Distribution, origin and cycling of carbon in the Tana River (Kenya): a dry season basin-scale survey from headwaters to the delta
The Tana River basin (TRB) is the largest in Kenya (~120 000 km<sup>2</sup>). We conducted a survey during the dry season throughout the TRB, analyzing a broad suite of biogeochemical parameters. Biogeochemical signatures in headwater streams were highly variable. Along t...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2009-11-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/6/2475/2009/bg-6-2475-2009.pdf |
| Summary: | The Tana River basin (TRB) is the largest in Kenya (~120 000 km<sup>2</sup>). We conducted a survey during the dry season throughout the TRB, analyzing a broad suite of biogeochemical parameters. Biogeochemical signatures in headwater streams were highly variable. Along the middle and lower river course, total suspended matter (TSM) concentrations increased more than 30-fold despite the absence of tributary inputs, indicating important resuspension events of internally stored sediment. These resuspended sediment inputs were characterized by a lower and <sup>14</sup>C-depleted OC content, suggesting selective degradation of more recent material during sediment retention. Masinga Dam (a large reservoir on the upper river) induced a strong nutrient retention (~50% for inorganic N, ~72% for inorganic phosphate, and ~40% for dissolved silicate). Moreover, while DOC pools and δ<sup>13</sup>C signatures were similar above, in and below the reservoir, the POC pool in Masinga surface waters was dominated by <sup>13</sup>C-depleted phytoplankton, which contributed to the riverine POC pool immediately below the dam, but rapidly disappeared further downstream, suggesting rapid remineralization of this labile C pool in the river system. Despite the generally high turbidity, the combination of relatively high oxygen saturation levels, low δ<sup>18</sup>O signatures of dissolved O<sub>2</sub> (all &lt;+24.2&permil;), and the relatively low <i>p</i>CO<sub>2</sub> values suggest that in-stream primary production was significant, even though pigment data suggest that phytoplankton makes only a minor contribution to the total POC pool in the Tana River. |
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| ISSN: | 1726-4170 1726-4189 |