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Nutrient retention in floodplains of the river Rhine

Nutrient retention in floodplains of the river Rhine. Jan Vermaat, Harry Olde Venterink, + Guda van der Lee [+ Harm Duel (Delft Hydraulics), Bert Higler (Alterra), Jos Verhoeven (UU) and several other colleagues)] Delft Cluster + IRMA. History: the gossipping part.

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Nutrient retention in floodplains of the river Rhine

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  1. Nutrient retention in floodplains of the river Rhine Jan Vermaat, Harry Olde Venterink, + Guda van der Lee [+ Harm Duel (Delft Hydraulics), Bert Higler (Alterra), Jos Verhoeven (UU) and several other colleagues)] Delft Cluster + IRMA

  2. History: the gossipping part • Got involved very late, had to provide ‘some sensible ecology’ to the cluster • Organize cooperation + matching with Delft Hydraulics and Alterra • All this settled (..), then by sheer luck I found the ideal postdoc and could appoint him 2 months before the campaign started ...

  3. What did we do? N, P, sediment I designed a threeway approach: • What is trapped in the floodplain? Different processes, floodplain habitats and seasons (2x HOV et al., Biogeochemistry and submitted) • What happens in the flowing water? Fliessende Welle between bridges: real flood events needed (HOV et al., J Env Qual) • Overall up-scaled modelling (Van der Lee et al., Riv Res & Appl; WL)

  4. Fliessende Welle 1 • Retention: (L1 – L2) / Distance [ g N or P km-1]

  5. Fliessende Welle 2 • N mainly nitrate, • P more particulate • P retention in IJssel • IJssel versus Waal

  6. Fliessende Welle 3 Repeated measures ANOVA: Rhine branch and months matter, note the interactions!

  7. Fliessende Welle 4: do the floodplains matter? • N = NO3, so nothing happened to N • Mainly retention of particulate P in IJssel, due to sedimentation: 20-45% disappeared • No retention in Waal: limited floodplains and fast flow: • 8 h travelling time vs 22 through the Ijssel, and • 19 vs 28% of the flow passed over the floodplains

  8. What happened insidethe floodplains? -1 • Sedimentation: laid out artificial grass sods before flooding events • Denitrification: soil core incubations via acetylene block method • Plant uptake: N, P -content in early spring and later summer • 5 floodplain wetland types, agric. grass, semi-natural grass, reed-beds, woodland and ponds

  9. Inside the floodplains - 2 • Sedimentation: considerable differences among habitat types

  10. Inside the floodplains - 3 • All floodplain habitats accumulate nutrients! Input > output; Also N! • Remaining plants and sediment/soil important sinks (no trees quantified) • inputs and outputs differ among habitats

  11. Via Habitats (kg ha-1 y-1) N-retention overall quite low (< 3%) P retention: Waal 5% IJssel 18% Fliessende Welle N-retention: not measurable P retention: Waal: not measurable IJsel: 20-45% Upscaling to whole river stretches and annual loads (Van der Lee)

  12. conclusions • This kind of complex studies is feasible: just 1 postdoc Harry, 1 trainee, 1 Jan, a little help from Alterra and Delft Hydraulics • 3 tracks-approach OK • This river: only (particulate) P retention, no loss of NO3 , unlike elsewhere and despite potentially substantial denitrification • Crucial: proportion of the flow through the floodplains (19-28%), and passage time (8-22h)

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