Freshwater Methane Emissions Offset the Continental Carbon Sink
Acornerstone of our understanding of the
contemporary global carbon cycle is that
the terrestrial land surface is an important
greenhouse gas (GHG) sink (1, 2). The global
land sink is estimated to be 2.6 T 1.7 Pg of C
year−1 (variability T range, excluding C emissions
because of deforestation) (1). Lakes, impoundments,
and rivers are parts of the terrestrial landscape,
but they have not yet been included in the
terrestrial GHG balance (3, 4). Available data
suggest, however, that freshwaters can be substantial
sources of CO2 (3, 5) and CH4 (6). Over time,
soil carbon reaches freshwaters by lateral hydrological
transport, where it can meet several fates,
including burial in sediments, further transport to
the sea, or evasion to the atmosphere as CO2 or
CH4 (7). CH4 emissions may be small in terms of
carbon, but CH4 is a more potent GHG than CO2
over century time scales. This study indicates that
global CH4 emissions expressed as CO2 equivalents
correspond to at least 25% of the estimated
terrestrial GHG sink.
Publication Date: 2011
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