The Dark Side of Light

September 24, 2019

Beneath the surface of one of Germany’s deepest lakes, researchers are studying the hidden effects of artificial light.

Martina Bauchrowitz put her back into it, swinging the oars in a wide arc, and the small boat lurched away from the lakeshore. I gripped the hull, shivering in the early-spring air, and watched our progress toward the rose-shaped metal platform floating on the surface of Lake Stechlin, one of the deepest lakes in northern Germany.

After a few minutes of rowing, we bumped against the side of the rosette. Bauchrowitz and I secured the boat and climbed out. Beneath the blue sky and puffy clouds, beneath the shiny platform and the dark, choppy waves, is another world—invisible in daylight and, more important, in darkness.

We stood on a floating plastic pontoon anchored among 24 aluminum cylinders, each protruding a few inches above the surface so that they resembled connected rings, like the petals of a flower. Each is a miniature ecosystem. They are, essentially, giant test tubes, each the size of a grain silo, nestled in Lake Stechlin. In this system of artificial lakes, scientists at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries can test their hypotheses in a natural environment.

“Watch your step,” Bauchrowitz said. I thought she was worried that I would fall, or worse, drop my notebook into one of the ringed enclosures, but that wasn’t what she meant. She gestured toward browning spots of caked-on guano.

“The birds are a problem. When they shit here, we have extra nutrients we would not have without the platform,” she said.

Most biologists conduct their laboratory experiments inside well-appointed rooms within nondescript buildings at research centers or on university campuses. But here, the lake is the lab. Every fish is counted, the density of microscopic plants and animals is carefully calibrated, and any excess bird crap must be cleaned up. The cylinders inside the lake are kept as pristine as possible until an experiment begins, and the scientists tinker with them the way their counterparts might meddle with the contents of a petri dish.

The Lake Lab was built so that ecologists could study a form of environmental change that rivals climate change in its scale and reach: the spread of artificial light at night.

Since 2010, the scientific literature has exploded with research examining light’s effects on individual species, from birds to fish to trees to humans. The news, in general, isn’t good. Artificial light changes animal migration and reproduction, tree leaf growth, bird nesting and fledging, pollination, human sleep, and much more. It even affects the spread of diseases. In July, researchers reported that West Nile–virus–infected house sparrows that live in light- polluted conditions are infectious for two days longer than those that live in darkness are, increasing the risk of a West Nile outbreak by 41 percent.

But none of this happens in a vacuum. The Lake Lab allows researchers to study how the effects of artificial light cascade through entire ecosystems—in this case, through bacteria, plankton, algae, and fish.

As a research station studying broad environmental change, the Lake Lab is a microcosm of the larger, uncontrolled experiment humans have been conducting on the planet since the start of the industrial age. But the lab is a version that we can control. It is a place where scientists can determine just how bad things have become, and how we can make them better.

Light is the basis for all life, but it is more than just a source of energy. It is also a source of information, telling organisms when to sleep, hunt, hide, migrate, metabolize, and reproduce. Since the advent of incandescent light bulbs, humans have been interfering with those messages. And the interference is worsening with the spread of LEDs, which consume less electricity and so are often brighter and stay on longer and later than their predecessors.

Since 2012, when a satellite began taking detailed measurements, light emissions have been rising at a rate of 2.2 percent a year on average. Previous work showed that light emissions are growing by as much as 20 percent in some regions. This is faster than the average annual growth of the global economy, the global population, and emissions of carbon dioxide.

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