 |
| Titel |
Distribution and origin of suspended matter and organic carbon pools in the Tana River Basin, Kenya |
| VerfasserIn |
F. Tamooh, K. Meersche, F. Meysman, T. R. Marwick, A. V. Borges, R. Merckx, F. Dehairs, S. Schmidt, J. Nyunja, S. Bouillon |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 8 ; Nr. 9, no. 8 (2012-08-02), S.2905-2920 |
| Datensatznummer |
250007225
|
| Publikation (Nr.) |
 copernicus.org/bg-9-2905-2012.pdf |
|
|
|
|
|
| Zusammenfassung |
| We studied patterns in organic carbon pools and their origin in the Tana
River Basin (Kenya), in February 2008 (dry season), September–November 2009
(wet season), and June–July 2010 (end of wet season), covering the full
continuum from headwater streams to lowland mainstream sites. A consistent
downstream increase in total suspended matter (TSM, 0.6 to
7058 mg l−1 and particulate organic carbon (POC, 0.23 to
119.8 mg l−1 was observed during all three sampling campaigns,
particularly pronounced below 1000 m above sea level, indicating that most
particulate matter exported towards the coastal zone originated from the mid
and low altitude zones rather than from headwater regions. This indicates
that the cascade of hydroelectrical reservoirs act as an extremely efficient
particle trap. Although 7Be / 210Pbxs ratios/age of
suspended sediment do not show clear seasonal variation, the gradual
downstream increase of suspended matter during end of wet season suggests its
origin is caused by inputs of older sediments from bank erosion and/or river
sediment resuspension. During wet season, higher TSM concentrations
correspond with relatively young suspended matter, suggesting a contribution
from recently eroded material. With the exception of reservoir waters, POC
was predominantly of terrestrial origin as indicated by generally high
POC : chlorophyll a (POC : Chl a) ratios (up to ~41 000).
Stable isotope signatures of POC (δ13CPOC ranged
between −32 and −20‰ and increased downstream, reflecting an
increasing contribution of C4-derived carbon in combination with an expected
shift in δ13C for C3 vegetation towards the more semi-arid
lowlands. δ13C values in sediments from the main reservoir
(−19.5 to −15.7‰) were higher than those found in any of the
riverine samples, indicating selective retention of particles associated with
C4 fraction. Dissolved organic carbon (DOC) concentrations were highest
during the end of wet season (2.1 to 6.9 mg l−1), with stable
isotope signatures generally between −28 and −22‰. A consistent
downstream decrease in % organic carbon (%OC) was observed for soils,
riverine sediments, and suspended matter. This was likely due to better
preservation of the organic fraction in colder high altitude regions, with
loss of carbon during downstream spiraling. δ13C values for soil
and sediment did not exhibit clear altitudinal patterns, but values reflect
the full spectrum from C3-dominated to C4-dominated sites. Very low ratios of
organic carbon to mineral surface area (OC : SA) were found in reservoir
sediments and suspended matter in the lower Tana River, indicating that these
are stable OC pools which have undergone extensive degradation. Overall, our
study demonstrates that substantial differences occur in both the quantities
and origin of suspended sediments and organic carbon along the river profile
in this tropical river basin, as well as seasonal differences in the
mechanisms causing such variations. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|