Original paper
Seasonal and extreme water level fluctuations impact methane concentrations and fluxes in two Amazon tributaries near Manaus
Silva, Jonismar S.; Pinel, Sébastien; van Asperen, Hella; Amaral, João H. F.; Pimental, Tania P.; da Cunha, Hillândia B.; Krusche, Alex V.; Forsberg, Bruce R.
Fundamental and Applied Limnology Volume 197 Nr. 4 (2025), p. 265 - 279
53 references
published: Aug 27, 2025
published online: Jan 31, 2025
manuscript accepted: Jan 14, 2025
manuscript revision received: Jan 13, 2025
manuscript revision requested: Jul 12, 2024
manuscript received: Jun 5, 2024
ArtNo. ESP141019704008, Price: 29.00 €
Abstract
Methane (CH4) is a potent greenhouse gas, mainly produced in anoxic environments through the degradation of organic matter. Measurements of dissolved CH4 concentrations and environmental variables were made in the two largest tributaries of the Amazon, the Negro and Solimões river, between 2005 and 2011, including years of exceptional high and low water levels. Diffusive CH4 emissions were estimated from CH4 concentrations. These rivers have distinct chemical and physical properties and are of unique economic and cultural significance to their riverine populations. Both rivers were consistently over-saturated with CH4 in relation to the atmosphere, with the Negro River generally presenting higher concentrations (between 0.004 µM and 0.223 µM) than the Solimões River (between 0.005 µM and 0.037 µM). Diffusive fluxes were also found to be larger for the Negro River (0.09 to 8.6 mmol m–2 d–1) than for the Solimões River (0.04 to 1.07 mmol m–2 d–1). A clear seasonal pattern was observed for both rivers with respect to dissolved CH4 concentrations and diffusive fluxes: the highest concentrations and diffusive fluxes of CH4 were found during LW, while the lowest concentrations and fluxes were found during HW. This seasonal trend was more pronounced in years of severe or atypical flood or drought events. Regression models indicated that water depth and temperature can explain the variation in the dissolved CH4 concentration in the Negro (70 %) and Solimões River (58 %). This study shows the potentially strong effects of interannual hydrological variation on river CH4 concentrations and the subsequent river CH4 outgassing.
Keywords
Negro River • Solimões River • methane • outgassing • river fluxes • Amazon • extreme events