Browsing by Autor "E. Walter Helbling"

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DNA damage and photosynthetic inhibition induced by solar ultraviolet radiation in tropical phytoplankton (Lake Titicaca, Bolivia)
(Taylor & Francis, 2001) E. Walter Helbling; Virginia E. Villafañe; Anita G. J. Buma; Marcos Andrade; Francesco Zaratti
Experiments were conducted during October 1998 in Lake Titicaca, Bolivia (16° S, 68° W, 3810 m a.s.l), to determine the effects of solar ultraviolet radiation (UVR) on phytoplankton photosynthetic rates and DNA damage. Water samples were taken daily and incubated in situ or in simulated in situ conditions using sharp cut-off filters to eliminate various portions of the UVR spectrum. The total inhibition of photosynthesis due to UVR in surface waters was 85%; the greatest part of this inhibition (65%) was due to UVAR (315–400 nm), the rest (20%) being due to UVBR (280–315 nm). The inhibition of photosynthesis decreased with depth so that there were no significant differences among treatments at 1.3 optical depths (K PAR). The loss of carbon assimilation in the integrated production over the euphotic zone (4.6 optical depths) was 17.4%, with 14% due to UVAR and an additional 3.4% due to UVBR. Lake Titicaca phytoplankton had a reshold for inhibition of photosynthesis at about 0.3 W m−2 for UVBR and 5 W m−2 for UVAR, below which no inhibition was detected. Above this threshold, photosynthetic inhibition increased steadily, with UVAR having the greatest effect. Analysis of biological weighting functions (BWFs) indicated that phytoplankton from Lake Titicaca was less sensitive to UVR than phytoplankton from other regions. DNA damage (evaluated through the formation of cyclobutane pyrimidine dimers, CPDs) was observed for a simulated worst-case situation (i.e. samples incubated in full sunlight) and significant CPD accumulation was found as a result of UVBR exposure, but not with UVAR. However, absolute levels of damage were relatively low when compared with results obtained at other locations, also suggesting the low sensitivity of Lake Titicaca phytoplankton to UVR. It seems that UVBR stress in these organisms acts via at least two cellular targets: the photosynthetic apparatus and nuclear DNA. Our results suggest that an eventual enhancement of UVBR, due to ozone depletion, would have little impact on the phytoplankton of Lake Titicaca.
DNA damage and photosynthetic inhibition induced by solar ultraviolet radiation in tropical phytoplankton (Lake Titicaca, Bolivia)
(Taylor & Francis, 2001) E. Walter Helbling; Virginia E. Villafañe; Anita G. J. Buma; Marcos Andrade; Francesco Zaratti
Experiments were conducted during October 1998 in Lake Titicaca, Bolivia (16° S, 68° W, 3810 m a.s.l), to determine the effects of solar ultraviolet radiation (UVR) on phytoplankton photosynthetic rates and DNA damage. Water samples were taken daily and incubated in situ or in simulated in situ conditions using sharp cut-off filters to eliminate various portions of the UVR spectrum. The total inhibition of photosynthesis due to UVR in surface waters was 85%; the greatest part of this inhibition (65%) was due to UVAR (315–400 nm), the rest (20%) being due to UVBR (280–315 nm). The inhibition of photosynthesis decreased with depth so that there were no significant differences among treatments at 1.3 optical depths (K PAR). The loss of carbon assimilation in the integrated production over the euphotic zone (4.6 optical depths) was 17.4%, with 14% due to UVAR and an additional 3.4% due to UVBR. Lake Titicaca phytoplankton had a reshold for inhibition of photosynthesis at about 0.3 W m−2 for UVBR and 5 W m−2 for UVAR, below which no inhibition was detected. Above this threshold, photosynthetic inhibition increased steadily, with UVAR having the greatest effect. Analysis of biological weighting functions (BWFs) indicated that phytoplankton from Lake Titicaca was less sensitive to UVR than phytoplankton from other regions. DNA damage (evaluated through the formation of cyclobutane pyrimidine dimers, CPDs) was observed for a simulated worst-case situation (i.e. samples incubated in full sunlight) and significant CPD accumulation was found as a result of UVBR exposure, but not with UVAR. However, absolute levels of damage were relatively low when compared with results obtained at other locations, also suggesting the low sensitivity of Lake Titicaca phytoplankton to UVR. It seems that UVBR stress in these organisms acts via at least two cellular targets: the photosynthetic apparatus and nuclear DNA. Our results suggest that an eventual enhancement of UVBR, due to ozone depletion, would have little impact on the phytoplankton of Lake Titicaca.
Inhibition of phytoplankton photosynthesis by solar ultraviolet radiation: studies in Lake Titicaca, Bolivia
(Wiley, 1999) VirginiaE. Villafa�e; Marcos Andrade; V. Lairana; Francesco Zaratti; E. Walter Helbling
1. Lake Titicaca is a large, high altitude (3810 m a.s.l.) tropical lake (16°S, 68°W) that lies on the border of Bolivia and Perú, receiving high fluxes of ultraviolet radiation (UVR) throughout the year. Our studies were conducted during September of 1997 with the main objective of studying the impact of solar UVR upon phytoplankton photosynthesis. 2. Water samples were taken daily and incubated in situ (down to 14 m depth) under three radiation treatments to study the relative responses to PAR (Photosynthetic Available Radiation, 400–700 nm), UV‐A (320–400 nm), and UV‐B (280–320 nm) radiation. 3. Photosynthetic inhibition by UVR in surface waters was about 80%, with UV‐A accounting for 60% and UV‐B for 20%; the inhibition by high levels of PAR was less than 20%. The inhibition due to UVR decreased with depth so that there were no significant differences between treatments at 8.5 m depth. 4. The amount of inhibition per unit energy received by phytoplankton indicates that even though there was a significant inhibition of photosynthesis due to UVR, species in Lake Titicaca seem to be better adapted than species in high latitude environments. 5. The cellular concentration of UV‐absorbing compounds, a possible mechanism of photoadaptation, was low in phytoplanktonic species. However, they were abundant in zooplankton, suggesting a high rate of bioaccumulation through the diet.