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| Titel |
A halocarbon survey from a seagrass dominated subtropical lagoon, Ria Formosa (Portugal): flux pattern and isotopic composition |
| VerfasserIn |
I. Weinberg, E. Bahlmann, T. Eckhardt, W. Michaelis, R. Seifert |
| 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 ; 12, no. 6 ; Nr. 12, no. 6 (2015-03-17), S.1697-1711 |
| Datensatznummer |
250117863
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| Publikation (Nr.) |
 copernicus.org/bg-12-1697-2015.pdf |
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| Zusammenfassung |
In this study we report fluxes of chloromethane (CH3Cl), bromomethane
(CH3Br), iodomethane (CH3I), and bromoform (CHBr3) from two
sampling campaigns (summer and spring) in the seagrass dominated subtropical
lagoon Ria Formosa, Portugal. Dynamic flux chamber measurements were
performed when seagrass patches were either air-exposed or submerged.
Overall, we observed highly variable fluxes from the seagrass meadows and
attributed them to diurnal cycles, tidal effects, and the variety of possible
sources and sinks in the seagrass meadows. The highest emissions with up to
130 nmol m−2 h−1 for CH3Br were observed during tidal
changes, from air exposure to submergence and conversely. Furthermore, during
the spring campaign, the emissions of halocarbons were significantly elevated
during tidal inundation as compared to air exposure.
Accompanying water sampling performed during both campaigns revealed elevated
concentrations of CH3Cl and CH3Br, indicating productive sources
within the lagoon. Stable carbon isotopes of halocarbons from the air and
water phase along with source signatures were used to allocate the
distinctive sources and sinks in the lagoon. Results suggest that CH3Cl
was rather originating from seagrass meadows and water column than from salt
marshes. Aqueous and atmospheric CH3Br was substantially enriched in
13C in comparison to source signatures for seagrass meadows and salt
marshes. This suggests a significant contribution from the water phase on
the atmospheric CH3Br in the lagoon.
A rough global upscaling yields annual productions from seagrass meadows of
2.3–4.5 Gg yr−1, 0.5–1.0 Gg yr−1, 0.6–1.2 Gg yr−1,
and 1.9–3.7 Gg yr−1 for CH3Cl, CH3Br, CH3I, and
CHBr3 respectively. This suggests a minor contribution from seagrass
meadows to the global production of CH3Cl and CH3Br with about 0.1
and 0.7%, respectively. In comparison to the known marine sources
for CH3I and CHBr3, seagrass meadows are rather small sources. |
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