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Sie sind hier: Uni. Fk.. Fk. V. ICBM-TM. FG Watt. Research. Projects. Former Structure (2001-2007)

BioGeoChemistry of Tidal Flats

Projects

Former Structure

Sub-Project 1: Nonlinear Dynamics	Phase 1	Phase 2
Sub-Project 2: Integrative Modeling	Phase 1	Phase 2
Sub-Project 3: Water Column States and Budget	Phase 1	Phase 2
Sub-Project 4: Hydrodynamics and Suspended Matter Budget	Phase 1	Phase 2
Sub-Project 5: Ecology of Suspended Particles	Phase 1	Phase 2
Sub-Project 6: Anaerobic Transformations	Phase 1	Phase 2
Sub-Project 7: Sediment-Water Boundary Layer	Phase 1	Phase 2
Sub-Project 8: Methane cycle		Phase 2
Sub-Project 9: Macroinfaunal colonization		Phase 2

Phase 1 (2001 - 2004)

Sub-Project 1 Ulrike Feudel

Nonlinear Dynamics in Models for Tidal Flats:
Pattern Formation, Complexity and Critical Transitions

It is the aim of the sub-project to study pattern formation processes in a hierarchy of ecosystem models and to investigate the interaction of biogeochemical and transport processes in tidal flat sediments. We focus on the investigation of the formation of structures in space and time due to nonlinear interactions of reaction, diffusion and advection. Critical transitions where characteristic parameters of the system exceed certain threshold values leading to a spontaneous, discontinuous formation of new structures or dynamics are of special interest. One important point is the inhomogeneity of the medium with regard to transport characteristics and the distribution patterns of microorganisms. The influence of such inhomogeneities and non-local interactions on the pattern formation process will be studied. Additionally, the effects of stochastic influences (weather), big disturbances (extreme weather events) and the coupling of different sub-models on different spatial and time scales will be studied.

Phase 2

Sub-Project 2 Wolfgang Ebenhöh

Integrative Modeling of Biogeochemical Processes in the Wadden Sediment

Different biogeochemical processes in the Wadden Sea sediment including exchange at the sediment-water interface are assessed in an integrative way. Mainly, two hierarchical levels are considered, (1) the back-barrier tidal flat ecosystem and (2) a sediment column connected to the sea water (1). The ecosystem model is based on established standards (ERSEM) and will integrate the hydrodynamical model of sub-project 4 as well as an aggregated version of the sediment model (2). Special emphasis will be given to the effects of asymmetric tidal transport of nutrients and microbial activities on suspended particles (2). On the level of biogeochemical sediment processes, a major task lies in developing new model equations. Additionally, the description of POM degradation as well as several transport mechanisms, including the cycling of chemical nitrogen-, iron-, manganese- and sulfur-species are investigated. The dynamics of these element cycles is dominantly mediated by aerobic and anaerobic bacterial communities implicitly accounted for in the model. Here, the innovation lies in the description of the effect of succession and adaptation processes by means of effective variables. These, for example, represent apparent kinetic characteristics in different pathways of POM degradation or reoxidation of reduced substances. The sub-project aims to develop further coupling and aggregation methods in order to merge the two model levels as efficiently as possible. Using the results of a model sensitivity analysis, key processes of the biogeochemistry of tidal flats will be identified. In this way and by offering a frame for integrating most experimental results obtained so far, the sub-project contributes to the general coherence of the project.

Phase 2

Sub-Project 3 Hans-Jürgen Brumsack and Rainer Reuter

Input/output budget and states of the backbarrier tidal flat water column

The East Frisian tidal flats are continuously influenced by open marine (from the North Sea) and on-shore processes. In this sub-project, we want to elucidate whether the input/output of dissolved and particulate matter between the backbarrier and offshore areas is presently in a steady state or whether the tidal flats suffer a net loss of material. We intend to study the seasonal dynamics of seaward and landward inputs as well as their relation to the retention or mobilisation of specific compounds. These questions will be addressed from three viewpoints:

characterisation, quantification and input/output balance of the dissolved and particulate load between the backbarrier tidal flats and the open North Sea through the inlet on tidal and seasonal cycles, also taking into account extreme events (severe storms and sea ice)
characterisation and quantification of the dissolved and particulate input from small coastal tributaries into the backbarrier tidal flat system on a seasonal scale
characterisation and quantification of the biogeochemical transformation of the dissolved and particulate matter in the water column of the backbarrier tidal area.

Phase 2

Sub-Project 4 Jörg-Olaf Wolff and Burghard W. Flemming

Hydrodynamics and Suspended Matter Budget in an Intertidal Basin of the East Frisian Wadden Sea

The East Frisian Wadden Sea can currently be characterized by a lack of accommodation space for imported fine-grained sediments. The depositional system reacts to sea-level rise by a landward movement of existing sediments. The dominant driving forces of this process are a combination of sea-level rise, tidal currents, waves and wind-induced sea-level changes. Human activities have modified the natural system by constructing dikes for coastal protection. This has resulted in higher energy levels near the dike and hence to an ongoing elimination of finer-grained sediments. We postulate that, because of the lack of accommodation space in the Wadden Sea, the net export of fine-grained sediments (and any material associated with the fine sediment fraction) will continue and possibly accelerate in the future. The main aim of this project, therefore, is to establish a suspended sediment budget for a typical tidal basin as a function of hydrodynamic forcing factors and, ultimately, to develop a mathematical model for its prediction. To reach this objective, a high-resolution three-dimensional circulation model will be developed which will eventually be coupled with a wave model. Both, the circulation model and the import-export model of suspended sediment will be validated by in-situ measurements. Special emphasis will be given to extreme events (e.g. ice-winters and storm surges). At the same time, the processes controlling deposition and resuspension of fine-grained sediments in the tidal basin will be investigated.

Phase 2

Sub-Project 5 Meinhard Simon and Gunther Wittstock

Ecology of Suspended Particles

This sub-project will investigate the spatio-temporal dynamics and the aggregation processes of suspended matter, its composition and microbial colonization as well as the substrate turnover in the backbarrier tidal flats of Spiekeroog island. This includes the analysis of the size structure of the suspended matter and its biochemical and microscopic composition (planktonic and benthic algae, zooplankton, detritus, mineral particles). The composition of the associated bacterial community will be analyzed with classical and molecular microbiological methods (16S rDNA clone libraries, DGGE, FISH). In order to determine the microbial turnover of the suspended matter, we will measure the biomass production of the associated bacteria and the concentration, release and turnover of amino acids and carbohydrates on the aggregated suspended matter. In addition to the field studies, we plan to carry out experiments in mesocosms and large-scale tanks under controlled conditions and simulating the tidal currents.

Sub-Project 6 Heribert Cypionka, Jürgen Rullkötter and Henrik Sass

Gradients and Microbial Transformations in the Anoxic Zone

In this project, microbial and chemical processes in the Wadden Sea sediments are investigated. We study the composition and activities of the microbial communities and their influence on the sediment chemistry. Microbiological, molecular biological and geochemical approaches are used in a combined manner. Sampling will focus on the anoxic zone down to the sulfate-free layers. New methods have to be developed to deal with the bacteria of the 'shallow biosphere' and to cultivate them as efficiently as possible. Microbial and geochemical processes and fluxes are compared as a function of depth, and limiting parameters will be identified. Organic and inorganic compounds will be analyzed in order to clarify whether the present (recalcitrant) organic matter can serve as substrate for microbial growth, and whether binding to the mineral matrix limits its availability.

Phase 2

Sub-Project 7 Bo Barker Jørgensen and Michael E. Böttcher

Biogeochemical Processes at the Sediment-Water Interface of Intertidal Sediments

In this project, the cycles of manganese, iron, and sulfur in the different sediment types will be investigated in a quantitative manner in order to understand the fluxes of matter and the biogeochemistry of the intertidal sediments. Through the interaction of geochemical and microbial processes, the decomposition of organic matter is tightly linked to the cycles of O, N, S, Mn, Fe and other elements. Manganese and iron are important for the electron transfer and are recirculated through various redox processes. However, our understanding of the role of these elements in the decomposition pathways is still poor. This project will address (1) the biogeochemical processes that are important at the sediment-water interface and in the uppermost sediment layer, (2) the mineralization rates of organic matter, (3) the influence of environmental factors on the mineralization and biogeochemical zonation, (4) the relationship between the distribution of microorganisms and the biogeochemical processes and (5) the role of the hydrodynamic processes. All processes will be investigated with respect to their variability on tidal, day-night and seasonal scales in situ as well as in laboratory experiments.

Phase 2

Phase 2 (2004-2007)

Sub-Project 1 Ulrike Feudel

Nonlinear Dynamics in Models for Tidal Flats: Pattern Formation, Complexity and Critical Transitions

Our study of the interaction of biological and physical processes in tidal flats focusses on the role of biological compared to physical processes. Firstly, we study the biogeochemical degradation of different substrates in the Wadden Sea sediment with respect to the emergence of temporal, spatial or spatio-temporal patterns, which result from a non-linear interaction between reaction, bioturbation, diffusion and advection. Within this study we estimate the influence of the sediment's structure (sand or mud flat) on the process of advection. Environmental conditions that change with time are of particular interest: We study the effect of seasonal fluctuations in the environmental conditions as well as the influence of changing penetration depths of specific chemicals (e.g. oxygen) that are affected by the tides. Our second goal is the modelling of the effect of aggregation on sedimentation processes, specifically on the size distribution of aggregates. We estimate the impact of the biological activity of microorganisms inhabiting the sedimenting particles on the size distribution and the velocities of sedimentation. In particular we investigate how this activity is affected by the strength of the antagonistic forces determining the size of the aggregates (coagulation, shear stress). From the results we derive an estimate how the sizes will change along the season.

Sub-Project 2 Wolfgang Ebenhöh

Integrative Modeling of Biogeochemical Processes in the Wadden Sediment

Mathematical models are used to investigate the biogeochemical processes in the Wadden Sea, particularly concerning the sediment and suspended particles as well as their connection to physical and ecosystem-related processes. Central questions and hypotheses align model-building with empirical work in other sub-projects. Among others, fields of research are the dynamics at and of suspended particles as well as their function in the nutrient cycle, the cause of horizontal nutrient gradients, the impact of extreme events and the role of microbial adaptability. To approach these problems, different model generations will be applied: (1) complex models developed at an earlier stage concerning the Wadden Sea ecosystem and early diagenesis will be (2) coupled with each other, resulting in a complete Wadden Sea model from which (3) variants, dedicated to special areas of interest, will be deduced. Some of these variants will then be compared to (4) prototypic and simple conceptual models. The model-building process will thereby rely on basic contributions to the fields of model aggregation and knowledge discovery/management. These methods are useful to streamline the complete Wadden Sea model for investigations on the central questions as well as for coupling to other models (e.g. concerning tidal basin morphology). Further emphasis will be placed on data integration and analysis, providing the validation of models (1)-(3). Finally, the data collected by the autonomous measurement station will be processed using (non-)linear time-series analysis, resulting in a characterisation in terms of information theoretical properties (e.g. measures of entropy) and correlation structure on short distances.

Sub-Project 3 Hans-Jürgen Brumsack and Rainer Reuter

Input/output budget and states of the backbarrier tidal flat water column

We want to elucidate whether the input/output of dissolved and particulate matter between backbarrier and offshore areas is presently in a steady state or whether the tidal flats suffer a net loss of material. We study the seasonal dynamics of seaward and landward inputs as well as their relation to the retention or mobilisation of specific compounds. These questions will be addressed from three viewpoints:

characterisation, quantification and input/output balance of the dissolved and particulate load between the backbarrier tidal flats and the open North Sea through the inlet on tidal and seasonal cycles, also taking into account extreme events (severe storms and sea ice)
characterisation and quantification of the dissolved and particulate input from small coastal tributaries and from the pore water of the sediments into the backbarrier tidal flat system on a seasonal scale
characterisation and quantification of the biogeochemical transformation of the dissolved and particulate matter in the water column of the backbarrier tidal area

Sub-Project 4 Jörg-Olaf Wolff and Burghard W. Flemming

Hydrodynamics and Suspended Matter Budget in an Intertidal Basin of the East Frisian Wadden Sea

The Wadden Sea responds to a rising sea level with a transgressive shoreward displacement of the whole depositional system while at the same time aggrading vertically. This process is driven by the combined action of sea-level rise, tidal currents, waves, and wind-induced water-level fluctuations. By constructing dikes along the mainland coast, man has not only deprived the system of its accommodation space for fine-grained sediments but has also erected an insurmountable barrier to the displacement process. As a consequence of this interference, a net export of suspended matter from the Wadden Sea is predicted in the long run. This hypothesis is being tested by quantifying suspended matter fluxes of a typical tidal basin on the one hand, and predictive modelling on the other. Besides in situ measurements of suspended matter concentrations and the derivation of import-export budgets, a high-resolution 3D numerical flow model has been developed for this purpose. This will now be expanded to incorporate the local wave climate. Both the flow model and the suspended sediment budget are continually being validated and calibrated by the measurements. In the future, the research will mainly focus on the effects of extreme events on the hydrodynamics, the sediment budget, and the deposition-resuspension behaviour of fine-grained sediments in the tidal basin.

Sub-Project 5 Meinhard Simon and Gunther Wittstock

Ecology of Suspended Particles

Aggregation processes as well as tidal and seasonal dynamics, size distribution and composition of suspended matter in the backbarrier tidals flats of Spiekeroog Island will be continued to be studied in the field like in the first phase of the research group. In addition, the essential regulation parameters for particle aggregation and transformation and the composition of the bacterial communities will be investigated in laboratory systems and by colonization experiments on well-defined model surfaces of varying complexity. The identification and analysis of suspended particles will reveal information on their size structure and their biochemical and microscopic composition (algae, detritus, mineral particles). A further key topic will be the investigation of the bacterial transformations (biomass production, transformation of labile organic matter) related to suspended particles and dissolved organic matter in the surrounding waters. The composition of the particle-associated bacterial communities will be analyzed by molecular biological methods (DGGE, FISH) and correlated with the nature and surface layer functionalities of the suspended particles. The measurement of transformation rates will be restricted to the most important bacterial populations.

Phase 1

Sub-Project 6 Heribert Cypionka, Jürgen Rullkötter and Henrik Sass

Gradients and Microbial Transformations in the Anoxic Zone

The investigation of bacterial communities in the deeper sedimentary layers of the tidal flats (shallow biosphere) will be continued. It is the main objective to determine and to quantify the activity and composition of the bacterial communities using molecular biological, microbiological and geochemical methods and to correlate the results with the geochemical gradients in the sediments. Active and inactive microorganisms, or vegetative cells and endospores, are to be distinguished by amplification and sequencing of ribosomal RNA and rRNA genes as well as by the analysis of intact phospholipids. We plan to study how the microbial activity is influenced by seasonal changes (temperature, porewater composition) or inflow of organic matter in the pore system (e.g. by groundwater transport). Among the microorganisms particularly those isolated from deeper sediment layers are to be identified and selected (groups of) representatives quantified in situ by real-time PCR amplification. The specific adaptation of the isolated organisms to extremely substrate-depleted habitats will be tested by cultivation and microcalorimetric experiments and by applying RNA probes and vitality indicators.

Phase 1

Sub-Project 7 Bo Barker Jørgensen and Michael E. Böttcher

Biogeochemical Processes at the Sediment-Water Interface of Intertidal Sediments

The interactions between biogeochemical and microbial processes lead to a coupling of the degradation of organic matter to the element cycles of oxygen, nitrogen, manganese, iron, and sulfur. The most important aerobic and anaerobic processes in intertidal surface sediments will be quantified to increase our understanding of their significance for element fluxes and the biogeochemistry of the Wadden Sea. Among others, a non-invasive technique will be applied for the first time in the Wadden Sea to measure oxygen exchange rates as a basis for a high-resolution data set (in space and time) on benthic activity of the whole study area. Additionally, biological hot spots will be identified for further biogeochemical studies. The main questions to be answered are: What is the quantitative importance of benthic primary productivity and different respiration processes in sediments, and what is the quantitative relation to element fluxes at the sediment-water interface? What are the microbial and abiotic processes and the corresponding microorganisms responsible for the reoxidation of initially formed reduced species which, therefore, are important links in the shuttle of electrons? Finally, what are the consequences of rapid sedimentation events on the rates of biogeochemical processes?

Phase 1

Sub-Project 8 Heribert Cypionka, Bert Engelen and Rudolf Amann

Methane cycle in the Wadden Sea

Methane concentrations in the Wadden Sea were observed a hundred times higher compared to the open ocean. Sources and sinks of this climatically active gas in the tidal flats have not yet been clarified. This sub-project will investigate the methane cycle in all parts of the tidal flats (sediment, particles and water column). Therefore, we will measure methane concentrations during tidal and seasonal cycles. Microorganisms that are involved in the methane cycle (methanogenic archaea, methanothrophic bacteria and anaerobically methane-oxidizing consortia) will be quantified, isolated and characterized physiologically. The consortia of methanogenic archaea (type ANME2) and sulfate-reducing bacteria (Desulfosarcinales) which have recently been discovered in the tidal flats are of special interest. The second focus of this project is the identification and structural analysis of whole genome sections encoding key enzymes of the methane cycle. We aim to elucidate by means of the metagenomic analyses whether the existing operon structures are similar to those of methanogens and (an)aerobic methane oxidizers of different sites (e.g. Hydrate ridge, Black Sea).

Sub-Project 9 Tilmann Harder and Katarzyna A. Palinska

Macroinfaunal colonization in Wadden Sediments: Interactions between microbial settlement cues and biogeochemical sediment characteristics

Surface-associated microorganisms have long been demonstrated to act as localized signposts in colonization events of benthic invertebrates. The analysis of sediment cores along transects in tidal flat sediments revealed distinctive abundance patterns of sessile, infaunal macroorganisms, many of which disperse via a pelagic larval stage. To test the potential of microorganisms to mediate larval settlement not only on hard substrata but also in soft sediments, we developed a laboratory-based culture of the infaunal polychaete Polydora cornuta, identified the criteria of larval competence, and designed a larval settlement bioassay. Based on this model system we analyze the potential of sediment-associated microorganisms to mediate larval settlement of benthic infauna. These works comprise the analysis of microbial community profiles on preferred and rejected natural patches, the individual assessment of bacterial isolates on larval settlement, and the correlation of sediment attractiveness with the abundance of particular bacterial types. The long term goal of these investigations is to identify cultivable bacteria for an isolation and elucidation of chemical signals involved in polychaete larval settlement. The influence of biogeochemical sediment parameters on infaunal colonization adds a second level of complexity to the mediation of larval settlement via microbial cues. The abundance of suitable electron acceptors for the microbial mineralization of organic matter may directly influence microbial community profiles in the upper sediment, and thus may pose an indirect effect on macroinfaunal colonization patterns. Hence, a second objective of this project will be a correlation of biogeochemical sediment parameters with infaunal colonization patterns and vice versa.