Seasonal dynamics in methane emissions from the Amazon River floodplain to the troposphere

Abstract

Methane fluxes to the troposphere from the three principal habitats of the floodplain of the Amazon River main stem (open waters, emergent macrophyte beds, and flooded forests) were determined along a 1700‐km reach of the river during the low‐water period of the annual flood cycle (November–December 1988). Overall, emissions averaged 68 (±20) mg CH4 m−2 d−1 and were significantly lower than similar emissions determined previously for the high‐water period, 184 (±41) mg CH4 m−2 d−1 (July–August 1986). This difference was due to significantly lower emissions from floating macrophyte environments. Low‐water emissions from open waters and flooded forest areas were not significantly different than at high water. A monthly time series of methane emissions from eight lakes located in the central Amazon basin showed similar results. Average annual emission from the lakes was 125 (±28) mg CH4 m−2 d−1. Methane emissions from lakes were significantly higher during the high water period, again primarily due to an increase in emissions from macrophyte habitats. The data were used to calculate a seasonally weighted annual emission to the troposphere from the Amazon River main stem floodplain of 5.1 Tg yr−1, which indicates the importance of the area in global atmospheric chemistry.