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The June 1995 of the Impacts Reporter is also available.
ISSN 1203-1429 The UVB Impacts Reporter: VOLUME 3: SAMPLE ISSUE
The following articles are selections from the first two volumes of The UVB Impacts Reporter.
Australia has the highest incidence of skin cancer in the world. An estimated two of every three will develop at least one skin cancer in their lifetime. However, many Australians continue to pursue activities contrary to recommended exposure to the sun. Following an extensive review of the psychological literature on suntanning and sun protection, psychologists Stephen Arthey and Valerie Clark of Deakin University and the Anti-Cancer Council of Victoria found that many people have a high degree of knowledge of the dangers of excessive sun exposure but do not transfer this knowledge into changes in behaviour. Indeed, many still actively desire and seek a tan.
The medical literature has rather conclusively shown that overexposure to the sun is damaging to the human body, especially the skin. Most well known are the effects of sunburn. Skin aging and cancer are also fairly well known effects of sun exposure while eye damage and impacts on the immune system are less well known. However, many people continue to hold deeply the beliefs that a suntan is necessary for looking and feeling attractive and healthy, and that it is easier to enjoy the summer with a tan.
A suntan has been a status symbol among Caucasians since the industrial revolution. Before that time, pale skin was fashionable because it indicated wealth and no need to work out- of-doors. With industrialization, however, the status of tanned skin reversed. It was now considered a sign of an abundance of leisure time to spend outdoors. Suntanning as a fashion statement began in the 1940s promoted by Coco Chanel, the French fashion designer.
The suntan's association with health began in the early 1900s as treatments known as "heliotherapy" came into vogue. Though mostly discredited in the 1940s and 1950s, the belief that sun exposure as a cure-all have persisted.
The popularity of suntanning as a symbol of health, wealth and fashion has risen almost unabated since the end of World War II. Only recently, spurred by a rapid rise in skin cancers and decline in the ozone layer, has there been an attempt to reverse this popularity. The campaign has been difficult - not so much in spreading information, but in affecting change in beliefs and behaviour.
While the level of knowledge concerning skin protection and the dangers of skin cancer is considered high, many continue to believe that the risks are outweighed by the benefits of a suntan. As the desire for a tan decreases, however, there is more willingness to engage in sun protective measures. Personal knowledge of someone with skin cancer also increases willingness to engage in skin protection practices.
Even for those who have a strong knowledge of the dangers, changes in behaviour are reluctant. Keesling and Friedman (1987) found that "sunbathers seem less concerned with their actual health than with the appearance of health." An additional factor is the 'optimistic bias' whereby an individual believes that something negative is less likely to happen to them than to their peers.
There is a marked difference in health beliefs, behaviour and choice of sun protection among groups segregated by occupation, age and/or gender. For example, younger people will more likely rely on a sunscreen for sun protection while older people prefer to cover-up with clothing. Such differences are important to consider when designing education campaigns. Arthey and Clarke suggest that it is perhaps better to produce several group-specific messages than a blanket message.
Females are more likely to be concerned with health and healthful behaviour and engage in more preventative medical behaviours than males. Females also generally have a higher level of knowledge of effects of sun on the skin. However, this does not seem to have a marked change in their desire for a suntan nor their belief that a tan is healthy.
Adolescents are more likely to spend the most time in the sun and are the most determined to get a suntan. They are also the most resistant to advice on what to wear and how to behave in the sun. Adolescents may have a sufficient knowledge of the dangers of excessive sun exposure but are highly susceptible to social pressure from the media and their peers with regard to the attractiveness and fashionability of suntans. Yet it is in adolescence that the greatest long-term damage to the skin is done.
Outdoor workers are another group at high risk for skin cancer and other sun-related skin and eye damage. Information campaigns aimed specifically at outdoor workers in Australia have been shown to have good success in changing behaviour. These campaigns can be further tailored to account for gender differences. Men, for example, are more likely to wear hats than women for sun protection and less likely to wear shirts or other upper body protection.
A major obstacle to sun/anti-cancer campaigns is the widespread belief that skin cancer is a disease of the elderly, one which will not occur for 20 years or more. Since the most distant practical timeframe that concerns most people is 10 to 15 years, the threat of skin cancer is beyond the timeframe for apprehension and practical action. In addition, people tend to over- evaluate short-term threats in relation to more distant ones and to value immediate gratification more than those in the distant future.
Arthey and Clarke thus suggest that "for people to begin to change their behaviour it is necessary to reduce the timeframe that they associate with the consequences of over-exposure to the sun, increase the urgency of the message on the dangers of over-exposure to the sun and demonstrate the existence of virtually immediate rewards for covering-up when in the sun."
They summarized their research by stating that "at present, the public has been found to have a high level of knowledge on the dangers of over-exposure to the sun, however many people still desire, and some go to great lengths to get, a suntan." Some of the major barriers in this area are that having a suntan is seen as being both healthy and attractive, and it is not 'cool' to cover-up. Interventions may be more effective if directed at specific high risk groups.
Arthey and Clarke conclude by noting that, "knowledge must precede any attempts to alter behaviour, but knowledge alone will not necessarily result in changes to behaviour." Educational programs which rely solely on increasing the public's level of knowledge are likely to have only limited success in changing behaviour.
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The study of UVB impacts on aquatic ecosystems has mainly focused on the marine environment, especially in polar waters under the Antarctic Ozone Hole. The role of UVB in freshwater ecosystems is complex and highly influenced by UVB-absorbing organic matter dissolved and suspended in the waters. These compounds in all but the clearest lakes limit the penetration of UVB radiation. The depth to which the UVB radiation has been reduced to 10% of its surface value is usually less than a few metres. On the other hand, the average depth of the world's lakes is less than 10 metres and the most favourable growth conditions are generally found in the mixed surface waters, a layer only a few metres thick. Rivers and streams often have much higher loadings of organic matter but are also much shallower than lakes, and thus potentially more vulnerable to damaging UVB radiation.
With the possible exception of some of the clearest lakes in the world, freshwater environments generally have a more rapid change with depth of light, temperature, oxygen, predators, food quantity and quality and other habitat characteristics than marine environments. Williamson (1995) suggests that "in these steep gradients strong selective pressure exists for lacustrine organisms to be finely tuned to changes in UVB radiation that it will interact with other environmental variables, and that it influences not only the primary producers, but also many trophic levels simultaneously, often with unexpected consequences."
Williamson (1995) has reviewed the literature and synthesized the complex role of UVB radiation on freshwater ecosystems into four impacts hypotheses: the solar ambush hypothesis, the solar bottleneck hypothesis, the solar cascade hypothesis and the acid transparency hypothesis.
Solar ambush hypothesis
Those aquatic organisms that cannot detect and respond to changes in UVB radiation are vulnerable to injury. Organisms that are able to detect and respond to UVA wavelengths or visible light but not to UVB may thus be "ambushed" and damaged by wavelength-selective changes in solar radiation. That is, they will remain in positions in their habitats which they perceive as benign while being damaged by UVB irradiance. Examples of freshwater invertebrates that are especially vulnerable are the euphausiid Thysanoessa and the midge fly larvae of Chironomidae.
Sessile or non-free moving organisms and organisms in high-elevation lakes may be particularly at risk to solar ambush. The latter are vulnerable to severe fluctuations in UVB because high-elevation lakes are generally shallow or lacking in absorptive organic matter. Most vertebrates do not have sensitive photoreceptors which extend below the UVA wavelengths and are thus also susceptible to solar ambush.
Solar bottleneck hypothesis
In lakes with low nutrient content (oligotrophic lakes) around the summer solstice, small zooplankton may encounter a bottleneck resulting from two conflicting pressures: the need to migrate toward the surface away from predatory invertebrates, who have moved to greater depths fleeing larger predators, and the need to avoid damaging solar radiation in the surface waters. In lakes where UVB penetration is greatest, small zooplankton are thus caught in the bottleneck between predation and solar/UVB damage. If the zooplankton are unable to detect and respond to UVB radiation, then the solar bottleneck is also a solar ambush.
In lakes with high levels of organic nutrients (eutrophic lakes), the upper layer absorbs enough radiation and remains a safe haven for the small zooplankton.
Solar cascade hypothesis
UVB can also have a strong indirect influence on organisms by its impact on food resources and predators. This hypothesis is an extension of the well-known ecological concept of cascading trophic interactions. That is, impacts on one level of the food chain by an outside agent have cascading effects into both lower and higher levels of the food chain.
Combined direct and indirect impacts of UVB may either accentuate the damage or decrease it. An example of the latter has been illustrated in the work of Bothwell et al. (1994) who found that algae biomass initially reduced by direct UVB impacts was able to rebound when the grazer population feeding upon it was also reduced by UVB.
Acid transparency hypothesis
Lakes acidified by human influences are a harsher UVB environment than naturally acidified lakes. Lakes which are naturally acidic often have high concentrations of humic substances which attenuate UVB radiation within a few centimetres of the surface. Lakes acidified through the deposition of anthropogenic emissions of sulphates and nitrate compounds tend to have reduced levels of humic materials and are thus much more transparent to UVB radiation. UVB may play some role in the changes in species diversity observed during lake acidification.
Conclusion
One of the most important concepts for assessing the impacts on freshwater ecosystems is that complex rather than simple responses are likely the rule. Responses will not be limited to simple decreases in primary production of biomass. In fact, shifts in the community structure may initially be more common and result in little detectible difference in ecosystem biomass.
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While a number of studies have reported adverse impacts on the growth and function in plants, there are only a few reports on the potential effects of UVB on the incidence and severity of plant diseases. Those studies which do exist show that UVB may either enhance or reduce disease depending on the species and even the cultivar. The timing of the exposure may also be critical (Caldwell et al., 1994).
Spore formation by many pathogenic fungi is activated by increases in levels of ultraviolet radiation (UVR), both in the UVA and UVB wavebands (between 310 and 400 nm). Exposure to UVR either initiated or increased spore formation and release (sporulation). It is believed that fungi use intense short-wave light as a signal to initiate their reproductive phase. Since extended periods of high UVR fluxes are often associated with dry weather conditions, using this signal may be a way in which fungi protect themselves from drying out and from radiation damage (Manning and Tiedemann, 1995). Such weather conditions are also conducive for spore dissemination by the wind.
Commercial greenhouse operators may use this UVR trigger to commence sporulation as a means of reducing fungal infection. By covering greenhouses with a UV-absorbing plastic film, they may reduce or prevent sporulation. The practice may be 90% effective in fungal disease control for certain foliar pathogens on vegetables. (Manning and Tiedemann, 1995)
Since UVB stimulates sporulation in fungi, one might speculate that an increase in UVB would enhance the incidence of fungal epidemics. However, Manning and Tiedemann (1995) believe that there is already sufficient UVR in sunlight to promote sporulation and the slight increase in UVR energy resulting from ozone depletion would not likely have a strong influence on the life cycle of pathogenic fungi. Too little is known at present to determine if a notable shift in the quality of solar radiation would have any additional influence.
Cucumbers inoculated with Colletotrichum lagenarium (anthracnose) or Cladosporum cucumerinum (scab) showed increased disease when exposed to enhanced UVB radiation prior to the infection. Irradiation after inoculation, however, showed no increase in the severity of either disease (Orth et al, 1990) Enhanced UVB had a negative impact on sugar beet infected with the fungus Cercospora beticola (Caldwell et al, 1994).
Increased infection of wheat by wheat rust (Puccunua recondita f. sp. tritici) under enhanced UVB irradiation varied with cultivar. The rust-resistant cultivar 'Florida 301' showed little effect whereas in the rust-susceptible cultivar 'Red Hart' added UVB increased the number of rust infections (Manning and Tiedemann, 1995).
Thus, Manning and Tiedemann concluded from a recent literature survey that studies have shown UVB radiation may increase or decrease the severity of biotic disease or may have no effect. In nine of the thirteen studies of necrotic fungi pathogens, UVB enhanced disease in host plants. In contrast, for three of four biotrophic fungi studied, disease was reduced. Like the direct impacts of UVB on plants, there is a wide variation in reactions to increased UVB radiation not only among species but also among cultivars (Manning and Tiedemann, 1995).
The principle effects of UVB on the course of plant diseases are likely due to alterations caused in the host plant rather than on the pathogens. For example, in many plant species, UVB produces or increases chemical compounds such as flavonoids and other phenolic compounds as a protective response to UV radiation. These compounds may also act as an antibiotic agent to disease organisms although there have as yet been no clear studies pointing to this effect (Manning and Tiedemann, 1995). On the other hand, UVB injury to cellular membranes and their functions may provide a site for pathogen entry.
UVB is also known to promote onset of maturity and death in plants. By changing the length of plant life cycles, UVB may open pathways for a variety of pathogens such as necrotrophic pathogen and latent infections (Manning and Tiedemann, 1995).
UVB may also have indirect impacts on the course of disease through alterations in the plant canopy structure through its influence over biomass production and allocation. A denser canopy would likely be moister and warmer than a more open canopy where wind speed and evaporation potential are higher. These conditions are conducive to the development and spread of many diseases. Such effects of a denser canopy on disease have been demonstrated in experiments where added fertilization resulted in greater biomass growth (Manning and Tiedemann, 1995).
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Outdoor exposure to solar ultraviolet radiation is the primary environmental cause of the degradation of non-metallic materials, particularly polymer material such as rubber and plastic. With increasing UVB radiation, many polymer materials will degrade more quickly, thus reducing their useful lifetime.
Materials used in outdoor applications which are most affected by UVR radiation include:
Damage to materials is caused by all UVR wavelengths with the shorter wavelengths having the greater impacts. The sensitivity to different wavelengths and dosages required for particular types of damage depend upon the composition of the particular material. Damage may be manifest through discoloration, chalking, blistering, brittleness, loss of strength, warping and cracking. Higher temperatures enhance the rate of photodegradation. Thus, darker surfaces degrade at a faster rate than white or light-coloured materials (Andrady et al., 1989).
To minimize degradation by UVR, chemical stabilizers are often added to rubber and plastic materials. Higher UVB levels will require a greater use of stabilizers, the design of new stabilizer compounds, the development of more resistant materials, or the substitution of alternate materials which are not degraded by UVB (Andrady et al., 1989)
Data available on polyvinyl chloride (PVC) materials indicate that damage increases exponentially with decreasing wavelengths of sunlight. The UVB portion of the solar spectrum is especially damaging to PVC (Andrady 1993).
Discoloration of materials and surface coverings is caused by photoreactions between the material and UVB radiation. In many cases this can dramatically reduce the lifetime of the product. Examples where discoloration is important include: building vinyl siding, lettering on signs, decorative art work and house paint (Andrady et al., 1994).
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While aquatic ecosystems have evolved under a wide range of solar ultraviolet radiation from the polar seas to the tropics. there is now overwhelming evidence that even small increases in UVB exposure is harmful, especially to the primary producers in the marine food chain: the phytoplankton. Adverse impacts on phytoplankton will have dramatic consequences on the global environment because these organisms annually produce more than one half of the Earth's biomass. UVB radiation affects biological adaptive strategies, impairs important physiological functions and threatens many marine organisms during their development stages. UVB has been shown to have deleterious effects on phytoplankton through impacts on DNA; direct impairment of photosynthetic systems, enzyme activity and nitrogen incorporation; bleaching of cellular pigments; and inhibition of the ability to move and orient with respect to solar irradiance (H„der et al., 1994)
Phytoplankton convert approximately 104 billion tons of atmospheric carbon annually into organic material (Houghton and Woodwell, 1989). Estimates of the reduction in phytoplankton productivity as a consequence of ozone depletion suggest a 16 percent depletion of the ozone layer may result in a 5 percent loss of productivity which translate to a loss in fish biomass of about 7 million tons per year. Because the sea provides more than 30 percent of human animal protein consumption, such losses have wide ranging effects on the health and welfare of humans (H„der et al., 1994).
The distribution of phytoplankton is not uniform around the world's oceans. With the exception of certain areas along the continental shelf where nutrient upwelling supports large populations, concentrations of phytoplankton are 10 to 100 times greater in high latitude than in the subtropical and tropical waters. UV radiation may play a role in this variation as well. In many temperate waters, phytoplankton blooms in the spring are followed by a secondary bloom in autumn. Concentrations of phytoplankton drop during summer when UVB levels are high. This temporal distribution pattern suggests that natural UVB radiation cycles may control phytoplankton populations (H„der et al., 1994).
Recently, populations of very small phytoplankton - nanoplankton and picoplankton - have been found to be much larger than previously estimated. They are now thought to make up 40 percent of the total biomass in the oceans. The role of bacterioplankton has also gained in significance, especially in the degradation and cycling of organic matter in the sea. UVB has been shown to significantly affect bacterial plankton and microplankton because of their size and short generation times. As a result, increases in UVB may play key roles in niche separation and distribution of species in the lower food-web processes (H„der et al., 1994).
Phytoplankton productivity is limited to the upper layer of the ocean (the euphotic zone) in which there is sufficient sunlight to support photosynthesis. The transparency of water to solar radiation is wavelength dependent and is strongly influenced by the concentration of particles and dissolved organic materials within it. In coastal waters where concentrations of these materials are high, the depth at which UVB is reduced to 1 percent of its surface strength is less than a metre. In clear ocean waters, this depth reaches several tens of metres (H„der et al., 1994). In very clear Antarctic waters UV penetration to a depth of 65 m has been measured (H„der et al., 1991).
The vertical position of phytoplankton in the surface layer is affected by wind and wave, and to some degree by the organism's ability to actively move within the water column in order to maximize productivity and to avoid hazardous levels of solar radiation. Phytoplankton use visible and UVA light to orient themselves; however, like humans, phytoplankton are unable to perceive, and thus avoid, UVB radiation. Even brief exposure to UVB may damage the organism's ability to react to visible and UVA light and may reduce the speed of its movement away from damaging light. Thus, UVB may not only have a direct impact on production but also an indirect one. UVB damage to the phytoplankton's ability to position itself to a favourable depth may allow UVA to impair its photosynthetic ability (H„der et al., 1994).
In both the Antarctic and tropical waters, photosynthesis is impaired approximately equally by both UVA and UVB light. Screening of most of the UV wavelengths below 378 nm results in an increase in photosynthesis by 10 percent to 20 percent (H„der et al., 1994).
Field studies of phytoplankton productivity in Antarctic waters under the spring ozone hole have given researchers the opportunity to study impacts under a wide range of UVB irradiation. Although the ozone column only modifies a narrow (40 nanometre-wide) band of the UV spectrum reaching the planet's surface, some phytoplankton species show negative responses to changes in radiation as small as 0.01 percent of incident UVB. As well, biological effects are very wavelength dependent.
Time for UV photoadaptation is one of the most critical aspects of a species' tolerance to UVB radiation. Antarctic organisms have the same UV tolerance mechanisms found in organisms worldwide. However, the rapid increase from the dark of polar winter to very high springtime UVB irradiance under the ozone hole, which are equivalent to mid-summer levels, provides little time for adaptation (Karentz, 1994).
For several years a field research program known as Icecolors has quantified changes in phytoplankton productivity as a function of UVR, UVA and UVB irradiance in the Antarctic Ocean along the marginal ice zone where phytoplankton blooms contribute significantly to the overall biomass production of the Antarctic Ocean and are subject to the rapid increase in solar radiation in the spring. These experiments have taken advantage of the movement of the ozone hole above them so that data can be collected under a wide range of ambient UVR levels (Pr‚zelin, et al., 1994). Icecolors '90 demonstrated, for the first time, the negative effect of ozone-dependent increases in UVB radiation on the primary production in natural marine communities. The results suggest: previous estimates of carbon production loss in the Antarctic waters have been conservative; UVB inhibition may be greatest in the morning and mitigated later by photoprotective mechanisms; and photoprotective mechanisms for UVB exposure may be regulated by UVA levels (Pr‚zelin, et al.., 1994).
Estimates of the ozone-related damage to phytoplankton productivity suggest decreases of 6 percent to 25 percent under the Antarctic Ozone Hole. Other studies which differentiated UVB and UVA impacts show that UVB impaired photosynthesis by 4.9 percent while UVA's effect was 6.2 percent (H„der et al., 1994.
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The global decline of amphibian species - toads, frogs and salamanders has puzzled and alarmed scientists in recent years. "Amphibians are like canaries in the mine shaft," commented Richard Wyman of the E.N. Huyck Preserve in Rensselaerville, NY. Possible causes for the decline include air and water pollution, climate change, bacteria and other diseases and UV radiation.
A study recently published by a team of Oregon State University scientists led by Dr. Andrew Blaustein (Blaustein, et al., 1994) suggests a link between the population decline of many amphibian species around the world and increased UVB damage. Their study included a laboratory study of the ability of 10 species to repair DNA damage in eggs caused by UV radiation and a field study to determine hatching success of three Oregon frog species.
Results from the laboratory study showed that the ability to repair UVB-induced damage to DNA in eggs and oocytes varied greatly among nine U.S. Pacific Coast amphibian species. While the activity of a key UVB-specific repair enzyme, photolyase, were reproducibly characteristic for any single species, the variation between species was over 80-fold. This showed that the impact of UVB on amphibians varied greatly among the species.
Key to this variation was the observation that the highest enzyme activity occurred in the Pacific tree frog (Hyla regilla), a frog whose population is not known to be in decline. In sharp contrast were the lower enzyme activities of the Western toad (Bufo boreas) and the Cascades frog (Rana cascadae). Populations of both the Western toad and Cascade frog have undergone such drastic declines in recent years that they are candidates for designation as threatened species.
A field study of the impacts of natural sunlight on the eggs of the three above-named frog species was conducted in the spring of 1993. All three species lay their eggs in open, shallow water. Four sites were selected in the Cascade Mountains of Oregon ranging in elevation from 1220m to 2000m. Eggs at each site were divided into three sunlight treatments: unfiltered sunlight; sunlight filtered to remove UVB and shorter wavelengths; and sunlight filtered to remove only wavelengths shorter than UVB. The experiment continued until all the original egg embryos either hatched or died. Survival was measured as the proportion of hatchlings produced.
Hatching survival rates for the eggs of the Pacific tree frog were high and similar for all three sun treatments. This result was expected given the high enzyme activity found in the laboratory for this species. For both the Western toad and Cascades frog, the survival rate was significantly higher for those eggs exposed to UVB-filtered sunlight than eggs exposed to sunlight containing UVB.
Blaustein et al. therefore concluded that the results supported the UV-sensitivity hypothesis that increased UVB radiation may contribute to population declines in certain species.
Blaustein has also suggested that the Western toad may be impacted by a known fungal disease common to fish raised in hatcheries. Studies in humans and other mammal species indicated that UVB radiation may suppress the immune system's ability to fight diseases which enter through the skin. If UVB radiation has a similar effect on frogs, it could make frogs and other amphibians more susceptible to fungal and other diseases and thus further reducing the population.
Reference:
Around the world, many amphibian species are declining due to a variety of environmental impacts: loss of habitat, disease, changing climate, and pollution. Research led by Andrew Blaustein of Oregon State University ( Blaustein et al., 1994) reported that exposure to natural levels of UVB radiation significantly reduced egg hatching success in two of three species of frogs from the Pacific Northwest. They concluded that increased levels of UVB radiation resulting from ozone depletion caused declines in populations of the Western toad (Bufo boreas) and Cascades frog (Rana cascadae) whereas the UVB-tolerant Pacific tree frog (Hyla regilla) population was stable. Further research by Blaustein has indicated a pathogenic fungus transmitted from introduced stocked fish when combined with UVB radiation killed embryos of the Cascades frog and Western toad.
In contrast to Blaustein's studies, research undertaken by Karen Grant and Lawrence Licht (1996) at York University in Ontario, Canada concluded that ecologically relevant dosages of UVB had no discernable effect on the early life stages of four species of Ontario frogs: Bufo americanus (American toad), Hyla versicolor (Grey tree frog), Rana clamitans (Green frog) and Rana sylvatica (Wood frog).
Grant and Licht collected eggs from these species from natural breeding areas around southern Ontario. Some eggs were used for hatching success experiments and others were hatched for experiments on larval and metamorphosed forms. Their intent was to determine lethal and sub-lethal levels of UVA and UVB for embryos, larvae and metamorphosed forms. Experiments were conducted in the laboratory using UVA from unshielded lamps (F20T12BLB Damar) and UVB from ChromatoVue Model UVM-57 lamps. Intensities of UVB were altered using varying layers of acetate filter under the lamps. Initial experiments used unshielded lamps which produced lethal intensities much higher than would be expected in natural settings. For control treatments, daylight fluorescent light was used. All UVR treatments were administered with a background of daylight fluorescent light to allow for photorecovery.
UVA had no effect on eggs or larvae at exposures as high as twice the normal outdoor intensity.
Eggs of R. sylvatica exposed to unshielded UVB for 30 minutes all died, but 63 percent or more survived 15 minutes at this level of irradiation. When exposed to natural levels of UVB radiation, there was little mortality. An interesting sidelight was the synergistic effect of temperature and UVB exposure. Eggs hatched in 20oC water and exposed to UVB were generally unaffected. However, eggs hatched in 12oC water and exposed to UVB for 10 to 15 minutes had "a high survival rate, but a high proportion of hatchlings subsequently showed morphological and behaviourial abnormalities." Grant and Licht suggest that at the lower temperature, the slower development rate of embryos or impeded photorepair may resulted in a higher cumulative irradiation before hatching, thus causing UVB damage in the larvae: curvature of the spine, outpocketing of the midsection and erratic, circular swimming behaviour.
Grant and Licht feel that the results of Blaustein et al. attributing UVB to population declines in frogs through reduced hatching success cannot be supported by their findings. They further suggest that Blaustein's experimental techniques may have exposed the eggs to abnormal levels of UVB by placing the eggs in water that was too shallow and devoid of protective vegetation or substrate debris. In addition, the eggs used in his studies apparently had their protective jelly matrix removed. Eggs of amphibians are surrounded by a number of jelly coats. Grant and Licht investigated the UV transmittance of jelly from R. sylvatica, B. americanus, and R. aurora (Red-legged frog from British Columbia) and found UV transmission reductions of 7, 14 and 6.5 percent, respectively.
Only 30 percent of the R. clamitans larvae survived when exposed to 2 or 3 minutes of unfiltered UVB whereas the other four species had a zero survival rate. The surviving larvae, however, showed delayed development which would have reduced their probability of metamorphosing successfully. Since most larvae died after receiving 2 or 3 minute high-intensity exposure while eggs survived even longer exposure, indicates that embryos may be more tolerant than larvae, perhaps through protection offered by the jelly capsules of the eggs.
Only high-intensity UVB affected tadpoles of the four species while the ecologically relevant levels had no obvious effect. In these experiments the tadpoles were fully exposed and not able to seek or receive shelter from UVB in their environment. All recently metamorphosed juvenile R. clamitans and R. sylvatica exposed to high-intensity UVB died while 32 percent of B. americanus survived the 2-week testing period.
In frogs and toads, the egg stage appears to be the most defenceless, being unable to flee from perceived dangers. However, the photorepair mechanism detected in eggs coupled with a copious protective jelly covering and physical protection afforded by the environment suggest, according to Grant and Licht, that dosages received even under projected increases in UVB should not be sufficient to have an effect on embryonic survival. In addition, given their ability for avoidance of open sunlight and natural protection features of the environment, advanced larval and adult stages are unlikely to be affected by natural levels and projected increases in UVB radiation.
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During late July and August, 1995, foliage on broad-leafed trees in two valleys (Coal River Valley and valley parallel to the south) in southern West Virginia exhibited widespread damage patterns. Concurrent with this damage, severe needle deflection and damage was observed on white pine during mid-August which Dr Orie Loucks of Miami (Ohio) University has linked to UVB effects. A survey of foliar damage conducted by John Flynn of the Appalachian Forest Action Project found injury on eight broad-leaf species: yellow poplar, sycamore, red maple, redbud, white oak, chestnut oak, chinkapin oak and shagbark hickory and possible injury to sweet buckeye and American elm.
The damage was expressed as blister-like lesions on petioles and anthracnose-like browning and curling on foliage in yellow poplar, sycamore, red maple and redbud; and as browning and curling in white oak, chestnut oak, chinkapin oak and shagbark hickory. The damage to the first four species was observed in the last 10 days of July. Damage to the latter four became apparent by early August at mid-elevation points of the ridges and by August 20 at all elevations and locations.
Damage found on these trees was expressed as follows:
Yellow Poplar - Yellow poplar is a species generally free of disease and insect problems. However, between July 20 and 25, leaves began browning and curling. The browning began on the sides or ends of leaves and advanced rapidly. By month's end, shedding of leaves of all ages littered lawns and roads. Foliage of the outer twigs of large trees in open settings was the most severely affected.
Sycamore - Damage was more difficult to assess since sycamore had retained some dead leaves from the spring anthracnose-related browning and mild mid-summer damage from the flea-beetle and ground-level ozone. The rapid browning of trees of all ages located in open settings was profound. By mid-August, many were uniformly brown save for new leaf growth that began after the suspected July event.
Red Maple - These trees appeared less affected than yellow poplar and sycamore. Leaf curl, browning and petiole lesions occurred on trees with diameters less than six inches.
Redbud - Young redbud leaves growing in open exposures were discoloured and curled, but mature leaves did not seem affected.
White, Chestnut and Chinkapin Oak and Shagbark Hickory - Foliage browned and curled from early to late August. Large open-grown oaks took on "impressionistic" hues of brown. The damage seemed to be a delayed response to the phenomenon which earlier injured other trees.
Sweet Buckeye and American Elm - These species may also have been affected but observations were confounded by the occurrence of already recognized "leaf splotch" on buckeye and a new strain of foliar disease in elm reported to be active in the valleys in question.
The first suspected causes for the damage were environmental factors other than solar radiation. However, weather records suggest that the leaf-fall was not likely drought-related nor temperature-related. No local industrial air emissions could be implicated as possible agents for the damage.
The spatial variability of the damage gave some clue that solar radiation may have played an important role. Yellow poplar, sycamore, red maple and redbud growing on moist soil in less open areas were significantly less affected. "So much so," according to Flynn, "that one could anticipate the location in which the damage would be expressed while driving in the hollows and on the main arteries of the narrow valleys of the Mixed Mesophytic Forest. On the other hand, black birch growing along the rivers and receiving both direct and reflected light showed severe damage on the exposed side only."
These observations lead to the suggestion that strong visible light along with heat scorched the leaves. Leaf curl and shedding similar to that observed on black birch is a classic symptom of scorch. However, the dark burn-like discoloration on the young leaves of yellow poplar, sycamore and redbud, and the petiole lesions are not consistent with scorch.
Specimens of damaged leaves were forwarded to the U.S. Forest Service laboratory in Morgantown, West Virginia for analysis. According to the chief plant pathologist, Dr Martin MacKenzie, "I saw nothing that suggests the damage was caused by insects or fungi. Nor do I believe it was from gaseous pollutant exposure. The damage I observed was sun-directed...This leaves the sun as the source."
The concurrence of needle deflection in white pine which Dr Loucks has attributed to UVB radiation led to the suggestion that the damage to broad-leafed species was caused by the UVB portion of the solar spectrum. Examination of satellite measurements indicated the ozone layer above southern West Virginia was at record or near-record low thickness during most of July.
Ozone layer thickness measured above southern West Virginia averaged 292 Dobson Units (DU) for the month of July and 282 DU for the last 20 days. The lowest single day measured 278 DU. The long-term (16 year) average for the area has been 330 DU. Thus, with ozone thickness 15% below normal for the latter days of July, UVB readings could have been 30 percent or more above normal.
Dr Art Neuendorffer of the National Oceanic and Atmospheric Administration believes "It's very likely the trees were getting record amounts of UVB. Important in relating the damage to UVB is whether the area had days of clear, dry air with relatively low humidities. Our records indicate that the air in that neck of the woods was drier than in surrounding regions when the damage took place...So you can add the dry air to the lack of clouds and the depleted upper ozone protection and you seem to have the setting for what took place."
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The Antarctic Ozone Hole emerged earlier and grew more rapidly in 1995 than the record Ozone Holes of 1993 and 1994, and was of equivalent maximum size and depth according to reports from the World Meteorological Organization. Observed by ground-based measurements at Antarctic research stations operated by Argentina, Finland, France, Italy, Germany, New Zealand, Russia and the United Kingdom and satellite readings from the U.S. TIROS Operational Vertical Sounder (TOVS) provide data for analysis of the 1995 hole.
Even before the onset of austral spring, there were indications that 1995 ozone depletion over the Antarctic would again be severe. During the late austral winter (July and August), average ozone levels over Antarctica were 10 percent below the "pre-hole" averages with individual periods (August 5 - 10 and August 10 - 20) as much as 30 percent below normal. The average 1995 ozone depths ranged from 210 to 240 Dobson Units (DU) in August.
The 1995 Ozone Hole rapidly deepened in August with ozone thickness 25 to 30 percent below pre-ozone-hole averages and 10 percent lower than August of 1994 which had a record deficiency. Most stations reported days with depths below 200 DU.
The rapid decline of August continued into September. By mid-month, the overall ozone deficiency above the Antarctic was 35 to 38 percent below pre-hole averages and greater than had been observed previously. The area where ozone depths were less than 220 DU exceeded 12 million square kilometres at mid-month and 22 million square kilometres by month's end. Most observing sites reported levels below 150 DU. Over 80 percent ozone loss was reported in the stratosphere from 16 - 20 km altitude.
The size of the Ozone Hole remained between 22 and 23 million square kilometres through October with most of the continent below 130 DU. Nearly complete destruction between 15 and 20 km was observed from mid-September to mid-October. The October mean levels at several sites reached record low levels slightly lower than the record low levels of last year.
In mid-October, (12-14) the Ozone Hole expanded in the direction of South America covering populated areas of the southern cone region of the continent. The station at Ushuaia, Argentina reported total ozone depth of 189 DU, about 50 percent below the long-term average. In late October, the areal extent of the Ozone Hole still covered the entire Antarctic continent and adjacent ocean waters to 64 degrees South latitude. The 1995 event reached size and ozone deficiencies similar to the record holes observed in 1993 and 1994.
The 1995 Ozone Hole began to fill in early November, but as of November 21, had not broken up. It has currently shrunk to 15 million square kilometres and become irregular in shape. Thus, areas of Antarctica under the hole report ozone from 150 - 170 DU while areas outside report levels above 300 DU. Measurements over New Zealand and Australia are 360 - 420 DU, close to normal for this time of year.
The strength of the polar vortex in late November indicates that the 1995 Ozone Hole will likely continue for some time. Since the event began in early August, it is now the longest lasting ozone hole event ever observed. The ozone depths above monitoring sites at Marambio, Nuemayer and Syowa have reported nearly complete annihilation of the ozone layer between 14 and 19 km for over nine consecutive weeks. This continued depletion has maintained temperatures in the lower stratosphere more than 10 Co below normal. These low temperatures facilitate the continued destruction of the ozone layer and maintain a strong polar vortex.
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In 1991 the eruption of Mt Pinatubo spewed tonnes of dust and gas high into the atmosphere which caused global reductions in the ozone layer for several years. By 1995, almost all of the volcanic material had settled out of the atmosphere. Thus, as austral spring approached, questions arose concerning the 1995 Antarctic Ozone Hole. Would the Hole be "healed" from the injury caused by Mt Pinatubo and less in depth and extent than the previous two seasons? Or would the deepening continue as the atmospheric concentration of ozone-depleting substances increased, pushing the Hole ever deeper and larger?
By mid-November, the news has been mixed. The 1995 Ozone Hole reached depletion levels and areal extent equivalent to the record holes of 1993 and 1994 with almost complete loss of ozone between 10 and 20 kilometres altitude lasting more than nine weeks. As of this writing (November 21), the 1995 event had not ended, making it the longest ozone hole event ever observed.
However, new computer models suggest that the depletion and size of the Antarctic Ozone Hole may have nearly reached its maximum. Scientists at NASA's Goddard Space Flight Center have built a computer model which simulates the variations of the Antarctic polar vortex and chemistry of ozone destruction. The model was able to reproduce year-to-year variations in the size and depth of the ozone hole from 1980 to the early 1990s. According to the model, future Antarctic Ozone Holes should be similar to the 1993-94 holes. The holes will "go down faster each year, but won't get deeper or wider," according to Dr Mark Schoeberl, atmospheric scientist at Goddard. The reason is that the region of the atmosphere where ozone-depleting reactions occur has already reached nearly complete depletion and the region is unlikely to expand.
Dr Arthur Neuendorffer of the US NOAA believes that future holes may not exceed the 22 to 23 million square kilometre area been reached the last three years. The growth of the hole now nearly fills the inner boundaries of the polar vortex, the strong winds which blow in the upper atmosphere around the southern pole. The vortex is known to act as a physical barrier to the mixing of air over the Antarctic with that outside the vortex region, and it is within the polar vortex that the ozone hole appears.
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Following the record ozone depletion during the Arctic Spring of 1995, the World Meteorological Organization (WMO) announced March 12, 1996 that large spring ozone deficiencies in the northern polar region have reappeared in 1996. At the time of the announcement, low ozone layer thicknesses had been measured during a short period in mid- January and again from mid-February through the first ten days of March. "Extremely low ozone values for a few days exceeding an unprecedented deficiency of 45% for the northern latitudes were observed by the WMO Global Ozone Observing System (GO3OS) stations and satellites over the sub-polar region from Greenland and Scandinavia to Western Siberia," reported Dr Rumen D. Bojkov, Special Advisor to the Secretary-General of WMO for Ozone and Global Environmental Issues.
During the period encompassing December, January, and February, the ozone layer above the northern middle and polar latitudinal belts averaged about 10% below the long-term (1957-1979) mean. However, briefly in mid-January and again from mid-February to early March, ozone levels over the region covering Greenland, the Northern Atlantic and Scandinavia to the western part of the Russian Arctic fell below 250 Dobson Units (DU), levels which correspond to monthly mean ozone deficiencies of 20% to 30%. The lowest ozone values reported by the WMO GO3OS stations in this region fell for the first time below 200 Dobson Units, the value defining the threshold of an ozone hole.
In contrast, ozone levels over North America (the Canadian sub-Arctic and Alaska) and the North Pacific to Eastern Siberia where the stratosphere was warmer, have been only a few percent less than the long-term normals (460-500 Dobson Units) for this time of year.
The large ozone depletion in 1996 has been caused by the polar stratospheric vortex with cold lower stratosphere temperatures becoming dominant over the region. Within the vortex, stratospheric temperatures lower than minus 78oC permit the formation of polar stratospheric clouds which, combined with the presence of chlorine and bromine compounds and rising solar radiation, facilitate severe ozone destruction. "One could expect even stronger ozone declines in the coming years with increasing chlorine and bromine concentrations. In contrast with Antarctica, these events over the Arctic are lasting for weeks but not for months", according to Dr Bojkov.
These low ozone values are in concurrence with the WMO/UNEP Assessment on the State of the Ozone Layer-1994. The assessment, made with contributions from hundreds of scientists, attributes chemicals from CFCs and halons as the main cause for the depletion. Measures taken by countries signatory to the Vienna Convention and its Montreal Protocol to reduce the use of ozone-depleting chemicals will begin the process of healing the damage to the ozone layer. However, not until the second half of the 21st century could one expect the disappearance of the Antarctic-spring ozone hole phenomena, reports the WMO.
The WMO results come on the heels of reports that, at the end of the first week in March, two British stations, Lerwick and Cornwall measured the lowest levels of ozone since the British Meteorological Office established ozone recording stations in the United Kingdom seventeen years ago. Dr. Farman, the British Antarctic Survey scientist who discovered the ozone hole over the Antarctic told the British newspaper Independent, "We've warned that things would get worse before they start to get better, but it's impossible to make any precise predictions. With the very cold winters we have been getting at high altitude, the ozone loss could well accelerate." According to Farman, global warming caused by the buildup of greenhouse gases appears to be aggravating the ozone loss. While temperatures rise in the lower atmosphere, those in the lower stratosphere drop. This makes sustained ozone destruction more likely, because it helps the formation of the polar stratospheric clouds and allows them to exist for longer periods.
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The UVB Impacts Reporter is written and edited by Keith C. Heidorn, PhD, ACM. 1996. Correspondence may be sent to #304-3220 Quadra St., Victoria, BC, Canada V8X 1G3. Phone 604-388-7847: email: see@AT@islandnet.com.
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