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The response of planktonic phosphate uptake and turnover to ultraviolet radiation in Lake Erie

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Abstract:

The hypothesis that ambient ultraviolet radiation (UVR), at near-surface intensities, may diminish phosphorus availability to phytoplankton was tested in Lake Erie in July and August of 1998 and 1999. Relative to samples exposed to photosynthetically active radiation (PAR, 400–700 nm) only, those exposed to ultraviolet-B (UVB, 280–320) and (or) ultraviolet-A (UVA, 320–400 nm) in natural sunlight, or kept in darkness, had diminished phosphate uptake rates at elevated (1 µM P) dissolved phosphate concentrations. By contrast, the specific uptake rate of dissolved phosphate at ambient concentrations (turnover rate) was not significantly affected by UVR or darkness. Turnover was usually dominated by particles smaller than 0.8 µm, whereas uptake from elevated concentrations was dominated by larger particles. The size distribution of turnover and uptake activity was not affected by radiation treatment. Chlorophyll a concentrations were decreased by sufficient exposure to UVB and (or) UVA and increased by deprivation of PAR (dark controls), but the concentration of bacterial cells was unaffected. The results showed that UVR inhibited the phosphate uptake potential of larger, probably algal, plankton but did not change the apparent severity of phosphate limitation at ambient concentrations.

L'hypothèse selon laquelle la radiation ultraviolette (UVR) ambiante, aux intensités qui prévalent près de la surface de l'eau, puisse diminuer la disponibilité du phosphore au phytoplancton a été mise à l'épreuve au lac Érié en juillet et août, en 1998 et 1999. Par comparaison à des échantillons exposés seulement à la radiation reliée à la photosynthèse (PAR, 400–700 nm), les échantillons exposés à l'ultraviolet-B (UVB, 280–320 nm) et (ou) à l'ultraviolet-A (UVA, 320–400 nm) sous un ensoleillement naturel, ou alors gardés à l'obscurité, affichent une diminution de l'incorporation du phosphate aux concentrations élevées (1 µM P) de phosphate dissous. En revanche, le taux spécifique d'incorporation de phosphate dissous aux concentrations ambiantes (le taux de renouvellement) n'est pas significativement affecté par la radiation UV ou par l'obscurité. Le renouvellement est dominé généralement par des particules de taille inférieure à 0,8 µm, alors que l'incorporation aux concentrations élevées l'est par des particules plus grandes. Les distributions de fréquence des tailles impliquées dans le renouvellement et l'incorporation ne sont pas modifiées par le traitement aux radiations. Les concentrations de chlorophylle a diminuent après une exposition suffisamment importante aux UVB et (ou) aux UVA et elles augmentent par pénurie de PAR (témoins gardés à l'obscurité), mais les concentrations de cellules bactériennes restent les mêmes. Nos résultats démontrent que la radiation UV inhibe le potentiel d'incorporation du phosphate du plancton de grande taille, sans doute essentiellement composé d'algues, mais elle ne change pas la gravité apparente de la pénurie de phosphate aux concentrations ambiantes.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: May 1, 2002

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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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