Methane from Some Wetlands May Lower Benefits of Carbon Sequestration

Sacramento, Calif. – Methane emissions from restored wetlands may offset the benefits of carbon sequestration a new study from the U.S. Geological Survey suggests. Wetlands are known to reduce atmospheric carbon dioxide through plant photosynthesis and also provide habitat and food sources for wildlife, act as biological filters for improving water quality and improve coastal protection in the face of sea level rise. What is not well understood is how wetland production of other more potent greenhouses gases like methane offset these benefits. Results from the new study show that restored wetlands can release enough methane to reduce or even negate the benefits the same wetlands offer of carbon sequestration.

In the study, USGS, California Water Science Center Hydrologist Frank Anderson and a team of scientists collected data in 2002-2003 and 2010-2011 to estimate trends of carbon fluxes from restored wetlands in the Sacramento-San Joaquin Delta. From measuring wind speeds and gas concentrations, and computing photosynthesis and respiration rates, they concluded that carbon dioxide uptake decreased between the two sampling periods, while carbon dioxide respiration and methane emissions remained relatively consistent. Results show that the restored wetlands were a small source of carbon in 2010-2011. However, given the potency of methane as a strong greenhouse gas, the wetlands will likely be long-term sources of global warming potential.

The research presented in this study is both important and timely as policy makers consider restoring wetlands not only for their environmental potential, but also their economic value for cap-and-trade carbon offset programs. Although the USGS study design was unique to the Sacramento-San Joaquin Delta restored wetlands and may not necessarily represent potential emissions in other restorative wetland designs, the study emphasizes the need for continual monitoring of restored wetlands when evaluating their long term impacts. 

The study, first published in the “Journal of Geophysical Research: Biogeosciences,” was featured as a “Research Spotlight” on the American Geophysical Union’s Earth & Space Science News website. “Variation of energy and carbon fluxes from a restored temperate freshwater wetland and implications for carbon market verification protocols” is available online.

To learn more about USGS Water Science, please visit the USGS Water Resources of the United States website or the USGS California Water Science Center website.