"The fact that lignin is proving to be this metabolically active is a big surprise," Richey said. "It's a mechanism for the rivers' role in the global carbon cycle it's the food for the river breath."
The Amazon alone discharges about one-fifth of the world's freshwater and plays a large role in global processes, but it also serves as a test bed for natural river ecosystems.
Richey and his collaborators have studied the Amazon River for more than three decades. Earlier research took place more than 500 miles upstream. This time the U.S. and Brazilian team sought to understand the connection between the river and ocean, which meant working at the mouth of the world's largest river a treacherous study site.
"There's a reason that no one's really studied in this area," Ward said. "Pulling it off has been quite a challenge. It's a humongous, sloppy piece of water."
The team used flat-bottomed boats to traverse the three river mouths, each so wide that you cannot see land, in water so rich with sediment that it looks like chocolate milk. Tides raise the ocean by 30 feet, reversing the flow of freshwater at the river mouth, and winds blow at up to 35 mph.
Under these conditions, Ward collected river water samples in all four seasons. He compared the original samples with ones left to sit for up to a week at river temperatures. Back at the UW, he used newly developed techniques to scan the samples for some 100 compounds, covering 95 percent of all plant-based lignin. Previous techniques could identify only 1 percent of the plant-based carbon in the water.
Based on the results, the authors estimate that about 45 percent of the Amazon's lignin breaks down in soils, 55 percent breaks down in the river system, and 5 percent reaches the ocean, where it may break down or sink to the o
|Contact: Hannah Hickey|
University of Washington