Amazon Wetlands and Carbon Dioxide

Floodplains are critical components of the biogeochemistry, ecology and hydrology of the lowland Amazon basin. They contain thousands of lakes and associated wetlands linked to one another and to the many rivers and streams of the basin. Floodplains modify hydrology, influence carbon and nutrient biogeochemistry, emit carbon dioxide and methane to the atmosphere, and support highly diverse ecosystems and productive fisheries.

Understanding that system is one key to determining how significantly naturally produced gases such as carbon dioxide and methane are contributing to atmospheric changes like global warming. It is also at the heart of research being conducted by UCSB’s John Melack, professor and associate dean of the Bren School of Environmental Science and Management.

Melack has been studying the Amazon basin for two decades and recently received an additional $640,000 from NASA to continue his work through 2009. His latest project, “Linking Remote Sensing of Variations in Inundation and Aquatic Vegetation with Regional Analysis of Carbon Dynamics,” uses remote sensing instruments to look at how the Amazon basin functions as a large system and its contribution to the global carbon cycle.

The project is a portion of the Brazilian government’s large, multi-national study called Large-scale Biosphere and Atmosphere Project, or LBA. NASA joined LBA to sponsor a series of projects under a research component called LBA-ECO. Melack has served on the LBA Scientific Steering Committee since the project began in 1998 and has been a principal investigator on three LBA-ECO projects, including this latest effort.

To look at something as large as the Amazon—at 7 million square kilometers—researchers needed to invoke new methodology. So Melack used remote sensing technology—synthetic aperture radar and passive microwave emissions—to determine where the water is and to quantify how much is there. Then he linked the data to the ecology and biogeochemistry of those areas.

There’s been a lot of study of the Amazon’s land and forests, but 20 percent of the Amazon is wetlands, and until now no one knew what the carbon contribution was of the wetlands to the carbon cycle, Melack says.

Carbon dioxide and methane are the two main greenhouse gases in the atmosphere. What Melack discovered is that the amount of carbon dioxide transferred from the fresh water wetlands is 10 times the amount that is transported down the river as organic carbon. The estimated amount of carbon being released by the wetlands into the atmosphere almost balances the net production of upland forests, which was a surprising finding, he says. It suggests the Amazon is less a sink for carbon than had previously been thought.

Additionally, Melack and his team did the first rigorous analysis of methane emissions from the basin.

“We did methane studies, and in terms of direct carbon balances, it’s smaller. But methane is about 20 times more potent as a greenhouse gas relative to CO2. Therefore, methane is about 40 percent relative to the carbon uptake by the forests.”

Understanding the Amazon’s contributions of greenhouse gases to the atmosphere will help scientists ultimately determine how much of global warming is, in fact, related to human activities.

There is much more to discover, and Melack’s work will continue seeking answers to questions this research has raised. For example, is the carbon that is respired coming from plants growing on land or in the water? It’s another piece of the Amazon’s carbon balance puzzle.