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Greenhouse gas emissions from stored liquid swine manure in a cold climate
ARTICLE IN PRESS
Atmospheric Environment 40 (2006) 618–627 www.elsevier.com/locate/atmosenv
Greenhouse gas emissions from stored liquid swine manure in a cold climate Kyu-Hyun Park, Andrew G. Thompson, Miche`le Marinier, Karen Clark, Claudia Wagner-Riddle Department of Land Resource Science, University of Guelph, Guelph, Ont., Canada N1G 2W1 Received 8 September 2005; accepted 8 September 2005
Abstract Current global warming has been linked to increases in greenhouse gas (GHG) concentrations. Animal manure is an important source of anthropogenic GHG, mostly of methane (CH4) and nitrous oxide (N2O). Country-specific emission estimates of these GHG can be obtained using IPCC 2000 guidelines, or suggested improvement, such as the USEPA approach for CH4 emissions, which is based on monthly air temperature (T air ). These approaches have not been validated against measured CH4 and N2O fluxes for liquid swine manure storage in cold climates due to the scarcity of year-round studies. A four-tower micrometeorological mass balance method was used at three swine farms (Arkell, Guelph, and Jarvis) in Ontario, Canada (annual T air o10 1C), from July 2000 to May 2002. Methane and N2O concentrations were measured using two tunable diode laser trace gas analyzers, and manure temperature (T man ), redox potential (E h ) and composition were also measured. Dry matter content and E h between sites and seasons varied from 0.6% to 3%, and 232 and 333 mV, respectively. Annual T air was 8.4 1C, and T man was on average 4 1C warmer. Mean N2O fluxes were not significantly different from zero, except for Jarvis with mean fluxes of 337.6 ng m2 s1 in summer and 101.8 ng m2 s1 in fall. Mean yearly N2O emission was estimated as 3.6 g head1 yr1, and was lower than the IPCC-based emission factor (EF) of 17 g head1 yr1. Our data suggests that N2O emissions from non-aerated liquid swine manure storage could be ignored in GHG inventories. Mean monthly CH4 fluxes obtained from half-hourly data varied between 4.6 103 and 1.05 mg m2 s1 (number of measurements per month ¼ 25–562). Measured CH4 emissions from May to October were mostly larger, and from January to April were lower than values predicted using the USEPA approach. Use of T man improved monthly CH4 emission prediction using the USEPA approach compared to T air with a lower limit of 7.5 1C (r2 ¼ 0:64 vs. 0.355). The methane conversion factor derived from measured fluxes was 0.23, comparable to the USEPA derived values of 0.22–0.25, but much lower than the IPCC recommended value for cold climates (0.39). r 2005 Elsevier Ltd. All rights reserved. Keywords: Methane; Nitrous oxide; Micrometeorological mass balance method; Manure temperature; IPCC methodology; Liquid swine manure
1. Introduction Corresponding author. Tel.: +1 519 824 4120x52787;
fax: +1 519 824 5730. E-mail address: [email protected] (C. Wagner-Riddle). 1352-2310/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2005.09.075
Human activities are changing the environment. Since the Industrial Revolution, concentration of greenhouse gases (GHG), such as carbon dioxide
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(CO2), methane (CH4), and nitrous oxide (N2O), have increased by 30%, 151%, and 17%, respectively, and have caused an increase in daily nighttime minimum air temperature, narrowing the gap between day and night temperatures (IPCC, 2001). Agriculture has played an important role in climate change. Animal manure is often held in liquid or solid form on the farm, awaiting disposal. During storage time the manure decomposes, and gaseous by-products are released, where the type of gas is determined largely on whether the decomposition is aerobic or anaerobic (Kirchmann and Lundvall, 1998). The handling system determines the moisture content and oxygen availability in the manure, with liquid systems producing predominantly CH4, and solid systems producing both CH4 and N2O. Globally, livestock manure contributes 5–10% to the total emission of CH4 (Rotmans et al., 1992) and 7% of N2O (Khalil and Rasmussen, 1992). In 2001, emissions of CH4 and N2O from stored manure accounted for 17% (10.1 Mt CO2-eq) of Canada’s total agricultural emissions (Olsen et al., 2003). Emissions of GHG from stored manure are affected by environmental factors such as temperature (Khan et al., 1997), wind speed (Sebacher et al., 1983), redox potential (Brown et al., 2000) and crust formation on the slurry surface (Sommer et al., 2000), as well as by animal factors (Hashimoto et al., 1980). Uncertainties in GHG estimation have been attributed to uncertainties in the types and size of manure storage and to the accuracy of yearround extrapolation of emissions from short-term studies (Kaharabata et al., 1998). IPCC (2000) recommends non-invasive and yearround measurements of GHG emissions in production systems, in order to reduce the large uncertainties in emission factors (EFs) used for calculating national GHG emission inventories. The Micrometeorological Mass Balance (MMB) method, a non-invasive measurement technique, is suitable for heterogeneous source distributions and/or elevated sources such as waste storage sites, where eddy correlation and flux-gradient approaches are not appropriate (Denmead et al., 1998). Most research concerning GHG emissions from stored manure has been conducted from spring to fall (Kaharabata et al., 1998) or in mild winters when an ice cover did not form on the surface of the liquid manure (Sharpe and Harper, 1999). As a result, insufficient data exists to evaluate year-round
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GHG emissions from stored manure in cold climates such as Canada. Currently, calculation of CH4 EFs using the IPCC (2000) approach with country-specific inputs (Tier 2) takes climate into account, through the use of a methane conversion factor (MCF). With a mean annual air temperature below 15 1C, Canada fits into the ‘cool climate’ designation. In an effort to fine-tune the calculation of MCF, the US Greenhouse Gas Inventory adopted a method which takes monthly air temperature into account (USEPA, 2003). These approaches have not been validated against measured CH4 and N2O fluxes for liquid swine manure storage in cold climates. The objectives of this study were: (1) to quantify CH4 and N2O emissions from stored liquid swine manure at three farms through a quasi-continuous year-round experiment in a cold climate region (annual mean air temperature o10 1C); (2) to compare the measured values to EFs derived using the IPCC (2000) and USEPA (2003) approaches. 2. Materials and methods 2.1. Experimental sites and instrument setup for MMB method Flux measurements were conducted at the liquid manure storage tanks of one research farm (Arkell) and two commercial swine farms (Guelph and Jarvis) in Ontario, Canada, over July 2000 to May 2002 (Table 1). A mobile instrumentation trailer was first stationed at Arkell, and then moved between Jarvis and Guelph. An attempt was made to measure fluxes over the different seasons, in order to characterize environmental effects. Pigs were fed a standard corn–soybean diet at all sites, with alfalfa added at Jarvis. At all sites, manure was collected in the barn in a below-ground holding tank through partially slatted floors and sent bi-weekly to outdoor concrete storage tanks. There were four outdoor storage tanks at Arkell, two at Jarvis, and one at Guelph, but only one tank was monitored at each site. Stored manure in the outside tanks was stirred prior to field application in spring (April–May) and fall (October– November). In the MMB method, measurements of wind speed and direction, and gas concentration in air samples are needed. A detailed description of the four-tower MMB method used in this experiment is given by Wagner-Riddle et al. (2005). Briefly, four
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Table 1 Description of swine farms where CH4 and N2O fluxes were measured in Ontario, Canada, over the 2000–2002 period Site Arkell
Guelph
Jarvis
Location Type of swine farm
431320 N 801100 W Farrow-to-finish
431330 N 801250 W Grower
421580 N 80140 W Farrow-to-wean
Number of swine Starters Growers Finishers Dry sows Lactating sows Boars
1500 400 250 450 275 75 50
490 0 430 0 30 0 0
2725 2000 0 0 75 650 0
Storage tank Diameter (m) Deptha (m) Total surface areab (m2)
18.7 3.5 1093.9
16.9 3.0 224.3
34.4 2.4 1858.8
Measurement period Summer Fall Winter Spring
2000/2001 Jun. 25–Jul. 18 Oct. 24–Nov. 5 Jan. 9–Jan. 14 Mar. 22–May 3
2001/2002 Jul. 28–Aug. 10 Oct. 11–Oct. 30 Feb. 1–Mar. 22 Mar. 22–Apr. 18
2001 May 28–Jul. 11 Nov. 8–Nov. 28 NDc NDc
a
Depth of manure in tank varied over the measurement period, but the tanks mostly were filled to within 0.3 m from the top. The number of tanks used in manure storage (four at Arkell, and two at Jarvis) was taken into account when calculating total surface area available for emissions. c Measurements were not carried out in winter and spring at Jarvis (ND ¼ not determined). b
air sampling towers and one tower collecting wind data were installed above the wall of the circular manure storage tanks. Four air-sampling intakes were located at heights of 0.25, 1.0, 2.0 and 3.5 m on each tower. The wind tower had cup anemometers (F460, Climatronics, Newton, PA) at the same heights used for air sampling. A wind vane (R.M. Young, Model 05102, Traverse, MI) was mounted on the top of the wind tower (4.0 m). Four thermocouples to measure manure temperature were mounted on a floating frame at depths of 0.03, 0.20, 0.60, and 1.0 m below the liquid surface at Jarvis and Guelph. A datalogger (CR7, Campbell Scientific, Edmonton, AB) recorded mean 5-min (for Arkell) and 1-min (for Jarvis and Guelph) wind direction, and half-hourly mean wind speed and liquid manure temperatures. Two tunable diode laser trace gas analyzers (TGA100, Campbell Scientific, Inc., Logan, UT), one for each CH4 and N2O concentration measurements, were used in an air sampling setup as described by Wagner-Riddle et al. (2005). The half-hourly mean gas flux ðF Þ was then calculated
from the rectangular gas flux calculation method (Wagner-Riddle et al., 2005): 4 1X ½ð¯ui D¯ci Þ Dzi , F¯ ¼ L i¼1
(1)
where L is the mean distance traveled by the horizontal air flow over the source, and i indicates the height of mean half-hourly gas concentration difference ðD¯ci Þ and wind speed ð¯ui Þ measurements, which were considered representative of the air layers ðDzi Þ of 0–0.5, 0.5–1.5, 1.5–2.5, and 2.5–4.5 m. The D¯ci was obtained from concentration measurements at upwind and downwind positions for each layer. These positions were determined based on 30-min mean wind direction. The 30-min mean fetch L was calculated from 5-, or 1-min fetch values determined according to the 5-, or 1-min wind direction data and the circular tank’s geometry (Wagner-Riddle et al., 2005). Note that the turbulent diffusive flux term, which is approximately 10–15% of total flux (Denmead et al., 1998), was ignored in Eq. (1) due to difficulties in obtaining this term.
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2.2. Chemical analysis Manure samples from 30 cm below the manure surface were taken at Guelph and Jarvis over the measurement periods at randomly selected locations within the storage tank. Redox potential and pH were immediately measured on-site. The pH was measured with a pH meter (Accumets pH meter model 610A, Fisher Scientific Int’l., NH) with electrode (Accumets 13-620-104, Fisher Scientific Int’l., NH). Redox potential was measured using a platinum and Ag–AgCl reference electrode (#599055, Cole-Parmer, Niles, IL), connected to a digital multivoltmeter (Orion pH/ISE meter, Model 710A, Orion Research Inc., Boston, MA). Collected samples were stored at 20 1C in a freezer and thawed before analysis. Each sample was analyzed for total solids (TS), total soluble nitrogen (TSN), total soluble organic carbon (TOC), nitrate, and ammonium concentration (Tel and Heseltine, 1990). Some results from routine manure composition analyses were available for the Arkell Research farm.
2.3. Measured and estimated CH4 emission factors Measured half-hourly CH4 fluxes were averaged to obtain monthly means, which were then converted to a monthly emission per animal, using the storage tanks’ total surface area and the number of animals at each farm (Table 1). Although measurements were carried out on one of the tanks at each farm, it was necessary to consider emissions from all tanks, in order to scale the emissions to a per animal basis. An annual CH4 EF was obtained by pooling all measured monthly values and interpolating between measured values for months with no measurements (September and December; Table 1). Measured CH4 EF were compared to calculated EF using Tier 2 IPCC (2000) and USEPA (2003) methodology. In the IPCC approach the annual EF for an animal population, in this case each farm, is equal to the product of yearly volatile solid excretion per animal (VS, kg head1 d1), maximum CH4 producing potential of manure (Bo , assumed 0.298 kg CH4 kg1 VS for swine), and a CH4 conversion factor dependent on the type of manure management system and climate (MCF, assumed 0.39 for liquid systems in climates with annual temperature o15 1C). The VS were calculated
according to a modified IPCC methodology: ASH ED 1 , VS ¼ DMI 1 100 100
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(2)
where DMI is the dry matter intake (kg head1 d1), ASH and ED are the ash content and energy digestibility of feed (%), respectively. Note that IPCC uses the mineral content of the manure, not feed for ASH. For each farm, typical DMI, ASH and ED for a corn–soybean diet were used for each animal class shown in Table 1: 0.8, 1.7, 2.2, and 2.5 kg head1 d1 for DMI of starters, growers, finishers, dry sows/boars, and lactating sows; 4.5%, 5%, and 5.5% for ASH in feed for starters, growers/finishers/dry sows/boars, and lactating sows; and 82%, 84%, 88%, and 86% for starters, growers/finishers, dry sows/boars, and lactating sows, respectively. The mean VS produced at each farm, obtained by a weighted average that took number of animals in each class into account, were similar at 0.283, 0.258 and 0.275 kg head1 d1 for Arkell, Guelph and Jarvis, respectively, despite differences in production systems. In the USEPA approach, monthly CH4 emission for liquid manure storage (other than anaerobic lagoons) is calculated as the product of VS produced on a monthly basis, Bo (as defined above) and a factor (f ), which describes the effect of monthly air temperature on CH4 emissions according to the Van’t Hoff–Arrhenius equation, as described in Safley and Westerman (1990). A minimum monthly air temperature of 7.5 1C is recommended in the calculation of f when air temperature drops to values o7.5 1C to account for differences in liquid manure and air temperature. For inventory purposes, an annual MCF is derived from the ratio of annual CH4 emission (equal to the sum of monthly values) and potential CH4 production (calculated as total VS Bo). This calculation assumes that VS do not accumulate in storage as is the case with frequent manure tank emptying. In cold climates VS may accumulate in manure storage due to regulations that prevent producers from applying manure to fields during the winter months. For anaerobic lagoons, the USEPA approach involves carry-over of non-consumed VS from month-to-month as well as the use of a management and design practices factor (MDP). This MDP factor determines which fraction of VS produced each month is available for CH4 production, and has been adjusted to 0.8 (USEPA, 2003). For comparison purposes, we estimated monthly CH4
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emission using both monthly VS production without carry-over effect (i.e. non-accumulated from month-to-month, VSn-acc) and monthly VS production with carry-over effect (i.e. accumulated from month-to-month, VSacc). In all calculations we assumed an MDP factor of 1. 2.4. Measured and estimated N2O emission factors The method outlined in IPCC (2000) for estimating N2O emissions from manure storage relies on the amount of N excreted for each animal type per year, and an EF for each type of manure handling system ( ¼ 1.57 g N2O kg1 N excreted for liquid systems). The amount of N excreted (Nex) was estimated using: Nex ¼ ðCP=6:25Þð1 Nret Þ,
(3)
where CP is the fraction of crude protein in the diet ( ¼ 0.19 for starters and 0.15 for other categories), and Nret is the proportion of N retained by the body ( ¼ 0.35). Annual N2O EFs were calculated for each farm based on the animal population and EF for each animal category. 3. Results and discussion 3.1. Chemical analysis The liquid swine manure stored at the three farms had a dry matter content between 0.6 and 3% (TS), and pH between 6.8 and 7.9 (Table 2). Jarvis had
the most dilute manure, consistent with its type of swine production (farrow-to-wean), and Guelph (summer) had the most concentrated manure, given its swine population (Table 1) and the fact that very little rain had occurred after its tank had been emptied 2 months earlier. The latter effect was also responsible for the higher TSN, NH+ 4 , and TOC, and lower pH recorded at Guelph in summer, when compared to other samplings dates. Jarvis had consistently low concentrations of TSN, NH+ 4 , and TOC, no doubt due to higher water use associated with farrow-to-wean systems. Measured redox potentials were typical of environments in which methanogenesis and sulfur reduction occur (o100 mV, Tate, 1995), and were lowest in summer, indicating most reduced conditions. This was most likely related to an increase in microbial activity during the warmer season, as higher temperature results in larger consumption of substrates, and hence larger oxygen consumption (Nozhevnikova et al., 1997). 3.2. Manure temperature and GHG fluxes The average monthly air temperature during the measurement period varied from 5.6 1C (January 2001) to 20.3 1C (July 2001), with an annual mean of 8.4 1C. Monthly liquid manure temperature at 60 cm depth was on average 4 1C warmer than air temperature, and strongly correlated to air temperature (Fig. 1). Lowest average manure temperature recorded was 2.7 1C, indicating that the lower
Table 2 Liquid swine manure composition as determined from samples (n) taken at 30 cm depth during each experimental period at Guelph and Jarvis farms Site/period
Manure composition pH
Redox (mV)
Total solids (mg kg1)
Total soluble N (mg kg1)
1 NH+ 4 (mg kg )
Total organic C (mg kg1)
Arkell
7.5
—
12 400 (4300)
—
1521
—
Guelph Summer Fall Winter Spring
6.8 7.5 7.4 7.4
30 519 17 126 9166 6610
2299 1874 1719 1342
Jarvis Summer Fall
7.7 (0.03) 7.9 (0.06)
(0.03) (0.02) (0.04) (0.01)
318.3 333.4 232.0 284.2
(1.7) (5.1) (6.4) (5.1)
333.7 (3.0) 259.7 (2.2)
(3086) (860.4) (771.4) (158.3)
6629 (403.6) 6252 (234.1)
(33.9) (101) (77.3) (230)
797.5 (17.9) 1074 (11.7)
2066 1398 1282 1167
(30.8) (61.7) (36.6) (78.9)
678 (13.0) 882 (20.4)
6281 2637 2965 3085
(48.8) (123.0) (144.3) (323.5)
376.6 (10.9) 439.8(4.0)
Exact dates of summer to spring periods are listed in Table 1. Also shown are values available from farm manure analysis at Arkell. Values in brackets show standard error of the mean. Number of observations for each mean varied between 12 and 18. NO 3 concentrations were always 1–2 mg kg1 or non-detectable, and are not shown.
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Fig. 1. Monthly manure temperature at 60 cm depth (y) as a function of monthly air temperature (x) measured at Guelph and Jarvis from May 2001 to April 2002, and plot of linear regression (dashed line, y ¼ 0:879x þ 4:24, n ¼ 10, r2 ¼ 0:946). Labels indicate month of measurement.
limit of 7.5 1C used by USEPA (2003) is not adequate for the region studied. The daily mean manure temperature measured at 3 cm was similar to the temperature recorded at 60 cm depth, except for short periods in the summer, and throughout January to March 2002, when the surface temperature was close to 0 1C (Fig. 2), and the presence of an ice cover was observed. Halfhourly CH4 fluxes over this latter period were quite small (o 0.3 mg m2 s1), in contrast to maximum fluxes larger than 1 mg m2 s1 measured during summer or fall (Fig. 2). Highest flux values were observed when manure was agitated before pumping from the storage tank to a manure spreader (Arkell day 302; Guelph day 304), or after barn manure addition to tank (Arkell, day 197). After tank emptying, fluxes decreased to much lower levels as illustrated for Arkell (day 308) and Guelph (day 305). In general, CH4 fluxes were strongly related to manure temperature with decreasing fluxes from July 2001 to April 2002 at Arkell, and higher fluxes in July 2001 when compared to November 2002 at Jarvis (Fig. 2). Results for August and October 2001 at Guelph did not fit this pattern, although January to April 2002 presented lowest fluxes as expected. When measurements were initiated at Guelph on day 210, the storage tank was only one-third full,
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with manure addition occurring on day 218 (Fig. 2), shortly before the instrumentation trailer was moved to another site as part of a separate experiment. In contrast to NH3 fluxes, which are related to surface area, CH4 fluxes are related to the volume or mass of liquid manure associated with the surface area over which fluxes are measured. Hence, the lower volume of the manure in storage would have resulted in less CH4 flux. In addition, the liquid manure for this period had a relatively low pH, high TS, and NH+ content (Guelph 4 summer, Table 2). Methanogenesis from acetate, which contributes 70% of manure-generated CH4 (Jeris and McCarty, 1965), is inhibited by pH o7 (Attal et al., 1988). In addition, increased NH+ 4 concentration has been shown to inhibit CH4 production (Kroeker et al., 1979), and a longer lag phase for CH4 production in a batch sewage digester was observed when NH+ 4 increased from 1210 to 2360 mg L1 (van Velsen, 1979). These combined effects could be the causes for lower CH4 fluxes observed at Guelph during the measurement period in August 2001 (mean 0.357 mg m2 s1), and fluxes probably would have increased over the subsequent months as the manure would have become more dilute through rainfall, and the methanogenic microbial community would have developed. Indeed, when measurements were resumed at Guelph in October 2001 (day 283, Fig. 2), 1 NH+ 4 concentration was o1400 mg kg , pH was 47, and CH4 fluxes were much larger (mean 1.05 mg m2 s1). These high fluxes occurred until the tank was completely emptied (day 305). Nitrous oxide fluxes were small with mean value for several of the measurement period not significantly different from zero (Po0:05; data not shown). The exception was mean fluxes obtained at Jarvis: 337.6 ng m2 s1 (SE ¼ 119 ng m2 s1, n ¼ 238) in summer, and 101.8 ng m2 s1 (SE ¼ 45 ng m2 s1, n ¼ 464) in fall. Brown et al. (2000) observed a non-linear increase in N2O emission from solid dairy manure when the redox potential increased from 200 to 200 mV, with values 300 ng N2O m2 s1 associated with 50 mV. In the liquid manure storage tank studied here, the redox potential at 30 cm depth was always o200 mV (Table 2). The storage tank at Jarvis had a relatively large surface area and was quite full during the measurement period (Table 1), possibly resulting in increased oxygen diffusion into, and higher manure redox potential in the surface manure layer, when compared to the other sites
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Arkell
4
30
Jarvis
Tair Tman at 3 cm
3
20
Tman at 60 cm 10
2 0 1
180 190 Jun 28
200
300 310 Oct 26
Guelph
4
10 20 80 90 Jan 10 Mar 21
100
110 120 Apr 20
Jarvis
150 160 May 30
170
180 190 Jun 29
-20
30
Guelph
20
3
Temperature ( oC)
CH4 Flux (mg m-2 s -1)
-10 0
10 2 0 1 -10 0 -20 210 220 Jul 29
280 290 Oct 7
300
310 320 Nov 6
330
20 30 Jan 20
40
50
60 70 Mar 1
80
90
100 Apr 10
Day of Year Fig. 2. Half-hourly CH4 fluxes (dots), daily CH4 fluxes (solid bold line), daily air temperature, and manure temperature at 3 and 60 cm depth as a function of day of year from July 2000 to July 2001 (top graph), and August 2001 to April 2002 (bottom graph), in Ontario, Canada. Site of measurements are indicated at the top of each graph. Note: manure temperature was not measured at Arkell. Upward pointing solid arrows indicate when manure was stirred and open arrows show when manure was flushed from barn to outdoor tank.
studied. Nitrous oxide production during aerobic treatment of pig slurry has been observed, particularly at high aeration levels (2–4 mg O2 L1), but also in a low aeration level control (redox potential ¼ 0 to 48 mV), although lower N2O levels were recorded in the latter treatment (Be´line et al., 1999). The required O2 levels for N2O production to take place in non-treated liquid swine manure do not appear to be met often, as our very small fluxes attest. Negligible or non-detectable N2O fluxes were also observed for anaerobic swine lagoons by Harper et al. (2000). In contrast, Sommer et al. (2000) found N2O emissions from stored dairy slurry with higher dry matter content than the liquid manure studied here were up to 10 940 ng m2 s1, but these emissions were only detected during the dry season when a crust formed on the surface.
3.3. Measured and estimated CH4 and N2O emission factors Mean monthly CH4 fluxes were obtained from half-hourly data, with number of observations per mean ranging from 25 (August at Guelph) to 562 (April at Arkell) (Fig. 3A). The large number of measurements (n ¼ 929 at Arkell, n ¼ 830 at Guelph, n ¼ 702 at Jarvis) indicates the suitability of the MMB for year-round studies of gas fluxes from manure storage tanks. Scaling of the measured means using storage tank surface area and number of animals at each site (Table 1) allowed for comparison of CH4 emission (expressed in kg head1 month1) with the USEPA approach (Fig. 3B). The measured CH4 emissions from May to October were mostly larger than values predicted with monthly air temperature (bold
ARTICLE IN PRESS K.-H. Park et al. / Atmospheric Environment 40 (2006) 618–627 Arkell Guelph Jarvis
Methane Flux (mg m-2 s-1)
1.2 225
0.8
105 32
0.4
100
106 47 30
25 464 47
562
0
39 77
99 394
95
Methane Emission (kg head-1 month-1)
(A)
(B)
3 VSacc
2
Tair Tman
VSn-acc Tair Tman
1
0 MayJun Jul AugSepOct NovDecJanFeb Mar Apr Month
Fig. 3. (A) Monthly mean methane emissions from stored liquid swine manure measured at Arkell, Jarvis, and Guelph (bars represent standard error of mean, and labels represent number of half-hourly flux measurements used to obtain each mean). (B) Values shown in (A) expressed on a per animal basis compared to estimated emissions based on the USEPA approach using monthly carry-over of non-consumed volatile solids (VSacc) and no carry-over of volatile solids (VSn-acc). For both approaches of VS estimates, curves are shown for calculations using air temperature (T air , set to ¼ 7.5 1C when o7.5 1C) and manure temperature (T man ).
solid line, Fig. 3B). From January to April measured emissions were clearly lower than the emissions estimated setting monthly air temperature for these months equal to 7.5 1C. Use of manure temperature improved prediction for both periods (comparison between observed vs. predicted values yielded r2 ¼ 0:64, Po0:05 vs. r2 ¼ 0:355, Po0:10 for air temperature). However, for reasons discussed above, some monthly means deviated considerably from predictions (August and October for Guelph), emphasizing the need for process-based models in order to refine predictions of CH4 emissions from manure. Manure composition as affected by animal diet and management is obviously an area that needs better algorithms linked to CH4 production. For illustration purposes
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we display the approach developed by USEPA for VS carry-over in anaerobic lagoon systems (Fig. 3B). Our data confirm the assumption that this approach is not adequate for manure holding tanks, as these are not designed for anaerobic manure decomposition, i.e. optimal CH4 production. Consistent over-prediction of CH4 emissions for the January to April period when using manure temperature in the USEPA approach, pointed to additional effects taking place (Fig. 3B). We suggest that formation of an ice layer suppressed the emission of the small CH4 production that occurred at manure temperatures of 2–3 1C at 60 cm depth (Figs. 1 and 2). This is corroborated by examination of the CH4 fluxes during the first spring thaw period in 2001 at Arkell, and 2002 at Guelph (Fig. 4). In both cases, CH4 fluxes increased significantly on the second day of air temperatures above 0 1C, when significant ice melting was observed. This burst was most likely a release of trapped CH4 as subsequent thaws did not show a similar effect (Fig. 2). Finally, the VS carry-over approach predicted relatively large CH4 emission for April, a direct consequence of large VS accumulation due to low CH4 production during the winter months (Fig. 3B). The question remains if such large emissions would occur in anaerobic lagoons during winters that result in ice formation. For GHG inventory purposes the USEPA approach yielded quite acceptable results, with annual EF of 6.5, and 7.5 kg CH4 head1 yr1 with use of air temperature 47.5 1C, and manure temperature, respectively. In contrast, the measured EF was 6.7 kg CH4 head1 yr1, as obtained through pooling of data and summation of monthly values with interpolations for September and December (Fig. 3B). Surprisingly, the USEPA recommended
Fig. 4. Methane flux (closed circles) and air temperature (solid line) measured during the main thawing event from March 27 (day 86) to April 1 (day 91) during spring 2001 at Arkell (left graph) and from March 5 (day 64) to 10 (day 69) during spring 2002 at Guelph (right graph).
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approach (air temperature 47.5 1C) was closest to the measured EF, a result of under-prediction for May to October, and over-prediction for December to April. Methane EF using IPCC Tier 2 for the three sites averaged 11.5 kg CH4 head1 yr1, an over-prediction consistent with the use of MCF ¼ 0:39, when compared to the value derived from measurements (MCF ¼ 0:23) and the USEPA derived values (MCF ¼ 0:2220:25). Clearly, the USEPA developed approach provides an improvement to the IPCC Tier 2 approach and should be adopted when possible. Using an estimate of monthly manure temperature, based on air temperature and a derived regression equation, further improved CH4 emission predictions, particularly on a monthly basis. However, when using monthly VS production with carry-over effect, as recommended for anaerobic lagoons, the calculated MCF of 0.50 was clearly an overestimate. This implies that although VS are accumulating in the manure tank the nonconsumed amounts are not all carried over to the next months. Indeed, the derived MDP factor in this case would be approximately 0.45 (obtained from the ratio of measured MCF and derived MCF for VS accumulation, i.e. 0.23/0.50). Mean yearly N2O emission was estimated as 3.6 g head1 yr1, based on the small fluxes measured at Jarvis in summer and fall 2001. This value is much lower than the average N2O EF of 17 g head1 yr1, calculated for the studied farms based on N excretion. 4. Conclusion The MMB method, a non-intrusive flux measurement method, was used in the quasi-continuous measurement of CH4 and N2O fluxes from stored liquid swine manure during a total of 2461 halfhours, over 13 months. The farms studied had contrasting swine production systems, which resulted in dry matter content ranging from 0.6% to 3%, and redox potential characteristic of very reducing environments (o200 mV). These conditions led to negligible or very small nitrous oxide fluxes, approximately 20% of the EF calculated using the IPCC recommended approach. Hence, we suggest that N2O emissions from non-aerated liquid swine manure storage could be ignored in GHG inventories. Monthly CH4 emissions were predicted reasonably well using the USEPA approach with measured
manure temperature (r2 ¼ 0:64, Po0:05). Discrepancies between measured and predicted CH4 fluxes can be attributed to several factors not considered in this approach, such as effect of manure composition (pH, NH+ 4 ), manure management (agitation, pumping) and the formation of an ice layer on the tank’s surface. Improvements in emission predictions requires modelling of processes and factors controlling nutrient cycling, and their interaction with environmental conditions. Sommer et al. (2004) proposed a process-based model for CH4 and N2O emission prediction and cited a lack of comprehensive, year-round data on trace gas emissions from manure for testing of their approach. Our data provide opportunity for testing some of the existing models in future initiatives. The annual CH4 EF derived from our data was within 10% of EF based on the USEPA approach using monthly manure temperature, which was approximately 4 1C warmer than air temperature for the liquid manure storage tanks studied. However, the measured EF was only 60% of the EF derived using IPCC Tier 2. This discrepancy is due to an MCF factor ( ¼ 0.39) recommended for climates with mean annual temperature o15 1C, which is clearly an over-estimate for cold climates (MCF o0.25). Acknowledgements Funding of this research provided by Climate Change Funding Initiative in Agriculture (CCFIA) from Agriculture Canada administered by the Canadian Agri-Food Research Council, Ontario Ministry of Agriculture and Food (OMAF), and Natural Science and Engineering Council (NSERC) are greatly acknowledged. A special thanks is extended to Robert Sweetman for technical assistance, and to the swine producers Harry Stam and Jim Whitehouse for allowing this research to take place on their farms. References Attal, A., Ehlinger, F., Audic, J.M., Faup, G.M., 1988. pH inhibition mechanisms of acetogenic, acetoclastic and hydrogenophilic populations. In: Hall, E.R., Hobson, P.N. (Eds.), Anaerobic Digestion 1988: Proceedings of the Fifth International Symposium on Anaerobic Digestion, Bologna, Italy, 22–26 May 1988. Pergammon Press, Oxford, pp. 71–78. Be´line, F., Martinez, J., Chadwick, D., Guiziou, F., Coste, C.-M., 1999. Factors affecting nitrogen transformations and related nitrous oxide emissions from aerobically treated piggery
ARTICLE IN PRESS K.-H. Park et al. / Atmospheric Environment 40 (2006) 618–627 slurry. Journal of Agricultural Engineering Research 73, 235–243. Brown, H.A., Wagner-Riddle, C., Thurtell, G.W., 2000. Nitrous oxide flux from solid dairy manure in storage as affected by water content and redox potential. Journal of Environmental Quality 29, 630–638. Denmead, O.T., Harper, L.A., Freney, J.R., Griffith, D.W.T., Leuning, R., Sharpe, R.R., 1998. A mass balance method for non-intrusive measurements of surface-air trace gas exchange. Atmospheric Environment 32, 3679–3688. Harper, L.A., Sharpe, R.R., Parkin, T.B., 2000. Gaseous nitrogen emissions from anaerobic swine lagoons: ammonia, nitrous oxide, and dinitrogen gas. Journal of Environmental Quality 29, 1356–1365. Hashimoto, A.G., Chen, Y.R., Varel, V.H., 1980. Theoretical aspects of methane production: state-of-the-art. In: Proceedings, Fourth International Symposium on Livestock Wastes. American Society of Agricultural Engineers, St. Joseph, MI, pp. 86–91. IPCC, 2000. Good practice guidance and uncertainty management in national greenhouse gas inventories [Online]. Available at www.ipcc-nggip.iges.or.jp/public/gp/english/ (verified 9 June 2005). IPCC, 2001. In: Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linden, P.J., Dai, X., Maskell, K., Johnson, C.A. (Eds.), Climate Change 2001: The Scientific Basis. Cambridge University Press, UK, and New York, USA, 881pp. Jeris, J.S., McCarty, P.L., 1965. The biochemistry of the methane fermentation using 14C tracers. Journal of Water Pollution Control Federation 37, 178–192. Kaharabata, S.K., Schuepp, P.H., Desjardins, R.L., 1998. Methane emissions from aboveground open manure slurry tanks. Global Biogeochemical Cycles 12, 545–554. Khalil, M.A.K., Rasmussen, R.A., 1992. The global source of nitrous oxide. Journal of Geophysical Research 97, 14651–14660. Khan, R.Z., Muller, C., Sommer, S.G., 1997. Micrometeorological mass balance technique for measuring CH4 emission from stored cattle slurry. Biology and Fertility of Soils 24, 442–444. Kirchmann, H., Lundvall, A., 1998. Treatment of solid animal manures: identification of low NH3 emission practices. Nutrient Cycling in Agroecosystems 51, 65–71. Kroeker, E.J., Schulte, D.D., Sparling, A.B., Lapp, H.M., 1979. Anaerobic treatment process stability. Journal of the Water Pollution Control Federation 51, 718–727.
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Nozhevnikova, A.N., Holliger, C., Ammann, A., Zehnder, A.J.B., 1997. Methanogenesis in sediments from deep lakes at different temperatures (2–70 1C). Water Science and Technology 36 (6–7), 57–64. Olsen, K., Wellisch, M., Boileau, P., Blain, D., Ha, C., Henderson, L., Liang, C., McCarthy, J., McKibbon, S., 2003. Canada’s Greenhouse Gas Inventory 1990–2001. Environment Canada, Greenhouse Gas Division. Rotmans, J., Den Elzen, M.G.J., Krol, M.S., Swart, R.J., van der Woerd, H.J., 1992. Stabilizing atmospheric concentrations: towards international methane control. Ambio 21, 404–413. Safley, L.M., Westerman, P.W., 1990. Psychrophillic anaerobic digestion animal manure: proposed design methodology. Biological wastes 34, 133–148. Sebacher, D.I., Harriss, R.C., Bartlett, K.B., 1983. Methane flux across the air–water interface: air velocity effects. Tellus 35B, 103–109. Sharpe, R.R., Harper, L.A., 1999. Methane emissions from an anaerobic swine lagoon. Atmospheric Environment 33, 3627–3633. Sommer, S.G., Petersen, S.O., Søgaard, H.T., 2000. Atmospheric pollutants and trace gases: greenhouse gas emission from stored livestock slurry. Journal of Environmental Quality 29, 744–751. Sommer, S.G., Petersen, S.O., Møller, H.B., 2004. Algorithms for calculating methane and nitrous oxide emissions from manure management. Nutrient Cycling in Agroecosystems 63, 143–154. Tate, R.L., 1995. Soil Microbiology. Wiley, New York. Tel, D.A., Heseltine, C., 1990. The analysis of KCl soil extracts for nitrate, nitrite and ammonium using a TRAACS 800 analyzer. Communications in Soil Science and Plant Analysis 21, 1681–1688. USEPA, 2003. Inventory of greenhouse gas emissions and sinks: 1990–2001 [Online]. Available at yosemite.epa.gov/OAR/ globalwarming.nsf/content/ResourceCenterPublicationsGH GEmissionsUSEmissionsInventory2003.html (verified 9 June 2005). van Velsen, A.F.M., 1979. Adaptation of methanogenic sludge to high ammonia-nitrogen concentrations. Water Research 13, 995–999. Wagner-Riddle, C., Park, K.-H., Thurtell, G.W., 2005. A micrometeorological mass balance approach for greenhouse gas flux measurements from stored animal manure. Agricultural and Forest Meteorology, in press.
Atmospheric Environment 40 (2006) 618–627 www.elsevier.com/locate/atmosenv
Greenhouse gas emissions from stored liquid swine manure in a cold climate Kyu-Hyun Park, Andrew G. Thompson, Miche`le Marinier, Karen Clark, Claudia Wagner-Riddle Department of Land Resource Science, University of Guelph, Guelph, Ont., Canada N1G 2W1 Received 8 September 2005; accepted 8 September 2005
Abstract Current global warming has been linked to increases in greenhouse gas (GHG) concentrations. Animal manure is an important source of anthropogenic GHG, mostly of methane (CH4) and nitrous oxide (N2O). Country-specific emission estimates of these GHG can be obtained using IPCC 2000 guidelines, or suggested improvement, such as the USEPA approach for CH4 emissions, which is based on monthly air temperature (T air ). These approaches have not been validated against measured CH4 and N2O fluxes for liquid swine manure storage in cold climates due to the scarcity of year-round studies. A four-tower micrometeorological mass balance method was used at three swine farms (Arkell, Guelph, and Jarvis) in Ontario, Canada (annual T air o10 1C), from July 2000 to May 2002. Methane and N2O concentrations were measured using two tunable diode laser trace gas analyzers, and manure temperature (T man ), redox potential (E h ) and composition were also measured. Dry matter content and E h between sites and seasons varied from 0.6% to 3%, and 232 and 333 mV, respectively. Annual T air was 8.4 1C, and T man was on average 4 1C warmer. Mean N2O fluxes were not significantly different from zero, except for Jarvis with mean fluxes of 337.6 ng m2 s1 in summer and 101.8 ng m2 s1 in fall. Mean yearly N2O emission was estimated as 3.6 g head1 yr1, and was lower than the IPCC-based emission factor (EF) of 17 g head1 yr1. Our data suggests that N2O emissions from non-aerated liquid swine manure storage could be ignored in GHG inventories. Mean monthly CH4 fluxes obtained from half-hourly data varied between 4.6 103 and 1.05 mg m2 s1 (number of measurements per month ¼ 25–562). Measured CH4 emissions from May to October were mostly larger, and from January to April were lower than values predicted using the USEPA approach. Use of T man improved monthly CH4 emission prediction using the USEPA approach compared to T air with a lower limit of 7.5 1C (r2 ¼ 0:64 vs. 0.355). The methane conversion factor derived from measured fluxes was 0.23, comparable to the USEPA derived values of 0.22–0.25, but much lower than the IPCC recommended value for cold climates (0.39). r 2005 Elsevier Ltd. All rights reserved. Keywords: Methane; Nitrous oxide; Micrometeorological mass balance method; Manure temperature; IPCC methodology; Liquid swine manure
1. Introduction Corresponding author. Tel.: +1 519 824 4120x52787;
fax: +1 519 824 5730. E-mail address: [email protected] (C. Wagner-Riddle). 1352-2310/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2005.09.075
Human activities are changing the environment. Since the Industrial Revolution, concentration of greenhouse gases (GHG), such as carbon dioxide
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(CO2), methane (CH4), and nitrous oxide (N2O), have increased by 30%, 151%, and 17%, respectively, and have caused an increase in daily nighttime minimum air temperature, narrowing the gap between day and night temperatures (IPCC, 2001). Agriculture has played an important role in climate change. Animal manure is often held in liquid or solid form on the farm, awaiting disposal. During storage time the manure decomposes, and gaseous by-products are released, where the type of gas is determined largely on whether the decomposition is aerobic or anaerobic (Kirchmann and Lundvall, 1998). The handling system determines the moisture content and oxygen availability in the manure, with liquid systems producing predominantly CH4, and solid systems producing both CH4 and N2O. Globally, livestock manure contributes 5–10% to the total emission of CH4 (Rotmans et al., 1992) and 7% of N2O (Khalil and Rasmussen, 1992). In 2001, emissions of CH4 and N2O from stored manure accounted for 17% (10.1 Mt CO2-eq) of Canada’s total agricultural emissions (Olsen et al., 2003). Emissions of GHG from stored manure are affected by environmental factors such as temperature (Khan et al., 1997), wind speed (Sebacher et al., 1983), redox potential (Brown et al., 2000) and crust formation on the slurry surface (Sommer et al., 2000), as well as by animal factors (Hashimoto et al., 1980). Uncertainties in GHG estimation have been attributed to uncertainties in the types and size of manure storage and to the accuracy of yearround extrapolation of emissions from short-term studies (Kaharabata et al., 1998). IPCC (2000) recommends non-invasive and yearround measurements of GHG emissions in production systems, in order to reduce the large uncertainties in emission factors (EFs) used for calculating national GHG emission inventories. The Micrometeorological Mass Balance (MMB) method, a non-invasive measurement technique, is suitable for heterogeneous source distributions and/or elevated sources such as waste storage sites, where eddy correlation and flux-gradient approaches are not appropriate (Denmead et al., 1998). Most research concerning GHG emissions from stored manure has been conducted from spring to fall (Kaharabata et al., 1998) or in mild winters when an ice cover did not form on the surface of the liquid manure (Sharpe and Harper, 1999). As a result, insufficient data exists to evaluate year-round
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GHG emissions from stored manure in cold climates such as Canada. Currently, calculation of CH4 EFs using the IPCC (2000) approach with country-specific inputs (Tier 2) takes climate into account, through the use of a methane conversion factor (MCF). With a mean annual air temperature below 15 1C, Canada fits into the ‘cool climate’ designation. In an effort to fine-tune the calculation of MCF, the US Greenhouse Gas Inventory adopted a method which takes monthly air temperature into account (USEPA, 2003). These approaches have not been validated against measured CH4 and N2O fluxes for liquid swine manure storage in cold climates. The objectives of this study were: (1) to quantify CH4 and N2O emissions from stored liquid swine manure at three farms through a quasi-continuous year-round experiment in a cold climate region (annual mean air temperature o10 1C); (2) to compare the measured values to EFs derived using the IPCC (2000) and USEPA (2003) approaches. 2. Materials and methods 2.1. Experimental sites and instrument setup for MMB method Flux measurements were conducted at the liquid manure storage tanks of one research farm (Arkell) and two commercial swine farms (Guelph and Jarvis) in Ontario, Canada, over July 2000 to May 2002 (Table 1). A mobile instrumentation trailer was first stationed at Arkell, and then moved between Jarvis and Guelph. An attempt was made to measure fluxes over the different seasons, in order to characterize environmental effects. Pigs were fed a standard corn–soybean diet at all sites, with alfalfa added at Jarvis. At all sites, manure was collected in the barn in a below-ground holding tank through partially slatted floors and sent bi-weekly to outdoor concrete storage tanks. There were four outdoor storage tanks at Arkell, two at Jarvis, and one at Guelph, but only one tank was monitored at each site. Stored manure in the outside tanks was stirred prior to field application in spring (April–May) and fall (October– November). In the MMB method, measurements of wind speed and direction, and gas concentration in air samples are needed. A detailed description of the four-tower MMB method used in this experiment is given by Wagner-Riddle et al. (2005). Briefly, four
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Table 1 Description of swine farms where CH4 and N2O fluxes were measured in Ontario, Canada, over the 2000–2002 period Site Arkell
Guelph
Jarvis
Location Type of swine farm
431320 N 801100 W Farrow-to-finish
431330 N 801250 W Grower
421580 N 80140 W Farrow-to-wean
Number of swine Starters Growers Finishers Dry sows Lactating sows Boars
1500 400 250 450 275 75 50
490 0 430 0 30 0 0
2725 2000 0 0 75 650 0
Storage tank Diameter (m) Deptha (m) Total surface areab (m2)
18.7 3.5 1093.9
16.9 3.0 224.3
34.4 2.4 1858.8
Measurement period Summer Fall Winter Spring
2000/2001 Jun. 25–Jul. 18 Oct. 24–Nov. 5 Jan. 9–Jan. 14 Mar. 22–May 3
2001/2002 Jul. 28–Aug. 10 Oct. 11–Oct. 30 Feb. 1–Mar. 22 Mar. 22–Apr. 18
2001 May 28–Jul. 11 Nov. 8–Nov. 28 NDc NDc
a
Depth of manure in tank varied over the measurement period, but the tanks mostly were filled to within 0.3 m from the top. The number of tanks used in manure storage (four at Arkell, and two at Jarvis) was taken into account when calculating total surface area available for emissions. c Measurements were not carried out in winter and spring at Jarvis (ND ¼ not determined). b
air sampling towers and one tower collecting wind data were installed above the wall of the circular manure storage tanks. Four air-sampling intakes were located at heights of 0.25, 1.0, 2.0 and 3.5 m on each tower. The wind tower had cup anemometers (F460, Climatronics, Newton, PA) at the same heights used for air sampling. A wind vane (R.M. Young, Model 05102, Traverse, MI) was mounted on the top of the wind tower (4.0 m). Four thermocouples to measure manure temperature were mounted on a floating frame at depths of 0.03, 0.20, 0.60, and 1.0 m below the liquid surface at Jarvis and Guelph. A datalogger (CR7, Campbell Scientific, Edmonton, AB) recorded mean 5-min (for Arkell) and 1-min (for Jarvis and Guelph) wind direction, and half-hourly mean wind speed and liquid manure temperatures. Two tunable diode laser trace gas analyzers (TGA100, Campbell Scientific, Inc., Logan, UT), one for each CH4 and N2O concentration measurements, were used in an air sampling setup as described by Wagner-Riddle et al. (2005). The half-hourly mean gas flux ðF Þ was then calculated
from the rectangular gas flux calculation method (Wagner-Riddle et al., 2005): 4 1X ½ð¯ui D¯ci Þ Dzi , F¯ ¼ L i¼1
(1)
where L is the mean distance traveled by the horizontal air flow over the source, and i indicates the height of mean half-hourly gas concentration difference ðD¯ci Þ and wind speed ð¯ui Þ measurements, which were considered representative of the air layers ðDzi Þ of 0–0.5, 0.5–1.5, 1.5–2.5, and 2.5–4.5 m. The D¯ci was obtained from concentration measurements at upwind and downwind positions for each layer. These positions were determined based on 30-min mean wind direction. The 30-min mean fetch L was calculated from 5-, or 1-min fetch values determined according to the 5-, or 1-min wind direction data and the circular tank’s geometry (Wagner-Riddle et al., 2005). Note that the turbulent diffusive flux term, which is approximately 10–15% of total flux (Denmead et al., 1998), was ignored in Eq. (1) due to difficulties in obtaining this term.
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2.2. Chemical analysis Manure samples from 30 cm below the manure surface were taken at Guelph and Jarvis over the measurement periods at randomly selected locations within the storage tank. Redox potential and pH were immediately measured on-site. The pH was measured with a pH meter (Accumets pH meter model 610A, Fisher Scientific Int’l., NH) with electrode (Accumets 13-620-104, Fisher Scientific Int’l., NH). Redox potential was measured using a platinum and Ag–AgCl reference electrode (#599055, Cole-Parmer, Niles, IL), connected to a digital multivoltmeter (Orion pH/ISE meter, Model 710A, Orion Research Inc., Boston, MA). Collected samples were stored at 20 1C in a freezer and thawed before analysis. Each sample was analyzed for total solids (TS), total soluble nitrogen (TSN), total soluble organic carbon (TOC), nitrate, and ammonium concentration (Tel and Heseltine, 1990). Some results from routine manure composition analyses were available for the Arkell Research farm.
2.3. Measured and estimated CH4 emission factors Measured half-hourly CH4 fluxes were averaged to obtain monthly means, which were then converted to a monthly emission per animal, using the storage tanks’ total surface area and the number of animals at each farm (Table 1). Although measurements were carried out on one of the tanks at each farm, it was necessary to consider emissions from all tanks, in order to scale the emissions to a per animal basis. An annual CH4 EF was obtained by pooling all measured monthly values and interpolating between measured values for months with no measurements (September and December; Table 1). Measured CH4 EF were compared to calculated EF using Tier 2 IPCC (2000) and USEPA (2003) methodology. In the IPCC approach the annual EF for an animal population, in this case each farm, is equal to the product of yearly volatile solid excretion per animal (VS, kg head1 d1), maximum CH4 producing potential of manure (Bo , assumed 0.298 kg CH4 kg1 VS for swine), and a CH4 conversion factor dependent on the type of manure management system and climate (MCF, assumed 0.39 for liquid systems in climates with annual temperature o15 1C). The VS were calculated
according to a modified IPCC methodology: ASH ED 1 , VS ¼ DMI 1 100 100
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(2)
where DMI is the dry matter intake (kg head1 d1), ASH and ED are the ash content and energy digestibility of feed (%), respectively. Note that IPCC uses the mineral content of the manure, not feed for ASH. For each farm, typical DMI, ASH and ED for a corn–soybean diet were used for each animal class shown in Table 1: 0.8, 1.7, 2.2, and 2.5 kg head1 d1 for DMI of starters, growers, finishers, dry sows/boars, and lactating sows; 4.5%, 5%, and 5.5% for ASH in feed for starters, growers/finishers/dry sows/boars, and lactating sows; and 82%, 84%, 88%, and 86% for starters, growers/finishers, dry sows/boars, and lactating sows, respectively. The mean VS produced at each farm, obtained by a weighted average that took number of animals in each class into account, were similar at 0.283, 0.258 and 0.275 kg head1 d1 for Arkell, Guelph and Jarvis, respectively, despite differences in production systems. In the USEPA approach, monthly CH4 emission for liquid manure storage (other than anaerobic lagoons) is calculated as the product of VS produced on a monthly basis, Bo (as defined above) and a factor (f ), which describes the effect of monthly air temperature on CH4 emissions according to the Van’t Hoff–Arrhenius equation, as described in Safley and Westerman (1990). A minimum monthly air temperature of 7.5 1C is recommended in the calculation of f when air temperature drops to values o7.5 1C to account for differences in liquid manure and air temperature. For inventory purposes, an annual MCF is derived from the ratio of annual CH4 emission (equal to the sum of monthly values) and potential CH4 production (calculated as total VS Bo). This calculation assumes that VS do not accumulate in storage as is the case with frequent manure tank emptying. In cold climates VS may accumulate in manure storage due to regulations that prevent producers from applying manure to fields during the winter months. For anaerobic lagoons, the USEPA approach involves carry-over of non-consumed VS from month-to-month as well as the use of a management and design practices factor (MDP). This MDP factor determines which fraction of VS produced each month is available for CH4 production, and has been adjusted to 0.8 (USEPA, 2003). For comparison purposes, we estimated monthly CH4
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emission using both monthly VS production without carry-over effect (i.e. non-accumulated from month-to-month, VSn-acc) and monthly VS production with carry-over effect (i.e. accumulated from month-to-month, VSacc). In all calculations we assumed an MDP factor of 1. 2.4. Measured and estimated N2O emission factors The method outlined in IPCC (2000) for estimating N2O emissions from manure storage relies on the amount of N excreted for each animal type per year, and an EF for each type of manure handling system ( ¼ 1.57 g N2O kg1 N excreted for liquid systems). The amount of N excreted (Nex) was estimated using: Nex ¼ ðCP=6:25Þð1 Nret Þ,
(3)
where CP is the fraction of crude protein in the diet ( ¼ 0.19 for starters and 0.15 for other categories), and Nret is the proportion of N retained by the body ( ¼ 0.35). Annual N2O EFs were calculated for each farm based on the animal population and EF for each animal category. 3. Results and discussion 3.1. Chemical analysis The liquid swine manure stored at the three farms had a dry matter content between 0.6 and 3% (TS), and pH between 6.8 and 7.9 (Table 2). Jarvis had
the most dilute manure, consistent with its type of swine production (farrow-to-wean), and Guelph (summer) had the most concentrated manure, given its swine population (Table 1) and the fact that very little rain had occurred after its tank had been emptied 2 months earlier. The latter effect was also responsible for the higher TSN, NH+ 4 , and TOC, and lower pH recorded at Guelph in summer, when compared to other samplings dates. Jarvis had consistently low concentrations of TSN, NH+ 4 , and TOC, no doubt due to higher water use associated with farrow-to-wean systems. Measured redox potentials were typical of environments in which methanogenesis and sulfur reduction occur (o100 mV, Tate, 1995), and were lowest in summer, indicating most reduced conditions. This was most likely related to an increase in microbial activity during the warmer season, as higher temperature results in larger consumption of substrates, and hence larger oxygen consumption (Nozhevnikova et al., 1997). 3.2. Manure temperature and GHG fluxes The average monthly air temperature during the measurement period varied from 5.6 1C (January 2001) to 20.3 1C (July 2001), with an annual mean of 8.4 1C. Monthly liquid manure temperature at 60 cm depth was on average 4 1C warmer than air temperature, and strongly correlated to air temperature (Fig. 1). Lowest average manure temperature recorded was 2.7 1C, indicating that the lower
Table 2 Liquid swine manure composition as determined from samples (n) taken at 30 cm depth during each experimental period at Guelph and Jarvis farms Site/period
Manure composition pH
Redox (mV)
Total solids (mg kg1)
Total soluble N (mg kg1)
1 NH+ 4 (mg kg )
Total organic C (mg kg1)
Arkell
7.5
—
12 400 (4300)
—
1521
—
Guelph Summer Fall Winter Spring
6.8 7.5 7.4 7.4
30 519 17 126 9166 6610
2299 1874 1719 1342
Jarvis Summer Fall
7.7 (0.03) 7.9 (0.06)
(0.03) (0.02) (0.04) (0.01)
318.3 333.4 232.0 284.2
(1.7) (5.1) (6.4) (5.1)
333.7 (3.0) 259.7 (2.2)
(3086) (860.4) (771.4) (158.3)
6629 (403.6) 6252 (234.1)
(33.9) (101) (77.3) (230)
797.5 (17.9) 1074 (11.7)
2066 1398 1282 1167
(30.8) (61.7) (36.6) (78.9)
678 (13.0) 882 (20.4)
6281 2637 2965 3085
(48.8) (123.0) (144.3) (323.5)
376.6 (10.9) 439.8(4.0)
Exact dates of summer to spring periods are listed in Table 1. Also shown are values available from farm manure analysis at Arkell. Values in brackets show standard error of the mean. Number of observations for each mean varied between 12 and 18. NO 3 concentrations were always 1–2 mg kg1 or non-detectable, and are not shown.
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Fig. 1. Monthly manure temperature at 60 cm depth (y) as a function of monthly air temperature (x) measured at Guelph and Jarvis from May 2001 to April 2002, and plot of linear regression (dashed line, y ¼ 0:879x þ 4:24, n ¼ 10, r2 ¼ 0:946). Labels indicate month of measurement.
limit of 7.5 1C used by USEPA (2003) is not adequate for the region studied. The daily mean manure temperature measured at 3 cm was similar to the temperature recorded at 60 cm depth, except for short periods in the summer, and throughout January to March 2002, when the surface temperature was close to 0 1C (Fig. 2), and the presence of an ice cover was observed. Halfhourly CH4 fluxes over this latter period were quite small (o 0.3 mg m2 s1), in contrast to maximum fluxes larger than 1 mg m2 s1 measured during summer or fall (Fig. 2). Highest flux values were observed when manure was agitated before pumping from the storage tank to a manure spreader (Arkell day 302; Guelph day 304), or after barn manure addition to tank (Arkell, day 197). After tank emptying, fluxes decreased to much lower levels as illustrated for Arkell (day 308) and Guelph (day 305). In general, CH4 fluxes were strongly related to manure temperature with decreasing fluxes from July 2001 to April 2002 at Arkell, and higher fluxes in July 2001 when compared to November 2002 at Jarvis (Fig. 2). Results for August and October 2001 at Guelph did not fit this pattern, although January to April 2002 presented lowest fluxes as expected. When measurements were initiated at Guelph on day 210, the storage tank was only one-third full,
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with manure addition occurring on day 218 (Fig. 2), shortly before the instrumentation trailer was moved to another site as part of a separate experiment. In contrast to NH3 fluxes, which are related to surface area, CH4 fluxes are related to the volume or mass of liquid manure associated with the surface area over which fluxes are measured. Hence, the lower volume of the manure in storage would have resulted in less CH4 flux. In addition, the liquid manure for this period had a relatively low pH, high TS, and NH+ content (Guelph 4 summer, Table 2). Methanogenesis from acetate, which contributes 70% of manure-generated CH4 (Jeris and McCarty, 1965), is inhibited by pH o7 (Attal et al., 1988). In addition, increased NH+ 4 concentration has been shown to inhibit CH4 production (Kroeker et al., 1979), and a longer lag phase for CH4 production in a batch sewage digester was observed when NH+ 4 increased from 1210 to 2360 mg L1 (van Velsen, 1979). These combined effects could be the causes for lower CH4 fluxes observed at Guelph during the measurement period in August 2001 (mean 0.357 mg m2 s1), and fluxes probably would have increased over the subsequent months as the manure would have become more dilute through rainfall, and the methanogenic microbial community would have developed. Indeed, when measurements were resumed at Guelph in October 2001 (day 283, Fig. 2), 1 NH+ 4 concentration was o1400 mg kg , pH was 47, and CH4 fluxes were much larger (mean 1.05 mg m2 s1). These high fluxes occurred until the tank was completely emptied (day 305). Nitrous oxide fluxes were small with mean value for several of the measurement period not significantly different from zero (Po0:05; data not shown). The exception was mean fluxes obtained at Jarvis: 337.6 ng m2 s1 (SE ¼ 119 ng m2 s1, n ¼ 238) in summer, and 101.8 ng m2 s1 (SE ¼ 45 ng m2 s1, n ¼ 464) in fall. Brown et al. (2000) observed a non-linear increase in N2O emission from solid dairy manure when the redox potential increased from 200 to 200 mV, with values 300 ng N2O m2 s1 associated with 50 mV. In the liquid manure storage tank studied here, the redox potential at 30 cm depth was always o200 mV (Table 2). The storage tank at Jarvis had a relatively large surface area and was quite full during the measurement period (Table 1), possibly resulting in increased oxygen diffusion into, and higher manure redox potential in the surface manure layer, when compared to the other sites
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Day of Year Fig. 2. Half-hourly CH4 fluxes (dots), daily CH4 fluxes (solid bold line), daily air temperature, and manure temperature at 3 and 60 cm depth as a function of day of year from July 2000 to July 2001 (top graph), and August 2001 to April 2002 (bottom graph), in Ontario, Canada. Site of measurements are indicated at the top of each graph. Note: manure temperature was not measured at Arkell. Upward pointing solid arrows indicate when manure was stirred and open arrows show when manure was flushed from barn to outdoor tank.
studied. Nitrous oxide production during aerobic treatment of pig slurry has been observed, particularly at high aeration levels (2–4 mg O2 L1), but also in a low aeration level control (redox potential ¼ 0 to 48 mV), although lower N2O levels were recorded in the latter treatment (Be´line et al., 1999). The required O2 levels for N2O production to take place in non-treated liquid swine manure do not appear to be met often, as our very small fluxes attest. Negligible or non-detectable N2O fluxes were also observed for anaerobic swine lagoons by Harper et al. (2000). In contrast, Sommer et al. (2000) found N2O emissions from stored dairy slurry with higher dry matter content than the liquid manure studied here were up to 10 940 ng m2 s1, but these emissions were only detected during the dry season when a crust formed on the surface.
3.3. Measured and estimated CH4 and N2O emission factors Mean monthly CH4 fluxes were obtained from half-hourly data, with number of observations per mean ranging from 25 (August at Guelph) to 562 (April at Arkell) (Fig. 3A). The large number of measurements (n ¼ 929 at Arkell, n ¼ 830 at Guelph, n ¼ 702 at Jarvis) indicates the suitability of the MMB for year-round studies of gas fluxes from manure storage tanks. Scaling of the measured means using storage tank surface area and number of animals at each site (Table 1) allowed for comparison of CH4 emission (expressed in kg head1 month1) with the USEPA approach (Fig. 3B). The measured CH4 emissions from May to October were mostly larger than values predicted with monthly air temperature (bold
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Fig. 3. (A) Monthly mean methane emissions from stored liquid swine manure measured at Arkell, Jarvis, and Guelph (bars represent standard error of mean, and labels represent number of half-hourly flux measurements used to obtain each mean). (B) Values shown in (A) expressed on a per animal basis compared to estimated emissions based on the USEPA approach using monthly carry-over of non-consumed volatile solids (VSacc) and no carry-over of volatile solids (VSn-acc). For both approaches of VS estimates, curves are shown for calculations using air temperature (T air , set to ¼ 7.5 1C when o7.5 1C) and manure temperature (T man ).
solid line, Fig. 3B). From January to April measured emissions were clearly lower than the emissions estimated setting monthly air temperature for these months equal to 7.5 1C. Use of manure temperature improved prediction for both periods (comparison between observed vs. predicted values yielded r2 ¼ 0:64, Po0:05 vs. r2 ¼ 0:355, Po0:10 for air temperature). However, for reasons discussed above, some monthly means deviated considerably from predictions (August and October for Guelph), emphasizing the need for process-based models in order to refine predictions of CH4 emissions from manure. Manure composition as affected by animal diet and management is obviously an area that needs better algorithms linked to CH4 production. For illustration purposes
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we display the approach developed by USEPA for VS carry-over in anaerobic lagoon systems (Fig. 3B). Our data confirm the assumption that this approach is not adequate for manure holding tanks, as these are not designed for anaerobic manure decomposition, i.e. optimal CH4 production. Consistent over-prediction of CH4 emissions for the January to April period when using manure temperature in the USEPA approach, pointed to additional effects taking place (Fig. 3B). We suggest that formation of an ice layer suppressed the emission of the small CH4 production that occurred at manure temperatures of 2–3 1C at 60 cm depth (Figs. 1 and 2). This is corroborated by examination of the CH4 fluxes during the first spring thaw period in 2001 at Arkell, and 2002 at Guelph (Fig. 4). In both cases, CH4 fluxes increased significantly on the second day of air temperatures above 0 1C, when significant ice melting was observed. This burst was most likely a release of trapped CH4 as subsequent thaws did not show a similar effect (Fig. 2). Finally, the VS carry-over approach predicted relatively large CH4 emission for April, a direct consequence of large VS accumulation due to low CH4 production during the winter months (Fig. 3B). The question remains if such large emissions would occur in anaerobic lagoons during winters that result in ice formation. For GHG inventory purposes the USEPA approach yielded quite acceptable results, with annual EF of 6.5, and 7.5 kg CH4 head1 yr1 with use of air temperature 47.5 1C, and manure temperature, respectively. In contrast, the measured EF was 6.7 kg CH4 head1 yr1, as obtained through pooling of data and summation of monthly values with interpolations for September and December (Fig. 3B). Surprisingly, the USEPA recommended
Fig. 4. Methane flux (closed circles) and air temperature (solid line) measured during the main thawing event from March 27 (day 86) to April 1 (day 91) during spring 2001 at Arkell (left graph) and from March 5 (day 64) to 10 (day 69) during spring 2002 at Guelph (right graph).
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approach (air temperature 47.5 1C) was closest to the measured EF, a result of under-prediction for May to October, and over-prediction for December to April. Methane EF using IPCC Tier 2 for the three sites averaged 11.5 kg CH4 head1 yr1, an over-prediction consistent with the use of MCF ¼ 0:39, when compared to the value derived from measurements (MCF ¼ 0:23) and the USEPA derived values (MCF ¼ 0:2220:25). Clearly, the USEPA developed approach provides an improvement to the IPCC Tier 2 approach and should be adopted when possible. Using an estimate of monthly manure temperature, based on air temperature and a derived regression equation, further improved CH4 emission predictions, particularly on a monthly basis. However, when using monthly VS production with carry-over effect, as recommended for anaerobic lagoons, the calculated MCF of 0.50 was clearly an overestimate. This implies that although VS are accumulating in the manure tank the nonconsumed amounts are not all carried over to the next months. Indeed, the derived MDP factor in this case would be approximately 0.45 (obtained from the ratio of measured MCF and derived MCF for VS accumulation, i.e. 0.23/0.50). Mean yearly N2O emission was estimated as 3.6 g head1 yr1, based on the small fluxes measured at Jarvis in summer and fall 2001. This value is much lower than the average N2O EF of 17 g head1 yr1, calculated for the studied farms based on N excretion. 4. Conclusion The MMB method, a non-intrusive flux measurement method, was used in the quasi-continuous measurement of CH4 and N2O fluxes from stored liquid swine manure during a total of 2461 halfhours, over 13 months. The farms studied had contrasting swine production systems, which resulted in dry matter content ranging from 0.6% to 3%, and redox potential characteristic of very reducing environments (o200 mV). These conditions led to negligible or very small nitrous oxide fluxes, approximately 20% of the EF calculated using the IPCC recommended approach. Hence, we suggest that N2O emissions from non-aerated liquid swine manure storage could be ignored in GHG inventories. Monthly CH4 emissions were predicted reasonably well using the USEPA approach with measured
manure temperature (r2 ¼ 0:64, Po0:05). Discrepancies between measured and predicted CH4 fluxes can be attributed to several factors not considered in this approach, such as effect of manure composition (pH, NH+ 4 ), manure management (agitation, pumping) and the formation of an ice layer on the tank’s surface. Improvements in emission predictions requires modelling of processes and factors controlling nutrient cycling, and their interaction with environmental conditions. Sommer et al. (2004) proposed a process-based model for CH4 and N2O emission prediction and cited a lack of comprehensive, year-round data on trace gas emissions from manure for testing of their approach. Our data provide opportunity for testing some of the existing models in future initiatives. The annual CH4 EF derived from our data was within 10% of EF based on the USEPA approach using monthly manure temperature, which was approximately 4 1C warmer than air temperature for the liquid manure storage tanks studied. However, the measured EF was only 60% of the EF derived using IPCC Tier 2. This discrepancy is due to an MCF factor ( ¼ 0.39) recommended for climates with mean annual temperature o15 1C, which is clearly an over-estimate for cold climates (MCF o0.25). Acknowledgements Funding of this research provided by Climate Change Funding Initiative in Agriculture (CCFIA) from Agriculture Canada administered by the Canadian Agri-Food Research Council, Ontario Ministry of Agriculture and Food (OMAF), and Natural Science and Engineering Council (NSERC) are greatly acknowledged. A special thanks is extended to Robert Sweetman for technical assistance, and to the swine producers Harry Stam and Jim Whitehouse for allowing this research to take place on their farms. References Attal, A., Ehlinger, F., Audic, J.M., Faup, G.M., 1988. pH inhibition mechanisms of acetogenic, acetoclastic and hydrogenophilic populations. In: Hall, E.R., Hobson, P.N. (Eds.), Anaerobic Digestion 1988: Proceedings of the Fifth International Symposium on Anaerobic Digestion, Bologna, Italy, 22–26 May 1988. Pergammon Press, Oxford, pp. 71–78. Be´line, F., Martinez, J., Chadwick, D., Guiziou, F., Coste, C.-M., 1999. Factors affecting nitrogen transformations and related nitrous oxide emissions from aerobically treated piggery
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