Impacts of Holocene Peat Deposits on Nearshore Biogeochemical Processes and Trace Gas Production Monographische Dissertation zur Erlangung des akademischen Grades doctor rerum naturalium (Dr. rer. nat.) der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Rostock vorgelegt von Matthias Kreuzburg Geboren am 03. November 1985 in Heidelberg Rostock den 24. Mai 2019 Thou canst not stir a flower, without troubling of a star. Francis Thompson, The Mistress of Vision I Table of contents Table of contents .............................................................................................................. II Eigenständigkeitserklärung ............................................................................................. VI Abstract ......................................................................................................................... VII Zusammenfassung ....................................................................................................... VIII Curriculum Vitae ............................................................................................................. IX Publications ..................................................................................................................... X Articles in peer-reviewed journals ................................................................................. X Conferences, workshops and presentations ................................................................. X Research stays abroad .............................................................................................. XII Grant .......................................................................................................................... XII Acknowledgement ........................................................................................................ XIII List of abbreviations, symbols and variables ................................................................. XIV List of Figures ............................................................................................................... XVI List of Tables .............................................................................................................. XVIII Motivation ..................................................................................................................... XIX 1. Introduction ................................................................................................................ 1 1.1. Climate relevant trace gases in coastal zones .................................................... 1 1.1.1. Methane ...................................................................................................... 1 1.1.2. Nitrous oxide ............................................................................................... 2 1.2. Geology and physical processes in coastal regions ............................................ 3 1.3. Hydrological processes across the terrestrial marine interface ........................... 5 1.3.1. Coastal interactions with peatlands ............................................................. 6 1.4. Study site ........................................................................................................... 7 1.4.1. Onshore area .............................................................................................. 7 1.4.2. Waterline and offshore area ........................................................................ 9 1.4.3. Warnow-river ............................................................................................... 9 2. Methods .................................................................................................................. 10 2.1. Geochemical field surveys ................................................................................ 10 2.1.1. Offshore water sampling ............................................................................ 10 2.1.1.1. Water column characteristics ................................................................. 10 2.1.1.2. Mini chamber lander system .................................................................. 11 2.1.2. Shoreline field campaigns.......................................................................... 12 2.1.3. Investigations of the Warnow-river system ................................................ 12 2.1.4. Analytical methods used for samples from the field campaigns ................. 12 II 2.1.4.1. Gas Chromatography ............................................................................. 12 2.1.4.2. Nutrients ................................................................................................ 14 2.2. Geophysical surveys ........................................................................................ 15 2.2.1. Geophysical data ....................................................................................... 15 2.2.2. Ground-truthing ......................................................................................... 16 2.2.3. Grain size distribution ................................................................................ 16 14 2.2.4. Geochemical sediment analysis and C age-determination ...................... 17 2.3. Column experiment study ................................................................................. 17 2.3.1. Column experiment and instrumentation ................................................... 18 2.3.2. Ground and seawater flow regimes ........................................................... 20 2.3.3. Analytical methods .................................................................................... 22 2.3.3.1. Gas fluxes among the air-water interface ............................................... 22 2.3.3.2. Porewater geochemical analysis ............................................................ 23 2.3.3.3. Monitoring of dissolved oxygen .............................................................. 24 2.3.3.4. Solid phase geochemistry ...................................................................... 25 2.3.3.5. Quantification of methanogens and sulfate reducers .............................. 25 3. Results .................................................................................................................... 27 3.1. Trace gas investigation within the study site ..................................................... 27 3.1.1. Offshore concentrations of CH4 and N2O ................................................... 27 3.1.2. Trace gas concentrations along the waterline ............................................ 30 3.1.3. Flux measurements from chamber lander incubations ............................... 31 3.1.4. Impacts of the Warnow-river on trace gas distribution ............................... 32 3.2. Geological surveys ........................................................................................... 34 3.2.1. Onshore .................................................................................................... 34 3.2.2. Bathymetry ................................................................................................ 35 3.2.3. Seafloor composition ................................................................................. 36 3.2.4. Sediment cores ......................................................................................... 38 3.2.5. Subsurface structure ................................................................................. 40 3.3. Column experiment .......................................................................................... 42 3.3.1. Aqueous phase geochemistry ................................................................... 42 3.3.1.1. Salinity ................................................................................................... 42 3.3.2. Porewater chemistry .................................................................................. 44 3.3.3. CO2 and CH4 fluxes ................................................................................... 45 3.3.4. Abundances of methanogenic archaea and sulfate reducing bacteria ....... 46 3.3.5. Solid phase geochemistry.......................................................................... 46 III 4. Discussion ............................................................................................................... 48 4.1. Hydrodynamics and trace gas distribution ........................................................ 48 4.1.1. Baltic Sea water ........................................................................................ 48 4.1.2. Warnow-river water ................................................................................... 50 4.1.3. Submarine groundwater discharge ............................................................ 51 4.2. Coastal development and geomorphology ........................................................ 52 4.2.1. Peatland formation and sea level rise ........................................................ 54 4.2.2. Submerged peat deposits in marine sediments ......................................... 56 4.3. Experimental investigation of the interaction of submerged peat with advective groundwater and seawater flow................................................................................... 58 4.3.1. Advective flow and solute transport ........................................................... 58 4.3.2. Solid phase geochemistry.........................................................................