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Reduced Mineralization of Terrestrial OC in Anoxic Sediment Suggests Enhanced Burial Efficiency in Reservoirs Compared to Other Depositional Environments
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.ORCID iD: 0000-0002-4634-527X
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Univ Fed Juiz de Fora, Dept Biol, Lab Aquat Ecol, Juiz De Fora, Brazil.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.ORCID iD: 0000-0003-1351-9277
2019 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 124, no 3, p. 678-688Article in journal (Refereed) Published
Abstract [en]

Freshwater reservoirs are important sites of organic carbon (OC) burial, but the extent to which reservoir OC burial is a new anthropogenic carbon sink is currently unclear. While burial of aquatic OC (by, e.g., phytoplankton) in reservoirs may count as a new C sink, the burial of terrestrial OC in reservoirs constitutes a new C sink only if the burial is more efficient in reservoirs than in other depositional environments. We carried out incubation experiments that mimicked the environmental conditions of different depositional environments along the land‐sea continuum (oxic and anoxic freshwater, oxic and anoxic seawater, oxic river bedload, and atmosphere‐exposed floodplain) to investigate whether reservoirs bury OC more efficiently compared to other depositional environments. For sediment OC predominantly of terrestrial origin, OC degradation rates were significantly lower, by a factor of 2, at anoxic freshwater and saltwater conditions compared to oxic freshwater and saltwater, river, and floodplain conditions. However, the transformation of predominantly terrestrial OC to methane was one order of magnitude higher in anoxic freshwater than at other conditions. For sediment OC predominantly of aquatic origin, OC degradation rates were uniformly high at all conditions, implying equally low burial efficiency of aquatic OC (76% C loss in 57 days). Since anoxia is more common in reservoirs than in the coastal ocean, these results suggest that reservoirs are a depositional environment in which terrestrial OC is prone to become buried at higher efficiency than in the ocean but where also the terrestrial OC most efficiently is transformed to methane.

Abstract [en]

Plain Language Summary

The widespread construction of dams disrupts the transport of sediment particles by rivers and traps sediment in reservoirs. The sediment contains organic carbon (OC) that can be degraded into greenhouse gas (carbon dioxide and methane) or buried in the sediment. In the absence of dams, sediment would be deposited in other environments, such as rivers, floodplains, or sea. In our study, we investigated through incubation experiments if the construction of reservoirs creates an environment that stores sediment OC more efficiently than other environments. We found that OC from terrestrial origin is buried more efficiently in anoxic conditions than in oxic conditions. Slowing down of water and high primary production makes reservoirs prone to anoxia, implying that they may be sites of highly efficient OC burial. However, anoxic reservoir conditions were also characterized by higher methane emissions than other environments. OC from aquatic origin was degraded extensively in all studied conditions. Our results suggest that the ~50% of the terrestrial OC that escapes degradation if it gets trapped in an anoxic reservoir may be accounted as a new carbon sink; however, whole‐system studies that account for site‐specific environmental conditions are necessary to calculate the magnitude of this effect.

Place, publisher, year, edition, pages
2019. Vol. 124, no 3, p. 678-688
Keywords [en]
sediment, burial, carbon, anoxic, reservoir, methane
National Category
Oceanography, Hydrology and Water Resources
Identifiers
URN: urn:nbn:se:uu:diva-375404DOI: 10.1029/2018JG004823ISI: 000464653200016OAI: oai:DiVA.org:uu-375404DiVA, id: diva2:1284083
Funder
EU, FP7, Seventh Framework Programme, 336642Available from: 2019-01-30 Created: 2019-01-30 Last updated: 2019-05-21Bibliographically approved

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