Instead of burning petroleum or coal, nitrogen comes from natural gas transformed into ammonia fertilizer and used to grow crops; what doesn’t absorb into the soil runs off into streams, which flow into rivers, which flow to the ocean, where the nitrogen fuels “dead zones” – areas where nitrogen (and phosphorus) fertilizes so much algae growth that it absorbs enough oxygen to make the water inhospitable to fish and other marine life. Jellyfish are about the only thing that thrives in these conditions; corals certainly do not.

There are other causes of dead zones; human sewage, inadequately treated, is another, as is the fallout from burning fossil fuels and certain industrial processes. Dead zones, which start as “eutrophic” zones (that is, over-rich with fertilizers), and end up as “hypoxic” areas (that is, short of oxygen), often shrink and grow with the seasons.

China’s environmental problems are mounting. Water pollution and water scarcity are burdening the economy, rising levels of air pollution are endangering the health of millions of Chinese, and much of the country’s land is rapidly turning into desert.

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The costs of inaction to China’s economy, public health and international reputation are growing. And the government is well aware of the increasing potential for environmental protest to ignite broader social unrest.

One event this spring particularly alarmed China’s leaders. For several days in May in the coastal city of Xiamen, after months of mounting opposition to the planned construction of a $1.4 billion petrochemical plant nearby, students and professors at Xiamen University, among others, are said to have sent out 1m text messages calling on their fellow citizens to take to the streets on June 1.

That day, and the following, protesters reportedly numbering between 7,000 and 20,000 marched peacefully through the city, some defying threats of expulsion from school or from the Communist party. The protest was captured on video and uploaded to YouTube.

Effective environmental protection requires transparent information, official accountability and an independent legal system. But these features are the building blocks of a political system fundamentally different from that of China today, and so far there is little indication that China’s leaders will risk the authority of the Communist party on charting a new environmental course.