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Quartz Tubes (quartz + tubes)
Selected AbstractsEffects of ultraviolet radiation on the eggs of landlocked Galaxias maculatus (Galaxiidae, Pisces) in northwestern PatagoniaFRESHWATER BIOLOGY, Issue 3 2000M. Battini Summary 1Ultraviolet radiation (UVR) damages early life stages of several fish species. Galaxias maculatus is a small catadromous fish, with landlocked forms occurring in many lakes within the Nahuel Huapi National Park (Patagonia, Argentina). In this work, the vulnerability of G. maculatus eggs exposed to both natural and artificial UVR was investigated in relation to water transparency. 2Field experiments were performed in two lakes differing in UVR attenuation. Galaxias maculatus eggs were exposed to in situ levels of UVR in quartz tubes incubated at various depths. For laboratory experiments, the eggs were exposed to five levels of artificial UVB radiation. 3Exposure to natural UVR causes various degrees of egg mortality depending on water transparency and incubation depth. In the less transparent lake (Kd320 = 3.08 m -1), almost complete mortality was observed near the surface. At a depth of 43 cm the observed mortality was only 22%, but was still significantly different from the dark control. In the most transparent lake (Kd320 = 0.438 m -1), almost total mortality was observed in tubes incubated at 2.56 m or shallower. A gradual decline in mortality was recorded from that depth to 3.78 m where the values approached those in the dark control treatments. 4A monotonic relationship between mortality and UV exposure could be observed both in field and laboratory experiments. Using the results from field incubations, a LD50 of 2.5 J cm -2 nm -1 was estimated. In a few mountain lakes, this value would be exceeded even if the eggs were laid at the maximum depth of the lake. Thus UVR seems a sufficient cause to explain the absence of G. maculatus populations in some mountain lakes. For most lakes, however, UVR is probably one of several important environmental factors, which together determine the habitat suitability. [source] Electron spin resonance studies on ,-irradiated coffee bean partsINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 1 2003Brij Bhushan Summary Using electron spin resonance (ESR) free radicals, present naturally or formed after ,-irradiation of parts of coffee bean, were examined by entrapping the sample in potassium chloride powder in ESR quartz tubes. The ESR signal at g=2.002 was more prominent in the spermoderm than in the whole seed portion of the coffee beans. The ,-irradiation of coffee beans with doses of 5 or 10 kGy, normally used for decontamination, resulted in a dose-dependent increase of a signal at g=2.002 which was accompanied by a weak triplet (aH c. 3.0 mT), and which was also more prominent in the spermoderm. While short-term storage (24 h at 25 ± 0.5 °C) of irradiated beans resulted in a substantial loss of signal at g=2.002, annealing at 50 ± 0.5 °C for 16 h increased this signal intensity in greater proportion than caused by irradiation alone, suggesting that generation of free radicals in the two varieties of coffee beans is not unique to the irradiation processing alone. [source] Variability of UVR Effects on Photosynthesis of Summer Phytoplankton Assemblages from a Tropical Coastal Area of the South China Sea,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Kunshan Gao From June to September 2005, we carried out experiments to determine the ultraviolet radiation (UVR) -induced photoinhibition of summer phytoplankton assemblages from a coastal site of the South China Sea. Variability in taxonomic composition was determined throughout the summer, with a peak chlorophyll a (chl a,20 ,g chl a L,1) dominated by the diatom Skeletonema costatum that was detected early in the study period; the rest of the time samples were characterized by monads and flagellates, with low chl a values (1,5 chl a ,g L,1). Surface water samples were placed in quartz tubes, inoculated with radiocarbon and exposed to solar radiation for 2,3 h to determine photosynthetic rates under three quality radiation treatments (i.e. PAB, 280,700 nm; PA, 320,700 nm and P, 400,700 nm) using different filters and under seven levels of ambient irradiance using neutral density screens (PvsE curves). UVR inhibition of samples exposed to maximum irradiance (i.e. at the surface) varied from ,12.2% to 50%, while the daytime-integrated UVR-related photoinhibition in surface seawater varied from ,62% to 7%. The effects of UVR on the photosynthetic parameters PBmax and Ek were also variable, but UV-B accounted for most of the observed variability. During sunny days, photosynthesis of microplankton (>20 ,m) and piconanoplankton (<20 ,m) were significantly inhibited by UVR (mostly by UV-B). However, during cloudy days, while piconanoplankton cells were still inhibited by UVR, microplankton cells used UVR (mostly UV-A) as the source of energy for photosynthesis, resulting in higher carbon fixation in samples exposed to UVR than the ones exposed only to photosynthetically active radiation (PAR). Our results indicate that size structure and cloudiness clearly condition the overall impact of UVR on phytoplankton photosynthesis in this tropical site of South China. In addition, model predictions for this area considering only PAR for primary production might have underestimated carbon fixation due to UVR contribution. [source] Vertical Migration and Motility Responses in Three Marine Phytoplankton Species Exposed to Solar Radiation,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Peter R. Richter ABSTRACT Diurnal vertical migration in the water column and the impact of solar radiation on motility were investigated in three marine phytoplankton species: Tetraselmis suecica, Dunaliella salina and Gymnodinium chlorophorum. Cells were exposed to solar radiation either in ultraviolet radiation (UVR, 280,400 nm) transparent Plexiglas tubes (45 cm length, 10 cm diameter) or in quartz tubes under three radiation treatments: PAB (280,700 nm), PA (320,700 nm) and P (400,700 nm). The three species displayed different behavior after exposure to solar radiation. Tetraselmis suecica was insensitive to UVR and under high solar radiation levels, cells accumulated preferentially near the surface. Exposure experiments did not indicate any significant changes in swimming speed nor in the percentage of motile cells after 5 h of exposure. On the other hand, D. salina was sensitive to UV-B displaying a significant decrease in swimming speed and percentage of motile cells after 2,3 h of exposure. Moreover, D. salina cells migrated deep in the water column when irradiance was high. The response of G. chlorophorum was in between that of the other two species tested, with a slight (but significant) decrease in swimming speed and percentage of motile cells in all radiation treatments after 5 h of exposure. While G. chlorophorum cells were more or less homogenously distributed in the water column, a slight (but significant) avoidance response to high radiation was observed at local noon, with cells migrating deep in the water column. Our data clearly indicate that these sub-lethal effects of solar radiation are species-specific and they might have important implications for the aquatic ecosystem. [source] | ||||||||||