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Ecological light pollution

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Ecological light pollution is the term used to describe how the presence of artificial light disrupts the lives of individual organisms and of the structure of ecosystems as a whole.

The effect that artificial light has upon organisms is highly variable, and ranges from beneficial (e.g. increased ability for predator species to observe prey) to immediately fatal (e.g. moths that are attracted to incandescent lanterns and are killed by the heat). It is also possible for light at night to be both beneficial and damaging for a species. As an example, humans benefit from using artificial light to extend the time available for work and play, but the light disrupts the human circadian rhythm, and the resulting stress is damaging to health.

Through the various effects that light pollution has on individual species, the ecology of regions is affected. In the case where two species occupy an identical niche, the population frequency of each species may be changed by the introduction of artificial light if they are not equally affected by light at night. For example, some species of spiders avoid lit areas, while other species are happy to build their spider web directly on a lamp post. Since lamp posts attract many flying insects, the spiders that don't mind light gain an advantage over the spiders that avoid it, and consequently become more common. Changes in these species frequencies can then have knock-on effects, as the interactions between these species and others in the ecosystem are affected and food webs are altered. These ripple effects can eventually affect even diurnal plants and animals. As an example, changes in the activity of night active insects can change the survival rates of night blooming plants, which may provide food or shelter for diurnal animals.

The study of ecological light pollution is still in its infancy, but it is already clear that the introduction of artificial light at night has had comparable, or perhaps greater, effect to other types of anthropogenic changes such as toxic pollution, land use change, and climate change due to increases in the concentration of green house gasses.

Natural light cycles

The introduction of artificial light disrupts several natural light cycles that arise from the movements of the Earth, Moon, and Sun, as well as from meteorological factors.

Diurnal (solar) cycle

The most obvious change in introducing light at night is the end of darkness in general. The day/night cycle is probably the most powerful environmental behavior signal, as almost all animals can be categorized as nocturnal or diurnal.

Seasonal (solar) cycles

The axial tilt of the Earth results in seasons outside of the tropics. The change in the length of the day is the key signal for seasonal behavior (e.g. mating season) in non-tropical animals. The presence of light at night can result in "seasons out of time" [1], changing the behavior and thermoregulation of affected organisms.

Lunar cycles

The behavior of some animals (e.g. coyotes[2], bats[3], toads[1], insects) is keyed to the lunar cycle. Near city centers the level of skyglow often exceeds that of the full moon[2], so the presence of light at night can alter these behaviors, potentially reducing fitness.

Cloud coverage

In pristine areas, clouds blot out the stars and darken the night sky, resulting in the darkest possible nights. In urban and suburban areas, in contrast, clouds enhance the effect of skyglow[3]. This means that the typical level of light is much higher near cities, but it also means that truly dark nights never occur in these areas.

The impact of clouds on light levels in urban and suburban ecosystems is completely reversed from what occurs in pristine areas.

Effects of light pollution on individual organisms

Insects

The attraction of insects to artificial light is one of the most well known examples of the effect of light at night on organisms. When insects are attracted to lamps they can be killed by exhaustion or contact with the lamp itself, and they are also vulnerable to predators like bats[4].

The compound eye of moths results in fatal attraction to light[4].

Birds

Lights on tall structures can disorient migrating birds. Estimates by the U.S. Fish and Wildlife Service of the number of birds killed after being attracted to tall towers range from 4 to 5 million per year to an order of magnitude higher.[55] The Fatal Light Awareness Program (FLAP) works with building owners in Toronto, Canada and other cities to reduce mortality of birds by turning out lights during migration periods.

Similar disorientation has also been noted for bird species migrating close to offshore production and drilling facilities. Studies carried out by Nederlandse Aardolie Maatschappij b.v. (NAM) and Shell have led to development and trial of new lighting technologies in the North Sea. In early 2007, the lights were installed on the Shell production platform L15. The experiment proved a great success since the number of birds circling the platform declined by 50 to 90%.[56]

Juvenile seabirds may also be disoriented by lights as they leave their nests and fly out to sea.[5]

Humans

At the turn of the century it was discovered that human eyes contain a non-imaging photosensor that is the primary regulator of the human circadian rhythm[5]. This photosensor is particularly affected by blue light, and when it observes light the pineal gland stops the secretion of melatonin. The presence of light at night in human dwellings (or for shift workers) makes going to sleep more difficult and reduces the overall level of melatonin in the bloodstream. Because melatonin is a powerful anti-oxidant, it is hypothesized that this reduction can result in an increased risk of breast and prostate cancer[6][7].

Other human health effects may include increased headache incidence, worker fatigue, medically defined stress, decrease in sexual function and increase in anxiety.[8][9][10][11] Likewise, animal models have been studied demonstrating unavoidable light to produce adverse effect on mood and anxiety.[12]

Turtles

Loggerhead sea turtles are attracted to street and hotel lights rather than to the ocean.[13]

Zooplankton

Zooplankton (e.g. Daphnia) exhibit diel vertical migration. That is, they actively change their vertical position inside of lakes throughout the day. In lakes with fish, the primary driver for their migration is light level, because small fish visually prey on them. The introduction of light through skyglow reduces the height to which they can ascend during the night[14]. Because zooplankton feed on the phytoplankton that form algae, the decrease in their predation upon phytoplankton may increase the chance of algal blooms, which can kill off the lakes' plants and lower water quality.

Polarized light pollution

Artificial planar surfaces, such as glass windows or asphalt reflect highly polarized light. Many insects are attracted to polarized surfaces, because polarization is usually an indicator for water. This effect is called polarized light pollution[15], and although it is certainly a form of ecological photopollution, "ecological light pollution" usually refers to the impact of artificial light on organisms.

References

  1. ^ Rachel A. Granta, Elizabeth A. Chadwick, and Tim Halliday (2009). "The lunar cycle: a cue for amphibian reproductive phenology?". Animal Behaviour. 78 (2): 349–357. doi:10.1016/j.anbehav.2009.05.007.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ^ C. C. M. Kyba and T. Ruhtz and J. Fischer and F Hölker (2011). ""Cloud Coverage Acts as an Amplifier for Ecological Light Pollution"". PLoS One. 6 (3). doi:10.1371/journal.pone.0017307. PMC 3047560. PMID 21399694.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  3. ^ C. C. M. Kyba and T. Ruhtz and J. Fischer and F Hölker (2011). ""Cloud Coverage Acts as an Amplifier for Ecological Light Pollution"". PLoS One. 6 (3). doi:10.1371/journal.pone.0017307. PMC 3047560. PMID 21399694.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  4. ^ Kenneth D. Frank (1988). "Impact of outdoor lighting on moths". Journal of the Lepidopterists' Society. 42. International Dark-Sky Association: 63–93.
  5. ^ RodrÍguez, Airam; RodrÍguez, Beneharo (2009). "Attraction of petrels to artificial lights in the Canary Islands: effects of the moon phase and age class". Ibis. 151 (2): 299. doi:10.1111/j.1474-919X.2009.00925.x.
  6. ^ Scott Davis, Dana K. Mirick, Richard G. Stevens (2001). "Night Shift Work, Light at Night, and Risk of Breast Cancer". Journal of the National Cancer Institute. 93 (20): 1557–1562. doi:10.1093/jnci/93.20.1557. PMID 11604479.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Eva S. Schernhammer, Francine Laden, Frank E. Speizer, Walter C. Willett, David J. Hunter, Ichiro Kawachi, Graham A. Colditz (2001). "Rotating Night Shifts and Risk of Breast Cancer in Women Participating in the Nurses' Health Study". Journal of the National Cancer Institute. 93 (20): 1563–1568. doi:10.1093/jnci/93.20.1563. PMID 11604480.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ^ Susan L. Burks, Managing your Migraine, Humana Press, New Jersey (1994) ISBN 0-89603-277-9
  9. ^ Cambridge Handbook of Psychology, Health and Medicine, edited by Andrew Baum, Robert West, John Weinman, Stanton Newman, Chris McManus, Cambridge University Press (1997) ISBN 0-521-43686-9
  10. ^ L. Pijnenburg, M. Camps and G. Jongmans-Liedekerken, Looking closer at assimilation lighting, Venlo, GGD, Noord-Limburg (1991)
  11. ^ Knez, I (2001). "EFFECTS OF COLOUR OF LIGHT ON NONVISUAL PSYCHOLOGICAL PROCESSES". Journal of Environmental Psychology. 21 (2): 201. doi:10.1006/jevp.2000.0198.
  12. ^ Fonken, L K; Finy, M S; Walton, James C.; Weil, Zachary M.; Workman, Joanna L.; Ross, Jessica; Nelson, Randy J. (28 December). "Influence of light at night on murine anxiety- and depressive-like responses". Behavioural Brain Research. 205 (2): 349–354. doi:10.1016/j.bbr.2009.07.001. PMID 19591880. {{cite journal}}: Check date values in: |date= and |year= / |date= mismatch (help)
  13. ^ M. Salmon (2003). "Artificial night lighting and sea turtles" (PDF). Biologist. 50: 163–168.
  14. ^ Marianne V. Moore, Stephanie M. Pierce, Hannah M. Walsh, Siri K. Kvalvik and Julie D. Lim (2000). "Urban light pollution alters the diel vertical migration of Daphnia" (PDF). Verh. Internat. Verein. Limnol. 27: 1–4.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  15. ^ Horváth, Gábor (2009). "Polarized light pollution: a new kind of ecological photopollution". Frontiers in Ecology and the Environment. 7:6 (2009/08). Accès Online: 317–325. doi:10.1890/080129. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
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