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Effect of Light Pollution on Rietvlei
The effects of light pollution is widely reported in scientific literature; but it is interesting to note that most of the studies report on the effects of light pollution on human physiology and behaviour, as well as the negative effect lighting has on the night sky in cities and urban areas. The effect of light pollution on natural ecosystems was first studied in 1938, but only during the past 10 years has this subject been more fully researched; most probably due to more rapid encroachments of the urban environment into the natural environment.
This is a short summary of information from various sources on the effects of light pollution on ecosystems; it is by no means meant to be a scientific report on light pollution. Some of the information here may not be directly applicable to the situation at Rietvlei, but it does show the wide-ranging effects artificial lights have on ecosystems.
Light pollution poses a serious threat to wildlife, having negative impacts on plant and animal physiology. Light pollution can confuse animal navigation, alter competitive interactions, change predator-prey relations, and cause physiological harm. The rhythm of life is orchestrated by the natural diurnal patterns of light and dark, so disruption to these patterns impacts on ecological dynamics.
Recent studies concentrating on the perturbation of polarised light, or the artificial polarisation of light (even during the day) suggests deleterious impacts on animals and ecosystems. Natural polarisation of sunlight and its reflection is a source of information for many animals, particularly in determining direction. Polarised light pollution can affect behaviour patterns in such animals and alter ecological interactions.
Studies suggest that light pollution around lakes and wetlands prevents zooplankton, such as Daphnia, from rising to the surface and feeding on surface algae, helping cause algal blooms that lower water quality and leads to a decline in numbers and variety of plant and animal species.
Artificial light at night may interfere with the ability of moths and other nocturnal insects to navigate; this can affect night-blooming flowers that depend on moths for pollination as there is no replacement pollinator that would not be affected by night lighting. The result is a decline in these plants as they are no longer able to reproduce, thus changing the area’s long-term ecology.
The negative effect of artificial lighting on sea turtle hatchlings have been well documented; but recent studies indicate that artificial lighting also interfere with the breeding activity and reproductive cycles of toads and frogs – in many species these cycles are cued by moonlight and artificial lighting confuses the animals. Lighting during normally dark periods can also disrupt the level of melatonin production in amphibians and reptiles. Melatonin is a hormone that regulates photoperiodic physiology and behaviour; some species of frogs and salamanders use a light-dependent ‘compass’ to orientate their migrations to breeding sites. A number of studies indicate that in many amphibians and reptiles artificial light causes developmental irregularities such as retinal damage, reduced sperm production, and genetic mutations.
Studies in the United States, Canada and the Netherlands have shown that lights on tall structures can disorient migrating birds. The US Fish and Wildlife Service estimate that from 4-5 million birds are killed each year in the US after being attracted to tall towers. In Canada there is a programme whereby lights on tall structures are turned off during bird migration periods. Similar disorientation has also been noted for bird species migrating close to offshore oil and gas production facilities in the North Sea – since 2007 researchers in the Netherlands have been experimenting with new lighting technologies to reduce the number of birds circling production platforms.
Juvenile seabirds may be disoriented by artificial lights as they leave their nests and fly out to sea. Studies in England have indicated that the numbers of insectivorous English songbirds and bats could decline as their main source of food are now attracted to artificial lights where large numbers of prey die each night. The birds mostly feed at dawn and dusk when they catch the insects from grass and shrubs near ground level. Bats would generally avoid artificial lights and feed in the dark, there will be less food for them because their prey is now diverted to artificial lights.
Light Pollution and Rietvlei
Situated in an urban environment, Rietvlei has been subjected to light pollution from surrounding residential areas for many years. This would have had negative effects on the ecosystem, most likely in the estuary portion where residential and street lighting is close to the water body. Above the Otto du Plessis bridge artificial lighting has been mostly confined to the eastern and northern shore of the wetland, most of this lighting is nor very high above ground level.
A positive factor has always been the lack of major artificial lighting on the western side of Rietvlei, at least the portion between Sunset Beach and Dolphin Beach has been unlighted. At night there are lights from traffic on the R27, but this is transitory and there are periods during the middle of the night when there is no traffic.
The effects of the street lighting now erected on the R27 along the western side of Rietvlei can only have negative effects on the ecosystem. What these effects will be is not known, but this should have been investigated before the lighting was installed. In view of the facts at our disposal on the effects of artificial lighting in other ecosystems, further investigation into this important issue with respect to Rietvlei is strongly recommended.
Barrett, K., & Guyer, C. (2008). Differential responses of amphibians and reptiles in riparian and stream habitats to land use disturbances in western Georgia, USA. Biological Conservation, 141(9), 2290-2300.
Frank, Kenneth D. (1988). Impact of outdoor lighting on moths. Journal of the Lepidopterists' Society 42: 63–93.
Granta, Rachel A., Elizabeth A. Chadwick, and Tim Halliday (2009). The lunar cycle: a cue for amphibian reproductive phenology?. Animal Behaviour 78: 349–357.
Horváth, Gábor, György Kriska, Péter Malik, Bruce Robertson (2009). Polarized light pollution: a new kind of ecological photopollution. Frontiers in Ecology and the Environment 7:6, 317-325
Longcore, T and C. Rich (2004). Ecological light pollution. Frontiers in Ecology and the Environment 2(4): 191–198.
Malakoff, D. (2001). Faulty towers. Audubon 103(5): 78–83.
Moore, Marianne V., Stephanie M. Pierce, Hannah M. Walsh, Siri K. Kvalvik and Julie D. Lim (2000). Urban light pollution alters the diel vertical migration of Daphnia. Verh. Internat. Verein. Limnol. 27: 1–4.
Perry, G.; Buchanan, B. W.; Fisher, R. N.; Salmon, M.; Wise, S. E. (2008). Effects of artificial night lighting on amphibians and reptiles in urban environments. Urban Herpetology, 3, Society for the Study of Amphibians and Reptiles, pp. 239–256.
Rich, Catherine and Travis Longcore (2006). Ecological consequences of artificial night lighting. Island Press.
Rowan, W. (1938). Light and seasonal reproduction in animals. Biological Reviews, 13(4), 374-401.
Salmon, M. (2003). Artificial night lighting and sea turtles. Biologist 50: 163–168.
Scheling, L. (2006). Ecological Consequences of Artificial Night Lighting. Natural Areas Journal, 27(3), 281–282.
Woltz, H. W., Gibbs, J. P., & Ducey, P. K. (2008). Road crossing structures for amphibians and reptiles: Informing design through behavioral analysis. Biological Conservation, 141(11), 2745-2750.
Article written by Niel van Wyk. March 2010
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