NH3 and NOx . Both Fig. 4 and Table 1 show clearly that emission rates for NH3 were higher at the Victorian site than at the Queensland site, while the reverse was true for NOx . The differences may well be linked to the surface wetness of the pens in the two locations. No direct measurements of surface wetness were made, but in the 2 weeks before the Victorian measurements, 17.2 mm of rain fell at the feedlot and another 2.2 mm fell during the observation period. The pens were largely undisturbed during this period and the surface remained visually moist throughout. Only 1.6 mm of rain fell at the Queensland site in the 2 weeks before the emission measurements were made and another 7.6 mm fell during the observation period. The surface appeared dry for most of the period. The measurements of evaporation during the observation periods at both feedlots provide more concrete evidence of their relative surface wetness. The daily evaporation rates for the two sites are in Fig. 5 and summarised for the acceptable study days in Table 1. For the most part, evaporation rates at the Victorian site were higher than at the Queensland site despite much cooler temperatures and lower solar radiation levels; hence, evaporation at the Victorian site represented a much higher proportion of the energy available for evaporation (the net solar radiation less changes in the heat energy stored in the ground). This could happen only if the soil surface was wetter at the Victorian site. The suggestion is that in these circumstances, NH3 would escape to the atmosphere more readily from the wet pen surface because of the smaller resistance to transport from the site of its formation. The fact that emissions of NOx were smaller in Victoria than in Queensland (Fig. 4b) may be simply because the rapid volatilisation of NH3 at the Victorian site left less nitrogen available for further transformation to nitrate with the consequent production of NOx . It may be also that the rates of further transformations were slower in Victoria because of the lower temperatures there (Table 1). NO fluxes from soils are known to be temperature dependent (Galbally 1989). Hutchinson et al. (1982) suggest a third possibility from their research: nitrification in the feedlot occurs under dry, aerobic conditions

500 Evaporation 400

Available energy

300

200

100

0 1 Aug.

11 Aug.

21 Aug.

31 Aug.

10 Sept.

Fig. 5. Daily evaporation rates and available energy supply during Victorian and Queensland studies, Australia, in 2006.

Emissions of NH3 and NOx from feedlots

whereas a wet feedlot pen causes the surface to be anaerobic, reducing the amount of nitrification and subsequently increasing NH3 volatilisation. Open-path measurements of NH3 emissions at these sites, described by Loh et al. (2008), were also made during the winter, with a partial overlap with the closed-path measurements. The sampling periods for the closed-path study covered about twice as many days as the open-path study. The open-path systems yielded rather higher emission rates than those in Table 1, but there is still some uncertainty attached to the open-path measurements, whose cause is under investigation. Apart from possible differences in instrument calibration, there are several reasons why the calculated closed-path emission rates could be lower than those from the open-path systems: a different and much smaller touchdown region, different wind directions and source areas, and different sampling periods, for instance. Less equivocal open-path measurements were made at the same two sites in summer (Loh et al. 2008). These also indicated higher NH3 emission rates than those reported in Table 1, and the summer rates measured at the Queensland site (170 g N/animal.day) were higher than those at the Victorian site (117 g N/animal.day). However, this result is still consistent with the suggestion that NH3 release is governed by the wetness of the surface. Rainfall for the 2 weeks before the measurements was near 22 mm at both sites, but a further 14.4 mm fell at the Queensland site during the measurement period and only 0.2 mm at the Victorian site. The average evaporation rate over the summer measurement period at the former site, determined by the same eddy covariance system as used in the winter, was 50% higher than in Victoria: 1.52 mm/day compared with 1.07 mm/day. Emissions of nitrogen gases from the feedlots were dominated by emissions of NH3 . Those of NOx were negligible in this context. To compare our results with others, we observe first that our measurements of NOx fluxes from feedlots appear to be unique. However, Mosier et al. (1998) suggest an emission factor for grazing animals of 0.2 kg NH3 -N + NOx -N/kg of N excreted by livestock. Accepting a value of 0.16 kg N/animal.day for N excretion by beef cattle (Mosier et al. 1998, Flesch et al. 2007) and assuming that the annual emissions of NH3 and NOx are the averages of the winter and summer rates reported here (∼95 g N/animal.day), our annual emission factor for NH3 and NOx is 0.59 kg N/kg N excreted, which is considerably higher than the emission factor suggested by Mosier et al. (1998). Results from mass balance studies in a feedlot conducted by Bierman et al. (1999) indicated emission factors between 0.56 and 0.71 while micrometeorological measurements by Flesch et al. (2007) and Loh et al. (2008) indicate emission factors of 0.90 to 0.94 kg NH3 -N/kg N excreted. It appears that in feedlot situations, most of the N excreted by the cattle escapes to the atmosphere as NH3 and the emission factor suggested by Mosier et al. (1998) for grazing animals might be too low. In a parallel study to that described by Loh et al. (2008), N2 O emissions were measured at both feedlots in summer using the bLs technique and open-path infra-red spectroscopy (M. Bai, pers. comm.). The emission rate at the Victorian site was 1.1 g N2 O-N/animal.day and at the Queensland site, 1.8 g N2 O-N/animal.day. If we assume as previously that the


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annual emissions of NH3 and NOx are 95 g N/animal.day, that all the emitted NH3 and NOx eventually return to the land, and that the Australian Greenhouse Office (2007) default emission factor for N2 O of 1.25% of nitrogen additions applies, potential emissions of N2 O from these indirect sources would be of the same magnitude as the direct emissions. On the assumptions of an overall (direct plus indirect) emission of 3 g N2 O-N/animal.day, a national feedlot population of 106 cattle, and a global warming potential for N2 O of 310, emissions of N2 O from Australian feedlots would amount to 533 Gg CO2 -e which is 2.6% of all N2 O emissions from agriculture or 2.2% of all Australian N2 O emissions, estimated by the Australian Greenhouse Office (2007) to be 20 734 and 24 295 Gg CO2 -e, respectively. Conclusions We have used a micrometeorological technique to measure emissions of the indirect greenhouse gases NH3 and NOx from feedlots in different environments. The database is still small and our conclusions are tentative. The results indicate that emissions of NH3 from Australian feedlots are considerable and amount to around 60% of the annual N excretion by the cattle. The study also suggests that NH3 emissions from feedlots are governed by the wetness of the pen surfaces. Pen-cleaning practices differed between the two feedlots. At one of them, pens were cleaned at intervals of 6 to 8 weeks and the surface was mostly wet and at the other, the dung was mounded in the middle of the pen at intervals of a few days and the surface was mostly dry. Measurements of evaporation rates and the solar energy available for evaporation confirmed these differences in surface wetness. In winter, emissions of NH3 from the first (wetter) feedlot were almost 3-times those from the second, despite similar evaporation rates at both sites and cooler temperatures and lower solar radiation levels at the first site. The order was reversed in a summer study when the second site was wet after substantial rain and its evaporation rate was 50% higher than that at the first site. Emissions of NOx were measured during the winter study. Those from the Victorian feedlot were less than half those from the Queensland feedlot. We suggest three possible reasons: (1) less nitrogen available for transformations that produce NOx at the Victorian site because of more rapid NH3 volatilisation; (2) lower soil temperatures at that site; and (3) the prevalence of anaerobic conditions in the wetter pen surfaces at the Victorian feedlot compared with more aerobic conditions in the drier pens in Queensland. Ammonia was the dominant nitrogen gas emitted at both sites. The average rate of emission of NH3 from both sites during the winter measurements reported here was 46 g N/animal.day and 0.36 g N/animal.day for NOx . When combined with measurements of NH3 and N2 O made by Loh et al. (2008) at the same sites during the summer, we estimate that potential emissions of N2 O arising from these indirect sources could be as large as the direct N2 O emissions. On the basis of our measurements, the estimate of annual direct plus indirect N2 O emissions from the two feedlots studied is 3 g N/animal.day. If applied to all Australian feedlots, their contribution would be 2.2% of all Australian N2 O emissions.

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Finally, we observe that the bLs technique that we and Loh et al. (2008) employed has much potential for measuring gas emissions in many agricultural situations where the source can be defined exactly. These include herds, feedlots, piggeries, poultry farms, waste lagoons, manure piles, fenced pastures and fertilised fields. Acknowledgements We thank the Australian Greenhouse Office and Meat and Livestock Australia for their interest and financial support and the management, and staff of the Victorian and Queensland feedlots for making their sites available and providing much material help.

References Australian Greenhouse Office (2007) ‘National greenhouse gas inventory 2005.’ (Department of the Environment and Water Resources: Canberra, Australia) 29 pp. Bierman S, Erickson GE, Klopfenstein TJ, Stock RA, Shain DH (1999) Evaluation of nitrogen and organic matter balance in the feedlot as affected by level and source of dietary fiber. Journal of Animal Science 77, 1645–1653. Conrad R, Dentener FJ (1999) The application of compensation point concepts in scaling of fluxes. In ‘Approaches to scaling of trace gas fluxes in ecosystems’. (Ed. AF Bouwman) pp. 205–216. (Elsevier: Amsterdam)


Flesch TK, Wilson JD, Harper LA, Todd RW, Cole NA (2007) Determining ammonia emissions from a cattle feedlot with an inverse dispersion technique. Agricultural and Forest Meteorology 144, 139–155. doi: 10.1016/j.agrformet.2007.02.006 Galbally IE (1989) Factors controlling NOx emissions from soils. In ‘Exchange of trace gases between terrestrial ecosystems and the atmosphere’. (Eds MO Andreae, DS Schimel) pp. 23–37. (John Wiley & Sons: Chichester) Hutchinson GL, Mosier AR, Andre CA (1982) Ammonia and amine emissions from a large cattle feedlot. Journal of Environmental Quality 11, 288–293. Loh Z, Chen D, Bai M, Naylor T, Griffith D, Hill J, Denmead T, McGinn S, Edis R (2008) Measurement of greenhouse gas emissions from Australian feedlot beef production using open-path spectroscopy and atmospheric dispersion modelling. Australian Journal of Experimental Agriculture 48, 244–247. McGinn SM, Chen D, Loh Z, Hill J, Beauchemin KA, Denmead OT (2008) Methane emissions from feedlot cattle in Australia and Canada. Australian Journal of Experimental Agriculture 48, 183–185. Mosier A, Kroeze C, Nevison C, Oenema O, Seitzinger S, van Cleemput O (1998) Closing the global N2 O budget: nitrous oxide emissions through the agricultural nitrogen cycle. Nutrient Cycling in Agroecosystems 52, 225–248. doi: 10.1023/A:1009740530221 Manuscript received 16 August 2007, accepted 28 October 2007

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