The key approach of the main research activities are focused on the process-oriented investigation of separated and connected biogeochemical element cycles with the use of special analytical approaches as stable isotope (S, O, C) and redox-sensitive element partitioning (e.g., S, C, O, P, Fe, Mn, Mo). It is reflected by the five main research areas:

• Aquatic Geochemistry
• Biogeochemistry
• Stable Isotope Geochemistry
• Sediment Geochemistry
• Environmental Geochemistry

Probennahme im Watt.   Referenz des Fotos links: Al-Raei et al. (2009) Seasonal dynamics of microbial sulfate reduction in temperate intertidal surface sediments: controls by temperature and organic matter. Ocean Dynamics 59: 351–370.   doi 10.1007/s10236-009-0186-5

Foto rechts: Probennahme in einer Lagune, Brasilien

Laufende Projekte

The general aim of AMBER is the implementation and application of the Ecosystem Approach to Management (EAM) to the Baltic Sea in the face of two closely intertwined environmental threats, eutrophication and climate change. Focus is on the coastal ecosystem (CE) because it supports most of the 85 mi inhabitants of nine nations around the Baltic Sea catchment. The CE receives most human derived nutrient loads from rivers, submarine ground water discharge (SGD), atmospheric deposition, and point sources and links the land with the open Baltic Sea. The CE controls the biogeochemical transformations of P-, N- compounds (phosphate, nitrate, DON, etc.) through the close coupling between water and sediments. Furthermore, it is crucial for fish as reproduction area, nursery and grazing ground and tightly connected to the open Baltic Sea. For an optimal integrated management, the implementation and application of EAM concepts on the CE it is necessary to study in a holistic approach the link between the catchment (including groundwater) and the open Baltic Sea and how climate change will affect the river water constituents and the biogeochemistry of the coastal waters and sediments. Unfortunately it is difficult to separate the signals of climate change from the direct impact of human activity. To understand and manage the future development of CE, the separation of these signals is necessary. Hence, one of the first steps of AMBER is the separation of climate from anthropogenic signals by means of a combinatorial variation in model’s boundary conditions using the output of existing regional climate change scenarios and the output of a watershed model simulating changes in land use.

• BIOACID
  Subproject 3.2.1 Impact of biogenic carbonates on pH buffering in an acidifying coastal sea (North Sea)
  BMBF (09.2009-08.2012)

We propose to investigate the influence of changing pH and carbon dioxide partial pressure, and alkalinity on carbonate dissolution in surface sediments of the Wadden Sea and the consequences for and relation to the carbonate system of the North Sea. Our hypothesis is that biogenic carbonates at the surface of intertidal sediments and the upper sediment layers play -to different extents- a role in modifying tidal waters that exchange with the shallow North Sea. This adds to carbonate fluxes caused by benthic organic matter degradation. The absolute and relative importances will change as the North Sea carbonate system will acidify in the future. One important aspect will be the reactivity (reaction rates and thermodynamic stability) of different biogenic carbonates and the experimental quantification of the different dissolution rates in pure and seawater media under different controlled laboratory conditions, i.e. pH, partial pressure of carbon dioxide (PCO2-stat and free-drift), and carbonate undersaturation. The reactive surface of the carbonate will be characterized to extract specific dissolution rates from experimental data on the development of liberated major minor and trace cations and the dissolved carbonate species. Experiments will be carried out at different fixed CO2 partial. This approach will include in parallel experiments geomicrobiological effects on microbial degradation of the organic matrix compared to purely abiotic reactions. Experimental laboratory-based approaches will be compared to field in-situ transformation experiments and will be followed by microscopic (e.g., SEM-EDX), inorganic geochemical (ICP-OES, photometry, microsensors) and stable isotope (C, O; irmMS) approaches. Experiments will also be carried out in collaboration with Dr. Hoppema (3.2.3) regarding benthic mesocosm experiments at AWI. Field work will additionally characterize the sources and surface textures of different carbonate fractions in surface sediments with geochemical methods and SEM-EDX. These results will allow to evaluate the time-dependent corrosion of biogenic carbonates as a function of burial time. Application of microsensors to characterize the chemical gradients will be carried out in collaboration with Dr. D. deBeer (MPI-MM; 3.2.2). From the side of carbonate formation, the influence of a changed carbonate system on growth of Mytilus and Crassostrea is planned to be assessed in a later phase of the project. Finally, pelagic measurements and experimental results will link the alkalinity and DIC exchange with the coastal North Sea and the possible ecosystem consequences via biogeochemical modelling. Parameters of the dissolved carbonate system (TA, DIC, PCO2, pH) will be measured in collaboration with PD Dr. Bernd Schneider (IOW) while d13C(DIC) will be determined via irmMS. These results will be provided for a collaborative integration in Theme 5 (Pätsch et al.) and the inclusion in the modelling of the North Sea carbonate system. The approach provides the base for a quantitative understanding of the role of the carbonate system in the water column on preservation, destruction and temporal authigenesis in the intertidal surface sediments, and the role of benthic metabolisms.

• WATT-II (DFG)

  Redox-sensitive Transformationen in Wassersäule und Sediment des nordfriesischen Wattenmeeres

  Laufzeit: 4.2009-3.2010

Zur Klärung des Stoffumsatzes im Wattenmeer soll geprüft werden, inwieweit Planktonblüten und die daran gekoppelte mikrobielle Aktivität sowie Sedimentumlagerungen (Sturmereignisse und Bioturbation) die Transformation in den biogeochemischen Kreisläufen von redox-sensitiven Elementen wie z. B. Mangan (Mn) und Molybdän (Mo) in der Wassersäule und im Oberflächensediment beeinflussen. Grundlage ist ein konzeptionelles Modell, nachdem es beim Zusammenbruch von Phytoplanktonblüten zur mikrobiell induzierten Aggregatbildung mit daraus resultierender Fixierung gelöster Elemente kommt. Die Einarbeitung der Aggregate in das Oberflächensediment und die anschließende Mineralisierung der Aggregate führt zu einer Freisetzung von Mn und Mo in das Porenwasser mit nachfolgendem Rücktransfer in die Wassersäule. Basierend auf Vorarbeiten im ostfriesischen Watt soll nun durch Feldkampagnen im nordfriesischen Wattenmeer, geprüft werden ob in den Küstengewässern verschiedener tidaler Systeme der Nordsee ein grundlegend verschiedenes Transferverhalten redox-sensitiver Elemente und DIC auftritt. Der geringere Eutrophierungsstatus des nordfriesischen Wattenmeeres könnte ursächlich zu einem verschiedenen Transferverhalten der Elemente führen. Die Felduntersuchungen werden durch Laborexperimente zu signifikanten Teilprozessen flankiert. Schließlich soll der Einfluss der ostfriesischen und nordfriesischen Wattsysteme für den Spurenelementeintrag in die Deutsche Bucht mittels Modellierung bilanziert werden.

Mitarbeiter: Kowalski, Dellwig, Böttcher (Kooperation AWI-Sylt: J. van Beusekom)