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Transient, tidal time-scale, nitrogen transformations in an estuarine turbidity maximum-fluid mud system (The Gironde, south-west France)
Abril, G.; Riou, S.A.; Etcheber, H.; Frankignoulle, M.; De Wit, R.; Middelburg, J.J. (2000). Transient, tidal time-scale, nitrogen transformations in an estuarine turbidity maximum-fluid mud system (The Gironde, south-west France). Est., Coast. and Shelf Sci. 50(5): 703-715. dx.doi.org/10.1006/ecss.1999.0598
In: Estuarine, Coastal and Shelf Science. Academic Press: London; New York. ISSN 0272-7714, more
Peer reviewed article  

Available in Authors | Datasets 
    VLIZ: Open Repository 280426 [ OMA ]

Keywords
    Denitrification; Nitrification; Nitrous oxide; Resuspension; Sedimentation; Tidal cycles; Turbidity; ANE, France, Gironde Estuary [Marine Regions]; Marine; Brackish water; Fresh water
Author keywords
    maximum turbidity zone; sedimentation; resuspension; tidal cycle; nitrification; denitrification; nitrous oxide; Gironde Estuary; France coast

Authors  Top | Datasets 
  • Abril, G., more
  • Riou, S.A.
  • Etcheber, H.
  • Frankignoulle, M., more
  • De Wit, R.
  • Middelburg, J.J., more

Abstract
    The maximum turbidity zone (MTZ) of the Gironde Estuary is a site of important mineralization of particulate organic nitrogen. Moreover, this MTZ is characterized by intense cycles of settling and resuspension of anoxic fluid mud at both tidal and neap-spring time-scales. In the upper layer of the fluid mud, which was deposited at tidal slack and eroded during each ebb and flood, a denitrification rate of up to 65 µmol l-1h-1 was measured during the transient period of settling. High concentrations of NO-2 (up to 13 µM), and N2O (up to 1500 nM) were observed in this layer at tidal slack, either due to an incomplete nitrification at low oxygen concentrations or to high denitrification activity. This suggests that deposition and erosion of the upper fluid mud at the tidal time-scale could be an important source of N2O for the estuarine overlying waters. The deepest layer of the fluid mud was more turbid, NO3- depleted and remained stable throughout tidal cycles, during several days. In this layer, ammonification was responsible for an increase of NH+4. Most probable number (MPN) counts of ammonium oxidizing bacteria in turbid water and fluid mud revealed that they were closely associated with particles, whereas potential nitrification rates were rather constant (10-14 µmol l-1 h- 1) irrespective of the suspended matter concentrations. In the MTZ of the Gironde, nitrogen behaves like in activated sludge reactors, with oxic/anoxic oscillations occurring at the tidal time scale. Nitrification takes place in the oxic water column and denitrification in the anoxic fluid mud. However at the whole estuarine scale the loss of particulate nitrogen and the gain of total dissolved inorganic nitrogen are in the same order of magnitude, which suggests that the net loss of nitrogen from the system is rather limited. This seems due to the fact that high denitrification rates are limited both in time (tidal slacks) and space (upper layers of fluid mud). However, our study emphasises the importance of settling/erosion transition periods on the nitrogen dynamics in estuarine maximum turbidity zones.

Datasets (2)
  • BIOGEST project dataset: Biogas Transfer in Estuaries, more
  • Publication data from Jack Middelburg for BIOGEST (particulate del13C, del15N, POC, PON, DOC, N2O and nitrogen uptake data), more

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