Showing papers on "Chlorococcum published in 1976"
TL;DR: Results were variable and atrazine, simazine, malathion and 2,4-D stimulated chlorophyll production by Chlorella when present individually at 0·1 and 0·5 μg/1, while results were variable when the pesticides were present individual at a concentration of 1 μg/l.
Abstract: An examination was made of the influence of atrazine, simazine, malathion and 2,4-D on total chlorophyll production by Chlorella vulgaris, Chlorococcum hypnosporum, Stigeoclonium tenue, Tribonema sp., Vaucheria geminata and Oscillatoria lutea. The herbicide 2,4-D in concentrations up to 100 mg/1 did not alter chlorophyll production by the algae. Chlorococcum was not influenced by the pesticides. When added individually, atrazine, simazine and malathion inhibited chlorophyll production at a concentration of 1 mg/l or greater except for Stigeoclonium, in which production was not influenced by 1 mg/1 simazine. Results were variable when the pesticides were present individually at a concentration of 1 μg/l. The three pesticides stimulated chlorophyll production by Chlorella when present individually at 0·1 and 0·5 μg/1. The same was true for simazine and malathion on Tribonema and Oscillaloria. A complete examination was not made for all the algae in these lower concentrations of pesticides. A signif...
88 citations
TL;DR: It is suggested that Chlamydomonas is at a selective advantage during the summer, yet during mixed water conditions with higher levels of nutrients growth of Chlorococcum is favoured.
Abstract: Growth of chlorophycean algae occurred during summer and autumn in the phytoplankton of Abbot's Pool. both motile and non-motile species were recorded during summer stratification and turbulent conditions in autumn. The largest standing crop in terms of biomass was produced by the growth of Pandorina and concurrently nitrate levels in the epilimnion decreased to below the level of chemical detection. Although nitrate-nitrogen and inorganic phosphorus levels in the epilimnion were severely depleted from July onwards, further growth of phytoplankton including Chlorococcum and Chlamydomas occurred. It is suggested that such nutrients may have become available from the hypolimnion via the process of eddy diffusion. From consideration of the biology of Chlorococcum and Chlamydomonas it is suggested that Chlamydomonas is at a selective advantage during the summer, yet during mixed water conditions with higher levels of nutrients growth of Chlorococcum is favoured. This hypothesis is supported by consideration o...
4 citations
01 Jan 1976
TL;DR: Molina et al. as discussed by the authors evaluated the effects of Zectran on photosynthetic rates of unicellular green algae, Chlorococcum sp. were assayed over a range of l ight intensities, temperatures and pH values to observe changes in tolerance under conditions of physio- logical stress.
Abstract: Molina, William R., 1976 Environmental Studies Toxicity of Zectran on Microalgae Subjected to Natural Environ mental Stress Toxic effects of the carbamate insecticide, Zectran, on photosynthetic rates of unicellular green algae, Chlorococcum sp. were assayed over a range of l ight intensities, temperatures and pH values to observe changes in tolerance under conditions of physio logical stress. At optimum conditions of 25 C, 1500 ft-c. and pH 7.5, Chlorococcum exhibited a tolerance threshold for photo synthesis and respiration between 1 and 10 parts per million (ppm) Zectran. One ppm Zectran showed no toxic effects at the stress temperatures 7 and 38 C. Toxicity greatly increased, how ever, with increasing time and temperature at 10 and 15 ppm. Light intensities of 250, 1500, and 10,000 foot candles (ft-c.) were used as suboptimal, optimal and supraoptimal conditions re spectively. Again, 1 ppm showed no toxic effects over 24 hours at sub-, supraor optimal l ight intensities. At 10,000 ft-c. , the higher concentrations 10 and 15 ppm showed 13 20% greater inhibition than at lower intensities. Exposure to 10 and 15 ppm for 1 hour at pH 10 reduced photo synthesis by 33% and 50% respectively over the control rates. Permutations of stress conditions were tested at the three Zectran concentrations. Photosynthesis was inhibited 27% by 1 ppm after 24 hours at conditions of 38 C and 10,000 ft-c. At all concentrations, combinations of high l ight and high tempera ture had similar detrimental effects. Temperature extremes proved to have the most influence governing toxicity. Low l ight reduced the toxic response of Chlorococcum and low temperature provided the greatest degree of protection for the organism. Exposure at pH 10 was protective at low light and temperature and detrimental at high l ight and temperature. In most cases, as the period of exposure increased, toxicity also increased. The results indicate that environmental conditions at the time of pesticide application can have an important effect on nontarget organism response. Director: Dr. Richard Sheridan