The ways climate change affects the Mississippi River have become undeniably more pronounced in recent years.
Floods are lasting longer and carrying more water than before, and droughts are becoming more intense. There's also a loss of habitat and biodiversity, said Olivia Dorothy, a restoration director for American Rivers, whose work focuses on the Mississippi.
“There is this flipside that we are starting to learn a lot more about, and that is: How does the alteration of river systems actually contribute to climate change?” she said.
It’s a newer consideration for environmentalists, who previously thought that river systems were relatively benign and don’t contribute many greenhouse gas emissions, Dorothy said. That perspective is changing now as new research demonstrates that reservoirs behind dams can release lots of methane, a potent greenhouse gas, she added.
“We have these really large methane reserves that are behind these dams,” Dorothy said. “As we do things like dredging or any kind of disturbance, as water fluctuations change, those methane bubbles come up to the surface and are emitted into the atmosphere.”
The upper Mississippi itself has more than two dozen locks and dams, which wind up slowing down the river’s flow and the organic material in it. Methane is released when that organic matter accumulates and decomposes, Dorothy said.
Just how many emissions come from the Mississippi River’s dams and reservoirs each year and historically over time is not yet clear, she said. It’s a question American Rivers is exploring with the help of researchers from Southern Illinois University Carbondale like Jonathan Remo.
“We have some information on how much methane the Mississippi River has produced today, but then we have to go back in time,” he said. “The challenge is going back in time and figuring out what that pre-condition [before any dams] may have looked like.”
Remo is an associate professor at SIU who studies rivers and humans’ impact on them and is developing a model that can estimate those methane emissions. It’s information that will help inform the tradeoffs of inland navigation, like on barges, which the damming of the Mississippi facilitates, he said.
“The mantra from the inland navigation system is that they’re so fuel efficient and therefore produce less greenhouse gases than other traditional forms of transportation,” Remo said. “That may be true on a per-mile basis, but overall, we fundamentally altered the Mississippi River system, and how has that changed the greenhouse gas production of the system?”
Dorothy argues the emissions figures for barge shipping are dubious at best as many come from industry-specific data that aren’t easily verifiable. She adds figures from the Environmental Protection Agency are based on estimates from oceangoing vessels and ferries, which are much different than the tows on the Mississippi.
There are also questions about fuel economy on different segments of the Mississippi River or different rivers entirely, a fully loaded tow versus an empty one and traveling upstream versus downstream, Dorothy said.
“Those questions have never been answered,” she said. “There’s huge amounts of money coming out of the federal government for navigation on the Mississippi River, and we don’t even know what this means in terms of carbon emissions.”
The Bipartisan Infrastructure and Jobs Act set aside billions of dollars for projects on the nation's inland water systems, some of which are meant to bolster shipping by barge.
“The river is the conduit for most of our agricultural products, corn and soybeans for example, as well as moving the commodities the farmers need to grow those products,” said Barry Drazkowski, a former deputy director of the Long Term Resource Monitoring Program for the Upper Mississippi River with the USGS.
With climate change, Drazkowski expects the soils in the parts of the Midwest that largely produce these commodity crops will dry out and may not have enough moisture to sustain a crop like corn, he said.
“We need to rethink our policy for the Mississippi River if navigation and the drivers for navigation are going to change,” he said. “The reality is we cannot put enough money into river management to actually stop the degradation.”
Dorothy agrees.
“It’s perplexing because we know these commodity crops are also a big driver of the climate crisis as well,” Dorothy said. “They’re very resource intensive in terms of fossil fuel emissions.”
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This story is being distributed in partnership with Harvest Public Media, a collaboration of public media newsrooms in the Midwest. It reports on food systems, agriculture and rural issues.