"You can work out the budget, and there is a phenomenal amount of nitrogen accumulating somewhere in the basin, " said Professor Tim Burt, also of Durham University.

BBC: Thames archive reveals long nitrate rise

The largest problem is the dangerous amount of nitrogen oxide (which mixes with vehicle-exhaust gas to create ozone, and then smog) coughed out by the state's industrial plants.

ECONOMIST: The Lone Smog State

But if these effects could be managed, then it is not clear that the amount of nitrogen being drawn out of the air would, of itself, be a problem.

ECONOMIST: The global environment

For years green groups have been trying to persuade the Environmental Protection Agency (EPA) to set a limit for the amount of nitrogen and phosphorus allowed in the states whose rivers feed the Mississippi.

ECONOMIST: Nutrient pollution

More stringent engine standards were already set to take effect three years hence, and the EPA was now requiring at least a 90% reduction in the amount of nitrogen oxides and soot emanating from diesel engines.

FORBES: Death By Hubris? The Catastrophic Decision That Could Bankrupt A Great American Manufacturer

So while the additional dissolved iron triggered an earlier-than-usual phytoplankton bloom, as the metal triggered growth in a greater number of phytoplankton cells, the bloom was only 15-20% larger than normal because the growth was limited by the amount of available nitrogen, another vital ingredient required for the organisms to develop.

BBC: Iceland volcano ash cloud triggers plankton bloom

The company is also experimenting with a new way of storing the hydrogen that will fuel its cells a fabric made of fibres of activated carbon that can (when cooled with liquid nitrogen) soak up the same amount of energy per kilogram as petrol.

ECONOMIST: Clean living in Iceland

Ms. PATTON: The Four Corners Power Plant and the Navajo Generating Station collectively discharge some 77, 000 tons of smog and haze-forming oxides of nitrogen each year, and that is comparable to the amount of pollution that would be discharged from some 80 million motor vehicles.

NPR: E.P.A Proposes New Rules on Haze