Bubble distribution along major rivers in the Amazon during the high-water season

Ebullition (gas bubbling) from aquatic ecosystems is an important pathway for gas transport from waterbodies to the atmosphere. The spatial and temporal variability of bubbles is typically high and often driven by the distribution of temporary or permanent hotspots. Understanding ebullition patterns remains key to adequately quantifying the exchange of poorly soluble gases like methane.

In this study, we performed a spatial analysis of bubble quantity and relative size using a scientific echosounder during the high-water season across black-, white-, and clearwater river floodplains, encompassing a wide variety of waterbody types such as lakes, main fluvial channels, tributaries, and flooded forests in the Amazon River basin. Our results revealed the dominance of a few spatially limited hotspots. While the number of bubbles per m² was highest in the Negro river system, the total bubble flux was dominated by a few measurement sections in the Amazon and Tapajós river systems with substantially higher ebullition. The relationships of river system, waterbody type, or depth with the bubble quantity or size were weak with no clear trends.

These findings highlight ebullition hotspots as an important component of regional gas emissions in the Amazon basin, emphasizing the spatial heterogeneity of ebullition and the importance of local conditions in regulating ebullition and associated gas fluxes.