Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 4, issue 1
Biogeosciences, 4, 11–26, 2007
https://doi.org/10.5194/bg-4-11-2007
© Author(s) 2007. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.
Biogeosciences, 4, 11–26, 2007
https://doi.org/10.5194/bg-4-11-2007
© Author(s) 2007. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

  11 Jan 2007

11 Jan 2007

Nitrogen assimilation and short term retention in a nutrient-rich tidal freshwater marsh – a whole ecosystem 15N enrichment study

B. Gribsholt1, E. Struyf2, A. Tramper1, L. De Brabandere*,3, N. Brion3, S. van Damme2, P. Meire2, F. Dehairs3, J. J. Middelburg1, and H. T. S. Boschker1 B. Gribsholt et al.
  • 1Netherlands Institute of Ecology, Center for Estuarine and Marine Ecology. P.O. Box 140, 4400AC Yerseke, The Netherlands
  • 2University of Antwerp, Department of Biology, Environmental Management Research Group, Universiteitsplein 1C, 2610 Wilrijk, Belgium
  • 3Vrije Universiteit Brussel, Department of Analytical and Environmental Chemistry, Pleinlaan 2, 1050 Brussel, Belgium
  • *now at: University of Florida, Dept. of Fisheries and Aquatic Sciences, 7922 NW 71st Street, Gainesville FL 32653, USA

Abstract. An intact tidal freshwater marsh system (3477 m2) was labelled by adding 15N-ammonium as a tracer to the flood water inundating the ecosystem. The appearance and retention of 15N-label in different marsh components (leaves, roots, sediment, leaf litter and invertebrate fauna) was followed over 15 days. This allowed us to elucidate the direct assimilation and dependence on creek-water nitrogen on a relatively short term and provided an unbiased assessment of the relative importance of the various compartments within the ecosystem. Two separate experiments were conducted, one in spring/early summer (May 2002) when plants were young and building up biomass; the other in late summer (September 2003) when macrophytes were in a flowering or early senescent state.

Nitrogen assimilation rate (per hour inundated) was >3 times faster in May compared to September. On both occasions, however, the results clearly revealed that the less conspicuous compartments such as leaf litter and ruderal vegetations are more important in nitrogen uptake and retention than the prominent reed (Phragmites australis) meadows. Moreover, short-term nitrogen retention in these nutrient rich marshes occurs mainly via microbial pathways associated with the litter and sediment. Rather than direct uptake by macrophytes, it is the large reactive surface area provided by the tidal freshwater marsh vegetation that is most crucial for nitrogen transformation, assimilation and short term retention in nutrient rich tidal freshwater marshes. Our results clearly revealed the dominant role of microbes in initial nitrogen retention in marsh ecosystems.

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