It's a summer night near Germany's forest lake and something
strange happens. Beyond the dark waters of the sea, a soft glow emanates from
the rings of light above the ocean.
Nearby, bobbing red torchlights — the visible spectrum's
least-disruptive component — reveal scientists' presence on the shoreline. They
're seeing what happens when they rob their night's lake animals. This experiment
near Berlin is the most ambitious of many ventures in dark countryside patches
across Europe, set up over the past few years to check what light pollution is
doing to ecosystems. Researchers are increasingly concerned about the problem.
While several studies have reported how artificial light
affects individual organisms, the impacts on entire ecosystems and their
services, such as crop pollination, are less evident. Several field studies aim
to provide answers by tracking how plant and animal populations react to both
direct and more subtle night sky luminance, known as skyglow.
Environmentalists face challenges such as accurately
measuring light and determining how multiple organisms respond. But early
studies indicate that light at night exerts omnipresent, long-term ecosystem
stress, from coasts to farmland to urban waterways, many of which are already
suffering from other, more well-known forms of pollution.
It's an significant blind spot, says Steve Long, a plant
biologist at Urbana University, Illinois, and author of Global Change Biology. We
know more about increasing CO2 impacts, he says. "Just how severe are
light pollution impacts? We 're playing our future with what we're doing to the
world.
Dutch physiologist Frans Verheijen started researching how
lights attract animals and interfere with their behaviour. And in the 1970s,
further biological findings of light impacts started to appear in literature.
Nevertheless, it took two lateral biogeographers — Catherine
Rich, member of the Urban Wildlands Group in Los Angeles, California, and
Travis Longcore, now at Los University of Southern California. Angeles — to see
the correlations between them and organize a conference in 2002, followed by a
book, Ecological Implications of Artificial Night Lighting (Island, 2006).
In the vast majority of organisms — human, cockroach, or
plankton wisp — the process of light and dark is an important behavior
regulator. This mediates courtship, reproduction, migration, etc.
"Earth has changed drastically since life developed,
but bright days and dark nights still existed," says Christopher Kyba, a
physicist at Potsdam's German Geoscience Research Centre. If you change it, you
're afraid some stuff could screw up.
This change 's speed is growing. Striking photos from space
over the past two decades show how vanishing the night is. Estimates say that
more than one-tenth of the planet's land area experiences artificial light at
night — and that increases to 23 percent if skyglow is included. The scale of artificially
illuminated outdoor areas expands from 2012 to 2016 by 2 percent annually.
An unforeseen trend factor is the widespread installation of
light-emitting diodes (LEDs), which rise in popularity because they are more
energy-efficient than other bulbs. They appear to emit a wide-spectrum white
light which includes most frequencies essential to the natural world.
The phenomenon has had significant impacts on certain
species; lights are well-known, for example, to disorient migrating birds and
sea turtles. Scientists have also found that vanishing darkness disturbs the
behavior of crickets, moths and bats, and also increases bird-borne disease
transmission.
Probably the most deadly impacts on insects — vital food
sources and pollinators in many habitats. An estimation of the impact of street
lamps in Germany indicated that over a single summer, the light could wipe out
more than 60 billion insects. Some insects fly straight into lamps and sizzle;
some die after hourly circles.
Fewer studies have studied plants, but some that indicate
that light often disrupts them. In a UK study , scientists took a 13-year
record of timing of bud opening in trees and matched it with night-time
satellite illumination.
They noticed, after adjusting for urban heat, that artificial
lighting was related to trees bursting their buds more than a week earlier — a
magnitude close to that expected for 2 ° C global warming. A study of soybean
farms in Illinois6 found that light from adjacent roads and cars could delay
crop maturation by up to seven weeks and reduce yield.
Ecosystem effects
Now, some innovative projects are coming in. One of the
biggest is a field experiment in the Netherlands, where eight reserves and dark
areas host several rows of street lamps. The rows are different colors — green,
red, white, and switched off control row — and run from a grassland or heat
field into a forest.
For six years now, scientists and volunteers have used
camera traps to track small mammal activity; automated bat detectors to record
echolocation calls; mist nets to capture birds; and nest boxes to determine
timing and breeding success. Under the lights, botanists research plants.
The team found empirical evidence of the adverse effects of
light exposure on wildlife health. Songbirds roosting around the white light
had restless night, less sleep, and metabolic changes that may suggest poorer
health.
The project also investigated how light affects bats, which
had mixed fortunes under the explosion of artificial lighting. Some animals,
such as the common pipistrelle (Pipistrellus pipistrellus), feast on the insect
buffet they find circling lamps. Other, light-shy bats lost habitat and
vanished from some areas.
In the Netherlands report, red light had no effect on any
bat species, meaning it could be used instead of white.
But the experiment gave some surprising findings. Several
urban experiments find that nighttime artificial light causes songbirds to sing
earlier in daytime. As females prefer to select early-singing males, the
shifted dawn chorus can influence which birds will reproduce.
But the Dutch team found no impact on any of 14 species10.
The lighting may have been too poor to create an effect — it is designed to
reflect the level on country roads and bike paths, rather than an urban park's
glare.
These kinds of findings are useful to local governments,
says Kamiel Spoelstra, who leads the project at the Netherlands Institute of
Ecology (NIOO-KNAW) in Wageningen. Outdoor lighting regulations incorporate the
results of his team.
For example, he says, some areas trying to help local bat
populations have turned to red light, a trend he expects to develop.
Colored light also graces grasslands in southwestern
England, where a project known as Ecolight seeks proof of 'cascade effects'
where light impacts on one species have knock-on effects on the environment.
Ecolight's flickering cubes can be mistaken for an art
installation. Scientists led by Kevin Gaston, Exeter University, UK
biodiversity and conservation expert, have just finished studying 54 grassland
artificial communities.
Within some containers, bugs, slugs, pea aphids and 18 plant
species muddled around for 5 years, separated from outside world. Certain boxes
were simpler — containing plants, herbivores, or plants alone. Some were lit
with white light at night, others with amber, others only saw raw sky.
Light effects on grasslands are significant, partly because
roadside grass provides wildlife refuges and corridors in built-up areas.
Scientists discovered that amber light and, to a lesser degree, green,
inhibited trefoil flowering (Lotus pedunculatus)
The amber-lit boxes had a cascade effect. When pea aphids
changed from consuming shoots to feasting on flower heads in August, their
numbers dropped, probably due to less plentiful food. think it's the first scientific proof of a
strong, bottom-up effect of artificial light exposure, Gaston says. The team
shows more effects in its new, unpublished research, cascading on machine
predators.
Another comprehensive experiment in a dark skies reserve in
Germany's Westhavelland Nature Park showed that these cascade effects would
spill into neighboring habitats. Street lamps built out of water near
water-filled ditches attract aquatic insects,12 says Franz Hölker, an
ecohydrologist at Berlin's Leibniz Institute of Freshwater Ecology and Inland
Fisheries.
The insects flock to the lamps and become fodder for nearby
predators. Meanwhile, the hinterland, which would otherwise have received
insect visits, is deprived of a significant food source, he says.
These studies, which lay these relationships bare in
well-controlled, small-scale experiments, indicate "such impacts are more
likely to be taken seriously in the field and by regulators evaluating lighting
impacts," says Longcore.
Artificial light can also impact ecosystem services — the
benefits ecosystems offer to humans. A research published in Nature last year
found that lighting a collection of Swiss meadows prevented plants pollinating
nocturnal insects.
A team led by Eva Knop of the University of Berne 's
Institute of Ecology and Evolution found that insect visits to plants fell by
almost two-thirds under artificial light and that daytime pollination couldn't
compensate: plants produced 13 percent less fruit. Knop's team predicted these
changes could spread through the daytime pollinator population by reducing the
amount of food available. "This is a very significant research that
clearly shows that night artificial light inhibits pollination," says
Hölker.
Light skies
Most of Earth remains free from direct artificial illumination,
but skyglow — illumination scattered back to Earth by aerosols and clouds — is
more common. It may be so small that humans can not see it, but researchers
estimate it may still threaten 30 percent of vertebrates and 60 percent of
nocturnal and exquisitely sensitive invertebrates.
Skyglow "almost definitely" affects biodiversity,
Gaston notes, since the amount is far above the levels to induce many
biological responses. And yet, he notes, It's very hard to do the conclusive
analysis.
That's where the project forest-lake comes in. Glowing light
circles float over cylinders sunk into Lake Stechlin, recreating skyglow. They
are Leibniz physicist Andreas Jechow 's job, who had to find a way to generate
low-level, even illumination without blocking daylight or hindering scientists
entry.
Using state-of-the-art photonics devices such as an advanced
ray-tracing device, he and his team did this. "As biologists, we were too
unaware of the nature of light as a physical phenomenon," says Mark
Gessner, project manager, known as The LakeLab, and co-leader of his
artificial-light project, ILES (Illuminating Lake Ecosystems). In the past,
several studies have also failed to account for shifting the Moon through the
sky, he says.
The concept for ILES was to expand results from a well-known
zooplankton study, which during the day live in deep, dark water and migrate
night into shallower waters to graze on algae.
This movement is the world's largest biomass migration. A
study14 in lakes near Boston , Massachusetts, in the late 1990s indicated that
skyglow decreases the zooplankton 's increase by 2 meters and the number of
species that grow by 10–20%. This behavioral shift can be an unrecognized
catalyst of essential lake processes including algal blooms.
The 24 cylinders, each 9 meters in diameter, look from the
surface like a fish farm. Lighting them with various 'skyglow' rates and
monitoring the distribution of the tiny plankton using video cameras,
scientists found that skyglow had no significant impact on zooplankton
movement.
"We may have a modified migration trend, but I'm not
sure yet," says Gessner. While there's an impact, it looks like it's not
the profound one we've been expecting.
The unexpected outcome characterizes these challenging
studies. Gessner points out their experiment just completed their first season.
Maybe we don't need to be worried or maybe less worried — we don't know, at
least as far as the effects of skyglow on lakes are concerned, he says.
Bright future
Soft, careful research, but the field coalesces as proof
accumulates, says Gaston. The last two or three years saw a drastic change in
our perception,he says.
Nevertheless, changes are required. Also calculating
exposure is difficult. In the field, the light an individual receives may be difficult
to measure; for example, a bird can migrate to a nearby tree's shadow to avoid
illumination. Some scientists tried to tie light meters to birds to get a
better understanding of dose.
As the results show, one thing ecologists frustrate and
encourage is that the solution is at hand.
Longcore also collects published data on how various
animals, such as shearwaters and sea turtles, react to different sections of
the spectrum and adapt the results to the spectra produced by different
lighting styles. He needs to advise lighting decisions — for example, which
type of lamp to use on a bridge, and which at a seaside resort.
Technicians and environmentalists know that well-considered
lighting can perform its task without, as Kyba puts it, "spraying light
into the sky." For certain areas of the spectrum, LEDs can be changed to
glow, dim, and turn off remotely. "My dream," Kyba says, "is
that in 30 years the streets will be beautifully lit — better than today — but
we will use one-tenth of the sun."
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