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Friday, February 08, 2008
The Mississippi's changing waters
Excess water produced by farming operations in Midwestern states is making its way into the Mississippi River and creating an alarming amount of carbon dioxide in the Mississippi River, according to a study published this week in the science journal Nature.

In fact, the effects are being felt all through the mighty water channel, even into Louisiana. Over the past 50 years, this farming-related runoff has injected the equivalent of five Connecticut Rivers' worth of water into the Mississippi River, based on the new research being funded by the National Science Foundation. "It's like the discovery of a new large river being piped out of the Corn Belt," says Peter Raymond, lead author of the study and an ecologist at Yale University. "Agricultural practices have significantly changed the hydrology and chemistry of the Mississippi."

The research team analyzed current data from the Mississippi River against comparative data from the river that is more than 100 years old. The older data had been warehoused at two New Orleans water treatment plants before being used for the study. "This impressive effort has led to important conclusions about the influence of land-use practices on carbon dioxide in the environment," says Martyn Caldwell, program director in NSF's division of environmental biology. For instance, researchers tracked changes in the levels of bicarbonate, which forms when carbon dioxide begins to dissolve minerals in the river. Bicarbonate plays an important, long-term role in absorbing atmospheric carbon dioxide, also known as greenhouse gas. Ocean bodies, like the Gulf of Mexico, then absorb the carbon dioxide when the river dumps into it. As a result, however, the ocean bodies become more acidic in the process.

Eugene Turner, a co-author of the paper and a marine ecologist at Louisiana State University, said this aftereffect makes it harder for some species to survive. "Ocean acidification makes it difficult, for example, for certain organisms to form hard shells," Turner said. The researchers concluded that liming and farming practices, such as changes in drainage and crop rotation, are likely responsible for the majority of the increase in water and carbon in the Mississippi River. The researchers also believe that increased nutrients in the Mississippi also are altering the chemistry of the Gulf of Mexico, into which the Mississippi flows. - Jeremy Alford