H. D. Kumar

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.

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.

Effects of UV irradiation on certain physiological and biochemical processes in cyanobacteria

The effects of artificial UV (280–400 nm, 5 W m−2) radiation on heterocyst differentiation, nitrogenase activity, 14CO2 uptake and protein profile of whole cell and isolated heterocysts have been studied in four cyanobacterial strains isolated from Indian rice paddy fields. Exposure of cells to UV for 1 h significantly affected the differentiation of vegetative cells into heterocysts in four cyanobacterial strains studied (Anabaena sp., Nostoc sp., Nostoc carmium and Scytonema sp). Almost 50% fewer heterocysts were recorded in Anabaena sp. and Scytonema sp. and nearly 70% fewer in Nostoc sp. and Nostoc carmium after UV radiation in comparison with controls without UV. Nitrogenase activity in Anabaena sp. was completely inhibited within 45 min of UV exposure. 14CO2 uptake in Anabaena sp. was also severely affected by UV radiation. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE) analyses of the total protein profile of Anabaena sp. showed a linear decrease in the protein content with increasing UV exposure time. Almost complete elimination of most of the protein bands occurred after 120 min of UV exposure. The SDS PAGE protein profile of isolated heterocysts of Anabaena sp. showed three prominent polypeptides of 26, 54 and 55 kDa, with a decrease in the first two and complete elimination of the last one after 1 h of UV radiation.

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.

DIFFERENTIAL EFFECT OF ULTRAVIOLET‐B RADIATION ON CERTAIN METABOLIC PROCESSES IN A CHROMATICALLY ADAPTING Nostoc

Abstract— The impact of UV‐B radiation on growth, pigmentation and certain physiological processes has been studied in a N2‐fixing chromatically adapting cyanobacterium, Nostoc spongiaeforme. A brownish form (phycoerythrin rich) was found to be more tolerant to UV‐B than the blue‐green (phycocyanin rich) form of N. spongiaeforme. Continuous exposure to UV‐B (5.5 W m‐2) for 90 min caused complete killing of the blue‐green strain whereas the brown strain showed complete loss of survival after 180 min. Pigment content was more strongly inhibited in the blue‐green strain than in the brown. Nitrogenase activity was completely abolished in both strains within 35 min of UV‐B treatment. Restoration of nitrogenase occurred upon transfer to fluorescent or incandescent light after a lag of 5–6 h, suggesting fresh synthesis of nitrogenase. Unlike the above processes, in vivo nitrate reductase activity was stimulated by UV‐B treatment, the degree of enhancement being significantly higher in the blue‐green strain. Like the effect of UV‐B on nitrogenase, 14CO2 uptake was also completely abolished by UV‐B treatment in both strains. Our findings suggest that UV‐B may produce a deleterious effect on several metabolic activities of cyanobacteria, especially in cells lacking phycoerythrin. Strains containing phycoerythrin appear to be more tolerant to UV‐B, probably because of their inherent property of adapting to a variety of light qualities.

Lipid and hydrocarbon production byBotryococcus spp. under nitrogen limitation and anaerobiosis.

The production of lipids and hydrocarbons in batch cultures of the algaeBotryococcus braunii andB. protuberans has been studied with respect to nitrogen limitation under aerobic and anaerobic conditions. Nitrogen deficiency significantly decreased the dry weight, chlorophylla and protein contents but the amounts of carotenoids, carbohydrates and lipids increased in both the species. Nitrogen starvation gave a 1.6-fold increase in lipid content. Anaerobiosis under nitrogen deficient conditions gave greater lipid production than anaerobiosis in nitrogen supplemented medium. Under nitrogen deficiency, the hydrocarbon fraction increased and the polar lipids decreased. Anaerobiosis induced hydrocarbon synthesis more significantly than nitrogen deficiency but decreased other non-polar and polar lipids.

Nitrogen fixation and hydrogen uptake in four cyanobacteria

Abstract Anabaena variabilis, Nostoc spongiaeforme, Westiellopsis prolifica , and Nostoc sp. isolated from diverse local habitats fixed nitrogen under aerobic conditions, but the nitrogenase activity was greater in anaerobic conditions. Nitrogenase activity was highest in fluorescent light in the case of A. variabilis, W. prolifica and Nostoc sp., but that of N. spongiaeforme was higher in incandescent light. N. spongiaeforme showed high nitrogenase activity in blue light also, whereas the other three species had stronger activity in red light than in blue light. A concentration of H 2 up to 20% enhanced the nitrogenase activity, but 25% was inhibitory in all of the four organisms. All the four strains were found capable of utilizing exogenous hydrogen. N. spongiaeforme showed higher H 2 uptake activity both under aerobic and anaerobic conditions and its capacity for chromatic adaptation may partly account for such behaviour. Addition of DCMU inhibited hydrogen uptake in A. variabilis, W. prolifica and Nostoc sp. but not in N. spongiaeforme .

Effect of monochromatic lights on nitrogen fixation and hydrogen evolution in the isolated heterocysts of Anabaena sp. strain CA

Abstract Photostimulation of nitrogen fixation (acetylene reduction) and nitrogenase catalysed H2 evolution was investigated using monochromatic lights in the heterocysts isolated from a mutant (hydrogen uptake-less N9C) strain of Anabaena CA. Nitrogenase activity was strictly light dependent, being maximum in fluorescent light, followed by 620 and 650 nm light respectively. Isolated heterocysts under fluorescent light evolved H2 in a biphasic manner. However, when the heterocysts were exposed to wavelengths of 620 and 650 nm, the pattern changed to monophasic without any initial burst. Fluorescence-emission spectra were also studied in the context of energy transfer from phycobilisomes to chlorophyll a.

Environmental effects of ozone depletion and its interactions with climate

The parties to the Montreal Protocol are informed by three panels of experts. One of these is the Environmental Effects Assessment Panel (EEAP), which deals with UV radiation and its effects on human health, animals, plants, biogeochemistry, air quality and materials. Since 2000, the analyses and interpretation of these effects have included interactions between UV radiation and global climate change. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than believed previously. As a result of this, human health and environmental problems will likely be longer-lasting and more regionally variable. Like the other panels, the EEAP produces a detailed report every four years; the most recent was that for 2006 (Photochem. Photobiol. Sci., 2007, 6, 201-332). In the years in between, the EEAP produces a less detailed and shorter progress report, as is the case for this present one for 2009. A full quadrennial report will follow for 2010.

Immobilization of cholesterol oxidase on Formvar using organic solvents

The present study describes a new immobilization support for the preparation of enzyme membrane in the presence of organic solvents. The support was composed of Formvar solubilization in organic solvents with enzyme. More than 90% of the enzyme was immobilized on the membrane. The membrane was prepared by mixing 4% Formvar in organic solvents and 1% cholesterol oxidase was immobilized by entrapment technique. Practically no leaching of the entrapped enzyme was observed. The resultant immobilized enzyme membrane was stored at 4 °C for 10 days without losing its activity. The pH and temperature stabilities were greater than those of the native enzyme. The immobilized enzyme membrane has a long life due to its hydrophobic nature, as compared with other membranes.