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removing the curtain

One of World’s Dirtiest Jobs : Removing ‘Curtain’ from Arctic Lake

In 1985, a “curtain” was installed to divide Lake N2 at the Arctic Long Term Ecological Research (LTER) site at Toolik Lake, Alaska. The goal was to produce a divided lake to study the effects of increased nutrients in an Arctic lake due to climate change and increased land use. The nutrients nitrogen and phosphorus were added to one side while the other side was the control side, free of any additions.

The curtain was made of polyethylene, with chains on the bottom to weigh it down in the relatively shallow (7-meter) lake and floats on the top to keep the top of the curtain floating. Ecosystems Center scientists and their LTER colleagues brought it across Toolik Lake by boat, then carried it the 300 or 400 yards to Lake N2. "The day the curtain was installed was very windy, recalls John Hobbie, principal investigator on the Arctic LTER project, and “the curtain came up in to the wind like a spinnaker.” It took some effort to bring it down and place it in the lake."

In June of this year, the curtain was removed. Senior scientist Anne Giblin was there. “It took 11 people six hours using five rubber rafts and four 55-gallon drums (for flotation) , three box cutters, two hack saws and one bolt cover to remove the curtain," she said.

The curtain had one length of 3/16" chain the entire length of the lake and another chain nearly as long attached to it. There were two other curtains which were put in to patch gaps and these were also weighted down with buckets of rocks. In order to remove the main curtain, Giblin and crew had to pull it up as much as possible, tie the lake end to the drums and cut it, then drag that piece onto shore. This process was repeated about four times and took three trips in a helicopter to sling the curtain back to camp.

“I don't know if anyone has an accurate weight on all that we moved, but the helicopter is able to carry 750 lbs and we needed three trips! The curtain was covered with slime and it resembled an episode of ‘world's dirtiest jobs’ for sure. The team of RAs, grad students and REUs was amazing, they never gave up in spite of the difficulties," said Giblin. Dan White , Wil Longo, Will Daniels and Marshall Moore of the MBL were part of the team, and spent the whole day kneeling in the rafts, pulling the curtain from the water.

For five years, from 1985 to 1990, the experimental side of the lake was fertilized with nitrogen and phosphorus at a rate that was approximately five times the natural rate. One of the early results, said Hobbie, was that most of the phosphorous ended up in the sediments. It wasn’t until the sediment was saturated with the phosphorus that other effects began to show in the lake, such as large amounts of algae.

One lesson from the experiment is that small amounts of nutrients do not create big changes in species. Another was that, to this day, the sediments have not returned to their previous chemical composition. The oxygen between the control and the fertilized sides is now similar but a bit lower than pre-fertilization. The fertilized side was deeper than the control side and oxygen in the deepest portions there did not fully recover. This was one reason the research team decided to remove the curtain to see if it impeded mixing and therefore, recovery.