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Factors regulating nitrification in aquatic sediments: effects of organic carbon, nitrogen availability, and pH

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We investigated the response in nitrification to organic carbon (C) availability, the interactive effects of the C: nitrogen (N) ratio and organic N availability, and differing pH in sediments from several streams in the upper midwestern United States. In addition, we surveyed 36 streams to assess variability in sediment nitrification rates. Labile dissolved organic carbon (DOC) additions of 30 mg C·L–1 (as acetate) to stream sediments reduced nitrification rates (P < 0.003), but lower concentration additions or dilution of ambient DOC concentration had no effect on nitrification. C:N and organic N availability strongly interacted to affect nitrification (P < 0.0001), with N availability increasing nitrification most at lower C:N. Nitrification was also strongly influenced by pH (P < 0.002), with maximum rates occurring at pH 7.5. A multiple regression model developed from the stream survey consisted of five variables (stream temperature, pH, conductivity, DOC concentration, and total extractable NH4+) and explained 60% of the variation observed in nitrification. Our results suggest that nitrification is regulated by several variables, with NH4+ availability and pH being the most important. Organic C is likely important at regulating nitrification only under high environmental C:N conditions and if most available C is relatively labile.

Nous avons étudié la nitrification en fonction de la disponibilité du carbone organique (C), les effets interactifs du rapport C:N et de la disponibilité de l'azote organique (N) ainsi que les différences de pH dans les sédiments de plusieurs cours d'eau du Midwest supérieur des États-Unis. De plus, nous avons inventorié 36 cours d'eau pour déterminer la variabilité des taux de nitrification dans les sédiments. L'addition de carbone organique dissous (DOC) labile à raison de 30 mg C·L–1 (sous forme d'acétate) aux sédiments des cours d'eau réduit les taux de nitrification (P < 0,003), mais l'addition de concentrations moindres ou la dilution des concentrations ambiantes de DOC restent sans effet sur la nitrification. Le rapport C:N et la disponibilité de N organique interagissent fortement pour affecter la nitrification (P < 0,0001) et c'est aux valeurs inférieures du rapport C:N que la disponibilité de N agit le plus sur la nitrification. La nitrification est aussi fortement influencée par le pH (P < 0,002), avec un taux maximal qui se situe à pH 7,5. Un modèle de régression multiple élaboré à partir des inventaires des cours d'eau contient cinq variables (température du cours d'eau, pH, conductivité, concentration de DOC et NH4+ total extractible) et explique 60% de la variation observée dans la nitrification. Il apparaît donc que la nitrification est contrôlée par plusieurs variables, dont les plus importantes sont la disponibilité de NH4+ et le pH. Le C organique n'a probablement de rôle important à jouer dans le contrôle de la nitrification que lorsque le rapport C:N dans l'environnement est élevé et que la plus grande partie du C disponible est relativement labile.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2002-03-01

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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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