In a remote valley in the Appalachian mountains, as the setting sun lit the tops of sycamore trees with gold light, Keith Eshleman strode down a ragged logging road, past yellow and white wildflowers, to his workplace.
Eshleman is a water quality scientist at the University of Maryland Center for Environmental Science’s lab in Frostburg. He stepped on mossy rocks through a stream called Black Lick, which has a water quality monitoring device in a box mounted atop a pipe.
It was here, nearly 200 miles from the Chesapeake Bay, that Eshleman made a discovery that turned the bay upside down. Over two decades of monitoring this and a dozen other streams that flow into the Potomac River, Eshleman found that levels of nitrogen – a pollutant that fertilizes algal blooms and dead zones in the bay -- plummeted as much as 70 percent in forested streams from 1995 to 2010.
“It was a complete shock,” said Eshleman, who earned a Ph.D. in water resources from the Massachusetts Institute of Technology. “You know, when we do things in hydrology and water quality, we expect to see a one or two percent improvement, or maybe a 10 percent improvement or a 10 percent decline. Those are pretty big numbers. So when we see a 50 to 70 percent reduction or something of that magnitude it’s absolutely, totally surprising.”
The combined effect from the drop in pollution in all these streams was a boost to the health of the Chesapeake. This was surprising, in part because the conventional wisdom was that wooded creeks like this had some nitrates in them, but that they were naturally-occurring from the decomposition of leaves caused by bacteria in the soil. Eshleman deduced that the huge change in nitrates must not have come not from the land, because the forests surrounding the streams had not changed.
“I said, ‘Oh my gosh. We’ve got something here we really can’t explain,” Eshleman said.
Instead, the water was being cleaned by the sky. Eshleman figured out the bulk of the nitrates in the soil and stream were not natural but instead had been carried by the wind from the smokestacks of coal-fired power plants in the Midwest, as well as from the tailpipes of cars and trucks. Altogether, about a third of the nitrogen pollution in the bay is from air pollution.
Back in 1990, President George H.W. Bush signed an amendment to the federal Clean Air Act that required air pollution control systems on coal-fired power plants to reduce sulfur dioxide emissions and acid rain. The intent of the law was to improve human health. But an unintended consequence of the filtration equipment on smokestacks was that they also substantially cut nitrogen water pollution in the Chesapeake Bay and other waterways.
Also helpful of also reducing nitrogen pollution in the bay, Eshleman said, were additional air regulations imposed by President Obama on power plants and vehicles, as well as a shift from coal generation to natural gas, which became cheaper with the advent of hydraulic fracturing.
“If there is one kind of interesting irony to this entire story it’s that it took air quality regulation to improve water quality,” Eshleman said. “So think about that. Water quality regulation is what should be working. But frankly, it appears to us – at least if you believe the data we are sharing – that it was really the air quality component that worked and not the water quality side of the house.”
Things in the bay are not what they seem. Upgrades to sewage treatment plants have been working to help the Chesapeake. But more than a decade of voluntary efforts to convince farmers to plant trees along streams and control runoff pollution in other ways on the land have not been as effective as attacking what’s falling from the sky.