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Greenhouse gas fluxes over managed grasslands in Central Europe

Hörtnagl, Lukas, Barthel, Matti, Buchmann, Nina, Eugster, Werner, Butterbach‐Bahl, Klaus, Díaz‐Pinés, Eugenio, Zeeman, Matthias, Klumpp, Katja, Kiese, Ralf, Bahn, Michael, Hammerle, Albin, Lu, Haiyan, Ladreiter‐Knauss, Thomas, Burri, Susanne, Merbold, Lutz
Global change biology 2018 v.24 no.5 pp. 1843-1872
animal manures, carbon dioxide, ecosystems, eddy covariance, emissions factor, environmental factors, environmental impact, grassland management, grasslands, greenhouse gas emissions, greenhouse gases, methane, nitrous oxide, plowing, prediction, soil, Central European region
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 (−1,783 to −91 g CO₂ m⁻² year⁻¹), but a N₂O source (18–638 g CO₂‐eq. m⁻² year⁻¹), and either a CH₄ sink or source (−9 to 488 g CO₂‐eq. m⁻² year⁻¹). The net GHG balance (NGB) of nine sites where measurements of all three GHGs were available was found between −2,761 and −58 g CO₂‐eq. m⁻² year⁻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 led to increased N₂O and CH₄ emissions, the CO₂ sink strength was generally the most dominant component of the annual GHG budget.