N 2 O emissions at municipal solid waste landﬁll sites: Effects of CH 4 emissions and cover soil Houhu Zhang, Pinjing He * , Liming Shao State Key Laboratory of Pollution Control and Resources Reuse, Key Laboratory of Yangtze River Water Environment, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, PR China article info Article history: Received 3 February 2009 Accepted 5 February 2009 Keywords: Municipal solid waste landﬁll N 2 O emissions CH 4 emissions Methanotrophic nitriﬁcation Cover soil type abstract Municipal solid waste landﬁlls are the signiﬁcant anthropogenic sources of N 2 O due to the cooxidation of ammonia by methane-oxidizing bacteria in cover soils. Such bacteria could be developed through CH 4 fumigation, as evidenced by both laboratory incubation and ﬁeld measurement. During a 10-day incu- bation with leachate addition, the average N 2 O ﬂuxes in the soil samples, collected from the three selected landﬁll covers, were multiplied by 1.75 (p < 0.01), 3.56 (p < 0.01), and 2.12 (p < 0.01) from the soil samples preincubated with 5% CH 4 for three months when compared with the control, respectively. Among the three selected landﬁll sites, N 2 O ﬂuxes in two landﬁll sites were signiﬁcantly correlated with the variations of the CH 4 emissions without landﬁll gas recovery (p < 0.001). N 2 O ﬂuxes were also elevated by the increase of the CH 4 emissions with landﬁll gas recovery in another landﬁll site (p > 0.05). The annual average N 2 O ﬂux was 176  566 mgN 2 O–N m 2 h 1 (p < 0.01) from sandy soil–covered landﬁll site, which was 72% (p < 0.05) and 173% (p < 0.01) lower than the other two clay soil covered landﬁll sites, respectively. The magnitude order of N 2 O emissions in three landﬁll sites was also coin- cident by the results of laboratory incubation, suggesting the sandy soil cover could mitigate landﬁll N 2 O emissions. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Nitrous oxide (N 2 O) is an atmospheric trace gas important in radiative forcing and contributes to the catalytic destruction of ozone in the stratosphere (IPCC, 2001, 2007). Atmospheric N 2 O has 296 times the radiative force per molecule of CO 2 , partly because of N 2 O’s long atmospheric lifetime of 127 years (Kiese and Butterbach-Bahl, 2002). N 2 O emissions have been investigated intensively in various ecosystems, e.g., agricultural ﬁelds, wetlands, forests, and grasslands (Chen et al., 2000; Kiese and Butterbach-Bahl, 2002; Ghosh et al., 2003; Erisman et al., 2008), whereas only a few investigations have been conducted about N 2 O emissions in municipal soil waste (MSW) landﬁlls (B} orjesson and Svensson, 1997; Rinne et al., 2005). N 2 O is produced predominantly by microbial processes in soils, as a by-product of nitriﬁcation (the oxidation of ammonia to nitrate via nitrite) and as an intermediate product of denitriﬁcation (the reduction of nitrate to molecular nitrogen via nitrite, nitric oxide, and nitrous oxide). Ammonia oxidation through the nitriﬁcation process is considered as the ﬁrst, often rate-limiting, step of N 2 O formation (Freitag and Prosser, 2003). Ammonia oxidation by methanotrophs as they oxidize CH 4 has been referred to as meth- anotrophic nitriﬁcation and represents an important pathway of the nitrogen cycle (Dalton, 1977; Yoshinari, 1985; Megraw and Knowles, 1989; King and Schnell, 1994). Landﬁll sites are widely reported as signiﬁcant CH 4 emission sources (B} orjesson et al., 2000; Barlaz et al., 2004; Powell et al., 2006; Lohila et al., 2007; Zhang et al., 2008a). In landﬁll cover soils, the microbial population of methane-oxidizing (methanotrophic) bacteria has been highly developed because of CH 4 fumigation, which was formed from anaerobic decomposition of the landﬁlled waste. Mandernack et al. (2000) reported that preincubation of a landﬁll topsoil with 1% CH 4 for 2 weeks resulted in higher rates of N 2 O production when subsequently amended with NH 3 (g) than the control without preincubation. However, the rate and extent of the N 2 O emissions inﬂuenced by the CH 4 in the environments of landﬁll cover have not yet, to our knowledge, been reported. The physicochemical properties of soils are intrinsic factors inﬂuencing N 2 O emissions (van der Weerden and Jarvis, 1997; Inubushi et al., 2000). Kravchenko et al. (2002) reported a more than sixfold gap on N 2 O ﬂuxes between loam and loamy sand soils amended with the same amount of (NH 4 ) 2 SO 4 . The highest N 2 O ﬂuxes from landﬁlls were reported at the H} ogbytorp landﬁll in * Corresponding author. Tel./fax: þ86 21 65986104. E-mail address: solidwaste@tongji.edu.cn (P. He). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2009.02.011 Atmospheric Environment 43 (2009) 2623–2631