Nov 13, 2013

The Sludge at the Bottom of the Sea

In March, 1986, when New York started loading up barges with human waste and dumping it into the Atlantic, 106 miles off the coast, the EPA told environmentalists not to worry, that sludge wasn’t going to affect the ocean -- hell, it wasn't even making its way to the bottom.

The EPA's argument was that the ocean was so vast, when the barges dumped the sludge it would disperse harmlessly into the trillions of gallons of saltwater. That’s when the benthic guys, those scientists that are very interested in the activity down on the sea floor, called their bluff.

Starting in 1989, a team of bacteriologists, ecologists, chemists, geologists, and biologists went out to the 106-mile site on multiple expeditions, diving over and over in a tiny submarine to gather data. What did they find? The waste had affected the ocean. It had settled on the bottom, 2,500 meters down. More than that, it had left a vast footprint, covering an area of 80 square nautical miles with a film 5 centimeters deep.

On October 30, 1991, Fred Grassle, the expedition team leader, presented Congress with a 200-page report detailing the effects of the sludge. In 1992, the 106-mile dumping finally stopped, but, all that poop? It's still out there.

The Spot

USGS/Mike Bothner

The map above was created from a computer model, before any dives began. Using data such as ocean current and particle size, the team predicted where the dumped sewage might have settled in the ocean. To confirm their suspicions, the team measured the amount of silver in the ocean soil. Why's that? You see, back on land, throughout the time of the dumping, silver was used in photography and x-ray development, and a lot of it was making its way into NYC's sewer system. By taking core samples and measuring silver levels, chemist Mike Bothner and the team, “were able to develop a plume, a contour of silver, that mirrored the [predicted] dispersion of sewage sludge.” The amount of silver in the soil in this area of the ocean was seen to increase by twenty percent.

The Descent



Collecting Samples

The incoming waste roughly doubled the amount of food on the sea floor by roughly doubling the amount of carbon. As a result, opportunistic “surface deposit feeders," or animals that feed directly on small specks of organic matter -- your polycheate worms, sea cucumbers, and sea urchins -- rushed in to this newly carbon-rich environment and began proliferating. “If you look around sewage outfall, there’s going to be some animals that really love that," says Rose Petrecca, a benthic ecologist and part of the 106-mile investigation. And once the deposit feeders were there, then came the larger animals that eat them, say for example your rattail fish. Though one can't say necessarily whether such changes are good or bad for the environment, Petrecca explains that benthic ecosystems are very fragile.

A rattail swims by the submarine:

A sea cucumber crawls out from the ocean floor:

Net Pull 

The team, self-named Sister Sludge and the Mud Studs for their muddy deep-sea exploits, wrangle a sea trawler that has pulled up a sample of the sea floor, and along with it larger marine life. In the video, you'll see them grab rattail fish, sea cucumbers, and sea urchins from the mud and throw them in buckets for lab testing. In the lab, oceanographer Cindy Van Dover will remove the gonads -- the area with the most tissue in the body -- of the sea urchin, freeze and pulverize them, and then test them for an isotope of sulphur present in human waste but not normally found in high levels on the sea floor. Ultimately, the isotope was found, showing that the waste had entered the benthic food chain.

ALVIN Dangles

To explore the sludge site, two scientists and a pilot are all crammed into ALVIN, a personnel sphere that’s six feet wide and six feet high. “The night before your dive, the pilot takes you into the sub for the first time," says marine bacteriologist Russell Hill, reflecting on what it was like to climb in to ALVIN that night, as a young scientist part of the team. "The pilots are checking you out to see if you’re okay in this confined space. They run through the safety issues with you. They explain what happens if something goes wrong. They show you where the fire extinguisher is." He laughs, "You’re in this tiny titanium sphere, thousands of meters below the ocean. If there’s a fire, it wouldn’t be a good outcome." Despite the odds, scientists have continued to use ALVIN for all types of ocean investigations, squeezing into that space for more than 4,300 dives and counting since 1964.

Special thanks to Mike Bothner, Rose Petrecca, Fred Grassle, Russell Hill, and Cindy Van Dover, the scientists who spoke with us for the story. 

Image of submarine ALVIN courtesy of Deep East 2001, NOAA/OER

Image of rattail courtesy of Deep East 2001, NOAA/OER

Image of sea cucumber courtesy of Woods Hole Oceanographic Institution Archives

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