The Responses of a Natural Bacterioplankton Community to Different Levels of Ultraviolet-B Radiation: A Food Web Perspective.

With the continuing increase of ultraviolet-B radiation (UVBR: 280-320 nm) fluxes toward the Earth's surface, there is concern regarding a possible negative impact on heterotrophic bacterioplankton. The effects of enhanced UVBR on a natural bacterioplankton community were studied during a 7-day experiment conducted in mesocosms (1500 L). Four light regimes were tested: natural light, 280 to 313 nm excluded UVBR, and two levels of UVBR enhancement. During the first 3 days of the experiment characterized by high inorganic nutrient concentrations (nitrates > 1 µmol L-1 and ammonium > 0.1 µmol L-l), UVBR had no effect on both bacterial abundances and activities. From day 4 to the end of the experiment, nitrate concentrations remained low (

[Not Available]. / Comparaison de trois methodes de dosage du cuivre par analyse statistique.

Three methods commonly used for copper measurements in the range 0.5-10 mug/l. were compared by statistical analysis of the data. Regression analysis was applied to the calibration curves and confidence intervals were calculated, providing a constant index of precision. The atomic-absorption method seems to be the best choice, especially because it permits much saving of time when several metals are to be determined in the same sample.