Natural Solar Radiation Research Articles

Oxidation of microcystin-LR and cylindrospermopsin by heterogeneous photocatalysis using a tubular photoreactor packed with different TiO2 coated supports

The photocatalytic degradation of cyanotoxins in aqueous solutions using slurry suspensions of TiO2 implies a post-filtration step to retain the photocatalyst. In this work, 2D and 3D TiO2 thin films supported in inert surfaces was proposed for the solar photocatalytic removal of cyanotoxins microcystin-LR (MC-LR) or cylindrospermopsin (CYN) in distilled and natural water under neutral pH conditions. The photocatalytic experiments were performed in a lab-scale tubular photoreactor with a compound parabolic collector (CPC) using simulated and natural solar radiation. The tubular photoreactor was packed with transparent cellulose acetate monoliths (CAM) coated with a P25 paste or sol–gel 2D TiO2 film or with a photocatalytic 3D TiO2-loaded exterior paint (PC500, VLP7000 and P25). The efficiency of the TiO2 photocatalytic system in the presence of hydrogen peroxide was also assessed. PVC or glass tubes and glass spheres, coated with a photocatalytic 3D TiO2-loaded exterior paint, were also tested as inert surfaces. The supports used in this work were chosen according to some characteristics, such as cost, surface resistance, surface area and transmissibility to UV radiation. The toxins MC-LR and CYN were purified from Microcysts aeruginosa and Cylindrospermopsis raciborskii cultures, respectively. The photocatalytic system P25-CAM/H2O2 can be considered the most effective process, considering the cyanotoxins removal efficiency, the cost and the simplicity of the preparation.

Survival of Pseudomonas aeruginosa exposed to sunlight resembles the phenom of persistence

During exposure of Pseudomonas aeruginosa stationary phase cells to natural solar radiation, a reduction in the rate of loss of bacterial viability was observed when survival fractions were lower than 1/10,000. This reduction was independent of the growth medium used and of the initial bacterial concentration, and was also observed when irradiation was performed with artificial UVA radiation (365nm, 47Wm−2). These results indicate the presence of a small bacterial subpopulation with increased tolerance to radiation. Such a tolerance is non-heritable, since survival curves comparable to those of the parental strain were obtained from survivors to long-term exposure to radiation. The radiation response described here resembles the phenomenon called persistence, which consists of the presence of a small subpopulation of slow-growing cells which are able to survive antibiotic treatment within a susceptible bacterial population. The condition of persister cells is acquired via a reversible switch and involves active defense systems towards oxidative stress. Persistence is probably responsible for biphasic responses of bacteria to several stress conditions, one of which may be exposure to sunlight. The models currently used to analyze the lethal action of sunlight overestimate the effect of high-dose irradiation. These models could be improved by including the potential formation of persister cells.

Application of heat stress in situ demonstrates a protective role of irradiation on photosynthetic performance in alpine plants.

The impact of sublethal heat on photosynthetic performance, photosynthetic pigments and free radical scavenging activity was examined in three high mountain species, Rhododendron ferrugineum, Senecio incanus and Ranunculus glacialis using controlled in situ applications of heat stress, both in darkness and under natural solar irradiation. Heat treatments applied in the dark reversibly reduced photosynthetic performance and the maximum quantum efficiency of photosystem II (Fv/Fm), which remained impeded for several days when plants were exposed to natural light conditions subsequently to the heat treatment. In contrast, plants exposed to heat stress under natural irradiation were able to tolerate and recover from heat stress more readily. The critical temperature threshold for chlorophyll fluorescence was higher under illumination (Tc′) than in the dark (Tc). Heat stress caused a significant de-epoxidation of the xanthophyll cycle pigments both in the light and in the dark conditions. Total free radical scavenging activity was highest when heat stress was applied in the dark. This study demonstrates that, in the European Alps, heat waves can temporarily have a negative impact on photosynthesis and, importantly, that results obtained from experiments performed in darkness and/or on detached plant material may not reliably predict the impact of heat stress under field conditions.

Synthesis of surfactant-assisted FeVO4 nanostructure: Characterization and photocatalytic degradation of phenol

Pure triclinic FeVO4 catalysts were synthesized by hydrothermal method and modified with Hexadecyltrimethylammonium Bromide (HTAB), Sodium Dodecyl Sulfate, Polyethylene Glycol (PEG) as surfactant. The materials were characterized by XRD, BET, FT-IR, DRS and SEM techniques. These catalysts were used for the photocatalytic degradation of phenol (Ph) under natural solar light irradiation. The effect of preparation parameters on the photocatalytic activity was also examined. It is found that the surfactant and pH value a significant influence on the particle morphology and even the crystalline structure of the product. Surfactant added products resulted an improve efficiency of the triclinic FeVO4. With HTAB as surfactant at an hydrothermal temperature of 75°C and the pH 3 value of the precursor solution the highest percentage of phenol degradation (100%) and highest reaction rate (1.24mgl−1min−1) were obtained in 45min. It is concluded that the excellent photocatlytic activity of the HTAB-assisted FeVO4 catalyst, with rod-like shaped morphology, was associated its small particle size, large surface area, the presence of more surface OH groups and lower band gap energy than pure FeVO4.

Influence of canopy fruit location on morphological, histochemical and biochemical changes in two oil olive cultivars

The influence of different irradiance conditions was evaluated under natural solar radiation by comparing well-exposed (in) and shaded fruit (out) in canopies of olive trees (Olea europaea L). Over a 2-year period, from 50 days after full bloom up to harvest time, “in” and “out” olive samples of two genotypes (“Frantoio Millennio” and “Coratina 5/19”) were periodically collected. Morphological, histochemical, and biochemical analysis were performed to study the changes on fruit morphometric traits, oil body accumulation, and β-glucosidase enzyme activity. Some parameters were modified by shading inside the canopy in which the proportion of incident photosynthetically active radiation intercepted by the crop was 47%. Shaded fruits developed at slow rate and were characterized by late darkgoing time, reduced size, with a tendency toward oblong shape. The rapid histochemical procedure proposed to estimate the oil body accumulation during fruit ripening showed that a reduced irradiance caused a decrease in oil body density. The canopy position influenced, in a different way, the β-glucosidase activity in relation to the fruit-ripening stage in both genotypes. These findings indicate that providing an adequate and uniform lighting of the olive canopy by careful choices of orchard management practices can be a key factor for several yield components.

Inactivation of MS2 coliphage in sewage by solar photocatalysis using metal-doped TiO2

The beneficial properties of metal-doped titania nanoparticles with respect to wastewater disinfection under solar irradiation were investigated. Mn-, Co- and binary Mn/Co-doped TiO2 catalysts were prepared by means of a co-precipitation method and were subsequently assessed in terms of their potential to inactivate MS2 bacteriophage in slurry reactor under simulated and natural solar irradiation. Disinfection effectiveness was evaluated in relation to influential operating parameters, like catalyst type (Mn-, Co- and Mn/Co), dopant concentration (0.02–1molwt%), artificial and natural solar light, wavelength (i.e. >420nm) and photon flux (4.93–5.8×10−7E/(Ls)). Metal doping led to considerable narrowing of the band gap and the spectral response of the catalysts extended well into the visible region. MS2 phage was readily inactivated in sewage samples under simulated solar irradiation in the presence of the prepared metal-doped catalysts. The latter proved to be superior to the commercial P25, under the current experimental conditions, resulting in an approximately 60% phage population decrease in almost 60min of simulated solar irradiation when initial MS2 concentration was 105PFU/mL. Catalysts with the binary dopant exhibited the best photocatalytic activity in all cases, as almost 99% of MS2 population was eliminated in less than 20min of irradiation highlighting the fact that composite dopants induce a synergistic effect. The effect of different dopants concentration was apparent up to a certain limit. Disinfection follows a pseudo-first order kinetic rate. Retardation of the process by a factor 1.6–3.8 was recorded under natural solar light, based on the kinetic rate constants of inactivation curves which were within the range of 0.032–0.057min−1. The corresponding range for inactivation under simulated solar irradiation was 0.053–0.221min−1. Moreover, testing the Mn-, Co-, and binary Mn/Co doped TiO2 in the absence of UV light, they were considerably sensitized making clear that they can be activated in the visible part of the spectrum.

Magnetizing of nano-materials on example of Degussa’s P-25 TiO2 photocatalyst: Synthesis of magnetic aggregates, characterization and possible use

This study deals with the production of a magnetic photocatalyst using a new magnetizing technique – growth of magnetite crystals onto P-25 TiO2 particles from Degussa. Magnetite (MT) crystals were grown via the synthesis of layered FeII–FeIII hydroxide sulfate (green rust) on the surfaces of TiO2. The magnetite/P-25 TiO2 aggregates (MT/P-25) were characterized with XRD and TEM. The structure of the P-25 TiO2 photocatalyst appeared to be unchanged by the treatment. The photocatalytic activity of MT/P-25 in aqueous suspensions were tested in the near neutral pH area where magnetite is stable and compared to the photoactivity of pure P-25 TiO2. Photooxidation of tartronic acid (TA) was first used to test the photooxidative efficiency of MT/P-25 followed by other more complex compounds: aqueous solution of 2,6 difluorobenzoic acid (2,6 DFBA) as well as the natural organic matter in water from the Hohloh Lake, Germany (NOM-HLW). For the TA photocatalytic oxidation with MT/P-25 similar oxidation rates were observed as for the P-25 TiO2, but for 2,6 DFBA and NOM-HLW the degradation rates were higher for pure P-25 TiO2. Two types of laboratory reactors were applied for photocatalytic degradation of 2,6 DFBA and NOM-HLW: a reactor (400mL) with an artificial UV radiation source and the other one (800mL) that was irradiated by natural solar radiation. Photonic efficiencies of organic substrates degradation processes for both types of the reactors were calculated and compared. The bigger reactor showed better results in degradation of organic substrates (photonic efficiency was more than 7 times higher for 2,6 DFBA).Magnetic separation using a simple separator (hand magnet, batch experiment) showed a mass loss less than 3% of MT/P-25 per experiment. However, using a high gradient magnetic separator (with continuous flow) less than 0.3% of MT/P-25 aggregates were lost with a suspension flow rate of 250mL/min. In both cases magnetically separated and reused MT/P-25 showed practically unchanged photoactivity.The mechanical stability of the MT/P-25 was checked comparing the photoactivity of MT/P-25 in TA solution without prior stirring and after stirring in the reactor “in the dark” for durations of 80 and 160h. No significant differences were observed in their photoactivity before and after stirring. However, ultrasonication of the MT/P-25 at 35kHz for 60min separated the MT/P-25 material into MT and TiO2. Nevertheless, for practical purposes the stability of the aggregates during the mechanical stirring and during the magnetic separation is of major importance.

Synthesis, features and solar-light-driven photocatalytic activity of TiO2 nanotube arrays loaded with SnO2.

In the present study TiO2 nanotube arrays (TNTs) were loaded with a post-transition metal oxide particles namely SnO2 via incipient wet impregnation method by varying its concentration (1.59 wt%, 2.25 wt% and 2.84 wt%). The photocatalytic activity of the prepared photocatalyst was evaluated for the degradation of methylene blue (MB) in presence of natural solar light irradiation. The morphological analyses revealed that the prepared TNTs had average inner diameter of 109 nm, wall thickness of 15 nm and tube length of 7-10 μm, respectively, while the crystalline phase and Raman spectra confirmed the 100% anatase mineral form of TiO2. Further, the presence of SnO2 in TNTs was confirmed by high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The visible light absorption properties of TNTs improved drastically with increasing SnO2 loadings. The coupling effect of SnO2 and TiO2 significantly enhanced degradation efficiency of MB. An 84% degradation of MB was achieved in 6 h of irradiation under clear sky condition.

Intensification of a solar photo-Fenton reaction at near neutral pH with ferrioxalate complexes: A case study on diclofenac removal from aqueous solutions

Abstract The kinetic degradation profile for diclofenac (DCF) antibiotic in aqueous solutions using the conventional photo-Fenton reaction is characterized by a very slow reaction rate mainly associated to DCF precipitation-redissolution-degradation mechanism at acidic conditions and DCF degradation via a ligand-to-metal charge mechanism that occurs on the surface of the iron precipitates, under neutral pH conditions. This work evaluates the intensification of a solar photo-Fenton reaction by using ferrioxalate complexes (Fe3+/H2O2/oxalic acid/UVA–vis) in the degradation of diclofenac (DCF) in aqueous solution at near neutral pH values, which avoids the precipitation of DCF and ferric hydroxide, and iron concentrations below the discharge limits into water bodies ([Fe] ⩽ 2.0 mg/L). The efficiency of the photo-Fenton process was evaluated at different iron/oxalate molar ratios (1:3; 1:6 and 1:9; [Fe3+] = 2 mg/L), under controlled conditions of pH (5.0 and 6.0), using a lab-scale photoreactor irradiated with artificial sunlight. At pH 6.0 ([DCF]0 = 20 mg/L), using an iron/oxalate molar ratio of 1:9 it was achieved complete degradation of DCF (below the detection limit) and 63.0% mineralization in 90 min, consuming 1.9 mM H2O2. A lower dose of oxalic acid (1:3 iron/oxalate molar ratio) was needed to attain similar results at pH 5.0. DCF degradation at pH 5.0, for an iron/oxalate molar ratio of 1:3, was also evaluated at different temperatures (15–45 °C), UVA irradiances (27.8–59.9 WUV/m2), DCF and iron concentrations ([DCF] = 2–20 mg/L, [Fe3+] = 1–2 mg/L), presence of inorganic ions (0.1 g/L; Cl−, SO42−, NO3−, HCO3−, NH4+) and radical scavengers (sodium azide 10 mM and d -mannitol 50 mM). DCF degradation kinetics at pilot plant scale under natural solar radiation, using the best conditions obtained at lab-scale (pH 5.0, iron/oxalate molar ratio of 1:3), showed similar results to those obtained in the lab-scale photoreactor. The nitrogen and chlorine atoms in the DCF molecule structure were easily released to the solution as chloride, ammonium and nitrite ions. Acetic acid was the main low-molecular-weight carboxylic acid detected during the reaction, stopping the photo-Fenton process due to the low photoactivity of ferric-acetate complexes and its recalcitrant character to further mineralization by hydroxyl radical attack.

Solar photo-Fenton treatment of winery effluents in a pilot photocatalytic reactor

A pilot-scale solar Fenton process has been applied for the treatment of winery wastewater collected during the vinification period. The importance of the experimental variables was investigated at lab-scale experiments through the application of experimental design methodology. The pilot-scale study was conducted on a pilot CPC photocatalytic reactor under natural solar irradiation. The results show that at low catalyst dose (i.e. [Fe2+]=5mgL−1) mineralization (i.e. ca. 50%) is dependent on the oxidant consumption (i.e. 500mgL−1), irrespective of the excess oxidant present; however, shorter reaction times are required under excess H2O2, indicating higher reaction rates due to higher availability of oxidant molecules in the bulk liquid. Increasing the catalyst dose enhances the reaction rate due to higher H2O2 decomposition and HO• production. This is corroborated with the lower H2O2 consumption (i.e. 1270mgL−1) occurring at low catalyst, signifying, however, a more effective use of the oxidant (i.e. less oxidant is required to achieve similar mineralization).

Use of Radiation Absorbing Materials for Clearing Snow in Mountainous Areas

A comparative study of melting of snow by spreading different materials such as charcoal power, boiler ash, saw dust and common salt etc. On its surface under exposure to natural solar radiation has been made. The observations were carried out at Gulmarg at a height of about 9,000 ft. above sea level in the months of January, February and March 1965. It was observed that with the help of boiler ash, the melting rate of snow was increased to about 4 in the half inches per day which is about twice the rate without boiler ash. This material therefore seems to be very much suited to snow clearing operations in the mountain terrain.

Sunlight-driven photochemical halogenation of dissolved organic matter in seawater: a natural abiotic source of organobromine and organoiodine.

Reactions of dissolved organic matter (DOM) with photochemically generated reactive halogen species (RHS) may represent an important natural source of organohalogens within surface seawaters. However, investigation of such processes has been limited by difficulties in quantifying low dissolved organohalogen concentrations in the presence of background inorganic halides. In this work, sequential solid phase extraction (SPE) and silver-form cation exchange filtration were utilized to desalt and preconcentrate seawater DOM prior to nonspecific organohalogen analysis by ICP-MS. Using this approach, native organobromine and organoiodine contents were found to range from 3.2-6.4 × 10(-4) mol Br/mol C and 1.1-3.8 × 10(-4) mol I/mol C (or 19-160 nmol Br L(-1) and 6-36 nmol I L(-1)) within a wide variety of natural seawater samples, compared with 0.6-1.2 × 10(-4) mol Br/mol C and 0.6-1.1 × 10(-5) mol I/mol C in terrestrial natural organic matter (NOM) isolates. Together with a chemical probe method specific for RHS, the SPE+ICP-MS approach was also employed to demonstrate formation of nanomolar levels of organobromine and organoiodine during simulated and natural solar irradiation of DOM in artificial and natural seawaters. In a typical experiment, the organobromine content of 2.1 × 10(-4) mol C L(-1) (2.5 mg C L(-1)) of Suwannee River NOM in artificial seawater increased by 69% (from 5.9 × 10(-5) to 1.0 × 10(-4) mol Br/mol C) during exposure to 24 h of simulated sunlight. Increasing I(-) concentrations (up to 2.0 × 10(-7) mol L(-1)) promoted increases of up to 460% in organoiodine content (from 8.5 × 10(-6) to 4.8 × 10(-5) mol I/mol C) at the expense of organobromine formation under the same conditions. The results reported herein suggest that sunlight-driven reactions of RHS with DOM may play a significant role in marine bromine and iodine cycling.

Solar energy for wastewater treatment: review of international technologies and their applicability in Brazil.

Several studies have reported the adverse effects of recalcitrant compounds and emerging contaminants present in industrial effluents, which are not degradable by ordinary biological treatment. Many of these compounds are likely to accumulate in living organisms through the lipid layer. At concentrations above the limits of biological tolerance, these compounds can be harmful to the ecosystem and may even reach humans through food chain biomagnification. In this regard, advanced oxidation processes (AOPs) represent an effective alternative for the removal of the pollutants. This study focused on the AOP involving the use of ultraviolet radiation in homogeneous and heterogeneous systems. Based on the literature review, comparisons between natural and artificial light were established, approaching photoreactors constructive and operational characteristics. We concluded that the high availability of solar power in Brazil would make the implementation of the AOP using natural solar radiation for the decontamination of effluents feasible, thereby contributing to clean production and biodiversity conservation. This will serve as an important tool for the enforcement of environmental responsibility among public and private institutions.

Interaction of extrinsic chemical factors affecting photodegradation of dissolved organic matter in aquatic ecosystems

Photochemical degradation of dissolved organic matter (DOM) plays an important role in the carbon cycle. Irradiation experiments were conducted to evaluate the influence of chemical factors, specifically those expected to be altered in natural waters by atmospheric acid deposition, on photodegradation of DOM. These included pH, nitrate, iron and calcium. The experiments were carried out using stream and lake water samples with a wide range of dissolved organic carbon (DOC) concentration. Decreasing DOC concentration along with decreasing absorbance was observed during three-week exposures to natural solar radiation as well as during laboratory experiments with artificial solar radiation. The pH of the samples significantly affected degradation rates of DOM especially with elevated iron, while no influence of nitrate or calcium concentration was observed. Addition of Fe(III) did not significantly affect photodegradation and photobleaching rate constants in samples at circumneutral pH. Acid pH increased photodegradation rates. The results suggest that photodegradation rates of DOM will decrease during recovery from acidification. Hence, lower photodegradation rates may be responsible for increases in DOM observed in some regions of North America and Europe.

Developmental toxicity and DNA damage from exposure to parking lot runoff retention pond samples in the Japanese medaka (Oryzias latipes)

Parking lot runoff retention ponds (PLRRP) receive significant chemical input, but the biological effects of parking lot runoff are not well understood. We used the Japanese medaka (Oryzias latipes) as a model to study the toxicity of water and sediment samples from a PLRRP in Morehead City, NC. Medaka exposed in ovo to a dilution series of PLRRP water had increased odds of death before hatching, but not teratogenesis or delayed hatching. Next, we adapted a long-amplicon quantitative PCR (LA-QPCR) assay for DNA damage for use with the Japanese medaka. We employed LA-QPCR to test the hypotheses that PLRRP water and sediments would cause nuclear and mitochondrial DNA damage with and without full-spectrum, natural solar radiation. Fluoranthene with and without natural sunlight was a positive control for phototoxic polycyclic aromatic hydrocarbon-induced DNA damage. Fluoranthene exposure did not result in detectable DNA damage by itself, but in combination with sunlight caused significant DNA damage to both genomes. PLRRP samples caused DNA damage to both genomes, and this was not increased by sunlight exposure, suggesting the DNA damage was unlikely the result of PAH phototoxicity. We report for the first time that PLRRP-associated pollutants cause both nuclear and mitochondrial DNA damage, and that fluoranthene-mediated phototoxicity results in similar levels of damage to the nuclear and mitochondrial genomes. These effects may be especially significant in sensitive marine ecosystems.

Enhancement of the photo-Fenton reaction at near neutral pH through the use of ferrioxalate complexes: A case study on trimethoprim and sulfamethoxazole antibiotics removal from aqueous solutions

Abstract Literature describes a kinetic degradation profile for sulfamethoxazole (SMX) and trimethoprim (TMP) antibiotics in aqueous solutions using a photo-Fenton reaction characterized by a very fast initial reaction rate followed by a slow degradation process. This work tries to elucidate that the slow decay on SMX and TMP concentration observed in the second part of the photo-Fenton kinetic degradation profile is not only entirely attributed to the competition of hydroxyl radicals between the initial intermediates generated and the antibiotic molecules, but also associated to the formation of strong and stable Fe(III)-antibiotic complexes, which limits the photoreduction of Fe3+, decreasing the decomposition of H2O2 in the Fenton reaction and the overall efficiency of the photo-Fenton process. Ferric speciation diagrams, including the ferric hydroxide complexes, antibiotic species and their interaction with ferric ions, showed the formation of those strong Fe(III)-antibiotic complexes. Process intensification of the photo-Fenton reaction with ferrioxalate complexes was able to reduce the formation of those Fe(III)-antibiotic complexes, enhancing the reaction efficiency at near neutral pH values (5.0) and using low iron concentration (5.0 mg/L). Ferrioxalate complexes are stronger than Fe(III)-antibiotic complexes, improving the quantum yield for ferrous ions production. The efficiency of the photo-Fenton reaction was also compared with the heterogeneous photocatalysis (TiO2/UV and TiO2/H2O2/UV), driven by natural solar radiation using photoreactors with compound parabolic collectors (CPCs) at pilot scale. The speciation of antibiotics molecules in solution as a function of pH plays also an important role in the reactivity of ROS.

About the possibility of calibrating optical detectors by solar radiation

Whereas information on absolute detected/emitted irradiation is not required for determination of absorbance or transmittance, this information is essential to quantitatively analyse nearly any photo-induced reaction. Some examples/applications are photo catalysis, photo degradation, optical materials, photo synthesis, photochemical kinetics and dynamics of solar energy – that is, all procedures for studying the influence of a large number of photons. The only way to control the irradiation is to have access to an optical radiometer with known and defined parameters. Due to aspects such as receiver quantum yield and construction influences, absolute and spectral calibrations must be considered. Fibre-couplet optical detectors based on the CCD technique are affordable and variability is a major advantage. But for spectral calibration no comparable procedure exists. Additionally, constructed stable reference light sources with known and suitable radiance (>200 W m−2), with sufficient illumination area and exactly known broadband wavelength distribution are not easily accessible or do not exist. A novel procedure is presented here using natural solar radiation for calibration of intensity and energy.

UV-induced carbon monoxide emission from living vegetation

Abstract. The global burden of carbon monoxide (CO) is rather uncertain. In this paper we address the potential for UV-induced CO emission by living terrestrial vegetation surfaces. Real-time measurements of CO concentrations were made with a cavity-enhanced laser spectrometer connected in closed loop to either a chamber on a field of grass or a plant-leaf scale chamber. Leaves of all plant species that were examined exhibited emission of CO in response to artificial UV radiation as well as the UV component of natural solar radiation. The UV-induced rate of CO emission exhibited a low dependence on temperature, indicating an abiotic process. The emission of CO in response to the UV component of natural solar radiation was also evident at the natural grassland scale.

Effect of ultraviolet irradiation on the production and composition of fatty acids in plankton in a sub-Antarctic environment

We investigated the effects of ultraviolet-B (UV-B) radiation on the natural phytoplankton assemblage in Marine Cove on King George Island, Antarctica, in December 2005. The amount of newly synthesized phytoplankton polyunsaturated fatty acids (PUFAs) was lower with exposure to full irradiation (PAR+UV-A+UV-B) than without such exposure (exposed instead to PAR+UV-A radiation) in an in situ incubation under the light conditions in two different types of incubation bottles: quartz bottles transmitting all light wavelengths including UV-B and polycarbonate bottles with no UV-B transmission and 20 % reduced PAR compared to the quartz bottle. However, the amount of newly synthesized saturated fatty acids was greater with than without UV-B radiation. Thus, UV-B radiation may have a significant influence on fatty acid synthesis in phytoplankton. In particular, the production of eicosapentaenoic acid [20:5(n-3)] and docosahexaenoic acid [22:6(n-3)] was reduced during incubation under the natural solar radiation including UV-B. To understand the indirect influence of UV-B on herbivores (the secondary producer), we conducted feeding experiments with amphipods fed in situ on the natural phytoplankton assemblage. The amphipods fed on the phytoplankton with the low PUFA values also exhibited a low PUFA accumulation rate, which could negatively affect their growth, development, and reproduction. Consequently, the diminished rate of essential fatty acid synthesis [especially 20:5(n-3) and 22:6(n-3)] in primary producers caused by UV-B exposure could affect the structure and function of the Antarctic marine ecosystem.

Distinct Optical Chemistry of Dissolved Organic Matter in Urban Pond Ecosystems

Urbanization has the potential to dramatically alter the biogeochemistry of receiving freshwater ecosystems. We examined the optical chemistry of dissolved organic matter (DOM) in forty-five urban ponds across southern Ontario, Canada to examine whether optical characteristics in these relatively new ecosystems are distinct from other freshwater systems. Dissolved organic carbon (DOC) concentrations ranged from 2 to 16 mg C L-1 across the ponds with an average value of 5.3 mg C L-1. Excitation-emission matrix (EEM) spectroscopy and parallel factor analysis (PARAFAC) modelling showed urban pond DOM to be characterized by microbial-like and, less importantly, by terrestrial derived humic-like components. The relatively transparent, non-humic DOM in urban ponds was more similar to that found in open water, lake ecosystems than to rivers or wetlands. After irradiation equivalent to 1.7 days of natural solar radiation, DOC concentrations, on average, decreased by 38% and UV absorbance decreased by 25%. Irradiation decreased the relative abundances of terrestrial humic-like components and increased protein-like aspects of the DOM pool. These findings suggest that high internal production and/or prolonged exposure to sunlight exerts a distinct and significant influence on the chemistry of urban pond DOM, which likely reduces its chemical similarity with upstream sources. These properties of urban pond DOM may alter its biogeochemical role in these relatively novel aquatic ecosystems.