Falling crop diversity leads to dead zone

By Jordan Blum
Feb 12, 2009; 2theadvocate.com


The dwindling amount of agricultural diversity along the Mississippi River basin is significantly contributing to the Gulf of Mexico’s “dead zone” off Louisiana’s coast, according to a new LSU-led report.

The study started as an LSU doctoral dissertation and ended up as an expanded research effort on crop biodiversity highlighted Wednesday in the Ecological Society of America’s “Frontiers in Ecology and the Environment” publication.

The results show that the evolution from smaller, more diverse farms to today’s homogenized, industrial farms has funneled much more nitrogen through the soil and into the river watershed, said author Whitney Broussard, a former LSU doctoral student now working as a post-doctoral researcher at the University of Louisiana at Lafayette.

“The biodiversity connection is an idea I had in my mind while I was flying over Kansas,” Broussard said. “It’s a homogenization issue. Looking at the patchwork from the air, it was easy to see.”

Nitrogen intrusion is a major cause of the so-called “dead zones,” also known as hypoxia, which are low-oxygen areas in the Gulf of Mexico that support little marine life, affecting shrimp, oysters and commercial fish.

The Gulf of Mexico dead zone measured 8,000 square miles last year and is one of the world’s largest.

The increased nitrogen comes from more mechanized farming machinery and more potent fertilizers, Broussard said.

R. Eugene Turner, LSU professor of coastal ecology, is the co-author and was Broussard’s doctoral adviser.

More crop rotation, smaller fields with sharper edges and more “perennial” plants could greatly reduce aquatic nitrate concentrations because they produce more buffers in the soil that stymie the underground trek of the nitrogen, Turner said.

There are many options, including more “far out” research, such as putting roots on corn, Turner said.

But much of these improvements would require federal public policy changes, he said.

That is where organizations like the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force come into play.

A year ago, Turner and Broussard co-authored an article in the journal Nature about agriculturally-caused increases in carbon in the Mississippi River.

So the idea of agricultural practices affecting water quality is far from new, Broussard said.

But Broussard studied agriculture census data dating back to the early 1900s and found “highly significant” correlations between farming practices and nitrogen concentration.

The changes were noticeable even in the early 1900s but significantly intensified as agriculture became more industrialized and mechanized, he said.

Broussard cautioned that agriculture only accounts for about half of the changes in nitrogen concentration in the watershed. Another cause includes urban sewerage problems, he said.

“This (research) points us in a general direction,” Broussard said. “But there’s still much work to be done to determine the specifics.”