Nav: Home

Unexpected culprit -- wetlands as source of methane

June 19, 2019

Wetlands are an important part of the Earth's natural water management system. The complex system of plants, soil, and aquatic life serves as a reservoir that captures and cleans water. However, as cities have expanded, many wetlands were drained for construction. In addition, many areas of land in the Midwest were drained to increase uses for agriculture to feed a growing world.

Draining wetlands disconnected the natural flow and retention of water, a system that had worked well for millennia. One solution to wetland draining was to rebuild these wetlands in another area (more convenient to humans). These are referred to as "constructed wetlands." In other cases, constructed wetlands are built to rebuild an area no longer used for agriculture.

How these constructed wetlands are built and managed can make a big environmental impact. Karla Jarecke and researchers from several universities have been studying wetlands' impact on greenhouse gas methane.

"Globally, wetlands are the largest natural source of methane to the atmosphere," says Jarecke. "Methane has a much bigger impact than carbon dioxide on global warming - an impact 25 times greater."

Both natural and constructed wetlands emit methane. Due to their nature - wetlands are, after all, wet - soil microbes and plants are forced to metabolize under anaerobic conditions. And, this leads to methane production.

The soil microbes are responsible for the production of methane in wetlands. The methane then gets to the atmosphere via diffusion, transport through plant tissue, and the episodic release of gas bubbles. The hydrologic stability of wetland soils, as well as the transport efficiency through plants, can affect how much and how often methane is released from the soil.

"Understanding the conditions under which methane is produced and released in wetlands could lead to solutions to reduce methane emissions," says Jarecke.

But, studying large areas like wetlands can prove impossible. So, Jarecke and her colleagues made "mesocosms" of wetlands - manageable, outdoor chambers where methane emissions could more easily be measured. Mesocosms are structural research areas that bridge the gap between lab studies and large field studies.

The study focused on two common wetland plants and their potential role in methane emissions: swamp milkweed and northern water plantain. Plants and soils were collected from a constructed wetland in Dayton, Ohio. They were then transported to Lincoln, Nebraska to create wetland mesocosms. The Dayton site had formerly been drained and used for agriculture and was rebuilt as wetland in 2012.

The researchers harvested seedlings of swamp milkweed and northern water plantain from the wetland and transplanted them into soils collected in PVC pipe. They covered individual plants with clear acrylic cylinders during gas sampling. This helped them measure and quantify methane emissions from the soil-plant mesocosms. The study was performed in the summer of 2013.

Besides comparing the emissions of the two plant species, the researchers studied the effects of hydrology - or the saturation of the soil. "While the controls of hydrology and plant species on methane emissions are individually well-studied, the two are rarely studied together," says Jarecke.

This recent study concluded that water level and saturation influenced methane emissions more than the type of plant species. While methane emissions differed between laboratory mesocosms with water plantain and mesocosms with swamp milkweed, methane emissions did not differ in field mesocosms with each of the two species. In the field, soil saturation had a greater effect on methane emissions.

Finding plant species that reduce microbial methane production could be a key to better wetland management. For example, plants that deliver oxygen to the rooting zone can suppress microbial methane production. In addition, future research is needed to understand how varying soil saturation affects methane emissions. This information could be valuable for designing wetland topography that creates hydrologic conditions for increased carbon storage and reduced methane emissions.

Future research might focus on longer periods of time. "Methane emissions likely change as restored wetlands mature," says Jarecke. "Organic matter from root systems, decaying plants and other materials will build up. This helps restore hydrologic stability. Other research indicates that it can take just a few years to restore hydrologic aspects of a restored wetland. However, biogeochemical and biodiversity aspects can take decades or longer to recover."
-end-
This research was published in the Soil Science Society of America Journal. Funding was provided by NASA/USDA joint program on Carbon Cycle Science (grants 2011-03007 and 2011-00829) NSF DEB-1457505, and a University of Nebraska-Lincoln Undergraduate Creative Arts and Research Experiences (UCARE) grant.

To read a blog about constructed wetlands and their history, visit https://soilsmatter.wordpress.com/2018/09/15/wait-dont-drain-the-swamp/

American Society of Agronomy

Related Methane Articles:

New 3D view of methane tracks sources
NASA's new 3-dimensional portrait of methane concentrations shows the world's second largest contributor to greenhouse warming.
Show me the methane
Though not as prevalent in the atmosphere as carbon dioxide, methane is a far more potent greenhouse gas.
Containing methane and its contribution to global warming
Methane is a gas that deserves more attention in the climate debate as it contributes to almost half of human-made global warming in the short-term.
Microorganisms reduce methane release from the ocean
Bacteria in the Pacific Ocean remove large amounts of the greenhouse gas methane.
Origin of massive methane reservoir identified
New research provides evidence of the formation and abundance of abiotic methane -- methane formed by chemical reactions that don't involve organic matter -- on Earth and shows how the gases could have a similar origin on other planets and moons, even those no longer home to liquid water.
Unexpected culprit -- wetlands as source of methane
Knowing how emissions are created can help reduce them.
Methane-consuming bacteria could be the future of fuel
Northwestern University researchers have found that the enzyme responsible for the methane-methanol conversion in methanotrophic bacteria catalyzes the reaction at a site that contains just one copper ion.
New measurement method for radioactive methane
The method developed by Juho Karhu in his PhD thesis work is a first step towards creating a precise measuring device.
New key players in the methane cycle
Methane is not only a powerful greenhouse gas, but also a source of energy.
Diffusing the methane bomb: We can still make a difference
The Arctic is warming twice as fast as the rest of the planet, causing the carbon containing permafrost that has been frozen for tens or hundreds of thousands of years to thaw and release methane into the atmosphere, thereby contributing to global warming.
More Methane News and Methane Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Teaching For Better Humans 2.0
More than test scores or good grades–what do kids need for the future? This hour, TED speakers explore how to help children grow into better humans, both during and after this time of crisis. Guests include educators Richard Culatta and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

Space
One of the most consistent questions we get at the show is from parents who want to know which episodes are kid-friendly and which aren't. So today, we're releasing a separate feed, Radiolab for Kids. To kick it off, we're rerunning an all-time favorite episode: Space. In the 60's, space exploration was an American obsession. This hour, we chart the path from romance to increasing cynicism. We begin with Ann Druyan, widow of Carl Sagan, with a story about the Voyager expedition, true love, and a golden record that travels through space. And astrophysicist Neil de Grasse Tyson explains the Coepernican Principle, and just how insignificant we are. Support Radiolab today at Radiolab.org/donate.