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Controls on phytoplankton physiology in Lake Ontario during the late summer: evidence from new fluorescence methods

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Fast repetition rate fluorescence (FRRF) and spectral fluorescence, together with measures of nutrients and pigments, were used to characterize the composition and photosynthetic physiology of Lake Ontario phytoplankton in late summer and relate them to environmental conditions. Two stations demonstrated effects from relatively heavy anthropogenic disturbance and showed that the response of phytoplankton physiology to different impacts is highly variable. Other stations were more similar in phytoplankton composition, and in situ fluorescence yields () in the lower surface mixed layer suggested good physiological condition (0.45–0.50). Nutrient ratios and mean irradiance indicated a general state of light saturation and slight phosphorus (P) deficiency, but physiological variations among stations were unrelated to measures of P deficiency. Fluorescence yields often decreased when surface layer samples were held in the dark, consistent with an induction of chlororespiration and prior exposure to supersaturating levels of irradiance. Comparative estimates of photosynthesis by FRRF and 14C revealed disparities suggestive of substantial differences between in situ and incubation methods, while spectral fluorescence appeared to underestimate cyanobacterial abundance. FRRF parameters, particularly , were effective in identifying higher-impact stations and showed promise as an efficient means of characterizing variations in phytoplankton condition that may underlie phenomena such as taste and odour production.

La fluorescence à haute fréquence de répétition (FRRF) et la fluorescence spectrale, combinées à des dosages des nutriments et des pigments, nous ont servi à caractériser la physiologie de la photosynthèse et la composition du phytoplancton du lac Ontario en fin d'été et de les relier aux conditions du milieu. Deux des stations montrent les effets d'une perturbation anthropique relativement forte et indiquent que la réaction de la physiologie du phytoplancton aux divers impacts est très variable. D'autres stations ont des compositions phytoplanctoniques plus semblables et les rendements in situ de la fluorescence () dans la surface inférieure de la couche de mélange indiquent que les conditions physiologiques sont bonnes (0,45–0,50). Les rapports de nutriments et l'irradiation moyenne montrent une situation générale de saturation lumineuse et une faible carence de le phosphore (P), mais les variations physiologiques entre les stations ne sont pas reliées aux mesures de carence de P. Les rendements de fluorescence décroissent souvent lorsque les échantillons de la couche superficielle sont gardés à l'obscurité, ce qui est compatible avec une induction de la chlororespiration et une exposition préalable à des niveaux de sursaturation d'irradiation. Une comparaison des estimations de la photosynthèse par les méthodes FRRF et 14C montre des disparités qui indiquent des différences importants entre la méthode in situ et l'incubation, alors que la fluorescence spectrale semble sous-estimer l'abondance des cyanobactéries. Les paramètres FRRF, particulièrement , servent à identifier de manière efficace les stations à plus fort impact et montrent un potentiel comme moyens valables de caractériser les variations de la condition du phytoplancton qui peuvent sous-tendre des phénomènes tels que la production de goûts et d'odeurs. [Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2007-01-01

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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