NewsGulf of Mexico hypoxia

NewsGulf of Mexico hypoxia

Nearly 10 millennia ago the great glaciers retreated from mid-America, and plant and animal
successions adjusted to the warmer wetter periods. Water from rain and snowmelt sought its way
to the oceans carving drainage basins from the glacial and wind deposited soil. Forests, wetlands
and especially the beautiful and functional mixed prairies evolved on the landscape. Deep soils
were formed in the prairie areas, giving us the most fertile and productive agricultural region in
the World.
The Mississippi and Missouri River basins form a huge drainage area; about 41 percent of the
continent is drained by the Mississippi by the time it meets the Gulf of Mexico. Before invasion
by humans, the grasses and trees slowed water flow and retained soil. Water seeped through
wetlands and sloughs, removing the accumulated nutrients and sediment. Rivers and streams
flowed clear and diverse aquatic life flourished.
This idyllic situation was not to last. Land was first cultivated on the hills near the well-drained
landscape around Dubuque that had not been glaciated. The wet, poorly drained soils, such as
those surrounding Ames, were bypassed. Only the hardy settlers tried to farm here. I recall my
grandfather telling how hard it was to run the plow, pulled by oxen, through the prairie. The huge
prairie plants roots would pop and snakes and rodents would scatter.
Soon a way was found to drain the prairie soils so they could be farmed. Tile drainage, now
done with large polyethylene tubes, revolutionized farming. Soils cultivated each year erode
rapidly once cleared, and the great Mississippi and its tributaries such as the Des Moines and
Skunk rapidly became more clogged with silt. The huge delta south of New Orleans was formed
from the eroded soil.
New technologies kept expanding our control of the land, more powerful tractors and efficient
machinery, corn hybrids, introduction of soybean, diet changes, wars, export markets, and now
ethanol, all increased the grain on the land.
As agriculture changed from mixed farming of crops, pastures and forages to mostly row crops,
the detritus of agriculture became greater. Much of this ran into the tiles, to the streams and on
down the river. Nitrogen, in particular the mobile species nitrate, was a major pollutant.
Nitrate is associated with the intense grain farming of today through the tillage of soil, and
addition of nitrogen fertilizers to maximize corn profits. In the Gulf, nitrate limits algae growth.
So when nitrate flows to the Gulf in the spring, which is when the streams are highest in nitrate,
algae form. They then die, sink to the bottom and decompose, pulling oxygen out of the water.
Oxygen can get so low that fish and shellfish cannot exist. This is called hypoxia (also called the
dead zone, but there is life there, just not fish and shellfish).
Hypoxia was not really prevalent until the 1970s when it seemed to show up in estuaries (the
shallow sea close to the shore) all over the world. One of the largest areas is the one in the
northern Gulf of Mexico. It now averages roughly the area of New Jersey but its size varies
depending on how much nitrate comes in the weather and disturbance by storms, especially
hurricanes. Monitoring by the United States Geological Service has shown that more than half of
the nitrate comes from the Corn Belt. Exhaustive committee meetings and studies have reached a
consensus to reduce the size of the hypoxic zone by about two-thirds in the next few years,
mainly by lowering the input of nitrate. This will take large changes in farming practices, in
particular far less corn. But at the same time, the government policies are promoting increases in
corn production for ethanol. This is another in the many examples of opposing government
policies. There are many good conservation programs available, but they have a hard time
competing with corn. And there are advanced perennial plant based biofuels that may help in the
future.
In the meantime, the river keeps rolling along, carrying nutrients and sediment to the Gulf. A lot
of scientific solutions have been proposed. But as Mark Twain said in his book, “Life on the
Mississippi,” “There is something fascinating about science. One gets such wholesale returns of
conjecture out of such a trifling investment of fact.”
Dennis Keeney was the first director of the Leopold Center for Sustainable Agriculture and is an
emeritus professor at Iowa State University. He resides in Ames and can be reached at
earthwatch@mchsi.com.
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