Thursday March 21, 2013 | 12:22 PM
Posted by Harold Johnson

Ever find one of these on your beach? 

It’s got quite a story.

On March 6, 2011, heavy rainfall hit NH’s Merrimack Valley.

A few days later, towns around the mouth of the Merrimack started reporting these strange 2” plastic discs washing up on their shores.

It turns out, the deluge overpowered the sewage treatment plant at the small town of Hooksett, north of Manchester. The plant couldn’t handle the flow, and it released 300,000 gallons of sewage into the Merrimack River.

But it wasn’t just sewage.

Hooksett had been trying out a new system to boost efficiency. It had placed millions of these discs into the sewage tanks. Their surfaces would give new habitat for the natural bacteria that breaks down sewage. More bacteria = more efficient treatment plant.

It all worked wonderfully. Until it didn’t.

When the deluge came, some 4.3 million discs were released into the Merrimack. Being buoyant polyethylene, they floated quickly downstream, and out into the Gulf of Maine.

There they dispersed, winding up on beaches farther and farther from home. The story of the spread of these disks is told by this Google Maps Web site. It was maintained through much of 2011 (I helped), with updates of the farthest-away sightings of these discs.

By March 11 they were seen all around Newburyport, MA. By the end of the month they had traveled to Cape Cod. By mid-May they had rounded the Cape and reached Nantucket. By June they were invading Rhode Island!

The northward trend is more interesting. By mid-April a few had reached York and Ogunquit, Maine. But then they stopped. The reason is simple. Maine & New Hampshire coastal currents run southward.

(Source)

Currents on our coast tend toward Cape Cod. From there they split, parts hugging the New England coast southwest, others turning east. (Sometimes going far east, to Ireland & England!)

Yet in the summer of 2011 -- almost all at once -- the discs started appearing all up and down the Maine coast. In July the first one was spotted in Saco. By early August they were in Casco Bay; a couple weeks later one was all the way up at Lubec!

What happened? The SCOPEX gyre happened.

(Source)

Just east of Cape Cod, this counterclockwise circulation grabs objects from one place and spits them out in another. Depending on where said object (like a sewage treatment disc) gets spat out, it can be on its way anywhere up and down the coast.

Of the original 4.3 million lost, the best estimate is that 400,000+ were never recovered after the initial cleanup. Every couple of months I find some. The blogger “Old Boatshoes” finds them in Marshfield, Duxbury, and Plymouth (http://oldboatshoes.org/2013/03/01/the-disk-2/). The “Trash Paddler” has found more than a thousand on Massachusetts rivers, and counting (http://www.trashpaddler.com/2013/02/riverside-visits-looking-for-spring.html). And look at them. After 2 years in the harshest of elements, they still look brand new. Our great-grandchildren will probably be finding these.

The tragedy of a plastic world is that every single accident like Hooksett dumps more nondegradable plastic junk into our ocean. But with this one, for once we know exactly where it came from, and when. That can help us tell the story of how plastic gets into our seas, how long it lasts, how it travels, and what on earth we can do about it.

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About the Author

Visiting a Maine beach in March 2010, Harold Johnson was shocked by the ocean-borne debris left by recent storms. He grabbed a garbage bag and a camera, and hasn’t looked back.

Since then he has spent most of his free time studying marine pollution, coastal ecosystems, and the mysteries and science of ocean and shore.

Copyeditor and writer by trade, historian and archaeologist at heart, Johnson’s philosophy is simple: Dig below the surface, travel the currents, make the connections, learn. Then share what you learn. He lives in Saco with his wife and young daughter. Follow on Twitter @FlotsamDiaries.

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