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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-246
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-246
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 05 Jul 2019

Submitted as: research article | 05 Jul 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Biogeosciences (BG).

High organic carbon burial but high potential for methane ebullition in the sediments of an Amazonian reservoir

Gabrielle R. Quadra1, Sebastian Sobek2, José R. Paranaíba1, Anastasija Isidorova2, Fábio Roland1, Roseilson do Vale3, and Raquel Mendonça1 Gabrielle R. Quadra et al.
  • 1Laboratório de Ecologia Aquática, Programa de Pós-Graduação em Ecologia, Universidade Federal de Juiz de Fora, 36036 900, Brazil
  • 2Department of Ecology and Genetics, Limnology, Uppsala University, 75236, Sweden
  • 3Universidade Federal do Oeste do Pará, Instituto de Engenharia e Geociências, 68040 255, Brazil

Abstract. Reservoir sediments sequester significant amounts of organic carbon (OC), but at the same time, high amounts of methane (CH4) can be produced during the degradation of sediment OC. Hydropower is expanding in the Amazon basin, but the potential effects of river damming on the biogeochemistry of the Amazon river system can at present not be gauged due to a lack of studies. Here we present results from the first investigation of OC burial and CH4 concentrations in the sediments of an Amazonian reservoir. We performed sub-bottom profiling, sediment coring and sediment pore water analysis in the Curuá-Una reservoir (Amazon, Brazil) during rising and falling water periods. A mean sediment accumulation rate of 0.6 cm yr−1 and a mean OC burial rate of 91 g C m−2 yr−1 were found, which is the highest OC burial rate on record for low-latitude reservoirs, probably resulting from high OC deposition onto the sediment compensating for high OC mineralization at 28–30 °C water temperature. Elevated OC burial was found near the dam, and close to major river inflow areas. C : N ratios between 10.3 and 17 (mean ± SD: 12.9 ± 2.1) indicate that both land-derived and aquatic OC accumulate in CUN sediments. About 29 % of the sediment pore water samples had dissolved CH4 close to saturation concentration, a higher share than other hydroelectric reservoirs, indicating a high potential for CH4 ebullition, particularly in river inflow areas.

Gabrielle R. Quadra et al.
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Gabrielle R. Quadra et al.
Gabrielle R. Quadra et al.
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Short summary
Hydropower is expanding in the Amazon basin, but the potential effects of river damming on carbon fluxes cannot be gauged due to a lack of studies. We quantified, for the first time in an Amazonian reservoir, both organic carbon burial and the concentrations of methane in the sediments. We found that the dual role of sediments as both carbon sink and methane source may be particularly pronounced in this Amazonian reservoir.
Hydropower is expanding in the Amazon basin, but the potential effects of river damming on...
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