Spatial and temporal variability of sediment organic matter recycling in two temperate eutrophicated estuaries
|Author(s)||Khalil Karima1, Raimonet Melanie2, Laverman Anniet M.2, Yan Chen2, Andrieux-Loyer Françoise3, Viollier Eric4, Deflandre Bruno5, Ragueneau Olivier6, Rabouille Christophe7|
|Affiliation(s)||1 : Univ Cadi Ayyad, Ecole Super Technol Essaouira, Essaouira, Aljadida, Morocco.
2 : Univ Paris 06, CNRS, UMR Sisyphe 7619, F-75252 Paris 05, France.
3 : IFREMER, Ctr Bres, Dept Dyneco Pelagos, Plouzane, France.
4 : Univ Paris Diderot, UMR CNRS 7154, Inst Phys Globe Paris, Sorbonne Paris Cite, F-75013 Paris, France.
5 : Univ Bordeaux 1, OASU UMR EPOC 5805, F-33405 Talence, France.
6 : Inst Univ Europe Mer, UMR CNRS 6539, F-29280 Plouzane, France.
7 : CEA, CNRS, Lab Mixte, Lab Sci Climat & Environm, F-91190 Gif Sur Yvette, France.
|Source||Aquatic Geochemistry (1380-6165) (Springer), 2013-11 , Vol. 19 , N. 5 , P. 517-542|
|WOS© Times Cited||9|
|Note||MOITEM I, Février 2009 (11/02/2009 au 16/02/2009), Côtes de la Manche MOITEM II, Mai 2009 (3/05/2009 au 8/05/2009), Côtes de la Manche MOITEM III, Juillet 2009 (23/07/2009 au 27/07/2009), Côtes de la Manche MOITEM IV, Octobre 2009 (28/10/2009 au 01/11/2005), Côtes de la Manche|
|Keyword(s)||Spatial and temporal variability, Estuarine sediment, Oxygen, Organic carbon and isotopic composition, Microelectrode, Organic matter recycling|
|Abstract||This paper deals with the spatial and seasonal recycling of organic matter in sediments of two temperate small estuaries (Elorn and Aulne, France). The spatio-temporal distribution of oxygen, nutrient and metal concentrations as well as the organic carbon and nitrogen contents in surficial sediments were determined and diffusive oxygen fluxes were calculated. In order to assess the source of organic carbon (OC) in the two estuaries, the isotopic composition of carbon (δ 13C) was also measured. The temporal variation of organic matter recycling was studied during four seasons in order to understand the driving forces of sediment mineralization and storage in these temperate estuaries. Low spatial variability of vertical profiles of oxygen, nutrient, and metal concentrations and diffusive oxygen fluxes were monitored at the station scale (within meters of the exact location) and cross-section scale. We observed diffusive oxygen fluxes around 15 mmol m−2 day−1 in the Elorn estuary and 10 mmol m−2 day−1 in the Aulne estuary. The outer (marine) stations of the two estuaries displayed similar diffusive O2 fluxes. Suboxic and anoxic mineralization was large in the sediments from the two estuaries as shown by the rapid removal of very high bottom water concentrations of NO x − (>200 μM) and the large NH4 + increase at depth at all stations. OC contents and C/N ratios were high in upstream sediments (11–15 % d.w. and 4–6, respectively) and decreased downstream to values around 2 % d.w. and C/N ≤ 10. δ 13C values show that the organic matter has different origins in the two watersheds as exemplified by lower δ 13C values in the Aulne watershed. A high increase of δ 13C and C/N values was visible in the two estuaries from upstream to downstream indicating a progressive mixing of terrestrial with marine organic matter. The Elorn estuary is influenced by human activities in its watershed (urban area, animal farming) which suggest the input of labile organic matter, whereas the Aulne estuary displays larger river primary production which can be either mineralized in the water column or transferred to the lower estuary, thus leaving a lower mineralization in Aulne than Elorn estuary. This study highlights that (1) meter scale heterogeneity of benthic biogeochemical properties can be low in small and linear macrotidal estuaries, (2) two estuaries that are geographically close can show different pattern of organic matter origin and recycling related to human activities on watersheds, (3) small estuaries can have an important role in recycling and retention of organic matter.|