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| Titel |
Environmental assessment of biofuel chains based on ecosystem modelling, including land-use change effects |
| VerfasserIn |
B. Gabrielle, N. Gagnaire, R. Massad, V. Prieur, Y. Python |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068456
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| Zusammenfassung |
| The potential greenhouse gas (GHG) savings resulting from the displacement of fossil energy
sources by bioenergy mostly hinges on the uncertainty on the magnitude of nitrous oxide
(N2O) emissions from arable soils occuring during feedstock production. These emissions are
broadly related to fertilizer nitrogen input rates, but largely controlled by soil and climate
factors which makes their estimation highly uncertain.
Here, we set out to improve estimates of N2O emissions from bioenergy feedstocks by using
ecosystem models and measurements and modeling of atmospheric N2O in the greater Paris
(France) area. Ground fluxes were measured in two locations to assess the effect of soil type
and management, crop type (including lignocellulosics such as triticale, switchgrass and
miscanthus), and climate on N2O emission rates and dynamics. High-resolution maps of N2O
emissions were generated over the Ile-de-France region (around Paris) with two ecosystem
models using geographical databases on soils, weather data, land-use and crop
management. The models were tested against ground flux measurements and the emission
maps were fed into the atmospheric chemistry-transport model CHIMERE. The
maps were tested by comparing the CHIMERE simulations with time series of N2O
concentrations measured at various heights above the ground in two locations in
2007.
The emissions of N2O, as integrated over the region, were used in a life-cycle assessment of
representative biofuel pathways: bioethanol from wheat and sugar-beet (1st generation), and
miscanthus (2nd generation chain); bio-diesel from oilseed rape. Effects related to direct and
indirect land-use changes (in particular on soil carbon stocks) were also included in the
assessment based on various land-use scenarios and literature references. The potential
deployment of miscanthus was simulated by assuming it would be grown on the current
sugar-beet growing area in Ile-de-France, or by converting land currently under permanent
fallow.
Compared to the standard methodology currently used in LCA, based on fixed emissions for
N2O, the use of model-derived estimates leads to a 10 to 40% reduction in the overall
life-cycle GHG emissions of biofuels. This emphasizes the importance of regional factors in
the relationship between agricultural inputs and emissions (altogether with biomass yields) in
the outcome of LCAs. When excluding indirect land-use change effects (iLUC), 1st
generation pathways enabled GHG savings ranging from 50 to 73% compared to
fossile-derived equivalents, while this figure reached 88% for 2nd generation bioethanol from
miscanthus. Including iLUC reduced the savings to less than 5% for bio-diesel from
rapeseed, 10 to 45% for 1st generation bioethanol and to 60% for miscanthus. These figures
apply to the year 2007 and should be extended to a larger number of years, but the magnitude
of N2O emissions was similar between 2007, 2008 and 2009 over the Ile de France region. |
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