Gulf of California - Excessive fertilizer use and algae blooms

Page - July 8, 2008
They are less than a millimetre in size yet you can see them from space. Each November and April, with clockwork precision, small algae start to multiply by the billion, forming gargantuan algae blooms in the pristine waters of the Gulf of California. It’s not because of an internal clock or lunar cycle. It is triggered by farmers’ excessive use of fertilizers in the neighbouring Yaqui Valley.

Each time farmers irrigate their wheat fields at the beginning and end of a crop cycle, they wash thousands of tonnes of nitrogen fertilizer into the Gulf of California, a body of water so rich in biodiversity that celebrated ocean explorer Jacques Cousteau once called it the "aquarium of the world." The farmers in the Yaqui Valley are proud to have some of the highest wheat yields in the world. But equally high are their fertilizer application rates: some 250 kilograms of nitrogen per hectare, which is far beyond the Mexican average.

The wheat plants can only use a small fraction of this nitrogen. Scientists estimate nearly two-thirds of the nitrogen applied in fertilizer in the Yaqui Valley is lost in the atmosphere and runs off into surface waters. Year after year, an estimated 11,000 to 22,000 tonnes of nitrogen are washed into the sea. This triggers a particularly dramatic effect in the nitrogen-deficient waters of the Gulf of California, stimulating algae blooms within days of fertilisation and irrigation.

In 2005, a team of researchers from Stanford University in the United States demonstrated the close correlation between overuse of nitrogen fertilizer and explosive algae growth in coastal waters (Beman et al., Nature 434:211) through satellite pictures. The images show thick algae bloom right off the coast, fuelled by nitrogen run-off from wheat fields.

The researcher measured algae blooms as big as 577 square kilometres in the Gulf of California, which is one of the most productive and biologically diverse marine ecosystems in the world. More species of whale and dolphin feed and breed here than anywhere else. Nearly 900 fish species and 34 species of marine mammals swim in these waters, and more than 800 of the Gulf's species are found nowhere else. Hundreds of species of birds, both migratory and resident, nest in mangroves and coastal lagoons. The effects of the regular algae blooms on this unique diversity are potentially significant

Algae Blooms

Algae blooms are not unique to Northern Mexico. They are occurring with more frequency and in more locations worldwide than ever before. Virtually every coast in the United States is now affected by regular algae blooms. In China, the average number of harmful blooms escalated within two decades, from less than 10 in 1980 to more than 80 in 2000. A recent European Environmental Agency report found that runoff from agricultural activities is the main source of nitrogen pollution, and that the accumulation of nutrients ('eutrophication') is "still one of the major environmental problems across Europe"

(, Report No. 7/2005).

This threat could be easily avoided by reducing the overuse of fertilizers and by farming more ecologically. A first and easily implemented step would be precision fertilizing. Applying smaller quantities of fertilizer at specific times in the crop cycle directly on the plants would ensure most of the fertilizer was used and not washed away. Farmers would save money while not compromising yields and the environment would be less exposed to harmful effects of nutrient overloading.

But farmers in the Yaqui Valley are reluctant to apply these methods, be it that precision fertilizing is deemed too complicated, or that they are too used to the high-input, high-output methods of the so-called Green Revolution - a revolution that started right here, in the heart of the Yaqui Valley. In the 1940s, future Nobel Peace Prize winner Norman Borlaug started a wheat breeding program here, which later led to the development of his much acclaimed high-input, high-yield varieties. The valley, with its 225,000 hectares of irrigated wheat, became one of Mexico's most productive breadbaskets.

But for the farmers and families in the Yaqui Valley, the Green Revolution highway is more and more becoming a road to perdition. The sustainability of the valley, which was once highly regarded for its advanced agro-technology and biological richness, is now in question. When drought hit the region in the late 1990s/early-2000s, the degraded soils were unable to cope with water shortage. In the 2003-2004 crop cycle, less than a quarter of the land in the Yaqui Valley could be planted. The abundant use of pesticides is also taking its toll.

In the early 1990s, a Mexican researcher found extremely high levels of pesticides in samples from children in the Yaqui Valley. A follow-up study was published in 1998 by Dr. Elizabeth Guillette, an anthropologist and research scientist from the United States. She compared children from the farming communities of the Yaqui Valley, where a wide mix of pesticides is applied 30 to 40 times a season, with those from a village in the Sierra Madre foothills, where far fewer pesticides are applied.

Pictures of people drawn by 4 year old Yaqui children. Pictures on the left by children living in the Sierra Madre foothills, which are less exposed to pesticides; pictures on the right children by from the Yaqui Valley that live close to farming areas with high pesticide application rates.

[Thanks to Elizabeth Guillette]

The research team found the Valley children had poor hand and eye coordination. The four and five-year-old children were below the standard level of three-year-olds at such simple tasks as catching a ball. One of Dr. Guillette's findings was particularly disturbing. She asked the children to draw a person, a standard way to measure a child's perceptual and motor abilities development. The four-year-olds from the foothills could draw a complete person. But of the Valley children, most four-year-olds just scribbled, and the five-year-olds only drew a head and a line or a circle and a line.

In the heartland of the Green Revolution, farmers and their families are losing out.

The only thing that still blooms here is the algae.