The role of methane oxidation in the carbon cycle of the lower Amazon River
Abstract
Inland waters are recognized as an important source of methane (CH4) to the atmosphere. Recent estimates have shown that the emissions from rivers and streams can be equivalent in order of magnitude to the uptake of CH4 by soils. The CH4 emitted to the atmosphere is a fraction of CH4 that is not subjected to methane oxidation (MOX). Aquatic MOX may represent an important sink of CH4. Microbial consumption of CH4 in large rivers in the Amazon basin can be responsible for the reduction in emissions to the atmosphere of up to 2 TgCH4 yr-1. The consumed CH4 is converted into partly CO2 and partly biomass, that becomes available to the food web along the river continuum and potentially in the ocean. The relative magnitude of these two CH4 fates and how they influence the aquatic carbon cycle is not well known. Here, we present ecosystem MOX estimates combined with 13C-CH4 enrichment incubations to evaluate the importance of MOX and the transformation rates of dissolved CH4 into biomass and CO2 in the water column of the lower Amazon River. Fluxes to the atmosphere were measured to better understand the CH4 dynamics and the role CH4 plays in the aquatic carbon cycle. Floating chamber measurements of CH4 fluxes, stable isotopic composition of the surface water dissolved CH4, and bubbles retrieved from shallow areas near the shore, along with surface water incubations with labeled 13C-CH4, were made during the rising water season in February 2016. The overall ecosystem MOX prevented approximately 56-74 % of the CH4 emissions. The incubations showed transfer of the 13C labeled CH4 into both biomass and CO2, indicating that the consumed CH4 is converted into biomass that can support downstream food webs.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2018
- Bibcode:
- 2018EGUGA..20.7740S