Management effects on ecosystem functions of salt marshes: silica cycling and sedimentation processes Dissertation zur Erlangung des Doktorgrades an der Fakultät für Mathematik, Informatik und Naturwissenschaften im Fachbereich Biologie der Universität Hamburg vorgelegt von Frauke Müller Hamburg, 2012 Contents Summary 777 Zusammenfassung 111111 111 Introduction 171717 1.1 Salt marshes ................................................................................................ 17 1.1.1 Typology and hydrology ................................................................... 17 1.1.1 Vegetation and zonation ................................................................... 19 1.1.2 Ecosystem functions and services...................................................... 20 1.1.3 Management ..................................................................................... 22 1.1.4 Environmental threats ...................................................................... 23 1.2 The Wadden Sea coast ................................................................................ 25 1.2.1 Geology ............................................................................................. 25 1.2.2 Human alterations of the coast line .................................................. 27 1.2.3 Schleswig-Holstein Wadden Sea National Park................................. 29 1.2.4 Salt marshes in the national park ..................................................... 31 1.2.5 Research project BASSIA ................................................................. 32 1.3 Silica cycling ................................................................................................ 33 1.3.1 Global silica cycling .......................................................................... 33 1.3.2 Silica as a nutrient ............................................................................ 33 1.3.3 Diatoms and silica limitation ............................................................ 34 1.3.4 Silica supply from tidal freshwater marshes ...................................... 35 1.4 Sedimentation processes .............................................................................. 36 1.4.1 Sedimentation in salt marshes .......................................................... 36 1.4.2 Terminology ...................................................................................... 37 1.4.3 Influencing factors............................................................................. 38 1.4.4 Measurement of sedimentation processes .......................................... 39 1.4.5 Storm surges and sea-level rise ......................................................... 41 1.5 Objectives of the study ................................................................................ 42 1.6 Outline of the author’s contribution ............................................................ 43 1 222 Silica export dynamics of salt marshes in the Wadden Sea area 454545 2.1 Abstract ...................................................................................................... 45 2.2 Introduction ................................................................................................ 46 2.3 Methods ...................................................................................................... 48 2.3.1 Study sites ........................................................................................ 48 2.3.2 Field and laboratory methods .......................................................... 49 2.3.3 Calculation of export rates ............................................................... 50 2.4 Results ........................................................................................................ 51 2.4.1 DSi and BSi concentrations .............................................................. 51 2.4.2 Seasonality of concentrations............................................................ 53 2.4.3 Impact of management on concentrations ........................................ 53 2.4.4 DSi and BSi exports ......................................................................... 55 2.4.5 Seasonality of exports ....................................................................... 56 2.4.6 Impact of management on exports ................................................... 56 2.5 Discussion ................................................................................................... 56 2.5.1 DSi and BSi concentrations .............................................................. 56 2.5.2 Seasonality of concentrations............................................................ 57 2.5.3 DSi uptake by benthic diatoms ........................................................ 57 2.5.4 Impact of management on concentrations ........................................ 58 2.5.5 Silica exports .................................................................................... 59 2.6 Conclusion .................................................................................................. 61 2.7 Acknowledgements ...................................................................................... 63 333 A comprehensive study of silica ppoolsools and fluxes in Wadden Sea salt marshes 676767 3.1 Abstract ...................................................................................................... 67 3.2 Introduction ................................................................................................ 68 3.3 Methods ...................................................................................................... 69 3.3.1 Study sites ........................................................................................ 69 3.3.2 Field and laboratory methods .......................................................... 71 3.3.3 Calculation of pools, fluxes and budgets........................................... 72 3.4 Results ........................................................................................................ 74 3.4.1 Concentrations ................................................................................. 74 3.4.2 Pools................................................................................................. 76 3.4.3 Fluxes ............................................................................................... 78 3.5 Discussion ................................................................................................... 79 3.5.1 Concentrations ................................................................................. 79 3.5.2 Pools................................................................................................. 80 3.5.3 Fluxes ............................................................................................... 81 3.5.4 Storm surges and tidal regime .......................................................... 82 3.5.5 Marsh maturity ................................................................................ 82 3.5.6 Grazing management........................................................................ 83 3.6 Conclusion .................................................................................................. 84 3.7 Acknowledgements ...................................................................................... 85 2 CONTENTS 444 Significance of dissolved silica inputs from salsaltt marshesmarshes in European coastal waters at regional scale 878787 4.1 Abstract ...................................................................................................... 87 4.2 Introduction ................................................................................................ 88 4.3 Data and methods ....................................................................................... 88 4.4 Results and discussion ................................................................................. 90 4.4.1 General results .................................................................................. 90 4.4.2 Local significance .............................................................................. 91 4.4.3 Seasonal significance ......................................................................... 92 4.4.4 Factors controlling DSi exports ........................................................ 93 4.4.5 Specific DSi fluxes............................................................................. 94 4.5 Conclusions.................................................................................................. 95 4.6 Acknowledgements ...................................................................................... 95 555 The vegetation silica pool in a developing tidal freshwater marsh 979797 5.1 Abstract ...................................................................................................... 97 5.2 Introduction ................................................................................................ 98 5.3 Methods....................................................................................................... 99 5.3.1 Study site.......................................................................................... 99 5.3.2 Cover-biomass conversion: the CBC-method .................................. 100 5.4 Results....................................................................................................... 101 5.4.1 Vegetation mapping ........................................................................ 101 5.4.2