Weeds coincide with toxic algae blooms


Special to The Progressive Populist

Do toxic algae blooms and common farm weeds have anything in common? According to Dr. Elaine Ingham of Oregon State University they do. Both result from too much nitrogen and phosphorus.

Scientists at the 16th International Botanical Congress meeting in St. Louis in August presented evidence of the proliferation of toxic algae blooms. Explosions of toxic algae kill thousands of fish and shellfish, and have even been known to kill people, said Dr. Julie Hambrook, a biologist at the U.S. Geological Survey (USGS). They contributed to the creation of "dead zones" in the oceans, areas where algae have killed all other life, now thought to number near 50. The largest dead zone in the Western Hemisphere covers 7,000 square miles in the Gulf of Mexico.

The frequency of hazardous algae blooms along the Atlantic and Gulf coasts has more than tripled since the 1970s, said Hambrook, to over 300 a year. The main culprits are nitrogen and phosphorus from fertilizers and human and animal waste.

For a long time the USGS assumed algal blooms were solely a salt water problem. It has no information on inland algal blooms.

At the same congress, however Dr. Wayne Carmichael of Wright State University in Ohio presented evidence that algal blooms are a potentially serious fresh water problem. In the first-ever study of municipal water systems in North America, he found widespread contamination with toxins from blue-green algal blooms, called microcystins. The most common toxins were liver poisons, but he also found algal-produced nerve poisons.

Carmichael took 1,000 water samples from reservoirs throughout the U.S. and Canada. Eighty percent contained algal toxins. Twenty percent had microcystin levels higher than the safety level specified by World Health Organization guidelines. And those guidelines, he said, are for toxin levels that cause acute illness. They don't take into account that, even at low levels, "microcystins are potent liver tumor promoters."

While it is fairly easy to remove microcystins from water with charcoal filters, not all water systems do that. "Some add chemicals to kill algae, but that leaves the toxins in the water," said Hambrook.

Carmichael and a colleague, Dr. Greta Fryxell of the University of Texas, called for restrictions on farm fertilizer use and total watershed management of nitrogen and phosphorus.

Just the mention of fertilizer controls usually prompts an uproar from farmers, but it shouldn't.

Cutting fertilizer use will cut farmers' weed problems, said Ingham, without hurting productivity. Many farmers do not know that too much fertilizer just gives them more weeds, she said. "They still think that all there is to soil science is nitrogen, phosphorus and potassium." Weeds are like a warning light, she said, but instead of determining the problem, too many farmers are simply disconnecting the signal by spraying herbicides.

Ingham developed techniques that improved the productivity of strawberry and lettuce farms in California's Salinas Valley, while simultaneously slashing the amount of chemical fertilizers and pesticides farmers used, said Frank Stances, president of Pacific Ag Research, a commercial agricultural research and development company.

"Weeds all require high levels of nitrogen," said Ingham. The magic number is 10 parts of nitrogen per million parts of soil. ""If you drop your nitrates to less than 10 parts per million, the weeds leave.... thistle, johnson grass, and nightshade all disappear," she said.

Ingham and scientists such as Dr. David Janos at the University of Miami and Dr. Nancy Johnson at Arizona State University have shown that a complex network of soil microorganisms can keep down weeds and help plants acquire nutrients, unless they are killed by excess fertilizer and other industrial farming techniques. Once you kill the beneficial microbes "you have to keep adding more fertilizer just to stay in place," added Janos. It can take up to three years to replace the microbial "soil food web," said Ingham, though some studies have shown farmers can jump start the process by inoculating their fields with beneficial bacteria.

Up to now, farmers have resisted calls to curtail fertilizer use to save the gulf. According to the Fertilizer Institute, American farmers last year applied over 45 billion pounds of fertilizer to their fields. Farmers in the main corn-producing states applied over 16 billion pounds to corn fields alone. That "corn belt" stretches from Pennsylvania to Colorado, with Michigan and Minnesota in the north and Tennessee in the south.

According to the U.S. Department of Agriculture, corn growers use the more fertilizer than anyone else, and they use herbicides more intensively than other farmers, too. Corn growers applied nitrogen fertilizer on 98 percent of their acreage in 1998, and they used herbicides on 95 percent of their acres.

A 50 percent cut in fertilizer use, which is much less of a cut than Ingham claimed is possible, farmers would save $5.5 billion. An equivalent cut in herbicide use would bring the savings up to $9.9 billion.

Peter Downs is a writer based in St. Louis.

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