Greenhouse gas fluxes over managed grasslands in Central Europe
Résumé
Central European grasslands are characterized by a wide range of different management practices
in close geographical proximity. Site-specific management strategies strongly affect the
biosphere-atmosphere exchange of the three greenhouse gases (GHG) carbon dioxide (CO2),
nitrous oxide (N2O) and methane (CH4). The evaluation of environmental impacts at site level is
challenging, because most in-situ measurements focus on the quantification of CO2 exchange,
while long-term N2O and CH4 flux measurements at ecosystem scale remain scarce.
Here, we synthesized ecosystem CO2, N2O and CH4 fluxes from 14 managed grassland sites,
quantified by eddy covariance or chamber techniques. We found that grasslands were on average
a CO2 sink (-1783 to -91 g CO2 m-2 yr-1), but a N2O source (18 – 638 g CO2-eq. m-2 yr-1), and
either a CH4 sink or source (-9 to 488 g CO2-eq. m-2 yr-1). The net GHG balance (NGB) of nine
sites where measurements of all three GHGs were available was found between -2761 and -58 g
CO2-eq. m-2 yr-1, with N2O and CH4 emissions offsetting concurrent CO2 uptake by on average
21 ± 6% across sites. The only positive NGB was found for one site during a restoration year with
ploughing. The predictive power of soil parameters for N2O and CH4 fluxes was generally low
and varied considerably within years. However, after site-specific data normalization we
identified environmental conditions that indicated enhanced GHG source/sink activity (‘sweet
spots’) and gave a good prediction of normalized overall fluxes across sites. The application of
animal slurry to grasslands increased N2O and CH4 emissions. The N2O-N emission factor across
sites was 1.8 ± 0.5%, but varied considerably at site level among the years (0.1 – 8.6%). Although
grassland management lead to increased N2O and CH4 emissions, the CO2 sink strength was
generally the most dominant component of the annual GHG budget.
Origine : Accord explicite pour ce dépôt
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