Interactive effects of ozone depletion and climate change on biogeochemical cycles

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2021

The Environmental Effects Assessment Panel of the Montreal Protocol under the United Nations Environment Programme evaluates effects on the environment and human health that arise from changes in the stratospheric ozone layer and concomitant variations in ultraviolet (UV) radiation at the Earth’s surface. The current update is based on scientific advances that have accumulated since our last assessment (Photochem and Photobiol Sci 20(1):1–67, 2021). We also discuss how climate change affects stratospheric ozone depletion and ultraviolet radiation, and how stratospheric ozone depletion affects climate change. The resulting interlinking effects of stratospheric ozone depletion, UV radiation, and climate change are assessed in terms of air quality, carbon sinks, ecosystems, human health, and natural and synthetic materials. We further highlight potential impacts on the biosphere from extreme climate events that are occurring with increasing frequency as a consequence of climate change. These and other interactive effects are examined with respect to the benefits that the Montreal Protocol and its Amendments are providing to life on Earth by controlling the production of various substances that contribute to both stratospheric ozone depletion and climate change.

Combined Effects of Trace Metals and Light on Photosynthetic Microorganisms in Aquatic Environment

In the present review, we critically examine the state-of-the-art of the research on combined effects of trace metals and light on photosynthetic microorganisms in aquatic environment. Light of different intensity and spectral composition affects the interactions between trace metals and photosynthetic microorganisms directly, by affecting vital cellular functions and metal toxicokinetics and toxicodynamics, and indirectly, by changing ambient medium characteristics. Light radiation and in particular, the ultraviolet radiation component (UVR) alters the structure and reactivity of dissolved organic matter in natural water, which in most of the cases decreases its metal binding capacity and enhances metal bioavailability. The increase of cellular metal concentrations is generally associated with increasing light intensity, however further studies are necessary to better understand the underlying mechanisms. Studies on the combined exposures of photosynthetic microorganisms to metals and UVR reveal antagonistic, additive or synergistic interactions depending on light intensity, spectral composition or light pre-exposure history. Among the light spectrum components, most of the research was performed with UVR, while the knowledge on the role of high-intensity visible light and environmentally relevant solar light radiation is still limited. The extent of combined effects also depends on the exposure sequence and duration, as well as the species-specific sensitivity of the tested microorganisms and the activation of stress defense responses.

Photochemical cleaving of allochthonous organic-metal complexes contributes to phosphorus immobilization in surface waters

The photochemical transformation of terrestrial dissolved organic carbon (DOC) in surface waters exposed to UV radiation causes the precipitation of metal (Al and Fe) bearing complexes with high phosphorus sorption capacities. To better elucidate this process, a series of laboratory experiments was performed with stream and river waters with pH range from 3.5 to 8.2 and concentrations of dissolved reactive phosphorus from 2 to 142 μg L^-1. Samples were filtered (0.4 μm) and UV (350 nm) irradiated for 24 h at 68 W m^-2, i.e. under conditions equivalent to ∼2 summer days of natural solar radiation. Irradiated samples and dark controls were then spiked with ³³P-phosphate and the kinetics of P adsorption on freshly formed particles was determined after separation by ultracentrifugation. Up to 68% of the added P was removed from the solution within 48 h of the spike. The P sorption was pH dependent, with the maximum sorption ability at pHs of 6-7. We hypothesize that this process can importantly contribute to the immobilization and lower bioavailability of P in the inlet areas of (especially circum-neutral) lakes due to the intensive photochemical degradation of allochthonous DOC-metal complexes.

Interactive effects of temperature, ultraviolet radiation and food quality on zooplankton alkaline phosphatase activity

Ultraviolet Radiation (UVR) is a stressor for aquatic organisms affecting enzyme activities in planktonic populations because of the increase in reactive oxygen species. In addition, UVR exposure combined with other environmental factors (i.e. temperature and food quality) could have even higher detrimental effects. In this work, we aimed to determine the effect of UVR on somatic Alkaline Phosphatase Activity (APA) and Glutathione S-Transferase (GST) activity on the cladoceran Daphnia commutata under two different temperatures (10 °C and 20 °C) and under three food qualities (carbon:phosphorus ratios: 1150, 850 and 550). APA is a biomarker that is considered as a P deficiency indicator in zooplankton. Since recovery from UVR damage under dark conditions is an ATP depending reaction we also measured APA during recovery phases. We carried out a laboratory experiment combining different temperatures and food qualities with exposition to UVR followed by luminic and dark phases for recovery. In addition, we exposed organisms to H2O2, to establish if the response on APA to UVR was a consequence of the reactive oxygen species produced these short wavelengths. Our results showed that somatic APA was negatively affected by UVR exposure and this effect was enhanced under high temperature and low food quality. Consistently, GST activity was higher when exposed to UVR under both temperatures. The H2O2 experiments showed the same trend as UVR exposure, indicating that APA is affected mainly by oxidative stress than by direct effect of UVR on the enzyme. Finally, APA was affected in the dark phase of recovery confirming the P demands. These results enlighten the importance of food quality in the interacting effect of UVR and temperature, showing that C:P food ratio could determine the success or failure of zooplanktonic populations in a context of global change.

Increased p53 and decreased p21 accompany apoptosis induced by ultraviolet radiation in the nervous system of a crustacean

Ultraviolet (UV) radiation can produce biological damage, leading the cell to apoptosis by the p53 pathway. This study evaluated some molecular markers of the apoptosis pathway induced by UVA, UVB and UVA+ UVB (Solar Simulator, SIM) in environmental doses, during five consecutive days of exposure, in the brain of the crab Ucides cordatus. We evaluated the central nervous system (CNS) by immunoblotting the content of proteins p53, p21, phosphorylated AKT, BDNF, GDNF, activated caspase-3 (C3) and phosphohistone H3 (PH3); and by immunohistochemical tests of the cells labeled for PH3 and C3. After the fifth day of exposure, UVB radiation and SIM increased the protein content of p53, increasing the content of AKT and, somehow, blocking p21, increasing the content of activated caspase-3, which led the cells to apoptosis. The signs of death affected the increase in neurotrophins, such as BDNF and GDNF, stimulating the apoptotic cascade of events. Immunohistochemical assays and immunoblotting showed that apoptosis was present in the brains of all UV groups, while the number of mitotic cells in the same groups decreased. In conclusion, environmental doses of UV can cause apoptosis by increasing p53 and decreasing p21, revealing an UV-damage pathway for U. cordatus.

Antioxidant activity stimulated by ultraviolet radiation in the nervous system of a crustacean

Ultraviolet (UV) radiation can produce biological damage, principally oxidative stress, by increasing the production of reactive oxygen species (ROS). This study evaluated biochemical impairments related to the oxidative stress induced by UVA, UVB and UVA+UVB (solar simulator-SIM) in environmental doses, during five consecutive days of exposure, in the brain and eyestalk of the crab Ucides cordatus. We evaluated these regions by sampling on the 1st, 3rd and 5th days of UV exposure for lipid peroxidation (LPO), antioxidant capacity against the peroxyl radical (ACAP), and the activities of catalase (CAT), glutathione peroxidase (GPX) and glutathione-S-transferase (GST). Immunohistochemical and immunoblotting assays were performed for anti-activated-caspase 3 in the brains. After the first day of exposure, LPO increased in the eyestalks and brains of the UV-exposed animals; ACAP, and CAT, GPX and GST activities also increased in the brains. On the third day, the LPO values in the eyestalk remained high in the UV-exposed groups, while ACAP decreased in the brain and eyestalk and CAT activity remained high in all irradiated groups in both regions. On the fifth day, LPO decreased in the eyestalk and brain of the UV-exposed groups. These results may have been a consequence of the antioxidant defense system (ADS) activity, since CAT activity was high in both regions, ACAP was high in the eyestalks of the SIM group, and GPX activity remained high in the eyestalks of the UVA and UVB groups. Immunohistochemical assays and immunoblotting showed that there was apoptosis in the brains of the UV-exposed crabs. In conclusion, environmental doses of UV can cause oxidative damage to the CNS cells, including apoptosis.

Blending remote sensing data products to estimate photochemical production of hydrogen peroxide and superoxide in the surface ocean

Hydrogen peroxide (H₂O₂) and its precursor, superoxide (O₂(-)), are well-studied photochemical products that are pivotal in regulating redox transformations of trace metals and organic matter in the surface ocean. In attempts to understand the magnitude of both H₂O₂ and O₂(-) photoproduction on a global scale, we implemented a model to calculate photochemical fluxes of these products from remotely sensed ocean color and modeled solar irradiances. We generated monthly climatologies for open ocean H₂O₂ photoproduction rates using an average apparent quantum yield (AQY) spectrum determined from laboratory irradiations of oligotrophic water collected in the Gulf of Alaska. Because the formation of H₂O₂ depends on secondary thermal reactions involving O₂(-), we also implemented a temperature correction for the H₂O₂ AQY using remotely sensed sea surface temperature and an Arrhenius relationship for H₂O₂ photoproduction. Daily photoproduction rates of H₂O₂ ranged from <1 to over 100 nM per day, amounting to ∼30 μM per year in highly productive regions. When production rates were calculated without the temperature correction, maximum daily rates were underestimated by 15-25%, highlighting the importance of including the temperature modification for H₂O₂ in these models. By making assumptions about the relationship between H₂O₂ and O₂(-) photoproduction rates and O₂(-) decay kinetics, we present a method for calculating midday O₂(-) steady-state concentrations ([O₂(-)]ss) in the open ocean. Estimated [O₂(-)]ss ranged from 0.1-5 nM assuming biomolecular dismutation was the only sink for O₂(-), but were reduced to 0.1-290 pM when catalytic pathways were included. While the approach presented here provides the first global scale estimates of marine [O₂(-)]ss from remote sensing, the potential of this model to quantify O₂(-) photoproduction rates and [O₂(-)]ss will not be fully realized until the mechanisms controlling O₂(-) photoproduction and decay are better understood.

Effects of selenium on agronomical characters of winter wheat exposed to enhanced ultraviolet-B

Enhanced ultraviolet-B (UV-B) is one of the most important abiotic stress factors that can influence almost every aspect of plant. Selenium (Se) can increase the tolerance of plants to stressful environment. The paper mainly reported the effects of enhanced UV-B, Se supply and their combination on agronomical characters of winter wheat under field conditions. Enhanced UV-B caused a marked decrease in chlorophyll content, plant height, spike length, weight per spike, grain yield and protein content, grain nitrogen (N) and iron (Fe) concentration, and increased hydrogen peroxide (H2O2), malondialdehyde (MDA) and proline content, and grain zinc (Zn) and manganese (Mn) concentration under without supplemental Se supply. However, it also decreased plant height, spike length, weight per spike, grain yield and Fe concentration, and increased H2O2 content, grain potassium (K), Zn and Mn concentration under supplemental Se supply. On the other hand, Se supply induced an evident increase in chlorophyll content, spike length, weight per spike, grain yield, grain protein content, grain N, Fe, copper (Cu), and Se concentration under both UV-B levels. Moreover, significant UV-B×Se interaction was found on plant height, chlorophyll, MDA, H2O2 and proline content, and grain protein, N, K, Cu and Mn concentrations in wheat. The obtained results supported the hypothesis that Se supply increased the yield and improved the quality of winter wheat exposed to enhanced UV-B to some extent.

Soil moisture effect on bacterial and fungal community in Beilu River (Tibetan Plateau) permafrost soils with different vegetation types

AIM

This study investigated the effects of environmental variables on the bacterial and fungal communities of the Beilu River (on the Tibetan Plateau) permafrost soils with different vegetation types.

METHODS AND RESULTS

Microbial communities were sampled from meadow, steppe and desert steppe permafrost soils during May, June, August and November, and they were analysed by both pyrosequencing and the use of Biolog EcoPlates. The dominant bacterial and fungal phyla in meadow and steppe soils were Proteobacteria and Ascomycota, whereas Actinobacteria and Basidiomycota predominated in desert steppe soils. The bacterial communities in meadow soils degraded amines and amino acids very rapidly, while polymers were degraded rapidly by steppe communities. The RDA patterns showed that the microbial communities differed greatly between meadow, steppe and desert steppe, and they were related to variations in the soil moisture, C/N ratio and pH. A UniFrac analysis detected clear differences between the desert steppe bacterial community and others, and seasonal shifts were observed. The fungal UniFrac patterns differed significantly between meadow and steppe soils. There were significant correlations between the bacterial diversity (H') and soil moisture (r = 0.506) and C/N (r = 0.527). The fungal diversity (Hf') was significantly correlated with the soil pH (r = 0.541).

CONCLUSION

The soil moisture, C/N ratio and pH were important determinants of the microbial community structure in Beilu River permafrost soils.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results may provide a useful baseline for predicting the variation in microbial communities in response to climate changes.

Effects of UV radiation on marine ectotherms in polar regions

Ozone-related increase in solar ultraviolet radiation (UVR) during the last decades provided an important ecological stressor, particularly for polar ecosystems since these are less adapted to such changes. All life forms appear to be susceptible to UVR to a highly variable extent that depends on individual species and their environment. Differences in sensitivity between organisms may relate to efficiency differences of their protection mechanisms and repair systems. UVR impacts are masked by large seasonal and geographic differences even in confined areas like the polar regions. UVR has effects and responses on various integration levels: from genetics, physiology, biology, populations, communities, to functional changes as in food webs with consequences on material and energy circulations through ecosystems. Even at current levels, solar UV-B affects consumer organisms, such as ectotherms (invertebrates and fish), particularly through impediments on critical phases of their development (early life history stages such as gametes, zygotes and larvae). Despite the overall negative implications of UVR, effect sizes vary widely in, e.g., molecular damage, cell and tissue damage, survival, growth, behavior, histology, and at the level of populations, communities and ecosystems.

Effects of enhanced UV-B radiation on the distribution of mineral elements in soybean (Glycine max) seedlings

In order to understand the effect of ultraviolet-B (UV-B) radiation on plant, the accumulated amount of dry matter and the distribution of the mineral elements in the different organs of soybean seedlings treated with UV-B radiation were investigated using the inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results indicated that the accumulated amount of dry matter in root, stem and leaf of soybean seedlings treated with UV-B radiation during the stress and recovery period was lower than that of the control soybean. Moreover, the content of macroelements in the root, stem and leaf of soybean seedlings during the stress period and recovery period were decreased comparing with that of the control soybean. The change in the contents of microelements depended on the intensity of UV-B radiation, the organs of soybean and the treating period. Finally, the results from the stepwise regression analysis indicated that the content of specific microelements also affected the accumulation of dry matter in the soybean seedlings treated with UV-B radiation comparing with the contents of macroelements in the control soybean. The relationship between the contents of mineral elements and the accumulation of dry matter depended on the intensity of UV-B radiation and the organs of soybean. These results demonstrated that UV-B radiation induced the change in the distribution of mineral elements in root, stem and leaf, leading to the decrease in the accumulation of dry matter and then the inhibition of soybean growth. It was a possible effect mechanism of UV-B radiation on plant.

Light-initiated transformations of fullerenol in aqueous media

We provide the first evidence that a fullerene derivative can be extensively mineralized under environmental conditions by direct photolysis. Dissolved inorganic carbon (DIC) was identified as a major photoproduct of fullerenol, a hydroxylated C(60) molecule and the ratio of moles DIC produced to moles of fullerenol reacted reached 28 or approximately 47% of complete mineralization on extensive irradiation by simulated solar radiation. The direct photoreaction kinetics of fullerenol in dilute aqueous solution can be described by pH-dependent biexponential rate expressions. This photoreaction slowed by a factor of 2 in nitrogen-saturated water. The oxygen dependence is attributed to photoinduced electron or hydrogen atom transfer from fullerenol to oxygen to produce superoxide ions with a quantum yield of 6.2 x 10(-4). Fullerenol can photosensitize the production of singlet oxygen ((1)O(2)) in dilute aqueous solution with quantum yields ranging from 0.10 in acidic water to 0.05 in neutral and basic solution. However our results indicate that chemical reactions involving diffusive encounters between (1)O(2) or superoxide and fullerenol are too slow to significantly contribute to the fast component of fullerenol photoreaction in sunlight. The pH dependence of the direct and sensitized photoreactions is attributed to changes in intramolecular hemiketal formation in fullerenol.

Humic substances-part 7: the biogeochemistry of dissolved organic carbon and its interactions with climate change

BACKGROUND, AIM, AND SCOPE

Dissolved organic matter, measured as dissolved organic carbon (DOC), is an important component of aquatic ecosystems and of the global carbon cycle. It is known that changes in DOC quality and quantity are likely to have ecological repercussions. This review has four goals: (1) to discuss potential mechanisms responsible for recent changes in aquatic DOC concentrations; (2) to provide a comprehensive overview of the interactions between DOC, nutrients, and trace metals in mainly boreal environments; (3) to explore the impact of climate change on DOC and the subsequent effects on nutrients and trace metals; and (4) to explore the potential impact of DOC cycling on climate change.

MAIN FEATURES

We review recent research on the mechanisms responsible for recent changes in aquatic DOC concentrations, DOC interactions with trace metals, N, and P, and on the possible impacts of climate change on DOC in mainly boreal lakes. We then speculate on how climate change may affect DOC export and in-lake processing and how these changes might alter nutrient and metal export and processing. Furthermore, the potential impacts of changing DOC cycling patterns on climate change are examined.

RESULTS

It has been noted that DOC concentrations in lake and stream waters have increased during the last 30 years across much of Europe and North America. The potential reasons for this increase include increasing atmospheric CO(2) concentration, climate warming, continued N deposition, decreased sulfate deposition, and hydrological changes due to increased precipitation, droughts, and land use changes. Any change in DOC concentrations and properties in lakes and streams will also impact the acid-base chemistry of these waters and, presumably, the biological, chemical, and photochemical reactions taking place. For example, the interaction of trace metals with DOC may be significantly altered by climate change as organically complexed metals such as Cu, Fe, and Al are released during photo-oxidation of DOC. The production and loss of DOC as CO(2) from boreal lakes may also be affected by changing climate. Climate change is unlikely to be uniform spatially with some regions becoming wetter while others become drier. As a result, rates of change in DOC export and concentrations will vary regionally and the changes may be non-linear.

DISCUSSION

Climate change models predict that higher temperatures are likely to occur over most of the boreal forests in North America, Europe, and Asia over the next century. Climate change is also expected to affect the severity and frequency of storm and drought events. Two general climate scenarios emerge with which to examine possible DOC trends: warmer and wetter or warmer and drier. Increasing temperature and hydrological changes (specifically, runoff) are likely to lead to changes in the quality and quantity of DOC export from terrestrial sources to rivers and lakes as well as changes in DOC processing rates in lakes. This will alter the quality and concentrations of DOC and its constituents as well as its interactions with trace metals and the availability of nutrients. In addition, export rates of nutrients and metals will also change in response to changing runoff. Processing of DOC within lakes may impact climate depending on the extent to which DOC is mineralized to dissolved inorganic carbon (DIC) and evaded to the atmosphere or settles as particulate organic carbon (POC) to bottom sediments and thereby remaining in the lake. The partitioning of DOC between sediments and the atmosphere is a function of pH. Decreased DOC concentrations may also limit the burial of sulfate, as FeS, in lake sediments, thereby contributing acidity to the water by increasing the formation of H(2)S. Under a warmer and drier scenario, if lake water levels fall, previously stored organic sediments may be exposed to greater aeration which would lead to greater CO(2) evasion to the atmosphere. The interaction of trace metals with DOC may be significantly altered by climate change. Iron enhances the formation of POC during irradiation of lake water with UV light and therefore may be an important pathway for transfer of allochthonous DOC to the sediments. Therefore, changing Fe/DOC ratios could affect POC formation rates. If climate change results in altered DOC chemistry (e.g., fewer and/or weaker binding sites) more trace metals could be present in their toxic and bioavailable forms. The availability of nutrients may be significantly altered by climate change. Decreased DOC concentrations in lakes may result in increased Fe colloid formation and co-incident loss of adsorbable P from the water column.

CONCLUSIONS

Climate change expressed as changes in runoff and temperature will likely result in changes in aquatic DOC quality and concentration with concomitant effects on trace metals and nutrients. Changes in the quality and concentration of DOC have implications for acid-base chemistry and for the speciation and bioavailability of certain trace metals and nutrients. Moreover, changes in DOC, metals, and nutrients are likely to drive changes in rates of C evasion and storage in lake sediments.

RECOMMENDATIONS AND PERSPECTIVES

The key controls on allochthonous DOC quality, quantity, and catchment export in response to climate change are still not fully understood. More detailed knowledge of these processes is required so that changes in DOC and its interactions with nutrients and trace metals can be better predicted based on changes caused by changing climate. More studies are needed concerning the effects of trace metals on DOC, the effects of changing DOC quality and quantity on trace metals and nutrients, and how runoff and temperature-related changes in DOC export affect metal and nutrient export to rivers and lakes.

Alteration of chromophoric dissolved organic matter by solar UV radiation causes rapid changes in bacterial community composition

We evaluated the effect of photochemical alterations of chromophoric dissolved organic matter (CDOM) on bacterial abundance, activity and community composition in a coastal lagoon of the Atlantic Ocean with high dissolved organic carbon concentration. On two occasions during the austral summer, bacteria-free water of the lagoon was exposed to different regions of the solar spectrum (full solar radiation, UV-A+PAR, PAR) or kept in the dark. Subsequently, dilution cultures were established with bacterioplankton from the lagoon that were incubated in the pre-exposed water for 5 h in the dark. Cell abundance, activity, and community composition of bacterioplankton were assessed before and after incubation in the different treatments. Changes in absorption, fluorescence, and DOC concentration were used as proxies for CDOM photoalteration. We found a significant CDOM photobleaching signal, DOC loss, as well as a stimulation of bacterial activity in the treatments pre-exposed to UV radiation, suggesting increased bioavailability of DOM. Bacterial community analysis by fluorescence in situ hybridization revealed that this stimulation was mainly accompanied by the specific enrichment of Alpha- and Betaproteobacteria. Thus, our results suggest that CDOM photoalteration not only stimulates bacterioplankton growth, but also induces rapid changes in bacterioplankton composition, which can be of relevance for ecosystem functioning, particularly considering present and future changes in the input of terrestrial CDOM to aquatic systems.

Introducing an integrated climate change perspective in POPs modelling, monitoring and regulation

This paper presents a review on the implications of climate change on the monitoring, modelling and regulation of persistent organic pollutants (POPs). Current research gaps are also identified and discussed. Long-term data sets are essential to identify relationships between climate fluctuations and changes in chemical species distribution. Reconstructing the influence of climatic changes on POPs environmental behaviour is very challenging in some local studies, and some insights can be obtained by the few available dated sediment cores or by studying POPs response to inter-annual climate fluctuations. Knowledge gaps and future projections can be studied by developing and applying various modelling tools, identifying compounds susceptibility to climate change, local and global effects, orienting international policies. Long-term monitoring strategies and modelling exercises taking into account climate change should be considered when devising new regulatory plans in chemicals management.

Chapter 4. Susceptibility of sharks, rays and chimaeras to global extinction

Marine biodiversity worldwide is under increasing threat, primarily as a result of over-harvesting, pollution and climate change. Chondrichthyan fishes (sharks, rays and chimaeras) have a perceived higher intrinsic risk of extinction compared to other fish. Direct fishing mortality has driven many declines, even though some smaller fisheries persist without associated declines. Mixed-species fisheries are of particular concern, as is illegal, unreported and unregulated (IUU) fishing. The lack of specific management and reporting mechanisms for the latter means that many chondrichthyans might already be susceptible to extinction from stochastic processes entirely unrelated to fishing pressure itself. Chondrichthyans might also suffer relatively more than other marine taxa from the effects of fishing and habitat loss and degradation given coastal habitat use for specific life stages. The effects of invasive species and pollution are as yet too poorly understood to predict their long-term role in affecting chondrichthyan population sizes. The spatial distribution of threatened chondrichthyan species under World Conservation Union (IUCN) Red List criteria are clustered mainly in (1) south-eastern South America; (2) western Europe and the Mediterranean; (3) western Africa; (4) South China Sea and Southeast Asia and (5) south-eastern Australia. To determine which ecological and life history traits predispose chondrichthyans to being IUCN Red-Listed, and to examine the role of particular human activities in exacerbating threat risk, we correlated extant marine species' Red List categorisation with available ecological (habitat type, temperature preference), life history (body length, range size) and human-relationship (whether commercially or game-fished, considered dangerous to humans) variables. Threat risk correlations were constructed using generalised linear mixed-effect models to account for phylogenetic relatedness. We also contrasted results for chondrichthyans to marine teleosts to test explicitly whether the former group is intrinsically more susceptible to extinction than fishes in general. Around 52% of chondrichthyans have been Red-Listed compared to only 8% of all marine teleosts; however, listed teleosts were in general placed more frequently into the higher-risk categories relative to chondrichthyans. IUCN threat risk in both taxa was positively correlated with body size and negatively correlated albeit weakly, with geographic range size. Even after accounting for the positive influence of size, Red-Listed teleosts were still more likely than chondrichthyans to be classified as threatened. We suggest that while sharks might not have necessarily experienced the same magnitude of deterministic decline as Red-Listed teleosts, their larger size and lower fecundity (not included in the analysis) predispose chondrichthyans to a higher risk of extinction overall. Removal of these large predators can elicit trophic cascades and destabilise the relative abundance of smaller species. Predator depletions can lead to permanent shifts in marine communities and alternate equilibrium states. Climate change might influence the phenology and physiology of some species, with the most probable response being changes in the timing of migrations and shifts in distribution. The synergistic effects among harvesting, habitat changes and climate-induced forcings are greatest for coastal chondrichthyans with specific habitat requirements and these are currently the most likely candidates for extinction. Management of shark populations must take into account the rate at which drivers of decline affect specific species. Only through the detailed collection of data describing demographic rates, habitat affinities, trophic linkages and geographic ranges, and how environmental stressors modify these, can extinction risk be more precisely estimated and reduced. The estimation of minimum viable population sizes, below which rapid extinction is more likely due to stochastic processes, is an important component of this endeavour and should accompany many of the current approaches used in shark management worldwide.

Interactive effects of solar UV radiation and climate change on biogeochemical cycling

This report assesses research on the interactions of UV radiation (280-400 nm) and global climate change with global biogeochemical cycles at the Earth's surface. The effects of UV-B (280-315 nm), which are dependent on the stratospheric ozone layer, on biogeochemical cycles are often linked to concurrent exposure to UV-A radiation (315-400 nm), which is influenced by global climate change. These interactions involving UV radiation (the combination of UV-B and UV-A) are central to the prediction and evaluation of future Earth environmental conditions. There is increasing evidence that elevated UV-B radiation has significant effects on the terrestrial biosphere with implications for the cycling of carbon, nitrogen and other elements. The cycling of carbon and inorganic nutrients such as nitrogen can be affected by UV-B-mediated changes in communities of soil organisms, probably due to the effects of UV-B radiation on plant root exudation and/or the chemistry of dead plant material falling to the soil. In arid environments direct photodegradation can play a major role in the decay of plant litter, and UV-B radiation is responsible for a significant part of this photodegradation. UV-B radiation strongly influences aquatic carbon, nitrogen, sulfur and metals cycling that affect a wide range of life processes. UV-B radiation changes the biological availability of dissolved organic matter to microorganisms, and accelerates its transformation into dissolved inorganic carbon and nitrogen, including carbon dioxide and ammonium. The coloured part of dissolved organic matter (CDOM) controls the penetration of UV radiation into water bodies, but CDOM is also photodegraded by solar UV radiation. Changes in CDOM influence the penetration of UV radiation into water bodies with major consequences for aquatic biogeochemical processes. Changes in aquatic primary productivity and decomposition due to climate-related changes in circulation and nutrient supply occur concurrently with exposure to increased UV-B radiation, and have synergistic effects on the penetration of light into aquatic ecosystems. Future changes in climate will enhance stratification of lakes and the ocean, which will intensify photodegradation of CDOM by UV radiation. The resultant increase in the transparency of water bodies may increase UV-B effects on aquatic biogeochemistry in the surface layer. Changing solar UV radiation and climate also interact to influence exchanges of trace gases, such as halocarbons (e.g., methyl bromide) which influence ozone depletion, and sulfur gases (e.g., dimethylsulfide) that oxidize to produce sulfate aerosols that cool the marine atmosphere. UV radiation affects the biological availability of iron, copper and other trace metals in aquatic environments thus potentially affecting metal toxicity and the growth of phytoplankton and other microorganisms that are involved in carbon and nitrogen cycling. Future changes in ecosystem distribution due to alterations in the physical and chemical climate interact with ozone-modulated changes in UV-B radiation. These interactions between the effects of climate change and UV-B radiation on biogeochemical cycles in terrestrial and aquatic systems may partially offset the beneficial effects of an ozone recovery.

Historical changes in arctic freshwater ecosystems

Various types of ecosystem-based climate proxies have been used to assess past arctic change. Although lotic records are relatively poor because of the constant reworking of riverine material, high-quality lentic data have been assembled back to the end of the Pleistocene and deglaciation of the circumpolar Arctic. In general, climatic variations in the Holocene, partly due to changes in the shrinking effect of glacier coverage, produced significant temporal and spatial variations in arctic hydrology and freshwater ecosystems. Of particular note were the vast expansions of northern peatlands during major protracted periods of wetting. More recent lake biota and sedimentiological data reflect the general warming trend that has occurred over the last one to two centuries and indicate major changes to freshwater characteristics such as ice-cover duration and thermal stratification. Such data provide an excellent baseline against which future effects of climate change can be both projected and measured.

Climate change effects on hydroecology of arctic freshwater ecosystems

In general, the arctic freshwater-terrestrial system will warm more rapidly than the global average, particularly during the autumn and winter season. The decline or loss of many cryospheric components and a shift from a nival to an increasingly pluvial system will produce numerous physical effects on freshwater ecosystems. Of particular note will be reductions in the dominance of the spring freshet and changes in the intensity of river-ice breakup. Increased evaporation/evapotranspiration due to longer ice-free seasons, higher air/water temperatures and greater transpiring vegetation along with increase infiltration because of permafrost thaw will decrease surface water levels and coverage. Loss of ice and permafrost, increased water temperatures and vegetation shifts will alter water chemistry, the general result being an increase in lotic and lentic productivity. Changes in ice and water flow/levels will lead to regime-specific increases and decreases in habitat availability/quality across the circumpolar Arctic.

The role of wetlands in the chromophoric dissolved organic matter release and its relation to aquatic ecosystems optical properties. A case of study: Katonga and Bunjako Bays (Victoria Lake; Uganda)

Chromophoric Dissolved Organic Matter (CDOM) is an important component in freshwater and marine ecosystems and plays direct and indirect role in biogeochemical cycles. CDOM originates from the degradation process of organic materials, usually macrophytes and planktons. The present work examines the importance of wetland derived CDOM on the optical and bio-optical properties of two bays of Lake Victoria (Uganda, Africa). This was achieved by determining the attenuation and extinction coefficients of filtered and unfiltered water samples from two equatorial bays on the Ugandan coastline of Lake Victoria. Katonga Bay is a wetland lined bay that receives water from the Katonga river, while Bunjako Bay is an outer bay between Katonga Bay and Lake Victoria. The results showed that attenuation was highest in Katonga Bay and the role of CDOM is most dominant near the river inlet. The quantity and quality of CDOM is extremely different in the two bays: in Katonga Bay it is possible to hypothesize a terrestrial origin of CDOM (transported by the wetland river). On the contrary, in Bunjako Bay, spectral measurements of absorption indicate a modified CDOM and/or alternative CDOM source. The terrestrial CDOM in Katonga Bay is more capable of absorbing harmful UV radiation than the CDOM present in the Bunjako Bay. The resulting optical environment in the former bay presented a water column with a very limited penetration of harmful UV radiation, while a higher penetration was observed in the Bunjako Bay.

UV Effects on Marine Planktonic Food Webs: A Synthesis of Results from Mesocosm Studies

UV irradiance has a broad range of effects on marine planktonic organisms. Direct and indirect effects on individual organisms have complex impacts on food-web structure and dynamics, with implications for carbon and nutrient cycling. Mesocosm experiments are well suited for the study of such complex interrelationships. Mesocosms offer the possibility to conduct well-controlled experiments with intact planktonic communities in physical, chemical and light conditions mimicking those of the natural environment. In allowing the manipulation of UV intensities and light spectral composition, the experimental mesocosm approach has proven to be especially useful in assessing the impacts at the community level. This review of mesocosm studies shows that, although a UV increase even well above natural intensities often has subtle effects on bulk biomass (carbon and chlorophyll), it can significantly impact the food-web structure because of different sensitivity to UV among planktonic organisms. Given the complexity of UV impacts, as evidenced by results of mesocosm studies, interactions between UV and changing environmental conditions (e.g. eutrophication and climate change) are likely to have significant effects on the function of marine ecosystems.