Ciencia

Biogeosciences, 7, 2673–2694, 2010
www.biogeosciences.net/7/2673/2010/
doi:10.5194/bg-7-2673-2010
© Author(s) 2010. CC Attribution 3.0 License.

Biogeosciences

Spatial and temporal patterns of CH4 and N2O fluxes in terrestrial
ecosystems of North America during 1979–2008: application of a
global biogeochemistry model
H. Tian1,2 , X. Xu1,2 , M. Liu1,2 , W. Ren1,2 , C. Zhang1 , G. Chen1,2, and C. Lu1,2
1 Ecosystem

Dynamics and Global Ecology (EDGE) Laboratory, School of Forestry and Wildlife Sciences, Auburn
University, Auburn, AL, 36849, USA
2 International Center for Climate and Global Change Research, Auburn University, Auburn, AL, 36849, USA
Received: 16 March 2010 – Published in Biogeosciences Discuss.: 21 April 2010
Revised: 30 August 2010 – Accepted: 1 September2010 – Published: 10 September 2010

Abstract.
Continental-scale estimations of terrestrial
methane (CH4 ) and nitrous oxide (N2 O) fluxes over a long
time period are crucial to accurately assess the global balance of greenhouse gases and enhance our understanding and
prediction of global climate change and terrestrial ecosystem feedbacks. Using a process-based global biogeochemical model, theDynamic Land Ecosystem Model (DLEM),
we quantified simultaneously CH4 and N2 O fluxes in North
America’s terrestrial ecosystems from 1979 to 2008. During the past 30 years, approximately 14.69 ± 1.64 T g C a−1
(1 T g = 1012 g) of CH4 , and 1.94 ± 0.1 T g N a−1 of N2 O
were released from terrestrial ecosystems in North America. At the country level, both the US and Canada acted
as CH4 sources tothe atmosphere, but Mexico mainly oxidized and consumed CH4 from the atmosphere. Wetlands
in North America contributed predominantly to the regional
CH4 source, while all other ecosystems acted as sinks for atmospheric CH4 , of which forests accounted for 36.8%. Regarding N2 O emission in North America, the US, Canada,
and Mexico contributed 56.19%, 18.23%, and 25.58%, respectively, to thecontinental source over the past 30 years.
Forests and croplands were the two ecosystems that contributed most to continental N2 O emission. The inter-annual
variations of CH4 and N2 O fluxes in North America were
mainly attributed to year-to-year climatic variability. While
only annual precipitation was found to have a significant effect on annual CH4 flux, both mean annual temperature and
annualprecipitation were significantly correlated to annual

Correspondence to: H. Tian
(tianhan@auburn.edu)

N2 O flux. The regional estimates and spatiotemporal patterns of terrestrial ecosystem CH4 and N2 O fluxes in North
America generated in this study provide useful information
for global change research and policy making.

1

Introduction

Methane (CH4 ) and nitrous oxide (N2 O) are twopotent
greenhouse gases which in sum contribute to more than one
fourth of global warming caused by anthropogenic activities
(Forster et al., 2007). Although the concentrations of CH4
and N2 O in the atmosphere are relatively low, their warming potentials are much higher than that of carbon dioxide
(Denman et al., 2007). CH4 and N2 O also play significant
roles in ozone layer chemistry(Denman et al., 2007; Forster
et al., 2007). Similar to the increase of atmospheric CO2
concentration, the concentrations of these two gases dramatically increased since the Industrial Revolution (Forster et
al., 2007; Tueut et al., 2007; Rigby et al., 2008). Although
the importance of CH4 and N2 O emissions in changing the
Earth’s climate has been recognized, scientific community
has placed largeemphasis on the CO2 problem. Understanding and quantifying CH4 and N2 O fluxes in terrestrial ecosystems at large spatial scales, therefore, becomes an urgent task
for accurately predicting the future climate change (Rigby et
al., 2008; Forster et al., 2007; Sheldon and Barnhart, 2009).
Terrestrial ecosystems could act as either sources or sinks
for atmospheric CH4 and N2 O, depending on the...