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| Titel |
Ecosystem-scale compensation points of formic and acetic acid in the central Amazon |
| VerfasserIn |
K. Jardine, A. Yañez Serrano, A. Arneth, L. Abrell, A. Jardine, P. Artaxo, E. Alves, J. Kesselmeier, T. Taylor, S. Saleska, T. Huxman |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 12 ; Nr. 8, no. 12 (2011-12-16), S.3709-3720 |
| Datensatznummer |
250006251
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| Publikation (Nr.) |
 copernicus.org/bg-8-3709-2011.pdf |
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| Zusammenfassung |
| Organic acids, central to terrestrial carbon metabolism and atmospheric
photochemistry, are ubiquitous in the troposphere in the gas, particle, and
aqueous phases. As the dominant organic acids in the atmosphere, formic acid
(FA, HCOOH) and acetic acid (AA, CH3COOH) control precipitation acidity
in remote regions and may represent a critical link between the terrestrial
carbon and water cycles by acting as key intermediates in plant carbon and
energy metabolism and aerosol-cloud-precipitation interactions. However, our
understanding of the exchange of these acids between terrestrial ecosystems
and the atmosphere is limited by a lack of field observations, the existence
of biogenic and anthropogenic primary and secondary sources whose relative
importance is unclear, and the fact that vegetation can act as both a source
and a sink. Here, we first present data obtained from the tropical
rainforest mesocosm at Biosphere 2 which isolates primary vegetation
sources. Strong light and temperature dependent emissions enriched in FA
relative to AA were simultaneously observed from individual branches (FA/AA = 3.0 ± 0.7) and mesocosm ambient air (FA/AA = 1.4 ± 0.3). We also
present long-term observations of vertical concentration gradients of FA and
AA within and above a primary rainforest canopy in the central Amazon during
the 2010 dry and 2011 wet seasons. We observed a seasonal switch from net
ecosystem-scale deposition during the dry season to net emissions during the
wet season. This switch was associated with reduced ambient concentrations
in the wet season (FA < 1.3 nmol mol−1, AA < 2.0 nmol mol−1)
relative to the dry season (FA up to 3.3 nmol mol−1, AA up to
6.0 nmol mol−1), and a simultaneous increase in the FA/AA ambient concentration
ratios from 0.3–0.8 in the dry season to 1.0–2.1 in the wet season. These
observations are consistent with a switch between a biomass burning
dominated source in the dry season (FA/AA < 1.0) to a vegetation dominated
source in the wet season (FA/AA > 1.0). Our observations provide the first
ecosystem-scale evidence of bidirectional FA and AA exchange between a
forest canopy and the atmosphere controlled by ambient concentrations and
ecosystem scale compensation points (estimated to be 1.3 ± 0.3 nmol mol−1:
FA, and 2.1 ± 0.4 nmol mol−1: AA). These results suggest
the need for a fundamental change in how future biosphere-atmosphere
exchange models should treat FA and AA with a focus on factors that
influence net exchange rates (ambient concentrations and ecosystem
compensation points) rather than treating emissions and deposition
separately. |
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