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| Titel |
Biogeochemical characterization of the riverine particulate organic matter transferred to the NW Mediterranean Sea |
| VerfasserIn |
M. Higueras, P. Kerhervé, A. Sanchez-Vidal, A. Calafat, W. Ludwig, M. Verdoit-Jarraya, S. Heussner, M. Canals |
| 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 ; 11, no. 1 ; Nr. 11, no. 1 (2014-01-10), S.157-172 |
| Datensatznummer |
250117111
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| Publikation (Nr.) |
 copernicus.org/bg-11-157-2014.pdf |
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| Zusammenfassung |
| A large amount of terrestrial organic matter is annually delivered by rivers
to the continental shelf, where this material is either degraded, buried or
transferred to the deep sea by hydrodynamic processes such as storms. The
relative amount of terrestrial organic matter in the marine sediments is
often determined by analysing the stable isotopes (δ13C and
δ15N) and the C / N ratio of organic matter because the various
particulate organic matter (POM) sources have distinct isotopic
compositions. With the objective to refine and better interpret POM sources
in the marine environment, we have characterized monthly terrestrial POM
delivered by eight rivers discharging to the NW Mediterranean Sea:
the Rhône, Hérault, Orb, Aude, Têt, Fluvià, Ter and Tordera rivers. These rivers were simultaneously sampled from November 2008 to
December 2009 and the concentrations of total suspended matter (TSM),
particulate organic carbon (POC) and nitrogen (PN), as well as their stable
isotopic ratios (δ13C and δ15N) were determined.
During the survey, three rainstorm events with winds coming from the E–NE and
the S–SE impacted the NW Mediterranean. Depending on the direction of
incoming winds, the fluvial response (amount of water discharge and TSM) was
different. Rivers draining the Alps (Rhône River) and Central Massif
(Hérault, Orb, and Aude rivers) were mostly impacted by rainstorms
associated with winds coming from the S–SE, while rivers draining the
Pyrenees (Têt, Fluvià, and Ter rivers) and the Montseny Massif
(Tordera River) were impacted by rainstorms associated with winds coming from
the E–NE. In addition, the spatial evolution of water discharges shows
a different hydrological regime of the Rhône River, with relatively
constant and high water stages and TSM concentrations when compared to
coastal rivers, characterized by long periods of low water stages. TSM
concentrations are positively correlated to water discharges (high water
flows resuspended riverbed sediments) but show an inverse relationship with
POC and PN relative contents (mostly due to dilution and by low availability
of light in river waters during flood events). TSM in most of the coastal
rivers have on average 2.5–3 times higher POC and PN mean contents than the
Rhône River (8.5 and 1.5%, respectively, for coastal rivers compared
to
3.6 and 0.5%, respectively, for the Rhône River). This discrepancy
may be caused by the long drought periods in small coastal Mediterranean
watersheds that enhance the eutrophication in studied coastal rivers. The
δ13C ratios of organic matter also reflect this discrepancy between
high and low water stages with values ranging from −33.2 to
−24.5‰. The enriched 13C values
(−26.3 ± 0.4‰ for the Rhône River and
−26.9 ± 1.2‰ for coastal rivers), measured during high
water stages, express mostly a mixture of terrestrial source (plant remains
and soils) whereas depleted 13C values (∼ −30‰)
associated with low water stages exhibit a source with predominant freshwater
algae. The high δ15N mean values (>8‰) found in
Têt, Ter and Tordera rivers may underline the importance of
denitrification processes as a consequence of the eutrophication and
anthropogenic impact. |
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