Atmospheric nitrogen deposition causes indirect NO and N2O emissions in (semi-)natural ecosystems

Tobias Bühlmann (University of Basel)

Beat Achermann (FOEN)Simon Liechti (FOEN)

Beat Rihm (Meteotest)Erika Hiltbrunner (University of Basel)Christian Körner (University of Basel)

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Indirect N2O and N emissions

• (Semi-)natural ecosystems are used extensively only or not at all; no net N input besides atmospheric N deposition

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Total atmospheric N deposition (wet + dry) 2010

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Exceedance of CLN

• Correlation between atmospheric N deposition and NO/N2O emission (Butterbach et al. 1998)

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Today’s methods

• Indirect N2O emissions (Guidelines for National Greenhouse Gas Inventories 2006, IPCC)

– N2O-N = (NH3-N + NOx-N emissions) x EF4

• EF4 = 1%

• Indirect NO emissions (Emission Inventory Guidebook 2013, EMEP/EEA)

– Simpler methodology (Skiba et al. 1997)

• NO = N input x EFNOx + 0.1 ng NO-N m-2 s-1

– EFNOx = 0.3%

– Detailed methodology (Novak and Pierce 1993)

• Not suitable for annual emissions

• Attention: EF4 and EFNOx are based on agriculture data only

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Methods

• Aim: Calculate indirect NO and N2O emissions of Swiss (semi-)natural ecosystems

– EMEP/EEA and IPCC compatibility: “Activity x EF”

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Methods

• Literature research– Studies measuring NO or N2O emission in (semi-)natural

ecosystems• Total N deposition known (measured or modelled)• Similar climatic conditions as Switzerland• Long time measurements• No fertilizer, no N2-fixing plants

• N deposition dependent emission rates- SWC, soil pH, soil temperature etc. could not be involved in

analyses

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Results & discussion

• 57 N2O long-term emission measurements

• N deposition inducessignificant N2O emissions;confirmed byMachefert et al. 2002and Skiba et al. 2012

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Bühlmann et al. 2015

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Results & discussion

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• 16 NO long-term emission measurements

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Results & discussion

• Emission rates differ between (semi-)natural ecosystems (Bühlmann et al. 2015; Groffman et al. 2000)

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de.wikipedia.org

N2O NO

N2

O NO

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Results & discussion

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Stehfest and Bouwman 2006

N input

EFN2O-N:0.9 %

EFNO-N:0.6 %

N input

EFN2O-N:3.7 %

EFNO-N:12.5 %

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Application

• Calculation of ecosystem specific indirect NO and N2O emissions– Indirect N emission = N deposition x emission rate– Ecosystem specific emission rate (this study)

• Ecosystem type: Land Use Statistics, WMG-100– 100 m resolution

– N deposition (Meteotest)• 100 m resolution, for the years 1990, 2000, 2007, 2010

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Results & discussion

• Indirect N2O emissions of (semi-)natural ecosystems

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Bühlmann et al. 2015

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Results & discussion

• Indirect NO emissions of (semi-)natural ecosystems

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Bühlmann et al. 2015

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Results & discussion

• Indirect N2O emissions of (semi-)natural ecosystems for the year 2000

• IPCC approach underestimates N2O emissions of (semi-) natural ecosystems in Switzerland

• In 2010 21 % of the total N2O emission were emitted from (semi-)natural ecosystems

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N2O (Gg N)This study

N2O (Gg N)IPCC (modified)

N2O (Gg N)Kesik et al. 2005

Forests 1.45 ± 0.40 0.18 0.75

Grass- and wetlands 0.24 ± 0.04 0.03 -

total 1.69 ± 0.34 0.21 -

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Results & discussion

• Indirect NO emissions of (semi-)natural ecosystems for the year 2000

• EMEP/EEA approach underestimates NOx emissions of (semi-) natural ecosystems in Switzerland

• In 2010 10 % of the total NOx emission were emitted from (semi-)natural ecosystems

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NO (Gg N)This study

NO (Gg N)EMEP/EAA

NO (Gg N)Kesik et al. 2005

Forests 2.56 ± 0.64 0.06 0.58

Grass- and wetlands 0.03 ± 0.04 0.03 -

total 2.61 ± 0.55 0.09 -

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Conclusion

• Indirect N2O and NO emissions from (semi-)natural ecosystems are substantial.

• EFs for indirect N emissions differ between ecosystems.– EFs for agricultural land are unsuitable for (semi-)natural

ecosystems.

• Indirect N2O and NO emissions of (semi-)natural ecosystems are currently underestimated by the international approaches.– High uncertainty for NO emissions.

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Acknowledgements

• University of Basel– Erika Hiltbrunner, Christian Körner

• FOEN– Beat Achermann, Richard Ballaman, Martin Schiess, Simon

Liechti

• Meteotest– Beat Rihm

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Application in emission inventories

• indEmistotal = indEmis(semi-)nat. ecosystems + indEmisrest

• N deposition missing in emission inventories– Relate indirect emissions of (semi-)natural ecosystems to

the sum of direct NOx-N and NH3-N emissions Efemis

• Switzerland– Indirect N2O emissions are calculated for direct emissions

of agriculture only.

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Application of results: NO

• Indirect NO emissionsNOind. = NOind. nat. ecosystems + NOind. rest

= Activity x EFnat. Ecosystems + activity x EFNOx

= Activity x (EFnat. Ecosystems + EFNOx)

• Activity = sum of national NOx-N and NH3-N emissions

• EFnat. ecosystems = (NO-Nnat. ecosystems)/(sum of national NOx-N and NH3-N emissions)– Available for the years 1990, 2000, 2007, 2010– Only valid for Switzerland!

• EFNOx = (NO-Nrest)/(sum of national NOx-N and NH3-N emissions)

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Application of results: N2O

• Indirect N2O emissionsN2Oind. = N2Oind. nat. ecosystems + N2Oind. rest

= Activity x EFnat. Ecosystems + activity x EF4 x 0.543

• Activity = sum of national NOx-N and NH3-N emissions

• EFnat. ecosystems = (N2O-Nnat. ecosystems)/(sum of national NOx-N and NH3-N emissions)– Available for the years 1990, 2000, 2007, 2010– Only valid for Switzerland!

• EF4 = 0.01

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