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Nutrient biogeochemistry in the water column (N, P, Si) and pore-water (N) of sandy sediment of the Scheldt estuary (SW-Netherlands)
Boderie, P.M.A.; Zwolsman, J.J.G.; van Eck, G.Th.M.; van der Weijden, C.H. (1993). Nutrient biogeochemistry in the water column (N, P, Si) and pore-water (N) of sandy sediment of the Scheldt estuary (SW-Netherlands). Neth. J. Aquat. Ecol. 27(2-4): 309-318.
Also appears in:
Meire, P.; Vincx, M. (Ed.) (1993). Marine and estuarine gradients: ECSA 21: Proceedings of the 21st symposium of the Estuarine and Coastal Sciences Association held in Gent, 9-14 september 1991. Netherlands Journal of Aquatic Ecology, 27(2-4). Netherlands Society of Aquatic Ecology: Bilthoven. 496 pp., more
Peer reviewed article  

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    Marine/Coastal; Brackish water

Authors  Top 
  • Boderie, P.M.A., more
  • Zwolsman, J.J.G., more
  • van Eck, G.Th.M., more
  • van der Weijden, C.H.

    The Scheldt river drains a densely populated and industrialized area in northern France, western Belgium and the south-west Netherlands. Mineralization of the high organic load carried by the river leads to oxygen depletion in the water column and high concentrations of dissolved nitrogen and phosphorus compounds. Upon estuarine mixing, dissolved oxygen concentrations are gradually restored due to reaeration and dilution with sea water. The longitudinal redox gradient present in the Scheldt estuary strongly affects the geochemistry of nutrients. Dissolved nutrients in the water column and dissolved nitrogen species in sediment porewaters were determined for a typical summer and winter situation. Water column concentration-salinity plots showed conservative behaviour of dissolved Si during winter. During summer (and spring) dissolved Si may be completely removed from solution due to uptake by diatoms. The geochemistry of phosphorus was governed by inorganic and biological processes. The behaviour of nitrogen was controlled by denitrification in the anoxic fluvial estuary, followed by nitrification in the upper estuary (prior to oxygen regeneration). In addition, nitrogen was taken up during phytoplankton blooms in the lower estuary. Dissolved inorganic nitrogen species in porewaters from the upper 20 cm of sediments were obtained from a subtidal site in the middle of the lower estuary. Dissolved nutrient concentrations were low in the upper 10-15 cm of the sandy and organic poor ( <1% POC) sediments mainly as a result of strong sediment mixing. The porewater profiles of ammonium and nitrate were evaluated quantitatively, using a one-dimensional steady-state diagenetic model. This coupled ammonium-nitrate model showed ammonification of organic matter to be restricted to the upper 4 to 7 cm of the sediments. Total nitrification ranged trom 3.7-18.1 mmol m-2 d-1, converting all ammonium produced by ammonification. The net balance between nitrification and denitrification depended on the season. Nitrate was released from the sediments during winter but is taken up from the water column during summer. These results are in good agreement with data obtained from the independently calibrated water column model for the Scheldt Estuary (VAN GILS et al., 1993).

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