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| Titel |
Dynamics of dissolved inorganic carbon and aquatic metabolism in the Tana River basin, Kenya |
| VerfasserIn |
F. Tamooh, A. V. Borges, F. J. R. Meysman, K. Meersche, F. Dehairs, R. Merckx, S. Bouillon |
| 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. 11 ; Nr. 10, no. 11 (2013-11-04), S.6911-6928 |
| Datensatznummer |
250085391
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| Publikation (Nr.) |
 copernicus.org/bg-10-6911-2013.pdf |
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| Zusammenfassung |
| A basin-wide study was conducted in the Tana River basin (Kenya) in February
2008 (dry season), September–November 2009 (wet season) and June–July 2010
(end of the wet season) to assess the dynamics and sources of dissolved
inorganic carbon (DIC) as well as to quantify CO2 fluxes, community
respiration (R), and primary production (P). Samples were collected along
the altitudinal gradient (from 3600 to 8 m) in several headwater streams,
reservoirs (Kamburu and Masinga), and the Tana River mainstream. DIC
concentrations ranged from 0.2 to 4.8 mmol L−1, with exceptionally
high values (3.5 ± 1.6 mmol L−1) in Nyambene Hills tributaries.
The wide range of δ13CDIC values (−15.0 to
−2.4‰) indicate variable sources of DIC, with headwater streams
recording more positive signatures compared to the Tana River mainstream.
With with only a few exceptions, the entire riverine network was
supersaturated in CO2, implying the system is a net source of CO2
to the atmosphere. pCO2 values were generally higher in the lower Tana
River mainstream compared to headwater tributaries, opposite to the pattern
typically observed in other river networks. This was attributed to high
suspended sediment in the Tana River mainstream fuelling in-stream community
respiration and net heterotrophy. This was particularly evident during the
2009 wet season campaign (median pCO2 of 1432 ppm) compared to the
2010 end of the wet season (1002 ppm) and 2008 dry season (579 ppm).
First-order estimates show that in-stream community respiration was
responsible for the bulk of total CO2 evasion (77 to 114%) in the
Tana River mainstream, while in the tributaries, this could only account for
5 to 68% of total CO2 evasion. This suggests that CO2 evasion
in the tributaries was to a substantial degree sustained by benthic
mineralisation and/or lateral inputs of CO2-oversaturated groundwater.
While sediment loads increased downstream and thus light availability
decreased in the water column, both chlorophyll a (0.2 to
9.6 μg L−1) and primary production (0.004 to
7.38 μmol C L−1 h−1) increased consistently
downstream. Diurnal fluctuations of biogeochemical processes were examined at
three different sites along the river continuum (headwater, reservoir and
mainstream), and were found to be substantial only in the headwater stream,
moderate in the reservoir and not detectable in the Tana River mainstream.
The pronounced diurnal fluctuations observed in the headwater stream were
largely regulated by periphyton as deduced from the low chlorophyll a in
the water column. |
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