Seasonal variation in stable C and N isotope ratios of the Rhone River inputs to the Mediterranean Sea (2004–2005)
- 381 Downloads
The temporal variation in the stable carbon and nitrogen isotope ratios of particulate organic matter (POM) in the Rhone River was investigated on a monthly basis during a 2-year period (2004–2005). In spite of high month-to-month variation, interannually consistent seasonal trends appeared, with significantly lower δ13C (<−28.2‰) in spring than in the other seasons. In contrast, δ15N did not exhibit significant temporal variation. In spring and summer, high chlorophyll a and b concentrations were associated with low C/N values (<8) and a high percentage of organic carbon (%C) and organic nitrogen (%N), testifying to high development of autochthonous riverine phytoplankton (mainly diatoms and chlorophytes). In fall and winter, higher δ13C (>−27.2‰) and C/N (>8) values, and lower %C, %N, and chlorophylls concentrations indicated the predominance of allochthonous terrestrial detritus material in the river POM. The lower δ13C values recorded in spring–summer, when the phytoplankton biomass was high, were related to the lower carbon isotopic signatures of freshwater diatoms and chlorophytes compared to those of terrestrial plants. Overall, Rhone River POM was mainly composed of terrestrially derived material (90%), with autochthonous phytoplankton representing only 10% as a mean, in spite of a higher mean contribution of phytoplankton (27%) to river POM in summer.
KeywordsChlorophyll C/N Freshwater organic matter Gulf of Lions Stable isotopes
This research was supported by the French National programmes PNEC-MEDOC and ECCO-PNBC. The second author was supported by a research stipend of the Okeanos foundation (Germany). We are grateful to Chantal Salen-Picard for assistance in sampling and to Charlie Scrimgeour (Mylnefield Lipid Analysis-SCRI) for stable isotope analyses. Thanks are expressed to the editor and two reviewers for their most valuable comments and improvement on the manuscript.
- Aminot A, Kerouel R (2004) Hydrologie des écosystèmes marins. Paramètres et analyses. Editions Ifremer, 336 ppGoogle Scholar
- Bravard JP, Clémens A (eds) (2008) Le Rhône en 100 questions. ZABR-GRAIE, LyonGoogle Scholar
- Finlay JC, Kendall C (2007) Stable isotope tracing of temporal and spatial variability in organic matter sources to freshwater ecosystems. In: Michener R, Lajtha K (eds) Stable isotopes in ecology and environmental science, 2nd edn. Blackwell Publications, USA, pp 283–333Google Scholar
- Harmelin-Vivien M, Loizeau V, Mellon C, Beker B, Arlhac D, Bodiguel X, Ferraton F, Hermand R, Philippon X, Salen-Picard C (2008) Comparison of C and N stable isotope ratios between surface particulate organic matter and microphytoplankton in the Gulf of Lions (NW Mediterranean). Cont Shelf Res 28:1911–1919CrossRefGoogle Scholar
- Hellings L, Dehairs F, Tackx M, Keppens E, Baeyens W (1999) Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition. Biogeochemistry 47:167–186Google Scholar
- Kerhervé P & Sanchez-Vidal A (2007) Stable isotopic tracers (delta13C and delta15N) of riverine inputs into the Gulf of Lions: results from a one-year survey. Rapp Comm Int Mer Médit 38:677Google Scholar
- Martinotti W, Camuso M, Guzzi L, Patrolecco L, Pettine M (1997) C, N and their stable isotopes in suspended and sedimented matter from the Po estuary (Italy). Water Air Soil Pollut 99:325–332Google Scholar
- Mook WG, Tan TC (1991) Stable carbon isotopes in rivers and estuaries. In: Degens ET, Kempe S, Richey JE (eds) Biogeochemistry of major world rivers. SCOPE. Wiley, Chichester, pp 245–264Google Scholar
- Ottle C, Etchevers P, Golaz C, Habets F, Noilhan J, Martin E, Ledoux E, Leblois E, Sauquet E, Amaraoui N, Artinian E, Champeaux JL, Guérin C, Lacarrère P, Le Moigne P, Saulnier GM, Thiéry D, Vidal-Madjar D, Voirin S (2001) Hydro-meteorological modelling of the Rhone Basin: general presentation and objectives. Phys Chem Earth B 26:443–453Google Scholar
- Tesi T, Miserocchi S, Goñi MA, Langone L (2007) Source, transport and fate of terrestrial organic carbon on the western Mediterranean Sea, Gulf of Lions. France Mar Chem 105:101–117Google Scholar