U.S. farming practices acidifying Mississippi

Midwestern farming practices in the United States have left the Mississippi River full of carbon dioxide, acidifying the downstream Gulf of Mexico and harming coral and other marine life, a new study finds.

Using data from as far back as 100 years ago, researchers tracked changes in the water level and in certain chemicals in the river, and found its chemistry has been significantly altered.

The researchers concluded that farming practices such as liming (adding calcium to the soil), changes in drainage and crop rotation have caused an increase in bicarbonate and the amount of water running off into the Mississippi.

The result is an injection of the equivalent of five Connecticut Rivers' worth of carbon dioxide into the Mississippi each year during the last 50 years, said study leader Peter Raymond of Yale University. The Connecticut River is the largest river in New England, at 407 miles (655 kilometers) long.

"It's like the discovery of a new large river being piped out of the Corn Belt," Raymond said. "Agricultural practices have significantly changed the hydrology and chemistry of the Mississippi."

The carbon dioxide build-up starts when water in the farmlands surrounding the river dissolves soil minerals. The important mineral in the carbon equation is bicarbonate, which forms when carbon dioxide in the farm water runoff dissolves the soil minerals.

Bicarbonate is a key player in the absorption of atmospheric carbon dioxide. When the Mississippi waters eventually run out into the Gulf of Mexico, these chemical changes cause the ocean waters to absorb more carbon dioxide and therefore become more acidic.