Nitrogen: too much of a good thing?

• Author: Halweil, Brian
• Position: Fertilizers result in dead zones

All things in moderation--especially when nitrogen fertilizer is being used near coastal areas, according to a new study from Stanford University scientists.

Coastal areas depend on nitrogen, phosphorous, and other nutrients from inland rivers to feed ocean plants, coastal fisheries, and other healthy sea life. But too many nutrients, nitrogen in particular, can provoke blooms of algae that rob the surrounding water of oxygen as they die and decompose. Such oxygen-depleted "dead zones" have multiplied in recent decades and now total some 146 worldwide. In the most severe cases, the zones exceed 20,000 square kilometers, as in the Gulf of Mexico, the East China Sea, and the Baltic Sea.

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Although scientists have long suspected that chemical fertilizers and manure from concentrated animal farms contribute to nitrogen overload, the Stanford researchers found a close correlation between pulses of irrigation in Mexico's heavily fertilized Yaqui Valley and subsequent algae blooms in the Gulf of California. Like other tropical and subtropical waters, the Gulf is naturally low in nitrogen and particularly vulnerable to nitrogen runoff. The researchers pointed out that these low-nutrient waters tend to be near locations where farmers in Latin America, Asia, and Africa are increasingly adopting chemical fertilizers and establishing large livestock farms. "We project that by the year 2050, 27 to 59...