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Influence of diel cycles of respiration, chlorophyll, and photosynthetic parameters on the summer metabolic balance of temperate lakes and rivers

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Abstract:

Primary production, planktonic respiration, bacterial abundance, and chlorophylla were measured in the epilimnion of two Canadian Shield lakes and in two large rivers to establish their metabolic balance and to contrast oligotrophic and oligo-mesotrophic systems. Pronounced diel respiration cycles were observed in all systems, with a minimum in the morning and a maximum in the evening. Respiration was positively correlated with water temperature, incident light, and chlorophylla concentration. Diel cycles of chlorophylla were discernible in both rivers and in the oligo-mesotrophic lake. Our results show that a single morning sampling underestimates both respiration and chlorophylla, whereas a single sample taken at noon generally agrees better with the average of four daily measurements. In oligotrophic Lac Croche, the photosynthetic parameter αB remained constant throughout the day, whereas PBm increased by 12.5% between 0600h and 1300h. Ignoring the diel community respiration cycle resulted in a ~25% underestimation of daily respiration, whereas ignoring the PBm cycle induced a ~9% underestimation of the daily primary production. The net balance between production(P) and respiration(R) of the oligotrophic lake epilimnion remained positive during two summers, and the P:R ratio showed net autotrophy for all systems except for the oligotrophic river, which was slightly net heterotrophic.

La production primaire, la respiration planctonique, l’abondance bactérienne et la chlorophyllea ont été mesurées dans l’épilimnion de deux lacs du Bouclier canadien et dans deux grandes rivières afin d’établir leur bilan métabolique et de comparer des milieux oligotrophes et oligo-mésotrophes. Des cycles journaliers de respiration ont été observés dans les quatre milieux aquatiques avec un minimum en matinée et un maximum en soirée. La respiration était corrélée positivement avec la température de l’eau, la lumière incidente et la concentration en chlorophyllea. Des cycles journaliers de la chlorophylle a ont été mis en lumière dans les deux systèmes fluviaux et dans le lac oligo-mésotrophe. Le prélèvement d’un seul échantillon en matinée sous-estime la respiration et la chlorophyllea, tandis qu’un seul prélèvement effectué à midi correspond généralement mieux à la moyenne de quatre mesures journalières. Dans le lac Croche qui est oligotrophe, le paramètre photosynthétique αB ne présentait pas de variation journalière, alors que PBm augmentait de 12,5% entre 0600h et 1300h. Ignorer la variation journalière de la respiration engendre une sous-estimation de la respiration journalière de ~25%, tandis que l’omission du cycle de PBm produit une sous-estimation ~9% de la production primaire journalière. Le bilan net entre la production(P) et la respiration(R) de l’épilimnion du lac oligotrophe est demeuré positif au cours de deux étés de mesure et le rapport P:R indique que tous les systèmes étaient autotrophes nets à l’exception de la rivière oligotrophe, faiblement hétérotrophe.

Document Type: Research Article

Publication date: July 1, 2009

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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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