Reference : Distribution and origin of suspended matter and organic carbon pools in the Tana River B...
Scientific journals : Article
Life sciences : Aquatic sciences & oceanology
http://hdl.handle.net/2268/128577
Distribution and origin of suspended matter and organic carbon pools in the Tana River Basin, Kenya
English
Tamooh, F []
Van den Meersche, K []
Meysman, F []
Marwick, TR []
Borges, Alberto mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Océanographie chimique >]
Merckx, R []
Dehairs, F []
Schmidt, S []
Nyunja, J []
Bouillon, S []
2012
Biogeosciences
European Geosciences Union
9
2905–2920
Yes (verified by ORBi)
International
1726-4170
Katlenburg-Lindau
Germany
[en] 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
1000m 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 ( 13CPOC)
ranged between −32 and −20‰and increased downstream,
reflecting an increasing contribution of C4-derived carbon
in combination with an expected shift in 13C for C3 vegetation
towards the more semi-arid lowlands. 13C 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. 13C 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.
Researchers ; Professionals ; Students
http://hdl.handle.net/2268/128577
10.5194/bg-9-2905-2012
http://www.biogeosciences.net/9/2905/2012/bg-9-2905-2012.html

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