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| Titel |
Dissolved black carbon along the land to ocean continuum of Paraiba do Sul River, Brazil |
| VerfasserIn |
Jomar Marques da Silva Junior, Thorsten Dittmar, Jutta Niggemann, Marcelo Gomes de Almeida, Carlos Eduardo de Rezende |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250130283
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| Publikation (Nr.) |
 EGU/EGU2016-10518.pdf |
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| Zusammenfassung |
| Rivers annually carry 25-28 Tg of pyrogenic dissolved organic matter (or dissolved black
carbon, DBC) into the ocean, which is equivalent to about 10% of the entire land-ocean flux
of dissolved organic carbon (Jaffé et al., Science 340, 345-347). Objective of this study was
to identify the main processes behind the release and turnover of DBC on a riverine
catchment scale. As model system we chose the land to ocean continuum of Paraíba do Sul
River (Brazil), the only river system for which long-term DBC flux data exist (Dittmar,
Rezende et al., Nature Geoscience 5, 618-622). The catchment was originally covered by
Atlantic rain forest (mainly C3 plants) which was almost completely destroyed over the past
centuries by slash-and-burn. As a result, large amounts of wood-derived charcoal reside in the
soils. Today, fire-managed pasture and sugar cane (both dominated by C4 plants) cover
most of the catchment. Water samples were collected at 24 sites along the main
channel of the river, at 14 sites of the main tributaries and at 21 sites along the salinity
gradient in the estuary and up to 35 km offshore. Sampling was performed in the wet
seasons of 2013 and 2014, and the dry season of 2013. DBC was determined on a
molecular level as benzenepolycarboxylic acids after nitric acid oxidation (Dittmar,
Limnology and Oceanography: Methods 6, 230–235). Stable carbon isotopes (δ13C) were
determined in solid phase extractable dissolved organic carbon (SPE-DOC) to distinguish
C4 and C3 sources. Our results clearly show a relationship between hydrology
and DBC concentrations in the river, with highest DBC concentrations in the wet
season and lowest in the dry season. This relationship indicates that DBC is mainly
mobilized from the upper soil horizons during heavy rainfalls. A significant correlation
between DBC concentrations and δ13C-SPE-DOC indicated that most of DBC in the
river system originates from C3 plants, i.e. from the historic burning event of the
Atlantic rain forest. A simple mixing model could largely reproduce the observed
concentrations within the catchment and the land to ocean continuum. Thus, within
the river system and estuary, DBC concentrations behaved mainly conservatively. |
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