『Abstract
We present the first study of the Si isotopic composition of
dry season river waters from the Tana River, Kenya. Data encompasses
the entire river basin, with samples collected from headwaters
to the estuary, thereby capturing a salinity gradient. In the
headwaters, the isotopic signature is affected by climate, as
a result of its control on soil drainage and weathering. The δ30Si
signatures in the basin range from +0.69‰ up to +2.23‰. Signatures
are clearly affected by dams: an increase in δ30Si
ratios of 0.54‰ and a decrease in the dissolved Si (DSi) concentration
by 41% were observed downstream of the Masinga dam, the largest
of a succession of 5 hydroelectric dams. This reduction in Si
load is most likely due to increased diatom productivity as the
corresponding change in δ30Si signature is consistent
with the known fractionation by these organisms. The δ30Si
composition of waters entering the estuary is ca. +2‰ and DSi
concentrations are 349μM. In the estuary, the DSi concentrations
decrease linearly following the salinity, while the δ30Si
ratio remains stable, indicating the absence of processes affecting
the DSi pool for the studied range of salinity.
Keywords: Tana River; Chemical weathering; Silicon isotopes; Dam
impact; Silicon cycle』
1. Introduction
2. General study area settings
3. Methods
3.1. Sampling
3.2. Element analyses
3.3. isotopic analyses
3.4. Rainfall
4. Results
5. Discussion
5.1. Headwater regions
5.2. Impact of the dams
5.3. Estuary
6. Conclusion
Acknowledgments
References