Ultraviolet Radiation Conditions Research Articles

Comparing the response of Antarctic, tropical and temperate microalgae to ultraviolet radiation (UVR) stress

The response of Antarctic, tropical and temperate microalgae of similar taxonomic grouping to ultraviolet radiation (UVR) stress was compared based on their growth and fatty acid profiles. Microalgae of similar taxa from the Antarctic (Chlamydomonas UMACC 229, Chlorella UMACC 237 and Navicula UMACC 231), tropical (Chlamydomonas augustae UMACC 246, Chlorella vulgaris UMACC 001 and Amphiprora UMACC 259) and temperate (Chlamydomonas augustae UMACC 247, Chlorella vulgaris UMACC 248 and Navicula incerta UMACC 249) regions were exposed to different UVR conditions. The cultures were exposed to the following conditions: PAR (42 μmol photons m−2 s−1), PAR + UVA (854 μW cm−2) and PAR + UVA + UVB (117 μW cm−2). The cultures were subjected to UVA doses of 46.1, 92.2 and 184.4 J cm−2 and UVB doses of 6.3, 12.6 and 25.2 J cm−2 by varying the duration of their exposure (1.5, 3 and 6 h) to UVR during the light period (12:12 h light-dark cycle). UVA did not affect the growth of the microalgae, even at the highest dose. In contrast, growth was adversely affected by UVB, especially at the highest dose. The dose that caused 50% inhibition (ID50) in growth was used to assess the sensitivity of the microalgae to UVB. Sensitivity of the microalgae to UVB was species-dependent and also dependent on their biogeographic origin. Of the nine microalgae, the Antarctic Chlorella was most tolerant to UVB stress (ID50 = 21.0 J cm−2). Except for this Chlorella, the percentage of polyunsaturated fatty acids of the microalgae decreased in response to high doses of UVB. Fatty acid profile is a useful biomarker for UVB stress for some microalgae.

Photoinduced toxicity of polycyclic aromatic hydrocarbons to Daphnia magna: Ultraviolet‐mediated effects and the toxicity of polycyclic aromatic hydrocarbon photoproducts

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants known for their photoinduced toxicity. This toxicity may occur through two mechanisms: Photosensitization, and photomodification. Photosensitization generally leads to the production of singlet oxygen, a reactive oxygen species that is highly damaging to biological molecules. Photomodification of PAHs, usually via oxidation, results in the formation of new compounds and can occur under environmentally relevant levels of actinic radiation. The toxicities of 16 intact PAHs to Daphnia magna were assessed under two ultraviolet radiation conditions. The toxicity of intact PAHs generally increased in the presence of full-spectrum simulated solar radiation relative to that in the presence of visible light plus ultraviolet A only. Despite the knowledge of a bipartite mechanism of phototoxicity that includes photosensitization and photomodification, few studies have examined the effects of PAH photoproducts on animals. To expand the existing data, 14 PAH photoproducts (oxy-PAHs) also were assayed, most of which were highly toxic without further photomodification. Two photoproducts of benzo[a]pyrene, 1,6- and 3,6-benzo[a]pyrenequinone, were the most toxic compounds tested, followed closely by benz[a]anthraquinone. Each of these three compounds had a median effective concentration in the low nanomolar range. The data presented highlight the effects of ultraviolet radiation on mediating PAH toxicity and the need to analyze absorption spectra of contaminants in the prediction of photoinduced toxicity. The importance of the role of photomodification also is stressed, because several oxy-PAHs, an unregulated group of contaminants, were highly toxic to D. magna, a key bioindicator species in aquatic ecosystems.

A Five‐year Study of Solar Ultraviolet Radiation in Southern Chile (39° S): Potential Impact on Physiology of Coastal Marine Algae?

This study reports 5 years of (1998-2003) data on continuous solar-irradiation measurements from a scanning spectroradiometer (SUV-100) in Valdivia, Chile (39 degrees S), accompanied by evaluation of the impact of ultraviolet radiation (UVR) on marine macroalgae of this site. UVR conditions showed a strong seasonal variation, which was less pronounced toward longer wavelengths. Daily maximum dose rates (clear days) averaged in winter-summer: UV-B(290-315 nm) 0.30-2.1, UV-B(290-320 nm) 0.70-3.7, UV-A(315-400 nm) 20.6-62.1, UV-A(320-400 nm) 20.2-60.5 W m(-2), and photosynthetically active radiation (PAR) 969-2423 micromol m(-2) s(-1). The corresponding daily doses (all the days) ranged: UV-B(290-315 nm) 2.6-40.7, UV-B(290-320 nm) 6.7-78.5, UV-A(315-400 nm) 228-1539, UV-A(320-400 nm) 224-1501, and PAR 2008-13308 kJ m(-2) d(-1). Taking into consideration action spectra of a biological interest, the risk of UV exposure could be up to 37 times higher in summer than in winter. The photosynthetic activity (as maximum quantum yield of chlorophyll fluorescence, F(v)/F(m)) of the brown alga Lessonia nigrescens from the infralittoral zone was markedly more sensitive to UVR than of the green alga Enteromorpha intestinalis from the upper midlittoral, and the UV-B wave band increased markedly photoinhibition. In L. nigrescens, maximal photoinhibition (40%) took place at weighted (the action spectrum for photoinhibition of photosynthesis) UVR doses of 800 kJ m(-2), irrespective of the season (corresponding midsummer daily dose in Valdivia is 480 kJ m(-2)). In winter, when this alga was at its most sensitive, the weighted UV dose causing 35-40% photoinhibition was around 200 kJ m(-2). In E. intestinalis, weighted doses of 800 kJ m(-2) resulted in low photoinhibition (<10 %) and no clear seasonal patterns could be inferred. These results confirm that midday summer levels of UV-B and their daily doses in southern Chile are high enough to produce stress to intertidal macroalgae.

Direct and Indirect Effects of Solar Ultraviolet Radiation on Attached Bacteria and Algae in Lotic Systems

I examined the effects of solar ultraviolet radiation (UVR) on attached bacteria and algal densities in lotic systems in outdoor artificial stream apparatus. Flumes were covered with four types of film for UVR screening treatments, and attached bacterial cell densities and their temporal variations were compared between conditions excluding and including solar UVR. Attached bacterial cell densities were depressed by solar UVR, and both accrual rate and saturated density were significantly lower in the +UVR (full solar radiation) condition than in −UVR and dark conditions. Solar UVR also indirectly affected the rate of algal accrual. Microscopic direct observations of attached bacterial cell density and algae on substrata showed that solar UVR depressed the accrual of attached bacteria and consequently the frequency of sites with high bacterial cell density that can trap suspended algae in the water. The final amount of algal accrual in the +UVR condition was one-fourth of that in the −UVR condition. Therefore, the effects of solar UVR may be more serious in systems where periphyton are frequently removed by floods.

Species-specific responses of freshwater diatoms to solar ultraviolet radiation

We studied species-specific growth responses of freshwater algae to solar ultraviolet radiation (UVR) by measuring growth-irradiance curves (G-E curves) of 17 algal diatoms (isolated from a periphyton community in a lotic system) in a solar simulator under photosynthetically available radiation plus UVR and minus UVR radiation condition. Algal growth responses to UVR were highly species-specific, and the photoinhibition parameter (β) of the +UVR condition differed greatly among species. We compared the degree of UVR effect on algal growth (UVR inhibition index: difference in between +UVR and -UVR conditions) with parameters derived from the G-E curve and with algal cell morphology. UVR inhibition indexes significantly correlated with the initial slope of light-limited portion of G-E curve (a) and with the irradiance at which the growth rate starts to saturate (E k ), but not with the cell surface to volume ratios. Low-light-adapted algae tended to be more susceptible to growth inhibition by UVR than high-light-adapted ones. Algae that formed dense colonies in the growth medium were relatively tolerant of UVR irrespective of E k values. Although past studies have emphasized that UVR effects on algae are algal-size dependent, the growth strategies dealing with solar radiation and algal growth forms appear to be more valid in correctly interpreting species-specific responses of algae to solar UVR.

Effects of solar ultraviolet radiation on the periphyton community in lotic systems: comparison of attached algae and bacteria during their development

The effects of solar ultraviolet radiation (UVR) on the development of a periphyton community were studied in an outdoor artificial stream apparatus. Algal biomass, species composition, and bacterial cell density were measured under full sunlight and non-UVR (photosynthetically active radiation [PAR]-only) conditions. Attachment of algae was detected on days 6–9. Although the chlorophyll-a concentration under non-UVR conditions was 2–4 times that under full sunlight (PAR + UVR) throughout the experiment, neither net algal growth rate nor species composition differed significantly between the two light conditions. The relative carotenoid pigment contents of attached algae in the PAR + UVR condition were 1.1–1.3 times those in the non-UVR condition. Rates of increase of bacterial cell densities under the PAR + UVR condition were depressed by solar UVR for the first few days, although there were no apparent differences in the rates of increase between the light conditions later in the experiment. The small effect of UVR on the development of this periphyton community may be attributable to low UV flux at this study site and to the experimental conditions under which the algae were kept: a high physiological state with high nutrient conditions. Attached bacteria and algae that colonize substrata first are likely to be sensitive to solar UVR, and the negative effects of UVR are mitigated by the development of a periphyton community.

Reproducible coating and testing techniques for large core luminescent clad optical fibre probes for UV detection

This paper describes a technique for the uniform and reproducible coating of unclad optical fibres with epoxies that have been doped with photoluminescent phosphors in order to create distributed optical fibre ultra violet sensors. The technique involves spinning the fibres both axially and radially simultaneously after application of the coating to create a coating of uniform thickness. The fibres are also tested for their responses to a range of ultra violet radiation conditions controlled using a test unit specifically designed for this purpose. The test unit involves an array of ultra violet LED's that can be switched on and off in specific sequences which are controlled through a graphical user interface on a PC. This method of testing enables the interrogation and comparison of outputs when specific points are irradiated along these distributed sensors.

Reproducible coating and testing techniques for large core luminescent clad optical fibre probes for UV detection

This paper describes a technique for the uniform and reproducible coating of unclad optical fibres with epoxies that have been doped with photoluminescent phosphors in order to create distributed optical fibre ultra violet sensors. The technique involves spinning the fibres both axially and radially simultaneously after application of the coating to create a coating of uniform thickness. The fibres are also tested for their responses to a range of ultra violet radiation conditions controlled using a test unit specifically designed for this purpose. The test unit involves an array of ultra violet LED's that can be switched on and off in specific sequences which are controlled through a graphical user interface on a PC. This method of testing enables the interrogation and comparison of outputs when specific points are irradiated along these distributed sensors.

Stage-dependent sensitivity to ultraviolet radiation in zygotes of the brown alga Fucus serratus.

Sensitivity to ultraviolet (UV) radiation (UV-A, lambda = 315-400 nm; plus UV-B, lambda = 280-315 nm) of zygotes of the brown alga Fucus serratus L. (Phaeophyta) has been assessed through effects on growth of developing germlings. Different stages of development were distinguished by considering 5 h periods of time after fertilisation. Both the stage of the zygote and the UV radiation condition significantly affected growth of developing germlings. The negative response of growth rate of early stages of the zygotes to UV radiation seemed to be caused by UV-B rather than UV-A radiation, as the lowest relative growth rates were always estimated for germlings developed from zygotes irradiated with UV-B radiation. As regards the stage of the zygote, those germlings that developed from zygotes irradiated at 5-10 h after fertilisation showed the strongest inhibition of growth compared with the other stages. These results point to polarisation as the most UV-sensitive process during the first 24 h of the development of the zygote. A non-linear relationship between the developmental stage of the zygote and the sensitivity to UV radiation is suggested.

Effects of temperature and ultraviolet radiation on microbial foodweb structure: potential responses to global change

Summary1. A series of growth experiments were conducted with natural plankton communities from a lake and river in northern Quebec, to evaluate the response of microbial foodweb structure to changes in ambient temperature and solar ultraviolet radiation (UVR).2. Bioassays were incubated for 6 days at two temperatures (10 and 20 °C) and three near‐surface irradiance conditions [photosynthetically active radiation (PAR) + UVA + UVB, PAR + UVA, and PAR only).3. The concentration of total bacteria showed no net response to temperature, but the percentage of actively respiring bacteria, as measured with the cellular redox probe5‐cyano‐2,3‐ditolyl tetrazolium chloride (CTC), was up to 57% higher at 20 °C relative to 10 °C. Chlorophyll a concentrations in the &lt; 2 μm size fraction also reacted strongly to temperature, with a net increase of up to 61% over the temperature range of 10–20 °C.4. The UVR effects were small or undetectable for most of the measured variables; however, the percentage of actively respiring bacteria was significantly inhibited in the presence of UVR at 20 °C, decreasing by 29–48% on day 6 in the lake experiments and by 59% on day 2 in one river experiment.5. The results show differential sensitivity to temperature among organisms of microbial communities in subarctic freshwaters, and a resilience by the majority of micro‐organisms to their present UVR conditions. Microbial foodwebs in northern freshwaters appear to be relatively unresponsive to short‐term (days) changes in UVR. However, the observed responses to temperature suggest that climate change could influence community structure, with warmer temperatures favouring picoplanktonic phototrophs and heterotrophs, and a shift in nanoplankton species composition and size structure.