Robert C. Worrest

Effects on aquatic ecosystems

Abstract Regarding the effects of UV-B radiation on aquatic ecosystems, recent scientific and public interest has focused on marine primary producers and on the aquatic web, which has resulted in a multitude of studies indicating mostly detrimental effects of UV-B radiation on aquatic organisms. The interest has expanded to include ecologically significant groups and major biomass producers using mesocosm studies, emphasizing species interactions. This paper assesses the effects of UV-B radiation on dissolved organic matter, decomposers, primary and secondary producers, and briefly summarizes recent studies in freshwater and marine systems. Dissolved organic carbon (DOC) and paniculate organic carbon (POC) are degradation products of living organisms. These substances are of importance in the cycling of carbon in aquatic ecosystems. UV-B radiation has been found to break down high-molecular-weight substances and make them available to bacterial degradation. In addition, DOC is responsible for short-wavelength absorption in the water column. Especially in coastal areas and freshwater ecosystems, penetration of solar radiation is limited by high concentrations of dissolved and particulate matter. On the other hand, climate warming and acidification result in faster degradation of these substances and thus enhance the penetration of UV radiation into the water column. Several research groups have investigated light penetration into the water column. Past studies on UV penetration into the water column were based on temporally and spatially scattered measurements. The process of spectral attenuation of radiant energy in natural waters is well understood and straightforward to model. Less known is the spatial and temporal variability of in-water optical properties influencing UV attenuation and there are few long-term observations. In Europe, this deficiency of measurements is being corrected by a project involving the development of a monitoring system (ELDONET) for solar radiation using three-channel dosimeters (UV-A, UV-B, PAR) that are being installed from Abisko (North Sweden, 68 °N, 19 °E) to Tenerife (Canary Islands, 27 °N, 17 °W). Some of the instruments have been installed in the water column (North Sea, Baltic Sea, Kattegat, East and Western Mediterranean, North Atlantic), establishing the first network of underwater dosimeters for continuous monitoring. Bacteria play a vital role in mineralization of organic matter and provide a trophic link to higher organisms. New techniques have substantially changed our perception of the role of bacteria in aquatic ecosystems over the recent past and bacterioplankton productivity is far greater than previously thought, having high division and turnover rates. It has been shown that bacterioplankton play a central role in the carbon flux in aquatic ecosystems by taking up DOC and remineralizing the carbon. Bacterioplankton are more prone to UV-B stress than larger eukaryotic organisms and, based on one study, produce about double the amount of cyclobutane dimers. Recently, the mechanism of nitrogen fixation by cyanobacteria has been shown to be affected by UV-B stress. Wetlands constitute important ecosystems both in the tropics and at temperate latitudes. In these areas, cyanobacteria form major constituents in microbial mats. The organisms optimize their position in the community by vertical migration in the mat, which is controlled by both visible and UV-B radiation. Cyanobacteria are also important in tropical and sub-tropical rice paddy fields, where they contribute significantly to the availability of nitrogen. Solar UV radiation affects growth, development and several physiological responses of these organisms. On a global basis, phytoplankton are the most important biomass producers in aquatic ecosystems. The organisms populate the top layers of the oceans and freshwater habitats where they receive sufficient solar radiation for photosynthetic processes. New research strengthens previous evidence that solar UV affects growth and reproduction, photosynthetic energy-harvesting enzymes and other cellular proteins, as well as photosynthetic pigment contents. The uptake of ammonium and nitrate is affected by solar radiation in phytoplankton, as well as in macroalgae. Damage to phytoplankton at the molecular, cellular, population and community levels has been demonstrated. In contrast, at the ecosystem level there are few convincing data with respect to the effects of ozone-related UV-B increases and considerable uncertainty remains. Following UV-B irradiation, shifts in phytoplankton community structure have been demonstrated, which may have consequences for the food web. Macroalgae and seagrasses are important biomass producers in aquatic ecosystems (but considerably smaller than phytoplankton). In contrast to phytoplankton, most of these organisms are sessile and can thus not avoid exposure to solar radiation at their growth site. Recent investigations showed a pronounced sensitivity to solar UV-B radiation, and effects have been found throughout the top 10–15 m of the water column. Photoinhibition can be quantified by oxygen exchange or by PAM (pulse amplitude modulated) fluorescence. Surface-adapted macroalgae, such as several brown and green algae, show a maximum of oxygen production at or close to the surface; whereas algae adapted to lower irradiances usually thrive best when exposed deeper in the water column. Mechanisms of protection and repair are being investigated. UV effects on aquatic animals are of increased interest. Evidence for UV effects has been demonstrated in Zooplankton activity. Other UV-B-sensitive aquatic organisms include sea urchins, corals and amphibians. Solar UV radiation has been known to affect corals directly. In addition, photosynthesis in their symbiotic algae is impaired, resulting in reduced organic carbon supply. Amphibian populations are in serious decline in many areas of the world, and scientists are seeking explanations for this phenomenon. Most amphibian population declines are probably due to habitat destruction or habitat alteration. Some declines are probably the result of natural population fluctuations. Other explanations for the population declines and reductions in range include disease, pollution, atmospheric changes and introduced competitors and predators. UV-B radiation is one agent that may act in conjunction with other stresses to affect amphibian populations adversely. The succession of algal communities is controlled by a complex array of external conditions, stress factors and interspecies influences. Freshwater ecosystems have a high turnover and the success of an individual species is difficult to predict, but the development of general patterns of community structure follows defined routes. There is a strong predictive relationship between DOC concentration and the depth to which UV radiation penetrates in lakes. Since DOC varies widely, freshwater systems display a wide range of sensitivity to UV penetration. In these systems, increased solar UV-B radiation is an additional stress factor that may change species composition and biomass productivity. The Arctic aquatic ecosystem is one of the most productive ecosystems on earth and is a source of fish and crustaceans for human consumption. Both endemic and migratory species breed and reproduce in this ocean in spring and early summer, at a time when recorded increases in UV-B radiation are maximal. Productivity in the Arctic ocean has been reported to be higher and more heterogeneous than in the Antarctic ocean. In the Bering Sea, the sea-edge communities contribute about 40–50% of the total productivity. Because of the shallow water and the prominent stratification of the water layer, the phytoplankton are more exposed and affected by solar UV-B radiation. In addition, many economically important fish (e.g., herring, pollock, cod and salmon) spawn in shallow waters where they are exposed to increased solar UV-B radiation. Many of the eggs and early larval stages are found at or near the surface. Consequently, reduced productivity of fish and other marine crops is possible but has not been demonstrated. There is increased consensus, covering a wide range of aquatic ecosystems, that environmental UV-B, independent of ozone-related increases, is an important ecological stress that influences the growth, survival and distribution of phytoplankton. Polar ecosystems, where ozone-related UV-B increases are the greatest and which are globally significant ecosystems, are of particular concern. However, these ecosystems are characterized by large spatial and temporal variability, which makes it difficult to separate out UV-B-specific effects on single species or whole phytoplankton communities. There is clear evidence for short-term effects. In one study a 4–23% photoinhibition of photosystem II activity was measured under the ozone hole. However, extrapolation of short-term effects to long-term ecological consequences requires various complex effects to be accounted for and quantitative evaluation remains uncertain.

EFFECTS OF ENHANCED SOLAR ULTRAVIOLET RADIATION ON AQUATIC ECOSYSTEMS

The total amount of ozone in the stratosphere is comparatively low: if it could be collected and compressed under atmospheric pressure, the thickness of the whole layer would amount to about 3 or 4 mm. Therefore it is not astonishing that gaseous pollutants such as man-made chlorinated fluorocarbons (CFC)?, even though emitted in relatively small amounts (exceeding 1 million tons per year), affect the ozone density. The chlorine atoms are liberated from the CFCs and catalytically break down many thousand ozone molecules each until they are washed out of the atmosphere.

Stratospheric ozone reduction, solar ultraviolet radiation, and plant life

Agents and Effects of Ozone Trends in the Atmosphere.- Inconsistencies in Current Photochemical Models Deduced from Considerations of the Ozone Budget.- Computation of Spectral Distribution and Intensity of Solar UV-B Radiation.- A New UV-B Handbook, Vol. 1.- Possible Errors Involved in the Dosimetry of Solar UV-B Radiation.- Action Spectra and Their Key Role in Assessing Biological Consequences of Solar UV-B Radiation Change.- Action Spectra for Inactivation and Mutagenesis in Chinese Hamster Cells and Their Use in Predicting the Effects of Polychromatic Radiation.- Dose and Dose-Rate Responses to UV-B Radiation: Implications for Reciprocity.- Cellular Repair and Assessment of UV-B Radiation Damage.- Repair of Genetic Damage Induced by UV-B (290-320 nm) Radiation.- Physiological Responses of Yeast Cells to UV of Different Wavelengths.- Effects of UV-B Radiation on Photosynthesis.- Effect of UV Irradiation on Different Partial Reactions of the Primary Processes of Photosynthesis.- Effects of Ultraviolet Radiation on Fluorescence Induction Kinetics in Isolated Thylakoids and Intact Leaves.- Fine Structural Effects of UV Radiation on Leaf Tissue of Beta vulgaris.- Comparative Sensitivity of Binucleate and Trinucleate Pollen to Ultraviolet Radiation: A Theoretical Perspective.- The Effect of Enhanced Solar UV-B Radiation on Motile Microorganisms.- UV-B Radiation and Adaptive Mechanisms in Plants.- Leaf UV Optical Properties of Rumex patientia L. and Rumex obtusifolius L. in Regard to a Protective Mechanism Against Solar UV-B Radiation Injury.- UV-B-Induced Effects upon Cuticular Waxes of Cucumber, Bean, and Barley Leaves.- Effects of UV-B Radiation on Growth and Development of Cucumber Seedlings.- Interaction of UV-A, UV-B and Visible Radiation on Growth, Composition, and Photosynthetic Activity in Radish Seedlings.- Effects of Enhanced Ultraviolet-B Radiation on Yield, and Disease Incidence and Severity for Wheat Under Field Conditions.- Effects of Ultraviolet-B Radiation on the Growth and Productivity of Field Grown Soybean.- Interaction Between UV-B Radiation and Other Stresses in Plants.- Models and Data Requirements for Measuring the Economic Consequences of UV-B Radiation on Agriculture.- Appendix 1: Subroutine for Schippnick and Green UV Spectral Irradiance Model.- List of Workshop Attendees.

Environmental effects of ozone depletion and its interactions with climate change: progress report, 2011

The Environmental Effects Assessment Panel (EEAP) is one of three Panels that regularly informs the Parties (countries) to the Montreal Protocol on the effects of ozone depletion and the consequences of climate change interactions with respect to human health, animals, plants, biogeochemistry, air quality, and materials. The Panels provide a detailed assessment report every four years. The most recent 2014 Quadrennial Assessment by the EEAP was published as a special issue of seven papers in 2015 (Photochem. Photobiol. Sci., 2015, 14, 1-184). The next Quadrennial Assessment will be published in 2018/2019. In the interim, the EEAP generally produces an annual update or progress report of the relevant scientific findings. The present progress report for 2015 assesses some of the highlights and new insights with regard to the interactive nature of the effects of UV radiation, atmospheric processes, and climate change.

Aquatic ecosystems: effects of solar ultraviolet radiation and interactions with other climatic change factors

Aquatic ecosystems are a key component of the Earths biosphere. A large number of studies document substantial impact of solar UV radiation on individual species, yet considerable uncertainty remains with respect to assessing impacts on ecosystems. Several studies indicate that the impact of increased UV radiation appears relatively low when considering overall ecosystem response, while, in contrast, effects on individual species show considerable responses. Ecosystem response to climate variability incorporates both synergistic and antagonistic processes with respect to UV-related effects, significantly complicating understanding and prediction at the ecosystem level. The impact of climate variability on UV-related effects often becomes manifest via indirect effects such as reduction in sea ice, changes in water column bio-optical characteristics, changes in cloud cover and shifts in oceanographic biogeochemical provinces.

IMPACT OF ENHANCED SIMULATED SOLAR ULTRAVIOLET RADIATION UPON A MARINE COMMUNITY

Abstract—There is evidence to indicate that an increased exposure to solar radiation in the UV‐B region (specifically, 290–320 nm) may occur as a result of anthropogenic degradation of stratospheric ozone. The fact that present levels of solar UV radiation can detrimentally affect marine organisms led to experiments to quantify the impact of increased UV radiation upon a marine community. Two 720–l seawater chambers (continuous flow‐through design) were exposed to simulated solar UV radiation. Fluorescent sunlamps filtered by a 290 nm cutoff filter (a 0.13 mm thickness of cellulose triacetate film) were used as the radiation source. Utilization of three different weighting factors for the spectral irradiances at the surface of the chambers yielded differences of 18%, 35% and 40% in biologically effective fluence rate between the two chambers. Analysis of attached forms of algae at various depths demonstrated that a surface exposure of 1.4W/m2 in the 290–315nm waveband as contrasted with the chamber receiving a surface exposure of 1.0W/m2 resulted in depressed Chl a concentrations, reduced biomass, increased autotrophic indices, and decreased community diversity. These results indicate a potential for adverse effects of increased solar UV‐8 radiation: decreased community diversity, community structure shifts, and decreased productivity.

Review of Literature Concerning the Impact of UV-B Radiation Upon Marine Organisms

UV-B radiation (e.g. 310 nm) penetrates approximately the upper 10% of the coastal marine euphotic zone before it is reduced to 1% of its surface irradiance (Jerlov, 1976). There is good evidence that current levels of solar UV radiation depress near-surface primary production in marine waters (e.g., Steemann Nielsen, 1964; Jitts et al., 1976). Marine animals may tolerate current levels of solar UV-B radiation by means of protective screens, avoidance behavior, and repair processes which reverse much of the potential damage inflicted by the radiation. However, as early as 1925, scientific investigators have documented the damage inflicted on marine animals by exposure to sunlight, especially the UV component of the sunlight (Huntsman, 1925; Klugh, 1929, 1930; Harvey, 1930). Utilizing currently available laboratory and field data the present contribution will review the literature relating to the impact of UV-B radiation upon marine organisms.

IMPACT OF UV‐B RADIATION UPON ESTUARINE MICROCOSMS

Abstract— Twelve flow‐through estuarine microcosms were exposed daily to four different levels of UV‐B radiation (290–320. nm)(1.57 ± 102, 6.43 ± 103, 6.86 ± 103 and 7.61 ± 103 J·m‐2d−1) in addition to a natural level of visible solar radiation (380‐800. nm). The parameters studied over a four week period were phytoplankton community composition, plankton biomass (ash‐free dry weight), chlorophyll a concentration and primary productivity (radiocarbon uptake). With increased exposure to UV‐B radiation there was an obvious alteration of the community composition. Daily exposure to enhanced levels of UV‐B radiation also depressed the biomass, the chlorophyll a concentration and the radiocarbon uptake of samples from the ecosystems.

SENSITIVITY OF MARINE PHYTOPLANKTON TO UV‐B RADIATION: IMPACT UPON A MODEL ECOSYSTEM

Abstract Human activities may cause a 16% reduction of stratospheric ozone. The concomitant increase in solar UV‐B radiation reaching the surface of the earth could detrimentally affect the phytoplankton that form the base of the food web in oceanic and estuarine ecosystems. In the current study acute exposure of seven species of marine phytoplankton to UV–B radiation depressed the radiocarbon estimate of primary production. A model of a marine ecosystem was constructed based on the differential sensitivities of the seven species of phytoplankton. Increasing the UV–B exposure within the model from 100 EffDNAJ/m2/day to 150 EffDNAJ/m2/day significantly altered the community composition of the ecosystem. In nature, alteration of the phytoplanktonic community structure could result in a significant impact upon successional patterns and primary producer–consumer trophodynamics.

Impact of UV-B radiation on the fecundity of the copepod Acartia clausii

It has recently been demonstrated that acute midultraviolet irradiation (UV-B, 290 to 320 nm) of the marine copepod Acartia clausii results in reduced survival and fecundity. In the present study, immature late copepodites were separted by sex and exposed to three UV-B exposure levels (0, 25, and 50 effectiveDNA Jm-2). The irradiated copepods were then reared to sexual maturity, and adult virgin survivors were mated according to prior exposure, supplying 7 different types of mating crosses (M0F0, M0F25, M25F0, M25F25, M0F50, M50F0, M50F50). Six replications of each cross were maintained for the duration of an experiment. Two experiments are documented. There was a significant effect of UV-B radiation on the survival of the parents as well as a reduction in the number of eggs and the number of living nauplii produced. For each experiment, 30 nauplii from each type of cross were separated, reared to maturity and counted, providing information on the survival capability of non-irradiated offspring from the 7 different mating types. Previous exposure of parental stock did not significantly affect the survival, and development to maturity, of these nauplii 15 d after separation.