Daniel Conley
Professor
Tracing silicon cycling in the Okavango Delta, a sub-tropical flood-pulse wetland using silicon isotopes
Author
Summary, in English
Chemical weathering of silicate minerals releases elements into solution whereas the neoformation of secondary minerals
works in the opposite direction, potentially confounding estimates of silicate weathering rates. Silicon isotopes (d30Si) may be
a useful tool to investigate these processes. Here, we present 82 d30Si measurements from surface waters, pore waters, biogenic
silica (BSi), clays, sand and vegetation from the Okavango Delta, Botswana, a freshwater sub-tropical, flood-pulse wetland.
Hydrologically, the Okavango is dominated by evapotranspiration water losses to the atmosphere. It receives an annual pulse
of water that inundates seasonal floodplains, while river baseflow is sufficient to maintain a permanent floodplain. d30Si in
dissolved silica (DSi) in surface waters along a 300 km transect at near-peak flood show a limited range (0.36–1.19&), imply-
ing the Delta is well buffered by a balance of processes adding and removing DSi from the surface water. A key control on DSi
concentrations is the uptake, production of BSi and recycling of Si by aquatic vegetation, although the net isotopic effect is
necessarily small since all BSi re-dissolves on short timescales. In the sediments, BSi d30Si (n = 30) ranges from
works in the opposite direction, potentially confounding estimates of silicate weathering rates. Silicon isotopes (d30Si) may be
a useful tool to investigate these processes. Here, we present 82 d30Si measurements from surface waters, pore waters, biogenic
silica (BSi), clays, sand and vegetation from the Okavango Delta, Botswana, a freshwater sub-tropical, flood-pulse wetland.
Hydrologically, the Okavango is dominated by evapotranspiration water losses to the atmosphere. It receives an annual pulse
of water that inundates seasonal floodplains, while river baseflow is sufficient to maintain a permanent floodplain. d30Si in
dissolved silica (DSi) in surface waters along a 300 km transect at near-peak flood show a limited range (0.36–1.19&), imply-
ing the Delta is well buffered by a balance of processes adding and removing DSi from the surface water. A key control on DSi
concentrations is the uptake, production of BSi and recycling of Si by aquatic vegetation, although the net isotopic effect is
necessarily small since all BSi re-dissolves on short timescales. In the sediments, BSi d30Si (n = 30) ranges from
Department/s
- Quaternary Sciences
Publishing year
2014
Language
English
Pages
132-148
Publication/Series
Geochimica et Cosmochimica Acta
Volume
142
Full text
Document type
Journal article
Publisher
Elsevier
Topic
- Geology
Status
Published
ISBN/ISSN/Other
- ISSN: 0016-7037