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

Abstract

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 δ(15) N and δ(13) C 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°N, Finland); in contrast, N loading increased fourfold in the Scorff River (47°N, France) over the same period. Archived scales of Atlantic salmon parr, a riverine life-stage that feeds on aquatic invertebrates, revealed high δ(15) N values in the Scorff River reflecting anthropogenic N inputs to that riverine environment. A strong correlation between dissolved inorganic N loads and δ(13) C 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.

Environmental influences on life history strategies in partially anadromous brown trout (Salmo trutta, Salmonidae)

“…Interestingly, intensive agriculture systems relying on a large quantity of nutrients led to an increase in productivity in River Scorff, France (Roussel et al, 2013). Interestingly, intensive agriculture systems relying on a large quantity of nutrients led to an increase in productivity in River Scorff, France (Roussel et al, 2013).…”

Chemical archives in fishes beyond otoliths: A review on the use of other body parts as chronological recorders of microchemical constituents for expanding interpretations of environmental, ecological, and life‐history changes

“…For example, researchers have used diet-induced Sr tags (i.e., diet enriched with Sr 89 ) and differences in scale Mn concentrations to distinguish farmed and wild salmon (Yamada et al 1979;Adey et al 2009). Furthermore, by recording concentrations of dissolved nitrogen, heavy metals, and pollutants, scales can provide historical information on water quality and human health hazards (Rashed 2001;Roussel et al 2014;Lake et al 2006).…”

Environmental predictability of taxonomic and functional community composition in high‐latitude streams

“…Therefore, understanding the relationship between different environmental variables and functional composition of communities today could help in predicting the possible changes in the functioning of the streams in the future. Northern headwater streams provide ideal settings for testing these ideas, as they are extremely heterogeneous environments with minimal anthropogenic disturbance (Wrona et al, 2013;Roussel et al, 2014).…”