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Biogenic Si analysis in volcanically imprinted lacustrine systems: the case of Lake Rutundu (Mt. Kenya)

(2015) BIOGEOCHEMISTRY. 125(2). p.243-259
Author
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Abstract
Diatoms are important primary producers in lake ecosystems and, as a sink for dissolved (DSi) and biogenic silica (BSi) originating from land, can significantly impact the global Si cycle. After burial in lake sediments, resistant diatom frustules can also be used for reconstructions of past ecosystem change. The BSi content of lake sediments is thus often used as a proxy for past diatom productivity, and measured using a time-step analysis of Si extracted in 0.1 M Na2CO3. However, studies in soils and ocean sediments have shown that also certain non-biogenic Si fractions are prone to dissolve in alkaline solutions, contributing to a potential overestimate of sedimentary BSi concentration. In lakes, volcanic and terrestrial Si compounds reactive at high pH are likely to interfere with the analysis. In this study we used a continuous analysis of Si and Al extracted in 0.5 M NaOH and a new mathematical model improved from Koning et al. (Aquat Geochem 8:37-67, 2002) to distinguish between biogenic and non-biogenic Si fractions in lake-sediment extracts. We tested this approach in 43 samples of a 19,000-year sediment sequence recovered from Lake Rutundu, a volcanic crater lake on Mt. Kenya. Our results show that a significant fraction of the extractable Si is of non-biogenic origin, especially in the part of the sequence deposited during the glacial period. We conclude that this technique is essential for the characterization of different Si phases, and in particular the diatom-derived BSi, in the sediment of lakes situated in volcanic catchments. It allows calculating a correction, based on the distinct Si:Al ratio of each of those Si phases, that eliminates the contribution from non-BSi fractions.
Keywords
Lakes, Diatoms, Volcanic interference, Continuous analysis, Alkaline extractions, LATE QUATERNARY CHANGES, LAND-USE CHANGE, EAST-AFRICA, ORGANIC-MATTER, CLIMATE VARIABILITY, ISOTOPE COMPOSITION, MARINE-SEDIMENTS, DIATOM SILICA, MOUNT-KENYA, RECORD

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Citation

Please use this url to cite or link to this publication:

MLA
Barão, Lúcia et al. “Biogenic Si Analysis in Volcanically Imprinted Lacustrine Systems: The Case of Lake Rutundu (Mt. Kenya).” BIOGEOCHEMISTRY 125.2 (2015): 243–259. Print.
APA
Barão, L., De Cort, G., Meire, P., Verschuren, D., & Struyf, E. (2015). Biogenic Si analysis in volcanically imprinted lacustrine systems: the case of Lake Rutundu (Mt. Kenya). BIOGEOCHEMISTRY, 125(2), 243–259.
Chicago author-date
Barão, Lúcia, Gijs De Cort, Patrick Meire, Dirk Verschuren, and Eric Struyf. 2015. “Biogenic Si Analysis in Volcanically Imprinted Lacustrine Systems: The Case of Lake Rutundu (Mt. Kenya).” Biogeochemistry 125 (2): 243–259.
Chicago author-date (all authors)
Barão, Lúcia, Gijs De Cort, Patrick Meire, Dirk Verschuren, and Eric Struyf. 2015. “Biogenic Si Analysis in Volcanically Imprinted Lacustrine Systems: The Case of Lake Rutundu (Mt. Kenya).” Biogeochemistry 125 (2): 243–259.
Vancouver
1.
Barão L, De Cort G, Meire P, Verschuren D, Struyf E. Biogenic Si analysis in volcanically imprinted lacustrine systems: the case of Lake Rutundu (Mt. Kenya). BIOGEOCHEMISTRY. 2015;125(2):243–59.
IEEE
[1]
L. Barão, G. De Cort, P. Meire, D. Verschuren, and E. Struyf, “Biogenic Si analysis in volcanically imprinted lacustrine systems: the case of Lake Rutundu (Mt. Kenya),” BIOGEOCHEMISTRY, vol. 125, no. 2, pp. 243–259, 2015.
@article{6914897,
  abstract     = {{Diatoms are important primary producers in lake ecosystems and, as a sink for dissolved (DSi) and biogenic silica (BSi) originating from land, can significantly impact the global Si cycle. After burial in lake sediments, resistant diatom frustules can also be used for reconstructions of past ecosystem change. The BSi content of lake sediments is thus often used as a proxy for past diatom productivity, and measured using a time-step analysis of Si extracted in 0.1 M Na2CO3. However, studies in soils and ocean sediments have shown that also certain non-biogenic Si fractions are prone to dissolve in alkaline solutions, contributing to a potential overestimate of sedimentary BSi concentration. In lakes, volcanic and terrestrial Si compounds reactive at high pH are likely to interfere with the analysis. In this study we used a continuous analysis of Si and Al extracted in 0.5 M NaOH and a new mathematical model improved from Koning et al. (Aquat Geochem 8:37-67, 2002) to distinguish between biogenic and non-biogenic Si fractions in lake-sediment extracts. We tested this approach in 43 samples of a 19,000-year sediment sequence recovered from Lake Rutundu, a volcanic crater lake on Mt. Kenya. Our results show that a significant fraction of the extractable Si is of non-biogenic origin, especially in the part of the sequence deposited during the glacial period. We conclude that this technique is essential for the characterization of different Si phases, and in particular the diatom-derived BSi, in the sediment of lakes situated in volcanic catchments. It allows calculating a correction, based on the distinct Si:Al ratio of each of those Si phases, that eliminates the contribution from non-BSi fractions.}},
  author       = {{Barão, Lúcia and De Cort, Gijs and Meire, Patrick and Verschuren, Dirk and Struyf, Eric}},
  issn         = {{0168-2563}},
  journal      = {{BIOGEOCHEMISTRY}},
  keywords     = {{Lakes,Diatoms,Volcanic interference,Continuous analysis,Alkaline extractions,LATE QUATERNARY CHANGES,LAND-USE CHANGE,EAST-AFRICA,ORGANIC-MATTER,CLIMATE VARIABILITY,ISOTOPE COMPOSITION,MARINE-SEDIMENTS,DIATOM SILICA,MOUNT-KENYA,RECORD}},
  language     = {{eng}},
  number       = {{2}},
  pages        = {{243--259}},
  title        = {{Biogenic Si analysis in volcanically imprinted lacustrine systems: the case of Lake Rutundu (Mt. Kenya)}},
  url          = {{http://dx.doi.org/10.1007/s10533-015-0125-0}},
  volume       = {{125}},
  year         = {{2015}},
}

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