Mississippi water flows see increase

By Amy Wold
Baton Rouge Advocate; January 27, 2008


Farming practices since ’50s found responsible for trend

Since the mid-1950s, changes in farming practices in the Mississippi River basin helped put more water and more carbon into the Mississippi River, a trend that continues today, according to a science article published this month in Nature.

The article, “Anthropogenically Enhanced Fluxes of Water and Carbon in the Form of Bicarbonate from the Mississippi River,” is a mouthful to pronounce, but comes down to the fact that farming practices since the 1950s, fields are being drained differently and the types and methods of crop planting have been updated.

This means that more water that used to be retained in the soil or sent back into the environment by plants, began to travel to streams and rivers faster, said Eugene Turner, professor with the School of Coast and Environment at LSU.

Normally, rain falls on the ground and as it seeps downward, it dissolves minerals which then flow into streams that eventually find their way to the Mississippi River and the Gulf of Mexico.

However, the article in Nature states that this process has increased in tempo and now there is 9 percent more water going into the Mississippi River and a 40 percent increase in its carbon load during the last 50 years, Turner said.

“For a given amount of rainfall, more water is getting into the river,” said Whitney Broussard, article co-author and LSU doctoral candidate.

Turner said this additional water carries with it additional carbon in the form of bicarbonate. This material becomes a water quality issue because it can increase the acidity of ocean waters by helping to absorb carbon dioxide from the atmosphere.

The article identifies several reasons for the cause of this additional water and accompanying carbon, which is related to the amount of land used for agriculture.

The first reason includes changes in agriculture methods that help drain water away from fields faster, such as underground drainage systems.

The research — funded by the National Science Foundation — got its start while Turner

was looking for historical nitrate levels in the Mississippi River.

That search led him and Broussard to New Orleans-area water treatment facilities at Carrollton and Algiers to look at water-testing records that date back to 1900.

The records were fairly complete and were done in a similar format down through  the years, meaning the numbers were comparable, Turner said.

“These guys didn’t change their format since 1905,” he said.

Broussard explained that the water treatment plants needed to test the water because they needed to know how much lime to add before processing the water for drinking, Broussard said. The lime helped separate materials in the water that could clog water pipes.

Testing would be done three times a day, he said.

“They’ve been doing this every day for 100 years,” Broussard said.

Using that information, the researchers partnered with lead author Peter Raymond and Neung-Hwan Oh with the Yale School of Forestry and Environmental Studies to compare carbon amounts — in the form of bicarbonate — with rainfall.

The results showed that more water is getting into the river faster and carrying with it a higher percentage of carbon.

Another factor related to the additional water and carbon is that crops aren’t in the ground year round, leaving the earth bare for periods of time.

In addition, nonagriculture ecosystems tend to put more water back into the air through a process called “evapotranspiration” than agriculture land does, Turner said.

“If you have more plants, they evaporate the water right there,” Turner said.

Now, with 18 percent more corn planted nationwide last year as part of the incentive program to produce ethanol fuel, the problem will likely continue or get worse, he said.

Broussard agreed.

“This (the article in Nature) is another way to say that the impact we have on the land affects the water,” Broussard said.