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| Titel |
Importance of intertidal sediment processes and porewater exchange on the water column biogeochemistry in a pristine mangrove creek (Ras Dege, Tanzania) |
| VerfasserIn |
S. Bouillon, J. J. Middelburg, F. Dehairs, A. V. Borges, G. Abril, M. R. Flindt, S. Ulomi, E. Kristensen |
| 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 ; 4, no. 3 ; Nr. 4, no. 3 (2007-06-12), S.311-322 |
| Datensatznummer |
250001728
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| Publikation (Nr.) |
 copernicus.org/bg-4-311-2007.pdf |
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| Zusammenfassung |
| We sampled a tidal creek (Ras Dege, Tanzania) during a 24-h cycle to
document the variations in a suite of creek water column characteristics and
to determine the relative influence of tidal and biological driving forces.
Since the creek has no upstream freshwater inputs, highest salinity was
observed at low tide, due to evaporation effects and porewater seepage.
Total suspended matter (TSM) and particulate organic carbon (POC) showed
distinct maxima at periods of highest water flow, indicating that erosion of
surface sediments and/or resuspension of bottom sediments were an important
source of particulate material. Dissolved organic carbon (DOC), in contrast,
varied in phase with water height and was highest at low tide. Stable
isotope data of POC and DOC displayed large variations in both pools, and
similarly followed the variations in water height. Although the variation of
δ13CDOC (−23.8 to −13.8‰) was higher than that of δ13CPOC (−26.2 to −20.5‰), due to the different end-member pool
sizes, the δ13C signatures of both pools differed only slightly
at low tide, but up to 9‰ at high tide. Thus, at low tide both DOC and POC
originated from mangrove production. At high tide, however, the DOC pool had
signatures consistent with a high contribution of seagrass-derived material,
whereas the POC pool was dominated by marine phytoplankton. Daily variations
in CH4, and partial pressure of CO2 (pCO2) were similarly
governed by tidal influence and were up to 7- and 10-fold higher at low
tide, which stresses the importance of exchange of porewater and diffusive
fluxes to the water column. When assuming that the high dissolved inorganic
carbon (DIC) levels in the upper parts of the creek (i.e. at low tide) are
due to inputs from mineralization, δ13C data on DIC indicate
that the organic matter source for mineralization had a signature of
−22.4‰. Hence, imported POC and DOC from the marine environment contributes
strongly to overall mineralization within the mangrove system. Our data
demonstrate how biogeochemical processes in the intertidal zone appear to be
prominent drivers of element concentrations and isotope signatures in the
water column, and how pathways of dissolved and particulate matter transport
are fundamentally different. |
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