Nutrients, Fla.’s red tide menace tied

By Amy Wold
The Advocate, Nov 15, 2007

Nutrients from fertilizer or urban runoff that travel down the Mississippi River are widely accepted as causing the annual summer low-oxygen "dead zone" off the coast of Louisiana.

Now it appears those nutrients play a role in the recurring "red tide" of algae blooms off the western coast of Florida, according to a recently released report from the National Oceanic and Atmospheric Administration.

"NOAA’s been forecasting the potential impacts of red tides for about three years now," said Richard Stumpf, NOAA oceanographer and NOAA Harmful Algal Bloom Forecasting coordinator.

The tough part with forecasting red tide episodes has been predicting when they will start, he said.

Researchers look at four characteristics that seem to be linked to these episodes: that algae blooms appear over large areas, that they appear in areas where nitrogen in the water is low, that the red tides form in fall and that they seem to be linked to ocean fronts.
In a Nov. 7 telephone news conference, Stumpf said he and other researchers decided to look at what role ocean fronts play in the red tide formation and why these blooms form in low-nitrogen areas.

What researchers found is that in the early summer every year, winds in the Gulf of Mexico shift and help bring Mississippi River outflow eastward, instead of the normal westward.

This flow brings nutrients to the Florida coast, he said. The nitrogen carried by the river water sinks and is transformed into a type of food for this particular type of algae.

Then the winds change in fall and upwelling helps bring these blooms to the surface and concentrate them in an area.

It doesn’t appear that ocean fronts create the blooms; the fronts just help concentrate the blooms in an area, he said.

Research that hasn’t been completed yet includes what effect hurricanes and tropical storms can have on the blooms, he said.

These nutrients are the same that help create the annual low-oxygen "dead zone" off the coast of Louisiana every summer.

In October, the National Research Council released a report stating that the increased use of corn crops for ethanol production could make the dead zone worse.

Corn — currently the primary source for ethanol production — requires a lot of fertilizer. As more acreage in the Mississippi River watershed is planted in corn, the potential increases that more of that fertilizer nutrient can make it down the river and into the Gulf of Mexico.

This fertilizer — along with urban runoff and nutrients from other sources— feeds small organisms which use of oxygen in the water as they die and decompose.

This low-oxygen water settles to the bottom of the water column in summer and creates a "dead zone" where there isn’t enough oxygen to support life.

This year, the "dead zone" off Louisiana‘s coast measured 7,900 square miles.

Amy Wold covers environmental issues for The Advocate.