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Volume 9, issue 11
Biogeosciences, 9, 4263–4278, 2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 9, 4263–4278, 2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 05 Nov 2012

Research article | 05 Nov 2012

Mimicking floodplain reconnection and disconnection using 15N mesocosm incubations

N. Welti1,2,*, E. Bondar-Kunze1,2, M. Mair1,2, P. Bonin4, W. Wanek3, G. Pinay5, and T. Hein1,2 N. Welti et al.
  • 1University of Natural Resources and Life Science, Institute of Hydrobiology and Aquatic Ecosystem Management, Vienna, Austria
  • 2WasserCluster Lunz Biologische Station GmbH, Lunz am See, Austria
  • 3University of Vienna, Department of Terrestrial Ecosystem Research, Vienna, Austria
  • 4Aix-Marseille Université, Mediterranean Institute of Oceanography (MIO), Marseille 9, France
  • 5ECOBIO-OSUR-CNRS, Avenue du General Leclerc, Rennes, France
  • *currently at: National Centre for Groundwater Research and Training, University of Queensland, Brisbane, Australia

Abstract. Floodplain restoration changes the nitrate delivery pattern and dissolved organic matter pool in backwaters, though the effects these changes have are not yet well known. We performed two mesocosm experiments on floodplain sediments to quantify the nitrate metabolism in two types of floodplains. Rates of denitrification, dissimilatory nitrate reduction to ammonium (DNRA) and anammox were measured using 15N-NO3 tracer additions in mesocosms of undisturbed floodplain sediments originating from (1) restored and (2) disconnected sites in the Alluvial Zone National Park on the Danube River downstream of Vienna, Austria. DNRA rates were an order of magnitude lower than denitrification and neither rate was affected by changes in nitrate delivery pattern or organic matter quality. Anammox was not detected at any of the sites. Denitrification was out-competed by assimilation, which was estimated to use up to 70% of the available nitrate. Overall, denitrification was higher in the restored sites, with mean rates of 5.7 ± 2.8 mmol N m−2 h−1 compared to the disconnected site (0.6 ± 0.5 mmol N m−2 h−1). In addition, ratios of N2O : N2 were lower in the restored site indicating a more complete denitrification. Nitrate addition had neither an effect on denitrification, nor on the N2O : N2 ratio. However, DOM (dissolved organic matter) quality significantly changed the N2O : N2 ratio in both sites. Addition of riverine-derived organic matter lowered the N2O : N2 ratio in the disconnected site, whereas addition of floodplain-derived organic matter increased the N2O : N2 ratio in the restored site. These results demonstrate that increasing floodplains hydrological connection to the main river channel increases nitrogen retention and decreases nitrous oxide emissions.

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