Midwest farming changing Mississippi chemistry
Researchers investigating agricultural pollution in the American Midwest have said that the volume of chemicals in the Mississippi is equivalent to another large river.A team of scientists from Yale and Louisiana State universities has concluded that over the past 50 years farming has poured the equivalent of five Connecticut Rivers - itself a major watercourse - into the mighty Mississippi.
This has led to very real changes in the chemistry and ecology of the river and its estuary.
"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 carbon dioxide but become more acidic in the process.
"Ocean acidification makes it more difficult, for example, 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 liming and farming practices, such as changes in tile drainage and crop type and rotation, are most likely responsible for the majority of the increase in water and carbon in the Mississippi River.
The research team analyzed 100-year-old data on the Mississippi River taken from two New Orleans water treatment plants, and combined it with data on precipitation and water extraction.
"A notable part of this finding is that changes in farming practices are more important than changes in precipitation to the increase in water being discharged into the river," said Mr Raymond.
The researchers used their data to demonstrate the effects of this excess water on the carbon content of the river, and argue that nutrients and pollution in the water are altering the chemistry of the Gulf of Mexico.