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Spatial heterogeneity of methane ebullition in a large tropical reservoir

Publikationsart Peer-reviewed
Publikationsform Originalbeitrag (peer-reviewed)
Autor/in Delsontro T., Kunz M.J., Kempter T., Wüest A., Wehrli B., Senn D.B.,
Projekt The role of lake sediments in the carbon cycle: organic carbon preservation and methane emission
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Originalbeitrag (peer-reviewed)

Zeitschrift Environmental Science and Technology
Volume (Issue) 45(23)
Seite(n) 9866 - 9873
Titel der Proceedings Environmental Science and Technology
DOI 10.1021/es2005545

Open Access

Abstract

Tropical reservoirs have been identified as important methane (CH4) sources to the atmosphere, primarily through turbine and downstream degassing. However, the importance of ebullition (gas bubbling) remains unclear. We hypothesized that ebullition is a disproportionately large CH4 source from reservoirs with dendritic littoral zones because of ebullition hot spots occurring where rivers supply allochthonous organic material. We explored this hypothesis in Lake Kariba (Zambia/Zimbabwe; surface area >5000 km2) by surveying ebullition in bays with and without river inputs using an echosounder and traditional surface chambers. The two techniques yielded similar results, and revealed substantially higher fluxes in river deltas (103 mg CH4 m–2 d–1) compared to nonriver bays (<100 mg CH4 m–2 d–1). Hydroacoustic measurements resolved at 5 m intervals showed that flux events varied over several orders of magnitude (up to 105 mg CH4 m–2 d–1), and also identified strong differences in ebullition frequency. Both factors contributed to emission differences between all sites. A CH4 mass balance for the deepest basin of Lake Kariba indicated that hot spot ebullition was the largest atmospheric emission pathway, suggesting that future greenhouse gas budgets for tropical reservoirs should include a spatially well-resolved analysis of ebullition hot spots. (with suppl. information S2-S19).
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