Stable isotope analyses on archived fish scales reveal the long-term effect of nitrogen loads on carbon cycling in rivers

• Published in: Global Change Biology
• Main Authors: Roussel, Jean-Marc, Perrier, Charles, Erkinaro, Jaakko, Niemela, Eero, Cunjak, Richard A., Huteau, Dominique, Riera, Pascal
• Other Authors: Écologie et santé des écosystèmes (ESE), Institut National de la Recherche Agronomique (INRA)-AGROCAMPUS OUEST, Département de Biologie, Institut de Biologie Intégrative et des Systèmes Québec (IBIS), Finnish Game and Fisheries Research Institute, Canadian Rivers Institute and the Department of Biology, Faculty of Forestry and Environmental Management, Adaptation et diversité en milieu marin (AD2M), Station biologique de Roscoff Roscoff (SBR), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2014
• Subjects: eutrophication; dissolved inorganic N; atmospheric CO2 diffusion; river food web; Atlantic salmon; Salmo salar; food webs; organic-matter; lake tanganyika; benthic; algae; trophic state; delta-n-15; delta-c-13; streams; rtielje r; 1995; limnology and oceanography; v40; p690; [SDV]Life Sciences [q-bio]; Teno
• Online Access: https://hal.science/hal-01123117; https://doi.org/10.1111/gcb.12293

Stable isotope analysis of organic matter in sediment records has long been used to track historical changes in productivity and carbon cycling in marine and lacustrine ecosystems. While flow dynamics preclude stratigraphic measurements of riverine sediments, such retrospective analysis is important for understanding biogeochemical cycling in running waters. Unique collections of riverine fish scales were used to analyse N-15 and C-13 variations in the food web of two European rivers that experience different degrees of anthropogenic pressure. Over the past four decades, dissolved inorganic N loading remained low and constant in the Teno River (70 degrees N, Finland); in contrast, N loading increased fourfold in the Scorff River (47 degrees N, France) over the same period. Archived scales of Atlantic salmon parr, a riverine life-stage that feeds on aquatic invertebrates, revealed high N-15 values in the Scorff River reflecting anthropogenic N inputs to that riverine environment. A strong correlation between dissolved inorganic N loads and C-13 values in fish scales was observed in the Scorff River, whereas no trend was found in the Teno River. This result suggests that anthropogenic N-nutrients enhanced atmospheric C uptake by primary producers and its transfer to fish. Our results illustrate for the first time that, as for lakes and marine ecosystems, historical changes in anthropogenic N loading can affect C cycling in riverine food webs, and confirm the long-term interactions between N and C biogeochemical cycles in running waters.