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23 July 2012 Variability in δ15N natural abundance of basal resources in fluvial ecosystems: a meta-analysis
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Variation in N stable isotope (δ15N) signatures of basal resources can influence interpretation of trophic relationships in ecosystems, and significant variation in δ15N signatures has been reported in streams and rivers. However, a comprehensive understanding of the main factors driving δ15N variability is lacking, and this variability confounds the consumer's trophic-level position during δ15N analysis. We conducted a meta-analysis to examine the variability in δ15N natural abundance of basal resources and dissolved inorganic N (DIN) in streams and rivers in relation to the environmental factors that may drive this variability. The meta-analysis was based on a literature review over the last 20 y (1989–2009) and contained signatures of δ15N-DIN (δ15N-NO3 and δ15N-NH4) and δ15N-basal resources (δ15N-detrital compartments, δ15N-biofilm, δ15N-algae, and δ15N-macrophytes) from >100 rivers or streams. Signatures of δ15N-DIN varied widely (−8.4–19.4‰), and we found fewer values for δ15N-NH4 than δ15N-NO3, even though NH4 is assimilated rapidly by basal resources. The range of δ15N-basal resources was also broad (−4–16‰) within and among compartments. Human land use was the most significant factor explaining variability in δ15N-DIN and δ15N-basal resource signatures. We found significant differences between δ15N signatures of photoautotrophic (i.e., autochthonous) and detrital (i.e., allochthonous) basal resources. Our results point out the difficulty in defining a baseline δ15N signature of the food web, and provide a basis to explain confounding results in studies using δ15N analysis to identify trophic linkages in fluvial food webs.

The Society for Freshwater Science
Marc Peipoch, Eugènia Martí, and Esperança Gacia "Variability in δ15N natural abundance of basal resources in fluvial ecosystems: a meta-analysis," Freshwater Science 31(3), 1003-1015, (23 July 2012).
Received: 17 November 2011; Accepted: 1 May 2012; Published: 23 July 2012

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