Mountain rivers in the Andes are hotspots for emissions

According to a new study led by the University of Liège in Belgium, streams and rivers in the Andean Mountains are hotspots for greenhouse gas emissions, contributing 35 percent and 72 percent of riverine emissions of carbon dioxide (CO2) and methane (CH4) in the Amazon basin, the largest river on our planet.

The Amazon River originates in the Andes Mountains and, after flowing through Peru, Colombia, Ecuador, and Brazil, it reaches the Atlantic Ocean. Due to the erosion of rocks at its headwaters in the Andes, mineral particles are transported over 3,000 kilometers across South America to the river’s mouth at Belem in Brazil, where they flow into the Atlantic. While all the previous studies of CO2 and CH4 emissions have been conducted in the plains of central Amazon – about 1,000 kilometers from the Andes – researchers have now examined the rates of emissions of mountain rivers, located close to Amazon’s origin.

According to the experts, the Amazon consists of three river systems nested in mountains and spread across plains, all of which have different emission rates. First, the small and rapidly flowing mountain streams pass over steep and rocky terrain, promoting a vigorous physical exchange of gases with the atmosphere, even though the steep terrain does not allow for a large accumulation of soils supporting the production of CO2 and CH4. 

Second, the lowland river is wide and winding, spreading over flat terrain. While the slower flow of water does not promote the exchange of gases with the atmosphere as vigorously as in the mountain rivers, the higher temperatures allow for thicker soils to accumulate, favoring the production and transport of CO2 and CH4 to lowland watercourses. Moreover, the floodplains connected to lowland rivers also supply them with these gases.

Finally, a third type of river system – the so-called piedmont rivers – located in the plains at the foot of mountain ranges resemble lowland rivers, but receive massive amounts of particles from upstream mountain rivers, which, after being temporarily deposited, are resuspended and transported further downstream until they reach the ocean. When these particles are deposited as sediment, they promote the production of CH4 through fermentation. 

By estimating river emissions across the whole Amazon basin using existing data for the lowland river, the scientists found that streams and rivers in the headwaters and piedmont of the Andean Mountains are major greenhouse gas emissions hotpots, accounting for 35 percent of CO2 and 72 percent of CH4 of integrated emissions at the basin scale.

“We found that mountain rivers in the Andes have higher emissions than piedmont rivers, and are hotspots for CO2 and CH4 emissions, with significantly higher flux intensities than in the lowland rivers of the central Amazon,” concluded lead author Gonzalo Chiriboga, a doctoral student in Chemical Oceanography at Liège. 

The study is published in the journal Nature Communications: Earth & Environment.

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By Andrei Ionescu, Earth.com Staff Writer

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