By Matthew Cimitile
Long valued for biological diversity and flood control, Great Lakes coastal wetlands are now seen as a tool to suck up and store excess carbon dioxide.
It’s an important function as researchers seek to blunt climate change caused by that greenhouse gas.
“Wetlands are at the top of the list of best systems for sequestering carbon on the landscape,” said William Mitsch, professor emeritus at Ohio State University and director of the Everglades Wetland Research Park at Florida Gulf Coast University.
There are more than 535,000 acres of coastal wetlands in the Great Lakes basin, according to the Great Lakes Coastal Wetlands Consortium. The nutrients, water and light flowing through these systems fuel a tremendous amount of photosynthesis, a process that absorbs carbon dioxide to produce energy for plant growth, said Donald Uzarski, director of the Institute of Great Lakes Research at Central Michigan University.
Once absorbed, wetlands can store that carbon in soils for centuries, even thousands of years.
“The major benefit of wetlands over other environments is that they provide a long term solution for carbon storage where it is kept in the muck of the soil,” said Mitsch. “Trees above ground retain carbon for a shorter time in comparison.”
Understanding how much carbon dioxide wetlands capture could help focus policy on preserving them to combat climate change.
Mitsch and other researchers are studying wetlands around Lake Erie in Ohio. They’ve found that coastal wetlands at sites such as Old Woman Creek, a 136-acre plot in northern Ohio, can take in 1,215 pounds of carbon dioxide per acre per year. That means Old Woman Creek is absorbing the emissions produced by 12 cars a year.
Wetlands also emit greenhouse gases of their own, most notably methane, which is 25 times more potent than carbon dioxide in terms of its warming effect. But Mitsch says because of how long wetlands can retain carbon that in the long run they act as sinks rather than sources of greenhouse gases.
“Much of the discussion about wetlands and climate change is on how they emit methane,” said Mitsch. “But their capability for sequestering carbon and especially storing it for long durations needs to be better recognized.”
Nationally, the U.S. Geological Survey is studying how well all ecosystems store carbon to counterbalance emissions from burning fossil fuels. This Congressionally mandated assessment has produced reports on ecosystems in the Great Plains and western U.S. The latter report concludes that wetlands have the highest carbon capture rate of all ecosystems.
A final report due out later this year will assess ecosystem sequestration rates throughout the eastern U.S., including the many coastal wetlands in the Great Lakes.
The studies can help target protection and restoration efforts, said Kristin Bird, a physical scientist at the U.S. Geological Survey. “At a regional level it can provide resource managers the ability to prioritize land in parks and forests for climate change mitigation,” she said.
Coastal wetlands seen as a beneficial tool for society would be a change. They were long regarded as mosquito-infested nuisances or as an obstruction for lake views. Typically they were dredged and filled. In the Great Lakes, nearly half of coastal wetlands were destroyed in a little over a century for agriculture and development, said Uzarski.
“We tend to develop the shoreline and people don’t want to live on a coastal wetland, they like to live on a beach or right on the water,” said Uzarski. “If you look around Saginaw Bay or Lake Huron, lawns go right to the water’s edge.”
Coastal development still threatens to destroy and fragment wetlands. We now know that not only reduces habitat, it releases into the atmosphere large amounts of carbon stored in these soils, said Bird.
Development creates a double whammy of releasing carbon that is already stored and of future carbon that could have been captured, said Mitsch.