Midwestern farming has introduced the equivalent of five Connecticut Rivers into the Mississippi River over the past 50 years and is adding more carbon dioxide annually into its waters, according to a study published in Nature by researchers at Yale and Louisiana State universities.

“It’s like the discovery of a new large river being piped out of the corn belt,” said Pete Raymond, lead author of the study and associate professor of ecosystem ecology at the Yale School of Forestry & Environmental Studies. “Agricultural practices have significantly changed the hydrology and chemistry of the Mississippi River.”

The researchers tracked changes in the levels of water and bicarbonate, which forms when carbon dioxide in soil water dissolves rock minerals. Bicarbonate plays an important, long-term role in absorbing atmospheric carbon dioxide, a greenhouse gas. Oceans then absorb the excess carbon dioxide and become more acidic in the process. “Ocean acidification makes it more difficult for organisms to form hard shells in coral reefs,” said R. Eugene Turner, a co-author of the study and a professor at the Coastal Ecology Institute at Louisiana State University.

The researchers concluded that farming practices, such as liming, changes in tile drainage and crop type and rotation, are responsible for the majority of the increase in water and carbon dioxide in the Mississippi River, which is North America’s largest river.

Raymond said that the research team analyzed 100-year-old data on the Mississippi River, warehoused at two New Orleans water treatment plants, along with data on precipitation and water export. “A notable finding is that changes in farming practices are more important than changes in precipitation to the increase in water being discharged into the river,” he said.

The researchers used their data to demonstrate the effects of excess water on the carbon content of the river, and to argue that nutrients and pollution in the water are altering the chemistry of the Gulf of Mexico.

Besides Raymond and Turner, the other authors of the study, “,” are Neung-Hwan Oh of the Yale School of Forestry & Environmental Studies, and Whitney Broussard of the Department of Oceanography and Coastal Sciences at Louisiana State University.

Citation: Peter A. Raymond, Neung-Hwan Oh, R. Eugene Turner & Whitney Broussard, Anthropogenically Enhanced Fluxes of Water and Carbon from the Mississippi River, Nature 451, 449 (2008). doi:10.1038/nature06505