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| Titel |
Organic carbon and nitrogen export from a tropical dam-impacted floodplain system |
| VerfasserIn |
R. Zurbrügg, S. Suter, M. F. Lehmann, B. Wehrli, D. B. Senn |
| 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 ; 10, no. 1 ; Nr. 10, no. 1 (2013-01-04), S.23-38 |
| Datensatznummer |
250007909
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| Publikation (Nr.) |
 copernicus.org/bg-10-23-2013.pdf |
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| Zusammenfassung |
| Tropical floodplains play an important role in organic matter transport,
storage, and transformation between headwaters and oceans. However, the
fluxes and quality of organic carbon (OC) and organic nitrogen (ON) in
tropical river-floodplain systems are not well constrained. We explored the
quantity and characteristics of dissolved and particulate organic matter
(DOM and POM, respectively) in the Kafue River flowing through the Kafue
Flats (Zambia), a tropical river-floodplain system in the Zambezi River
basin. During the flooding season, > 80% of the Kafue River
water passed through the floodplain, mobilizing large quantities of OC and
ON, which resulted in a net export of 69–119 kg OC km−2 d−1 and
3.8–4.7 kg ON km−2 d−1, 80% of which was in the dissolved form.
The elemental C : N ratio of ~ 20, the comparatively high
δ13C values of −25‰ to
−21‰, and its spectroscopic properties
(excitation-emission matrices) showed that DOM in the river was mainly of
terrestrial origin. Despite a threefold increase in OC loads due to inputs
from the floodplain, the characteristics of the riverine DOM remained
relatively constant along the sampled 410-km river reach. This suggests that
floodplain DOM displayed properties similar to those of DOM leaving the
upstream reservoir and implied that the DOM produced in the reservoir was
relatively short-lived. In contrast, the particulate fraction was
13C-depleted (−29‰) and had a C : N ratio of
~ 8, which indicated that POM originated from phytoplankton
production in the reservoir and in the floodplain, rather than from plant
debris or resuspended sediments. While the upstream dam had little effect on
the DOM pool, terrestrial particles were retained, and POM from algal and
microbial sources was released to the river. A nitrogen mass balance over
the 2200 km2 flooded area revealed an annual deficit of 15 500–22 100 t N
in the Kafue Flats. The N isotope budget suggests that these N losses are
balanced by intense N-fixation. Our study shows that the Kafue Flats are a
significant local source of OC and ON to downstream ecosystems and
illustrates how the composition of riverine OM can be altered by dams and
floodplains in tropical catchments. |
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