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Trophic structure and energy flow in backwater lakes of two large floodplain rivers assessed using stable isotopes

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Carbon and nitrogen stable isotopes (13C and 15N, respectively) were measured for locally abundant primary producers, detritus, aquatic invertebrates, and fish in backwater lakes of two large floodplain rivers in an effort to understand patterns of energy dependence and trophic structure within these habitats. We observed trophic enrichment values for 15N that were within the ranges observed for other aquatic systems but were often considerably lower than the 3.4‰ typically assumed in stable isotope studies. Production based on benthic and terrestrial material, combined with planktonic production for larval fish, appears to be an important energy source supporting consumers in backwater lakes of large floodplain rivers. Our isotopic data challenge the conventional wisdom that macrophytes are centrally involved in supplying carbon to aquatic consumers in shallow lakes and that food webs in most lakes are sustained almost exclusively by carbon fixed by phytoplankton.

Nous avons mesuré les isotopes stables de carbone et d'hydrogène (13C et 15N) chez les producteurs primaires, le détritus, les invertébrés aquatiques et les poissons communs des lacs situées sur la plaine de débordement de deux grandes rivières dans le but de comprendre les patterns de dépendance énergétique et la structure trophique de ces habitats. Nous avons observé des valeurs d'enrichissement trophique de 15N comprises dans la même gamme que celles des autres systèmes aquatiques, mais ces valeurs étaient souvent considérablement plus faibles que le 3,4 ‰ qu'on assume communément dans les études sur les isotopes stables. Une production basée sur du matériel benthique et terrestre et une production planctonique utilisée par les larves de poissons semblent être les sources d'énergie qui supportent les consommateurs dans ces lacs situés sur les plaines de débordement de grandes rivières. Nos données sur les isotopes mettent en doute la croyance commune que les macrophytes jouent un rôle central dans l'apport de carbone aux consommateurs dans les lacs peu profonds et que les réseaux trophiques de la plupart des lacs sont alimentés par le carbone fixé par le phytoplancton.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2004-01-01

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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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