Universiteit Antwerpen Faculteit wetenschappen Departement Biologie Silica cycling and vegetation development in a restored freshwater tidal marsh Siliciumcyclering en vegetatie- ontwikkeling in een hersteld zoetwaterschor Proefschrift voorgelegd tot het behalen van de graad van doctor in de wetenschappen aan de Universiteit Antwerpen te verdedigen door Sander Jacobs Promotor Prof. dr. P. Meire Universiteit Antwerpen Faculteit Wetenschappen Departement Biologie Onderzoeksgroep Ecosysteembeheer Silica cycling and vegetation development in a restored freshwater tidal marsh Siliciumcyclering en vegetatie-ontwikkeling in een hersteld zoetwaterschor Proefschrift voorgelegd tot het behalen van de graad van doctor in de Wetenschappen aan de Universiteit Antwerpen te verdedigen door Sander Jacobs Promotor Prof. Dr. P. Meire Copromotor Dr. E. Struyf Antwerpen 2009 Rivers know this: there is no hurry. We shall get there some day. Pooh 's Little Instruction Book inspired by A. A. Milne Contents Chapter 1 Introduction............................................................................................................. 1 1.1 Estuaries.................................................................................................................2 1.2 Estuarine degradation ..........................................................................................5 1.3 Tidal marsh restoration ...................................................................................... 7 1.4 Silica in estuaries and tidal m arshes ................................................................. 9 1.5 The silica management hypothesis ................................................................. 13 1.6 Restoration in the Schelde estuary ................................................................. 14 1.6.1 The Schelde estuary ...................................................................... 14 1.6.2 The Sigma-plan ..............................................................................16 1.6.3 Controlled reduced tid e ............................................................... 17 1.7 This thesis ............................................................................................................ 25 Chapter 2 Plant communities in European tidal freshwater wetlands......................39 2.1 A bstract................................................................................................................40 2.2 Introduction ........................................................................................................ 40 2.3 Vegetation pattem of the Schelde, Rhine-Meuse, and Elbe .................... 42 2.3.1 Schelde (Belgium) ..........................................................................45 2.3.2 Biesbosch and Oude Maas (The Netherlands) .......................48 2.3.3 Elbe (Germany) .............................................................................57 2.4 Conclusions ......................................................................................................... 63 2.5 Acknowledgements ........................................................................................... 64 Chapter 3 Restoration of tidal freshwater vegetation using controlled reduced tide (CRT) along the Schelde Estuary (Belgium)................................................ 73 3.1 A bstract ................................................................................................................74 3.2 Introduction ........................................................................................................ 75 3.3 Methods ................................................................................................................78 3.3.1 Site description and design scheme ........................................... 78 3.3.2 M onitoring ...................................................................................... 79 3.3.3 Data analysis................................................................................... 81 3.4 Results...................................................................................................................82 3.4.1 Effect of remnant vegetation and elevation ............................ 82 3.4.2 Species composition ......................................................................84 3.4.3 Temporal development and system trajectory ........................85 3.5 Discussion ........................................................................................................... 87 3.5.1 Which species established ...........................................................87 3.5.2 importance of flooding vs. remnant vegetation .....................89 3.5.3 plant community composition through time ..........................90 3.6 Conclusions ......................................................................................................... 91 3.7 Acknowledgements............................................................................................93 Chapter 4 The silica pool in freshwater tidal marsh vegetations............................... 103 4.1 A bstract ............................................................................................................. 104 4.2 Introduction ...................................................................................................... 105 4.3 Methods ............................................................................................................. 106 4.3.1 Site description ............................................................................. 106 4.3.2 Sampling plan ............................................................................... 107 4.4 Results.................................................................................................................109 4.4.1 Vegetation mapping ................................................................... 109 4.4.2 Cover-biomass relationships .....................................................109 4.4.3 Silica content per species ........................................................... I l l 4.4.4 BSi pool in the entire marsh vegetation .................................I l l 4.5 Discussion ......................................................................................................... 113 Chapter 5 Amorphous and dissolved silica patterns in freshwater tidal marshes . 121 5.1 A bstract ............................................................................................................. 122 5.2 Introduction ...................................................................................................... 122 5.3 Methods ............................................................................................................. 125 5.3.1 Data analysis................................................................................. 128 5.4 Results.................................................................................................................129 5.4.1 ASi contents ................................................................................. 129 5.4.2 DSi concentrations ......................................................................131 5.5 Discussion ......................................................................................................... 132 5.5.1 Build-up o f ASi-stock ................................................................ 132 5.5.2 ASi-recycling................................................................................. 133 5.5.3 Conclusions .................................................................................. 134 5.6 Acknowledgements ......................................................................................... 135 5.7 Appendix 1 ........................................................................................................ 141 Chapter 6 Spatiotemporal aspects of silica buffering in restored tidal marshes.... 145 6.1 A bstract ............................................................................................................. 146 6.2 Introduction ...................................................................................................... 146 6.3 Materials and Methods ...................................................................................149 6.3.1 Study area.......................................................................................149 6.3.2 Sampling ........................................................................................151 6.3.3 Water and Silica mass Balances................................................154 6.4 Results.................................................................................................................155 6.4.1 Concentration profiles................................................................155 6.4.2 Mass balances ............................................................................... 157 6.4.3 Ephemeral and Diurnal aspects .............................................. 159 6.4.4 Spatial Aspects ............................................................................. 161 6.5 D iscussion ......................................................................................................... 164 6.5.1 Diffusive and advective transport ............................................ 164 6.5.2 Sedimentation and resuspension ..............................................166 6.5.3 Diatom die-back and frustule dissolution ..............................167 6.5.4 Si-uptake