 |
| Titel |
Influence of distributary channels on sediment and organic matter supply in event-dominated coastal margins: the Po prodelta as a study case |
| VerfasserIn |
T. Tesi, S. Miserocchi, M. A. Goñi, M. Turchetto, L. Langone, A. Lazzari, S. Albertazzi, A. Correggiari |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 2 ; Nr. 8, no. 2 (2011-02-15), S.365-385 |
| Datensatznummer |
250005448
|
| Publikation (Nr.) |
 copernicus.org/bg-8-365-2011.pdf |
|
|
|
|
|
| Zusammenfassung |
From November 2008 through May 2009, the Po river (Italy) experienced
several floods exceeding 5000 m3 s−1. This long series of events
ended with a large flood in early May 2009 (~8000 m3 s−1).
An event-response sampling was carried out in the Po prodelta in April–May 2009
to characterize the preservation of this series of floods in the sediment record
and to describe the event-supply and deposition of riverborne particulate material
during the May 2009 flood. The water sampling was carried out early in the event
under conditions of moderate river flow (~5000 m3 s−1) and 24 h later
during the peak discharge (~8000 m3 s−1). Sediment cores were collected
in the prodelta before and after the peak flood. At each station, profiles of conductivity,
transmittance, and fluorescence were acquired. Surface and bottom waters were sampled
to collect sediments in suspension. In addition, a few days before the May 2009 event,
suspended sediments were collected at Pontelagoscuro gauging station, ~90 km
upstream from the coast. Biogeochemical compositions and sedimentological
characteristics of suspended and sediment samples were investigated using
bulk and biomarker analyses. Furthermore, 7Be and radiographs were used
to analyze the internal stratigraphy of sediment cores.
During moderate flow, the water column did not show evidence of plume
penetration. Stations re-occupied 24 h later exhibited marked physical and
biogeochemical changes during the peak flood. However, the concentration of
terrestrially-derived material in surface waters was still less than
expected. These results suggested that, since material enters the Adriatic
as buoyancy-driven flow with a reduced transport capacity, settling and
flocculation processes result in trapping a significant fraction of
land-derived material in shallow sediments and/or within distributary
channels.
Although numerous discharge peaks occurred from November 2008 through April
2009 (4000–6000 m3 s−1), sediment cores collected in late April 2009 showed lack of
event-strata preservation and reduced 7Be penetrations. This suggested
that only a small fraction of the sediment supply during ordinary
events reaches the deepest region of the prodelta (12–20 m water depth). As
a result, these event-strata have a thickness not sufficient to be preserved
in the sediment record because of post-depositional processes that destroy
the flood signal.
Stations in the northern and central prodelta were re-occupied after the
peak of the May 2009 flood. Based on 7Be and radiographs, we estimated
event layers of 17 and 6 cm thickness, respectively. Selective trapping of
coarse material occurred in the central prodelta likely because of the
geomorphologic setting of the central outlet characterized by an
estuary-like mouth. Despite these settling processes, lignin-based
parameters indicated that the composition of the terrigenous OC was fairly
homogenous throughout the network of channels and between size-fractions. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|