Starting early in the morning of May 31, volunteers from Falmouth will fan out to estuaries along the Buzzards Bay coastline, where they will measure water temperature, dissolved oxygen, salinity and water clarity.

Just over a month later, beginning in early July, these same volunteers will return, but this time—and three more times over the summer—they will collect and filter water samples. These go to a laboratory at the Marine Biological Laboratory, where a team that I oversee painstakingly measures their nitrogen content.

These collections are part of the Buzzards Bay Coalition’s “Baywatchers” program. The program—started in 1992—now provides a long-running and invaluable look at the health of waters along half of Falmouth’s 68 miles of coastline. Falmouth Water Stewards volunteers make similar measurements of temperature, salinity and oxygen across 15 estuaries, including bays on the Vineyard Sound coast. Every four years, the Buzzards Bay Coalition compiles these data in a report on the health of Buzzards Bay.

The latest “State of the Bay” based on data through 2015 reported good news—an “encouraging pause in nitrogen pollution.”

One of the main reasons for this hiatus in decades-long worsening nitrogen pollution has little to do with anything we did in Falmouth. Rather, it has a great deal to do with what the United States did over many decades under a bipartisan consensus to clean up air pollution.

In 1970 Congress passed the Clean Air Act. That legislation authorized federal and state regulations to limit emissions from both power plants and vehicles. Congress created the Environmental Protection Agency the same year. Congress’s logic was that air pollution crosses state boundaries and can’t be regulated solely by states.

In 1990, under President George H.W. Bush, Congress passed amendments to the Clean Air Act that authorized control of acid rain. The amendments set limits on sulfur and nitrogen emissions, and allowed utilities and industries to trade emissions allowances. The final emissions caps were phased in in 2010.

This cap-and-trade approach was a resounding success. We now see the benefits to Falmouth’s waters. And here’s the evidence:

MBL scientists Javier Lloret and Ivan Valiela compiled and analyzed information on nitrogen deposited from the atmosphere—the fallout of air pollution—from 1980 to 2013 collected under the National Atmospheric Deposition Program. What they found and published in the journal Biogeochemistry last year was that starting in 1996, the deposition of nitrogen in New England started to decline. Today, atmospheric nitrogen deposition is half of what it was as recently as 2000.

This translates to direct benefits to Falmouth’s estuaries. Nitrogen coming from the atmosphere is the largest single input to most Cape Cod watersheds. Some of this nitrogen falls directly on open bay waters. Other falls inland, where soils and growing plants fortunately absorb about 90 percent of this nitrogen before it reaches estuaries. But a lot still gets through. Valiea estimated atmospheric deposition contributed 30 percent of the total nitrogen load to Waquoit Bay in the early 1990s.

We now likely see the beneficial effects of the success of the Clean Air Act nitrogen pollution reductions in the Buzzards Bay water quality data. The “pause” in the decline of our local water quality would almost certainly not have occurred without a strong national environmental policy. Thanks, EPA.

Declining nitrogen deposition buys us time. It does not clean up the other sources of nitrogen—particularly wastewater from septic systems—that cause our number one environmental problem. That job remains a high priority. Falmouth Water Stewards will continue to work with groups like the Buzzards Bay Coalition to advocate for better town-wide nitrogen removal treatment and continued monitoring.

But right now we in Falmouth owe the Clean Air Act and the EPA more than an acknowledging nod. We should thank them for saving us real dollars—dollars that we won’t have to spend in the future to clean up nitrogen that no longer reaches our estuaries.

(Christopher Neill is a senior scientist at the Woods Hole Research Center and a fellow at the MBL. He sits on the board of Falmouth Water Stewards and the Buzzards Bay Coalition.)

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